How Leqembi became the biggest news in Alzheimer’s disease in 40 years, and what comes next
A few months ago, Betsy Groves traveled less than a mile from her home in Cambridge, Mass. to give a talk to a bunch of scientists. The scientists, who worked for the pharmaceutical companies Biogen and Eisai, wanted to know how she lived her life, how she thought about her future, and what it was like when a doctor’s appointment in 2021 gave her the worst possible news. Groves, 73, has Alzheimer’s disease. She caught it early, through a lumbar puncture that showed evidence of amyloid, an Alzheimer’s hallmark, in her cerebrospinal fluid. As a way of dealing with her diagnosis, she joined the Alzheimer’s Association’s National Early-Stage Advisory Board, which helped her shift into seeing her diagnosis as something she could use to help others.
After her talk, Groves stayed for lunch with the scientists, who were eager to put a face to their work. Biogen and Eisai were about to release the first drug to successfully combat Alzheimer’s in 40 years of experimental disaster. Their drug, which is known by the scientific name lecanemab and the marketing name Leqembi, was granted accelerated approval by the U.S. Food and Drug Administration last Friday, Jan. 6, after a study in 1,800 people showed that it reduced cognitive decline by 27 percent over 18 months.
It is no exaggeration to say that this result is a huge deal. The field of Alzheimer’s drug development has been absolutely littered with failures. Almost everything researchers have tried has tanked in clinical trials. “Most of the things that we've done have proven not to be effective, and it's not because we haven’t been taking a ton of shots at goal,” says Anton Porsteinsson, director of the University of Rochester Alzheimer's Disease Care, Research, and Education Program, who worked on the lecanemab trial. “I think it's fair to say you don't survive in this field unless you're an eternal optimist.”
As far back as 1984, a cure looked like it was within reach: Scientists discovered that the sticky plaques that develop in the brains of those who have Alzheimer’s are made up of a protein fragment called beta-amyloid. Buildup of beta-amyloid seemed to be sufficient to disrupt communication between, and eventually kill, memory cells. If that was true, then the cure should be straightforward: Stop the buildup of beta-amyloid; stop the Alzheimer’s disease.
It wasn’t so simple. Over the next 38 years, hundreds of drugs designed either to interfere with the production of abnormal amyloid or to clear it from the brain flamed out in trials. It got so bad that neuroscience drug divisions at major pharmaceutical companies (AstraZeneca, Pfizer, Bristol-Myers, GSK, Amgen) closed one by one, leaving the field to smaller, scrappier companies, like Cambridge-based Biogen and Tokyo-based Eisai. Some scientists began to dismiss the amyloid hypothesis altogether: If this protein fragment was so important to the disease, why didn’t ridding the brain of it do anything for patients? There was another abnormal protein that showed up in the brains of Alzheimer’s patients, called tau. Some researchers defected to the tau camp, or came to believe the proteins caused damage in combination.
The situation came to a head in 2021, when the FDA granted provisional approval to a drug called aducanumab, marketed as Aduhelm, against the advice of its own advisory council. The approval was based on proof that Aduhelm reduced beta-amyloid in the brain, even though one research trial showed it had no effect on people’s symptoms or daily life. Aduhelm could also cause serious side effects, like brain swelling and amyloid related imaging abnormalities (known as ARIA, these are basically micro-bleeds that appear on MRI scans). Without a clear benefit to memory loss that would make these risks worth it, Medicare refused to pay for Aduhelm among the general population. Two congressional committees launched an investigation into the drug’s approval, citing corporate greed, lapses in protocol, and an unjustifiably high price. (Aduhelm was also produced by the pharmaceutical company Biogen.)
To be clear, Leqembi is not the cure Alzheimer’s researchers hope for. While the drug is the first to show clear signs of a clinical benefit, the scientific establishment is split on how much of a difference Leqembi will make in the real world.
So far, Leqembi is like Aduhelm in that it has been given accelerated approval only for its ability to remove amyloid from the brain. Both are monoclonal antibodies that direct the immune system to attack and clear dysfunctional beta-amyloid. The difference is that, while that’s all Aduhelm was ever shown to do, Leqembi’s makers have already asked the FDA to give it full approval – a decision that would increase the likelihood that Medicare will cover it – based on data that show it also improves Alzheimer’s sufferer’s lives. Leqembi targets a different type of amyloid, a soluble version called “protofibrils,” and that appears to change the effect. “It can give individuals and their families three, six months longer to be participating in daily life and living independently,” says Claire Sexton, PhD, senior director of scientific programs & outreach for the Alzheimer's Association. “These types of changes matter for individuals and for their families.”
To be clear, Leqembi is not the cure Alzheimer’s researchers hope for. It does not halt or reverse the disease, and people do not get better. While the drug is the first to show clear signs of a clinical benefit, the scientific establishment is split on how much of a difference Leqembi will make in the real world. It has “a rather small effect,” wrote NIH Alzheimer’s researcher Madhav Thambisetty, MD, PhD, in an email to Leaps.org. “It is unclear how meaningful this difference will be to patients, and it is unlikely that this level of difference will be obvious to a patient (or their caregivers).” Another issue is cost: Leqembi will become available to patients later this month, but Eisai is setting the price at $26,500 per year, meaning that very few patients will be able to afford it unless Medicare chooses to reimburse them for it.
The same side effects that plagued Aduhelm are common in Leqembi treatment as well. In many patients, amyloid doesn’t just accumulate around neurons, it also forms deposits in the walls of blood vessels. Blood vessels that are shot through with amyloid are more brittle. If you infuse a drug that targets amyloid, brittle blood vessels in the brain can develop leakage that results in swelling or bleeds. Most of these come with no symptoms, and are only seen during testing, which is why they are called “imaging abnormalities.” But in situations where patients have multiple diseases or are prescribed incompatible drugs, they can be serious enough to cause death. The three deaths reported from Leqembi treatment (so far) are enough to make Thambisetty wonder “how well the drug may be tolerated in real world clinical practice where patients are likely to be sicker and have multiple other medical conditions in contrast to carefully selected patients in clinical trials.”
Porsteinsson believes that earlier detection of Alzheimer’s disease will be the next great advance in treatment, a more important step forward than Leqembi’s approval.
Still, there are reasons to be excited. A successful Alzheimer’s drug can pave the way for combination studies, in which patients try a known effective drug alongside newer, more experimental ones; or preventative studies, which take place years before symptoms occur. It also represents enormous strides in researchers’ understanding of the disease. For example, drug dosages have increased massively—in some cases quadrupling—from the early days of Alzheimer’s research. And patient selection for studies has changed drastically as well. Doctors now know that you’ve got to catch the disease early, through PET-scans or CSF tests for amyloid, if you want any chance of changing its course.
Porsteinsson believes that earlier detection of Alzheimer’s disease will be the next great advance in treatment, a more important step forward than Leqembi’s approval. His lab already uses blood tests for different types of amyloid, for different types of tau, and for measures of neuroinflammation, neural damage, and synaptic health, but commercially available versions from companies like C2N, Quest, and Fuji Rebio are likely to hit the market in the next couple of years. “[They are] going to transform the diagnosis of Alzheimer's disease,” Porsteinsson says. “If someone is experiencing memory problems, their physicians will be able to order a blood test that will tell us if this is the result of changes in your brain due to Alzheimer's disease. It will ultimately make it much easier to identify people at a very early stage of the disease, where they are most likely to benefit from treatment.”
Learn more about new blood tests to detect Alzheimer's
Early detection can help patients for more philosophical reasons as well. Betsy Groves credits finding her Alzheimer’s early with giving her the space to understand and process the changes that were happening to her before they got so bad that she couldn’t. She has been able to update her legal documents and, through her role on the Advisory Group, help the Alzheimer’s Association with developing its programs and support services for people in the early stages of the disease. She still drives, and because she and her husband love to travel, they are hoping to get out of grey, rainy Cambridge and off to Texas or Arizona this spring.
Because her Alzheimer’s disease involves amyloid deposits (a “substantial portion” do not, says Claire Sexton, which is an additional complication for research), and has not yet reached an advanced stage, Groves may be a good candidate to try Leqembi. She says she’d welcome the opportunity to take it. If she can get access, Groves hopes the drug will give her more days to be fully functioning with her husband, daughters, and three grandchildren. Mostly, she avoids thinking about what the latter stages of Alzheimer’s might be like, but she knows the time will come when it will be her reality. “So whatever lecanemab can do to extend my more productive ways of engaging with relationships in the world,” she says. “I'll take that in a minute.”
How a Deadly Fire Gave Birth to Modern Medicine
On the evening of November 28, 1942, more than 1,000 revelers from the Boston College-Holy Cross football game jammed into the Cocoanut Grove, Boston's oldest nightclub. When a spark from faulty wiring accidently ignited an artificial palm tree, the packed nightspot, which was only designed to accommodate about 500 people, was quickly engulfed in flames. In the ensuing panic, hundreds of people were trapped inside, with most exit doors locked. Bodies piled up by the only open entrance, jamming the exits, and 490 people ultimately died in the worst fire in the country in forty years.
"People couldn't get out," says Dr. Kenneth Marshall, a retired plastic surgeon in Boston and president of the Cocoanut Grove Memorial Committee. "It was a tragedy of mammoth proportions."
Within a half an hour of the start of the blaze, the Red Cross mobilized more than five hundred volunteers in what one newspaper called a "Rehearsal for Possible Blitz." The mayor of Boston imposed martial law. More than 300 victims—many of whom subsequently died--were taken to Boston City Hospital in one hour, averaging one victim every eleven seconds, while Massachusetts General Hospital admitted 114 victims in two hours. In the hospitals, 220 victims clung precariously to life, in agonizing pain from massive burns, their bodies ravaged by infection.
The scene of the fire.
Boston Public Library
Tragic Losses Prompted Revolutionary Leaps
But there is a silver lining: this horrific disaster prompted dramatic changes in safety regulations to prevent another catastrophe of this magnitude and led to the development of medical techniques that eventually saved millions of lives. It transformed burn care treatment and the use of plasma on burn victims, but most importantly, it introduced to the public a new wonder drug that revolutionized medicine, midwifed the birth of the modern pharmaceutical industry, and nearly doubled life expectancy, from 48 years at the turn of the 20th century to 78 years in the post-World War II years.
The devastating grief of the survivors also led to the first published study of post-traumatic stress disorder by pioneering psychiatrist Alexandra Adler, daughter of famed Viennese psychoanalyst Alfred Adler, who was a student of Freud. Dr. Adler studied the anxiety and depression that followed this catastrophe, according to the New York Times, and "later applied her findings to the treatment World War II veterans."
Dr. Ken Marshall is intimately familiar with the lingering psychological trauma of enduring such a disaster. His mother, an Irish immigrant and a nurse in the surgical wards at Boston City Hospital, was on duty that cold Thanksgiving weekend night, and didn't come home for four days. "For years afterward, she'd wake up screaming in the middle of the night," recalls Dr. Marshall, who was four years old at the time. "Seeing all those bodies lined up in neat rows across the City Hospital's parking lot, still in their evening clothes. It was always on her mind and memories of the horrors plagued her for the rest of her life."
The sheer magnitude of casualties prompted overwhelmed physicians to try experimental new procedures that were later successfully used to treat thousands of battlefield casualties. Instead of cutting off blisters and using dyes and tannic acid to treat burned tissues, which can harden the skin, they applied gauze coated with petroleum jelly. Doctors also refined the formula for using plasma--the fluid portion of blood and a medical technology that was just four years old--to replenish bodily liquids that evaporated because of the loss of the protective covering of skin.
"Every war has given us a new medical advance. And penicillin was the great scientific advance of World War II."
"The initial insult with burns is a loss of fluids and patients can die of shock," says Dr. Ken Marshall. "The scientific progress that was made by the two institutions revolutionized fluid management and topical management of burn care forever."
Still, they could not halt the staph infections that kill most burn victims—which prompted the first civilian use of a miracle elixir that was being secretly developed in government-sponsored labs and that ultimately ushered in a new age in therapeutics. Military officials quickly realized this disaster could provide an excellent natural laboratory to test the effectiveness of this drug and see if it could be used to treat the acute traumas of combat in this unfortunate civilian approximation of battlefield conditions. At the time, the very existence of this wondrous medicine—penicillin—was a closely guarded military secret.
From Forgotten Lab Experiment to Wonder Drug
In 1928, Alexander Fleming discovered the curative powers of penicillin, which promised to eradicate infectious pathogens that killed millions every year. But the road to mass producing enough of the highly unstable mold was littered with seemingly unsurmountable obstacles and it remained a forgotten laboratory curiosity for over a decade. But Fleming never gave up and penicillin's eventual rescue from obscurity was a landmark in scientific history.
In 1940, a group at Oxford University, funded in part by the Rockefeller Foundation, isolated enough penicillin to test it on twenty-five mice, which had been infected with lethal doses of streptococci. Its therapeutic effects were miraculous—the untreated mice died within hours, while the treated ones played merrily in their cages, undisturbed. Subsequent tests on a handful of patients, who were brought back from the brink of death, confirmed that penicillin was indeed a wonder drug. But Britain was then being ravaged by the German Luftwaffe during the Blitz, and there were simply no resources to devote to penicillin during the Nazi onslaught.
In June of 1941, two of the Oxford researchers, Howard Florey and Ernst Chain, embarked on a clandestine mission to enlist American aid. Samples of the temperamental mold were stored in their coats. By October, the Roosevelt Administration had recruited four companies—Merck, Squibb, Pfizer and Lederle—to team up in a massive, top-secret development program. Merck, which had more experience with fermentation procedures, swiftly pulled away from the pack and every milligram they produced was zealously hoarded.
After the nightclub fire, the government ordered Merck to dispatch to Boston whatever supplies of penicillin that they could spare and to refine any crude penicillin broth brewing in Merck's fermentation vats. After working in round-the-clock relays over the course of three days, on the evening of December 1st, 1942, a refrigerated truck containing thirty-two liters of injectable penicillin left Merck's Rahway, New Jersey plant. It was accompanied by a convoy of police escorts through four states before arriving in the pre-dawn hours at Massachusetts General Hospital. Dozens of people were rescued from near-certain death in the first public demonstration of the powers of the antibiotic, and the existence of penicillin could no longer be kept secret from inquisitive reporters and an exultant public. The next day, the Boston Globe called it "priceless" and Time magazine dubbed it a "wonder drug."
Within fourteen months, penicillin production escalated exponentially, churning out enough to save the lives of thousands of soldiers, including many from the Normandy invasion. And in October 1945, just weeks after the Japanese surrender ended World War II, Alexander Fleming, Howard Florey and Ernst Chain were awarded the Nobel Prize in medicine. But penicillin didn't just save lives—it helped build some of the most innovative medical and scientific companies in history, including Merck, Pfizer, Glaxo and Sandoz.
"Every war has given us a new medical advance," concludes Marshall. "And penicillin was the great scientific advance of World War II."
This Boy Struggled to Walk Before Gene Therapy. Now, Such Treatments Are Poised to Explode.
Conner Curran was diagnosed with Duchenne's muscular dystrophy in 2015 when he was four years old. It's the most severe form of the genetic disease, with a nearly inevitable progression toward total paralysis. Many Duchenne's patients die in their teens; the average lifespan is 26.
But Conner, who is now 10, has experienced some astonishing improvements in recent years. He can now walk for more than two miles at a time – an impossible journey when he was younger.
In 2018, Conner became the very first patient to receive gene therapy specific to treating Duchenne's. In the initial clinical trial of nine children, nearly 80 percent reacted positively to the treatment). A larger-scale stage 3 clinical trial is currently underway, with initial results expected next year.
Gene therapy involves altering the genes in an individual's cells to stop or treat a disease. Such a procedure may be performed by adding new gene material to existing cells, or editing the defective genes to improve their functionality.
That the medical world is on the cusp of a successful treatment for a crippling and deadly disease is the culmination of more than 35 years of work by Dr. Jude Samulski, a professor of pharmacology at the University of North Carolina School of Medicine in Chapel Hill. More recently, he's become a leading gene therapy entrepreneur.
But Samulski likens this breakthrough to the frustrations of solving a Rubik's cube. "Just because one side is now all the color yellow does not mean that it is completely aligned," he says.
Although Conner's life and future have dramatically improved, he's not cured. The gene therapy tamed but did not extinguish his disorder: Conner is now suffering from the equivalent of Becker's muscular dystrophy, a milder form of the disease with symptoms that appear later in life and progress more slowly. Moreover, the loss of muscle cells Conner suffered prior to the treatment is permanent.
"It will take more time and more innovations," Samulski says of finding an even more effective gene therapy for muscular dystrophy.
Conner's family is still overjoyed with the results. "Jude's grit and determination gave Conner a chance at a new life, one that was not in his cards before gene therapy," says his mother Jessica Curran. She adds that "Conner is more confident than before and enjoys life, even though he has limitations, if compared to his brothers or peers."
Conner Curran holding a football post gene therapy treatment.
Courtesy of the Curran family
For now, the use of gene therapy as a treatment for diseases and disorders remains relatively isolated. On paper at least, progress appears glacially slow. In 2018, there were four FDA-approved gene therapies (excluding those reliant on bone marrow/stem cell transplants or implants). Today, there are 10. One therapy is solely for the cosmetic purpose of reducing facial lines and folds.
Nevertheless, experts in the space believe gene therapy is poised to expand dramatically.
"Certainly in the next three to five years you will see dozens of gene therapies and cell therapies be approved," says Dr. Pavan Cheruvu, who is CEO of Sio Gene Therapies in New York. The company is developing treatments for Parkinson's disease and Tay-Sachs, among other diseases.
Cheruvu's conclusion is supported by NEWDIGS, a think tank at the Massachusetts Institute of Technology that keeps tabs on gene therapy developments. NEWDIGS predicts there will be at least 60 gene therapies approved for use in the U.S. by the end of the decade. That number could be closer to 100 if Chinese researchers and biotech ventures decide the American market is a good fit for the therapies they develop.
"We are watching something of a conditional evolution, like a dot-com, or cellphones that were sizes of shoeboxes that have now matured to the size of wafers. Our space will follow along very similarly."
Dr. Carsten Brunn, a chemist by training and CEO of Selecta Biosciences outside of Boston, is developing ways to reduce the immune responses in patients who receive gene therapy. He observes that there are more than 300 therapies in development and thousands of clinical trials underway. "It's definitely an exciting time in the field," he says.
That's a far cry from the environment of little more than a decade ago. Research and investment in gene therapy had been brought low for years after the death of teenager Jesse Gelsinger in 1999 while he had been enrolled in a clinical trial to treat a liver disease. Gene therapy was a completely novel concept back then, and his death created existential questions about whether it was a proper pathway to pursue. Cheruvu, a cardiologist, calls the years after Gelsinger's death an "ice age" for gene therapy.
However, those dark years eventually yielded to a thaw. And while there have been some recent stumbles, they are considered part of the trial-and-error that has often accompanied medical research as opposed to an ominous "stop" sign.
The deaths of three patients last year receiving gene therapy for myotubular myopathy – a degenerative disease that causes severe muscle weakness – promptly ended the clinical trial in which they were enrolled. However, the incident caused few ripples beyond that. Researchers linked the deaths to dosage sizes that caused liver toxicity, as opposed to the gene therapy itself being an automatic death sentence; younger patients who received lower doses due to a less advanced disease state experienced improvements.
The gene sequencing and editing that helped create vaccines for COVID-19 in record time also bolstered the argument for more investment in research and development. Cheruvu notes that the field has usually been the domain of investors with significant expertise in the field; these days, more money is flowing in from generalists.
The Challenges Ahead
What will be the next step in gene therapy's evolution? Many of Samulski's earliest innovations came in the laboratory, for example. Then that led to him forming a company called AskBio in collaboration with the Muscular Dystrophy Association. AskBio sold its gene therapy to Pfizer five years ago to assure that enough could be manufactured for stage 3 clinical trials and eventually reach the market.
Cheruvu suggests that many future gene therapy innovations will be the result of what he calls "congruent innovation." That means publicly funded laboratories and privately funded companies might develop treatments separately or in collaboration. Or, university scientists may depend on private ventures to solve one of gene therapy's most vexing issues: producing enough finished material to test and treat on a large scale. "Manufacturing is a real bottleneck right now," Brunn says.
The alternative is referred to in the sector as the "valley of death": a lab has found a promising treatment, but is not far enough along in development to submit an investigational new drug application with the FDA. The promise withers away as a result. But the new abundance of venture capital for gene therapy has made this scenario less of an issue for private firms, some of which have received hundreds of millions of dollars in funding.
There are also numerous clinical challenges. Many gene therapies use what are known as adeno-associated virus vectors (AAVs) to deliver treatments. They are hollowed-out husks of viruses that can cause a variety of mostly mild maladies ranging from colds to pink eye. They are modified to deliver the genetic material used in the therapy. Most of these vectors trigger an antibody reaction that limits treatments to a single does or a handful of smaller ones. That can limit the potential progress for patients – an issue referred to as treatment "durability."
Although vectors from animals such as horses trigger far less of an antibody reaction in patients -- and there has been significant work done on using artificial vectors -- both are likely years away from being used on a large scale. "For the foreseeable future, AAV is the delivery system of choice," Brunn says.
Also, there will likely be demand for concurrent gene therapies that can lead to a complete cure – not only halting the progress of Duchenne's in kids like Conner Curran, but regenerating their lost muscle cells, perhaps through some form of stem cell therapy or another treatment that has yet to be devised.
Nevertheless, Samulski believes demand for imperfect treatments will be high – particularly with a disease such as muscular dystrophy, where many patients are mere months from spending the remainder of their lives in wheelchairs. But Samulski believes those therapies will also inevitably evolve into something far more effective.
"We are watching something of a conditional evolution, like a dot-com, or cellphones that were sizes of shoeboxes that have now matured to the size of wafers," he says. "Our space will follow along very similarly."
Jessica Curran will remain forever grateful for what her son has received: "Jude gave us new hope. He gave us something that is priceless – a chance to watch Conner grow up and live out his own dreams."