Development of a novel, potent, safe, long-lasting lentivirus-based gene therapy for cystic fibrosis

Cystic Fibrosis (CF) is a common genetic disease that affects over 8000 people in the UK. It is the result of a mutation in a single gene called CFTR that causes the build up of thick sticky mucus in the lungs. Eventually the lungs become repeatedly infected and inflamed, leading to lung failure and premature death. All current therapies are aimed at coping with the symptoms; there is no cure. In 2001, three research groups in the UK formed the CF Gene Therapy Consortium to develop a new kind of treatment based on introducing new (healthy) copies of the CFTR gene into the lungs of people with CF. Many advances have been made, and we have learned a great deal about the obstacles to this approach, but we are not yet in a position to offer an effective gene therapy for CF lung disease. The aim of this research application is to use a new kind of gene therapy based on a virus called lentivirus, which we think has the potential to be more efficient at delivering the gene into the lungs and to provide an effective treatment for CF lung disease. In order to make the lentivirus carrying the CF gene as effective as possible, it is wrapped up in two new coat proteins called F and HN, a process known as 'pseudotyping'. We have shown that when the lentivirus is pseudotyped with F and HN it is efficient at entering lung cells and the gene it carries can be expressed for many months, even years in some situations. Another key feature that this pseudotyped virus displays is that it can be repeatedly administered, a property we have not seen previously with other viruses. This has an important advantage for treating chronic diseases, such as CF where the effects last for the life-time of the individual. The objectives of this application are i) to engineer the virus so it is suitable for use in patients; ii) to improve virus production methods so that it can be made in sufficient quantities to use as a therapy; and iii) to understand the potential for side-effects associated with administering the virus. The research project is 18 months long and at the end of it we hope to have selected a final version of the virus that we can take forward to test in patients. If we are successful in manufacturing the virus and selecting a suitable version to give to patients, we envisage that it could be delivered to the lungs of CF individuals using a device called a nebuliser, which generates a fine mist that can be breathed in. The increased efficiency of this virus along with the ability to have an effect that is long-lived effect means that this could form the basis of a new, more effective treatment for CF.

Cystic fibrosis (CF) is the most common lethal inherited disease of Caucasian populations, affecting ~80,000 individuals worldwide. In the UK, the current median age at death is ~25 years. Current treatments are focused on symptomatic relief and are associated with a huge treatment burden, and high individual NHS patient costs. No treatment is available that targets the genetic defect.

We have developed a novel, IP-protected, lentiviral gene transfer vector, specifically pseudotyped to enable efficient airway cell uptake. We hypothesise that CFTR gene transfer into the CF lung by this vector system will provide an effective treatment for CF lung disease.

The vector directs stable gene expression in lung models at levels thought to be within the therapeutic range. Uniquely, this vector system suffers no loss of efficacy upon repeated administration; with transgene expression remaining ~2 logs higher than current competing vector technologies.

Prior to final candidate selection key aspects of the vector system must be enhanced. Firstly, the current vector system is not fully compliant with pharmacopoeial regulations; however, straightforward sequence manipulation will rectify this issue. Secondly, the current vector purification methodology is difficult to scale. Simple method development, utilising steps previously applied in the field, will provide a scaleable GMP compatible production process. Thirdly, concerns driven by clinical findings from the use of early-generation retroviral vectors, requires an understanding of the effect of the vector transgene expression cassette upon theoretical insertion site-specific clonal expansion. Consequently, insertion site profiling is prudent prior to seeking regulatory approval for clinical studies. We outline a milestone-driven, 18 months translational research programme to bridge our current pre-clinical data package to regulatory toxicology studies and first-in-man trials.

Who will benefit from this research?
The ultimate objective of this research is to develop a treatment for the serious life threatening disease cystic fibrosis (CF). CF is the most common lethal inherited disease of Caucasian populations, International patient registries indicate that there are ~80,000 CF subjects in the EU, North America and Australia/New Zealand. Approximately 10% of this population live in the UK. In addition, some estimates suggest that an additional ~200K CF subjects are unidentified in emerging pharmaceutical markets. Typically, CF individuals suffer from repeated bacterial infections of the conducting airways leading to lung failure. Current treatments are focused on symptomatic relief and are associated with a huge treatment burden, requiring several hours of self-administered therapy daily. In the UK, the median age at death is ~25 years. NHS costs per patient range from £15 - £50K per year, with an annual direct healthcare cost of ~£200M. No treatment is available that targets the genetic defect; bridging this gap has been shown to be the highest priority of patients and carers.

Our solution to this problem is a novel, lentiviral gene transfer vector (termed F/HN-SIV), specifically engineered to enable efficient airway cell uptake. F/HN-SIV directs stable gene expression in cells relevant to CF lung disease for ~2 years following a single application. We hypothesise that gene transfer of a copy of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene into the CF lung by this repeatedly administrable vector will provide an effective treatment for CF lung disease.

The F/HN-SIV vector is the class leading solution to the problem of delivering nucleic acid-based therapeutics to the lung. As a platform for lung delivery additional therapeutic intervention options include: (1) the delivery of CFTR or other transgenes to treat acquired or inherited lung diseases - eg alpha 1-antitrypsin to treat emphysema/ chronic obstructive pulmonary disease (COPD), (2) the delivery of inhibitory molecules to treat viral infections or pre-existing lung disease - eg RNAi/miRNA class sequences to teat influenza/asthma, and (3) the delivery of transgenes to lung cells acting as a secreted protein factory to treat systemic disease - eg Factor VIII or IX to treat haemophilias.

How will end-users benefit from this research?
While modern CF treatment regimens have extended the life expectancy of a CF child, CF remains a lethal disease with no cure. Typically, CF patients require twice-daily regimens of physiotherapy and nebuliser treatments, supplemented with numerous orally delivered medications, imposing a high therapeutic burden (3-4 hours treatment/day is not unusual) on them and their carers. Successful gene therapy will provide benefits ranging from a reduction in (i) the conventional treatment burden, and (ii) time in hospital, manifesting through an increased life expectancy, to prevention of lung disease if treatment is started early after diagnosis. Our experience is that there is enthusiasm for gene therapy amongst CF individuals, but also a sense of realism. If successful CF gene therapy will have a dramatic effect on patient well-being, and the potential benefits to end users are large.

Following this 18 month project, we estimate it will take ~2.5 years to complete the required safety toxicology studies before a first-in-man clinical trial can be initiated. If successful, a CF treatment based on F/HN-SIV technology could be marketed within 10 years.