Leishmania amazonensis promastigote surface antigen expressed on virus-like particles elicits cross-protective immunity against L. donovani in mice

The immunogenicity of promastigote surface antigens (PSA) derived from Leishmania spp. has been well-documented and the efficacy of various vaccine platforms, including virus-like particles (VLPs) that express this antigen has been explored. However, many PSA-expressing vaccine studies involved homologous challenge infection and cross-species protection elicited by PSA-expressing leishmaniasis vaccines remains largely unexplored. To address this gap in our understanding, we evaluated the cross-protective efficacy of VLP vaccines expressing the L. amazonensis PSA (LaPSA-VLP) against L. donovani infection in mice. Influenza VLPs expressing the PSA of L. amazonensis were self-assembled in Spodoptera frugiperda insect cells. The VLPs were characterized by SDS-PAGE, western blotting, and transmission electron microscopy to confirm successful assembly and antigen expression. L. amazonensis parasites expressing mCherry fluorescence were cultured, and the peak growth time point was selected. To evaluate heterologous protection, mice were immunized three times at 3-week intervals, and blood was collected 1 week after each immunization. Three weeks after the final immunization, mice were challenge-infected and killed 2 weeks post-infection for sample collection. Antibody responses, immune cell analysis, cytokine production measurement, and parasite burden were assessed. Nucleotide and amino acid sequences for the PSA of L. amazonensis and L. donovani were highly similar, signifying that cross-reactivity between the two species can occur. Intramuscular LaPSA-VLP immunization elicited cross-reactive IgG antibody production that reacted with L. donovani antigens. Compared to the unimmunized controls, LaPSA-VLP vaccines enabled the induction of germinal center B cells and CD4 + /CD8 + T cells. VLP vaccines significantly reduced hepatic inflammation by limiting IFN-γ and IL-6 cytokine production. LaPSA-VLP immunization drastically reduced the parasite burden in the visceral organs, implying that the PSA antigen derived from L. amazonensis can confer cross-protection against L. donovani infection.