β2 microglobulin-deficient (B2mnull) NOD/SCID mice are excellent recipients for studying human stem cell function

Human SCID repopulating cells (SRC) are defined based on their functional ability to repopulate the bone marrow of NODI SCID mice with both myeloid and lymphoid cell populations. The frequency of SRC in umbilical cord blood cells is 1 in 9.3 x 10(5) mononuclear cells. We report that as few as 8 x 10(4) human cord blood mononuclear cells transplanted into NOD/SCID/B2m(null) mice resulted in mutlilineage differentiation in the murine bone marrow, revealing a more than 11-fold higher SRC frequency than in NOD/SCID mice. Moreover, as few as 2 to 5 x 10(3) CD34(+) cells recovered from the bone marrow of primary transplanted NODI SCID mice were sufficient for engrafting secondary NOD/SCID/B2m(null) mice with SRC, suggesting SRC self-renewal. Thus, by using NOD/SCID/B2m(null) mice as recipients, we established a functional assay for human stem cells capable of engrafting the bone marrow of primary and secondary transplanted immune-deficient mice with SRC, providing a model that better resembles autologous stem cell transplantation. (C) 2000 by The American Society of Hematology.