ANALYSIS OF HUMAN HEMATOPOIETIC STEM-CELL POPULATIONS

Purification of human hematopoietic stem cells (HSC) may be useful cli nically for preparation of tumor-free grafts to be used for autologous transplantation and as targets for gene therapy, To analyze the pheno type of the human HSC, assays were used that measure the unique proper ties of stem cells, i.e., their long-term repopulating ability and the ir multilineage potential, These assays include: (1) an in vitro long- term hematopoietic culture system, using the murine bone marrow stroma l cell line SyS1, which supports both B lymphopoiesis and myelopoiesis ; (2) fetal human bone grafts implanted in SCID-hu mice, in which main tenance of CD34(+) cells and B and myeloid differentiative capacity of candidate stem cell populations may be measured; (3) fetal human thym us grafts in SCID-hu mice, which allow the analysis of in vivo T-cell potential of a candidate stem cell population, Stem cells in adult bon e marrow (ABM) or cytokine-mobilized peripheral blood (MPB) are though t to express CD34 but lack expression of markers indicating lineage co mmitment, This CD34(+) Lineage(-) (Lin(-)) subpopulation has been isol ated by fluorescence-activated cell sorting and tested for activity in the assays described here. CD34(+) Lin(-) cells from both ABM and MPB demonstrated long-term engraftment in the SCID-hu bone model, This CD 34(+) Lin(-) population can be subfractionated further using an antibo dy to Thy-1. The Thy-(1+) subset of CD34(+) Lin(-) cells is enriched f or both long-term culture-initiating cells (LTC-1C) and has the abilit y to engraft in vivo.