title: Tolerance induction by megadose hematopoietic progenitor cells: expansion of veto cells by short-term culture of purified human CD34(+) cells.
abstract: Stem cell-dose escalation is one way to overcome immune rejection of incompatible stem cells. However, the number of hematopoietic precursors required for overcoming the immune barrier in recipients pretreated with sublethal regimens cannot be attained with the state-of-the-art technology for stem cell mobilization. This issue was addressed by the observation that cells within the human CD34(+) population are endowed with veto activity. In the current study, we demonstrated that it is possible to harvest about 28- to 80-fold more veto cells on culturing of purified CD34(+) cells for 7 to 12 days with an early-acting cytokine mixture including Flt3-ligand, stem cell factor, and thrombopoietin. Analysis of the expanded cells with fluorescence-activated cell-sorter scanning revealed that the predominant phenotype of CD34(+)CD33(-) cells used at the initiation of the culture was replaced at the end of the culture by cells expressing early myeloid phenotypes such as CD34(+)CD33(+) and CD34(-)CD33(+). These maturation events were associated with a significant gain in veto activity as exemplified by the minimal ratio of veto to effector cells at which significant veto activity was detected. Thus, whereas purified unexpanded CD34(+) cells exhibited veto activity at a veto-to-effector cell ratio of 0.5, the expanded cells attained an equivalent activity at a ratio of 0.125. The availability of novel sources of veto cells such as those in this study might contribute to the realization of immunologic tolerance in "minitransplants," without any risk of graft-versus-host disease.
authors: Department of Immunology, Weizmann Institute of Science, Rehovot, Israel.
authors: Hilit
authors: H
authors: Gur
authors: Rita
authors: R
authors: Krauthgamer
authors: Alain
authors: A
authors: Berrebi
authors: Tirza
authors: T
authors: Klein
authors: Arnon
authors: A
authors: Nagler
authors: Antonio
authors: A
authors: Tabilio
authors: Massimo F
authors: MF
authors: Martelli
authors: Yair
authors: Y
authors: Reisner
mesh_terms: D015703:Antigens, CD / Q000032:analysis*; D018952:Antigens, CD34 / Q000032:analysis*; D015214:Antigens, Differentiation, Myelomonocytic / Q000032:analysis; D002450:Cell Communication; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance / Q000502:physiology*; D007371:Interferon-gamma / Q000032:analysis; D063268:Sialic Acid Binding Ig-like Lectin 3
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D015214:Antigens, Differentiation, Myelomonocytic; C571163:CD33 protein, human; D063268:Sialic Acid Binding Ig-like Lectin 3; D007371:Interferon-gamma