KIR-associated protection from CMV replication requires pre-existing immunity: a prospective study in solid organ transplant recipients

The impact of HLA polymorphism on herpesvirus infection and disease

Human Leukocyte Antigens (HLA) are cell surface molecules, central in coordinating innate and adaptive immune responses, that are targets of strong diversifying natural selection by pathogens. Of these pathogens, human herpesviruses have a uniquely ancient relationship with our species, where coevolution likely has reciprocating impact on HLA and viral genomic diversity. Consistent with this notion, genetic variation at multiple HLA loci is strongly associated with modulating immunity to herpesvirus infection. Here, we synthesize published genetic associations of HLA with herpesvirus infection and disease, both from case/control and genome-wide association studies. We analyze genetic associations across the eight human herpesviruses and identify HLA alleles that are associated with diverse herpesvirus-related phenotypes. We find that whereas most HLA genetic associations are virus- or disease-specific, HLA-A*01 and HLA-A*02 allotypes may be more generally associated with immune susceptibility and control, respectively, across multiple herpesviruses. Connecting genetic association data with functional corroboration, we discuss mechanisms by which diverse HLA and cognate receptor allotypes direct variable immune responses during herpesvirus infection and pathogenesis. Together, this review examines the complexity of HLA-herpesvirus interactions driven by differential T cell and Natural Killer cell immune responses.

Cohort profile: The Swiss Transplant Cohort Study (STCS): A nationwide longitudinal cohort study of all solid organ recipients in Switzerland

PURPOSE

The Swiss Transplant Cohort Study (STCS) is a prospective multicentre cohort study which started to actively enrol study participants in May 2008. It takes advantage of combining data from all transplant programmes in one unique system to perform comprehensive nationwide reporting and to promote translational and clinical post-transplant outcome research in the framework of Swiss transplantation medicine.

PARTICIPANTS

Over 5500 solid organ transplant recipients have been enrolled in all six Swiss transplant centres by end of 2019, around three-quarter of them for kidney and liver transplants. Ninety-three per cent of all transplanted recipients have consented to study participation, almost all of them (99%) contributed to bio-sampling. The STCS genomic data set includes around 3000 patients.

FINDINGS TO DATE

Detailed clinical and laboratory data in high granularity as well as patient-reported outcomes from transplant recipients and activities in Switzerland are available in the last decade. Interdisciplinary contributions in diverse fields of transplantation medicine such as infectious diseases, genomics, oncology, immunology and psychosocial science have resulted in approximately 70 scientific papers getting published in peer-review journals so far.

FUTURE PLANS

The STCS will deepen its efforts in personalised medicine and digital epidemiology, and will also focus on allocation research and the use of causal inference methods to make complex matters in transplant medicine more understandable and transparent.

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.

Molecular Signatures of Natural Killer Cells in CMV-Associated Anterior Uveitis, A New Type of CMV-Induced Disease in Immunocompetent Individuals

Cytomegalovirus (CMV) causes clinical issues primarily in immune-suppressed conditions. CMV-associated anterior uveitis (CMV-AU) is a notable new disease entity manifesting recurrent ocular inflammation in immunocompetent individuals. As patient demographics indicated contributions from genetic background and immunosenescence as possible underlying pathological mechanisms, we analyzed the immunogenetics of the cohort in conjunction with cell phenotypes to identify molecular signatures of CMV-AU. Among the immune cell types, natural killer (NK) cells are main responders against CMV. Therefore, we first characterized variants of polymorphic genes that encode differences in CMV-related human NK cell responses (Killer cell Immunoglobulin-like Receptors (KIR) and HLA class I) in 122 CMV-AU patients. The cases were then stratified according to their genetic features and NK cells were analyzed for human CMV-related markers (CD57, KLRG1, NKG2C) by flow cytometry. KIR3DL1 and HLA class I combinations encoding strong receptor–ligand interactions were present at substantially higher frequencies in CMV-AU. In these cases, NK cell profiling revealed expansion of the subset co-expressing CD57 and KLRG1, and together with KIR3DL1 and the CMV-recognizing NKG2C receptor. The findings imply that a mechanism of CMV-AU pathogenesis likely involves CMV-responding NK cells co-expressing CD57/KLRG1/NKG2C that develop on a genetic background of KIR3DL1/HLA-B allotypes encoding strong receptor–ligand interactions.

The Role of HLA and KIR Immunogenetics in BK Virus Infection after Kidney Transplantation

BK virus (BKV) is a polyomavirus with high seroprevalence in the general population with an unremarkable clinical presentation in healthy people, but a potential for causing serious complications in immunosuppressed transplanted patients. Reactivation or primary infection in kidney allograft recipients may lead to allograft dysfunction and subsequent loss. Currently, there is no widely accepted specific treatment for BKV infection and reduction of immunosuppressive therapy is the mainstay therapy. Given this and the sequential appearance of viruria-viremia-nephropathy, screening and early detection are of utmost importance. There are numerous risk factors associated with BKV infection including genetic factors, among them human leukocyte antigens (HLA) and killer cell immunoglobulin-like receptors (KIR) alleles have been shown to be the strongest so far. Identification of patients at risk for BKV infection would be useful in prevention or early action to reduce morbidity and progression to frank nephropathy. Assessment of risk involving HLA ligands and KIR genotyping of recipients in the pre-transplant or early post-transplant period might be useful in clinical practice. This review summarizes current knowledge of the association between HLA, KIR and BKV infection and potential future directions of research, which might lead to optimal utilization of these genetic markers.

Challenges and Clinical Implications of the Diagnosis of Cytomegalovirus Lung Infection in Children

PURPOSE OF REVIEW

Pulmonary cytomegalovirus (CMV) infection is a potential lethal disease in children, but it remains a diagnostic challenge. The differentiation between latent CMV infections with viral shedding and active infections is difficult and may lead to false positives in bronchoalvolar lavage (BAL) PCR detection. This review summarizes current diagnostic approaches for CMV lung infection in children including progress in the identification of underlying immune defects linked to this condition.

RECENT FINDINGS

There is increasing literature supporting that the combined assessment of host risk factors and lung disease pattern is essential for the diagnosis of pulmonary CMV infection in children. The most important host risk factor is an immunecompromised state that has expanded from primary or acquired immunodeficiency (e.g., HIV) to include a myriad of immune-dysregulation syndromes (e.g., CTLA4, PIK3 defects). Newborns, paricularly those born premature, are also a high-risk group. At the pulmonary level, active CMV infection is typically characterized by alveolar compromise leading to hypoxemia, ground-glass opacities, and intra-alveolar infiltrates with CMV inclusions in lung biopsy. The identification of active CMV lung infection should trigger additional evaluation of immune defects (primary or secondary) impairing T and NK cell function or innate antiviral responses as well as other immune dysregulation disorders. Lung CMV infections in children are more prevalent in immunocompromised hosts and premature newborns. Lung CMV infections should prompt further investigation into conditions altering immune mechanisms usually in place to contain CMV infections. Common clinical and radiological patterns such as hypoxemia and ground-glass pulmonary opacities may allow early identification and treatment of CMV lung infection and underlying causes in the pediatric population.

Killer Immunoglobulin-Like Receptor 2DS2 (KIR2DS2), KIR2DL2-HLA-C1, and KIR2DL3 as Genetic Markers for Stratifying the Risk of Cytomegalovirus Infection in Kidney Transplant Recipients

Infection with cytomegalovirus (CMV) remains a major problem in kidney transplant recipients, resulting in serious infectious complications and occasionally mortality. Accumulating evidence indicates that natural killer cell immunoglobulin-like receptors (KIRs) and their ligands affect the susceptibility to various diseases, including viral infections (e.g., CMV infection). We investigated whether KIR genes and their ligands affect the occurrence of CMV infection in a group of 138 kidney transplant recipients who were observed for 720 days posttransplantation. We typed the recipients for the presence of KIR genes (human leukocyte antigen C1 [HLA-C1], HLA-C2, HLA-A, HLA-B, and HLA-DR1) by polymerase chain reaction with sequence-specific primers. The multivariate analysis revealed that the lack of KIR2DS2 (p = 0.035), the presence of KIR2DL3 (p = 0.075), and the presence of KIR2DL2–HLA-C1 (p = 0.044) were risk factors for posttransplant CMV infection. We also found that a lower estimated glomerular filtration rate (p = 0.036), an earlier time of antiviral prophylaxis initiation (p = 0.025), lymphocytopenia (p = 0.012), and pretransplant serostatus (donor-positive/recipient-negative; p = 0.042) were independent risk factors for posttransplant CMV infection. In conclusion, our findings confirm that the KIR/HLA genotype plays a significant role in anti-CMV immunity and suggest the contribution of both environmental and genetic factors to the incidence of CMV infection after kidney transplantation.

The Third International Consensus Guidelines on the Management of Cytomegalovirus in Solid-organ Transplantation

Despite recent advances, cytomegalovirus (CMV) infections remain one of the most common complications affecting solid organ transplant recipients, conveying higher risks of complications, graft loss, morbidity, and mortality. Research in the field and development of prior consensus guidelines supported by The Transplantation Society has allowed a more standardized approach to CMV management. An international multidisciplinary panel of experts was convened to expand and revise evidence and expert opinion-based consensus guidelines on CMV management including prevention, treatment, diagnostics, immunology, drug resistance, and pediatric issues. Highlights include advances in molecular and immunologic diagnostics, improved understanding of diagnostic thresholds, optimized methods of prevention, advances in the use of novel antiviral therapies and certain immunosuppressive agents, and more savvy approaches to treatment resistant/refractory disease. The following report summarizes the updated recommendations.

NK cell and Th17 responses are differentially induced in murine cytomegalovirus infected renal allografts and vary according to recipient virus dose and strain

Human cytomegalovirus (HCMV) donor positive (D+) serostatus with acute rejection is associated with renal allograft loss, but the impact of recipient positive (R+) serostatus is unclear. In an allogeneic renal transplant model, antiviral natural killer (NK) and CD8+ T cell memory responses in murine CMV (MCMV) D+/R+ transplants were compared to D-/R- and D+/R- transplants, with recipient infection varied by MCMV dose and strain. D+/R- transplants had high primary antiviral cytolytic (interferon-γ+) and cytotoxic (granzyme B+) NK responses, whereas NK memory responses were lower in D+/R+ recipients receiving a high primary MCMV dose. Despite MCMV immunity, D+/R+ recipients receiving a low MCMV dose showed primary-like high cytolytic and cytotoxic NK responses. D+/R+ transplants infected with different D/R strains had low cytolytic NK responses but high cytotoxic NK responses. NK memory also induced a novel TNF-α+ NK response among high-dose virus recipients. MCMV+ transplants had greater Th17 responses than MCMV-uninfected transplants and Th17 inhibition ameliorated graft injury. All MCMV+ recipients had similar CD8+ T cell responses. In sum, NK and Th17 responses, but not CD8+ T cells, varied according to conditions of primary recipient infection. This variability could contribute to variable graft outcomes in HCMV D+/R+ renal transplantation.

LILRB1 polymorphisms influence posttransplant HCMV susceptibility and ligand interactions

UL18 is a human CMV (HCMV) MHC class I (MHCI) homolog that efficiently inhibits leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1)+ NK cells. We found an association of LILRB1 polymorphisms in the regulatory regions and ligand-binding domains with control of HCMV in transplant patients. Naturally occurring LILRB1 variants expressed in model NK cells showed functional differences with UL18 and classical MHCI, but not with HLA-G. The altered functional recognition was recapitulated in binding assays with the binding domains of LILRB1. Each of 4 nonsynonymous substitutions in the first 2 LILRB1 immunoglobulin domains contributed to binding with UL18, classical MHCI, and HLA-G. One of the polymorphisms controlled addition of an N-linked glycan, and that mutation of the glycosylation site altered binding to all ligands tested, including enhancing binding to UL18. Together, these findings indicate that specific LILRB1 alleles that allow for superior immune evasion by HCMV are restricted by mutations that limit LILRB1 expression selectively on NK cells. The polymorphisms also maintained an appropriate interaction with HLA-G, fitting with a principal role of LILRB1 in fetal tolerance.

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.

A significant effect of the killer cell immunoglobulin-like receptor ligand human leucocyte antigen-C on fibrosis progression in chronic C hepatitis with or without liver transplantation

BACKGROUND & AIMS

The interaction of killer cell immunoglobulin-like receptors with their human leucocyte antigen ligands drives the activation and inhibition of natural killer cells. Natural killer cells could be implicated in the development of liver fibrosis in chronic hepatitis C.

METHODS

We analysed 206 non-transplanted and 53 liver transplanted patients, selected according to their Metavir fibrosis stage. Several variables such as the number of activator killer cell immunoglobulin-like receptors or the human leucocyte antigen ligands were considered in multinomial and logistic regression models. Possible confounding variables were also investigated.

RESULTS

The killer cell immunoglobulin-like receptors were not significant predictors of the fibrosis stage. Conversely, a significant reduction of the human leucocyte antigen-C1C2 genotype was observed in the most advanced fibrosis stage group (F4) in both cohorts. Furthermore, the progression rate of fibrosis was almost 10 times faster in the subgroup of patients after liver transplantation, and human leucocyte antigen-C1C2 was significantly reduced in this cohort compared with non-transplanted patients.

CONCLUSION

This study suggests a possible role of killer cell immunoglobulin-like receptors and their ligands in the development of liver damage. The absence of C1 and C2 ligands heterozygosity could lead to less inhibition of natural killer cells and a quicker progression to a high level of fibrosis in patients infected with hepatitis C virus, especially following liver transplantation.

Killer-cell immunoglobulin-like receptors and cytomegalovirus reactivation during late pregnancy

Human cytomegalovirus (CMV) represents an important public health concern as it is associated with severe morbidity and mortality in transplant recipients, HIV-infected individuals and pregnant women given the risk of congenital infection. Congenital CMV is a leading cause of neurological sequelae, developmental delay and birth defects worldwide. Cytomegalovirus can be transmitted to the foetus following maternal infection or reactivation. NK cells expressing killer-cell immunoglobulin-like receptors (KIR) are part of the innate immune system and the first line of defence against viral incursions. Previous reports have shown that KIR genes are associated with CMV infections in the post-transplant setting. In this study, we set out to determine whether a protective effect of KIR genes over CMV infection is seen in Mexican pregnant women. Cytomegalovirus infection was assessed through nucleic acid testing in 200 pregnant women and 600 healthy blood donors comprising the Mexican mestizo reference population. Killer-cell immunoglobulin-like receptors and HLA-C genotypes were obtained from 200 pregnant women and 300 reference samples using a comprehensive PCR-SSP approach. We observed statistically lower carrier frequencies of cB03|tA01 gene-content haplotype, of cB03 haplotype motif, of the KIR2DL5 + 2DS3/2DS5 gene pair and of KIR2DL5 amongst CMV-positive pregnant women in comparison with those CMV negative. None of these were associated with CMV status in the reference population. Logistic regression analysis revealed that the most important factor determining CMV status during third-trimester pregnancies was the KIR2DL5 + 2DS3/2DS5 gene pair (OR 0.376 (95%CI 0.174, 0.811, P = 0.013). Our results indicate that CMV-protective KIR gene associations described in Caucasoid populations are also present in the genetically distinct Mexican mestizo population. Our results suggest that certain KIR gene combinations provide protection against CMV infections occurring during late-term pregnancies, a finding of utmost epidemiological importance given its implication with congenital CMV infections.

Activating KIRs and NKG2C in Viral Infections: Toward NK Cell Memory?

Natural killer (NK) cells are important players in the immune defense against viral infections. The contribution of activating killer immunoglobulin-like receptors (KIRs) and CD94/NKG2C in regulating anti-viral responses has recently emerged. Thus, in the hematopoietic stem cell transplantation setting, the presence of donor activating KIRs (aKIRs) may protect against viral infections, while in HIV-infected individuals, KIR3DS1, in combination with HLA-Bw4-I80, results in reduction of viral progression. Since, studies have been performed mainly at the genetic or transcriptional level, the effective size, the function, and the "licensing" status of NK cells expressing aKIRs, as well as the nature of their viral ligands, require further investigation. Certain viral infections, mainly due to Human cytomegalovirus (HCMV), can deeply influence the NK cell development and function by inducing a marked expansion of mature NKG2C(+) NK cells expressing self-activating KIRs. This suggests that NKG2C and/or aKIRs are involved in the selective proliferation of this subset. The persistent, HCMV-induced, imprinting suggests that NK cells may display unexpected adaptive immune traits. The role of aKIRs and NKG2C in regulating NK cell responses and promoting a memory-like response to certain viruses is discussed.

The swiss transplant cohort study: lessons from the first 6 years

Prospective cohort studies significantly contribute to answering specific research questions in a defined population. Since 2008, the Swiss Transplant Cohort Study (STCS) systematically enrolled >95 % of all transplant recipients in Switzerland, collecting predefined data at determined time points. Designed as an open cohort, the STCS has included >3900 patients to date, with a median follow-up of 2.96 years (IQR 1.44-4.73). This review highlights some relevant findings in the field of transplant-associated infections gained by the STCS so far. Three key general aspects have crystallized: (i) Well-run cohort studies are a powerful tool to conduct genetic studies, which are crucially dependent on a meticulously described phenotype. (ii) Long-term real-life observations are adding a distinct layer of information that cannot be obtained during randomized studies. (iii) The systemic collection of data, close interdisciplinary collaboration, and continuous analysis of some key outcome data such as infectious diseases endpoints can improve patient care.

Haploidentical Haematopoietic Stem Cell Transplantation: Role of NK Cells and Effect of Cytomegalovirus Infections

Natural killer cells play an important role in the immune responses against cancer and viral infections. In addition, NK cells have been shown to exert a key role in haploidentical hematopoietic stem cell (HSC) transplantation for the therapy of high-risk leukemias. The anti-leukemia effect is mostly related to the presence of "alloreactive" NK cells, i.e., mature KIR(+) NK cells that express inhibitory KIR mismatched with HLA class I (KIR-L) of the patient. In addition, an important role is played by certain activating KIR (primarily, but not only, KIR2DS1) upon interaction with their HLA class I ligand (C2 alleles). In general, the presence of activating KIR correlates with a better prognosis. Beside the infusion of "pure" CD34(+) cells, a novel protocol has been recently developed in which depletion of αβ T cells and CD19(+) B cells makes it possible to infuse into the patient, together with donor CD34(+) HSCs, important effector cells including mature PB NK cells and γδ T cells. Recent studies revealed that cytomegalovirus (CMV) infection/reactivation may induce rapid NK cell maturation and greatly influence the NK receptor repertoire. The remarkable expansion of a subset expressing the activating receptor NKG2C, together with a more efficient virus-specific effector response after rechallenge with CMV (i.e., antigen specificity), and the longevity of the expanded population are all features consistent with an adaptive type of response and support the notion of a memory-like activity of NK cells.

Global scientific vision with local vigilance: renal transplantation in developing countries

CONTEXT

Renal Transplantation is the most effective treatment for patients with end-stage renal disease, which is fortunately available in the developing countries, even for poor people. Nonetheless, the way forward should be the implementation of advanced science of transplantation, allograft monitoring abilities, knowledge about the epidemiology of renal disease in any specific region, awareness about the influence of ethenic and genetic factors immunosuppressant bioavailability, and post-transplant complications all strongly affecting the patients and allograft survival.

EVIDENCE ACQUISITIONS

In this process we searched mainly in PubMed, Web of Science and Google Scholar data bases for key words of renal allograft monitoring, post-transplant infections, renal/kidney transplantation and Iran. We followed the cross articles to follow our main idea to find a connection between modern advancement in renal allograft monitoring and our practice in developing countries. Another focus was on the special infectious and non-infection complication that do exist in specific region and need specific considerations.

RESULTS

Implementation of modern techniques of immune monitoring, allograft function, awareness about the specific infectious and non-infectious disease in each region improves the quality of renal transplantation.

CONCLUSIONS

We need to combine the advance scientific vision with local vigilance to achieve the best outcome in renal allograft recipients.