Person:

Anderson, Ana

The immune response plays an important role in staving off cancer; however, mechanisms of immunosuppression hinder productive anti-tumor immunity. T cell dysfunction or exhaustion in tumor-bearing hosts is one such mechanism. PD-1 has been identified as a marker of exhausted T cells in chronic disease states, and blockade of PD-1–PD-1L interactions has been shown to partially restore T cell function. We have found that T cell immunoglobulin mucin (Tim) 3 is expressed on CD8(^+) tumor-infiltrating lymphocytes (TILs) in mice bearing solid tumors. All Tim-3(^+) TILs coexpress PD-1, and Tim-3(^+)PD-1(^+) TILs repre- sent the predominant fraction of T cells infiltrating tumors. Tim-3(^+)PD-1(^+) TILs exhibit the most severe exhausted phenotype as defined by failure to proliferate and produce IL-2, TNF, and IFN-(\gamma). We further find that combined targeting of the Tim-3 and PD-1 pathways is more effective in controlling tumor growth than targeting either pathway alone.

T-cell immunoglobulin mucin 3 (TIM3) is an inhibitory molecule that has emerged as a key regulator of dysfunctional or exhausted CD8+ T cells arising in chronic diseases such as cancer. In addition to exhausted CD8+ T cells, highly suppressive regulatory T cells (Tregs) represent a significant barrier against the induction of antitumor immunity. We have found that the majority of intratumoral FOXP3+ Tregs express TIM3. TIM3+ Tregs co-express PD-1, are highly suppressive and comprise a specialized subset of tissue Tregs that are rarely observed in the peripheral tissues or blood of tumor-bearing mice. The co-blockade of the TIM3 and PD-1 signaling pathways in vivo results in the downregulation of molecules associated with TIM3+ Treg suppressor functions. This suggests that the potent clinical efficacy of co-blocking TIM3 and PD-1 signal transduction cascades likely stems from the reversal of T-cell exhaustion combined with the inhibition of regulatory T-cell function in tumor tissues. Interestingly, we find that TIM3+ Tregs accumulate in the tumor tissue prior to the appearance of exhausted CD8+ T cells, and that the depletion of Tregs at this stage interferes with the development of the exhausted phenotype by CD8+ T cells. Collectively, our data indicate that TIM3 marks highly suppressive tissue-resident Tregs that play an important role in shaping the antitumor immune response in situ, increasing the value of TIM3-targeting therapeutic strategies against cancer.

SUMMARY The inhibitory receptor Tim-3 has emerged as a critical regulator of the T cell dysfunction that develops in chronic viral infections and cancers. However, little is known regarding the signaling pathways that drive Tim-3 expression. Here, we demonstrate that IL-27 induces NFIL3, which promotes permissive chromatin remodeling of the Tim-3 locus and induces Tim-3 expression together with the immunosuppressive cytokine IL-10. We further show that the IL-27/NFIL3 signaling axis is crucial for the induction of Tim-3 in vivo. IL-27-conditioned Th1 cells exhibit reduced effector function and are poor mediators of intestinal inflammation. This inhibitory effect is NFIL3 dependent. In contrast, tumor-infiltrating lymphocytes (TILs) from IL-27R−/− mice exhibit reduced NFIL3, less Tim-3 expression and failure to develop dysfunctional phenotype, resulting in better tumor growth control. Thus, our data identify an IL-27/NFIL3 signaling axis as a key regulator of effector T cell responses via induction of Tim-3, IL-10, and T cell dysfunction.