Tofacitinib has been reported to inhibit a spectrum of cytokines from diverse cellular origins across a range of diseases, including IL-4, IL-5, IL-6, IL-10, IL-17, IL-21, IL-23, IL-8, TNF-α, and IL-1 (229–232), all of which are intricately linked to PV pathogenesis. The gene discussed is IL21; the disease is acquired polycythemia vera.