Gene therapy is easy, in theory.

Born with a bad gene? No prob!! Just replace it with one that works! We have lots of ways of doing that! I mean, retroviruses plop new genes into our cells all the time! Half of your genome is made of leftover retroviruses! So why dont we just put a functional version of your ‘bad’ gene in a retrovirus, and let it do all the work? Yay!

Wait… no yay.

Retroviruses are still wild broncos. We cant tame them yet. Force them to insert here, but not here… so our previous efforts to use retroviruses as gene therapy vectors ended in disaster (cancer).

Luckily retroviruses arent our only hope. A potential solution to the problems retroviruses bring to the table could be a different virus– Adeno-associated virus. Wild-type AAV is completely harmless, and if we replaced the viral genome with a ‘good’ gene for gene therapy, we would know exactly where the ‘good’ gene will insert (a region on chromosome 19).

Unfortunately AAVs have their own gene therapy issues. One major problem is that up to 96% of us already have antibodies to the AAV researchers would like to use as a vector, AAV-2. And ~67.5% of us already have AAV-2 neutralizing antibodies. Inject a gene therapy AAV-2 into someone, and odds are the viruses will never reach their intended targets. Itll be creamed by the patient immune system.

Solution to this problem?

EVOLUTION, BABY!


A super sweet paper came out in Journal of Virology earlier this year, where they took the basic tenants of evolution, mutation and natural selection, and figured out a way to make a kick ass gene therapy vector:
In Vitro and In Vivo Gene Therapy Vector Evolution via Multispecies Interbreeding and Retargeting of Adeno-Associated Viruses

STEP 1: MUTATION
Previous efforts to get around all these AAV-2 antibodies was to mutate the protein these antibodies target, capsid (the structural protein). Its been kinda scatter-shot. Mutation here, mutation there, sometimes the virus cant even work anymore, meh.

Grimm et al tried something radically different. Get this. They took the capsid genes from lots of different AAVs:
AAV-2– Works great in humans
AAV-8 and AAV-9– Work super friggen great in liver cells (theyre going to try to make an ‘ideal’ vector for gene therapy for liver genes)
AAV-4, AAV-5, avian AAV, bovine AAV, caprine AAV– not prevalent in humans, we wont already have antibodies to them

They chopped up the capsid genes from each of those viruses, and smushed them back together again different combinations. So what they ended up with, is a population of viruses with lots of different kinds of capsids– each virus with different mixture than the next. One might have gotten a lot of AAV-2 and no avian. Another might have equal bits from all of the viruses, etc.

STEP 2: NATURAL SELECTION
So Grimm has a vat of viruses with different capsids. But all that diversity doesnt mean anything until you make those viruses perform a task, and let natural selection pick the variants that perform the task the best.

Grimm wanted to end up with a virus that could replicate super friggen awesome in liver cells, so he took his vat-o-virus and passaged them several times in primary liver cells, and liver cell lines. Towards the end of those passages (just five), out of that huuuuuge mix of viruses, only the viruses with a capsid combination that could replicate in liver cells the best were left. The rest had been outcompeted, and went extinct.

Well Grimm took those winner viruses and looked at their capsids– what did the mix look like? Shit. The viruses were all pretty different. Still too hard to pick ‘one’ combination that could be the best candidate for liver gene therapy.

STEP 3: MOOOOOOORE NATURAL SELECTION!!
Grimm repeated his initial experiments with another layer of selection– the viruses had to replicate really well in liver cells… AND they had to replicate really well in the presence of anti-AAV antibodies from people. Who cares if you replicate well in liver cells, if the patient will most likely neutralize the virus before it can do its job (the problem with AAV-2 in the first place).

Making the vat-o-viruses do two tricks at once narrowed the population down to one survivor. A viral variant they named AAV-DJ (I think the authors named it after themselves– Dirk and Joyce. hehe!)

Grimm replaced the wild-type AAV viral genome with the human Factor IX gene (theoretically if hFIX were given to someone with hemophilia B in a liver specific AAV, they could be ‘cured’). He then gave the viruses to mice (who were also injected with human antibodies to AAV).

Those mouse livers then made a shit load of hFIX.

The viruses got into some muscles (heart and regular muscles) and kidneys a little, but the vast majority of the new hFIX expression was confined to the liver, the place it was supposed to be.

And, AAV-DJ performed much better than the parent viruses (AAV-2, AAV-8, etc).

WHOOO!!

There is a ton more to this paper (its one of the longest I have read in a long time), but I had to write a post on their basic premise: Using evolution to make medicine better.

Suck it, Egnor.

Comments

  1. #1 D. C. Sessions
    December 4, 2008

    Damn. That is some sweet work, and it’s way outside of my field. It sounds like it represents two serious masterworks:

    1) Some serious kick-ass science, and
    2) A masterpiece of grantsmanship. Props to the PI.

  2. #2 Joshua Zelinsky
    December 4, 2008

    That just shows how evolution can only remove information not add it! And that’s not really evolution because it was done by humans. That’s evidence of Intelligent Design helping medicine. And obviously God designed humans and the AAV virus so that the AAV virus would work well for gene delivery after humans had gone through much effort to modify it to a workable form! This should be all obvious to you. Godless biologists!1111oneEleventyone!FactorialFactorial!!11!

  3. #3 Lycosid
    December 4, 2008

    w00t.

  4. #4 Cody
    December 4, 2008

    This is just god damn cool. I love it when results like these show up, not least because they are intrinsically interesting, but also because I can explain them to someone like my mother and they can appreciate the significance.

  5. #5 dreikin
    December 4, 2008

    Bah. I’m slightly disappointed.
    (if only because they got there before I did ;-) )

    On the other hand,
    Yay! New tool for me!

    As for “Gene therapy is easy, in theory.”…No. Nonono…
    There is SO friggin much to take into consideration.
    o The vector
    o Getting the vector past the immune system (immunosuppression==BAD idea)
    o The vector not clogging things up (heart attack, anyone?)
    o The vector not replicating uncontrollably/undesirably
    o Being able to ‘clean up’ the vector when you’re done, and/or automagically
    o The vector not interfering with the rest of the body (non-conductive in heart tissue, doesn’t mess with osmotic balance, etc)
    o Getting the vector into all cells/all the ‘right’ cells/only some cells and when to use which

    …and that’s (mostly) before it even gets inside the cell. Then you have such stuff as:
    o Make sure the package is inserted ONLY in certain places
    o Make sure cells don’t get overwhelmed with too much vector (either by auto-production or invasion)
    o Make sure insertions are appropriately limited (including to the point of only one per cell)
    o Make sure you’ve got the right control elements along with the base gene(s) (sure, give the diabetic an insulin gene! but if it never turns off.. X.X)
    o Make sure it can/can’t be passed to offspring
    o Make sure it can’t cause cancer, and
    o Even then you still have to have countermeasures in place (eg, certain anti-cancer genes also in the vector, with their own control elements, et al)
    o Make sure the insertion target is actually exposed in the cell (not everything is easy to get to, or even used, per cell)

    etc etc etc…

    (yeah, I figure you’re prolly aware of this abby, but some of the reader’s prolly aren’t)

  6. #6 Paper Hand
    December 5, 2008

    This is way over my head, but what little I understood was pretty cool. :-)

  7. #7 clinteas
    December 5, 2008

    The viruses got into some muscles (heart and regular muscles) and kidneys a little

    That wouldnt have been so awesome for the little mouseys,I imagine….

    Otherwise good stuff tho.

  8. #8 Stephen Wells
    December 5, 2008

    Um, tenets, not tenants, of evolution, I think. This is a great piece of work.

  9. #9 Reynold
    December 5, 2008

    So, evolution proves useful again, while Intelligent Design can’t even pass the explanatory filter.

  10. #10 Christophe Thill
    December 5, 2008

    You forgot :
    STEP 4 – PROFIT !

    (Yes, I know. Tired joke. No reason not to use it)

  11. #11 ZacharySmith
    December 5, 2008

    Evolution, schmevolution.

    It’s still just a virus.

    I’m sure Engor (or is it Egnor?) will be smacking this down in short order.

  12. #12 Rev. BigDumbChimp, KoT, OM
    December 5, 2008

    Have you seen Denise “Buy my Book” O’Weary’s latest on this?

    Of course. The whole concept of evolutionary medicine is a waste of time for a very simple reason:

    Medicine can never be a discipline without a subject. Astrobiology can be a discipline without a subject because there are no space aliens to complain that their needs are not attended to. But medicine can�t be a discipline without a subject (conventionally, a patient) because medicine must offer solutions, not just theories.

    Supposed ancestors, just like space aliens, are not a subject, as far as medicine is concerned.

    If you go to your doctor with severe chest pain, you will hardly wish to hear that some professor somewhere has theorized that Pleistocene man did not suffer from your condition because his selfish genes gave him lots of exercise bopping his numerous squeezes around, so

    So you are supposed to pay for this information, if – out of charity – it can be called information?

    Medicine exists, in the words of William Osler to provide cure sometimes, relief often, and comfort always – but never mere theories.

    In my view, “evolutionary medicine” is another example of people trying to find a use for something that isn’t really any particular use.

    you can almost hear the wind rushing through there

  13. #13 Dustin
    December 5, 2008

    Who wants to help me pin O’Weary down and shove some Bean-O up her nose?

  14. #14 Tatarize
    December 5, 2008

    This is certainly cool. But, I wouldn’t call it evolution proper. It’s certainly heredity and selection to find which potential vector does the best for the given situation. It lacks the sort of long term mutation and wow-factor of real evolution. You can move genes into bacteria, exert a selection force on them, and then later on take out a much better gene from them. That sort of has the wow factor of making a better gene without actually doing anything. This suggests that some viruses do better in certain situations than others. And that’s true but it lacks the real oompf and power of evolution.

    I’m not saying it’s wrong, I’m just saying that I want my evolution in medicine to knee creationists in the groin.

    However, the main thrust of the post is look at this cool thing. And hey, that’s fricking cool. AAV vectors for gene insertion, awesome. I suppose the main thrust of my comment is that it won’t make creationists look stupid enough.

  15. #15 Ian
    December 5, 2008

    You say, “Wild-type AAV is completely harmless”, but then go on to say, “One major problem is that up to 96% of us already have antibodies to the AAV”.

    So is AAV harmless because we have antibodies or is it simply harmless? If it’s the antibodies which render it harmless to us and then we’re bypassing those by modifying the virus, doesn’t this entail a risk in and of itself?

  16. #16 deep
    December 5, 2008

    I’m glad this is looking up…but no matter how fundamental evolution is to medicine those that don’t want to believe it won’t. I’ve wasted hours of my life on trying to convince this one creationist that evolution can be used for anything.

  17. #17 martin
    December 6, 2008

    Abbie – get off your butt and post about your appearance on BloggingheadsTV! Spread the word to your loyal minions. Did you forget about it after it was recorded back on November 23? So it took Bob Wright two weeks to release it – you still look good. Ed Yong – meh. Next time, more cleavage – no teasing.
    http://brainwaveweb.com/diavlogs/16352

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