hematopoietic progenitors in sickle cell disease differ phenotypically and functionally from normal and suggest distinct subpopulations that generate F cells

Objective. Sickle cell disease (SCD) is remarkable for stress erythropoiesis. We investigated the progenitor populations contributing to erythroid stress. Materials andMethods. We characterizedhematopoieticprogenitor cells in sicklebone marrow and sickle peripheral blood from patients with SCD compared to those in normal bone marrow. Results. There were increased proportions of sickle bone marrow and sickle peripheral blood CD34 cells that coexpressed glycophorin A (GlyA), normally expressed late during erythroid differentiation when CD34 is down-regulated. Remarkably, increased numbers of CD34CD38 hematopoietic progenitor cells from sickle bone marrow (p 0.03) and sickle peripheral blood (p 0.004) coexpressed GlyA, compared to normal bone marrow CD34CD38 hematopoietic progenitor cells. At a molecular level, even the sickle bone marrow and sickle peripheral blood CD34CD38 hematopoietic progenitor cells not expressing GlyA by fluorescence-activated cell sorting or reverse transcriptase-polymerase chain reaction expressed the erythroid-specific gene GATA-1, unlike normal bone marrow, suggestingdesynchronizederythroidgeneexpressionintheSCDhematopoieticprogenitorcells. We also generated red blood cells in vitro from GlyA and GlyACD34 cells. GlyACD34 produced more F cells (p 0.02) and had lower clonogenicity (p 0.01) and erythroid expansion potential. Increased F cells were generated only from sickle CD34 hematopoietic progenitor cells (p 0.04), as occurs in vivo. Conclusion. Stress erythropoiesis in SCD has been postulated to accelerate erythropoiesis and production of F cells. Thus, CD34CD38 expressing GlyA may represent the “stress progenitor” population. This is the first study characterizing CD34 and CD34CD38 hematopoietic progenitor cells in sickle bone marrow, comparing them to sickle peripheral blood and normal bone marrow and using them to generate sickle red blood cells that recapitulate F cell production observed in vivo. We identified a unique population of GlyACD34 cells in SCD, which is in an accelerated erythroid differentiation pathway, has not down-regulated CD34 antigen expression, and predominantly generates F cells. 2004