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Dr. Kelvin and colleague Dr. Mark Cameron have established a technical and academic core at the heart of Transnet. The facility is open for business and is performing research on innovation in organ and cell transplantation in collaboration with Transnet members across Canada. |
The holy grail of transplant research is tolerance. To learn how to tell the body to accept a transplanted organ as though it were its own, to limit or cease the use of immunosuppressants, and to save lives-such are the ultimate goals of Transnet, a successful team in the 2002 Institute of Infection and Immunity Health Research Programs of Excellence (HRPE) grant competition.
Very little is known about the mechanisms, or "molecular programs," taking place between the transplanted organ and the recipient's immune system. "The organs don't last forever, and there probably isn't a good reason for that-they were designed to last for a long time, why don't they last a long time after transplantation?" says Dr. Anthony Jevnikar, a member of Transnet (see table). It's a central question for the team. Transnet's basic approach is to monitor gene expression in a graft, or transplanted organ, in order to describe transplantation rejection and tolerance at the molecular level.
Without immunosuppression, an organ will likely be rejected within seven to 10 days. But the concept of tolerance isn't based in myth: a small number of individuals, who for whatever reason must discontinue immunosuppressant treatment, do not reject their organs-ever. Currently, there's no way of telling who has this ability. "You can't say to somebody today, let's take the drugs away and see if your organ's going to survive," says Dr. David Kelvin, Transnet principal investigator.
To illuminate the molecular mechanisms involved in transplant tolerance or rejection, Transnet investigators are using microarrays to allow them to develop gene expression profiles for tissues of interest. "Looking at a specimen under a microscope simply isn't enough to understand what's happening," says Jevnikar. DNA microarray technology was the original idea behind the project according to Kelvin. By taking an early snapshot of a transplanted organ's gene expression profile and comparing it against further snapshots taken over time, the profile could highlight factors involved in chronic rejection-the slow process of organ damage that happens to almost every transplant recipient, beginning as early as one year after the transplant. Some of these mechanisms originate with the donor and with the physical trauma to the organ during the transplantation process, while other mechanisms include recipient immune responses to the organ. An understanding of these causes would allow clinicians to more closely monitor the state of transplanted organs, finding infection before it's even clinically visible, perhaps tailoring immunosuppressive treatment to suit rejection mechanisms unique to each patient. For example, if the expression of certain genes appeared to be linked to rejection, drugs to suppress those genes could be developed, and vice versa, thus prolonging the life of the organ.
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Health Research Programs of Excellence Team Transnet: Molecular modeling of alloantigen independent and alloantigen dependent transplantation injury | |
| Investigator | Affiliation |
| David Kelvin, Principal Investigator | Division of Experimental Therapeutics, Toronto General Research Institute, University Health Network, University of Toronto |
| Huifang Chen | Dept. of Surgery, Centre Hopital de l'Université de Montréal |
| Philip Halloran | Division of Nephrology and Immunology, University of Alberta |
| Anthony Jevnikar | Depts. Of Medicine, Microbiology and Immunology, University of Western Ontario Robarts Research Institute Transplantation Nephrology, Division of Nephrology, LHSC-UC |
| Gary Levy | Multi-organ Transplant Program, Toronto General Hospital |
| Joaquin Madrenas | Robarts Research Institute Dept. of Microbiology and Immunology, The University of Western Ontario |
| Peter Nickerson | Internal Medicine, University of Manitoba Immunogenetics Laboratory, Canadian Blood Services |
| James Woodgett | Dept. of Experimental Therapeutics, Ontario Cancer Institute |
| Jiangping Wu | Laboratory of Transplantation Immunology Dept. of Medicine, Centre Hopital de l'Université de Montréal |
| Li Zhang | Division of Cellular and Molecular Biology, Toronto General Hospital Research Institute |
| Robert Zhong | Experimental Surgery, Transplant Program LHSC Dept. of Surgery, The University of Western Ontario |
Team members will take advantage of the microarray technology to shed light on the immune response from various angles. Jevnikar is particularly interested in the organ's response to injury and inflammation. "You have a smoking gun, and you have a bunch of dead cells around, but you don't actually know what happened." Transnet members Li Zhang and Jiangping Wu are also taking unique tacks at unearthing mechanisms of increasing longevity of transplanted organs, studying a unique species of lymphocyte and a lymphocyte activation molecule respectively (see sidebar).
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A member of Dr. David Kelvin's research team prepares a slide for microarray analysis. Dr. David Kelvin, based at the University Health Network, an affiliate of the University of Toronto, is the principal investigator of a successful team in the CIHR Institute of Infection and Immunity's Health Research Programs of Excellence competition. |
The arrays carry 18,000 human genes. The gene expression profile referred to by Kelvin will reveal the up-regulation, down-regulation, or status quo of immunology genes in infected or injured tissue versus healthy tissue. Data will be collected for organs which undergo acute rejection (i.e. rejection within two to three weeks' time from transplantation), chronic rejection, and healthy organs as a baseline, generating millions of data points.
The data will be organized into gene families-groups of genes about which information is already available. But Kelvin describes the one-third of the human genome about which nothing is known as a gold mine. "This is absolute discovery. .That's the wonderful thing about this technology: it allows us to generate and look at things that we've never imagined before."
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Spotlight on Tolerance  |
Dr. Li Zhang is a member of Transnet"What's the molecular basis for the cell to be able to induce transplantation tolerance? We found that tolerant animals who do not reject grafts-such as skin grafts and heart grafts-have a unique population of T cells we call CD4(-) CD8(-) double negative T regulatory lymphocytes (DN Treg). We found that this type of cell increased in the tolerant recipient.We found these double negative cells to be "good" cells, and when we boost them, they overcome the "bad" cells and the graft is not rejected. We now want to extend our findings from rodents to primates, and hopefully to some humans, and we want to identify the genes involved in this regulation. We want to see whether the genes important for those regulatory cells to function also exist in a tolerant human graft.Currently, one of the clinical diagnostic parameters of graft rejection is based on biopsies that show infiltrating lymphocytes and tissue damage. If lymphocytes are present, that's interpreted as a bad sign, and the clinician will increase immunosuppression. But our findings show the infiltrating lymphocytes can be "good" or "bad." The good ones, the regulatory cells, actually try to protect the graft.I think Transnet is exciting.nowadays it's very limiting if you want to work alone, because the knowledge is exploding - you really need collaboration and joint efforts if you want to do something big." |
The investigators are looking forward to explaining many of the factors known to affect transplant success. At the molecular level, why do organs harvested within the same hospital as the transplant operation survive longer? Why do transplants between identical twins survive longer? Why do liver transplants fare better than those of other organs-a chronic rejection rate of two percent compared to up to 20 per cent for other organs?
According to Kelvin, most transplanted organs have a half-life of about five years, so improved diagnostic ability would have immeasurable impact on transplant recipients. In 2002, more than 1,800 Canadians received a transplanted organ. Often suffering end-stage organ failure, they were fortunate. But for most recipients, this new lease on life ends-due to various factors which include recurrence of the original disease, immunosuppressant drug toxicity, or the slow rejection process. In the case of kidneys, most people go back to the waiting list. But for those waiting for something else, "they'll never see another organ," says Kelvin. As of December 31, 2002, more than 4,000 Canadians were waiting for transplants. Yet even the thousands on the waiting list are not indicative of true need. As Transnet member Dr. Gary Levy points out, speaking for clinician colleagues, no clinician puts everyone on the transplant wait list that would benefit - particularly for the heart - because the disparity between supply and demand is so tremendous.
Transnet's original mandate was to form an interactive network of transplantation clinicians and scientists from across Canada utilizing functional genomic approaches to transplantation research. The core team included 11 scientists with expertise in small and large animal models of allotransplantation (intra-species transplantation), transplantation injury, clinical outcomes, genomics and gene expression profiling. When the CIHR-III HRPE grant was submitted, the team's aim was to examine gene expression patterns in normal renal tissues and cells and those from renal transplant patients. However, the team leveraged its
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Transnet's success in transforming from an idea to a functioning and highly productive research network is evident in its sponsors-the team is also supported by the Canadian Network of Vaccines and Immunotherapeutics (CANVAC) and Toronto's University Health Network-and its member scientists, clinicians and equipment. But Jevnikar says: "Without the patient samples, it probably won't mean much. Because we're not interested, actually, in preserving transplants in animals. Having buy-in by clinicians that are in the trenches looking after patients is very important." And there is buy-in, as Transnet members have found: after her seminars, Li Zhang is often surrounded by clinicians and pathologists eager to become involved. Citing the cohesiveness of the Canadian transplant community, Jevnikar says Canada provides an ideal environment for the research Transnet is doing. "The Canadian transplant community is big enough and yet small enough that we can do something in Canada that would be very difficult in the U.S."
To learn more about Transnet, visit: www.transnet.ca
