You all might have heard about ‘delta32’ or ‘delta-CCR5’ people in association with HIV infection.
People who naturally, by chance, have deletions and mutations in the CCR5 gene of their DNA dont make functional CCR5 proteins. It doesnt appear to be ‘a big deal’, and people who have this particular mutation seem to live normal lives. But the absence of the CCR5 protein means that in these people, HIV does not have one of its favorite co-receptors (note: there are others! CCR5 is just HIVs favorite!). Thus people with this phenotype are resistant to HIV infection.
That is SUPER for them… but how this information is useful to others, particularly HIV+ individuals has been somewhat limited.
I mean, you cant change someones DNA, right?
So the first idea was to try to make everyone ‘delta CCR5’ by making therapeutics that block the CCR5 receptor. If we have a drug in someone, binding up all the CCR5 molecules, then there isnt any left for HIV to infect cells.
But these havent worked out as an HIV treatment, for many reasons– from unacceptable side-effect profiles to good old-fashioned HIV evolution.
Another idea was to fry the patients immune system, then to replace their normal immune cells with bone marrow from a delta-CCR5 donor. NOTE: This was done to treat blood cancers in HIV/AIDS patients, NOT to ‘cure HIV/AIDS’. For example, the famous ‘Berlin Patient’ was given a bone marrow transplant from someone who had the delta-CCR5 phenotype, and he is doing fantastic, with no evidence of HIV infection at this point… but bone marrow transplants are risky and costly, and again, only done in the context of HIV+blood cancer. Bone marrow transplants for everyone is not a viable world-wide ‘cure for HIV/AIDS’.
So, how the hell can we make everyone (or, at least, HIV+ people) delta-CCR5?
Again, we cant cant change someones DNA, right?
STEP 1– Make an artificial enzyme to cut the CCR5 gene out of ‘normal’ (non-delta-CCR5) human DNA.
Zinc finger nucleases are fun proteins that work together to cut DNA. We can modify/alter these proteins to recognize any stretch of DNA we want (we can also modify the ‘cutting’ portion of these proteins to snip any way we like).
In this case, the zinc fingers were designed ‘see’ the human CCR5 gene. Add these proteins to the target cells of HIV, CD4+ T-cells, and they chop the CCR5 DNA and only the CCR5 DNA. The DNA naturally ‘heals’ itself, and thats it.
No more CCR5 DNA, then no more CCR5 RNA, and no more CCR5 protein. No more CCR5 protein, then HIV doesnt have one of the handles it wants to infect cells.
But how the hell do you get these zinc finger nucleases INTO cells?
STEP 2– Make an artificial virus to deliver DNA encoding the instructions for making the anti-CCR5 zinc finger nucleases.
We need to get proteins into a cell. Getting proteins produced, purified, and delivered into a human, to be subsequently taken up and used by cells, is really, really hard. Sometimes quite impossible.
So an alternative means of getting proteins into cells, is getting DNA into cells. Cells do DNA–>RNA–> Protein all day long. Get the DNA into a cell, you get the cell to make the protein you want.
Well, viruses are these handy creatures that deliver DNA/RNA into cells. That is what they do. Bonus: They are also really conducive to genetic modification. We can swap out their viral genes for genes we are interested in without much difficulty, and the virus doesnt mind in the slightest!
In this case, they convinced an adenovirus to deliver the anti-CCR5 zinc finger nucleases.
I asked the adenovirus for a comment:
*shug* Whatever. I dont care, man.
But, how do we get the virus to the cells we are interested in, CD4+ T-cells? I mean its really nice of the andenovirus to deliver the anti-HIV zinc finger nucleases for us, but they arent really ‘reliable’. We cant just inject someone with the GMO adenovirus and expect the genes to get to CD4+ T-cells. They will kinda go everywhere. Or nowhere. And while bystander cells being delta-CCR5 wont hurt anything, we *do* want this process to be as efficient as possible.
STEP 3– Purify CD4+ T-cells from HIV+ individuals. Genetically modify them by infecting them with the GMO virus containing the GMO zinc finger nucleases.
Thats pretty much it 🙂 Purify only the CD4+ T-cells from patients, put the virus on those cells to make sure the virus gets where it is supposed to go, and then put those cells back into the patients.
If the virus does its job, and the zinc finger nucleases do their job, then the GMO CD4+ T-cells should then lack the CCR5 protein, thus be resistant to HIV infection when they go back into the HIV+ patient. And maybe, these patients can maintain their CD4+ T-cell counts and not progress to AIDS.
So did it work?
Kinda! Well, sorta.
This was a very small group of patients, but we can still make some conclusions.
1– Genetically modifying human cells is not efficient, yet. In the cases of like, the anti-tumor Cytotoxic T-cells, that inefficiency doesnt matter much because even a few cells doing their job is enough. But in this case, we need as many CD4+ T-cells as possible to be protected. We also need to keep the GMO CD4+ T-cells alive as long as possible. The protocol needs to be maximized, and its not there yet.
2– It does work to preserve some CD4+ T-cells. One of the cohorts was taken off antiretrovirals. Their viral loads (viral RNA) skyrocketed… but there was no correlated skyrocket in viral DNA (new infected cells). That means that some of the CD4+ T-cells were protected/not infected. Furthermore, it looks like most (but not all) of the patients saw an overall increase in CD4+ T-cells over the course of the trial.
3– It didnt protect everyone. One patient (of six) did have an increase in HIV DNA when they were taken off HAART… luckily they did maintain their CD4+ counts over the course of the trial. We do need to figure out why this happened.
4– No way this is a viable world-wide ‘cure for HIV/AIDS’. But it is more viable than bone marrow transplants, and optimizing this protocol could get it cheaper/faster/safer for the developing world, aka, the place we really need a cure for HIV/AIDS.
But this is really cool. Really cool step in a positive direction.