Bypassing immunization in an attempt to develop beta 1 specific monoclonal human antibodies from semi-synthetic repertoires

Abstract

Immune selection can be mimiced 'in vitro' by displaying antibody repertoires on the surface of a filamentous bacteriophage and selecting phage by binding to antigen. The development of recombinant DNA methods and the knowledge that antibody fragments could be functionally expressed and assembled in 'E. coli' have led to the development of phage-antibody display technology. Integrins are conserved proteins involved in tissue morphogenesis, tissue integrity, develop ent, inflammation, control of cell growth, and cell mobility. Highly conserved regions of the integrins are thought to play an important role in their function. Failure to raise antibodies against those regions using conventional hybridoma technology has led to the use of semi-synthetic repertoires in an attempt to develop B1 integrin specific monoclonal antibodies. Large diversity is an essential feature of semi-synthetic repertoires of antibodies. Seven semi-synthetic phage-antibody human libraries were used, where HCDR3 was randomised over 7 or 13 amino acid residues. These randomized heavy chains where cloned with a unique Humkv 325 light chain as Fab fragments into pComb 3H vector for phage display. The libraries were panned by binding to a biotinylated B1 integrin peptide known to be the epitope of an inhibitory antibody called JB1A, or to purified human B1 integrin. Seven rounds of panning, with increasing stringency, were done in an attempt to increase the proportion of highly specific clones. Modest enrichment was observed for the selection on peptide and no enrichment was observed on purified human B1 integrin. Clones selected using these semi-synthetic antibody libraries do not seem to have any specificity for the desired epitope. Improvement of the method of selection and system outlined in this thesis should be done in any future attempt of selection. Nevertheless phage-antibody display technology has a promising future as a complement to the well established hybridoma technology.