FETAL HEMOGLOBIN EXPRESSION IN TRANSPLANT RECIPIENTS OF PLACENTAL BLOOD HEMATOPOIETIC PROGENITOR CELLS

Patients who achieved bone marrow engraftment of cord blood-derived pr ogenitor cells provided an opportunity to examine the expression of fe tal Hb by neonatal hematopoietic progenitors in a postneonatal host. C ord blood cells from histocompatible siblings were successfully transp lanted in two children with the Fanconi anemia syndrome. One of the tr ansplant donors had heterocellular hereditary persistence of fetal Hb, apparently due to gamma-globin gene triplication; the other donor was hematologically normal. The (G) gamma/(A) gamma ratio of the patient who received his transplant from the donor with hereditary persistence of fetal Hb was markedly elevated, similar to that of the transplant donor's cord blood, and this ratio remained elevated in subsequent mon ths. In the other child, the (G) gamma/(A) gamma ratio immediately aft er her transplant was typical of the normal newborn, and over the next several months it reverted to the adult pattern. Globin synthesis stu dies performed shortly after engraftment demonstrated ratios of fetal Hb/adult Hb synthesis in both patients that were typical of those of n ormal newborns. Over the next several months, both patients converted to the adult pattern. Fetal Hb to adult Hb switching in these patients seemed to follow a temporal sequence intrinsic to the transplanted ne onatal progenitor cells, without discernible influence of postneonatal environmental factors. The program for Hb switching seems to be an in herent feature of neonatal hematopoietic progenitor cells.