CD8A and colorectal carcinoma: An orally applied mixture of four Clostridiales strains (CC4), namely Anaerostipes caccae, Eubacterium hallii, F. prausnitzii, and Roseburia intestinalis, effectively prevented and treated CRC in mice by promoting the intratumoral infiltration and activation of CD8+ T cells and NK cells indicated by increased production of IFN-γ and granzyme B. The anticancer effect of the CC4 mix could be completely abolished in mature B/T cell-deficient mice.