Translational Applications of New Insights into Immunoreceptor Signalling

The aim of the T-cell biology group, in its translational work, is to develop new antibodies for use as therapies in autoimmune diseases. To achieve this we are working towards an understanding of the biology of the leukocyte cell surface, and to apply this understanding to the development of new drug-like antibodies. Leukocytes are white blood cells that are involved in defending the body against infectious disease and foreign materials found in the blood and lymphatic circulatory systems. The surface of leukocytes is covered in protein molecules, some of which are receptors that interact with fragments of specific foreign proteins either from infectious agents or other foreign materials, such as allergens, or, as in the case of some autoimmune diseases, to self-antigens. When the receptors interact with their target molecules, we propose that they undergo a reorganization that causes them to trigger immune response pathways. If these pathways are triggered inappropriately, then autoimmune disease can develop. The process of receptor triggering by native ligands can be mimicked with antibodies, which means that, when we fully understand the process, we may be in a position to design new antibody-based receptor agonists for use in the treatment of autoimmune diseases.

Goals To understand the cell biology of the leukocyte surface and to use the insights to alter the behaviour of leukocytes in autoimmune settings. The T-cell biology group is working towards an understanding of the biology of the leukocyte surface and the mechanism of receptor triggering, both for its intrinsic cell biological interest and as the basis for developing new types of immunotherapy. For the last several years we have focused on understanding the composition of the T-cell surface and how receptors expressed there are organized and then ‘triggered’ by ligand binding (1-3). The expression of transcripts encoding known cell surface molecules by a human CD8+ T-cell clone was characterized by a transcriptomic approach (SAGE) and the results suggested that existing models of receptor triggering are unlikely to be wrong because key components remain to be discovered (1). Determination of an anti-CD28 superagonistic antibody Fab fragment bound to CD28 (2) provided insights as to how antibody superagonists work and incorporated CD28 into the family of receptors triggered via kinase/phosphatase segregation – a family that includes the T cell receptor (for a review see reference 3). Assembly of proteins expressed at the cell surface has been studied by bioluminescence resonance energy transfer (BRET), which has been used to characterize the quaternary structures of cell surface molecules. Our new experimental framework for detecting transfected receptor dimers revealed that most proteins expressed at the cell surface are likely to be monomers, undermining the notion that important groups of receptors inexorably form dimers (4). Together with our collaborators we have established a new method for studying the organization of native receptor complexes (two-colour coincidence detection). Analysis of the composition of protein complexes on the surface of live T cells has shown that the TCR is monovalent (5). Recent work has focused on determination of the stoichiometries of each key component of the T cell triggering apparatus – MHC class II, CD4, CD45 – and these too have been shown to be monovalent (6). Future research plans Future work will concentrate on understanding receptor triggering by native ligands and by antibodies and to use this knowledge in the development of new receptor agonist-based therapeutic antibodies – for example against inhibitory receptors such as PD-1 that suppress immune responses both in vivo and in vitro. A key objective is to target molecules that may offer new opportunities to intervene in autoimmunity. References: (1) Evans et al 2003 Immunity 19: 213 (2) Evans 2005 Nature Immmunol 6: 271 (3) Davis and van der Merwe 2006. Nature Immunol 7: 803 (4) James et al. 2006 Nature Methods 3: 1001 (5) James et al 2007 Proc Natl Acad Sci USA 104: 17662 (6) James et al. 2011 J Biol Chem. 2011 16:31993