photopheresis

Photopheresis, formally extracorporeal photopheresis (ECP), is a medical procedure used to modulate the immune system by treating a patient’s white blood cells outside the body and returning them afterward. In the common form, leukocytes are collected through leukapheresis, exposed to a photosensitizing agent such as methoxsalen (a psoralen) and ultraviolet A (UVA) light, and then reinfused into the patient. The treatment is typically performed as an outpatient procedure over several hours per session.

The procedure is most commonly applied for cutaneous T-cell lymphomas, including mycosis fungoides and Sézary syndrome, and for graft-versus-host disease (GVHD) following hematopoietic stem cell transplantation. It is also used in some cases of solid organ transplant rejection risk and certain immunologic or inflammatory conditions, though evidence varies by condition. ECP is generally considered to have a favorable safety profile and is often chosen when systemic immunosuppression poses risks or inadequate responses occur.

Mechanistically, photopheresis is thought to induce immunomodulation rather than direct cytotoxicity. The treated leukocytes undergo apoptosis and, upon reinfusion, promote a shift in immune regulation through altered antigen presentation and cytokine patterns, which may enhance tolerance and reduce pathological immune activity.

Commonly reported advantages include the potential for symptom improvement with relatively low systemic toxicity. Side effects can include infusion-related reactions, fatigue, hypotension, fever, and increased photosensitivity; infections are uncommon but monitored, especially in immunocompromised patients. Treatment plans vary by condition and response, often requiring several weeks to months of therapy followed by maintenance sessions.