Human dendritic cells transfected with RNA encoding prostate-specific antigen stimulate prostate-specific CTL responses in vitro

Although immunological tolerance to self Ags represents an important mechan ism to prevent normal tissue injury, there is growing evidence that toleran ce to tumor Ags, which often represent normal peripherally expressed protei ns, is not absolute and can be effectively reverted. Prostate-specific Ag ( PSA) is a self Ag expressed by both normal and malignant prostatic epitheli um, and therefore offers a unique opportunity to examine the ability of sel f Ags to serve as specific CTL targets. In this study, we investigated the efficacy of autologous dendritic cells (DC) transfected with mRNA encoding PSA to stimulate CTL against PSA Ags in vitro, Ag in form of RNA carries th e advantage to encode multiple epitopes for many HLA alleles, thus permitti ng induction of CTL responses among many cancer patients independent of the ir HLA repertoire. In this study, we show that PSA mRNA-transfected DC were capable of stimulating primary CTL responses against PSA Ags in vitro. The PSA-specific CTL did not cross-react with kallikrein Ags, a protein, which shares significant homology with PSA, suggesting that harmful autoimmune t oxicity may not represent a significant problem with this approach, PSA RNA -transfected DC generated from male or female healthy volunteers or from ca ncer patients were equally effective in stimulating PSA-specific CTL in vit ro, implying that neither natural tolerance to PSA Ags nor tumor-mediated T cell anergy may represent major barriers for CTL generation against the se lf Ag PSA, This study provides a preclinical rationale for using PSA RNA-tr ansfected DC in active or adoptive immunization protocols.