CD34+ cells from first-trimester fetal blood are enriched in primitive hemopoietic progenitors

Objective: The purpose of this study was to investigate whether purified CD34+ cells from first-trimester fetal blood are a source of primitive and committed hemopoietic progenitors. Study Design: CD34+ cells from first-trimester fetal blood and term cord blood were assayed for committed hemopoietic progenitor cells, high proliferative potential colony-forming cells, and long-term cultureinitiating cells. Results: First-trimester CD34+ cells that were compared with cells at term generated fewer hemopoietic progenitor cells and fewer high proliferative potential colony-forming cells with lower recloning efficiency (P< .001). First-trimester CD34+ cells tended to contain more long-term culture-initiating cells, both in bulk cultures and by limiting dilution analysis. The ratio between committed and primitive progenitors was 3 in the first-trimester and 20 in the term cord blood, respectively. Conclusion: First-trimester fetal blood is enriched in primitive (compared with committed) hemopoietic progenitors and may be an advantageous source of stem cells for prenatal therapy.