Thursday, 29 March 2012

Gene Therapy for Cystic Fibrosis


Gene Therapy for Cystic Fibrosis


By Eleanor Sondergeld 42906401

Recently the ‘United Kingdom Cystic Fibrosis Gene Therapy Consortium’ has confirmed that in the coming months they will undertake the largest trial yet of a gene therapy treatment for Cystic Fibrosis (McKie 2012).

Cystic fibrosis (CF) is a heritable genetic disease, caused by a mutation in the gene which generates the protein; cystic fibrosis transmembrane conductance regulator (CFTR) (Yankaskas et.al 2004). This protein is involved in the transport of ions across epithelial cell membranes which line secretory cells. 

(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012)

As the ions are not able to move freely in and out of these cells, blockage occurs and a thick salty mucus forms (National Heart Lung and Blood Institute 2011) (Yankaskas et.al 2004). 

(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012

This cellular secretion commonly leads to severe inflammation and chronic infection in the respiratory, and gastrointestinal systems (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012). As there is currently no cure for CF, on going treatment involves managing inflammation and infection through a combination of medication, physiotherapy and in many cases lung transplants (National Heart Lung and Blood Institute 2011).

This new treatment involves the delivery of DNA expressing a functioning CFTR gene, into cells within the respiratory tract, in the form of a nebulized aerosol (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012). 

(BBC, 2012)


The DNA is taken up by the cell membranes and then transported to the cell’s nucleolus where it can express its copy of the CFTR gene(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012). Through translation the CFTR gene from this DNA, the CFTR protein can be manufactured and regular lung function is returned (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012) (McKie, 2012). This general principle of replacing non-functioning genetic material with functioning versions of that DNA is the basis of this research (Genetic Home Reference, 2012)(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).

The immune systems of CF patients are highly developed due to the constant infections that accompany the disease; thus introducing foreign bodies, particularly into the respiratory system is problematic (Hickman, 2012). Viral vectors that have been successfully developed as a carrier of DNA in other gene therapy treatments (Genetics Home reference, 2012) are targeted by the immune system and are therefore largely ineffective in delivering genetic material into the cells of CF patients (Hickman, 2012). For this reason, non-viral vehicles were developed; in this case liposomal transport has been shown in preliminary research to be the most effective vector for the CFTR gene (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).

The product used in this trial is GL67A/pGM169, a mixture of the cationic liposome GL67A and the plasmid DNA which expresses CFTR pGM169 (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012). This is delivered into the lungs of patients when they inhale this product as an aerosol through a jet nebulizer(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).

The plasmid used is a single stranded “complimentey” DNA (cDNA) and is used because the entire CFTR gene contains DNA that is not essential to CFTR synthesis and can interrupt the protein coding sequence (Hickman, 2012)(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012). It is then mixed with the compound hCEFI which has been shown to promote the longest period of CFTR expression in cells reached by the treatment (Hyde et.al 2008) as well as the liposomal GL67A vector (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).


A western blot to detect CFTR protein expression from human cell lines. pGM169 is in the two right hand lanes.

(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012)


Liposomes comprise a synthetically manufactured fatty substance which is able to encapsulate aqueous solutions (the cDNA plasmid pGM169) (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012), and which can be designed to include ligands on its surface (Mady, 2011). According to Prokop; the addition of specific ligands to these molecules allow for the more exact targeting of specific cell types (which for CF sufferers are epithelial cells) as well as a ‘stealth’ like property which prevents the immediate engulfment of the molecule by phagocytic cells (Prokop, 2012). Furthermore the liposomes are able to mix with the phospholipid cell membrane (Prokop, 2012) and efficiently deposit the genetic material into the cell, which can then be taken into the cell’s nucleus (Mady, 2011)(United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).

When mixed, the positively charged fatty liposomes (GL67A) and negatively charged plasmid cDNA form small, strongly bound particles; stable enough to resist aerosolisation and pass through the mucus covered membrane of cells of the respiratory tract (United Kingdom Cystic Fibrosis Gene Therapy Consortium, 2012).

This study is based the culmination of findings from numerous preliminary studies using the most current techniques and products available. If successful it potentially may lead to the development of a treatment that can be made available to the thousands of CF sufferers globally.











 BBC, 2012, Cystic Fibrosis, Viewed 16 March 2012
 <http://www.bbc.co.uk/learningzone/clips/gene-therapy-and-cystic-fibrosis/6014.html>


Yankaskas, JR; Marshall, BC; Sufian, B; Simon, RH; Rodman, D 2004, ‘Cystic Fibrosis Adult Care Consensus Conference Report’, Chest, vol.125, no.1, viewed 16th March 2012,
<http://chestjournal.chestpubs.org/content/125/1_suppl/1S.long>

McKie, R 2012, Cystic fibrosis treatment saved by last-minute £4 bailout, The Guardian, viewed 18th March 2012,
<http://www.guardian.co.uk/science/2012/mar/18/cystic-fibrosis-research-saved>

Mady, MM 2011,’Cationic liposomes as gene delivery system’, African Journal of Pharmacy and Pharmacology, vol. 5, no.17, pp. 2008-2012

UK Cystic Fibrosis Gene Therapy Consortium, 2012, Multi-dose Clinical Trial, viewed 16 March 2012, <http://www.cfgenetherapy.org.uk/clinical/multidose.html>

Prokop, A 2011, Intracellular Delivery: Fundamentals and Application, Springer Publishing, New York.

Hyde, SC, Pringle, IA, Abdullah, S, Lawton, AE, Davies, LA, Varathalingam, A, Nunez-Alonso, G, Green, AM, Bazzani, RP, Sumner-Jones, SG, Chan, M, Li, H, Yew, NS, Cheng, SH, Boyd, AC, Davies, JC, Griesenbach, U, Porteous, DJ, Sheppard, DN, Munkonge, FM, Alton, EW & Gill, DR 2008, ‘CpG-free plasmids confer reduced inflammation and sustained pulmonary gene expression’, Nature Biotechnology, vol.26, pp. 549-551

National Heart Lung and Blood Institute 2011, What is Cystic Fibrosis?,  viewed 16 March 2012,
< http://www.nhlbi.nih.gov/health/health-topics/topics/cf/> 

Genetics Home Refference 2012, What is gene therapy?, viewed 16 March 2012
<http://ghr.nlm.nih.gov/handbook/therapy/genetherapy>

Hickman, M 2012, Cystic Fibrosis in Detail, Podcast, Changing Futures, viewed 16 March 2012,
<http://www.youtube.com/watch?v=z7tbEuYS1JY>

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