WAYNE, Pa. (June 2, 2025) — Aclaris Therapeutics, Inc. (NASDAQ: ACRS), a clinical-stage biopharmaceutical company focused on developing treatments for immuno-inflammatory diseases, has announced the initiation of a Phase 2 clinical trial of its leading drug candidate, bosakitug (ATI-045).
This investigational monoclonal antibody will be evaluated for its efficacy and safety in patients with moderate-to-severe atopic dermatitis (AD), a chronic and often debilitating inflammatory skin condition that affects more than 200 million people globally.
The trial follows strong results from a previous open-label Phase 2a study, where bosakitug showed high clinical response:
-
94% of participants achieved EASI-75 (75% improvement in eczema severity),
-
88% achieved clear or almost clear skin as measured by Investigator Global Assessment (IGA) scores of 0 or 1.
“We believe bosakitug could be a best-in-class anti-TSLP therapy,” said Dr. Jesse Hall, Chief Medical Officer at Aclaris.
“Its strong efficacy profile, superior binding characteristics, and potential for longer dosing intervals position it well to address a significant unmet need in the AD treatment landscape.”
About Aclaris Therapeutics
Aclaris Therapeutics is a U.S.-based clinical-stage biopharmaceutical company developing treatments for immune-mediated conditions with high unmet needs. Its diverse pipeline includes monoclonal antibodies, oral kinase inhibitors, and next-gen bispecifics targeting key inflammatory pathways.
As of Q1 2025, Aclaris has $190.5 million in cash reserves, supporting operations through 2028 without additional financing.
The company is actively seeking strategic partnerships to co-develop respiratory indications of bosakitug outside China.
About Bosakitug (ATI-045)
Bosakitug is a humanized monoclonal antibody designed to block thymic stromal lymphopoietin (TSLP), a cytokine that plays a central role in allergic and inflammatory responses. TSLP is a validated target in multiple diseases, including eczema, asthma, and nasal polyps.
Bosakitug stands out due to:
-
High binding affinity to TSLP
-
Very low dissociation rate, enabling long residence time
-
High neutralization potency
-
A half-life that supports extended dosing intervals
In addition to AD, bosakitug has shown promise in respiratory diseases. Aclaris’ Chinese partner Chia Tai Tianqing (CTTQ) has already advanced bosakitug into Phase 3 trials for severe asthma and chronic rhinosinusitis with nasal polyps (CRSwNP).
About Atopic Dermatitis (AD)
Atopic dermatitis is the most common type of eczema. In the U.S. alone, it affects around 27 million people, with nearly 40% experiencing moderate-to-severe symptoms. Patients often suffer from:
-
Dry, itchy, cracked skin
-
Raised bumps and redness
-
Sleep disruption
-
Social stigma and emotional stress
There remains a critical need for new treatment options that offer improved efficacy and longer-lasting relief with fewer side effects.
Details of the Phase 2 Trial
The ongoing Phase 2 trial is randomized, double-blind, and placebo-controlled. It will enroll approximately 90 patients with moderate-to-severe AD across multiple global sites. The primary endpoint is percent change in Eczema Area and Severity Index (EASI) at week 24.
Secondary endpoints include:
-
EASI-50, EASI-75, and EASI-90 response rates
-
Investigator Global Assessment (IGA) scores
-
Body Surface Area (BSA) improvements
-
Peak Pruritus Numerical Rating Scale (PP-NRS) scores
-
Overall safety and tolerability profile
Note: Top-line results are expected in the second half of 2026.
How Bosakitug for Atopic Dermatitis Impacts the Pharmaceutical Industry
Aclaris Therapeutics’ launch of a Phase 2 trial for bosakitug (ATI-045) marks a pivotal moment in the pharmaceutical industry. The drug targets thymic stromal lymphopoietin (TSLP)—an upstream immune trigger—signaling a strategic shift toward more precise biologic therapies. This direction could reshape treatment paradigms for chronic inflammatory diseases.
New frontiers in precision immunology
Bosakitug reflects a broader industry trend toward upstream immune modulation, specifically through targeting TSLP—a key master switch in the inflammatory cascade. Unlike downstream inhibitors that address only parts of the problem, upstream TSLP inhibition can potentially suppress multiple proinflammatory pathways at once.
This makes bosakitug a blueprint for precision immunology approaches in treating complex diseases like atopic dermatitis, asthma, and beyond.
Biologics investment is set to rise
The positive momentum behind Bosakitug could further accelerate industry-wide investments in monoclonal and bispecific antibodies. As small-molecule R&D faces higher costs and diminishing returns, biologics are becoming more attractive due to their specificity, lower side effects, and patent durability.
Bosakitug’s progress may lead to more venture capital deals, R&D alliances, and licensing activity in immuno-dermatology and respiratory therapeutics.
Dosing innovation will influence market adoption
Bosakitug's unique pharmacokinetic profile—including its long residence time and low dissociation rate—could support extended dosing intervals.
Fewer injections mean better patient adherence and potentially reduced treatment costs. In an increasingly value-driven market, dosing convenience is a major competitive advantage. This innovation is likely to influence how future biologics are designed and evaluated by both providers and payers.
Pipeline expansion through dual-target strategies
Aclaris is already advancing ATI-052, a bispecific antibody that combines TSLP and IL-4R targeting. This dual-pathway inhibition represents a new wave of therapies designed to block multiple immune signals simultaneously.
Such strategies could redefine standard care in diseases where a single-target biologic fails to deliver lasting results. Bosakitug is a stepping stone toward this more sophisticated pipeline development.
Smart global commercialization through partnerships
Rather than pursue every market independently, Aclaris has chosen a selective licensing strategy. The company retains global rights outside Greater China while partnering with Chia Tai Tianqing (CTTQ) for development in Asia.
This approach lowers risk, reduces time-to-market in high-potential regions, and increases the chance of success by tapping local expertise. It sets an example for mid-sized biotech companies with breakthrough assets.
Challenging current biologics with a new mechanism
If approved, bosakitug could either rival or complement existing therapies like Sanofi's Dupixent®, which also treats AD via IL-4/IL-13 inhibition. However, bosakitug’s upstream mechanism may offer broader immune modulation, improved durability, and fewer injections.
Its success could shift market dynamics, forcing larger players to re-evaluate their positioning or explore combination therapies involving upstream and downstream immune blockers.
