Formation of donor-specific human leukocyte antigen antibodies after kidney transplantation: correlation with acute rejection and tapering of immunosuppression

Diseases association with the polymorphic major histocompatibility complex class I related chain a: MICA gene

The Major Histocompatibility Complex class I chain-related molecule A (MICA) genes encode a highly polymorphic glycoprotein among the cell surface antigens that trigger an immune response after allograft transplantation. It is encoded by the MICA gene, a member of the glycosylated MIC genes. Discovered in 1994, the MICA gene is located within the MHC class I region. Moreover, its biological function is achieved through the interaction with the NKG2D receptor. Unlike the classical HLA molecules, MICA protein is not associated with β2- microglobulin nor binds peptides. MICA gene expression may result in a cytotoxic response and IFN-γ secretion through the up-regulation by heat shock proteins in response to infection (Human Cytomegalovirus HCMV), mediated by NKG2D-expressing cells. Anti-MICA antibodies were identified as significant risk factors for antibody mediated rejection after being detected in sera of patients with graft rejection. In addition, soluble MICA proteins (sMICA) has been detected in the serum of transplant recipients with cancers. Furthermore, the association of MICA polymorphisms with infectious diseases, various autoimmune diseases, cancer, and allograft rejection or graft-versus-host disease (GVHD) has been studied. Moreover, numerous advanced disease studies centered on MICA polymorphism are independent of HLA association. In this review, we discussed the up-to-date data about MICA and the association of MICA polymorphism with infections, autoimmune diseases, graft-versus-host disease, and cancer.

An overview of T follicular cells in transplantation: spotlight on their clinical significance

Introduction: For late stage organ failure patients, transplantation is the best option to increase life expectancy with a superior quality of life. Unfortunately, after transplantation many patients are at risk of cellular and antibody-mediated rejection (ABMR). The latter is initiated by donor specific antibodies (DSA) which depend on the actions of B cells, T follicular helper (Tfh) cells and T follicular regulatory (Tfr) cells that are present in the germinal center of lymphoid organs.Areas covered: In this overview paper, we discuss the biology and function of Tfh and Tfr cells in lymphoid tissues, transplanted organs and their circulating counterparts. We report on their relevance to alloimmunity and on the effects of immunosuppressive drugs on these immunocompetent cell populations.Expert opinion: Growing knowledge about the actions of Tfh and Tfr allows for a better understanding of the immunological mechanisms of ABMR after organ transplantation. This understanding feeds the hypothesis that immunosuppressive drugs targeting the actions of Tfh cells have huge therapeutic potential. This new concept in the treatment of the humoral rejection response will improve graft and patient survival after organ transplantation.

The Impact of Withdrawal of Maintenance Immunosuppression and Graft Nephrectomy on HLA Sensitization and Calculated Chance of Future Transplant

Background

The development of HLA antibodies towards a failing renal allograft is a barrier to retransplantation. This study aimed to compare the formation of HLA donor-specific antibodies (DSA) in patients undergoing graft nephrectomy and in those with a failed graft left in situ who had maintenance immunosuppression (IS) stopped, and assess the relative impact of IS cessation and graft nephrectomy on future relative chance of transplant (R-CoT).

Methods

A single-center retrospective study of patients with failed grafts between 2005 and 2015 was performed. Samples were tested for DSA pre-IS wean, post-IS wean, and post-IS cessation. Nephrectomy patients additionally had samples tested for DSA before and after nephrectomy. Calculated reaction frequency (cRF) was determined at each timepoint and entered into the UK Organ Donation and Transplant R-CoT calculator.

Results

Forty-one patients were included in the study: 24 with nephrectomy and 17 with a failed graft in situ. Patient demographics and duration of IS wean were similar between groups. There was a higher rate of blood transfusion (54% vs 24%) in nephrectomy patients. In patients whose graft remained in situ, cRF rose from 13% pre-IS wean to 40% post-IS wean and 62% after IS cessation. This equated to a reduction in mean R-CoT from 54% to 46% at 5 years. In patients undergoing nephrectomy mean cRF rose from 31% pre-IS wean to 69% post-IS wean and 89% post-IS cessation. Mean R-CoT fell from 54% to 42% at 5 years.

Conclusions

A stepwise increase in cRF with reduced chance of transplant was observed in both groups as IS was withdrawn, with a similar pattern irrespective of graft nephrectomy. Calculated reaction frequency was higher in the nephrectomy group. The risks and benefits of stopping IS need to be carefully considered on an individual basis to maximize chance of future transplant.

The Calcineurin Inhibitor Tacrolimus Specifically Suppresses Human T Follicular Helper Cells

Background

T follicular helper (Tfh) cells are key players in the production of antibody-producing B cells via the germinal center reaction. Therapeutic strategies targeting Tfh cells are important where antibody formation is implicated in disease, such as transplant rejection and autoimmune diseases. We investigated the impact of the immunosuppressive agent tacrolimus on human Tfh cell differentiation and function in transplant recipients.

Methods

Paired blood and lymph node (LN) samples were obtained from 61 transplant recipients immediately prior to organ implantation. Living-donor recipients received a week of tacrolimus prior to kidney transplantation. Deceased-donor recipients served as controls, as tacrolimus was not administered until after the transplant operation. Flow cytometry was used to compare LN and circulating cell subsets.

Results

The calcineurin inhibitor (CNIs) tacrolimus specifically suppresses both LN Tfh cells and circulating Tfh cells, but not their regulatory counterparts or other CD4 T cell subsets.

Conclusion

Our findings suggest that CNIs may have a more important role in the prevention of antibody formation than previously understood and, therefore, have potential for antibody-associated conditions in which aberrant Tfh function has been implicated in disease.

Regulatory B cells: Phenotype, function and role in transplantation

While B cells are traditionally known for their roles in antibody production, antigen presentation and cytokine production, recent studies have highlighted the existence of B cells with regulatory properties, which have been termed Bregs, analogous to regulatory T cells (Tregs). Bregs have been found to play a role in autoimmune disease, malignancies, infections, and may also be involved in solid organ transplantation. Their main mechanism of action is by promoting the development of Tregs while suppressing effector CD4⁺ and CD8⁺ T cells, primarily by IL-10 secretion. In the field of transplantation evidence for an active role of Bregs is scarce. While the presence of Bregs has been associated with improved graft survival and operational tolerance in kidney transplant recipients, these findings are not without controversy. Since the majority of fundamental research on Bregs has been performed in the fields in autoimmunity and infectious diseases, we will first focus on what these fields taught us on basic Breg biology, after which the relevance for the transplant setting is discussed.

Can a combined screening/treatment programme prevent premature failure of renal transplants due to chronic rejection in patients with HLA antibodies: study protocol for the multicentre randomised controlled OuTSMART trial

BACKGROUND

Renal transplantation is the best treatment for kidney failure, in terms of length and quality of life and cost-effectiveness. However, most transplants fail after 10 to 12 years, consigning patients back onto dialysis. Damage by the immune system accounts for approximately 50% of failing transplants and it is possible to identify patients at risk by screening for the presence of antibodies against human leukocyte antigens. However, it is not clear how best to treat patients with antibodies. This trial will test a combined screening and treatment protocol in renal transplant recipients.

METHODS/DESIGN

Recipients>1 year post-transplantation, aged 18 to 70 with an estimated glomerular filtration rate>30 mL/min will be randomly allocated to blinded or unblinded screening arms, before being screened for the presence of antibodies. In the unblinded arm, test results will be revealed. Those with antibodies will have biomarker-led care, consisting of a change in their anti-rejection drugs to prednisone, tacrolimus and mycophenolate mofetil. In the blinded arm, screening results will be double blinded and all recruits will remain on current therapy (standard care). In both arms, those without antibodies will be retested every 8 months for 3 years. The primary outcome is the 3-year kidney failure rate for the antibody-positive recruits, as measured by initiation of long-term dialysis or re-transplantation, predicted to be approximately 20% in the standard care group but <10% in biomarker-led care. The secondary outcomes include the rate of transplant dysfunction, incidence of infection, cancer and diabetes mellitus, an analysis of adherence with medication and a health economic analysis of the combined screening and treatment protocol. Blood samples will be collected and stored every 4 months and will form the basis of separately funded studies to identify new biomarkers associated with the outcomes.

DISCUSSION

We have evidence that the biomarker-led care regime will be effective at preventing graft dysfunction and expect this to feed through to graft survival. This trial will confirm the benefit of routine screening and lead to a greater understanding of how to keep kidney transplants working longer.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN46157828.

The effect of MICA antigens on kidney transplantation outcomes

Good HLA matches do not guarantee rejection-free kidney transplantation, indicating that other antigens might be targets for rejection. The major histocompatibility complex class I-related antigens A (MICA) are polymorphic. Mismatched MICA epitopes may lead to antibodies against MICA antigens and induce immune response. Establishment of detection technique for MICA, including solid-phase, immunofluorescence, flow-crossmatch, make it possible to detect the types of MICA antibodies. Therefore, the pathological role of MICA antibodies has received an increased attention in kidney transplantation. This review describes and summarizes the data from recent studies related to the impact of MICA antibodies on kidney allografts rejection and survival. And also provides evidence that the presence of MICA antibodies before or after transplantation, as a risk factor, is likely to be responsible for transplant outcomes.

Post Transplant Development of MICA and Anti-HLA Antibodies is Associated with Acute Rejection Episodes and Renal Allograft Loss

This study was undertaken with the primary aim of analyzing the clinical relevance of posttransplant appearance of anti-human leukocyte antigen (HLA) and major histocompatibility (MHC) class I related chain A (MICA) antibodies in response to live related donor (LRD) renal transplantation. A total of 185 consecutive post renal transplant recipient serum samples were analyzed for the detection of anti-HLA by enzyme-linked immunoabsorbent assay (ELISA) and MICA antibodies using Luminex techniques. Patients with IgG HLA class I antibodies had more acute rejection episodes compared to the negative group (67% vs. 20%, chi(2) = 7.95, p = 0.005) and also had poor graft survival (44% vs 86%, chi(2) = 6.67, p = 0.01). Similarly, patients with anti-HLA class II antibodies also had significantly lower graft survival and a higher number of rejection episodes as compared to the antibody negative group (p = 0.002 and p = 0.000, respectively). Following transplantation, 30 patients (16%) developed antibodies against any of the MICA alleles (MICA*001, MICA*002, MICA*004, MICA*008, or MIC*009). The graft survival was significantly compromised in these patients as compared to the negative group (60% vs 86%, chi(2) = 10.26, p = 0.001). Further, patients carrying both antibodies (MICA+/HLA+) were the worst affected and showed significantly poor graft survival as compared to the MICA-/HLA- group (17% vs 89%, chi(2) = 19.63, p = 0.000). Similarly, patients with only MICA antibodies or those with only HLA antibodies also had significantly lower graft survival and a higher number of acute rejection episodes (p = 0.035 and p = 0.001, respectively) as compared to the nonsensitized group. The study illustrates that posttransplant monitoring of antibodies to both MICA as well as HLA could be an important prognostic marker in renal transplant subjects.

Relevance of Posttransplant Flow Cytometric T- and B-cell Crossmatches in Tacrolimus-Treated Renal Transplant Patients

BACKGROUND

De novo development of anti-human leukocyte antigen (HLA) antibodies after transplantation is associated with increased rejection and decreased graft survival. In this study, the effect of posttransplant HLA antibodies on clinical outcome was evaluated in patients treated with tacrolimus by means of flow cytometric crossmatches (FCXm).

METHODS

T- and B-cell FCXm were performed retrospectively on posttransplant sera of patients who received a graft between 1997 and 1999. Ninety-four kidney-only recipients were tested and all FCXm positive sera were investigated for the presence of HLA class I and II antibodies by Flow panel reactive antibodies.

RESULTS

From 94 patients with a negative pretransplant complement-dependent cytotoxicity crossmatch, seven (7%) showed a positive pretransplant FCXm. After transplantation the FCXm became positive in five patients (6%). The predictive value of a positive FCXm after transplantation, and the log-transformed relative change in fluorescence ratio between pretransplant and posttransplant serum, were not significant to rejection within six months, nor to graft survival censored for death.

CONCLUSIONS

The presence of HLA antibodies before rejection or graft failure could only be shown in a minority of patients; most antibodies were detected after graft failure, especially after transplantectomy. Monitoring through antibody testing after transplantation on the basis of our results has no added value with tacrolimus-based immunosuppression.

Human Leukocyte Antigen Antibodies for Monitoring Transplant Patients

Human leukocyte antigen (HLA) antibody-mediated hyperacute rejection has dramatically decreased since the clinical introduction of crossmatch technology. However, the role of HLA antibody in acute and chronic rejection remains unclear. In this article, we cite publications to show the correlation between HLA antibody and allograft rejection. Potential pathological mechanisms of antibody-mediated rejection are also proposed and the rationale of commonly used HLA antibody detection techniques are introduced. The advantages and disadvantages of these technologies are further discussed in detail. We conclude that owing to the recent availability of improved antibody detection methods, a causal relationship between HLA antibodies and allograft rejection is now considered to exist.

Anti-HLA class II antibodies in kidney retransplant patients

The relevance of anti-HLA class II antibodies for kidney graft survival is still controversial. In part, this can be attributed to difficulties to detect and differentiate anti-HLA class II antibodies. Anti-HLA class II IgG antibody screening was performed by enzyme-linked immunosorbent assay. Subsequently, all anti-HLA class II-positive sera were subjected to the determination and specification using color-coded microspheres coated with purified HLA antigens. In a cohort of 934 patients awaiting kidney transplantation, 41 sera (4.4%) were positive for IgG anti-HLA class II antibodies. The presence was confirmed in 90.2% sera by retesting. Subsequently, all anti-HLA class II-positive patients (n = 27) who in the past had undergone a kidney transplantation with an HLA-DR and/or -DQ-mismatched graft were selected. In 25 of 27 sera (92.6%), the alloantibody specificities corresponded to the known previous transplant mismatches on a broad antigen level. In 20 of 27 sera (74.1%), anticlass I antibodies were detected as well. Anti-HLA-DP antibodies were seen in 24 of the 27 sera of this cohort. In the majority of the cases, the reactivities with different DPB1 alleles could be explained by involvement of a single, specific DPB1 epitope. Donor-specific anti-HLA-DR and -DQ antibodies were seen in the majority of cases with graft failure following HLA class II alloantigen exposure in prior kidney transplantations. In addition, HLA-DP may serve as a transplantation antigen in kidney transplantation, leading to a humoral response.

Effective donor lymphohematopoietic reconstitution after haploidentical CD34+-selected hematopoietic stem cell transplantation in children with refractory severe aplastic anemia

Peritransplant toxicity and a delay in effective immune reconstitution have limited the utility of alternate donor transplantation for children with refractory severe aplastic anemia. We have assessed the effectiveness of infusing large numbers of highly purified haploidentical CD34+ cells after immunoablative conditioning in three patients who had failed intensive immunosuppression, lacked unrelated donors, and had active or recent serious infections. One patient rejected the first infusion, but engrafted after a second infusion from the same donor. This patient died 4 months after hematopoietic stem cell transplantation with no evidence of lymphoid reconstitution. Two patients experienced mixed chimerism requiring treatment with antibodies and/or donor lymphocyte infusion. Both currently survive more than 1 year after transplantation with normal blood counts, 100% donor engraftment, effective lymphoid reconstitution, and no chronic graft-versus-host disease. We observed functional thymopoiesis as measured by lymphocyte immunophenotyping, T cell receptor excision circles and T cell receptor Vbeta spectratyping complexity analysis. Further study is required to validate the initial promise of these preliminary observations.