The results of this study showed that IL-35 could significantly increase the proportion of CD4+ Foxp3+ Treg cells and decrease the proportion of CD4+ and CD8+ T in the spleen, blood and tumour tissue of mice with prostate cancer, indicating that IL-35 could promote CD4+ Foxp3+ Treg cells, inhibiting antitumour immunity and promoting the progression of PCA. The gene discussed is FOXP3; the disease is prostate carcinoma.