Musami, Mathew Mwata; (1999) Role of CD44-dependent pathway in the adhesion and homing of human haemopoietic stem cells and progenitors. Masters thesis (M.Phil), UCL (University College London).

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Abstract

Although the presence of cell adhesion molecules on primitive haemopoietic cells are known and well characterised, adhesion pathways mediated by many of these CAMs remain a matter of intense investigation. This thesis explores the adhesive interactions of haemopoietic stem cells (HSC) and progenitors with ECM ligands and stroma with particular emphasis on characterising the CD44:HA adhesion pathways. The myeloid cell line, KGla, expressing the CD34 molecule demonstrated significant binding to stroma and less so to HA, this was mediated by CD44. Long-term culture-initiating cell (LTC-IC) and plastic adherent (PA) cells (defined as stem cells) were quantified, in adult BM and peripheral blood (PB), using either limiting dilution assay (LDA) or single dilutions and both showed frequencies similar to previous studies. Adhesion assays using BM MNC and PB CD34+ cells on ligand-coated surfaces, showed that the frequencies of stem cells (either LTC-IC or PA cells), in the nonadherent fraction were less compared with those in the original cell suspension. These data suggest that there was 2-3 fold enrichment of of the two stem cell population by HA.The role of CD44 in the adherence of the stem cells to the ligands was investigated by including anti-CD44 moAb in adhesion assays and in two experiments both stem cells populations showed partial inhibition of adhesion to HA, compared with control antibody.Adhesion of these stem cell populations to fibronectin were also studied. Similar to HA, the frequencies in the two stem cells were higher in the original than in the nonadherent cell suspension suggesting enrichement by FN. The adhesion was blocked by anti-integrin pi antibody but not by anti-CD44 antibody. CFU-GM progeny assayed from PB CD34+ cells were shown to adhere to HA, furthermore this adhesion was partially inhibited by anti-CD44 antibody. Similarly theadhesion of CFU-C progeny assayed from UCB cell fractions was inhibited by the antibody.These findings suggest that the majority of stem cells in BM, PB and progeny in UCB cell populations are adherent to HA and that this is dependent, at least in part, on CD44.

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