TAPBP (tapasin) is a molecular chaperone essential for MHC class I antigen presentation. It functions as a bridge linking MHC class I molecules to the TAP transporter in the endoplasmic reticulum, facilitating peptide loading onto MHC class I complexes 1. This process is critical for immune recognition of intracellular antigens by CD8+ T cells. Genetically, TAPBP variants influence disease susceptibility across multiple conditions. Loss-of-function mutations cause MHC class I deficiency type 3, an inborn error of immunity predisposing to recurrent bacterial infections including pneumococcal pneumonia and Haemophilus influenzae 2. Conversely, increased TAPBP expression associates with enhanced malaria resistance through improved antigen presentation by tapasin-dependent HLA allotypes 3. TAPBP upregulation promotes anti-tumor immunity in colorectal cancer by activating type I interferon pathways and enhancing CD8+ T cell infiltration 4. Clinically, TAPBP emerges as a multi-cancer biomarker. A genetic variant (rs1059288) increases cervical cancer susceptibility through enhanced m6A modification, with elevated TAPBP promoting tumor growth and chemotherapy resistance 5. Conversely, decreased circulating TAPBP associates with increased ankylosing spondylitis risk 6, and TAPBP shows cross-cancer effects as a potential therapeutic target 7. These findings highlight TAPBP's dual role: essential for protective immunity while potentially contributing to cancer progression when dysregulated.