Is pathogen reduction an acceptable alternative to irradiation for risk mitigation of transfusion-associated graft versus host disease?

Transfusion-associated graft versus host disease (TA-GVHD) is a highly morbid and often fatal adverse event associated with transfusion of cellular blood products [platelets, red blood cells (RBCs) and whole blood] and more rarely with never-frozen plasma products. It is caused by residual viable donor T-lymphocytes that proliferate and actively target recipient tissues. Selective or universal irradiation of blood components using gamma-irradiation and more recently, X-ray irradiation, are the most commonly applied interventions and have been validated by the demonstration of in vitro T-lymphocyte inactivation, in murine models of TA-GVHD and by years of clinical experience. Irradiation, however, has multiple limitations including a sharp dose-response curve that renders quality control of dosage critically important, the use of radioactive radiation sources that are a terrorism risk, and selective implementation in many countries that leads to inadvertent omission and patient risk exposure. Certain pathogen reduction technologies (PRT) for platelets have been approved by regulatory authorities and endorsed by professional societies as an alternative to irradiation for reducing the risk of TA-GVHD, and PRT for RBCs and whole blood are in development. While the mechanism of action of T-lymphocyte inactivation differs from gamma/X-ray irradiation, the impact on T-lymphocyte inactivation for PRT is equivalent or superior to that of irradiation as demonstrated by sensitive in vitro lymphocyte proliferation assays and in vivo mouse models that approximate human TA-GVHD. Clinical trials and cumulative routine-use experience attest to the efficacy of PRT when used as an alternative to irradiation. While T-lymphocyte inactivation efficacy varies between PRT platforms, the implementation of PRT for platelets increases blood safety for patients beyond the mitigation of TA-GVHD, by decreasing the risk of transfusion transmitted infections with known viruses, bacteria and parasites as well as emerging pathogens.