Hemopoietic stem cells from human fetal liver were transplanted in utero into preimmune fetal sheep (48-54 days of gestation). The fate ofdonor cells was followed using karyotype analysis, by immunofluorescence labelingwith anti-CD antibodies, and by fluorescent in situ hybridization using human-specific DNA probes. Engrftment occurred in 13 of 33 recipients. Of five live born sheep that exhibited chimerism, all expressed human cells in the marrow, whereas three expressed them in blood as well.Engraftment was multilineage (erythroid, myeloid, and lymphoid) and human hemopoietic progenitors (multipotent colony-forming units, colony-forming units-granulocyte, macrophage, and erythroid burst-forming units) capable of forming colonies in vitro were detected in all five lambs for > 2 yr. These progenitors responded to human-specific growth-factors both in vitro and in vivo. Thus the administration of recombinanthumanIL-3andgranulocytemacrophage-colony-stimulating factor to chimeric sheep resulted in a 2.1-3.4-fold increase in the relative expression of donor (human) cells. These results demonstrate that the permissive environment ofthe preimmune fetal sheep provides suitable conditions for the engraftment and long-term multilineage expression of human hemopoietic stem cells in a large animal model. In this model, donor human cells appear to retain certain phenotypic and functional characteristics that can be used to manipulate the size of donor cell pool.

Autologous fragments of transplanted marrow have survived in various extramedullary sites in the rat, rabbit, and dog. Survival of the fragments occurs with a complete reconstitution of the hemopoietic and adventitial structures. The process originates from a network of surviving reticular cells which proliferate and differentiate into osteoblasts and give rise to trabecular bone. Later, the reticular cells reconstruct the marrow's microcirculation. Hemopoietic repopulation of the marrow implant takes place only after its sinusoidal microcirculation has been established.

We previously reported on the successful engraftment and long-term multilineage expression (erythroid, myeloid, lymphoid) of human fetal liver hematopoietic stem cells in sheep after transplantation in utero. That the engraftment of longterm repopulating pluripotent stem cells occurred in these animals was shown here by the fact that transplantation of human CD45 + cells isolated from bone marrow of these chimeric animals into preimmune fetal sheep resulted in engraftment and expression of human cells. Marrow cells were obtained from three chimeric sheep at 3.2-3.6 yr after transplant. The relative percentage of human CD45+ cells present in these marrows was 3.3±0.32%. A total of 29 X 106 CD45+ cells were isolated by panning, pooled, and transplanted into six preimmune sheep fetuses (4.8 x 106 cells/fetus). All six recipients were born alive. Hematopoietic progenitors exhibiting human karyotype were detected in marrows of two lambs soon after birth. Cells expressing human CD45 antigen were also detected in blood and marrow of both lambs. Human cell expression has been multilineage and has persisted for > 1 yr. These results demonstrate that the expression of human cells in this large animal model resulted from engraftment of long-term repopulating pluripotent human stem cells. (J. Clin. Invest. 1994. 93:1051-1055.) Key words: hematopoietic stem cells * human/sheep xenograft -in utero transplantation -preimmune fetus * fetal liver

The clinical records of all patients with granular cell tumor seen at our institution over a 20-year period were reviewed. Three patients with malignant, and 37 with benign tumor, were identified. Eleven patients had multiple benign lesions. Three had a history of familial occurrence. Clinical and pathologic features and the management of this nebulous entity, in both its benign and malignant forms, are reviewed and discussed.

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