Infex Therapeutics Achieves Positive Phase IIa Results for RESP-X in Pseudomonas-Colonised Bronchiectasis Patients

Quarterly inhaled dosing of a monoclonal antibody is no longer a theoretical fill-finish challenge: Infex Therapeutics has reported positive Phase IIa data for RESP-X (INFEX702), a first-in-class anti-virulence mAb targeting Pseudomonas aeruginosa in non-cystic fibrosis bronchiectasis (NCFB), with results presented at the American Thoracic Society 2026 International Conference on 20 May in Orlando.

The randomised, double-blinded, placebo-controlled study, conducted at Liverpool University Hospitals NHS Foundation Trust, evaluated two dose levels, 6 mg/kg and 10 mg/kg, across two cohorts. The trial met its primary and all secondary objectives. No severe or life-threatening treatment-emergent adverse events related to the study drug were recorded, no patients withdrew due to adverse events, and no infusion reactions were observed at either dose level. All potentially related TEAEs were mild to moderate and showed no dose-responsive pattern.

Pharmacokinetic data are directly relevant to biologics manufacturing planning. RESP-X demonstrated a half-life of 28.8 days, with dose-proportional exposure increases across the dosing range and PK profiles in NCFB patients consistent with Phase I healthy volunteer data. That long half-life underpins the quarterly dosing interval and will shape batch sizing, cold-chain logistics, and fill-finish scheduling as the program advances. No immunogenicity was detected, removing a common regulatory hurdle for mAb programs at this stage.

Lung deposition data confirmed target coverage, and exploratory efficacy endpoints showed reduced exacerbation rates in Pa-positive patients, an early signal in a population for which no approved preventative treatment currently exists. For regulatory affairs leads, the absence of an approved comparator in NCFB will bear on Phase III trial design, endpoint selection, and eventual labelling strategy.

Infex has indicated the data support advancement into the next efficacy study, though specific Phase III timelines and trial sites have not yet been disclosed. Manufacturing teams and CMOs engaged in inhaled biologics should note that the delivery format, combined with quarterly dosing, will impose distinct process validation and sterility assurance requirements under 21 CFR Part 211 and ICH Q10 frameworks as the program scales.

The Phase III design, including dose selection between the two tested levels and primary endpoint definition, will be the next measurable checkpoint for teams tracking this program.

Source: Infex Therapeutics via company press release, 21 May 2026. Data presented at ATS 2026 International Conference, Orlando, Florida, 20 May 2026.