Using gene scissors to correct CGD

Dr Linzhao Cheng will research a new way to mend defective CGD genes using state of the art DNA-scissor technology. Awarded in October 2010

Project leaders: Dr Linzhao Cheng, Dr Harry Malech and Dr Jizhong Zou
Locations: Johns Hopkins University-School of Medicine, Baltimore and Laboratory of Host Defences, National Institute of Allergy and Infectious Diseases, National Institutes of Health, USA
Duration: 1 year
Total project cost: £50,000
Official title: Developing Novel Gene Therapy of X-linked CGD by Targeted Correction in Patient-specific Induced Pluripotent Stem Cells

Conventional gene therapy for CGD uses viruses to carry the corrective gene into a patient’s stem cells.  This project explores an exciting new approach to gene therapy using special DNA-scissor proteins, called zinc finger nucleases (ZFNs). This new technology has the ability to place the genes in ‘safe harbours’ of the cell’s DNA. 

These gene scissor proteins attach or bind to specific places on chromosomes (an organized structure of DNA and protein found in cells). Working like a pair of scissors they can be used to cut out areas of DNA that do not work properly, allowing it to be repaired by the cell’s repair own machinery when a normal, healthy copy of DNA is delivered into the cells. 

What this research means to people with CGD 

Most work involving gene therapy is aimed at the most common form of CGD, X-linked CGD. However, this approach has the potential to help all forms of CGD regardless of the mutation involved and can be regarded as patient specific gene medicine.

This technology has potential advantages over virally delivered gene therapy in that it is more highly targeted and specific. By repairing the genetic fault where it occurs in a person’s DNA the gene remains exactly where it is meant to be in a person’s genetic makeup and because of this it has the potential in the long term to improve safety of gene correction treatment substantially.

Background to the work

Zinc finger nucleases were originally developed in 1986 in the UK's Medical Research Council's Laboratory of Molecular Biology in Cambridge. They are proteins that attach or bind to specific places on chromosomes and can cut DNA at specific locations - hence the name DNA scissors.  They can be used to cut out the bad gene allowing it be repaired by the cell’s own machinery.

Zinc finger nucleases have to be designed specifically to do the precise ‘cutting’ needed.  Until recently this was very expensive and the ZFNs could only be obtained through a commercial company. However through a collaboration of scientists in the field a consortium has been set up at the Massachusetts General Hospital in Boston that produces these reagents at a fraction of their commercial cost www.zincfingers.org Dr Cheng is an active member of this group: ‘This new technology, using ZFNs, has the ability to place the affected gene affected in X-linked CGD in ‘safe harbours’ of the cell’s DNA’.

To date the technology has only worked in a laboratory setting and it is very much at a developmental stage to treat genetic disorders such as CGD however its potential is widely acknowledged and may allow the benefits of gene therapy to be realised. 

Researchers believe it is the pairing of the two technologies of induced pluripotent stem cells and gene therapy to treat genetic disorders such as CGD that offers the real promise for the future.  To treat CGD this would involve producing patient specific iPSCs, repair of the specific genetic defect in CGD using ZFNs and then differentiating these gene corrected cells into stem cells capable of making all the different types of blood cells. These cells would then be transplanted back into the CGD patient to restore their ability to fight off infections.

To date ZFNs are being used to test approaches to gene therapy for conditions such as X-SCID, haemophilia, sickle cell anaemia, HIV and amyotrophic lateral sclerosis.

Further information and links

‘Putting the fingers on gene repair’ www.sciencemag.org/content/310/5756/1894.full

‘New Way to Edit DNA, Hope for Treating Disease’ New York Times Article www.nytimes.com/2009/12/29/health/research/29zinc.html?_r=2