This study aims to investigate the effect of anti-PD-1 antibody expressed in mouse mammary gland on the surface antigen protein of spleen T cells, cytokine expression, spleen CD4⁺ T cell proliferation and proliferation related pathways of transgenic mice at the cellular level. Transgenic mice expressing anti-human PD-1 antibody at 8 weeks of age without pregnancy and 18 weeks of age with lactation were divided into two groups, with transgenic negative mice in each group as the control. Spleen lymphocytes were extracted and the changes of spleen lymphocytes were detected. Compared with transgenic negative mice, the proportion of effector T cells of spleen T cells in the immune system of transgenic mice with anti-PD-1 antibody expressed in breast increased, the proportion of Treg cells decreased, and the IFN-g, IL-17 and IL-2 expressed in CD4⁺ T cells increased in varying degrees. Moreover, IL-4, IL-10 and TGF-b in CD4⁺ T cells did not change, nor did some cell surface protein molecules related to T cell stimulate. There was no significant difference in T cell proliferation between transgenic positive and transgenic negative mice. In transgenic positive mice, the expression of phosphorylated proteins in PI3K/Akt/mTOR and RAS/MEK/ERK pathways were partially up-regulated, but the whole pathway was not completely up-regulated. Therefore, it is feasible to use transgenic mice as host to express monoclonal antibodies related to immune system such as anti-PD-1 antibody.