Background/Purpose: Axial spondyloarthritis (axSpA) is a chronic inflammatory disease which requires optimal management.1 In clinical trials, Assessment of SpondyloArthritis international Society ≥40% improvement (ASAS40) is a stringent outcome used to assess efficacy, while in clinical practice, focus is on axSpA Disease Activity Score (ASDAS) low disease activity (LDA; < 2.1). Maintenance of response, an internationally recommended axSpA treatment target,1 can be measured by these outcomes.Bimekizumab (BKZ) is a monoclonal IgG1 antibody that selectively inhibits interleukin (IL)-17F in addition to IL-17A. In patients (pts) across the full disease spectrum of axSpA (i.e., non-radiographic [nr-] and radiographic [r-]axSpA), BKZ has demonstrated sustained clinical efficacy to 2 years in the phase 3 studies BE MOBILE 1 and 2, and their combined open-label extension (OLE).2 This analysis assessed the maintenance of response to BKZ over 3 years in pts who achieved responses at Week (Wk) 16 in these studies, including in pts who never lost their response at any subsequent visit.

Methods: BE MOBILE 1 (NCT03928704; nr-axSpA) and 2 (NCT03928743; r-axSpA) both comprised a 16-wk double-blind, placebo-controlled period followed by a 36-wk maintenance period.3 From Wk 16, all pts received subcutaneous BKZ 160 mg every 4 wks. At Wk 52, eligible pts could enroll in the OLE (BE MOVING; NCT04436640). The proportion of pts achieving ASAS40 or ASDAS LDA at Wk 164 was assessed among BKZ-randomized pts that achieved each respective outcome at Wk 16. The proportion of pts who achieved ASDAS LDA at Wk 16 and never lost their response at every subsequent visit from Wk 16 to Wk 164 is also reported, including those who achieved ASDAS major improvement (ASDAS-MI; ≥2.0-unit change from baseline [CfB]) and ASDAS clinically important improvement (ASDAS-CII; ≥1.1-unit CfB).Presented data, pooled across studies, use non-responder imputation (NRI), modified non-responder imputation (mNRI) or multiple imputation (MI; ASDAS only). Observed case (OC) data are also reported.

Results: A total of 128 pts and 221 pts were randomized to BKZ across BE MOBILE 1 and 2, respectively (N&#3f349). A high proportion of pts who achieved a response at Wk 16 maintained their response at Wk 164 (Figure 1).Of the 160 pts (45.8%; NRI) who achieved ASAS40 at Wk 16, 80.4% still achieved ASAS40 at Wk 164 (mNRI). Of the 152 pts (43.6%; NRI) who achieved ASDAS LDA at Wk 16; 78.8% still achieved ASDAS LDA at Wk 164 (MI; Figure 1). From Wk 16 through to Wk 164, 50% of pts never lost their ASDAS LDA status at any assessed visit (MI), with a further 22.4% only losing their ASDAS LDA status at one visit, and 6.1% at two visits, respectively (MI). The majority of pts who never lost their ASDAS LDA status from Wk 16 and entered the OLE achieved ASDAS-MI or ASDAS-CII at Wk 52, 104 and 164 (94.5%, 94.5%, and 90.9%, respectively; Figure 2).

Conclusion: A high proportion of BKZ-randomized pts who achieved stringent clinical responses at Wk 16 maintained these to Wk 164 across the full disease spectrum of axSpA. Half of pts achieving ASDAS LDA at Wk 16 never lost their response up to Wk 164. References: 1. Ramiro S. Ann Rheum Dis 2023;82:19–34; 2. Baraliakos X. Rheumatology 2025;keaf009; 3. Baraliakos X. Ann Rheum Dis 2024;83:199–213.

Figure 1. Maintenance of (A) ASAS40 and (B) ASDAS LDA to Week 164 among BKZ-randomized patients who achieved each respective outcome at Week 16

Figure 2. BKZ-randomized patients who achieved ASDAS LDA ( < 2.1) at Week 16 and (A) never lost their ASDAS LDA status to Week 164 or (B) lost their ASDAS LDA status at least once to Week 164 (OC)

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/bimekizumab-treatment-resulted-in-patients-with-axial-spondyloarthritis-maintaining-their-clinical-responses-over-3-years-results-from-two-phase-3-studies-and-their-open-label-extension/