CD155 on Tumor Cells Drives Resistance to Immunotherapy by Inducing the Degradation of the Activating Receptor CD226 in CD8+ T Cells.

The activating receptor CD226 is expressed on lymphocytes, monocytes, and platelets and promotes anti-tumor immunity in pre-clinical models. Here, we examined the role of CD226 in the function of tumor-infiltrating lymphocytes (TILs) and resistance to immunotherapy. In murine tumors, a large proportion of CD8+ TILs had decreased surface expression of CD226 and exhibited features of dysfunction, whereas CD226hi TILs were highly functional. This correlation was seen also in TILs isolated from HNSCC patients. Mutation of CD226 at tyrosine 319 (Y319) led to increased CD226 surface expression, enhanced anti-tumor immunity and improved efficacy of immune checkpoint blockade (ICB). Mechanistically, tumor-derived CD155, the ligand for CD226, initiated phosphorylation of Y319 by Src kinases, thereby enabling ubiquitination of CD226 by CBL-B, internalization, and proteasomal degradation. In pre-treatment samples from melanoma patients, CD226+CD8+ T cells correlated with improved progression-free survival following ICB. Our findings argue for the development of therapies aimed at maintaining the expression of CD226.

Eomes-Dependent Loss of the Co-activating Receptor CD226 Restrains CD8+ T Cell Anti-tumor Functions and Limits the Efficacy of Cancer Immunotherapy.

CD8+ T cells within the tumor microenvironment (TME) are exposed to various signals that ultimately determine functional outcomes. Here, we examined the role of the co-activating receptor CD226 (DNAM-1) in CD8+ T cell function. The absence of CD226 expression identified a subset of dysfunctional CD8+ T cells present in peripheral blood of healthy individuals. These cells exhibited reduced LFA-1 activation, altered TCR signaling, and a distinct transcriptomic program upon stimulation. CD226neg CD8+ T cells accumulated in human and mouse tumors of diverse origin through an antigen-specific mechanism involving the transcriptional regulator Eomesodermin (Eomes). Despite similar expression of co-inhibitory receptors, CD8+ tumor-infiltrating lymphocyte failed to respond to anti-PD-1 in the absence of CD226. Immune checkpoint blockade efficacy was hampered in Cd226-/- mice. Anti-CD137 (4-1BB) agonists also stimulated Eomes-dependent CD226 loss that limited the anti-tumor efficacy of this treatment. Thus, CD226 loss restrains CD8+ T cell function and limits the efficacy of cancer immunotherapy.

The NK cell granule protein NKG7 regulates cytotoxic granule exocytosis and inflammation.

Immune-modulating therapies have revolutionized the treatment of chronic diseases, particularly cancer. However, their success is restricted and there is a need to identify new therapeutic targets. Here, we show that natural killer cell granule protein 7 (NKG7) is a regulator of lymphocyte granule exocytosis and downstream inflammation in a broad range of diseases. NKG7 expressed by CD4+ and CD8+ T cells played key roles in promoting inflammation during visceral leishmaniasis and malaria-two important parasitic diseases. Additionally, NKG7 expressed by natural killer cells was critical for controlling cancer initiation, growth and metastasis. NKG7 function in natural killer and CD8+ T cells was linked with their ability to regulate the translocation of CD107a to the cell surface and kill cellular targets, while NKG7 also had a major impact on CD4+ T cell activation following infection. Thus, we report a novel therapeutic target expressed on a range of immune cells with functions in different immune responses.

MAIT Cells Promote Tumor Initiation, Growth, and Metastases via Tumor MR1.

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that require MHC class I-related protein 1 (MR1) for their development. The role of MAIT cells in cancer is unclear, and to date no study has evaluated these cells in vivo in this context. Here, we demonstrated that tumor initiation, growth, and experimental lung metastasis were significantly reduced in Mr1 -/- mice, compared with wild-type mice. The antitumor activity observed in Mr1 -/- mice required natural killer (NK) and/or CD8+ T cells and IFNγ. Adoptive transfer of MAIT cells into Mr1 -/- mice reversed metastasis reduction. Similarly, MR1-blocking antibodies decreased lung metastases and suppressed tumor growth. Following MR1 ligand exposure, some, but not all, mouse and human tumor cell lines upregulated MR1. Pretreatment of tumor cells with the stimulatory ligand 5-OP-RU or inhibitory ligand Ac-6-FP increased or decreased lung metastases, respectively. MR1-deleted tumors resulted in fewer metastases compared with parental tumor cells. MAIT cell suppression of NK-cell effector function was tumor-MR1-dependent and partially required IL17A. Our studies indicate that MAIT cells display tumor-promoting function by suppressing T and/or NK cells and that blocking MR1 may represent a new therapeutic strategy for cancer immunotherapy. SIGNIFICANCE: Contradicting the perception that MAIT cells kill tumor cells, here MAIT cells promoted tumor initiation, growth, and metastasis. MR1-expressing tumor cells activated MAIT cells to reduce NK-cell effector function, partly in a host IL17A-dependent manner. MR1-blocking antibodies reduced tumor metastases and growth, and may represent a new class of cancer therapeutics.This article is highlighted in the In This Issue feature, p. 1.

CD155 loss enhances tumor suppression via combined host and tumor-intrinsic mechanisms.

Critical immune-suppressive pathways beyond programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) require greater attention. Nectins and nectin-like molecules might be promising targets for immunotherapy, since they play critical roles in cell proliferation and migration and exert immunomodulatory functions in pathophysiological conditions. Here, we show CD155 expression in both malignant cells and tumor-infiltrating myeloid cells in humans and mice. Cd155-/- mice displayed reduced tumor growth and metastasis via DNAM-1 upregulation and enhanced effector function of CD8+ T and NK cells, respectively. CD155-deleted tumor cells also displayed slower tumor growth and reduced metastases, demonstrating the importance of a tumor-intrinsic role of CD155. CD155 absence on host and tumor cells exerted an even greater inhibition of tumor growth and metastasis. Blockade of PD-1 or both PD-1 and CTLA4 was more effective in settings in which CD155 was limiting, suggesting the clinical potential of cotargeting PD-L1 and CD155 function.

Reactive Neutrophil Responses Dependent on the Receptor Tyrosine Kinase c-MET Limit Cancer Immunotherapy.

Inhibitors of the receptor tyrosine kinase c-MET are currently used in the clinic to target oncogenic signaling in tumor cells. We found that concomitant c-MET inhibition promoted adoptive T cell transfer and checkpoint immunotherapies in murine cancer models by increasing effector T cell infiltration in tumors. This therapeutic effect was independent of tumor cell-intrinsic c-MET dependence. Mechanistically, c-MET inhibition impaired the reactive mobilization and recruitment of neutrophils into tumors and draining lymph nodes in response to cytotoxic immunotherapies. In the absence of c-MET inhibition, neutrophils recruited to T cell-inflamed microenvironments rapidly acquired immunosuppressive properties, restraining T cell expansion and effector functions. In cancer patients, high serum levels of the c-MET ligand HGF correlated with increasing neutrophil counts and poor responses to checkpoint blockade therapies. Our findings reveal a role for the HGF/c-MET pathway in neutrophil recruitment and function and suggest that c-MET inhibitor co-treatment may improve responses to cancer immunotherapy in settings beyond c-MET-dependent tumors.

Glucocorticoids alleviate intestinal ER stress by enhancing protein folding and degradation of misfolded proteins.

Endoplasmic reticulum (ER) stress in intestinal secretory cells has been linked with colitis in mice and inflammatory bowel disease (IBD). Endogenous intestinal glucocorticoids are important for homeostasis and glucocorticoid drugs are efficacious in IBD. In Winnie mice with intestinal ER stress caused by misfolding of the Muc2 mucin, the glucocorticoid dexamethasone (DEX) suppressed ER stress and activation of the unfolded protein response (UPR), substantially restoring goblet cell Muc2 production. In mice lacking inflammation, a glucocorticoid receptor antagonist increased ER stress, and DEX suppressed ER stress induced by the N-glycosylation inhibitor, tunicamycin (Tm). In cultured human intestinal secretory cells, in a glucocorticoid receptor-dependent manner, DEX suppressed ER stress and UPR activation induced by blocking N-glycosylation, reducing ER Ca(2+) or depleting glucose. DEX up-regulated genes encoding chaperones and elements of ER-associated degradation (ERAD), including EDEM1. Silencing EDEM1 partially inhibited DEX's suppression of misfolding-induced ER stress, showing that DEX enhances ERAD. DEX inhibited Tm-induced MUC2 precursor accumulation, promoted production of mature mucin, and restored ER exit and secretion of Winnie mutant recombinant Muc2 domains, consistent with enhanced protein folding. In IBD, glucocorticoids are likely to ameliorate ER stress by promoting correct folding of secreted proteins and enhancing removal of misfolded proteins from the ER.

A peptide nucleic acid-aminosugar conjugate targeting transactivation response element of HIV-1 RNA genome shows a high bioavailability in human cells and strongly inhibits tat-mediated transactivation of HIV-1 transcription.

The 6-aminoglucosamine ring of the aminoglycoside antibiotic neomycin B (ring II) was conjugated to a 16-mer peptide nucleic acid (PNA) targeting HIV-1 TAR RNA. For this purpose, we prepared the aminoglucosamine monomer 15 and attached it to the protected PNA prior to its cleavage from the solid support. We found that the resulting PNA-aminoglucosamine conjugate is stable under acidic conditions, efficiently taken up by the human cells and fairly distributed in both cytosol and nucleus without endosomal entrapment because cotreatment with endosome-disrupting agent had no effect on its cellular distribution. The conjugate displayed very high target specificity in vitro and strongly inhibited Tat mediated transactivation of HIV-1 LTR transcription in a cell culture system. The unique properties of this new class of PNA conjugate suggest it to be a potential candidate for therapeutic application.