Gene therapy is increasingly achieving success and major strides are being made. The 2020 Nobel Prize in Chemistry goes to the developers of the gene scissors Crispr-Cas. From January 1, 2020, Spinraza is available to all patients with Spinal Muscular Atrophy (SMA). In 2020, the European Medicines Agency EMA issued a conditional positive advice for the authorization of Zolgensma (muscle disease SMA). By mid-2020, 350 gene therapies will be investigated in clinical trials. Gene therapy is expected to be used with increasing success, but what exactly is gene therapy?
The success of gene therapy
- What is gene therapy?
- Purpose of gene therapy
- A virus as a transmitter (vector)
- Capecchi and Smithies
- Zolgensma and Spinraza
- Big steps forward, but still much to investigate
What is gene therapy?
Gene therapy is treatment with a medicine that contains as active substance a piece of DNA that is capable of correcting, replacing or removing the hereditary mutation in the non-working gene. When replacing the gene that does not work properly, the hereditary mutation in the gene is not corrected or repaired, but an extra working copy of the gene is introduced into the body. This extra gene makes the body able to produce the necessary and working protein itself. This allows a very specific response to all kinds of ailments and incurable hereditary diseases. It is now known where on the chromosomes the responsible faulty gene is located for many diseases. Gene editing (for example Crispr-Cas) is also receiving a lot of attention. Emmanuelle Charpentier and Jennifer Doudna won the Nobel Prize for Chemistry in 2020 with this technique, applied in crop breeding.
Purpose of gene therapy
The aim of the treatment is to reduce the symptoms of a hereditary disease as much as possible with no or minimal side effects. The intention is that one treatment will indicate lifelong improvement. By comparison, diabetes or hemophilia requires repeated injections. It would be nice if this could be replaced by a treatment that is one-off and repairs the errors in the body forever.
A virus as a transmitter (vector)
But how do you get a working gene into the body in such a way that it can also do its job? Well, it is known that a virus can be an excellent transporter of genetic material. In gene therapy,
two groups of viruses can be used as transmitters and vectors and thus two techniques:
- The adeno-associated virus (AAV).
- The lentivirus.
In addition, AAV can be used quite easily as a vector, but it is not always clear how long it provides protection (logical long-term effects are not yet known). The disadvantage of the spring virus is that the treatment is more complex. First, the patient’s bone marrow stem cells must also be harvested and treated with the lentiviral vector, after which the bone marrow is restored. Research is being used to improve both treatments.
Capecchi and Smithies
Already in the early 1980s, the treatment of rats and mice showed that genes can be transferred with viruses. Mario Capecchi, Oliver Smithies and Martin Evans received the Nobel Prizes in Medicine and Physiology in connection with Genetic Modification. Mario Capecchi, Oliver Smithies worked on a technique to replace genes on one chromosome with another. And Nobel Prize winner Evans worked on embryonic stem cells in mice and discovered how to extract them from an embryo. They collected a lot of information. The combination of the research results led to a leap forward in gene modification and gene therapy.
Zolgensma and Spinraza
Much is not yet known. For example, techniques can be improved, the long-term effects are unknown and the medicines are often expensive. Zolgensma will cost 2 million in 2020. Zolgensma is administered with a single injection, but that is not the end of it. Thorough preparation and aftercare are necessary to prevent serious side effects. Spinraza is given by epidural injection and is not a one-off treatment but must be repeated three times a year. In addition, there are side effects such as head and back pain and possibly increased pressure in the head due to reduced cerebrospinal fluid flow. Most side effects with Spinraza appear to be transient.
Big steps forward, but still much to investigate
There are estimated to be more than 7,500 different hereditary diseases, of which approximately 3,000 hereditary diseases could in principle be candidates for gene therapy. So there is still a lot to gain and a lot to learn, even though gene therapy is making great strides forward.