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Treating sickle cell disease with gene therapy

Dr Derrick Aarons

Sunday, March 12, 2017    

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After nearly two years of debate about its possible benefits and risks, the gene editing technique is now here to stay.

An article in the December 27, 2015 edition of the Sunday Observer told of the first recorded use of the inexpensive CASPR-Cas9 gene editing technology to cut and ‘splice out’ bad genes and replace them with healthy genes.

INHERITED DISEASE

A gene is a unit of heredity that is passed down from parent to child, and which carries characteristics that become apparent in the child. Each cell of the human body has around 25,000 genes, and each of those genes carry information that determines the individual traits or features of the person. So there is a gene for eye colour, hair colour, skin colour, and so on.


However, when some genes are defective or they undergo changes or mutation, illnesses can occur. Illnesses may also occur when there are missing genes which should have played a particular role. Some of the problems with genes may also be inherited from a parent.

One such illness well known to us in Jamaica is sickle cell disease. This is a severe hereditary disease in which the haemoglobin protein that is present in red blood cells to carry oxygen around the body is mutated and abnormal. Red blood cells are customarily round and circular in shape to flow smoothly through our blood vessels, but when oxygen levels are low in the bloodstream, the abnormal haemoglobin that is present in people with sickle cell disease cause the red blood cells to bend into a sickle crescent shape, making it difficult for them to flow through the tiny blood vessels of the body, and consequently may cause severe joint pains and other complications.

GENE THERAPY

The concept behind gene therapy is to use the technology of genetic engineering to replace abnormal genes with healthy ones.

Whilst this concept has been around for 30 years, the process became much more accessible with the development of the inexpensive CASPR-Cas9 gene editing technology around two years ago.

In April 2015, scientists in China were able to use the technology to splice out ‘bad’ genes that were present in human embryonic stem cells and replace them with healthy ones. The stem cells, however, were never implanted into women at the time for their development into humans.

In December 2015, a speaker at the annual symposium of the American Society of Hematology described possible work in which an infant with sickle cell disease would have his or her blood stem cells edited to repair the haemoglobin gene, thereby preventing the formation of blood cells that would have caused sickling. The specific work would involve harvesting the blood stem cells of the diseased infant, editing them outside the body with a normal DNA sequence, then returning them to the infant in a bone marrow transplant.

ETHICAL CONCERNS

As this technique involved editing the haemoglobin gene within the somatic stem cell rather than in the embryonic stem cell, this choice was deemed by many to be the more ethically acceptable approach. Many people are very concerned that the gene editing technique may be used to make long-lasting hereditable changes at the embryo stage or on germ cells (human sperm or eggs), and some find this unacceptable.

This notwithstanding, in February 2016, the United Kingdom Fertilisation and Embryology Authority, who are the UK regulators on fertility matters, granted permission for scientists in London to edit the genomes (the complete set of genetic instructions, which includes all genes) of human embryos for research purposes. The developmental biologists were allowed to use the gene editing technique in healthy embryos to alter genes that are active within the first few days after fertilisation of the egg.

The approved research would utilise healthy human embryos that had been left over from in vitro fertilisation procedures performed in fertility clinics. However, the caveat was that the researchers should stop the research after seven days of study, and the researched embryos destroyed. The study would illuminate how the modification of genes could assist in developing treatments for infertility.

MOST RECENT SUCCESS

A report in the most recent edition of the New England Journal of Medicine informed that a teenage boy with sickle cell disease appeared to have been cured using the gene therapy technique. The treatment had stopped the painful symptoms of the disease, and the teenager was doing well.

Success stories such as this are normally the first step in efforts to reproduce the benefits obtained in individual cases by conducting clinical trials of the treatment on large groups of affected people. Hopefully we will hear of such studies and their outcomes in the near future.

Until preliminary results are verified, however, scepticism will exist regarding whether the positive results obtained in one person will be translated to many more people. Time will tell.

Derrick Aarons MD, PhD is a consultant bioethicist/family physician, a specialist in ethical issues in medicine, the life sciences and research, and is the Ethicist at the Caribbean Public Health Agency – CARPHA. (The views expressed here are not written on behalf of CARPHA)

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