Overproduction of TGF-β1 in 4T1/TGF-β1 tumor-bearing mice was associated with a higher percentage of CD4+CD25+Foxp3+ cells in the lungs and CD103+CD4+Foxp3+ cells in the spleens, compared with 4T1/RFP tumor-bearing mice and tumor-free mice. The gene discussed is TGFB1; the disease is neoplasm.