Pimozide enhances antigen cross-presentation and promotes cytotoxic CD8+ T cell immunity by stimulating dendritic cells.

The activation of cytotoxic CD8+ T cells requires antigen presentation in the context of major histocompatibility complex class I (MHC-I). While endogenous antigens can directly access this pathway, the priming of CD8+ T cells against exogenous antigens-such as those derived from tumors or internalized pathogens-depends on dendritic cell (DC)-mediated antigen cross-presentation. Strategies capable of enhancing DC cross-presentation are therefore of considerable interest for the development of next-generation immunotherapies. Here, we demonstrate that pimozide, a clinically approved antipsychotic with reported antitumoral and immunomodulatory properties, acts as a pharmacological enhancer of antigen cross-presentation. We show that pimozide-treated DCs display improved cross-presentation of soluble antigens, leading to stronger CD8+ T cell activation and proliferation in vivo, enhanced IFN-γ production by antigen-specific CD8+ T cells in vitro, and augmented cytotoxic T lymphocyte responses in vivo. Mechanistically, pimozide reshapes antigen-processing pathways in DCs by increasing reactive oxygen species production and altering endosomal physiology, thereby creating a biochemical environment that favors antigen cross-presentation. Moreover, pimozide treatment reduces STAT5 levels in DCs, and pharmacological inhibition of STAT5 with an independent inhibitor recapitulates the enhancement of cross-presentation and CD8+ T cell activation, suggesting STAT5 signaling as a mediator of this effect. Together, these findings reveal an unrecognized immunomodulatory activity of pimozide on DCs and establish a conceptual framework for the pharmacological repositioning of small molecules to reprogram DC function. This work ultimately opens new avenues for amplifying cytotoxic CD8+ T cell immunity in the context of next-generation cancer immunotherapies.