Interestingly, gain of function (GOF) mutations of Stat3 in humans can result in early stages of autoimmunity (e.g., type I diabetes, arthritis) but can also cause some types of immunodeficiencies such as hypogammaglobulinemia, as well as increased recurrent infections [32,35], but the underlined mechanisms for this effect remain unclear. Here, STAT3 is linked to Immunodeficiency.