CRISPR Gene Editing Tool Linked to Unexpected Collateral DNA Damage

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Photo Credit: Genetic Literacy Project

 

CRISPR–Cas9 has been widely hailed as the gene editing tool of the future. But research, published in the journal Nature Biotechnology,  about the effects of CRISPR/Cas9, have found it can cause unexpected genetic damage which could lead to dangerous changes in some cells.

Scientists have also learned there may be some safety implications for gene therapies that are being developed using CRISPR/Cas9.

These results come on the heels of a few studies published last month which suggested the CRISPR gene editing tool may inadvertently increase cancer risk in some cells.

“We found that changes in the DNA have been seriously underestimated before now,” said Allan Bradley, a professor at Britain’s Wellcome Sanger Institute who co-led the research published on Monday.

CRISPR/Cas9 can alter sections of DNA in cells by cutting at specific points and introducing changes at that location and is seen by many as a promising way to create treatments for diseases such as HIV or cancer.

Bradley’s team carried out a full systematic study in both mouse and human cells and discovered that CRISPR/Cas9 frequently caused extensive mutations including large genetic rearrangements such as DNA deletions and insertions.

These could lead to important genes being switched on or off – as intended by the therapies – but could also have major unexpected implications, the scientists said.

While experts say treatments like these could inactivate a disease-causing gene, or correct a genetic mutation, much more research is still needed to ensure techniques are safe.

Gene-editing Technique in Mice Shows Promise for Genetic Disorder in Utero

 

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New research presents a promising new avenue for research into treating genetic conditions during fetal development.
Credit: © llhedgehogll / Fotolia

Each year roughly 16 million parents receive the heartbreaking news that their child is likely to be born with a severe genetic disorder or birth defect. And while these genetic conditions can often be detected during pregnancy, using amniocentesis, there haven’t been any treatment options to correct these genetic conditions before birth. Well – thanks to a group of researchers at Carnegie Mellon University and Yale University that could one day change and offer alternative treatment options for children with genetic disorders while they are still in the womb.

For the first time ever, according to a Carnegie Melon press release, scientists used a gene editing technique to successfully cure a genetic condition in a mouse in utero. Their findings, published in Nature Communications, not only present a promising new avenue for research into treating genetic conditions, but they also open the doors for additional treatment options in the future.

In this study, the researchers used a synthetic molecule called a peptide nucleic acid (PNA) as the basis for a gene editing technique. They had previously used this method to cure beta-thalassemia, a genetic blood disorder that results in the reduced production of hemoglobin, in adult mice. Their technique uses an FDA-approved nanoparticle to deliver PNA molecules, paired with donor DNA, to the site of a genetic mutation. When the PNA-DNA complex identifies a designated mutation, the PNA molecule binds to the DNA and unzips its two strands. The donor DNA then binds with the faulty DNA and spurs the cell’s DNA repair pathways into action, correcting the error.

The researchers believe that their technique might even be able to achieve higher success rates if they can administer it multiple times during gestation. They also hope to see if their technique can be applied to other conditions.

While this research is promising there is a long way to go before the team will be ready to test it in people. However, one CIRM-supported project has already reached that milestone. Dr. Tippi MacKenzie and her team at UCSF are using in utero blood stem cell transplants from the mother to the fetus to help treat alpha thalassemia major, a blood disorder that is almost always fatal.

We recently blogged about this research and how it helped one couple deliver a healthy baby.

https://blog.cirm.ca.gov/2018/06/04/cirm-funded-study-results-in-the-first-ever-in-utero-stem-cell-transplant-to-treat-alpha-thalassemia/

 

 

CIRM Supported Scientist Makes Surprising Discovery with Parasitic Gut Worms

 

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Image of gut lining and parasites.  Photo courtesy of UCSF/ Michael Fortes

 

It’s no secret that researchers have long believed adult stem cells could contribute to wound healing in the gut and skin, but in a new paper in Nature — a group of scientists at UC San Francisco made a surprising discovery.

Through several experiments using parasitic worms in the mouse gut, they found that as parasites dug into the intestinal walls of mice, the gut responded in an unexpected way – by reactivating a type of cell growth previously seen in fetal tissues.

So why is this important?

Simply put, it gives scientists new targets to go after. According to UCSF CIRM supported scientist Ophir Klein, MD, Ph.D., this discovery could be paradigm-shifting in terms of our understanding of how the mammalian body can repair damage and could help scientists develop more ways to enhance the body’s natural healing abilities.

Adult stem cells in the intestines are vital for maintaining the digestive status quo. The gut lining is made up of epithelial cells which absorb nutrients and produce protective mucus. These cells are replaced every few days by the stem cells at the base of crypts — indentations in the gut lining. Researchers expected that the same stem cells could also help repair tears in the gut.

How did they do it?

Larvae from parasites like H. polygyrus invade the gut lining in a mouse’s intestine, burying themselves to develop in the tissue. Based on prevailing ideas in the field, the scientists predicted that, in response, nearby stem cells would increase their productivity and patch up the worm-created wounds, but that is not what happened.

Instead, signs of the stem cells in worm-infected areas disappeared entirely; fluorescent markers that should have been expressed by one of the genes in the regular stem cell program completely vanished. And yet, even with no identifiable stem cells in the area, the wounded tissue regenerated more quickly than ever.

Researchers spent years trying to resolve this mystery and after a number of false starts and dead ends, the team eventually noticed the recurrence of a different gene, known as Sca-1.

Using antibody staining for the Sca-1 protein, the researchers realized that where the stem cell genes had disappeared, a different gene program was expressed instead: one that resembled the way that mouse guts develop in utero.

Upon their discovery, the researchers wondered whether the reactivation of this fetal program was a specific response to parasite infections, or if it could be a general strategy for many kinds of gut injury. Additional experiments showed that shutting down gut stem cells with irradiation or genetically targeting them for destruction triggered aspects of the same response: despite an absence of detectable stem cell activity, undifferentiated tissue grew rapidly nonetheless.

Later, once the acute injury is repaired, the gut may return to the normal stem cell program of producing differentiated cells that perform specific functions.

Many other injured tissues could benefit from the ability to quickly and efficiently make generalized repairs before returning to specialized adult cell production, opening up therapeutic opportunities. For example, developing treatments that bestow an ability to control the change between adult and fetal genetic programs might offer new strategies to manage conditions such as inflammatory bowel disease (IBD).