Aclaris Therapeutics Announces Positive Phase 1b Proof-of-Concept Primary Analysis Results for its Anti-TSLP/IL-4Rα Bispecific ATI-052 in Atopic Dermatitis (AD) and Asthma

Development priorities now center on eosinophilic esophagitis following early clinical results in two other inflammatory diseases.

Rhea-AI Summary

Aclaris Therapeutics (ACRS) reported Phase 1b results for ATI-052 in atopic dermatitis and asthma, with both trials meeting their primary safety objective. The trials enrolled 14 and 16 patients, respectively. No Grade 3 or 4 treatment-emergent adverse events, adverse-event discontinuations or conjunctivitis were observed.

In atopic dermatitis, the day-57 mean improvement in the Eczema Area and Severity Index was 45% placebo-adjusted; itch improvement was 43% placebo-adjusted. In asthma, a single dose reduced exhaled nitric oxide, an airway inflammation marker, by 59% at day 15 versus 15% with placebo. Mean improvement in one-second exhaled air volume was 200 ml, both absolute and placebo-adjusted, at day 15. Aclaris intends to prioritize a Phase 2b trial in eosinophilic esophagitis early next year and update plans for a potential additional indication in the near term.

16 points · 1 major

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Hollow bars mark forward-looking points. How the balance works

Positive

• Major pointBoth ATI-052 trials achieved the primary safety objective, with no Grade 3 or 4 treatment-emergent adverse events.
• Moderate pointAD skin severity improved 45% placebo-adjusted at day 57: 58% in the active arm versus 13% with placebo.
• Moderate pointDay-57 itch improvement was 43% placebo-adjusted: 38% improvement with ATI-052 versus 5% worsening with placebo.
• Moderate pointAsthma airway inflammation marker fell 59% (45 ppb) at day 15 versus 15% with placebo; reduction was 40% at day 29.
• Moderate pointAsthma one-second exhaled air volume improved 200 ml at day 15, both absolute and placebo-adjusted.
• Moderate point. Forward-looking: it has not happened yet and may not happen.Aclaris plans to prioritize Phase 2b development in eosinophilic esophagitis early next year.

10 minor points

• Minor pointSafety findings included no conjunctivitis or adverse-event discontinuations; injection-site reactions were transient and almost exclusively Grade 1.
• Minor pointAD patients achieved 78% placebo-adjusted EASI-50, a response indicating at least 50% skin-severity improvement, at day 57.
• Minor pointEASI-50 responses at day 57 were 100% for baseline vIGA 3 versus 71% for vIGA 4, placebo-adjusted.
• Minor pointAD skin responses were durable through week 16 in the subset with available data; follow-up remains ongoing.
• Minor pointItch relief emerged in the first week and deepened through week 10 in patients with available data.
• Minor pointWeek-4 itch improvement was 40%, both placebo-adjusted and absolute.
• Minor pointDay-57 itch results included a 33% placebo-adjusted response for improvement of at least four points.
• Minor pointAD skin protein measurements showed 95% normalization at week 8, with inflammatory pathway suppression across several immune pathways.
• Minor pointAsthma patients receiving ATI-052 achieved 58% exhaled nitric oxide normalization at day 15 after one dose.
• Minor pointPost hoc asthma subgroup lung-function improvement was 350 ml at day 15, versus a 140 ml worsening with placebo.

Negative

• Minor pointEvidence comes from small Phase 1b populations: 14 AD patients and 16 asthma patients.
• Minor pointAD per-protocol analysis excluded four patients for prespecified reasons before unblinding.
• Minor pointThe larger asthma subgroup lung-function response came from a post hoc analysis, rather than a prespecified subgroup analysis.

News Explained

The Phase 1b atopic dermatitis efficacy results are per-protocol: four of the 14 enrolled patients were excluded, two from each arm, for prespecified eligibility or early rescue-medication reasons.

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Key Figures

AD trial enrollment: 14 patients AD dosing regimen: Five weekly doses of 480 mg Placebo-adjusted EASI change: 45% +5 more

AD trial enrollment

14 patients

Phase 1b trial in severe atopic dermatitis

AD dosing regimen

Five weekly doses of 480 mg

Weeks 0 through 4

Placebo-adjusted EASI change

45%

At day 57 from baseline

Placebo-adjusted EASI-50

78%

At day 57

Placebo-adjusted itch improvement

43%

PP-NRS at day 57

Lesional skin proteome normalization

95%

At week 8 in ATI-052 recipients

FeNO reduction

59% (45 ppb)

Mean absolute reduction 15 days after a single dose

FEV1 improvement

200 ml

Placebo-adjusted and absolute mean improvement 15 days after a single dose

Previous Clinical trial Reports

1 past event · Latest: Apr 28

Same Type 1 event

1. Apr 28

   Phase 1a data

   24h Move

   -4.3%

   ATI-052 Phase 1a results reported an approximately 45-day half-life and sustained pharmacodynamic activity supporting up to three-month dosing.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Key Terms

bispecific antibody, treatment-emergent adverse events, fractional exhaled nitric oxide, forced expiratory volume in one second, +1 more

5 terms

bispecific antibody technical

"anti-TSLP/IL-4Rα bispecific antibody ATI-052"

A bispecific antibody is a specially designed protein that can attach to two different targets at the same time. Think of it as a custom-made connector that brings two things together—such as a disease cell and an immune system component—helping the body fight illnesses more effectively. For investors, understanding bispecific antibodies is important because they represent innovative therapies that could lead to new treatments and potentially lucrative market opportunities.

treatment-emergent adverse events medical

"Treatment-emergent adverse events (TEAEs) observed in these POC trials"

Events or symptoms that either appear for the first time or get worse after a patient starts a treatment; think of new or intensified side effects that show up once medicine or a medical device is used. Investors watch these closely because they affect whether a therapy can gain regulatory approval, be prescribed widely, or face legal and commercial setbacks—similar to how early customer complaints can sink a new product’s prospects.

fractional exhaled nitric oxide medical

"baseline fractional exhaled nitric oxide (FeNO) of at least 35 parts per billion"

Fractional exhaled nitric oxide is a simple breath test that measures the small amount of nitric oxide a person exhales, which rises when the airways are inflamed. For investors, it acts like a smoke alarm for airway inflammation: it helps doctors decide who needs or is responding to asthma treatments and influences demand, reimbursement and market size for related drugs, devices and diagnostic services.

forced expiratory volume in one second medical

"Forced Expiratory Volume in One Second (FEV1)"

Forced expiratory volume in one second (FEV1) is the volume of air a person can forcefully exhale in the first second after taking a full breath in, measured by spirometry. It is reported as an absolute volume (liters) and often as a percentage of a predicted value based on a person’s age, sex, height and ethnicity; clinicians use changes or percentages of predicted FEV1 to assess and quantify airflow obstruction or improvement in lung function. The measure depends on patient effort and correct testing technique, so repeatable, standardized spirometry is required for reliable results.

eczema area and severity index medical

"Eczema Area and Severity Index (EASI) Score"

A standardized clinical score that measures how much skin is affected by eczema and how severe the lesions are, combining area and intensity into one number much like a report card for a skin condition. Investors care because changes in this score are often used as a primary measure of a treatment’s effectiveness in clinical trials, influencing regulatory approval chances, market potential, and the perceived value of companies developing eczema therapies.

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- Results Demonstrated Breadth and Rapidity of Response to ATI-052 in Heterogeneous Patient Populations; Pharmacodynamic Results Demonstrated Potential for Additivity/Synergy of Targeting TSLP and IL-4Rα -

- Rapid and Durable Improvement in Skin and Itch Observed in Severe AD Population with ATI-052; Single Dose Rapidly Improved Airway Inflammation and Lung Function in Diverse Asthma Population -

- ATI-052 Demonstrated Favorable Safety and Tolerability Profile Including No Observations of Conjunctivitis -

- Aclaris to Prioritize Development in Eosinophilic Esophagitis (EoE), Consistent with Development Strategy -

- Aclaris to Host Conference Call this Morning at 8:00 AM ET-

WAYNE, Pa., Oct. 27, 2026 (GLOBE NEWSWIRE) -- Aclaris Therapeutics, Inc. (NASDAQ: ACRS), a clinical-stage biopharmaceutical company focused on developing novel product candidates for immuno-inflammatory diseases, today announced positive primary analysis results from the Phase 1b proof-of-concept (POC) trials of its anti-TSLP/IL-4Rα bispecific antibody ATI-052 in atopic dermatitis and asthma. Both trials demonstrated strong proof-of-concept with rapid and broad responses to ATI-052, further validating the additive/synergistic potential of simultaneously targeting TSLP, IL-4, and IL-13 with a bispecific anti-TSLP/IL-4Rα antibody, and achieved the primary objective, showing a favorable safety profile including no observations of conjunctivitis. Slides accompanying this announcement will be available for download at the time of the conference call here.

Aclaris intends to prioritize Phase 2b development of ATI-052 initially in EoE, where the Company believes a focused development program is well aligned with its development strategy and disciplined capital management.

“These strong results convey ‘the art of the possible’ with this bispecific mechanism in heterogeneous diseases across diverse patient populations and support that this is a potent, broadly acting compound with potential best-in-class activity,” said Dr. Neal Walker, Chief Executive Officer of Aclaris. “Across heterogeneous patient populations, we observed breadth and depth of response, normalization of the immune proteome, encouraging early durability, evidence of potential synergy of targets, and a favorable safety profile associated with ATI-052 – all of which clarify its potential across indications. Consistent with our development strategy, we intend to prioritize initiating a Phase 2b trial in EoE early next year and provide an update on plans for a potential additional indication in the near term.”

Primary Analysis Results: Safety

ATI-052 was well tolerated across both trials and demonstrated a favorable safety profile. Treatment-emergent adverse events (TEAEs) observed in these POC trials were predominantly Grade 1. There were no Grade 3 or 4 TEAEs, and no adverse events led to study discontinuation. Injection site reactions (ISR) were transient, almost exclusively Grade 1, and observed at a low frequency. No conjunctivitis was observed.

Phase 1b POC Trial in Atopic Dermatitis (AD)

The randomized (3:1), double-blind, placebo-controlled Phase 1b trial evaluated the safety and tolerability of ATI-052 compared with placebo in 14 patients with severe AD. Enrolled patients received five weekly doses of 480 mg of ATI-052 or placebo from weeks 0 through 4, and endpoints for the primary analysis were assessed at day 57. Four patients were excluded from the prespecified per-protocol analysis for reasons defined before unblinding: Two in the ATI-052 arm (only two doses taken; eligibility criteria not met) and two in the placebo arm (both began rescue medication early on). Among per-protocol patients in the active arm, 78% had severe disease at baseline, as defined by a score of 4 on the Validated Investigator’s Global Assessment (vIGA), setting a high bar for success.

Primary Analysis Results: AD

Eczema Area and Severity Index (EASI) Score

• Patients treated with ATI-052 experienced a 45% placebo-adjusted mean change in EASI score from baseline at day 57 (absolute change of 58% in the active arm vs 13% in the placebo arm). Responses were durable for the subset of patients with available data at week 16 (follow up ongoing).
• Patients treated with ATI-052 experienced a 78% placebo-adjusted EASI-50 at day 57. Of those, 100% of patients with a baseline severity of vIGA 3 achieved placebo-adjusted EASI-50 at day 57 compared to 71% of patients with a baseline severity of vIGA 4.

Peak Pruritus Numerical Rating Scale (PP-NRS)

• Itch relief emerged in the first week and continued to deepen through week 10 in patients with available data despite high baseline disease severity. At week 4, patients that received ATI-052 experienced a 40% placebo-adjusted and absolute mean improvement from baseline in itch (PP-NRS).
• Patients that received ATI-052 experienced a 43% placebo-adjusted mean improvement in itch (PP-NRS) at day 57 (38% absolute improvement in the active arm vs a 5% worsening in the placebo arm).
• At day 57, 33% of patients experienced a placebo-adjusted mean improvement of ≥4-points in itch (PP-NRS4).
  
  

“These ATI-052 data in AD are very noteworthy, not only in strength of response at day 57 but also in rapidity and durability of response,” said Dr. Michael Cameron, M.D., FAAD, CEO of Equity Medical and Assistant Clinical Professor, Department of Dermatology at Mount Sinai in New York, and an investigator in the trial. “Given the mechanism of ATI-052, one would expect reductions in EASI and itch from baseline to be rapid and sustained due to blockade of IL-4 and IL-13 via their shared receptor IL-4Rα, and durable through blockade of the TSLP alarmin. This is consistent with my experience during the trial. For example, one of my longstanding refractory patients responded quickly to ATI-052 and had a durable response that lasted months beyond their last dose. This bodes well for the mechanism in future clinical trials.”

Pharmacodynamic (PD) Results

• 95% normalization in the lesional skin proteome was observed at week 8 in patients that received ATI-052, with immune protein expression resembling that of non-lesional skin.
• ATI-052 broadly downregulated pathways, with modulation across multiple inflammatory mediators in AD, including Th1, Th2 and Th17/Th22, fibrosis/ECM remodeling, and itch-associated molecular pathways.
• ATI-052 produced a pronounced reduction of the established dupilumab biomarkers, additionally suppressing Th1, Th17 innate, and myeloid pathways, suggesting a potential best-in-class footprint.
  
  

“These ATI-052 pharmacodynamic biomarker results in patients with AD are clear, and significantly correlated to the efficacy results,” said Emma Guttman, M.D., Ph.D., Waldman Professor of Dermatology and Immunology and Health System Chair of the Kimberly and Eric J. Waldman Department of Dermatology at the Icahn School of Medicine at Mount Sinai in New York City. “Among the most important findings were the overall improvements to the immune proteome in patients receiving ATI-052; key immune proteins were significantly downregulated by ATI-052 compared to placebo, potentially highlighting the contribution of added benefit of blocking TSLP in this indication, with the proteomic phenotype of lesional skin closely resembling that of non-lesional skin already at week 8. These results, including ATI-052’s ability to modulate all three T helper cell related markers, are suggestive of early potent anti-inflammatory clinical activity.”

Phase 1b POC Trial in Asthma

The randomized (3:1), double-blind, placebo-controlled Phase 1b trial evaluated the safety and tolerability of a single 480 mg dose of ATI-052 compared with placebo in 16 patients with mild-to-moderate asthma and baseline fractional exhaled nitric oxide (FeNO) of at least 35 parts per billion (ppb). Endpoints were assessed through day 29.

Primary Analysis Results: Asthma

Fractional Exhaled Nitric Oxide (FeNO)

• Following a single dose of ATI-052, patients experienced a rapid 59% mean absolute reduction in FeNO (45 ppb) only 15 days after administration compared to 15% in the placebo arm, and a 40% reduction at day 29.
• 58% of patients on ATI-052 achieved FeNO normalization (≤25 ppb) at day 15 after a single dose, highlighting the rapid onset of response.

Forced Expiratory Volume in One Second (FEV1)

• Following a single ATI-052 dose, patients responded rapidly, experiencing a placebo adjusted and absolute mean improvement of 200 ml in FEV1 only 15 days after administration.
• In a post hoc subgroup analysis of the enrolled patients with FEV1 of <80% at baseline with reversibility, which models the typical Phase 2b/3 eligible population of patients, an absolute mean improvement in FEV1 of 350 ml from baseline was observed at day 15 compared to a worsening of FEV1 of -140 ml in the placebo arm.
  
  

“In such a Phase 1b trial, the goals are to ensure safety and to develop some encouraging signals; in this case, the results are significantly better than encouraging,” said Dr. Chris Brightling, Clinical Professor in Respiratory Medicine at the University of Leicester and Deputy Director and Respiratory and Infection Theme Lead, NIHR Biomedical Research Centre: Leicester. “Of particular interest are the rapid improvements in the breath biomarker FeNO, both in the overall population and when stratified by baseline eosinophils, and the lung function test FEV1, with maximum effects that are at least as good if not improving on those seen by comparator compounds.”

Webcast and Conference Call

Aclaris will host a webcast and conference call with slides today at 8:00 AM ET to discuss the Phase 1b POC primary analysis results in asthma and AD. The live and archived webcast will be available on the Events page of the Company’s website: https://investor.aclaristx.com/events. The webcast will be archived on the same page for 30 days following the event. If you would rather access the call via telephone: To register and receive a dial in number and unique PIN to access the live conference call, please follow this link to register online. Upon registering you will receive the dial-in info and a unique PIN to join the call as well as an email confirmation with the details.

About ATI-052

ATI-052 is an investigational humanized anti-TSLP and anti-IL-4Rα bispecific antibody that simultaneously inhibits thymic stromal lymphopoietin (TSLP) and interleukin-4 receptor (IL-4Rα) with high affinity and potency. By targeting TSLP, which sits at the top of the inflammatory cascade, it inhibits a broad range of inflammation; by targeting IL-4Rα, it blocks downstream signaling of both IL-4 and IL-13, which are key cytokines involved in Th2-mediated inflammation and allergic diseases. The TSLP binding interface of ATI-052 allows it to extensively bind TSLP, uniquely binding all six light chain and heavy chain CDRs. ATI-052 demonstrates very slow dissociation kinetics from TSLP with a residence time up to 116x longer than comparator antibodies. It exhibits potential best-in-class potency and utilizes the same TSLP antigen-binding fragment (Fab) region as the Company’s monoclonal antibody bosakitug (ATI-045), retaining the dissociation kinetics, long residence time, and high potency advantages over comparator antibodies, but is engineered to bind more tightly to the neonatal Fc receptor (FcRn) to extend its half-life. ATI-052 has the potential to treat a variety of atopic, immunologic and respiratory diseases. Aclaris has the exclusive worldwide rights to ATI-052, excluding Greater China.

About Aclaris Therapeutics, Inc.

Aclaris Therapeutics, Inc. is a clinical-stage biopharmaceutical company developing a pipeline of novel product candidates to address the needs of patients with immuno-inflammatory diseases who lack satisfactory treatment options. The company has a multi-stage portfolio of product candidates powered by a robust R&D engine. For additional information, please visit www.aclaristx.com and follow Aclaris on LinkedIn.
        
Cautionary Note Regarding Forward-Looking Statements

Any statements contained in this press release that do not describe historical facts may constitute forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. These statements may be identified by words such as “anticipate,” “believe,” “expect,” “intend,” “may,” “plan,” “potential,” “will,” and similar expressions, and are based on Aclaris’ current beliefs and expectations. These forward-looking statements include expectations regarding its development plans for ATI-052, including its intention to prioritize development of ATI-052 initially in EoE, the timing to initiate a Phase 2b trial of ATI-052 in EoE and the timing and plans to pursue development of ATI-052 in additional indications, the therapeutic potential for ATI-052, including the potential for ATI-052 to be best-in-class, the potential for ATI-052 to provide additive or synergistic activity through the simultaneous inhibition of TSLP and IL-4Rα, and the potential for ATI-052 to treat atopic, immunologic, and respiratory diseases. These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements. Risks and uncertainties that may cause actual results to differ materially include uncertainties inherent in the conduct of clinical trials, risks associated with interim, topline and preliminary data, Aclaris’ reliance on third parties over which it may not always have full control, Aclaris’ ability to enter into strategic partnerships on commercially reasonable terms, the uncertainty regarding the macroeconomic environment and other risks and uncertainties that are described in the Risk Factors section of Aclaris’ Annual Report on Form 10-K for the year ended December 31, 2025 and other filings Aclaris makes with the U.S. Securities and Exchange Commission from time to time. These documents are available under the “SEC Filings” page of the “Investors” section of Aclaris’ website at www.aclaristx.com. Any forward-looking statements speak only as of the date of this press release and are based on information available to Aclaris as of the date of this release, and Aclaris assumes no obligation to, and does not intend to, update any forward-looking statements, whether as a result of new information, future events or otherwise.

Aclaris Therapeutics Contact:

Will Roberts
Senior Vice President
Corporate Communications and Investor Relations
(484) 329-2125
wroberts@aclaristx.com

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Aclaris ATI-052 show in the Phase 1b atopic dermatitis trial?

ATI-052 produced a 45% placebo-adjusted mean improvement in skin severity at day 57, measured by the Eczema Area and Severity Index. The active arm improved 58% versus 13% with placebo. Mean itch improvement was 43% placebo-adjusted at day 57.

What is Aclaris planning next for ATI-052?

Aclaris intends to prioritize initiating a Phase 2b trial in eosinophilic esophagitis early next year. The company also plans to provide an update on a potential additional indication in the near term.

Why were patients excluded from Aclaris ATI-052 atopic dermatitis analysis?

Four patients were excluded from the prespecified per-protocol analysis for reasons defined before unblinding. In the ATI-052 arm, one took only two doses and another did not meet eligibility criteria. Two placebo patients began rescue medication early.

How were the Aclaris ATI-052 Phase 1b trials designed?

Both trials were randomized 3:1, double-blind and placebo-controlled. AD patients received five weekly 480 mg doses or placebo during weeks 0 through 4, with primary analysis at day 57. Asthma patients received one 480 mg dose or placebo, with endpoints assessed through day 29; eligibility required mild-to-moderate asthma and baseline exhaled nitric oxide of at least 35 parts per billion.