Immune regulation and graft survival in kidney transplant recipients are both enhanced by human leukocyte antigen matching

An exome-wide study of renal operational tolerance

Background

Renal operational tolerance is a rare and beneficial state of prolonged renal allograft function in the absence of immunosuppression. The underlying mechanisms are unknown. We hypothesized that tolerance might be driven by inherited protein coding genetic variants with large effect, at least in some patients.

Methods

We set up a European survey of over 218,000 renal transplant recipients and collected DNAs from 40 transplant recipients who maintained good allograft function without immunosuppression for at least 1 year. We performed an exome-wide association study comparing the distribution of moderate to high impact variants in 36 tolerant patients, selected for genetic homogeneity using principal component analysis, and 192 controls, using an optimal sequence-kernel association test adjusted for small samples.

Results

We identified rare variants of HOMER2 (3/36, FDR 0.0387), IQCH (5/36, FDR 0.0362), and LCN2 (3/36, FDR 0.102) in 10 tolerant patients vs. 0 controls. One patient carried a variant in both HOMER2 and LCN2. Furthermore, the three genes showed an identical variant in two patients each. The three genes are expressed at the primary cilium, a key structure in immune responses.

Conclusion

Rare protein coding variants are associated with operational tolerance in a sizable portion of patients. Our findings have important implications for a better understanding of immune tolerance in transplantation and other fields of medicine.ClinicalTrials.gov, identifier: NCT05124444.

Operational tolerance in kidney transplantation and associated biomarkers

In the 1960s, our predecessors won a historical battle against acute rejection and ensured that transplantation became a common life-saving treatment. In parallel with this success, or perhaps because of it, we lost the battle for long-lived transplants, being overwhelmed with chronic immune insults and the toxicities of immunosuppression. It is likely that current powerful treatments block acute rejection, but at the same time condemn the few circulating donor cells that would have been able to elicit immunoregulatory host responses towards the allograft. Under these conditions, spontaneously tolerant kidney recipients - i.e. patients who maintain allograft function in the absence of immunosuppression - are merely accidents; they are scarce, mysterious and precious. Several teams pursue the goal of finding a biomarker that would guide us towards the 'just right' level of immunosuppression that avoids rejection while leaving some space for donor immune cells. Some cellular assays are attractive because they are antigen-specific, and provide a comprehensive view of immune responses toward the graft. These seem to closely follow patient regulatory capacities. However, these tests are cumbersome, and require abundant cellular material from both donor and recipient. The latest newcomers, non-antigen-specific recipient blood transcriptomic biomarkers, offer the promise that a practicable and simple signature may be found that overcomes the complexity of a system in which an infinite number of individual cell combinations can lead possibly to graft acceptance. Biomarker studies are as much an objective - identifying tolerant patients, enabling tolerance trials - as a means to deciphering the underlying mechanisms of one of the most important current issues in transplantation.

A New Window into the Human Alloresponse

Alloreactive T lymphocytes are the primary mediators of allograft rejection. The size and diversity of the HLA-alloreactive T cell repertoire has thus far precluded the ability to follow these T cells and thereby to understand their fate in human transplant recipients. This review summarizes the history, challenges, and recent advances in the study of alloreactive T cells. We highlight the historical development of assays to measure alloreactivity and discuss how high-throughput T cell receptor (TCR) sequencing-based assays can provide a new window into the fate of alloreactive T cells in human transplant recipients. A specific approach combining a classical in vitro assay, the mixed lymphocyte reaction, with deep T cell receptor sequencing is described as a tool to track the donor-reactive T cell repertoire for any specific HLA-mismatched donor-recipient pair. This assay can provide mechanistic insights and has potential as a noninvasive, highly specific biomarker for rejection and tolerance.

Th17 Responses to Collagen Type V, kα1-Tubulin, and Vimentin Are Present Early in Human Development and Persist Throughout Life

T helper 17 (Th17)-dependent autoimmune responses can develop after heart or lung transplantation and are associated with fibro-obliterative forms of chronic rejection; however, the specific self-antigens involved are typically different from those associated with autoimmune disease. To investigate the basis of these responses, we investigated whether removal of regulatory T cells or blockade of function reveals a similar autoantigen bias. We found that Th17 cells specific for collagen type V (Col V), kα1-tubulin, and vimentin were present in healthy adult peripheral blood mononuclear cells, cord blood, and fetal thymus. Using synthetic peptides and recombinant fragments of the Col V triple helical region (α1[V]), we compared Th17 cells from healthy donors with Th17 cells from Col V-reactive heart and lung patients. Although the latter responded well to α1(V) fragments and peptides in an HLA-DR-restricted fashion, Th17 cells from healthy persons responded in an HLA-DR-restricted fashion to fragments but not to peptides. Col V, kα1-tubulin, and vimentin are preferred targets of a highly conserved, hitherto unknown, preexisting Th17 response that is MHC class II restricted. These data suggest that autoimmunity after heart and lung transplantation may result from dysregulation of an intrinsic mechanism controlling airway and vascular homeostasis.

HLA Genotyping in Patients with End-Stage Renal Disease Waiting For Cadaveric Renal Transplantation in Federation of Bosnia and Herzegovina

AIM

The research was conducted by genotyping two Human Leukocyte Antigen (HLA) gene classes. The main objective of this research was to investigate distribution and frequency of the allelic groups, genotypes and haplotypes in the gene loci of HLA class I (HLA-A*, -B*, -C*) and HLA class II (HLA-DRB1*, -DQB1*) in patients included in the program of cadaveric renal transplantation.

MATERIAL AND METHODS

Our study covered 186 blood samples of patients who are registered on the list for cadaveric renal transplantation in Federation of Bosnia and Herzegovina and included 59 control, healthy unrelated individuals. For the HLA typing, we have used three different methods: micro lymphocyte cytotoxicity test (MLCT), Polymerase Chain Reaction (PCR) - Sequence Specific Primers (SSP) and PCR - Sequence-Specific Oligonucleotides (SSO) or Luminex technology. All patients and cadaveric donors were tested using the three methods because the system is polymorphic.

RESULTS

Analysis of the results of genotyping HLA class I gene loci identified dominant HLA-A*02, HLA-B*35, HLA-C*07 allelic groups. Analysis of the HLA class II gene loci genotyping showed that HLA-DRB1*11 and HLA-DQB1*03 loci had the highest incidence in HLA class II.

CONCLUSION

Based on our results and previous research, there were no observed differences between allelic frequencies and genotypes of healthy people and people with ESRD. Differences between allelic groups occurred, but they were not statistically significant, except HLA-C*01 (p = 0.020).

Immunologic prognostic factors of renal allograft survival

INTRODUCTION

Successful outcome of renal transplantation depends on various factors, of which immunologic is one of the most important. Accumulated experience of a single center, with the same surgical and immunological team contributes significantly to safe conclusions. Purpose of this study was the evaluation of potential factors, in particular immunologic, that influence renal allograft survival.

PATIENTS AND METHODS

During the period 1991-2013, 20,784 surgical operations have been performed in our Department of Surgery - Transplant Unit, of which 575 were renal transplantations. We examined donor and recipient demographic factors, immunologic characteristics along with patient and graft survival.

RESULTS

Renal allograft was retrieved from living-related donor in 103 cases and in 472 from cadaveric donor. Donor age was 46.7 ± 18.5 years old and 49.9% (287) were male. Recipient age was 48 ± 12.3 years old and 402 were male. HLA histocompatibility was carefully matched resulting in 85.5% renal transplants with 2-4 HLA mismatches and 93.8% renal transplants with at least one HLA-DR. Renal graft survival the first, fifth and tenth year was 89%, 76%, and 67% and patient survival was respectively 95%, 89% and 83%. Statistical analysis revealed that only donor age influenced renal graft survival (P < .05). HLA mismatches were not correlated with graft survival (log rank P = .495), but identification of panel reactive antibodies (PRA) class I and class II post transplantation had a statistically significant impact on long term renal graft survival (log rank P < .001 and P = .021, accordingly).

CONCLUSIONS

Analysis of potential prognostic factor showed that only donor age was correlated with allograft survival. Development of PRA following renal transplantation influenced long term graft survival. Good HLA matching with at least one HLA DR resulted in excellent graft and patient survival.

Differential requirement for P2X7R function in IL-17 dependent vs. IL-17 independent cellular immune responses

IL17-dependent autoimmunity to collagen type V (Col V) has been associated with lung transplant obliterative bronchiolitis. Unlike the T helper 1 (Th1)-dependent immune responses to Tetanus Toxoid (TT), the Th17 response to Col V in lung transplant patients and its Th1/17 variant observed in coronary artery disease patients requires IL-1β, tumor necrosis factor α and CD14(+) cells. Given the involvement of the P2X7 receptor (P2X7R) in monocyte IL-1β responses, we investigated its role in Th17-, Th1/17- and Th1-mediated proinflammatory responses. Transfer of antigen-pulsed peripheral blood mononucleated cells (PBMCs) from Col V-reactive patients into SCID mouse footpads along with P2X7R antagonists revealed a selective inhibition of Col V-, but not TT-specific swelling responses. P2X7R inhibitors blocked IL-1β induction from monocytes, including both Col V-α1 peptide-induced (T-dependent), as well as native Col V-induced (T-independent) responses. Significantly higher P2X7R expression was found on CXCR3(neg) CCR4(+)/6(+) CD4(+) [Th17] versus CXCR3(+)CCR4/6(neg) CD4(+) [Th1] subsets in PBMCs, suggesting that the paradigm of selective dependence on P2X7R might extend beyond Col V autoimmunity. Indeed, P2X7R inhibitors suppressed not only anti-Col V, but also Th1/17-mediated alloimmunity, in a heart transplant patient without affecting anti-viral Epstein-Barr virus responses. These results suggest that agents targeting the P2X7R might effectively treat Th17-related transplant pathologies, while maintaining Th1-immunity to infection.

Trans-vivo delayed type hypersensitivity assay for antigen specific regulation

Delayed-type hypersensitivity response (DTH) is a rapid in vivo manifestation of T cell-dependent immune response to a foreign antigen (Ag) that the host immune system has experienced in the recent past. DTH reactions are often divided into a sensitization phase, referring to the initial antigen experience, and a challenge phase, which usually follows several days after sensitization. The lack of a delayed-type hypersensitivity response to a recall Ag demonstrated by skin testing is often regarded as an evidence of anergy. The traditional DTH assay has been effectively used in diagnosing many microbial infections. Despite sharing similar immune features such as lymphocyte infiltration, edema, and tissue necrosis, the direct DTH is not a feasible diagnostic technique in transplant patients because of the possibility of direct injection resulting in sensitization to donor antigens and graft loss. To avoid this problem, the human-to-mouse "trans-vivo" DTH assay was developed (1,2). This test is essentially a transfer DTH assay, in which human peripheral blood mononuclear cells (PBMCs) and specific antigens were injected subcutaneously into the pinnae or footpad of a naïve mouse and DTH-like swelling is measured after 18-24 hr (3). The antigen presentation by human antigen presenting cells such as macrophages or DCs to T cells in highly vascular mouse tissue triggers the inflammatory cascade and attracts mouse immune cells resulting in swelling responses. The response is antigen-specific and requires prior antigen sensitization. A positive donor-reactive DTH response in the Tv-DTH assay reflects that the transplant patient has developed a pro-inflammatory immune disposition toward graft alloantigens. The most important feature of this assay is that it can also be used to detect regulatory T cells, which cause bystander suppression. Bystander suppression of a DTH recall response in the presence of donor antigen is characteristic of transplant recipients with accepted allografts (2,4-14). The monitoring of transplant recipients for alloreactivity and regulation by Tv-DTH may identify a subset of patients who could benefit from reduction of immunosuppression without elevated risk of rejection or deteriorating renal function. A promising area is the application of the Tv-DTH assay in monitoring of autoimmunity(15,16) and also in tumor immunology (17).

Bidirectional alloreactivity: A proposed microchimerism-based solution to the NIMA paradox

The NIMA paradox is the observation that in transplants of allogeneic kidneys or hematopoietic stem cells, siblings benefit from re-exposure to non-inherited maternal antigens (NIMA), whereas re-exposure to a transplant from mother herself, theoretically the ideal "NIMA" donor, does not yield clinical results superior to a father-donated allograft. Recent observations of bidirectional alloreactivity in kidney and cord blood transplantation offer a possible solution to this paradox. If correct, the proposed solution points the way to clinical applications of microchimerism in solid organ and hematopoetic transplants.

Monitoring tolerance and rejection in organ transplant recipients

To avoid toxic side effects caused by permanent immunosuppressive treatment, research in transplantation focuses on new treatment strategies inducing tolerance or allowing drug weaning. Implementing drug minimization into clinical routine can be only safely achieved when guided by biomarkers reflecting the individual immune reactivity. We review recently described biomarkers and assays allowing identification of patients suitable for drug weaning or at risk of rejection. However, the majority of described biomarkers and assays have not been validated in prospective clinical trials. Thus, collaborative efforts are needed to design and perform prospective multicenter trials to validate the identified biomarkers across different laboratories.

Approaching the promise of operational tolerance in clinical transplantation

Long-term acceptance of transplanted organs without requirement for indefinite immunosuppression remains the ultimate goal of transplant clinicians and scientists. This clinical state of allograft acceptance termed "operational tolerance" has been elusive in routine practice. However, there are published reports of recipients where immunosuppression has been discontinued, by intention or patient noncompliance, in which the outcome is a nondestructive immune response and normal function. The question now arises how clinical operational tolerance might be achieved in the majority of recipients. This review provides an overview of current approaches to achieve operational tolerance, including the use of donor bone marrow and depletion of recipient T cells and the resistance of liver transplants to rejection. It also describes the key role of clinical immune monitoring and future approaches to tolerance induction including inhibition of T-cell signaling, manipulation of costimulatory pathways, and expansion of regulatory T cells. The principles of these experimental approaches may ultimately be extended to provide safe and effective control of transplant rejection and induction of clinical operational tolerance.

Anticardiac myosin immunity and chronic allograft vasculopathy in heart transplant recipients

Chronic allograft vasculopathy (CAV) contributes to heart transplant failure, yet its pathogenesis is incompletely understood. Although cellular and humoral alloimmunity are accepted pathogenic mediators, animal models suggest that T cells and Abs reactive to graft-expressed autoantigens, including cardiac myosin (CM), could participate. To test the relationship between CAV and anti-CM autoimmunity in humans, we performed a cross-sectional study of 72 heart transplant recipients: 40 with CAV and 32 without. Sera from 65% of patients with CAV contained anti-CM Abs, whereas <10% contained Abs to other autoantigens (p < 0.05), and only 18% contained anti-HLA Abs (p < 0.05 versus anti-CM). In contrast, 13% of sera from patients without CAV contained anti-CM Abs (p < 0.05; odds ratio [OR], associating CAV with anti-CM Ab = 13, 95% confidence interval [CI] 3.79-44.6). Multivariable analysis confirmed the association to be independent of time posttransplant and the presence of anti-HLA Abs (OR = 28, 95% CI 5.77-133.56). PBMCs from patients with CAV responded more frequently to, and to a broader array of, CM-derived peptides than those without CAV (p = 0.01). Detection of either CM-peptide-reactive T cells or anti-CM Abs was highly and independently indicative of CAV (OR = 45, 95% CI 4.04-500.69). Our data suggest detection of anti-CM immunity could be used as a biomarker for outcome in heart transplantation recipients and support the need for further studies to assess whether anti-CM immunity is a pathogenic mediator of CAV.

Steroid avoidance in two-haplotype-matched living donor renal transplants with basiliximab induction therapy

BACKGROUND

Induction therapy and haplotype matching are utilized to mitigate immunologic risk in renal transplantation. The incidence of acute rejection (AR) of renal allografts has been reported to be as low as 9.3% within the first year among two-haplotype-matched siblings with no induction and triple-drug maintenance immunosuppression. We report our use of basiliximab induction in a series of two-haplotype-matched living donor renal transplants (LDRT).

METHODS

We retrospectively reviewed 25 patients who received a two-haplotype-matched LDRT with basiliximab induction therapy. The primary endpoints were acute rejection (AR) episodes at 6 and 12 months and 1-year patient and graft survival rates. The secondary endpoints were the incidence of delayed graft function (DGF), cytomegalovirus (CMV), and BK virus (BKV).

RESULTS

The rate of AR at 6 months was 0% (0/25) and 4% (1/25) at 12 months. The 1-year graft and patient survival rates were 100%. The incidence of DGF was 4% (1/25), while the incidences of CMV and BKV were 0%.

CONCLUSION

Basiliximab induction therapy with a steroid-sparing regimen yields favorable results in two-haplotype-matched LDRT, including a notable reduction in the rates of AR as compared to triple-drug maintenance immunosuppression without induction. These patients have excellent graft survival with no increased incidences of secondary infections.

HLA-A, -B, and -DR zero-mismatched kidneys shipped to the University of Wisconsin, Madison, 1993-2006: superior graft survival despite longer preservation time

BACKGROUND

To determine the impact at a single center of the United Network for Organ Sharing-mandated sharing program for human leukocyte antigen (HLA)-A/-B/-DR 0-mismatched (0MM) kidneys, we analyzed the results of 264 kidney transplants from 0MM distant donors between 1993 and 2006, with a follow-up through January 31, 2007. We compared these results with that of concurrent kidneys transplanted from HLA more than 0MM local donors and with shipped more than 0MM kidneys from "payback" donors.

RESULTS

Despite a significantly longer preservation time, we found an 11% increase in 8-year graft survival (63% vs. 52%; P<0.003) of 0MM shipped versus locally procured, >0MM donor kidneys. Graft survival of 0MM shipped kidneys at 8 years was significantly better in nonsensitized (<20% panel reactive antibodies; 68% vs. 55%; P<0.0005) but not in sensitized (>or=20% panel reactive antibodies) recipients, who showed an early (2 years) but short-lived benefit. The benefit of receiving a HLA-A, -B, and -DR 0MM shipped kidney remained strong and statistically significant (0.71 relative risk of graft loss vs. local; P<0.02) when adjusted for 22 potentially confounding variables in a Cox proportional hazards analysis.

CONCLUSIONS

The recent change in United Network for Organ Sharing policy restricting mandated sharing of 0MM kidneys to sensitized and pediatric recipients will give greater flexibility to the local organ procurement organization in allocating organs. However, the survival benefit to nonsensitized patients is real and long lasting and will be lost.

Interleukin-17-dependent autoimmunity to collagen type V in atherosclerosis

RATIONALE

Considerable evidence shows atherosclerosis to be a chronic inflammatory disease in which immunity to self-antigens contributes to disease progression. We recently identified the collagen type V [col(V)] α1(V) chain as a key autoantigen driving the Th17-dependent cellular immunity underlying another chronic inflammatory disease, obliterative bronchiolitis. Because specific induction of α1(V) chains has previously been reported in human atheromas, we postulated involvement of col(V) autoimmunity in atherosclerosis.

OBJECTIVE

To determine whether col(V) autoimmunity may be involved in the pathogenesis of atherosclerosis.

METHODS AND RESULTS

Here, we demonstrate Th17-dependent anti-col(V) immunity to be characteristic of atherosclerosis in human coronary artery disease (CAD) patients and in apolipoprotein E-null (ApoE(-/-)) atherosclerotic mice. Responses were α1(V)-specific in CAD with variable Th1 pathway involvement. In early atherosclerosis in ApoE(-/-) mice, anti-col(V) immunity was tempered by an interleukin (IL)-10-dependent mechanism. In support of a causal role for col(V) autoimmunity in the pathogenesis of atherosclerosis, col(V) sensitization of ApoE(-/-) mice on a regular chow diet overcame IL-10-mediated inhibition of col(V) autoimmunity, leading to increased atherosclerotic burden in these mice and local accumulation of IL-17-producing cells, particularly in the col(V)-rich adventitia subjacent to the atheromas.

CONCLUSIONS

These findings establish col(V) as an autoantigen in human CAD and show col(V) autoimmunity to be a consistent feature in atherosclerosis in humans and mice. Furthermore, data are consistent with a causative role for col(V) in the pathogenesis of atherosclerosis.

Decreased T-cell responses to influenza vaccination in patients with heart failure

STUDY OBJECTIVE

To determine whether T-cell immune responses to influenza vaccination in patients with chronic heart failure (CHF) are less vigorous than the responses of healthy control subjects.

DESIGN

Prospective, single-center study.

SETTING

University hospital and research laboratory.

PARTICIPANTS

Eighteen adults with stable CHF receiving optimal treatment and 16 healthy control subjects.

INTERVENTION

Participants were immunized with the 2006-2007 trivalent inactivated (killed) influenza vaccine during October-December of 2006.

MEASUREMENTS AND MAIN RESULTS

Blood samples were taken from the participants before and 2-4 weeks after vaccination to measure antibody titers, which were measured with a hemagglutination inhibition assay, then 3-4 months after vaccination to assess T-cell responses, measured by using the trans vivo delayed-type hypersensitivity method. As part of this method, which mimics physiologic conditions, peripheral blood mononuclear cells were isolated from the blood samples. The cells were mixed with influenza vaccine antigens A/H1N1, A/H3N2, and B type and injected into the footpads of SCID mice (mice with severe combined immunodeficiency), as their resulting swelling is an index of human T-cell sensitization. Median T-cell-mediated immune responses to A/H3N2 were less vigorous in patients with CHF than in control subjects (62.5 vs 87.5 microm, unadjusted p=0.031, age-adjusted p=0.006). Median responses to A/H1N1 were not significantly different between the groups (56.3 vs 75 microm, p=0.11). Median responses to B type were also similar between the groups (62.5 vs 75 microm, p=0.47). All participants mounted an antibody response to the influenza vaccine.

CONCLUSION

Patients with CHF had reduced T-cell responses to the influenza vaccine compared with healthy control subjects, as demonstrated by a lower response to A/H3N2, the newest antigen in the 2006-2007 vaccine. However, differences in T-cell immune responses to the A/H1N1 and B type strains were not found to be significant between the two groups, which suggests that patients with CHF can mount an appropriate response to vaccine antigens to which they have been previously exposed, but less so to new antigens. These findings suggest that patients with CHF may be at increased risk for influenza infection, and clinicians may want to investigate other or additional strategies for influenza vaccination.

Successful reduction of immunosuppression in older renal transplant recipients who exhibit donor-specific regulation

BACKGROUND

We hypothesized that T-regulatory cells specific for donor alloantigens would protect a renal transplant during partial withdrawal of immunosuppression.

METHODS

To test this hypothesis, 32 renal transplant recipients aged 55 years and older with excellent renal function were tested for donor-specific regulation (DSR) by trans-vivo delayed type hypersensitivity assay at the time of enrollment (T=0) and 6 months later (T=6). Twenty-two patients had prednisone withdrawn during a 3-month period, whereas 10 controls were maintained on triple therapy (prednisone, cyclosporine, and mycophenolate).

RESULTS

Of 22 patients in the steroid withdrawal group, 10 were DSR+ and 12 were DSR- at the time of enrollment (T=0). None of the DSR+ patients experienced acute rejection, nor did any have donor-specific human leukocyte antigen (HLA) antibody during or after withdrawal. Of 12 DSR- patients, three developed acute rejection, which were reversed with bolus steroid treatment, and four were donor-specific antibody+ at T=0 or T=6. Two years later, 80% (8 of 10) of DSR+ patients in the withdrawal group remain steroid free while maintaining excellent renal function, as compared with only 58% (7 of 12) DSR- patients. Patient survival at 4 years was similar for DSR+ (9 of 10) and DSR- (11 of 12) patients in the withdrawal group. Patients maintained on triple therapy remained rejection free during the 4-year follow-up regardless of initial DSR status, with patient survival rate of 70% (7 of 10).

CONCLUSIONS

DSR before steroid withdrawal may identify a subset of transplant patients who could benefit from reduction of immunosuppression without elevated risk of rejection or deteriorating renal function.

Early and limited use of tacrolimus to avoid rejection in an alemtuzumab and sirolimus regimen for kidney transplantation: clinical results and immune monitoring

Alemtuzumab induction with 60 days of tacrolimus treatment and continuous sirolimus treatment prevented acute rejection in nine of 10 consecutive renal allograft recipients. All patients are alive with a functioning kidney graft at 27-39 months of follow-up. Extensive immune monitoring was performed in all patients. Alloantibody detection, cytokine kinetics assay (CKA), and trans vivo delayed-type hypersensitivity (DTH) assay were performed every 6 months showing correlation with clinical evolution. Despite alloantibody presence in five patients, eight patients remain without the need for specific treatment and only sirolimus monotherapy in decreasing dosage. Four patients take only 1 mg sirolimus daily with levels of 3-4 ng/mL. One patient showed clinical signs of rejection at month 9 post-transplant, with slow increase in serum creatinine and histological signs of mixed cellular (endarteritis) and humoral rejection (C4d positivity in peritubular capillaries and donor-specific antibody (DSA)). In summary, the addition of tacrolimus therapy for 2 months to a steroid-free, alemtuzumab induction and sirolimus maintenance protocol limited the previously shown acute rejection development. Nevertheless, alloantibody was present in serum and/or C4d present on 1-year biopsy in half the patients. The combination of CKA and DSA monitoring or the performance of transvivo DTH correlated with immune status of the patients.

Analysis of indirect pathway CD4+ T cells in a patient with metastable tolerance to a kidney allograft: possible relevance to superior graft survival of HLA class II closely matched renal allografts

MHC class I mismatched, but class II matched kidney transplants are tolerogenic in large animal models. CD4(+) T regulatory cells specific for HLA-B1501-derived peptide p37-MA (DSDAASPRMAPRAPWIEQ) developed in a long term (>12 years) tolerant patient who received an HLA-B1501 mismatched, HLA class II closely matched renal allograft. We hypothesized that class II matching favored T regulatory cell development by allowing allopeptide presentation on either recipient (DR4/DQ7(+)) or donor (DR4/DQ8(+)) antigen presenting cells (APC). Indirect pathway CD4(+) T cell clones were generated from recipient PBMC by sorting antigen-stimulated, proliferating cells. Most clones responded to p37-MA-pulsed B1501(-) autologous, but not to DQ8(+)B1501(+) donor B-lymphoblastoid cell lines (B-LCL). However, some clones responded to both; in fact, one responded even more strongly to donor B-LCL than to p37-MA-pulsed autologous B-LCL. P37-MA contained a DQ8-binding motif and induced strong TH1 responses from DQ8 but not DQ6 transgenic mice. Microchimerism was found to be enriched in the dendritic cells (DC) cultured from adherent PBMC. This indicates donor APC could possibly present p37-MA peptide directly to p37-MA specific T cells. These data support the concept that, when the donor is MHC class II closely matched, a "hybrid" form of allorecognition (direct/indirect) occurs. This may favor the generation of a beneficial form of indirect pathway alloreactivity, i.e. allopeptide-specific CD4(+) T regulatory cells, in the context of long term DC microchimerism.

A model for human leukocyte antigen-matched donor-swap transplantation in India

BACKGROUND

In developing countries such as India, extending donor-swap transplantation (DSTx) to human leukocyte antigen (HLA)-mismatched patient-donor pairs would increase well-matched living donor kidney transplantation rates, resulting in use of less immunosuppression and less expenses, lower infective morbidity, and better survival. A model for DSTx based on HLA matching is presented.

METHODS

Consecutive HLA class 1 antigen (A, B) tests of prospective renal allograft recipients and their related donors, performed at a single center in India was analyzed retrospectively using an HLA matching program to determine the proportion of prospective recipients with poorly matched related donors who could have benefited by DSTx based on HLA matching.

RESULTS

Over the past 17.5 years, 2,129 prospective renal allograft recipients and 2,890 donors were tested for HLA class I (A and B) antigens. Of the prospective recipients, 33% did not have well-matched donors (defined as blood group compatible and sharing > or =2 of 4 HLA class I antigens). Among such recipients, 19.2% could have found a well-matched donor-swap pair within a year at a single center. This number would increase to 38% if four major national centers were involved with a shared HLA registry.

CONCLUSIONS

Nearly 40% of prospective recipients without well-matched donors would find a donor-swap pair based on HLA matching within a year, with coordination among four national centers and a shared HLA registry, increasing the well-matched living donor renal transplant rates and improving transplant outcomes. This finding is relevant in the context of Indian government amending the Transplantation of Human Organs Act to encourage DSTx.

IL-17-dependent cellular immunity to collagen type V predisposes to obliterative bronchiolitis in human lung transplants

Bronchiolitis obliterans syndrome (BOS), a process of fibro-obliterative occlusion of the small airways in the transplanted lung, is the most common cause of lung transplant failure. We tested the role of cell-mediated immunity to collagen type V [col(V)] in this process. PBMC responses to col(II) and col(V) were monitored prospectively over a 7-year period. PBMCs from lung transplant recipients, but not from healthy controls or col(IV)-reactive Goodpasture's syndrome patients after renal transplant, were frequently col(V) reactive. Col(V)-specific responses were dependent on both CD4+ T cells and monocytes and required both IL-17 and the monokines TNF-alpha and IL-1beta. Strong col(V)-specific responses were associated with substantially increased incidence and severity of BOS. Incidences of acute rejection, HLA-DR mismatched transplants, and induction of HLA-specific antibodies in the transplant recipient were not as strongly associated with a risk of BOS. These data suggest that while alloimmunity initiates lung transplant rejection, de novo autoimmunity mediated by col(V)-specific Th17 cells and monocyte/macrophage accessory cells ultimately causes progressive airway obliteration.

Th-17, monokines, collagen type V, and primary graft dysfunction in lung transplantation

RATIONALE

The pathogenesis of primary graft dysfunction (PGD), a serious complication of lung transplantation, is poorly understood. Human studies and rodent models have shown that collagen type V (col[V]), stimulates IL-17-dependent cellular immunity after lung transplantation.

OBJECTIVES

To determine whether patients with end-stage lung disease develop pretransplant col(V)-specific cellular immunity, and if so, the impact of this response on PGD.

METHODS

Trans-vivo delayed-type hypersensitivity (TV-DTH) assays were used to evaluate memory T-cell responses to col(V) in 55 patients awaiting lung transplantation. Pa(O(2))/Fi(O(2)) index data were used to assess PGD. Univariate risk factor analysis was performed to identify variables associated with PGD. Rats immunized with col(V) or irrelevant antigen underwent lung isografting to determine if prior anti-col(V) immunity triggers PGD in the absence of alloreactivity.

MEASUREMENTS AND MAIN RESULTS

We found that 58.8% (10/17) of patients with idiopathic pulmonary fibrosis, and 15.8% (6/38) of patients without idiopathic pulmonary fibrosis tested while on the wait list for a lung transplant were col(V) DTH positive. Col(V) reactivity was CD4(+) T-cell and monocyte mediated, and dependent on IL-17, IL-1beta, and tumor necrosis factor (TNF)-alpha. Pa(O(2))/Fi(O(2)) indices were impaired significantly 6-72 hours after transplantation in col(V)-reactive versus nonreactive patients. Univariate risk factor analysis identified only preoperative TV-DTH to col(V) and ischemic time as predictors of PGD. Finally, in a rat lung isograft model, col(V) sensitization resulted in significantly lower Pa(O(2))/Fi(O(2)), increased local TNF-alpha and IL-1beta production, and a moderate-to-severe bronchiolitis/vasculitis when compared with control isografts.

CONCLUSIONS

The data suggest that activation of innate immunity by col(V)-specific Th-17 memory cells represents a novel pathway to PGD after lung transplantation.

Mouse strain and injection site are crucial for detecting linked suppression in transplant recipients by trans-vivo DTH assay

Chemokine-driven accumulation of lymphocytes, mononuclear and polymorphonuclear proinflammatory cells in antigenic tissue sites is a key feature of several types of T-cell-dependent autoimmunity and transplant rejection pathology. It is now clear that the immune system expends considerable energy to control this process, exemplified by the sequential layers of regulatory cell input, both innate and adaptive, designed to prevent a classical Type IV or 'delayed-type' hypersensitivity (DTH) reaction from occurring in the visual field of the eye. Yet, despite an abundance of in vitro assays currently available to the human T-cell immunologist, none of them adequately models the human DTH response and its various control features. The theme of this article is that it is relatively easy to model the effector side of the human DTH response with xenogeneic adoptive transfer models. However, we show that in order to detect inhibition of a recall DTH in response to colocalized donor antigen (linked suppression)--a characteristic feature of peripheral tolerance to an organ transplant--both the challenge site and the immunocompetence of the mouse adoptive host are critical factors limiting the sensitivity of the trans-vivo DTH test.

A novel approach to detect donor/recipent immune responses between HLA-identical pairs

Renal transplant rejection and graft versus host reactions between HLA genetically-identical sibling (HLAgi) donor/recipient (D/R) pairs are thought to result from minor histocompatibility antigen (mHAg) disparities. We have compared two methods of measuring HLAgi D/R T lymphocyte responses to "matured" dendritic cells: 1.) a modified Cylex assay of CD4(+) ATP levels (MLDC-ATP) versus 2.) (3)H-thymidine uptake (MLDC-(3)H). The MLDC-ATP kinetics peaked at 48 hours versus the MLDC-(3)H at 7 days, and appeared more sensitive. We tested HLAgi (normal) volunteer siblings (NLs), and D/R sibling pairs before and after renal transplantation (pre-Tx and post-Tx). The overall frequencies of positive responses in the MLDC-ATP for HLAgi NLs, pre-Tx, and post-Tx D/R pairs were 63%, 50%, and 42%, respectively. The percentage with reciprocal responses was 37.5%, 20%, and 22.22%, respectively. In one set of three HLAgi (NLs) siblings (two males and one female), there was a nongender-associated differential response. There was no MLDC correlation with class I MHC-associated mHAg (SSP) incompatibility, nor could some MLDC positive reactive pairs theoretically process the necessary HLA-class I restriction molecules for presentation of known (nanomeric) mHAg peptides. Speculatively, the MLDC reflects class II MHC-restricted mHAg reactions (not yet definable), with possible effects of other polymorphic (nonhistocompatibility) immune response genes, and thereby may be a useful measurement of CD4(+) T-cell HLAgi transplantation immunity.

CD4+CD25bright+ regulatory T cells can mediate donor nonreactivity in long-term immunosuppressed kidney allograft patients

CD4+ CD25bright+ FoxP3+ T cells are potent regulators of T-cell reactivity, but their possible involvement in donor-specific nonresponsiveness after clinical kidney transplantation remains to be elucidated. We assessed the proliferative donor-reactivity in 33 kidney allograft recipients who were maintained on a combination of proliferation inhibitors (mycophenolate mofetil (MMF) or Azathioprine (Aza)) and prednisone, long (> 5 years) after transplantation. Of the 33 patients, 8 still exhibited donor-reactivity, whereas 25 were classified as donor nonreactive patients. Within these 25 donor nonreactive patients, we assessed the involvement of CD4+ CD25bright+ regulatory T cells both by depleting them from the responder population as well as by reconstituting them to the CD25(-/dim) effector population. The absence of proliferation in these 25 patients, was abolished in 7 (28%) recipients upon depletion of the CD4+ CD25bright+ T cells. Reconstitution of these cells suppressed the donor-reactivity in a dose-dependent manner. Adding-back CD4+ CD25bright+ T cells inhibited the anti-third party response in all recipients, indicating that functional CD4+ CD25bright+ T cells circulate despite more then 5 years of immunosuppressive treatment. Altogether, we conclude that in long-term immunosuppressed kidney allograft patients functional regulatory CD4+ CD25bright+ T cells circulate but that these cells mediate donor non reactivity only in a subset of patients.

Monitoring tolerance after human liver transplantation

The validation of reliable, non-invasive immunological assays evaluating anti-donor responsiveness in allograft recipients would provide a clinically relevant tool for the early detection of ongoing rejection process as well as for the identification of operational tolerance in the long term. A sequential approach towards immunological monitoring of allografts is proposed in this review: (i) investigations exploring the initial donor-recipient alloresponses, including the analysis of the cytokine network; (ii) investigations regarding graft acceptance and operational tolerance in long-term transplant patients, consisting in the analysis of regulatory T cells and of circulating precursors of dendritic cells, in the measurement of T cell alloreactivity as well as in the study of T cell receptor repertoires. Beside the conventional in vivo and in vitro immunological techniques, the potential applications of molecular imaging in transplantation also deserve further exploration, with particular respect to allograft immune monitoring. Enforced collaboration between transplant clinicians and immunologists will be required to develop the translational research protocols required for the development of immunological monitoring, within an international multicentric network.

How can we measure immunologic tolerance in humans?

Prevention and treatment of allograft rejection in organ transplant recipients relies primarily on non-antigen-specific immunosuppression, with all its associated potential hazards and costs. Currently, the status of the recipient immune response is measured by monitoring pharmacologic drug levels and clinical/pathologic evaluation of graft function. Development of reliable assays that can measure accurately the status of the immune response not only would help clinicians customize the prescription of immunosuppressive drugs in individual patients but also may allow their complete withdrawal in some patients with immunologic tolerance. Furthermore, these assays would facilitate the safe evaluation of novel tolerogenic regimens. Achieving this goal has proved to be very difficult because it requires both a more in-depth understanding of complex mechanisms of tolerance and also identification of transplant patients with acquired tolerance to an allograft that can be studied. This review discusses the current understanding of tolerance mechanisms and outlines the unique and specific challenges in development of tolerance/monitoring assays in the field of transplantation. In addition, several of the most promising candidate assays are discussed in detail.

Can unresolved infection precipitate autoimmune disease?

Autoimmune diseases are frequently postulated to arise as post-infectious phenomena. Here we survey the evidence supporting these theories, with particular emphasis on Crohn's disease and ankylosing spondylitis. Direct proof that infection establishes persistent autoimmunity remains lacking, although it may provoke a prolonged inflammatory response when occurring on a susceptible immunological background. The argument of infective causality is by no means trivial, since it carries important consequences for the safety of vaccine development.

Tolerance Assays: Measuring the Unknown

Distinguishing transplant recipients who will benefit from a reduction in, or even the withdrawal of, immunosuppression from those who require intensive, lifelong immunosuppression will be dependent on developing strategies for immune monitoring. Currently, no assays have been shown to accurately predict the development or presence of donor-specific tolerance in humans after transplantation. In this overview we describe and discuss those assays that we believe may be useful for identifying tolerant transplant recipients. Validation of "tolerance" assays will be critical for the safe development of tolerance regimens in humans.

The immunological monitoring of alloreactive responses in liver transplant recipients: a review

The aim of this work is to review the current knowledge in the field of immunological monitoring of allogenic responsiveness in clinical liver transplantation. When compared to other solid-organ transplants, liver allografts are considered as immunologically privileged, and, accordingly, constitute a favorable setting to develop experimental as well as clinical strategies for minimization of immunosuppression and even induction of operational tolerance. The validation of simple, reliable, noninvasive assays exploring antidonor alloreactivity will constitute a crucial step toward implementing such approaches in the clinic. In contrast to research in rodents claiming the development of donor-specific tolerance in case of graft survivals of over 100 days without immunosuppression, it is impractical to confirm tolerance induction in this way in humans. Promising candidate assays include the detection of post-transplant immune deviation, of circulating precursors of dendritic cells subtypes, and of regulatory T cells. A conceptual framework for the development of tolerance assays in clinical liver transplantation is also proposed.

Development of tolerogenic strategies in the clinic

The study of tolerance in the clinic can be divided into three areas: (i) focused evaluation of existing tolerant transplant recipients as to their mechanism of tolerance; (ii) prospective tolerance trials, such as combined bone marrow and kidney transplantation as well as T cell depletion followed by subsequent weaning of immunosuppression; and (iii) immunologic assays to assess the likelihood of rejection or tolerance. Frankly, a very small number of patients have been transplanted with the intention of removing all immunosuppressive therapy, but several clinical trials with this aim are currently in progress, largely sponsored by the Immune Tolerance Network, a joint venture between the National Institutes of Health and the Juvenile Diabetes Research Foundation. Similarly, a reliable assay to assess tolerance has not yet been developed but a variety of approaches towards assessing rejection, and in some cases tolerance, are being developed. It would be accurate to state that many of the experimental and preclinical approaches to the induction of tolerance have resulted in better immunosuppression for human transplantation, but reliable tolerance strategies in humans have not yet been achieved. Combined bone marrow and kidney transplantation may be considered as one exception to this, but such a strategy is not generally applicable to the vast majority of solid organ transplant recipients. This review will summarize efforts to date, particularly focusing on kidney transplantation.

In vitro parameters of donor-antigen-specific tolerance

Donor-antigen-specific tolerance to the allograft is increasingly considered a reachable goal in the field of transplantation. As our understanding of the processes that govern donor-specific tolerance increases, so must our understanding of ways to detect this state of affairs. Unfortunately, this is not a straightforward procedure, as the mechanisms which govern tolerance are multiple and varied. Previously, the mixed lymphocyte reaction was used as standard to detect unresponsiveness. This approach is not valid for detecting tolerance because it only measures both direct pathway, naïve and memory responses, whereas the indirect pathway and 'pure' memory responses are more informative parameters for detecting tolerance. Techniques, such as the trans vivo delayed-type hypersensitivity assay, ELISPOT and antigen-specific HLA tetramer analysis address this problem, and the numbers of cell subsets, such as dendritic cells and NKT cells, can also aid us in detecting donor-antigen-specific tolerance.

The effect of a first kidney transplant on a subsequent transplant outcome: An experimental and clinical study

BACKGROUND

Second kidney transplantations have a roughly similar clinical outcome to first transplantations. Nevertheless, the effect of the presence of the first, nonfunctional transplant at the time of the second transplantation may also influence its outcome and has not yet been specifically studied.

METHODS

We analyzed the effect of the presence of a first graft on the outcome of a second graft in a rodent allograft model and in a cohort of 240 human second kidney allograft recipients.

RESULTS

In rodents, 100 days subsequent to the rejection of the first graft, we observed an increase in blood but not spleen CD4(+)CD25(+) T cells, whereas no differences were observed in transcriptional patterns. Adoptive transfer of day 100 splenocytes did not prolong graft survival. Moreover, the presence of a first rejected graft does not prolong the survival of a second graft performed at a later date. In the human context, a higher incidence of patients with anti-HLA immunization and a higher % of PRA were observed in retransplant recipients with primary allograft nephrectomy. Despite a relatively low statistical power, our data do not suggest significant differences in graft outcome between recipients of second transplants with primary allograft nephrectomy and those without.

CONCLUSION

Collectively, the data from both an experimental model and a large cohort of human recipients of a second graft do not suggest a beneficial effect of the presence of a first rejected graft at the time of a second transplantation.

Metastable tolerance to rhesus monkey renal transplants is correlated with allograft TGF-beta 1+CD4+ T regulatory cell infiltrates

Approaches that prevent acute rejection of renal transplants in a rhesus monkey model were studied to determine a common mechanism of acceptance. After withdrawal of immunosuppression, all 14 monkeys retained normal allograft function for >6 mo. Of these, nine rejected their renal allograft during the study, and five maintained normal function throughout the study period. The appearance of TGF-beta 1(+) interstitial mononuclear cells in the graft coincided with a nonrejection histology, whereas the absence/disappearance of these cells was observed with the onset of rejection. Analysis with a variety of TGF-beta 1-reactive Abs indicated that the tolerance-associated infiltrates expressed the large latent complex form of TGF-beta 1. Peripheral leukocytes from rejecting monkeys lacking TGF-beta 1(+) allograft infiltrates responded strongly to donor Ags in delayed-type hypersensitivity trans-vivo assays. In contrast, allograft acceptors with TGF-beta 1(+) infiltrates demonstrated a much weaker peripheral delayed-type hypersensitivity response to donor alloantigens (p < 0.01 vs rejectors), which could be restored by Abs that either neutralized active TGF-beta 1 or blocked its conversion from latent to active form. Anti-IL-10 Abs had no restorative effect. Accepted allografts had CD8(+) and CD4(+) interstitial T cell infiltrates, but only the CD4(+) subset included cells costaining for TGF-beta 1. Our data support the hypothesis that the recruitment of CD4(+) T regulatory cells to the allograft interstitium is a final common pathway for metastable renal transplant tolerance in a non-human primate model.