4'-Aminomethyltrioxsalen hydrochloride (AMT) is a psoralen derivative used primarily in extracorporeal photopheresis (ECP) for treating conditions such as cutaneous T-cell lymphoma (CTCL), graft-versus-host disease (GVHD), and other immune-mediated disorders. It intercalates into DNA of leukocytes or pathogens and, upon UVA irradiation, forms covalent crosslinks, inducing apoptosis in targeted cells and modulating immune responses. This enables the reinfusion of treated blood components to achieve therapeutic effects. Additionally, it is employed in molecular biology research to study DNA structure, function, and gene expression through photochemical crosslinking mechanisms.