Phase 2/3 study did not meet primary or key secondary endpoints; ulviprubart showed a favorable safety and tolerability profile compared to placebo

Clinically meaningful slowing of disease progression observed in patients with mild to moderate disease; establishes basis for advancing ulviprubart in this segment of the population

Study results to be presented at the 6^th Global Conference on Myositis

Abcuro, Inc., today announced topline results 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), a rare, debilitating and relentlessly progressive chronic autoimmune disease that currently has no approved treatment options. The MUSCLE study did not meet its primary endpoint, assessed by the IBM Functional Rating Scale (IBMFRS) total score at Week 76 compared to placebo, or key secondary endpoints. While the results did not achieve statistical significance, a pre-specified subgroup analysis in patients with mild to moderate disease at baseline showed trends in improvement in the IBMFRS total score and key secondary endpoints, suggesting the potential of ulviprubart’s disease modifying activity in such patients. Importantly, ulviprubart showed a favorable safety and tolerability profile compared to placebo, and no safety signals were identified at the doses studied.

Abcuro plans to present the study results from the MUSCLE trial at the upcoming 6^th Global Conference on Myositis (GCOM) meeting, being held March 23-26, 2026, in Lisbon, Portugal.

“While we are disappointed that the MUSCLE trial did not reach statistical significance in the overall study population, we are encouraged by the clear and meaningful magnitude of improvements observed in patients with mild to moderate disease, as well as its favorable safety and tolerability profile overall,” said H. Jeffrey Wilkins, Chief Medical Officer of Abcuro. “Ulviprubart was designed to target cytotoxic T-cells expressing KLRG1, a pathology we believe is a potential driver of muscle destruction in IBM. This is the first study to investigate this mechanism of action in IBM, and we believe further study of ulviprubart in patients with less severe disease is an important next step towards being able to provide an effective treatment option for patients with IBM. We plan to discuss our approach with the FDA in the near future.”

“Abcuro remains committed to the IBM community, and we are extremely grateful to the clinical study participants, investigators, and study site teams that supported this important clinical study,” said Alex Martin, Chief Executive Officer of Abcuro. “With insights derived from this study, we hope to continue developing ulviprubart for patients with IBM.”

MUSCLE (NCT05721573) was a global Phase 2/3 clinical trial evaluating ulviprubart in 272 patients with IBM, randomized across two drug levels and placebo cohorts with the primary endpoint of IBMFRS at week 76. Key secondary endpoints included Manual Muscle Test 12 (MMT-12) and dynamometry measurements for hand grip and quadricep strength. Nearly all patients who completed the MUSCLE study are currently being dosed in an ongoing open-label extension study.

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 believe there are approximately 40,000 patients 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’s lead program, ulviprubart, is a potential first-in-class, 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 expressed, while sparing other immune cells, which may offer improvements in safety and tolerability as compared to other T cell depleting approaches. For more information, visit us on LinkedIn and at abcuro.com.

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