Vaccination with plasmid DNA encoding KMPII, TRYP, LACK and GP63 does not protect dogs against Leishmania infantum experimental challenge

Abstract

Vaccination of dogs, the domestic reservoir of Leishmania infantum, is the best method for controlling zoonotic visceral leishmaniasis. This strategy would reduce the incidence of disease in both the canine and, indirectly, the human population. Different vaccination approaches have been investigated against canine leishmaniasis (CaL) but to date there is only one licensed vaccine against this disease in dogs, in Brazil. DNA immunization is a promising method for inducing both humoral and cellular immune responses against this parasitic disease. Here, we report the results of a multiantigenic plasmid DNA vaccine encoding KMPII, TRYP, LACK and GP63 L. infantum antigens against experimentally induced CaL. Twelve dogs were randomly assigned to two groups receiving, at a 15 days interval, either four doses of plasmid DNA or similar injections of PBS. After vaccination, dogs were intravenously challenged with 5 x 10(7) promastigotes of L. infantum. The vaccine showed to be safe and well-tolerated. Neither cellular immune response nor antibodies directed against whole Leishmania antigen were detected after immunization in vaccinated dogs, although anti-LACK-specific antibodies were sporadically detected in two vaccinated dogs before challenge, thus suggesting that antigens were indeed expressed. A delay in the development of detectable specific immune response and parasite multiplication in vaccinated dogs was observed after challenge. Nevertheless, the multiantigenic Leishmania DNA vaccine was unable to induce protection against parasite dissemination or disease. This study emphasizes the need to strengthen DNA vaccines in order to obtain effective immune responses in models other than the murine.