Amlitelimab: Sanofi's OX40L Antibody Bets on Fewer Shots and a Response That Grows Over Time (September 23, 2026)
Table of Contents
- What amlitelimab is, in one line
- Why OX40L, and why 'upstream' matters
- The COAST 1, COAST 2 and SHORE Phase 3 results
- The unusual part: a response that deepens over time
- How it compares with dupilumab and the anti-OX40 receptor antibodies
- Beyond eczema - promise and a caution from asthma
- What to watch, and the bottom line
What amlitelimab is, in one line
Amlitelimab (development codes SAR445229 and KY1005) is an investigational antibody from Sanofi being developed mainly for moderate-to-severe atopic dermatitis - the most common form of eczema - in people aged 12 and older. Instead of blocking a single inflammatory messenger the way most modern eczema biologics do, it blocks a switch called OX40 ligand (OX40L) that helps turn on and keep on the immune cells behind the disease. It is given as an injection under the skin, and its headline feature is how rarely you need it: after a starting dose, maintenance can be as infrequent as once every 12 weeks - about four injections a year. Amlitelimab is not approved by the FDA or any regulator; it is available only through clinical trials.
Why OX40L, and why 'upstream' matters
To activate, a T cell needs more than one signal. The first tells it what to react to; the second, a 'costimulatory' signal, tells it how strongly and how long to respond. OX40 (on activated T cells) and its partner OX40L (on antigen-presenting cells) are one of those second-signal pairs, and they especially amplify the memory T cells that keep chronic inflammation smoldering. Amlitelimab binds OX40L and blocks that handshake. Because this pair feeds several inflammatory programs at once - not only the Type 2 (Th2) pathway that drives classic eczema, but also Th1, Th17 and Th22 - blocking it acts more broadly than an antibody aimed at a single cytokine such as IL-4, IL-13 or IL-5. And crucially, amlitelimab is 'non-depleting': it dials the T cells down without killing them, aiming to calm the immune system rather than remove part of it.
The COAST 1, COAST 2 and SHORE Phase 3 results
Amlitelimab's pivotal evidence comes from three Phase 3 trials in moderate-to-severe atopic dermatitis, each testing dosing every 4 weeks (Q4W) and every 12 weeks (Q12W) against placebo at week 24. COAST 1 (NCT06130566, 601 patients, monotherapy) met all its primary and key secondary endpoints: EASI-75 - a 75% improvement in eczema severity - reached 35.9% (Q4W) and 39.1% (Q12W) versus 19.1% for placebo, and clear-or-almost-clear skin (vIGA-AD 0/1) reached 21.1% and 22.5% versus 9.2%. COAST 2 (547 patients, monotherapy) also met its primary endpoint but with more modest numbers - vIGA-AD 0/1 of 25.3% and 25.7% versus 14.8%, EASI-75 of 41.8% and 40.5% versus 24.2% - a readout some analysts called mixed. SHORE (596 patients), which added amlitelimab on top of topical steroids, did best: vIGA-AD 0/1 of 28.7% (Q4W) and 32.3% (Q12W) versus 16.8%, and EASI-75 of 48.1% and 46.8% versus 32.3%. A consistent point across all three: the Q12W schedule held up remarkably well against Q4W.
The unusual part: a response that deepens over time
Most biologics hit their peak effect early and then plateau. Amlitelimab looks different. Across the program - and especially in the open-label long-term extension ATLANTIS (NCT05769777) - responses kept climbing for months. By week 52 in that extension, clear/almost-clear skin reached roughly 50% of patients and EASI-75 about 77%, well above the week-24 figures. Dermatologists have described this as 'progressive efficacy.' The proposed explanation ties back to the mechanism: if you are quieting the costimulatory memory that sustains the disease rather than just mopping up one cytokine, the benefit may build as that overactive memory gradually resets. It also fits the earlier Phase 2 finding that responses persisted for a while even after dosing stopped - the observation that pushed Sanofi toward such infrequent maintenance dosing in the first place.
How it compares with dupilumab and the anti-OX40 receptor antibodies
The eczema field is crowded. Dupilumab (anti-IL-4/IL-13) set the modern standard and clears skin in a larger share of patients faster than amlitelimab does at week 24; the anti-IL-13 antibodies tralokinumab and lebrikizumab are also established. Amlitelimab's pitch is not 'higher peak numbers' but a different profile: a broad, upstream, non-depleting mechanism, a response that grows over time, and dosing as seldom as four times a year - a real convenience and adherence advantage. It also has direct mechanistic rivals: rocatinlimab and telazorlimab hit the other side of the same pair, the OX40 receptor on T cells, and are in their own late-stage programs. The open question the head-to-head data have not fully answered is whether amlitelimab's convenience and durability outweigh the higher early clearance rates of the cytokine blockers for a given patient.
Beyond eczema - promise and a caution from asthma
Because OX40L costimulation is a general lever on T-cell inflammation, Sanofi is testing amlitelimab as a potential 'platform' across immune-mediated diseases: asthma, systemic sclerosis, celiac disease, alopecia areata and hidradenitis suppurativa. That breadth is the bull case. But breadth is not guaranteed: a Phase 2 asthma study (TIDE-Asthma) had its highest dose miss the primary goal of reducing severe exacerbations, even though a middle dose showed nominally significant reductions. It is a useful reminder that an elegant upstream mechanism does not automatically win in every disease, and that each indication needs its own data.
What to watch, and the bottom line
The things to watch next are the remaining Phase 3 readouts (including AQUA and ESTUARY), how the full 52-week and longer durability data hold up, real-world adherence given the four-shots-a-year schedule, and Sanofi's regulatory submissions and timing in atopic dermatitis - which the company has signaled it intends to pursue despite the mixed COAST 2 numbers. On safety, amlitelimab was generally well tolerated across the trials, with adverse-event rates similar to placebo and only mild, uncommon injection-site reactions; as with any immunomodulator, longer-term infection and vaccine-response data will keep accumulating. The bottom line: amlitelimab is a mechanistically distinctive, convenient and durable option for moderate-to-severe eczema whose efficacy is real but partial at six months and grows thereafter - a credible new entry rather than an outright replacement for today's leading biologics, and still an investigational drug available only through clinical trials. This article is educational and not medical advice. (Sanofi acquired amlitelimab through its 2021 purchase of Kymab.)
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Citations
- [1] Sanofi's amlitelimab met all primary and key secondary endpoints in the COAST 1 phase 3 study in atopic dermatitis (September 2025) - Sanofi Source
- [2] Sanofi's amlitelimab confirms its potential in atopic dermatitis (COAST 2 and SHORE, January 2026) - Sanofi Source
- [3] AAD late-breaking: new results from Sanofi's amlitelimab phase 3 studies in atopic dermatitis (March 2026) - Sanofi Source
- [4] COAST 1 - Amlitelimab in participants aged 12+ with moderate-to-severe atopic dermatitis - ClinicalTrials.gov NCT06130566 Source
- [5] Phase 2b randomized clinical trial of amlitelimab, an anti-OX40 ligand antibody, in moderate-to-severe atopic dermatitis - Journal of Allergy and Clinical Immunology (2024) Source
- [6] Sanofi to Acquire Kymab, Adding KY1005 (amlitelimab) to Pipeline (2021) - Sanofi Source
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