PHENOTYPE AND FUNCTION OF HUMAN HEMATOPOIETIC-CELLS ENGRAFTING IMMUNE-DEFICIENT CB17-SEVERE COMBINED IMMUNODEFICIENCY MICE AND NONOBESE DIABETIC-SEVERE COMBINED IMMUNODEFICIENCY MICE AFTER TRANSPLANTATION OF HUMAN CORD-BLOOD MONONUCLEAR-CELLS

In an attempt to understand better the regulation of stem cell functio n in chimeric immunodeficient mice transplanted with human cells, and the filiation between progenitor cells identified in vitro and in vivo , we assessed the different compartments of hematopoietic progenitors found in the marrow of CB17-severe combined immunodeficiency (SCID) mi ce (34 mice, 9 experiments) after intravenous injection of 2 to 3 x 10 (7) cord blood mononuclear cells. On average 6.3 +/- 4 x 10(5) human c ells were detected per four long bones 4 to 6 weeks after the transpla nt predominantly represented by granulomonocytic (CD11b(+)) and B lymp hoid (CD19(+)) cells. Twenty five percent of these human cells express ed the CD34 antigen, of which 90% coexpressed the CD38 antigen and 50% the CD19 antigen. Functional assessment of progenitor cells (both clo nogenic and long-term culture-initiating cells [LTC-IC]) was performed after human CD34(+) cells and CD34(+)/CD38(-) cells have been sorted from chimeric CB17-SCID marrow 3 to 10 weeks after intravenous (IV) in jection of human cells. The frequency of both colony-forming cells and LTC-IC was low (4% and 0.4%, respectively in the CD34(+) fraction) wh en compared with the frequencies of cells with similar function in CD3 4(+) cells from the starting cord blood mononuclear cells (26% +/- 7% and 7.2% +/- 5%, respectively). More surprisingly, the frequency of LT C-IC was also low in the human CD34(+) CD38(-) fraction sorted from ch imeric mice. This observation might be partly accounted for by the exp ansion of the CD34(+) CD19(+) B-cell precursor compartment. Despite th eir decreased frequency and absolute numbers, the differentiation capa bility of these LTC-IC, assessed by their clonogenic progeny output af ter 5 weeks in coculture with murine stromal cells was intact when com pared with that of input LTC-IC. Furthermore the ratio between clonoge nic progenitor cells and LTC-IC was similar in severe combined immunod eficiency (SCID) mice studied 4 weeks after transplant and in adult ma rrow or cord blood suspensions. Results generated in experiments where nonobese diabetic (NOD)-SCID mice were used as recipients indicate a higher level of engraftment but no change in the distribution of clono genic cells or LTC-IC. These results suggest that the hierarchy of hem atopoietic differentiation classically defined in human hematopoietic tissues can be reconstituted in immunodeficient SCID or NOD-SCID mice. (C) 1996 by The American Society of Hematology.