STAT3 and hyper-IgE syndrome: Indeed, Th17 cells differentiation was abrogated in the absence of STAT3, both in vitro and in vivo [31,71], corroborated by the finding that patients with hyper immunoglobulin E syndrome (HIES), who show STAT3 inactivating mutations [72,73] display impaired Th17 differentiation that may also explain their recurrent infections [74,75].