Immune thrombocytopenia more than a year after allogeneic marrow transplantation due to antibodies against donor platelets with anti-PlA1 specificity: evidence for a host-derived immune reaction.

We report on a male patient transplanted from his HLA-matched sister for Ph1-chromosome positive chronic myelogenous leukaemia who developed immune thrombocytopenia more than 1 year after transplantation. The platelet antibody reacted with the platelet specific antigen PlA1 on donor platelets, and also on recipient platelets after engraftment. A presumed host-versus-donor induced thrombocytopenia was supported by Southern blot analysis using a Y-chromosome specific probe demonstrating residual host-origin cells in the patient's excised spleen.