photopheresis
Meaning of photopheresis: Only the white cell layer is treated, and the cells sent back work by retraining the immune system rather than by being destroyed.
Definition of photopheresis
Photopheresis is a procedure in which blood is drawn through a machine that separates out the white cells, exposes them to a light-sensitive drug and ultraviolet A light, then returns them to the circulation. Red cells and plasma go back untreated. It is established treatment for cutaneous T-cell lymphoma and for graft-versus-host disease after a stem cell transplant.
What happens during a session?
Blood leaves through a needle or a central line and enters a machine that spins it, skimming off the pale layer of white cells and giving back everything else. A drug of the psoralen family is mixed into that collected layer. Psoralen slides between the two strands of DNA and does nothing until ultraviolet A light strikes it, at which point it locks the strands together. The treated cells are then reinfused. They are not destroyed on the spot; the damage commits them to a slow, orderly death over the following day.
Why does it not suppress the whole immune system?
The answer lies in what happens to those dying cells after they go back. Scavenging cells swallow them, display fragments of what they contained, and the immune response that follows is a damping one, expanding the regulatory cells that hold other immune cells in check. The effect is therefore selective for whatever the treated cells were reacting against. Ordinary blood counts do not fall, and the broad vulnerability to infection that comes with drugs suppressing the whole immune system is not a feature of it. That tolerance-building action, rather than simple cell killing, is the current understanding of how it works.
What is it used for?
| Setting | Role |
|---|---|
| Cutaneous T-cell lymphoma | Longest established use, for widespread skin and blood involvement |
| Chronic graft-versus-host disease | Widely used when steroids fail to control it |
| Heart and lung transplant rejection | Added when rejection recurs despite standard drugs |
Two treatments on consecutive days make up one cycle, repeated over months. The name extracorporeal photopheresis refers to the same procedure and stresses that the light exposure happens outside the body, which spares the skin and eyes the light sensitivity that swallowing the drug would cause. Its use after bone marrow transplantation accounts for most sessions performed.
Also known as
Used in a sentence
Photopheresis was started for chronic graft-versus-host disease of the skin.
Good to know
Whole blood is not treated: only the separated white cell fraction is exposed to the drug and light, and the response is attributed to a shift toward immune tolerance rather than to destruction of the treated cells.
Word origin
Where “photopheresis” comes from
From the Greek photos, meaning light, and apheresis, meaning a taking away, which is the word for drawing off one component of blood.