{"gene":"CD19","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":1995,"finding":"CD19 forms a multimolecular complex on the B cell surface with complement receptor CR2 (CD21) and tetraspanin TAPA-1 (CD81). Cross-linking CD19 to membrane immunoglobulin (mIg) lowers by two orders of magnitude the number of mIg molecules that must be ligated to activate phospholipase C or induce DNA synthesis. CD19 is coupled via protein tyrosine kinases to PLC and PI3-kinase and interacts with the Src-type nonreceptor PTK Lyn.","method":"Biochemical co-association studies, crosslinking experiments, signaling assays (PLC activation, DNA synthesis, Ca2+ responses)","journal":"Annual review of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal biochemical methods (co-immunoprecipitation, functional crosslinking assays, kinase assays), replicated across labs","pmids":["7542009"],"is_preprint":false},{"year":1997,"finding":"CD19 and CD22 reciprocally regulate tyrosine phosphorylation of Vav protein during B lymphocyte BCR signaling. CD19 crosslinking is more efficient than BCR crosslinking at inducing Vav phosphorylation; simultaneous crosslinking of CD19 with the BCR resulted in decreased Vav phosphorylation when CD22 was expressed. This differential regulation of Vav by CD19 and CD22 provides a molecular mechanism for adjusting BCR signaling thresholds.","method":"BCR crosslinking in CD22-deficient and CD19-deficient mouse B cells, immunoblotting for Vav tyrosine phosphorylation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout models (CD19-/- and CD22-/- mice) combined with biochemical phosphorylation assays, reciprocal loss-of-function comparison","pmids":["9371816"],"is_preprint":false},{"year":2001,"finding":"CD19 is necessary for efficient activation of Akt kinase following BCR or Igβ crosslinking in B cells. In the absence of CD19, Akt kinase activity is reduced and transient. Coligation of CD19 with surface immunoglobulin leads to augmented Akt activity in a dose-dependent manner, placing CD19 as a key regulator of PI3K-dependent Akt activity and cell survival signaling.","method":"CD19-deficient B-lymphoma cell lines and CD19-deficient mouse splenic B cells; Akt kinase activity assays after BCR/Igβ crosslinking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — loss-of-function genetic model (CD19-/- cells) with direct kinase activity assays, dose-dependent coligation experiments","pmids":["11042164"],"is_preprint":false},{"year":2001,"finding":"CD19 establishes a Src-family kinase activation loop requiring Lyn for CD19 phosphorylation. In Lyn-deficient mice, CD19 deficiency suppresses hyperresponsive B cell phenotype and autoimmunity (serum autoantibodies and glomerulonephritis). CD19 deficiency in Lyn-/- mice reduced Fyn and other cellular protein tyrosine phosphorylation following BCR ligation while Syk phosphorylation remained normal, demonstrating that CD19 amplifies signals through Src family PTKs other than Lyn.","method":"Double-knockout mice (CD19/Lyn-/-); BCR-induced Ca2+ responses, tyrosine phosphorylation immunoblots, humoral immune response assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — compound genetic epistasis with double-knockout mouse model and multiple orthogonal biochemical and functional readouts","pmids":["11509585"],"is_preprint":false},{"year":2002,"finding":"CD19 cytoplasmic tyrosines Y482 and Y513 are essential for all CD19 functions in vivo, including B1 and marginal zone B cell differentiation, T-dependent and -independent antibody responses, and germinal center B cell maturation/cell cycle progression. Mutation of these residues blocks germinal center maturation associated with retarded cell cycle progression.","method":"CD19-knockout mice expressing transgenic CD19 constructs with tyrosine mutations; in vivo immunization, flow cytometry, cell cycle analysis","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-directed mutagenesis in vivo with multiple functional readouts (B cell subsets, antibody responses, germinal center maturation, cell cycle)","pmids":["12387743"],"is_preprint":false},{"year":2002,"finding":"Bruton's tyrosine kinase (Btk) physically associates with CD19 following BCR engagement in B cells. CD19 expression maintains Btk in an activated state following BCR engagement but is not required for initial Btk phosphorylation. CD19-induced intracellular Ca2+ responses require downstream Btk function. CD19 and Btk regulate partially overlapping but also independent signaling pathways.","method":"Co-immunoprecipitation of Btk with CD19 in A20 B cells; CD19-/- and Xid (Btk-mutant) compound mouse models; Ca2+ flux assays; PI3K and Akt activation assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP plus compound genetic epistasis (CD19-/- × Xid double mutant), multiple orthogonal biochemical readouts","pmids":["12023340"],"is_preprint":false},{"year":2003,"finding":"CD19 facilitates the pro-B to pre-B cell transition by promoting proliferation downstream of pre-BCR signaling. In CD19-/- mice, the large cycling pre-B cell fraction is reduced. Signaling through the pre-BCR is impaired in the absence of CD19, as shown by reduced activation of Bruton's tyrosine kinase and ERK/MAPK.","method":"CD19-/- mouse model; sublethal irradiation reconstitution experiments; BrdU labeling and cell cycle analysis; IL-7-dependent pre-B cell cultures; Btk and ERK activation assays","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout model with multiple orthogonal methods (cell cycle analysis, BrdU incorporation, kinase activation assays, in vitro culture)","pmids":["14634103"],"is_preprint":false},{"year":2009,"finding":"CD21 (CR2) interaction with CD19 is necessary for coreceptor activity in humoral immunity. Knockin mice expressing mutant CR2 receptors that bind C3 ligands but cannot signal through CD19 showed significantly diminished germinal center B cell survival and secondary antibody titers, but B memory formation was less impaired than in complete CR deficiency.","method":"Knockin mouse model (Cr2-Delta/Delta-gfp); germinal center B cell survival analysis, antibody titer measurements, B memory assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockin model with separation-of-function mutation plus multiple immunological readouts","pmids":["19706534"],"is_preprint":false},{"year":2015,"finding":"CD19 is required for TLR9-induced B cell activation. TLR9 ligands induce phosphorylation of CD19 through MYD88/PYK2/LYN complexes, which enables recruitment of PI3K and subsequent phosphorylation of Btk and Akt in human B cells with different kinetics than BCR signaling. Loss of one or both CD19 alleles impairs upregulation of CD86, TACI, and CD23 after TLR9 stimulation.","method":"CD19-deficient patient B cells (mono- and biallelic mutations); phospho-flow cytometry; immunoblotting; co-immunoprecipitation; lentiviral CD19 knockdown B-cell line; PI3K/AKT/BTK inhibitors","journal":"The Journal of allergy and clinical immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — human genetic loss-of-function (patient samples with defined mutations) combined with pharmacological inhibition and co-IP, multiple orthogonal methods","pmids":["26478008"],"is_preprint":false},{"year":2016,"finding":"Mst1 kinase positively regulates BCR signaling by modulating CD19 transcriptional levels. Mst1 upregulates CD19 mRNA via the transcription factor TEAD2, which directly binds to a consensus motif in the 3' UTR of cd19. Mst1-deficient mice show reduced BCR signaling concurrent with defective BCR clustering and B cell spreading, and defective MZ and germinal center B cell differentiation due to disruption of CD19-mediated Btk signaling.","method":"Mst1 knockout mouse model; TIRF microscopy for BCR clustering; chromatin immunoprecipitation/transcription factor binding assay (TEAD2 on cd19 3'UTR); Btk phosphorylation assays","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout with TIRF microscopy and transcription factor binding evidence, single lab, mechanistic pathway established","pmids":["29296937"],"is_preprint":false},{"year":2018,"finding":"CD19 exon 2 variants generated by in-frame insertions or exon skipping (as resistance mechanisms after CAR T therapy) cause protein misfolding and retention in the endoplasmic reticulum rather than epitope loss per se. CD19 exon 2 variants acquire ER-specific high-mannose glycans but not Golgi-synthesized complex-type glycans, colocalize with ER markers, fail to bind the tetraspanin CD81, and instead interact with ER-resident chaperones (calnexin) and ER transporters.","method":"Retroviral transduction and genome editing to generate VSVg-tagged CD19 exon 2 variants; live-cell flow cytometry; pulse-chase glycosylation assays; alpha-mannosidase inhibitor assays; GFP fusion colocalization with ER markers; mass spectrometric profiling of CD19-interacting proteins","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal biochemical methods (glycosylation assays, subcellular localization, MS interactome) with functional validation (ADC killing resistance), rigorous controls","pmids":["30104252"],"is_preprint":false},{"year":2022,"finding":"Hyperglycosylation of CD19 caused by loss of the Golgi-resident intramembrane protease SPPL3 in malignant B cells directly inhibits CAR T cell effector function and suppresses anti-tumor cytotoxicity, representing a post-translational mechanism of antigen escape. Conversely, over-expression of SPPL3 drives loss of CD19 protein.","method":"SPPL3 loss-of-function and overexpression in malignant B cells; in vitro CAR T cell cytotoxicity assays; glycosylation analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic manipulation (loss and gain of function) with direct functional CAR T cell killing assays, single lab, pre-clinical model","pmids":["35690611"],"is_preprint":false},{"year":2023,"finding":"Cryo-EM structures of CD19 antigen bound to the FMC63 scFv (used in four FDA-approved CAR T therapies) and to SJ25C1 scFv were determined. Molecular dynamics simulations guided by structures enabled creation of lower- or higher-affinity binders. CAR T cells with different affinity binders exhibited distinct antigen density requirements for cytolysis and differed in propensity to trigger trogocytosis upon contacting tumor cells.","method":"Cryo-EM structure determination; molecular dynamics simulations; generation of affinity-tuned CAR variants; in vitro CAR T cell cytolysis assays at varying antigen densities; trogocytosis assays","journal":"Science immunology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure plus molecular dynamics plus functional CAR T cell validation with mutagenesis-derived affinity variants, multiple orthogonal methods in one study","pmids":["36867678"],"is_preprint":false},{"year":2019,"finding":"The FMC63 conformational epitope on the CD19 extracellular domain spans spatially adjacent but genetically distant loops encoded by exons 3 and 4. The epitopes of FMC63, 4G7-2E3, and 3B10 antibodies are partially overlapping but distinct, near the B43 epitope. All N-linked glycosylation sites can be removed from CD19 while retaining antibody binding in a yeast display context.","method":"Comprehensive single-site saturation mutagenesis library of CD19 extracellular domain; yeast display; flow cytometric screening for antibody binding; thermal stability selection","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — comprehensive saturation mutagenesis with functional binding screen, rigorous epitope mapping","pmids":["31702909"],"is_preprint":false},{"year":1999,"finding":"Enforced CD19 expression in tumorigenic human myeloma cells (which normally lack CD19) inhibits growth in vitro and reduces tumorigenicity in vivo. This growth-inhibitory effect requires the CD19 cytoplasmic signaling domain, as a truncated CD19 lacking this domain does not produce the effect, establishing CD19 signaling as a growth suppressor in myeloma.","method":"CD19 transfection of KMS-5 myeloma cell line; in vitro growth and anchorage-independent colony assays; in vivo tumorigenicity in SCID-hIL-6 transgenic mice; truncation mutant controls","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 / Strong — gain-of-function transfection with cytoplasmic domain truncation control, both in vitro and in vivo functional readouts","pmids":["10552966"],"is_preprint":false},{"year":2014,"finding":"CD19 deficiency in humans impairs selection of immunoglobulin reactivity in memory B cells. CD19-deficient patients show decreased activation-induced cytidine deaminase and increased uracil-DNA glycosylase 2 activity but decreased mismatch repair during somatic hypermutation, demonstrating a role for CD19 signaling in transcriptional regulation of DNA repair genes during germinal center reactions.","method":"CD19-deficient patient samples (n=8); flow cytometry of B cell subsets; molecular analysis of IgA and IgG transcripts; somatic hypermutation analysis; B cell activation studies","journal":"The Journal of allergy and clinical immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetic loss-of-function (defined patient mutations), molecular transcript analysis, single study","pmids":["24418477"],"is_preprint":false},{"year":2022,"finding":"CAR-induced internalization of CD19 is coupled with lysosome-mediated degradation, leading to emergence of transiently CD19-negative leukemic cells that evade CAR T19 immune responses. In contrast, bispecific T-cell engager (STAb-T19) strategy does not induce CD19 downmodulation and forms canonical immunological synapses, preventing this escape mechanism.","method":"In vitro coculture of CAR-T19 and STAb-T19 cells with leukemic cells; CD19 surface expression tracking; lysosome inhibitor assays; immunological synapse imaging; in vivo patient-derived xenograft mouse models","journal":"Cancer immunology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mechanistic comparison with lysosome inhibition, live imaging of synapse, in vivo validation, single lab","pmids":["35362043"],"is_preprint":false},{"year":2018,"finding":"Dock8 regulates BCR signaling through CD19. Dock8 deficiency reduces phosphorylated CD19 (pCD19) and phosphorylated Btk (pBtk) levels. WASP positively regulates cd19 transcription, and Dock8 regulates cd19 transcription through WASP. Dock8-deficient B cells show defective BCR clustering and B cell spreading on stimulatory lipid bilayers.","method":"Dock8 knockout mouse model; peripheral blood from Dock8-deficient patients; TIRF microscopy; confocal microscopy for BCR clustering/spreading; phospho-flow cytometry for pCD19 and pBtk","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout (mouse and human) with imaging and phospho-flow, single lab, mechanistic pathway established","pmids":["29472447"],"is_preprint":false}],"current_model":"CD19 is a transmembrane co-receptor that forms a signaling complex with CD21 (CR2), CD81 (TAPA-1), and CD225 on B cells; upon BCR engagement, it is phosphorylated on cytoplasmic tyrosines Y482 and Y513 by Lyn, establishing a Src-family PTK amplification loop that recruits PI3K, activates Akt and Btk, promotes Vav phosphorylation, and lowers the B cell activation threshold by orders of magnitude; it also integrates TLR9 signaling via MYD88/PYK2/LYN/PI3K/BTK and regulates CD19 transcription through Mst1-TEAD2 and WASP/Dock8 axes, with the cytoplasmic signaling domain required for growth regulation in plasma cells, and CD19 surface localization dependent on interaction with CD81 such that exon 2 alterations cause ER misfolding and loss of surface expression."},"narrative":{"mechanistic_narrative":"CD19 is a B-cell transmembrane co-receptor that lowers the antigen-receptor activation threshold and amplifies B-cell signaling, integrating multiple inputs to govern B-cell development, germinal center maturation, and humoral immunity [PMID:7542009, PMID:12387743]. On the cell surface it assembles into a multimolecular complex with complement receptor CR2 (CD21) and the tetraspanin TAPA-1 (CD81); cross-linking CD19 to membrane immunoglobulin reduces by two orders of magnitude the number of receptors that must be engaged to activate phospholipase C and drive DNA synthesis, and the CR2-CD19 interaction is required for germinal center B-cell survival and secondary antibody responses [PMID:7542009, PMID:19706534]. Signal amplification depends on a Src-family kinase loop in which Lyn phosphorylates CD19, which in turn sustains phosphorylation of Fyn and other Src-family PTKs to drive a hyperresponsive, autoimmune-prone phenotype [PMID:11509585]. Phosphorylated CD19 couples to PI3K, promoting efficient and sustained Akt activation, physically associates with Btk to maintain it in an active state for intracellular Ca2+ responses, and reciprocally regulates Vav phosphorylation to tune BCR signaling thresholds [PMID:9371816, PMID:11042164, PMID:12023340]. The cytoplasmic tyrosines Y482 and Y513 are essential for all CD19 functions in vivo, including B1 and marginal zone B-cell differentiation, T-dependent and -independent antibody responses, and germinal-center cell-cycle progression [PMID:12387743], and the cytoplasmic signaling domain confers growth suppression when CD19 is expressed in myeloma cells [PMID:10552966]. Beyond the BCR, CD19 is required for TLR9-induced activation, becoming phosphorylated via MYD88/PYK2/LYN to recruit PI3K and activate Btk and Akt [PMID:26478008]. CD19 transcription is positively controlled by an Mst1-TEAD2 axis acting on the cd19 3'UTR and by a WASP/Dock8 pathway, both of which feed back to support CD19-mediated Btk signaling and BCR clustering [PMID:29296937, PMID:29472447]. Human CD19 deficiency impairs somatic hypermutation and selection of immunoglobulin reactivity in memory B cells [PMID:24418477]. Surface localization requires CD81 binding: exon 2 alterations prevent CD81 association, trap CD19 with calnexin in the ER as a high-mannose glycoform, and abolish surface expression [PMID:30104252]. The extracellular domain presents a conformational FMC63 epitope spanning exon 3- and exon 4-encoded loops, structurally defined by cryo-EM, and CD19 antigen density and glycosylation state critically modulate CAR T-cell cytolysis, trogocytosis, and antigen escape [PMID:30104252, PMID:35690611, PMID:36867678, PMID:31702909, PMID:35362043].","teleology":[{"year":1995,"claim":"Established CD19 as a threshold-setting co-receptor by defining its surface complex and signaling couplings, answering how B cells could be activated by far fewer antigen-receptor engagements.","evidence":"Biochemical co-association, crosslinking, and signaling assays (PLC, DNA synthesis, Ca2+) in B cells","pmids":["7542009"],"confidence":"High","gaps":["Stoichiometry and dynamics of the CD19/CD21/CD81 complex not resolved","Direct kinase-substrate steps inferred rather than fully reconstituted"]},{"year":1997,"claim":"Showed CD19 and CD22 reciprocally control Vav phosphorylation, providing a molecular rheostat for adjusting BCR signaling thresholds.","evidence":"BCR crosslinking in CD19-/- and CD22-/- mouse B cells with Vav phospho-immunoblotting","pmids":["9371816"],"confidence":"High","gaps":["Direct versus indirect link between CD19 and Vav not defined","Downstream consequences of altered Vav phosphorylation not quantified"]},{"year":1999,"claim":"Demonstrated that CD19 signaling can suppress growth in non-B-lineage myeloma cells, revealing a context-dependent growth-regulatory function dependent on the cytoplasmic domain.","evidence":"CD19 transfection of myeloma cells with cytoplasmic truncation controls; in vitro growth and SCID xenograft assays","pmids":["10552966"],"confidence":"High","gaps":["Effector pathway of growth suppression not identified","Relevance to normal plasma cells unaddressed"]},{"year":2001,"claim":"Placed CD19 upstream of PI3K-Akt survival signaling and within a Lyn-dependent Src-family amplification loop, mechanistically linking the co-receptor to hyperresponsiveness and autoimmunity.","evidence":"CD19-/- B cells and CD19/Lyn double-knockout mice; Akt kinase assays, Ca2+ responses, phospho-immunoblots, autoimmunity readouts","pmids":["11042164","11509585"],"confidence":"High","gaps":["Direct PI3K recruitment site on CD19 not defined in these studies","How Lyn-phosphorylated CD19 amplifies other Src-family PTKs mechanistically unresolved"]},{"year":2002,"claim":"Identified the essential cytoplasmic tyrosines and the physical CD19-Btk association, establishing the specific signaling residues and a Btk-maintenance mechanism required for in vivo B-cell function.","evidence":"CD19-/- mice reconstituted with Y482/Y513 mutants; co-IP of Btk with CD19; CD19-/- x Xid compound mice; Ca2+ and kinase assays","pmids":["12387743","12023340"],"confidence":"High","gaps":["Identity of effectors recruited specifically to Y482 versus Y513 not delineated","Mechanism by which CD19 sustains active Btk not structurally defined"]},{"year":2003,"claim":"Extended CD19 function to early B-cell development, showing it promotes the pro-B to pre-B transition via pre-BCR-driven proliferation.","evidence":"CD19-/- mice; BrdU/cell-cycle analysis; IL-7 pre-B cultures; Btk and ERK activation assays","pmids":["14634103"],"confidence":"High","gaps":["Whether pre-BCR-CD19 coupling uses the same complex as mature BCR not established"]},{"year":2009,"claim":"Demonstrated that CR2 must signal through CD19 for coreceptor activity in humoral immunity, separating ligand binding from signaling output.","evidence":"Cr2-Delta/Delta-gfp knockin mice with separation-of-function mutation; germinal center, antibody titer, and memory assays","pmids":["19706534"],"confidence":"High","gaps":["Molecular interface enabling CR2-to-CD19 signal transfer not defined"]},{"year":2014,"claim":"Linked human CD19 signaling to the somatic hypermutation machinery, showing it regulates AID, UNG2, and mismatch repair activities during memory B-cell selection.","evidence":"CD19-deficient patient B cells; SHM and immunoglobulin transcript analysis; flow cytometry","pmids":["24418477"],"confidence":"Medium","gaps":["Transcriptional pathway from CD19 to DNA-repair gene regulation not mapped","Single patient cohort"]},{"year":2015,"claim":"Showed CD19 is also required for TLR9 signaling, integrating innate and antigen-receptor pathways through a distinct MYD88/PYK2/LYN-initiated phosphorylation route.","evidence":"CD19-deficient patient B cells, phospho-flow, co-IP, knockdown lines, PI3K/AKT/BTK inhibitors","pmids":["26478008"],"confidence":"High","gaps":["How TLR9-driven CD19 phosphorylation differs in kinetics/sites from BCR-driven phosphorylation not fully resolved"]},{"year":2016,"claim":"Identified transcriptional control of CD19 by an Mst1-TEAD2 axis and a WASP/Dock8 pathway, showing CD19 abundance is actively set to tune BCR signaling and B-cell clustering.","evidence":"Mst1 and Dock8 knockout mice and patient cells; TIRF/confocal imaging; TEAD2 3'UTR binding; phospho-CD19/Btk assays","pmids":["29296937","29472447"],"confidence":"Medium","gaps":["Single-lab transcriptional mechanisms","Direct versus indirect TEAD2 and WASP effects on cd19 not fully separated"]},{"year":2018,"claim":"Defined CD81-dependent surface trafficking of CD19 and the molecular basis of exon 2-driven CAR T resistance as ER misfolding rather than epitope loss.","evidence":"VSVg-tagged exon 2 variants; pulse-chase glycosylation, ER colocalization, MS interactome (calnexin), ADC killing assays","pmids":["30104252"],"confidence":"High","gaps":["Structural basis of CD19-CD81 association not resolved","Folding intermediates and quality-control kinetics not detailed"]},{"year":2019,"claim":"Mapped the conformational FMC63 epitope to exon 3/4-encoded loops and showed N-glycosylation is dispensable for antibody binding, informing CAR and antibody recognition.","evidence":"Saturation mutagenesis library, yeast display, flow cytometric epitope mapping, thermal stability selection","pmids":["31702909"],"confidence":"High","gaps":["Native membrane context of the epitope not addressed","Relationship of epitope loops to coreceptor signaling untested"]},{"year":2022,"claim":"Revealed post-translational and trafficking mechanisms of antigen escape: SPPL3-dependent hyperglycosylation blunts CAR T killing, and CAR-induced lysosomal degradation of CD19 yields transiently antigen-negative cells.","evidence":"SPPL3 loss/gain in B cells with CAR T cytotoxicity assays; CAR-T19 vs STAb-T19 cocultures with lysosome inhibition, synapse imaging, and PDX models","pmids":["35690611","35362043"],"confidence":"Medium","gaps":["Single-lab pre-clinical models","In vivo clinical relevance of SPPL3-driven escape not established","Reversibility kinetics of CD19 downmodulation not fully quantified"]},{"year":2023,"claim":"Provided cryo-EM structures of CD19 bound to clinically used scFvs and showed affinity tuning dictates antigen-density thresholds and trogocytosis, connecting CD19 structure to CAR T efficacy.","evidence":"Cryo-EM, molecular dynamics, affinity-variant CARs, cytolysis assays at varying antigen densities, trogocytosis assays","pmids":["36867678"],"confidence":"High","gaps":["Structure of full-length CD19 in its native coreceptor complex not determined","In vivo correlation of affinity tuning with durable response not shown"]},{"year":null,"claim":"How the CD19 cytoplasmic signaling module, its transcriptional regulators, and its CD81-dependent trafficking are mechanistically integrated within the native coreceptor complex at atomic resolution remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the assembled CD19/CD21/CD81 signaling complex","Direct CD19 cytoplasmic-domain interactome incompletely defined","Causal hierarchy among transcriptional inputs (Mst1-TEAD2, WASP/Dock8) unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,4,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,10]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,4,8]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,3,5]}],"complexes":["CD19/CD21(CR2)/CD81(TAPA-1) B-cell coreceptor complex"],"partners":["CD21","CD81","LYN","BTK","VAV","CR2","CALNEXIN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P15391","full_name":"B-lymphocyte antigen CD19","aliases":["B-lymphocyte surface antigen B4","Differentiation antigen CD19","T-cell surface antigen Leu-12"],"length_aa":556,"mass_kda":61.1,"function":"Functions as a coreceptor for the B-cell antigen receptor complex (BCR) on B-lymphocytes (PubMed:29523808). Decreases the threshold for activation of downstream signaling pathways and for triggering B-cell responses to antigens (PubMed:1373518, PubMed:16672701, PubMed:2463100). Activates signaling pathways that lead to the activation of phosphatidylinositol 3-kinase and the mobilization of intracellular Ca(2+) stores (PubMed:12387743, PubMed:16672701, PubMed:9317126, PubMed:9382888). Is not required for early steps during B cell differentiation in the blood marrow (PubMed:9317126). Required for normal differentiation of B-1 cells (By similarity). Required for normal B cell differentiation and proliferation in response to antigen challenges (PubMed:1373518, PubMed:2463100). Required for normal levels of serum immunoglobulins, and for production of high-affinity antibodies in response to antigen challenge (PubMed:12387743, PubMed:16672701, PubMed:9317126)","subcellular_location":"Cell membrane; Membrane raft","url":"https://www.uniprot.org/uniprotkb/P15391/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CD19","classification":"Not Classified","n_dependent_lines":28,"n_total_lines":1208,"dependency_fraction":0.023178807947019868},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CD19","total_profiled":1310},"omim":[{"mim_id":"621523","title":"SPONDYLOCOSTAL DYSOSTOSIS 7, AUTOSOMAL RECESSIVE; SCDO7","url":"https://www.omim.org/entry/621523"},{"mim_id":"621234","title":"ICHAD SYNDROME; ICHAD","url":"https://www.omim.org/entry/621234"},{"mim_id":"621097","title":"IMMUNODEFICIENCY 131; IMD131","url":"https://www.omim.org/entry/621097"},{"mim_id":"621068","title":"NEURODEVELOPMENTAL DISORDER WITH HYPOTONIA, POOR GROWTH, DYSMORPHIC FACIES, AND AGAMMAGLOBULINEMIA; NEDHGFA","url":"https://www.omim.org/entry/621068"},{"mim_id":"620532","title":"HYPER-IgE SYNDROME 6, AUTOSOMAL DOMINANT, WITH RECURRENT INFECTIONS; HIES6","url":"https://www.omim.org/entry/620532"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"intestine","ntpm":31.2},{"tissue":"lymphoid tissue","ntpm":70.8}],"url":"https://www.proteinatlas.org/search/CD19"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P15391","domains":[{"cath_id":"2.60.40.10","chopping":"21-135_154-279","consensus_level":"medium","plddt":83.4136,"start":21,"end":279},{"cath_id":"1.20.5","chopping":"280-315","consensus_level":"medium","plddt":84.1953,"start":280,"end":315}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P15391","model_url":"https://alphafold.ebi.ac.uk/files/AF-P15391-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P15391-F1-predicted_aligned_error_v6.png","plddt_mean":62.22},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CD19","jax_strain_url":"https://www.jax.org/strain/search?query=CD19"},"sequence":{"accession":"P15391","fasta_url":"https://rest.uniprot.org/uniprotkb/P15391.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P15391/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P15391"}},"corpus_meta":[{"pmid":"32023374","id":"PMC_32023374","title":"Use of CAR-Transduced Natural Killer Cells in CD19-Positive Lymphoid Tumors.","date":"2020","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32023374","citation_count":1730,"is_preprint":false},{"pmid":"29849141","id":"PMC_29849141","title":"Disruption of TET2 promotes the therapeutic efficacy of CD19-targeted T cells.","date":"2018","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/29849141","citation_count":737,"is_preprint":false},{"pmid":"27571406","id":"PMC_27571406","title":"Dual CD19 and CD123 targeting prevents antigen-loss relapses after CD19-directed immunotherapies.","date":"2016","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/27571406","citation_count":485,"is_preprint":false},{"pmid":"23210908","id":"PMC_23210908","title":"CD19: a biomarker for B cell development, lymphoma diagnosis and therapy.","date":"2012","source":"Experimental hematology & oncology","url":"https://pubmed.ncbi.nlm.nih.gov/23210908","citation_count":439,"is_preprint":false},{"pmid":"7542009","id":"PMC_7542009","title":"The CD19/CR2/TAPA-1 complex of B lymphocytes: linking natural to acquired immunity.","date":"1995","source":"Annual review of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/7542009","citation_count":396,"is_preprint":false},{"pmid":"38238616","id":"PMC_38238616","title":"Safety, efficacy and determinants of response of allogeneic CD19-specific CAR-NK cells in CD19+ B cell tumors: a phase 1/2 trial.","date":"2024","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38238616","citation_count":394,"is_preprint":false},{"pmid":"8528044","id":"PMC_8528044","title":"CD19 antigen in leukemia and lymphoma diagnosis and immunotherapy.","date":"1995","source":"Leukemia & lymphoma","url":"https://pubmed.ncbi.nlm.nih.gov/8528044","citation_count":260,"is_preprint":false},{"pmid":"9708202","id":"PMC_9708202","title":"Levels of expression of CD19 and CD20 in chronic B cell leukaemias.","date":"1998","source":"Journal of clinical pathology","url":"https://pubmed.ncbi.nlm.nih.gov/9708202","citation_count":258,"is_preprint":false},{"pmid":"11086109","id":"PMC_11086109","title":"Quantitative genetic variation in CD19 expression correlates with autoimmunity.","date":"2000","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/11086109","citation_count":245,"is_preprint":false},{"pmid":"27761200","id":"PMC_27761200","title":"Catch me if you can: Leukemia Escape after CD19-Directed T Cell Immunotherapies.","date":"2016","source":"Computational and structural biotechnology journal","url":"https://pubmed.ncbi.nlm.nih.gov/27761200","citation_count":244,"is_preprint":false},{"pmid":"30387077","id":"PMC_30387077","title":"Neurotoxicity Associated with CD19-Targeted CAR-T Cell Therapies.","date":"2018","source":"CNS drugs","url":"https://pubmed.ncbi.nlm.nih.gov/30387077","citation_count":209,"is_preprint":false},{"pmid":"26325036","id":"PMC_26325036","title":"CAR therapy: the CD19 paradigm.","date":"2015","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/26325036","citation_count":181,"is_preprint":false},{"pmid":"16505143","id":"PMC_16505143","title":"Lineage specification and plasticity in CD19- early B cell precursors.","date":"2006","source":"The Journal of experimental medicine","url":"https://pubmed.ncbi.nlm.nih.gov/16505143","citation_count":153,"is_preprint":false},{"pmid":"19798033","id":"PMC_19798033","title":"CD19: a promising B cell target for rheumatoid arthritis.","date":"2009","source":"Nature reviews. Rheumatology","url":"https://pubmed.ncbi.nlm.nih.gov/19798033","citation_count":151,"is_preprint":false},{"pmid":"33010231","id":"PMC_33010231","title":"CART19-BE-01: A Multicenter Trial of ARI-0001 Cell Therapy in Patients with CD19+ Relapsed/Refractory Malignancies.","date":"2020","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/33010231","citation_count":131,"is_preprint":false},{"pmid":"22003072","id":"PMC_22003072","title":"SAR3419: an anti-CD19-Maytansinoid Immunoconjugate for the treatment of B-cell malignancies.","date":"2011","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/22003072","citation_count":128,"is_preprint":false},{"pmid":"31316055","id":"PMC_31316055","title":"Super-resolution microscopy reveals ultra-low CD19 expression on myeloma cells that triggers elimination by CD19 CAR-T.","date":"2019","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/31316055","citation_count":125,"is_preprint":false},{"pmid":"35482927","id":"PMC_35482927","title":"Preinfusion factors impacting relapse immunophenotype following CD19 CAR T cells.","date":"2023","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/35482927","citation_count":120,"is_preprint":false},{"pmid":"30784102","id":"PMC_30784102","title":"Toxicities of CD19 CAR-T cell immunotherapy.","date":"2019","source":"American journal of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/30784102","citation_count":114,"is_preprint":false},{"pmid":"28780238","id":"PMC_28780238","title":"T-cell receptor αβ+ and CD19+ cell-depleted haploidentical and mismatched hematopoietic stem cell transplantation in primary immune deficiency.","date":"2017","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/28780238","citation_count":114,"is_preprint":false},{"pmid":"29593838","id":"PMC_29593838","title":"B cell-based therapies in CNS autoimmunity: differentiating CD19 and CD20 as therapeutic targets.","date":"2018","source":"Therapeutic advances in neurological disorders","url":"https://pubmed.ncbi.nlm.nih.gov/29593838","citation_count":111,"is_preprint":false},{"pmid":"33558546","id":"PMC_33558546","title":"Single-cell profiling identifies pre-existing CD19-negative subclones in a B-ALL patient with CD19-negative relapse after CAR-T therapy.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/33558546","citation_count":107,"is_preprint":false},{"pmid":"12387743","id":"PMC_12387743","title":"The physiologic role of CD19 cytoplasmic tyrosines.","date":"2002","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/12387743","citation_count":105,"is_preprint":false},{"pmid":"24667955","id":"PMC_24667955","title":"CD19-CAR trials.","date":"2014","source":"Cancer journal (Sudbury, Mass.)","url":"https://pubmed.ncbi.nlm.nih.gov/24667955","citation_count":94,"is_preprint":false},{"pmid":"29245005","id":"PMC_29245005","title":"CD19 CAR T Cells.","date":"2017","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/29245005","citation_count":94,"is_preprint":false},{"pmid":"9371816","id":"PMC_9371816","title":"CD19 and CD22 expression reciprocally regulates tyrosine phosphorylation of Vav protein during B lymphocyte signaling.","date":"1997","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/9371816","citation_count":87,"is_preprint":false},{"pmid":"11042164","id":"PMC_11042164","title":"Cd19-dependent activation of Akt kinase in B-lymphocytes.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11042164","citation_count":82,"is_preprint":false},{"pmid":"9695183","id":"PMC_9695183","title":"CD19 regulates B lymphocyte responses to transmembrane signals.","date":"1998","source":"Seminars in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/9695183","citation_count":80,"is_preprint":false},{"pmid":"32894185","id":"PMC_32894185","title":"Efficacy and safety of CD19 CAR T constructed with a new anti-CD19 chimeric antigen receptor in relapsed or refractory acute lymphoblastic leukemia.","date":"2020","source":"Journal of hematology & oncology","url":"https://pubmed.ncbi.nlm.nih.gov/32894185","citation_count":78,"is_preprint":false},{"pmid":"30890546","id":"PMC_30890546","title":"Novel CD19-targeted TriKE restores NK cell function and proliferative capacity in CLL.","date":"2019","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/30890546","citation_count":78,"is_preprint":false},{"pmid":"15778510","id":"PMC_15778510","title":"CD19 function in central and peripheral B-cell development.","date":"2005","source":"Immunologic research","url":"https://pubmed.ncbi.nlm.nih.gov/15778510","citation_count":72,"is_preprint":false},{"pmid":"22820352","id":"PMC_22820352","title":"CD19 as an attractive target for antibody-based therapy.","date":"2012","source":"mAbs","url":"https://pubmed.ncbi.nlm.nih.gov/22820352","citation_count":70,"is_preprint":false},{"pmid":"28153605","id":"PMC_28153605","title":"CD19, from bench to bedside.","date":"2017","source":"Immunology letters","url":"https://pubmed.ncbi.nlm.nih.gov/28153605","citation_count":69,"is_preprint":false},{"pmid":"30104252","id":"PMC_30104252","title":"CD19 Alterations Emerging after CD19-Directed Immunotherapy Cause Retention of the Misfolded Protein in the Endoplasmic Reticulum.","date":"2018","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/30104252","citation_count":69,"is_preprint":false},{"pmid":"33077866","id":"PMC_33077866","title":"Donor-derived CD19 CAR-T cell therapy of relapse of CD19-positive B-ALL post allotransplant.","date":"2020","source":"Leukemia","url":"https://pubmed.ncbi.nlm.nih.gov/33077866","citation_count":68,"is_preprint":false},{"pmid":"14634103","id":"PMC_14634103","title":"CD19 function in early and late B cell development. II. CD19 facilitates the pro-B/pre-B transition.","date":"2003","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/14634103","citation_count":68,"is_preprint":false},{"pmid":"11913948","id":"PMC_11913948","title":"CD19, CD21, and CD22: multifaceted response regulators of B lymphocyte signal transduction.","date":"2001","source":"International reviews of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/11913948","citation_count":65,"is_preprint":false},{"pmid":"35690611","id":"PMC_35690611","title":"Antigen glycosylation regulates efficacy of CAR T cells targeting CD19.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/35690611","citation_count":61,"is_preprint":false},{"pmid":"32514351","id":"PMC_32514351","title":"Mechanisms underlying CD19-positive ALL relapse after anti-CD19 CAR T cell therapy and associated strategies.","date":"2020","source":"Biomarker research","url":"https://pubmed.ncbi.nlm.nih.gov/32514351","citation_count":59,"is_preprint":false},{"pmid":"36867678","id":"PMC_36867678","title":"CD19 CAR antigen engagement mechanisms and affinity tuning.","date":"2023","source":"Science immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36867678","citation_count":58,"is_preprint":false},{"pmid":"34196410","id":"PMC_34196410","title":"CAR T cells: Building on the CD19 paradigm.","date":"2021","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/34196410","citation_count":56,"is_preprint":false},{"pmid":"24418477","id":"PMC_24418477","title":"Human CD19 and CD40L deficiencies impair antibody selection and differentially affect somatic hypermutation.","date":"2014","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/24418477","citation_count":54,"is_preprint":false},{"pmid":"37976456","id":"PMC_37976456","title":"Sequential antigen loss and branching evolution in lymphoma after CD19- and CD20-targeted T-cell-redirecting therapy.","date":"2024","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/37976456","citation_count":52,"is_preprint":false},{"pmid":"33808645","id":"PMC_33808645","title":"CD19 Chimeric Antigen Receptor-Exosome Targets CD19 Positive B-lineage Acute Lymphocytic Leukemia and Induces Cytotoxicity.","date":"2021","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/33808645","citation_count":52,"is_preprint":false},{"pmid":"15624204","id":"PMC_15624204","title":"Diminished expression of CD19 in B-cell lymphomas.","date":"2005","source":"Cytometry. Part B, Clinical cytometry","url":"https://pubmed.ncbi.nlm.nih.gov/15624204","citation_count":49,"is_preprint":false},{"pmid":"33228221","id":"PMC_33228221","title":"Complications after CD19+ CAR T-Cell Therapy.","date":"2020","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/33228221","citation_count":47,"is_preprint":false},{"pmid":"24442430","id":"PMC_24442430","title":"CD19 and CD32b differentially regulate human B cell responsiveness.","date":"2014","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/24442430","citation_count":46,"is_preprint":false},{"pmid":"26478008","id":"PMC_26478008","title":"CD19 controls Toll-like receptor 9 responses in human B cells.","date":"2015","source":"The Journal of allergy and clinical immunology","url":"https://pubmed.ncbi.nlm.nih.gov/26478008","citation_count":46,"is_preprint":false},{"pmid":"30479356","id":"PMC_30479356","title":"Genome-wide DNA methylation changes in CD19+ B cells from relapsing-remitting multiple sclerosis patients.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30479356","citation_count":45,"is_preprint":false},{"pmid":"31201998","id":"PMC_31201998","title":"Transcriptome and Regulatory Network Analyses of CD19-CAR-T Immunotherapy for B-ALL.","date":"2019","source":"Genomics, proteomics & bioinformatics","url":"https://pubmed.ncbi.nlm.nih.gov/31201998","citation_count":44,"is_preprint":false},{"pmid":"23885836","id":"PMC_23885836","title":"Therapeutic targeting of CD19 in hematological malignancies: past, present, future and beyond.","date":"2013","source":"Leukemia & lymphoma","url":"https://pubmed.ncbi.nlm.nih.gov/23885836","citation_count":42,"is_preprint":false},{"pmid":"37744005","id":"PMC_37744005","title":"Cytokine and reactivity profiles in SLE patients following anti-CD19 CART therapy.","date":"2023","source":"Molecular therapy. Methods & clinical development","url":"https://pubmed.ncbi.nlm.nih.gov/37744005","citation_count":40,"is_preprint":false},{"pmid":"39589371","id":"PMC_39589371","title":"Aggressive Lymphoma after CD19 CAR T-Cell Therapy.","date":"2024","source":"The New England journal of medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39589371","citation_count":39,"is_preprint":false},{"pmid":"34478871","id":"PMC_34478871","title":"A novel and efficient tandem CD19- and CD22-directed CAR for B cell ALL.","date":"2021","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/34478871","citation_count":38,"is_preprint":false},{"pmid":"25993197","id":"PMC_25993197","title":"CD19 CAR Therapy for Acute Lymphoblastic Leukemia.","date":"2015","source":"American Society of Clinical Oncology educational book. American Society of Clinical Oncology. Annual Meeting","url":"https://pubmed.ncbi.nlm.nih.gov/25993197","citation_count":38,"is_preprint":false},{"pmid":"12023340","id":"PMC_12023340","title":"Complementary roles for CD19 and Bruton's tyrosine kinase in B lymphocyte signal transduction.","date":"2002","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/12023340","citation_count":38,"is_preprint":false},{"pmid":"31702909","id":"PMC_31702909","title":"Fine Epitope Mapping of the CD19 Extracellular Domain Promotes Design.","date":"2019","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31702909","citation_count":36,"is_preprint":false},{"pmid":"10552966","id":"PMC_10552966","title":"Enforced CD19 expression leads to growth inhibition and reduced tumorigenicity.","date":"1999","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/10552966","citation_count":36,"is_preprint":false},{"pmid":"34831430","id":"PMC_34831430","title":"Sensitivity and Specificity of CD19.CAR-T Cell Detection by Flow Cytometry and PCR.","date":"2021","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/34831430","citation_count":35,"is_preprint":false},{"pmid":"11509585","id":"PMC_11509585","title":"A CD19-dependent signaling pathway regulates autoimmunity in Lyn-deficient mice.","date":"2001","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/11509585","citation_count":35,"is_preprint":false},{"pmid":"23360526","id":"PMC_23360526","title":"A CD19/Fc fusion protein for detection of anti-CD19 chimeric antigen receptors.","date":"2013","source":"Journal of translational medicine","url":"https://pubmed.ncbi.nlm.nih.gov/23360526","citation_count":34,"is_preprint":false},{"pmid":"31899793","id":"PMC_31899793","title":"How I treat adults with advanced acute lymphoblastic leukemia eligible for CD19-targeted immunotherapy.","date":"2020","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/31899793","citation_count":34,"is_preprint":false},{"pmid":"16430470","id":"PMC_16430470","title":"Loss of CD19 expression in B-cell neoplasms.","date":"2006","source":"Histopathology","url":"https://pubmed.ncbi.nlm.nih.gov/16430470","citation_count":33,"is_preprint":false},{"pmid":"35421218","id":"PMC_35421218","title":"CD34+CD19-CD22+ B-cell progenitors may underlie phenotypic escape in patients treated with CD19-directed therapies.","date":"2022","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/35421218","citation_count":32,"is_preprint":false},{"pmid":"12403344","id":"PMC_12403344","title":"Role of CD19 signal transduction in B cell biology.","date":"2002","source":"Immunologic research","url":"https://pubmed.ncbi.nlm.nih.gov/12403344","citation_count":32,"is_preprint":false},{"pmid":"19706534","id":"PMC_19706534","title":"Uncoupling CD21 and CD19 of the B-cell coreceptor.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19706534","citation_count":32,"is_preprint":false},{"pmid":"28821531","id":"PMC_28821531","title":"CD28 and 41BB Costimulation Enhances the Effector Function of CD19-Specific Engager T Cells.","date":"2017","source":"Cancer immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/28821531","citation_count":31,"is_preprint":false},{"pmid":"31242389","id":"PMC_31242389","title":"Retargeting CD19 Chimeric Antigen Receptor T Cells via Engineered CD19-Fusion Proteins.","date":"2019","source":"Molecular pharmaceutics","url":"https://pubmed.ncbi.nlm.nih.gov/31242389","citation_count":31,"is_preprint":false},{"pmid":"37095120","id":"PMC_37095120","title":"Which one is better for refractory/relapsed acute B-cell lymphoblastic leukemia: Single-target (CD19) or dual-target (tandem or sequential CD19/CD22) CAR T-cell therapy?","date":"2023","source":"Blood cancer journal","url":"https://pubmed.ncbi.nlm.nih.gov/37095120","citation_count":31,"is_preprint":false},{"pmid":"27186412","id":"PMC_27186412","title":"CD19 chimeric antigen receptor (CD19 CAR)-redirected adoptive T-cell immunotherapy for the treatment of relapsed or refractory B-cell Non-Hodgkin's Lymphomas.","date":"2016","source":"American journal of cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/27186412","citation_count":30,"is_preprint":false},{"pmid":"36945773","id":"PMC_36945773","title":"Dual targeting of CD19 and CD22 against B-ALL using a novel high-sensitivity aCD22 CAR.","date":"2023","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/36945773","citation_count":29,"is_preprint":false},{"pmid":"33656536","id":"PMC_33656536","title":"HLA-haploidentical TCRαβ+/CD19+-depleted stem cell transplantation in children and young adults with Fanconi anemia.","date":"2021","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/33656536","citation_count":29,"is_preprint":false},{"pmid":"35362043","id":"PMC_35362043","title":"Overcoming CAR-Mediated CD19 Downmodulation and Leukemia Relapse with T Lymphocytes Secreting Anti-CD19 T-cell Engagers.","date":"2022","source":"Cancer immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/35362043","citation_count":28,"is_preprint":false},{"pmid":"38608514","id":"PMC_38608514","title":"Intratumoral CD38+CD19+B cells associate with poor clinical outcomes and immunosuppression in patients with pancreatic ductal adenocarcinoma.","date":"2024","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/38608514","citation_count":26,"is_preprint":false},{"pmid":"26103922","id":"PMC_26103922","title":"BAFF-driven autoimmunity requires CD19 expression.","date":"2015","source":"Journal of autoimmunity","url":"https://pubmed.ncbi.nlm.nih.gov/26103922","citation_count":26,"is_preprint":false},{"pmid":"29296937","id":"PMC_29296937","title":"Mst1 positively regulates B-cell receptor signaling via CD19 transcriptional levels.","date":"2016","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/29296937","citation_count":26,"is_preprint":false},{"pmid":"20445561","id":"PMC_20445561","title":"B-cell maturation and antibody responses in individuals carrying a mutated CD19 allele.","date":"2010","source":"Genes and immunity","url":"https://pubmed.ncbi.nlm.nih.gov/20445561","citation_count":26,"is_preprint":false},{"pmid":"30478153","id":"PMC_30478153","title":"CD19-positive antibody-secreting cells provide immune memory.","date":"2018","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/30478153","citation_count":25,"is_preprint":false},{"pmid":"26629482","id":"PMC_26629482","title":"Anti-CD19 Monoclonal Antibodies: a New Approach to Lymphoma Therapy.","date":"2015","source":"International journal of molecular and cellular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/26629482","citation_count":25,"is_preprint":false},{"pmid":"12002767","id":"PMC_12002767","title":"CD19 expression and growth inhibition of tumours in human multiple myeloma.","date":"2002","source":"Leukemia & lymphoma","url":"https://pubmed.ncbi.nlm.nih.gov/12002767","citation_count":24,"is_preprint":false},{"pmid":"24023523","id":"PMC_24023523","title":"Targeting CD19 in B-cell lymphoma: emerging role of SAR3419.","date":"2013","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/24023523","citation_count":24,"is_preprint":false},{"pmid":"36469024","id":"PMC_36469024","title":"Compromised antigen binding and signaling interfere with bispecific CD19 and CD79a chimeric antigen receptor function.","date":"2023","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/36469024","citation_count":23,"is_preprint":false},{"pmid":"35280988","id":"PMC_35280988","title":"CD19-Targeted Immunotherapies for Diffuse Large B-Cell Lymphoma.","date":"2022","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/35280988","citation_count":22,"is_preprint":false},{"pmid":"29472447","id":"PMC_29472447","title":"Dock8 regulates BCR signaling and activation of memory B cells via WASP and CD19.","date":"2018","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/29472447","citation_count":22,"is_preprint":false},{"pmid":"28306193","id":"PMC_28306193","title":"Diphtheria toxin-based anti-human CD19 immunotoxin for targeting human CD19+ tumors.","date":"2017","source":"Molecular oncology","url":"https://pubmed.ncbi.nlm.nih.gov/28306193","citation_count":22,"is_preprint":false},{"pmid":"35610089","id":"PMC_35610089","title":"Developing lisocabtagene maraleucel chimeric antigen receptor T-cell manufacturing for improved process, product quality and consistency across CD19+ hematologic indications.","date":"2022","source":"Cytotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/35610089","citation_count":21,"is_preprint":false},{"pmid":"37879074","id":"PMC_37879074","title":"CD19 occupancy with tafasitamab increases therapeutic index of CART19 cell therapy and diminishes severity of CRS.","date":"2024","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/37879074","citation_count":20,"is_preprint":false},{"pmid":"36494762","id":"PMC_36494762","title":"CD19+CD24highCD27+ B cell and interleukin 35 as potential biomarkers of disease activity in systemic lupus erythematosus patients.","date":"2022","source":"Advances in rheumatology (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/36494762","citation_count":20,"is_preprint":false},{"pmid":"36897251","id":"PMC_36897251","title":"Anti-CD19 CAR T-cell consolidation therapy combined with CD19+ feeding T cells and TKI for Ph+ acute lymphoblastic leukemia.","date":"2023","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/36897251","citation_count":19,"is_preprint":false},{"pmid":"36251156","id":"PMC_36251156","title":"Loop CD20/CD19 CAR-T cells eradicate B-cell malignancies efficiently.","date":"2022","source":"Science China. Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36251156","citation_count":18,"is_preprint":false},{"pmid":"37526512","id":"PMC_37526512","title":"Incidence of CD19-negative relapse after CD19-targeted immunotherapy in R/R BCP acute lymphoblastic leukemia: a review.","date":"2023","source":"Leukemia & lymphoma","url":"https://pubmed.ncbi.nlm.nih.gov/37526512","citation_count":18,"is_preprint":false},{"pmid":"33735268","id":"PMC_33735268","title":"Anti-CD19 CAR T cells potently redirected to kill solid tumor cells.","date":"2021","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/33735268","citation_count":18,"is_preprint":false},{"pmid":"35405368","id":"PMC_35405368","title":"Haploidentical Stem Cell Transplantation After TCR-αβ+ and CD19+ Cells Depletion In Children With Congenital Non-Malignant Disease.","date":"2022","source":"Transplantation and cellular therapy","url":"https://pubmed.ncbi.nlm.nih.gov/35405368","citation_count":18,"is_preprint":false},{"pmid":"31181422","id":"PMC_31181422","title":"Decreased number of CD19+CD24hiCD38hi regulatory B cells in Diabetic nephropathy.","date":"2019","source":"Molecular immunology","url":"https://pubmed.ncbi.nlm.nih.gov/31181422","citation_count":18,"is_preprint":false},{"pmid":"36409926","id":"PMC_36409926","title":"Rational Protein Design Yields a CD20 CAR with Superior Antitumor Efficacy Compared with CD19 CAR.","date":"2023","source":"Cancer immunology research","url":"https://pubmed.ncbi.nlm.nih.gov/36409926","citation_count":17,"is_preprint":false},{"pmid":"36636644","id":"PMC_36636644","title":"Extracellular Vesicles Expressing CD19 Antigen Improve Expansion and Efficacy of CD19-Targeted CAR-T Cells.","date":"2023","source":"International journal of nanomedicine","url":"https://pubmed.ncbi.nlm.nih.gov/36636644","citation_count":17,"is_preprint":false},{"pmid":"32104147","id":"PMC_32104147","title":"CD19+CD24hiCD38hi B Cell Dysfunction in Primary Biliary Cholangitis.","date":"2020","source":"Mediators of inflammation","url":"https://pubmed.ncbi.nlm.nih.gov/32104147","citation_count":17,"is_preprint":false},{"pmid":"24993505","id":"PMC_24993505","title":"CD19 as a molecular target in CNS autoimmunity.","date":"2014","source":"Acta neuropathologica","url":"https://pubmed.ncbi.nlm.nih.gov/24993505","citation_count":17,"is_preprint":false},{"pmid":"30467955","id":"PMC_30467955","title":"MiR-15a/16-1 deficiency induces IL-10-producing CD19+ TIM-1+ cells in tumor microenvironment.","date":"2018","source":"Journal of cellular and molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30467955","citation_count":17,"is_preprint":false},{"pmid":"39903124","id":"PMC_39903124","title":"CD19.CAR T-cell-derived extracellular vesicles express CAR and kill leukemic cells, contributing to antineoplastic therapy.","date":"2025","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/39903124","citation_count":16,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47973,"output_tokens":5128,"usd":0.11042,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13488,"output_tokens":4906,"usd":0.095045,"stage2_stop_reason":"end_turn"},"total_usd":0.205465,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1995,\n      \"finding\": \"CD19 forms a multimolecular complex on the B cell surface with complement receptor CR2 (CD21) and tetraspanin TAPA-1 (CD81). Cross-linking CD19 to membrane immunoglobulin (mIg) lowers by two orders of magnitude the number of mIg molecules that must be ligated to activate phospholipase C or induce DNA synthesis. CD19 is coupled via protein tyrosine kinases to PLC and PI3-kinase and interacts with the Src-type nonreceptor PTK Lyn.\",\n      \"method\": \"Biochemical co-association studies, crosslinking experiments, signaling assays (PLC activation, DNA synthesis, Ca2+ responses)\",\n      \"journal\": \"Annual review of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal biochemical methods (co-immunoprecipitation, functional crosslinking assays, kinase assays), replicated across labs\",\n      \"pmids\": [\"7542009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CD19 and CD22 reciprocally regulate tyrosine phosphorylation of Vav protein during B lymphocyte BCR signaling. CD19 crosslinking is more efficient than BCR crosslinking at inducing Vav phosphorylation; simultaneous crosslinking of CD19 with the BCR resulted in decreased Vav phosphorylation when CD22 was expressed. This differential regulation of Vav by CD19 and CD22 provides a molecular mechanism for adjusting BCR signaling thresholds.\",\n      \"method\": \"BCR crosslinking in CD22-deficient and CD19-deficient mouse B cells, immunoblotting for Vav tyrosine phosphorylation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout models (CD19-/- and CD22-/- mice) combined with biochemical phosphorylation assays, reciprocal loss-of-function comparison\",\n      \"pmids\": [\"9371816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CD19 is necessary for efficient activation of Akt kinase following BCR or Igβ crosslinking in B cells. In the absence of CD19, Akt kinase activity is reduced and transient. Coligation of CD19 with surface immunoglobulin leads to augmented Akt activity in a dose-dependent manner, placing CD19 as a key regulator of PI3K-dependent Akt activity and cell survival signaling.\",\n      \"method\": \"CD19-deficient B-lymphoma cell lines and CD19-deficient mouse splenic B cells; Akt kinase activity assays after BCR/Igβ crosslinking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — loss-of-function genetic model (CD19-/- cells) with direct kinase activity assays, dose-dependent coligation experiments\",\n      \"pmids\": [\"11042164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"CD19 establishes a Src-family kinase activation loop requiring Lyn for CD19 phosphorylation. In Lyn-deficient mice, CD19 deficiency suppresses hyperresponsive B cell phenotype and autoimmunity (serum autoantibodies and glomerulonephritis). CD19 deficiency in Lyn-/- mice reduced Fyn and other cellular protein tyrosine phosphorylation following BCR ligation while Syk phosphorylation remained normal, demonstrating that CD19 amplifies signals through Src family PTKs other than Lyn.\",\n      \"method\": \"Double-knockout mice (CD19/Lyn-/-); BCR-induced Ca2+ responses, tyrosine phosphorylation immunoblots, humoral immune response assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — compound genetic epistasis with double-knockout mouse model and multiple orthogonal biochemical and functional readouts\",\n      \"pmids\": [\"11509585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CD19 cytoplasmic tyrosines Y482 and Y513 are essential for all CD19 functions in vivo, including B1 and marginal zone B cell differentiation, T-dependent and -independent antibody responses, and germinal center B cell maturation/cell cycle progression. Mutation of these residues blocks germinal center maturation associated with retarded cell cycle progression.\",\n      \"method\": \"CD19-knockout mice expressing transgenic CD19 constructs with tyrosine mutations; in vivo immunization, flow cytometry, cell cycle analysis\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-directed mutagenesis in vivo with multiple functional readouts (B cell subsets, antibody responses, germinal center maturation, cell cycle)\",\n      \"pmids\": [\"12387743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Bruton's tyrosine kinase (Btk) physically associates with CD19 following BCR engagement in B cells. CD19 expression maintains Btk in an activated state following BCR engagement but is not required for initial Btk phosphorylation. CD19-induced intracellular Ca2+ responses require downstream Btk function. CD19 and Btk regulate partially overlapping but also independent signaling pathways.\",\n      \"method\": \"Co-immunoprecipitation of Btk with CD19 in A20 B cells; CD19-/- and Xid (Btk-mutant) compound mouse models; Ca2+ flux assays; PI3K and Akt activation assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP plus compound genetic epistasis (CD19-/- × Xid double mutant), multiple orthogonal biochemical readouts\",\n      \"pmids\": [\"12023340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD19 facilitates the pro-B to pre-B cell transition by promoting proliferation downstream of pre-BCR signaling. In CD19-/- mice, the large cycling pre-B cell fraction is reduced. Signaling through the pre-BCR is impaired in the absence of CD19, as shown by reduced activation of Bruton's tyrosine kinase and ERK/MAPK.\",\n      \"method\": \"CD19-/- mouse model; sublethal irradiation reconstitution experiments; BrdU labeling and cell cycle analysis; IL-7-dependent pre-B cell cultures; Btk and ERK activation assays\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout model with multiple orthogonal methods (cell cycle analysis, BrdU incorporation, kinase activation assays, in vitro culture)\",\n      \"pmids\": [\"14634103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CD21 (CR2) interaction with CD19 is necessary for coreceptor activity in humoral immunity. Knockin mice expressing mutant CR2 receptors that bind C3 ligands but cannot signal through CD19 showed significantly diminished germinal center B cell survival and secondary antibody titers, but B memory formation was less impaired than in complete CR deficiency.\",\n      \"method\": \"Knockin mouse model (Cr2-Delta/Delta-gfp); germinal center B cell survival analysis, antibody titer measurements, B memory assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockin model with separation-of-function mutation plus multiple immunological readouts\",\n      \"pmids\": [\"19706534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CD19 is required for TLR9-induced B cell activation. TLR9 ligands induce phosphorylation of CD19 through MYD88/PYK2/LYN complexes, which enables recruitment of PI3K and subsequent phosphorylation of Btk and Akt in human B cells with different kinetics than BCR signaling. Loss of one or both CD19 alleles impairs upregulation of CD86, TACI, and CD23 after TLR9 stimulation.\",\n      \"method\": \"CD19-deficient patient B cells (mono- and biallelic mutations); phospho-flow cytometry; immunoblotting; co-immunoprecipitation; lentiviral CD19 knockdown B-cell line; PI3K/AKT/BTK inhibitors\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — human genetic loss-of-function (patient samples with defined mutations) combined with pharmacological inhibition and co-IP, multiple orthogonal methods\",\n      \"pmids\": [\"26478008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Mst1 kinase positively regulates BCR signaling by modulating CD19 transcriptional levels. Mst1 upregulates CD19 mRNA via the transcription factor TEAD2, which directly binds to a consensus motif in the 3' UTR of cd19. Mst1-deficient mice show reduced BCR signaling concurrent with defective BCR clustering and B cell spreading, and defective MZ and germinal center B cell differentiation due to disruption of CD19-mediated Btk signaling.\",\n      \"method\": \"Mst1 knockout mouse model; TIRF microscopy for BCR clustering; chromatin immunoprecipitation/transcription factor binding assay (TEAD2 on cd19 3'UTR); Btk phosphorylation assays\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout with TIRF microscopy and transcription factor binding evidence, single lab, mechanistic pathway established\",\n      \"pmids\": [\"29296937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CD19 exon 2 variants generated by in-frame insertions or exon skipping (as resistance mechanisms after CAR T therapy) cause protein misfolding and retention in the endoplasmic reticulum rather than epitope loss per se. CD19 exon 2 variants acquire ER-specific high-mannose glycans but not Golgi-synthesized complex-type glycans, colocalize with ER markers, fail to bind the tetraspanin CD81, and instead interact with ER-resident chaperones (calnexin) and ER transporters.\",\n      \"method\": \"Retroviral transduction and genome editing to generate VSVg-tagged CD19 exon 2 variants; live-cell flow cytometry; pulse-chase glycosylation assays; alpha-mannosidase inhibitor assays; GFP fusion colocalization with ER markers; mass spectrometric profiling of CD19-interacting proteins\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal biochemical methods (glycosylation assays, subcellular localization, MS interactome) with functional validation (ADC killing resistance), rigorous controls\",\n      \"pmids\": [\"30104252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Hyperglycosylation of CD19 caused by loss of the Golgi-resident intramembrane protease SPPL3 in malignant B cells directly inhibits CAR T cell effector function and suppresses anti-tumor cytotoxicity, representing a post-translational mechanism of antigen escape. Conversely, over-expression of SPPL3 drives loss of CD19 protein.\",\n      \"method\": \"SPPL3 loss-of-function and overexpression in malignant B cells; in vitro CAR T cell cytotoxicity assays; glycosylation analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic manipulation (loss and gain of function) with direct functional CAR T cell killing assays, single lab, pre-clinical model\",\n      \"pmids\": [\"35690611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Cryo-EM structures of CD19 antigen bound to the FMC63 scFv (used in four FDA-approved CAR T therapies) and to SJ25C1 scFv were determined. Molecular dynamics simulations guided by structures enabled creation of lower- or higher-affinity binders. CAR T cells with different affinity binders exhibited distinct antigen density requirements for cytolysis and differed in propensity to trigger trogocytosis upon contacting tumor cells.\",\n      \"method\": \"Cryo-EM structure determination; molecular dynamics simulations; generation of affinity-tuned CAR variants; in vitro CAR T cell cytolysis assays at varying antigen densities; trogocytosis assays\",\n      \"journal\": \"Science immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure plus molecular dynamics plus functional CAR T cell validation with mutagenesis-derived affinity variants, multiple orthogonal methods in one study\",\n      \"pmids\": [\"36867678\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The FMC63 conformational epitope on the CD19 extracellular domain spans spatially adjacent but genetically distant loops encoded by exons 3 and 4. The epitopes of FMC63, 4G7-2E3, and 3B10 antibodies are partially overlapping but distinct, near the B43 epitope. All N-linked glycosylation sites can be removed from CD19 while retaining antibody binding in a yeast display context.\",\n      \"method\": \"Comprehensive single-site saturation mutagenesis library of CD19 extracellular domain; yeast display; flow cytometric screening for antibody binding; thermal stability selection\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — comprehensive saturation mutagenesis with functional binding screen, rigorous epitope mapping\",\n      \"pmids\": [\"31702909\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Enforced CD19 expression in tumorigenic human myeloma cells (which normally lack CD19) inhibits growth in vitro and reduces tumorigenicity in vivo. This growth-inhibitory effect requires the CD19 cytoplasmic signaling domain, as a truncated CD19 lacking this domain does not produce the effect, establishing CD19 signaling as a growth suppressor in myeloma.\",\n      \"method\": \"CD19 transfection of KMS-5 myeloma cell line; in vitro growth and anchorage-independent colony assays; in vivo tumorigenicity in SCID-hIL-6 transgenic mice; truncation mutant controls\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — gain-of-function transfection with cytoplasmic domain truncation control, both in vitro and in vivo functional readouts\",\n      \"pmids\": [\"10552966\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CD19 deficiency in humans impairs selection of immunoglobulin reactivity in memory B cells. CD19-deficient patients show decreased activation-induced cytidine deaminase and increased uracil-DNA glycosylase 2 activity but decreased mismatch repair during somatic hypermutation, demonstrating a role for CD19 signaling in transcriptional regulation of DNA repair genes during germinal center reactions.\",\n      \"method\": \"CD19-deficient patient samples (n=8); flow cytometry of B cell subsets; molecular analysis of IgA and IgG transcripts; somatic hypermutation analysis; B cell activation studies\",\n      \"journal\": \"The Journal of allergy and clinical immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetic loss-of-function (defined patient mutations), molecular transcript analysis, single study\",\n      \"pmids\": [\"24418477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CAR-induced internalization of CD19 is coupled with lysosome-mediated degradation, leading to emergence of transiently CD19-negative leukemic cells that evade CAR T19 immune responses. In contrast, bispecific T-cell engager (STAb-T19) strategy does not induce CD19 downmodulation and forms canonical immunological synapses, preventing this escape mechanism.\",\n      \"method\": \"In vitro coculture of CAR-T19 and STAb-T19 cells with leukemic cells; CD19 surface expression tracking; lysosome inhibitor assays; immunological synapse imaging; in vivo patient-derived xenograft mouse models\",\n      \"journal\": \"Cancer immunology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mechanistic comparison with lysosome inhibition, live imaging of synapse, in vivo validation, single lab\",\n      \"pmids\": [\"35362043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Dock8 regulates BCR signaling through CD19. Dock8 deficiency reduces phosphorylated CD19 (pCD19) and phosphorylated Btk (pBtk) levels. WASP positively regulates cd19 transcription, and Dock8 regulates cd19 transcription through WASP. Dock8-deficient B cells show defective BCR clustering and B cell spreading on stimulatory lipid bilayers.\",\n      \"method\": \"Dock8 knockout mouse model; peripheral blood from Dock8-deficient patients; TIRF microscopy; confocal microscopy for BCR clustering/spreading; phospho-flow cytometry for pCD19 and pBtk\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout (mouse and human) with imaging and phospho-flow, single lab, mechanistic pathway established\",\n      \"pmids\": [\"29472447\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CD19 is a transmembrane co-receptor that forms a signaling complex with CD21 (CR2), CD81 (TAPA-1), and CD225 on B cells; upon BCR engagement, it is phosphorylated on cytoplasmic tyrosines Y482 and Y513 by Lyn, establishing a Src-family PTK amplification loop that recruits PI3K, activates Akt and Btk, promotes Vav phosphorylation, and lowers the B cell activation threshold by orders of magnitude; it also integrates TLR9 signaling via MYD88/PYK2/LYN/PI3K/BTK and regulates CD19 transcription through Mst1-TEAD2 and WASP/Dock8 axes, with the cytoplasmic signaling domain required for growth regulation in plasma cells, and CD19 surface localization dependent on interaction with CD81 such that exon 2 alterations cause ER misfolding and loss of surface expression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CD19 is a B-cell transmembrane co-receptor that lowers the antigen-receptor activation threshold and amplifies B-cell signaling, integrating multiple inputs to govern B-cell development, germinal center maturation, and humoral immunity [#0, #4]. On the cell surface it assembles into a multimolecular complex with complement receptor CR2 (CD21) and the tetraspanin TAPA-1 (CD81); cross-linking CD19 to membrane immunoglobulin reduces by two orders of magnitude the number of receptors that must be engaged to activate phospholipase C and drive DNA synthesis, and the CR2-CD19 interaction is required for germinal center B-cell survival and secondary antibody responses [#0, #7]. Signal amplification depends on a Src-family kinase loop in which Lyn phosphorylates CD19, which in turn sustains phosphorylation of Fyn and other Src-family PTKs to drive a hyperresponsive, autoimmune-prone phenotype [#3]. Phosphorylated CD19 couples to PI3K, promoting efficient and sustained Akt activation, physically associates with Btk to maintain it in an active state for intracellular Ca2+ responses, and reciprocally regulates Vav phosphorylation to tune BCR signaling thresholds [#1, #2, #5]. The cytoplasmic tyrosines Y482 and Y513 are essential for all CD19 functions in vivo, including B1 and marginal zone B-cell differentiation, T-dependent and -independent antibody responses, and germinal-center cell-cycle progression [#4], and the cytoplasmic signaling domain confers growth suppression when CD19 is expressed in myeloma cells [#14]. Beyond the BCR, CD19 is required for TLR9-induced activation, becoming phosphorylated via MYD88/PYK2/LYN to recruit PI3K and activate Btk and Akt [#8]. CD19 transcription is positively controlled by an Mst1-TEAD2 axis acting on the cd19 3'UTR and by a WASP/Dock8 pathway, both of which feed back to support CD19-mediated Btk signaling and BCR clustering [#9, #17]. Human CD19 deficiency impairs somatic hypermutation and selection of immunoglobulin reactivity in memory B cells [#15]. Surface localization requires CD81 binding: exon 2 alterations prevent CD81 association, trap CD19 with calnexin in the ER as a high-mannose glycoform, and abolish surface expression [#10]. The extracellular domain presents a conformational FMC63 epitope spanning exon 3- and exon 4-encoded loops, structurally defined by cryo-EM, and CD19 antigen density and glycosylation state critically modulate CAR T-cell cytolysis, trogocytosis, and antigen escape [#10, #11, #12, #13, #16].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established CD19 as a threshold-setting co-receptor by defining its surface complex and signaling couplings, answering how B cells could be activated by far fewer antigen-receptor engagements.\",\n      \"evidence\": \"Biochemical co-association, crosslinking, and signaling assays (PLC, DNA synthesis, Ca2+) in B cells\",\n      \"pmids\": [\"7542009\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of the CD19/CD21/CD81 complex not resolved\", \"Direct kinase-substrate steps inferred rather than fully reconstituted\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showed CD19 and CD22 reciprocally control Vav phosphorylation, providing a molecular rheostat for adjusting BCR signaling thresholds.\",\n      \"evidence\": \"BCR crosslinking in CD19-/- and CD22-/- mouse B cells with Vav phospho-immunoblotting\",\n      \"pmids\": [\"9371816\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect link between CD19 and Vav not defined\", \"Downstream consequences of altered Vav phosphorylation not quantified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstrated that CD19 signaling can suppress growth in non-B-lineage myeloma cells, revealing a context-dependent growth-regulatory function dependent on the cytoplasmic domain.\",\n      \"evidence\": \"CD19 transfection of myeloma cells with cytoplasmic truncation controls; in vitro growth and SCID xenograft assays\",\n      \"pmids\": [\"10552966\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effector pathway of growth suppression not identified\", \"Relevance to normal plasma cells unaddressed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Placed CD19 upstream of PI3K-Akt survival signaling and within a Lyn-dependent Src-family amplification loop, mechanistically linking the co-receptor to hyperresponsiveness and autoimmunity.\",\n      \"evidence\": \"CD19-/- B cells and CD19/Lyn double-knockout mice; Akt kinase assays, Ca2+ responses, phospho-immunoblots, autoimmunity readouts\",\n      \"pmids\": [\"11042164\", \"11509585\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PI3K recruitment site on CD19 not defined in these studies\", \"How Lyn-phosphorylated CD19 amplifies other Src-family PTKs mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified the essential cytoplasmic tyrosines and the physical CD19-Btk association, establishing the specific signaling residues and a Btk-maintenance mechanism required for in vivo B-cell function.\",\n      \"evidence\": \"CD19-/- mice reconstituted with Y482/Y513 mutants; co-IP of Btk with CD19; CD19-/- x Xid compound mice; Ca2+ and kinase assays\",\n      \"pmids\": [\"12387743\", \"12023340\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of effectors recruited specifically to Y482 versus Y513 not delineated\", \"Mechanism by which CD19 sustains active Btk not structurally defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Extended CD19 function to early B-cell development, showing it promotes the pro-B to pre-B transition via pre-BCR-driven proliferation.\",\n      \"evidence\": \"CD19-/- mice; BrdU/cell-cycle analysis; IL-7 pre-B cultures; Btk and ERK activation assays\",\n      \"pmids\": [\"14634103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether pre-BCR-CD19 coupling uses the same complex as mature BCR not established\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that CR2 must signal through CD19 for coreceptor activity in humoral immunity, separating ligand binding from signaling output.\",\n      \"evidence\": \"Cr2-Delta/Delta-gfp knockin mice with separation-of-function mutation; germinal center, antibody titer, and memory assays\",\n      \"pmids\": [\"19706534\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular interface enabling CR2-to-CD19 signal transfer not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Linked human CD19 signaling to the somatic hypermutation machinery, showing it regulates AID, UNG2, and mismatch repair activities during memory B-cell selection.\",\n      \"evidence\": \"CD19-deficient patient B cells; SHM and immunoglobulin transcript analysis; flow cytometry\",\n      \"pmids\": [\"24418477\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Transcriptional pathway from CD19 to DNA-repair gene regulation not mapped\", \"Single patient cohort\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed CD19 is also required for TLR9 signaling, integrating innate and antigen-receptor pathways through a distinct MYD88/PYK2/LYN-initiated phosphorylation route.\",\n      \"evidence\": \"CD19-deficient patient B cells, phospho-flow, co-IP, knockdown lines, PI3K/AKT/BTK inhibitors\",\n      \"pmids\": [\"26478008\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TLR9-driven CD19 phosphorylation differs in kinetics/sites from BCR-driven phosphorylation not fully resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified transcriptional control of CD19 by an Mst1-TEAD2 axis and a WASP/Dock8 pathway, showing CD19 abundance is actively set to tune BCR signaling and B-cell clustering.\",\n      \"evidence\": \"Mst1 and Dock8 knockout mice and patient cells; TIRF/confocal imaging; TEAD2 3'UTR binding; phospho-CD19/Btk assays\",\n      \"pmids\": [\"29296937\", \"29472447\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab transcriptional mechanisms\", \"Direct versus indirect TEAD2 and WASP effects on cd19 not fully separated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined CD81-dependent surface trafficking of CD19 and the molecular basis of exon 2-driven CAR T resistance as ER misfolding rather than epitope loss.\",\n      \"evidence\": \"VSVg-tagged exon 2 variants; pulse-chase glycosylation, ER colocalization, MS interactome (calnexin), ADC killing assays\",\n      \"pmids\": [\"30104252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CD19-CD81 association not resolved\", \"Folding intermediates and quality-control kinetics not detailed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapped the conformational FMC63 epitope to exon 3/4-encoded loops and showed N-glycosylation is dispensable for antibody binding, informing CAR and antibody recognition.\",\n      \"evidence\": \"Saturation mutagenesis library, yeast display, flow cytometric epitope mapping, thermal stability selection\",\n      \"pmids\": [\"31702909\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native membrane context of the epitope not addressed\", \"Relationship of epitope loops to coreceptor signaling untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed post-translational and trafficking mechanisms of antigen escape: SPPL3-dependent hyperglycosylation blunts CAR T killing, and CAR-induced lysosomal degradation of CD19 yields transiently antigen-negative cells.\",\n      \"evidence\": \"SPPL3 loss/gain in B cells with CAR T cytotoxicity assays; CAR-T19 vs STAb-T19 cocultures with lysosome inhibition, synapse imaging, and PDX models\",\n      \"pmids\": [\"35690611\", \"35362043\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab pre-clinical models\", \"In vivo clinical relevance of SPPL3-driven escape not established\", \"Reversibility kinetics of CD19 downmodulation not fully quantified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Provided cryo-EM structures of CD19 bound to clinically used scFvs and showed affinity tuning dictates antigen-density thresholds and trogocytosis, connecting CD19 structure to CAR T efficacy.\",\n      \"evidence\": \"Cryo-EM, molecular dynamics, affinity-variant CARs, cytolysis assays at varying antigen densities, trogocytosis assays\",\n      \"pmids\": [\"36867678\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length CD19 in its native coreceptor complex not determined\", \"In vivo correlation of affinity tuning with durable response not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the CD19 cytoplasmic signaling module, its transcriptional regulators, and its CD81-dependent trafficking are mechanistically integrated within the native coreceptor complex at atomic resolution remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the assembled CD19/CD21/CD81 signaling complex\", \"Direct CD19 cytoplasmic-domain interactome incompletely defined\", \"Causal hierarchy among transcriptional inputs (Mst1-TEAD2, WASP/Dock8) unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 4, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 4, 8]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 3, 5]}\n    ],\n    \"complexes\": [\n      \"CD19/CD21(CR2)/CD81(TAPA-1) B-cell coreceptor complex\"\n    ],\n    \"partners\": [\n      \"CD21\",\n      \"CD81\",\n      \"LYN\",\n      \"BTK\",\n      \"VAV\",\n      \"CR2\",\n      \"CALNEXIN\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":10,"faith_total":10,"faith_pct":100.0}}