CD4 and melanoma: We sought to comprehensively evaluate the relative expression of CTLA-4 on circulating and tumor-infiltrating CD4+FoxP3+, CD4+FoxP3−, and CD8+ T lymphocytes across multiple murine models of transplantable syngeneic tumor cell lines of variable immunogenicity, including B16 melanoma, MCA205 sarcoma, MC38 colonic adenocarcinoma, CT26 colorectal carcinoma (Figures 1A–1C), and human solid tumor subtypes including advanced melanoma, early-stage non-small cell lung cancer (NSCLC), and renal cell carcinoma (RCC) (Figures 1D–1F).