Conference Scene: Autoimmunity and Transplantation: Basic Science and Clinic Translation Meet in Geneva

Abstract

Scientists interested in the field of immunomodulation meet every 2 years to discuss new regulatory mechanisms and targets of intervention for the treatment of autoimmunity and transplant rejection. This article highlights the 9th International Conference on New Trends in Immunosuppression and Immunotherapy, which was held in February 2010 in Geneva, Switzerland.

Research in the field of transplantation immunology and autoimmune diseases aims to develop strategies to restore tolerance and improve long-term survival without the occurrence of severe side effects related to chronic immunosuppression. Targeting pathogenic cells via new biological agents or different drug regimens, transferring regulatory cells or enhancing their suppressive effect in vivo are currently pursued strategies to accomplish this aim in preclinical studies and clinical trials. Although immunosuppression can be minimized in some cases, tolerance is rarely achieved and the molecular mechanisms underlying tolerance induction are not fully understood.

The International Conference on New Trends in Immunosuppression and Immunotherapy was founded in 1991 by Alexander Yussim (Israel) and Claus Hammer (Germany). This biannual meeting highlights the latest developments in the field of preclinical and translational immunomodulation, as well as in immunotherapy. This year, it was held in Geneva, Switzerland, and was chaired by Hans-Dieter Volk (Germany). Scientists and clinicians were brought together again to share common interests in defining new therapeutic approaches to treat transplantation rejections and autoimmune diseases. The congress was organized around plenary sessions, oral presentations and poster displays. This article focuses on selected topics discussed, in particular molecular mechanisms of tolerance, targeting pathogenic cells via new biological agents or different drug regimens and the possible use of regulatory T cells to achieve tolerance in transplanted or autoimmune patients.

Autoimmunity & transplantation: preclinical targets

Andreas Radbruch (Deutsches Rheuma Forschungszentrum, Germany) has discussed the possible options and limitations of targeting B cells and plasma cells for the treatment of autoimmune diseases. His group has pioneered the concept that antibody-secreting plasma cells are long-lived and represent an independent component of immunological memory [1]. Long-lived plasma cells are generated during an immune response and migrate to the bone marrow, where they persist for years and decades. Their survival is dependent on receiving distinct signals provided by cells forming a plasma cell survival niche. They can also migrate to, and survive in, inflamed tissues. In autoimmune diseases, depletion of long-lived plasma cells secreting autoantibodies is still a therapeutic challenge because they are resistant to conventional treatments, in particular to immunosuppression and anti-inflammatory drugs. However, immunoablation followed by reconstitution of the patient‘s immune system from hematopoietic stem cells induces long-term remissions in many patients with autoimmune diseases, suggesting that immunoablation with anti-thymocyte globulin may succeed in targeting autoreactive long-lived plasma cells. Nonetheless, specific treatments for the elimination of such cells are needed to avoid the complete temporary immune incompetence induced by immunoablation, and to decipher the role of long-lived autoreactive plasma cells in human autoimmune diseases in more detail.

NK cells not only mediate the graft-versus-leukemia effect but can also be beneficial to prevent transplant-related complications such as graft-versus-host disease and graft rejection [2]. Chiara Romagnani (Deutsches Rheuma Forschungszentrum, Germany) reported that while NK cells have been long considered to be innate cells ready to display effector functions, it appears clear that, similar to T cells, they undergo a complex differentiation program and need to be primed in order to acquire the ability to respond to activating ligands. Moreover, a Phase I/II clinical trial with patients undergoing haploidentical stem cell transplantation showed that the adoptive transfer of donor NK cells is indeed safe and appeared to display a beneficial effect in terms of overall survival, especially in acute myeloid leukemia patients.

Regulatory T cells play an essential role in controlling immunity. Two main subsets of regulatory CD4⁺ T cells (Tregs), namely the Foxp3⁺CD25^high natural Treg (nTreg) and the T-inducible regulatory type 1 (Tr1) cells, characterized by the expression of IL-10 and of low levels of IFN-γ, have been extensively studied in preclinical models as well as in humans. Treg-based therapy of autoimmune diseases and transplantation appears to be a very promising approach [3]. Maria Grazia Roncarolo (San Raffaele Telethon Institute for Gene Therapy, Italy) presented key data on both subsets of Tregs, Foxp3⁺CD25^high Tregs and Tr1 cells. She demonstrated that the number and phenotype of CD4⁺CD25^high T cells from patients affected by immune dysregulation polyendocrinopathy enteropathy X-linked (IPEX) was comparable with those of normal donors and that CD4⁺CD25^high T cells from IPEX patients who express FOXP3 protein suppressed the in vitro proliferation of effector T cells from normal donors. By contrast, the suppressive function of CD4⁺ CD25^high T cells from IPEX patients who do not express Foxp3 protein was profoundly impaired. Importantly, CD4⁺CD25^high T cells from either Foxp3⁺ or Foxp3^- IPEX patients showed altered suppression toward autologous effector T cells [4]. The analysis of active wild-type (WT) versus mutated FOXP3 allele distribution in healthy female carriers of FOXP3 mutations revealed a random pattern of X-chromosome inactivation in naive and memory CD4⁺ T cells. Conversely, nTregs expressed only the active WT-Foxp3, thus suggesting that the expression of WT-Foxp3 is indispensable for the presence of a normal nTreg compartment but not for effector T-cell differentiation in humans [5]. In the final part of the presentation, Roncarolo addressed the efficacy of Tr1-cell therapy in preclinical models of islet transplant. Transfer of polyclonal Tr1 cells engendered graft tolerance only in a nonstringent mouse model. Conversely, cell therapy with antigen-specific Tr1 cells induced an IL-10-dependent tolerance in the stringent mouse model of islet transplant, demonstrating for the first time that Tr1-cell therapy leads to tolerance in settings of islet transplant and that its therapeutic efficacy is highly dependent on the antigen specificity of these cells [6].

The potential and limitations of treating autoimmune diseases with autoantigen-specific Foxp3⁺ Tregs was the main subject of discussion in the presentation held by Todd M Brusko (Diabetes Center at the University of California, CA, USA). Although transfer of Tregs has been shown to control autoimmunity in preclinical models, the limited access to sufficient amounts of autoantigen-specific Tregs displaying stable suppressive phenotypes in vitro and in vivo may limit the translation of this approach to treat autoimmune diseases. Indeed, the group of Jeffrey A Bluestone has previously shown in genetic lineage tracing studies using a Foxp3–GFP–Cre × ROSA26–YFP dual reporter mice that a fraction of Tregs are capable of losing Foxp3 protein and suppressive function. These ‘exFoxp3‘ cells had an activated-memory phenotype, produced inflammatory cytokines such as IL-17 and IFN-γ and were able to transfer diabetes [7]. In line with these data in vivo, Brusko has shown that a fraction of in vitro expanded human Tregs produced IFN-γ. Foxp3⁺ IFN-γ⁺ cells displayed highly methylated FOXP3 Treg-specific demethylated regions and reduced suppressive activity. Similarly, IFN-γ production could also be observed when Foxp3⁺ CD45RA⁺ Tregs were cultured under Th1-polarizing conditions. Therefore, one possible approach proposed by their group to obtain sufficient amounts of autoantigen-specific Tregs displaying a stable suppressive phenotypes is to transduce Tregs with autoantigen-specific T-cell receptors derived from effector T cells and to overexpress Foxp3 in order to reinforce their suppressive phenotype.

Transplantation & induction of tolerance

Operational tolerance, defined as long-term freedom from all immunosuppression in transplanted patients with normal graft function, is rarely achieved. Minimizing immunosuppression in long-term stable solid organ transplant (SOT) patients in order to reduce adverse effects and costs is a common goal discussed in this conference. However, in order to perform a safe weaning of immunosuppressive drugs, we urgently need reliable biomarkers that identify operational-tolerant patients [8]. Hans-Dieter Volk (Institute of Medical Immunology, Charité University, Germany) reported on new biomarkers that emerged from the collaborative work of several groups within the European Networks Indices of Tolerance and Reprogramming the Immune System for the Establishment of Tolerance. Preliminary data suggest that drug-free stable transplant patients express a particular ‘tolerance signature‘, with restricted similarities between kidney and liver transplant patients. The tolerance signature is more frequent in liver than in kidney transplant patients and this may explain why complete weaning is more successful in liver than in kidney transplant patients. Conversely, patients who experienced failure of calcineurin inhibitor weaning expressed a ‘rejection signature‘ before calcineurin inhibitor weaning was initiated as compared to nonrejecters. The rejection signature was defined by different approaches such as microarrays/real-time PCR, TcLand (quantitative and qualitative analysis of T-cell receptor profiles), urinary IP-10 levels and ELISPOT of donor-reactive T cells. Randomized validation studies are ongoing.

Herman Waldmann (Sir William Dunn School of Pathology, UK) discussed the multiple mechanisms operating in transplantation tolerance. Short pulses of therapeutic nonablative antibodies directed to the T-cell coreceptors CD4 and CD8 can produce long-term acceptance and tolerance of genetically mismatched grafts. Tolerance is mediated by natural and induced Tregs and is dependent on TGF-β signaling to T cells. Tregs can convert naive T cells into Tregs when they encounter antigens presented by the same antigen-presenting cell, a process defined as linked suppression or infectious tolerance. The tissue context or ‘microenvironment‘ may be crucial to achieve linked suppression, and tissue integrity appears to be necessary for dominant tolerance to be expressed. Among the molecular mechanisms by which Tregs may mediate immune regulation and infectious tolerance in vivo, the expression of TGF-β, the generation of extracellular adenosine and catabolism of tryptophan have been implicated [9]. Importantly, the group of Waldmann could show that antigen-specific Tregs induce the expression of enzymes that consume different essential amino acids (EAAs) in skin grafts and dendritic cells. When any of these EAAs is limiting, T cells fail to proliferate in response to antigen, and Foxp3 expression is induced in synergy with TGF-β. Similar effects could be achieved by inhibition of the mammalian target of rapamycin pathway, which is involved in sensing EAA concentrations, thus showing the strong link between induced consumption of EAAs, the mammalian target of rapamycin pathway and TGF-β, as well as their crucial role in immune regulation and infectious tolerance [10].

Before proceeding to clinical trials in humans, it is essential to test the clinical efficacy of human Tregs in appropriate in vivo models. Kathryn J Wood (University of Oxford, UK) presented her results from a model in which immunodeficient mice were reconstituted with human peripheral blood mononuclear cells and then transplanted with human vessels autologous or allogeneic to the human peripheral blood mononuclear cell donor. Regulatory T cells isolated and expanded according to different protocols (CD25^high or CD25^highIL-7Rα^low) were compared for their ability to suppress graft rejection in vivo as measured by development of intimal expansion as a sign of transplant arteriosclerosis. Although CD25^highIL-7Rα^low cells displayed less fold expansion in vitro, they were more effective in suppressing in vivo.

Flavio Vincenti (University of California, CA, USA) reported from the Belatacept Evaluation of Nephroprotection and Efficacy as First-line Immunosuppression Trial (BENEFIT), which compared belatacept-based regimens with cyclosporine (CsA)-based regimens in adults receiving a kidney transplant from a living or standard-criteria deceased donor. Belatacept is a second-generation CTLA-4-Ig, which was rationally designed to bind with more avidity to CD86, therefore blocking interaction with CD28 and providing the more potent immunosuppressive properties required for immunosuppression in transplantation [11]. All patients (n = 666) received basiliximab induction, mycophenolate mofetil and corticosteroids and were then randomized to a more intensive or less intensive regimen of belatacept or CsA. After 12 months, patient/graft survival with belatacept regimens was noninferior to CsA, despite an increase in acute rejection in the early post-transplant period. Importantly, belatacept regimens demonstrated superior renal function, therefore representing a promising non-nephrotoxic therapy option in kidney transplant patients. However, belatacept was associated with an increased risk of post-transplant lymphoproliferative disease, especially in Epstein–Barr virus (EBV)-negative recipients; and therefore, costimulation blockade with belatacept should be used only in EBV-positive patients.

Petra Reinke (Department of Nephrology and Intensive Care, Charité-University Medicine, Germany) discussed adoptive T-cell therapy for the treatment of cytomegalovirus (CMV) and EBV infections in patients undergoing SOT. Adoptive cell therapy of infections in SOT patients is still a challenge, considering that the donors are not lymphopenic and they are chronically immunosuppressed. The group has developed a novel modular protocol for the fast generation of virus-specific T cells, with broad application in all patients independent of HLA/epitope restriction [12], and demonstrated that the isolation and expansion of virus-specific T cells from SOT patients is feasible [13]. Adoptive transfer of EBV-specific cells in SOT patients at high risk for post-transplant lymphoproliferative disease, or with active disease resulted in 50% long-lasting control of EBV load over years [14]. T-cell adoptive transfer in SOT patients with severe human CMV disease was performed after isolation and expansion of CMV-specific effector T cells according to the same molecular protocol established by the group. Such an approach has a dramatic impact on human CMV viremia and clinical outcome, but relapse of viral load and drop of IFN-γ-producing T cells occurred within 6 weeks after T-cell infusion [15]. This effect appears to be related to a higher frequency of Foxp3⁺ Tregs as well as CMV-specific Tr1 cells in the peripheral blood of patients compared with healthy controls, as well as lower percentages of multifunctional central memory T cells.

Conclusion

Owing to space limitations, we could not summarize all the other interesting talks held at this meeting, which addressed new immune regulatory mechanisms as well as novel possible targets of immune intervention. These topics are of great interest in the field of autoimmunity and transplantation, and the balanced combination of these themes provided a wonderful opportunity for scientists interested in basic and translational immunomodulation to interact at the meeting. Interested readers may want to attend the next meeting of this group, which will be held in 2012.

Financial & competing interests disclosure

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.