Abstract
The aim of this study was to assay the efficacy of cytokine gene-transduced tumor vaccines and DNA vaccines for prostate cancer. In this study, we used probasin (PB), a prostate specific antigen of mice, as a model target antigen and interleukine-3 (IL-3) and granulocyte-monocyte-colony stimulating factor (GM-CSF) as immune modulating cytokine. This study includes three parts: (1) the establishment of murine prostate cancer cells that can express probasin antigen, (2) the construction of DNA vaccines and tumor vaccines that express both cytokine and probasin, and (3) the examination of the in vivo effects of these vaccines in mouse model.To establish the murine prostate cancer cell permanently expressing probasin antigen, PT67-PB packaging cell line which could produce retrovirus containing PB gene was first established. After confirming the production of retrovirus-PB by PCR and plaque assay, Tramp-C1 tumor cells were infected by retrovirus-PB. This modified tumor cells, Tramp-PB, were demonstrated to expresses the probasin in both mRNA and protein levels, by RT-PCR and ELISA, respectively.To construct DNA and tumor vaccines, a bi-cistronic vector, pIRES, was used to co-express probasin gene and a cytokine gene, IL-3 or GM-CSF. The constructed IRES-PB-IL3 and IRES-PB-GM-CSF plasmids were either used as DNA vaccines, or further transfected into Tramp-C1 tumor cells. Tramp-PB-IL3 and Tramp-PB-GM-CSF cell lines were established following 2 weeks of G418 selection after liposome transfection. The expression of IL-3 and probasin in TRAMP-PB-IL3 cells were identified by RT-PCR and ELISA.To test the immunity of DNA vaccines, the DNA plasmids of IRES-PB-IL-3 and IRES-PB-GM-CSF were injected intramuscular into flanks of C57BL/6J and C3H/HeN mice. Histology demonstrated that these vaccines could not induce autoimmunity in the prostate of these mice.To further examine the efficacy of these vaccines in vivo, we were surprise to find that Tramp-PB cell line did not grow in vivo. We further demonstrated that Tramp-PB cells had lost their tumorgenicity in both tumor growth delay and lung colony formation models. Due to the lack of tumorgenicity of Tramp-PB cells, the efficacy of these vaccines could not be confirmed in this model. We are currently using a murine prostate cancer mouse model, TRAMP transgenic mice, to test whether these DNA and tumor vaccines can prevent or delay the progression of the prostate cancers in these mice.