Persistence of human multilineage, self-renewing lymphohematopoietic stem cells in chimeric sheep

Abstract

We have previously reported the ability of uncharacterized human bone marrow (BM) cells to engraft into preimmune fetal sheep, thereby creating sheep-human chimera suitable for in vivo examination of the properties of human hematopoietic stem cells (HSC). Adult human bone marrow CD34+ HLA-DR- cells have been extensively characterized in vitro and have been demonstrated to contain a number of primitive hematopoietic progenitor cells (PHPC). However, the capacity of such highly purified populations of human marrow CD34+ HLA-DR- cells to undergo in vivo self-renewal and multipotential lymphohematopoietic differentiation has not been previously demonstrated. To achieve that, human CD34+ HLA-DR- cells were transplanted in utero into immunoincompetent fetal sheep to investigate the BM-populating potential of these cells. Long-term chimerism, sustained human hematopoiesis, and expression of human cells belonging to all human blood cell lineages were demonstrated in two animals for more than 7 months' posttransplantation. Chimeric BM contained erythroid, granulocytic/monocytic, and megakaryocytic hematopoietic progenitor cells, as well as the primitive high proliferative potential colony- forming cell (HPP-CFC). Under a variety of in vitro experimental conditions, chimeric BM cells gave rise to human T cells expressing T- lymphocyte-specific markers, human natural killer (NK) cells, and human IgG-producing B cells. In vivo expansion and possibly self-renewal of transplanted PHPC was confirmed by the detection in chimeric BM 130 days' posttransplantation of CD34+ HLA-DR- cells, the phenotype of human cells constituting the stem-cell graft. These studies demonstrate not only the BM-populating capacity, multipotential differentiation, and most likely self-renewal capabilities of human CD34+ HLA-DR- cells, but also that this BM population contains human HSC. Furthermore, it appears that this animal model of xenogeneic stem-cell transplantation is extremely useful for in vivo examination of human hematopoiesis and the behavioral and functional characteristics of human HSC.

The Biological Basis of and Strategies for Clinical Xenotransplantation

“…It is particularly noteworthy that xenogeneic cells can be engrafted more easily than complex tissues and organs (HuUett et al 1987, Ricordi et al 1987, Faiqui et al 1991, Michejda et al 1992, Srour et al 1993). This has been illustrated by a recently reported experiment (Fontes et al 1994b) in which 2 baboons preconditioned with 7.5 Gy total lymphoid irradiation were given 6xlO^/kg unaltered human bone marrow cells, and provided with no subsequent treatment.…”

In Utero Transplantation for Thalassemia

“…30 In contrast, adult BM enriched for CD34, or more highly enriched populations, have the ability to engraft the fetus without causing GVHD. 28,29,[31][32][33]…”

Delineation of the human hematolymphoid system: potential applications of defined cell populations in cellular therapy

“…Human stem cells can engraft sheep fetuses if they are injected intraperitoneally prior to the development of a functional thymus and during the time fetal HSC are believed to migrate from the fetal liver to bone marrow (days 48-54 of gestation). Tbe transplanted human CD34+Tby-1+ bone marrow cells were shown to home to the bone marrow and differentiate along both myeloid and lymphoid lineages (28)(29)(30)(31)(32)(33)(34)(35). Mature human T lymphocytes were also detected, with no evidence for active human thymopoiesis in the sheep thymus, raising the possibility of extrathymic maturation of human T cells.…”