Intramuscular electroporation of a P1A-encoding plasmid vaccine delays P815 mastocytoma growth

• We constructed DNA vaccines directed to P815 mastocytoma.
• The vaccine encoding the P1A full-length protein induced antitumor response.
• Minigene vaccines coding for P1A35–43 failed to promote response.
• Electroporation is an efficient method to deliver DNA vaccines against P815.

This study aimed to construct DNA vaccines encoding the mouse P1A tumor antigen and to generate a protective immune response against the P815 mastocytoma, as a model for vaccines against human MAGE-type tumor antigens. DNA vaccines were constructed and delivered to mice by intramuscular electroporation before tumor challenge. Immunization with a plasmid coding for the full-length P1A significantly delayed tumor growth and mice survived at least 10 days longer than untreated controls. 10% of the mice completely rejected the P815 tumors while 50% of them showed a regression phase followed by tumor regrowth. Mice immunized by electroporation of a P1A35–43 minigene-encoding plasmid failed to reject tumor and even delay tumor growth. The P1A35–43-encoding plasmid was modified and helper epitope sequences were inserted. However, these modified plasmids were not able to improve the response against P815 mastocytoma. Consistent with these results, a 12-fold higher CTL activity was observed when the plasmid coding for full-length P1A was delivered as compared to the plasmid encoding the P1A35–43 epitope. Our results demonstrated that electroporation is an efficient method to deliver DNA vaccines against P815 and suggested the superiority of full-length as compared to minigene constructs for DNA vaccines.

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