Circulating CFU-E during hematopoietic recovery after allogeneic bone marrow transplantation: relationship to erythroid engraftment.

The more mature erythroid progenitor assayable in vitro, the colony-forming unit-erythroid (CFU-E), is normally found in the bone marrow (BM) but is virtually absent from peripheral blood (PB), unlike the more immature progenitor, the burst-forming unit-erythroid (BFU-E). We report on the detection of CFU-E in the PB of six of 18 patients during hematopoietic recovery following allogeneic bone marrow transplantation (BMT); three of six patients with PB CFU-E were under treatment with recombinant human erythropoietin (rhEpo) as well as six of 12 who did not present with PB CFU-E. PB CFU-E were found as early as day 14 following BMT, reached a peak on day 28, and were still detectable on day 60. The presence of PB CFU-E was associated with signs of stimulated erythroid engraftment--an accelerated reticulocyte recovery, an increased number of reticulocytes, higher levels of serum transferrin receptor, and a reduction in transfusional requirements were found in these patients compared to those without PB CFU-E. The numbers of PB and BM BFU-E were similar in the two groups, as well as the numbers of PB and BM CFU-granulocyte/macrophage (CFU-GM) and multipotential CFU (CFU-GEMM); on the other hand, the percentage of BM BFU-E in S phase of the cell cycle was higher in the group of patients with PB CFU-E. While there was no difference between the two groups in serum Epo levels assayed on days 14 and 28 after BMT, patients with PB CFU-E had higher Epo levels in serum samples collected before starting the BMT procedure. These data suggest that the appearance of circulating CFU-E early after BMT is characteristic of a group of patients with an accelerated erythroid engraftment, although the mechanisms leading to the circulation of CFU-E after BMT remain unclear.