Tumor blood vessel-associated antigens, DLK-1 and DLK-2, as targets for anti-cancer immunotherapy

Abstract Tumors induce pathological angiogenesis that results in a tumor vascular network that is highly abnormal. These aberrant blood vessels support tumor growth and progression and also immunosuppression by promoting a hypoxic and high interstitial fluid pressure-environment that impedes immune trafficking to the tumor bed. Hence, normalization of tumor blood vessels is essential in ensuring success of anti-cancer therapy. We have previously shown that pericytes in tumor blood vessels of murine renal cell carcinoma (RENCA) express the Notch antagonist delta-like homolog-1 (DLK1). DLK1-targeted vaccination of RENCA-bearing mice resulted in vascular normalization and CD8+ T cell-dependent inhibition of tumor growth. Here we show that DLK2, a homolog of DLK1, is upregulated in RENCA pericytes after DLK-1 vaccine-induced removal of DLK1 in the tumor microenvironment (TME). Using recombinant lentiviruses and adenoviruses encoding full-length DLK1 and DLK2, we demonstrate that coordinate vaccination against these two antigens leads to superior antigen-specific CD8+ T cell-induced tumor growth inhibition than vaccination with either antigen alone. We also show that DLK-1 and DLK-2 coordinate vaccination shifts the TME to a more “immunocompetent” phenotype by normalizing tumor vasculature and decreasing the immunosuppressive cell population. We conclude that specific vaccination targeting DLK-1 and DLK-2 is a promising approach for the treatment of vascularized tumors.