Mechanism of transfusion-associated graft-versus-host disease.

Recent investigations have revealed that transfusion-associated graft-versus-host disease (TA-GVHD) occurs in patients whose immune system is immature or impaired, but also in immunocompetents. The mechanism of TA-GVHD in immunocompromised patients is that donor's viable lymphocytes can not be rejected by the recipient because of defects in cellular immunity. While, even in immunocompetent patients, TA-GVHD may occur when an HLA-heterozygous recipient receives blood from a donor who is homozygous for one of the patient's haplotypes. Engraftment of donor's lymphocytes may be established without rejection, as the donor's homozygous lymphocytes are identical with one of the patient's haplotypes in HLA. Our calculations show that the Japanese have a greatest risk of TA-GVHD than other populations among relatives and unrelated donors.