KIR Gene and KIR Ligand Analysis to Predict Graft Rejection After Renal Transplantation

Orchestrating the Impact of KIR/HLA Interactions on Kidney Transplant

This study examines the interplay between human leukocyte antigen (HLA) compatibility and killer-cell immunoglobulin-like receptor (KIR) genotypes in influencing kidney transplantation outcomes. Understanding these interactions is crucial for improving graft survival and minimizing rejection risks. We evaluated 84 kidney transplant recipients, dividing them into two groups based on post-transplant outcomes: there were 68 with stable graft function (SGF) and 16 who experienced chronic rejection (CR). Patients were selected based on specific inclusion criteria. HLA mismatches (Class I: HLA-A, -B; Class II: HLA-DR) and KIR genotypes were determined using standard genotyping techniques. Statistical analyses, including logistic regression, were performed to correlate these factors with transplant outcomes. Significant age differences were observed, with younger patients more likely to experience graft rejection, while no significant gender-based differences were noted. A significant correlation was found between Class II mismatches and increased rejection rates, highlighting the importance of HLA-DR compatibility. Further analysis revealed that certain inhibitory KIRs, such as KIR3DL1, were associated with favorable outcomes, suggesting a protective role against graft rejection. These findings were corroborated by evaluating serum creatinine levels over multiple years, serving as a biomarker for renal function post transplant. This study underscores the critical need for meticulous HLA matching and the consideration of KIR genotypes in pre-transplant evaluations to enhance graft survival and minimize rejection risks. Integrating these genetic factors into routine clinical assessments could significantly improve personalized transplant medicine strategies, ultimately enhancing patient outcomes. Further research is needed to explore the underlying mechanisms and validate these findings in larger, diverse populations.

Allorecognition and the spectrum of kidney transplant rejection

Detection of mismatched human leukocyte antigens by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection or antibody-mediated rejection. This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several observations have recently emerged that question this dichotomization between T-cell mediated rejection and antibody-mediated rejection, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-human leukocyte antigen antibodies, the immunogenicity of donor-recipient non-human leukocyte antigen mismatches, and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies, and better outcome after kidney transplantation.

Missing Self-Induced Microvascular Rejection of Kidney Allografts: A Population-Based Study

BACKGROUND

Circulating anti-HLA donor-specific antibodies (HLA-DSA) are often absent in kidney transplant recipients with microvascular inflammation (MVI). Missing self, the inability of donor endothelial cells to provide HLA I-mediated signals to inhibitory killer cell Ig-like receptors (KIRs) on recipient natural killer cells, can cause endothelial damage in vitro, and has been associated with HLA-DSA-negative MVI. However, missing self's clinical importance as a nonhumoral trigger of allograft rejection remains unclear.

METHODS

In a population-based study of 924 consecutive kidney transplantations between March 2004 and February 2013, we performed high-resolution donor and recipient HLA typing and recipient KIR genotyping. Missing self was defined as the absence of A3/A11, Bw4, C1, or C2 donor genotype, with the presence of the corresponding educated recipient inhibitory KIR gene.

RESULTS

We identified missing self in 399 of 924 transplantations. Co-occurrence of missing self types had an additive effect in increasing MVI risk, with a threshold at two concurrent types (hazard ratio [HR], 1.78; 95% confidence interval [95% CI], 1.26 to 2.53), independent of HLA-DSA (HR, 5.65; 95% CI, 4.01 to 7.96). Missing self and lesions of cellular rejection were not associated. No HLA-DSAs were detectable in 146 of 222 recipients with MVI; 28 of the 146 had at least two missing self types. Missing self associated with transplant glomerulopathy after MVI (HR, 2.51; 95% CI, 1.12 to 5.62), although allograft survival was better than with HLA-DSA-associated MVI.

CONCLUSION

Missing self specifically and cumulatively increases MVI risk after kidney transplantation, independent of HLA-DSA. Systematic evaluation of missing self improves understanding of HLA-DSA-negative MVI and might be relevant for improved diagnostic classification and patient risk stratification.

HLA Class I Molecules as Immune Checkpoints for NK Cell Alloreactivity and Anti-Viral Immunity in Kidney Transplantation

Natural killer (NK) cells are innate lymphocytes that can kill diseased- or virally-infected cells, mediate antibody dependent cytotoxicity and produce type I immune-associated cytokines upon activation. NK cells also contribute to the allo-immune response upon kidney transplantation either by promoting allograft rejection through lysis of cells of the transplanted organ or by promoting alloreactive T cells. In addition, they protect against viral infections upon transplantation which may be especially relevant in patients receiving high dose immune suppression. NK cell activation is tightly regulated through the integrated balance of signaling via inhibitory- and activating receptors. HLA class I molecules are critical regulators of NK cell activation through the interaction with inhibitory- as well as activating NK cell receptors, hence, HLA molecules act as critical immune checkpoints for NK cells. In the current review, we evaluate how NK cell alloreactivity and anti-viral immunity are regulated by NK cell receptors belonging to the KIR family and interacting with classical HLA class I molecules, or by NKG2A/C and LILRB1/KIR2DL4 engaging non-classical HLA-E or -G. In addition, we provide an overview of the methods to determine genetic variation in these receptors and their HLA ligands.

Allograft recognition by recipient's natural killer cells: Molecular mechanisms and role in transplant rejection

The current transplant immunology dogma defends that allograft rejection is initiated by recipient's adaptive immune system. In this prevalent model, innate immune cells in general, and natural killer (NK) cells in particular, are merely considered as downstream effectors which participate in the destruction of the graft only upon recruitment by adaptive effectors: alloreactive T cells or donor-specific antibodies (DSA). Challenging this vision, recent data demonstrated that recipients' NK cells are capable of a form of allorecognition because they can sense the absence of self HLA class I molecules on the surface of graft endothelial cells. Missing-self triggers mTORC1-dependent activation of NK cells, which in turn promote the development of graft microvascular inflammation and detrimentally impact graft survival. The fact that some patients develop chronic vascular rejection in absence of DSA or genetically-predicted missing self suggests that other molecular mechanisms could underly NK cell allorecognition. This review provides an overview of these proven and putative molecular mechanisms and discusses future research directions in this emerging field in organ transplant immunology.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Missing self triggers NK cell-mediated chronic vascular rejection of solid organ transplants

Current doctrine is that microvascular inflammation (MVI) triggered by a transplant -recipient antibody response against alloantigens (antibody-mediated rejection) is the main cause of graft failure. Here, we show that histological lesions are not mediated by antibodies in approximately half the participants in a cohort of 129 renal recipients with MVI on graft biopsy. Genetic analysis of these patients shows a higher prevalence of mismatches between donor HLA I and recipient inhibitory killer cell immunoglobulin-like receptors (KIRs). Human in vitro models and transplantation of β2-microglobulin-deficient hearts into wild-type mice demonstrates that the inability of graft endothelial cells to provide HLA I-mediated inhibitory signals to recipient circulating NK cells triggers their activation, which in turn promotes endothelial damage. Missing self-induced NK cell activation is mTORC1-dependent and the mTOR inhibitor rapamycin can prevent the development of this type of chronic vascular rejection.

‘Missing self’ is a mode of natural killer (NK) cell activation aimed to detect the lack of HLA-I molecules on infected or neoplastic cells. Here, the authors show that mismatch between donor HLA-I and cognate receptors on recipient NK cells mediates microvascular inflammation-associated graft rejection, a pathology that is preventable by mTOR inhibition.

Putative role of KIR3DL1/3DS1 alleles and HLA-Bw4 ligands with end stage renal disease and long term renal allograft survival

BACKGROUND

Killer immunoglobulin receptors (KIR) are highly polymorphic in nature. KIR3DL1/3DS1 genes are known to affect HLA-B antigen binding affinity causing natural killer (NK) cell inhibition, which results into successful renal transplantation. In this study we have examined whether alleles of KIR3DL1/3DS1 play any role in changing the binding affinity with HLA-Bw4 antigen and if so then how are they associated with long term renal allograft survival. We have also evaluated plausible association of KIR3DL1 with HLA-A23/A24/A32 with renal pathophysiology.

MATERIALS AND METHODS

KIR3DL1/3DS1 allelic diversity was examined in 501 renal transplant cases and 507 controls. PCR-SSP was used to determine the incidence of KIR3DL1/3DS1 genes and HLA class-I antigens. KIR3DL1/3DS1 alleles were determined by sequencing. Expression at transcription level for KIR3DL1/3DS1 genes was evaluated in the presence of HLA-Bw4. Different statistical analyses were performed using SPSS v 22.0. p≤0.05 was considered significant. Sequence based variant effect was predicted using Variant Effect Predictor. To evaluate whether variation in KIR3DL1 and HLA interaction changes the binding affinity structure based effect prediction was carried out using MutaBind and BindProf software.

RESULTS

For KIR3DL1*0010101, no-risk and low mRNA expression was seen among antibody mediated acute rejection (ABMR) and chronic rejection (CR) cases. Whereas, 3DS1*01301, 3DL1*00401, and 3DL1*00402 showed susceptibility and elevated mRNA expression with ABMR and CR. Two mutations c.320C>T (rs143159382) and c.911G>T (rs35974949), present in alleles 3DL1*00402 and 3DL1*00401 were predicted to be deleterious. Reduced renal allograft survival was observed for individuals possessing KIR3DL1*00401-HLA-Bw4+. In relation to HLA-A locus no significance was observed with ESRD, ABMR, and CR.

DISCUSSION

The experimental and computational data corroborated with each other suggesting susceptibility for renal allograft in presence of 3DL1*00402 and 3DL1*00401 alleles.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

Dual Role of Natural Killer Cells on Graft Rejection and Control of Cytomegalovirus Infection in Renal Transplantation

Allograft rejection constitutes a major complication of solid organ transplantation requiring prophylactic/therapeutic immunosuppression, which increases susceptibility of patients to infections and cancer. Beyond the pivotal role of alloantigen-specific T cells and antibodies in the pathogenesis of rejection, natural killer (NK) cells may display alloreactive potential in case of mismatch between recipient inhibitory killer-cell immunoglobulin-like receptors (KIRs) and graft HLA class I molecules. Several studies have addressed the impact of this variable in kidney transplant with conflicting conclusions; yet, increasing evidence supports that alloantibody-mediated NK cell activation via FcγRIIIA (CD16) contributes to rejection. On the other hand, human cytomegalovirus (HCMV) infection constitutes a risk factor directly associated with the rate of graft loss and reduced host survival. The levels of HCMV-specific CD8⁺ T cells have been reported to predict the risk of posttransplant infection, and KIR-B haplotypes containing activating KIR genes have been related with protection. HCMV infection promotes to a variable extent an adaptive differentiation and expansion of a subset of mature NK cells, which display the CD94/NKG2C-activating receptor. Evidence supporting that adaptive NKG2C⁺ NK cells may contribute to control the viral infection in kidney transplant recipients has been recently obtained. The dual role of NK cells in the interrelation of HCMV infection with rejection deserves attention. Further phenotypic, functional, and genetic analyses of NK cells may provide additional insights on the pathogenesis of solid organ transplant complications, leading to the development of biomarkers with potential clinical value.

Impact of killer immunoglobulin-like receptor-human leukocyte antigens ligand incompatibility among renal transplantation

Killer immunoglobulin-like receptor (KIR) gene shows a high degree of polymorphism. Natural killer cell receptor gets activated once they bind to self-human leukocyte antigens (HLAs) with specific ligand. KIR gene and HLA ligand incompatibility due to the presence/absence of KIR in the recipient and the corresponding HLA ligand in the allograft may impact graft survival in solid organ transplantation. This study evaluates the effect of matches between KIR genes and known HLA ligands. KIR genotypes were determined using sequence specific primer polymerase chain reaction. Presence of certain KIR in a recipient, where the donor lacked the corresponding HLA ligand was considered a mismatch. The allograft was considered matched when both KIR receptor and HLA alloantigen reveald compatibility among recipient and donor. The data revealed better survival among individuals with matched inhibitory KIR receptors and their corresponding HLA ligands (KIR2DL2/DL3-HLAC2, KIR3DL1-HLABw4). On the contrary, no adverse effect was seen for matched activating KIR receptors and their corresponding HLA ligands. One of the activating gene KIR2DS4 showed risk (P = 0.0413, odds ratio = 1.91, 95% confidence interval = 1.02-3.57) association with renal allograft rejection. We conclude that the presence of inhibitory KIR gene leads to better survival; whereas activating motifs show no significant role in renal allograft survival.

Are killer cell immunoglobulin-like receptor genes important for the prediction of kidney graft rejection?

Killer cell immunoglobulin-like receptors (KIRs) are expressed on natural killer cells and minor subpopulations of thymus-derived (T) lymphocytes. KIRs may have a long cytoplasmic tail and inhibit cell activation upon ligand (HLA class I) binding, or they may have a short cytoplasmic tail and activate a cell after ligand binding. They are encoded by up to 14 genes present in different individuals in different combinations, whence their associations with several human diseases. KIR involvement in the fate of kidney allograft has not been extensively studied; nevertheless some associations had already been noticed. Their results are not concordant: some authors found no effect of KIR genotype, whereas others detected protective effect of KIR2DL2/KIR2DS2 or KIR-KIR ligand mismatch. We found an association of KIR2DS4 gene with acute rejection and a protective effect of KIR2DS5 gene. Interestingly, in patients, whose end-stage renal disease was caused by glomerulonephritis, the effect of KIR2DS4 was stronger than HLA mismatch, whereas opposite was true for recipients with other causes of renal failure.

No impact of KIR-ligand mismatch on allograft outcome in HLA-compatible kidney transplantation

Natural killer (NK) cell function can be modulated by the killer cell immunoglobulin-like receptors (KIR) which interact with human leukocyte antigen (HLA) class I molecules on target cells. KIR-ligand mismatching has recently been shown by van Bergen et al. (American Journal of Transplantation 2011; 11(9): 1959-1964) to be a significant risk factor for long-term graft loss in HLA-A, -B and -DR compatible kidney transplants. To verify this potentially important finding, we performed genotyping of 608 deceased-donor kidney graft recipients and their HLA-A, -B and -DR compatible donors for KIR and HLA, using samples and clinical data provided by the Collaborative Transplant Study. Graft survival of KIR-ligand-matched and -mismatched transplants was compared. We found no impact of KIR-ligand mismatching on 10-year graft survival in HLA-A, -B, -DR compatible kidney transplants. Further analysis did not reveal a significant effect of recipient activating/inhibitory KIR or KIR genotypes on graft survival. Our data do not support the concept that KIR-HLA matching might serve as a tool to improve long-term renal allograft survival.

Killer immunoglobulin-like receptor (KIR) and HLA genotypes affect the outcome of allogeneic kidney transplantation

Background

Recipient NK cells may detect the lack of recipient's (i.e., self) HLA antigens on donor renal tissue by means of their killer cell immunoglobulin-like receptors (KIRs). KIR genes are differently distributed in individuals, possibly contributing to differences in response to allogeneic graft.

Methodology/Principal Findings

We compared frequencies of 10 KIR genes by PCR-SSP in 93 kidney graft recipients rejecting allogeneic renal transplants with those in 190 recipients accepting grafts and 690 healthy control individuals. HLA matching results were drawn from medical records. We observed associations of both a full-length KIR2DS4 gene and its variant with 22-bp deletion with kidney graft rejection. This effect was modulated by the HLA-B,-DR matching, particularly in recipients who did not have glomerulonephritis but had both forms of KIR2DS4 gene. In contrast, in recipients with glomerulonephritis, HLA compatibility seemed to be much less important for graft rejection than the presence of KIR2DS4 gene. Simultaneous presence of both KIR2DS4 variants strongly increased the probability of rejection. Interestingly, KIR2DS5 seemed to protect the graft in the presence of KIR2DS4fl but in the absence of KIR2DS4del.

Conclusions/Significance

Our results suggest a protective role of KIR2DS5 in graft rejection and an association of KIR2DS4 with kidney rejection, particularly in recipients with glomerulonephritis.

KIR-ligand mismatches are associated with reduced long-term graft survival in HLA-compatible kidney transplantation

Natural killer (NK) cells are cytotoxic lymphocytes of the innate immune system with the ability to detect HLA class I disparities via killer-cell immunoglobulin-like receptors (KIR). To test whether such KIR-ligand mismatches contribute to the rejection of human solid allografts, we did a retrospective cohort study of 397 HLA-DR-compatible kidney transplantations and determined the KIR and HLA genotypes of recipients and the HLA genotypes of donors. In transplantations compatible for HLA-A, HLA-B and HLA-DR (n = 137), in which a role for T cells and HLA antibodies in rejection was minimized, KIR-ligand mismatches were associated with an approximately 25% reduction in 10-year death-censored graft survival (p = 0.043). This effect was comparable to the effect of classical HLA-A and HLA-B incompatibility, and in HLA-A,-B-incompatible transplantations (n = 260) no significant additional effect of KIR-ligand mismatches was observed. Multivariate Cox regression analysis confirmed the effect of KIR-ligand mismatching as an independent risk factor in HLA-A,-B,-DR-compatible transplantations (hazard ratio 2.29, range 1.03-5.10, p = 0.043). This finding constitutes the first indication that alloreactive NK cells may thwart the success of HLA-compatible kidney transplantations, and suggests that suppression of NK-cell activity can improve the survival of such kidney grafts.

Donor and recipient HLA/KIR genotypes do not predict liver transplantation outcome

Whether or not Natural Killer (NK) cells affect the immune response to solid organ allografts is still controversial. Main determinants of NK-cell activation are specific HLA/killer-cell immunoglobulin-like receptors (KIR) interactions that, in transplantation, may induce NK-cell alloreactivity. So far, in liver transplantation (LTX) donor-versus-recipient alloreactivity has not been investigated; in addition, studies of predicted recipient-versus-donor NK-cell alloreactivity have led to contradicting results. We typed a cohort of LTX donors and recipients for HLA-C/Bw4 and KIRs. We estimated the effect of NK-cell alloreactivity, as predicted by classically used models, in the donor-versus-recipient direction. The results indicate that HLA/KIR mismatches in the donor-versus-recipient direction do not predict graft rejection nor graft or patient survival, suggesting that donor-derived NK cells do not play a major role in LTX outcome. In addition, when considering predicted NK-cell alloreactivity in the reverse direction (recipient-versus-donor), we first confirmed that donor HLA-C genotype was not associated with acute rejection, graft or patient survival and secondly we found that none of the models describing NK-cell alloreactivity could predict LTX outcome. Overall our observations suggest that, in contrast to what is shown in haematopoietic stem cell transplantation, donor-derived NK cells may not contribute in preventing liver graft rejection, and that recipient-versus-donor NK-cell alloreactivity does not predict LTX outcome.

Natural killer cells and the immune response in solid organ transplantation

Natural killer (NK) cells have been characterized classically for their cytotoxicity against pathogen infected or stressed cells as well as for their role in monitoring the expression of self MHC I. However, the participation of NK cells in solid organ transplantation (SOT) is poorly defined due to conflicting clinical and animal model data. Preclinical models have shown that NK cells exacerbate T-cell allogeneic responses during rejection, but can also promote tolerance induction under immunosuppressive conditions. Further, while protocols such as costimulatory blockade effectively induce tolerance by blocking T-cell activation and promoting Treg generation, how such regimens regulate other innate and adaptive immune cells, including NK cells, is incomplete. This review examines NK cells and the regulation of their effector functions in SOT.

The number of activating KIR genes inversely correlates with the rate of CMV infection/reactivation in kidney transplant recipients

Viral infection is a common complication after kidney transplantation. The role of natural killer cells (NK cells) in this setting remains unknown. NK cells express activating and inhibitory killer cell immunoglobulin-like receptors (KIR). We analyzed whether activating KIR genes carried by kidney transplant-recipients influence the rate of viral infection during the first year after transplantation. In patients with a KIR A/A genotype (n = 40, KIR2DS4 only activating KIR) the rate of cytomegalovirus (CMV) infection and reactivation was 36%, as compared to 20% in transplant recipients with more than one activating KIR gene (KIR B/X genotype, n = 82, p = 0.04). Adjusting for other risk factors in Cox regression, the relative risk of B versus A genotype patients was 0.34 (95% CI 0.15-0.76, p = 0.009). The degree of protection increased with the number of activating KIR genes. Symptomatic CMV disease was only observed in four individuals, all carrying a KIR A/A genotype. As for viral infections other than CMV, and for bacterial infections, no KIR-linked protective effect could be detected. Also, graft function and the rate-rejection episodes were similar in KIR A/A and KIR B/X genotype individuals. This study supports a role for activating KIR in the control of CMV infection after kidney transplantation.