MoonLake Immunotherapeutics has kicked off a year of readouts for its much-hyped inflammatory disease prospect with a midstage win in a type of arthritis.
The Swiss biotech evaluated a 60-mg subcutaneous dose of the IL-17 inhibitor, called sonelokimab, in a phase 2 study of 26 adults with axial spondyloarthritis (axSpA), a chronic inflammatory arthritis. Patients in the study either had the more serious form of radiographic axSpA—also known as ankylosing spondylitis, which is characterized by damage to the sacroiliac joints and can be recognized on X-rays—or non-radiographic axSpA, which is detected by an MRI or another method of clinical investigation.
At Week 12, 81% of participants achieved an improvement of at least 40% across a wide-ranging spondyloarthritis measurement—hitting the primary goal of the trial. This Assessment of Spondyloarthritis International Society 40 (ASAS40) measurement has been the primary endpoint for the “latest approved therapies” in the axSpA space, MoonLake noted in its Feb. 22 release.
AxSpA typically strikes young adults in their 20s and affects joints in the chest, spine and pelvis. The condition affects roughly 1% of the people in the world, causing significant pain, stiffness and reduced mobility.
There are already a range of drugs approved for axSpA, including AbbVie’s TNF-blocking antibody Humira, the IL-23 inhibitor Skyrizi and JAK inhibitor Rinvoq. With nanobodies like sonelokimab, MoonLake has been hoping to deliver the targeting ability of conventional antibodies with the advantages of an antibody fragment, including easier manufacturing.
MoonLake said PET imaging during the phase 2 trial demonstrated “significant reduction of inflammation and osteoblast activity in sacroiliac joints affected by axSpA, a key driver of irreversible ossification in the disease.”
Meanwhile, blood and tissue biomarker analyses also showed “rapid and sustained effects of the treatment with SLK in inhibiting key immune pathways known to drive inflammation and ossification in affected patients,” the biotech explained.
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“The complementary data from clinical outcomes, MRI and PET imaging as well as peripheral blood and tissue biomarkers confirm our hypothesis of sonelokimab’s ability to access deeper tissue, which is essential to optimally control this chronic rheumatological condition and prevent irreversible mobility restriction,” MoonLake’s founder and chief scientific officer Kristian Reich, M.D., Ph.D., said in a statement.
“In our view, the impact of sonelokimab on clinical parameters and key disease pathways observed in S-OLARIS already within the first 12 weeks of treatment highlight the potential of the drug to elevate clinical outcomes and to achieve disease modification in axSpA,” Reich added. “With millions of patients affected by this devastating condition and limited impact of current therapies in improving relevant disease mechanisms, sonelokimab has the potential to change the treatment paradigm in axSpA.”
Yesterday’s axSpA readout is just the latest in a conveyor belt of mid- and late-stage readouts for sonelokimab across a range of inflammatory diseases. While most of the data to date have been positive, MoonLake’s share price was shattered last September when the drug missed the key goal of one of a pair of phase 3 studies for its joint-lead indication of severe hidradenitis suppurativa (HS).
Despite MoonLake claiming a win across the totality of data for those two HS studies, the company’s stock plunged almost 90% at the time and is yet to fully recover. Still, MoonLake has plenty of opportunities this year to continue to redeem sonelokimab. The rest of 2026 is set to see a flurry of readouts including a phase 3 study of adolescents with HS and two phase 3 readouts in sonelokimab’s other lead indication of psoriatic arthritis.
The company is hoping to file an approval application for sonelokimab to treat psoriatic arthritis in the second half of the year, MoonLake affirmed in yesterday’s release. The biotech entered 2026 with $394 million in the bank that it expects to last into the second half of next year. The biotech saw its shares up more than 9% in premarket trading Monday morning.
MoonLake licensed sonelokimab from Germany’s Merck KGaA in 2021. The molecule originated at nanobody specialist Ablynx, which is now part of Sanofi.
