Immune thrombocytopenia in dogs after fetal liver hematopoietic cell transplantation

Immune thrombocytopenia occurred in 6 of 33 engrafted dogs (18%) after fetal liver hematopoietic cell transplantation. Concurrent granulocytopenia occurred in three of six dogs and anemia in one. All dogs were receiving cyclosporin to prevent graft rejection and graft-versus-host disease (GVHD). None of the dogs had signs of GVHD. Bone marrow obtained at the time of platelet nadir was hypercellular with megakaryocyte hyperplasia. All dogs exhibited anti-megakaryocyte antibodies detected by direct immunofluorescence of bone marrow smears. Treatment with oral prednisolone resulted in normalization of platelet counts in five of six dogs and granulocyte and erythrocyte counts in dogs exhibiting concurrent leukopenia or anemia. Two long-term survivors (> 2.5 years) have not developed further hematologic abnormalities since initial diagnosis and treatment.