Association of HLA Alleles with IgA Nephropathy and Its Recurrence After Kidney Transplantation

Introduction

IgA nephropathy (IgAN) is the most common primary glomerulopathy and causes end-stage kidney disease (ESKD) in adults worldwide [1]. The mean renal survival time is 10.8 years, and the median age at the time of kidney failure is 49 years [2]. Kidney transplantation (KT) is the best option for renal replacement therapy in most patients with chronic kidney disease (CKD). Patients with IgAN are ideal candidates for KT because of the relatively young mean age and fewer associated comorbidities compared with other causes. Recurrence of primary glomerulopathy after KT is the third most common cause of graft failure [3]. The recurrence rate of IgAN after KT varies between 8% and 53%, depending on the rate of performing graft biopsies or the overall length of follow-up. In contrast to complement-mediated membranoproliferative glomerulopathy (MPGN), IgAN recurrence usually occurs late after KT, with an often subtle and slowly progressive nature [4–6]. Long-term graft survival is a major challenge in patients after KT, whereas the current short-term survival is relatively high due to highly effective antirejection therapy. Recurrence of the underlying glomerulopathy is one of the main reasons why we have not yet been able to increase long-term graft survival rates. An Italian study from 2013, which had 15-year follow-up after KT, clearly showed that graft survival in patients with IgAN recurrence is significantly lower compared to those without [7].

Several studies suggested a significant association between genetic aspects and the development of IgAN. These include differences in IgAN prevalence between ancestral groups, higher prevalence in relatives of affected individuals, or reports of large pedigrees containing multiple affected individuals [8]. Previous research on the association between the human leukocyte antigen (HLA) system and the development of IgAN has most often pointed to an association with HLA class II genes. The strongest association was inverse to the HLA-B, -DQA, -DQB, and -DRB1 loci [9]. Regarding IgAN recurrence, a broad spectrum of risk factors has been described. The most frequently mentioned are low recipient age, rapidly progressive disease course before KT, living-related donor, donor-specific antibodies (DSA) presence, or zero HLA mismatches [8,10]. A clear association with specific HLA alleles has not been demonstrated. Since there is still no effective treatment for recurrent IgAN in clinical practice, it is very important to identify patients at high risk of recurrence prior to KT. Identifying patients who are at increased risk of IgAN recurrence may be key to their future management. An individualized approach to choice of induction and maintenance immunosuppression may be the best way to strike the right balance between preventing recurrence of glomerulopathy while minimizing the risk of infectious or metabolic complications.

The primary aim of our study was to identify risk and protective HLA class I and II alleles for the development of IgAN and its subsequent recurrence after KT. A secondary aim was to describe patient demographic and clinical characteristics associated with recurrence and the diagnostic and therapeutic methods used.

Material and Methods

This retrospective single-center analysis included all adult patients who underwent primary or higher KT until July 2024 at the Transplant-Nephrology Department of the University Hospital in Martin, Slovakia. The study group’s primary inclusion criterion was histologically confirmed IgAN as the underlying cause of CKD and the subsequent native kidney failure. Exclusion criteria were loss of patient to follow-up at our center and unavailability of complete histological finding from the patient’s native kidney biopsy, which could skew the incidence of IgAN. Baseline patient characteristics were recorded (sex, age at the time of transplantation, and transplant characteristics), as well as primary/higher, donor type, type of induction immunosuppression, and onset of graft function. We identified patients with IgAN in native kidneys who underwent graft biopsy after KT and evaluated the recurrence of IgAN. Patients underwent either a protocol graft biopsy, which was performed at 3 and 12 months after KT, or an indication biopsy at any time after KT. Indications for biopsy were deteriorating graft function, as reflected by a decrease in estimated glomerular filtration rate (eGFR), progressive proteinuria, and detection of de novo DSA by Luminex. In these patients, in addition to the baseline characteristics listed above, we recorded the time to confirmation of recurrence, biopsy type, indication for biopsy, treatment of recurrent IgAN, incidence of graft rejection, and its treatment in the post-transplantation period.

We detected HLA typing in IgAN patients who underwent KT. HLA typing was investigated in all patients in the cohort at the time of listing on the waiting list before KT. HLA typing was performed using a real-time polymerase chain reaction (PCR) system, which included the LinkSēq™ HLA-ABCDRDQB1 384 diagnostic kit, PCR water (Solis Biodyne), Quanstudio™ 6 pro (Thermo Fisher Scientific), Fluorometer Qubit 4.0 (Thermo Fisher Scientific), Qubit dsDNA BR kit (Thermo Fisher Scientific), Design and Analysis™ 2.6.0 software (Thermo Fisher Scientific), and SureTyper™ evaluation software (Thermo Fisher Scientific). We used a virtual calculated panel-reactive antibody (cPRA) calculator to assess potential risk and protective alleles of the HLA system for the occurrence of IgAN in our cohort, and the control group consisted of 10 000 healthy donors from the Eurotransplant registry. We assessed the potential risk or protectiveness of the identified HLA alleles as linkage disequilibrium.

Statistical analyses were performed using a certified statistical program, MedCalc version 13.1.2 (MedCalc Software VAT registration number BE 0809 344 640, Member of International Association of Statistical Computing, Ostend, Belgium). Descriptive statistics were used to summarize patient characteristics, including means with standard deviations and percentages. Odds ratios and the chi-squared test were used to compare the frequency of HLA alleles between selected groups. Multivariate analysis used Cox proportional hazards regression to identify specific HLA alleles as an independent predictor of IgAN recurrence. Correlation coefficients were calculated to assess the relationships between IgAN recurrence and variables. A P value <0.05 was considered statistically significant.

All procedures involving human participants were approved according to the ethical standards of the institutional research committee, including the 1964 Helsinki Declaration and its later amendments, or comparable ethical standards. The study protocol was checked and approved by University Hospital’s and Jessenius Faculty of Medicine’s Ethics Committees (EK 73/2024). The clinical and research activities being reported are consistent with the Principles of the Declaration of Istanbul as outlined in the Declaration of Istanbul on Organ Trafficking and Transplant Tourism.

Results

The primary screening included 470 patients after KT at the Transplant-Nephrology Department in Martin. IgAN as the primary cause of failure of the native kidneys and verified histologically was identified in 7.2% of them (n=48). Patients with IgAN were male in 77.1% of cases (n=37), and their mean age at the time of KT was 42.6 years.

Table 1 shows the prevalence of selected alleles of HLA-DRB1 and HLA-DQB1 loci in the IgAN patient group and the population of healthy donors. Comparing their frequency of occurrence in each group, we found that the HLA-DRB1*11 allele was present in 47.92% of patients with confirmed IgAN (n=23), which was significantly more frequent (OR 2.09) than in the healthy donor group (22.98%). We also observed the HLA-DRB1*04 allele more frequently in the IgAN group, and it was present in 33.33% (n=16) compared with 24.58% in the healthy control group (OR 1.33). Using the chi-squared test, we confirmed that the HLA-DRB1*11 allele is statistically significantly more prevalent in the IgAN-confirmed patient population (P=0.0048) and is thus a risk factor for developing this disease. The HLA-DRB1*04 allele was not statistically significantly more frequently associated with the development of IgAN (P=0.3061).

However, the HLA-DRB1*03 allele was identified as potentially protective against IgAN development. We observed the occurrence of this allele in 4.17% of the IgAN group (n=2), which was significantly lower compared to the healthy control group, where the prevalence was 21.73% (OR 0.2). However, using the chi-squared test, we did not confirm that its prevalence was statistically significantly correlated with a lower incidence of IgAN (P=0.5472). At the HLA-DQB locus, we observed a frequent HLA-DQB1*03 allele in both groups: 66% in the IgAN group versus 55.58% in the control group (OR 1.19). The HLA-DQB1*02 allele was present in 16.67% of IgAN patients compared to 36.39% of healthy donors (OR 0.47) (Table 1).

Of the IgAN patients (n=48), 70.8% (n=34) underwent graft biopsy at various times after KT, with 47 biopsies performed. Most cases involved protocol biopsies (61.7%, n=29), of which 25 were performed in the third month after KT and 4 in the twelfth month after KT. An indication biopsy was performed in 38.3% (n=18) and in a total of 13 patients. Recurrence of IgAN in the transplanted graft was confirmed 10 times and in 9 patients, as 1 patient had recurrence after both primary and secondary KT. The overall incidence of recurrent IgAN in our analysis was 20.8%, but in the analysis of only patients who underwent graft biopsy, it was 29.4%. Recurrent IgAN in the graft was confirmed in 80% (n=8) by indication biopsy and in 20% by protocol biopsy (n=2), with 1 in the third and 1 in the twelfth month after KT. All patients who experienced a recurrence of IgAN were male, with a mean age of 37.5 years at the time of KT. The mean time from KT to confirmation of IgAN recurrence was 56.1 months. Graft failure in the study population occurred in 1 patient because of recurrent IgAN. The mean follow-up time from KT in the entire cohort was 89.6 months (range 6–236 months), and it was 70.2 months in the group of patients who underwent graft biopsy after KT.

Potential risk alleles of the HLA system for IgAN recurrence in the graft after KT were evaluated in multivariate analysis. The HLA-DRB1*11 allele, which we confirmed as a risk allele for IgAN in the native kidneys, was identified in 77.8% of patients (n=7) with IgAN recurrence in the graft. However, using a Cox regression hazard model, we did not identify it as an independent risk factor for IgAN recurrence (HR 2.3967; P=0.3956) (Table 2).

All patients who had a recurrence of IgAN underwent KT from a deceased donor, and we observed delayed onset of graft function in only 1 of them. There were no differences in the induction immunosuppressive regimen; antithymocyte globulin was used in 50% (n=5), basiliximab in 40% (n=4), and no induction was used in 10% (n=1). All patients were on the same maintenance immunosuppression consisting of tacrolimus, mycophenolic acid, and prednisone. All patients maintained the same range of serum tacrolimus concentrations depending on the time after KT and had the same dose of mycophenolic acid, which held constant. Of the corticosteroids, all patients received 2 pulses of methylprednisolone at 500 mg during induction, followed by switching to prednisone at 20 mg daily for the first 14 days, 15 mg daily until the end of the first month, 10 mg daily until the end of the 4th month, 7.5 mg daily until the end of the 12th month, and then were maintained on a dose of 5 mg daily thereafter. In terms of the primary presentation of the disease on which graft biopsy was indicated, 55.6% of patients (n=5) had worsening proteinuria combined with microhematuria, 22.2% (n=2) had worsening proteinuria and eGFR, 11.1% (n=1) had worsening eGFR and microhematuria, and 11.1% (n=1) had progressive proteinuria only. Three patients, after confirmation of IgAN recurrence, underwent steroid pulse therapy in which they received a total of 1.5 g of methylprednisolone. In 2 of them, a good effect of this treatment was observed, as the proteinuria disappeared or was reduced to the previous chronic level. In terms of supportive IgAN therapy, 100% (n=9) of the patients had the maximum tolerated dose of renin-angiotensin-aldosterone system (RAAS) inhibitor, and 55.6% (n=5) also had an SGLT2 inhibitor. The other 4 patients did not meet the indication criteria for this agent at that time.

We also recorded the history, type, treatment of graft rejection, and incidence of de novo DSA in patients who underwent graft biopsy after KT (n=33). We found that in the group of patients with no IgAN recurrence (n=24), 8.3% (n=2) had acute cellular rejection (ACR) and 8.3% (n=2) had antibody-mediated rejection (ABMR), and of these, 1 had serum-detected DSA (4.2%). In the group of patients with confirmed IgAN recurrence (n=9), 11.1% (n=1) had ACR, 22.2% (n=2) had ABMR, and we detected DSA in 33.3% (n=3). Due to the number of patients and the different sizes of these groups, it was impossible to compare them statistically. However, Table 3 shows the correlations of these variables with IgAN recurrence. We found a significant correlation between IgAN recurrence in the graft and the development of de novo DSA after KT (r=0.3980, P=0.0218), Table 3.

Discussion

In our retrospective single-center analysis of IgAN patients who underwent KT, we found that the HLA-DRB1*11 allele was identified as a risk factor for development of this glomerulopathy in native kidneys. This allele was present in 77.8% of patients with a recurrence of IgAN in the transplanted graft, but multivariate analysis did not confirm it as an independent risk factor for recurrence. However, the HLA-DRB1*03 allele was more common in the healthy population than in the IgAN patient group, which suggests its potential protective effect. Recurrence of IgAN after KT was confirmed in most cases by indication biopsy (80%) at a mean of 56.1 months after KT. All patients with confirmed IgAN recurrence were male, with a mean age of 37.5 years. The most common indication for biopsy after KT was a combination of worsening proteinuria and microhematuria (55.6%), and management mainly involved optimizing supportive care.

The most extensive study to date that has examined the association of IgAN and genetic aspects is a 2010 genome-wide analysis by Feehally et al, which compared 914 samples of IgAN patients with healthy controls. The study group included patients who also had ancestors affected by IgAN and patients who had incident IgAN. The authors found that the strongest single-nucleotide polymorphism (SNP) association signal was present at the major histocompatibility complex (MHC), clearly confirming the association of IgAN with HLA loci. Subsequent analysis of the inserted HLA alleles showed significant positive and negative correlations with HLA-DQB*0501 and HLA-DQB*0201, respectively. The HLA-DRB1*0301 allele was scarce among IgAN patients [9]. Our analysis also found a significantly lower representation of HLA-DRB1*03 group alleles, which may suggest an association with reduced susceptibility to IgAN. This is supported by the findings of an analysis by Vuong et al, who compared 213 White patients with confirmed IgAN with 1569 healthy individuals, and found that HLA-DRB1*03 was significantly protective against the development of disease [11]. A significantly lower abundance of this allele in IgAN patients was also identified in a retrospective analysis of 1620 patients from the Eurotransplant database [12]. On the other hand, a systematic review from 2022, which included 35 studies in the final analysis that investigated the association of HLA alleles and CKD, shows that several papers identified HLA-DRB1*03 as a risk allele for the development of CKD. However, none of these papers specifically associated it with the risk of developing IgAN, and this risk of developing CKD has been found in non-European populations [13].

Several genome-wide association studies have shown that SNPs bound to the HLA-DRB1 and -DQB1 loci are strongly associated with IgAN [9,14,15]. However, none of the previous studies identified HLA-DRB1*11 as an IgAN risk allele, as we did. The systematic review summarizes several papers linking it to a higher risk of CKD without identifying a specific risk etiology [13]. The results of studies on patients with systemic sclerosis, thrombotic thrombocytopenic purpura, or autoimmune myopathy clearly show its association with a higher susceptibility to immune-mediated diseases [16–18]. Our center’s analysis found that most patients who experienced a recurrence of IgAN after KT had this risk allele. Previous research has focused on identifying clinical risk factors for recurrence, the most common of which were young recipient age, living-donor kidney, or the presence of DSA [8,10]. None demonstrated a relationship between IgAN recurrence and a specific HLA allele. The incidence of IgAN recurrence in our cohort was 20.8%. When considering only those who underwent graft biopsy after KT, the incidence was 29.4%, which is at the lower end of the range for the incidence described in other studies. This probably is due to several reasons. One is that we started performing protocol graft biopsies at our center in 2018. Thus, patients with longer follow-up have not yet undergone a graft biopsy, which may underdiagnose recurrence. In addition, until recently we performed protocol biopsies only at 3 months after KT for early detection of subclinical graft rejection. IgAN typically recurs after KT, and its incidence increases with a longer follow-up time [10]. Protocol biopsy at 12 months was performed only in 4 of them, and in 1 case, we were also able to detect IgA recurrence. Another reason is the rate of performing native kidney biopsies of CKD patients. In our cohort of post-transplant patients, only 7.2% had biopsy-verified IgAN as the cause of their own renal failure, which is far below the average prevalence in the White population [1]. We hypothesize that in the past, patients with mild urinary findings and slow progression of CKD were not routinely referred for biopsy, which likely led to underdiagnosis of IgAN and subsequent recurrence after KT in our cohort. When looking at the characteristics of our patients with IgAN recurrence, we identified its correlation with serum de novo DSA incidence. Their possible association was suggested by the 2021 international TANGO study, which demonstrated a significant association of de novo DSAs arising after KT with IgAN recurrence rate (HR 6.65) [10]. In such a case, whether the maintenance immunosuppressive regimen was sufficient in these patients is pertinent. There were no differences in induction and maintenance immunosuppression between our cohort and the TANGO study. The TANGO study did not show a higher recurrence rate in patients with early steroid withdrawal from treatment [10]. Given that there is no effective treatment for IgAN recurrence after KT to date, we consider it important to identify the risk phenotype of patients before KT. The typing of the specific alleles of the HLA system may be crucial in this regard, as the present study and previous research clearly demonstrate their very strong association with IgAN in the native kidneys. Therefore, larger, ideally multicenter, studies on a cohort of patients with proven recurrence of IgAN is needed to confirm the association with HLA alleles, especially HLA-DRB1*11.

Our study has several limitations. The main limitation is the number of patients who had confirmed recurrence of IgAN in the graft after KT. Another limitation is that not all patients had graft biopsies performed after KT, especially after KT, for the most extended period. Patients who underwent protocol biopsy had it performed 3 months after KT, which is a short time for recurrence to occur, and few had it performed 12 months after KT. The low incidence of IgAN in our transplanted population may also be a limiting factor, which is highly likely due to the low biopsy rate in past years. Therefore, there was likely a significant percentage of patients with IgAN in our cohort who were also at risk for its recurrence in the graft. A strength of our study is that it was a comprehensive single-center analysis that suggests the important role of HLA system alleles in the risk of IgAN recurrence after KT. To the best of our knowledge, this is the first study identifying IgAN risk alleles.

Conclusions

Our single-center analysis confirmed the recurrence of IgAN in 29.4% of patients after KT. The HLA-DRB1*11 allele was identified as a risk allele for IgAN in the native kidneys and was present in most patients who experienced recurrence. IgAN recurrence in the graft was correlated with the incidence of de novo DSA after KT in our study; all these patients were male and younger. In clinical practice, it will be essential to identify patients with the IgAN risk phenotype to optimize immunosuppressive and supportive therapy and to use regular screening to reduce the high incidence of IgAN recurrence and its negative impact on graft survival.