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Title: Engineering antibodies to study and improve immunomagnetic isolation of tumour cells
Author: Jain, Jayati
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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Cell separation based on antibody-targeted magnetic beads has been widely used in a number of applications in immunology, microbiology, oncology and more recently, in the isolation of circulating tumour cells (CTCs) in cancer patients. Although other cell separation techniques such as size based cell filtration and Fluorescence Activated Cell Sorting have also been in popular use, immunomagnetic cell isolation possesses the advantages of high throughput, good specificity and reduced cell stress. However, certain fundamental features of the cell-bead interface are still unknown. In this study, some of the key features of the cell-bead synapse were investigated in an effort to improve the efficiency of immunomagnetic cell isolation and reduce its dependence on high expressing cell surface markers. A clinically relevant antibody fragment (Fab) against tyrosine kinase receptor HER2 was applied to study the immunomagnetic isolation of HER2 expressing cancer cells. First, the minimum number of target proteins required on a cell for it to be isolated was determined. Second, the importance of the primary antibody affinity was investigated, using a series of Fab mutants with known kinetics and it was shown that despite starting with sub-nanomolar affinity, improving Fab affinity increased cell isolation. Third, the influence of the connection between the primary antibody and the bead was studied by comparing Fab bridged to the magnetic bead via a secondary antibody, Protein L or streptavidin; the high affinity biotin-streptavidin linkage increased isolation sensitivity by an order of magnitude. Fourth, the effect of manipulating cytoskeletal polymerization and cell membrane fluidity using small molecules was tested; cholesterol depletion decreased isolation and cholesterol loading increased cell isolation. The insights from these observations were then applied to isolate a panel of cell lines expressing a wide range of surface HER2. While the standard approach isolated less than 10% of low HER2 expressing cancer cells from spiked rabbit and human blood, our enhanced approach with the optimized cholesterol level, antibody affinity and antibody-bead linkage could specifically isolate more than 80% of such cells. The final part of this work focussed on developing an antibody clamp that could physically restrict the antigen within its binding site on the Fab and prevent antigen dissociation, using the HER2-Fab complex and the anti-myc peptide antibody 9E10. Work from this thesis provides useful insights into the molecular and cellular parameters guiding immunomagnetic cell isolation and can be used to extend the range of target receptors and biomarkers for tumour cell isolation and other types of cell separation, thereby enhancing the power and capacity of this approach.
Supervisor: Howarth, Mark; Brockdorff, Neil Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry ; Molecular biophysics (biochemistry) ; Bioinformatics (life sciences) ; Biology ; Cell Biology (see also Plant sciences) ; Genetics (life sciences) ; Nano-biotechnology ; Genetics (medical sciences) ; Immunology ; Membrane proteins ; Molecular genetics ; Protein chemistry ; Protein folding ; antibodies ; protein engineering ; HER2 ; Herceptin ; 4D5 ; microbiology ; cancer ; immunomagnetic ; cell isolation ; cholesterol ; Fab ; tumour cell ; magnetic bead ; circulating tumour cell ; biotinylation ; 9E10 ; BT474 ; clamping ; periplasmic expression ; cell sorting ; myc peptide ; streptavidin ; flow cytometry