RGB-19, a proposed biosimilar to tocilizumab, is being evaluated in a phase III trial to assess clinical equivalence in efficacy, pharmacokinetics, pharmacodynamics (PD), safety, and immunogenicity for the treatment of adults with active rheumatoid arthritis (RA) inadequately controlled by methotrexate. In this interview, Professor Ernest Choy (Cardiff University School of Medicine, Cardiff, Wales, UK) discusses the aims, inclusion criteria and design of the phase III study, and covers the efficacy and safety findings, as well as their potential impact on clinical practice.
The abstract “Efficacy, safety and immunogenicity of the proposed tocilizumab biosimilar RGB-19, intravenously administered to participants with active rheumatoid arthritis: Week 24 data from a Phase 3 study.” was presented at EULAR 2025, Barcelona, 11–14 June 2025.
Q. What were the aims and inclusion criteria of your study?
Tocilizumab is an interleukin-6 (IL-6) receptor anti-monoclonal antibody that is effective in the treatment of RA; this has been demonstrated in both randomized controlled trials and real-world studies. RGB-19 is a proposed biosimilar to tocilizumab. The objective of this study was to demonstrate the clinical equivalence in efficacy, PD, safety and immunogenicity of RGB-19 and tocilizumab. The study was conducted in Japan. Adults aged ≥20 to ≤75 years with active RA and an inadequate response to methotrexate were recruited.
Q. Could you give a brief overview of the trial design, including the clinical outcomes?
The study was a phase III, randomized, double-blind, multicentre study. 368 patients were randomized 1:1 to intravenous (IV) infusions of RGB-19 8 mg/Kg or IV tocilizumab 8 mg/Kg every 4 weeks. The primary outcome and endpoint was mean change from baseline (CfB) in DAS28-ESR at W12. Secondary endpoints were: DAS28-ESR; American College of Rheumatology (ACR) 20, ACR50, ACR70, and European League Against Rheumatism (EULAR) response rates; Clinical Disease Activity Index (CDAI) and Simple Disease Activity Index (SDAI) remission rates and serum drug concentrations, absolute neutrophil count (ANC), CRP, soluble IL-6 receptor (sIL-6R), safety and antidrug antibodies (ADA), including neutralising antibodies (NAb).
Q. How well were the primary and secondary endpoints met?
The primary endpoint analysis demonstrated equivalence in efficacy between RGB-19 and tocilizumab. Change from baseline in DAS28-ESR was −3.62 (0.09) and −3.41 (0.09) for RGB-19 and tocilizumab, respectively. Secondary endpoint analyses showed that ACR20, ACR50, ACR70, EULAR, CDAI, and SDAI achievement/response rates at W12 and W24 were similar for RGB-19 and tocilizumab.
Q. What was the safety profile of RGB-19?
Overall, 4/182 (2.2%) participants in the RGB-19 group and 6/186 (3.2%) in the tocilizumab group had a treatment-emergent adverse event. Safety profiles were similar between treatments with no new safety signals identified. Both treatments had similarly low immunogenicity.
Q. What impact will these findings have on clinical practice?
Biologics are associated with high costs that may limit patient access. Biosimilars may offer a more cost-effective option. RGB-19 demonstrated equivalent efficacy and safety to tocilizumab originator.
Further content in rheumatoid arthritis.
This content has been developed independently by Touch Medical Media for touchIMMUNOLOGY. It is not affiliated with the European Alliance of Associations for Rheumatology (EULAR). Views expressed are the speaker’s own and do not necessarily reflect the views of Touch Medical Media.
Cite: Ernest Choy. RGB-19 Matches Tocilizumab in Efficacy and Safety: Promising Phase III Data from RA Biosimilar Trial. touchIMMUNOLOGY. 4 July 2025.
Editor: Victoria Smith, Senior Content Editor.
Abstract: Choy E, Emery P, Matsuno H, et al. POS0659 EFFICACY, SAFETY AND IMMUNOGENICITY OF THE PROPOSED TOCILIZUMAB BIOSIMILAR RGB-19, INTRAVENOUSLY ADMINISTERED TO PARTICIPANTS WITH ACTIVE RHEUMATOID ARTHRITIS: WEEK 24 DATA FROM A PHASE 3 STUDY. Annals of the Rheumatic Diseases. 2025;84(Suppl. 1): 844–845.
Disclosures: This short article was prepared by touchIMMUNOLOGY in collaboration with Ernest Choy. touchIMMUNOLOGY utilize AI as an editorial tool (ChatGPT (GPT-4o) [Large language model]. https://chat.openai.com/chat.) The content was developed and edited by human editors. No fees or funding were associated with its publication.
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