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gp63 in Stable Cationic Liposomes Confers Sustained Vaccine Immunity to Susceptible BALB/c Mice Infected with Leishmania donovani

Swati Bhowmick, Rajesh Ravindran, and Nahid Ali^*

Indian Institute of Chemical Biology, Infectious Diseases and Immunology Division, Kolkata 700032, India

Received 30 April 2007/ Returned for modification 13 July 2007/ Accepted 4 January 2008

Visceral leishmaniasis is deadly if not treated, and development of a vaccine with long-term immunity remains a challenge. In this study, we showed that cationic distearoyl phosphatidylcholine (DSPC) liposomes, when used as vaccine adjuvant with the immunodominant 63-kDa glycoprotein (gp63) of Leishmania donovani promastigotes, induced significant protection against progressive visceral leishmaniasis in susceptible BALB/c mice. gp63 used without adjuvant elicited partial protection but in association with liposomes exhibited marked resistance in both the livers and spleens of the mice challenged 10 days after the last vaccination. The protective efficacy of liposomal gp63 vaccination was dose dependent, with 2.5 µg of protein showing optimal protection. The immunity conferred by this vaccine formulation was durable, as mice challenged 12 weeks after immunization were still protected, and the infection was controlled for at least 3 months postchallenge. Production of gamma interferon (IFN-) and interleukin-4 (IL-4) by splenic T cells, and of serum immunoglobulin G1 (IgG1) and IgG2a following immunization, suggested that a mixed Th1/Th2 response had been induced following immunization. However, control of disease progression and parasitic burden in mice vaccinated with gp63 in cationic DSPC liposomes was associated with enhancement of antigen-specific IFN- and downregulation of IL-4, demonstrating a Th1 bias. Long-term immunity elicited by this vaccine corresponded to, in addition to the presence of antigen-specific Th1, CD8⁺ T-cell responses. Our results demonstrated that stable cationic liposomes containing gp63 acted as a potent adjuvant for protein antigen to induce long-term protection against L. donovani that represents an alternative to DNA vaccination.

Published ahead of print on 14 January 2008.

Editor: J. F. Urban, Jr.

Present address: Department of Pathology, Emory Vaccine Center, 954 Gatewood Road, Atlanta, GA 30329.