At the 2026 European Respiratory Society (ERS) International Congress, Infex Therapeutics presented a new analysis of Phase IIa results for RESP-X (INFEX702) in P. aeruginosa (Pa)-colonized non-cystic fibrosis bronchiectasis (NCFB). This matters because, despite the 2025 approval of Insmed’s Brinsupri (brensocatib) as the first therapy for NCFB, no approved treatment yet targets Pa, the disease’s most consequential pathogen. The ERS 2026 data position RESP-X at the forefront of the Pa-colonized NCFB space, with a clean safety profile and encouraging preliminary efficacy signals, according to GlobalData, a leading intelligence and productivity platform.

RESP-X is a first-in-class, humanized IgG4 monoclonal antibody, in-licensed by Infex from Shionogi, that targets PcrV, the needle-tip protein of Pa’s type 3 secretion system (T3SS), which injects toxins into host cells and enables chronic infection. By capping this protein, RESP-X blocks toxin delivery and allows the immune system to clear the pathogen. Pa colonization in NCFB drives more frequent exacerbations, faster lung function decline, worse quality of life, and higher mortality, yet antibiotic strategies extrapolated from cystic fibrosis have failed to reliably control it in non-CF patients.

Connor Daniels, Healthcare Analyst at GlobalData, comments: “RESP-X is mechanistically distinct from both antibiotics and brensocatib’s DPP1 inhibition, positioning it as complementary rather than competitive. The target population is NCFB patients chronically colonized with Pa with a history of infective exacerbations, a subgroup responsible for a disproportionate share of disease burden and healthcare costs.”

The Phase IIa study enrolled nine patients in a randomized, double-blind, dose-ranging trial at a single UK site (Liverpool University Hospitals NHS Foundation Trust). It tested single IV doses of RESP-X at 6mg/kg and 10mg/kg against placebo, with topline results announced in May 2026 showing the study met both its primary and secondary objectives, with RESP-X proving both safe and well tolerated.

RESP-X showed a half-life of 23.0 days (6mg/kg) and 28.8 days (10mg/kg), with the 10mg/kg dose achieving 1.9% serum-to-lung exposure, supporting three-month dosing. Bronchoscopy confirmed drug presence in lung epithelial lining fluid within 48 hours, addressing a common failure point for systemic antibodies targeting pulmonary pathogens. All Pa isolates collected encoded PcrV and were confirmed to bind RESP-X. No infusion reactions, severe adverse events, or anti-drug antibodies were observed.

Pa-positive patients experienced 1.2 annualized exacerbations from Day 1 to Day 180, versus 3.4 in the prior 12 months, a reduction that did not reach statistical significance (P=0.08), unsurprising for an exploratory endpoint in a small, single-site study not powered for efficacy. Quality-of-life also improved, with SGRQ score reductions of 2.93 points (6mg/kg) and 6.91 points (10mg/kg).

RESP-X enters a bronchiectasis field newly validated by Brinsupri’s approval (FDA, August 2025; European Commission, November 2025), which establishes a regulatory and commercial pathway but does not itself address Pa colonization, leaving a distinct opportunity for RESP-X.

Daniels continues: “This raises a strategic question for Infex as to whether to position RESP-X as a combination or sequential option alongside DPP1 inhibition, which will shape its Phase IIb/III design. RESP-X also sits within a growing anti-virulence class alongside AstraZeneca’s gremubamab, which met its primary endpoint in the Phase II GREAT-2 trial.”

Daniels concludes: “Infex’s next steps are progressing to a larger, multi-center Phase IIb trial and securing the investment needed for late-stage development, as competition from larger players like AstraZeneca intensifies.”