• While not reaching statistical significance, there was a slowing of disease progression relative to placebo, as measured by IBMFRS, in the overall patient population at the lower dose of ulviprubart, with a 50% slowing of disease progression relative to placebo across both doses in a pre-specified subgroup of patients with less severe disease

• Ulviprubart demonstrated a favorable safety and tolerability profile compared with placebo in the study

• Study validates ulviprubart’s mechanism of targeted depletion of cytotoxic T cells expressing KLRG1

• Abcuro plans to meet with FDA to discuss next steps to advance ulviprubart in IBM

Abcuro, Inc., a clinical stage biotechnology company, today presented results at the 6^th Global Conference on Myositis (GCOM) meeting, being held March 23-26, 2026 in Lisbon, Portugal from the Phase 2/3 MUSCLE clinical study of ulviprubart (ABC008), an investigational monoclonal antibody in development for the treatment of patients with inclusion body myositis (IBM). IBM is a rare, debilitating and relentlessly progressive chronic autoimmune disease that currently has no approved treatment options.

“A trend towards slowing of disease progression in patients with less severe disease is encouraging based on the biological hypothesis of how KLRG1+ T cells destroy muscle fibers over time. This pattern is consistent with observations in other diseases, where therapeutic effects are more readily detected in earlier stages,” said Namita Goyal, MD, Director of the Neuromuscular Center at the University of California, Irvine School of Medicine, and principal investigator of the MUSCLE study. “It also underscores ulviprubart’s unique mechanism targeting highly differentiated cytotoxic T cells expressing KLRG1. IBM is a devastating, progressive disease with no approved treatment options that affects tens of thousands of patients around the world. The significant unmet need in IBM cannot be overstated, and patients, care partners, and healthcare providers are united in seeking a safe and effective treatment.”

Key Highlights from Oral Presentation:

MUSCLE (NCT05721573) was a global Phase 2/3 clinical trial evaluating ulviprubart, dosed once every eight weeks (Q8W), in patients with IBM. The primary endpoint was change from baseline in IBM Functional Rating Scale (IBMFRS) total score at Week 76 compared to placebo. Key secondary endpoints included Manual Muscle Test 12 (MMT-12), dynamometry measurements for hand grip (Grip Dynamometry) and quadricep strength (Quad Dynamometry) and Modified Timed Up and Go (mTUG).

• 272 patients were randomized to one of two dose cohorts, 0.5 mg/kg (n=94, Low Dose Cohort) and 2.0 mg/kg (n=92, High Dose Cohort), or placebo (n=86).
• Across all patients, the primary endpoint of mean change from baseline in IBMFRS score at Week 76 demonstrated a trend for slower decline in the Low Dose Cohort with a decrease of 1.7 points in IBMFRS compared to a decrease of 2.4 in the placebo cohort (p=0.086), and a decrease of 2.1 in the High Dose Cohort (p=0.373).
• In the pre-specified analysis of patients with a baseline IBMFRS score of ≥29, there was a trend in both dose cohorts suggesting slower decline in the IBMFRS score over 76 weeks compared to placebo.
  • The mean change from baseline of IBMFRS at Week 76 was a decrease of 1.3 points for both doses, compared to placebo which decreased by 2.6 points (p=0.066 and p=0.075 for the Low Dose and High Dose groups, respectively).
  • This reflects a 50% slowing of disease progression relative to placebo in this subpopulation with less severe disease, suggesting a greater potential of ulviprubart’s disease modifying activity in patients with a baseline IBMFRS score of ≥29.
• Ulviprubart was observed to have a favorable safety and tolerability profile across all patients. The most common adverse event was fall (52.2% and 55.3% in the Low Dose Cohort and High Dose Cohort, respectively, compared to 51.2% in the placebo cohort). Common treatment emergent adverse events (in ≥10% of patients) that occurred at least twice as often with ulviprubart versus placebo were chills, headache, pyrexia, and nasopharyngitis.
• No patient dosed with ulviprubart experienced a treatment-emergent adverse event (TEAE) that led to discontinuation; overall, 2% of ulviprubart dosed patients discontinued the study early compared to 7% in the placebo group.
• Nearly all patients who completed the MUSCLE study are currently being dosed in an ongoing open-label extension (OLE) study.

“We would like to thank all the participating patients and care partners, along with the clinical investigators and their staff for their support of the MUSCLE study,” said H. Jeffrey Wilkins, Chief Medical Officer of Abcuro. “While the study did not achieve statistical significance, ulviprubart was generally well-tolerated and demonstrated a promising trend toward slowing of disease progression in less severe patients as assessed by IBMFRS. Based on the data, we believe ulviprubart has the potential to provide meaningful therapeutic benefit in such patients and we plan to meet with the FDA to discuss next steps for the advancement of ulviprubart in IBM.”

About Ulviprubart

Ulviprubart is a first-in-class, potent, monoclonal antibody that targets pathogenic T cells that express killer cell lectin-like receptor G1 (KLRG1) on their cell surface, referred to as KLRG1+ T cells. Ulviprubart is designed to selectively target and deplete well-differentiated cytotoxic KLRG1+ T cells where KLRG1 is highly expressed, while sparing other immune cells, which may offer improvements in safety and tolerability as compared to other T cell depleting approaches.

About Inclusion Body Myositis (IBM)

IBM is a rare, debilitating and relentlessly progressive chronic autoimmune muscle disease with no approved pharmacologic treatments and a significant unmet need. It is mediated by highly differentiated T cells that are chronically or aberrantly overstimulated and can have detrimental long-term effects including destruction of healthy muscle tissue. People living with IBM progressively lose muscle function, including loss of grip, dexterity and mobility. Based on published epidemiology literature, the ICD-10 code for IBM and an estimate for those misdiagnosed or undiagnosed, we estimate there are approximately 40,000 patients diagnosed with IBM in the United States and we estimate the prevalence of IBM to be approximately 35,000 patients across major European countries and Japan.

About Abcuro

Abcuro is a clinical stage biotechnology company developing potentially first-in-class immunotherapies designed to benefit people living with debilitating and progressive rare autoimmune diseases and for other indications where certain cytotoxic T cells are pathogenic. We believe that by selectively targeting and depleting highly cytotoxic T cells, which are key drivers of chronic inflammation and damage, we can advance our mission to deliver potentially life-transforming, disease-modifying therapies to patients facing these devastating conditions. The company’s lead program, ulviprubart, is currently being evaluated in a long-term open label study of inclusion body myositis (IBM) patients previously treated on another ulviprubart trial and a Phase 1/2 clinical trial in patients with T cell large granular lymphocytic leukemia (T-LGLL). For more information, visit us on LinkedIn and at abcuro.com.

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