• Cystic Fibrosis

Cystic fibrosis (CF), a common inherited disease, is caused by mutations in the gene CF transmembrane conductance regulator (CFTR). This gene encodes the CFTR protein, which  is located on the apical surface of the epithelial cells and has many functions, the most important of which is thought to be ion transport. Abnormal ion transport leads to accumulation of thick secretions in the airways, infection, inflammation and eventually irreversible lung damage. There is currently no treatment that has been demonstrated to halt the natural progression of the disease; all available successful therapies merely slow down the rate of decline in clinical condition, which still leads to premature death. The first therapy to target the CFTR defect directly has recently been approved in the USA and the European Union: treatment with ivacaftor (marketed as Kalydeco) resulted in significant improvements in lung function, exacerbation rate, weight gain and quality of life in patients with the G551D mutation.1 Although this mutation is relatively rare, affecting 4%–5% of the global CF population, these results have proved the principles that direct targeting of CF at its root cause and restoring CFTR protein function can be clinically beneficial.

In contrast to the mutation-specific small molecule approach, gene therapy, which seeks to introduce a normal copy of the CFTR gene into the cells of the conducting airways, will be applicable for CF patients with any genetic defect. The many trials conducted to date have provided proof of principle for gene transfer to the airways based on molecular or electrophysiological measures.2 Most of the clinical trials assessing gene therapy have been with a single dose and were not designed to assess clinical benefit. In one case where this was the focus with a recombinant viral vector, results were disappointing. In addition, there are clearly immune recognition barriers to repeated application of most viral vectors including adenovirus and adeno-associated virus. Such an issue has not been observed with non-viral vectors.

The UK Cystic Fibrosis Gene Therapy Consortium (UKCFGTC, Imperial College, University of Edinburgh and University of Oxford; http://www.cfgenetherapy.org.uk) was formed over a decade ago from the three UK groups that had conducted CF clinical gene therapy trials. We work cohesively on a structured programme to bring CF gene therapy to clinical reality. Our initial efforts (as part of the Wave 1 programme) led to the selection of the best, currently available, gene transfer agent (a CFTR-expressing plasmid complexed with a cationic lipid), which has recently been assessed in a single-dose phase I and IIa safety study (Evaluation of safety and gene expression with a single dose of pGM169 or GL67A administered to the nose and lungs of the individuals with CF. EudraCT reference: 2007-004050-85). In parallel, we have performed a number of non-interventional studies, including tracking the responsiveness of outcome measures to intravenous antibiotics for an infective exacerbation and a larger, longitudinal observational study (run-in study) of multiple outcomes (such as physiological, structural, inflammatory and patient reported) in almost 200 CF patients. Based on these studies, we have identified outcome measures as well as patient characteristics for a subsequent trial involving the application of multiple doses of the gene transfer vector.

As CF is a lifelong disease and because the respiratory epithelial cells have only a limited life span, we reason that any gene therapy with a chance of clinical success will require repeated application. As, to date, no viral gene transfer agents retain efficacy upon repeated administration in man due to immune responses, we have conducted extensive work to identify the best currently available non-viral gene transfer agent. Extensive preclinical studies of different non-viral vectors indicated that the cationic lipid formulation, GL67A, was the most effective agent.3 GL67A has been aerosolised into healthy volunteers and CF patients.4 In our recent single-dose trial, the plasmid (pGM169) incorporated novel features specifically designed for prolonged duration of expression including the hCEFI transcriptional element consisting of CpG-free versions of the human cytomegalovirus enhancer and human elongation factor 1 α promoter. Preclinical studies demonstrated sustained levels of expression (to at least 2 months) with this new promoter, which could permit less frequent dosing. In addition, the DNA usually used in gene therapy trials is rich in unmethylated CpG dinucleotides, which are likely recognised by cellular defence mechanisms in humans and to which an inflammatory response is mounted. Such a response is thought to have contributed to the flu-like illness, reported in our previous trial in the group receiving DNA or lipid but not lipid alone.4 The new plasmid has been rendered entirely CpG free in an attempt to reduce such an inflammatory response.5 Data from the single-dose study indicate that, using such a CpG-free plasmid, a dose can be achieved at which such inflammatory responses are negligible.

Here, we describe the protocol of our current phase IIB clinical trial, a double-blind placebo-controlled parallel group study. This trial is being undertaken by the UKCFGTC incorporating the universities of Oxford, Edinburgh, Imperial College London and their associated National Health Service centres (NHS Lothian and Royal Brompton and Harefield NHS Foundation Trust). The aim of the trial is to assess the clinical benefit of repeated doses of nebulised, non-viral CFTR gene therapy over a 12-month period with forced expiratory volume in 1 second (FEV₁) as the primary outcome measure.

Inclusion and exclusion criteria are as shown in table 1.