IL-12 as an immunopotentiator in leishmaniasis

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Leishmaniasis is a major public health problem in large parts of the world, due in part to the lack of a vaccine and inadequate chemotherapy. Studies of the immune responses in humans and mice following Leishmania infection have provided an understanding of many of the cells and cytokines that contribute to the control of this disease. Nevertheless, a vaccine for human leishmaniasis does not exist. Understanding how memory T cells develop will be crucial in the development of such vaccines. Two types of memory T cells have been described: T effector memory cells, which produce effector cytokines and migrate through the tissues, and central memory T cells that do not produce effector cytokines and migrate through lymph nodes. C57BL/6 mice infected with Leishmania major are immune to rechallenge after they resolve their infections, but this immunity was thought to be dependent upon residual parasites. Now an attenuated L. major parasite that is eliminated after eight weeks has been shown to stimulate the development of long- lived protective memory T cells. These cells have the characteristics of central memory T cells, and the studies in this proposal will characterize these cells and assess whether we can generate memory T cells with an effector phenotype. The studies will include a comparison of the ability of a Listeria expressing a leishmanial antigen and L. major to stimulate effector memory T cells, assessment of the role that parasite persistence plays in blocking the development of effector memory cells, and how dendritic cells influence memory T cell generation. The experiments utilize state-of-the art tools that will allow qualitative and quantitative assessment of memory T cell development. Overall, the experiments described in this proposal will determine what type of immunologic memory can be induced in leishmaniasis, which will provide direction for the field in establishing what are reasonable goals for a leishmaniasis vaccine.