Fetal erythropoiesis following bone marrow transplantation

'Fetal' erythrocytes are present in older children and certain adults with hematologic disorders. To determine if regenerating bone marrow produces such cells, the blood of 7 allogeneic bone marrow transplant recipients was examined. Six patients were engrafted with donor cells, while one patient recovered autologous bone marrow after rejection of a marrow transplant. All 7 patients had fetal hemoglobin levels of up to 10% by 100 days after transplantation. In 3 patients, the Gγ to Aγ ratio in the fetal hemoglobin was 'newborn', while in one it was 'adult'. Gamma chain synthesis in blood and bone marrow never exceeded 20% of total non alpha globin synthesis. The fetal hemoglobin was heterogeneously distributed in the cells. High titer i antigen also appeared. All fetal characteristics declined by 200 days. Erythropoiesis during bone marrow recovery appears to be associated with an accelerated, albeit partial, recapitulation of ontogeny.