Generation of two high affinity anti-mouse FcRn antibodies: Inhibition of IgG recycling in wild type mice and effect in a mouse model of immune thrombocytopenia.

Primary immune thrombocytopenia (ITP) is an autoimmune disease characterized by pathogenic immunoglobulin G (IgG) autoantibodies that bind to platelets, causing their phagocytic removal and leading to reductions in platelet number. The neonatal Fc receptor (FcRn) selectively salvages and recycles IgG, including pathogenic IgG, thereby extending the half-life of IgG in plasma. Two anti-mouse FcRn monoclonal antibodies (mAb) (4470 and 4464) were generated to evaluate the effect of inhibiting IgG recycling. Statistically significant reductions in plasma IgG concentration were observed upon administration of 4470 (10, 30 and 100 mg/kg) in wild-type mice. In a passive mouse model of ITP, 4464 alleviated the reduction in platelet number and/or preserved newly produced platelets when dosed prophylactically as well as in a therapeutic dosing regimen once platelet numbers had already been reduced. These results support the investigation of anti-FcRn therapy as a potential treatment for ITP.

Engineered hexavalent Fc proteins with enhanced Fc-gamma receptor avidity provide insights into immune-complex interactions.

Autoantibody-mediated diseases are currently treated with intravenous immunoglobulin, which is thought to act in part via blockade of Fc gamma receptors, thereby inhibiting autoantibody effector functions and subsequent pathology. We aimed to develop recombinant molecules with enhanced Fc receptor avidity and thus increased potency over intravenous immunoglobulin. Here we describe the molecular engineering of human Fc hexamers and explore their therapeutic and safety profiles. We show Fc hexamers were more potent than IVIG in phagocytosis blockade and disease models. However, in human whole-blood safety assays incubation with IgG1 isotype Fc hexamers resulted in cytokine release, platelet and complement activation, whereas the IgG4 version did not. We used a statistically designed mutagenesis approach to identify the key Fc residues involved in these processes. Cytokine release was found to be dependent on neutrophil FcγRIIIb interactions with L234 and A327 in the Fc. Therefore, Fc hexamers provide unique insights into Fc receptor biology.

A short treatment with an antibody to sclerostin can inhibit bone loss in an ongoing model of colitis.

Chronic inflammation leads to bone loss, and increased fracture rates have been reported in a number of human chronic inflammatory conditions. The study reported here investigates the skeletal effects of dosing a neutralizing antibody to the bone regulatory protein sclerostin in a mouse model of chronic colitis. When dosed prophylactically, an antibody to sclerostin (Scl-AbI) did not reduce the weight loss or histological changes associated with colitis but did prevent inflammation-induced bone loss. At the end of the experiment, Scl-AbI-treated animals had a significantly higher femoral BMD (+27%, p < 0.05) than control antibody (Cntrl-Ab)-treated animals. In a second experiment, treatment with Scl-AbI was delayed until colitis had developed, by which time the mechanical properties of femurs in colitic animals were significantly worse than those of healthy age-matched control mice (maximum load, -26%, p < 0.05; energy, -37%, p < 0.05; ultimate strength, -33%, p < 0.05; elastic modulus, -17%, p < 0.05). A short treatment with Scl-AbI halted bone loss and reversed the decline of both intrinsic and extrinsic mechanical properties of the femur such that, after 19 days of treatment, the bone mechanical properties in the Scl-AbI-treated animals were not significantly different from those of noncolitic age-matched controls. Serum markers of bone formation and resorption suggested that the antibody to sclerostin stimulated osteoblast activity and inhibited osteoclast-mediated bone resorption.