To date, reduced numbers of circulating Vγ9Vδ2 T cells expressing skin-homing cutaneous lymphocyte-associated antigen (CLA) (8), and genes controlling IFN-γ/TNF signaling, T cell activation, and proliferation have been found in PV patients (19), and their transition from naïve to terminally differentiated phenotype has been linked to disease severity (19). The gene discussed is IFNG; the disease is acquired polycythemia vera.