PD-1 Blockade Reduces Parasite Load and Restores Anti-Parasitic Immunity in Murine Visceral Leishmaniasis

Immune checkpoint blockade holds therapeutic potential in visceral leishmaniasis; its underlying mechanism remains unclear. This study aimed to investigate the therapeutic potential and underlying immune mechanisms of Programmed cell death protein 1 (PD-1) blockade in experimental visceral leishmaniasis.

BALB/c mice infected with Leishmania donovani received anti-PD-1 antibody at 35–44 days post-infection. Parasite burden in target organs, serum antibodies, hepatopathology, and transcriptome of the liver were analyzed. T cell exhaustion, activation, apoptosis, and inflammation genes were quantified in target organs.

PD-1 blockade reduced splenic parasite load (reduction rate = 82.6%, ***p < 0.001), enhanced hepatic granulomatous maturation, and elevated anti-Leishmania IgG/IgG1/IgG2a levels. qPCR analysis revealed that the expressions of exhaustion marker genes Programmed cell death 1 (Pdcd1) and B and T lymphocyte attenuator (Btla) were upregulated in the liver and spleen following Leishmania infection, indicating an exhausted state. After PD-1 blockade, the expression of pro-inflammatory cytokine genes Tumor necrosis factor alpha (Tnfa), Interferon gamma (Ifng), and Nitric Oxide Synthase 2 (Nos2) was upregulated in the spleen, while the expression of anti-inflammatory cytokine genes Interleukin 4 (Il4) and Interleukin 10 (Il10) was downregulated in the liver. Transcriptome suggested that antigen processing & presentation, Natural Killer cell-mediated cytotoxicity, and neutrophil extracellular trap formation pathways were restored after blockade. Six hub genes associated with immune restoration were identified, of which Activating transcription factor 3 (Atf3) was chosen to be overexpressed in RAW 264.7 and manifested a reduced infection rate and average Leishmania at 12 h post-infection.

This study demonstrated PD-1 blockade reinvigorated anti-parasitic immunity through multimodal mechanisms and illuminated both the potential and intricate dynamics of immune checkpoint modulation in leishmaniasis, where treatment success hinges on coordinated immune activation.