A recently described long-term culture system for early human progenitor cells was established with the murine preadipocyte stromal line FBMD-1 grown in 96-well plates; cobblestone areas formed by inoculated hematopoietic cells are determined in a limiting dilution setting after five weeks' culture. To compare the capacity of cobblestone-area-forming cell (CAFC) formation by bone marrow and leukapheresis products in this system, mononuclear cells (MNC) of both origins were cultured. As related to CD34 + cell content, CAFC yields after five weeks' culture were in the same range in bone marrow and leukapheresis stemming from patients with efficient mobilization of hematopoietic cells. In purified CD34 + cell fractions, the CAFC yield per inoculated cell number was considerably higher than in MNC; however, if the CAFC number was related to the inoculated CD34 + cell number in MNC and after purification, the yield was four to eight times decreased in purified fractions. Addition of the mature cells brought the CAFC yield back up to the numbers obtained in the unseparated MNC fraction. By contrast, slightly more advanced progenitors per CAFC were found in cultures of purified hematopoietic cells from both origins than in whole MNC. The results suggest that mature human accessory cells give noticeable support to recruitment of early progenitors on this feeder but lead to lower yield of GM progenitors.
Using three different statistical tests in parallel, we showed in a preliminary study that neither mononuclear cells, CD34+33+ or 33− cells, nor CD34+38+ cells significantly correlated with engraftment kinetics following autologous blood cell transplantation (ABCT). We additionally demonstrated here, in a series of patients suffering from malignant diseases, that the graft content in CD34+38− cells is individually a more sensitive indicator of the earliest, as well as the latest post‐ABCT trilineage hematopoietic recovery than the colony‐forming units‐granulocyte‐macrophage and even the total CD34+ cell content. This suggests that the CD34+38− cell population is itself subdivided into two more subsets, one being already lineage‐committed and responsible for short‐term engraftment, the other containing only very primitive hematopoietic cells responsible for sustained engraftment. Strong arguments favor the probability that these subsets correspond to HLA‐DR+ and DR− cells, respectively. We also defined an optimal threshold value of 0.05 × 106 CD34+38− cells/kg of the patient's body weight (b.w.) above which a rapid and sustained trilineage engraftment safely occurs. In fact, infusion of lower numbers of cells seems to have a more significant impact on long‐term compared to short‐term neutrophil recovery and on platelet kinetics engraftment. We additionally looked for the eventual influence on engraftment time of the type of disease, and of post‐ABCT administration of hematopoietic growth factors (HGF). When the type of disease appeared to have no influence on the engraftment time, posttransplant HGF administration significantly reduced the time to trilineage engraftment in patients transplanted with < 0.05 × 106 CD34+38+ cells, thus justifying it in case of reinfusion of low numbers of CD34+38+ cells. On the other hand, the administration of HGF after infusion of more than 0.05 × 106 CD34+38− cells/kg b.w. did not hasten more, or only very little, the engraftment time, thus becoming not only unprofitable for the patients but costly as well.
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