Ustekinumab Mechanism of Action: How Ustekinumab Works | Elicit

Ustekinumab Mechanism of Action

How Ustekinumab (Stelara) Works: IL-12/IL-23 (p40) blockade to inhibit immune signaling and cytokine production.

Last updated: March 2026

Quick Summary

Ustekinumab (Stelara) is a human monoclonal antibody that targets the p40 subunit shared by interleukin (IL)-12 and IL-23. By preventing IL-12/IL-23 from interacting with the IL-12 receptor complex, it inhibits downstream signaling and cytokine production involved in immune activation. This IL-12/IL-23 blockade underpins its use in plaque psoriasis, psoriatic arthritis, Crohn’s disease, and ulcerative colitis.

Properties

Details
Generic Name Ustekinumab
Brand Names Stelara, Wezlana, Imuldosa, Otulfi, Pyzchiva, Selarsdi, Steqeyma, Yesintek
Drug Class Interleukin-12/23 antagonist
Primary Target Interleukin-12/interleukin-23 p40 subunit (IL12B)
Approved Indications Moderate-to-severe plaque psoriasis (adults and pediatric patients ≥6 years), psoriatic arthritis (PsA), moderately to severely active Crohn's disease, moderately to severely active ulcerative colitis
Key Effect Blocks IL-12/IL-23 signaling by binding the shared p40 subunit, preventing cytokine-driven immune activation.

Development History

Ustekinumab was developed by Centocor Research & Development (now Janssen Biotech, a Johnson & Johnson company) as a fully human IgG1κ monoclonal antibody generated in human immunoglobulin-transgenic mice and originally designated CNTO 1275. Rather than targeting tumor necrosis factor like the dominant biologics of the late 1990s, the program was designed around the then-newly-appreciated IL-12/IL-23 axis: ustekinumab binds the shared p40 subunit common to IL-12 and IL-23, simultaneously blunting Th1 and Th17 effector programs upstream of TNF-driven inflammation. The transgenic-mouse origin gave the molecule endogenous human IgG1 effector properties and low immunogenicity, while the long serum half-life conferred by the p40-binding mechanism enabled every-12-week subcutaneous maintenance dosing, the most convenient schedule among approved psoriasis biologics at launch.

The pivotal program for first approval comprised two Phase 3 trials in moderate-to-severe plaque psoriasis. In PHOENIX 1, 45 mg and 90 mg subcutaneous doses at weeks 0 and 4 produced PASI 75 responses at week 12 of 67.1% and 66.4% respectively versus 3.1% for placebo; PHOENIX 2 reproduced the effect at 66.7% and 75.7% with the primary endpoint of PASI 75 at week 12. On the basis of those data, the FDA approved STELARA® in September 2009 for adults with moderate-to-severe plaque psoriasis, marking the first-in-class IL-12/23p40 antagonist to reach the market.

Indication expansion followed the same Th17-driven biology into adjacent diseases. The PSUMMIT 1 trial demonstrated ACR20 responses of 42.4% (45 mg) and 49.5% (90 mg) versus 22.8% for placebo at week 24, supporting FDA approval for active psoriatic arthritis in September 2013. In Crohn's disease, the UNITI-1, UNITI-2 and IM-UNITI program delivered week-6 response rates up to 55.5% and week-44 remission of 53.1% on every-8-week subcutaneous maintenance, leading to FDA approval for moderately-to-severely active Crohn's disease in September 2016. Most recently, the UNIFI Phase 3 trial achieved clinical remission in 15.6–15.5% of induction patients at week 8 and 43.8% of maintenance patients at week 44, supporting FDA approval for moderately-to-severely active ulcerative colitis in October 2019 under the STELARA® brand, extending the label across four major IL-12/23-driven immune-mediated indications.

Detailed Mechanism of Action

Ustekinumab is administered by subcutaneous injection using a loading schedule at weeks 0 and 4, followed by maintenance dosing every 12-week maintenance interval. After subcutaneous dosing, the antibody is slowly absorbed, reaching a terminal elimination half-life of approximately about 3 weeks in the PHOENIX phase 3 program. This prolonged systemic exposure is explained, at least in part, by FcRn-mediated salvage that protects the antibody from lysosomal degradation. Subcutaneous bioavailability has been estimated at approximately 57%, consistent with the slow absorption and sustained serum concentrations that support infrequent maintenance dosing.

Shared p40 neutralization. At the molecular level, ustekinumab is a fully human IgG1 kappa monoclonal antibody that binds the IL-12p40 subunit, a structural component shared by both IL-12 (p35+p40 heterodimer) and IL-23 (p19+p40 heterodimer). Structural studies characterizing a Fab/IL-12 co-crystal structure place the ustekinumab epitope in the D1 domain of p40, with mutational analysis identifying specific residues in D1 required for antibody binding. Because p40 is the common subunit, this single binding event provides dual recognition of IL-12 and IL-23 — explaining why a molecule originally designed to target IL-12 simultaneously modulates IL-23.

Receptor-mediated cytokine signaling blockade. The immediate functional consequence of p40 binding is steric prevention of cytokine engagement with IL-12Rβ1-containing receptor complexes on NK cells and T cells. IL-12 ordinarily signals through an IL-12Rβ1/IL-12Rβ2 heterodimeric receptor in which IL-12Rβ1 contacts p40; IL-23 similarly requires IL-12Rβ1 as its proximal receptor subunit before associating with IL-23R for intracellular signaling. Ustekinumab prevents human IL-12 and IL-23 from binding to the IL-12Rβ1 receptor chain of both receptor assemblies — a single blocking event that simultaneously interrupts both cytokine axes at their shared receptor-proximal step.

Dual JAK–STAT pathway suppression. Preventing IL-12 from engaging its receptor abolishes downstream activation of STAT4, the transcription factor that drives T-bet expression and Th1 lineage commitment — the primary source of IFN-gamma production in adaptive immune responses. In parallel, preventing IL-23 from engaging IL-23R abolishes JAK2/TYK2-dependent phosphorylation of STAT3, which otherwise drives induction of RORgammat and Th17 lineage commitment, with consequent secretion of IL-17A, IL-17F, and IL-22. The net effect is simultaneous attenuation of both Th1-associated and Th17-associated effector cytokine outputs from a single upstream target.

Pathway selectivity and Fc considerations. Because ustekinumab targets soluble cytokine prior to receptor engagement, it cannot bind IL-12 or IL-23 that is already docked to receptor complexes on cell surfaces. This constrains the mechanism to cytokine neutralization and makes it unlikely to mediate Fc effector functions such as antibody-dependent cellular cytotoxicity or complement-dependent cytotoxicity. The drug therefore does not affect immune responses driven by other cytokines or unrelated cellular programs — a targeted axis inhibitor rather than a global immunosuppressant.

Clinical translation. The molecular events map onto outcomes across three approved indications. In psoriasis, suppression of IL-12-driven IFN-gamma and IL-23-driven IL-17A/IL-17F reduces the cytokine milieu that sustains epidermal keratinocyte activation and plaque formation; controlled trials demonstrated attainment of PASI 75 responses exceeding placebo at week 12. In Crohn disease, blockade of the p40 axis interrupts intestinal immune programs driven by Th1 and Th17 effectors, translating to induction of clinical response and remission in phase 3 trials. In psoriatic arthritis, attenuation of IL-23-driven Th17 biology reduces synovial inflammation. The ~3-week half-life enables the once-every-12-weeks maintenance schedule to sustain continuous pathway suppression across all three disease settings.

Clinical Relevance

Approved Indications

Key Drug Interactions (Mechanism-Based)

Special Populations

Emerging Indications

Endocrinology / Metabolic

Immunology

Hepatology

Oncology

Reproductive Health

Clinical Trials of Ustekinumab

Trial Name Phase Design N Enrolled Intervention Indication Primary Endpoint Key Result Status
PSOLAR 4 observational registry (postmarketing long-term safety signal detection) 12090 International observational registry of systemic/biologic psoriasis therapies including ustekinumab (comparators include non-biologics and other biologics, as used in routine care). Time to major adverse cardiovascular events (MACE), analyzed using adjusted hazard ratios in time-to-event models. A prespecified analysis suggested higher MACE risk for ustekinumab vs non-biologics (adjusted HR 1.533, 95% CI 1.103–2.131); after revised post hoc methods, the HR was 0.820 (95% CI 0.532–1.265), indicating no meaningful increase in MACE risk with ustekinumab. Ongoing
STARDUST 3b RCT (treat-to-target vs standard of care) with ongoing follow-up/extension 440 IV ustekinumab ~6 mg/kg at baseline plus SC ustekinumab 90 mg at week 8; week-16 responders randomized to treat-to-target vs standard-of-care maintenance with protocol-driven dose adjustment (q12w/q8w with escalation as needed). Endoscopic response at week 48, defined as ≥50% decrease from baseline in SES-CD, analyzed by non-responder imputation. At week 48, endoscopic response was not significantly different with treat-to-target vs standard of care (38% vs 30% ; p=0.087). Clinical response was significantly lower with treat-to-target (68% vs 78% ; p=0.020). Ongoing
SEAVUE 3b randomized, double-blind, active-comparator trial 386 Ustekinumab (~6 mg/kg IV day 0 then 90 mg SC every 8 weeks) vs adalimumab (160 mg day 0, 80 mg at week 2, then 40 mg SC every 2 weeks) through week 56. Clinical remission (CDAI <150) at week 52 in the intention-to-treat population. At week 52, clinical remission was 65% (124/191) with ustekinumab vs 61% (119/195) with adalimumab (between-group difference 4%, 95% CI −6 to 14; p=0.42), showing no significant difference in the primary endpoint. Completed
UNIFI 3 RCT (8-week induction and 44-week maintenance, double-blind placebo-controlled) 961 Induction: single IV infusion of ustekinumab 130 mg or weight-range–based ~6 mg/kg vs placebo; maintenance (responders): SC ustekinumab 90 mg every 12 weeks or every 8 weeks vs placebo. Clinical remission at week 8 (induction) and week 44 (maintenance). Week 8 clinical remission was 15.6% (130 mg) and 15.5% (~6 mg/kg) vs 5.3% with placebo (P<0.001 for both). Among induction responders, week 44 clinical remission was 38.4% (SC q12w) and 43.8% (SC q8w) vs 24.0% with placebo (P=0.002 and P<0.001, respectively). Completed
IM-UNITI 3 RCT (maintenance therapy in induction responders) with long-term extension follow-up 397 SC maintenance: placebo vs ustekinumab 90 mg every 12 weeks vs ustekinumab 90 mg every 8 weeks (in patients who responded to IV ustekinumab induction). Clinical remission at week 44 (CDAI <150). At week 44, clinical remission was 48.8% (UST q12w) and 53.1% (UST q8w) vs 35.9% with placebo (absolute differences +12.9 and +17.2 percentage points). At week 252, clinical remission was 34.4% (q8w) vs 28.7% (q12w) (absolute difference +5.7 percentage points). Completed
PSUMMIT 1 3 randomized, placebo-controlled trial 615 Ustekinumab 45 mg or 90 mg vs placebo at weeks 0 and 4 and every 12 weeks (with early escape/crossover). Proportion of patients achieving ACR20 response at week 24. In PSUMMIT1, the mean percentage difference for ACR20 at week 24 was +20% (95% CI 11% to 28%) for ustekinumab 45 mg vs placebo and +27% (95% CI 18% to 36%) for ustekinumab 90 mg vs placebo (both P<0.001 vs placebo). Completed
UNITI-2 3 RCT (double-blind, placebo-controlled induction trial) 628 Single IV induction dose of ustekinumab 130 mg or weight-range–based ~6 mg/kg vs placebo. Clinical response at week 6 (CDAI decrease ≥100 points or CDAI <150). At week 6, clinical response was 51.7% (130 mg) and 55.5% (~6 mg/kg) vs 28.7% with placebo (P<0.001 for both comparisons). Completed
UNITI-1 3 RCT (double-blind, placebo-controlled induction trial) 741 Single IV induction dose of ustekinumab 130 mg or weight-range–based ~6 mg/kg vs placebo. Clinical response at week 6 (CDAI decrease ≥100 points or CDAI <150). At week 6, clinical response was 34.3% (130 mg) and 33.7% (~6 mg/kg) vs 21.5% with placebo (absolute differences +12.8 and +12.3 percentage points; P=0.002 and P=0.003, respectively). Completed

Ustekinumab Competitive Landscape

Drug Class Representative Drug(s) Primary Molecular Target Mechanism of Action Key Efficacy Outcomes Route & Dosing Safety / Risk Profile Key Limitations
TNF-alpha inhibitors "Infliximab (Remicade), Adalimumab (Humira), Etanercept (Enbrel)" Tumor Necrosis Factor-alpha (TNF-α) Binds to and neutralizes both soluble and membrane-bound TNF-α, which blocks its interaction with cell surface receptors and inhibits the downstream inflammatory cascade. In Crohn's disease, a single infliximab dose led to a clinical response in 65% of patients vs 17% for placebo. In vedolizumab-experienced IBD patients, 52-week treatment persistence was lower for anti-TNF drugs (52.3%) compared to ustekinumab (91.7%), particularly in UC (35% vs 75%). Varies by agent; includes IV infusion every 4-8 weeks (Infliximab) and subcutaneous injection every 1-2 weeks (Adalimumab) or weekly (Etanercept). Carries a boxed warning for increased risk of serious infections, including tuberculosis and invasive fungal infections, and for malignancies like lymphoma. Common adverse events include upper respiratory infections, headache, and infusion or injection site reactions. Primary non-response occurs in 20-40% of patients, with an additional 5-15% losing response each year. In patients with prior vedolizumab failure, ustekinumab demonstrates superior 52-week treatment persistence compared to anti-TNF agents.
IL-12/23 inhibitors "Ustekinumab (Stelara)" The p40 protein subunit shared by Interleukin-12 (IL-12) and Interleukin-23 (IL-23) Binds to the shared p40 subunit of IL-12 and IL-23 cytokines, disrupting their signaling and preventing the activation of Th1 and Th17 inflammatory pathways. In plaque psoriasis, PASI 75 response at week 12 was achieved in 66-76% of patients vs 3-4% for placebo. In Crohn's disease, clinical remission at week 8 was 34-40% vs 20-22% for placebo, and in ulcerative colitis, clinical remission at week 8 was 19% vs 7% for placebo. IV infusion for induction in IBD followed by subcutaneous injection every 8 weeks for maintenance; subcutaneous injection at weeks 0, 4, and then every 12 weeks for psoriasis. Most common adverse events include nasopharyngitis, upper respiratory tract infection, headache, and fatigue. Carries warnings for an increased risk of serious infections, malignancy, and rare cases of Posterior Reversible Encephalopathy Syndrome (PRES). More selective IL-23p19 inhibitors may offer superior efficacy and a better safety profile in some IBD populations. The development of anti-drug antibodies can be associated with reduced efficacy.
IL-17 inhibitors "Secukinumab (Cosentyx), Ixekizumab (Taltz), Bimekizumab (Bimzelx)" Interleukin-17A (IL-17A), Interleukin-17F (IL-17F), or the IL-17A receptor Binds to and neutralizes IL-17 cytokines (e.g., IL-17A, IL-17F) or blocks the IL-17 receptor, inhibiting the release of proinflammatory cytokines and chemokines. In plaque psoriasis, IL-17 inhibitors demonstrate high efficacy, with PASI 90 rates at Week 12-16 ranging from approximately 59% to 91%. In a head-to-head trial (IXORA-S), ixekizumab showed superior PASI 90 rates compared to ustekinumab at 52 weeks (76.5% vs 59.0%). Subcutaneous injection, with a loading dose phase followed by maintenance dosing every 2 to 8 weeks, depending on the agent. Most common adverse reactions include nasopharyngitis, upper respiratory tract infections, and injection site reactions. The class is associated with an increased risk of mucocutaneous candidiasis and may cause exacerbation or new onset of inflammatory bowel disease. Not recommended for patients with active inflammatory bowel disease due to risk of exacerbations. Dosing is generally more frequent than for IL-12/23 or some IL-23 inhibitors.
IL-23 inhibitors "Guselkumab (Tremfya), Risankizumab (Skyrizi), Tildrakizumab (Ilumya)" The p19 subunit of Interleukin-23 (IL-23) Selectively binds to the p19 subunit of the IL-23 cytokine, inhibiting its interaction with the IL-23 receptor and blocking the release of pro-inflammatory cytokines and chemokines. In Crohn's disease, guselkumab achieved clinical remission in 59% of patients vs. 17% for placebo at Week 48. In plaque psoriasis, PASI 90 response rates at Week 16 are high, with guselkumab achieving ~70-73%. In Crohn's disease, IL-23p19 inhibitors may be more effective than ustekinumab in achieving clinical and endoscopic remission. IV infusion or subcutaneous injection for induction, followed by subcutaneous maintenance injections every 4, 8, or 12 weeks depending on the agent and indication. Common adverse reactions include upper respiratory infections, headache, injection site reactions, and arthralgia. May increase the risk of infection, and patients should be evaluated for tuberculosis before starting treatment. Liver enzyme monitoring is recommended for IBD indications. Efficacy may be superior to ustekinumab in biologic-experienced IBD patients, but not in biologic-naive patients. While highly effective for skin and gut inflammation, the class has fewer approvals for psoriatic arthritis compared to other classes.
JAK inhibitors "Tofacitinib (Xeljanz), Upadacitinib (Rinvoq), Filgotinib (Jyseleca)" Intracellular Janus kinases (JAK1, JAK2, JAK3, TYK2) Blocks the JAK-STAT signaling pathway, which transmits signals from cytokines and growth factors, thereby preventing the phosphorylation of STATs and reducing inflammatory gene expression. In ulcerative colitis, upadacitinib induction (45 mg) achieved clinical remission in 26-33% of patients vs 5-7% for placebo. In Crohn's disease, upadacitinib induction (45 mg) achieved clinical remission in 39-50% vs 21-29% for placebo. Real-world data suggests upadacitinib has higher odds of achieving clinical response and remission in UC vs ustekinumab. Oral tablets or solution, taken once or twice daily. Carries a class-wide boxed warning for serious infections, increased mortality, malignancy, major adverse cardiovascular events (MACE), and thrombosis. Common adverse reactions include upper respiratory tract infections, nausea, headache, and herpes zoster. Not recommended for use with biologic DMARDs or other potent immunosuppressants. Safety concerns and boxed warnings may limit use to patients who have failed other therapies, such as TNF inhibitors.
Integrin inhibitors "Vedolizumab (Entyvio)" α4β7 integrin Specifically binds to the α4β7 integrin on a subset of memory T-lymphocytes, blocking their interaction with MAdCAM-1 on endothelial cells and thus inhibiting their migration into inflamed gastrointestinal tissue. In ulcerative colitis (UC Trial I), vedolizumab achieved clinical response in 47% of patients vs 26% for placebo at Week 6, with clinical remission in 17% vs 5%. In maintenance (UC Trial II), clinical remission at Week 52 was 42% vs 16% for placebo. IV infusion, 300 mg at weeks 0, 2, and 6, then every 8 weeks; a subcutaneous option is also available. Most common adverse reactions include nasopharyngitis, headache, arthralgia, and nausea. Carries warnings for infusion-related and hypersensitivity reactions, an increased risk of infections, and a potential risk of Progressive Multifocal Leukoencephalopathy (PML), though no cases were observed in clinical trials. Indicated only for ulcerative colitis and Crohn's disease, not for psoriatic conditions. Therapy is discontinued if there is no evidence of therapeutic benefit by Week 14.

Open Research Questions

What is the optimal strategy for managing secondary loss of response to ustekinumab in Crohn's disease - dose escalation versus switching to an IL-23p19 selective inhibitor?

The decision affects a substantial minority of patients on maintenance therapy and lacks head-to-head trial guidance. A 2025 editorial in Inflammatory Bowel Diseases frames the dilemma as POWER through or switch treatment, noting that interval shortening or IV reinduction can recapture response in observational cohorts but has not been benchmarked prospectively against transitioning to risankizumab or mirikizumab.

To what extent should ustekinumab therapeutic drug monitoring rely on personalized trough thresholds rather than a single universal cutoff?

Reactive TDM is established for anti-TNFs, but ustekinumab exposure-response relationships are noisier, leaving clinicians without firm dose-intensification targets. A 2024 review concluded that the clinical role of TDM in patients on ustekinumab remains unclear, and emerging data suggest target trough concentrations may need to differ between biologic-naïve and biologic-experienced patients.

What early immunological signatures predict ustekinumab response in Crohn's disease, and can they enable treatment selection before week 24?

Primary non-response wastes 8-16 weeks of induction, so biomarkers reading out at week 8 would meaningfully shorten the trial-and-error cycle. A 2026 study reported that elevated serum IL-12/IL-23 at week 8 associated with favourable clinical and endoscopic outcomes, but the signature has not yet been validated in independent cohorts.

How does ustekinumab compare with selective IL-23p19 inhibitors when used sequentially or as a first-line biologic in psoriasis and IBD?

With guselkumab, risankizumab, and mirikizumab now approved across overlapping indications, optimal positioning of IL-12/23p40 versus IL-23p19 blockade is unresolved. A 3-year Italian multicentre cohort found that partial responders to ustekinumab achieved meaningful PASI improvement after switching to guselkumab, though prospective head-to-head comparisons in biologic-naïve populations remain limited.

What is the safest interval between in-utero ustekinumab exposure and administration of live-attenuated vaccines to the infant?

Maternal IgG biologics persist in newborns and current guidelines defer live vaccines variably; a clearer pharmacokinetic anchor would standardize practice. A Danish-Dutch prospective cohort observed infant ustekinumab cleared at a mean of 6.7 months with no associated infection signal, supporting live vaccination from 6 months pending confirmation in larger registries.