Brain donation programs – now perhaps at risk of losing funding – are key to a Huntington's disease cure: a family's story

 

In July 2022 Dorlue Schulte of San Diego died at home after a long struggle with Huntington’s disease. To benefit HD research, Dorlue donated her brain to the Harvard Brain Tissue Resource Center (HBTRC) at the nonprofit McLean Hospital in suburban Boston.

 

“They can get hundreds of samples from one donation, so it’s truly the gift that keeps on giving,” said Dorlue’s husband and main caregiver Doug in a presentation last October at the Huntington’s Disease Society of America (HDSA) San Diego chapter’s “Family is Everything” Education Day.

Doug observed that HD researchers are “coming up with great ways to inspect the brain to learn from them.”

 

Dorlue Schulte (family photo)

 

“Scientists now have the ability to look at every cell in the brain and look at the mRNA and the proteins in the cells to see if they are resistant or not resistant to Huntington’s disease and, more importantly, probably, the timing of when (cell) death occurs,” Doug explained. “They’ve got to compare it with a brain that’s not diseased.”

 

For his outstanding advocacy Doug received the 2021 Woody Guthrie Award at the HDSA national convention. He served on the HDSA-San Diego board from 2019-2022. A retired firefighter, Doug has raised awareness about HD among police officers to make them “a friend, not a foe,” when encountering affected individuals.

 

You can watch Doug’s 30-minute talk in the video below.

 

 

‘Precious’ human data

 

Besides research on HD mice and many other non-human species, study of HD brains provides “precious” human data in the quest for treatments, in the words of Robert Pacifici, Ph.D., the chief scientific officer of the key, HD-focused CHDI Foundation, Inc.

 

At meetings like CHDI’s Annual HD Therapeutic Conference scientists discuss the growing body of knowledge coming from these brains.

 

Doug was inspired to present Dorlue’s story in part by Dr. Pacifici’s statements about the importance of research in humans. Although the huntingtin gene exists in many species, only humans develop HD.

 

Over 10,000 brains collected

 

Founded in 1978 and one of the first brain banks in the U.S., Harvard Brain Tissue Resource Center is one of six repositories that are part of the federal National Institutes of Health (NIH) NeuroBioBank, a centralized resource for the collection and distribution of human brain specimens for research.

  

According to the HBTRC website, it has collected over 10,000 brain donations from across the U.S. and distributed over a hundred thousand samples, both nationally and globally, that have resulted in hundreds of publications. More than 45 different brain disorders are represented in the HBTRC collection, including HD.

 

HDSA endorses HBTRC. The two have a long-standing collaboration, and HBTRC has one of the largest collections of brains donated by persons diagnosed with HD in the U.S. if not the world.

 

The HBTRC’s home, McLean Hospital, is the largest psychiatric teaching hospital of Harvard Medical School.

 

The sole funder of the HBTRC is the federal NIH, HBTRC director Sabina Berretta, M.D., wrote in an e-mail interview with me on July 25. An associate professor of psychiatry at Harvard Medical School, she carries out HD research on the team of investigator Steve McCarroll, Ph.D., whose lab has created precise techniques for measuring the impact of HD on single brain cells.

 

As Doug pointed out, this type of research is only possible because of brain donations.

 

The uncertainty of future public funding

 

Harvard University has sued the federal government to try to block the Trump administration’s freezing of nearly $3 billion in research funds. The government also seeks to eliminate $783 million in NIH funding.

 

A statement on the NeuroBioBank website reads: “This repository is under review for potential modification in compliance with Administration directives.”

 

Responding to my questions about this situation, Dr. Berretta wrote that the cuts at Harvard and the NIH have not currently impacted the HBTRC. The government has not flagged current funds, she added. She noted, however, that “we are not sure at the moment” about potential restrictions arising from government concerns about diversity, equity, and inclusion. 

 

Dr. Berretta explained that the HBTRC NIH contract “will end in October 2025. It is not known at this time whether and how the new contract, expected to start in November 2025, will be impacted.”

 

Dr. Berretta explained that “the current funding uncertainty creates some challenges, particularly for talent retention and long-term planning, both critical to our work.”

 

“The other 5 brain banks part of the NIH NeuroBioBank are in our same situation,” she added.

 

Dr. Sabina Berretta (McLean Hospital photo)

 

A family discussion and a decision

 

Dorlue was 63 and had been married to Doug for 32 years. After graduating from high school in 1976, she worked for 20 years in a Pacific Bell office. She volunteered at her church, participated in her son Ryan’s school PTA, and enjoyed family camping trips. As a young adult, Ryan tested negative for the HD gene.

 

Dorlue was remembered as having “a fighting spirit that never wavered in the face of her diagnosis” with HD, including participation in clinical trials in hopes of a cure.

 

Doug and Dorlue discussed, and then agreed to, donating her brain when she was no longer in “denial” about her disease and learning that Ryan was now free of the disease, Doug said in his presentation. Dorlue registered for the donation in 2012.

 

“It should be your decision and no one else’s,” Doug emphasized, noting that contemplating a donation can be “very stressful” because of all of the difficulties already involved in HD.

 

The decision must involve the person’s legal first of kin, who will see through the donation after the person has died.

 

There are many reasons to donate – or not donate, said Doug, noting that some might have religious reasons against the process.

 

He recommended that families start conversations about donations “early.”

 

“You can cancel at any time,” he said of the process. The opportunity to donate is “a blessing,” he added.

 

A ‘very professional’ organization

 

A person can pre-register their donation on the HBTRC website or register any time over the phone, even after an individual has died, Doug explained.

 

Doug spoke several times with Dr. Berretta.

 

“She’s very compassionate,” he said. “The organization is very professional. I really felt that they understood how difficult it was to go through that process, especially right after your loved one died.”

 

Doug noted several exclusionary criteria that might prevent a brain from being accepted, such as a delay of more than 24 hours in getting the brain to the bank; a stroke or penetrating head injury; or testing positive for HIV, hepatitis B, or hepatitis C.

 

Although “it costs a lot of money for the brain to be put on a plane and sent to Harvard,” the only charges covered by the family are the usual funeral costs, such as cremation or embalming, Doug said.

 

Just 24 hours to get the brain delivered

 

The 24-hour clock for the donation to be received starts at the moment the last person saw the deceased alive, Doug continued.

 

Dorlue died at 6 a.m., when a hospice nurse declared her dead. Doug contacted the funeral home, which needed to transport the body to the facility that “harvests” the brain. The funeral home worker took four hours to arrive, Doug said.

 

“We were ten hours into this before they even took the body out of the house,” he recalled. “I was pretty anxious that we get this thing off.”

 

The brain is packed in ice for transport and placed in the luggage area of the plane so that it stays cold throughout the flight, Doug explained.

Once it arrives at the HBTRC laboratories, the brain is immediately dissected. Part of it is immediately frozen and kept at minus 80 degrees centrigrade. Another part is immersed in formalin. It is then assessed by a neuropathologist, who generates a neuropathology report. Both preparations are made available to investigators.

 

Once the brain arrived at Harvard, Doug received a call reassuring him that it had arrived undisturbed and on time. To preserve the integrity of the tissue for research, the brain is ultimately frozen at minus 80 degrees centigrade.

 

Doug also sent the HBTRC Dorlue’s medical records to assist in their research on her brain.

 

“That’s a big part of what the scientists look at,” he said. “They compare the brain with the symptoms and see if there’s any similarities or not.”

 

Crucial work towards a cure

 

The HBTRC website has an FAQ, donation forms, and phone numbers for making a donation.

 

This HBTRC does crucial work in the quest for a cure.

 

Doug has signed up to donate his brain. I will do the same.

 

As Doug put it, the bank collects brains from around the U.S. and sends samples around the world.

 

“Who knows who’s going to find a cure,” he said.

More optimistic than ever, CHDI head scientist sees unprecedented mobilization in the fight to treat Huntington’s disease

 

In the wake of last week’s 20th Annual Huntington’s Disease Therapeutics Conference, the chief scientific officer for CHDI Foundation, Inc., declared that HD scientists had mustered unprecedented efforts toward therapies (treatments).

 

“I’ve been in the drug discovery business for over 30 years now,” Robert Pacifici, Ph.D., the CHDI head scientist, told me in a 37-minute video interview after the conference, referring to the key theme of crucial modifier genes, a focus of the meeting. “I’ve never seen the mobilization of efforts as quickly and as deliberately – from the identification of those genes to the understanding of how those genes mechanistically are having their effect – to actually developing candidate therapies that are modifying those processes.”

 

Dr. Pacifici observed that, in the HD field, “everybody’s pushing wherever they can to accelerate therapeutics. But we all know that sometimes you just hit roadblocks, you hit bottlenecks.”

 

He said that those difficulties can be overcome with “new technologies, new methods, new techniques,” which often result in “breakthrough moments. They allow you to do things that you just could never contemplate doing before.”

 

Dr. Robert Pacifici, wearing a Team Hope shirt from the Huntington's Disease Society of America, overseeing the 20th Annual HD Therapeutics Conference (photo by Gene Veritas, aka Kenneth P. Serbin)

 

The efforts forming around this hottest of topics in the HD field are “incredibly exciting,” Dr. Pacifici said. The “big news” over the next two years should include getting drugs that imitate the effect of the modifier genes – which research has demonstrated delay the onset of HD symptoms – into clinical trial programs.

 

As reported in this blog, the now defunct Triplet Therapeutics had aimed from 2020-2022 to develop and test a modifier gene drug (click here to read more).

 

Dr. Pacifici said that he is “more optimistic” than ever that HD drugs will get approved.

 

I attended the conference. Below you can watch a video of my interview with Dr. Pacifici.

 

 

 

Attacking the harmful protein

 

While this year’s Therapeutics Conference did not include any major positive announcements like the approval of a drug, Dr. Pacifici observed that it also did not bring the kind of disappointing news experienced by the HD community in 2021 with negative results from trials run by Roche and Wave Life Sciences.

 

The conference did bring reports from both Roche and Wave about their revised clinical trial programs. PCT Therapeutics and uniQure also reported on their ongoing clinical trials.

 

All four programs use drugs to lower the amount of harmful mutant huntingtin protein in the brain cells of patients. This is the first of three approaches to defeating HD, Dr. Pacifici recalled.

 

I will detail these updates soon.

 

‘Lucky’ and ‘unlucky’ genes

 

The second, more recent approach involves the search for drugs to imitate the modifier genes, as Dr. Pacifici noted above. These genes are related to somatic instability – the tendency of the expanded HD gene to expand further with time. This process can be triggered by negative modifier genes.

 

Dr. Pacific described those genes as “lucky” or “unlucky.” A good modifier gene can delay HD onset, whereas the bad one can hasten the start of the disease, he explained.

 

These genes act as “sentinels” in the bookkeeping of our DNA, Dr. Pacifici added. “We want our DNA to stay clean and error-free.”

 

Dr. Pacifici emphasized how more than 12,000 HD-affected individuals and their relatives in genetic research helped lead to the discovery of the modifier genes a decade ago. A study of a large group of people’s DNA is known as a Genome Wide Association Study (GWAS).

 

Fixing broken cells

 

The third approach to treating HD involves yet another set of genes that emerged from the HD GWAS. They were a key topic at the conference.

 

Dr. Pacifici stated that these genes are “every bit as validated” as the ones involving somatic instability. “We just don’t know the effect yet,” he said.

 

Dr. Pacifici added that understanding these genes will help answer a key unanswered question about HD: “what is it actually inside a cell at the molecular level that’s broken” and how to fix it.

 

All three of these areas could be targeted by an eventual cocktail of HD drugs, Dr. Pacifici said.

 

Key new genetic research and ‘rock star’ HD families

 

“We keep on thinking of ways of getting even more information out of persons with HD,” Dr. Pacifici said.

 

CHDI has announced that all 22,000 participants in Enroll-HD, the global registry of HD patients and relatives, will be full-genome-sequenced. That means their entire DNA will be  mapped.

 

“That’s a lot of data,” Dr. Pacifici noted. “It’s going to be the next set of breakthroughs, where we understand not just little bits of DNA information but the whole story for every participant.”

 

This will be “incredibly impactful,” he said.

 

The HD families that have provided all of this crucial data underlying these approaches to treatments are true “rock stars,” Dr. Pacifici said. Their interaction with HD scientists is critical, he concluded, to advancing scientific breakthroughs.

Savoring 20 years of my Huntington’s disease blog

 

This month I am celebrating the 20 years of this blog.

 

I began At Risk for Huntington’s Disease on January 10, 2005, wanting to “squeeze as much life into my days as possible” before experiencing the debilitating HD symptoms that led to my mother’s death a year later. Because I lived in what I called the “terrible and lonely HD closet” – fearful of genetic discrimination – I used the pseudonym “Gene Veritas,” “the truth in my genes.” That name reflected the fact that I had tested positive for the HD gene in 1999.

 

My mother died at 68, after two decades of debilitating symptoms, which was very painful to watch.

 

I turned 65 last month. By this age, I had expected to have full-blown HD, which would have left me unable to work, drive, or write.

 

But, according to my latest neurological checkup, I don’t yet have apparent HD symptoms!

 

In general, the more abnormal the gene, the earlier the age of disease onset. My mother and I have the same gene mutation, suggesting a similar disease path. However, although my mother’s symptoms started in her late 40s, one or more modifier genes, the functions of which were discovered a decade ago, have perhaps delayed my disease onset.

 

This article is number 336. Each day of good health is a blessing.

 

Gene Veritas (aka Kenneth P. Serbin) with his blog (photo by Regina Serbin)

 

The impact

 

In 2012, I exited the HD closet by publishing an essay – and using my real name, Kenneth P. Serbin – in The Chronicle of Higher Education. It was titled “Racing Against the Genetic Clock.” Going public opened new vistas of advocacy and enabled me to blog with greater transparency.

 

In December 2022. I published a detailed analysis of the blog in “Striving for a Realistic and Unapologetic View of Huntington’s Disease” in the Journal of Huntington’s Disease. It described how the blog has helped give voice to the HD community by exploring the major challenges faced by HD families, becoming a key reference for those families, and chronicling the quest to defeat the disorder.

 

As I observed, the blog has also “helped document the new and harrowing experience of living in the gray zone between a genetic test result and disease onset.”

 

At Risk for HD has addressed multiple topics including advocacy, caregiving, family trauma, coping strategies, genetic testing, discrimination, leaving the HD closet, participation in research and clinical trials, as well as religion, faith, and spirituality.

 

When my mother was diagnosed with HD in 1995 – two years after the discovery of the gene – little hope existed for treatments that could slow the progression of HD. However, in the past decade, advances in academic labs and biopharma firms have led to key clinical trials that show potential for affecting the course of HD and perhaps even a cure (click here to read more).

Telling the story of those complex developments has become a major focus of At Risk for HD. With the growing number of research projects, I have necessarily highlighted those that appear closest to producing actual drugs such as the Roche gene silencing program, which I have covered extensively.

 

In 2021, the first Roche trial showed lack of efficacy. In 2023 Roche started enrolling volunteers in a more focused trial to see if the drug might work at least in some patients. Other key trials are in progress or being planned.

 

Hoping for an HD-free world, savoring life

 

Writing the entries of At Risk for HD has given me great meaning and purpose, which researchers have identified as increasing well-being and positively impacting the course of the disease.

 

For now, I plan to continue blogging as long health permits – and until the quest for a cure is complete.

 

In February, I hope to attend the crucial 20th Annual HD Therapeutics Conference at the Parker Hotel in Palm Springs, CA. The conference is sponsored by CHDI Foundation, Inc., the largest private funder of HD research.

 

In 2011, I delivered the conference keynote speech before 250 scientists, physicians, and biopharma reps – a decisive step towards my complete exit from the closet in 2012 and chronicled in this blog.

 

I have described the conference as the “Super Bowl of HD research,” covered in many blog articles and videos of scientists (see, for example, this one).

 

With the rest of the HD community, I hope for the announcement of effective treatments. I very much look forward to reporting on progress.

 

Just as important is the need to savor life – another key lesson of my journey with the HD community, this blog, and my friends and family.

At Harvard-MGH’s Mouro Pinto Lab, deploying CRISPR in the quest to cure Huntington’s disease

 

With a $1 million grant from the Hereditary Disease Foundation (HDF), a team of top researchers led by Ricardo Mouro Pinto, Ph.D., of Harvard Medical School, is deploying CRISPR to target genetic modifiers of Huntington’s disease.

 

In brain cells, these modifiers accelerate or slow so-called somatic expansions in HD.

 

The Mouro Pinto Lab at Harvard-affiliated Massachusetts General Hospital (MGH) specializes in research on these expansions. Scientists describe this process as the tendency of the mutant, expanded, disease-causing huntingtin gene to keep expanding abnormally. This causes the dysfunction – and possibly also death – of brain cells, leading to HD symptoms  (click here to read more). As scientists now see somatic expansion as a key driver of HD, research on this process has burgeoned.

 

Investigators have identified the modifier genes affecting expansion through deep research in human data. In speeding or slowing somatic expansion, those genes can hasten or delay disease onset. Many academic and biopharma groups, including the Mouro Pinto Lab, are investigating modifiers as potential drug targets.

 

The Mouro Pinto Lab is focusing on how one modifier gene, MLH3, acts harmfully as a “scissors” in HD. (By convention, human MLH3 gene is always capitalized and italicized; in contrast, the non-human gene is rendered as Mlh3.)

 

In an August 7 interview at his lab, Dr. Mouro Pinto described an experimental drug his team is testing in mice to deactivate the MLH3 scissors, a potential first step in seeking a treatment in people.

 

“I'm extremely optimistic about our approach,” Dr. Mouro Pinto said. “We can see what our drug does to somatic expansions. Can it slow it down? And our preliminary data is very encouraging in the sense that we can do that.”

 

On August 10, Dr. Mouro Pinto provided an update on the project at HDF’s HD2024: Milton Wexler Biennial Symposium. Announced in October 2023, the foundation’s two-year Transformative Research Award supports his team’s research of “therapeutic targeting of somatic CAG expansions with CRISPR base editing.” A group of anonymous donors funds the award.

 

 

Above, at the HDF symposium, Dr. Mouro Pinto displays a slide demonstrating how his lab’s experimental drug slowed somatic expansion in the striatum of mouse brains. In humans, the striatum is one of the areas most affected by HD. Below, a Mouro Pinto slide illustrates how a drug could impact somatic expansion and therefore prevent or delay HD onset, or slow progression of the disease in humans (photo of Dr. Mouro Pinto by Gene Veritas, aka Kenneth P. Serbin, image of slide courtesy of Dr. Mouro Pinto). (To make it larger, click on an image.)

 

Innovative collaborators

 

Seven innovative labs are collaborating with the Mouro Pinto team.

 

James Gusella, Ph.D., whose Harvard lab discovered the huntingtin gene in 1993, is one of three co-investigators on the project.

 

Gusella’s team has developed the human cell line that “allows us to model somatic instability so we can test the drugs,” Dr. Mouro Pinto explained.  That cell line has the expansions of the segment of the DNA code CAG (cytosine, adenine, and guanine), identified in 1993 as the underlying cause of HD.

 

At the symposium the HDF awarded Gusella the Leslie Gehry Prize for Innovation in Science, including $100,000 for research and a plaque with a small sculpture by the renowned architect Frank Gehry.

 

Specialists in somatic expansion

 

A native of Porto, Portugal, Dr. Mouro Pinto received his Ph.D. in molecular genetics at Brunel University in England in 2010, focusing on Friedreich’s ataxia, a debilitating genetic neuromuscular disorder. Along with HD, Friedreich’s is one of more than 50 repeat expansion disorders. In Friedreich’s and others, somatic expansion also plays a role. Scientists also refer to this process as somatic instability.

 

From 2010-2015, Dr. Mouro Pinto worked as a postdoctoral fellow in the lab of Vanessa Wheeler, Ph.D., an associate professor of neurology at Harvard, MGH researcher, and pioneer in the study of somatic instability. The Wheeler lab is collaborating with the Mouro Pinto group on the HDF project.

 

For Portuguese-speaking advocates, in 2022 I interviewed Dr. Mouro Pinto in his native tongue, discussing his work and outlook for HD therapies. We spoke at the 17th HD Therapeutics Conference, sponsored by CHDI Foundation, Inc., the largest private funder of HD research and a backer of the Mouro Pinto Lab.

 

On August 6, the HDF and MGH co-hosted a tour of the Mouro Pinto Lab for about 20 HDF officials, donors, and HD family members. Dr. Wheeler participated, too. I took part at the invitation of the HDF. At the start, Dr. Mouro Pinto presented an overview of the HDF project.

 

 

Above, before the tour of his lab, Dr. Mouro Pinto presents a slide demonstrating the path of his scientific studies. Below, Dr. Mouro Pinto explains the purpose of a PCR (polymerase chain reaction) workstation, where they isolate and make billions of copies of the CAG repeat so they can study it in more detail (photos by Gene Veritas). 

 

 A key task: measuring the expansion

 

In 2016 Dr. Mouro Pinto won the first Berman-Topper Family HD Career Development Fellowship from the Huntington’s Disease Society of America. That funding allowed him to conduct research demonstrating that modifier genes can speed or slow somatic expansion in mice, he said.

 

According to Dr. Mouro Pinto, his lab’s more recent examination of postmortem tissue from HD patients revealed that somatic expansion had occurred in about 30 different brain regions. In all, 50 different tissues were examined, showing different rates of somatic expansion in the liver, muscle, kidney, and others. Some of the fastest expansion was in the brain, he added.

 

To measure a drug’s effect in a clinical trial, brain biopsies are currently not an option, Dr. Mouro Pinto pointed out. However, measuring somatic expansion in blood, liver, and cerebrospinal fluid, which bathes the brain, could serve as biomarkers. A biomarker is a sign of a disease or effect of a drug. He noted that other researchers are already investigating somatic expansion in the blood.

 

“What is the right tissue, bio fluid to obtain from the patient?” Dr. Mouro Pinto asked. “And then what is the right test to be sensitive and accurate? So those two things are actually other aspects of research in our lab that we're trying to develop.”

 

Having those biomarkers will be crucial if the potential CRISPR drug reaches a human clinical trial, he observed.

 

CRISPR: a one-time, permanent edit of the gene

 

CRISPR stands for “clustered regularly interspaced short palindromic repeats,” a strand of RNA that, when activated by an enzyme, can edit DNA. Bacteria evolved this technique to defend against viruses.

 

Jennifer Doudna, Ph.D., and Emmanuelle Charpentier, Ph.D., won the 2020 Nobel Prize in Chemistry for their work in identifying and understanding CRISPR. Click here to read more about CRISPR, its potential for treating HD, and its powerful implications for the future of humanity.

 

Scientists have now used CRISPR to edit human genes in labs and in clinical trials that have resulted in drugs approved by the U.S. Food and Drug Administration (FDA). In December 2023 the FDA approved two CRISPR drugs for sickle cell disease, an inherited disorder that primarily affects people of African descent.

 

This first wave of CRISPR clinical trials has started with the “lowest-hanging fruit,” diseases that “affect the liver or the eye or the ear,” Dr. Mouro Pinto pointed out. The brain is far more difficult to research, so it has been challenging to address brain diseases with CRISPR drugs, he said.

 

“You're doing it at the level of the DNA and that causes a permanent change,” he emphasized. “Once you treat and you introduce the change you made, that will stay in that cell forever.”

 

A CRISPR clinical trial “will look, essentially, the same as any other HD trial,” he explained. “You'll need to collect samples. And you'll need to conduct a battery of physical tests, cognitive tests and behavioral tests. It will still be evaluated exactly by the same standards as any other clinical trial.”

 

In contrast with most other HD drug approaches, CRISPR has a key, beneficial difference. “It’s a one-time treatment,” Dr. Mouro Pinto said.

 

An ‘amazing toolbox’

 

Dr. Mouro Pinto underscored that in addition to serving as a drug, CRISPR has provided an “amazing toolbox” for less costly and more efficient and precise lab research.

 

In contrast with the old, very expensive process of breeding large numbers of mice over years, CRISPR “has accelerated the rate of research tremendously” and dramatically reduced the numbers needed, he said. With CRISPR, they can much more quickly pursue tasks such as making mutations in mice or screening a large number of genes to see which might modify somatic expansion, he said. The lab’s paper on this topic will be published in Nature Genetics.

 

The lab also can deliver a CRISPR reagent to a young mouse, transforming it into a model for study and producing results in a few weeks.

 

A unique ‘humanized Mlh3 mouse’

 

Use of CRISPR enabled a “really critical” step in the HDF project: creation of what Dr. Mouro Pinto described as a “humanized Mlh3 mouse,” a unique research step. To prepare the potential CRISPR drug for testing in mice for efficacy against HD and safety, the lab introduced into the animals a small sequence of human DNA from the MLH3 gene.

 

The scientists have crossed these mice with engineered HD mice. After a few generations downstream, this will result in mice with the expanded and the humanized modifier gene, which will be tested with the CRISPR reagent to see if it stops somatic expansion, Dr. Mouro Pinto continued.

 

The crossing was also necessary to assure that the humanized segment of DNA itself does indeed experience somatic instability, because the goal of the research is to stop instability, he added.

 

Another key step will involve measuring the CRISPR reagent’s impact on somatic expansion, irregular movements, and behavioral symptoms in the mice, Dr. Mouro Pinto said. For this stage, the lab will have the key assistance of the “extremely experienced” Cathleen Lutz, Ph.D., M.B.A., vice president of  The Jackson Laboratory Rare Disease Translational Center, he noted.

 

‘Promoting the flavor without the scissors’

 

As it develops greater precision, the Mouro Pinto Lab has found that one of two MLH3 variants has the scissors that cause harmful genetic cutting. That gets closer to solving the HD puzzle.

 

In a February HDF webinar about the project, Dr. Mouro Pinto explained that in people without HD, the MLH3 variant without scissors – the good variant – is present.

 

He said that he is confident that promoting expression (activation) of the good variant over the bad would be better tolerated as a treatment than simply turning off the bad. He described this approach as “promoting the flavor without the scissors, as opposed to completely getting rid of the protein” that results from the gene.

 

“In a mouse that doesn’t have the scissors, you completely stabilize the repeat,” Dr. Mouro Pinto stated in the webinar. “We know that the scissors component of this protein is essential for promoting CAG expansions.”

 

Furthermore, in human HD cells the team not only reduced but eliminated the bad version of MLH3.

 

They achieved this using a technique known as base editing.

 

Dr. Mouro Pinto noted that with standard CRISPR editing, a sequence of DNA can be broken up, potentially causing unwanted effects. In contrast, in base editing, no breakage occurs, because scientists edit the DNA by simply changing a letter of the genetic code, for example, from A (adenine) to G (guanine), or C (cytosine) to T (thymine).

 

Significantly, his team edited both copies of the MLH3 gene and completely shifted expression from the “bad” version towards only making the “good” “scissor-less” version of MLH3 protein. As a result, the experiment completely stabilized the CAG repeat (i.e. the CAG stopped expanding in edited cells), Dr. Mouro Pinto stressed.

 

There are two bases because, as Dr. Mouro Pinto reminded, every cell has two copies of each gene – a copy from each parent.

 

Partnering on more precise gene editing

 

Only a few projects have started exploring base editing for HD, and most are happening in research labs such as his, Dr. Mouro Pinto said.

 

To maximize the benefits for HD patients, the HDF project will seek to improve on this editing.

 

Recognizing the many other labs are examining directly targeting the CAG expansion, Dr. Mouro Pinto believes that, instead, deactivating a modifier gene such as the MLH3 scissors is a safer and easier strategy.

 

On this aspect, the Mouro Pinto Lab will partner with co-investigator David Liu, Ph.D., of both Harvard and the Massachusetts Institute of Technology (MIT). Dr. Liu invented both base editing and prime editing.

 

As Dr. Mouro Pinto pointed out in our interview, base editing allows for more “precise base changes.” In the HDF webinar, he noted that this method prevents breaking up of the DNA.

 

Harvard’s Benjamin Kleinstiver, Ph.D., another innovative co-investigator, has engineered CRISPR enzymes that “literally can go anywhere in the genome,” Dr. Mouro Pinto added. This enables the team to target any sequence of DNA it needs to, he said.

 

The lab continues to seek improvements in its enzyme to “achieve highest specificity and maximum efficacy,” he said.

 

The potential path to a clinical trial

 

“It's too early” to gauge whether the experimental CRISPR reagent can undergo testing in humans and have a “therapeutic impact,” Dr. Mouro Pinto told me, noting that four key questions must be answered in mice first. The lab aims to answer them in the coming months.

 

He described the outcome needed in the series of mouse experiments: “Did we change the DNA? Yes. Okay. Did we change which version of MLH3 is made? Yes. Okay. Next. Did we reduce the CAG instability? Yes. And then do we have any impact on HD symptoms?”

 

Currently the lab is working on the first step, with “promising” indications so far, Dr. Mouro Pinto said.

 

If the project proves successful, other, distinct projects testing the reagent in other animals, such as nonhuman primates, would follow, Dr. Mouro Pinto explained. The HDF grant does not include funds for those steps.

 

Emphasizing safety, avoiding unwanted edits

 

Dr. Mouro Pinto underscored that the team strives to find the safest CRISPR drug possible.

 

In line with more stringent FDA standards and bioethical concerns regarding gene editing, the project must carry out “due diligence” to avoid “very serious adversity.” That includes so-called off-target effects of gene editing, in which a gene such as one for cancer is accidentally activated or turned off, Dr. Mouro Pinto cautioned.

 

“It is not uncommon for these drugs to have some activity in unwanted regions of the genome,” he explained.  “We need to spend a lot of time looking for unwanted modifications.”

 

The CRISPR agent is “not yet ready for the clinic,” Dr. Mouro Pinto added.

 

He noted that the project is not doing edits in the sex cells; offspring therefore cannot inherit any genetic changes.

 

 

Finding the best way to deliver the cargo

 

The lab has no name yet for the experimental reagent, that is, its CRISPR enzyme.

 

“This is still an experimental reagent,” Dr. Mouro Pinto stressed. “I don't want to create false expectations. We are primarily putting effort into making sure that our cargo is good, that it's really doing what we want.”

 

The “cargo,” the potential drug, needs to be delivered safely and effectively into the brain and to the right cells, Dr. Mouro Pinto said. A common strategy in gene therapy is using a virus, specifically, an adeno-associated virus (AAV).

 

The Mouro Pinto Lab is using an AAV that works well in mice but not possible for humans, he said. As part of the HDF project, the team is searching for the ideal delivery system, which could be an AAV, a lipid nanoparticle, or extracellular vesicle, he continued. All three are tiny.

 

“There are many people now working on AAVs that you inject systemically,” Dr. Mouro Pinto said. “You give it into a vein, they go everywhere in your body including crossing the blood-brain barrier and entering the brain.” They can reach “almost every single neuron in the brain,” he added.

 

The blood-brain barrier is a membrane that protects the brain from harmful substances and germs.

 

Another project collaborator, Benjamin Deverman, Ph.D., of Vector Engineering and Harvard and MIT, has greatly improved the ability of AAVs to cross the blood-brain barrier in humans. In May, these critical findings for solving brain disorders were published in Science magazine.

 

“It's going to unlock this sort of roadblock that we have with delivery,” Dr. Mouro Pinto said of this breakthrough.

 

Lipid nanoparticles also can be injected into the blood. Some researchers are exploring oral administration of extracellular vesicles.

 

These vehicles pose less burden on clinical trial participants and patients in comparison with other methods, such as spinal taps or direct injection into the brain, a “complex surgical procedure,” Dr. Mouro Pinto observed.

 

“We're a little bit agnostic to the delivery strategy,” Dr. Mouro Pinto said, noting that the science of these delivery methods is evolving rapidly. By the time the project concludes in October 2025, “there might be a variety of different delivery options that we may want to consider.”

 

“Synergizing” with other HDF awardees

 

Dr. Mouro Pinto sees “opportunities to synergize” with the team that also received a 2023 Transformative Research Award, under the leadership of Beverly Davidson, Ph.D., of the University of Pennsylvania and Jang-Ho Cha, M.D., Ph.D., the chief scientific officer of Latus Biosciences. Latus focuses on precision delivery of gene therapy. An expert in AAVs, Dr. Davidson presented the team’s work at the HDF symposium.

 

Titled “Advancing gene therapies for HD” and focusing on AAVs, that project could potentially provide a delivery system for the CRISPR reagent, Dr. Mouro Pinto said.

 

 

Dr. Beverly Davidson presenting her team’s work on AAVs at the 2024 HDF symposium (photo by Gene Veritas).

 

Getting to market, looking beyond HD

 

In the event of the CRISPR reagent’s success in the lab, MGH will assist in commercializing it, Dr. Mouro Pinto said.

 

The hospital could license the technology to a biopharma company or, as in the case of the Davidson-Cha project, to start a company like Latus to bring the drug through a clinical trial and to market.

 

“We're open to those conversations and we've been fortunate to have a very collaborative interaction with industry partners so far,” Dr. Mouro Pinto told me.

 

The problem of somatic expansion “is shared across a large number of repeat expansion diseases,” he observed. “Individually, they're rare diseases. Collectively, they're not a rare disease. They actually affect a large number of patients around the world.”

 

“If our hypothesis is correct, the therapeutic benefit will not be limited to HD patients,” he concluded.

 

Disclosure: the Hereditary Disease Foundation covered my travel expenses to tour the Mouro Pinto Lab and attend the 2024 symposium.

 

Sadly, Michael McCabe, a 62-year-old Boston HD man who told his story at this year’s HDF symposium, died suddenly on September 12. Donations in Michael’s memory are suggested to the Huntington’s Disease Society of America.

 

 

Gene Veritas (left) and Dr. Mouro Pinto in the MGH lab (personal photo)