This thesis examines the potential of a cytotoxic monoclonal antibody (mAb) which targets activated human antigen presenting cells (APCs) as a novel strategy for the prophylaxis of Graft versus Host Disease (GVHD). GVHD is a major limitation to the treatment of leukaemia with allogeneic (i.e. non-self donor) hematopoietic stem cell transplantation (HSCT), as following transplantation, grafted immune cells recognise the host as foreign and stimulate an inflammatory attack. Traditional immunosuppressant drugs prevent GVHD, but also increase post-transplant complications, most notably, the incidence and severity of infection. The lack of an effective treatment strategy for GVHD limits the number of allogeneic transplants worldwide to 15,000 per year, despite the hundreds of thousands of people who are diagnosed with blood disorders each year that could potentially benefit from HSCT.
The significance of this work is two-fold, as from a clinical standpoint, this research may potentiate a more effective treatment for GVHD, a disease with currently a small market that is of limited immediate commercial interest to the biopharmaceutical industry. Secondly, this research is scientifically novel, exploring the possibility of targeting of activated APCs (i.e. upstream initiators of inflammation), as opposed to traditional targets on T cell, which directly produce the inflammatory GVHD cascade.
To investigate the potential of an APC-targeted therapy for GVHD prophylaxis, target antigen candidates expressed by the professional APC type, dendritic cells (DCs), were evaluated. Activation marker, CD83 was selected as an attractive cell surface biomarker and a panel of single chain variable fragment (scFv) antibodies specific for human CD83 were isolated from antibody display libraries. Antibody display technology underpinned both the initial generation of the mAb, and was further utilised to perform affinity maturation for a lead candidate mAb. Cellular proliferation assays and cytotoxic assays for antibody dependant cell-mediated cytotoxicity (ADCC) were key metrics used to draw comparisons between distinct mAb clones and a polyclonal anti-CD83 preparation.
The salient findings from this research derive from the characterisation of several new anti-human CD83 monoclonal antibodies. This anti-CD83 mAb panel has demonstrable efficacy across a range of in vitro assays. A single lead candidate mAb was further optimised using affinity maturation and glyco-engineering strategies and the engineered mAbs provided insight into the immunobiology of targeting CD83+ cells for the purpose of immunosuppression. In particular, antigen density is shown to be a significant factor controlling ADCC of CD83 target cells. Finally, engineered CD83 mAbs are shown to be as efficacious as a polyclonal anti-CD83 antibody both in vitro and in a xenogeneic mouse model of GVHD, which illustrates the potential of anti-CD83 mAb as an attractive lead candidate antibody worthy of further pre-clinical development.