Regression of a donor atheroma after cardiac transplantation: serial observations with intravascular ultrasound

Failing Heart Transplants and Rejection-A Cellular Perspective

The median survival of patients with heart transplants is relatively limited, implying one of the most relevant questions in the field—how to expand the lifespan of a heart allograft? Despite optimal transplantation conditions, we do not anticipate a rise in long-term patient survival in near future. In order to develop novel strategies for patient monitoring and specific therapies, it is critical to understand the underlying pathological mechanisms at cellular and molecular levels. These events are driven by innate immune response and allorecognition driven inflammation, which controls both tissue damage and repair in a spatiotemporal context. In addition to immune cells, also structural cells of the heart participate in this process. Novel single cell methods have opened new avenues for understanding the dynamics driving the events leading to allograft failure. Here, we review current knowledge on the cellular composition of a normal heart, and cellular mechanisms of ischemia-reperfusion injury (IRI), acute rejection and cardiac allograft vasculopathy (CAV) in the transplanted hearts. We highlight gaps in current knowledge and suggest future directions, in order to improve cellular and molecular understanding of failing heart allografts.

Treatment of allograft vasculopathy in heart transplantation

Cardiac allograft vasculopathy remains one of the main causes of morbidity and mortality after heart transplantation, although its impact is becoming somewhat smaller as prophylactic measures are implemented. Advances in the understanding of the molecular and cellular mechanisms involved in the genesis and development of cardiac allograft vasculopathy are opening ways for new diagnostic and therapeutic strategies. Successful prophylaxis of the early stages of the disease has been demonstrated with the use of newer immunosuppressive agents, such as sirolimus and everolimus, that will probably be included in future protocols. For most patients with established cardiac allograft vasculopathy, currently available revascularisation methods and retransplantation are not appropriate options. Antiproliferative agents could provide significant improvement in terms of symptom relief and prognosis, but their definite value must be proven in well-designed trials.

Progress in heart transplantation

The field of heart transplantation was built upon the discoveries of immunity and tolerance by Landsteiner, Medawar, Burnet, and others, as well as technical advancements in surgical technique by Carrel. Since the first successful human heart transplant performed by Christiaan Barnard in 1967, there has been substantial progress in the field of heart transplantation, especially over the last several decades. With advances in immunosuppression and surgical techniques, the rates of acute rejection and infection leading to graft failure have declined. However, the detection of acute and chronic allograft rejection remains one of the most important yet unsettled matters. As such, many new horizons exist for further advancement of the field of heart transplantation and for improving the outcomes of the patients we serve.

Cardiac allograft vasculopathy: central role of endothelial injury leading to transplant "atheroma"

Endothelial injury plays a central role in the pathophysiologic mechanisms underlying cardiac allograft vasculopathy (CAV). Although the accelerated course of CAV and its localization to the allograft support an important role for the alloimmune response, there is considerable evidence implicating lipoprotein abnormalities, metabolic disturbances, viral infections, and systemic inflammation in the process. This multifactorial basis for CAV may be put into a pathophysiologic context in which endothelial cell injury is the triggering event that initiates and drives the proliferative and fibrotic processes characteristic of CAV. In the transplant setting, endothelial cell injury is induced by multiple factors, including brain death, ischemia-reperfusion, alloimmune responses, and viral infections. Once initiated, propagation of the proliferative processes that ultimately lead to vascular occlusion is enhanced by the abnormal metabolic environment of elevated lipoproteins and insulin resistance encountered in most patients. This review examines the evidence for the role of potential triggers of endothelial injury in the pathophysiology of CAV and discusses the central role of the nitric oxide pathway in the disease process.