STAT3 and Autoimmunity: Altogether, these findings would support the existence of underlying autoimmunity mechanisms that lead to the abnormally decreased numbers of many different myeloid- and lymphoid-cell populations reported here and in previous studies in LGLL [1,9,10,46], suggesting the potential existence of shared pathogenic mechanisms for the cytopenias observed in both STAT3-mutated PID and LGLL.