—  SHORT COURSE #61  —

Kidney and Liver Transplant - Update and Issues

Arthur H. Cohen, Juan Lechago and Cynthia C. Nast

Introduction
The purpose of this short course is to introduce the attendees to some basic concepts of the immunopathology of organ transplant rejection, the structural manifestations of the rejection process in the transplanted kidneys and livers, and effects of drugs, viral infections and recurrent diseases on these transplanted organs. It will also discuss philosophies and practices of tissue processing and classification schema for pathologies in these allografts.

This course will focus almost exclusively on changes in the transplanted organ in tissue sections. It should be kept in mind that aspiration cytology of the allografts have an important but not commonly used role; this is especially true and effective in the early post-transplant period in distinguishing acute rejection from drug toxicity or infection in kidneys. For livers, this technique is useful to identify acute cellular rejection, and possibly drug effects, including intracellular cholestasis and fatty change.

Rapid processing of core biopsies of both livers and kidneys is routinely used in most transplant centers; the major legitimate indication for kidneys is a recent decline in renal function. Typically this is during the initial post-transplant period although it may occur many years later. For livers, it is for abnormal function test. Most institutions use short processing times often following microwave fixation. If necessary, a method for frozen sections on fixed and cryo-protected tissue with excellent results is well described.

Tissue Processing
In general, decisions of both a professional nature and a financial nature concerning the type(s) of handling and processing of diagnostic transplant tissues are easier for liver in comparison to kidney. This is, of course, a manifestation of tissue handling in the non-transplant setting and a question of what further information may be obtained using methods such as electron microscopy (EM) and immunofluorescence (IF) in addition to the standard practices for light microscopy (LM). As livers are routinely evaluated only by light microscopy with a battery of stains, this is not an issue. On the other hand, in most centers native kidneys are usually evaluated by EM and IF in addition to light microscopy with a routine set of stains. Because certain lesions and changes may not be detectable by LM, we have elected to evaluate transplant biopsies with EM and IF under certain circumstances and at other times use LM only. However, we obtain tissues for all three modalities in all instances. In practice, the first biopsy is evaluated by all three methods; this allows for baseline information including the remote possibility of an undetected immune mediated or other disease in the donor. With repetitive biopsies over a short period of time, only the specimen for LM is processed completely and evaluated; the IF portion is processed for C4d stain (see case 2) and the EM portion is embedded only or thick sections only are prepared. It should be pointed out that an immunoperoxidase method for identifying C4d in paraffin embedded sections is successfully used in some laboratories. Consequently, in selected circumstances, IF may not be necessary. With a long duration between biopsies (greater than one year) or with clinical or pathological features in the LM specimen which suggest a process that requires the other two methods, then all three modalities are used. We have been fortunate in that the nephrology and renal transplant communities with whom we interact have supported this approach. We are fully aware that many transplant centers, institutions or pathology departments encourage or insist upon LM only for financial reasons. Under these circumstances in order to try to identify, for example, recurrent or de novo glomerular lesions it would be necessary to reprocess all or a portion of the paraffin embedded tissue or to rebiopsy the patient.

Basic Aspects of Transplant Rejection
Transplant rejection may be consequent to cell-mediated and/or antibody-mediated immune mechanisms; cellular rejection is most common although variations on classical forms of humoral rejection are probably underrecognized. This portion of the syllabus will provide a brief and directed review of the mechanisms of rejection and their morphological patterns of injury. More detailed information will be discussed in the appropriate sections.

Cell mediated rejection
The initial event is the recognition of foreign antigens; in humans the main histocompatibility antigens (MHC) are expressed by endothelial cells in small vessels and some parenchymal cells. Activation of the antigen-specific T-cells follows; this is achieved when the MHC antigen engages the T-cell antigen receptor leading to expression of the IL-2R receptor on the cell surface. A second signal from the antigen-presenting cell is necessary to initiate IL-2 production. The activated T-cells produce lymphokines which cause chemotoxis and activation of macrophages, eosinophils and T-cells and induction of MHC antigens and adhesion molecules on parenchymal cells. Cytokines (TNF-α,TNF-β) produced by T-cells and macrophages indirectly mediate cellular injury. Cytotoxic T-cells directly mediate injury to endothelial and parenchymal cells. The morphological expression of these events is manifested primarily by accumulation of T-cells in capillaries (best observed in kidneys), migration into the stroma and further migration into the structures containing the major MHC-bearing cells. In the liver, these are primarily bile duct epithelium and secondarily hepatocytes, whereas in the kidneys, tubular cells are the primary target. When endothelial cells of arterial vessels of all sizes and glomerular capillaries (in the kidneys) are the target, the T-cells adhere to the luminal surfaces, infiltrate between and ultimately undermine these cells producing the lesion known as endothelialitis or endarteritis. This is, of course, cell-mediated vascular rejection (see case 2).

Antibody mediated rejection
The antibodies are directed against endothelial cells and result in inflammation with or without necrosis of the affected vascular structures. This form of rejection is rare in transplanted livers but is not particularly uncommon in renal allografts. If antibodies are preformed, the resulting pathology and clinical manifestations are known as hyperacute rejection and occur within a few minutes of establishing recipient circulation to the graft. It is characterized by widespread endothelial damage, vascular thrombosis and acute necrosis with cessation of renal function. When antibodies are formed following establishment of function, usually 1 to 10-12 weeks after engraftment, the process is known as acute humoral (or, incorrectly, acute vascular or accelerated acute, delayed humoral) rejection and is characterized by arterial necrosis or inflammation, glomerular inflammation, and vascular thrombosis, with all of the consequences. More recently a form of antibody-mediated rejection with peritubular capillary endothelium as the target has been described in kidneys. This requires the use of antibody directed against C4d. Because of considerations to be discussed later in this Short Course, current practice of renal transplant pathology mandates a routine search for C4d deposits in peritubular capillaries. Although most laboratories use indirect immunofluorescence on frozen tissue, some use an immunoperoxidase method on paraffin-embedded specimens. Morphological counterpart of this process is quite variable. It is important to appreciate that cell mediated and antibody mediated mechanisms of rejection are not mutually exclusive.

Chronic rejection
Pathogenic mechanisms responsible for this process in either organ are multifactorial. It is likely that all of the abnormalities are not truly a manifestation of rejection; some are likely related to other factors. Invariably, there is involvement of arteries and other vascular structures with inflammation and fibrosis leading to luminal narrowing obliterative endarteritis changes. Abnormalities of epithelial structures (tubules in the kidney, bile ducts in the liver) are also an integral feature of the pathology. The common theme is for vascular structures thought to be repetitive immunological injury (repeated episodes of acute rejection). It is usually associated with chronic parenchymal changes. In these two organs, immunology for the pathologic features is often varied and reflects the predominant or important findings. Antibody mediated chronic renal transplant rejection, diagnosed largely by a search for C4d in peritubular capillaries, is increasingly recognized as an important cause of chronic allograft failure.

It should be appreciated that the definition of chronic rejection is not necessarily time-related, for the changes can occur as early as a few months post-transplantation. What is important is that it implies irreversible organ damage which is usually progressive.




Case 1 - Acute Tubular Necrosis and Calcineurin Inhibitor Nephrotoxicity
Case 2 - Hyperacute and Acute Renal Transplant Rejection
Case 3 - Renal Transplant: Chronic Rejection and Chronic Nephropathy
Case 4 - Acute and Hyperacute Liver Transplant Rejection
Case 5 - Recurrent Disease after Liver Transplantation
Case 6 - Vanishing Bile Ducts and Chronic Rejection of Liver Transplant
Case 7 - Renal and Hepatic Transplant Infections
Classifications and Schemas




References
  1. Colvin RB Renal transplant pathology in Heptinstall's Pathology of the Kidney, 5th ed. Jennette JC, Olson JL, Schwartz MM, Silva FG (eds) Lippincott-Raver, Philadelphia, 1998, pp. 1409-1540. Perhaps the best and most comprehensive treatise on all aspects of pathology affecting the transplanted kidney.

  2. Transplant Pathology Internet Services (TPIS) from the University of Pittsburgh (http://tpis.upmc.edu) An excellent resource with useful links.

  3. Cohen AH, Gonzalez S, Nast CC, Wilkinson A, Danovitch GM. Frozen-section analysis of allograft renal biopsy specimens. Reliable histopathologic data for rapid decision making. Arch Pathol Lab Med 115:386-389, 1991.

  4. Collins AB, Schneeberger EE, Pascual MA, Saidman SL, Williams WW, Colvin RB et al. Complement activation in acute humoral renal allograft rejection: diagnostic significance of C4d deposits in peritubular capillaries. J Am Soc Nephrol 10:2208-2214, 1999.

  5. Danovitch GM, Nast CC, Wilkinson A, Rosenthal T. Evaluation of fine-needle aspiration biopsy in the diagnosis of renal transplant dysfunction. Am J Kidney Dis 17:206-210, 1991.

  6. Hayry P, Von Willebrand E, Lautenschlager I. Transplant aspiration cytology: applications to kidney and liver transplantations. Transplant Proc 23:1760-1761, 1991.

  7. Jain A, Reyes J, Kashyap R, Dodson SF, Demetris AJ, Ruppert K et al. Long-term survival after liver transplantation in 4,000 consecutive patients at a single center. Ann Surg 232:490-500, 2000.

  8. Kirby RM, Young JA, Hubscher SG, Elias E, McMaster P. The accuracy of aspiration cytology in the diagnosis of rejection following orthotopic liver transplantation. Transpl Int 1:119-126, 1988.

  9. Kubota K, Ericzon BG, Reinholt FP. Comparison of fine-needle aspiration biopsy and histology in human liver transplants. Transplantation 51:1010-1013, 1991.

  10. Lorenz M, Regele H, Schillinger M et al. Risk factors for capillary C4d deposition in kidney allografts: evaluation of a large study cohort. T ransplantation 78:447-452, 2005.

  11. Mauiyyedi S, Pelle PD, Saidman S, Collins AB, Pascual M, Cosimi AA, Colvin RB et al. Chronic humoral rejection: identification of antibody mediated chronic renal allograft rejection by C4d deposits in peritubular capillaries. J Am Soc Nephrol 12:574-582, 2001.

  12. Minamiguchi S, Sakurai T, Fujita S, Okuno T, Haga H, Mino M et al. Living related liver transplantation: histopathologic analysis of graft dysfunction in 304 patients. Hum Pathol 30:1479-1487, 1999.

  13. Nast CC, Blifeld C, Danovitch GM, Fine RN, Ettenger RB. Evaluation of cyclosporine nephrotoxicity by renal transplant fine needle aspiration. Mod Pathol 2:577-582, 1989.

  14. Nast CC, Wilkinson A, Rosenthal JT, Barba L, Bretan PN, Beaumont P, Danovitch GM. Differentiation of cytomegalovirus infection from acute rejection using renal allograft fine needle aspirates. J Am Soc Nephrol 1:1204-1211, 1991.

  15. Nast CC, Zuo XJ, Prehn J, Danovitch GM, Wilkinson A, Jordan SC. Gamma-interferon gene expression in human renal allograft fine-needle aspirates. Transplantation 57:498-502, 1994.

  16. Nast CC. Renal transplant fine needle aspiration and cytokine gene expression. Pediatr Nephrol 9:S56-60, 1995.

  17. Nickeleit V, Mihatsch MJ. Kidney transplants, antibodies and rejection: is C4d a magic marker? Nephrology Dialysis Transplant 18:2232-2239, 2003.

  18. Pascual M, Vallhonrat H, Cosimi AB, Tolkoff-Rubin N, Colvin RB et al. The clinical usefulness of the renal allograft biopsy in the cyclosporine era: a prospective study. Transplantation 67:737-741, 1999.

  19. Vierling JM. Immunology of acute and chronic hepatic allograft rejection. Liver Transpl Surg 5:S1-S20, 1999.