An indoleamine 2, 3-dioxygenase siRNA nanoparticle-coated and Trp2-displayed recombinant yeast vaccine inhibits melanoma tumor growth in mice

Therapeutic vaccine is a promising approach in cancer therapy. But tumor-associated antigen peptides have weak immunogenicity and cancer patients are often characterized by immunosuppression and tolerance, leading to less efficiency of immunotherapy. We here successfully developed indoleamine 2, 3-dioxygenase (IDO) siRNA nanoparticle-coated and tyrosinase-related protein 2 (Trp2)-displayed recombinant Saccharomyces cerevisiae (YCP). YCPs had positive charges with a diameter of approximately 5 mu m, resulting in selective phagocytosis by APC cells. YCP-delivered siRNA and Trp2 successfully escaped from phagosomes, efficiently inhibited IDO expression in DCs, promoted the immune reaction of T cell against Trp2, increased the secretion of proin-flammatory cytokines such as IFN-gamma, TNF-alpha, and IL-6, and decreased the generation of regulatory T cells. Moreover, YCPs significantly inhibited melanoma tumor growth by alleviating immune tolerance and promoting Trp2-specific CD8(+) T cell immune response. These results suggest that Saccharomyces cerevisiae as a combined immunotherapeutic platform to simultaneously delivery IDO-siRNA and Trp2 epitope peptide is a promising vaccine system for melanoma treatment.