STAT3 and interstitial lung disease: On the other hand, the intrinsic immune dysregulation typical of CVID may favor the development of interstitial lung disease, as observed in CVID-like monogenic diseases such as cytotoxic T lymphocyte associated protein-4 (CTLA-4) deficiency and signal transducer and activator of transcription 3 (STAT3) gain-of-function mutations.