Vertex Discontinues mRNA-Based Cystic Fibrosis Program

May 04, 2026-

Vertex Pharmaceuticals has discontinued development of VX-522, an inhaled mRNA-based cystic fibrosis therapy developed in partnership with Moderna, after persistent tolerability issues led to the winding down of its Phase 1/2 clinical trial. The program was designed for people with cystic fibrosis who are not eligible for currently approved CFTR modulator therapies, a population Vertex previously estimated at approximately 5,000 patients.

VX-522 was intended to deliver CFTR mRNA to lung cells using lipid nanoparticles, enabling cells to produce functional copies of the CFTR protein that is defective or absent in cystic fibrosis. Unlike CFTR modulators, which improve function of certain mutant CFTR proteins, an mRNA-based approach could theoretically benefit patients whose mutations do not produce a protein that can be modulated. The therapy was being evaluated as an inhaled treatment in adults with cystic fibrosis whose mutations are not responsive to CFTR modulators.

According to the company, the program was stopped because of persistent tolerability concerns. Vertex CEO Reshma Kewalramani said the tolerability issue involved lung inflammation, likely in response to the LNP delivery system. Vertex noted that early termination of the study prevents full assessment of VX-522’s efficacy and safety, leaving open questions about whether the mRNA payload itself could have provided meaningful clinical benefit if delivery had been better tolerated.

The discontinuation underscores one of the central challenges facing RNA and DNA therapies for pulmonary diseases: delivery to the lung without triggering local irritation or inflammatory responses. For cystic fibrosis, the need remains especially urgent for patients who cannot benefit from existing CFTR modulators. While VX-522’s termination is a setback, Vertex indicated that delivery remains the key scientific problem to solve for future nucleic acid-based approaches in this patient population.

Other companies continue to pursue genetic medicine strategies for cystic fibrosis, including DNA- and RNA-based approaches using alternative delivery systems. Krystal Biotech, for example, has been developing a modified herpes viral vector approach to deliver CFTR and is evaluating repeat dosing, with plans for a pivotal study expected to begin in 2027. Together, these programs reflect continued momentum in the field, but also reinforce that success in cystic fibrosis genetic medicine will depend not only on choosing the right nucleic acid payload, but on solving the delivery, tolerability, and repeat-dosing challenges unique to the lung.