HDAC9 and colorectal carcinoma: Butyrate, in particular, activates cytotoxic CD8+ T cells by inhibiting HDAC, which upregulates IFN-γ and granzyme B production (148); in CRC, R. intestinalis-derived butyrate correlates with improved anti-PD-1 responses by increasing intratumoral CD8+ T cell infiltration (148).