Chapter 16 - Irradiated Components

Abstract

In transfusion associated graft-versus-host (TA-GVHD) patients, the intensity of the mixed lymphocyte reaction can be decreased by either reducing the number of unirradiated responding cells or increasing the dose of gamma irradiation to responding cells. For an institutional policy of blood component irradiation to fulfill its preventive function, patients at risk for TA-GVHD must be reliably identified prospectively. Blood components that must be irradiated for categories of patients at risk include packed red blood cells (PRBCs), granulocytes, platelets, platelet-rich plasma, freshly separated plasma, and buffy coats used to treat neonatal sepsis. Frozen deglycerolized PRBCs can also be a source of immunocompetent lymphocytes capable of causing TA-GVHD and therefore must be irradiated for indicated categories of patients. Human leukocyte antigen (HLA)-matched apheresis platelets must always be irradiated. Donor lymphocyte infusions (DLIs) may or may not be irradiated 0depending on the indication for their use: those used to treat viral infections should be irradiated, while those used as therapy for disease recurrence post-allograft should not be irradiated. Although some variation in dosing of irradiation still exists, with centers using anywhere from 15 to 50 Gy, the data with respect to the ability of lymphocytes to proliferate in mixed lymphocyte cultures or in response to mitogens indicate that a small fraction of T-lymphocytes retain some proliferative capacity even at 30 Gy. Current standards require a dose not less than 25 Gy to the central midplane of the irradiation field, and this dose appears to be appropriate for clinical indications.