Protective efficacy of heat-killed Leishmnaia donovani vaccine adjuvanted with Toll Like Receptor 7/8 agonist in BALB/c mice.

Visceral leishmaniasis, caused by the protozoan parasite Leishmania donovani is one of the most life threatening neglected tropical disease with no licensed human vaccine and increasing risks of resistance to chemotherapeutic agents. Current vaccine approaches are hindered by suboptimal immunogenecity, underscoring the need for potent adjuvant that can steer a durable and protective immune response. Here, we reported for the first time immunotherapeutic potential of a synthetic TLR7/8 agonist, 1-(4-(aminomethyl)benzyl)-2-butyl-1H-imidazo[4,5-c]quinolin-4 aminedihydrochloride (p-AM-BBIQ), in combination with heat-killed L. donovani antigen (HKA) in a murine model. Mice immunized with the adjuvanted formulation exhibited significant reduction in splenic parasite load, alongside enhanced production of nitric oxide and reactive oxygen species. Trancriptional profiling revealed increased upregulation of iNOS and Nf-κB, indicating activation of innate immune response. Flow cytometric analysis demonstrated increased frequencies of CD4+ and CD8+ T cells in splenocytes, while serum cytokine analysis showed elevated Th1-associated cytokines (IFN-γ and TNF-α) and reduced Th2 (IL-10 and IL-13) and regulatory cytokine (IL-27). These findings highlight the ability of p-AM-BBIQ to potentiate innate and adaptive immune responses, supporting its translational potential as a TLR7/8-targeted adjuvant to enhance killed vaccine efficacy against VL and other intracellular infections requiring strong Th1 immunity.