Comparison between 8-methoxypsoralen and 5-aminolevulinic acid in killing T cells of photopheresis patients ex vivo.

Background And Objective: Extracorporeal photopheresis (ECP), an established modality for cutaneous T-cell lymphoma (CTCL) and graft-versus-host disease, involves ex vivo treatment of isolated leukocytes of a patient with the photosensitizing drug 8-methoxypsoralen (8-MOP) and ultraviolet-A (UV-A) exposure before reinfusion back to the patient. However, 8-MOP binds to both diseased and normal cells and thus kills both types of the cells after UV-A illumination with little selectivity. Clinically, this modality gives only partial response in the majority of treated patients. 5-Aminolevulinic acid (5-ALA), a precursor of the potent photosensitizer protoporphyrin IX (PpIX), has been shown to selectively induce PpIX in activated T lymphocytes (T cells) and could be an alternative for 8-MOP. The objectives of this study were to investigate ex vivo 5-ALA dark toxicity, 5-ALA-induced PpIX production, and photodynamic effect on T cells obtained from clinical ECP patients after the treatment of 5-ALA or 8-MOP plus a built-in certified UV-A source in the commercial Therakos™ Photopheresis System.

Materials And Methods: Flow cytometry was used to study dark cytotoxic effects of 5-ALA on human leukocytes, to measure the production of 5-ALA-induced PpIX in CD25 activated T cells from both diluted mononuclear cells and undiluted buffy coat samples of ECP patients and to compare photodynamic effects on CD4 and CD8 T cells with 5-ALA/UV-A or 8-MOP/UV-A.

Results: No dark toxicity of 5-ALA on the leukocytes of ECP patients was seen at concentrations up to 10 mM for an incubation of up to 20 hours. 5-ALA-induced PpIX was produced more in CD25 activated T cells than resting T cells in both diluted mononuclear cells and undiluted buffy coat samples, although there was a huge variation of samples from different individual patients. The CD4 and CD8 T cells treated with 5-ALA/UV-A were killed more than those treated with 8-MOP/UV-A.

Conclusion: These results suggest that 5-ALA/UV-A may have the potential for improving the efficacy of ECP. Lasers Surg. Med. 50:469-475, 2018. © 2018 Wiley Periodicals, Inc.