RF35 | PSAT269 Double-Blind, Randomized, Placebo-controlled, Multicenter, Phase 2b Study of Batoclimab in Active and Moderate-to-Severe Thyroid Eye Disease

Clinical manifestations of thyroid eye disease (TED) are mainly caused by the binding of immunoglobulin G (IgG) thyrotropin receptors (TSHR) autoantibodies (TSHR-Ab) on orbital fibroblasts. Batoclimab (IMVT-1401) is an anti-neonatal Fc receptor (FcRn) human monoclonal antibody that prevents normal IgG recycling, leading to reduced levels of circulating IgG. Thus, batoclimab may provide benefit for patients with TED by reducing pathogenic anti-TSHR-Ab. In this Phase 2b, double-blind, randomized study (NCT03938545), subjects with active and moderate-to-severe TED received weekly subcutaneous (SC) injections of batoclimab (680mg, 340mg, 255mg) or placebo for 12-weeksSixty-five subjects were randomized and received batoclimab (680mg [n=18], 340mg [n=19], 255mg [n=10]) or placebo (n=18). Recruitment and treatment were stopped because of an unanticipated increase in LDL cholesterol levels, not included in subject informed consent. Hence, forty-five of 77 planned subjects completed the 12-week treatment period. Serum IgG and anti-TSHR-Ab were reduced from baseline to Week-12 with batoclimab (680mg [-77.9%; -65.5%], 340mg [-65.8%; -70.1%], 255mg [-56.6%; -42.1%]) versus placebo (-4.67%; -3.23%), respectively. Substantial reductions were also observed at Week-12 in stimulatory anti-TSHR-Ab. Fifty-one of 65 subjects had proptosis ≥ upper level of normal at baseline. At Week-12 (primary outcome), greater proportions of 680mg (30%; p=0.2197) and 340mg (30.8%; p=0.1311) subjects were proptosis responders (≥2mm reduction) versus placebo (8.3%). Absolute risk reduction (ARR [95% CI]) versus placebo was 21.4 (-11.3, 54.1) for 680mg and 24.2 (-4.8, 53.2) for 340mg at Week 12. Earlier proptosis responses were statistically different from placebo for 680mg at Weeks-four (35.7%; ARR [95% CI] 36.0 [10.9, 61.1]), five (42.9%; 43.0 [17.1, 68.9]), and 11 (41.7%; 34.5 [3.4, 65.6]) and for 340mg at Weeks-five (29.4%; 29.6 [7.9, 51.3]), nine(35.7%; 30.6 [3.0, 58.2]), and 11 (46.2%; 40.2 [10.2, 70.1]) (all p<0.05). Changes in clinical activity at Week-12 were not significantly different from placebo.The proportion of subjects with an adverse event (AE) were similar across treatment groups; most were mild or moderate in severity. Two subjects reported serious AEs not related to treatment (optic neuropathy, autoimmune encephalitis [occurring after treatment period]). No subjects withdrew from the study due to an AE during the 12-week treatment period. There was a reversible dose-dependent reduction in serum albumin during the treatment period. Post-hoc lipid analysis demonstrated a reversible increase in mean serum LDL during treatment (680-mg: 58.7%; 340-mg: 30.8%; 255-mg: 19.0%) vs placebo (-3.9%),.In conclusion, batoclimab reduced circulating IgG and especially the pathogenic anti-TSHR-Ab. Although the proptosis response was not statistically significant at the primary endpoint, significance was seen at earlier time points. This is probably related to early study termination which reduced the numbers of patients available for efficacy assessment at the primary endpoint. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m., Monday, June 13, 2022 12:54 p.m. - 12:59 p.m.