Biomarkers of Tolerance in Kidney Transplantation: Are We Predicting Tolerance or Response to Immunosuppressive Treatment?

We and others have previously described signatures of tolerance in kidney transplantation showing the differential expression of B cell-related genes and the relative expansions of B cell subsets. However, in all of these studies, the index group-namely, the tolerant recipients-were not receiving immunosuppression (IS) treatment, unlike the rest of the comparator groups. We aimed to assess the confounding effect of these regimens and develop a novel IS-independent signature of tolerance. Analyzing gene expression in three independent kidney transplant patient cohorts (232 recipients and 14 tolerant patients), we have established that the expression of the previously reported signature was biased by IS regimens, which also influenced transitional B cells. We have defined and validated a new gene expression signature that is independent of drug effects and also differentiates tolerant patients from healthy controls (cross-validated area under the receiver operating characteristic curve [AUC] = 0.81). In a prospective cohort, we have demonstrated that the new signature remained stable before and after steroid withdrawal. In addition, we report on a validated and highly accurate gene expression signature that can be reliably used to identify patients suitable for IS reduction (approximately 12% of stable patients), irrespective of the IS drugs they are receiving. Only a similar approach will make the conduct of pilot clinical trials for IS minimization safe and hence allow critical improvements in kidney posttransplant management.

Cross-validation of IFN-γ Elispot assay for measuring alloreactive memory/effector T cell responses in renal transplant recipients.

Assessment of donor-specific alloreactive memory/effector T cell responses using an IFN-γ Elispot assay has been suggested to be a novel immune-monitoring tool for evaluating the cellular immune risk in renal transplantation. Here, we report the cross-validation data of the IFN-γ Elispot assay performed within different European laboratories taking part of the EU RISET consortium. For this purpose, development of a standard operating procedure (SOP), comparisons of lectures of IFN-γ plates assessing intra- and interlaboratory assay variability of allogeneic or peptide stimuli in both healthy and kidney transplant individuals have been the main objectives. We show that the use of a same SOP and count-settings of the Elispot bioreader allow low coefficient variation between laboratories. Frozen and shipped samples display slightly lower detectable IFN-γ frequencies than fresh samples. Importantly, a close correlation between different laboratories is obtained when measuring high frequencies of antigen-specific primed/memory T cell alloresponses. Interestingly, significant high donor-specific alloreactive T cell responses can be similarly detected among different laboratories in kidney transplant patients displaying histological patterns of acute T cell mediated rejection. In conclusion, assessment of circulating alloreactive memory/effector T cells using an INF-γ Elispot assay can be accurately achieved using the same SOP, Elispot bioreader and experienced technicians in kidney transplantation.

Promoting transplantation tolerance; adoptive regulatory T cell therapy.

Transplantation is a successful treatment for end-stage organ failure. Despite improvements in short-term outcome, long-term survival remains suboptimal because of the morbidity and mortality associated with long-term use of immunosuppression. There is, therefore, a pressing need to devise protocols that induce tolerance in order to minimize or completely withdraw immunosuppression in transplant recipients. In this review we will discuss how regulatory T cells (T(regs)) came to be recognized as an attractive way to promote transplantation tolerance. We will summarize the preclinical data, supporting the importance of these cells in the induction and maintenance of immune tolerance and that provide the rationale for the isolation and expansion of these cells for cellular therapy. We will also describe the data from the first clinical trials, using T(regs) to inhibit graft-versus-host disease (GVHD) after haematopoietic stem cell transplantation and will address both the challenges and opportunities in human T(reg) cell therapy.

An analysis of lymphocyte phenotype after steroid avoidance with either alemtuzumab or basiliximab induction in renal transplantation.

Several studies have analyzed the phenotype of repopulated T-lymphocytes following alemtuzumab induction; however there has been less scrutiny of the reconstituted B-cell compartment. In the context of a randomized controlled trial (RCT) comparing alemtuzumab induction with tacrolimus monotherapy against basiliximab induction with tacrolimus and mycophenolate mofetil (MMF) therapy in renal transplantation, we analyzed the peripheral B- and T-lymphocyte phenotypes of patients at a mean of 25 +/- 2 months after transplantation. We examined the relationship between peripheral lymphocyte phenotype and graft function. Patients who received alemtuzumab had significantly higher numbers of B cells including naïve, transitional and regulatory subsets. In contrast, the CD4(+) T-cell compartment was dominated by a memory cell phenotype. Following either basiliximab or alemtuzumab induction patients with lower numbers of B cells or B subsets had significantly worse graft function. For alemtuzumab there was also a correlation between these subsets the stability of graft function and the presence of HLA-specific antibodies. These results demonstrate that a significant expansion of regulatory type B cells is associated with superior graft function and that this pattern is more common after alemtuzumab induction. This phenomenon requires further prospective study to see whether this phenotype could be used to customize immunotherapy.

Donor-specific indirect pathway analysis reveals a B-cell-independent signature which reflects outcomes in kidney transplant recipients.

To investigate the role of donor-specific indirect pathway T cells in renal transplant tolerance, we analyzed responses in peripheral blood of 45 patients using the trans-vivo delayed-type hypersensitivity assay. Subjects were enrolled into five groups-identical twin, clinically tolerant (TOL), steroid monotherapy (MONO), standard immunosuppression (SI) and chronic rejection (CR)-based on transplant type, posttransplant immunosuppression and graft function. The indirect pathway was active in all groups except twins but distinct intergroup differences were evident, corresponding to clinical status. The antidonor indirect pathway T effector response increased across patient groups (TOL < MONO < SI < CR; p < 0.0001) whereas antidonor indirect pathway T regulatory response decreased (TOL > MONO = SI > CR; p < 0.005). This pattern differed from that seen in circulating naïve B-cell numbers and in a cross-platform biomarker analysis, where patients on monotherapy were not ranked closest to TOL patients, but rather were indistinguishable from chronically rejecting patients. Cross-sectional analysis of the indirect pathway revealed a spectrum in T-regulatory:T-effector balance, ranging from TOL patients having predominantly regulatory responses to CR patients having predominantly effector responses. Therefore, the indirect pathway measurements reflect a distinct aspect of tolerance from the recently reported elevation of circulating naïve B cells, which was apparent only in recipients off immunosuppression.

Relative resistance of human CD4(+) memory T cells to suppression by CD4(+) CD25(+) regulatory T cells.

Successful expansion of functional CD4(+) CD25(+) regulatory T cells (T(reg)) ex vivo under good manufacturing practice conditions has made T(reg) -cell therapy in clinical transplant tolerance induction a feasible possibility. In animals, T(reg) cells home to both transplanted tissues and local lymph nodes and are optimally suppressive if active at both sites. Therefore, they have the opportunity to suppress both naïve and memory CD4(+) CD25(-) T cells (Tresp). Clinical transplantation commonly involves depleting therapy at induction (e.g. anti-CD25), which favors homeostatic expansion of memory T cells. Animal models suggest that T(reg) cells are less suppressive on memory, compared with naïve Tresp that mediate allograft rejection. As a result, in the context of human T(reg) -cell therapy, it is important to define the effectiveness of T(reg) cells in regulating naïve and memory Tresp. Therefore, we compared suppression of peripheral blood naïve and memory Tresp by fresh and ex vivo expanded T(reg) cells using proliferation, cytokine production and activation marker expression (CD154) as readouts. With all readouts, naïve human Tresp were more suppressible by approximately 30% than their memory counterparts. This suggests that T(reg) cells may be more efficacious if administered before or at the time of transplantation and that depleting therapy should be avoided in clinical trials of T(reg) cells.

Differential role of naïve and memory CD4 T-cell subsets in primary alloresponses.

The T cell response to major histocompatibility complex (MHC) alloantigens occurs via two main pathways. The direct pathway involves the recognition of intact allogeneic MHC:peptide complexes on donor cells and provokes uniquely high frequencies of responsive T cells. The indirect response results from alloantigens being processed like any other protein antigen and presented as peptide by autologous antigen-presenting cells. The frequencies of T cells with indirect allospecificity are orders of magnitude lower and comparable to other peptide-specific responses. In this study, we explored the contributions of naïve and memory CD4(+) T cells to these two pathways. Using an adoptive transfer and skin transplantation model we found that naive and memory CD4(+) T cells, both naturally occurring and induced by sensitization with multiple third-party alloantigens, contributed equally to graft rejection when only the direct pathway was operative. In contrast, the indirect response was predominantly mediated by the naïve subset. Elimination of regulatory CD4(+)CD25(+) T cells enabled memory cells to reject grafts through the indirect pathway, but at a much slower tempo than for naïve cells. These findings have implications for better targeting of immunosuppression to inhibit immediate and later forms of alloimmunity.

Clinical operational tolerance after kidney transplantation: a short literature review.

The clinical era of solid organ transplantation started with a renal transplantation (RT) performed between identical twins in Boston in 1954. The patient did not receive any immunosuppression, thus representing the very first case of operational tolerance (Tol). However, more than half a century later, we must admit the inadequacy of our knowledge regarding such a fundamental aspect of transplant immunology, as demonstrated by the fact that Tol has never been achieved in an intention-to-treat protocol. Herein we aim to shortly review the worldwide experience on clinical operational Tol after RT. Thus far, reports on successful cases of Tol after RT have been anecdotal: the largest series included no more than 10 individuals. We will understand that Tol can develop even in the presence of either HLA mismatches or blood group incompatibility at baseline, in the presence of anti-HLA antibodies during follow-up, as well as in patients having experienced acute rejection. Despite the lack of robust evidence, the fact that Tol is often accidentally discovered by transplant physicians during follow-up in noncompliant patients justifies the hypothesis that the real number of Tol cases might be much higher than currently reported.

Significant frequencies of T cells with indirect anti-donor specificity in heart graft recipients with chronic rejection.

BACKGROUND: The purpose of this study was to determine whether T cells with indirect allospecificity could be detected in heart transplant recipients with chronic rejection. METHOD AND RESULTS: Human T-cell clones were used to determine the most effective way to deliver major histocompatibility complex alloantigens for indirect presentation. Seven allograft recipients with evidence of progressive, chronic rejection were selected. Four heart graft recipients with no evidence of chronic rejection were used as controls. Peripheral blood T cells and antigen-presenting cells from the recipients were cultured with frozen/thawed stored donor cells or major histocompatibility complex class I-derived synthetic peptides in limiting dilution cultures and then compared with controls using tetanus toxoid and frozen/thawed third-party cells with no human leukocyte antigens in common with the donor. In 5 of 7 patients analyzed who had chronic rejection, elevated frequencies of T cells with indirect, anti-donor specificity (iHTLf) were detected. No such elevated iHTLf were detected in recipients without chronic rejection. DISCUSSION: iHTLf can be obtained from human transplant recipients, which supports the contention that the indirect pathway is involved in chronic transplant rejection.

Loss of lineage antigens is a common feature of apoptotic lymphocytes.

The analysis of apoptosis in cell populations involves the detection of their specific lineage antigen (LAg) expression. This experimental approach relies on their assumed constant expression, but it is unclear whether such expression is actually maintained during cell death. We examined whether the loss of LAgs is a common feature of apoptotic lymphocytes and whether some might completely lose their LAgs. The changes in the expression of CD3, CD5, CD8, CD4, CD28, CD56, and CD19 were monitored in highly purified lymphocyte populations obtained by negative selection in a fluorescence-activated cell sorter. These were cultured for 24 h with or without phytohemagglutinin or staurosporin. For each LAg-positive subset studied, apoptosis was consistently more common among cells showing partial or total loss of LAg expression compared with cells maintaining their initial LAg levels. The kinetics of expression loss was rapid for CD8, CD56, and CD28, and more than 80% of initial expression was lost in the early stages of apoptosis but was slower for CD3, CD5, and CD4. For CD3 and CD5, expression was dependent on the apoptotic stimulus used. It is interesting that loss of antigen expression was independent of cell size. This phenomenon was also found in nonmanipulated, highly pure CD19 B lymphocytes of peripheral blood mononuclear cells from B chronic lymphocytic leukemia patients. Loss of LAg expression appeared to be a common feature of apoptotic lymphocytes under all the conditions assayed. The different kinetic patterns of LAg loss suggest apoptotic cells might actively regulate this process.

The role of the allograft in the induction of donor-specific T cell hyporesponsiveness.

BACKGROUND: With adequate immunosuppression the majority of renal allografts are accepted, despite the exceptional vigour of the T cell alloimmune response. Previous work from this laboratory has demonstrated that this is accompanied by significant reductions in the precursor frequencies of anti-donor T cells. We have also shown that parenchymal cells are tolerogenic in vitro. We propose that the reduction in T cell frequencies may be due to the interaction between circulating T cells and potentially tolerogenic graft parenchymal cells. Primed/memory T cells (CD45RO+) are the only subset capable of reaching the allograft and therefore we would predict that T cell hyporesponsiveness would develop predominantly in the CD45RO+ subset due to their trafficking properties. METHODS: Frequencies of IL-2 secreting CD45RA+ and CD45RO+ CD4+ T cells in response to donor and third party stimulator cells were estimated in a series of renal transplant recipients, both before and after transplantation. RESULTS: There were highly significant reductions in the frequencies of donor-specific CD4+CD45RO+ T cells, when adjusted to control for the generalised effects of immunosuppression. There were no significant alterations in the frequencies of donor-specific CD4+CD45RA+ T cells. CONCLUSIONS: In renal transplant recipients, donor-specific CD4+ T cell hyporesponsiveness occurs predominantly in CD4+ CD45RO+ T cells which is the subset capable of trafficking through the graft.

Allorecognition and the alloresponse: clinical implications.

The artificial transfer of tissues or cells between genetically diverse individuals elicits an immune response that is adaptive and specific. This response is orchestrated by T lymphocytes that are recognizing, amongst others, major histocompatibility complex (MHC) molecules expressed on the surface of the transferred cells. Three pathways of recognition are described: direct, indirect and semi-direct. The sets of antigens that are recognized in this setting are also discussed, namely, MHC protein products, the MHC class I-related chain (MIC) system, minor histocompatibility antigens and natural killer cell receptor ligands. The end product of the effector responses are hyperacute, acute and chronic rejection. Special circumstances surround the situation of pregnancy and bone marrow transplantation because in the latter, the transferred cells are the ones originating the immune response, not the host. As the understanding of these processes improves, the ability to generate clinically viable immunotherapies will increase.

Multiparameter immune profiling of operational tolerance in liver transplantation.

Immunosuppressive drugs can be completely withdrawn in up to 20% of liver transplant recipients, commonly referred to as 'operationally' tolerant. Immune characterization of these patients, however, has not been performed in detail, and we lack tests capable of identifying tolerant patients among recipients receiving maintenance immunosuppression. In the current study we have analyzed a variety of biological traits in peripheral blood of operationally tolerant liver recipients in an attempt to define a multiparameter 'fingerprint' of tolerance. Thus, we have performed peripheral blood gene expression profiling and extensive blood cell immunophenotyping on 16 operationally tolerant liver recipients, 16 recipients requiring on-going immunosuppressive therapy, and 10 healthy individuals. Microarray profiling identified a gene expression signature that could discriminate tolerant recipients from immunosuppression-dependent patients with high accuracy. This signature included genes encoding for gammadelta T-cell and NK receptors, and for proteins involved in cell proliferation arrest. In addition, tolerant recipients exhibited significantly greater numbers of circulating potentially regulatory T-cell subsets (CD4+ CD25+ T-cells and Vdelta1+ T cells) than either non-tolerant patients or healthy individuals. Our data provide novel mechanistic insight on liver allograft operational tolerance, and constitute a first step in the search for a non-invasive diagnostic signature capable of predicting tolerance before undergoing drug weaning.

The alloresponse.

The alloresponse can be divided into two components. The first of these is allorecognition, which refers to the recognition of antigens, expressed on the surface of cells of non-self origin, by the host's lymphocytes. The second part is the immune effector mechanisms generated by this recognition process. The molecules recognised have been termed histocompatibility antigens and fall into two categories. The strongest responses are provoked by allogeneic major histocompatibility complex (MHC) antigens. T cells recognise these antigens either directly or after being processed like conventional antigens by antigen-presenting cells, in what has been termed indirect presentation. In the context of MHC identity, responses are observed against the second category of antigens, namely minor histocompatibility antigens (mHAgs). Although weaker, these responses are of clinical importance, particularly in bone marrow transplant recipients. CD4+ T cells play a central role in orchestrating the immune response to alloantigens. They secrete cytokines to attract effector cells, such as macrophages and CD8+ T cells, into the graft and are able to interact with B cells that will secrete highly specific alloreactive antibodies. In clinical terms, the result of the immune response to transplanted allografts can be classified as hyperacute rejection, acute and chronic rejection. The immunological effector mechanisms involved in each of these processes are discussed.

A low blood lymphocyte count is associated with an expansion of activated cytotoxic lymphocytes in patients with B-cell chronic lymphocytic leukaemia.

In order to determine the relationships between CD2+ lymphocyte subpopulations and tumour mass, the immunophenotype of natural killer (NK) cells and T lymphocyte subsets was studied in 56 B-chronic lymphocytic leukaemia (B-CLL) patients and 38 healthy subjects. The patients were classified according to their blood lymphocyte count (BLC). Forty patients had BLC<30x10(9)/l (low BLC, less tumour mass) and 16 patients had BLC>30x10(9)/l (high BLC, larger tumour mass). The percentage of CD3- CD56+ cells, as well as of CD8+, CD8+ CD45RO+ and CD3+ CD57+ T subsets in low BLC patients, were higher than those found in high BLC patients. Conversely, the percentages of CD3+ HLA x DR+, CD4+ and CD4+ CD45RO+ lymphocytes were higher in high BLC patients than in low BLC patients. The CD4/CD8 ratio was decreased in low BLC patients while it was increased in high BLC patients and a significant positive correlation was found between their CD4/CD8 ratio and their BLC. We conclude that in low BLC B-CLL patients there is a decreased percentage of activated helper lymphocytes and an increased percentage of NK cells and activated cytotoxic T lymphocytes. These results suggest a role for NK cells, and helper and cytotoxic T lymphocytes in the control of tumour burden in B-CLL patients.