CAR-T Cell Re-engineering: Why is HIV preferred over CRISPR?

In what was termed as a breakthrough cancer treatment, FDA approved the first gene therapy treatment in the US recently in August this year. Called CAR T cell therapy, in this technique, patients T cells are removed from the body, and new genes are introduced in these T cells using HIV (Human Immunodeficiency Virus). Thereafter, these re-designed T cells, which have the ability to find and kill cancer cells, are injected back into the patient’s body. These T cells multiply in the body and start to identify and kill cancerous cells by spotting the CD19 antigen on them.

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CureTalks had a chance for an exclusive interview with Dr Carl June of University of Pennsylvania, the pioneer of this breakthrough, this November, where he shared with us, how this #newincancer therapy will change the way we fight cancer.  

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Named “Kymriah” by Novartis, this therapy was approved for treatment of an aggressive type of Leukemia (specifically Acute Lymphoblastic Leukemia) in children and young adults up to 25 years of age who did not respond to other treatments.

Dr. June talked about his work with HIV and explained why was HIV ideal for re-engineering CAR-T cells that are used in this cancer immunotherapy. He elaborates:

One thing about this is, it shows that if you can work in different fields, seemingly disparate fields, like in infection and cancer, you can sometimes have lessons or low hanging fruit, that applies in one field to help solve the problem in another field. So, in the cancer field the problem was how to make T cells attack your own cancer, but not attack your body. And we didn’t have an efficient way to genetically alter those T-cells. And it turns out that HIV is evolved to do exactly that. I mean, it infects people, it goes in their immune system, into T cells. But, the natural HIV virus, as people know, destroys T cells eventually, and so the number of investigators over the years developed HIV and modified it so that it would be a tool to insert genes into T-cells rather than kill them.

So what they did was basically, got the virus of the genes, and material that would allow the virus to kill T cell, but retain the ability to insert new genes into T cells. And so we were the group to first test that in humans. In 2006, we treated patients who had late stage HIV with their own T cells – but then, using this modified form of HIV which we called Lentivirus –  to insert a new gene into their T cells and that’s what we ended up using in cancer patients because it works with very high efficiency and has been very safe in hundreds of patients. We never had a side effect from this virus.


Answering one of the panelists concern over the use of HIV and not CRISPR – which sounds safer – in the whole process of making re-engineered T cells, Dr June explained how these two technologies differ – One is to “bring in new genes to the cell” and the other “which can change target genes to achieve a benefit in the patient. He says, “They are really very complementary.”

Here is how he simplifies it:

It is just an example of how basic research is led. We are at the cusp of ways where we think we can actually cure diseases, even inherited diseases, which were unthinkable in the past. So called genetic editing is the ability to change the code. Our DNA is about 3 times 10 to the power of 9, or 3 billion different base pairs in length. Sometimes mistakes in just one of the those can lead to even lethal diseases or cause cancer. So you can have congenital diseases that you can inherit, or you can have acquired ones which happen, for instance, and lead to cancer through mutations after you are born.

So genetic editing offers the ability to repair these, and it can be done in 2 forms. In basic terms, in the lab you can take the cells out, genetically edit them and then return them so that, that could be in  bone marrow derived cells like T cells. It happens to be that today the first ever in vivo gene editing was reported by the team lead by Sangamo. They used a gene editing technology called Zinc Finger Nucleases. They injected it into a patient who had a congenital disease, to attempt to repair the gene. So too early to know if that is going to work, but in the lab, in mice it does.

So when you actually look down at the different technologies, they alter DNA sequences. We are fortunate to have a number of tools. The first one ever used in patients was the Zinc Finger Nucleases, and we actually did that beginning 2009 in patients with HIV. And we edited their T cells to make them so that the HIV virus could no longer infect their T cells. So that was done in the laboratory, much like our CAR-T cell engineering. This is going to be complementary to them. We will not replace technologies like using Lentiviral vectors or HIV to introduce genes. So there is one which is technology which can bring in new genes to the cell. There is another which can change target genes to achieve a benefit in the patient. They are really very complementary.

CRISPR technology uses an enzyme derived from bacteria called Cas9. It will cut in the DNA and you can target it with amazing precision. It is truly the needle in the haystack. So, of these 3 times 10 to power of 9 or 3 billion different base pairs in our DNA, you can target which one you want to change with this CRISPR Cas9 system. Its real advantage over the previous gene editing technologies like Zinc Finger Nucleases- is that it is more rapid in the laboratory to test many different targets. So it is very flexible. I am quite sure, we are going to see many of these technologies used both in the laboratory – for instance bone marrow cells are altered and then given back to the patients. Or, in certain tissues, they will be injected directly injected, and those areas will be modified as desired by systems like CRISPR Cas9.


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You can read more about CRISPR technique here.

In the nutshell, using Lentiviral vectors or HIV to bring in new genes to a cell is a harmless method since the HIV used is a disabled one and will not cause HIV infection. Dr. June asserts,

It’s a disabled virus, but it retains the one essential feature of HIV, which is the ability to insert new genes into cells.

CRISPR is altogether a different technology, which can change or edit target genes, by cutting desired DNA sequences precisely, to achieve desired results. These 2 technologies are going to be used in a complementary way in the future.

Listen to Dr. Carl June’s CAR-T Cell Therapy Journey and the Cancer Treatment Revolution here.


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