Abstract Previous studies suggest that by improving Notch signaling in the tumor microenvironment (TME), one may rescue tumor infiltrating T lymphocyte function and inhibit tumor growth in vivo. Delta-like homolog 1 (DLK-1) and Delta-like homolog 2 (DLK-2) are homologous transmembrane proteins whose ectodomains may be shed from the cell surface by the action of the tumor necrosis factor alpha converting enzyme. Both the membrane-associated and soluble forms of DLK-1/-2 serve as antagonists of Notch receptor-mediated signaling. We report that DLK-1 is differentially expressed by vascular pericytes of murine renal cell carcinomas (RENCA) and have shown that vaccination of RENCA-bearing BALB/c mice with DLK-1-derived peptides or cDNA results in the activation of specific CD8+ T cells, the recruitment of these T cells into the TME and the normalization of tumor vasculature in vivo. However, DLK-1 and DLK-2 have been reported to counter-modulate each other’s expression. Here we show that DLK-1-based vaccination leads to the T cell-dependent loss of DLK-1 expression in RENCA tumors, but to an apparent compensatory increase in TME expression of DLK-2. We have recently defined H-2d class I-presented peptide epitopes recognized by CD8+ T cells and are currently evaluating the therapeutic benefits of vaccines targeting both DLK-1 and DLK-2 in our RENCA model. We believe that such vaccines will have significant translational value for the treatment of many solid, vascularized forms of cancer.