Infex Therapeutics reported positive Phase IIa results for RESP‑X, an investigational anti‑virulence monoclonal antibody targeting Pseudomonas aeruginosa in non‑CF bronchiectasis. The therapy was safe, well tolerated, showed complete target coverage, and reduced exacerbation rates, supporting next‑phase development.
Written By: Farha Farheen, PharmD
Reviewed By: Pharmacally Editorial Team
Infex Therapeutics has announced encouraging Phase IIa data (ISRCTN17978477) for RESP‑X (INFEX702), its investigational anti‑virulence monoclonal antibody targeting Pseudomonas aeruginosa (Pa) in patients with non‑cystic fibrosis bronchiectasis (NCFB). Results presented at the 2026 American Thoracic Society International Conference showed the therapy was safe, well tolerated, and associated with reduced exacerbation rates alongside complete target coverage.
Novel Anti‑Virulence Approach
RESP‑X is a humanized IgG4 monoclonal antibody licensed from Shionogi that binds the PcrV protein within Pa’s Type III Secretion System (T3SS), a critical virulence pathway enabling toxin delivery and immune evasion. Unlike antibiotics, RESP‑X does not kill bacteria directly but blocks toxin translocation, potentially lowering selective pressure that drives antimicrobial resistance.
Trial Design and Safety Outcomes
The randomized, double‑blind, placebo‑controlled Phase IIa study enrolled NCFB patients chronically colonised with Pa at the Liverpool University Hospitals NHS Foundation Trust Clinical Research Facility. Two dose levels, 6 mg/kg and 10 mg/kg, were evaluated across separate cohorts over a 180‑day study period.
No severe or life‑threatening treatment‑emergent adverse events (TEAEs) related to RESP‑X were reported. There were no infusion‑related reactions or discontinuations due to adverse events. All treatment‑related AEs were mild to moderate, with no dose‑dependent increase observed.
Pharmacokinetics and Immunogenicity
Pharmacokinetic analyses demonstrated a half‑life of 28.8 days, supporting quarterly dosing intervals. Bronchoscopy and bronchoalveolar lavage confirmed drug exposure in lung epithelial lining fluid 48 hours post‑administration. No anti‑drug antibodies were detected during the study.
All Pa isolates collected during the trial encoded the RESP‑X target PcrV, confirming complete target coverage. Pa‑positive patients experienced fewer exacerbations over the 180‑day study period compared with the prior year before dosing. While the reduction in exacerbation rate did not reach statistical significance (p=0.08), investigators highlighted the trend as encouraging in a population with no approved preventative therapies for Pa‑driven exacerbations.
Executive Commentary
Chief Executive Officer Dr. Peter Jackson said the results support continued development of RESP‑X: “These findings reinforce the potential of anti‑virulence strategies in chronic pseudomonal disease, where patients currently lack preventative options.”
Chief Clinical Officer Prof. Colm Leonard added that the respiratory community has shown strong interest in novel approaches targeting Pa virulence mechanisms.
Next Steps and Broader Potential
Infex plans to engage regulators on a next‑phase efficacy study in NCFB patients colonised with Pa. The company also sees broader development potential across cystic fibrosis, COPD, asthma, ventilator‑associated pneumonia, bloodstream infections, burns, and diabetic foot infections linked to Pa.
References
About the Writer
Farha Farheen, PharmD (LinkedIn) is a pharmacy professional with a strong interest in pharmacovigilance and clinical research. She has completed her Doctor of Pharmacy (Pharm.D) along with her internship as a Clinical Pharmacist. She has hands-on experience in adverse drug reaction (ADR) reporting, safety data documentation, and pharmacovigilance workflows, and is proficient in using VigiFlow. She is also a patent holder for an antibacterial formulation enriched with bioactive substances, granted by the German Patent and Trademark Office.