The potential of autologous regulatory T cell (Treg) therapy to prevent Cardiac Allograft Vasculopathy (CAV) in paediatric heart transplant recipients

Abstract

Paediatric heart transplant is an established treatment for end stage heart failure in children, however patients have to commit to lifelong medical surveillance and adhere to daily immunosuppressants to minimise the risk of rejection. Compliance with immunosuppressants can be burdensome with their toxic side effects and need for frequent blood monitoring especially in children. Though the incidence of early rejection episodes has significantly improved overtime, the long-term allograft health and survival is determined by Cardiac Allograft Vasculopathy (CAV) which affects a vast number of post-transplant patients. Once CAV has set in, there is no medical or surgical treatment to reverse it and graft survival is significantly compromised across all age groups. Current treatment strategies include novel immunosuppressant agents and drugs to lower blood lipid levels to address the underlying immunological pathophysiology and to manage traditional cardiac risk factors. Translational researchers are seeking novel immunological approaches that can lead to permanent acceptance of the allograft such as using regulatory T cell (Tregs) immunotherapy. Clinical trials in the setting of graft versus host disease, autoimmunity and kidney and liver transplantation using Tregs have shown the feasibility and safety of this strategy. This review will summarise current knowledge of the latest clinical therapies for CAV and pre-clinical evidence in support of Treg therapy for CAV. We will also discuss the different Treg sources and the considerations of translating this into a feasible immunotherapy in clinical practice in the paediatric population.

Keywords: cardiac allograft vasculopathy (CAV); cell therapy; paediatric; regulatory T cells; thymic; transplantation.

Figure 1

Underlying Pathophysiology of CAV with the cascading effect of initial endothelial cell injury and activation of immune cells. Immune and non-immune mediated factors contribute to this process with the resulting diseased vessel becoming occluded and resulting in graft ischaemia and loss.

Figure 2

Schematic diagram to demonstrate the different ways in which Tregs can suppress immune cells. Cell to cell contact mechanisms include producing perforin/granzyme and directly influencing dendritic cells and B cells with surface receptors but also directly influencing neutrophils by reducing expression of chemoattractants. Indirect mechanisms include uptake of IL-2 by Tregs and depleting the microenvironment which in turn will reduce NK cell and effector cells proliferation.