Abstracts of the 19th International Congress on Neuromuscular Diseases 7th – 11th July 2026

Background: Inclusion body myositis (IBM) is a rare, progressive disorder characterized by invasion of muscle by highly differentiated cytotoxic CD8+ T cells.IBM can cause difficulty walking, loss of grip strength, and dysphagia.There are no pharmacological treatments approved for IBM.Ulviprubart, a humanized monoclonal antibody, selectively depletes cytotoxic CD8+ KLRG1+ T cells by targeting KLRG1 expressed on most IBM-muscle-infiltrating T cells.Here, we describe the study design and results of a phase 2/3 study of ulviprubart for treatment of IBM.Methods: This randomized, double-blind, placebo-controlled trial (NCT05721573) included patients aged ≥40 years with an IBM diagnosis otherwise fulfilling 2011 European Neuromuscular Center criteria.Ulviprubart (0.5 or 2.0 mg/kg) or placebo (1:1:1) was administered subcutaneously every 8 weeks for 76 weeks, with the option to receive treatment at 2.0 mg/kg in an open-label extension study.Efficacy endpoints included mean changes from baseline to week 76 in Inclusion Body Myositis Functional Rating Scale (IBMFRS; primary), manual muscle testing (MMT) of 23 muscle groups converted to a Kendall score, hand grip and quadriceps strength by dynamometry, and modified Timed Up and Go (mTUG).Safety monitoring included assessment of treatment-emergent adverse events.Results: Overall, 272 patients were enrolled.Mean (SD) patient age at baseline was 68.1 (7.8) years, and 186 patients were male (68%).Mean (SD) age at diagnosis was 65.1 (8.1) years.Mean (SD) baseline IBMFRS score was 27.3 (5.0); 14 patients had baseline IBMFRS scores of