ABSTRACT
Merkel cell carcinomas (MCCs) are rare but highly malignant skin cancers associated with a recently described polyomavirus. MCC tumors were infiltrated by T cells, including effector, central memory, and regulatory T cells. Infiltrating T cells showed markedly reduced activation as evidenced by reduced expression of CD69 and CD25. Treatment of MCC tumors in vitro with IL-2 and IL-15 led to T-cell activation, proliferation, enhanced cytokine production, and loss of viable tumor cells from cultures. Expanded tumor-infiltrating lymphocytes showed TCR repertoire skewing and upregulation of CD137. MCC tumors implanted into immunodeficient mice failed to grow unless human T cells in the tumor grafts were depleted with denileukin diftitox, suggesting that tumor-specific T cells capable of controlling tumor growth were present in MCC. Both CD4(+) and CD8(+) FOXP3(+) regulatory T cells were frequent in MCC. Fifty percent of nonactivated T cells in MCC-expressed PD-1, a marker of T-cell exhaustion, and PD-L1 and PD-L2 were expressed by a subset of tumor dendritic cells and macrophages. In summary, we observed tumor-specific T cells with suppressed activity in MCC tumors. Agents that stimulate T-cell activity, block regulatory T cell function, or inhibit PD-1 signaling may be effective in the treatment of this highly malignant skin cancer.
Subject(s)
Carcinoma, Merkel Cell/pathology , Programmed Cell Death 1 Receptor/metabolism , Skin Neoplasms/pathology , T-Lymphocytes, Regulatory/metabolism , T-Lymphocytes, Regulatory/pathology , T-Lymphocytes/metabolism , T-Lymphocytes/pathology , Animals , Antigens, CD/metabolism , Antigens, Differentiation, T-Lymphocyte/metabolism , CD8 Antigens/metabolism , Carcinoma, Merkel Cell/metabolism , Carcinoma, Squamous Cell/metabolism , Carcinoma, Squamous Cell/pathology , Cell Proliferation/drug effects , Cells, Cultured , Cytokines/metabolism , Forkhead Transcription Factors/metabolism , Humans , In Vitro Techniques , Interleukin-15/pharmacology , Interleukin-2/pharmacology , Interleukin-2 Receptor alpha Subunit/metabolism , Lectins, C-Type/metabolism , Mice , Mice, Inbred NOD , Mice, SCID , Signal Transduction/physiology , Skin/metabolism , Skin/pathology , Skin Neoplasms/metabolism , T-Lymphocytes/drug effects , Transplantation, HeterologousABSTRACT
Squamous cell carcinomas (SCCs) are sun-induced skin cancers that are particularly numerous and aggressive in immunosuppressed individuals. SCCs evade immune detection at least in part by downregulating E-selectin on tumor vessels, thereby restricting entry of skin-homing T cells into tumors. We find that nitric oxide (NO) potently suppresses E-selectin expression on human endothelial cells and that SCCs are infiltrated by NO-producing iNOS(+) CD11b(+) CD33(+) CD11c(-) HLA-DR(-) myeloid-derived suppressor cells (MDSCs). MDSCs from SCCs produced NO, transforming growth factor-ß (TGF-ß), and arginase, and inhibited endothelial E-selectin expression in vitro. MDSCs from SCCs expressed the chemokine receptor CCR2 (chemokine (C-C motif) receptor 2) and tumors expressed the CCR2 ligand human ß-defensin 3 (HBD3), suggesting that CCR2/HBD3 interactions may contribute to MDSC recruitment to SCCs. Treatment of SCCs in vitro with the inducible nitric oxide synthase (iNOS) inhibitor N(ω)-nitro-L-arginine(L-NNA) induced E-selectin expression at levels comparable to imiquimod-treated SCCs undergoing immunologic destruction. Our results suggest that local production of NO in SCCs may impair vascular E-selectin expression. We show that MDSCs are critical producers of NO in SCCs and that NO inhibition restores vascular E-selectin expression, potentially enhancing T-cell recruitment. The iNOS inhibitors and other therapies that reduce NO production may therefore be effective in the treatment of SCCs and their premalignant precursor lesions, actinic keratoses.
