Although PD-1 blockade inhibits pre-existing CD8+ T cells from immune resistance against tumors (44), and since 4T1 is a “cold” tumor with an immune-excluded phenotype (45, 46), monotherapy with anti–PD-1 Ab was not sufficient for tumor-specific CD8+ T cells to infiltrate into the primary tumor and inhibit tumor growth during treatment. Here, CD8A is linked to neoplasm.