CIITA (class II major histocompatibility complex transactivator) is the master regulator of MHC class II gene expression and a founding member of the nucleotide-binding oligomerization domain-like receptor (NLR) family 1. As a transcription factor, CIITA activates MHC-II genes essential for adaptive immunity by interacting with chr16-modifying enzymes and DNA-binding proteins that regulate histone acetylation and methylation 2. CIITA expression is controlled by cell-type-specific promoters regulated by transcription factors like ZBTB48, particularly in B cells 3. Beyond its canonical role in adaptive immunity, CIITA functions uniquely as a restriction factor against retroviruses including HIV-1 and HTLV-1 through multiple molecular mechanisms, exemplifying a dual link between intrinsic and adaptive immunity 4. CIITA also regulates butyrophilin family genes involved in unconventional T cell responses 5. In disease contexts, CIITA dysregulation contributes to pathology: elevated CIITA drives hepatocyte conversion to antigen-presenting cells in nonalcoholic steatohepatitis 6, while epigenetic suppression of CIITA in multiple myeloma reduces MHC expression and immunogenicity 7. Clinically, CIITA-engineered tumor cells effectively present tumor antigens and induce cross-protective anti-tumor immunity, showing therapeutic potential for cancer immunotherapy 8. Mutations in CIITA cause MHC class II deficiency, underscoring its essential role in immune function.