Phenotypic Definition of the Progenitor Cells with Erythroid Differentiation Potential Present in Human Adult Blood

In Human Erythroid Massive Amplification (HEMA) cultures, AB mononuclear cells (MNC) generate 1-log more erythroid cells (EBs) than the corresponding CD34(pos) cells, suggesting that MNC may also contain CD34(neg) HPC. To clarify the phenotype of AB HPC which generate EBs in these cultures, flow cytometric profiling for CD34/CD36 expression, followed by isolation and functional characterization (colony-forming-ability in semisolid-media and fold-increase in HEMA) were performed. Four populations with erythroid differentiation potential were identified: CD34(pos)CD36(neg) (0.1%); CD34(pos)CD36(pos) (barely detectable-0.1%); CD34(neg)CD36(low) (2%) and CD34(neg)CD36(neg) (75%). In semisolid-media, CD34(pos)CD36(neg) cells generated BFU-E and CFU-GM (in a 1 : 1 ratio), CD34(neg)CD36(neg) cells mostly BFU-E (87%) and CD34(pos)CD36(pos) and CD34(neg)CD36(low) cells were not tested due to low numbers. Under HEMA conditions, CD34(pos)CD36(neg), CD34(pos)CD36(pos), CD34(neg)CD36(low) and CD34(neg)CD36(neg) cells generated EBs with fold-increases of ≈9,000, 100, 60 and 1, respectively, and maturation times (day with >10% CD36(high)CD235a(high) cells) of 10–7 days. Pyrenocytes were generated only by CD34(neg)/CD36(neg) cells by day 15. These results confirm that the majority of HPC in AB express CD34 but identify additional CD34(neg) populations with erythroid differentiation potential which, based on differences in fold-increase and maturation times, may represent a hierarchy of HPC present in AB.