Which stem cells should be used for transplantation?

In view of the ever-increasing demand for human stem cells for transplantation, we initiated in vitro and in vivo studies of human fetal bone marrow stem/progenitor cells derived from lost pregnancies at 16-20 weeks. Utilizing non-human primates as models, we demonstrated that fetal tissue has distinctive biological and therapeutic properties that are optimal for transplantation. Subsequently, we tested and compared the phenotypic and functional characteristics of fetal bone marrow (FBM), adult bone marrow (ABM), and cord blood (CB) and peripheral blood (PB) sources of the most primitive stem/progenitor cells. A striking ontogenic difference in the proportion of CD34+ cells in FBM, ABM, PB and CB was observed (24.6 vs. 2.1 vs. 0.5 vs. 2%). The clonogenic potential, as measured by the CFU-c assay, was also higher in FBM when compared with ABM, PB and CB (202.5 vs. 73.5 vs. 40.8 vs. 65.5 colonies/10(5 )cells). Moreover, there was a significant decrease in proliferative responsiveness in the mixed lymphocyte reaction (MLR) assay of FBM and CB as compared to ABM and PB. The cytokinetic profiles of the cells from the four sources were also analyzed. This study revealed that both FBM and ABM had a higher proportion of S-phase (21.7 and 11.5%, respectively), compared to PB and CB cells (1.2 and 2.8%, respectively). FBM and ABM also showed a higher proportion of cells in the G(2)-M phase (6.4 and 2.6%, respectively) compared with PB and CB (1.7 and 1.2%, respectively). These data show that FBM has the highest number of proliferating cells. We have also investigated the ontogenic differences in stromal cells derived from FBM, ABM and CB, with a special focus on the expression of selected cytokines, such as CSF, GM-CSF, G-CSF, M-CSF, IL-3, IL-6, IL-10 and IL-11. FBM showed the highest levels of expression of CSF, IL-6 and IL-11 when compared to the other sources. These cytokines may have an important role in engraftment and homing of stem cells. The levels of expression of the other cytokines were similar in all sources of stromal cells, with the exception of G-CSF, which was not detected in CB. Moreover, the number of colonies FBM and ABM cells was higher when inoculated with fetal stromal cells. These results suggested an important regulatory role of cytokines in ontogeny of hematopoiesis. In summary, the foregoing observations indicate that each source of hematopoietic and stromal cells has different intrinsic properties, closely correlated with ontogenetic age, which is a vital determinant for phenotypic characteristics, lineage commitments, immunogenicity as well as proliferative potentials. Our data clearly indicate that FBM is the best source of stem cells for engraftment and therapeutic reconstitution due to its very high proliferative capacity, low immunogenicity and highest number of primitive stem/progenitor cells. It should also be stressed that FBM stem cells retrieved at their optimal stage of hematopoiesis (16-20 weeks) may be the cells of choice for both therapeutic cellular reconstitution and gene targeting.