How Guselkumab (Tremfya) Works: IL-23 pathway blockade to disrupt downstream inflammatory signaling.
Last updated:
March 2026
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Quick Summary
Guselkumab (Tremfya) is a human IgG1λ monoclonal antibody that binds selectively to interleukin-23 (IL-23) with high specificity and affinity. By blocking IL-23’s interaction with the cell-surface IL-23 receptor, it disrupts IL-23–mediated signaling and cytokine cascades, contributing to normalization of downstream inflammatory responses. Guselkumab exerts clinical effects in plaque psoriasis, psoriatic arthritis, ulcerative colitis, and Crohn’s disease through blockade of the IL-23 cytokine pathway.
Properties
Details
Generic Name
Guselkumab
Brand Names
Tremfya
Drug Class
IL-23 inhibitor (monoclonal antibody)
Primary Target
Interleukin-23 (IL-23) (IL23A) / IL-23 receptor (IL23R)
Approved Indications
Moderate-to-severe plaque psoriasis in adults, active psoriatic arthritis (PsA) in adults
Development History
Guselkumab was developed by Janssen Biotech as a fully human IgG1λ monoclonal antibody that selectively binds the p19 subunit of interleukin-23, neutralizing IL-23 signaling without engaging the shared p40 subunit targeted by predecessor ustekinumab. The antibody was isolated from a fully synthetic human Fab library using MorphoSys's HuCAL GOLD phage-display platform, yielding a high-affinity human sequence that sidestepped the immunogenicity risk of murine-derived scaffolds. By restricting blockade to IL-23 alone, the design preserved IL-12/Th1 signaling implicated in host defense while disrupting the IL-23/Th17 axis that drives plaque psoriasis, addressing the principal pharmacological liability of dual IL-12/IL-23 inhibition.
The pivotal program supporting first approval consisted of the Phase 3 VOYAGE 1 and VOYAGE 2 trials, both placebo- and adalimumab-controlled studies in adults with moderate-to-severe plaque psoriasis. In VOYAGE 1, 73.3% of guselkumab-treated patients achieved PASI 90 at week 16 versus 49.7% with adalimumab and 2.9% with placebo, with superiority over adalimumab sustained through week 48. VOYAGE 2 reproduced the effect, with 70.0% of patients reaching PASI 90 versus 2.4% on placebo at week 16. On the basis of these data together with the NAVIGATE switch study, the FDA approved guselkumab on July 13, 2017 under the brand name Tremfya for moderate-to-severe plaque psoriasis, administered as a 100 mg subcutaneous injection every eight weeks following starter doses at weeks 0 and 4.
Indication expansion followed a deliberate cadence across immune-mediated disease. In the Phase 3 DISCOVER-1 trial, 59% and 52% of patients on every-4-week and every-8-week guselkumab achieved ACR20 at week 24 versus 22% on placebo, supporting FDA approval of Tremfya for active psoriatic arthritis in July 2020. The Phase 2b/3 QUASAR program then established efficacy in inflammatory bowel disease, with 50% of patients on 200 mg subcutaneous maintenance achieving clinical remission at week 44 versus 19% on placebo, supporting FDA approval in ulcerative colitis on September 11, 2024. The GALAXI and GRAVITI Phase 3 programs subsequently demonstrated superiority versus ustekinumab on pooled endoscopic endpoints and supported FDA approval for moderately to severely active Crohn's disease on March 20, 2025, bringing the current Tremfya label to four indications spanning dermatology, rheumatology, and inflammatory bowel disease.
Detailed Mechanism of Action
Guselkumab is a fully human IgG1λ monoclonal antibody that selectively targets the p19 subunit of interleukin-23, leaving the shared p40 subunit — and therefore IL-12 signalling — intact. Following subcutaneous injection, the antibody distributes systemically and reaches inflamed tissue. Because its Fc region is native and unmodified, guselkumab also binds with high affinity to FcγRI (CD64), a receptor constitutively expressed on IL-23-producing inflammatory myeloid cells in lesional psoriatic skin. This dual engagement — p19 blockade on the one hand and Fc-mediated anchoring to CD64+ macrophages on the other — positions the antibody directly at its primary cellular source of target cytokine.
Primary binding event and Fc-dependent IL-23 capture. At the molecular level, guselkumab occludes the p19 epitope on the IL-23 heterodimer, sterically preventing IL-23 from engaging its cognate receptor complex (IL-23R/IL-12Rβ1). Simultaneously, CD64-anchored guselkumab captures IL-23 as it is secreted from the same myeloid cell, and the entire antibody–cytokine complex is internalized into low-pH endolysosomal compartments in a time-dependent manner. In co-culture assays pairing IL-23-producing CD64+ THP-1 cells with an IL-23-responsive reporter line, this Fc-dependent mechanism conferred approximately 10-fold greater potency for inhibiting IL-23 signalling compared with risankizumab, a structurally analogous anti-p19 antibody whose Fc region is mutated to ablate FcγR binding. CD64 engagement by guselkumab does not trigger cytokine release from myeloid cells, indicating that the ITAM signalling arm of CD64 activation is not recruited.
JAK–STAT3 pathway blockade. When IL-23 binds its receptor, IL-12Rβ1 associates with TYK2 and IL-23R associates with JAK2; cytokine binding triggers transphosphorylation of both kinases. Functional association of IL-12Rβ1 with TYK2 and of IL-23R with JAK2 is mandatory for IL-23 signalling. Activated JAK2 and TYK2 then phosphorylate STAT3 at its canonical tyrosine residues within the IL-23R intracellular domain — Tyr-484 and Tyr-611 in the human IL-23R mediate STAT3 activation, with additional non-canonical phosphotyrosine-independent activation sites contributing to a characteristically slow but sustained STAT3 phosphorylation profile that resists negative feedback by SOCS proteins. By blocking IL-23 at its source, guselkumab prevents this entire receptor-proximal signalling cascade from initiating.
RORγt induction and Th17/Th22 amplification. STAT3 phosphorylation induced by IL-23 is the principal driver of RORγt up-regulation in CD4+ T cells; RORγt in turn transcriptionally activates IL-17A, IL-17F, and related effector cytokines. IL-23 also promotes STAT3-dependent up-regulation of IL-23R and IL-12Rβ1 expression itself, establishing a positive-feedback loop that amplifies Th17 responsiveness. IL-23 additionally sustains Th22 cells and, together with IL-1β, shifts the Th17/Th22 balance toward the IL-17A-dominant phenotype relevant to psoriatic inflammation. By neutralising IL-23 at the myeloid source, guselkumab dismantles this amplification circuit upstream of both the IL-17 and IL-22 arms of the effector response.
Downstream cytokine suppression and keratinocyte effects. IL-17A released by Th17 cells, γδ T cells, and innate lymphoid cells acts on keratinocytes to drive proliferation and the production of antimicrobial peptides, neutrophil-recruiting chemokines (CXCL1, CXCL2, CXCL8), and CCL20, which in turn chemoattracts additional CCR6+ IL-17-producing cells — a feed-forward inflammatory loop. IL-17A accelerates keratinocyte proliferation and up-regulates CXCL1, CXCL2, CXCL8, and CCL20, perpetuating the IL-17-rich psoriatic milieu. In parallel, IL-22 directly drives keratinocyte hyperplasia and inhibits terminal differentiation via JAK1/TYK2–STAT3 signalling at the IL-22R1/IL-10R2 receptor complex. Guselkumab rapidly suppresses both axes: in VOYAGE 1 pharmacodynamic analyses, guselkumab produced greater reductions in serum IL-17F and IL-22 levels than secukinumab at weeks 24 and 48, consistent with upstream pathway regulation rather than point-of-action cytokine blockade.
Selective IL-23 inhibition versus dual IL-12/IL-23 blockade. Because guselkumab spares p40, IL-12-dependent Th1 differentiation, IFN-γ production, and IL-10-mediated anti-inflammatory signalling remain intact. Comparative skin biopsy analyses showed that guselkumab elicited greater reductions in Th17-related serum cytokines and more completely normalised the psoriasis skin transcriptomic profile than ustekinumab. In patients switching from ustekinumab to guselkumab, suppression of IL-17A and IL-17F and resolution of psoriasis-related gene markers in skin were substantially greater than in those who continued ustekinumab, demonstrating that residual IL-23-driven signalling under p40 blockade is pharmacologically addressable. At the histological level, guselkumab treatment produced greater than 90% reductions in CD3+ T cells and CD11c+ myeloid dendritic cells in lesional skin by week 12, compared with approximately 70% reductions with ustekinumab, translating the upstream molecular advantage into measurable cellular clearance of the psoriatic plaque.
Clinical Relevance
Approved Indications
Moderate-to-severe plaque psoriasis: Guselkumab is approved for adults with moderate-to-severe plaque psoriasis who are candidates for systemic therapy or phototherapy.
Active psoriatic arthritis: Based on the DISCOVER-1 and DISCOVER-2 phase 3 trials, guselkumab received FDA approval for active psoriatic arthritis in 2020, the first selective IL-23 inhibitor approved for this indication.
Moderately to severely active ulcerative colitis: Subcutaneous guselkumab induction and maintenance was reported safe and efficacious for 24 weeks in a fully subcutaneous regimen, establishing it as a treatment option in this population.
Crohn's disease: Versus placebo, guselkumab was associated with higher rates of clinical remission and improved endoscopic outcomes during both induction and maintenance.
Key Drug Interactions (Mechanism-Based)
CYP450 substrates: An exploratory DDI study demonstrated low potential for clinically relevant CYP interactions for CYP3A4, CYP2C9, CYP2C19, and CYP1A2; however, interaction potential for CYP2D6 substrates could not be ruled out and narrow therapeutic index drugs warrant monitoring.
Concomitant DMARDs, NSAIDs, and corticosteroids: Population pharmacokinetic analyses confirmed these agents did not affect the clearance of guselkumab, supporting co-administration without guselkumab dose adjustment.
Live vaccines: Live vaccines are not recommended during guselkumab treatment due to immunomodulatory activity; non-live vaccines may be used.
Contraindications
Serious hypersensitivity: Serious hypersensitivity reactions including anaphylaxis have been reported post-marketing; guselkumab is contraindicated in patients with a prior serious reaction to it or any excipient.
Tuberculosis screening: Evaluate all patients for tuberculosis before initiating therapy; across guselkumab clinical trials, no cases of active TB were reported.
Emerging Indications
Immunology
Hidradenitis suppurativa (Phase 2): IL-23 drives the Th17 axis implicated in HS lesion formation, providing a rationale for selective p19 blockade. In the NCT03628924 randomized Phase 2 study of guselkumab in moderate-to-severe HS, results were modest, and a recent multicentre real-world Spanish cohort reported HiSCR achievement in roughly half of treated patients at week 16, supporting continued development.
Palmoplantar pustulosis (Phase 2, Europe): Pustular lesions on palms and soles are driven by IL-23/IL-17 signaling in non-classical psoriasis variants, where guselkumab is approved in Japan but not in the U.S. or EU. The single-arm GAP Phase 2 trial in 50 European patients met its primary endpoint with a 59.6% median PPPASI reduction at week 24 (P<0.001) and PPPASI-75 in 34% of patients.
Giant cell arteritis (Phase 2, terminated): IL-23-driven Th17 expansion in arterial walls implicates the pathway in GCA vasculitis. The Janssen-sponsored NCT04633447 trial randomized 53 patients but missed its primary endpoint of glucocorticoid-free remission at week 28 (40% guselkumab vs. 33% placebo, P=0.64), and the sponsor concluded results do not support use in GCA.
Nephrology
Lupus nephritis (Phase 2, terminated): IL-23 has been linked to Th17-mediated renal inflammation in proliferative lupus, motivating exploration of p19 blockade as steroid-sparing add-on therapy. The NCT04376827 study was terminated early after enrolling 33 of a planned 60 patients, and at week 24 guselkumab+SOC did not improve proteinuria reduction versus placebo+SOC (35.3% vs. 56.3%).
Hepatology
Alcohol-associated liver disease (Phase 1): IL-23 contributes to hepatic neutrophilic inflammation and IL-17–driven fibrogenesis in alcohol-related steatohepatitis, suggesting upstream blockade could attenuate progression. The completed NCT04736966 dose-escalation study (Loomba, UCSD) evaluated 30, 70, and 100 mg subcutaneous guselkumab in up to 24 ALD patients to establish safety and explore inflammation and fibrosis biomarkers as a foundation for later-phase work.
Reproductive Health
Pyoderma gangrenosum (Phase 2, recruiting): Neutrophilic ulceration in PG is driven by IL-23-amplified IL-17 and IL-36 signaling, and multiple case series report responses to guselkumab in refractory disease. The Phase 2 open-label NCT06563323 trial is enrolling 17 adults at OHSU and Ohio State for 28 weeks of every-4-week dosing with prednisone, with healing as the primary endpoint, building on case-level evidence of higher-dose guselkumab in medically complex PG.
Clinical Trials of Guselkumab
Phase Design
N Enrolled
Intervention
Indication
Primary Endpoint
Key Result
Status
Trial data synthesized by Elicit's AI research agent from peer-reviewed publications and ClinicalTrials.gov filings.
Guselkumab Competitive Landscape
This table shows how Guselkumab compares to other IL-23 inhibitors and biologic therapies for psoriasis and psoriatic arthritis. Each entry breaks down the representative drugs, their molecular targets, and how they actually work in the body.
Drug Class
Representative Drug(s)
Primary Molecular Target
Mechanism of Action
Key Efficacy Outcomes
Route & Dosing
Safety / Risk Profile
Key Limitations
Competitive landscape synthesized by Elicit's AI research agent from peer-reviewed pharmacology literature and regulatory filings.
Open Research Questions
What is the clinical significance of guselkumab's CD64-mediated IL-23 internalization, and does this Fc-dependent mechanism translate into superior tissue-level efficacy over other IL-23p19 inhibitors?
Understanding whether a mechanistic in vitro advantage produces better patient outcomes is critical for positioning IL-23 inhibitors against each other. A 2025 study in Frontiers in Immunology demonstrated that guselkumab's native IgG1 Fc domain enables binding to CD64⁺ myeloid cells and mediates approximately 10-fold greater IL-23 signaling inhibition in co-culture versus risankizumab, but head-to-head clinical trials with tissue biomarker endpoints have not yet been conducted to confirm this advantage in vivo.
To what extent does guselkumab achieve true disease modification rather than sustained suppression, and what biomarkers predict durable remission after discontinuation?
If guselkumab can reset immunological memory rather than merely suppress it, tapering or stopping therapy could become a viable strategy for a subset of patients - with significant implications for long-term risk-benefit calculations. Real-world claims analyses report that guselkumab is associated with approximately twice the 18-month persistence and 31-40% higher remission likelihood versus IL-17 inhibitors, yet the biological basis for this durability and the patient-level predictors of off-drug remission remain undefined.
How does guselkumab remodel the gut microbiome, and can microbiome signatures serve as predictive biomarkers of treatment response?
Given the bidirectional gut-skin axis and IL-23's central role in intestinal immune regulation, characterizing guselkumab's microbiome effects could both explain heterogeneity in clinical response and inform combination strategies. A 48-patient longitudinal 16S rRNA study found that guselkumab-treated patients showed distinct shifts in microbial taxa and augmented taurine/hypotaurine pathway abundance in responders compared with IL-17 inhibitors, though sample sizes were small and causal directionality remains unresolved.
What are the determinants of primary and secondary non-response to guselkumab, and how effective is within-class IL-23 inhibitor switching after guselkumab failure?
Identifying immunological mechanisms driving inadequate response - whether anti-drug antibodies, alternative pathway upregulation, or baseline disease architecture - is needed to guide sequencing decisions. A five-year real-world cohort of 1,024 patients confirmed that prior biologic exposure and obesity are independent negative predictors of PASI response, but prospective studies delineating the molecular basis of non-response and the utility of in-class switching are still limited.
How does guselkumab affect the pharmacodynamics of the IL-23/Th17 axis in axial psoriatic arthritis, and does upstream IL-23 blockade provide comparable benefit to TNF inhibition in axial disease?
Axial involvement in psoriatic arthritis remains an area of clinical uncertainty for all IL-23 inhibitors, as their efficacy lags behind that observed in peripheral joint and skin domains. A 2024 ECLIPSE substudy reported that guselkumab produced greater sustained reductions in IL-17F and IL-22 serum levels than secukinumab at weeks 24 and 48, yet whether this upstream suppression translates to structural protection in axial disease requires dedicated imaging studies and longer trial follow-up.
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This mechanism of action page was generated using Elicit's AI research agent, which synthesizes explanations from peer-reviewed pharmacology literature. Every pathway description and citation is traceable — because in pharmacology, accuracy isn't optional.
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