It is difficult to say at the moment that the virus did or didn’t cause the cancer—this requires testing to see if there is a clear link to genomic changes that can be attributed to the AAV
The firm behind the therapy has kicked off such testing, and it could take a few months to indict or acquit the therapy.
This may or may not eventually prove the anti-GM/gene therapy lobby’s ‘gotcha!’ moment, but news of a person in the US who had received gene therapy for haemophilia developing liver tumour is going to fuel a lot of scepticism. Science reports that the US Food and Drug Administration has pushed the pause button for clinical trials of the therapy. To be sure, the patient had conditions that made them susceptible to liver cancer—the person was elderly and had a liver disease that carries significant cancer-risk. The person had also, in the past, suffered from Hepatitis B and C infections; chronic infections of these pathogens have a strong link with the type of cancer the patient in the present instance has been detected with. Many experts, thus, believe that the chances of the therapy having caused the cancer are low.
But it is also a fact that adeno-associated virus (AAV), the virus used to deliver the edited gene in this particular therapy, has been reported to cause cancer in mouse studies. Studies have also shown that the AAV-delivered DNA that is otherwise found floating freely within the host cell’s nucleus can sometimes integrate into the host cell’s chromosome and cause liver cancer. There have been reports of dogs treated with AAV-mediated gene therapy being detected with foreign DNA in their chromosomes at locations that trigger rapid cell growth.
It is difficult to say at the moment that the virus did or didn’t cause the cancer—this requires testing to see if there is a clear link to genomic changes that can be attributed to the AAV; if the tumour has cells that are clones of each other with respect to containing AAV DNA near a growth or cancer gene, then the therapy’s link to the cancer be established.
The firm behind the therapy has kicked off such testing, and it could take a few months to indict or acquit the therapy. But, some believe it may not be as cut and dry as that—it needs to be seen if AAV in any way accelerated or catalysed a tumour seeded by pre-existing factors. With so many uncertainties, critics and advocates of gene therapy need to let the full picture emerge.