PHOTOINACTIVATION OF LYMPHOHEMOPOIETIC CELLS - STUDIES IN TRANSFUSION MEDICINE AND BONE-MARROW TRANSPLANTATION

Ultraviolet (UV) irradiation affects eukaryotic cells in numerous ways. Exposure of blood transfusion products to UVC (200-280 nm) or UVB (280-320 nm) reduces or abrogates their immunogenicity and thereby prevents allosensitization and transfusion refractoriness in several models. Although the exact mechanism is not known, in vitro studies suggest that UV exposure results in a loss of class II histocompatibility antigens from the cell surface, alterations of calcium homeostasis, and a lack of interaction between antigen presenting and responding cells. In the UVB and UVA (320-400 nm) range, lymphocytes appear to be more sensitive than hemopoietic cells. In murine transplant models, UVB irradiation of spleen and marrow cells can be used to prevent the development of graft-versus-host disease while allowing for complete hemopoietic reconstitution. Furthermore, in clinical marrow transplantation, pilot studies of UVA in conjunction with psoralen administration have yielded encouraging results in patients with steroid refractory graft-versus-host disease of the skin. Thus, UV irradiation provides an interesting tool to study cell/cell and donor/host interactions and may have some applications in transfusion medicine and bone marrow transplantation.