CD5 and neoplasm: That, along with our observation of reduced CD5 on T cells within the tumor microenvironment and our previous report that experimental reduction of CD5 leads to increased CD8+ T cell activation (25), collectively suggest that T cells with low CD5 within tumors (due wholly or in part to the poorly immunogenic 4T1 tumor microenvironment) may have increased sensitivity to poorly immunogenic 4T1 tumor antigens.