什么叫体外光除去疗法？

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In medicine, photopheresis or extracorporeal photopheresis is a form of apheresis in which blood is treated with photoactivable drugs which are then activated with ultraviolet light.
Photopheresis is currently standard FDA-approved therapy for cutaneous T-cell lymphoma（淋巴瘤）. In this procedure, buffy coat (WBC + platelets) （白细胞和血小板）is separated from whole blood, chemically treated with 8-Methoxypsoralen (instilled into collection bag or given per os in advance), exposed to ultraviolet light, and returned to the patient. 8-Methoxypsoralen irreversibly binds covalently to both strands of the DNA of nucleated cells following photoactivation. 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. Minimal observed side effects for patients receiving photopheresis include hypotension and syncope resulting from volume shifts during leukapheresis phase of treatment. Photopheresis is also used as an experimental treatment in patients with cardiac, pulmonary and renal allograft rejection, graft-versus-host disease, autoimmune diseases, nephrogenic systemic fibrosis and ulcerative colitis.
From Wikipedia