PD-1
An Evolutionary Guide to New Immunotherapies
Posted on by Dr. Francis Collins
One of the best ways to learn how something works is to understand how it’s built. How it came to be. That’s true not only if you play a guitar or repair motorcycle engines, but also if you study the biological systems that make life possible. Evolutionary studies, comparing the development of these systems across animals and organisms, are now leading to many unexpected biological discoveries and promising possibilities for preventing and treating human disease.
While there are many evolutionary questions to ask, Brenda Bass, a distinguished biochemist at University of Utah, Salt Lake City, has set her sights on a particularly profound one: How has innate immunity evolved through the millennia in all living things, including humans? Innate immunity is the immune system’s frontline defense, the first responders that take control of an emerging infectious situation and, if needed, signal for backup.
Exploring the millennia for clues about innate immunity takes a special team, and Bass has assembled a talented one. It includes her Utah colleague Nels Elde, a geneticist; immunologist Dan Stetson, University of Washington, Seattle; and biochemist Jane Jackman, Ohio State University, Columbus.
With a 2020 NIH Director’s Transformative Research Award, this hard-working team will embark on studies looking back at 450 million years of evolution: the point in time when animals diverged to develop very distinct methods of innate immune defense [1]. The team members hope to uncover new possibilities encoded in the innate immune system, especially those that might be latent but still workable. The researchers will then explore whether their finds can be repurposed not only to boost our body’s natural response to external threats but also to internal threats like cancer.
Bass brings a unique perspective to the project. As a postdoc in the 1980s, she stumbled upon a whole new class of enzymes, called ADARs, that edit RNA [2]. Their function was mysterious at the time. It turns out that ADARs specifically edit a molecule called double-stranded RNA (dsRNA). When viruses infect cells in animals, including humans, they make dsRNA, which the innate immune system detects as a sign that a cell has been invaded.
It also turns out that animal cells make their own dsRNA. Over the years, Bass and her lab have identified thousands of dsRNAs made in animal cells—in fact, a significant number of human genes produce dsRNA [3]. Also interesting, ADARs are crucial to marking our own dsRNA as “self” to avoid triggering an immune response when we don’t need it [4].
Bass and others have found that evolution has produced dramatic differences in the biochemical pathways powering the innate immune system. In vertebrate animals, dsRNA leads to release of the immune chemical interferon, a signaling pathway that invertebrate species don’t have. Instead, in response to detecting dsRNA from an invader, and repelling it, worms and other invertebrates trigger a gene-silencing pathway known as RNA interference, or RNAi.
With the new funding, Bass and team plan to mix and match immune strategies from simple and advanced species, across evolutionary time, to craft an entirely new set of immune tools to fight disease. The team will also build new types of targeted immunotherapies based on the principles of innate immunity. Current immunotherapies, which harness a person’s own immune system to fight disease, target infections, autoimmune disorders, and cancer. But they work through our second-line adaptive immune response, which is a biological system unique to vertebrates.
Bass and her team will first hunt for more molecules like ADARs: innate immune checkpoints, as they refer to them. The name comes from a functional resemblance to the better-known adaptive immune checkpoints PD-1 and CTLA-4, which sparked a revolution in cancer immunotherapy. The team will run several screens that sort molecules successful at activating innate immune responses—both in invertebrates and in mammals—hoping to identify a range of durable new immune switches that evolution skipped over but that might be repurposed today.
Another intriguing direction for this research stems from the observation that decreasing normal levels of ADARs in tumors kickstarts innate immune responses that kill cancer cells [5]. Along these lines, the scientists plan to test newly identified immune switches to look for novel ways to fight cancer where existing approaches have not worked.
Evolution is the founding principle for all of biology—organisms learn from what works to improve their ability to survive. In this case, research to re-examine such lessons and apply them for new uses may help transform bygone evolution into a therapeutic revolution!
References:
[1] Evolution of adaptive immunity from transposable elements combined with innate immune systems. Koonin EV, Krupovic M. Nat Rev Genet. 2015 Mar;16(3):184-192.
[2] A developmentally regulated activity that unwinds RNA duplexes. Bass BL, Weintraub H. Cell. 1987 Feb 27;48(4):607-613.
[3] Mapping the dsRNA World. Reich DP, Bass BL. Cold Spring Harb Perspect Biol. 2019 Mar 1;11(3):a035352.
[4] To protect and modify double-stranded RNA – the critical roles of ADARs in development, immunity and oncogenesis. Erdmann EA, Mahapatra A, Mukherjee P, Yang B, Hundley HA. Crit Rev Biochem Mol Biol. 2021 Feb;56(1):54-87.
[5] Loss of ADAR1 in tumours overcomes resistance to immune checkpoint blockade. Ishizuka JJ, Manguso RT, Cheruiyot CK, Bi K, Panda A, et al. Nature. 2019 Jan;565(7737):43-48.
Links:
Bass Lab (University of Utah, Salt Lake City)
Elde Lab (University of Utah)
Jackman Lab (Ohio State University, Columbus)
Stetson Lab (University of Washington, Seattle)
Bass/Elde/Jackman/Stetson Project Information (NIH RePORTER)
NIH Director’s Transformative Research Award Program (Common Fund)
NIH Support: Common Fund; National Cancer Institute
Insulin-Producing Organoids Offer Hope for Treating Type 1 Diabetes
Posted on by Dr. Francis Collins
For the 1 to 3 million Americans with type 1 diabetes, the immune system destroys insulin-producing beta cells of the pancreas that control the amount of glucose in the bloodstream. As a result, these individuals must monitor their blood glucose often and take replacement doses of insulin to keep it under control. Such constant attention, combined with a strict diet to control sugar intake, is challenging—especially for children.
For some people with type 1 diabetes, there is another option. They can be treated—maybe even cured—with a pancreatic islet cell transplant from an organ donor. These transplanted islet cells, which harbor the needed beta cells, can increase insulin production. But there’s a big catch: there aren’t nearly enough organs to go around, and people who receive a transplant must take lifelong medications to keep their immune system from rejecting the donated organ.
Now, NIH-funded scientists, led by Ronald Evans of the Salk Institute, La Jolla, CA, have devised a possible workaround: human islet-like organoids (HILOs) [1]. These tiny replicas of pancreatic tissue are created in the laboratory, and you can see them above secreting insulin (green) in a lab dish. Remarkably, some of these HILOs have been outfitted with a Harry Potter-esque invisibility cloak to enable them to evade immune attack when transplanted into mice.
Over several years, Doug Melton’s lab at Harvard University, Cambridge, MA, has worked steadily to coax induced pluripotent stem (iPS) cells, which are made from adult skin or blood cells, to form miniature islet-like cells in a lab dish [2]. My own lab at NIH has also been seeing steady progress in this effort, working with collaborators at the New York Stem Cell Foundation.
Although several years ago researchers could get beta cells to make insulin, they wouldn’t secrete the hormone efficiently when transplanted into a living mouse. About four years ago, the Evans lab found a possible solution by uncovering a genetic switch called ERR-gamma that when flipped, powered up the engineered beta cells to respond continuously to glucose and release insulin [3].
In the latest study, Evans and his team developed a method to program HILOs in the lab to resemble actual islets. They did it by growing the insulin-producing cells alongside each other in a gelatinous, three-dimensional chamber. There, the cells combined to form organoid structures resembling the shape and contour of the islet cells seen in an actual 3D human pancreas. After they are switched on with a special recipe of growth factors and hormones, these activated HILOs secrete insulin when exposed to glucose. When transplanted into a living mouse, this process appears to operate just like human beta cells work inside a human pancreas.
Another major advance was the invisibility cloak. The Salk team borrowed the idea from cancer immunotherapy and a type of drug called a checkpoint inhibitor. These drugs harness the body’s own immune T cells to attack cancer. They start with the recognition that T cells display a protein on their surface called PD-1. When T cells interact with other cells in the body, PD-1 binds to a protein on the surface of those cells called PD-L1. This protein tells the T cells not to attack. Checkpoint inhibitors work by blocking the interaction of PD-1 and PD-L1, freeing up immune cells to fight cancer.
Reversing this logic for the pancreas, the Salk team engineered HILOs to express PD-L1 on their surface as a sign to the immune system not to attack. The researchers then transplanted these HILOs into diabetic mice that received no immunosuppressive drugs, as would normally be the case to prevent rejection of these human cells. Not only did the transplanted HILOs produce insulin in response to glucose spikes, they spurred no immune response.
So far, HILOs transplants have been used to treat diabetes for more than 50 days in diabetic mice. More research will be needed to see whether the organoids can function for even longer periods of time.
Still, this is exciting news, and provides an excellent example of how advances in one area of science can provide new possibilities for others. In this case, these insights provide fresh hope for a day when children and adults with type 1 diabetes can live long, healthy lives without the need for frequent insulin injections.
References:
[1] Immune-evasive human islet-like organoids ameliorate diabetes. [published online ahead of print, 2020 Aug 19]. Yoshihara E, O’Connor C, Gasser E, Wei Z, Oh TG, Tseng TW, Wang D, Cayabyab F, Dai Y, Yu RT, Liddle C, Atkins AR, Downes M, Evans RM. Nature. 2020 Aug 19. [Epub ahead of publication]
[2] Generation of Functional Human Pancreatic β Cells In Vitro. Pagliuca FW, Millman JR, Gürtler M, Segel M, Van Dervort A, Ryu JH, Peterson QP, Greiner D, Melton DA. Cell. 2014 Oct 9;159(2):428-39.
[3] ERRγ is required for the metabolic maturation of therapeutically functional glucose-responsive β cells. Yoshihara E, Wei Z, Lin CS, Fang S, Ahmadian M, Kida Y, Tseng T, Dai Y, Yu RT, Liddle C, Atkins AR, Downes M, Evans RM. Cell Metab. 2016 Apr 12; 23(4):622-634.
Links:
Type 1 Diabetes (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)
Pancreatic Islet Transplantation (National Institute of Diabetes and Digestive and Kidney Diseases)
“The Nobel Prize in Physiology or Medicine 2012” for Induced Pluripotent Stem Cells, The Nobel Prize news release, October 8, 2012.
Evans Lab (Salk Institute, La Jolla, CA)
NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases; National Cancer Institute
Fighting Cancer with Natural Killer Cells
Posted on by Dr. Francis Collins
Credit: Michele Ardolino, University of Ottawa, and Brian Weist, Gilead Sciences, Foster City, CA
Cancer immunotherapies, which enlist a patient’s own immune system to attack and shrink developing tumors, have come a long way in recent years, leading in some instances to dramatic cures of widely disseminated cancers. But, as this video highlights, new insights from immunology are still being revealed that may provide even greater therapeutic potential.
Our immune system comes equipped with all kinds of specialized cells, including the infection-controlling Natural Killer (NK) cells. The video shows an army of NK cells (green) attacking a tumor in a mouse (blood vessels, blue) treated with a well-established type of cancer immunotherapy known as a checkpoint inhibitor. What makes the video so interesting is that researchers didn’t think checkpoint inhibitors could activate NK cells.
Precision Oncology: Gene Changes Predict Immunotherapy Response
Posted on by Dr. Francis Collins
Caption: Adapted from scanning electron micrograph of cytotoxic T cells (red) attacking a cancer cell (white).
Credits: Rita Elena Serda, Baylor College of Medicine; Jill George, NIH
There’s been tremendous excitement in the cancer community recently about the life-saving potential of immunotherapy. In this treatment strategy, a patient’s own immune system is enlisted to control and, in some cases, even cure the cancer. But despite many dramatic stories of response, immunotherapy doesn’t work for everyone. A major challenge has been figuring out how to identify with greater precision which patients are most likely to benefit from this new approach, and how to use that information to develop strategies to expand immunotherapy’s potential.
A couple of years ago, I wrote about early progress on this front, highlighting a small study in which NIH-funded researchers were able to predict which people with colorectal and other types of cancer would benefit from an immunotherapy drug called pembrolizumab (Keytruda®). The key seemed to be that tumors with defects affecting the “mismatch repair” pathway were more likely to benefit. Mismatch repair is involved in fixing small glitches that occur when DNA is copied during cell division. If a tumor is deficient in mismatch repair, it contains many more DNA mutations than other tumors—and, as it turns out, immunotherapy appears to be most effective against tumors with many mutations.
Now, I’m pleased to report more promising news from that clinical trial of pembrolizumab, which was expanded to include 86 adults with 12 different types of mismatch repair-deficient cancers that had been previously treated with at least one type of standard therapy [1]. After a year of biweekly infusions, more than half of the patients had their tumors shrink by at least 30 percent—and, even better, 18 had their tumors completely disappear!
A Surprising Match: Cancer Immunotherapy and Mismatch Repair
Posted on by Dr. Francis Collins
How Anti-PD-1 Immunotherapy Works. Before immunotherapy (top), the tumor cell’s PD-1 ligand, or PD-L1, molecule (red) binds to a type of white blood cell called a T-cell in a way that enables the tumor cell to evade destruction by the immune system. During immunotherapy (bottom), an anti-PD-1 inhibitor drug (bright green) blocks PD-L1 binding, enabling the T cell to target the tumor cell for destruction.
Credit: NIH
Mismatch repair genes have long been a source of fascination to basic biologists. Normally, these genes serve to fix the small glitches that occur when DNA is copied as cells divide. Most of the original work was done in bacteria, with no expectation of medical relevance. But, as often happens, basic science studies can provide a profoundly important foundation for advances in human health. The relevance of mismatch repair to cancer was dramatically revealed in 1993, when teams led by Bert Vogelstein of Johns Hopkins University School of Medicine, Baltimore, and Richard Kolodner, then of Harvard Medical School, Boston, discovered that mutations in human mismatch repair genes play a key role in the development of certain forms of colorectal cancer [1, 2].
That discovery has led to the ability to identify individuals who have inherited misspellings in these mismatch repair genes and are at high risk for colorectal cancer, providing an opportunity to personalize screening by starting colonoscopy at a very early age and, thereby, saving many lives. But now a new consequence of this work has appeared. Vogelstein and his colleagues report that mismatch repair research may help fight cancer in a way that few would have foreseen two decades ago: predicting which cancer patients are most likely to respond to a new class of immunotherapy drugs, called anti-programmed death 1 (PD-1) inhibitors.
