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Liver Transplantation: Where We Are and Where We Are Heading
Liver Transplantation: Where We Are and Where We Are Heading C.O. Esquivel ABSTRACT Outcomes after liver transplantation are outstanding; however, the limiting factor is the shortage of organs. Recently, the utilization of donors after cardiac death has been encouraged; however, such transplants are associated with a high complication rate, mainly a high incidence of biliary complications, particularly ischemic cholangiopahty, a serious complication that often leads to retransplantation. The second problem is the morbidity associated with the use of immunosuppressive drugs. In this manuscript, the current status of clinical protocols for induction of tolerance is briefly discussed. Furthermore, the future of research in transplantation will involve basic scientists and clinical scholars working in concert as has been developed at Stanford School of Medicine with the creation of the Institute for Immunity, Transplantation and Infection. HE FIRST ATTEMPTS at human liver transplantation were carried out by Thomas E. Starzl in 1963. Progress was slow until the advent of cyclosporine in 1979. Before cyclosporine, the maintenance immunosuppression consisted of a combination of azathioprine and prednisone. Once cyclosporine was introduced to clinical practice, patient and graft survivals after hepatic replacement more than doubled almost overnight. For the next 25 years, the evolution of liver transplantation took place at lightening speed.1 Discoveries may be grouped in 2 categories: those related to improvements in the immunosuppression regimens and those related to the surgical aspects of liver transplantation.
T
DISCOVERIES IN IMMUNOSUPPRESSION
The combination of cyclosporine and prednisone became the mainstay for daily immunosuppression in liver transplantation. There have been several multi-institutional trials comparing tacrolimus with cyclosporine in the United States, Europe, and Japan. The results have shown that tacrolimus, a potent immunosuppressive agent, was as effective, if not better than cyclosporine.2 Further investigations began to show that the potency of tacrolimus was resulting in overimmunosuppression, leading to the development of posttransplant lymphoproliferative disease, particularly in children. With more experience, it became clear that tacrolimus could effectively be used as a single agent, at least in liver transplantation.3 Other immunosuppressive agents that have been added to the immunosuppression armamentarium are mycophenolate, rapamycin, as well as mono- and polyclonal antibody 0041-1345/10/$–see front matter doi:10.1016/j.transproceed.2010.02.013 610
preparations such as OKT3, antithymocyte globulin (ATG), interleukin-2 inhibitors such as daclizumab, everolimus, sirolimus, and alemtuzumab. Several comprehensive reviews of the mechanism of action as well as the clinical experience associated with the use of these agents exist in the transplant literature.4 A significant problem relates to noncompliance, particularly among teenagers. This is not unique to liver transplant recipients. It is also seen in chronic medical conditions such as type 1 diabetes and cystic fibrosis. In a recent study, almost 50% of adolescent liver transplant recipients admitted not taking the immunosuppressive drugs. Of those noncompliant patients, 70% experienced an episode of rejection. Predictors of noncompliance are those patients who come from a low socioeconomic status as well as those patients who enjoyed normal health until transplantation, for example, patients who underwent transplantation for acute liver failure.5 To tackle this problem of noncompliance, a “Teen Clinic” was created at Lucile Packard Children’s Hospital at Stanford University. In these clinics, adolescents are seen without their parents by transplant physicians, psychologists, and coordinators. Other consultants, such as psychiaFrom the Stanford University School of Medicine, Palo Alto, California. Supported in part by the Arnold and Barbara Silverman Endowed Fund. Address reprint requests to Carlos O. Esquivel, MD, PhD, 750 Welch Road, Suite # 319, Palo Alto, CA 94304. E-mail: esquivel@ stanford.edu © 2010 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710 Transplantation Proceedings, 42, 610 – 612 (2010)
LIVER TRANSPLANTATION
trists, are available on an ad hoc basis. The patients receive education as a group and individually. The environment also serves as a venue for a “support group” meeting. Their parents are seen in a separate room and they are informed if any changes were made to their child’s medical regimen. This clinic has been very successful in lowering the incidence of noncompliance and in helping these patients transition to adulthood. The ultimate solution for noncompliance and elimination of all the side effects of the immunosuppressive drugs is the induction of tolerance. It is likely to first achieve tolerance in liver transplant recipients as opposed to other organs because of the liver being a tolerogenic organ. However, most of the clinical trials involve tolerance induction in adult kidney transplant recipients. Although there may be multiple ongoing protocols for tolerance induction, the concept of tolerance induction falls into 3 categories: (1) pretreatment of the transplant recipient, (2) pre- and posttransplant immune manipulation, and (3) posttransplant induction. Pretransplant Tolerance Induction
This protocol has been championed by Thomas E. Starzl. He observed that several patients, recipients of kidney transplants in the 1960s, went on to develop tolerance. The mechanism for induction of tolerance in this group of patients was by the administration of immunosuppression (usually a combination of azathioprine and steroids) before transplantation. This resulted in the induction of tolerance. Several of these patients also acquired a stable chimerism. Over the years, the pretreatment was substituted by an intense posttransplant immunosuppressive regimen. The rationale for this switch in approach of immunosuppression was to lower the incidence of acute rejection episodes. By doing so, according to Starzl, the incidence of acute rejection was lowered, as was the incidence of tolerance induction.6 The high intensity of the posttransplant immunosuppression prevented these patients from developing tolerance. In recent years, Starzl’s group has modified the protocol by administering ATG; lately, alemtuzumab has replaced ATG in the pretransplant induction protocol. Such protocols have been used in liver, kidney, intestinal, and lung transplantation. The initial results are encouraging. Improvements in patient and graft survival have been observed in kidney, liver, lung, and intestinal transplantation. In intestinal transplantation a 25% gain in patient survival was immediately noted. Likewise, the patient survival in lung transplantation has improved from 60% to 90%.7,8 Perioperative Induction Protocol
Tolerance induction has been observed in 4 out of 5 kidney transplant recipients with a combination regimen. In brief, this protocol consists of a nonmyeloablative approach using cyclophosphamide, a single dose irradiation of the thymus, interleukin-2 antibody, and more recently CD20 antibody. The CD20 antibody was added because one of their early
611
patients experienced graft-versus-host disease. Tolerance was observed in 4 patients. All patients were alive at the time of publication of the study, but 1 kidney graft was lost to chronic rejection.9 Postoperative Induction Protocol
Tolerance induction is under investigation at Stanford University. It consists of a nonmyeloablative approach using a low-dose total lymphoid irradiation (TLI), ATG, and infusion of the donor progenitor cells after completion of the TLI treatments. Of 10 kidney transplant recipients involved, 5 are no longer taking immunosuppressive drugs, 2 out of 10 are in the weaning process, and 3 out of 10 experienced acute rejection. The acute rejection in these 3 patients was treated uneventfully and their kidney function continues to be excellent under minimal immunosuppression.10,11 A modified TLI protocol for liver transplantation is underway. This protocol does not use progenitor cell infusions because the liver allograft carries a large number of passenger lymphocytes.12 DISCOVERIES RELATED TO SURGICAL ASPECTS
An important breakthrough in the mid-1980s was the development of a much improved preservation solution known as “University of Wisconsin” solution (ViaSpan). This solution resulted in better organ function immediately posttransplantation and, consequently, a reduced need for transfusion of blood and blood products, lower incidence of hepatic artery thrombosis, decreased need for retransplantation, and shorter ICU and hospital stays. As outcomes continue to improve, liver transplantation became the therapy of choice for patients with end-stage acute and chronic liver disease. The lists of patients on the waiting list grew astronomically and the demand for organs became the limiting factor in liver transplantation. To alleviate the organ shortage, innovative techniques were developed, such as living donor liver transplantation, split liver transplantation (a liver is divided into 2 functioning parts to be used in 2 recipients), and domino transplants. It is out of the scope of this paper to discuss the techniques related to these procedures; suffice to say that the outcomes with living donor and split livers are similar to those of full-size liver transplants. However, the impact on the waiting list has been negligible. Patients continue to linger for years waiting for organs and many succumb without ever having an opportunity for a liver transplant. To increase the donor pool, efforts are being channeled to the utilization of donors after cardiac death (DCD).13 Such donors are patients who have sustained an irreversible brain injury resulting in a vegetative state. Procurement of the organs is done 5 minutes after circulatory arrest. Studies have shown that about 1000 per year DCD may qualify for donation in the United States. The result will be 3000 additional organs for transplantation. In 1993, there were 42 DCD out of a total of 4861 donors. In 2002, the number had increased to 191 DCD out of 5992 donors. From these
612
191 DCD, 310 kidneys, 81 livers, 10 pancreata, and 1 lung were transplanted. The majority of these donors (80%) were between the ages of 18 and 65 years. In this particular study, the 3-year graft survival for kidneys was 78% for DCDs compared with 78.1% for brain-dead donors. For livers, the 3-year actuarial survival was 66.9% for DCD compared with 73.2% for brain-dead donors. Although the survival was similar, the biliary complications among recipients of DCD livers were 3-fold greater than those of brain-dead donors. Biliary complications have been documented in additional studies. Biliary complications, particularly those associated with multiple extra- and intrahepatic strictures (ischemic cholangiopathy) are associated with a higher retransplantation rate and multiple readmissions, resulting in higher costs compared to recipients of livers from brain-dead donors.14 THE FUTURE OF RESEARCH IN TRANSPLANTATION
Transplantation is a young medical discipline that has undergone a light speed transformation from rudimentary immunosuppression to highly sophisticated, target-driven therapies to control rejection. Nevertheless, the current immunosuppression is associated with significant morbidity and mortality. Induction of tolerance is the main goal for research. However, the complexity of the immune system requires the participation of basic scientists and clinical scholars. At Stanford University, the Institute for Immunity, Transplantation and Infection (ITI; http://iti.stanford.edu) was launched to foster the collaboration of investigators from diverse disciplines. The institute’s collaborative research environment consists of working groups tackling many ravaging diseases such as hepatitis C infection, rheumatoid arthritis, and type 1 diabetes. One of these working group’s goals is to eliminate the need for taking toxic immunosuppressive drugs in transplantation, that is, tolerance induction, known in the transplant community as the “holy grail of transplantation.” The Human Immune Monitoring Center is a unique facility created under the auspices of ITI and charged with developing and implanting molecular tests to monitor the health of the human immune system and to make them available to the research community. Other centers, such as bioinformatics, bioengineering, genomics, and imaging, provide the resources for bringing research projects
ESQUIVEL
from bench to the bedside. Until recently, research by and large was specialty driven; now it is and will continue to be disease driven. REFERENCES 1. Starzl TE, Iwatsuki S, Van Thiel DH, et al: Evolution of liver transplantation. Hepatology 2:614, 1982 2. Mayer AD, Dmitrewski J, Squifflet JP, et al: Multicenter randomized trial comparing tacrolimus (FK506) and cyclosporine in the prevention of renal allograft rejection: a report of the European Tacrolimus Multicenter Renal Study Group. Transplantation 65:436, 1997 3. Rolles K, Davidson BR, Burroughs AK: A pilot study of immunosuppressive monotherapy in liver transplantation: tacrolimus versus microemulsified cyclosporine. Transplantation 68:1195, 1999 4. Sayegh MH, Remuzzi G, eds: Current and future immunosuppressive therapies following transplantation. Boston: Kluwer Academic Publishers; 2001 5. Berquist RK, Berquist WE, Esquivel CO, et al: Non-adherence to post-transplant care: prevalence, risk factors and outcomes in adolescent liver transplant recipients. Pediatr Transpant 12:194, 2008 6. Starzl TE: Acquired immunologic tolerance with particular reference to transplantation. Immunol Res 38:6, 2007 7. Reyes J, Mazariegos GV, Abu-Elmagd K, et al: Intestinal transplantation under tacrolimus monotherapy after perioperative lymphoid depletion with rabbit anti- thymocyte globulin (Thymoglobulin®). Am J Transplant 5:1430, 2005 8. McCurry K, Iacano A, Zeevi A, et al: Early outcomes in human lung transplantation with thymoglobulin or Campath-1H for recipient pre-treatment followed by post- transplant tacrolimus near-monotherapy. J Thorac Cardiovasc Surg 130:528, 2005 9. Kawai T, Cosimi B, Spitzer TR, et al: HLA-mismatched renal transplantation without maintenance immunosuppression. N Engl J Med 358:353, 2008 10. Scandling JD, Busque S, Dejbakhsh-Jones S, et al: Tolerance and chimerism after renal and hematopoietic-cell transplantation. N Engl J Med 358:362, 2008 11. Scandling J, Busque S, Dejbakhsh-Jones S, et al: Inducing and predicting tolerance after kidney transplantation. N Engl J Med. Forthcoming 12. Bonham A, Esquivel C, Concepcion W, et al: Study of complete immunosuppressive drug withdrawal from liver transplant patients conditioned with posttransplant total lymphoid irradiation (TLI) and anti-thymocyte globulin (ATG). Transplantation 86(suppl):74, 2008 13. Bernat JL, D’Alessandro AM, Port FK, et al: Report of a National Conference on Donation after cardiac death. Am J Transplant 6:281, 2006 14. Skaro AI, Jay CL, Baker TB, et al: The impact of ischemic cholangiopathy in liver transplantation using donors after cardiac death: the untold story. Surgery 146:543, 2009
T
DISCOVERIES IN IMMUNOSUPPRESSION
The combination of cyclosporine and prednisone became the mainstay for daily immunosuppression in liver transplantation. There have been several multi-institutional trials comparing tacrolimus with cyclosporine in the United States, Europe, and Japan. The results have shown that tacrolimus, a potent immunosuppressive agent, was as effective, if not better than cyclosporine.2 Further investigations began to show that the potency of tacrolimus was resulting in overimmunosuppression, leading to the development of posttransplant lymphoproliferative disease, particularly in children. With more experience, it became clear that tacrolimus could effectively be used as a single agent, at least in liver transplantation.3 Other immunosuppressive agents that have been added to the immunosuppression armamentarium are mycophenolate, rapamycin, as well as mono- and polyclonal antibody 0041-1345/10/$–see front matter doi:10.1016/j.transproceed.2010.02.013 610
preparations such as OKT3, antithymocyte globulin (ATG), interleukin-2 inhibitors such as daclizumab, everolimus, sirolimus, and alemtuzumab. Several comprehensive reviews of the mechanism of action as well as the clinical experience associated with the use of these agents exist in the transplant literature.4 A significant problem relates to noncompliance, particularly among teenagers. This is not unique to liver transplant recipients. It is also seen in chronic medical conditions such as type 1 diabetes and cystic fibrosis. In a recent study, almost 50% of adolescent liver transplant recipients admitted not taking the immunosuppressive drugs. Of those noncompliant patients, 70% experienced an episode of rejection. Predictors of noncompliance are those patients who come from a low socioeconomic status as well as those patients who enjoyed normal health until transplantation, for example, patients who underwent transplantation for acute liver failure.5 To tackle this problem of noncompliance, a “Teen Clinic” was created at Lucile Packard Children’s Hospital at Stanford University. In these clinics, adolescents are seen without their parents by transplant physicians, psychologists, and coordinators. Other consultants, such as psychiaFrom the Stanford University School of Medicine, Palo Alto, California. Supported in part by the Arnold and Barbara Silverman Endowed Fund. Address reprint requests to Carlos O. Esquivel, MD, PhD, 750 Welch Road, Suite # 319, Palo Alto, CA 94304. E-mail: esquivel@ stanford.edu © 2010 by Elsevier Inc. All rights reserved. 360 Park Avenue South, New York, NY 10010-1710 Transplantation Proceedings, 42, 610 – 612 (2010)
LIVER TRANSPLANTATION
trists, are available on an ad hoc basis. The patients receive education as a group and individually. The environment also serves as a venue for a “support group” meeting. Their parents are seen in a separate room and they are informed if any changes were made to their child’s medical regimen. This clinic has been very successful in lowering the incidence of noncompliance and in helping these patients transition to adulthood. The ultimate solution for noncompliance and elimination of all the side effects of the immunosuppressive drugs is the induction of tolerance. It is likely to first achieve tolerance in liver transplant recipients as opposed to other organs because of the liver being a tolerogenic organ. However, most of the clinical trials involve tolerance induction in adult kidney transplant recipients. Although there may be multiple ongoing protocols for tolerance induction, the concept of tolerance induction falls into 3 categories: (1) pretreatment of the transplant recipient, (2) pre- and posttransplant immune manipulation, and (3) posttransplant induction. Pretransplant Tolerance Induction
This protocol has been championed by Thomas E. Starzl. He observed that several patients, recipients of kidney transplants in the 1960s, went on to develop tolerance. The mechanism for induction of tolerance in this group of patients was by the administration of immunosuppression (usually a combination of azathioprine and steroids) before transplantation. This resulted in the induction of tolerance. Several of these patients also acquired a stable chimerism. Over the years, the pretreatment was substituted by an intense posttransplant immunosuppressive regimen. The rationale for this switch in approach of immunosuppression was to lower the incidence of acute rejection episodes. By doing so, according to Starzl, the incidence of acute rejection was lowered, as was the incidence of tolerance induction.6 The high intensity of the posttransplant immunosuppression prevented these patients from developing tolerance. In recent years, Starzl’s group has modified the protocol by administering ATG; lately, alemtuzumab has replaced ATG in the pretransplant induction protocol. Such protocols have been used in liver, kidney, intestinal, and lung transplantation. The initial results are encouraging. Improvements in patient and graft survival have been observed in kidney, liver, lung, and intestinal transplantation. In intestinal transplantation a 25% gain in patient survival was immediately noted. Likewise, the patient survival in lung transplantation has improved from 60% to 90%.7,8 Perioperative Induction Protocol
Tolerance induction has been observed in 4 out of 5 kidney transplant recipients with a combination regimen. In brief, this protocol consists of a nonmyeloablative approach using cyclophosphamide, a single dose irradiation of the thymus, interleukin-2 antibody, and more recently CD20 antibody. The CD20 antibody was added because one of their early
611
patients experienced graft-versus-host disease. Tolerance was observed in 4 patients. All patients were alive at the time of publication of the study, but 1 kidney graft was lost to chronic rejection.9 Postoperative Induction Protocol
Tolerance induction is under investigation at Stanford University. It consists of a nonmyeloablative approach using a low-dose total lymphoid irradiation (TLI), ATG, and infusion of the donor progenitor cells after completion of the TLI treatments. Of 10 kidney transplant recipients involved, 5 are no longer taking immunosuppressive drugs, 2 out of 10 are in the weaning process, and 3 out of 10 experienced acute rejection. The acute rejection in these 3 patients was treated uneventfully and their kidney function continues to be excellent under minimal immunosuppression.10,11 A modified TLI protocol for liver transplantation is underway. This protocol does not use progenitor cell infusions because the liver allograft carries a large number of passenger lymphocytes.12 DISCOVERIES RELATED TO SURGICAL ASPECTS
An important breakthrough in the mid-1980s was the development of a much improved preservation solution known as “University of Wisconsin” solution (ViaSpan). This solution resulted in better organ function immediately posttransplantation and, consequently, a reduced need for transfusion of blood and blood products, lower incidence of hepatic artery thrombosis, decreased need for retransplantation, and shorter ICU and hospital stays. As outcomes continue to improve, liver transplantation became the therapy of choice for patients with end-stage acute and chronic liver disease. The lists of patients on the waiting list grew astronomically and the demand for organs became the limiting factor in liver transplantation. To alleviate the organ shortage, innovative techniques were developed, such as living donor liver transplantation, split liver transplantation (a liver is divided into 2 functioning parts to be used in 2 recipients), and domino transplants. It is out of the scope of this paper to discuss the techniques related to these procedures; suffice to say that the outcomes with living donor and split livers are similar to those of full-size liver transplants. However, the impact on the waiting list has been negligible. Patients continue to linger for years waiting for organs and many succumb without ever having an opportunity for a liver transplant. To increase the donor pool, efforts are being channeled to the utilization of donors after cardiac death (DCD).13 Such donors are patients who have sustained an irreversible brain injury resulting in a vegetative state. Procurement of the organs is done 5 minutes after circulatory arrest. Studies have shown that about 1000 per year DCD may qualify for donation in the United States. The result will be 3000 additional organs for transplantation. In 1993, there were 42 DCD out of a total of 4861 donors. In 2002, the number had increased to 191 DCD out of 5992 donors. From these
612
191 DCD, 310 kidneys, 81 livers, 10 pancreata, and 1 lung were transplanted. The majority of these donors (80%) were between the ages of 18 and 65 years. In this particular study, the 3-year graft survival for kidneys was 78% for DCDs compared with 78.1% for brain-dead donors. For livers, the 3-year actuarial survival was 66.9% for DCD compared with 73.2% for brain-dead donors. Although the survival was similar, the biliary complications among recipients of DCD livers were 3-fold greater than those of brain-dead donors. Biliary complications have been documented in additional studies. Biliary complications, particularly those associated with multiple extra- and intrahepatic strictures (ischemic cholangiopathy) are associated with a higher retransplantation rate and multiple readmissions, resulting in higher costs compared to recipients of livers from brain-dead donors.14 THE FUTURE OF RESEARCH IN TRANSPLANTATION
Transplantation is a young medical discipline that has undergone a light speed transformation from rudimentary immunosuppression to highly sophisticated, target-driven therapies to control rejection. Nevertheless, the current immunosuppression is associated with significant morbidity and mortality. Induction of tolerance is the main goal for research. However, the complexity of the immune system requires the participation of basic scientists and clinical scholars. At Stanford University, the Institute for Immunity, Transplantation and Infection (ITI; http://iti.stanford.edu) was launched to foster the collaboration of investigators from diverse disciplines. The institute’s collaborative research environment consists of working groups tackling many ravaging diseases such as hepatitis C infection, rheumatoid arthritis, and type 1 diabetes. One of these working group’s goals is to eliminate the need for taking toxic immunosuppressive drugs in transplantation, that is, tolerance induction, known in the transplant community as the “holy grail of transplantation.” The Human Immune Monitoring Center is a unique facility created under the auspices of ITI and charged with developing and implanting molecular tests to monitor the health of the human immune system and to make them available to the research community. Other centers, such as bioinformatics, bioengineering, genomics, and imaging, provide the resources for bringing research projects
ESQUIVEL
from bench to the bedside. Until recently, research by and large was specialty driven; now it is and will continue to be disease driven. REFERENCES 1. Starzl TE, Iwatsuki S, Van Thiel DH, et al: Evolution of liver transplantation. Hepatology 2:614, 1982 2. Mayer AD, Dmitrewski J, Squifflet JP, et al: Multicenter randomized trial comparing tacrolimus (FK506) and cyclosporine in the prevention of renal allograft rejection: a report of the European Tacrolimus Multicenter Renal Study Group. Transplantation 65:436, 1997 3. Rolles K, Davidson BR, Burroughs AK: A pilot study of immunosuppressive monotherapy in liver transplantation: tacrolimus versus microemulsified cyclosporine. Transplantation 68:1195, 1999 4. Sayegh MH, Remuzzi G, eds: Current and future immunosuppressive therapies following transplantation. Boston: Kluwer Academic Publishers; 2001 5. Berquist RK, Berquist WE, Esquivel CO, et al: Non-adherence to post-transplant care: prevalence, risk factors and outcomes in adolescent liver transplant recipients. Pediatr Transpant 12:194, 2008 6. Starzl TE: Acquired immunologic tolerance with particular reference to transplantation. Immunol Res 38:6, 2007 7. Reyes J, Mazariegos GV, Abu-Elmagd K, et al: Intestinal transplantation under tacrolimus monotherapy after perioperative lymphoid depletion with rabbit anti- thymocyte globulin (Thymoglobulin®). Am J Transplant 5:1430, 2005 8. McCurry K, Iacano A, Zeevi A, et al: Early outcomes in human lung transplantation with thymoglobulin or Campath-1H for recipient pre-treatment followed by post- transplant tacrolimus near-monotherapy. J Thorac Cardiovasc Surg 130:528, 2005 9. Kawai T, Cosimi B, Spitzer TR, et al: HLA-mismatched renal transplantation without maintenance immunosuppression. N Engl J Med 358:353, 2008 10. Scandling JD, Busque S, Dejbakhsh-Jones S, et al: Tolerance and chimerism after renal and hematopoietic-cell transplantation. N Engl J Med 358:362, 2008 11. Scandling J, Busque S, Dejbakhsh-Jones S, et al: Inducing and predicting tolerance after kidney transplantation. N Engl J Med. Forthcoming 12. Bonham A, Esquivel C, Concepcion W, et al: Study of complete immunosuppressive drug withdrawal from liver transplant patients conditioned with posttransplant total lymphoid irradiation (TLI) and anti-thymocyte globulin (ATG). Transplantation 86(suppl):74, 2008 13. Bernat JL, D’Alessandro AM, Port FK, et al: Report of a National Conference on Donation after cardiac death. Am J Transplant 6:281, 2006 14. Skaro AI, Jay CL, Baker TB, et al: The impact of ischemic cholangiopathy in liver transplantation using donors after cardiac death: the untold story. Surgery 146:543, 2009