No abstract

Elevating Akt activation is an obvious clinical strategy to prevent progressive neuronal death in neurological diseases. However, this endeavor has been hindered because of the lack of specific Akt activators. Here, from a cell-based high-throughput chemical genetic screening, we identified a small molecule SC79 that inhibits Akt membrane translocation, but paradoxically activates Akt in the cytosol. SC79 specifically binds to the PH domain of Akt. SC79-bound Akt adopts a conformation favorable for phosphorylation by upstream protein kinases. In a hippocampal neuronal culture system and a mouse model for ischemic stroke, the cytosolic activation of Akt by SC79 is sufficient to recapitulate the primary cellular function of Akt signaling, resulting in augmented neuronal survival. Thus, SC79 is a unique specific Akt activator that may be used to enhance Akt activity in various physiological and pathological conditions.

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.

Both data in preclinical cancer models and data with T cells from patients with advanced cancer support a role for Tim-3 blockade in promoting effective anti-tumor immunity. Consequently, there is considerable interest in the clinical development of antibody-based therapeutics that target Tim-3 for cancer immunotherapy. A challenge to this clinical development is the fact that several ligands for Tim-3 have been identified: galectin-9, phosphatidylserine, HMGB1, and most recently, CEACAM1. These observations raise the important question of which of these multiple receptor:ligand relationships must be blocked by an anti-Tim-3 antibody in order to achieve therapeutic efficacy. Here, we have examined the properties of anti-murine and anti-human Tim-3 antibodies that have shown functional efficacy and find that all antibodies bind to Tim-3 in a manner that interferes with Tim-3 binding to both phosphatidylserine and CEACAM1. Our data have implications for the understanding of Tim-3 biology and for the screening of anti-Tim-3 antibody candidates that will have functional properties .

TIGIT is a co-inhibitory molecule that limits T cell proliferation and activation. TIGIT expression has been recently shown to identify a subset of regulatory T cells (Treg) that specifically suppresses Th1 and Th17 responses; however its role in tumor immunity has not been examined. Here, we determined whether TIGIT has a role in the suppression of anti-tumor immune responses. We found that TIGIT is highly up-regulated on Treg and CD8+ tumorinfiltrating lymphocytes (TILs) in multiple pre-clinical cancer models. Importantly, TIGIT expression is strongly associated with expression of other co-inhibitory molecules; PD-1, Tim-3 and Lag-3 and with production of IL-10 in Treg and CD8+ TILs. Moreover, TIGIT+ CD8+ TILs display an exhausted phenotype determined by decreased production of IL-2 and TNF-α. To understand whether TIGIT acts as a checkpoint in anti-tumor response, we monitored growth of implanted B16 melanoma in TIGIT -/mice and found that absence of TIGIT significantly delayed tumor growth. As TIGIT is expressed on both T cells (Treg and CD8+) and NK cells in cancer, we addressed the role of TIGIT in these subsets in driving immune suppression. Our data indicate that TIGIT may play a dominant role in Treg in that deficiency of TIGIT in Treg alone results in better control of tumor growth and a heightened proliferative response in the draining lymph nodes and spleens of tumor-bearing mice. Finally, we show that a TIGIT blocking antibody can be used therapeutically to decrease tumor growth and that blockade of TIGIT synergizes with Tim-3 blockade to maximally decrease tumor growth. Our study is the first report showing that TIGIT acts as an immune checkpoint in cancer. Importantly, our data indicate that TIGIT and Tim-3 synergize to suppress anti-tumor responses and targeting these two molecules could provide a therapeutic effect on tumor growth.

In the Discussion section of this Article, we inadvertently stated that 'endogenous IL-27 signalling results in reduced tumour burden'. This should have read: 'lack of IL-27 signalling results in reduced tumour burden'.

Genetic variants in il2 and il2ra have been associated with autoimmune disease susceptibility in both genome-wide association studies (GWAS) in humans and in genetic linkage studies in experimental models of autoimmunity. Specifically, genetic variants resulting in a low IL-2 phenotype are susceptibility alleles while variants resulting in a high IL-2 phenotype are resistance alleles. The association of high IL-2 phenotypes with resistance has been attributed primarily to the T cell intrinsic promotion of regulatory T cell development, maintenance, and function; however, IL-2 can also act T cell intrinsically to dampen differentiation of pathogenic IL-17-producing Th17 cells. Here, we have uncovered a novel T cell extrinsic mechanism whereby IL-2 promotes both IFN-γ and IL-27 production from tissue resident macrophages which in turn dampen the differentiation of pathogenic Th17 cells.