[Transfusion-associated graft-versus-host disease. Increased risk when using HLA matched donors]

For 30 years it has been known that immunodeficient patients can have a fatal reaction to transfused blood components containing viable lymphocytes. This risk of a transfusion-associated graft-versus-host reaction can be totally eliminated by irradiation of the blood prior to transfusion. Immunocompetent individuals can have this potentially fatal reaction if the blood donor is homozygous for one of the HLA-haplotypes of the recipient. The probability of this coincidence is low when donor and recipient are unrelated, but considerably higher when they are genetically related. When HLA-matched blood platelets are indicated for transfusing patients refractory to random platelets, the platelets must always be irradiated with minimum 25 Gy, since a large proportion of the donors will be homozygous with one of the HLA-haplotypes of the recipient.