Microenvironment and Immunology Targeting the Immunoregulator SRA/CD204 Potentiates SpecificDendritic Cell Vaccine-Induced T-cell Response and Antitumor Immunity

Although dendritic cell (DC) vaccines offer promise as cancer immunotherapy, further improvements are needed to amplify their clinical therapeutic efficacy. The pattern recognition scavenger receptor SRA/CD204 attenuates the ability of DCs to activate CD8þT-cell responses. Therefore, we examined the impact of SRA/CD204 on antitumor responses generated by DC vaccines and we also evaluated the feasibility of enhancing DC vaccine potency by SRA/CD204 blockade. DCs from SRA/CD204-deficient mice were more immunogenic in generating antitumor responses to B16 melanoma, compared with DCs from wild-type mice. Similarly, siRNA-mediated knockdown of SRA/CD204 by lentiviral vectors improved the ability of wild-type DCs to stimulate the expansion and activation of CD8þT cells specific for idealized or establishedmelanoma antigens inmice. Using SRA/CD204silenced DCs to generate antigen-targeted vaccines, we documented a marked increase in the level of antitumor immunity achieved against established B16 tumors and metastases. This increase was associated with enhanced activation of antigen specific CTLs, greater tumor infiltration by CD8þ T cells and NK cells, and increased intratumoral ratios of both CD4þ and CD8þ T-effector cells to CD4þCD25þ T-regulatory cells. Our studies establish that downregulating SRA/CD204 strongly enhances DC-mediated antitumor immunity. In addition, they provide a rationale to enhance DC vaccine potency through SRA/CD204-targeting approaches that can improve clinical outcomes in cancer treatment. Cancer Res; 71(21); 6611–20. 2011 AACR.