Eltrekibart

Eltrekibart is Eli Lilly's investigational monoclonal antibody that neutralizes a whole family of neutrophil-recruiting chemokines (the ELR+ CXC chemokines, including IL-8). Lilly is testing it on top of mirikizumab (Omvoh, Lilly's approved IL-23 blocker for ulcerative colitis) in a 143-patient Phase 2 trial, NCT06598943, now listed as active, not recruiting [1]. The commercial thesis is straightforward: Omvoh already works in UC, but a chunk of patients still fail to reach remission; add a neutrophil-blocking antibody and you might rescue them. The first disclosed Phase 2 efficacy readout in any indication was published by Forman and colleagues in JAAD in February 2026 in hidradenitis suppurativa (NCT06046729). Critically, that trial missed its prespecified primary endpoint: HiSCR50 was 48.9% on eltrekibart vs 31.8% on placebo at week 16, p=0.19 [2][3]. A prespecified Bayesian augmented-control analysis using historical placebo data was positive (65.6% vs 32.3%, 99.9% posterior probability of superiority), but the hard, prespecified comparison was negative. For Lilly, this is a hedge against the IL-23 class commoditizing: Omvoh runs behind AbbVie's Skyrizi, generating roughly $102M in Q2 2025 sales vs Lilly's $65.2B total 2025 company revenue [4]. An incremental UC product only matters if it meaningfully stretches Omvoh's label into harder-to-treat patients. The failed primary endpoint in HS makes the UC combo read materially less probable than it looked before publication.

Eltrekibart (LY3041658) is a novel first-in-class investigational antibody. It has not been approved anywhere for any indication. No FDA breakthrough, fast track, orphan, or priority review designations have been publicly disclosed for the UC program. The Phase 2 trial in ulcerative colitis, NCT06598943, is an eltrekibart plus mirikizumab combination study of 143 adults with moderate to severe active disease, currently active, not recruiting [1]. Primary endpoint is the percentage of patients achieving clinical remission. Based on the status change to active, not recruiting, topline data could land in 2026 or 2027, though Lilly has not guided a specific date. In parallel, Lilly ran a Phase 2 trial in hidradenitis suppurativa (NCT06046729, n=234 randomized 2:1 eltrekibart to placebo, completed) with HiSCR50 as the primary endpoint [3]. Results were published by Forman and colleagues in the Journal of the American Academy of Dermatology, volume 94, issue 2, pages 530-538, in February 2026 [2]. The primary endpoint failed to reach statistical significance. A Phase 1 bioavailability study of two eltrekibart formulations in healthy volunteers in Singapore (NCT07545590) completed in September 2026 [5]. No AE breakdown from that Phase 1 is publicly disclosed. Lilly disclosed the compound in its 2024 and 2025 10-Ks among immunology pipeline assets [4][6]. No Phase 3 has been initiated or publicly scheduled in UC. The next value-moving event is the NCT06598943 topline.

IL-8 (encoded by CXCL8) is one of the body's main signals for calling neutrophils, the fast-response white blood cells that chew up pathogens and, when overactive, chew up healthy tissue [7]. CXCL1, 2, 3, 5, 6, and 7 are its chemical siblings. All of them share a three-letter sequence (Glu-Leu-Arg, or ELR+) that lets them signal through chemokine receptors on neutrophils. CXCR2, found on neutrophil surfaces, is activated by all seven ELR+ CXC chemokines. CXCR1 is a second receptor with narrower ligand specificity, mainly responding to IL-8 (CXCL8) and CXCL6. Because any of the seven chemokines can trigger CXCR2-mediated recruitment, blocking a single chemokine leaves the others free to compensate. Eltrekibart binds and neutralizes the whole set at once, so neutrophils stop getting the recruitment signal regardless of which chemokine the tissue is pumping out. In ulcerative colitis, biopsies from active disease are stuffed with neutrophils forming crypt abscesses, the small pus pockets that mark flares. Reducing that neutrophil traffic should calm mucosal damage. The mechanism is biologically grounded, but the drug class has a thin win column. Earlier anti-IL-8 antibodies (BMS-986253/HuMax-IL8) and small-molecule CXCR1/2 antagonists (reparixin, navarixin) have mostly produced modest or failed signals [8]. Pairing eltrekibart with mirikizumab, which blocks IL-23 and the Th17 axis (a subset of T helper cells that drive chronic inflammation in the skin and gut), targets a different cytokine lane entirely, so the two drugs should hit non-overlapping drivers of UC. Whether that layered approach beats mirikizumab monotherapy is the question Phase 2 is built to answer.

NCT06598943 is a Phase 2 study of eltrekibart plus mirikizumab in 143 adults with moderately to severely active ulcerative colitis, sponsored by Eli Lilly [1]. The primary endpoint is the percentage of participants achieving clinical remission, the standard regulatory bar in UC (defined by stool frequency, rectal bleeding, and endoscopic subscores on the modified Mayo scale). The trial is active, not recruiting, meaning enrollment is closed and patients are being dosed and followed. A key design question not fully resolved in public registry text is whether the comparator is mirikizumab alone or placebo plus mirikizumab, and whether randomization is 1:1 or weighted. A 143-patient study is adequately powered to detect a large remission delta (say, 15 to 20 percentage points over mirikizumab monotherapy) but underpowered for smaller effects. The HS Phase 2 (NCT06046729) was a 2:1 randomized, double-blind, placebo-controlled study of eltrekibart 600 mg IV every 2 weeks with HiSCR50 (a 50% or greater reduction in abscess and inflammatory nodule count without worsening of abscesses or draining fistulas) at week 16 as primary [3]. Reported results: 48.9% HiSCR50 on eltrekibart vs 31.8% on placebo, p=0.19, 95% CI for the difference -7.3 to 41.4 [2]. The prespecified Bayesian augmented-control analysis incorporating historical Phase 3 placebo data yielded 65.6% vs 32.3% with 99.9% posterior probability of superiority. The prespecified classical primary analysis was negative; the Bayesian analysis was positive. The UC program should be interpreted against that mixed dermatology signal. Design concerns: no biomarker-stratified subgroups are prespecified for neutrophil-high UC, which would be the most mechanistically rational enrichment strategy.

Our model estimates a 17% chance this drug is eventually approved. It starts from the historical base rate for Phase 2 drugs in this area (about 30%), then adjusts using ten facts about the trial and sponsor. What moves the number most: it is helped by the sponsor's strong record of getting drugs approved and more secondary endpoints than usual; it is held back by weak or limited earlier-phase results and a randomized design. The other facts land near average for this stage, so they leave the estimate roughly where the base rate put it.

Efficacy risk is the biggest concern and has grown after HS. The prespecified HS primary analysis missed statistical significance [2]. Prior attempts to drug the IL-8 axis have produced thin signals: BMS-986253 as monotherapy and in combinations with checkpoint inhibitors generated limited oncology activity, and small-molecule CXCR1/2 antagonists have not cleared Phase 3 in any major indication [8]. Neutralizing seven chemokines at once is a differentiator, but the biology may still find a workaround through CCR-family receptors or complement-driven neutrophil recruitment. Safety risk is on-target: neutrophils are the primary defense against bacterial infection. Chronic suppression raises infection concern, particularly in a UC population where many patients are already on immunosuppressants and biologics. The combination design with mirikizumab compounds that risk. The published HS paper reported eltrekibart was generally well-tolerated at 16 weeks, but no long-term safety data are yet in the public record [2]. Trial design risk centers on comparator ambiguity and the absence of a biomarker-enriched arm, which could produce an uninterpretable topline if effect sizes are modest. Execution risk is low given Lilly's immunology trial machinery. Commercial risk is substantial even if the drug works. Omvoh itself is a late entrant in the IL-23 class, generating approximately $102M in Q2 2025 sales [4], and runs well behind AbbVie's Skyrizi, which is a multi-billion-dollar franchise with growing UC share. Adding a second antibody on top raises the cost of therapy well beyond any single biologic, and payers are already resistant to biologic combos in IBD without large incremental efficacy. A combo product would also need to clear the burden of showing it beats sequential therapy. The addressable population shrinks to Omvoh-treated UC patients with inadequate response.

Watch with lowered expectations. The HS Phase 2 (JAAD February 2026) is the first disclosed efficacy readout for eltrekibart, and the hard prespecified primary endpoint missed: 48.9% HiSCR50 vs 31.8% placebo, p=0.19 [2]. The Bayesian augmented-control analysis was clean (65.6% vs 32.3%, 99.9% posterior probability), but relying on historical controls to rescue a failed primary is not a strong basis for extrapolating to UC, where neutrophil dominance is less pronounced than in HS. For the UC program specifically, the signal to look for is topline from NCT06598943 showing a remission delta of at least 15 percentage points over mirikizumab monotherapy. Anything smaller gets lost in the noise of real-world IBD care and will not clear payer scrutiny. HS as a standalone opportunity is non-trivial on its own: dupilumab was approved for HS in 2024 and bimekizumab (Bimzelx) in 2025, with secukinumab also competing. HS market is estimated at mid-single-digit billions globally and growing fast. However, with Lilly's HS primary missed on classical analysis, a Phase 3 go-decision in HS is not guaranteed and would likely require Lilly's internal Bayesian conviction to override the headline miss. Check back when Lilly reports Q2 or Q3 2027 earnings or issues an immunology pipeline update, whichever comes first [4]. For Lilly at $65B in annual revenue, this asset is a pipeline hedge rather than a franchise-maker: it only matters commercially if it stretches Omvoh into harder-to-treat UC patients and creates a differentiated combination label that AbbVie cannot easily match with Skyrizi.