Boehringer Ingelheim Discontinues Inhaled Gene Therapy for Cystic Fibrosis After Phase 1/2 Trial

Feb. 17, 2026 —Boehringer Ingelheim has discontinued development of its inhaled lentiviral gene therapy for cystic fibrosis (CF) following the termination of a Phase 1/2 study.

The halted trial, known as Lenticlair 1, evaluated BI 3720931, an investigational inhaled lentiviral vector designed to deliver gene therapy directly to the lungs. According to a company spokesperson, the study did not generate clinical data sufficient to support further development.

Launched in late 2024, the trial enrolled five CF patients. The first portion tested three escalating dose levels in an open-label format, while the second part was a double-blind, placebo-controlled dose-expansion phase. Phase 1 focused on safety and adverse events, and Phase 2 assessed changes in forced expiratory volume (FEV1) at Week 8.

The company reported that the therapy’s safety profile aligned with expectations for an inhaled genetic treatment. However, efficacy outcomes did not justify continuation. The primary data readout occurred on February 3.

Boehringer stated that discontinuation of BI 3720931 does not affect other internal programs, though no additional clinical-stage gene therapies are currently listed in its pipeline.

The setback underscores ongoing challenges in developing genetic medicines for CF. In October, Arcturus Therapeutics reported lack of efficacy in a Phase 2 trial of its inhaled mRNA therapy. Earlier, Vertex Pharmaceuticals paused a Phase 1/2 study of VX-522, an mRNA therapy partnered with Moderna, due to tolerability concerns, with updated data expected in the second half of 2026.

Meanwhile, Sionna Therapeutics continues advancing multiple CF candidates, supported by a recent $135 million IPO.

Despite scientific advances in gene and mRNA delivery technologies, cystic fibrosis remains a complex and difficult target for inhaled genetic therapies.