This project is being helped by a generous donation in loving memory of Kade Jeffries.
Research helped by CGDRT funding has shown for the first time that special gene cutting enzymes known as zinc finger nucleases (ZFNs) can be used to correct X-CGD. This method of gene therapy may have advantages over the use of conventional gene therapy using viruses.
Researchers from the National Institutes of Health (NIH) and at the John Hopkins University School of Medicine used this new gene scissor technique to correct X-CGD by inserting a single healthy corrective gene at a safe, specifically defined location in a cell’s DNA. The work published in the journal ‘Blood’ holds promise in treating not only CGD, but also many other genetic disorders.
Dr Harry Malech, who heads the Genetic Immunotherapy Section at the NIH and senior study author said ‘We now know that when viruses are used to carry corrective genes into cells they can insert new genetic material at random locations within a cell’s DNA and that this can put patients at risk of developing of developing genetic mutations that may lead to serious blood disorders. The aim of this new approach is to develop a more precise and safer way of performing gene therapy for CGD that is not dependent on the use of viruses’.
What the researchers did
Bone marrow stem cells of a patient with X-CGD were genetically reprogrammed to become induced pluripotent stem cells (iPS cells). These are cells produced by turning back the biological clock of adult cells reverting them into a primitive state. These patient-specific iPS cells can be grown in large numbers in culture and retain their ability to differentiate into any cell type of the body, including blood stem cells known as haematopoietic stem cells (HSC).
Specific growth factors were then added to the iPS cells to make them become mature neutrophils, a cell type affected in CGD. The researchers then confirmed that these cells carried the same genetic defect as the starting cells. That is they couldn’t produce the superoxide signal necessary to kill microbes.
‘This is the first study in which the disease phenotype has been reproduced in neutrophils differentiated from X-CGD patient specific stem cells’, said Dr Malech.
‘We used a gene scissor enzyme known as a zinc finger nuclease to cut the patient’s DNA so that the gene gp91phox could be inserted at an exact location into the DNA of the patient derived iPS cells to correct the mutation causing X-linked CGD. We then selected the iPS cells with the desired gene insertion. Next we made the selected cells ‘differentiate’ i.e. grow into a certain type of cell, in this instance, neutrophils. These were then found to be able to produce superoxide as normal healthy cells.’
Although successfully using the repaired iPS cells to permanently restore the patient's immune system is still many years away. Dr Malech highlights the significance of their study:
‘Performing gene therapy on the patient's cells means that there is no need to search for a matching donor; patients provide their own means for treatment. Using ZFNs to insert the normal gene also improves control and testing of the gene correction process, leaving no new genetic materials or changes to the iPS cell's genome except for the desired repair.
This is the first study that has used ZFNs in specifically targeted gene transfer to correct X-CGD. Demonstrating that this approach to gene therapy works with a single-gene disease such as X-CGD means that the results from our study offer not only a potential treatment for this disease, but more importantly, a technique by which other single-gene diseases can be corrected using specifically targeted gene therapy on iPS cells.’
Publication
Zou J, Sweeney CL, Chou BK, Choi U, Pan J, Wang H, Dowey SN, Cheng L, Malech HL. Oxidase deficient neutrophils from X-linked chronic granulomatous disease iPS cells: functional correction by zinc finger nuclease mediated safe harbor targeting. Blood. 117(17): 4434-4441 (2011).
IMPORTANT NOTE :
The information contained on this website is intended only as a guideline, not as a substitute for medical advice. Always consult your doctor if you or your child has any CGD symptoms or concerns.
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Registered Charity No. 1003425 email:cgd@cgdrt.co.uk
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