Our research focuses on discovering biomarkers for diagnosis, prognosis, and targeted therapy for primary graft dysfunction, acute rejection, and chronic allograft dysfunction after heart and lung transplantation. In order to improve quality of life and patient survival, we must be able to predict, which transplants are doomed to be lost and which recipients will face an untimely death. We aim to establish biomarkers for transplant dysfunction and the side effects of immunosuppressive drugs based on peripheral blood samples and transplant biopsies and employing both classical pathology and new precision medicine tools integrated with electronic health records and eHealth. Moreover, to address the unmet need for heart and lung transplants, we will develop treatment algorithms for the utilization of marginal donors and organs from non-heart beating donors for heart and lung transplantation.
Heart and lung transplantation are the primary life-saving treatment option for patients diagnosed with either end-stage heart or lung diseases, respectively. The first successful heart transplantation was performed at Groote Schuur Hospital, Cape Town, South Africa in 1967 and first successful lung transplantation in Toronto General Hospital, Toronto, Canada in 1983. With advances in surgical techniques, intensive care, control of infection diseases, and the discovery of calcineurin inhibitors, heart and lung transplantations have become a plausible treatment for many end-stage heart and lung diseases. Due to the organ shortage, marginal donors are increasingly used. Primary graft dysfunction is the leading cause of death within the first 30 days after transplantation. Thereafter, chronic allograft dysfunction with infection and malignancy account for the majority of deaths. According to the International Society of Heart and Lung Transplantation, the average life expectancy is 11.9 years after heart transplantation and 7.3 years after lung transplantation.
Donor brain-death with the subsequent catecholamine and cytokine storm may induce hemodynamic and microvascular dysfunction in the donor organs. At the time of organ procurement, donated organs are disconnected from blood circulation and preserved in ice-cold solution before transplantation. Re-establishment of blood circulation is vital, but may paradoxically result in primary graft dysfunction. We hypothesize that these early events may initiate microvascular dysfunction and pro-inflammatory and pro-fibrotic processes and may lead to primary graft dysfunction, acute rejection, and chronic allograft dysfunction. Clinically, chronic allograft dysfunction usually manifests as cardiac fibrosis or cardiac allograft vasculopathy, or as obliterative bronchiolitis or restrictive allograft syndrome, and results in poor quality of life and untimely death.
Donor microvascular blood endothelial cells form the first line barrier between the recipient circulating inflammatory cells and the allograft. On top of regulating tissue perfusion, they are extremely important in immunological recognition and inflammatory cell recruitment, and contribute to transplant fibrosis by undergoing endothelial-mesenchymal cell transition. Their counterparts in the lymphatic system, lymphatic endothelial cells, are critical in immune surveillance and resolution of inflammation by regulating the drainage of extravasated fluid and inflammatory cells from the allograft. In microvascular dysfunction, junctional complex proteins dissociate thus rendering these junctions leaky.
Hypoxia-inducible factor is the master regulator of gene transcription during low oxygen tension and forms the molecular link between shortage of oxygen and cellular adaptation mechanisms in response to hypoxia. The transcriptional activity of HIF is enhanced by stabilization of the HIF1a proteins under hypoxic conditions. There is extensive interplay between hypoxia and inflammation, and the pro-inflammatory transcription factor NF-kB is a critical activator of HIF1a. We have used animal models with small molecule inhibitors, monoclonal antibodies, gene transfer, and cell-specific conditional knockout mice and found that HIF1a and several of its downstream growth factors such as VEGFA, VEGFB, VEGFC, PDGFs, ANG1, ANG2, and ET1 may have important clinical implications in the prevention of pro-inflammatory and pro-fibrotic processes after heart transplantation.
The new immunosuppressive drugs do not prevent primary graft dysfunction or chronic allograft dysfunction. On the other hand, acute rejection and side-effects of these drugs still affect about half of all transplant recipients. It is believed that the incidence of the side-effects depends on the type and intensity of the immunosuppressive drugs. There are no biomarkers or liquid biopsies available to monitor the level of individual immunosuppression other than measurement of their trough levels. The most common and reliable technique to evaluate rejection is the acquisition of histological evidence of inflammation and cell necrosis via invasive endomyocardial biopsy or transbronchial biopsy after heart and lung transplantation, respectively. However, the histological evaluation in the presence or absence of inflammation and cell necrosis does not reveal if the transplant in pro-inflammatory or profibrotic process leading to chronic allograft dysfunction. Therefore, a better understanding of the molecular profiles of biopsies is required. We believe that using clinical studies with multiomics approach and bioinformatics will help us find novel molecular pathways and develop diagnostic and prognostic methods as well as targeted therapy to prevent and to treat the disease processes after heart and lung transplantation.
Our research is focused on developing novel biomarkers and liquid biopsies for diagnosis, prognosis, and targeted therapy for primary graft failure, acute rejection, and chronic allograft dysfunction. The specific aims are:
- to study the effect of donor simvastatin treatment on primary graft failure, acute rejection, and chronic allograft dysfunction after heart transplantation in a randomized single center clinical trial, and to develop biomarkers for primary graft dysfunction;
- to study the effect of genetic diversity between the donor and recipient on the response to immunosuppressive drugs and the development of complications after heart and lung transplantation;
- to develop liquid biopsies for diagnosis, prognosis, and treatment for acute rejection, and chronic allograft dysfunction, and to monitor immunosuppression after heart and lung transplantation; and
- to test the novel molecular pathways in animal models using small molecule inhibitors, monoclonal antibodies, gene transfer, and cell-specific conditional knockout mice.