CD4 and myeloproliferative disorder: Indeed, the proportion, phenotype and function of circulating CD4 + CD25 + Foxp3 + T lymphocytes did not significantly differ between untreated MPN patients (6.9%), healthy subjects (6.1%) and MPN patients treated with hydroxyurea (5.8%), while a remarkable expansion of Tregs (13%) was detected in MPN patients undergoing long-term IFN-α therapy [108].