STXBP2 and Wiskott-Aldrich syndrome: Previous work has shown that the presence of IL-2 during in vitro culturing of hCTLs or NK cells can restore cytotoxicity in hCTLs from familial hemophagocytic lymphohistiocytis 5 (FHL5, due to STXBP2 defect) or WAS patients (32–34).