New Hope for Organ Transplantation: Life Without Anti-Rejection Drugs
Rob Waddell dreaded getting a kidney transplant. He suffers from a genetic condition called polycystic kidney disease that causes the uncontrolled growth of cysts that gradually choke off kidney function. The inherited defect has haunted his family for generations, killing his great grandmother, grandmother, and numerous cousins, aunts and uncles.
But he saw how difficult it was for his mother and sister, who also suffer from this condition, to live with the side effects of the drugs they needed to take to prevent organ rejection, which can cause diabetes, high blood pressure and cancer, and even kidney failure because of their toxicity. Many of his relatives followed the same course, says Waddell: "They were all on dialysis, then a transplant and ended up usually dying from cancers caused by the medications."
When the Louisville native and father of four hit 40, his kidneys barely functioned and the only alternative was either a transplant or the slow death of dialysis. But in 2009, when Waddell heard about an experimental procedure that could eliminate the need for taking antirejection drugs, he jumped at the chance to be their first patient. Devised by scientists at the University of Louisville and Northwestern University, the innovative approach entails mixing stem cells from the live kidney donor with that of the recipient to create a hybrid immune system, known as a chimera, that would trick the immune system and prevent it from attacking the implanted kidney.
The procedure itself was done at Northwestern Memorial Hospital in Chicago, using a live kidney donated by a neighbor of Waddell's, who camped out in Chicago during his recovery. Prior to surgery, Waddell underwent a conditioning treatment that consisted of low dose radiation and chemotherapy to weaken his own immune system and make room for the infusion of stem cells.
"The low intensity chemo and radiation conditioning regimen create just enough space for the donor stem cells to gain a foothold in the bone marrow and the donor's immune system takes over," says Dr. Joseph Levanthal, the transplant surgeon who performed the operation and director of kidney and pancreas transplantation at Northwestern University Feinberg School of Medicine. "That way the recipient develops an immune system that doesn't see the donor organ as foreign."
"As a surgeon, I saw what my patients had to go through—taking 25 pills a day, dying at an early age from heart disease, or having a 35% chance of dying every year on dialysis."
A week later, Waddell had the kidney transplant. The following day, he was infused with a complex cellular cocktail that included blood-forming stem cells derived from his donor's bone marrow mixed what are called tolerance inducing facilitator cells (FCs); these cells help the foreign stem cells get established in the recipient's bone marrow.
Over the course of the following year, he was slowly weaned off of antirejection medications—a precaution in case the procedure didn't work—and remarkably, hasn't needed them since. "I felt better than I had in decades because my kidneys [had been] degrading," recalls Waddell, now 54 and a CPA for a global beverage company. And what's even better is that this new approach offers hope for one of his sons who has also inherited the disorder.
Kidney transplants are the most frequent organ transplants in the world and more than 23,000 of these procedures were done in the United States in 2019, according to the United Network for Organ Sharing. Of this, about 7,000 operations are done annually using live organ donors; the remainder use organs from people who are deceased. Right now, this revolutionary new approach—as well as a similar strategy formulated by Stanford University scientists--is in the final phase of clinical trials. Ultimately, this research may pave the way towards realizing the holy grail of organ transplantation: preventing organ rejection by creating a tolerant state in which the recipient's immune system is compatible with the donor, which would eliminate the need for a lifetime of medications.
"As a surgeon, I saw what my patients had to go through—taking 25 pills a day, dying at an early age from heart disease, or having a 35% chance of dying every year on dialysis," says Dr. Suzanne Ildstad, a transplant surgeon and director of the Institute for Cellular Therapeutics at the University of Louisville, whose discovery of facilitator cells were the basis for this therapeutic platform. Ildstad, who has spent more than two decades searching for a better way, says, "This is something I have worked for my entire life."
The Louisville group uses a combination of chemo and radiation to replace the recipient's immune and blood forming cells with that of the donor. In contrast, the Stanford protocol involves harvesting the donor's blood stem cells and T-cells, which are the foot soldiers of the immune system that fight off infections and would normally orchestrate the rejection of the transplanted organ. Their transplant recipients undergo a milder form of "conditioning" that only radiates discrete parts of the body and selectively targets the recipient's T-cells, creating room for both sets of T-cells, a strategy these researchers believe has a better safety profile and less of a chance of rejection.
"We try to achieve immune tolerance by a true chimerism," says Dr. Samuel Strober, a professor of medicine for immunology and rheumatology at Stanford University and a leader of this research team. "The recipients immune system cells are maintained but mixed in the blood with that of the donor."
Studies suggest both approaches work. In a 2018 clinical trial conducted by Talaris Therapeutics, a Louisville-based biotech founded by Ildstad, 26 of 37 (70%) of the live donor kidney transplant recipients no longer need immunosuppressants. Last fall, Talaris began the final phase of clinical tests that will eventually encompass more than 120 such patients.
The Stanford group's cell-based immunotherapy, which is called MDR-101 and is sponsored by the South San Francisco biotech, Medeor Therapeutics, has had similar results in patients who received organs from live donors who were either well matched, such as one from siblings, meaning they were immunologically identical, or partially matched; Talaris uses unrelated donors where there is only a partial match.
In their 2020 clinical trial of 51 patients, 29 were fully matched and 22 were a partial match; 22 of the fully matched recipients didn't need antirejection drugs and ten of the partial matches were able to stop taking some of these medications without rejection. "With our fully matched, roughly 80% have been completely off drugs up to 14 years later," says Strober, "and reducing the number of drugs from three to one [in the partial matches] means you have far fewer side effects. The goal is to get them off of all drugs."
But these protocols are limited to a small number of patients—living donor kidney recipients. As a consequence, both teams are experimenting with ways to broaden their approach so they can use cadaver organs from deceased donors, with human tests planned in the coming year. Here's how that would work: after the other organs are removed from a deceased donor, stem cells are harvested from the donor's vertebrae in the spinal column and then frozen for storage.
"We do the transplant and give the patient a chance to recover and maintain them on drugs," says Ildstad. "Then we do the tolerance conditioning at a later stage."
If this strategy is successful, it would be a genuine game changer, and open the door to using these protocols for transplanting other cadaver organs, including the heart, lungs and liver. While the overall procedure is complex and costly, in the long run it's less expensive than repeated transplant surgeries, the cost of medications and hospitalizations for complications caused by the drugs, or thrice weekly dialysis treatments, says Ildstad.
And she adds, you can't put a price tag on the vast improvement in quality of life.
Naked Mole Rats Defy Aging. One Scientist Has Dedicated Her Career to Finding Out How.
Rochelle "Shelley" Buffenstein has one of the world's largest, if not the largest, lab-dwelling colonies of the naked mole rat. (No one has done a worldwide tabulation, but she has 4,500 of them.) Buffenstein has spent decades studying the little subterranean-dwelling rodents. Over the years, she and her colleagues have uncovered one surprising discovery after another, which has led them to re-orient the whole field of anti-aging research.
Naked mole rats defy everything we thought we knew about aging. These strange little rodents from arid regions of Africa, such as Kenya, Ethiopia and Somalia, live up to ten times longer than their size would suggest. And unlike virtually every other animal, they don't lose physical or cognitive abilities with age, and even retain their fertility up until the end of life. They appear to have active defenses against the ravages of time, suggesting that aging may not be inevitable. Could these unusual creatures teach humans how to extend life and ameliorate aging?
Buffenstein, who is senior principle investigator at Calico Life Sciences, has dedicated her life to finding out. Her early interest in the animals of what is now Zimbabwe led to her current position as a cutting-edge anti-aging researcher at Calico, the Google-funded health venture launched in 2013. The notoriously secretive company is focused on untangling the mysteries of why animals and people age, and whether there are ways to slow or temporarily arrest the process.
The small, wrinkly animal, which lives in underground burrows in the hot, arid regions of Africa, is hardly the beauty queen of the mammalian kingdom. Furless, buck-toothed and tiny-eyed, the creatures look like they could use a good orthodontist, a protective suit of clothes and possibly, some spectacles to enhance their eyesight. But these rats more than make up for their unimpressive looks with their superlative ability to adapt to some of the most inhospitable conditions on earth.
Based on the usual rule that body size predicts lifespan, naked mole rats shouldn't live that long. After all, similarly-sized rodents like mice have a life expectancy of two years or less. But Buffenstein was one of the first scientists to recognize that naked mole rats live an extraordinarily long time, with her oldest animal approaching 39 years of age. In addition, they never become geriatric in the human sense, defying the common signs of aging — age-related diseases, cognitive decline and even menopause. In fact, the queens, or females that do all the breeding in a bee-like underground colony, remain fertile and give birth to healthy pups up until what would be considered very old age in humans. And the naked mole rat has other curious abilities, such as the ability to endure extreme low-oxygen, or hypoxic, conditions like those they encounter in their underground nests.
"One thing we've learned from these animals is that they stay healthy until the very end."
It's not that the naked mole rat isn't subject to the vicissitudes of life, or the normal wear and tear of biological processes. Over the years, Buffenstein and her colleagues have discovered that, while the process of oxidative stress — thought for 50 years to be the main cause of aging — occurs in the naked mole rat just as in any other animal, its damage does not accumulate with age. Oxidative stress occurs during normal cell metabolism when oxygen "free radicals" with one or more unpaired electrons wreak havoc on large cellular molecules, leaving microscopic debris in their wake that clogs up the gears of healthy cell function. Somehow, naked mole rats have an enhanced ability to clear out the damaged cells and molecules before they can set off the usual chain reaction of cell dysfunction and death, according to a 2013 paper in which Buffenstein is the lead author.
Oxidative stress is not the only factor known to be problematic in aging. Slowly accumulating damage to DNA typically leads to protein malfunction and improper folding. In humans and most other animals, these protein fragments can accumulate in cells and gum up the works. Only not so much in naked mole rats, which are able to maintain normal protein folding throughout their long life. After years of discoveries like these, Buffenstein has gradually reframed her focus from "what goes wrong to produce aging?" to "what goes right in the naked mole rat to help it defy the normal wear and tear of life?" Buffenstein's research suggests that the tiny mammals have a unique ability to somehow clear out damaged protein fragments and other toxic debris before they can cause disease and aging.
How She Got Here
Buffenstein ascribes her initial acquaintance with the naked mole rat to serendipity. Back in 1979, her postgraduate mentor Jenny Jarvis at the University of Cape Town in South Africa kept a small colony of rats in her office while studying the mechanisms that lead to the animals' unusual adaptive capabilities. It was Buffenstein's job to take care of them. Working with Jarvis, Buffenstein focused on understanding their unique adaptations to the extreme conditions of their natural habitat.
They studied the unusual behaviors regulating the rat colonies. For instance, they observed that designated "workers" dig the entire colony's underground tunnels and a single reproducing female breeds with only a small number of males. Buffenstein also examined how these animals are able to survive without the "sunshine hormone" — vitamin D — and their unusual modes of regulating their internal temperatures and converting food into energy. Though classified as mammals, the rodents simply don't conform to the mammalian handbook, having found ingenuous ways to alter their bodies and behavior that is fine-tuned to the scorching heat and aridity of their environment.
To escape the heat, they simply burrow underground and live in elaborate tunnels. To cope with the low-oxygen conditions underground, they slowed their metabolism and learned to live for extended periods of time in such hypoxic conditions that an ordinary animal would quickly suffocate. But it was slowly dawning on Buffenstein that the small creatures were exceptional in additional ways.
When Buffenstein got her first academic position at the University of Witwatersrand in Johannesburg, Jarvis said she could take some of the naked mole rats with her. When she did, Buffenstein noticed that the animals were living far longer than similarly sized rodents. "At that stage, they were about ten years old. Little did I know how long they would eventually show us they could live," she says.
In 1997, after accepting a position at the City College of New York, Buffenstein moved to the U.S. and took her rat colony with her. There she was able to pursue an evolving narrative about the humble naked mole rat that continued to defy expectations. As the years passed, it was becoming more and more evident that her observations could have major implications for aging research. Eventually, she took a position at the Barshop Institute for Aging and Longevity Studies in San Antonio, Texas.
One early observation of Buffenstein's suggested that the species most often used in aging research—mice, roundworms, fruit flies and yeast—have short lifespans and poor defenses against aging. These animals provide important insights into how aging works, and have revealed possible targets for intervention. But they don't show what goes right in apparently non-aging animals like the naked mole rat.
Buffenstein's years of studying the rats has laid the foundation for a whole new perspective in aging research.
"My hypothesis," she says, "is that naked mole rats are very good at removing damaged macromolecules and cells, thereby maintaining homeostasis and cell and tissue function. All the repair pathways examined by us and others in the field point to more efficient repair and more rapid responses to damaging agents." These include things like free radicals and radiation.
Buffenstein’s Legacy
Some researchers today are building on Buffenstein's foundational discoveries to home in on possible anti-aging mechanisms that lead to the extraordinary resilience of naked mole rats. University of Cambridge researcher and co-founder of the institution's Naked Mole-Rat Initiative, Ewan St. John Smith, is studying the animal's resistance to cancer.
In a 2020 paper published in Nature, Smith and his colleagues established that naked mole rats harbor cancer-causing genes, and these genes occasionally create cancer cells. But something in the rats shuts the multiplication process down before the cells can grow out of control and form tumors. Now, scientists want to know what mechanisms, exactly, are at play in preventing the cells from invading healthy tissues. Smith has hypothesized that the answer is somehow embedded in interactions in the cells' microenvironment.
He also thinks the animal's immune system could just be very effective at seeking out and destroying cancer cells. Several current cancer therapies work by boosting the body's immune system so it can attack and eliminate the toxic cells. It's possible that the naked mole rat's immune system naturally goes into hyper-drive when cancer cells appear, enabling it to nip the disease in the bud before tumors can form. A pharmacologist by training, Smith thinks that if there is some chemical mediator in the naked mole rat that supercharges its immune cells, perhaps that mediator can be synthesized in a drug to treat humans for cancer.
The naked mole rat's extreme tolerance to hypoxia could also play a role. "Interestingly," he says, "when cells become cancerous, they also become hypoxic, and naked mole rats are known to be very resistant to hypoxia.
He notes that a form of low-level hypoxia is also present in the bodies and brains of both aged mice and older humans. It's commonly seen in the brains of humans with Alzheimer's disease and other forms of age-related dementia. This suggests that hypoxia in humans — and in other mammals — may have a role to play in Alzheimer's and the aging process itself. Resistance to hypoxia could be why the naked mole rat, in Smith's words, "chugs along quite happily" in conditions that in humans are associated with disease and decline.
Smith cheerfully acknowledges his debt to Buffenstein for laying so much of the groundwork in a field rife with possible implications for anti-aging. "Shelley is amazing," he says. "Naked mole rats have a queen and I always refer to her as the queen of the naked mole rat world." In fact, Buffenstein gave Smith his first colony of rats, which he's since grown to about 150. "Some of them will still be around when I retire," he jokes.
Vera Gorbunova, a professor of biology and oncology at the University of Rochester who studies both longevity and cancer in naked mole rats, credits Buffenstein with getting others to study the animals for anti-aging purposes. Gorbunova believes that "cancer and aging go hand-in-hand" and that longer-lived animals have better, more accurate DNA repair.
Gorbunova is especially interested in the naked mole rat's ability to secrete a superabundance of a "super-sugar" molecule called hyaluronan, a ubiquitous additive to skin creams for its moisturizing effect. Gorbunova and others have observed that the presence of high concentrations of hyaluronan in the naked mole rat's extracellular matrix — the chemical-rich solution between cells — prevents the overcrowding of cells. This, perhaps, could be the key to the animal's ability to stop tumors from forming.
Hyaluronan is also present in the extracellular matrix of humans, but the naked mole rat molecule is more than five times larger than the versions found in humans or mice, and is thought to play a significant part in the animal's DNA repair. But just rubbing a cream containing hyaluronan over your skin won't stop cancer or aging. High concentrations of the substance in the extracellular matrix throughout your body would likely be needed.
Gorbunova notes that the naked mole rat offers a multitude of possibilities that could eventually lead to drugs to slow human aging. "I'm optimistic that there are many different strategies, because the naked mole rat likely has many processes going on that fight aging," she says. "I think that in a relatively short time, there will be bonafide treatments to test in animals. One thing we've learned from these animals is that they stay healthy until the very end."
So if naked mole rats don't become frail with age or develop age-related diseases, what does kill them? The answer, unfortunately, is usually other naked mole rats. Buffenstein has long noted that even though they live in highly cooperative colonies, they can be quite cantankerous when there's a disruption in the hierarchy, a sentiment echoed by Gorbunova. "Sometimes there are periods of peace and quiet, but if something happens to the queen, all hell breaks loose," she says. "If the queen is strong, everybody knows their place," but if the queen dies, the new queen is inevitably decided by violent competition.
To the casual observer, a strange, wrinkly rodent like the naked mole rat might seem to have little to teach us about ourselves, but Buffenstein is confident that her discoveries could have major implications for human longevity research. Today, at Calico's labs in San Francisco, she's focused entirely on the determining how anti-aging defense mechanisms in the rats could lead to similar defenses being stimulated or introduced in humans.
"The million-dollar question is, what are the mechanisms protecting against aging, and can these be translated into therapies to delay or abrogate human aging, too?"
Buffenstein fired up a new generation of scientists with multiple discoveries, especially the fundamental one that naked mole rats are subject to the same wear and tear over time as the rest of us, but somehow manage to reverse it. These days, the trailblazer is at work on untangling the molecular mechanisms involved in the animal's resistance to cardiac aging. On top of everything else, the small creature has a unique ability to fight off the scourge of heart disease, which is the leading cause of death in the industrialized world.
After all, the point is not to extend old age, but to slow down aging itself so that frailty and disability are compressed into a brief period after a long-extended period of vitality. By switching the focus from what goes wrong to mechanisms that defend against aging in the first place, the discoveries of Buffenstein and a new generation of researchers who are building on her groundbreaking research promise to be a driving force in the quest to extend not only life, but healthy, vigorous life in humans.
This article was first published by Leaps.org on June 23, 2021.
The Friday Five covers five stories in research that you may have missed this week. There are plenty of controversies and troubling ethical issues in science – and we get into many of them in our online magazine – but this news roundup focuses on scientific creativity and progress to give you a therapeutic dose of inspiration headed into the weekend.
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Here are the promising studies covered in this week's Friday Five:
- A new target for drugs to treat dementia
- Using math to stay a step ahead of aneurysms
- Putting human cells into rat brains
- Hunting a deadly superbug
- The best sports for kids to avoid lifelong health risks
And an honorable mention this week: The benefits of intermittent fasting when it comes to sleeping better