Engraftment of cultured human hematopoietic cells in sheep. Blood 91:3688–3692

In an effort to expand human hematopoietic progenitors and stem cells in vitro, we cultured human CD341c-kitlow bone marrow cells in suspension in the presence of KIT ligand, FLK2/FLT3 ligand, interleukin-6 (IL-6), and erythropoietin with or without IL-3 and tested their engrafting capabilities by injecting them into sheep fetuses. As markers for engraft-ment, we analyzed CD451 cells and karyotypes of the colo-nies grown in methylcellulose culture. In three separate experiments, day-60 engraftment in the bone marrow was seen with both fresh cells and cells cultured in the presence or absence of IL-3. When fetuses were allowed to be born and analyzed for CD451 cells, no long-term engraftment was seen with cultured cells. We then pooled the CD451 cells of the fetal samples and transplanted them into secondary recipient fetuses. Day-60 engraftment in the secondary recipi