CD4 and renal fibrosis: Importantly, combined with existing literatures [27–32], these findings in this study provide a hypothesis that PMSCs may circulate to the spleen, subsequently inhibiting mTOR phosphorylation of Naïve CD4+ T cells, further promoting Naïve CD4+ T cells to differentiate into Tregs, thereby leading to the recruitment of Tregs in the kidney, ultimately inhibiting inflammatory process and effectively alleviating renal fibrosis.