Photopheresis is a treatment that removes a portion of your white blood cells, exposes them to ultraviolet light, and returns them to your body to reset part of your immune system. Its full name is extracorporeal photopheresis (ECP), meaning “outside the body.” First approved by the FDA in 1988 for a type of skin lymphoma, it was the first cellular immunotherapy approved for cancer and has since become a key treatment for transplant rejection and other immune-driven conditions.
How Photopheresis Works
The procedure follows three main steps. First, blood is drawn and run through a machine that separates out your white blood cells, specifically a layer called mononuclear cells, which includes the immune cells driving disease. Second, those cells are mixed with a light-sensitive compound and exposed to UVA light (the same wavelength range found in sunlight, between 320 and 400 nanometers). Third, the treated cells are infused back into your bloodstream.
Once those treated cells return to your body, several things happen. Many of the problematic immune cells undergo a controlled form of cell death called apoptosis. Your body’s cleanup crew, a type of immune cell called monocytes, processes these dying cells and matures into a more regulatory form. This shifts your overall immune balance: the mix of signaling molecules in your blood changes, and certain T cell populations that were driving inflammation or attacking healthy tissue get dialed back. The net effect is targeted immune suppression without broadly wiping out your ability to fight infections, which is a significant advantage over many conventional immunosuppressive drugs.
Conditions Treated With Photopheresis
The FDA originally approved photopheresis for cutaneous T-cell lymphoma (CTCL), a group of cancers where abnormal T cells accumulate in the skin. The two most common forms are mycosis fungoides and Sézary syndrome. A retrospective study found that contemporary photopheresis therapy achieved an overall response rate of 77% in Sézary syndrome and advanced-stage mycosis fungoides. At six months, 65% of patients on photopheresis alone showed measurable improvement in blood markers. Many patients achieved durable remission, with 58% remaining progression-free at five years.
Beyond CTCL, photopheresis has become widely used for several other conditions:
- Graft-versus-host disease (GvHD): After a bone marrow or stem cell transplant, donated immune cells can attack the recipient’s body. Photopheresis is recommended as a second-line therapy when patients don’t respond to steroids, can’t tolerate them, or become dependent on them. It’s used for both the acute form (appearing soon after transplant) and the chronic form (developing months or years later).
- Solid organ transplant rejection: Photopheresis helps prevent and treat rejection in lung, heart, and liver transplants. In lung transplant patients specifically, a condition called chronic lung allograft dysfunction (CLAD) causes progressive scarring of the airways. A study of 105 lung transplant recipients treated with photopheresis found that starting treatment early, while dysfunction was still mild, led to significantly better long-term survival (a median of 105 months compared to 15 months when started late).
- Systemic sclerosis: An autoimmune condition that hardens skin and can damage internal organs.
- Crohn’s disease: An inflammatory bowel condition, treated with photopheresis in severe or refractory cases.
What a Treatment Session Looks Like
Each session takes between 2 and 4 hours. You sit in a treatment chair while blood is drawn, usually from a vein in your arm, and cycled through the photopheresis machine. The machine separates the white blood cell layer, treats it with UVA light and the photosensitizing compound, then returns your blood. Some centers use an integrated system that does everything in one device, which averages about 99 minutes total. Others use a multi-step setup with separate collection and irradiation equipment, which takes closer to 122 minutes.
During the procedure, you’re mostly sitting still. Some people read, watch something on their phone, or nap. The process doesn’t feel dramatically different from donating blood or undergoing dialysis, though the time commitment is longer than a standard blood draw.
Treatment Schedule and Duration
Most people start with weekly sessions, typically two days in a row or two sessions per week. As your condition improves, treatments taper to biweekly, then monthly. Your doctor will usually reassess how things are going after 2 to 3 months. The overall duration depends on your response, but many people continue for several months or longer. Some patients with chronic conditions like GvHD or CTCL stay on a maintenance schedule for a year or more.
Side Effects and Safety
Photopheresis is one of the better-tolerated immune therapies. No severe (grade III or IV) side effects have been reported across published guidelines. A small number of people experience a temporary drop in blood pressure during the session. Mild anemia or a slight decrease in platelet counts can occur over the course of treatment, since the process involves handling blood components repeatedly.
The most important precaution comes after treatment. Because the photosensitizing compound remains in your system briefly, your skin and eyes become very sensitive to sunlight. You need to avoid sunlight for at least 24 hours after each session, including indirect sun through windows. During that period, wear sunscreen with at least SPF 15, a hat, and wraparound sunglasses that block light from the sides.
Who Should Not Have Photopheresis
Certain conditions rule out photopheresis. People with a known sensitivity to psoralen compounds (the light-activated substance used in treatment) cannot undergo the procedure. Those who’ve had their natural eye lenses removed (a condition called aphakia) face a significantly increased risk of retinal damage from the treatment. Other contraindications include pregnancy, a history of heparin-related blood clotting problems, poor heart or circulatory function, and very low red blood cell levels. Any condition that causes unusual sensitivity to light also raises concerns, since the treatment relies on UV exposure to the collected cells.