Predictive value of the original content of CD34(+) cells for enrichment of hematopoietic progenitor cells from bone marrow harvests by the apheresis procedure.

We retrospectively investigated the feasibility of the apheresis procedure for red blood cell (RBC) reduction with a closed-bag system. We also sought to determine the optimal processing volume for the maximal recovery of hematopoietic progenitor cells (HPC). Twelve bone marrow (BM) harvests were processed for major ABO-incompatible allogeneic transplantation and one BM harvest was processed for autologous transplantation. The processing was performed through seven apheresis cycles with a two-bag system using COBE Spectra Version 6.1. The mean recovery rates were compared in the products after four cycles and seven cycles of BM processing. Mean cell recovery rates were 79.2% (67.6-97.5%) and 87.3% (68.9-111.9%) for the mononuclear cells (MNC) and 84.5% (69.4-109.5%) and 92.0% (79.0-107.7%) for the CD34(+) cells after four and seven cycles, respectively. A mean of 96.3% (93.0-98.1%) of the RBCs were finally removed. The yield of CD34(+) cells after seven cycles of processing (median: 10.35 x 10(7) cells) was 7.9% greater than that after four cycles of processing (median: 9.65 x 10(7) cells), exhibiting a less-than-significant enhancement in yield. The CD34(+) cell contents recovered in the concentrates up to four cycles (r = 0.989) and up to seven cycles (r = 0.993) were strongly correlated with the original content of the CD34(+) cells. Engraftment was obtained in all patients except one patient infused with purified CD34(+) cells. This latter result confirmed the hematopoietic potential of the cell populations recovered. Granulocyte recovery (defined as an absolute neutrophil cell count > or = 500/microL for a period of three consecutive days) ranged from 8 to 25 days (median: 16 days) post-transplantation. No hemolytic reaction was observed in any of the patients. Our results confirmed the efficacy of BM processing cycles with the COBE Spectra device. However, we could not conclude that the large-volume apheresis for BM processing significantly enhanced the yields of HPC. The final recovery of CD34(+) cells after processing could be predicted from the CD34(+) cell content of the original collected marrow.

Graded levels of GATA-1 expression modulate survival, proliferation, and differentiation of erythroid progenitors.

Transcription factor GATA-1 plays an important role in gene regulation during the development of erythroid cells. Several reports suggest that GATA-1 plays multiple roles in survival, proliferation, and differentiation of erythroid cells. However, little is known about the relationship between the level of GATA-1 expression and its nature of multifunction to affect erythroid cell fate. To address this issue, we developed in vitro embryonic stem (ES) culture system by using OP9 stromal cells (OP9/ES cell co-culture system), and cultured the mutant (GATA-1.05 and GATA-1-null) and wild type (WT)ES cells, respectively. By using this OP9/ES cell co-culture system, primitive and definitive erythroid cells were developed individually, and we examined how expression level of GATA-1 affects the development of erythroid cells. GATA-1.05 ES-derived definitive erythroid cells were immature with the appearance of proerythroblasts, and highly proliferated, compared with WT and GATA-1-null ES-derived erythroid cells. Extensive studies of cell cycle kinetics revealed that the GATA-1.05 proerythroblasts accumulated in S phase and expressed lower levels of p16(INK4A) than WT ES cell-derived proerythroblasts. We concluded that GATA-1 must achieve a critical threshold activity to achieve selective activation of specific target genes, thereby influencing the developmental decision of an erythroid progenitor cell to undergo apoptosis, proliferation, or terminal differentiation.

Identification and characterization of 2 types of erythroid progenitors that express GATA-1 at distinct levels.

Transcription factor GATA-1 is essential for the development of the erythroid lineage. To ascertain whether strict control of GATA-1 expression level is necessary for achieving proper erythropoiesis, we established transgenic mouse lines expressing green fluorescent protein (GFP) under the control of the GATA-1 gene hematopoietic regulatory domain. We examined the GATA-1 expression level by exploiting the transgenic mice and found 2 GFP-positive hematopoietic progenitor fractions in the bone marrow. One is the GFPhigh fraction containing mainly CFU-E and proerythroblasts, which coexpress transferrin receptor, while the other is the GFPlow/transferrin receptor-negative fraction containing BFU-E. Since the intensity of green fluorescence correlates well with the expression level of GATA-1, these results indicate that GATA-1 is highly expressed in erythroid colony-forming unit (CFU-E) but low in erythroid burst-forming unit (BFU-E), suggesting that the incremental expression of GATA-1 is required for the formation of erythroid progenitors. We also examined GFP-positive fractions in the transgenic mouse spleen and fetal liver and identified fractions containing BFU-E and CFU-E, respectively. This study also presents an efficient method for enriching the CFU-E and BFU-E from mouse hematopoietic tissues.

Aberrant iron accumulation and oxidized status of erythroid-specific delta-aminolevulinate synthase (ALAS2)-deficient definitive erythroblasts.

Alas2 encodes the erythroid-specific delta-aminolevulinate synthase (ALAS2 or ALAS-E), the first enzyme in heme biosynthesis in erythroid cells. Mice with the Alas2-null phenotype showed massive cytoplasmic, but not mitochondrial, iron accumulation in their primitive erythroblasts. Because these animals died by day 11.5 in utero, studies of iron metabolism in definitive erythroblasts were not possible using the in vivo model. In this study, embryonic stem (ES) cells lacking the Alas2 gene were induced to undergo differentiation to the definitive erythroblast stage in culture, and the phenotype of Alas2-null definitive erythroblasts was examined. Alas2-null definitive erythroblasts cell pellets were entirely colorless due to a marked deficiency of heme, although their cell morphology was similar to that of the wild-type erythroblasts. The level of expression of erythroid-specific genes in Alas2-null definitive erythroblasts was also similar to that of the wild-type erythroblasts. These findings indicate that Alas2-null definitive erythroblasts developed to a stage similar to that of the wild-type erythroblasts, which were also shown to be very similar to the bone marrow erythroblasts in vivo. In contrast, Alas2-null definitive erythroblasts contained 15 times more nonheme iron than did the wild-type erythroblasts, and electron microscopy found this iron to be distributed in the cytoplasm but not in mitochondria. Consistent with the aberrant increase in iron, Alas2-null definitive erythroblasts were more peroxidized than wild-type erythroblasts. These findings suggest that ALAS2 deficiency itself does not interfere with the development of definitive erythroid cells, but it results in a profound iron accumulation and a peroxidized state in erythroblasts.