Baculovirus-infected insect cells expressing peptide-MHC complexes elicit protective antitumor immunity

Evaluation of T cell responses to tumor- and pathogen-derived peptides in preclinical models is necessary to define the characteristics of efficacious peptide vaccines. We show in this study that vaccination with insect cells infected with baculoviruses expressing MHC class I linked to tumor peptide mimotopes results in expansion of functional peptide-specific CD8+ T cells that protect mice from tumor challenge. Specific peptide mimotopes selected from peptide-MHC libraries encoded by baculoviruses can be tested using this vaccine approach. Unlike other vaccine strategies, this vaccine has the following advantages: peptides that are difficult to solublize can be easily characterized, bona fide peptides without synthesis artifacts are presented, and additional adjuvants are not required to generate peptide-specific responses. Priming of antitumor responses occurs within 3 days of vaccination and is optimal 1 wk after a second injection. After vaccination, the Ag-specific T cell response is similar in animals primed with either soluble or membrane-bound Ag, and CD11c+ dendritic cells increase expression of maturation markers and stimulate proliferation of specific T cells ex vivo. Thus, the mechanism of Ag presentation induced by this vaccine is consistent with cross-priming by dendritic cells. This straightforward approach will facilitate future analyses of T cells elicited by peptide mimotopes.