The monoclonal antibody ma6 identifies a cell surface antigen expressed on late bone marrow megakaryocytic progenitor cells

M. J. Horsfall, A. C W Zannettino, J. L. Nichol, P. Dyson, P. J. Simmons

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Abstract

To date the cell surface antigens expressed on progenitors of the megakaroycytic Uncage are relatively unknown. To facilitate the identification of such antigens we have generated marine monoclonal antibodies by immunising mice with megakaryocytic cell lines and megakaryocytic cells generated ex vivo following culture of CD34cells. One such antibody, MA6, was identified on the basis of its reactivity with a minor (1-6%) subpopulation of bone marrow (BM) CD34+ cells. In vitro liquid culture assays initiated with CD34tMA6+ cells gave rise to mature megakaryocytes in 2-3 days. The rapidity of megakaryocyte production under these conditions suggests that the mAb MA6 identifies a late precursor of megakaryocytes within the BM CD34 subpopulation. In support of this, preliminary data suggests that megakaryocytic colony forming potential measured by in vitro clonogenic assay is confined to the CD34 MA6 phenotype. Moreover, CD34 MA6+ cells coexpress CD38, but not Thy-1, consistent with the phenotypic characteristics of committed progenitor cells. Inummohistochemical staining of BM sections indicates that the antigen recognised by MA6 is initially expressed by megakaryocytes but is lost as they develop. The mature cells of this lineage, the platelets, do not express the MA6 antigen providing strong evidence that MA6 does not identify well known platelet/endothelial membrane antigens such as CD61. CD41, or CD36. These results indicate that the MA6 mAb uniquely indcntifics a cell surface antigen expressed by täte stage CD34 megakaryocytic progenitors which is lost at some stage during megakaryocyte maturation and it is absent on platelets. In addition, 20% of BFU-E are recovered by the CD34 MA6 phenotype. Studies are currently underway to determine if this mAb recognises a bipotent megakaryocytic/erythroid BM progenitor cell. In contrast to the limited binding of MA6 to CD34cells in steady state adult BM, initial studies of 17 patients mobilised with G-CSF alone or in combination with SCF demonstrated that 13.9 + 3.8% (n=17, range 3.2%-60.5%) of mobilised CD34cells co-expressed the MA6 antigen. We are therefore examining whether MA6 may provide a means to assess by flow cytometry the quality of mobilised blood stem cell collections for providing platelet engraftment.

Original languageEnglish
Number of pages1
JournalExperimental Hematology
Volume26
Issue number8
Publication statusPublished or Issued - 1 Dec 1998
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Hematology
  • Genetics
  • Cell Biology
  • Cancer Research

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