Using viruses as vectors in gene therapy


Viruses are modified to prevent disease before they are used as vehicles to deliver the required genes in gene therapy. — Pixnio

We previously talked about people using genes to treat diseases nowadays. We also talked about scientists using certain “vectors” like viruses to deliver the gene into my body. But these vectors are viruses, right? What is to stop these viruses from causing diseases in my body?
The most common viruses used as vectors in gene therapy are lentiviruses – one of which is HIV (human immunodeficiency virus) – and adenoviruses, which cause the common cold.

In gene therapy, these virus vectors are disabled beforehand,

This is similar to viruses being used as vaccines.

Researchers will remove the original disease-causing genes from the viruses and replace them with the genes the viruses now need to carry into your body to stop the targeted disease.

These modified or attenuated viruses would have been research-ed extensively in the lab and in animals before going on to be used in human clinical trials.

Only when the modified virus is deemed safe and effective, will it be used in gene therapy.

OK, but are there any side effects? We know vaccines that use viruses (like the Covid-19 vaccines) have certain side effects on some people, right?

Even for established vaccines, like those for influenza and hepatitis, there will always be a very small percentage of the population that will have some adverse reaction to them.

This is also true for any medication you introduce into your body.

Some people will experience no side effects whatsoever.

Some people will experience mild side effects.

And a small group will experience moderate to severe side effects, but this will involve very, very few people.

But people tend to focus too much on side effects; they forget that the main reason for you to take any vaccine, therapy or medication is to prevent or cure the disease in the first place or treat it to make you feel better.

The symptoms and complications of the disease are far worse than the side effects of the medication used to treat it most of the time.

Therefore, it is worthwhile to treat the disease.

And if you have any side effects from the medications, therapies or vaccines, doctors should be able to treat those side effects accordingly, e.g. by lowering the dose of the medication, adjusting the timing of the doses and so on.

OK, I get that. But does gene therapy itself have any side effects?

There are always risks in using virus vectors in the human body.

Some of these include:

  • An unwanted immune system reaction: Like with any vaccine, your body may see the newly-introduced viruses as invaders and attack them instead. This may lead to your own immune system attacking your own tissues and organs in rare cases.
  • Targetting the wrong cells: It is always possible that the attenuated virus will affect more than just the targetted cells. This may lead to healthy cells being damaged, and even mutating to form cancer.
  • Infection: The attenuated virus may recover its original ability to cause disease once it is in your body.
  • New tumour formation: If the new genes get inserted into the wrong spot in your DNA, it may lead to a new tumour.

That is why gene therapy has to undergo so many clinical trials, like all medicines and vaccines.

Regulatory bodies around the world, like the US Food and Drug Administration (FDA) and Malaysian Drug Control Authority review all the trials and literature very stringently before approving a new therapy for the general public.

Effectiveness and safety are always on the top of the minds of regulators.

Are viruses the only vectors for gene therapy? Why can’t we use something else that didn’t previously cause a disease?

Viruses are the easiest and most convenient vectors because of the way they are built.

But because of all the reasons above, scientists are studying other ways of introducing genes into our bodies.

The vectors currently being studied are:

  • Stem cells: These are the cells from which all other cells in your body originate from. They usually reside in your bone marrow. Some stem cells can be trained or altered in a lab to carry therapeutic genes into your body.
  • Liposomes: These are fatty particles. They also have the ability to carry therapeutic genes and pass it on to your cell’s DNA. (Yes, we know fat travels well!)
If I were to undergo gene therapy, what sort of procedure would I expect?

It will depend on the type of gene therapy.

It may be as easy as getting your blood drawn.

A more difficult procedure would involve getting your bone marrow drawn (but this will only take a few minutes).

Then your blood or bone marrow cells are taken to a lab and exposed to a virus vector that will pass on the therapeutic gene.

Your blood or bone marrow cells will then be injected back into your body through a vein or directly into a certain tissue.

Your cells will take up the new genes, which will treat your disease as time goes by.

Dr YLM graduated as a medical doctor, and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, email starhealth@thestar.com.my. The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.

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Genetics , immunotherapy , gene therapy

   

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