Identification of novel Leishmania donovani antigens that help define correlates of vaccine-mediated protection in visceral leishmaniasis.

Visceral leishmaniasis (VL), caused by the intracellular parasite Leishmania donovani is a major public health problem in the developing world. But there is no effective and safe vaccine approved for clinical use against any form of leishmaniasis. Through reactivity with kala-azar patient and cured sera, polypeptides ranging from 91 to 31-kDa from L. donovani promastigotes were previously identified as potential protective vaccine candidates. In this study four polypeptides 91(LD91), 72 (LD72), 51(LD51) and 31 (LD31)-kDa were purified using sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by electroelution. We compared the vaccine efficacy of these antigens encapsulated in cationic liposomes in BALB/c mice against challenge infection with L. donovani. Our results demonstrated that liposomal LD31 (74%-77%) and LD51 (72%-75%) vaccination reduced parasite burden to the greatest degree followed by liposomal LD72 (65%-67%) and LD91 (46%-49%). Analysis of the cytokine responses in immunized mice revealed that all the vaccinated groups produced prechallenge interferon-gamma, interleukin-12 and interleukin-4. Interestingly, the degree of reduction in parasite load could be predicted by the magnitude of the cytokine responses which correlated inversely with the parasite burden both in liver and spleen. The 31, 51 and 72-kDa bands were identified as ATP synthase alpha chain, beta-tubulin and heat shock 70-related protein 1 precursor of L. major, respectively using matrix-assisted laser desorption ionization-time of flight (MALDI-TOF/TOF) mass spectrometry. These three leishmanial antigens have not been described before as successful vaccine candidates examined against in vivo VL model. Thus, these antigens can be potential components of future antileishmaniasis vaccines.