UVB IRRADIATION OF HUMAN PLATELET CONCENTRATES DOES NOT PREVENT HLA ALLOIMMUNIZATION IN RECIPIENTS

Exposure of platelet concentrates (PCs) to ultraviolet B radiation (UV B) has been advocated as an alternative method for prevention of the o nset of HLA sensitization in recipients. In this study, pooled PCs wer e irradiated in a Haemonetics UV irradiator (Haemonetics corp, Braintr ee, MA) at a dose that did not induce platelet activation. The effect of UVB irradiation on prevention of primary HLA sensitization was eval uated in a prospective controlled clinical study performed in cardiac patients undergoing cardiopulmonary bypass. Patients were treated with filtered red blood cells and a single transfusion of either standard (control group) or UVB-irradiated (UVB group) pooled platelets prepare d from 12 donors. Five of 39 patients in the control group and 6 of 62 patients in the UVB group developed allo-antibodies against HLA antig ens, which is not significantly different (P = .62). This unexpected f inding prompted us to check the efficacy of UVB irradiation. We determ ined UVB-specific DNA damage in cells by measuring the fluorescence fr om a labeled specific monoclonal antibody against thymine dimers. With this novel flow cytometer technique, we estimated in UVB-irradiated l eukocytes in saline that a mean fluorescence intensity (MFI) of 47 +/- 2 arbitrary units (n = 6) correlated with abolition of alloreactivity in mixed lymphocyte cultures and delayed cell death (within 72 hours) . MFI in leukocytes suspended in plasma and exposed to the clinical do se of UVB was sixfold higher (310 +/- 41 arbitrary units) and resulted in early cell death (within 24 hours). We hypothesize that this high level of UVB radiation induces fragmentation of the leukocytes. As a c onsequence, the poor results of UVB irradiation may be explained by th e onset of HLA-alloimmunization induced by soluble donor HLA class I a ntigens processed and presented by host antigen-presenting cells. (C) 1994 by The American Society of Hematology.