Identification of lymphomyeloid primitive progenitor cells in fresh human cord blood and in the marrow of nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice transplanted with human CD34(+) cord blood cells

Transplantation of genetically marked donor cells in mice have unambiguousl y identified individual clones with full differentiative potential in all l ymphoid and myeloid pathways. Such evidence has been lacking in humans beca use of limitations inherent to clonal stem cell assays. In this work, we us ed single cell cultures to show that human cord blood (CB) contains totipot ent CD34(+) cells capable of T, B, natural killer, and granulocytic cell di fferentiation. Single CD34(+) CD19(-)Thy1(+) (or CD38(-)) cells from fresh CB were first induced to proliferate and their progeny separately studied i n mouse fetal thymic organotypic cultures (FTOCs) and cocultures on murine stromal feeder layers. 10% of the clones individually analyzed produced CD1 9(+), CD56(+), and CD15(+) cells in stromal cocultures and CD4(+)CD8(+) T c ells in FTOCs, identifying totipotent progenitor cells. Furthermore, we sho wed that totipotent clones with similar lymphomyeloid potential are detecte d in the bone marrow of nonobese diabetic severe combined immunodeficient ( NOD-SCID) mice transplanted 4 mo earlier with human CB CD34(+) cells. These results provide the first direct demonstration that human CB contains toti potent lymphomyeloid progenitors and transplantable CD34(+) cells with the ability to reconstitute, in the marrow of recipient mice, the hierarchy of hematopoietic compartments, including a comparment of functional totipotent cells. These experimental approaches can now be exploited to analyze mecha nisms controlling the decisions of such primitive human progenitors and to design conditions for their ampification that can be helpful for therapeuti c purposes.