Viral vector for flu-blocking antibody
This week, US-based scientist Maria Limberis and her team have inserted the gene coding for an antibody that can neutralise various forms of flu into a harmless virus called AAV9. Squirted into the nose, this triggers cells lining the airways to make anti-flu antibodies, theoretically blocking infection for up to months afterwards, as she explained to Chris Smith...
Maria - We used a virus that's non-pathogenic it's called adeno-associated virus vector to actually carry the genetic information for broadly neutralising antibody that was isolated back in 2011 put it into a vector. And then use the expertise that we have to target specific cells of the airway to transform the cells of our nose into almost mini factories that could actually produce antibody.
Chris - So basically, you take this antibody or at least the gene for the antibody that someone else has discovered what that gene is and you put that into this adeno-associated virus vector. This then goes into the nose, into the airways, and the cells that take up that virus get the gene for the antibody so they start making and secreting the antibody.
Maria - That's right.
Chris - That then defends that mucosal surface against any flu viruses that come in, does it?
Maria - Exactly. So, what will happen is that that cell will continuously for its life produce antibodies that will then be secreted into the airway and so, you can just imagine that amount of antibody becoming more and more concentrated. So upon introduction, whether you are exposed to a sneeze or someone's cough with virus and you breathe that in, that will get deposited in your nose but the antibodies that are there will fight that virus and neutralise it before it has a chance to replicate in the nose.
Chris - So, does it work?
Maria - We have a mouse adapted H1N1 which again, H1N1, we've had cases of pandemic 1918, the Spanish Flu. So, what we did is used the vector expressing the antibody, gave it to the mice and then after a set period of time, anything from 3 days after the vaccine to 14 days, we challenged these mice with the actual H1N1 and then monitored for survival or any onset of symptoms.
Animals that get H1N1 start losing weight quite rapidly and in most cases, have to be euthanized within 8 days. In contrast, when you see animals that were given this vector-based vaccine, the animals look completely healthy and normal. No weight loss. In fact, they actually gain weight and have no signs of behavioural distress. So then, we collaborated with researchers over in Canada, Dr. Kobinger and we did similar experiments with different strains of pandemic flu, and our mice were completely protected.
Chris - What about animals that are regarded as a better model of human infection because traditionally, when we've looked at flu and flu was actually first in fact discovered in ferrets? Have you looked in them?
Maria - Yes. So, wehen transitioned based on those data, we then transitioned and did some other studies using both H1N1 and H5N1. Both of which have been associated with pandemic and H5N1 is typically associated with bird flu. What we found in those particular experiments that were done both in Canada and in the US is that we saw complete protection of the ferrets which got us even more excited because it is a model that actually mimics the human airway response to influenza.
Chris - So, we're at the stage where you make this vector, you put it into these airway cells, it clearly has the ability to protect animals of a range of different mammalian species from what would otherwise be lethal doses of flu. So, that's looking very encouraging, but do you know how this actually works because there's a lot more to the respiratory tract than just a few cells in the nose. So, why are these animals getting so comprehensively protected by what you're doing?
Maria - So, we think that it's simply that we're creating a bio mask, an invisible bio mask where you would have such a high concentration of protective antibodies at the surface of the nose that upon inhalation, it basically just attaches to the virus and neutralise it, as simple as that. That's the theory that we are basically basing our work on and it seems to be falling in that category, that we're creating an invisible shield in the nasal cavity.
Chris - And how long do you think it will express for? How long could a person who, if we did translate this to humans, how long could a person be protected by this for?
Maria - So, we estimate that we are probably getting expression of the antibodies for a minimum of 6 months. And so, you would expect your patient to be protected from anything, from days following the delivery of this vector to at least 6 months.
Chris - And is there any downside to this? Is it possible that the antibodies could, through sheer numbers or chronically being present, actually do damage to the host?
Maria - Those are issues that we are really thinking about and in terms of the immunology of having way too much antibody in a site that otherwise would not, the beauty of this particular aspect of what we're doing is that the airway epithelium is not long-lived. And so, even though we have a fast onset of expression of the antibodies, they don't stay at the same level for a very long time. In fact, with time, anything from 3 months towards 6 months, we get a sort of progressive diminution of the expression of the antibody. And so far, in the models that we've tested including macaques, we haven't seen any side effects associated with having antibody present there in terms of somehow damaging the integrity of the epithelium or somehow making the particular species or model more susceptible to a particular infection.