Flow cytometry showed that the number of CD3 + CD8 + cells in the spleen of normal mice was about 29.8%, whereas the cells in the spleen of 4T1 tumour‐bearing mice were decreased to 2.9% (Figure 1D,E), indicating that the reduced killer T lymphocytes in spleen of 4T1 tumour‐bearing mice might be benefit to the formation of immunosuppressive microenvironment. The gene discussed is CD8A; the disease is neoplasm.