The effects of gamma irradiation versus white cell reduction on the mixed lymphocyte reaction.

The risk of transfusion-associated graft-versus-host disease (TA-GVHD) is related to the number of viable T cells transfused. Whether white cell (WBC)-reduced blood components would carry a decreased risk of TA-GVHD was considered, and the allogeneic mixed lymphocyte reaction was used as an in vitro model for TA-GVHD. An exponential decline in the mixed lymphocyte reaction was found to occur, as a result of either an arithmetic increase in the dose of gamma irradiation given to responding cells or a logarithmic decrease in the number of unirradiated responding cells. Irradiation of responding cells with 600 cGy or a 0.6 log10 reduction in the number of responding cells produced a 95-percent decline in the mixed lymphocyte reaction. Although these studies do not validate the use of WBC reduction as a substitute for gamma irradiation for the prevention of TA-GVHD, they suggest that the relative risk of TA-GVHD resulting from the use of standard cellular components versus WBC-reduced components merits further investigation.