LIVERPOOL, ENGLAND — The IRIS-RA study of the investigational monoclonal antibody drug nipocalimab in patients with rheumatoid arthritis (RA) did not meet its primary endpoint, but there could still be people with moderate to severe RA who might benefit from treatment with the drug, according to information reported at the British Society for Rheumatology (BSR) 2024 Annual Meeting.
The primary endpoint for the phase 2A trial was the least squares mean change in Disease Activity Score in 28 joints using C-reactive protein (DAS28-CRP) from baseline to 12 weeks of treatment. This was reduced by −1.03 with nipocalimab and by −0.58 with placebo, giving a mean difference of just −0.45 (P = .224).
However, one of the key secondary endpoints was the proportion of patients who had 20% improvement in American College of Rheumatology response criteria (ACR20). Results for this endpoint showed a greater difference in response to nipocalimab vs placebo, with a respective 45.5% and 20.0% (P = .055) of individuals achieving ACR20.
Moreover, an analysis stratifying for anti-citrullinated protein autoantibody (ACPA) levels at baseline found that people with higher levels had a better response to nipocalimab.
Choice of Endpoint
"The way this study was powered was to look at a change between the treatment groups of a DAS28-CRP reduction of 1.0," said Peter Taylor, BMBCh, PhD, the Norman Collisson chair of musculoskeletal medicine at the University of Oxford in Oxford, England.
DAS28-CRP was often chosen as the primary endpoint in small proof-of-concept studies, such as IRIS-RA, because it was a "measure of continuous change [that] theoretically, would allow greater sensitivity to change," Taylor added.
"Ironically, it has to be said that had we chosen ACR20, we would have hit the primary endpoint. One lives and learns," noted Taylor.
Proof of Concept
IRIS-RA was billed as a "proof-of-concept" study because it was the first time that a monoclonal antibody targeting the neonatal fragment crystallizable receptor (FcRn) was being tested in an RA population.
The study was a randomized double-blind trial in which 33 people with moderate to severe RA who had an inadequate response to tumor necrosis factor (TNF) inhibitors were treated with nipocalimab at a dose of 15 mg/kg given intravenously every 2 weeks, and 20 received a matching placebo. Participants were treated for 10 weeks, and then the primary follow-up was at 12 weeks, with additional follow-up for safety undertaken at 18 weeks.
Nipocalimab is a fully human, immunoglobulin G1 (IgG1) monoclonal antibody that is designed to selectively block the FcRn. By doing so, it essentially stops IgG from being recycled within the immune system, and this in turn lowers IgG levels. That includes potentially harmful ACPAs, among other pathogenic antibodies, Taylor and fellow investigators explained in their abstract.
"We've known for a long time that ACPA have prognostic value, but there's been controversy about whether or not ACPA are actually pathogenic," Taylor said. "So, one of the hypotheses that this study gives rise to is that by blocking FcRn, and thereby reducing, potentially, the concentration of ACPA in the blood, will we actually have efficacy in patients?"
Are ACPA Really Lowered?
Paul Emery, MD, Versus Arthritis professor of rheumatology and director of the Leeds Biomedical Research Centre at the University of Leeds in Leeds, England, questioned the reduction in antibody levels during the discussion that followed.
Although these data had not been presented, Emery observed that the reduction in IgG was actually greater than that in ACPA, "which is fairly critical. Is it feasible to look to selectively lower normal immunoglobulin over pathogenic autoantibodies?"
Emery also wanted to know if there "was a floor on the reduction of immunoglobulin" with long-term therapy, "which would be a worry."
Taylor responded that total IgG had been reduced by about 65% and ACPA by about 40%. Why this difference exists is not yet clear. It could be because ACPA are part of complexed antibodies.
"Most of these patients are rheumatoid factor [RF]–positive," said Taylor, pointing out that although IgM "wouldn't normally be affected by FcRn blockade," there was a 10% reduction in RF IgM, probably because it was complexed to IgG.
"So, the hypothesis here is that if you look at the clearance of complexes, they're handled differently in the cytoplasm from the clearance of monomeric IgG. But that's a hypothesis. It needs further investigation. In vitro, there's very good, confirmatory evidence to support that. But we've yet to explore that more fully in vivo," Taylor said.
As for long-term effects, Taylor responded: "All I can tell you is [that] after the 10-week intervention, that up to an 18-week observation period, immunoglobulin levels recovered very rapidly afterwards. And you mustn't forget that other isotypes are not affected, unlike rituximab."
Safety and Other Results
With regard to safety, 27 (82%) of nipocalimab- and 12 (60%) of placebo-treated participants experienced at least one treatment-emergent adverse event (TEAE). The most common, occurring in 10% or more of cases, were RA flares (36.4% for nipocalimab vs 15.0% with placebo), headache (12.1% vs 5.0%), and COVID-19 (12.1% vs 0.0%).
There were three serious TEAEs, all in the nipocalimab-treatment group: One was an infection of a burn that had been present at inclusion, another was a deep vein thrombosis that resolved with apixaban treatment, and the other was an infusion-related reaction that resolved with supportive treatment.
Another notable efficacy finding was the proportion of patients achieving DAS28-CRP remission at 12 weeks in the nipocalimab vs the placebo group was substantially greater if considering only people with high baseline ACPA levels, at a respective 40.0% vs 16.7%, when compared with the total population (21.2% vs 10.0%).
Similar findings were seen for the proportion of patients achieving an ACR50, and there were numerically greater reductions in the components of the ACR response criteria such as tender and swollen joints with nipocalimab vs placebo. All of these were exploratory observations, Taylor emphasized.
Combination and Further Trials
Further trials of nipocalimab are planned or are already ongoing in systemic lupus erythematosus, active lupus nephritis, Sjögren disease, and five other diseases.
In RA, nipocalimab is now being tested in combination with the TNF inhibitor certolizumab pegol (Cimzia) in the DAISY-RA trial. This is another proof-of-concept, phase 2A trial with a target accrual of 104 patients.
The IRIS-RA study was funded by Janssen Research & Development.
Taylor serves as a consultant to AbbVie, Biogen, Eli Lilly, Fresenius, Galapagos, Gilead Sciences, GlaxoSmithKline, Janssen, Nordic Pharma, Pfizer, Sanofi, Aqtual, and UCB and received research funding from Galapagos, among others.
Emery received research grants paid to his institution from AbbVie, Bristol Myers Squibb (BMS), Pfizer, MSD, and Roche; received consultant fees from BMS, AbbVie, Pfizer, MSD, Novartis, Roche, and UCB; and has undertaken clinical trials and provided expert advice to Pfizer, MSD, AbbVie, BMS, UCB, Roche, Novartis, Samsung, Sandoz, and Lilly.
Sara Freeman is a freelance medical journalist based in London, England.