Analysis of blood samples from a small number of clinical trial patients showed that the novel method -- which inactivates specific immune cells from the donor that would attack the recipient's body -- also unleashes a surge of T-cells that further dampen the immune reaction.
The previously unrecognized specificity of these regulatory T-cells (also called Tregs) helps explain why the patients treated with the new strategy -- known as "co-stimulatory blockade" -- have shown a gratifyingly low level of graft-vs-host disease, according to the report published online by the new journal Science Translational Medicine.
The findings also suggest that optimizing the activity of Tregs in this manner might prove valuable in transplants of kidneys and other solid organs, as well as in treating autoimmune disease, say the scientists, led by Eva Guinan, MD, senior author, of Dana-Farber and Children's Hospital Boston, and Jeff Davies, MD, PhD, first author, of Dana-Farber. Both are also on the Harvard Medical School faculty.
The innovative method for improving mismatched bone-marrow and stem-cell transplants was first described clinically 10 years ago in the New England Journal of Medicine by Guinan, Lee Nadler, MD, also at Dana-Farber and a co-author on the new publication, and others. They employed a technique called "co-stimulatory blockade" to prevent certain T-cells in the donor material from recognizing and attacking cells in the patient's body, causing graft-vs-host inflammatory reactions that can affect the gastrointestinal system, skin, and other organs. The need for techniques that can reduce complications in mismatched transplants is great; the odds of a patient having a perfectly matched sibling for a donor are only about 25 percent.
"Originally we thought that using this method to specifically block the harmful response by donor T-cells explained the decrease in graft-vs-host disease and the rapid recovery of immune function we have seen in the clinical trials," said Guinan. "Now we learn that there is another powerful mechanism that is induced -- the generation and rapid expansion of Treg cells in the three months following the transplant."
Regulatory T-cells are a special population of T-cells that suppress immunity. They have two important functions: Turning off immune reactions following a successful defense against infectious organisms, and preventing immune cells from attacking the body's own tissues, which are identified by distinctive "self-antigen" markers.
In the past five years or so, scientists have used new tools to study Tregs and consider ways they could be harnessed for therapy in transplantation and autoimmune disease. In 2008, Davies and Guinan reported low levels of graft-vs-host disease in a small number of mismatched transplants using co-stimulatory blockade, which not only neutralized the T-cells that cause the harmful graft-vs-host response but also led to rapid reconstitution of the patients' bone marrow.
The researchers then designed experiments to learn more molecular details about how the blockade strategy had reduced graft-vs-host complications. Based on few reports in the literature, "We wondered whether Tregs were playing an additional role," said Davies.
Davies analyzed frozen blood samples taken from five patients and donors at various intervals after the transplants. The analysis showed that during the first three months, the level of Tregs in the patients rapidly rose to very high levels, which helped explain why the recipients experienced only mild graft-vs-host symptoms. The Tregs, they confirmed, were generated from the donated T-cells – not remnants of the recipient's immune system.
"We found there was something about co-stimulatory blockade that caused this rapid expansion of Tregs," said Davies, adding that further studies are exploring this question.
Importantly, the researchers noted, the Tregs acted in a highly specific fashion: They turned off only the donor T-cells that would have triggered the immune attack on the recipient's tissues -- other T-cells that help the patients fight off infections were spared. This specificity appears to have developed in the recipient's body, where the Tregs were "educated" to respond only to a harmful T-cell reaction.
As a result, said Guinan, this technique "creates a good balance of effects -- inactivating the T-cells that cause graft-vs-host disease (GVHD), revving up the Tregs to turn off any incipient GVHD, while bringing about a rapid reconstitution of the recipient's immune system."
The scientists expect the new findings to influence the design of further clinical tests of the co-stimulatory blockade technique. And, they said, it opens a window on other potential applications of co-stimulatory blockade, which is already being used clinically to treat rheumatoid arthritis (an autoimmune disease) and is being tested in mismatched kidney transplants.
Guinan is the associate director of the Center for Clinical and Translational Research at Dana-Farber and an associate professor of pediatrics at Harvard Medical School.
The research was funded by grants from the National Institutes of Health, the Leukemia & Lymphoma Society, and the American Society of Blood and Marrow Transplantation.
Dana-Farber Cancer Institute (www.dana-farber.org) is a principal teaching affiliate of the Harvard Medical School and is among the leading cancer research and care centers in the United States. It is a founding member of the Dana-Farber/Harvard Cancer Center (DF/HCC), designated a comprehensive cancer center by the National Cancer Institute. It is the top ranked cancer center in New England, according to U.S. News & World Report, and one of the largest recipients among independent hospitals of National Cancer Institute and National Institutes of Health grant funding.
Bill Schaller | EurekAlert!
Study tracks inner workings of the brain with new biosensor
16.08.2018 | Rheinische Friedrich-Wilhelms-Universität Bonn
Foods of the future
15.08.2018 | Georg-August-Universität Göttingen
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
17.08.2018 | Physics and Astronomy
17.08.2018 | Information Technology
17.08.2018 | Life Sciences