They include cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) haploinsufficiency [5, 6], signal transducer and activator of transcription 3 (STAT3) gain-of-function (GOF) disease [7], activated phosphoinositide 3-kinase δ syndrome (APDS) [8–11], and nuclear factor kB1 (NF-κB1) haploinsufficiency [12]. Here, STAT3 is linked to activated PI3K-delta syndrome.