The change of HLA phenotype from heterozygous to homozygous one occurred in two postoperative patients developing posttransfusion GVHD. One haplotype was shared in the homozygous and heterozygous phenotype. A blood donor whose HLA phenotype was identical to the homozygous phenotype of the patient was found.
For preventing posttransf usion GVHD, blood preparations to be transfused within 10 days after collection were irradiated in a dose more than 15Gy. The two patient described above developed GVHD after the tranfsuion with non-irradiated fresh blood. On the other hand, no patients developed GVHD after the transfusion with irradiated blood.
