Interferon-γ promotes SMAP production by cytotoxic T lymphocytes in a thrombospondin 4 dependent manner

Cytotoxic T lymphocytes (CTLs) eliminate infected and cancerous cells by exocytosing cytotoxic granules, either as single-core granules (SCGs) releasing diffusible Granzyme B and Perforin, or as multi-core granules (MCGs) releasing these effectors as thrombospondin-1/4-encapsulated supramolecular attack particles (SMAPs). How CTLs differentially deploy these granule types remains unclear. We demonstrate that prolonged in vitro expansion and restimulation selectively enhance SMAP release, correlating with increased MCG maturation and thrombospondin-4 expression. Using high-resolution imaging, we identify fusion-competent MCG intermediates lacking SMAPs but releasing granzyme B diffusively. Mechanistically, interferon-{gamma} upregulates thrombospondin-4, driving MCG maturation and SMAP biogenesis, enhancing late-phase CTL killing efficiency against resistant targets. Consistent with this, THBS1 and THBS4 transcript levels appear elevated in melanoma-infiltrating CTLs compared with those during acute adenovirus infection. These findings define a stimulus-dependent, interferon-{gamma}-driven pathway tailoring CTL responses to chronic pathology and highlight opportunities for SMAP-targeted immunotherapies.