316. Dendritic Cell-Based Genetic Immunotherapy for Prostate Cancer

Abstract

Top of pageAbstract Human prostate tumor vaccine and gene therapy trials using ex vivo methods to prime dendritic cells (DCs) with prostate specific membrane antigen (PSMA) have been somewhat successful, but heretofore the lengthy ex vivo manipulation of DCs has limited the utility of this approach. Our goal was to improve upon DC vaccination with tumor antigens by delivering PSMA via a CD40-targeted adenoviral (Ad) vector expressing PSMA directly to DCs in situ as an efficient means for activation and antigen presentation to T-cells. We initially developed a mouse model of prostate cancer by generating several clonal derivatives of the mouse RM-1 prostate cancer cell line that express high levels of human PSMA (RM-1-PSMA). We then tested the efficacy of the CD40-targeted Ad-PSMA vector to stimulate a cytotoxic T-cell (CTL) response in vivo. In order to maximize antigen presentation in target cells, we induced both MHC class I and Tap protein expression in RM-1 cells by treatment with interferon-gamma (IFN-g). Using RM-1-PSMA cells pretreated with IFN-g as target cells, we demonstrated that DCs infected ex vivo with Ad-PSMA, as well as those infected by direct intraperitoneal injection of the CD40-targeted Ad-PSMA resulted in high levels of tumor-specific CTL responses, compared to responses with a control adenovirus (Ad-luc1). Thus, we have demonstrated that direct immunization of DCs in situ with a CD40-targeted Ad together with IFN-g treatment of target cells is effective in inducing an antigen-specific CTL response to PSMA. We have initiated animal studies to test the efficacy of the CD40-targeted PSMA vector versus a non-targeted vector with and without stimulation by IFN-g in protecting against a lethal RM-1-PSMA tumor challenge. At day 14 post-tumor inoculation, only those animals treated with the CD40-targeted adenovirus and IFN-g were resistant to challenge with RM-1-PSMA tumor cells. Our next aim is to determine the lowest effective dosage of targeted vector and the optimal combination of cytokine/chemokine stimulation to protect against tumor challenge as well as test the efficacy of the targeted vector strategy in a minimal residual disease model. The in vitro studies coupled with the syngeneic tumor survival model will allow us to systematically analyze this approach and generate data directly applicable for a human Phase I clinical trial.