Skip Navigation


NDT Advance Access originally published online on February 27, 2006
Nephrology Dialysis Transplantation 2006 21(5):1170-1173; doi:10.1093/ndt/gfl055
This Article
Right arrow Extract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
21/5/1170    most recent
gfl055v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (2)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fändrich, F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fändrich, F.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Editorial Review

Induction of tolerance in clinical organ transplantation

F. Fändrich

Department of General and Thoracic Surgery, University of Kiel, Arnold-Heller-Str. 7, 24105 Kiel, Germany

Correspondence and offprint requests to: Prof. Dr med. F. Fändrich, FRCS, Department of General and Thoracic Surgery, University of Kiel, Arnold-Heller-Str. 7, 24105 Kiel, Germany. Email: ffaendrich{at}surgery.uni-kiel.de

Keywords: mixed chimerism; regulatory cells; tolerance



   Introduction
Top
 Introduction
References
 
Human organ transplantation is still less than fully beneficial because of the need for continual immunosuppressive medication and the hazards associated with it, poor long-term graft survival rates and the discrepancy between the demand for and supply of organs. Our developing understanding of the immune system is encouraging, and it favours new strategies in the field of tolerance induction. This article will give an overview of the challenges and actual clinical concepts that bear upon the modulation of the body's natural tolerogenic mechanisms involved in long-term graft acceptance, and it will make a briefly stated contribution to the prospects of reducing immunosuppressive treatment or, eventually, the weaning of transplant recipients off their drugs.

The successful experiment by Billingham and colleagues [1] to induce organ tolerance in an allogenic animal model by infusing foreign marrow into a newborn mouse, unequivocally demonstrated that the immune system of higher vertebrates can be reprogrammed to selectively accept major and minor histocompatibility non-self antigens. This finding allowed the inference that the immunologic tolerance that an individual has must not be considered as a fixed, genetically encoded property, rather, it should be regarded as the expression of a dynamic and flexible process—of a complex network comprising molecules and cellular and soluble components that serve as important tools that survey and react to the host's immune and health status.

Tolerance-promoting strategies
To date, the prevention of graft rejection across histocompatibility barriers can only be achieved by the long-term use of non-selective immunosuppressive drugs, which subjugate the entire immune system—whereas, only a fraction of the alloreactive cytotoxic lymphocytes, which, depending on the extent of HLA disparity, can be rather large, are responsible for initiating graft destruction. Therefore, tolerance induction continues to be a highly desirable goal in the transplant community.

Transplantation tolerance can be defined as the indefinite acceptance of the grafted tissue by the host without any dependence on the ongoing immunosuppressive treatment. One of the difficulties of designing trials of clinical tolerance is that innovative strategies that aim at minimizing the dose and number of administered immunosuppressive drugs may be associated with compromised short-term success rates. Organ recipients and clinicians thus end up facing an ethical dilemma: the possibility that the experimental design in the quest of better long-term organ survival will sacrifice excellent short-term results. In this context, it is not possible to use short-term graft survival or acute rejection rates as reliable endpoints in clinical trials. In turn, the identification of candidate genes and related proteins as surrogate markers of clinical tolerance is of eminent importance for surveying and monitoring patients who might be undergoing discontinuation/withdrawal of their immunosuppressive medication.

Mixed chimerism, co-receptor blockade and co-stimulation blockade
A possible strategy to establish long-term, drug-free graft acceptance, one that has been successfully demonstrated in animal models, is the creation of a state of donor/host chimerism [2–4]—defined as the co-existence of donor and recipient haematopoietic tissues following the transplantation of donor bone marrow (BM) as a conditioning regimen to allow subsequent BM engraftment. The availability of monoclonal antibodies (mAbs) to specifically deplete T lymphocyte subsets by blocking co-receptors (such as CD4 or CD8) or co-stimulatory molecules (such as CD28, CD154 or PD-1), without the complete, and potentially lethal, ablation of host bone marrow, has nourished the current concepts of inducing a permanent or transient state of chimerism [5,6]. An attractive aspect of these concepts has been the demonstration in rodents that the engraftment of allogenic bone marrow was achieved without the necessity to interfere with host haemopoiesis. In the clinical context, however, there are concerns, for lymphocytes reconstitute poorly in adult life following their depletion, thus raising the spectre of long-term immunodeficiency. Moreover, the use of mAb-based protocols, though successfully applied in rodents, in humans can lead to disastrous clinical outcomes, such as lethal thromboembolic complications—as evidenced after the application of anti-CD40L mAbs in early clinical pilot studies [7]. Another factor limiting the successful application of these concepts is the still-unresolved problem of how a firm non-myeloablative regimen could achieve a substantial level of donor chimerism (>5% donor cells in the host's peripheral blood compartment) for each and all possible (highly variable) constellations of donor–recipient HLA disparities. Beyond that, the long-term persistence of macrochimerism does not necessarily represent a prerequisite for successful, stable tolerance induction. In fact, the lack of sustained significant donor macrochimerism was one of the most remarkable findings in clinical studies of combined kidney and donor BM transplantation [8,9]. However, it is impossible to predict which patients will develop tolerance and which will suffer from rejections once the donor chimerism disappears from the peripheral blood compartment.

Regulatory T lymphocytes: potential tools for peripheral tolerance induction
The existence of regulatory T cells has been the subject of discussion for more than two decades. Whereas Awwad and North [10] demonstrated the tumour promoting role of the cells in experimental cancer studies, it was Sakaguchi and colleagues [11,12] who observed that the adoptive transfer of T cells, depleted of the so-called ‘naturally occurring thymus-derived CD4+/CD25+ double-positive Tregs’, caused multi-organ auto-immunity in recipient animals. Regulatory T lymphocytes (Tregs) can also be induced in vivo or in vitro under particular antigen and cytokine exposures [13–17]. These induced Tregs are not necessarily CD4+/CD25+ double-positive, and they can be classified as T regulatory 1 (TR1) [18,19] and T helper 3 cells [20] according to their cytokine profile—either IL-10 alone, or TGF-ß, IL-4 and IL-10, respectively. Besides their capacity to suppress a variety of different immune responses in vitro and in vivo [21,22], it is also important to address the functional role of Tregs in promoting allograft survival in long-term tolerant mice. For example, Tregs isolated from tolerant mice can be transferred to naive recipients where they can prevent alloreactive T lymphocyte responses in a donor-specific fashion when the recipient is challenged with an allograft [23–25]. The role of CD8+ T cells with regulatory properties in controlling immune homoeostasis is still not clarified. It is known that their regulatory function does not involve CTLA4, but can be linked to a subpopulation of CD8+CD28– T lymphocytes, which upon interaction with professional APCs induce ILTR3 and -4 upregulation and subsequent tolerogenic mechanisms [26].

From a clinical point of view, the use of Tregs is severely limited by their paucity—they comprise only 4–8% of peripheral CD4+ blood lymphocytes. It follows that, reliable protocols that effectively expand Treg populations while maintaining their biological properties are urgently needed. Several strategies to trigger Treg expansion are being investigated: among them, CD3 and CD28 antibodies coupled to magnetic beads, high-dose IL-2, IL-10 and others [26–28] have been demonstrated to efficiently yield Tregs endowed with phenotypic cell markers that are specific for Tregs, markers such as CD25, CD62L, HLA-DR (human), CTLA4 (cytotoxic T-lymphocyte antigen 4), (glucocorticoid-induced tumour-necrosis factor receptor-related protein), and most importantly, for the intracellular expression of Foxp3, the forkhead box P3 transcription factor. In view of the potential clinical applications of Tregs for establishing donor-specific tolerance, the use of polyclonally expanded Tregs appears unjustified, because the frequency of the available precursor for a dedicated donor-antigen presumably will be low. Therefore an alternative strategy, which takes advantage of leukapheresis-derived monocytes, which upon ex-situ modification act as regulatory cells on their own (unpublished data), may be the route to take.

Induction of immunoregulatory monocytes
Plasticity and functional polarization are the hallmarks of mononuclear cells of myelomonocytic lineage. It is well-known that the versatility of the response of monocytes and macrophages to microbial products, chemokines and cytokines differentially affects their immunological function with regard to resistance to, or promotion of, pathogens, tumours, immunoregulation and tissue repair and remodelling [29,30]. Based on original work with rat-derived embryonic stem cell-like cells [31], we have developed a method for the in vitro expansion of M-CSF and {gamma}-IFN-modified monocytes (Mmod), which have regulatory functions. In a rat model of allogenic kidney transplantation, we were able to demonstrate that the intravenous injection of 106 of these M-CSF- and IFN{gamma}-stimulated monocytes (over a 5 day culture period) was sufficient to establish long-term (>150 days) donor-specific tolerance in non-immunosuppressed recipient animals, if administered on day 7 before the transplantation (unpublished data). The tolerogenic mechanism underlying this process is based on the elimination of alloreactive T lymphocytes upon cellular engagement with donor-derived Mmod. In addition to this eliminative property, we are also able to demonstrate that donor-derived Mmod share regulatory functions, as they are able to transform naïve CD4+ T lymphocytes into CD4+-/Foxp3+-positive T cells after a period of 4 days in co-culture. These inducible Tregs bear regulatory functions themselves, suppressing MLR-responses and inducing tolerance in vivo, upon adoptive transfer into naïve host animals. A pilot clinical study has just been initiated where, under the umbrella of induction therapy with three doses of ATG, an immunosuppressive regimen—including steroids (given for 8 weeks) and tacrolimus (given for 24 weeks)—is combined with the pre-transplant injection of donor-derived Mmod plus co-cultivated, recipient-borne, antigen-primed Tregs on day 5 prior to living-related kidney transplantation. This protocol will investigate the safety and efficacy of regulatory cells of both monocytic and lymphocytic origin for establishing long-term graft acceptance with minimized immunosuppressive treatment, or none at all. It is still open to speculation what will be the impact of and the role played by T and B memory cells, the degree of HLA disparity, the frequency of panel-reactive antibodies, the choice of immunosuppressive drugs and the viral status of donor and recipient in humans, in a similar setting. These studies of the factors that could be involved, in conjunction with large-scale genetic studies and detailed functional immune assays to survey enrolled patients, are obligatory; and they will be performed in an integrated European Immune Network (RISET) funded by the European Union.

Conflict of interest statement. None declared.



   References
Top
 Introduction
 References
 

  1. Billingham RE, Brent L, Medawar PB. Actively acquired tolerance of foreign cells. Nature 1953; 172: 603–606[CrossRef][Medline]
  2. Ildstad ST, Sachs DH. Reconstitution with syngeneic plus allogeneic or xenogeneic bone marrow leads to specific acceptance of allografts or xenografts. Nature 1984; 307: 168–170[CrossRef][Medline]
  3. Sharabi Y, Sachs DH. Mixed chimerism and permanent specific transplantation tolerance induced by a nonlethal preparative regimen. J Exp Med 1989; 169: 493–502[Abstract/Free Full Text]
  4. Kawai T et al. Mixed allogeneic chimerism and renal allograft tolerance in cynomolgus monkeys. Transplantation 1995; 59: 256–262[Medline]
  5. Wekerle T et al. Allogeneic bone marrow transplantation with co-stimulatory blockade induces macrochimerism and tolerance without cytoreductive host treatment. Nat Med 2000; 6: 464–469[CrossRef][ISI][Medline]
  6. Durham MM et al. Cutting edge: administration of anti-CD40 ligand and donor bone marrow leads to hemopoietic chimerism and donor-specific tolerance without cytoreductive conditioning. Immunol 2000; 165: 1–4
  7. Kawai T, Andrews D, Colvin RB, Sachs DH, Cosimi AB. Thromboembolic complications after treatment with monoclonal antibody against CD40 ligand. Nat Med 2000; 6: 114[ISI][Medline]
  8. Spitzer TR et al. Combined histocompatibility leukocyte antigen-matched donor bone marrow and renal transplantation for multiple myeloma with end stage renal disease: the induction of allograft tolerance through mixed lymphohematopoietic chimerism. Transplantation 1999; 68: 480–484[CrossRef][ISI][Medline]
  9. Buhler LH et al. Induction of kidney allograft tolerance after transient lymphohematopoietic chimerism in patients with multiple myeloma and end-stage renal disease. Transplantation 2002; 74: 1405–1409[CrossRef][ISI][Medline]
  10. Awwad M, North RJ. Immunologically mediated regression of a murine lymphoma after treatment with anti-L3T4 antibody. A consequence of removing L3T4+ suppressor T cells from a host generating predominantly Lyt-2+ T cell-mediated immunity. J Exp Med 1988; 168: 2193–2206[Abstract/Free Full Text]
  11. Sakaguchi S, Takahashi T, Nishizuka Y. Study on cellular events in post-thymectomy autoimmune oophoritis in mice. II. Requirement of Lyt-1 cells in normal female mice for the prevention of oophoritis. J Exp Med 1982; 156: 1577–1586[Abstract/Free Full Text]
  12. Sakaguchi S. Regulatory T cells: key controllers of immunologic self-tolerance. Cell 2000; 101: 455–458[CrossRef][ISI][Medline]
  13. Horwitz DA et al. Regulatory T cells generated ex vivo as an approach for the therapy of autoimmune disease. Semin Immunol 2004; 16: 135–143[CrossRef][ISI][Medline]
  14. Roncarolo MG, Bacchetta R, Bordignon C, Narula S, Levings MK. Type 1 T regulatory cells. Immuno Rev 2001; 182: 68–79
  15. Taylor PA, Lees CJ, Blaza BR. The infusion of ex vivo activated and expanded CD4+CD25+ immune regulatory cells inhibits graft-versus-host disease lethality. Blood 2002; 99: 3493–3499[Abstract/Free Full Text]
  16. Levings MK et al. Human CD25+CD4+ T suppressor cell clones produce transforming growth factor ß, but not interleukin 10, and are distinct from type 1 T regulatory cells. J Exp Med 2002; 196: 1335–1346[Abstract/Free Full Text]
  17. Godfrey WR et al. In vitro-expanded human CD4+CD25+ T-regulatory cells can markedly inhibit allogeneic dendritic cell-stimulated MLR cultures. Blood 2004; 104: 453–461[Abstract/Free Full Text]
  18. Groux H et al. A CD4+ T-cell subset inhibits antigen-specific T-cell responses and prevents colitis. Nature 1997; 389: 737–742[CrossRef][Medline]
  19. Barrat FJ et al. In vitro generation of interleukin 10-producing regulatory CD4+ T cells is induced by immunosuppressive drugs and inhibited by T helper type 1 (TH1)- and TH2-inducing cytokines. J Exp Med 2002; 195: 603–616[Abstract/Free Full Text]
  20. Weiner HL, Induction and mechanism of action of transforming growth factor-ß-secreting TH3 regulatory cells. Immunol Rev 2001; 182: 207–214[CrossRef][ISI][Medline]
  21. Thornton AM, Shevach EM. CD4+CD25+ immunoregulatory T cells suppress polyclonal T cell activation in vitro by inhibiting interleukin 2 production. J Exp Med 1998; 188: 287–296[Abstract/Free Full Text]
  22. Tang Q et al. Distinct roles of CTL-4 and TGF-ß in CD4+CD25+ regulatory T cell function. Eur J Immunol 2004; 34: 2996–3005[CrossRef][ISI][Medline]
  23. Liu J et al. Rat CD8+FOXP3+ T suppressor cells mediate tolerance to allogeneic heart transplants, inducing PIR-B in APC and rendering the graft invulnerable to rejection. Transpl Immunol 2004; 13: 239–247[CrossRef][ISI][Medline]
  24. Kingsley CI, Karim M, Bushell AR, Wood KJ. CD25+CD4+ regulatory T cells prevent graft rejection: CTLA-4- and IL-10-dependent immunoregulation of alloresponses. J Immunol 2002; 168: 1080–1086[Abstract/Free Full Text]
  25. Waldmann H et al. Regulatory T cells and organ transplantation. Semin Immunol 2004; 16: 119–126[CrossRef][ISI][Medline]
  26. Chang CC, Ciubotariu R, Manavalan JS et al. Tolerization of dendritic cells by T cells: the crucial role of inhibitory receptors ILT3 and ILT4. Nat Immunol 2002; 3: 237–243[CrossRef][ISI][Medline]
  27. Hoffmann P, Eder R, Kunz-Schughart LA, Andreesen R, Edinger M. Large-scale in vitro expansion of polyclonal human CD4+CD25+ regulatory T cells. Blood 2004; 104: 895–903[Abstract/Free Full Text]
  28. Tang Q et al. In vitro-expanded antigen-specific regulatory T cells suppress autoimmune diabetes. J Exp Med 2004; 199: 1455–1465[Abstract/Free Full Text]
  29. Mantovani A, Sica A, Sozzani S, Allavena P, Vecchi A, Locati M. The chemokine system in diverse forms of macrophage activation and polarization. Trends Immunol 2004; 25: 677–686[CrossRef][ISI][Medline]
  30. Mosser DM. The many faces of macrophage activation. J Leuk Biol 2003; 73: 209–212[Free Full Text]
  31. Fändrich F, Lin X, Chai GX et al. Preimplantation-stage stem cells induce long-term allogeneic graft acceptance without supplementary host conditioning. Nat Med 2002; 8: 171–178[CrossRef][ISI][Medline]
Received for publication: 26.10.05
Accepted in revised form: 31. 1.06


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?



This Article
Right arrow Extract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
21/5/1170    most recent
gfl055v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (2)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Fändrich, F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fändrich, F.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?