Immunization with recombinant DNA and modified vaccinia virus Ankara (MVA) vectors delivering PSCA and STEAP1 antigens inhibits prostate cancer progression

Despite recent advances in early detection and improvement of conventional therapies, there is an urgent need for development of additional approaches for prevention and/or treatment of prostate cancer, and the use of immunotherapeutic modalities, such as cancer vaccines, is one of the most promising strategies. In this study, we evaluated the prophylactic efficacy of an active immunization protocol against prostate cancer associated antigens mPSCA and mSTEAP1 in experimental prostate cancer. Two antigen delivery platforms, recombinant DNA and MVA vectors, both encoding either mPSCA or mSTEAP1 were used in diversified DNA prime/MVA boost vaccination protocol. Antitumour activity was evaluated in TRAMP-C1 subcutaneous syngeneic tumour model and TRAMP mice. DNA prime/MVA boost immunization against either mPSCA or mSTEAP1, delayed tumour growth in TRAMP-C1 cells-challenged mice. Furthermore, simultaneous vaccination with both antigens produced a stronger anti-tumour effect against TRAMP-C1 tumours than vaccination with either mPSCA or mSTEAP1 alone. Most importantly, concurrent DNA prime/MVA boost vaccination regimen with those antigens significantly decreased primary tumour burden in TRAMP mice without producing any apparent adverse effects. Histopathological analysis of prostate tumours from vaccinated and control TRAMP mice revealed also that mPSCA/mSTEAP1 based-vaccination was effective at reducing the severity of prostatic lesions and incidence of high-grade poorly differentiated prostate cancer. Suppression of the disease progression in TRAMP mice was correlated with decreased proliferation index and increased infiltration of T-cells in prostate tissue. Active immunization against PSCA and STEAP1 using DNA prime/MVA boost strategy is a promising approach for prevention and/or treatment of prostate cancer.