Cystic fibrosis is a genetic condition where epithelial cells, including from the respiratory tract, have an abnormal function of a surface protein, the cystic fibrosis transmembrane conductance regulator (CFTR) protein resulting from abnormal gene expression. The trial will assess the clinical efficacy, safety & tolerability and gene expression following repeated nebulised doses of a gene product coding for a normal CFTR protein, with the primary outcome of the trial assessing lung function.

Cystic fibrosis (CF), a common, genetically inherited disease, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This gene encodes the CFTR protein, which is expressed on the apical surface of epithelial cells, and which has many functions, the most important of which is thought to be ion transport. Abnormal ion transport leads to thick secretions in the airways, infection, inflammation and eventually irreversible lung damage. There is currently no treatment that halts the natural progression of the disease; all available successful therapies merely slow the rate of decline in clinical condition.

To date, no viral gene transfer agents retain efficacy upon repeated administration. Our study will assess the safety and efficacy of a lipid-mediated vector harbouring a normal CFTR gene in repeated nebulised administrations. We have completed a single dose safety study which evaluated the safety and gene expression of a single dose of pGM169/GL67A administered to the nose and lung of individuals with cystic fibrosis.

This trial is will randomise 130-patients to receive either a gene product (pGM169/GL67A)encoding for CFTR or placebo in a double-blinded fashion. All subjects will receive 12 doses of nebulised gene therapy at intervals of 4 weeks over a 48 week period. After dose 12 there will be 2 formal follow up visits, at 14 and 28 days post-dose. In addition, patients will be followed up long-term.

Subgroups of patients will be enrolled for gene expression measurement in both nose (at least n=20) and lower airway via bronchoscopy (at least n=20).

The primary outcome of the trial is to evaluate the relative change in predicted Forced Expiratory Volume in 1-second (FEV1) after 12-doses. Secondary outcome measures will assess the efficacy of the gene product (by assessment of patients' physiological function, serological indices, radiological appearances of the lungs and self-reported assessment of quality of life), on the degree of gene expression and on the product safely.

Inclusion Criteria:

1. Cystic fibrosis confirmed by sweat testing or genetic analysis

2. Males and females aged 12 years and above

3. Forced expiratory volume in the 1st second (FEV1) between 50 & 90% predicted inclusive (Stanojevic reference equations).

4. Clinical stability at screening defined by:

   1. Not on any additional antibiotics (excluding routine, long-term treatments) for the previous 2 weeks
   2. No increase in symptoms such as change in sputum production/colour, increased wheeze or breathlessness over the previous 2 weeks
   3. No change in regular respiratory treatments over the previous 4 weeks
   4. If any of these apply, entry into the study can be deferred

5. Prepared to take effective contraceptive precautions for the duration of their participation in the study and for 3 months thereafter (as stated in GTAC guidelines)

6. If taking regular rhDNase (pulmozyme) is willing, and considered able by independent medical carers, to withhold treatment for 24 hours before and 24 hours after the gene therapy dose (nebulised doses only)

7. Written informed consent obtained

8. Permission to inform their general practitioner of participation in study

Exclusion Criteria:

1. Infection with Burkholderia cepacia complex organisms, MRSA or M. abscessus

2. Significant nasal pathology including polyps, clinically-significant rhinosinusitis, or recurrent severe epistaxis (nose bleeds) (nasal cohort only)

3. Chloride secretory response on nasal PD of > 5 mV (nasal cohort only; will only be known after first measurement)

4. Acute upper respiratory tract infection within the last 2 weeks (entry can be deferred)

5. Previous spontaneous pneumothorax without pleurodesis (bronchoscopic subgroup only)

6. Recurrent severe haemoptysis (bronchoscopic subgroup only)

7. Current smoker

8. Significant comorbidity including:

   1. Moderate/severe CF liver disease (varices or significant, sustained elevation of transaminases: ALT/ AST>100 IU/l)
   2. Significant renal impairment (serum creatinine > 150 mmol/l)
   3. Significant coagulopathy (bronchoscopic group only)

9. Receiving 2nd line immunosuppressant drugs such as methotrexate, cyclosporine, intravenous immunoglobulin preparations

10. Pregnant or breastfeeding