Transient JAK/STAT inhibition by ruxolitinib modulates malaria-specific CD4+ T cell responses and enhances recall immunity in volunteers experimentally infected with Plasmodium falciparum.

Type I interferon (IFN) signalling promotes development of type 1 regulatory (Tr1) CD4+ T cells, which suppress inflammation but may limit protective immunity in malaria by constraining effector Th1 cells and antibody-promoting T follicular helper (Tfh) cells. We tested whether transiently blocking IFN-driven JAK/STAT signalling with ruxolitinib would reduce Tr1 cell development and enhance protective Th1 and Tfh cell responses. Using controlled human malaria infection, we investigated the impact of ruxolitinib on CD4+ T cell activation and antigen-specific immunity. Whole blood stimulation with IFN{beta}, IL-2, or PMA/Ionomycin revealed that ruxolitinib suppressed pSTAT1, pSTAT3, and pSTAT5 in CD4+ T cells following treatment. However, antigen-specific CD4+ T cell responses were preserved. Further, ruxolitinib enhanced recall CD4+ T cell responses during a second infection, with increased frequencies of antigen-specific Th1, Tfh, and Tr1 cell subsets. Transcriptional analysis revealed overlapping gene signatures and clonal sharing between Th1, Tfh and Tr1 cells. These findings show transient JAK inhibition can modulate development of Th1, Tfh and Tr1 cell subsets in malaria, suppressing inhibitory signalling while enhancing the magnitude and durability of the CD4+ T cell recall response following a second infection. Targeting IFN-driven Tr1 cell activity therefore represents a promising host-directed strategy to improve malaria immunity. Type I interferon (IFN) signalling promotes type 1 regulatory (Tr1) CD4+ T cells, which suppress inflammation but may also limit protective Th1 and T follicular helper (Tfh) cell responses in malaria. We tested whether transient blockade of IFN-driven JAK/STAT signalling with ruxolitinib would reduce Tr1 cell activity and enhance protective CD4+ T cell responses. In controlled human malaria infection, we assessed the impact of ruxolitinib on CD4+ T cell activation and antigen-specific responses. Ruxolitinib suppressed pSTAT1, pSTAT3, and pSTAT5 in CD4+ T cells during treatment but preserved antigen-specific responses. Notably, ruxolitinib treatment in first infection enhanced recall CD4+ T cell responses during second infection, with increased frequencies of antigen-specific Th1, Tfh, and Tr1 cell subsets. These findings indicate that transient JAK inhibition reshapes the balance of Th1, Tfh and Tr1 cell subsets, and enhances the magnitude and durability of the CD4+ T cell recall response following a second infection. SummaryBlocking type I IFN signalling with ruxolitinib transiently reduces Tr1 cell activity while enhancing Th1 and Tfh cell recall responses, reshaping anti-parasitic CD4+ T cell-mediated immune responses in malaria.