ABCB9 (ATP-binding cassette subfamily B member 9) is an ATP-dependent peptide transporter localized to the lysosomal membrane that mediates the translocation of cytosolic peptides into the lysosomal lumen for degradation 1. The protein functions as a homodimer and displays broad peptide length specificity ranging from 6-mers to at least 59-mers, with optimal transport of 23-mers 2. ABCB9 exhibits low-affinity but high-efficiency peptide transport, showing preference for positively charged, aromatic, or hydrophobic residues at peptide termini 2. Structurally, ABCB9 is a "half" ABC transporter closely related to the endoplasmic reticulum-resident TAP1/TAP2 proteins 1. Dysfunction of ABCB9 is implicated in multiple pathologies. A genome-wide association study identified ABCB9 as a potential causal gene for schizophrenia 3, while another study found shared genetic associations between ABCB9 and Alzheimer's disease alongside immune-mediated diseases 4. Clinically, miR-31-mediated downregulation of ABCB9 confers cisplatin resistance in non-small cell lung cancer by reducing drug-induced apoptosis 5. Additionally, ABCB9 modulation via novel anticancer agents shows therapeutic potential in manipulating regulatory T cell function to inhibit cancer metastasis 6.