OVERVIEW OF THE DEVELOPMENT AND CURRENT STATUS OF TRANSPLANT IMMUNOLOGY

Many of the historical and persistent barriers to successful transplantation derive from the complex immunological events that are set in motion once an organ or tissue from one individual is placed within the body of another. From a clinical standpoint, the immune interface between transplanted organs and their hosts dictates much of the need for pretransplant tissue typing and cross-match testing, lifelong posttransplant immunosuppressive therapy, regular monitoring of allograft function, and intermittent histological sampling of the graft. From a scientific perspective, the fields of immunology and transplantation have developed together in symbiotic fashion over the past century with experimentation and discovery in each influencing the other. Among the major immunological insights that have arisen partly or entirely from transplant-related experiments are the biology of natural and acquired antibodies, the significance of major histocompatibility complex (MHC) genetic diversity, the function of the thymus and other lymphoid organs, the nature of antigen presentation, the role of costimulation in T-Cell activation, and the mechanisms underlying self-tolerance. Recently, the parallel progress of the two fields has entered a new stage of productivity, the translation of mechanistic immunological discovery into novel targeted interventions, and treatment strategies for improving overall success in human transplantation. The purposes of this chapter are to succinctly describe our current understanding of the major elements of human protective immunity and to link these pathways with important aspects of the immune response to allogeneic organ transplants.