TAP2 is an ATP-binding cassette transporter that functions as a critical component of the antigen presentation machinery. In complex with TAP1, TAP2 mediates unidirectional translocation of cytosolic peptide antigens (8-13 amino acids) into the endoplasmic reticulum for loading onto MHC class I molecules 1. The transporter alternates between inward-facing and outward-facing conformations, with ATP hydrolysis driving the conformational switch necessary for peptide export against concentration gradients 12. TAP2 exhibits specificity for peptides with hydrophobic residues at position 3 and C-terminal anchor positions, while proline at position 2 destabilizes binding 3. Beyond canonical antigen presentation, TAP2 downregulation emerges as a dominant immune evasion mechanism in non-small cell lung cancer, driven by IL-4-mediated suppression of TAP2 expression and associated with reduced surface HLA-peptide complexes and resistance to CD8+ T-cell killing 4. TAP2 expression serves as a prognostic marker across multiple cancer types and correlates with immunotherapy response 5. Genetically, TAP2 polymorphisms associate with multiple autoimmune and infectious diseases. Specific variants (TAP2-379Ile, TAP2-565Thr) increase susceptibility to rheumatoid arthritis 6 and ankylosing spondylitis 7. TAP2 variants also interact epistatically with LILR locus variants in Crohn's disease risk 8 and influence hepatitis C treatment responses 9. These associations highlight TAP2's central role in immune regulation beyond its canonical antigen-processing function.