Extracorporeal Photopheresis

Extracorporeal Photopheresis Principles

ECP is an immunomodulation procedure that results in an antigen-specific immune response directed to autoreactive or pathogenic T cells without causing generalized immunosuppression. The precise mechanisms of ECP are unknown, but the desired therapeutic effects are believed to result from multiple synergistic actions ( Fig. 79.1 ).

Methods

In the United States, two ECP systems are FDA-approved, UVAR XTS (Mallinckrodt Pharmaceuticals, Bedminster, NJ) and CellEx (Mallinckrodt Pharmaceuticals, Bedminster, NJ). The UVAR XTS system, which is soon phasing out, uses single-needle venous access, operating in a discontinuous flow. The newer device, the CellEx system, allows for single- or double-venous access. The extracorporeal volume (ECV) in the CellEx is ∼255–865 mL, depending on the patient’s hematocrit, single- or double-access, and the return bag threshold volume. The manufacturer recommends the procedure be performed only in patients with a hematocrit >27%; however, many institutions allow procedures to be done in patients with a hematocrit >25%, as long as the ECV is tolerated. If the device’s ECV exceeds 10%–15% of the patient’s total blood volume, then procedure modification may be required, which includes priming the apheresis system with RBCs or giving a fluid (normal saline or 5% albumin). 8-MOP is added after MNC collection, then the MNC-psoralen product is exposed to UVA light to activate psoralen, intercalate into DNA, and trigger photooxidation and cell death. This mixture is then reinfused into the patient. The CellEx takes about ∼1.5 hours to complete. ECP is typically performed on 2 consecutive days, every 2–4 weeks, depending on the indication and clinical status of the patient.

Anticoagulant

ECP typically requires heparin; citrate may be used if heparin is contraindicated.

Adverse Effects

ECP is a safe and well-tolerated procedure with limited side effects. A low-grade fever may occur within 2–12 hours after MNC reinfusion, most likely due to cytokine release. Psoralen compounds are contraindicated in patients with aphakia and in those who have exhibited reactions to psoralen compounds or who have a history of photosensitive disease (e.g., porphyria cutanea tarda). Patients should avoid sun exposure for 24+ hours postprocedure and a high fat diet preprocedure that renders opacity to the plasma, which can potentially interfere with establishing the MNC interface during the separation process and during penetration with the UVA in the photoactivation process. Of note, based on a recent FDA warning, ECP may increase the risk of venous thromboembolism, including pulmonary embolism.

Indications