Immunotherapeutic potential of PD-1 blockade in chronic Leishmania mexicana infection through the enhancement of progenitor-like CXCR5+ and intermediate CXCR5+TIM-3+ exhausted T cells.

Diffuse cutaneous leishmaniasis (DCL), caused by Leishmania mexicana, is a chronic, treatment-refractory form of leishmaniasis characterized by multiple nodular lesions and high parasite load. During chronic infection, T cells acquire an exhausted immune state marked by elevated expression of PD-1 and comprise progenitor-like (CXCR5+TIM-3-), intermediate (CXCR5+TIM-3+), and terminally-differentiated (CXCR5-TIM-3+) exhausted T-cell (Tex) subsets. It remains unknown whether anti-PD-1 immune checkpoint therapy is effective during chronic L. mexicana infection and how it affects the Tex landscape. To address this, C57BL/6 mice chronically infected with L. mexicana were treated from day 45 post-infection with a variable-dose anti-PD-1 mAb regimen consisting of three 250 μg/dose induction doses followed by five 100 μg/dose maintenance doses. Anti-PD-1 immunotherapy limited lesion progression and reduced parasite burden in chronically infected mice. This effect was associated with enhanced antigen-specific Th1 immune response and functional reinvigoration of CD8+ and CD4+ T cells in draining lymph nodes, as evidenced by increased expression of CD69, Ki-67, IFN-γ, and GrzmB. Consistent with these findings, confocal microscopy analysis of footpad lesions revealed increased IFN-γ- and TNF-α-co-producing T cells. This study provides the first evidence that PD-1 blockade enhanced PD-1+CXCR5+ and PD-1+TIM-3+ Tex cells within lesion sites of L. mexicana-infected mice. In draining lymph nodes, anti-PD-1 treatment expanded progenitor-like CXCR5+TIM-3- Tex cells in both CD4+ and CD8+ T-cell compartments, as well as intermediate CXCR5+TIM-3+ Tex cells within the CD8+ T-cell compartment. Overall, these findings demonstrate that anti-PD-1 immunotherapy improves clinical and parasitological outcomes during chronic L. mexicana infection in association with enhanced Th1-type immunity and remodeling of the exhausted T-cell compartment, supporting further investigation of PD-1/PD-L1 checkpoint blockade as a potential immunotherapeutic strategy for DCL.