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 CD 34 ^pos cells, suggesting that MNC may also contain CD 34 ^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: CD 34 ^pos CD 36 ^neg (0.1); CD 34 ^pos CD 36 ^pos (barely detectable-0.1); CD 34 ^neg CD 36 ^low (2) and CD 34 ^neg CD 36 ^neg (75). In semisolid-media, CD 34 ^pos CD 36 ^neg cells generated BFU-E and CFU-GM (in a 1:1 ratio), CD 34 ^neg CD 36 ^neg cells mostly BFU-E (87) and CD 34 ^pos CD 36 ^pos and CD 34 ^neg CD 36 ^low cells were not tested due to low numbers. Under HEMA conditions, CD 34 ^pos CD 36 ^neg, CD 34 ^pos CD 36 ^pos, CD 34 ^neg CD 36 ^low and CD 34 ^neg CD 36 ^neg cells generated EBs with fold-increases of 9,000, 100, 60 and 1, respectively, and maturation times (day with >10 C D 36 h i g h C D 235 a h i g h cells) of 107 days. Pyrenocytes were generated only by CD 34 ^neg / CD 36 ^neg cells by day 15. These results confirm that the majority of HPC in AB express CD34 but identify additional CD 34 ^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.