Effectiveness and safety of BCD180, anti-TRBV9<sup>+</sup> T-lymphocytes monoclonal antibody in patients with active radiographic axial spondyloarthritis: 36-week results of double-blind randomized placebo-controlled phase II clinical study ELEFTA

The aim – to evaluate the clinical effectiveness, safety, pharmacokinetics, pharmacodynamics, and immunogenicity of seniprutug (BCD-180) in patients with radiographic active axial spondyloarthritis (r-axSpA, or ankylosing spondylitis). Subjects and methods . 260 patients with active r-axSpA and inadequate response to nonsteroidal anti-inflammatory drugs (NSAIDs) were randomized into three groups: seniprutug (BCD-180) at doses of 5 mg/kg or 7 mg/kg, or placebo. BCD-180 was administered on weeks 0–12–36. Patients in the placebo group were switched to BCD-180 at a dose of 5 mg/kg at week 24 and continued therapy at week 36. The primary endpoint was the proportion of patients achieving 40% improvement by Assessment in Spondyloarthritis International Society scale (ASAS40) at week 24. Secondary endpoints were proportion achieving ASAS20/40, improvement of 5 out of 6 criteria of ASAS (ASAS5/6), ASAS partial remission, clinically important improvement in ASDAS-CRP (Ankylosing Spondylitis Disease Activity Score with C-reactive protein) (ASDAS-CII) and major improvement in ASDAS-CRP (ASDAS-MI). The dynamics of the disease activity status according to ASDAS-CRP, the BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) and BASFI (Bath Ankylosing Spondylitis Functional Index) indices, as well as the dynamics of laboratory markers (C-reactive protein anderythrocyte sedimentation rate (ESR)) were analyzed. Safety was assessed by the frequency and profile of adverse events (AEs) and adverse reactions (ARs). Results . The proportion of patients achieving ASAS40 at week 24 with seniprutug (BCD-180) at the dose of 7 mg/kg and 5 mg/kg was 51.4% and 40.8%, respectively, compared with 24% in the placebo group (p=0.0012 and p=0.0417, respectively). Analysis of secondary endpoints showed that in patients with r-axSpA, BCD-180 at both study doses was significantly superior to placebo at week 24 in the following measures: decrease in the proportion of subjects with very high disease activity (ASDAS-CRP>3.5) achieving ASDAS-CII, ASAS20, ASAS5/6. A statistically significant decrease in the ASDAS-CRP, BASDAI, BASFI indices, as well as the concentration of CRP and ESR were demonstrated. Tolerability of seniprutug therapy was assessed as acceptable. Infusion reactions were the most common observed adverse events, the vast majority of which were mild to moderate in severity according to CTCAE 5.0 (Common Terminology Criteria for Adverse Events) and developed predominantly during the first administration. The proportion of patients with binding antibodies was 5.1%. However, no neutralizing antibodies were detected. Conclusion . Seniprutug (BCD-180) demonstrated superiority over placebo in clinical efficacy with a favorable safety profile and low immunogenicity as a treatment of r-axSpA.