Abstracts Biological Sciences

HOW STEM CELLS ROLL: A MICROFLUIDIC CHARACTERISATION OF THE CD44-HYALURONIC ACID INTERACTION AND ITS ROLE IN LEUKAEMIA

by Maximilian Paul Hanke

Acute myeloid leukaemia is a malicious disease. Although the initial chemotherapeutic treatment often leads to a complete remission (a disappearance of all manifestations of disease), the effective survival rate is only (30-40) % over 4 years due to a high relapse rate. This relapse is attributed to leukaemic stem cells residing in the protective environment of the bone marrow niche. There are two major approaches aiming at achieving better long-term therapeutic results. The first is to make the leukaemic stem cells more susceptible to chemotherapeutic agents and the second is to increase the efficiency of haematopoietic stem cell transplants, which are used to regenerate the haematopoietic system after failure due to chemotherapy. When searching for a receptor-ligand pair suitable as target for therapeutic agents, the prerequisite is that it must exhibit differences between the interaction it mediates in healthy and leukaemic cells. A detailed understanding of the mediated interaction and the differences would then allow exploitation of these to selectively mobilise the leukaemic stem cells increasing their susceptibility for chemotherapeutic drugs. In this work the flow-induced rolling interaction of leukaemic cells with hyaluronic acid was studied in detail using a suspension and an epithelial model cell line. It could be demonstrated, that the flow induced rolling interaction on hyaluronic acid observed for these cells was solely mediated by the cell surface receptor CD44 and that it was independent of the cell type tested. Next to a detailed validation and characterisation of this dependency and the properties of the interaction, the relevance of this interaction for the haematopoietic system and for leukaemic cells was evaluated. Therefore, the CD44 mediated interaction with hyaluronic acid of healthy haematopoietic progenitor cells from umbilical cord blood, mobilised peripheral blood and the bone marrow with that of leukaemic blasts was compared. Throughout the cell types tested two forms of interaction with hyaluronic acid were observed; a flow induced rolling and an immobile adhesion. It could be shown that while the rolling interaction was comparable for all cell types tested, the immobile adhesion to hyaluronic acid and its susceptibility to a monoclonal CD44 antibody (clone BU52) were not. The immobile adhesion was found predominantly in leukaemic cells, only playing a subordinate role in the interaction of healthy cells with hyaluronic acid. It could be demonstrated that a vicinity of the cells to the bone marrow upon isolation was directly correlated to an incomplete suppression of the immobile adhesion by BU52. Furthermore, this incomplete suppression could be linked to a non-response to induction chemotherapy and subsequently to a poor therapeutic outcome. Besides investigating the interaction with surfaces artificially coated with hyaluronic acid, the possibility of using surfaces covered with mesenchymal stromal cells isolated from the bone marrow as more realistic binding partners was …