JNJ Tremfya: First IL-23 Spinal Benefit in Axial PsA

Johnson & Johnson (JNJ) said its IL-23 inhibitor Tremfya (guselkumab) hit its primary and key secondary endpoints in the Phase 4 STAR study in axial psoriatic arthritis (PsA), making it the first IL-23 drug to show a spinal pain and stiffness benefit in a dedicated, placebo-controlled trial with MRI-confirmed enrollment.

Tremfya blocks the p19 subunit of IL-23, a cytokine that drives the inflammation behind PsA, and is J&J’s only drug designed to also bind CD64 on IL-23-producing cells. The company leans on that dual-action design to argue the drug neutralizes inflammation at its source.

STAR enrolled 411 biologic-naive adults with active PsA and axial involvement. Tremfya beat placebo on the primary endpoint, change in the BASDAI composite score covering spinal pain, stiffness, fatigue, and joint symptoms at week 24, and also reduced inflammation on MRI, the study’s objective measure. No new safety signals emerged.

Axial PsA is the under-treated piece of psoriatic arthritis: inflammation of the spine and sacroiliac joints that drives back pain, morning stiffness, and reduced mobility. It affects roughly 5% to 28% of early PsA patients and up to 70% of those with long-standing disease, and there are no universally accepted classification criteria, which is part of why so few trials target it.

The claim is competitive differentiation, not a new approval. Tremfya is already approved for PsA, plaque psoriasis, ulcerative colitis, and Crohn’s disease, and J&J recently added a label for slowing structural joint damage. The STAR result builds clinical rationale into the axial subpopulation where AbbVie’s Skyrizi (risankizumab) and Lilly’s Taltz (ixekizumab) have not run a comparable MRI-based study. Taltz targets IL-17 rather than IL-23, so the “first IL-23” framing is technically narrow but accurate against the class, and MoonLake’s sonelokimab IZAR-1 PsA program is largely still chasing that spinal signal. Tremfya is a key growth asset in J&J’s immunology franchise, where it competes with Skyrizi across psoriasis and PsA, so this axial data is J&J’s bid for a clinical edge the rival has not yet shown.

The honest caveat is that this is a post-marketing Phase 4 study, so the commercial effect is incremental and no new FDA filing was announced. Detailed efficacy and MRI data will be presented at an upcoming congress.

J&J shares closed at $271.22. The risk is that rivals respond with their own axial PsA data, or that physicians wait for the full MRI readout before shifting prescribing.

What to watch next: the detailed STAR data at the next rheumatology congress.

Source: Johnson & Johnson Tremfya STAR axial PsA press release STAR trial on ClinicalTrials.gov (NCT04929210)

What It Means for the Trade

Set expectations correctly: this is a Phase 4 label-support study, not a new approval, so the stock impact on a $271.22 mega-cap was always going to be near zero. The value is competitive positioning inside J&J’s immunology franchise, where Tremfya is a designated growth asset tasked with holding share while Stelara’s biosimilar erosion accelerates. STAR gives the sales force something Skyrizi and Taltz reps cannot claim — a dedicated, placebo-controlled, MRI-confirmed axial PsA dataset — and in specialty immunology, detail-with-data is how biologics defend price and share. The commercial effect is incremental, not transformative: it keeps patients with spinal involvement from defaulting to the IL-17 or IL-23 competitors on narrative and nudges the rheumatologists who treat axial disease toward a drug they already know.

The trade-relevant timeline is short: detailed efficacy and MRI data at the next rheumatology congress, then nothing until the rivals respond. AbbVie and Lilly both have the balance sheet to run their own axial PsA studies, so the first-mover label may have a shelf life measured in a few quarters. The structural joint damage label J&J recently added matters more commercially than STAR itself, because “slows damage” is a durability claim payers and rheumatologists act on.

Mechanism and Pipeline Context

Guselkumab blocks the p19 subunit of IL-23, upstream of the Th17 inflammatory cascade that drives psoriatic disease — the same node Skyrizi targets. Its differentiator is dual binding: the molecule also engages CD64, a receptor on myeloid cells that produce IL-23, so Tremfya neutralizes both the cytokine and a factory that makes it. Whether that translates to clinically meaningful superiority is unproven; STAR’s MRI-confirmed spinal data is the first evidence the design earns something concrete in the hardest-to-treat PsA compartment.

Axial PsA is a commercial orphan-within-a-franchise: inflammation of the spine and sacroiliac joints affects 5% to 28% of early PsA patients and up to 70% of long-standing ones, yet the lack of universal classification criteria means most trials skip it and most rheumatologists manage it off-label with axial spondyloarthritis tools. The IL-17 class (Taltz) has established spinal efficacy in ankylosing spondylitis, and MoonLake’s sonelokimab is chasing the same compartment — so STAR is J&J claiming the IL-23 lane before the field’s data catches up.

Risks and What Could Go Wrong

1. Rivals publish their own axial PsA data quickly, erasing the “first and only” claim before it compounds into share.
2. Full MRI results underwhelm — the topline said “reduced inflammation”; if the delta is small, the differentiation pitch weakens.
3. Prescriber inertia — rheumatologists may wait for published data before changing axial prescribing patterns.
4. This was never the needle — Tremfya moving the needle requires franchise-level share dynamics and a clean launch cadence, not a Phase 4 subpopulation win.