Evaluation of the immunoprophylactic potential of a killed vaccine candidate in combination with different adjuvants against murine visceral leishmaniasis.

Despite a large number of field trials, till date no prophylactic antileishmanial vaccine exists for human use. Killed antigen formulations offer the advantage of being safe but they have limited immunogenicity. Recent research has documented that efforts to develop effective Leishmania vaccine have been limited due to the lack of an appropriate adjuvant. Addition of adjuvants to vaccines boosts and directs the immunogenicity of antigens. So, the present study was done to evaluate the effectiveness of four adjuvants i.e. alum, saponin, cationic liposomes and monophosphoryl lipid-A in combination with Autoclaved Leishmania donovani (ALD) antigen against murine visceral leishmaniasis (VL). BALB/c mice were immunized thrice with respective vaccine formulation. Two weeks after last booster, challenge infection was given. Mice were sacrificed 15 days after last immunization and on 30, 60 and 90 post infection/challenge days. A considerable protective efficacy was shown by all vaccine formulations. It was evident from significant reduction in parasite load, profound delayed type hypersensitivity responses (DTH), increased IgG2a titres and high levels of Th1 cytokines (IFN-γ, IL-12) as compared to the infected controls. However, level of protection varied with the type of adjuvant used. Maximum protection was achieved with the use of liposome encapsulated ALD antigen and it was closely followed by group immunized with ALD+MPL-A. Significant results were also obtained with ALD+saponin, ALD+alum and ALD antigen (alone) but the protective efficacy was reduced as compared to other immunized groups. The present study reveals greater efficacy of two vaccine formulations i.e. ALD+liposome and ALD+MPL-A against murine VL.