Investigation of Serum Angiotensin II Type 1 Receptor Antibodies at the Time of Renal Allograft Rejection

Biomarkers for Kidney-Transplant Rejection: A Short Review Study

Kidney transplantation is the preferred treatment for end-stage renal failure, but the limited availability of donors and the risk of immune rejection pose significant challenges. Early detection of acute renal rejection is a critical step to increasing the lifespan of the transplanted kidney. Investigating the clinical, genetic, and histopathological markers correlated to acute renal rejection, as well as finding noninvasive markers for early detection, is urgently needed. It is also crucial to identify which markers are associated with different types of acute renal rejection to manage treatment effectively. This short review summarizes recent studies that investigated various markers, including genomics, histopathology, and clinical markers, to differentiate between different types of acute kidney rejection. Our review identifies the markers that can aid in the early detection of acute renal rejection, potentially leading to better treatment and prognosis for renal-transplant patients.

Rejection and graft outcomes in kidney transplant recipients with and without angiotensin II receptor type 1 antibodies

AIM

Angiotensin II type 1 receptor antibody (AT1R Ab) is a non-Human Leucocyte Antigen (HLA) antibody that is maybe associated with early severe kidney transplant rejection and worse graft outcomes. This study aimed to assess the association between AT1R Ab and kidney transplant rejection and graft outcomes.

METHODS

We performed a retrospective analysis of all adult kidney transplant recipients in an Australian centre who had an AT1R Ab test between 1 January 2015 to 30 June 2020. AT1R Ab positive patients were compared to AT1R Ab negative patients. Primary outcomes were rejection risk, type and histopathological severity scores. Secondary outcomes were 8-week graft function and graft loss.

RESULTS

Of 965 kidney transplants that were performed during the study period, 73 patients had AT1R Ab tested; 16 (22%) were positive and 57(78%) were negative. Positive patients were on average younger and had higher level of donor-specific HLA antibodies. Rejection occurred in 13 (81%) positive patients and 41 (72%) negative patients (P = 0.45). No significant differences in rejection type or severity were found. HLA mismatch and peak panel reactive antibody ≥80%, but not AT1R Ab, independently predicted rejection. Average (132 vs. 177 mmol/L, P = 0.302) and graft loss were not significantly different between groups.

CONCLUSION

The study found no evidence that AT1R Ab is associated with rejection type, severity or worse graft function. Future studies should assess its relationship with graft outcomes to help complement immunological risk assessment and potentially provide therapeutic options to alter outcomes.

Relationship Between Angiotensin II Type 1 Receptor Antibody Positivity and Cytokine Gene Polymorphism in Renal Transplant Patients When Organ Rejection Occurs

OBJECTIVES

Kidney transplant remains the gold standard for the treatment of end-stage renal disease. Relationships between the presence of non-HLA antibodies, antibodies to AT1R, and cytokine gene polymorphisms with rejection have recently been shown. We sought to determine whether the presence of antibodies to AT1R and cytokine gene polymorphisms affected the development of rejection in pediatric and adult patients, whether a relationship is present between cytokine polymorphism and level of antibodies to AT1R, and whether their presence can be a biomarker pretransplant.

MATERIALS AND METHODS

Our study included 100 pediatric and adult kidney transplant patients plus 50 healthy controls. Levels of AT1R antibodies (by enzyme-linked immunosorbent assay) and gene polymorphisms of the cytokines transforming growth factor β, tumor necrosis factor α, interleukins 6 and 10, and interferon gamma cytokines (by sequence- specific primer-polymerase chain reaction) were studied retrospectively and evaluated with the SPSS statistical program.

RESULTS

We found no statistically significant relationship between levels of antibodies to AT1R and gene polymorphisms among the studied cytokines in patients with rejection compared with the healthy controls and patients with uneventful courses posttransplant. However, higher levels of antibodies to AT1R were observed in pediatric compared with adult transplant recipients (P < .001). A statistically significant relationship was also observed between transforming growth factor β1 C/C G/C low-release and interleukin 6 G/C high-release gene polymorphism and levels of antibodies to AT1R (P < .001).

CONCLUSIONS

Because we observed that some gene polymorphisms among the studied cytokines may affect AT1R antibody levels, future studies are needed to understand the mechanism of the relationship. In addition, studies with larger groups are required to sufficiently confirm that higher antibody levels are present in pediatric versus adult patients.

Effect of anti-angiotensin II type-1 receptor antibodies on the outcomes of kidney transplantation: a systematic review and meta-analysis

BACKGROUND

Anti-angiotensin II type 1 receptor antibodies (AT1R-Abs) have been recognized as non-HLA antibodies associated with allograft rejection and poor allograft outcomes after kidney transplantation. The aim of this study was to assess the risk anti-AT1R-Abs pose for rejection and graft loss among kidney transplant populations.

METHODS

We systematically searched PubMed, EMBASE, and the Cochrane Library databases for relevant articles published from inception until June 2021 to identify all studies concerning the role AT1R-Abs play in the clinical outcome after kidney transplantation. Two reviewers independently identified studies, abstracted outcome data, and assessed the quality of the studies. The meta-analysis was summarized using the fixed-effects models or random-effects models, according to heterogeneity. The major outcomes included delayed graft function, acute rejection, graft loss, or patient death after transplantation.

RESULTS

Twenty-one eligible studies involving a total of 4,023 kidney transplantation recipients were included in the evaluation to identified. Meta-analysis results showed that the AT1R-Ab positive kidney transplant (KT) group had a greater incidence of antibody-mediated rejection (RR = 1.94, 95%CI: 1.61-2.33, P < 0.00001) and graft loss (RR = 2.37, 95%CI: 1.50-3.75, P = 0.0002) than did the AT1R-Abs negative KT group. There was no significant statistical difference in delayed graft function rate, T-cell mediated rejection, mixed rejection, acute cellular rejection, acute rejection, and patient death rate between AT1R-Ab positive KT and AT1R-Ab negative KT groups.

CONCLUSIONS

Our study shows that the presence of anti-AT1R-Abs was associated with a significantly higher risk of antibody-mediated rejection and graft loss in kidney transplantation. Future studies are still needed to evaluate the importance of routine anti-AT1R monitoring and therapeutic targeting. These results shows that assessment of anti-AT1R-Abs would be helpful in determining immunologic risk and susceptibility to immunologic events for recipients.

Causes of Positive Pretransplant Crossmatches in the Absence of Donor-Specific Anti-Human Leukocyte Antigen Antibodies: A Single-Center Experience

Pretransplant crossmatch (XM) testing is widely used for detecting preformed donor-specific antibodies (DSAs) against human leukocyte antigen (HLA). However, in some cases, there is a positive XM result in the absence of HLA-DSAs, the cause of which was rarely identified. We reviewed the causes of sequential positive XM results at a single center and analyzed the presence of non-HLA antibodies in patients with an unexplained positive pretransplant XM result. Among 251 patients with T-cell/B-cell complement-dependent cytotoxicity (CDC) or flow cytometric crossmatch (FCXM) positivity, HLA-DSAs were confirmed in 88 (35.1%) by a single antigen bead (SAB) assay, 150 (59.8%) used rituximab (anti-CD20), and 13 (5.2%) had neither HLA-DSAs nor a desensitization history. Anti-angiotensin II type 1 receptor IgG and 33 non-HLA antibodies were tested in the 13 patients with an unexplained positive pretransplant XM result, and more than one non-HLA antibody were revealed in all these patients; 11 patients had non-HLA antibodies reported to be associated with graft rejection, and two patients experienced rejection episode after kidney transplantation. Our study suggests considering non-HLA antibodies testing when a CDC or FCXM test is positive without a definite cause. Assessing non-HLA antibodies might be useful for interpreting XM results and evaluating immunologic risk in transplant recipients.

Non-HLA Abs in Solid Organ Transplantation

The role of anti-HLA antibodies in solid organ rejection is well established and these antibodies are routinely monitored both in patients in the waiting list and in the post-transplant setting. More recently, the presence of other antibodies directed towards non-HLA antigens, or the so-called minor histocompatibility antigens, has drawn the attention of the transplant community; however, their possible involvement in the graft outcome remains uncertain. These antibodies have been described to possibly have a role in rejection and allograft failure. This review focuses on the most studied non-HLA antibodies and their association with different clinical outcomes considered in solid organ transplantation with the aim of clarifying their clinical implication and potential relevance for routine testing.

Clinical Impact of Pre-transplant Antibodies Against Angiotensin II Type I Receptor and Major Histocompatibility Complex Class I-Related Chain A in Kidney Transplant Patients

Background

Evidence of antibody-mediated injury in the absence of donor-specific HLA antibodies (HLA-DSA) has recently emerged, suggesting a role of antibodies in targeting non-HLA antigens expressed on renal allograft tissue. However, the clinical significance of pre-transplant non-HLA antibodies remains unclear. We compared the histological and clinical impact of pre-transplant HLA-DSA and non-HLA antibodies, especially angiotensin II type I receptor (anti-AT1R) and MHC class I-related chain A (anti-MICA), in kidney transplant patients.

Methods

Pre-transplant HLA-DSA, anti-AT1R, and anti-MICA were retrospectively examined in 359 kidney transplant patients to determine the effect of each antibody on allograft survival and clinical characteristics.

Results

Pre-transplant HLA-DSA, anti-AT1R, and anti-MICA were detected in 37 (10.3%), 174 (48.5%), and 50 patients (13.9%), respectively. Post-transplant antibody-mediated rejection was associated with a pre-transplant HLA-DSA (+) status only. The development of microvascular inflammation (MVI) was associated with pre-transplant HLA-DSA (P=0.001) and anti-AT1R (P=0.036). Anti-AT1R (+) patients had significantly lower allograft survival compared with anti-AT1R (−) patients (P=0.042). Only pre-transplant anti-AT1R positivity was an independent risk factor for allograft failure (hazard ratio 4.824, confidence interval 1.017–24.888; P=0.038). MVI was the most common histological feature of allograft failure in patients with pre-transplant anti-AT1R.

Conclusions

Pre-transplant anti-AT1R is an important risk factor for allograft failure, which may be mediated by MVI induction in the allograft tissue.

The clinicopathological relevance of pretransplant anti-angiotensin II type 1 receptor antibodies in renal transplantation

Background

Anti-angiotensin II type 1 receptor antibodies (AT1R-Abs) have been suggested as a risk factor for graft failure and acute rejection (AR). However, the prevalence and clinical significance of pretransplant AT1R-Abs have seldom been evaluated in Asia.

Methods

In this multicenter, observational cohort study, we tested the AT1R-Abs in pretransplant serum samples obtained from 166 kidney transplant recipients. Statistical analysis was used to set a threshold AT1R-Abs level at 9.05 U/mL.

Results

Pretransplant AT1R-Abs were detected in 98/166 (59.0%) of the analyzed recipients. No graft loss or patient death was reported during the study period. AT1R-Abs (+) patients had a significantly higher incidence of biopsy-proven AR than AT1R-Abs (-) patients (27.6 versus 10.3%, P = 0.007). Recipients with pretransplant AT1R-Abs had a 3.2-fold higher risk of AR within a year of transplantation (P = 0.006). Five study subjects developed microcirculation inflammation (score ≥2). Four of them were presensitized to AT1R-Abs. In particular, three patients had a high titer of anti-AT1R-Abs (>22.7 U/mL).

Conclusions

Pretransplant AT1R-Abs is an independent risk factor for AR, especially acute cellular rejection, and is possibly associated with the risk of antibody-mediated injury. Pretransplant assessment of AT1R-Abs may be useful for stratifying immunologic risks.

Pre-transplant Screening for Non-HLA Antibodies: Who should be Tested?

Retrospective studies of angiotensin II type 1 receptor antibodies (AT1R-Ab) and anti-endothelial cell antibodies (AECA) have linked these antibodies to allograft injury. Because rising healthcare costs dictate judicious use of laboratory testing, we sought to define characteristics of kidney transplant recipients who may benefit from screening for non-HLA antibodies. Kidney recipients transplanted between 2011 and 2016 at Johns Hopkins, were evaluated for AT1R-Ab and AECA. Pre-transplant antibody levels were compared to clinical and biopsy indications of graft dysfunction. Biopsies were graded using the Banff' 2009-2013 criteria. AT1R-Ab and AECA were detected using ELISA and endothelial cell crossmatches, respectively. AT1R-Ab levels were higher in patients who were positive for AECAs. Re-transplanted patients (p < 0.0001), males (p = 0.008) and those with FSGS (p = 0.04) and younger (p = 0.04) at time of transplantation were more likely to be positive for AT1R-Ab prior to transplantation. Recipients who were positive for AT1R-Ab prior to transplantation had increases in serum creatinine within 3 months post-transplantation (p < 0.0001) and developed abnormal biopsies earlier than did AT1R-Ab negative patients (126 days versus 368 days respectively; p = 0.02). Defining a clinical protocol to identify and preemptively treat patients at risk for acute rejection with detectable non-HLA antibodies is an important objective for the transplant community.

Self-antigens and rejection: a proteomic analysis

PURPOSE OF REVIEW

Allo- and autoantibodies have been found to play important roles in both acute and chronic allograft rejection in organ transplantation, although only recently have non-human leukocyte antigen (non-HLA), nondonor-specific antibodies been given a more in-depth treatment. This review summarizes recent reports about investigations and proteomic approaches to identify self-antigens and corresponding autoantibodies that are associated with acute and chronic allograft rejection. Finally, we discuss the insights gained from these, challenges, and future prospects.

RECENT FINDINGS

Significant discoveries have been made regarding the presence and role of autoantibodies and alloantibodies, both those formed pretransplant and posttransplant, in acute and chronic rejection. These discoveries are made possible because of the publication of the human genome and subsequent development in the ability of expression and analysis of human proteome.

SUMMARY

Antibodies play a critical role in survival and dysfunction of a transplanted kidney. Even though HLA antibodies have been given the majority of the scientific community's attention for the past few decades, antibodies against autoantigens and that of non-HLA origin are gaining attention. Recent publications have identified novel self-antigens that are associated with acute and chronic rejection that have added to our understanding of new players in immune-related transplant rejection.

Angiotensin II Type 1 receptor antibodies are associated with inflammatory cytokines and poor clinical outcomes in pediatric kidney transplantation

Angiotensin II type 1 receptor (AT1R) antibody has been linked to poor allograft outcomes in adult kidney transplantation. However, its clinical consequences in children are unknown. To study this, we examined the relationship of AT1R antibody with clinical outcomes, biopsy findings, inflammatory cytokines, and HLA donor-specific antibodies (DSA) in a cohort of pediatric renal transplant recipients. Sixty-five patients were longitudinally monitored for AT1R antibody, HLA DSA, IL-8, TNF-α, IL-1β, IFN-γ, IL-17, and IL-6, renal dysfunction, hypertension, rejection, and allograft loss during the first two years post transplantation. AT1R antibody was positive in 38 of the 65 of children but was not associated with HLA DSA. AT1R antibody was associated with renal allograft loss (odds ratio of 13.1 [95% confidence interval 1.48-1728]), the presence of glomerulitis or arteritis, and significantly higher TNF-α, IL-1β, and IL-8 levels, but not rejection or hypertension. AT1R antibody was associated with significantly greater declines in eGFR in patients both with and without rejection. Furthermore, in patients without rejection, AT1R antibody was a significant risk factor for worsening eGFR over the two-year follow-up period. Thus, AT1R antibody is associated with vascular inflammation in the allograft, progressive decline in eGFR, and allograft loss. AT1R antibody and inflammatory cytokines may identify those at risk for renal vascular inflammation and lead to early biopsy and intervention in pediatric kidney transplantation.

Circulating angiotensin type II receptor: Possible marker for antibody mediated rejection after renal transplantation?

BACKGROUND

Presence of antibody [Ab] against angiotensin receptor [AT1R] indicates heightened risk for antibody mediated rejection [AMR] after transplantation but is insufficient as a marker. We speculated AT1R might be released systemically because of AMR and might be a useful biomarker.

METHODS

AT1R was measured in blood from 73 Normals and 72 renal patients pre- and post-transplantation. Patients were stratified as AMR-free [Gp1], AMR<1yr [Gp2] and AMR>1yr [Gp3].

RESULTS

AT1R was higher [13±26vs.367±537, p<0.01)] and more prevalent [20% vs. 92%, p<0.01] among renal patients than Normals. Pretransplant levels were similar [p=ns] between groups. One-year posttransplant levels approached [p<0.01] normalcy for Gps1+3 but spiked during AMR and remained elevated [155±58, p<0.01] for 50% Gp2 patients. One-year AT1R levels were higher among subsequent graft failures than surviving grafts [171±267vs. 38±50, p<0.01].

CONCLUSIONS

Pretransplant AT1R was abnormally elevated: possibly indicating ongoing tissue injury. Pretransplant AT1R didn't predict risk for AMR. However, AT1R spiked during early AMR and sustained elevations were associated with poorer outcomes.

Pretransplant angiotensin II type 1-receptor antibodies are a risk factor for earlier detection of de novo HLA donor-specific antibodies

BACKGROUND

Angiotensin II type 1 receptor antibodies (AT1Rabs) have been associated with significantly reduced graft survival. Earlier graft loss has been observed in patients who had pretransplant AT1Rabs and posttransplant donor-specific antibodies (DSA).

METHODS

The main goal of this retrospective cohort study was to examine the association between AT1Rabs and the time period to detection of de novo human leukocyte antigen (HLA-DSA) posttransplantation in living donor kidney transplant recipients (KTR). The analysis included 141 KTRs. Pretransplant frozen serum samples were tested for AT1Rabs by ELISA and HLA-DSA by SAB (Luminex) at both the pre- and post-KT time points.

RESULTS

The median AT1Rab level was 9.13 U (interquartile range 5.22-14.33). After a mean follow-up period of 3.55 years, 48 patients were found to harbour de novo HLA-DSAs. The presence of AT1Rabs [hazard ratio (HR) 1.009, 95% confidence interval (CI) 1.002-1.01, P = 0.010], male-to-male transplantation (HR 2.57, 95% CI 1.42-4.67, P = 0.002) and antecedent borderline changes or acute cellular rejection (ACR) (HR 2.47, 95% CI 1.29-4.75, P = 0.006) were significantly associated with de novo DSA detection. A dose-dependent association between AT1Rab levels (<10 U, 10.1-16.9 U, 17-29.9 U and >30 U) and de novo DSA detection was observed (log-rank P = 0.0031). After multivariate analysis of AT1Rab levels (continuous variable), AT1Rabs >30 U, male-to-male transplantation, donor age, higher class I percentage of Panel Reactive Antibody and antecedent borderline changes or ACR remained as independent significant risk factors for the detection of de novo DSAs.

CONCLUSIONS

The findings suggest that higher levels of pretransplant circulating antibodies against AT1R (>30 U) in kidney graft recipients constitute an independent risk factor for earlier de novo HLA-DSA detection during the posttransplant period.