Transplantation Immunology: Introduction

Transplantation Immunology

INTRODUCTION

The replacement of defective organs with transplants was one of the impossible dreams of medicine for many centuries. Its realization required a multitude of important steps: surgi-cal asepsis, development of surgical techniques of vascular anastomosis, understanding of the cellular basis of the rejection phenomena, and introduction of drugs and antisera effec-tive in the control of rejection.

By the early 1970s tissue and organ transplantation emerged as a major area of inter-est for surgeons and physicians. Kidney and bone marrow transplants have become routine in most industrialized countries and lead in frequency, followed by liver, heart, pancreas, lung, and small bowel transplants, in order of decreasing frequency. Transplantation of tra-chea and extremities are still in experimental development. Transplant of other tissues and organs will certainly follow.

The success of an organ transplant is a function of several variables. However, the major determinant of acceptance or nonacceptance (rejection) of a technically perfect graft is the magnitude of the immunologically mediated response against the graft. The likeli-hood of acceptance or rejection is closely related to the extent of genetic differences be-tween the donor and recipient of the graft. While transplantation of organs between animals of the same inbred strain or between homozygous (syngeneic) twins is successful and does not elicit an immune rejection response, transplants between distantly related individuals (allogenic) or across species barriers (xenogeneic) are always rapidly rejected. Thus, in hu-mans, genetic diversity between individuals is currently the main obstacle to successful transplantation.

However, there has been significant progress in the development of new immuno-suppressive drugs and administration regimens that has had a very significant impact on transplantation outcome. For example, the half-life of kidneys transplanted from a living donor increased from 12.7 years in 1988 to 35.9 years in 1996, and the half-life of cadav-eric kidneys increased from 11.0 to 19.5 years during the same period. This was not a con-sequence of better donor-recipient matching, but rather a reflection of better medical man-agement.