Stem cells are nestled deep inside certain tissues in the body and constantly replace old cells. They dictate how long and healthy your life is. When it comes to treating genetic diseases, fixing the stem cells is how it’s done. In recent years, such a feat has been possible. Scientists have been able to correct genetic diseases by removing these stem cells, editing their genomes and then implanting them back into the patient. However, it is a procedure full of complications, thus unreliable.
But now, Harvard scientist Amy Wagers, the Forst Family Professor of Stem Cell and Regenerative Biology, has lead brilliant new research that succeeded in demonstrating how gene-editing machinery can be delivered straight to stem cells where they live, rather than in a lab dish. Her team’s findings bring about major implications for biotechnology research and the development of therapeutics for genetic diseases.
The research was published in the journal Cell Reports.
Clean Up
Treating diseased cells won’t help much if you don’t address the stem cells, which will quickly replace the healthy cells with new diseased ones. In other words, you can clean up the mess of all the infected cells but the stem cells that are producing the infected cells will only make a mess again.
Wagers said:
If you want to change a genome to correct a disease-causing gene mutation, you have to change it in the relevant stem cells. If you don’t change the stem cells, whatever cells you do fix may eventually be replaced with diseased cells fairly quickly. If you do fix the stem cells, they will create healthy cells that can eventually replace the diseased cells.
There are different types of stem cells and they each live in their own “niche” – well-protected, hard-to-reach areas such as bone marrow. This makes it quite difficult to fix them. As of today, how the scientists fix them involves extracting them from their hideouts deep inside the body, then genetically altering them and putting them back into the patient; and all the while keeping the cells alive and healthy.
The process is highly disruptive for the cells, and there’s the chance that the modified cells may ultimately be rejected or fail to engraft back into the patient. The potential failure points in that complicated procedure include: the stem cells can die in the culture dish, the patient’s immune system can reject them once transplanted, or they can just fail to fire back up.
Wagers said:
When you take stem cells out of the body, you take them out of the very complex environment that nourishes and sustains them, and they kind of go into shock. Isolating cells changes them. Transplanting cells changes them. Making genetic changes without having to do that would preserve the regulatory interactions of the cells — that’s what we wanted to do.
Transport By AAV
An adeno-associated virus (AAV) infects human (and mouse) cells (mammal cells) but does not cause disease. These viruses have been specially altered to deliver a payload of gene-editing machinery. Wagers’ group used this AAV as a transport vehicle.
They created various AAV packages to deliver gene-editing cargo (the CRISPR gene-editing system) into several different types of skin, blood, and muscle stem and progenitor cells. To test whether their AAV complexes managed to deliver, the stem cells were edited to activate “reporter” genes, which would glow a fluorescent red.
Jill Goldstein, a postdoctoral fellow in the Wagers lab and co-first author of the study, said:
This was a true collaboration between labs specializing in several different organs. We set up experiments in our organs of interest, analyzed them, compared notes, and made adjustments in a kind of scientific assembly line. None of us could have done it alone — it takes a lot of hands, and the team approach made it really fun.
Effectiveness
- In skeletal muscle, up to 60% of the stem cells turned fluorescent red.
- In cells that give rise to different types of skin cells (skin progenitor cells), up to 27 percent of the cells turned red.
- Of the stem cells in bone marrow (which make blood), up to 38% were changed.
Sharif Tabebordbar, an alumnus of Harvard’s Department of Stem Cell and Regenerative Biology and now a postdoctoral fellow at the Broad Institute, said:
So far, the concept of delivering healthy genes to stem cells using AAV hasn’t been practical because these cells divide so quickly in living systems — so the delivered genes will be diluted from the cells rapidly. Our study demonstrates that we can permanently modify the genome of stem cells, and therefore their progenies, in their normal anatomical niche. There is a lot of potential to take this approach forward and develop more durable therapies for different forms of genetic diseases. That includes different forms of muscular dystrophy, where tissue regeneration is such an important factor.
Follow Up
Following up, researchers also noted that other dermal cells also appeared to be edited, indicating that changes to the skin stem cells were being passed down the line.
Ya-Chieh Hsu, Alvin and Esta Star Associate Professor of Stem Cell and Regenerative Biology, said:
We looked at the skin of these AAV-transduced mice from the Wagers lab, and were pleased to see that many dermal cells were successfully edited as well. Those included cells that give rise to dermal adipocytes, and cells that help regulate other stem cells in the skin. We’ve always needed a tool that lets us manipulate dermal cells in vivo rapidly — so for us, this is like a dream come true.
Conclusion
The team says this breakthrough has immense potential to lead to new treatments for genetic diseases; in particular, those like muscular dystrophy which hinge on tissue regeneration. As of yet, biotech companies have not been able to develop therapies for diseases like spinal muscular atrophy. Delivering gene therapy directly into a living system has been a barrier. This new research could be a total game changer.
Wagers said:
This is a really important resource for the community for two reasons. First, it changes the way we can study stem cells in the body. The AAV approach lets researchers investigate the importance of different genes for stem cells in their native environment, much more quickly than ever before. Because the delivery system is so robust, it can also be used to target genes that affect many different tissues.
Secondly, it’s an important step toward developing effective gene therapies. The approach we developed gets around all the problems you introduce by taking stem cells out of a body and allows you to correct a genome permanently. AAVs are already being used in the clinic for gene therapy, so things might start to move very quickly in this area.
