Non-HLA donor-recipient mismatches in kidney transplantation-A stone left unturned

Dynamics of HLA and angiotensin II type 1 receptor antibodies during pregnancy

BACKGROUND

Alloantibodies, especially anti-human leukocyte antigen antibodies (HLA antibodies), and autoantibodies, as angiotensin II type 1 receptor antibodies (AT1R antibodies), may complicate the access and the course of transplantation. Pregnancy is a known source of HLA antibodies, with most studies evaluating pregnancy-induced sensitization by complement-dependent cytotoxicity assays, mainly after childbirth. AT1R antibodies have been evaluated in the context of preeclampsia. We aimed to evaluate pregnancy as a natural source of HLA antibodies and AT1R antibodies, their dynamics along gestation and the potential factors involved in antibody appearance.

METHODS

Serum samples from pregnant women were collected during the three trimesters of pregnancy (1T, 2T, 3T). Presence of HLA antibodies was assessed by screening beads on Luminex and AT1R antibodies by ELISA.

RESULTS

A cohort of 138 pregnant women were included. Samples from all were tested in 1T, 127 in 2T and 102 in 3T. HLA antibodies increased from 29.7 % (1T) to 38.2 % (3T). AT1R antibodies were stable around 30 % along pregnancy. Up to 43.2 % multiparous women had HLA antibodies, with a similar proportion of class I and class II antibodies. In primiparous women HLA antibodies increased along pregnancy (from 17.6 % to 34.1 %), with predominance of class II HLA antibodies. AT1R antibodies were not different in primiparous and multiparous women.

CONCLUSIONS

Pregnancy is a relevant source of HLA antibodies sensitization, but not of AT1R antibodies. HLA antibodies increased clearly in primiparous women with predominance of class II. The use of newer solid-phase techniques on Luminex evidence a higher degree of HLA sensitization during pregnancy.

A non-muscle myosin heavy chain 9 genetic variant is associated with graft failure following kidney transplantation

BACKGROUND

Despite current matching efforts to identify optimal donor-recipient pairs for kidney transplantation, alloimmunity remains a major source of late transplant failure. Additional genetic parameters in donor-recipient matching could help improve longterm outcomes. Here, we studied the impact of a non-muscle myosin heavy chain 9 gene (MYH9) polymorphism on allograft failure.

METHODS

We conducted an observational cohort study, analyzing the DNA of 1,271 kidney donor-recipient transplant pairs from a single academic hospital for the MYH9 rs11089788 C>A polymorphism. The associations of the MYH9 genotype with risk of graft failure, biopsy-proven acute rejection (BPAR), and delayed graft function (DGF) were estimated.

RESULTS

A trend was seen in the association between the MYH9 polymorphism in the recipient and graft failure (recessive model, p = 0.056), but not for the MYH9 polymorphism in the donor. The AA-genotype MYH9 polymorphism in recipients was associated with higher risk of DGF (p = 0.03) and BPAR (p = 0.021), although significance was lost after adjusting for covariates (p = 0.15 and p = 0.10, respectively). The combined presence of the MYH9 polymorphism in donor-recipient pairs was associated with poor long-term kidney allograft survival (p = 0.04), in which recipients with an AA genotype receiving a graft with an AA genotype had the worst outcomes. After adjustment, this combined genotype remained significantly associated with 15-year death-censored kidney graft survival (hazard ratio, 1.68; 95% confidence interval, 1.05-2.70; p = 0.03).

CONCLUSION

Our results reveal that recipients with an AA-genotype MYH9 polymorphism receiving a donor kidney with an AA genotype have significantly elevated risk of graft failure after kidney transplantation.

Glomerular macrophage index (GMI) in kidney transplant biopsies is associated with graft outcome

BACKGROUND

Macrophages in renal transplants have been shown to participate in antibody-mediated rejection and are associated with impaired renal function. We calculated the glomerular macrophage index (GMI) in a large transplant biopsy cohort, studied its quantity in different diagnostic groups, to clarify its possible impact on graft survival.

METHODS

GMI, defined as the mean number of macrophages in 10 glomeruli, was prospectively quantified in 1440 renal transplant biopsies over a 10-year period. The main histopathological diagnoses were grouped into eight disease entities, and GMI was compared to normal transplant biopsies as the reference group. The impact of GMI on graft survival was analyzed.

RESULTS

GMI was highest in chronic (mean 9.4) and active (9.7) antibody mediated rejections (ABMR), mixed rejections (7.6), and recurrent or de novo glomerulonephritis (7.5) and differed significantly from normal transplants (1.3) in almost all diagnostic groups. Hazard ratios for graft loss were significantly increased for all biopsies with GMI ≥1.9 compared to GMI < .5 (reference group) in an adjusted Cox regression model and increased with higher GMI levels. Biopsies with GMI ≥ 4.6 had < 60% 10-year graft-survival, compared to > 80% with GMI ≤ 1.8.

CONCLUSION

GMI levels were predictive of graft loss independent of histological diagnoses and may guide clinicians to decide follow-up and therapy.

Donor–Recipient Non-HLA Variants, Mismatches and Renal Allograft Outcomes: Evolving Paradigms

Despite significant improvement in the rates of acute allograft rejection, proportionate improvements in kidney allograft longevity have not been realized, and are a source of intense research efforts. Emerging translational data and natural history studies suggest a role for anti-donor immune mechanisms in a majority of cases of allograft loss without patient death, even when overt evidence of acute rejection is not identified. At the level of the donor and recipient genome, differences in highly polymorphic HLA genes are routinely evaluated between donor and recipient pairs as part of organ allocation process, and utilized for patient-tailored induction and maintenance immunosuppression. However, a growing body of data have characterized specific variants in donor and recipient genes, outside of HLA loci, that induce phenotypic changes in donor organs or the recipient immune system, impacting transplant outcomes. Newer mechanisms for “mismatches” in these non-HLA loci have also been proposed during donor–recipient genome interactions with transplantation. Here, we review important recent data evaluating the role of non-HLA genetic loci and genome-wide donor-recipient mismatches in kidney allograft outcomes.

Noninvasive Assessment of the Alloimmune Response in Kidney Transplantation

Transplantation remains the optimal mode of kidney replacement therapy, but unfortunately long-term graft survival after 1 year remains suboptimal. The main mechanism of chronic allograft injury is alloimmune, and current clinical monitoring of kidney transplants includes measuring serum creatinine, proteinuria, and immunosuppressive drug levels. The most important biomarker routinely monitored is human leukocyte antigen (HLA) donor-specific antibodies (DSAs) with the frequency based on underlying immunologic risk. HLA-DSA should be measured if there is graft dysfunction, immunosuppression minimization, or nonadherence. Antibody strength is semiquantitatively estimated as mean fluorescence intensity, with titration studies for equivocal cases and for following response to treatment. Determination of in vitro C1q or C3d positivity or HLA-DSA IgG subclass analysis remains of uncertain significance, but we do not recommend these for routine use. Current evidence does not support routine monitoring of non-HLA antibodies except anti-angiotensin II type 1 receptor antibodies when the phenotype is appropriate. The monitoring of both donor-derived cell-free DNA in blood or gene expression profiling of serum and/or urine may detect subclinical rejection, although mainly as a supplement and not as a replacement for biopsy. The optimal frequency and cost-effectiveness of using these noninvasive assays remain to be determined. We review the available literature and make recommendations.

A Multi-Marker Test for Analyzing Paired Genetic Data in Transplantation

Emerging evidence suggests that donor/recipient matching in non-HLA (human leukocyte antigen) regions of the genome may impact transplant outcomes and recognizing these matching effects may increase the power of transplant genetics studies. Most available matching scores account for either single-nucleotide polymorphism (SNP) matching only or sum these SNP matching scores across multiple gene-coding regions, which makes it challenging to interpret the association findings. We propose a multi-marker Joint Score Test (JST) to jointly test for association between recipient genotype SNP effects and a gene-based matching score with transplant outcomes. This method utilizes Eigen decomposition as a dimension reduction technique to potentially increase statistical power by decreasing the degrees of freedom for the test. In addition, JST allows for the matching effect and the recipient genotype effect to follow different biological mechanisms, which is not the case for other multi-marker methods. Extensive simulation studies show that JST is competitive when compared with existing methods, such as the sequence kernel association test (SKAT), especially under scenarios where associated SNPs are in low linkage disequilibrium with non-associated SNPs or in gene regions containing a large number of SNPs. Applying the method to paired donor/recipient genetic data from kidney transplant studies yields various gene regions that are potentially associated with incidence of acute rejection after transplant.

Murine Cytomegalovirus-induced Complement-fixing Antibodies Deposit in Murine Renal Allografts During Acute Rejection

BACKGROUND

Human cytomegalovirus (CMV) infection is associated with renal allograft dysfunction and loss, particularly in combination with acute rejection. Emerging literature suggests that non-HLA antibodies may contribute to antibody-mediated rejection, but pathogen-induced antibodies have not been investigated in this context. This study examines the presence of CMV-induced antibodies in murine CMV (MCMV)-infected renal allografts during acute rejection.

METHODS

Intragraft immunoglobulin G (IgG) and complement C3 immunostaining were compared among allogeneic MCMV D-/R-, D+/R-, and D+/R+ renal transplants. Intragraft antibody deposition was examined in B cell-deficient recipients treated with MCMV immune sera. Antibody binding and complement-dependent cytotoxicity (CDC) of D-/R- and D+/R+ sera against infected renal tubular epithelial cells (TECs) were measured in vitro. IgG immunostaining was performed in D+/R+ allografts and native kidneys and in D+/R- allografts treated with ganciclovir to inhibit viral replication.

RESULTS

D+/R- and D+/R+ transplants had more abundant IgG and C3 deposition compared with D-/R- recipients. Greater IgG deposition was associated with more severe allograft injury in B cell-deficient recipients treated with MCMV immune sera compared with nonimmune sera. D+/R+ sera induced greater CDC of infected TECs compared with D-/R- sera. Native kidneys had lower IgG deposition compared with allografts, despite similar organ viral loads. Ganciclovir-treated allografts had reduced IgG deposition compared with untreated allografts.

CONCLUSIONS

In this murine model, complement-fixing antibodies can deposit into MCMV-infected renal allografts, are associated with allograft damage, and can induce CDC of MCMV-infected renal TECs. The allogeneic response and viral replication may also contribute to intragraft antibody deposition.

Endothelin A Receptors Expressed in Glomeruli of Renal Transplant Patients May Be Associated with Antibody-Mediated Rejection

BACKGROUND

Non-human leukocyte antigen (HLA) anti-endothelin A receptor antibodies are presented as being potentially important, but the expression of the endothelin A receptor in glomeruli (ETA receptor (g+)) has not yet been described. We decided to evaluate the presence and relevance of the ETA receptor in for-cause renal transplant biopsies. The aim of our study was to evaluate the immunoreactivity of the ETA receptor and its significance in patients who underwent a renal transplant biopsy due to the deterioration of transplant function, with detailed characterization of staining in glomeruli.

METHODS

The immunohistochemical expression of ETA receptor (ETAR) was analyzed in renal transplant biopsies. Microscopic evaluation was performed on paraffin sections in glomeruli. The analysis was performed using a two-step scale (0: lack of ETAR expression; 1: the presence of ETAR expression-mild to moderate immunoreactivity).

RESULTS

We analyzed 149 patients who underwent renal allograft biopsy after renal transplantation. Positive staining of ETA receptors in glomeruli (ETA receptor (g+)) was noticed in 13/149 (8.7%) patients. Five of these 13 (38.5%) patients with ETA receptor (g+) developed antibody-mediated rejection (AMR), while 13 of the remaining 136 (9.5%) ETA receptor (g-) patients developed AMR (p = 0.0022). Graft loss was noticed in all but one ETA receptor (g+) patient with AMR (4/5; 80%), but only in 2/13 (15%) ETA receptor (g-) patients with AMR (p = 0.009) during the first year after biopsy.

CONCLUSIONS

The expression of endothelin A receptors in glomeruli seems to be a potentially important feature in the diagnosis of damage during antibody-mediated rejection. It may help to identify patients at a higher risk of allograft rejection and injury.

Antibody-mediated rejection with and without donor-specific anti-human leucocyte antigen antibodies: performance of the peripheral blood 8-gene expression assay

BACKGROUND

Recently a peripheral blood 8-gene expression assay was developed for non-invasive detection of antibody-mediated rejection (ABMR) after kidney transplantation. Its value has not yet been evaluated in detail in clinical scenarios with different baseline disease probability [human leucocyte antigen donor-specific antibodies (HLA-DSA)-positive versus HLA-DSA-negative cases at the time of stable graft function versus graft dysfunction].

METHODS

Here we investigated the diagnostic accuracy of the 8-gene expression assay for histology of ABMR (ABMRh) with or without HLA-DSA in a cross-sectional cohort study of 387 blood samples with a concomitant graft biopsy.

RESULTS

In patients with HLA-DSA (n = 64), the 8-gene expression assay discriminated DSA-positive ABMRh (DSAposABMRh) cases (n = 16) with good diagnostic performance {area under the receiver operating characteristic curve [AUROC] 83.1% [95% confidence interval (CI) 70.8-95.3]}. Also, in HLA-DSA-negative samples (n = 323), a clinically relevant diagnostic performance for DSAnegABMRh cases was found (n = 30) with an AUROC of 75.8% (95% CI 67.4-84.4). The 8-gene assay did not discriminate DSAposABMRh cases from DSAnegABMRh cases. There was a net benefit for clinical decision-making when adding the 8-gene expression assay to a clinical model consisting of estimated glomerular filtration rate, proteinuria, HLA-DSA and age.

CONCLUSION

The 8-gene expression assay shows great potential for implementation in the clinical follow-up of high-risk HLA-DSA-positive patients and clinical relevance in HLA-DSA-negative cases.

Chronic Histologic Changes Are Present Regardless of HLA Mismatches: Evidence from HLA Identical Living Donor Kidney Transplants

BACKGROUND

At 5 and 10 years after kidney transplantation, chronic histologic changes such as arteriolar hyalinosis and mesangial expansion are common, however, determining etiology is difficult. We compared surveillance biopsies in living donor kidney transplants (LDKTx) from HLA matched siblings (termed HLA-identical (HLA-ID)) to HLA non-ID to investigate which histologic changes were likely due to alloimmune injury and which were due to non-alloimmune injury.

METHODS

We performed a retrospective, cohort study comparing HLA-ID sibling LDKTx (n=175) to HLA non-ID LDKTx (n=175; matched for age, sex and year of transplant +/- 2 years) performed at a single institution from 03/1999 to 11/2018.

RESULTS

Baseline characteristics and maintenance immunosuppression were similar. Mortality rates were similar, but in the HLA-ID group, 10-year death-censored graft survival was higher (93.8% vs 80.9% HLA non-ID LDKTx, p<0.001), rejection rates were lower (after 1 year 9.6% vs 27.1%; p<0.001) and Banff inflammation scores including glomerulitis and peritubular capillaritis were lower on surveillance biopsies at 1, 5 and 10 years. In contrast, chronic Banff scores (interstitial fibrosis, arteriolar hyalinosis, mesangial expansion, etc.) were similar in prevalence and severity on surveillance biopsies at 1, 5 and 10 years.

CONCLUSIONS

HLA-ID LDKTx have less inflammation and less transplant glomerulopathy, but most chronic histologic changes were similar to less-well matched LDKTx. We conclude that these types of chronic changes are not associated with HLA mismatches and may be due to non-immunologic causes (hypertension, obesity, etc.) suggesting that new management approaches to prevent these lesions may be needed.

Recent Advances and Clinical Outcomes of Kidney Transplantation

Recent advances in surgical, immunosuppressive and monitoring protocols have led to the significant improvement of overall one-year kidney allograft outcomes. Nonetheless, there has not been a significant change in long-term kidney allograft outcomes. In fact, chronic and acute antibody-mediated rejection (ABMR) and non-immunological complications following kidney transplantation, including multiple incidences of primary kidney disease, as well as complications such as cardiovascular diseases, infections, and malignancy are the major factors that have contributed to the failure of kidney allografts. The use of molecular techniques to enhance histological diagnostics and noninvasive surveillance are what the latest studies in the field of clinical kidney transplant seem to mainly focus upon. Increasingly innovative approaches are being used to discover immunosuppressive methods to overcome critical sensitization, prevent the development of anti-human leukocyte antigen (HLA) antibodies, treat chronic active ABMR, and reduce non-immunological complications following kidney transplantation, such as the recurrence of primary kidney disease and other complications, such as cardiovascular diseases, infections, and malignancy. In the present era of utilizing electronic health records (EHRs), it is strongly believed that big data and artificial intelligence will reshape the research done on kidney transplantation in the near future. In addition, the utilization of telemedicine is increasing, providing benefits such as reaching out to kidney transplant patients in remote areas and helping to make scarce healthcare resources more accessible for kidney transplantation. In this article, we discuss the recent research developments in kidney transplants that may affect long-term allografts, as well as the survival of the patient. The latest developments in living kidney donation are also explored.