Aclaris Therapeutics Details TSLP/ITK Pipeline with Multiple Clinical Readouts Expected in Late 2026

Aclaris Therapeutics outlined development priorities and upcoming milestones for its biologics and oral small-molecule pipeline during a fireside chat at Guggenheim's Emerging Outlook Biotech Summit, with multiple clinical readouts anticipated in the back half of 2026. The company is executing a two-pronged strategy spanning a TSLP-targeted antibody platform and an ITK-focused kinase inhibition franchise.

On the biologics side, Aclaris is developing a TSLP monoclonal antibody, referred to as "bosakitug," in a 90-patient randomized Phase II study for moderate-to-severe atopic dermatitis (AD), with results expected in late 2026. The study is powered on EASI reduction, uses a 2-to-1 randomization against placebo, is monotherapy, and runs for 24 weeks. The antibody has a 20–23 day half-life and a long "residence time" on TSLP of more than 400 hours. The company benchmarked the molecule against clinical candidates and Tezspire, stating the antibody was "70 times more potent than Tezspire" in those tests.

Results from an earlier Phase IIa open-label study (conducted while the CEO was at Biogen) showed that after six months of therapy, the program demonstrated a "94% EASI-75" score reduction and an Investigator's Global Assessment (IGA) 0/1 rate of 88%. The company expects the molecule could potentially support a dosing interval of two to three months, noting that in the earlier IIa study, EASI-75 responses persisted 12 weeks after the last dose at week 24.

Aclaris is also developing a bispecific antibody, ATI-052, built from the same TSLP monoclonal antibody paired with an IL-4 receptor (IL-4R) construct. The molecule includes a YTE mutation, and the company observed a 26-day half-life in the dataset recently reported from the first three single-ascending dose (SAD) cohorts. The bispecific retains the TSLP antibody's long residence time and showed strong target engagement in healthy volunteers. Injection site reactions were the most common adverse event in the healthy volunteer study, described as mostly Grade 1 and resolving within a day or two without medication. Additional data from the rest of the study are expected in the coming months.

Two Phase 1b studies are planned for ATI-052. The first is a placebo-controlled study in severe atopic dermatitis already underway, enrolling 9 active and 3 placebo patients, with five weekly doses intended to assess population pharmacokinetics, target engagement on both TSLP and IL-4R, and early efficacy signals including EASI metrics. The second is a moderate asthma study expected to start "imminently," enrolling a higher T2 population (FeNO > 35 and eosinophils > 150) in a single-dose study looking at FEV1 and FeNO reduction.

On the oral small-molecule side, Aclaris is advancing an ITK franchise led by ATI-2138, a first-generation covalent inhibitor described as a Phase IIb-ready asset. ATI-2138 has "high single-digit nanomolar potency" for ITK as well as JAK3, and is designed to hit JAK3 without cross-reacting to other JAK family members. In an open-label AD study, ATI-2138 produced approximately 70% EASI reduction and meaningful itch improvement.

Aclaris is also advancing next-generation ITK-selective compounds toward IND filings, with IND-enabling activities ongoing and entry into the clinic expected after an IND in the coming months for the lead program. The company is focused on covalent inhibitors that target a cysteine in the kinase pocket, described as a key differentiator from reversible ATP-competitive approaches that have historically struggled.

Aclaris will also announce full results from its Phase 1a trial of ATI-052 and the selection of its lead indication for the ITK/JAK3 inhibitor ATI-2138 on April 28, 2026, before market opening. The company will hold a conference call and webcast that morning at 8:30 AM EST to discuss these updates.