An AAV6-based multi-antigen vaccine for treatment of murine melanoma

Abstract

Abstract We recently showed that a vaccine with optimized AAV6 vector generates a superior immune response against strong antigens (Ag) such as Ovalbumin. However, tumor-associated antigens (TAA) are typically non-mutated self-proteins with low immunogenicity. To increase vaccine efficacy and to reduce tumor evasion of immune attack, we developed a multivalent AAV vaccine that targets four previously characterized melanoma TAA: tyrosinase, premelanosome protein gp100, tyrosinase-related protein 1, and dopachrome tautomerase. The vaccine represents a combination of individual AAV-based vaccines specific to unique TAA. The strength of cytotoxic T cell response against each TAA was shown via IFNγ ELISPOT analysis of re-stimulated splenocytes from immunized mice. Additionally, we showed that vaccine-induced Ag-specific antibodies directed B16F10 melanoma cells to complement-dependent lysis. The vaccine’s therapeutic potential was analyzed in prevention and treatment of B16F10 mouse melanoma. The preventative vaccination significantly reduced the number of metastatic tumor nodules in lungs. Since B16F10 melanomas are immunologically resistant tumors, we combined vaccination with aPD-1 and aPD-L1 checkpoint inhibitors for treatment of established solid tumor. The combination of both vaccine and checkpoint inhibitors significantly delayed tumor growth and extended animal survival. In summary, our preliminary data suggest that a multivalent vaccine based on modified AAV6 vectors generates strong immune responses against endogenous self-proteins, and vaccination may have a therapeutic benefit against both metastatic and solid tumor development.