Organ transplantation has been one of the greatest therapeutic advances of the second half of the 20th century. It is a procedure that can save and prolong the life of individuals with advanced diseases of vital organs. The success of transplantation has involved almost all medical specialties that have required extensive cooperation and exchange of knowledge and experience among basic scientists, surgeons, clinicians, and pathologists. The ideal goal of transplantation is not only to ensure survival of the patient, but also to provide an adequate quality of life after the procedure. Health care providers face a constant challenge in the management of patients after organ transplantation. Organ transplantation has forced us to learn pathology in a way that is not seen in “native organs,” such as the various histopathologic manifestations of rejection, the recurrence of initial disease in the transplanted organs, and the complications arising from immunosuppressive drugs, infectious diseases, and cancer. Increased survival rates in recent years have been achieved through a better understanding of the immunopathologic mechanisms of rejection. There are no clinical, physiologic, or serologic markers of rejection; therefore, the current gold standard for assessment of rejection or other complications of solid organ transplant is the biopsy.

This issue of Archives of Pathology & Laboratory Medicine provides a review of current problems in transplant pathology, with updated information on various issues that are of top priority for the understanding and management of patients undergoing transplantation. Tan et al provide a comprehensive review of heart transplant pathology. The authors give important guidelines to handle and interpret myocardial biopsies. Their review underscores the importance of a good understanding of what myocyte injury means to the general surgical pathologist. A common pitfall to the pathologist unfamiliar with heart transplantation biopsies is the Quilty lesions. Quilty lesions, named after the first patient in whom they were diagnosed and also known as endocardial lymphocytic infiltrates, can be misinterpreted as rejection. The importance of obtaining several levels and examination of consecutive sections should be kept in mind in these cases. Review of opportunistic organisms and a comparison between the International Society for Heart & Lung Transplantation grading systems of 1990 and 2004 systems are also important tools for the practicing pathologist.

In the review by Gaber, the criteria for cellular and humoral, acute, and chronic rejection in pancreas allografts are reviewed. Pancreas biopsies require special attention to the different compartments; islet cell infiltrates can be missed by the inexperienced observer in the hematoxylin-eosin–stained sections but, as the authors point out, staining for T lymphocytes demonstrates the lesion. Special attention is given to the presence of thrombosis, which is the major source of pancreas graft failure in the first 2 weeks after transplantation. Pancreatitis as a cause of failure is also discussed, and donor selection is also noted. Frequently, combined pancreas and kidney transplantation is performed, and this poses special challenges to clinicians and pathologists. It has been assumed that kidney rejection in these patients also reflects their pancreas status; however, as pointed out by Gaber, that is not always the case, since there is some level of disconcordance that justifies biopsy of both organs when indicated.

Truong et al review a current and important topic in transplant pathology: the role of antibody-mediated rejection in kidney allografts. Antibody-mediated rejection, which occurs as a result of activation of the complement system, is a topic that is covered also in the reviews for heart and pancreas allografts. It has been recognized only recently as a clinicopathologic entity. The reviews in this issue cover the history, techniques, and problems in interpretation of this still-difficult area. It was first recognized in kidney transplantation, and therefore it is the area in which most experience has been accumulated. C4d interpretation in lung biopsies has not been standardized, and the current reports are controversial. Hopefully a more precise discussion of C4d interpretation in nonrenal biopsies will appear in future special issues of the Archives dedicated to this topic; certainly, more research is needed in this area.

Tsao and Hsi review the topic of posttransplantation lymphoproliferative disorders. The authors provide the reader with an excellent overview of these disorders, which should be considered as a heterogeneous group of lymphoid proliferations with a wide spectrum that varies from reactive polyclonal to frank lymphomas. Risk factors for the development of these entities are well covered in their review. The final section of this review provides an excellent guide for the pathologic evaluation of these lesions.

Last, but not least, an elegant and well-illustrated review on pulmonary infections in transplantation pathology by Stewart gives us a good idea of the current opportunistic infections seen in organ transplantation. It reminds us that although histology is “pivotal in early diagnosis,” a multidisciplinary approach from clinicians, radiologists, and pathologists, as well as complementary molecular methods, is frequently necessary. We are reminded that although Pneumocystis pneumonia currently is uncommon due to chemoproxilaxis, the pathologist should be aware that Pneumocystis pneumonia can present in various morphologic patterns. The value of polymerase chain reaction is discussed.

The scientific landscape has certainly changed since Merrill, Murray, and colleagues clarified the problem of solid organ transplantation in 1954, when a kidney transplanted from a healthy twin into the other twin suffering from chronic glomerulonephritis was not rejected, but it was not until the 1960s and 1970s that disparity at the major histocompatibility complex was recognized as a genetic basis for rejection. Now the field of organ transplantation faces other challenges. New immunosuppressive schemes are being tested, histopathologic changes due to therapeutic agents are a continuous challenge, and resistant strains of opportunistic infections evolve. In this present and future environment, the pathologist plays a major role.

Roberto Barrios, MD Dr Roberto Barrios is professor of Pathology and Laboratory Medicine at Weill Medical College of Cornell University and a practicing pathologist at The Methodist Hospital in Houston, Tex, where his primary interests are pulmonary and renal pathology. Dr Barrios received his MD from the Faculty of Medicine, Universidad Nacional Autónoma de México in Mexico City; he did his residency at the Institute of Pathology, Case Western Reserve University in Cleveland, Ohio. Subsequently, Dr Barrios completed a fellowship at the Institute of Pathology, McGill University in Montreal, Canada, under the legendary pulmonary pathologist and researcher Dr James C. Hogg. He did molecular pathology research in the laboratory of Dr Michael Lieberman for more than 10 years. Dr Barrios served as chair of the Departments of Pathology at the Heart and the Lung Institutes in Mexico City. He has published in the areas of pulmonary and renal pathology as well as transgenic mouse models of prostate cancer. He is editor of several pulmonary pathology textbooks and is a section editor of Archives of Pathology & Laboratory Medicine.
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 Dr Roberto Barrios is professor of Pathology and Laboratory Medicine at Weill Medical College of Cornell University and a practicing pathologist at The Methodist Hospital in Houston, Tex, where his primary interests are pulmonary and renal pathology. Dr Barrios received his MD from the Faculty of Medicine, Universidad Nacional Autónoma de México in Mexico City; he did his residency at the Institute of Pathology, Case Western Reserve University in Cleveland, Ohio. Subsequently, Dr Barrios completed a fellowship at the Institute of Pathology, McGill University in Montreal, Canada, under the legendary pulmonary pathologist and researcher Dr James C. Hogg. He did molecular pathology research in the laboratory of Dr Michael Lieberman for more than 10 years. Dr Barrios served as chair of the Departments of Pathology at the Heart and the Lung Institutes in Mexico City. He has published in the areas of pulmonary and renal pathology as well as transgenic mouse models of prostate cancer. He is editor of several pulmonary pathology textbooks and is a section editor of Archives of Pathology & Laboratory Medicine.
Roberto Barrios, MD Dr Roberto Barrios is professor of Pathology and Laboratory Medicine at Weill Medical College of Cornell University and a practicing pathologist at The Methodist Hospital in Houston, Tex, where his primary interests are pulmonary and renal pathology. Dr Barrios received his MD from the Faculty of Medicine, Universidad Nacional Autónoma de México in Mexico City; he did his residency at the Institute of Pathology, Case Western Reserve University in Cleveland, Ohio. Subsequently, Dr Barrios completed a fellowship at the Institute of Pathology, McGill University in Montreal, Canada, under the legendary pulmonary pathologist and researcher Dr James C. Hogg. He did molecular pathology research in the laboratory of Dr Michael Lieberman for more than 10 years. Dr Barrios served as chair of the Departments of Pathology at the Heart and the Lung Institutes in Mexico City. He has published in the areas of pulmonary and renal pathology as well as transgenic mouse models of prostate cancer. He is editor of several pulmonary pathology textbooks and is a section editor of Archives of Pathology & Laboratory Medicine.
View largeDownload slide
 Dr Roberto Barrios is professor of Pathology and Laboratory Medicine at Weill Medical College of Cornell University and a practicing pathologist at The Methodist Hospital in Houston, Tex, where his primary interests are pulmonary and renal pathology. Dr Barrios received his MD from the Faculty of Medicine, Universidad Nacional Autónoma de México in Mexico City; he did his residency at the Institute of Pathology, Case Western Reserve University in Cleveland, Ohio. Subsequently, Dr Barrios completed a fellowship at the Institute of Pathology, McGill University in Montreal, Canada, under the legendary pulmonary pathologist and researcher Dr James C. Hogg. He did molecular pathology research in the laboratory of Dr Michael Lieberman for more than 10 years. Dr Barrios served as chair of the Departments of Pathology at the Heart and the Lung Institutes in Mexico City. He has published in the areas of pulmonary and renal pathology as well as transgenic mouse models of prostate cancer. He is editor of several pulmonary pathology textbooks and is a section editor of Archives of Pathology & Laboratory Medicine.
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The author has no relevant financial interest in the products or companies described in this article.

Reprints: Roberto Barrios, MD, Department of Pathology, The Methodist Hospital, Room M227, 6565 Fannin St, Houston, TX 77030 ([email protected])

College of American Pathologists
2007