GZMB and neoplasm: Pan-cancer studies further validate IPA’s causal role: its supplementation improves ICI response rates across malignancies (110, 159), while ATB-induced microbiota depletion reduces IPA levels and blunts γδ T cell-mediated tumor control—an effect reversed by exogenous IPA, which directly upregulates granzyme B/perforin in γδ T cells (111).