In medicine, photopheresis (aka extracorporeal photopheresis or ECP) is a form of apheresis and photodynamic therapy in which blood is subject to apheresis to separate buffy coat (WBC + platelets) from whole blood, chemically treated with 8-methoxypsoralen (instilled into a collection bag or given per os in advance), exposed to ultraviolet light (UVA), and then returned to the patient. Activated 8-methoxypsoralen crosslinks DNA in exposed cells, ultimately resulting apoptosis of nucleated cells. The photochemically damaged T-cells returned to the patient appear to induce cytotoxic effects on T-cell formation. The mechanism of such “antitumor” action has not been elucidated.
