Xenotransplantation: Basic Research and Clinical Applications

XENOTRANSPLANTATION BASIC RESEARCH AND CLINICAL APPLICATIONS EDITED BY

JEFFREY L. PLATT, MD

HUMANA PRESS

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Xenotransplantation

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Xenotransplantation Basic Research and Clinical Applications

Edited by

Jeffrey L. Platt, MD Transplantation Biology, Mayo Clinic Rochester, MN

HUMANA PRESS TOTOWA, NEW JERSEY

iv © 2002 Humana Press Inc. 999 Riverview Drive, Suite 208 Totowa, New Jersey 07512

www.humanapress.com For additional copies, pricing for bulk purchases, and/or information about other Humana titles, contact Humana at the above address or at any of the following numbers: Tel.: 973-256-1699; Fax: 973-256-8341, E-mail: [email protected]; or visit our Website: http://humanapress.com All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise without written permission from the Publisher. All articles, comments, opinions, conclusions, or recommendations are those of the author(s), and do not necessarily reflect the views of the publisher. Due diligence has been taken by the publishers, editors, and authors of this book to assure the accuracy of the information published and to describe generally accepted practices. The contributors herein have carefully checked to ensure that the drug selections and dosages set forth in this text are accurate and in accord with the standards accepted at the time of publication. Notwithstanding, as new research, changes in government regulations, and knowledge from clinical experience relating to drug therapy and drug reactions constantly occurs, the reader is advised to check the product information provided by the manufacturer of each drug for any change in dosages or for additional warnings and contraindications. This is of utmost importance when the recommended drug herein is a new or infrequently used drug. It is the responsibility of the treating physician to determine dosages and treatment strategies for individual patients. Further it is the responsibility of the health care provider to ascertain the Food and Drug Administration status of each drug or device used in their clinical practice. The publisher, editors, and authors are not responsible for errors or omissions or for any consequences from the application of the information presented in this book and make no warranty, express or implied, with respect to the contents in this publication. Cover design by Patricia F. Cleary. This publication is printed on acid-free paper. ' ANSI Z39.48-1984 (American National Standards Institute) Permanence of Paper for Printed Library Materials. Photocopy Authorization Policy: Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Humana Press Inc., provided that the base fee of US $10.00 per copy, plus US $00.25 per page, is paid directly to the Copyright Clearance Center at 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license from the CCC, a separate system of payment has been arranged and is acceptable to Humana Press Inc. The fee code for users of the Transactional Reporting Service is: [0-89603-674-X/02 $10.00 + $00.25]. Printed in the United States of America. 10 9 8 7 6 5 4 3 2 1 Library of Congress Cataloging-in-Publication Data Xenotransplantation: basic research and clinical applications / edited by Jeffrey L. Platt. p. cm. Includes bibliography and index. ISBN 0-89603-674-X 1. Xenografts. I. Platt, Jeffrey L. QR188.8.X453 2002 617.9’5–dc21 2001051652

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Preface No field of medicine has engendered greater excitement or enjoyed greater success than the field of transplantation. Organ transplantation allows the “cure” of disease by replacing failing organs with physiologically normal organs. Tissue transplantation and tissue engineering allow not only the replacement of abnormal cells, such as bone marrow cells, but also the possibility of using a transplant to impart novel physiologic functions. The major limitation to applying transplantation for the treatment of disease is a shortage of human donors. This shortage limits transplant procedures to as few as five percent of those that would be carried out if the supply of organs and tissues were unlimited. Because of this shortage and because of recent advances in fundamental knowledge, there has been a crescendo of interest in xenotransplantation, the use of animals in lieu of humans as organ and tissue donors. For many years, xenotransplantation has seemed only a distant prospect because of the severe immune responses of the host against the graft. Recent studies, however, have revealed the molecular basis of these immune responses and have given rise to novel therapeutic approaches for circumventing them. For example, the generation of transgenic animals expressing human complement regulatory proteins or human glycosyltransferases raises the prospect that the severest type of rejection can be avoided without manipulating the xenograft recipient. Thus, xenotransplantation has quickly moved to center stage in the field of transplantation, engaging the interest of clinicians, basic scientists, and academicians. Xenotransplantation: Basic Research and Clinical Applications compiles and explains the fundamental molecular and cell biology that has been applied with such advantage in the emerging fields of transplant immunology and xenotransplantation. The contributors to this book are established authorities in transplant immunology and molecular and cell biology. This book provides a base of knowledge for the practitioner, fellow, and student, and those involved in biotechnology and related sciences. Jeffrey L. Platt, MD v

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Contents Preface ................................................................................................ v Contributors ..................................................................................... ix 1

Molecular and Cellular Hurdles to Xenotransplantation Jeffrey L. Platt ......................................................................... 1

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Pathological Responses to Xenotransplantation Matilde Bustos and Jeffrey L. Platt ...................................... 45

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Natural Xenoreactive Antibodies Uri Galili ............................................................................... 57

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Specificity of Xenoreactive Natural Antibodies William Parker, Paul B. Yu, and Yuko C. Nakamura ..........73

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Biophysical Properties of Xenoreactive Natural Antibodies William Parker, Ryan C. Fields, and Yuko C. Nakamura..................................................... 87

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The Origin of Xenoreactive Natural Antibodies Paul B. Yu............................................................................ 103

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Synthesis of Carbohydrate Antigens Recognized by Xenoreactive Antibodies Mauro S. Sandrin and Ian F. C. McKenzie ........................119

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The Complement Barrier to Xenotransplantation Agustin P. Dalmasso ...........................................................139

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Defects and Amplification of Costimulation Across the Species Nicola Rogers and Robert Lechler .....................................173

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Contents

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Antibody-Dependent Effects on Cellular Immunity Antonello Pileggi, R. Damaris Molano, Thierry Berney, and Luca Inverardi .........................................................199

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Disordered Regulation of Coagulation and Platelet Activation in Xenotransplantation Simon C. Robson .................................................................215

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Current Applications of Cellular Xenografts Albert S. B. Edge .................................................................247

Index ...............................................................................................265

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Contributors THIERRY BERNEY • Diabetes Research Institute, University of Miami School of Medicine, Miami, FL MATILDE BUSTOS • Department of Surgery, Universidad de Navarra, Pamplona, Spain AGUSTIN P. DALMASSO • Departments of Surgery and Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis, MN ALBERT S. B. EDGE • Diacrin, Inc., Charlestown, MA RYAN C. FIELDS • Department of Surgery, Duke University Medical Center, Durham, NC URI GALILI • Departments of Cardiovascular-Thoracic Surgery and Immunology and Microbiology, Rush Medical College, Chicago, IL LUCA INVERARDI • Diabetes Research Institute, University of Miami School of Medicine, Miami, FL ROBERT LECHLER • Department of Immunology, Imperial College of Science, Technology, and Medicine, London, UK B RUCE L OVELAND • Molecular Immunogenetics Laboratory, Austin Research Institute, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia IAN F. C. MCKENZIE • Molecular Immunogenetics Laboratory, Austin Research Institute, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia R. DAMARIS MOLANO • Diabetes Research Institute, University of Miami School of Medicine, Miami, FL YUKO C. NAKAMURA • Department of Surgery, Duke University Medical Center, Durham, NC WILLIAM PARKER • Department of Surgery, Duke University Medical Center, Durham, NC ANTONELLO PILEGGI • Diabetes Research Institute, University of Miami School of Medicine, Miami, FL JEFFREY L. PLATT • Transplantation Biology and the Departments of Surgery, Immunology, and Pediatrics, Mayo Clinic, Rochester, MN ix

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Contributors

SIMON C. ROBSON • Center for Immunobiology, Department of Medicine, Beth Israel-Deaconess Medical Center, Boston, MA NICOLA ROGERS • Department of Immunology, Imperial College of Science, Technology, and Medicine, London, UK MAURO S. SANDRIN • Molecular Immunogenetics Laboratory, Austin Research Institute, Austin and Repatriation Medical Centre, Heidelberg, Victoria, Australia PAUL B. YU • Division of Cardiology, Massachusetts General Hospital, Boston, MA

Hurdles to Xenotransplantation

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Molecular and Cellular Hurdles to Xenotransplantation Jeffrey L. Platt, MD, PhD INTRODUCTION

The transplantation of organs, tissues, or cells between individuals of different species has been of increasing interest in recent years because the use of animals as organ and tissue donors as a source of transplants would overcome the severe and worsening shortage of human organs available for transplantation. This shortage restricts the application of organ transplantation to 5–15% of the patients who might benefit in the United States (1). Indeed, the shortage of donor organs is now widely acknowledged to be the major limitation of transplantation. Interest in xenotransplantation also arises because a xenotransplant might, in principle, be less susceptible to infection by viruses or other agents that caused the primary disease. Avoiding viral infection was the rationale for several baboon-to-human liver transplants (2) and for the transplantation of baboon bone marrow in a human patient with AIDS. Interest in xenotransplantation may further arise because the animal source can be subjected to genetic engineering, and such engineering might provide a vehicle for delivery of genes or enduring expression of genes (3). For example, genetic engineering might be used to express therapeutic genes in stem cells.

TISSUE SOURCE AND DONOR FACTORS IN XENOTRANSPLANTATION The type of organ or tissue transplanted and the phylogenetic distance between the donor and the recipient have profound importance for the immune response to xenotransplantation (Fig. 1). The type of organ

From: Xenotransplantation: Basic Research and Clinical Applications Edited by: Jeffrey L. Platt © Humana Press Inc., Totowa, NJ

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Fig. 1. The immunological response to xenotransplantation. The immune response to xenotransplantation can be classified according to whether the graft consists of isolated cells or free tissues, such as islets of Langerhans or of a primarily vascularized organ such as the kidney or heart. (A) Vascularized organ grafts are subject to hyperacute and acute vascular rejection caused by the action of antidonor antibodies on donor endothelium. If hyperacute or acute vascular rejection are averted, the graft may undergo accommodation, a condition in which the graft appears to resist injury despite the return of anti-donor antibodies to the circulation and the presence of an intact complement system. A vascularized organ graft may also be subject to cellular rejection and chronic rejection more or less like the corresponding types of rejection observed in allografts. (B) Free tissue grafts are subject to failure caused by primary nonfunction, failure of neovascularization or failure of the microenvironment to support the survival and function of the foreign tissue. If the free tissue or isolated cells engraft, they are then subject to cellular or humoral rejection.

or tissue grafted determines the nature of the blood supply and, thus, the nature of the contact between the transplant and the immune system of the host (Fig. 2). The type of transplant also determines the relative importance of “growth” factors for engraftment and the survival and function of the graft. The phylogenetic distance determines the compatibility of growth factors and growth factor receptors between donor and recipient (4,5). The type of graft, i.e., cell, tissue, or organ, also determines how donor antigen comes to be presented to the immune system of the recipient. Xenografts consisting of isolated cells, such as hepatocytes, derive their vascular supply entirely by the in-growth of blood vessels of the recipient (6) (Table 1). Free tissue grafts, such as pancreatic islets or

Hurdles to Xenotransplantation

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Fig. 2. Antigen presentation in a free tissue graft: implications for the immunogenicity of xenografts. Free tissue xenografts are generally vascularized by spontaneous anastomosis of donor and recipient blood vessels and by neovascularization. Spontaneous anastomosis allows the presentation of foreign antigen by foreign MHC as modeled in the upper left of the figure. Neovascularization results in presentation of foreign antigen by recipient MHC as in the upper right and lower parts of the figure. If neovascularization or spontaneous anastomosis were to be impaired, the mechanism of antigen presentation might differ from the mechanism that would predominate in a free tissue allograft.

Table 1 Classification of xenografts Type of xenograft (example) isolated cells (hepatocytes, bone marrow) free tissue (pancreatic islets, skin) organ (kidney, heart)

Type of vascular supply

Microenvironment

neovascularization

recipient

neovascularization + anastomosis of donor and recipient vessels primary anastomosis of donor and recipient vessels

donor and recipient donor

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skin, derive their vascular supply in part from the host and in part from the spontaneous anastomosis of donor and recipient blood vessels. The blood vessels of the recipient in cell and tissue grafts pose a barrier between the graft and the immune system of the recipient. This barrier may be sufficient to allow survival of xenografts with no more immunosuppression than allografts (7). Blood vessels of recipient origin might, in principle, take up and present antigen of the donor. Antigen presented in this way to T lymphocytes is said to be presented through the “indirect” pathway (8) (Fig. 3). The type of rejection typically seen in cell and tissue xenografts is cellular rejection. In contrast to cellular xenografts, organ xenografts provide their own blood vessels. The interaction of the immune system of the recipient with donor blood vessels gives rise to distinct types of vascular or humoral rejection (Fig. 1). Organ xenografts are also subject to cellular rejection. The donor blood vessels of organ xenografts may present antigen to T lymphocytes through the “direct” pathway (Fig. 3). The nature of the blood supply and the microenvironment may also determine the biological viability of the graft (Table 1). Cell and tissue grafts may depend on growth factors of recipient origin. If these growth factors are not compatible with the xenogeneic cells, the graft may fail. An important example of such incompatibility can be found in the transplantation of xenogeneic bone marrow (5). In contrast, organ xenografts generally provide the factors needed for survival of the xenogeneic cells in the graft. Genetic differences between the donor and the recipient are another important factor in xenotransplantation (Table 2). Phylogenetic distance between the donor and the recipient, of course, determines the number of antigens that might serve as a target of the immune response. However, certain genetically controlled traits have a disproportionate impact on the outcome of a xenograft. For example, the expression of a functional _1,3-galactosyltransferase gene in lower mammals leads to the synthesis of Gal_1-3Gal as the terminus of certain oligosaccharide chains. Gal_1-3Gal is recognized by certain naturally occurring antibodies made by humans, apes, and Old World monkeys (9). Although this antigen–antibody system constitutes a severe immunological barrier to xenotransplantation, the distribution of that glycosyltransferase in phylogeny is not a function of genetic distance (Table 3). Another trait under genetic control is the regulation of the complement system. The complement system is regulated by plasma and cell surface proteins

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Fig. 3. Antigen presentation in xenotransplantation. Antigen may be presented by the direct or indirect pathways. When direct antigen presentation occurs, the T cells of the recipient recognize undenatured MHC antigen of the donor expressed by donor APC or other donor cells. The peptide associated with MHC is of donor origin and may either dictate specificity or may be nominal with regard to specificity of recognition. For indirect antigen presentation, the T cells of the recipient recognizes donor peptide expressed in association with MHC of the recipient.

Table 2 Phylogeny and the Susceptibility to Hyperacute Rejection

Donor

Organ

Recipient

hamster guinea pig pig dog pig NW monkey OW monkey

heart heart kidney kidney heart heart heart

rat rat dog pig baboon baboon baboon

a

Graft a Survival

Histology of Rejected Graft

Selected Reference

4 1/4 d 1/4 h 1/3 h 2 1/2 h 3h 1h 6d

AVRb HAR HAR HAR HAR HAR AVR

211 212 25 25 213 57 214

The graft survival and histology shown are typical for this type of transplant in a recipient receiving a “routine” immunosuppression regimen. b Abbreviations used: NW, New World; OW, Old World; AVR, acute vascular rejection; HAR, hyperacute rejection.

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Table 3 Phylogeny of Gal_1-3Gal and Natural Antibodies Specific for that Saccharide

Species chicken mouse rat pig dog New world monkey Old world monkey Baboon human

_1,3-galactosyl transferase

Expression of Gal_1-3Gal

Natural antiGal_1-3Gal antibodies

– + + + + + – – –

– + + + + + – – –

+ – – – – – + + +

that function in a species-specific fashion (10) (Table 4). For example, the cells of the guinea pig allow the unrestrained activation of the rat alternative pathway of complement, and, as a result, organs of guinea pigs transplanted into rats are subject to very rapid and vigorous rejection (11,12). Fortunately, the alternative pathway of the human complement system is not primarily activated on porcine cell surfaces (13–15), and, thus, pigs may serve as a useful source of cells and organs for xenotransplantation into humans. Other genetic differences that may contribute to the outcome of xenografts include the species-specific functioning of cell-associated complement regulatory proteins such as decay accelerating factor (DAF), CD59 (16), and the potential speciesspecific functioning of the thrombomodulin vis-à-vis thrombin and protein C (17).

THE BIOLOGICAL RESPONSES TO ORGAN XENOTRANSPLANTATION Figure 1 shows a model for the biological responses to xenotransplantation, which manifest predominantly as rejection reactions. The sections that follow will summarize the molecular and cellular mechanism underlying these rejection reactions and how this information can be used to develop strategies for the prevention and treatment of rejection.

Serum

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Cells

Cow Rabbit Horse Pigeon Pig Human Dog Rat Guinea Pig Sheep

Hurdles to Xenotransplantation

Table 4 Activation of Complement on Xenogeneic Cells Via the Alternative Pathway

Cow

Rabbit

Horse

Pigeon

Pig

Human

Dog

Rat

Guinea Pig

Sheep

_ 2.6 0.59 2.34 4.4 4.4