Characterizing and modulating the canine T-cell costimulatory molecules CTLA-4 and CD28

Abstract

Current treatments for graft versus host disease, a major side effect of hematopoietic stem cell transplantation, have serious harmful side effects. The complexity of the cellular mechanisms leading to effector T-cell activation and deactivation is a hindrance to attempts to create more specifically acting immunosuppressive drugs. T-cell costimulation receptors CD28 and CTLA-4 and their associated antigen presenting cell ligands CD80 and CD86 have a poorly understood relationship. In particular, the mechanisms by which CTLA-4 expressed on the surface of effector and regulatory T-cells leads to suppression of T-cell activity is still unclear. In this project I attempted to characterize the relationships between these proteins including the canine analogues, which have so far been neglected, despite the importance of the canine model for development of treatments for graft versus host disease. I developed cell based reagents that will be useful tools for addressing these questions. I also attempted to develop and validate a specific CTLA-4 agonist for the purpose of suppressing active T-cells. This reagent is based around a soluble multivalent CD80 or CD86 molecule. I was able to produce milligram amounts of a reagent with desirable and functional binding properties. Further optimization of the expression system is required to produce sufficient product for in vivo testing.