Therapeutic effect of dendritic cells loaded with a fusion mRNA encoding tyrosinase-related protein 2 and enhanced green fluorescence protein on B16 melanoma.

Dendritic cells (DCs) loaded with messenger RNA (mRNA) have been proposed to be useful for inducing specific cytotoxic T lymphocytes against tumor antigens. It is now also apparent that tumor antigen-specific T cell tolerance limits the efficacy of active immunotherapy. To improve the efficacy of mRNA-loaded DCs, we constructed a fusion mRNA encoding tyrosinase-related protein 2 (TRP2), which has a late endosomal/lysosomal sorting signal and enhanced green fluorescence protein (EGFP), and evaluated its effect in a murine melanoma model. C57BL/6 mice were challenged subcutaneously (s.c.) with 3 x 10(5) B16 tumor cells, and 3 and 10 days later, 3 x 10(5) DCs loaded with mRNA (DC/mRNA) were injected s.c. in the vicinity of the tumor site. Treatment with DC/TRP2 mRNA or DC/TRP2-EGFP mRNA significantly inhibited tumor growth compared to DC/PBS on day 17 after B16 challenge (DC/PBS vs. DC/TRP2 mRNA, p = 0.0411; DC/PBS vs.DC/TRP2-EGFP mRNA, p = 0.0253), whereas no antitumor effect was observed in mice treated with DC/EGFP mRNA or DC/TRP2 peptide. Moreover, the survival rate in mice immunized with DC/TRP2 mRNA or DC/TRP2-EGFP mRNA was significantly improved as compared with that in mice receiving DC/PBS (DC/PBS vs. DC/TRP2 mRNA, p = 0.0228; DC/PBS vs. DC/TRP2-EGFP mRNA, p = 0.0049). Depletion of CD4+ T cells or CD8+ T cells with antibody administration completely abrogated the therapeutic effectiveness of DC/TRP2-EGFP mRNA, suggesting the induction of a T cell immune response against the B16 tumor.