FVIII tolerance induction in hemophilia A mice utilizing low dose IL2 treatment

Abstract

Abstract Hemophilia A patients lack or possess low levels of functional FVIII protein, which results in an inability for the blood to clot when injury occurs. The current treatment for hemophilia A patients is FVIII protein replacement, but this treatment is expensive and often results in anti-FVIII immune responses, neutralizing the clotting effect. Regulatory T (Treg) cells help balance T effector (Teff) cells through their suppressive function during an immune response and keep autoimmunity in check. Treg cells possess a high affinity epitope of the IL2 receptor. With a low dose of IL2, the Treg population outcompetes the Teff cells, leading to an increase in activation and number. The increased suppressive activity may induce tolerance in hemophilia A mice treated with FVIII. Hemophilia A mice were hydrodynamically injected with IL2 and FVIII plasmids. Cell staining data showed a marked increase in Treg cell population and activation. In addition, the Treg/Teff ratio was significantly increased in the first 3 weeks and maintained at increased levels over several weeks afterwards. On Day 28-post FVIII injection, control mice had started to develop inhibitors associated with significant decrease of FVIII expression, while mice treated with IL2 showed no inhibitors with persistent FVIII expression. The treated mice are monitored to determine the potential long term tolerance induced by low dose IL2. Combined gene transfer of FVIII and IL2 plasmids can produce therapeutic FVIII and simultaneously prevent inhibitory antibody formation, thus providing a potentially effective treatment of hemophilia A.