CD8A and neoplasm: CD8+ T lymphocytes, which are the primary cytotoxic T lymphocytes (CTLs) responsible for the direct elimination of tumor cells [37], were more abundant in the tumors of the mice treated with SRF@Fe(III)-COF + PD-1 than in those treated with SRF@Fe(III)-COF or PD-1 alone (Fig. 7E and F).