PROLIFERATION OF INDIVIDUAL HEMATOPOIETIC PROGENITORS PURIFIED FROM UMBILICAL-CORD BLOOD

In previous studies, we described long-term cultures of subpopulations of CD34(+) cord blood cells that were fractionated using antibodies s pecific for CD45RA and CD71. In the present study, we plated the most primitive CD34(+)CD45RA(low)CD71(low) cells individually and analyzed the proliferation and expansion kinetics of the various hematopoietic progenitors included in this subpopulation. The proliferation capacity of single progenitors was assessed by the total number of cells produ ced, and their expansion capacity was assessed by the production of CD 34(+) and colony-forming cells. Monolineage progenitors (erythroid, gr anulocyte, and macrophage progenitors) showed the lowest expansion cap acity, which correlated with a relatively short life span (<37 days) o f the generated colonies. Among these cells, erythroid progenitors sho wed the highest proliferative potential. Based on their relative cell content and proliferation/expansion capacities, two types of both gran ulo-macrophagic (GM) and multipotent (Mix) progenitors were identified . GM progenitors producing colonies with >70% granulocytes had a low e xpansion capacity and gave rise to colonies that were sustained for <4 2 days. A second type of GM progenitors, giving rise to colonies with >90% macrophages, had a higher expansion capacity and the colonies the y produced were sustained for >72 days. On the other hand, Mix progeni tors producing colonies with >70% erythroid cells had a lower expansio n capacity and life span (<46 days in culture), than Mix progenitors p roducing colonies with >90% myeloid cells (life span of >72 days). The se results demonstrate, at the single-cell level, a correlation betwee n the type of progenitor cell and its expansion capacity. In turn, the expansion capacity of the progenitors was correlated with the life sp an of the colonies produced. Furthermore, our results suggest that in cord blood, at least two types of bipotential myeloid (GM) progenitors and two types of multipotent (Mix) progenitors can be distinguished, that have respectively low and high proliferative and expansion capaci ty.