SCID-repopulating cell activity of human cord blood-derived CD34- cells assured by intra-bone marrow injection

Abstract

Precise analysis of human CD34-negative (CD34-) hematopoietic stem cells (HSCs) has been hindered by the lack of a simple and reliable assay system of these rare cells. Here, we successfully identify human cord blood-derived CD34- severe combined immunodeficiency (SCID)-repopulating cells (SRCs) with extensive lymphoid and myeloid repopulating ability using the intra-bone marrow injection (IBMI) technique. Lineage-negative (Lin-) CD34- cells did not show SRC activity by conventional tail-vein injection, possibly due to their low levels of homing receptor expression and poor SDF-1/CXCR4-mediated homing abilities, while they clearly showed a high SRC activity by IBMI. They generated CD34+ progenies not only in the injected left tibia but also in other bones following migration. Moreover, they showed slower differentiating and reconstituting kinetics than CD34+ cells in vivo. These in vivo-generated CD34+ cells showed a distinct SRC activity after secondary transplantation, clearly indicating the long-term human cell repopulating capacity of our identified CD34- SRCs in nonobese diabetic (NOD)/SCID mice. The unveiling of this novel class of primitive human CD34- SRCs by IBMI will provide a new concept of the hierarchy in the human HSC compartment and has important implications for clinical HSC transplantation as well as for basic research of HSC. © 2003 by The American Society of Hematology.