CD4 and neoplasm: Studies on coculture of tumor-derived exosomes and CD25− CD4+ T cells show that exosomes promote the production and proliferation of Tregs by transforming CD25− CD4+ T cells into FoxP3+ CD4+ CD25high T cells via microRNA-214-dependent suppression of PTEN in T cells and induction of Tregs to secrete IL-10, which ultimately leads to the promotion of tumor growth [114].