Skin resident memory cells generated by the L. major centrin gene deleted parasites mediate protective immune response analogous to leishmanization

Leishmaniasis is a vector-borne parasitic disease transmitted through the bite of a sand fly with no available vaccine for humans. Recently, we have developed a live attenuated Leishmania major centrin gene deleted parasite strain (LmCen-/-) that induced protection against a homologous and heterologous challenges. The protection is mediated by IFN{gamma} secreting CD4+ T effector cells and multifunctional T cells, which is analogous to leishmanization. Previously, skin tissue resident memory T cells (TRM cells) were shown to be crucial for host protection in a leishmanization model. In this study, we evaluated generation and function of skin TRM cells following immunization with LmCen-/- parasites and compared those with leishmanization. In the absence of recoverable LmCen-/- parasites, the skin of immunized mice showed functional TRM cells comparable to leishmanized mice. The generation of the skin TRM cells was supported by the induction of cytokines and chemokines essential for their production and survival. Following challenge infection with wild type L. major, TRM cells specific to L. major were rapidly recruited and proliferated at the site of infection in the immunized mice which was similar to leishmanization. Further, upon challenge, CD4+ TRM cells induced higher levels of IFN{gamma} and Granzyme B in the immunized and leishmanized mice than non-immunized mice. Taken together, our studies demonstrate that a genetically modified live attenuated Leishmania vaccine generates functional CD4+ TRM cells that mediate protection and can be a safer alternative to leishmanization.