CD4⁺ T cells are major effector cells during host immune responses against protozoan parasites. The ability of CD4⁺ T cells to produce pro-inflammatory cytokines is crucial for mediating protection. However, these cells can become functionally impaired during chronic disease. Visceral leishmaniasis (VL) is an important parasitic disease with unmet medical needs. An experimental model of VL caused by infection of C57BL/6 mice with the human parasite Leishmania donovani provides a unique opportunity to understand molecular changes in CD4⁺ T cells during acute and chronic infection within the same host. In this model, an acute infection develops in the liver, associated with the emergence of potent anti-parasitic CD4⁺ T cells, while a chronic infection becomes established in the spleen with the accumulation of dysfunctional CD4⁺ T cells. In this study, we hypothesised that transcriptional differences between CD4⁺ T cells from the spleen and liver would allow us to identify molecules associated with CD4⁺ T cell dysfunction that can be targeted to restore immune function. To test this, we identified transcriptional signatures associated with CD4⁺ T cells isolated from the spleen and liver of L. donovani-infected C57BL/6 mice. We also identified a transcriptional signature associated with CD4⁺ T cells isolated from the blood of VL patients with active disease and overlapped this data set with our mouse data to discover a set of differentially expressed genes from CD4⁺ T cells associated with immune dysfunction. These gene products have been ranked and prioritised as potential targets for immune checkpoint blockade and studies are currently underway to functionally validate several of these molecules using small molecule inhibitors, genetically-modified mice and genetic manipulation of primary CD4⁺ T cells using CRISPR/Cas9. Results from these studies will be presented.