Abcuro Highlights Phase 2/3 MUSCLE Study Results of Ulviprubart in Inclusion Body Myositis at GCOM 2026
Abcuro, Inc. has announced new clinical data from its Phase 2/3 MUSCLE study evaluating ulviprubart (ABC008), an investigational monoclonal antibody therapy for inclusion body myositis (IBM). The results were presented at the Global Conference on Myositis, held from March 23–26, 2026, in Lisbon. The findings provide important insights into the potential of ulviprubart to address a rare and debilitating autoimmune disease that currently has no approved treatment options.
Inclusion body myositis is a chronic, progressive neuromuscular disorder characterized by inflammation and degeneration of skeletal muscle. Over time, patients experience worsening muscle weakness, particularly in the arms and legs, leading to difficulties with mobility, swallowing, and daily functioning. The disease is widely recognized as one of the most challenging inflammatory myopathies to treat, with limited therapeutic progress despite decades of research. The absence of approved disease-modifying therapies underscores the urgent need for innovative approaches that can alter the course of the disease rather than simply manage symptoms.
Ulviprubart, also known as ABC008, represents one such novel approach. The therapy is a monoclonal antibody designed to selectively target KLRG1-positive (KLRG1+) cytotoxic T cells, which are believed to play a central role in the pathogenesis of IBM. These highly differentiated immune cells are thought to attack and destroy muscle fibers over time, contributing to the progressive muscle weakness observed in patients. By specifically targeting this cell population, ulviprubart aims to interrupt the underlying immune-driven damage and potentially slow disease progression.
The MUSCLE study (NCT05721573) was a global, randomized, placebo-controlled Phase 2/3 clinical trial designed Abcuro to evaluate the safety, tolerability, and efficacy of ulviprubart in patients with IBM. A total of 272 participants were enrolled and randomized into three groups: a low-dose cohort receiving 0.5 mg/kg (94 patients), a high-dose cohort receiving 2.0 mg/kg (92 patients), and a placebo group (86 patients). The drug was administered once every eight weeks, reflecting a relatively infrequent dosing schedule that could offer convenience for patients if proven effective.
The primary endpoint of the study was the change from baseline in the Inclusion Body Myositis Functional Rating Scale (IBMFRS) total score at Week 76 compared to placebo. The IBMFRS is a widely used clinical tool that assesses patients’ ability to perform daily activities, including swallowing, mobility, and hand function. Secondary endpoints included measures such as the Manual Muscle Test 12 (MMT-12), grip strength assessed through dynamometry, quadriceps strength measurements, and the Modified Timed Up and Go (mTUG) test, all of which provide a comprehensive evaluation of muscle function and physical performance.
Across the overall study population, the primary endpoint showed a trend toward slower disease progression in patients treated with ulviprubart, although the results did not reach statistical significance. Specifically, Abcuro patients in the low-dose cohort experienced a mean decline of 1.7 points in IBMFRS score over 76 weeks, compared to a decline of 2.4 points in the placebo group (p=0.086). In the high-dose cohort, the mean decline was 2.1 points (p=0.373). While these findings indicate a numerical improvement relative to placebo, the lack of statistical significance suggests that further investigation is needed to confirm the therapy’s efficacy.
More encouraging results emerged from a pre-specified subgroup analysis focusing on patients with less severe disease at baseline, defined as those with an IBMFRS score of 29 or higher. In this subgroup, both dosing regimens Abcuro demonstrated a stronger trend toward slowing disease progression compared to placebo. Patients receiving ulviprubart in either dose group showed a mean decline of 1.3 points in IBMFRS score over 76 weeks, whereas the placebo group experienced a decline of 2.6 points. These results correspond to an approximate 50% reduction in the rate of disease progression relative to placebo, with p-values of 0.066 and 0.075 for the low-dose and high-dose groups, respectively.
This pattern suggests that ulviprubart may have greater therapeutic impact when administered earlier in the disease course, before extensive muscle damage has occurred. Such findings are consistent with observations in other chronic Abcuro conditions, Abcuro where interventions tend to be more effective in earlier stages. The data therefore support the biological hypothesis underlying ulviprubart’s mechanism of action and highlight the importance of early diagnosis and intervention in IBM.
Dr. Namita Goyal, Director of the Neuromuscular Center at the University of California, Irvine School of Medicine and principal investigator of the MUSCLE study, commented on these findings. She noted that the observed trend toward slowing disease progression in patients with less severe disease aligns with the understanding of how KLRG1+ T cells contribute to muscle fiber destruction. Dr. Goyal emphasized that IBM is a devastating condition with significant unmet medical need, and that patients, caregivers, and clinicians are united in their efforts to identify safe and effective treatments.
In addition to efficacy outcomes, the Abcuro MUSCLE study provided important information on the safety and tolerability of ulviprubart. Overall, the therapy was well tolerated across both dose cohorts. The most commonly reported adverse event was falls, occurring in 52.2% of patients in the low-dose group and 55.3% in the high-dose group, compared to 51.2% in the placebo group. Abcuro Other treatment-emergent adverse events that occurred in at least 10% of patients and were observed at higher rates with ulviprubart than placebo included chills, headache, fever (pyrexia), and nasopharyngitis.
Importantly, no patients receiving ulviprubart discontinued treatment due to adverse events, indicating a favorable tolerability profile. Overall, only 2% of patients in the treatment groups discontinued the study early, compared to 7% in the placebo group. These findings suggest that ulviprubart can be administered safely over an extended period, which is a critical consideration for a chronic condition like IBM that may require long-term therapy.
Another notable aspect of the study is the high level of patient retention and continued participation in follow-up research. Nearly all patients who completed the MUSCLE trial have enrolled in an ongoing open-label extension (OLE) study, where they continue to receive ulviprubart. This extension study will provide additional long-term data on safety and efficacy, helping to further characterize the therapy’s potential benefits and risks.
H. Jeffrey Wilkins, Chief Medical Officer of Abcuro, expressed gratitude to the patients, caregivers, and clinical investigators who contributed to the study. He acknowledged that while the trial did not meet its primary endpoint with statistical significance, the observed trends—particularly in patients with less advanced disease—are promising. According to Wilkins, these findings support the continued development of ulviprubart as a potential disease-modifying therapy for IBM.
Abcuro plans to engage with the U.S. Food and Drug Administration (FDA) to discuss the next steps for advancing ulviprubart in clinical development. These discussions are expected to focus on the design of future studies, potential regulatory pathways, and strategies for confirming the therapy’s efficacy in targeted patient populations. Given the rarity of IBM and the challenges associated with conducting large clinical trials, regulatory guidance will be critical in determining the most efficient path forward.
The broader implications of these findings extend beyond IBM itself. The selective targeting of KLRG1+ T cells represents a novel therapeutic strategy that could have applications in other autoimmune and inflammatory diseases. If validated, this approach may open new avenues for the development of targeted immunotherapies that address the underlying drivers of disease rather than merely alleviating symptoms.
In conclusion, the Phase 2/3 MUSCLE study results presented by Abcuro provide a meaningful step forward in the search for effective treatments for inclusion body myositis. While the primary endpoint was not met with statistical significance, the observed trends toward slowing disease progression—particularly in patients with less severe disease—offer hope for a condition that has long lacked viable therapeutic options. Combined with a favorable safety profile and strong patient engagement in ongoing studies, ulviprubart emerges as a promising candidate in the evolving landscape of neuromuscular and autoimmune disease research.
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 Abcuro 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 Abcuro 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 Abcuro 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).
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