Herewith, we showed that intravenous application of MSCs in tumor-bearing mice significantly suppressed systemic antitumor immune response, reduced total number of lung-infiltrated DCs, macrophages, CD4+ T lymphocytes, CTLs, and NK cells, and attenuated antitumor cytotoxicity of CTLs and NK cells resulting with the expansion of metastatic lesions in the lungs. The gene discussed is CD4; the disease is neoplasm.