Executive Summary

Interleukin-11 (IL-11) is increasingly viewed as a key driver of tissue fibrosis, prompting development of IL-11-targeting therapies. As of 2026, the only approved IL-11-related drug is oprelvekin (Neumega), a recombinant IL-11 analog used to prevent chemotherapy-induced thrombocytopenia. By contrast, IL-11 pathway inhibitors are entirely experimental. Several pharmaceutical companies have entered this space: Boehringer Ingelheim, Lassen Therapeutics, and Mabwell are developing IL-11 or IL-11 receptor antibodies for conditions like idiopathic pulmonary fibrosis (IPF), thyroid eye disease, and pathological skin scarring. Preclinical research indicates IL-11 blockade can halt or reverse fibrosis and may even influence aging biology. This report reviews the approved products, pipeline candidates, clinical trials, safety signals, and commercial context of IL-11 therapies.

Approved IL-11 Therapy

Oprelvekin (brand name Neumega) is a recombinant human IL-11 that was FDA-approved in 1997 for the prevention of severe chemotherapy-induced thrombocytopenia1. It is indicated for patients with non-myeloid malignancies at high risk of platelet loss. Oprelvekin is administered subcutaneously (50 µg/kg/day for 10–21 days per cycle1) and increases platelet production. Its safety profile is dominated by fluid retention: common adverse effects include peripheral edema, dyspnea, pleural effusions, tachycardia, and cardiac arrhythmias1. These side effects have limited oprelvekin’s uptake in practice. Notably, the first IL-11-neutralizing antibody only entered clinical trials in 20232, so no IL-11 inhibitor is approved as of 2026.

No other IL-11-related therapy has regulatory approval. Oprelvekin remains the sole marketed IL-11 agent, and its usage is specialized. All anti-IL-11 drugs in development (antibodies or receptor blockers) must progress through clinical testing before any new approvals.

Clinical Pipeline of IL-11-Targeting Agents

Several companies are actively developing IL-11 or IL-11 receptor antagonists. Boehringer Ingelheim licensed Enleofen Bio’s IL-11 antibody platform and initiated clinical trials of BI-765423 (a human anti-IL-11 monoclonal antibody) in 20232. BI-765423 is designed to bind IL-11 and block its interaction with the IL-11 receptor. The company describes this as a first-in-class fibrotic disease treatment2. A Phase 1 study (NCT05658107) in healthy volunteers has been completed, and a Phase 2a trial (NCT07036523) in patients with idiopathic pulmonary fibrosis (IPF) is currently recruiting. Boehringer’s focus is on IL-11-driven fibrosis across organs; preclinical studies show anti-IL-11 can halt and even reverse fibrosis3. The company initially targets IPF and nonalcoholic steatohepatitis (NASH) as key indications.

Lassen Therapeutics is developing LASN01, a monoclonal antibody targeting the IL-11 receptor (IL-11R). LASN01 launched into clinical testing in late 20224. The Phase 1 single-ascending-dose trial in healthy volunteers was completed and demonstrated a favorable safety and pharmacokinetic profile5. Based on those results, the program expanded to patient cohorts: LASN01 is now being evaluated in Phase 1 studies of patients with IPF and with thyroid eye disease (TED)5. An Investigational New Drug (IND) clearance has been obtained for a planned Phase 2 trial in TED. Lassen reports that LASN01 is its lead candidate and is considered “best-in-class” by the company.

Mabwell (a biotech based in China) is developing 9MW3811, a humanized antibody that neutralizes IL-11. In preclinical studies, 9MW3811 potently inhibited IL-11 signaling and showed robust anti-fibrotic activity in models of lung and skin fibrosis6. 9MW3811 completed Phase 1 trials in healthy subjects in Australia and China with no dose-limiting toxicity6. The first patient was dosed in a Phase 2 trial (CTR20254857) in January 2026, evaluating 9MW3811 for pathological scarring (eg keloids)6. Regulatory submissions indicate that China’s NMPA, the US FDA, and Australia’s regulators have cleared 9MW3811 for clinical development in idiopathic pulmonary fibrosis and oncology indications6. In summary, Boehringer’s BI-765423, Lassen’s LASN01, and Mabwell’s 9MW3811 are the lead clinical-stage IL-11–targeting therapies in 2026.

Mechanistic Insights and Preclinical Rationale

IL-11 is a pro-fibrotic cytokine in the IL-6 family, produced by stromal and epithelial cells during tissue injury. It signals via the IL-11Rα/gp130 complex to activate ERK/MAPK pathways in fibroblasts. Multiple studies have implicated IL-11 in organ fibrosis: blocking IL-11 in animal models prevented or reversed collagen deposition in the lung, heart, liver, kidney, and other tissues2. Notably, a 2024 Nature study found that IL-11 levels increase with age in mice and that long-term anti–IL-11 treatment extended median lifespan by ~25%7. This indicates IL-11 drives chronic fibro-inflammatory and aging processes. These mechanistic data support the idea that IL-11 neutralization could have broad therapeutic benefit in fibrotic and age-related diseases.

In the context of fibrosis, IL-11’s central role has been termed “unprecedented” by researchers. By inhibiting IL-11 signaling, preclinical studies reported reduced production of fibrotic markers (such as collagen and TIMP-1) and improved organ function26. These findings provide a strong biological rationale for the current clinical programs. However, it is important to note that translation from animal models to human disease remains to be demonstrated.

Safety and Early Clinical Data

Safety profiles of IL-11-targeting therapies must be considered in two parts: the agonist oprelvekin and the new antagonists. For oprelvekin, toxicities are well-documented (fluid retention, cardiac events)1. For IL-11 inhibitors, data so far are limited to phase 1 trials. Lassen reported that LASN01 was well-tolerated in healthy volunteers; no serious adverse events were noted in single- or multiple-dose cohorts5. Mabwell similarly noted that 9MW3811 had a positive safety profile in phase 1 subjects, with a long serum half-life (>30 days)6. Boehringer has not publicly disclosed detailed Phase 1 results for BI-765423, but no unexpected safety signals have been reported. As development proceeds, phase 2 trials will closely monitor lung function (in IPF) or scar metrics (in dermatology) to assess both efficacy and potential toxicity.

Overall, the IL-11 inhibitors under investigation have not shown prohibitive safety issues in early trials. Their safety may ultimately be compared to existing fibrotic disease treatments: for example, approved IPF drugs like nintedanib and pirfenidone have known tolerability challenges. If IL-11 blockade proves safe, it could be combined with or sequenced after current therapies. At present, efficacy endpoints remain the critical unknowns pending ongoing trials.

Commercial Landscape and Outlook

Interest in IL-11 drugs is high among investors and big pharma. Boehringer Ingelheim’s deal with Enleofen reportedly included up to $1 billion in payments per product, reflecting confidence in the IL-11 approach3. Lassen’s progress has also attracted capital; a Series B financing in late 2023 raised $85 million to advance LASN015. Mabwell’s 9MW3811 is being developed under an exclusive license agreement with Calico Life Sciences, indicating interest in exploring IL-11 across aging-related diseases6. These collaborations and financings suggest strong commercial belief in IL-11 as a target.

However, commercial success will depend on clinical proof. No IL-11 antagonist has yet demonstrated efficacy in a pivotal trial. Regulatory approvals will hinge on trial outcomes. Region-specific pathways also play a role: for instance, China and the US have both granted clearance for IL-11 trials, but harmonizing global development will be important. Pricing and market size are uncertain. Fibrotic diseases affect millions, but any IL-11 therapy would likely be specialty-priced. The next few years of trial readouts will reveal whether IL-11–targeting drugs can translate their preclinical promise into patient benefit.