TOX2

TOX2 is an HMG-box transcription factor that programs lymphocyte identity, persistence, and functional state across multiple immune cell lineages. In CD8+ T cells, TOX2 cooperates with TOX downstream of NFAT to impose the exhaustion transcriptional program—dual knockout of both factors opens chromatin at NFκB and bZIP motifs, restores cytokine production, and enhances antitumor CAR T cell efficacy—yet TOX2 also independently promotes central memory T cell differentiation by binding TCM-associated gene promoters (PMID:31152140, PMID:37467321). In T follicular helper cells, TOX2 directly binds and activates the Bcl6 locus to establish a feed-forward loop that drives Tfh differentiation and sustains germinal center and memory Tfh populations, while in gut ILC3 it supports tissue residency by transcriptionally upregulating Hexokinase-2 to enable glycolytic metabolic adaptation (PMID:31732165, PMID:34623911, PMID:38677292). In the nucleus of T-ALL cells, TOX2 forms a repressive complex with TOX, the corepressor LCOR, and the deacetylase HDAC3 to suppress HAVCR2 (TIM3) transcription, with its nuclear retention regulated by SIRT1-mediated deacetylation and TBK1-dependent phosphorylation (PMID:39080376).

1. 2014 Medium

   Establishing TOX2 as a transcription factor active in early lymphocyte development, this work showed that TOX2 directly upregulates TBX21 to control NK cell developmental transitions, a function independent of ETS-1.

   Evidence shRNA knockdown and T-BET rescue in cord blood CD34+ progenitor-derived NK cell differentiation assays

   PMID:25352127

   Open questions at the time

   • Direct binding of TOX2 to the TBX21 promoter was not demonstrated by ChIP
   • Role of TOX2 in mature NK cell function beyond developmental transitions is unknown
   • Whether TOX2 controls NK development in vivo was not tested
2. 2019 High

   Two studies established TOX2 as a key transcriptional regulator in CD4+ and CD8+ T cell fate decisions: in CD8+ T cells, TOX2 cooperates with TOX downstream of NFAT to enforce the exhaustion program, while in CD4+ T cells, TOX2 directly binds the Bcl6 locus to initiate a feed-forward loop driving Tfh differentiation.

   Evidence Tox/Tox2 double-KO CAR T cells with ATAC-seq, flow cytometry, and in vivo tumor models (CD8+ exhaustion); ChIP-seq, ATAC-seq, and Tox2−/− mice with ectopic overexpression (Tfh differentiation)

   PMID:31152140 PMID:31732165

   Open questions at the time

   • Whether TOX2 has distinct or redundant chromatin targets compared to TOX was not resolved
   • The precise DNA-binding specificity of TOX2's HMG-box domain versus TOX was not defined
   • Relative contributions of TOX versus TOX2 to exhaustion versus memory programs remained unclear
3. 2021 Medium

   Extending the Tfh role, TOX2 was shown to be required not only for initial Tfh differentiation but also for maintaining germinal center Tfh identity and generating durable memory Tfh populations capable of recall responses.

   Evidence Tox2-deficient mice with reimmunization and heterologous influenza infection; Tox2 overexpression in human GC Tfh cells preventing TH1 conversion

   PMID:34623911

   Open questions at the time

   • Direct TOX2 chromatin targets in GC Tfh versus pre-Tfh were not distinguished
   • Whether TOX2 collaborates with the same or different cofactors in GC Tfh maintenance is unknown
4. 2023 Medium

   Two studies reframed TOX2's functional versatility: in NKTL, RUNX3 drives TOX2 expression through a super-enhancer to activate the oncogenic effector PRL-3; separately, in human CAR T cells, loss of TET2 elevates TOX2 expression and TOX2 promotes central memory T cell differentiation by binding TCM gene promoters, distinguishing its memory-promoting role from its exhaustion-associated function.

   Evidence ChIP-PCR, CRISPR-dCas9 SE interference, xenograft models (NKTL); TET2 knockdown with ATAC-seq, TOX2 ChIP-seq, shRNA in human CAR T cells (TCM)

   PMID:37032358 PMID:37467321

   Open questions at the time

   • Whether the RUNX3–TOX2 super-enhancer axis operates in non-malignant lymphocytes is untested
   • How TOX2 discriminates between memory versus exhaustion target gene sets is mechanistically undefined
   • The relationship between TET2-mediated demethylation at the TOX2 locus and TOX2 protein activity is correlative
5. 2024 High

   Two advances revealed TOX2 functions in innate lymphoid cells and in leukemic gene repression: in gut ILC3, TOX2 promotes tissue residency by transcriptionally activating Hexokinase-2 to support glycolytic metabolism required for protein translation; in T-ALL, nuclear TOX2 forms a repressive complex with TOX, LCOR, and HDAC3 to suppress HAVCR2 (TIM3), with nuclear-cytoplasmic shuttling controlled by SIRT1-mediated deacetylation and TBK1 phosphorylation.

   Evidence Tox2−/− mice with scRNA-seq, HK2 rescue, and Citrobacter rodentium infection (ILC3); Co-IP, luciferase reporter, shRNA, subcellular fractionation, and xenograft model (T-ALL)

   PMID:38677292 PMID:39080376

   Open questions at the time

   • Whether the TOX2–LCOR–HDAC3 repressive complex operates in normal T cells or is specific to T-ALL is unknown
   • The acetylation sites on TOX2 targeted by SIRT1 have not been mapped
   • Whether TOX2's glycolytic reprogramming role extends to other tissue-resident lymphocyte populations is untested

• Key unresolved questions include how TOX2's HMG-box domain selects among its diverse target loci in different lineage contexts, the structural basis for TOX2–TOX heterodimerization, and whether TOX2 post-translational modifications (acetylation, phosphorylation) gate its transcriptional outputs in non-malignant lymphocyte subsets.
• No structural model of TOX2 or the TOX–TOX2 complex exists
• Genome-wide binding maps in primary cells lack functional validation of individual target genes
• Post-translational regulation of TOX2 has only been studied in T-ALL cells