Cystic fibrosis research has entered its most productive era. The median predicted survival for someone born with CF between 2020 and 2024 is now 65 years, according to the Cystic Fibrosis Foundation’s 2024 Registry data. That number was in the low 40s just two decades ago. The shift is driven largely by a class of drugs called CFTR modulators, which treat the underlying protein defect rather than just managing symptoms. But significant gaps remain, and dozens of experimental therapies are working through clinical trials to close them.
How CFTR Modulators Changed the Landscape
Cystic fibrosis is caused by mutations in a gene that produces a protein responsible for moving salt and water across cell surfaces. When that protein is missing or misfolded, thick mucus builds up in the lungs, pancreas, and other organs. CFTR modulators work by fixing or enhancing the defective protein so it can do its job.
The most significant of these drugs is the triple combination of elexacaftor, tezacaftor, and ivacaftor, widely known by its brand name Trikafta. In clinical trials, people with the most common CF mutation who took this combination saw their lung function improve by roughly 14 percentage points compared to placebo. Real-world studies in France confirmed the effect, with patients gaining around 13 to 15 points of lung function after starting the drug. Sweat chloride levels, a direct measure of how well the CFTR protein is working, dropped by more than 40 units in multiple studies.
The downstream effects have been dramatic. In 2024, only 61 lung transplants were reported among CF patients in the U.S. registry, a steep decline from the numbers seen before Trikafta’s approval in 2019. Earlier modulators like ivacaftor alone (approved in 2012) had shown strong results for a small subset of patients with specific gating mutations, improving lung function by about 10 to 11 percentage points. But those drugs helped far fewer people. Trikafta is eligible for roughly 90% of the CF population, which is what makes it transformative.
The 10% Who Don’t Have a Treatment
About 10% of people with CF carry mutations that don’t respond to any available modulator. Many of these are nonsense mutations, which essentially insert a premature “stop sign” into the genetic instructions for building the CFTR protein. The cell reads the instructions, hits the stop sign too early, and never produces a functional protein. Since modulators work by fixing or stabilizing a protein that already exists, they have nothing to act on in these cases.
The leading strategy for these mutations involves “read-through” agents, compounds that coax the cell’s machinery to skip past the premature stop sign and finish building the protein. One candidate, ELX-02, is a modified version of an older antibiotic class that was found to promote read-through. In lab studies using human bronchial cells, it restored about 7% of normal CFTR activity, enough to potentially make a clinical difference. It’s currently in Phase 2 trials for patients carrying the G542X nonsense mutation. Notably, when read-through agents are combined with standard CFTR modulators, the amount of rescued protein activity roughly doubles, suggesting future treatments may layer both approaches.
Other strategies for nonsense mutations include antisense oligonucleotides, short synthetic molecules that can prevent the cell from destroying the faulty genetic message before it gets read. One such therapy, SPL-84, is in a Phase 1/2 trial. Researchers are also exploring ways to block a cellular quality-control process called nonsense-mediated decay, which normally destroys messages containing premature stop signs. Suppressing that process could leave more raw material available for read-through drugs to work on.
Gene Therapy and mRNA Approaches
The ultimate goal for CF research is a one-time genetic fix. Rather than patching a broken protein, gene therapy would deliver a correct copy of the CFTR gene directly into lung cells. A Phase 1/2 trial of 4D-710, a single-dose inhaled gene therapy using a modified viral delivery vehicle, is currently enrolling adults with CF at multiple centers including UCSF. The challenge has always been getting the therapy deep enough into lung tissue and making it last, since the cells lining the airways naturally turn over every few months.
A parallel approach uses messenger RNA (mRNA), the same technology behind some COVID-19 vaccines, to deliver temporary instructions for building normal CFTR protein. The advantage is that mRNA therapy would work regardless of which mutation a patient carries, since it provides entirely new instructions rather than trying to fix existing ones. A Phase 1/2 trial of an inhaled mRNA therapy called MRT5005 tested this concept in 42 participants. The treatment was generally safe, though about a quarter of those receiving it developed mild to moderate febrile reactions that resolved within a day or two. However, no consistent improvements in lung function were observed. The results confirmed the delivery concept is feasible but highlighted the need for more potent formulations.
Fighting Lung Infections With Phages
Chronic lung infections remain one of the biggest threats to people with CF, even those benefiting from modulators. Pseudomonas aeruginosa, a bacterium that thrives in the thick mucus of CF airways, is notoriously difficult to eliminate and increasingly resistant to antibiotics. Bacteriophage therapy, which uses viruses that specifically infect and kill bacteria, is now being formally tested.
An NIH-supported clinical trial has begun enrolling adults with CF who carry Pseudomonas in their lungs. The trial starts as a Phase 1b safety study and will expand into a Phase 2 trial with up to 50 participants randomized to receive either a phage cocktail or placebo. The goal is first to confirm safety, then to measure whether the phages can meaningfully reduce the bacterial load in the lungs. If successful, phage therapy could become a targeted alternative for infections that no longer respond to conventional antibiotics.
Personalized Medicine Through Organoids
More than 2,000 distinct CFTR mutations have been identified, and roughly 1,000 of them are so rare they each affect fewer than five people worldwide. Running a traditional clinical trial for mutations that rare is impossible. Researchers have found a workaround: growing miniature organ models, called organoids, from a patient’s own cells and testing drugs on those models instead.
The process starts with a simple nasal brushing, a far less invasive procedure than collecting tissue from the lungs or intestines. The collected cells are cultured into three-dimensional organoids that mimic how airway tissue behaves. When a working CFTR modulator is added, the organoids swell with fluid, a measurable response that indicates the drug is restoring protein function. This “forskolin-induced swelling” assay has already validated responses to the triple modulator therapy and detected mutation-specific differences. For instance, organoids from a patient with a particular gating mutation responded to ivacaftor, while organoids from a patient with a severe nonsense mutation did not respond to the triple combination.
This technology opens the door to testing not just existing modulators but also experimental treatments like gene editing tools and read-through agents on an individual patient’s cells before prescribing anything. It’s the closest thing CF care has to a true personalized medicine platform.
Tackling Chronic Inflammation
Even when infections are controlled, the lungs of people with CF sustain damage from their own immune system. The inflammatory response in CF airways is disproportionately intense, driven by signals from bronchial cells, neutrophils (a type of white blood cell), and disrupted calcium signaling inside cells. Researchers are investigating multiple molecular targets to dampen this response without compromising the body’s ability to fight infection.
One line of research focuses on mitochondria, the energy-producing structures inside cells that also play a role in triggering inflammation. In CF airway cells, abnormal calcium flow into mitochondria ramps up production of damaging reactive oxygen species and activates inflammatory cascades. Drugs targeting these specific calcium channels are in preclinical development. Another approach looks at pro-resolving mediators, natural molecules like lipoxins and resolvins that the body uses to wind down inflammation after an infection. In CF, these resolution pathways appear to be impaired, and restoring them could help break the cycle of chronic damage. Researchers are also testing inhaled modified heparins (stripped of their blood-thinning properties) as a way to block elastase, a destructive enzyme released by neutrophils that is a major driver of CF lung tissue breakdown.
The Broader Pipeline
Beyond these major categories, roughly 14 compounds are in Phase 2 or Phase 3 clinical trials for CF. On the modulator side, a next-generation combination featuring a novel corrector called vanzacaftor is in Phase 3 testing, aiming to offer an alternative or improvement to current triple therapy. A new potentiator, deuticaftor, is in Phase 2. For infections, intravenous gallium is being studied for its ability to disrupt Pseudomonas metabolism, and inhaled nitric oxide is in trials targeting particularly stubborn mycobacterial infections that sometimes complicate CF. An antifungal agent designed specifically for inhaled delivery is being tested as a preventive treatment after lung transplantation.
The overall picture is one of a disease that has shifted from universally fatal in childhood to a chronic condition increasingly managed into middle age and beyond, with an active research effort focused on reaching the patients current drugs cannot help and addressing the complications that persist even when the underlying defect is partially corrected.