Replacement of 8-MOP/UV-A treatment by UV-C irradiation for further development of Extracorporeal Photopheresis

Abstract

Extracorporeal photopheresis (ECP) has been used for more than 30 years to treat inflammatory disorders such as graft-versus-host disease (GvHD). The central step is the ex vivo treatment of the patient´s leukocytes with 8-Methoxypsoralen (8-MOP) and UV-A irradiation, resulting in cellular apoptosis. However, the injection of 8-MOP into the irradiation bag poses a risk of contamination. UV-C radiation is more energetic than UV-A radiation and is able to induce apoptosis without photosensitizers such as 8-MOP. Hence, we compared the effects of both treatments on leukocytes in vitro and in vivo. We analyzed the cell-specific pattern of apoptosis in human mononuclear cells treated with 8-MOP/UV-A and UV-C in cell culture for 72 hours. In addition, we investigated the therapeutic potential of UV-C irradiated leukocytes in a mouse model of acute GvHD. In vitro we observed equal or only slightly decreased levels of apoptosis in cells treated with UV-C compared to 8-MOP/UV-A. Both, the kinetic and final level of apoptosis after 72 h were similar in T cells, monocytes, B cells, regulatory T cells and NK(T) cells. The therapeutic in vivo analysis in a murine GvHD model revealed no clear benefit of the UV-C treatment compared to the non-therapeutic control group, but also no adverse survival or clinical GVHD score compared to the 8-MOP/UV-A group. Our in vitro and in vivo data support the notion that 8-MOP/UV-A could be replaced by UV-C treatment in ECP and thus contribute to a safer GvHD therapy. The investigation of the therapeutic in vivo potential should be continued in further studies.

Extracorporeal photopheresis and the cellular mechanisms: Effects of 8‐methoxypsoralen and UVA treatment on red blood cells, platelets and reactive oxygen species

“…With our annexin V apoptosis assay, we could demonstrate that the apoptosis of the leukocytes in the cell sample was strongly induced already 24 h after the 8-MOP and UVA treatment. In concordance with our previous studies, the leucocytic apoptosis level reached a level of more than 90% after 72 h in culture [11,19]. This finding was confirmed by several other groups, too [10,12].…”