It was late January and the temperature was in the mid-seventies without a cloud in the sky – one reason to love being in San Diego. Another reason? The Pediatric Diabetes Research Center (PDRC) at the University of California, San Diego was holding its third-annual symposium. The PDRC aims to bring together the numerous research efforts around type 1 diabetes in the San Diego community in order to improve the lives of patients and push us towards a cure, and so their big event of the year, the annual symposium, draws a heterogeneous audience of academics, clinicians, nurses, biotech scientists, and community members like me with a vested interest in diabetes research.
This year’s theme was beta cells– how to make them, and how to put them where they belong– and the speakers throughout the day presented their recent results from the lab. In type 1 diabetes, the immune system attacks and kills off the insulin-producing beta cells in the pancreas, meaning the body can no longer produce the crucial hormone insulin. Finding a new and plentiful source of insulin production that works naturally within the body, then, is one half of a cure for diabetes. Further, as some speakers touched on throughout the day, as type 2 diabetes progresses, scientists have seen that beta cells begin to die off, probably a result of cellular stress and toxicity. So, beta cell replacement will be important for the treatment of diabetics at large, and a working replacement system would be a huge boon to global health.
More details of some of the talks are below, but I want to begin with two of the major takeaways for me:
1. The body knows so much more than we do.
For all that scientists have learned about beta cell biology– and they’ve learned a lot– we still understand only the basics of the concert of cells and hormones that goes into natural regulation of insulin production and secretion. We can trace the progress of a single beta cell from embryonic stem cell to a series of interim progenitors to the final state of beta cell, but we can only name a fraction of the proteins and genes that are involved in the process. And, if we try to explain how each protein or gene is involved, we find we know even less.
The body, however, induces a working system without having to understand or control each player along the way. Dr. Maike Sander, one of the key researchers in beta cell differentiation from embryonic stem cells, described a set of experiments in which she and her team took pancreatic progenitor cells, capable of turning into many different cells of the pancreas, and tried to turn them into beta cells in a petri dish. They got insulin-producing cells, but they weren’t quite beta cells; they produced other hormones like glucagon, and didn’t produce insulin specifically in response to glucose. But, when they took the same pancreatic progenitors and stuck them inside mice, the cells naturally differentiated into happy little pancreases, with beta cells that produced only insulin, and only in response to glucose stimulation. Like magic.
So what does the body know that we don’t? A lot, it seems. The good news is we don’t have to wait until we learn everything before we have a working system. The successful implantation of progenitor cells, rather than mature beta cells, that will then turn into beta cells within the body, is the basis of the current beta cell replacement strategy that the company ViaCyte is executing (see below). The more we understand about the mechanisms behind the physiology, the better, but it’s nice to know we can also leverage the body’s existing systems to achieve our desired ends.
2. It ain’t over till it works in the clinic.
Speaking of ViaCyte, every time I hear someone from ViaCyte speak about their progress, I think, “Wow, well, they’re almost there! They almost have a working system to replace beta cells!” And indeed, listening to Dr. Olivia Kelly from ViaCyte, speaking, full of optimism for an inevitable successful product, I couldn’t help but wonder why all these other academics– self-deprecating and skeptical in comparison to Dr. Kelly– were trying other methods with varying degrees of success. Why don’t we all just jump on the ViaCyte bandwagon?
The answer came from Maike Sander, during her closing remarks. She pointed out that until we have a replacement strategy that works in the clinic, we need to keep trying different methods, because we don’t know for sure what will work all the way through the end until it actually does. And I realized the truth of that sentiment, as it’s often the last mile that proves the most difficult. This is true to some degree already in beta cell biology, as getting from embryonic stem cell to pancreatic progenitor proved very possible, but taking that next step from progenitor to beta cell is still a work in progress. And getting from mature beta cell to working treatment is a very long last mile.
So, until we figure out what the right answer is, it is important not to limit our options to just one precocious strategy. The PDRC symposium was faithful to that end, giving voice to an array of beta cell replacement studies and strategies.
Here are some summaries from just a few of the many speakers:
Michael Brehm, Assistant Professor at the University of Massachusetts Medical School
Development of Humanized Mouse Models for Diabetes Research
Dr. Brehm presented research and recent results from his experiments with humanized mice. Humanized mice are just about as bizarre and Frankenstein as the name sounds—mice bred to lack crucial components of the immune system are then engrafted with human cells and tissues such that the cells and tissues survive in the mouse and can be studied. Such mice serve as a bridge between murine studies and human trials—they are mouse enough to allow us to ethically experiment, but human enough that we can get an accurate picture of how the processes we observe or drugs we test will act in actual humans. The system is by no means perfect, but it seems we will see more and more humanized mice as scientists try to more efficiently create treatments that will reliably work in the clinic, rather than just in the lab.
Humanized mice have the potential to greatly advance our understanding of many diseases, one of which is type 1 diabetes. Brehm’s lab has been working to create mouse lines that imitate as closely as possible the human disease. Starting with mice that lack essential cells of the immune system (T cells, B cells, and Natural Killer [NK] cells), the researchers then transplant in human hematopoietic stem cells (HSCs), which differentiate inside the mouse into a full suite of immune cells. Importantly, however, these cells are human in origin, rather than mouse, and therefore we can observe how human cells respond to certain stimuli or hyperglycemia or even human beta cells in islets that are transplanted.
Currently, Brehm’s lab is working on creating a mouse that takes this idea one step further—they are creating a humanized mouse that has human immune cells that carry the HLA haplotype that is highly associated with type 1 diabetes. In other words: there is a genetic region that we know is highly correlated with the development of type 1 diabetes in humans, and Brehm and his team are trying to put cells with that genetic region into the mice such that we can see how this particular region changes the way immune cells behave and leads to the development of an autoimmune reaction against the cells of the pancreas. This is no small task, but if they succeed, these mice could give researchers much insight into how exactly a genetic region leads to a particular autoimmune reaction, which could in turn give researcher hints as to how to stop the process.
Olivia Kelly, Research Scientist at ViaCyte, Inc.
Developing an Encapsulated Stem Cell Therapy for Diabetes
ViaCyte has inspired much excitement and press in the scientific community over the past few years. Their aim is to develop an implantable source of insulin-producing cells from embryonic stem cells for use by diabetics who no longer produce insulin. Though a for-profit company, they are widely respected in the academic world, as they developed the now widely-used protocol that takes embryonic stem cells in a petri dish from pluripotency down to being pancreatic progenitors, cells much closer to being insulin-producing beta cells.
Dr. Kelly spoke at the symposium to give an update on the progress made by ViaCyte thus far towards its goal. She described the three key components of the end product that they are working on—a renewable cells source (a special line of human embryonic stem cells), a therapeutic cell product (the insulin-producing cells derived from the stem cells), and an encapsulation device to hold the cells when implanted into the patient.
In contrast to the academic speakers, who as a tribe are trained to be skeptical, Kelly was very optimistic about the progress so far and the prospect of a product for human use in the near future. Despite several years of effort, ViaCyte has not succeeded in making true insulin-producing cells entirely in the petri dish, but, Kelly reported, they’ve done something else that may prove just as good: they’ve designed a repeatable system for creating pancreatic progenitor cells in a petri dish, and once these cells, which ViaCyte calls pro-islets, are implanted into mice, they mature in vitro into different pancreatic cells, including glucose-responsive beta cells. ViaCyte researchers and associated academics are thus far unsure what exactly is happening after implantation to induce the pro-islet cells to become operational, but, luckily for us, that lack of insight will not stop progress toward a marketable product.
Indeed, Kelly described the ways in which progress was being made at ViaCyte. They are currently fine-tuning their processes such that the cells that worked in the lab with mice can be produced at scale in a reliable, FDA-approvable fashion. They are setting up a pipeline that starts with frozen human embryonic stem cells, differentiates the cells over a several weeks into pro-islet cells, freezes the pro-islets for storage for up to ten months, then thaws the pro-islets, transfers them into specially designed implantable envelopes, and ships them to the clinic for implantation.
Importantly, they are extensively testing the product at each stage to ensure expected quality, behavior, and safety. ViaCyte has completed a FDA-required Good Laboratory Practice (GLP) safety study, and has assessed a number of safety endpoints for the implanted device in mice and rat studies. They have even attached Dexcom continuous glucose monitors to rats to show that, after administering a toxin that kills beta cells, the implanted cells are able to maintain normoglycemia in the rats for extended periods of time.
Kelly preached the promise of the ViaCyte therapy, but some of the experts in the audience were so not easily convinced. Dr. Fred Levine , director of the Sanford Children’s Health Research Center and Associate Professor at UCSD, asked Kelly why there were so many delta cells showing up in the images taken of pro-islet filled devices that were implanted into mice, then removed after the cells matured. Levine saw the beta cells, but also saw an abundance of other pancreatic cells that begged for an explanation. Kelly did not have a direct answer, but noted that researchers were investigating the various ways in which cell maturation in the device was governed. And when Levine asked where the implanted devices would go, and how big they would be, Kelly noted that there were no clear answers on dosing yet, but that they could estimate the number of cells needed from the size of the patient.
In sum, it seemed, ViaCyte has an extremely promising product making good progress, but, as Dr. Sander said, we won’t know for sure what the answer is until it we’re done.
Timothy Kieffer, Professor at the University of British Columbia
Reprogramming Intestinal Cells for Insulin Replacement Therapy
Dr. Kieffer presented recent research from his lab on an alternate way to develop an abundant source of beta cells—differentiating them not from stem cells, but from other mature cells. The particular mature cells that Kieffer and his team work with are the gut K cells in the interendocrine system. These are cells that make up about 1 – 2 % of the lining of the intestines. Other researchers are working with liver cells and even gall bladder cells, but Kieffer thinks the K cells of the interendocrine system are a particularly promising home for insulin production because they are close to the pancreas to begin with, and, crucially, they are already glucose-responsive. You see, interendocrine cells are the cells responsible for secreting the incretins like the hormone GLP-1 in response to ingested glucose—so, rather than take a stem cell or liver cell and teach it to respond to glucose and secrete insulin, Kieffer aims to hijack the existing secretion mechanisms of K cells and teach them to secrete both incretins and insulin.
Though still in its infancy, the idea is intriguing and clever. Thus far, Kieffer’s lab has created an insulin transgene that they can deliver to mice such that many cells in the mouse harbor the gene, but only the K cells of the gut actually start to express the gene and make protein from it. They have shown that mice indeed start to make insulin in their K cells after the delivery of the transgene, and, further, that Non-Obese Diabetic (NOD) mice, which spontaneously develop autoimmune diabetes, are able to produce insulin from the gut without inducing an immune attack on gut K cells.
One of the initial hurdles that Kieffer’s team must overcome is figuring out how to safely and reliably get the insulin transgene into the K cells. The normal process for doing this in cells in the lab, using viral vectors, has been used clinically in a few cases, but this sort of gene therapy is considered risky and prone to causing immune reactions. The researchers are therefore investigating non-viral methods for introducing gene-carrying DNA into cells, including most recently chitosan-based nanoparticles that deliver the insulin transgene to cells throughout the body.
Thus far, Kieffer and his lab have demonstrated the successful induction of glucose-responsive insulin production in mice and even pigs for up to 150 days, and are currently continuing to push this alternate means of beta cell replacement forward.
All in all, I was sincerely impressed by the creativity and excitement in the room for the PDRC’s Annual Symposium. We’re not there yet, but every day we get closer thanks to the concerted efforts of a great number of scientists who, for whatever reason, can’t help but try to solve this problem of missing beta cells. So, from one person waiting for a new set of beta cells—thanks!
Full disclosure: The PDRC Annual Symposium was free to attend, and I have not been paid or asked to write about what I heard. However, I am very much a fan of the PDRC and the research they fund, so consider me biased.
Islet cell image courtesy of Wikipedia under Wikimedia Commons.