Infex Therapeutics has announced positive Phase 2a clinical trial results for RESP-X, its first-in-class anti-virulence monoclonal antibody being developed to address infections caused by Pseudomonas aeruginosa in patients with Non-Cystic Fibrosis Bronchiectasis (NCFB).

The company said the dose-ranging study achieved its primary and secondary endpoints, demonstrating that RESP-X was safe and well tolerated while also showing encouraging early signs of clinical benefit. The findings strengthen the case for advancing the therapy into the next phase of efficacy-focused studies.

The Phase 2a trial evaluated RESP-X across several parameters, including safety, pharmacokinetics, immunogenicity, lung deposition and exploratory efficacy measures. According to Infex Therapeutics, the treatment displayed favourable pharmacokinetic properties and showed no evidence of immunogenicity, supporting a convenient quarterly dosing schedule.

Importantly, patients colonised with Pseudomonas aeruginosa experienced reduced exacerbation rates, while the therapy also demonstrated complete target coverage. The results build upon previously reported Phase I data involving healthy volunteers.

Dr. Peter Jackson, Chief Executive Officer, Infex Therapeutics, said the findings mark a milestone for the company and reinforce RESP-X’s potential to address a major unmet clinical need.

He noted that the therapy’s safety profile, quarterly dosing capability and early efficacy signals support its continued clinical advancement, particularly for patients with limited treatment options.

Prof Colm Leonard, Chief Clinical Officer at Infex Therapeutics, highlighted growing interest in RESP-X among clinicians and researchers, describing the treatment as a potentially important advancement for bronchiectasis patients affected by Pseudomonas aeruginosa.

The randomised, double-blind, placebo-controlled trial was conducted at the Liverpool University Hospitals NHS Foundation Trust Clinical Research Facility in the UK. Researchers tested RESP-X at two dose levels—6 mg/kg and 10 mg/kg—in patients with NCFB colonised with the pathogen.

The company reported an encouraging safety profile across both treatment groups. No severe or life-threatening treatment-related adverse events were observed, and no patients withdrew from the study due to side effects. Any treatment-emergent adverse events linked to RESP-X were mild to moderate in severity.

Additionally, researchers found no infusion-related complications and confirmed effective lung deposition of the drug through bronchoscopy and bronchoalveolar lavage assessments.

Pharmacokinetic analysis demonstrated dose-proportional exposure levels and a long half-life of approximately 28.8 days. The higher-dose regimen achieved serum exposure levels that could support dosing every three months.

The study also confirmed complete coverage of the therapy’s biological target, known as PcrV, a protein associated with Pseudomonas aeruginosa’s Type 3 Secretion System—a mechanism the pathogen uses to establish infection and evade immune responses.

Patients treated with RESP-X recorded fewer disease exacerbations during the six-month follow-up period compared with the year prior to treatment.

Infex Therapeutics said it plans to engage with regulatory authorities to initiate the next stage of clinical development.

RESP-X, licensed from Japanese pharmaceutical company Shionogi, is being developed initially as a long-term therapy aimed at reducing flare-ups and disease progression in NCFB patients carrying Pseudomonas aeruginosa. The company also sees potential for broader applications across respiratory and infectious diseases, including cystic fibrosis, Chronic Obstructive Pulmonary Disease (COPD), asthma and hospital-acquired infections.

Non-cystic fibrosis bronchiectasis is a chronic respiratory condition characterised by irreversible airway damage and recurring lung infections. The disease affects up to six million people across major global markets, with approximately 30 percent of patients experiencing chronic Pseudomonas aeruginosa colonisation.

The bacterium remains a major healthcare challenge globally because of its resistance to multiple drugs and its ability to cause persistent and severe infections, particularly in patients with underlying respiratory conditions.

Despite the significant burden associated with these infections, there are currently no approved therapies specifically designed to prevent infection-related exacerbations in NCFB patients colonised with Pseudomonas aeruginosa, highlighting a major unmet need in respiratory medicine.