A Trypanothione Synthetase-Based Subunit Vaccine Induces Protective Th1 Immunity against Visceral Leishmaniasis in Mice

Leishmaniasis, caused by Leishmania species, remains a major global health challenge due to limited therapeutic options, drug resistance, and relapse. To achieve long-term protection, an effective vaccine is urgently needed. In this work, we evaluated Leishmania donovani trypanothione synthetase as a vaccine candidate in BALB/c mice, formulated with CpG oligodeoxynucleotides and interleukin-2 to enhance immunogenicity. Mice were immunized with LdTryS alone or in combination with CpG and IL-2, followed by a challenge infection. Immunological parameters assessed included parasite burden, cytokine profiling, NO production, IgG isotype, T-cell proliferation, and intracellular cytokine production. We observed a significant reduction in parasite load in the spleen and liver. Higher IgG2a-associated absorbance values and an increased IgG2a/IgG1 ratio were observed at the tested serum dilution, consistent with a trend toward a Th1-associated humoral response. Splenocytes from vaccinated animals produced higher levels of IFN-γ, TNF-α, and IL-2, whereas the levels of IL-4 and IL-5 were significantly lowered. Collectively, these findings underscore that LdTryS alone, and even more effectively in combination with CpG and IL-2, triggers potent Th1-oriented humoral and cellular immunity and thus could be a promising vaccine candidate against VL.