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The transcription factors nuclear factor of activated T cells (NFAT) and activator protein 1 (AP-1; Fos-Jun) cooperate to promote the effector functions of T cells, but NFAT in the absence of AP-1 imposes a negative feedback program of T cell hyporesponsiveness (exhaustion). Here, we show that basic leucine zipper ATF-like transcription factor (BATF) and interferon regulatory factor 4 (IRF4) cooperate to counter T cell exhaustion in mouse tumor models. Overexpression of BATF in CD8+ T cells expressing a chimeric antigen receptor (CAR) promoted the survival and expansion of tumor-infiltrating CAR T cells, increased the production of effector cytokines, decreased the expression of inhibitory receptors and the exhaustion-associated transcription factor TOX and supported the generation of long-lived memory T cells that controlled tumor recurrence. These responses were dependent on BATF-IRF interaction, since cells expressing a BATF variant unable to interact with IRF4 did not survive in tumors and did not effectively delay tumor growth. BATF may improve the antitumor responses of CAR T cells by skewing their phenotypes and transcriptional profiles away from exhaustion and towards increased effector function.

T cells expressing chimeric antigen receptors (CAR T cells) have shown impressive therapeutic efficacy against leukemias and lymphomas. However, they have not been as effective against solid tumors because they become hyporesponsive (“exhausted” or “dysfunctional”) within the tumor microenvironment, with decreased cytokine production and increased expression of several inhibitory surface receptors. Here we define a transcriptional network that mediates CD8 + T cell exhaustion. We show that the high-mobility group (HMG)-box transcription factors TOX and TOX2, as well as members of the NR4A family of nuclear receptors, are targets of the calcium/calcineurin-regulated transcription factor NFAT, even in the absence of its partner AP-1 (FOS-JUN). Using a previously established CAR T cell model, we show that TOX and TOX2 are highly induced in CD8 + CAR + PD-1 high TIM3 high (“exhausted”) tumor-infiltrating lymphocytes (CAR TILs), and CAR TILs deficient in both TOX and TOX2 ( Tox DKO) are more effective than wild-type (WT), TOX-deficient, or TOX2-deficient CAR TILs in suppressing tumor growth and prolonging survival of tumor-bearing mice. Like NR4A-deficient CAR TILs, Tox DKO CAR TILs show increased cytokine expression, decreased expression of inhibitory receptors, and increased accessibility of regions enriched for motifs that bind activation-associated nuclear factor κB (NFκB) and basic region-leucine zipper (bZIP) transcription factors. These data indicate that Tox and Nr4a transcription factors are critical for the transcriptional program of CD8 + T cell exhaustion downstream of NFAT. We provide evidence for positive regulation of NR4A by TOX and of TOX by NR4A, and suggest that disruption of TOX and NR4A expression or activity could be promising strategies for cancer immunotherapy.

T cells expressing chimeric antigen receptors (CAR T cells) have shown impressive therapeutic efficacy against leukemias and lymphomas. However, they have not been as effective against solid tumors because they become hyporesponsive ("exhausted" or "dysfunctional") within the tumor microenvironment, with decreased cytokine production and increased expression of several inhibitory surface receptors. Here we define a transcriptional network that mediates CD8

Cooperative interactions among transcription factors are essential for gene transcription. We previously showed that NFAT and AP-1 (Fos-Jun) transcription factors cooperate to promote the effector functions of T cells, but that under conditions where it is unable to cooperate with AP-1, NFAT imposes a negative feedback programme of T cell hyporesponsiveness (“exhaustion”). Here we show that BATF and IRF4 cooperate to counter T cell exhaustion. Overexpression of Batf in CD8+ T cells expressing a chimeric antigen receptor (CAR) promoted the survival and expansion of tumour-infiltrating CAR T cells, increased their production of effector cytokines, decreased their expression of inhibitory receptors and the exhaustion-associated transcription factor TOX, and led to the generation of long-lived memory T cells that controlled tumour recurrence. These responses were dependent on the BATF-IRF interaction, since cells expressing a Batf mutant unable to interact with Irf4 did not survive in tumours and did not effectively delay tumour growth. We suggest that BATF overexpression is a therapeutically viable option for improving the anti-tumour responses of CAR TILs, by skewing their phenotypes and transcriptional profiles away from exhaustion and towards increased effector function.

TET enzymes facilitate DNA demethylation by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and other oxidation products in DNA. Loss-of-function mutations in TET enzymes are associated with increased proliferation and increased stem cell function in many cellular lineages. Moreover, there are several hints that inhibition of TET enzymes in tumor-infiltrating T cells might enhance anti tumor immune responses in solid tumors. For instance, TET2 deficiency in mouse T cells increased the number of CD8+ central memory T cells, and TET deficiency human CD8 chimeric antigen receptor (CAR) T cells increased their antigen-specific proliferation and capacity to reject tumor cells in a patient with chronic lymphocytic leukemia. Furthermore, we previously showed that TET deficiency in regulatory T cells decreased the stability of Foxp3 expression; hence TET deficiency would be expected to counter the ability of regulatory T cells to suppress anti-tumor responses. In this study, we found that TET loss of function in CD8 TILs indeed slowed tumor growth and promoted anti tumor responses in a mouse CAR T cell model. The function of TET proteins and other Fe(II) and a-ketoglutarate dependent dioxygenases is inhibited by L-2-Hydroxyglutarate (L2HG), which is normally kept at low levels by the enzyme L-2HG dehydrogenase (L2HGDH). We found that when CAR T cells were rendered low in TET activity in any one of three ways: (i) deficiency of the TET enzymes, (ii) depletion of L2HGDH and (iii) pretreatment of L2HG, they showed decreased expression of inhibitory receptors as well as increased secretion of inflammatory cytokines. Based on these results, we suggest that TET inhibition in T cells might be a promising general approach in cancer immunotherapy.