New Gene-Delivery Therapy Restores Partial Hearing, Balance in Deaf Mice

Haha! I was just about to post a new thread about this.

 

Adeno-associated virus, or AAV for short has been discussed before. It's a type of virus used as a delivery vehicle for gene therapy. What's new is a new, revised version of that virus called Exosome adeno-associated virus, or exo-AAV for short. The authors of the news article I read refer to it as "super-charged" because it's a big improvement over the previous version. It allows much better hair cell penetration. Findings were published in Molecular Therapy.

Harvard Medical School: A Better Carrier
Harvard Gazette: New gene-delivery therapy restores partial hearing, balance in deaf mice
Molecular Therapy: Rescue of Hearing by Gene Delivery to Inner-Ear Hair Cells Using Exosome-Associated AAV
Molecular Therapy: It’s All in the Delivery: Improving AAV Transfection Efficiency with Exosomes

That's impressive! Just to give you an idea what this translates to visually, have a look at the illustration below. The top part of the image represents the previous AAV, and the bottom part represents the new exo-AAV.



We may be still long way from the final destination and seeing therapies based on these findings used in the clinics on a day to day basis. But remember that the flowers of tomorrow are hidden in the seeds that are sown today.
Go science, go!

 

"Research is to see what everyone has seen, but to think what no one else has thought."

My English translation of some quote I found in Swedish! Origin unknown, but I think it captures the Eureka! moment, the moment of discovery quite nicely.

This is surprisingly what happened in case of exo-AAV. Someone looked at the old AAV approach and said, Oh! I see! But what if I do this?! I think that someone is disclosed by name in the linked articles. He's one of the professors working at the lab.

I agree! Let's not underestimate the importance of these discoveries. To reuse the old Neil Armstrong quote;

That's one small step for Pharma, a giant leap for hearing impaired and (hopefully) for tinnitus patients likewise.

 

It is regenerative medicine! It just may not be the kind you are thinking of.

There is basically two in-roads for regenerating cells. One is gene therapy, and the other is stem cell therapy which is probably what you had in mind. My understanding is that gene therapy is even more promising than stem cell therapy, and is therefore thought to be much more advanced and will require a lot more research, understanding, and therefore may be used far off in the future. So for that reason most focus is on stem cell therapy. But if findings like these keep coming fast enough, gene therapy may not be so far off in the future as we think.

Assuming I understand this (somewhat) correctly, the difference is in that stem cell therapy is about reusing existing, healthy, supporting cells and turning them into hair cells for example. Gene therapy on the other hand is about repairing the damaged hair cells and making them work once again.

I will try giving you an analogy here. Think of it as driving a car on a highway and all of a sudden your radiator blows up! Bang! Dead! Because you pushed it to hard and you maintained it badly. You have two options. A: You can call in a mechanic to have it fixed on site. Or! B: You can ditch the dead car and hitchhike into town in a different car. Stem cell therapy is the hitchhiker approach, option B. Gene therapy is the mechanic approach, option A. You can guess which one takes most time, effort, money, and which one is the safest.

Assuming I have cellular damage in my inner ear(s) I would pick any one of these two approaches. Any one of them is much better than what's currently being offered. Everyone seems to be too focused on hair cells, the sensory part of hearing. But for neural damage, I think stem cell therapy is likely to bite the dust. Repairing sensory hair cells is a big undertaking! Or rather creating new ones from supporting cells. But how will these cells help you hear if you can't connect them to the brain because of neural degeneration? This is something that gene therapy has the best potential to solve for us. Not only can gene therapy repair damaged sensory cells, but it also has a much better chance at repairing nerve cells.

Gene therapy is considered risky and it is very much experimental at this point in time, because we know so little about the mechanisms that are involved in ears and hearing. But we are constantly making progress. Albeit in baby steps, but we are pushing the envelope of knowledge all the time. The exo-AAV is just one of these small baby steps in getting closer to a therapy that actually works nearly 100%.

 

Transduction is what I mentioned earlier. It's the connection between the hair cells and the nerve cells. If you can't connect those hair cells to something useful and make use of them, then they are merely a cellular art exhibition. You have to make the connection to the nerve cells and nerve fibre in order to send the information to the brain.

Gene therapy promotes transduction like nothing else. Mainly because it aims to repair and restore the damaged hair cells rather than sidestep them and make use of supporting cells like stem cell therapy is doing. There is greater chance that nerve endings are still there, and intact where hair cell used to be. What stem cell therapy is doing is like using mashed potato to form perfect fusilli spirals.

I don't want to undermine the importance of stem cell therapies. As I said earlier, i would gladly take any one of these options. Even fusilli spirals made of mashed potato is better than what audiologists and ENT doctors currently have to offer.

Also, I am not too eager to drug the brain to make the ringing stop. If the root cause of the ringing is in the ears, why would I want to drug my brain? It makes no sense to me. In lack of better options? My tinnitus is not that sever that I would take brain drugs. I love my brain! Me and my brain are best pals! Like in any relationship we have our ups and downs, and this tinnitus monster is currently tearing us apart. But I'm sure with time we will conquer this monster, together.

 

Don't we all!

Sadly, you don't know what you have until you have lost it. So try to be mindful and appreciate the things you still have, and keep your hopes up. Sometimes hope is what saves the day.

 

I got the impression that these cells are left as they are. Like scar tissue. But they no longer have any function, and the connecting nerve endings start to degenerate.

Not sure what you mean? All cells die eventually by aging. If cells are damaged to the point where they can no longer perform their function they are dead indeed, since hair cells in humans do not promote natural regeneration, unlike in chicken for example.

But what happens to the corpse of these dead cells so to speak I do not know. Are there like janitor cells that come and clean up the mess? I do not know. I like to think of it like a graveyard of dead cells. The images of damaged hair cells come to mind, as you said. Perhaps those images are taken shortly after the damage?...



Just to help us orientate, I will add this nice illustration of the organ of Corti.



My understanding is that once hair cells are damaged beyond natural restoration or repair, the nerve endings that connect to the cell start to die off, or to degenerate as it's called.

My understanding is that gene therapy targets these scarred and damaged cells and starts a process of induced regeneration, essentially rebuilding the cells at the same site where the old ones used to be. Stem cell therapy on the other hand sidesteps the corpse of the dead cells and targets their neighboring healthy supporting and non-hair cells and turns them into hair cells. At least that's my understand.

It's difficult to picture this in words. So it's time for yet another analogy! Think of a burned down house! That will serve as a dead cell. Just like our hair cells, a burned down house can't spontaneously rebuild itself! We have to do that job. We have two options. A: Clean up the ground, reuse the old foundation and start building the same house all over again using the blueprints and other documentation we have about it. B: Move to a new ground, build a new foundation, have someone prefabricate the house according to old blueprints and documentation, and have it assembled at the new location. Option A is the gene therapy approach, option B is the stem cell therapy approach.

That actually turned out to be a pretty good analogy! Better than I expected.

The benefit of option A is that you can reuse a lot of the old stuff that used to be at the old site where the house stood. You have the foundation, you have the plumbing, the electrical power lines, etc. This is analog to existing nerve fibre endings in dead hair cells. As opposed to having a new foundation, new plumbing work, new electrical installation done, etc. There is a lot more work involved with this option. Reconnecting the power lines at the new site would be analog to growing and extending new nerve fibre and making the connection to the brain.

Stem cell therapy is about using pluripotent stem cells in the lab and having them turned (differentiated) into the desired cell type. In this case that's hair cell type. You then injecting them into the target organ and tissue where they will continue to grow inside the animal, and hopefully be accepted and make the necessary connections.

Note that this is different from the general "rejuvenation" type of stem cell therapy where you get IV injections in your blood... somehow hoping that if the dose is big enough a small number of these stem cells will find their way through your body up to your inner ear and create new hair cells. That's only short of believing in magic. That's like having gold dust on your belly to cure all kinds of conditions, like in middle ages. If may help cure your other ailments, but hardly the one you are after. Note that Chloe Sohl who had her hearing repaird with stem cell therapy received a target injection for the inner ear. Targeting specific organs and tissues is one of the things that scientists have to overcome before we see stem cell therapy used in clinics to repair hearing.

With stem cell therapy you are injecting whole cells. All the information is there. In fact the entire cell is there! You take pluripotent stem cells and turn them into hair cells in lab, and then inject them at the target area where they continue to develop. With gene therapy you use a virus to carry a DNA with genes responsible for hair cell development. You are injecting this virus at the target area. These genes are then turned on (expressed) at the target area which starts the repair or cell growth process. Unlike with stem cells, the new cells are grown in the animal not in the lab. What kind of cells are grown is aided by the gene expression. This is much more advanced technique. Also, sometimes a combination of stem cell and gene therapy is used.

Stem cell therapy is the old technology, dating back to the first blood transfers in the 1940s. Gene therapy is the new technology dating back to 1970s. The Human Genom Project (HGP) of the 1990s has had a big impact and helped us get a deeper understanding of gene based therapy. Brain projects like the BRAIN Initiative, International BRAIN Initiative, and Human Brain Project, and the Canadian equivalent (don't recall the name), are expected to have the same kind of impact if not even more so for our understanding of the brain. Our knowledge and understanding is progressively growing and it's only a matter of time now before we have cures and treatments for several types of diseases that are currently untreatable.

 

If we would stop doing dumb things like making war and building walls we would already have had a cure for total deafness by now. Those millions and billions of dollars could have gone to research, awareness, protection and support. Or why not building homes for the homeless and weakest in our society.

 

One of the first gene therapies used to cure deafness in 2005:
https://www.newscientist.com/article/dn7003-gene-therapy-is-first-deafness-cure/

Expressing ATOH1 in DNA starts the process of hair cell generation:

Using growth factors in lab to differentiate embryonic stem cells into hair cells:

There were obstacles in using these therapies in humans in 2005:

There still were obstacles in 2015 (and there still are):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3755754/

And of course, now we have exo-AAV which is a big improvement over previous AAV.

Gene therapy for Ototoxicity is difficult:

Note, "the atonal gene product Atoh1 (Math1 in the mouse), that encodes a transcription factor inducing the development of sensory hair cells from supporting cells in the cochlea." It induces "development of sensory hair cells from supporting cells". More details can be found by following the link, but in conclusion:

Note the last part, as "gene delivery methods improve, we can expect to see important advances in the treatment of a variety of causes of hearing loss over the coming decade." Little did they know that exo-AAV would show such improvement just one year later.