Monophosphoryl Lipid A Based Cationic Liposome Facilitates Vaccine Induced Expansion of Polyfunctional T Cell Immune Responses against Visceral Leishmaniasis

Numerous experimental DNA vaccines have been tested against Leishmania, whose clinical use is mostly limited due to insufficient CD8(+) T cell-mediated immunity arising from poor gene delivery or presentation. Hence, there remains an important public health demand for a better vaccine adjuvant to combat leishmaniasis: ensuring proper antigen delivery coupled with strong cell mediated immune (CMI) response. To this end, we herein report, for the first time, novel cationic liposomes containing monophosphoryl lipid A (MPLA) intercalated into the 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) lipid bilayer as an adjuvant for a DNA vaccine to enhance antileishmanial immunity. Interestingly, this MPLA-liposomal formulation strongly amplified the Leishmania donovani cysteine protease C (Ldcpc) DNA vaccine (i.e., pVAX1-cpc)-induced endogenous T cell and antibody responses with a Th1 biased profile. MPLA-liposomes could activate the splenic DCs in vivo and increased magnitude of antigen-specific polyfunctional CD4(+) and CD8(+) T cells together with CD8(+) IFN-gamma(+) memory generation in BALB/c mice. Most importantly, in comparison to the mice receiving 'naked' pVAX1-cpc, immunization with MPLA-liposomal pVAX1-cpc DNA resulted in substantial reduction in parasite load, in association with reduced IL-10, IL-4 and TGF-beta along with enhanced IFN-gamma/IL-4 and IFN-gamma/IL-10 cytokine ratios. Parasite burden inversely correlated with frequency of CD4(+) and CD8(+) T cells producing postinfection IFN-gamma, IL-2, and TNF-alpha simultaneously, resulting in almost sterile protection (>98%) conferred by the DNA vaccine entrapped in MPLA-liposomes. This DNA vaccine afforded potent central and effector memory cell formation required for long-lasting immunity. Hence, this novel MPLA-DSPC adjuvant formulation approach could be a safe, biocompatible, and amenable choice as a strong immunostimulating agent delivery system holding promise against leishmaniasis and several other infectious diseases in the near future.