PD-L1 engagement on T cells promotes self-tolerance and suppression of neighboring macrophages and effector T cells in cancer.

Programmed cell death protein 1 (PD-1) ligation delimits immunogenic responses in T cells. However, the consequences of programmed cell death 1 ligand 1 (PD-L1) ligation in T cells are uncertain. We found that T cell expression of PD-L1 in cancer was regulated by tumor antigen and sterile inflammatory cues. PD-L1+ T cells exerted tumor-promoting tolerance via three distinct mechanisms: (1) binding of PD-L1 induced STAT3-dependent 'back-signaling' in CD4+ T cells, which prevented activation, reduced TH1-polarization and directed TH17-differentiation. PD-L1 signaling also induced an anergic T-bet-IFN-γ- phenotype in CD8+ T cells and was equally suppressive compared to PD-1 signaling; (2) PD-L1+ T cells restrained effector T cells via the canonical PD-L1-PD-1 axis and were sufficient to accelerate tumorigenesis, even in the absence of endogenous PD-L1; (3) PD-L1+ T cells engaged PD-1+ macrophages, inducing an alternative M2-like program, which had crippling effects on adaptive antitumor immunity. Collectively, we demonstrate that PD-L1+ T cells have diverse tolerogenic effects on tumor immunity.

γδ T Cells Promote Steatohepatitis by Orchestrating Innate and Adaptive Immune Programming.

BACKGROUND AND AIMS: The recruitment and activation of inflammatory cells in the liver delineates the transition from hepatic steatosis to steatohepatitis (SH). APPROACH AND RESULTS: We found that in SH, γδT cells are recruited to the liver by C-C chemokine receptor (CCR) 2, CCR5, and nucleotide-binding oligomerization domain-containing protein 2 signaling and are skewed toward an interleukin (IL)-17A+ phenotype in an inducible costimulator (ICOS)/ICOS ligand-dependent manner. γδT cells exhibit a distinct Vγ4+ , PD1+ , Ly6C+ CD44+ phenotype in SH. Moreover, γδT cells up-regulate both CD1d, which is necessary for lipid-based antigens presentation, and the free fatty acid receptor, CD36. γδT cells are stimulated to express IL-17A by palmitic acid and CD1d ligation. Deletion, depletion, and targeted interruption of γδT cell recruitment protects against diet-induced SH and accelerates disease resolution. CONCLUSIONS: We demonstrate that hepatic γδT cells exacerbate SH, independent of IL-17 expression, by mitigating conventional CD4+ T-cell expansion and modulating their inflammatory program by CD1d-dependent vascular endothelial growth factor expression.

BTLA+CD200+ B cells dictate the divergent immune landscape and immunotherapeutic resistance in metastatic vs. primary pancreatic cancer.

Response to cancer immunotherapy in primary versus metastatic disease has not been well-studied. We found primary pancreatic ductal adenocarcinoma (PDA) is responsive to diverse immunotherapies whereas liver metastases are resistant. We discovered divergent immune landscapes in each compartment. Compared to primary tumor, liver metastases in both mice and humans are infiltrated by highly anergic T cells and MHCIIloIL10+ macrophages that are unable to present tumor-antigen. Moreover, a distinctive population of CD24+CD44-CD40- B cells dominate liver metastases. These B cells are recruited to the metastatic milieu by Muc1hiIL18hi tumor cells, which are enriched >10-fold in liver metastases. Recruited B cells drive macrophage-mediated adaptive immune-tolerance via CD200 and BTLA. Depleting B cells or targeting CD200/BTLA enhanced macrophage and T-cell immunogenicity and enabled immunotherapeutic efficacy of liver metastases. Our data detail the mechanistic underpinnings for compartment-specific immunotherapy-responsiveness and suggest that primary PDA models are poor surrogates for evaluating immunity in advanced disease.

Specialized dendritic cells induce tumor-promoting IL-10+IL-17+ FoxP3neg regulatory CD4+ T cells in pancreatic carcinoma.

The drivers and the specification of CD4+ T cell differentiation in the tumor microenvironment and their contributions to tumor immunity or tolerance are incompletely understood. Using models of pancreatic ductal adenocarcinoma (PDA), we show that a distinct subset of tumor-infiltrating dendritic cells (DC) promotes PDA growth by directing a unique TH-program. Specifically, CD11b+CD103- DC predominate in PDA, express high IL-23 and TGF-ß, and induce FoxP3neg tumor-promoting IL-10+IL-17+IFNγ+ regulatory CD4+ T cells. The balance between this distinctive TH program and canonical FoxP3+ TREGS is unaffected by pattern recognition receptor ligation and is modulated by DC expression of retinoic acid. This TH-signature is mimicked in human PDA where it is associated with immune-tolerance and diminished patient survival. Our data suggest that CD11b+CD103- DC promote CD4+ T cell tolerance in PDA which may underscore its resistance to immunotherapy.