What exactly is gene therapy and gene editing, how do they differ and crucially how do they treat disease?

Gene therapy and gene editing are treatments that use our own cells to correct mistakes in our DNA letters that cause disease. The exact approach used depends on the condition and the type and number of mistakes in question. This takes us from first generation gene therapy for rare genetic disorders that only need one faulty gene to be corrected to the use of advanced gene editing techniques that modify multiple genes in complex cancers.  Since the discovery in 2013 of the Crispr/Cas9 technology, which cuts and pastes our DNA much like a word processor, the field has been advancing at breakneck speeds. The ease and precision of this new technology means that excited scientists are working late into the night: inserting, deleting, inactivating and generally moving our genes around like never before. Such developments can be applied to numerous fields, thus creating a new industry that can not only better treat humanity but better feed and fuel our world as well.

GENE THERAPY

MARGAUX MOREELS, WHO WAS CURED OF A FATAL IMMUNE DISORDER WITH THE GENE THERAPY STRIMVELIS.

Scientists first started thinking about rewriting our genes half a century ago but it wasn’t until 1990 that the first gene therapy was officially tested on a patient. It initiated the first wave of gene therapy treatments that has enabled scientists to correct faulty cells so completely that today such patients are able to live normal lives.

To do this, scientists withdraw the patient’s faulty cells and in the lab they take the DNA letters of a normal gene and put them into a virus. As naked DNA cannot be directly injected into humans, viruses are used because they naturally take their DNA into human cells when infecting them. Once some nifty genetic engineering has removed the virus’s dangerous properties, they become the perfect delivery vehicle for the corrected genes.

Therefore, the virus containing the corrected genes infects the patient’s faulty cells. In doing so, it literally dumps the correct genetic cargo to where the patient’s DNA letters are kept in the cell’s control centre, known as its nucleus. Scientists specifically target stem cells: they are the mother cells of the body and can develop into many different kinds of cells and self-renew. This means they act like factories of cells, constantly churning out normal cells for the entire life of the patient.

THE NUCLEUS OF A CELL - CREDIT: NICOLLE RAGER FULLER

Once this infection process, known as transduction, has been done with billions of cells, the doctor reinfused them back into the patient. These corrected cells flood the patient’s blood system and correct the disease. This first generation of gene therapy can treat numerous inherited diseases where there is just one faulty gene. Several of these kinds of treatment are already in human trials, others are reaching the marketplace and one has been approved for government funding in European countries.

Such gene therapies can vary in their technique. One such treatment that has helped restore sight to blind patients, doesn’t take the diseased cells out of the patient (known as autologous ex vivo gene therapy) but injects normal genes (also using the virus delivery vehicle) directly under the retina inside the eye. Although it is not yet considered to be a curative treatment, the improvements seen by thirty-one patients in a study are such that it been FDA approved. With those previously blind suddenly able to play sports and read books, customers were ready and waiting when the treatment, called Luxturna, became available this month. Scientists in London and Oxford have even managed to get virus corrected cells into a liquid aerosol so that it can be breathed into the lungs to treat Cystic Fibrosis. If all goes to plan, patient trials will get underway within the next two years. Other methods of gene therapy are being tested all the time and cover a huge range of conditions beyond genetic diseases including: HIV, arthritis and even spinal cord injuries, to name a few. But one advancement that is gaining huge ground is gene editing.

GENE EDITING

Recently scientists have discovered pioneering gene editing techniques, whereby instead of merely dumping the corrected DNA letters roughly in the correct place in the cell’s nucleus (on a strip of DNA know as a chromosome), and hoping that they are taken up, they are using molecular scissors which can cut out the faulty DNA letters and paste in the corrected ones in exactly the right spot. This is an important breakthrough for many diseases where there are several DNA faults as it means they can be corrected more precisely. Furthermore, it also lends itself to more complicated gene modifications for more complex diseases, like cancer.

Scientists in London dramatically saved the lives of patients with final stage leukaemia using molecular scissors called TALENS (transcription activator-like effector nucleases). As this blood cancer had totally ravaged the patients’ own immune cells, it was hugely beneficial that donor’s immune cells were used for the treatment. First, the scientists reprogrammed the cells to recognise and destroy the leukaemia. With a second edit, they removed any genes that could cause the donor cells to be rejected by the patient: all with the help of a virus delivery vehicle. Four treated patients who were at death’s door are in remission today making this a landmark moment for both cancer and gene editing.

The unprecedented precision another gene editing technique called Crispr/Cas9 (clustered regulatory interspaced short palindromic repeats), means that for the first time scientists are able modified human reproductive cells (egg, sperm and embryos). We now have a way to change the DNA of our off-spring, who controversially, have no say in whether they want these changes. This is all very well when obliterating a fatal heredity disease, but other conditions like Dwarfism and Down Syndrome are less clear cut. Sufferers, like the famous actress Kiruna Stamell, oppose it; stating that they would not be themselves if they had been altered from the offset. 

This also gives rise to genetic engineering for enhancement purposes as well; giving people extra muscly genes to make them a great athlete or for choosing other traits like the hair and eye colour for one’s children, hence the notion of designer babies. There are concerns that this could lead to a more unequal society where parents who can afford to pay for gene editing do so. Bioterrorism is another problem that could arise - the possibility that gene editing is used to create new diseases, the likes of which we have no cures.

Proceed with caution is the mantra coming from the research community. Those in the know recognise that this powerful new technology could be a double-edged sword. As scientists sharpen these genetic tools to better serve humanity, they are calling for a robust public debate. For this science to reach its full potential, it needs to be accepted by the public and for this to happen it first needs to be understood.

Gene therapy has started to treat patients of previously incurable diseases, but its imperfections mean so far it doesn’t work every time. Gene editing is striving to over come those failures but it’s our job to protect the human race and ensure it’s fail-safe.