Graft arteriosclerosis: molecular features of macrophage activation

Natural killer cells in rejection and tolerance of solid organ allografts

PURPOSE OF REVIEW

A series of recent studies defy conventional wisdom by showing that natural killer (NK) cells exert a powerful and long-lasting influence on the immune response to whole organ allografts. The early activation of NK cells following transplantation is associated with killing of allogeneic target cells and release of immunomodulatory chemokines and cytokines, which can contribute to either rejection or tolerance. Here, we review findings describing NK cell receptors, potential mediators and mechanisms underlying the dual influence of NK cells in solid organ transplantation.

RECENT FINDINGS

New studies show that NK cells can discriminate between self and foreign tissues and play a key role in the initiation and regulation of adaptive immune responses after solid organ transplantation. Depending upon the types of NK cell receptors engaged and the nature of cytokines released, early NK cell activation can promote either rejection or tolerance.

SUMMARY

Solid organ transplantation is associated with the early activation of NK cells, which are then licensed to kill allogeneic target cells directly or via antibody-dependent cellular cytotoxicity and release various chemokines and immunomodulatory cytokines. Depending upon the nature of NK cell subsets activated and their ability to kill allogeneic target cells and release certain types of cytokines, NK cells can promote the activation/expansion of pro-inflammatory Th1 cells or regulatory Th2/Treg cells thus tilting the balance of alloimmunity towards rejection or tolerance. An in-depth understanding of these mechanisms will be necessary in order to design therapies targeting NK cells in human transplantation.

CD28 family and chronic rejection: "to belatacept...And beyond!"

Kidneys are one of the most frequently transplanted human organs. Immunosuppressive agents may prevent or reverse most acute rejection episodes; however, the graft may still succumb to chronic rejection. The immunological response involved in the chronic rejection process depends on both innate and adaptive immune response. T lymphocytes have a pivotal role in chronic rejection in adaptive immune response. Meanwhile, we aim to present a general overview on the state-of-the-art knowledge of the strategies used for manipulating the lymphocyte activation mechanisms involved in allografts, with emphasis on T-lymphocyte costimulatory and coinhibitory molecules of the B7-CD28 superfamily. A deeper understanding of the structure and function of these molecules improves both the knowledge of the immune system itself and their potential action as rejection inducers or tolerance promoters. In this context, the central role played by CD28 family, especially the relationship between CD28 and CTLA-4, becomes an interesting target for the development of immune-based therapies aiming to increase the survival rate of allografts and to decrease autoimmune phenomena. Good results obtained by the recent development of abatacept and belatacept with potential clinical use aroused better expectations concerning the outcome of transplanted patients.

Coronary artery vasculopathy in pediatric cardiac transplant patients: the therapeutic potential of immunomodulators

The single largest cause of late graft loss in pediatric cardiac transplantation is transplant coronary artery vasculopathy (CAV). The mechanism of CAV remains unknown; it appears to have both immune and non-immune causes. The final common pathway of these mechanisms is endothelial activation, a prothrombotic environment, and endothelial damage with subsequent diffuse intimal proliferation. The disease process has largely been thought to be progressive and unresponsive to treatment. Re-transplantation has been advocated as the only definitive treatment. The appropriate management is largely unknown; intervention or surgical management has had limited utility, while medical management appears to have the most promise. Improvement in outcome can be achieved by optimizing non-immune factors and aggressive management of the immune mechanisms. Long-term survival of transplant patients after diagnosis with CAV is now being reported.