MSD’s anti-TL1A mAb from $10.8bn acquisition wins in Phase III trial

MSD's Tulisokibart Achieves Phase III Success in Ulcerative Colitis

MSD's investigational humanised monoclonal antibody, tulisokibart, acquired through a $10.8 billion buyout of Prometheus Therapeutics, has successfully met all primary and key secondary endpoints in its Phase III ATLAS-UC induction-only study (NCT06052059). The trial demonstrated significant improvements in patients with moderately to severely active ulcerative colitis (UC), achieving clinical remission at week 12 as defined by the Modified Mayo Score (MMS). This marks the first positive Phase III induction results for an anti-TL1A biologic, reinforcing its potential to address immuno-fibrosis in UC. The drug was also found to be safe and well-tolerated, with no new safety signals reported.

• The ATLAS-UC induction-only study (NCT06052059) for tulisokibart achieved its primary endpoint of clinical remission at week 12, as measured by the Modified Mayo Score (MMS), in patients suffering from moderately to severely active ulcerative colitis. All key secondary endpoints were also successfully met. This outcome is particularly significant as it represents the first positive Phase III induction results for an anti-TL1A biologic, highlighting a novel therapeutic approach designed to target immuno-fibrosis, a key driver of chronic immune dysregulation and disease progression in UC.
• Tulisokibart demonstrated a favorable safety and tolerability profile in the ATLAS-UC study, with no new safety signals identified. Beyond its success in ulcerative colitis, tulisokibart is being evaluated in the broadest development program within the novel anti-TL1A class, encompassing seven disease indications. This includes a Phase III trial in Crohn’s disease (ARES-CD) and Phase II trials for systemic sclerosis-associated interstitial lung disease, rheumatoid arthritis, psoriatic arthritis, radiographic axial spondyloarthritis, and hidradenitis suppurativa, underscoring its potential across a wide range of immune-mediated conditions.
• MSD strategically acquired tulisokibart through its $10.8 billion buyout of clinical-stage biotechnology firm Prometheus Biosciences. The definitive agreement was signed in April 2023, with the deal completing in June 2023, involving the purchase of all outstanding shares for $200 each. This acquisition positions MSD to capitalize on the growing ulcerative colitis market, which GlobalData projects to increase from $11.1 billion in 2021 to $14.7 billion by 2031 across 68 markets, validating the substantial investment with positive Phase III results.

Tulisokibart's Landmark Phase III Results in Ulcerative Colitis

The LUCENT program for mirikizumab, an anti-interleukin-23 p19 monoclonal antibody, has generated some of the most comprehensive long-term efficacy data in ulcerative colitis to date. The pivotal Phase III LUCENT-1 and LUCENT-2 trials (NCT03518086, NCT03524092) demonstrated that disease clearance — defined as concurrent symptomatic, endoscopic, and histologic remission — was achieved in 16.0% of patients at week 12, rising to 36.4% at week 52 and 51.3% at week 104. Early achievement of disease clearance at week 12 was associated with significantly improved clinical outcomes at subsequent time points, underscoring the prognostic value of rapid deep response. The LUCENT-3 open-label extension (OLE) study extended follow-up through week 212, representing four years of continuous treatment. Among patients who achieved clinical remission at week 52 and entered the OLE, 77.7% maintained clinical remission at week 212, with 81.3% achieving endoscopic remission, 66.0% achieving histologic-endoscopic mucosal remission, and 97.1% sustaining clinical response. Quality-of-life metrics as measured by the IBDQ were similarly durable, with response and remission rates exceeding 66–70% at week 212. Crucially, no new safety signals emerged over 160 weeks of OLE exposure, and efficacy outcomes were broadly consistent across biologic-naïve and biologic-experienced subgroups.

In the JAK inhibitor space, a multicenter retrospective cohort study conducted between 2018 and 2024 compared tofacitinib, filgotinib, and upadacitinib across 270 patients with moderate-to-severe UC. At six months, upadacitinib demonstrated the highest rates of clinical remission (91%), biochemical remission (71%), and endoscopic remission (80%), compared with filgotinib (78%, 67%, 50%) and tofacitinib (73%, 51%, 44%), with statistically significant advantages for upadacitinib over tofacitinib in clinical response (P=0.027) and remission (P=0.037). Drug persistence at 12 months also favored upadacitinib at 86%, versus 72% for filgotinib and 69% for tofacitinib. A separate upadacitinib versus tofacitinib meta-analysis, encompassing ten retrospective studies and 2,021 patients, reinforced these findings, with upadacitinib demonstrating superior steroid-free clinical remission at weeks 8–14 (OR 1.98; 95% CI 1.32–3.97), weeks 48–60 (OR 2.32; 95% CI 1.50–3.58), and at end of study follow-up (OR 3.60; 95% CI 1.73–3.92). Treatment discontinuation was less frequent with upadacitinib (OR 0.51; 95% CI 0.34–0.77), though acne occurred at significantly higher odds (OR 4.30; 95% CI 1.86–9.95).

Complementing the mechanism-specific analyses, an individual patient-level data meta-analysis of ten RCTs evaluated the impact of age on the efficacy and safety of advanced therapies — including TNF antagonists, vedolizumab, ustekinumab, and tofacitinib — across 6,192 patients, of whom 634 (10.2%) were aged 60 years or older. Efficacy was comparable between older and younger adults across all drug classes, with no statistically significant treatment effect modification observed for induction of clinical remission (TNF antagonists: RRR 0.94 [95% CI 0.41–2.15]; non-TNF-targeting agents: RRR 1.26 [0.60–2.62]). However, older adults were significantly more likely to experience infections when treated with advanced therapies versus placebo compared to younger adults, with relative risk ratios of 1.52 (95% CI 1.12–2.05) for TNF antagonists and 2.04 (95% CI 1.45–2.87) for non-TNF-targeting agents. These findings have direct implications for benefit-risk stratification in elderly UC populations, particularly when selecting between immunosuppressive mechanisms with differing infection profiles.

Unpacking the Novel Anti-TL1A Mechanism in Ulcerative Colitis

Monoclonal antibodies selectively targeting the p19 subunit of IL-23 — including risankizumab, mirikizumab, and guselkumab — have emerged as a bona fide therapeutic class in ulcerative colitis. Landmark phase 3 trials have demonstrated high efficacy and durable responses across both UC and Crohn's disease, culminating in recent regulatory approvals. These agents display favorable safety profiles and support convenient subcutaneous dosing regimens, broadening their applicability across diverse patient populations. Notably, a case report documented that guselkumab administered at the psoriasis-labeled regimen (100 mg every 8 weeks), in combination with mesalazine 4 g daily, achieved sustained endoscopic remission of UC (Mayo endoscopic score 1, UCEIS 1) in a patient with UC-psoriasis comorbidity — without the need for additional biologic therapy. This provides exploratory evidence that IL-23-targeted agents may serve patients with overlapping inflammatory conditions. Looking ahead, the integration of serological and multi-omics biomarkers is anticipated to enable prediction of treatment success and guide personalized selection among IL-23p19 inhibitors.

Janus kinase inhibitors (JAKi) represent another actively evaluated therapeutic avenue, with real-world data drawn from a propensity score–matched cohort of 3,186 patients (85.7% UC, 72% tofacitinib) demonstrating no significant difference in the risk of bacterial, viral, or fungal infections, major adverse cardiovascular events (MACE), malignancy, or venous thromboembolism compared to biologic therapy. However, JAKi use was associated with a higher risk of LDL ≥ 190 mg/dL (aOR 1.78; 95% CI 1.03–3.05) and grade 3 or higher lymphopenia (aOR 2.28; 95% CI 1.60–3.26), warranting ongoing lipid and hematological monitoring in clinical practice. No difference in 4-year risk of MACE or malignancy was observed in the tofacitinib subgroup versus the biologic cohort, offering some reassurance regarding longer-term cardiovascular and oncologic safety signals.

Beyond immune-targeted biologics and small molecules, emerging strategies are increasingly focused on the microbiome-metabolic axis as a root-cause therapeutic target. Approaches under investigation include fecal microbiota transplantation, probiotic and postbiotic formulations, bacteriophage therapy, helminth-based therapies, and precision genome editing — all aimed at restoring functional microbial metabolism, particularly in pathways governing short-chain fatty acids, bile acids, and redox homeostasis. Complementing this, multi-ancestry genome-wide and transcriptome-wide association analyses have uncovered 506 high-confidence IBD risk genes — 384 of which were not previously reported — with 46 of these genes targeted by 225 approved or Phase II/III drugs, including sulfasalazine. These genes converge on immune regulation and microbial interaction pathways, with over half showing transcriptional dysregulation supported by single-cell and spatial omics analyses, collectively pointing toward a richer target landscape for next-generation UC therapeutics.

Tulisokibart's Broad Pipeline Beyond Ulcerative Colitis

Tulisokibart's clinical development extends meaningfully beyond ulcerative colitis, with active investigation across inflammatory indications driven by the TL1A/DR3 signalling axis. Two additional indications — Crohn's disease and hidradenitis suppurativa — are currently in clinical evaluation, spanning Phase 2a through Phase 3 development. The intervention models vary by indication, reflecting differing stages of evidence generation.

Anti-TL1A Breakthrough: Reshaping Ulcerative Colitis Therapy

The recent announcement of tulisokibart's successful Phase III ATLAS-UC induction study marks a significant advancement in the treatment of moderately to severely active ulcerative colitis. This investigational humanized monoclonal antibody, targeting TL1A, has demonstrated significant improvements in clinical remission at week 12, reinforcing its potential to address the complex pathology of inflammatory bowel disease (IBD).

TL1A, a tumor necrosis factor-like cytokine, plays a critical role in chronic mucosal inflammation by costimulating T-helper 1 and T-helper 17 cells. Crucially, research indicates that TL1A also mediates intestinal fibrosis, a severe complication often associated with IBD. This dual mechanism of action—addressing both inflammation and fibrosis—positions tulisokibart as a promising therapeutic option, potentially offering more comprehensive disease control than existing treatments.

One of the most compelling aspects of this development is the potential for a precision medicine approach. Earlier Phase 2 trials for tulisokibart utilized a genetic-based diagnostic test to identify patients with an increased likelihood of response. This strategy could revolutionize patient selection, ensuring that the right therapy reaches the right patient, thereby optimizing treatment outcomes and potentially reducing healthcare costs associated with non-responders. However, the successful integration of such a diagnostic into routine clinical practice will be crucial for its widespread adoption.

While the short-term safety profile appears favorable, as no new safety signals were reported, the long-term safety and sustained efficacy of TL1A inhibition will be critical considerations as the drug progresses. The IBD therapeutic landscape is increasingly competitive, with numerous novel agents targeting various pathways. Tulisokibart's success, however, validates the TL1A pathway as a viable target, not only for UC but also for other immune-mediated conditions like Crohn's disease and Hidradenitis suppurativa, where TL1A is also implicated. This broad potential underscores the strategic importance of this breakthrough, suggesting that anti-TL1A therapies could become a cornerstone in the evolving paradigm of IBD management.