Universal or selective irradiation: a comparison of approaches

Pathological mechanisms proposed for transfusion-associated graft-versus-host diseases (TA-GVHD) include HLA homozygosity in donor cells of the transfusion unit that is shared by the recipient (one-way HLA match) and immunosuppression in the transfusion recipient. Which of these factors is indispensable or to what degree each factor contributes to the development of TA-GVHD has been the issue of debate. In countries like Japan with higher HLA homogeneity, TA-GVHD occurrence was thought to be primarily dependent on the one-way HLA match mechanism regardless of immunosuppression. Accordingly, universal irradiation of blood components has been conducted with no further TA-GVHD cases. In other developed countries, in contrast, TA-GVHD was thought to be a sort of extrapolation of GVHD observed among heavily immunosuppressed patients. Guidelines with the detailed list of diseases with the indication for irradiated components have been established in those countries. Although TA-GVHD occurrence decreased markedly after the introduction of universal leukoreduction, a considerable number of TA-GVHD cases have occurred among immunocompetent patients mostly by the one-way HLA match mechanism. Because one-way HLA matching with donor homozygosity is thought to be a ubiquitous and independent mechanism for TA-GVHD, it could occur in any transfusion setting regardless of immunosuppression. It would be thoughtful to select an area-specific strategy considering the drawbacks of irradiation and the frequency of TA-GVHD in that area. However, if complete abolition of TA-GVHD is required from the perspective of the high fatality of the disorder, universal irradiation of cellular components will be necessary.