An Immunotherapeutic CD137 Agonist Releases Eomesodermin from ThPOK Repression in CD4 T Cells

Agonists to the TNF/TNFR costimulatory receptors CD134 (OX40) and CD137 (4-1BB) elicit antitumor immunity. Dual costimulation with anti-CD134 plus anti-CD137 is particularly potent because it programs cytotoxic potential in CD8⁺ and CD4⁺ T cells. Cytotoxicity in dual-costimulated CD4 T cells depends on the T-box transcription factor eomesodermin (Eomes), which we report is induced via a mechanism that does not rely on IL-2, in contrast to CD8⁺ CTL, but rather depends on the CD8 T cell lineage commitment transcription factor Runx3, which supports Eomes expression in mature CD8⁺ CTLs. Further, Eomes and Runx3 were indispensable for dual-costimulated CD4 T cells to mediate antitumor activity in an aggressive melanoma model. Runx3 is also known to be expressed in standard CD4 Th1 cells where it fosters IFN-γ expression; however, the CD4 T cell lineage commitment factor ThPOK represses transcription of Eomes and other CD8 lineage genes, such as Cd8a Hence, CD4 T cells can differentiate into Eomes⁺ cytotoxic CD4⁺CD8⁺ double-positive T cells by terminating ThPOK expression. In contrast, dual-costimulated CD4 T cells express Eomes, despite the continued expression of ThPOK and the absence of CD8α, indicating that Eomes is selectively released from ThPOK repression. Finally, although Eomes was induced by CD137 agonist, but not CD134 agonist, administered individually, CD137 agonist failed to induce CD134^-/- CD4 T cells to express Eomes or Runx3, indicating that both costimulatory pathways are required for cytotoxic Th1 programming, even when only CD137 is intentionally engaged with a therapeutic agonist.

Costimulation Endows Immunotherapeutic CD8 T Cells with IL-36 Responsiveness during Aerobic Glycolysis

CD134- and CD137-primed CD8 T cells mount powerful effector responses upon recall, but even without recall these dual-costimulated T cells respond to signal 3 cytokines such as IL-12. We searched for alternative signal 3 receptor pathways and found the IL-1 family member IL-36R. Although IL-36 alone did not stimulate effector CD8 T cells, in combination with IL-12, or more surprisingly IL-2, it induced striking and rapid TCR-independent IFN-γ synthesis. To understand how signal 3 responses functioned in dual-costimulated T cells we showed that IL-2 induced IL-36R gene expression in a JAK/STAT-dependent manner. These data help delineate a sequential stimulation process where IL-2 conditioning must precede IL-36 for IFN-γ synthesis. Importantly, this responsive state was transient and functioned only in effector T cells capable of aerobic glycolysis. Specifically, as the effector T cells metabolized glucose and consumed O2, they also retained potential to respond through IL-36R. This suggests that T cells use innate receptor pathways such as the IL-36R/axis when programmed for aerobic glycolysis. To explore a function for IL-36R in vivo, we showed that dual costimulation therapy reduced B16 melanoma tumor growth while increasing IL-36R gene expression. In summary, cytokine therapy to eliminate tumors may target effector T cells, even outside of TCR specificity, as long as the effectors are in the correct metabolic state.

Tumor-Unrelated CD4 T Cell Help Augments CD134 plus CD137 Dual Costimulation Tumor Therapy

The ability of immune-based cancer therapies to elicit beneficial CD8(+) CTLs is limited by tolerance pathways that inactivate tumor-specific CD4 Th cells. A strategy to bypass this problem is to engage tumor-unrelated CD4 Th cells. Thus, CD4 T cells, regardless of their specificity per se, can boost CD8(+) CTL priming as long as the cognate epitopes are linked via presentation on the same dendritic cell. In this study, we assessed the therapeutic impact of engaging tumor-unrelated CD4 T cells during dual costimulation with CD134 plus CD137 that provide help via the above-mentioned classical linked pathway, as well as provide nonlinked help that facilitates CTL function in T cells not directly responding to cognate Ag. We found that engagement of tumor-unrelated CD4 Th cells dramatically boosted the ability of dual costimulation to control the growth of established B16 melanomas. Surprisingly, this effect depended upon a CD134-dependent component that was extrinsic to the tumor-unrelated CD4 T cells, suggesting that the dual costimulated helper cells are themselves helped by a CD134(+) cell(s). Nevertheless, the delivery of therapeutic help tracked with an increased frequency of tumor-infiltrating granzyme B(+) effector CD8 T cells and a reciprocal decrease in Foxp3(+)CD4(+) cell frequency. Notably, the tumor-unrelated CD4 Th cells also infiltrated the tumors, and their deletion several days following initial T cell priming negated their therapeutic impact. Taken together, dual costimulation programs tumor-unrelated CD4 T cells to deliver therapeutic help during both the priming and effector stages of the antitumor response.

CD134 plus CD137 dual costimulation induces Eomesodermin in CD4 T cells to program cytotoxic Th1 differentiation

Cytotoxic CD4 Th1 cells are emerging as a therapeutically useful T cell lineage that can effectively target tumors, but until now the pathways that govern their differentiation have been poorly understood. We demonstrate that CD134 (OX40) costimulation programs naive self- and virus-reactive CD4 T cells to undergo in vivo differentiation into cytotoxic Th1 effectors. CD137 (4-1BB) costimulation maximized clonal expansion, and IL-2 was necessary for cytotoxic Th1 differentiation. Importantly, the T-box transcription factor Eomesodermin was critical for inducing the cytotoxic marker granzyme B. CD134 plus CD137 dual costimulation also imprinted a cytotoxic phenotype on bystanding CD4 T cells. Thus, to our knowledge, the current study identifies for the first time a specific costimulatory pathway and an intracellular mechanism relying on Eomesodermin that induces both Ag-specific and bystander cytotoxic CD4 Th1 cells. This mechanism might be therapeutically useful because CD134 plus CD137 dual costimulation induced CD4 T cell-dependent tumoricidal function in a mouse melanoma model.

The E3 ubiquitin ligase Cbl-b regulates expansion but not functional activity of self-reactive CD4 T cells

Cbl-b is an E3 ubiquitin ligase that limits Ag responsiveness in T cells by targeting TCR-inducible signaling molecules. Cbl-b deficiency thus renders T cells hyperresponsive to antigenic stimulation and predisposes individuals toward developing autoimmunity. In part because Cbl-b(-/-) T cells do not require CD28 costimulation to become activated, and insufficient costimulation is a critical parameter that confers anergy induction over effector differentiation, it has been hypothesized that Cbl-b(-/-) T cells are resistant to anergy. This possibility has been supported in models in which anergy is normally induced in vitro, or in vivo following exposure to soluble Ag boluses. In the current study, we characterized the response of Cbl-b(-/-) CD4 T cells in an in vivo system in which anergy is normally induced by a constitutively expressed peripheral self-Ag. Cbl-b expression increased in self-Ag-induced anergic wild-type CD4 T cells, and Cbl-b(-/-) CD4 T cells underwent more robust proliferation and expansion upon initially encountering cognate self-Ag compared with wild-type counterparts. Nevertheless, both wild-type and Cbl-b(-/-) CD4 T cells ultimately developed the same impaired ability to respond to antigenic restimulation. The more extensive expansion that occurred during the initial induction of anergy did, however, allow the anergic CD4 T cells to expand to greater numbers when they were functionally resuscitated following replacement of the initial source of tolerizing self-Ag with a viral form of the same Ag.