BIDMC's Division of Transplant Immunology has international reputations for excellence and innovation. The center attracts students, fellows and post-doctoral individuals from around the world.
Terry B. Strom, MD, Co-Chief
Laurence Turka, MD, Co-Chief
Xian C. Li, MD, PhD
Wenda Gao, MD, PhD
The Challenge: Organ Rejection
Transplant patients and physicians face a significant challenge: organ rejection. Our bodies' immune systems are naturally designed to do battle with "foreign invaders." Under normal circumstances, this system is highly effective, protecting us from viruses, bacteria and other infections. However, our immune systems are not as successful at differentiating between dangerous foreign bodies (for instance, bacterial infections) and beneficial intruders (such as a new kidney, liver or pancreas). For organ transplant patients, the normally protective immune response can threaten the longevity and function of the transplanted organ.
Currently, organ transplant patients must take immunosuppressive or anti-rejection medication to prevent the immune system from fighting against the new, transplanted organ. However, over the long-term, these drugs pose a number of risks, and side effects that are particularly devastating to children.
The Mission: Prevent Rejection, Improve Function
Scientists in the Division of Transplant Immunology are working to:
- Develop new methods to prevent rejection
- Develop new methods to diagnose rejection before injury to the transplant
- Improve the function of organs after transplantation
- Reduce the number of medications patients must take to prevent rejection, including reducing steroid use
- Minimize the side effects of therapy
- Create immune tolerance to the transplant to totally eliminate the need for use of immunosuppressive medications
The center's basic or bench research is directed toward a broader understanding about transplant science and immunology (the body's ability to accept or reject foreign tissue), and how medicines can protect and maximize donor organ function and endurance. We are leaders in one) developing new approaches to overcome organ rejection without the use of highly toxic immunosuppressive drugs, and two) diagnosing early rejection and enabling application of medication before the transplant is damaged.
Principal Areas of Investigation
The interests of the research group include immune tolerance and T-cell biology, cytoprotection (the role of protective genes in transplantation), molecular diagnostics, and bioinformatics, as well as a number of subspecialties within these key areas.
Immune Tolerance and T-Cell Biology
Immune tolerance refers to the ability of the immune system to accept or tolerate new organs without taking life-long medications. By creating tolerance, researchers hope to ensure long-term transplant function without life-long drug therapy (which carries a number of risks). Scientists investigate the T-lymphocyte cells, or T cells, which are among the body's key infection-fighting cells. Normally T cells circulate through the blood in a resting or naïve state. When they encounter a foreign invader (such as a virus or bacteria) or foreign tissue (a transplanted organ), they receive a chemical signal to attack and destroy the "intruder." Researchers are working to understand this signal - how is it triggered, how can it be disarmed, and how can the T cell be disabled against (or help protect) the donor transplant (to maximize organ function), while remaining vigilant and ready to destroy truly harmful microbes and other infectious agents that enter the body.
BIDMC scientists are leading the way in refining immunosuppressive protocols, or treatment guidelines, to target T cells. They are learning how to train T cells to protect, rather than attack, transplanted organs. They are studying a new combination of immunosuppressive drugs, some of which have been developed in the Division of Transplant Immunology, called "power mix." Administered for a very short time after transplant, this power mix has been shown to prevent islet cell rejection in monkeys. Islet cells are the insulin producing cells in the pancreas that are deficient in people who have diabetes. Short-term power mix therapy has proven useful in permanently restoring normal blood sugar level and tolerance to islet cells in a mouse model of juvenile diabetes. In a parallel study this same team has determined that a short course of treatment with alpha1 anti-trypsin, a human protein that is normally produced in response to inflammation, is also curative in this model of juvenile diabetes. These studies are paving the way for clinical trials in the near future for patients with diabetes. The power mix also has exciting potential for other autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease and psoriasis.
Another area of T-cell investigation involves a better use of anti-lymphocyte antibodies, to reduce the number of aggressive T cells in the immune system, in combination with donor bone marrow cells. Patients undergoing a kidney transplant, for example, would receive anti-lymphocyte antibodies to knock out the aggressive T-cells, in combination with the kidney donor's bone marrow. This approach has shown great promise in improving organ tolerance.
Cyto or "cell" protection is another significant research area and has to do with protecting the graft, or donor organ, from damage. Scientists examine a process called apoptosis, or programmed cell death. Every cell in our body comes equipped with a unique life-cycle program. Cells survive and thrive until they are no longer useful and then they automatically die. Scientists are looking for the switch: What turns on the death program, and how do cells disappear without notice? With cancer, this orderly process goes haywire, allowing cancer cells to grow unchecked into tumors. In transplanted organs, researchers look to turn off the death program and turn on the survival signal, to keep the organ vital, functioning and less vulnerable to injury.
Researchers also study gene therapy to help protect and fortify the cells in the transplanted organ. Genes, located within the nucleus of each cell, contain our unique hereditary information, a personal blueprint, which is passed from cell to cell. The Division of Transplant Immunology has succeeded in identifying protective genes that have proved useful in fortifying the transplanted organ, helping to prevent chronic rejection and increasing graft survival.
Experiments have also shown that carbon monoxide can prevent the delay in kidney function that sometimes occurs after transplantation. This delay is attributed, in part, to how the organ must be preserved once it is removed from the donor.
Molecular diagnostics examines how proteins and genes interact within a cell, and captures this information as a "molecular signature." Researchers study these gene and protein patterns for early warning signs that predict the likelihood of organ rejection or tolerance. The goal is to disarm the T-cell attackers before the body's immune system can mount a defense and destroy the transplanted organ, thereby short-circuiting the rejection process before it even begins.
To check gene expression, we perform real-time quantitative PCR assay (qRT-PCR) using standard curve method. We custom design the primers and probes (P&P) for our qRT-PCR assays. We extract RNA from the biopsies, peripheral blood, and urine specimens. For quality control, RNA quantity and purity is tested by Nanodrop spectrophotometer. RNA integrity is examined by bio-analyzer. 1ug/100ul of the quality control passed total RNA is used to synthesize cDNA.
We developed pre-amplification technique that increases the sensitivity and allows measuring over 20 targets by qRT-PCR using samples as small as 30 ng of total RNA. For miniscule specimens such as core-biopsies and urine pellets
, where RNA is limited, pre-amplification technique is extremely useful. The pre-amplified cDNA is used to perform qRT-PCR. Standard curve method of qRT-PCR is performed using 18s rRNA amplicon as standard. The following performance characteristics are used as quality control measures for the qRT-PCR assay: (1) the slope of the standard curve must be between -3.320 to -3.500, and the correlation co-efficient must be greater than 0.990 (Fig); (2) the highest copy number in the standard curve (2.5 million copies) is adjusted to be 18 threshold cycles (Ct) and the minimum copy number (25 copies) is at 35Ct;(3) the differences between replicate Ct must be less than 0.5 Ct; and (4) the Ct of endogenous controls should always be statistically invariant. The results are shown in normalized copies per 1μg of total RNA/100μl. The samples that do not have atleast 50 million copies of 18s rRNA are considered to have failed the quality test.
Researchers use bioinformatics, which incorporates chemistry, statistics, and computer science among other techniques, to address biological challenges from the molecular perspective. At BIDMC, researchers are studying the genome, the complete set of genes that make up our hereditary information and account for how we develop, look and behave. Armed with this information about donors and recipients, doctors can more accurately predict and anticipate organ rejection and hopefully tolerance. The information is also likely to be valuable to guide doctors in tempering the use of immunosuppressive drugs or in selecting the most effective drugs based on the genetic makeup of individual patients.