Elsevier

Human Immunology

Volume 81, Issue 4, April 2020, Pages 141-146
Human Immunology

HLA-G 3′ untranslated region gene variants are promising prognostic factors for BK polyomavirus replication and acute rejection after living-donor kidney transplant

https://doi.org/10.1016/j.humimm.2019.09.011Get rights and content

Abstract

The immunosuppressive non-classical human leukocyte antigen-G (HLA-G) promotes transplant tolerance as well as viral immune escape. HLA-G expression is associated with regulatory elements targeting certain single nucleotide polymorphisms (SNPs) in the HLA-G 3 untranslated region (UTR). Thus, we evaluated the impact of HLA-G 3′UTR polymorphisms as surrogate markers for BK polyomavirus (BKPyV) replication or nephropathy (PyVAN) and acute cellular and antibody mediated rejection (ACR/AMR) in 251 living-donor kidney-transplant recipient pairs. After sequencing of the HLA-G 3UTR, fourteen SNPs between +2960 and +3227 and the 14 bp insertion/deletion polymorphism, which arrange as UTR haplotypes, were identified. The UTR-4 haplotype in donors and recipients was associated with occurrence of BKPyV/PyVAN compared to the other UTR haplotypes. While the UTR-4 recipient haplotype provided protection against AMR, the UTR-2 donor haplotype was deleteriously associated with ACR/AMR. Deduction of the UTR-2/4 haplotypes to specific SNPs revealed that the +3003C variant (unique for UTR-4) in donors as well as in recipients is responsible for BKPyV/PyVAN and also provides protection against AMR; whereas the +3196G variant (unique for UTR-2) promotes allograft rejection. Thus, HLA-G 3′UTR variants are promising genetic predisposition markers both in donors and recipients that may help to predict susceptibility to either viral infectious complication of BKPyV or allograft rejection.

Introduction

BK polyomavirus (BKPyV), an ubiquitous human virus, has emerged as one of the most challenging infectious pathogens in kidney transplant in the last decade [1], [2], [3]. After primary infection, BKPyV preferentially establishes latency from which it can reactivate during episodes of immunosuppression. BKPyV replication occurs in up to 60% of all kidney-transplant recipients [4]. The most serious clinical syndrome is the BK polyomavirus-associated nephropathy (PyVAN), a severe allograft dysfunction, which shows progressive decline in kidney function potentially resulting in allograft loss [5]. Currently, there is no direct antiviral treatment approved to limit BKPyV replication and treat PyVAN. Thus, the two pillars of PyVAN management are an active surveillance for BKPyV reactivation as well as in case of BKPyV replication a reduction or modification of immunosuppression in order to reestablish sufficient antiviral control by cellular immunity [2]. At present, little is known on the pathogenesis of BKPyV and it is not clear which factors besides level of immunosuppression and donor BKPyV-seropositivity determine the clinical course of the disease. Viruses have developed various strategies to avoid recognition and destruction by immune effectors. In fact, aberrant expression of the non-classical human leukocyte antigen G (HLA-G) has been reported for several virus infections [6], [7], [8], [9], [10]. Accordingly, we showed that HLA-G 3412 SNP facilitates immune evasion of cytomegalovirus infection after kidney transplant [10].

The important checkpoint molecule HLA-G exerts inhibitory signaling on immune effector cells by interacting with the inhibitory receptors immunoglobulin-like transcript (ILT)2, ILT4 or killer-cell immunoglobulin-like receptor (KIR)2DL4. Thus, HLA-G has the capacity to suppress the function of natural killer (NK) cells and T cells, reduce B cell activation and induce expansion of regulatory T cells. In addition, soluble HLA-G triggers the apoptosis of activated CD8+ T and NK cells [11]. Under physiological conditions, HLA-G cell surface expression is restricted to the maternal-fetal interface and to immune privileged adult tissues where it mediates immune tolerance [12], [13]. However, aberrant expression of HLA-G and its soluble forms has been associated with a vast variety of pathological situations such as cancer, autoimmune, and infectious diseases where HLA-G molecules favor escape from immune surveillance. Studies in transplant cohorts have repeatedly associated an up-regulated HLA-G expression with allograft tolerance [13], [14], [15]. Only few studies have elucidated the impact of HLA-G in the combined context of infectious diseases in transplant recipients [10], [16], [17]. Therefore, it seems reasonable that although the presence of the inhibitory HLA-G molecule may be beneficial for allograft tolerance, it may be detrimental for immune surveillance of viral infections as well.

In contrast to classical HLA molecules, HLA-G displays limited allelic variations. However, at least seven distinct HLA-G isoforms are generated as result of alternative splicing [18]. These isoforms comprise membrane-bound (HLA-G1, -G2, -G3 and -G4) and soluble molecules (HLA-G5, -G6, and -G7) [19], [20], [21]. HLA-G is located on chromosome 6p21.3 and is composed of eight exons and seven introns and to date 69 HLA-G allelic variations have been identified [22]. Notably, the regulation of local HLA-G expression and its soluble forms encompasses post-transcriptional processes such as alternative splicing, altered mRNA stability, microRNA-mediated regulation of translation, and impaired protein transport to the cell surface [23]. Especially the polymorphic 3′untranslated region (UTR) shared by the HLA-G1 to HLA-G6 transcripts plays a pivotal role in HLA-G expression by interfering with transcription, splicing, mRNA stability, and translation [24]. Here, 14 single nucleotide polymorphisms (SNP; +3001C/T, +3003C/T, +3010C/G, +3027C/A, +3032C/G, +3035C/T, +3052C/T, +3092G/T, +3111A/G, +3121C/T, +3142C/G, +3187A/G, +3196C/G, and +3227A/G) and the well-studied 14 bp insertion/deletion (INS/DEL) located at position +2961 have been identified in the 3′UTR potentially modifying the affinity of sequence-specific regulators of gene expression for post-transcriptional factors [24], [25]. These polymorphisms arrange as haplotypes, named UTRs (Table S1). Six already identified microRNA (miR), miR-148a, miR-148b, miR-152, miR-133a, miR-628-5p, and miR-548q, have been reported to bind to certain SNPs in the 3′UTR in a sequence-specific manner, leading to downregulation of HLA-G expression [22].

To our knowledge, there are no studies on the association between BKPyV replication and HLA-G 3UTR polymorphisms in kidney transplant donor and recipients. Considering the functional differences between the HLA-G polymorphisms within the 3′UTR, we hypothesized that the genetic background affects the clinical occurrence BKPyV replication and PyVAN as well as rejection after kidney transplantation, and might serve as a predictive parameter to identify patients at risk.

Section snippets

Study population, BKPyV, and PyVAN screening

In total, 251 living-donor kidney transplant recipients and their corresponding donors from the living-kidney donor program at University Hospital Essen, Germany, were enrolled in this retrospective study. Transplantations were performed from 2005 till 2017. Exclusion criteria were CMV disease during follow-up (n = 33) and immunosuppression containing an mTOR inhibitor (n = 10) [26]. Informed consent was obtained from all patients in accordance with the Declaration of Helsinki, and the local

Results

In total, 30 recipients (14.4%) were tested positive for BKPyV viremia. Nine out of these 30 recipients had at least one biopsy proven PyVAN after kidney transplantation.

Discussion

HLA-G is a naturally occurring immune suppressive molecule that plays an important role in the modulation of immunity. Its expression is regulated at transcriptional, co-, and post-transcriptional levels. Co- and post-transcriptional regulation is achieved by alternative splicing or binding of certain miRNAs within the HLA-G 3UTR [31]. A number of studies highlighted the differential modulation of HLA-G gene expression as a prognostic factor for clinical outcome in a variety of pathological

Conclusion

The present data highlight the complexity of the genetic background of HLA-G affecting the clinical course of kidney transplantation. Improved understanding of HLA-G regulation will contribute to the development of strategies detecting BKPyV or rejection-susceptible recipients prior to kidney transplant, thus helping to improve allograft survival.

Author contributions

HR, PAH, OW, VR: conceived and designed research. HR, ES, RTM, SS: performed the experiments. FMH: contributed reagents. SD, AG, BW, JK: collected and provided clinical data. HR, ES, RTM, VR: interpreted data and HR, ES, AG, VR: performed statistical analysis. HR and VR: wrote the initial draft. HR, ES, RTM, SS, SD, AG, MT, BW, JK, FMH, PAH, AK, OW, VR: read and approved the final article.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank the living-donor and recipient pairs participating in this study.

HR was supported by the “IFORES Research fellowship-program of the University Duisburg-Essen Medical School”. OW is supported by an unrestricted grant of the Rudolf-Ackermann-Stiftung (Stiftung für Klinische Infektiologie).

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