Some Types of Obesity Might be Caused by a Faulty Immune System

When we think of our Immune systems, we normally entertain visions of white blood cells that fight off invading viruses and bacteria. However, recent work suggests that our immune systems may also being fighting a war against fat.

When laboratory mice are engineered to lack a specific type of immune cell, they become obese and show signs of high blood pressure, high cholesterol, and diabetes. Even though these findings have yet to be replicated in humans, they are already helping scientists understand the triggers of metabolic syndrome, a cluster of conditions associated with obesity.

A new study “definitely moves the field forward,” says immunologist Vishwa Deep Dixit of the Yale School of Medicine, who was not involved in the work. “The data seem really solid.”

Scientists have known for some time now that there is a correlation between inflammation—a heightened immune response—and obesity. Fat cells have the ability to release inflammatory molecules, which complicates these findings, since it is difficult to distinguish if the inflammation causes weight gain or is a side effect of weight gain.

Immunologist Yair Reisner of the Weizmann Institute of Science in Rehovot, Israel, came upon this new cellular link between obesity and the immune system while he was studying autoimmune diseases. Reinser was interested in an immune molecule called perforin, which kills diseased cells by boring a hole in their outer membrane. Reisner’s group suspected that perforin-containing dendritic cells might also be destroying the body’s own cells in some autoimmune diseases. To test their hypothesis, Reisner and his colleagues engineered mice that lacked perforin-wielding dendritic cells. Then they waited to see whether they developed any autoimmune conditions.

“We were looking for conventional autoimmune diseases,” Reisner says. “Quite surprisingly, we found that the mice gained weight and developed metabolic syndrome.”

Mice lacking the dendritic cells with perforin had high levels of cholesterol, early signs of insulin resistance, and molecular markers in their bloodstreams associated with heart disease and high blood pressure. Furthermore, the immune systems of these laboratory animals revealed that they also had a peculiar balance of T cells—a type of white blood cell that directs immune responses.

Reisner and his colleagues report online in the journal Immunity that when they removed these T cells from the mice, the absence of dendritic cells no longer caused the animals to become obese or develop metabolic syndrome.

The results, according to Reisner, suggest that the normal role of the perforin-positive dendritic cells is to keep certain populations of T cells under control. In the same way that perforin acts to kill cells infected with viruses, it can be directed to kill subsets of unnecessary T cells. When the brakes are taken off those T cells, they cause inflammation in fat cells, which leads to altered metabolism and weight gain.

“We are now working in human cells to see if there is something similar going on there,” Reisner says. “I think this is the beginning of a new focus on a new regulatory cell.” If these results turn out to be true in humans, they could point toward a way to use the immune system to treat obesity and metabolic disease.

Daniel Winer, an endocrine pathologist at the University of Toronto in Canada and the lead author of a January Diabetes paper that links perforin to insulin resistance, says the new results overlap with his study. Winer and his group found that mice whose entire immune systems lack perforin developed the early stages of diabetes when fed a high-fat diet. This new paper builds on that by homing in on perforin-positive dendritic cells and showing the link even in the absence of a high-fat diet. “It provides further evidence that the immune system has an important role in the regulation of both obesity and insulin resistance.”

Even if the results hold true in humans, however, a treatment for Type 2 diabetes, obesity or metabolic disease are far off. Dixit said. “Talking about therapeutics at this point would be a bit of a stretch.” Injecting perforin into the body could kill cells beyond those T cells that promoting obesity. We can’t live without any T cells at all, since they are vital to fight diseases and infections.

However, research on what these T cells are recognizing when they seek out fat cells and cause inflammation in fat tissue could eventually reveal drug targets.

An Entire Organ Grown Inside an Animal

For the first time, scientists from Scotland have reported that an entire, functional organ has been grown from scratch inside a laboratory animal. A Scottish research group successfully transplanted a small quantity of cells into a laboratory mouse that grew and developed into a functional thymus.

These findings were published in the journal Nature Cell Biology, and might open the door to new alternatives to organ transplantation. This research certainly shows great promise, but is still years away from clinical trials and reproducible human therapies.

If you are wondering what the thymus is, it serves as an integral part of the immune system. The thymus is located just above and slightly over the heart and produces a vital component of the immune system, called T-cells, which fight infections and regulate the immune response.

The thymus
The thymus

thymus location


A research team from the Medical Research Council Centre for Regenerative Medicine at the University of Edinburgh began this experiment with mouse embryonic fibroblasts.  These fibroblasts are found in the skin and connective tissue of the embryo.  These mouse embryonic fibroblasts were genetically engineered to expressed the FOXN1 gene, which encodes a transcription factor known as the “forkhead box N1″ protein.  The forkhead box N1 protein binds to DNA and activates the expression of genes necessary to make thymic epithelial cells.  Mice that do not have a functional copy of the FOXN1 gene a “nude” mice.  They are nude because they have no hair and have no thymus.  

Once engineered to express FOXN1, the fibroblasts began to differentiate into thymic epithelial cells.  The Scottish team mixed these genetically engineered fibroblasts with some other support cells and transplanted them into laboratory mice where they summarily formed a fully functional thymus.  Structurally the animal-grown thymus contained the two main regions – the cortex and medulla – and it also produced T-cells.

Prof Clare Blackburn, who was part of the research team, said it was “tremendously exciting” when the team realized what they had accomplished.  Blackburn told the BBC: “This was a complete surprise to us, that we were really being able to generate a fully functional and fully organised organ starting with reprogrammed cells in really a very straightforward way.  This is a very exciting advance and it’s also very tantalising in terms of the wider field of regenerative medicine.”

Such a procedure could benefit patients who need a bone marrow transplant and children who are born without a functioning thymus.  Likewise because our immune response diminishes as we age and out thymus shrivels, such a procedure might boost the waning immune system of aged patients.   could all benefit from such a procedure.

However, there are a number of problems to solve before this procedure can cross the bridge from animal studies to hospital therapies.  First of all, the recipient of these implants were nude mice that had no thymus and could not reject transplanted tissue.  Also, the use of embryonic fibroblasts would cause a robust immune response against them.  Some other cell type must be found for this procedure that grows robustly and does not cause transplantation rejection.

Researchers also need to be sure that the transplant cells do not pose a cancer risk by growing uncontrollably.  Prof Robin Lovell-Badge, from the National Institute for Medical Research, said: “This appears to be an excellent study.  This is an important achievement both for demonstrating how to make an organ, albeit a relatively simple one, and because of the critical role of the thymus in developing a proper functioning immune system.  However… the methods are unlikely to be easy to translate to human patients.”

This experiment is a testimony of just how far the field of regenerative medicine has come.  Already patients with lab-grown blood vessels, windpipes and bladders have benefited from advances in regenerative medicine. These tissue engineered structures have been made by “seeding” a patient’s cells into a scaffold which is then implanted.  The thymus in this case only required one injection of a cluster of cells.  While it is doubtful that other organs will be this easy to grow, it is an encouraging start.

Also, this experiment utilized “direct reprogramming” that did not require taking cells through the embryonic stage.  Instead one-gene reprogramming directed the cells to make thymus epithelium cells.  This almost certainly promises to be a much safer way to make cells for regenerative treatments.

Dr Paolo de Coppi, who pioneers regenerative therapies at Great Ormond Street Hospital, said: “Research such as this demonstrates that organ engineering could, in the future, be a substitute for transplantation.  Engineering of relatively simple organs has already been adopted for a small number of patients and it is possible that within the next five years more complex organs will be engineered for patients using specialised cells derived from stem cells in a similar way as outlined in this paper.  It remains to be seen whether, in the long-term, cells generated using direct reprogramming will be able to maintain their specialised form and avoid problems such as tumour formation.”

Engineered Stem Cells from Human Umbilical Cord Blood Eradicates Pancreatic Tumor

Tissue-specific stem cells called mesenchymal stem cells (MSCs) are a very efficient way to delivery new drugs to cancer sites. One of the reasons these cells do such a good job with cancers in that MSCs have a liking for tumors, and once MSCs are injected into a patient or laboratory animal with tumors, the MSCs make a “B-line” for the tumor and get cozy with it.

Interleukin-15 (IL-15) is a small protein synthesized by white blood cells in our bodies, and IL-15 has a demonstrated ability to stop tumors in their tracks. Unfortunately, IL-15 is broken down quickly once it is injected into the body and consequently, has to be given in very high quantities for it to work. At such high concentrations, IL-15 causes severe side effects, and therefore, it has not been pursued as an anti-tumor agent to the degree that it deserves.

To get around this problem, a Chinese group led by Kexing Fan from the International Joint Cancer Institute in Shanghai, China, genetically engineered MSCs isolated from human umbilical cord blood so that they expressed IL-15. When these engineered MSCs that expressed a mouse version of IL-15 were subjected to experimental verification, the expressed IL-15 activated white blood cells to divide just like native IL-15.

Next, Fan’s group used these souped-up cells to treat In mice afflicted with pancreatic tumors. Pancreatic cancer is an indiscriminate killer, since by the time it causes any symptoms, it is usually so advanced, that there is little to be done in order to treat it. Thus new strategies to treat this yep of cancer are eagerly being sought. Systemic administration of IL-15-expressing MSCs significantly inhibited tumor growth and prolonged the survival of tumor-bearing mice. The tumors of these mice showed extensive cell death, and other types of immune cells known to fight tumor cells (NK and T cells) had also accumulated around the tumor. Other experiments confirmed that the injected MSCs did indeed migrate toward the tumors and secrete IL-15 at the site of the tumors.

Interestingly, those mice that were cured from the pancreatic tumors, appeared to have a kind of resistance of these tumors. Namely, when Fan and his colleagues tried to reintroduce the same tumor cells back into the cured mice, the tumor cells would not grow. Thus the engineered MSCs not only tuned the immune system against the tumor, but they effectively vaccinated the mice against it as well.

Overall, these data seem to support the use of IL-15-producing MSCs as an innovative strategy for the treatment of pancreatic tumors.

Differentiation of Induced Pluripotent Stem Cells Decreases Immune Response Against Them

The goal of regenerative medicine is to replace dead or damaged cells, tissues and even organs with living, properly functioning cells tissues and organs. However, this goal has a few genuine barriers that include tumor formation in the case of pluripotent stem cells, poor cell survival, or even immunological rejection of the transplanted cells before they can render any long-term benefits. Induced pluripotent stem cells (iPSCs), which are made from adult cells by a combination of genetic engineering and cell culture techniques, can be made from a patient’s own mature cells and the differentiated into almost any tissue in the adult body. However, research with mouse iPSCs has shown that even stem cells produced from the subject’s own tissues can be rejected by the subject’s own immune system.

Immune rejection of iPSCs is a legitimate concern, but research from the Stanford University School of Medicine has shown that differentiation of iPSCs into more mature cells before transplantation into mice allows them to be tolerated by the immune system.

Joseph Wu, MD, PhD, director of the Stanford Cardiovascular Institute, said, “Induced pluripotent stem cells have tremendous potential as a source for personalized cellular therapeutics for organ repair. This study shows that undifferentiated iPS cells are rejected by the immune system upon transplantation in the same recipient, but that fully differentiating these cells allows for acceptance and tolerance by the immune system without the need for immunosuppression.”

Wu is the senior author of this publication, which appeared online on May 30th in Nature Communications. Lead authorship of this paper is shared by Patricia Almeida, PhD, and Nigel Kooreman, MD, and assistant professor of medicine Everett Meyer, MD, PhD.

Several other studies have suggested that differentiation of iPSCs can reduce their tendency to activate the immune system after transplantation. However, this study of Wu and others is the first to closely examine, at the molecular and cellular level, how this works.

“We’ve demonstrated definitively that, once the cells are differentiated, the immune response to iPS-derived cells is indistinguishable from its response to unmodified tissue derived from elsewhere in the body,” said lead author Nigel Kooreman.

Pluripotent stem cells have the capacity to differentiate into any cell in the adult body. Of the two types of pluripotent stem cells, embryonic stem cells are made from embryos and iPSCs are made in the laboratory from existing adult cells (e.g., skin or blood). Induced pluripotent stem cells are easier to come by than embryonic stem cells, they match the genetic background of the person from whom they were obtained, and they are not as ethically dubious as embryonic stem cells. Thus, in theory, iPSCs are a good option for any physician who wants to make patient-specific stem cells for potential therapies.

Previous studies in mice have shown, however, that even genetically identicaliPSCs can trigger an immune response after transplantation. Thus, Wu and his colleagues have, for the past six years, been investigating how to use immunosuppressive medications to dampen the body’s response to both embryonic andiPSCs and render them more amenable for clinical use (see AS Lee, et al., J Biol Chem 2011 286(37):32697-704; Durruthy-Durruthy L, et al.,PLoS One, 2014 9(4):e94231 and others).

In this recent study, Kooreman and his co-lead authors decided to examine the immune response against transplanted stem cells. They first transplanted undifferentiated iPS cells into the leg muscles of genetically identical recipient mice. These grafts were rejected and no iPSCs were detected six weeks after transplantation.

Next, Wu and his co-workers differentiated the iPSCs into blood vessel-making endothelial cells that line the interior of the heart and blood vessels and then transplanted them into genetically-identical mice. Kooreman, Almeida, and Meyer then compared the acceptance by the immune system of these iPSC-derived endothelial cells with that of naturally occurring endothelial cells derived from the aortic lining of genetically-identical donor mice. To emphasize once again, all the transplanted cells were genetically identical to the mice in which they were injected. Unlike the undifferentiated iPS cells, both the iPS-derived endothelial cells and the aortic endothelial cells survived for at least nine weeks after transplantation.

Next, Wu and his group repeated the experiment, but they removed the grafts 15 days after transplantation. They observed immune cells called lymphocytes in all grafts, but these immune cells were much more prevalent in the grafts of undifferentiated iPS cells. When the lymphocytes that infiltrated the grafts of undifferentiated iPSCs were compared with those in the differentiated iPSC-derived grafts and the endothelial grafts, their gene expression profiles differed significantly. Those lymphocytes in the undifferentiated iPSC grafts expressed high levels of genes known to be involved in robust immune responses, but lymphocytes in both types of endothelial cell grafts expressed higher levels of genes known to be involved in dampening the immune response and inducing self-tolerance.

Finally, Wu and others directly examined a specific type of lymphocyte called a T cell. Grafts of undifferentiated iPS cells harbored large numbers of T cells that were largely homogeneous, which is characteristic of a robust immune response. Conversely, T cell from grafts of the two types of endothelial cells were more diverse, which suggests a more limited immune response which is typically associated with a phenomenon known as self-tolerance.

“The immune response to the iPS-derived endothelial cells and the aortic endothelial cells, and the longevity of the grafts, was very similar,” said Kooreman. “If we specifically look at the T cells, we see they’re also very similar and that they look much different from grafts that are rejected.”

Wu, who is also a professor of cardiovascular medicine and of radiology, said, “This study certainly makes us optimistic that differentiation — into any nonpluripotent cell type — will render iPS cells less recognizable to the immune system. We have more confidence that we can move toward clinical use of these cells in humans with less concern than we’ve previously had.”

Preventing Rejection of Embryonic Stem Cell-Based Tissues

Embryonic stem cells (ESCs) are derived from human embryos. Because they are pluripotent, or have the capacity to make any adult cell type, ESCs are thought to hold great promise for cell therapy as a source of differentiated cell types.

One main drawback to the use of ESCs in regenerative medicine is the rejection of ESC-derived cells by the immune system of the patient. Transplantation of ESC-derived tissues would require the patient to take powerful anti-rejection drugs, which tend to have a boatload of severe side effects.

However, a paper reports a strategy to circumvent rejection of ESC-derived cells. If these strategies prove workable, then they might clear the way to the use of ESCs in regenerative medicine.

The first paper comes from the journal Cell Stem Cell, by Zhili Rong, and others (Volume 14, Issue 1, 121-130, 2 January 2014). In this paper, Rong and his colleagues from the laboratory of Yang Xu at UC San Diego and their Chinese collaborators used mice whose immune systems had been reconstituted with a functional human immune system. These humanized mice mount a robust immune response against ESCs and any cells derived from ESCs.

In their next few experiments, Xu and others genetically engineered human ESCs to routinely express two proteins called CTLA4-Ig and PD-L1. Now this gets a little complicated, but stay with me. The protein known as CTLA4-Ig monkeys with particular cells of the immune system called T cells, and prevents those T cells from mounting an immune response against the cells that display this protein on their surfaces. The second protein, PD-L1, also targets T cells and when T cells bind to cells that have this protein on their surfaces, they are completely prevented from acting.

CTLA-4 mechanism

Think of it this way: T cells are the “detectives” of the immune system. When they find something fishy in the body (immunologically speaking), they get on their “cell phones” and call in the cavalry. However, when these detectives come upon these cells, their cell phones are inactivated, and their memories are wiped. The detectives wander away and then do not remember that they ever came across these cells.

Further experiments showed that any derivatives of these engineered ESCs, (teratomas, fibroblasts, and heart muscle cells) were completely tolerated by the immune system of these humanized mice.

This is a remarkable paper. However, I have a few questions. Genetic engineering of these cells might be potentially dangerous, depending upon how it was done, where in the genome the introduced genes insert, and how they are expressed. Secondly, if cells experience any mutations during the expansion of these cells, these mutations might cause the cells to be detected by the immune system. Third, do these types of immune repression last long-term? Clearly more work will need to be done, but these questions are potentially addressable.

My final concern is that if this procedure is used widespread, it might lead to the wholesale destruction of human embryos. Human embryos, however, are the youngest, weakest, and most vulnerable among us. What does that say about us if we do not value the weakest among us and dismember them for their cells? Would we allow this with toddlers?

Thus my interest and admiration for this paper is tempered by my concerns for human embryos.

Gene Therapy Makes Huge Advance in Cancer Fight

Gene therapy has been used to transform patients’ blood cells into soldiers that seek and destroy cancer. A small group of leukemia patients were given a one-time, experimental therapy several years ago and today, some remain cancer-free today. As a follow-up, at least six research groups have treated more than 120 patients with many types of blood and bone marrow cancers, with stunning results.

“It’s really exciting,” says Janis Abkowitz, blood diseases chief at the Univ. of Washington in Seattle and president of the American Society of Hematology. “You can take a cell that belongs to a patient and engineer it to be an attack cell.”

In one study, all five adults and 19 of 22 children with acute lymphocytic leukemia (ALL) showed complete remission of their cancer (i.e. no cancer could be found after treatment), although a few patients have relapsed since then.

These were gravely ill patients who were out of options. Some of them had tried multiple bone marrow transplants and up to 10 types of chemotherapy or other treatments. In the case of eight-year-old Emily Whitehead of Philipsburg, Pa., her cancer was so advanced that her doctors said Emily’s major organs would fail within days. Ms. Whitehead was the first child given the gene therapy and nearly two years later, shows no sign of cancer.

Physicians think that this has the potential to become the first gene therapy approved in the U.S. and the first for cancer worldwide. Only one gene therapy is approved in Europe, for a rare metabolic disease.

This gene therapy involves filtering patients’ blood to remove millions of T-cells, a type of white blood cell. These T-cells are then genetically engineered in the laboratory with a gene that targets cancer. These cells were subsequently returned to the patient in infusions, given over three days.

“What we are giving essentially is a living drug” – permanently altered cells that multiply in the body into an army to fight the cancer, says David Porter, a Univ. of Pennsylvania scientist who led one study.

Several drug and biotech companies are working hard to develop these therapies. The University of Pennsylvania has patented its method and licensed it to the Switzerland-based company Novartis AG. Novartis AG is building a research center on the Penn campus in Philadelphia and plans a clinical trial next year that could lead to federal approval of the treatment as soon as 2016. Hervé Hoppenot, president of Novartis Oncology, the division leading the work, said that “there is a sense of making history… a sense of doing something very unique.” Lee Greenberger, chief scientific officer of the Leukemia and Lymphoma Society, agrees: “From our vantage point, this looks like a major advance. We are seeing powerful responses… and time will tell how enduring these remissions turn out to be.”

This group has given $15 million to various researchers who are testing this strategy. Since there are nearly 49,000 new cases of leukemia, 70,000 cases of non-Hodgkin lymphoma and 22,000 cases of myeloma expected to be diagnosed in the U.S. in 2013, there are no shortage of potential subjects.

Many patients are successfully treated with chemotherapy or bone marrow or stem cell transplants, but transplants are risky and donors can’t always be found. Thus, gene therapy has been used as a fallback strategy for patients who were in danger of dying once all the other treatments failed.

The gene therapy must be made individually for each patient, since laboratory costs now are about $25,000, without a profit margin. That’s still less than many drugs to treat these diseases and far less than a transplant. The treatment can cause severe flu-like symptoms and other side effects, but these have been reversible and temporary, according to the physicians who administer the gene therapy treatment and observe the patients afterwards.

Penn doctors have treated 59 patients so far, which is the most of any center so far. Of the first 14 patients with B-cell chronic lymphocytic leukemia (CLL), four showed complete remissions, four showed partial remission, and the remaining patients did not respond to the treatment. However, some of the patients who showed partial remission continued to see their cancer shrink a year after treatment. “That’s very unique to this kind of therapy” and gives hope the treatment may still purge the cancer, says Porter.

Another 18 CLL patients were treated and half have responded so far. University of Pennsylvania doctors also treated 27 ALL patients. All five adults and 19 of the 22 children had complete remissions, which is an “extraordinarily high” success rate, according to Stephan Grupp at the Children’s Hospital of Philadelphia (CHOP). Six patients have, since then, suffered relapse of their cancer. The attending physicians are considering administering a second gene therapy treatment.

At the National Cancer Institute, James Kochenderfer and others have treated 11 patients with lymphoma and four with CLL, starting roughly two years ago. Six showed complete remission, six patients had partial remission, and one has stable disease but it is too soon to tell for the rest.

Ten other patients were given gene therapy to try to kill the leukemia or lymphoma cells that remained after bone marrow transplants. These patients received infusions of gene-treated blood cells from their transplant donors instead of using their own blood cells. One had a complete remission and three others had significant reduction of their disease.

“They’ve had every treatment known to man. To get any responses is really encouraging,” Kochenderfer says. The cancer institute is working with a Los Angeles biotech firm, Kite Pharma Inc., on its gene therapy approach.

Patients are encouraged that relatively few have relapsed.

“We’re still nervous every day because they can’t tell us what’s going to happen tomorrow,” says Tom Whitehead, eight-year-old Emily’s father.

Doug Olson, 67, a scientist for a medical device maker, shows no sign of cancer since his gene therapy in September 2010 for CLL he has had since 1996. “Within one month he was in complete remission. That was just completely unexpected,” says Porter, his doctor at Penn. Olson ran his first half-marathon in January and no longer worries about how long his remission will last. “I decided I’m cured. I’m not going to let that hang over my head anymore,” he says.

Embryonic Stem Cells Used to Make Laboratory-Created Thymus

Medical researchesr from UC San Francisco have used embryonic stem cells to construct a functioning mouse thymus in the laboratory. When implanted into a living mouse, this laboratory-made thymus can successfully foster the development of T cells, which the body needs to fight infections and prevent autoimmune reactions.

This achievement marks a significant step toward developing new treatments for autoimmune disorders such as type 1 diabetes and other autoimmune diseases, such as systemic lupus erythematosis and ulcerative colitis.

This research team was led by immunologist Mark Anderson and stem cell researcher Matthias Hebrok. They used a unique combination of growth factors to push the embryonic stem cells into a particular developmental trajectory. After a period of trial and error, they eventually found a formula that produced functional thymus tissue.

In our bodies, the thymus lies just over the top of our heart, and it serves to instruct T lymphocytes (a type of white blood cell) what to attack and what to leave alone. Because T cells serve a vital role in the immune response, the thymus serves a vital function.


Typically, each T cell attacks a foreign substance that it identifies by binding the foreign substance to its cell surface receptor. This T cell-specific receptor is made in each T cell by a set of genes that are randomly shuffled, and therefore, each T cell has a unique cell receptor that can bind particular foreign molecules. Thus each T cell recognizes and attacks a different foreign substance.

With in the thymus, T cells that attack the body’s own proteins are eliminated. Thymic cells express major proteins from elsewhere in the body. The T cells that enter the thymus first undergo “Positive Selection” in which the T cell comes in contact with self-expressed proteins that are found in almost every cell of the body and are used to tell “you” from something that is not from “you.” In order to destroy cells that do not bear these self-expressed proteins, they must be able to properly identify them. If T cells that enter the thymus cannot properly recognize those self-expressed proteins (known as MHC or major histocompatibility complex proteins for those who are interested), the thymus destroys them. Second, T cells undergo “Negative Selection” in which if the T cell receptor binds to self MHC proteins, that T cell is destroyed to avoid autoimmunity.

The thymus tissue grown in the laboratory in this experiment was able to nurture the growth and development of T cells. It could act as a model system to study patients with fatal diseases from which there are no effective treatments, according the Mark Anderson.

As an example, DiGeorge Syndrome is caused by a small deletion of a small portion of chromosome 22 and infants born with DiGeorge Syndrome are born without a thymus and they usually die during infancy.

Other applications include manipulating the immune system to accept transplanted tissues such as implanted stem cells or organs from donors that are not a match to the recipient.

Anderson said, “The thymus is an environment in which T cells mature and where they also are instructed on the difference between self and nonself.” Some T cells are prepared by the thymus to attack foreign invaders and that includes transplanted tissue. Other T cells that would potentially attack our own tissues are eliminated by the thymus.

Laboratory-induced thymus tissue could be used to retrain the immune system in autoimmune diseases so that the T cells responsible for the autoimmune response eventually ignore the native tissues they are attacking.

Hebrok warns that he and his team have not perfectly replicated a thymus. Only about 15% of the cells are successfully directed to become thymus tissue with the protocols used in this study. Nevertheless, Anderson asserted, “We now have developed a tool that allows us to modulate the immune system in a manner that we never had before.”