How Does It Work?
ZolgensmaTM uses harmless, genetically engineered viruses to increase SMN protein levels. Upon injection into the blood (through “intravenous injection”), the viruses are able to travel around the body and get to a variety of different cells to help restore some of the SMN protein that is missing due to the condition.
Viruses are usually combatted by our immune systems. For example, we may suffer from a flu virus, but then our immune system starts to work and we get better after a week or so. What happens after this is that our bodies then produce proteins called antibodies that will very specifically recognise that particular virus in the future and prevent us from getting sick from the same flu virus at a later date. We develop an immunity to that particular flu virus.
The virus used in ZolgensmaTM gene therapy works in just the same way so as soon as it is introduced to a patient, their body starts to produce antibodies. If they have a second injection of the virus, it won’t work as they will have developed an immunity to it / antibodies will fight against it. This means that only a single injection of the treatment can be effectively used.
The virus that is packaged with the SMN gene to create ZolgensmaTM can be found in the environment; so, some people, including people with SMA, will have a natural immunity to the virus and will therefore not benefit from the ZolgensmaTM therapy.
Any child, young person or adult being considered for a trial or treatment with ZolgensmaTM always has a screening blood test to see if they have this immunity and would therefore not benefit from or be eligible for the treatment.