Regulatory T cells: Therapeutic Potential for Treating Transplant Rejection and Type I Diabetes

My name's Jeff Bluestone. I'm the director of the UCSF Diabetes Center. We're at a laboratory here and oversee the immune tolerance network.

My work is involved in basic understanding of how the immune system distinguishes self from non-self and how we can use therapies to try to induce what we call immune tolerance, which is the ability of the immune system being modulated and protect itself from recognizing itself as foreign and attacking things like its own pancreas or brain or joints. That happens in many autoimmune diseases. We're particularly interested in therapies, both drug and cellular therapies that might be used to educate or reeducate the immune system so that we don't block or destroy our own ability To protect our own tissue.

So whenever A a T cell comes through the thymus or B cell comes out of the bone marrow, it has to learn to distinguish self from non-self, and this is what we call immune tolerance, which is that ability to tolerate one's own tissue and not destroy it or attack it. What often happens in many disease settings is that the immune system because of environmental and genetic reasons, starts attacking one's own tissue and tolerance is broken and it's that system that we're trying to reestablish with some of our therapies. And the ultimate goal of immune tolerance therapies as opposed to generalized immunosuppression is to try to develop therapies or drugs that will in fact reestablish tolerance without requirement for ongoing therapy.

So that today where somebody with a kidney transplant or a liver transplant might require 20 or 30 pills a day to keep the immune system from attacking the, the kidney or pancreas or, or or liver in the future. And we might be able to just provide some kind of therapy that would change the immune system so that it becomes tolerant to the kidney or liver And doesn't reject it. So one of the more Interesting elements of immune tolerance has been to discovery that there are specialized cells in the body whose job it is to protect the organs of the body and and to regulate the immune system so that it doesn't attack those tissues.

These so-called regulatory T cells have become a very important and central part of understanding immune tolerance over the last decade or so. In fact, regulatory T cells are often known as suppressor. T cells have been around for 30 years since early discovery and and descriptions by people like Dick Han.

Unfortunately, in the eighties, these cells came in some disrepute because of the absence of unique biological or biochemical markers that could distinguish them from other cells and data that was difficult to interpret given our current understanding of how T cells recognize proteins and how the immune system works. But then starting in the mid nineties through seminal work by investigators like Shimon Succi and others, we started to understand both the cellular as well as biochemical basis for regulatory T cells, such that when a transcription factor called Fox P three was discovered in early two thousands, we're able to finally put a specialized tag on these cells and really understand them. And ever since we've really been able to exploit those cells by expanding em, isolating em, and reintroducing em into animals to demonstrate that they are capable of inducing immune tolerance, which is what we are All about.

One of the Most important questions that is challenge the field is trying to understand what the mechanism of tregs are, both in immune responses as well as during tolerance induction. And there have been a number of questions related to do the cells act on other T cells that are pathogenic? Do they act on antigen presenting cells or do they make cytokines that ultimately regulate the immune response?

Our own studies have suggested based on in vi, in vivo imaging that in fact these cells act directly on the major antigen presenting cell in in the pancreas, and that is a dendritic cell. And we demonstrated that in fact we could label regulatory T cells one color green while the dendritic cells were labeled another color, and show that in fact these regulatory T cells interacted directly with the dendritic cells and by doing so, fundamentally altered the ability of those dendritic cells to activate the pathogenic T cell response. So we think that either directly or through some intermediate cytokine like IL 10 or TGF beta that the tregs educate or change the dendritic cells to make them less able to activate a pathogenic T cell response.

Yeah, So one of the more interesting aspects of regulatory T cells has been the notion that in addition to this very specialized subset that exists in the thymus and develops during thymic development, the so-called natural T-Rex that during the course of an immune response, other T cells may in fact turn into regulatory T cells either through direct upregulation of Fox P three due to cytokines like TGF beta, which are known to turn on FOX P three or even other cells which are not Fox P three positive, but take on regulatory T-cell characteristics. Those so-called adaptive tregs are generally very important in in regulating an inflammatory response because they're interacting with the antigens that are present locally in that inflamed tissue. And those adaptive cells are probably critical in maintaining tolerance locally in a targeted tissue, whereas the natural tregs are probably more useful or important in maintaining a, a, a immune homeostasis or generalized suppression of auto reactivity in the whole animal Or patient.

So now that we know That these regulatory cells are essential in in maintaining immune homeostasis, we can imagine what would happen if they're disrupted. And in fact, if you destroy Fox P three and either mouse models using knockout technology, or in fact there's a human disease called I pex, the individual animals die in a short period of time of a massive autoimmune disease where each targeted tissue, liver, kidney, heart are in infiltrated with T cells and the tissues are destroyed. So that's the fundamental immuno immune homeostasis that's required that these cells Really protect the individual.

One of the important Discoveries with regards to regulatory T cells is the possibility that we might be able to both isolate them and expand them in a specific way to reintroduce into individuals with diseases to bring the immune system back into a homeostatic equilibrium. And in fact, work in our laboratory and others have been able to take these cells out and expand them up to a thousand fold and show that they retain their suppressor activity and can be reintroduced into individual animals to induce an a regulatory response. Where that's been most successful at, at this time has been in treating autoimmune disease and animal models of diabetes, for instance, we can prevent or even reverse diabetes by putting in small numbers of these antigen specific eyelid antigen specific regulatory T cells that we've expanded ex vivo and we hope that we can get into people soon with similar populations that have been expanded in in a similar manner.

Now the future hopefully will go beyond autoimmune diseases and into more broad based immunological settings and perhaps the most daunting of which is transplantation. Today we transplant over a half a dozen organs into people, but still are required to give them lifelong immunosuppression to prevent those transplants from being rejected. The hope is that we can take regulatory cells that see the donor tissue from these kidney, liver, pancreas, eyelet transplants and be able to target those regulatory cells to those tissues and prevent the immune system from recognizing those tissues as far and now take this alloimmune response and convert it into a safe self response and prevent rejection without ongoing immunosuppressive Drug therapy.

So What we hope is, is that this particular therapy is going to be very appropriate, appropriate for treating people with type one diabetes. Once all of the insulin producing beta cells have been destroyed, the only way we're ultimately gonna be able to treat the disease is by both reconstituting the individual with an eyelet or some insulin producing cell, and at the same time prevent the autoimmune and alloimmune responses from destroying it. So our approach is to take people with long-term diabetes and transplant eyelets at present from cric donors, but in the future, perhaps from stem cells or other sources to actually replace the insulin producing capability, we hope to introduce regulatory T cells into that setting to prevent those eyelets that are coming from foreign sources, from being rejected.

As I mentioned, this notion that we can induce tolerance in these individuals will require not just the source of an insulin producing cell, but some combination of drugs and cellular therapies. We hope like regulatory cells to put the individual into a state of tolerance in homeostasis so that these foreign tissues are not recognized and destroyed once introduced into the diabetic patient. Specifically, our approach to actually reconstituting insulin producing beta cells in patients starts out with the kind of experiments we're doing in animal models, which is to take eyelets that have been prepared from a pancreas, remembering that only about 0.5%of all of the cells in the pancreas actually are the eyelets to make insulin to isolate those cells and purify them in a way that we can reintroduce them into a recipient.

We reintroduce them either by putting them under the kidney capsule, which is routinely the way we do it in animal models are directly into the liver, which is the way we do it in humans. And once those cells go into that site, either kidney or liver, they then seed that site and start getting the blood and other nutrients that they need in order to survive and make the insulin that then gets circulated to other tissues and organs as needed. And the goal is to obviously, once those cells are in that tissue, to then treat with our various immunotherapeutics to prevent the immune system from attacking the cells Within those tissues.

So of course there are a Number of challenges for all novel immunotherapies and tregs are no exception. We need to worry about a number of things as we try to this for a therapeutic. We need to worry about cell numbers at present, that we can only identify small numbers of cells that have the antigen specificity that we need to block both auto and allo immunity.

So we'll need to figure out ways to both isolate those cells and expand them to sufficient numbers to treat an individual. In addition, we need to be careful that these cells are truly pure regulatory T cells. We don't wanna make the mistake of putting in cells that have the ability to be pathogenic and attack the foreign tissue as opposed to the regulatory cells which protect.

And so understanding the stability and the robustness of these cells and how how they survive in various inflammatory settings will be critical. The third thing we need to worry about is non-specific immunosuppression that could be caused. These regulatory cells are designed to shut down broadly in immune response.

And so we don't want to, at the same time we're blocking graft rejection, block the ability of an individual to recognize a bacteria or a virus or cancer cells that might come up, but instead stay targeted and focused on the tissue that we've transplanted into the individual. And then finally, I think the, the other challenge with any cellular therapy is being able to do it robustly and routinely many, many, many times over because each patient is gonna require their own set of cells. This is not a drug you can just take off the shelf.

And so we're gonna have to work technologies out that are, use good manufacturing practices that are approved by the food and drug administration that allow us to grow these up the same way every time and be sure that we're working with a, a truly homogeneous and and well-defined population of Cells. When one Thinks about funding for projects like this, it's always a mix between the federal funding that we get through the NIH to support the basic science that's important in moving this forward. And then for us, fortunately, other organizations such as the Juvenile Diabetes Foundation who have been very supportive having raised an enormous amount of money from the community to help in these highly risky projects.

And so we've been fortunate in being able to partner with both the NIH and JDRF as well as with pharmaceutical companies on occasion to be able to move these kinds of projects along. So at present, I think the funding is actually adequate and we really hope that we will be able to drive this project forward Effectively. We've been lucky in the diabetes community having such a strong, both federal and non-federal interest in the disease.

Of course, that's not inappropriate given the fact that disease is really growing and reaching epidemic proportions, but we hope that the funding that exists will be sufficient for us to move This project. So Like all scientists, we always feel as if we are underfunded and underappreciated when you look at how much money is being spent to, to deal with problems around the world, to deal with war in Iraq, to deal with our, our military, and know that just a couple of days of that funding could support the NIH for a year. It's hard to imagine how we've placed our priorities because we think as scientists that there are a lot of things that we can do to change human health, human, the human state.

So we only continue to hope that the advances in the science look in in 50 years. We're not gonna be talking about health insurance, we're not gonna be talking about HMOs and management. We're gonna talk about the amazing discoveries that have been made that are gonna change health in in our country that's gonna change health in the world.

And just like the industrial revolution of turn of the last century, that in this century the, the major impact is gonna be on how we've changed diseases, both acute and chronic diseases. And so we hope that the public appreciates that and appreciates our efforts to try to make that kind of Difference.