Background ABP 501 has been approved by the US FDA as the first biosimilar to the fully human recombinant monoclonal antibody, adalimumab. Totality of evidence to date suggests that ABP 501 is highly similar to adalimumab. Subjects receiving either ABP 501 or adalimumab in the active-controlled, comparative, pivotal phase 3 study in rheumatoid arthritis (parent study) continued on to this open-label extension (OLE) study if they had completed the final week 26 visit of that study.

Objectives To describe the safety, immunogenicity, and efficacy outcomes of ABP 501 in the OLE study.

Methods Subjects who completed the parent study were screened and were included if they met the eligibility requirements. All subjects included in the OLE were treated with ABP 501 40 mg subcutaneously every other week for 68 weeks followed by disease assessments at week 70 and the follow-up safety assessment at week 72 (or early termination). Data were summarized descriptively and no inferential analyses were performed.

Results Of the 467 subjects enrolled in the OLE study, 466 were treated with ABP 501. Of these, 237 transitioned from the adalimumab arm of the parent study; 412/467 completed the study. Demographics and disease characteristics were balanced between subjects who transitioned from adalimumab and those who continued on ABP 501 from the parent study. Overall, the incidence of treatment-emergent adverse events (TEAEs) was 63.7% (297/466) and that of grade ≥3 TEAEs was 9.0% (42/466); incidence of TEAEs leading to discontinuation of investigational product was 3.6% (17/466). TEAEs with incidence ≥5% were nasopharyngitis (9.2%), upper respiratory tract infection (8.6%), bronchitis (6.4%), rheumatoid arthritis (6.2%), hypertension (4.7%), and pharyngitis (4.1%). The incidence of serious adverse events was 9.9% (46/466). Most common TEAEs of interest were infections (40.8%), liver enzyme elevations (5.4%), and hypersensitivity (4.3%).

Overall, 18.2% (85/466) of subjects developed binding antidrug antibodies (ADAs) and 6.9% (32/466) developed neutralizing ADAs in the OLE study. The rates of ADA formation were similar between subjects who transitioned from adalimumab and those who continued on ABP 501.

The ACR20 response rate (using the parent study baseline) was 73.3% (340/464) at the OLE study baseline, 77.6% (361/465) at week 4, 74.2% (336/453) at week 24, 77.6% (337/434) at week 48, and 78.8% (327/415) at week 70. The overall mean DAS28-CRP change from parent study baseline was −2.25 (n=440) at the OLE study baseline, −2.36 (n=463) at week 4, −2.41 (n=450) at week 24, −2.55 at week 48 (n=433), and –2.60 at week 70 (n=412).

Conclusions In this OLE study of ABP 501, efficacy documented in the parent study was maintained with no new safety findings. Long-term safety, immunogenicity, and efficacy results were similar between subjects who transitioned from adalimumab and those who continued on ABP 501 from the parent study.

Disclosure of Interest S. Cohen Consultant for: Amgen Inc, J. L. Pablos Consultant for: Amgen Inc, H. Wang Shareholder of: Amgen Inc, Employee of: Amgen Inc, G. Müller Consultant for: Amgen Inc, A. Kivitz Consultant for: Amgen Inc, A. Matsumoto Consultant for: Amgen Inc, E. Krishnan Shareholder of: Amgen Inc, Employee of: Amgen Inc