Photopheresis

In medicine, photopheresis (aka extracorporeal photopheresis or ECP) is a form of apheresis and photodynamic therapy in which blood is treated with a photosensitizing agent and subsequently irradiated with specified wavelengths of light to achieve an effect. Specifically, buffy coat (WBC + platelets) is separated from whole blood, chemically treated with 8-methoxypsoralen (instilled into collection bag or given per os in advance), exposed to ultraviolet light (UVA), and 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.

Photopheresis involving 8-methoxypsoralen was first described in a 1987 New England Journal of Medicine publication. Photopheresis is currently standard therapy approved by the U.S. Food and Drug Administration (FDA) for cutaneous T-cell lymphoma. Evidence suggests that this treatment might be effective in the treatment of graft-versus-host disease, though this evidence is largely observational and controlled trials are needed to support this use. Photopheresis has also been used successfully in the treatment of epidermolysis bullosa acquisita when all other treatments have been ineffective.

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.