Division of Cardiothoracic Surgery
GANDY / DOMEN LAB
Laboratory Interest.
Dr Domen has a long-standing interest in the biology of Hematopoietic Stem Cells and their regulation by apoptosis. Dr Gandy has studied aspects of allogeneic hematopoietic cell transplantation with a focus on their use in tolerance induction, in addition to her interest in and practice of pediatric cardiac surgery.
Drs Gandy and Domen have recently joined the Children's Research Institute/Medical College of Wisconsin and have initiated a joint lab effort. This is currently focused on two area's.
(i) The use of hematopoietic stem cells and bone marrow cells in tolerance induction for solid organ transplantation. Organ transplantation is successful, but requires continued immunosuppression to prevent rejection of the transplanted organ. This leads to complications, including ongoing vulnerability to infection. It is known that a bone marrow transplantation from the organ donor can result in acceptance of the transplanted organ. We are investigating ways to improve bone marrow transplantation to the point that use for tolerance induction can become clinically accepted. This in addition to the already widespread use of bone marrow transplantations in cancer patients, which have different needs than transplantation patients.
(ii) The unexplained ability of bone marrow cells to contribute to recovery of myocardial function. This has been documented mostly in myocardial infarct models in different animal systems, and also in clinical studies in humans. Our research in this area uses mouse models of congenital cardiomyopathy. We observe improved function after bone marrow injection, without clear evidence of engraftment in the heart of bone marrow-derived cells. We are currently investigating possible mechanisms that could help explain these observations
We approach these two area's using mouse models. Mice have the advantage of being well characterized, and of being relevant predictors of clinical usefulness.
Tolerance Induction.
In large part due to the development of immunosuppressive drugs, organ transplantation has become an effective therapy for the treatment of end-stage organ disease. Long term graft and patient survival, however, continue to be limited.
Despite advances in immunosuppressants, most grafts eventually succumb to rejection. The figure below shows one year (gray) and five year (blue) graft survival data from the 2005 OPTN/SRTR report for different types of solid organ transplantations in humans. Only 40-60% of the most successful graft types continue to function at 10 years. In addition, the need for continued immunosuppression leads to many, potentially lethal, complications. Transplantation tolerance is a phenomenon defined as the lack of destructive immunological activity to a foreign graft in an otherwise immunocompetent host. Achieving tolerance means that the lifespan of the transplanted organ will be extended. It also abolishes the need for immunosupressants and the accompanying side effects. For the last fifty years clinical implementation has been an elusive goal, largely due to the complexity and redundancy of the immune system. Multiple methods of tolerance induction have been proposed. The most reproducible method appears to be hematopoietic reconstitution. In this method, blood cells from the organ donor are infused into a genetically disparate recipient (allogeneic HCT) and the recipient's blood system is reconstituted in large part with donor blood cells. The effectiveness of this method may result from the fact that hematopoietic reconstitution addresses a variety of central and peripheral tolerance induction mechanisms, and thus the redundancy in the system.
However, despite the fact that the potential has been recognized for a long time, hematopoietic cell transplantation has not seen general clinical use, due to the attendant morbidity and mortality of the procedure. Our efforts are focused on ways to reduce the complications associated with Hematopoietic Cell Transplantation beyond what has already been achieved in recent years by the development of procedures such as "mini-transplants". In the past research by Dr Gandy has focused on the use of so-called facilitator cells to reduce the risk of hematopoietic graft failure. Our current focus is on reducing the immune incompetence that follows especially allogeneic hematopoietic reconstitution. The central hypothesis of our ongoing research is that high levels of donor-derived chimaerism will result in clinically robust tolerance to subsequently transplanted organs. The clinical application of this principle is limited by the morbidity and mortality associated with allogeneic Hematopoietic Cell Transplantation (HCT). Graft-versus-Host disease, potentially a major problem in allogeneic hematopoietic cell transplantations, can be resolved by the use of highly purified grafts. The risk of engraftment failure (to which purified grafts are prone) can reduced by "mega"dose HCT and by the use of facilitators. However, this still leaves patients exposed to a period of neutropenia, and prolonged immuno-incompetence. Recently, infusion of a population of
cells known as Myeloid Progenitors (MP) in neutropenic hosts has been shown to provide transient resistance to fungal and bacterial pathogens in a non-MHC-restricted fashion. This could significantly reduce HCT-related complications and has the potential to become an important component of future HCT protocols. We aim to investigate systematically whether addition of Myeloid Progenitors can alter tolerance induction by hematopoietic cell transplantation. In addition to myeloid progenitors we aim to investigate other adjuvant cell populations that can improve immune competence, such as memory T cells. The experimental approach is depicted schematically in the left panel below.
A second approach (right panel above) that is currently being pursued studies the use of autologous Hematopoietic Cell transplantation as a way to achieve tolerance for a previously transplanted allogeneic solid organ. In this approach the hematopoietic cell transplantation is used to "reset" the immune system after the solid organ transplantation and remove graft-reactive immune cells. New immune cells that are generated following the autologous Hematopoietic Cell transplantation are expected to recognize the transplanted solid organ as self. While initial experiments have shown promise the outcome is determined by many variables (such as solid organ graft size and type, timing of organ and hematopoietic transplantation, method used to precondition for Hematopoietic Cell transplantation, to name but a few). A systematic investigation of their influence is needed to determine the potential of this approach.
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Rescue of Cardiac Function in Models of Congenital Cardiomyopathy.
Most pediatric cardiomyopathy is non-ischemic in origin, with a significant portion having a genetic etiology. We have established a model of congenital cardiomyopathy, induced by tropomodulin overexpression (TMOD), in which injection of bone marrow (WBM) results in improved myocardial function. We find that intravenous injection of WBM at four weeks of age largely prevents the development of heart damage that is normally seen in these mice. Analysis of heart function by echocardiography 10 weeks after WBM injection demonstrates function approaching that of normal mice. Our initial analysis, using GFP-expressing bone marrow cells, did not reveal myocardial engraftment of donor cells. This would indicate that an indirect mechanism, such as the induction of growth factor expression, prevents development of cardiac damage. This type of analysis, however, can be deceptive, as loss of GFP expression is not uncommon after transplantation. Therefore, we propose to evaluate engraftment more rigorously using cells labeled intensely with quantum dots. Quantum dot fluorescence is not dependent on continued gene-expression. In addition to our studies in TMOD mice we aim to expand our observations to a second congenital mouse model of cardiomyopathy in order to broaden the observations and evaluate the potential for rescue in other models of cardiomyopathy.
Links
Community of Science profile: Jos Domen
Clinical link: Kimberly Gandy
Division of Cardiothoracic Surgery
Department of Surgery
Program in Regenerative Medicine and Stem Cell Biology
Children's Research Institute
Medical College of Wisconsin
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