Adaptive natural killer cell expression in response to cytomegalovirus infection in blood and solid cancer

Natural Killer (NK) cells are conventionally thought to be an indefinite part of innate immunity. However, in a specific subset of NK cells, recent data signify an extension of their "duties" in immune surveillance and response, having characteristics of adaptive immunity, in terms of persistence and cytotoxicity. These cells are known as the adaptive or memory-like NK cells, where human cytomegalovirus (HCMV) infection has been shown to drive the expansion of adaptive NKG2C+ NK cells. HCMV is a ubiquitous pathogen whose prevalence differs worldwide with respect to the socioeconomic status of countries. The adaptive NK cell subpopulation is often characterized by the upregulated expression of NKG2C, CD16, and CD2, and restricted expression of NKG2A, FCεRγ and killer immunoglobulin-like receptors (KIR), although these phenotypes may differ in different disease groups. The reconfiguration of these receptor distributions has been linked to epigenetic factors. Hence, this review attempts to appraise literature reporting markers associated with adaptive or memory-like NK cells post-HCMV infection, in relation to solid cancers and hematological malignancies. Adaptive NK cells, isolated and subjected to ex vivo modifications, have the potential to enhance anti-tumor response which can be a promising strategy for adoptive immunotherapy.

Innate and adaptive effector immune drivers of cytomegalovirus disease in lung transplantation: a double-edged sword

Up to 90% of the global population has been infected with cytomegalovirus (CMV), a herpesvirus that remains latent for the lifetime of the host and drives immune dysregulation. CMV is a critical risk factor for poor outcomes after solid organ transplant, though lung transplant recipients (LTR) carry the highest risk of CMV infection, and CMV-associated comorbidities compared to recipients of other solid organ transplants. Despite potent antivirals, CMV remains a significant driver of chronic lung allograft dysfunction (CLAD), re-transplantation, and death. Moreover, the extended utilization of CMV antiviral prophylaxis is not without adverse effects, often necessitating treatment discontinuation. Thus, there is a critical need to understand the immune response to CMV after lung transplantation. This review identifies key elements of each arm of the CMV immune response and highlights implications for lung allograft tolerance and injury. Specific attention is paid to cellular subsets of adaptive and innate immune cells that are important in the lung during CMV infection and reactivation. The concept of heterologous immune responses is reviewed in depth, including how they form and how they may drive tissue- and allograft-specific immunity. Other important objectives of this review are to detail the emerging role of NK cells in CMV-related outcomes, in addition to discussing perturbations in CMV immune function stemming from pre-existing lung disease. Finally, this review identifies potential mechanisms whereby CMV-directed treatments may alter the cellular immune response within the allograft.

Is HLA-E with its receptors an immune checkpoint or an antigenic determinant in allo-HCT?

Hematopoietic cell transplantation (HCT) represents a potentially curative therapeutic approach for various hematologic and non-hematologic malignancies. Human leukocyte antigen (HLA) matching is still the central selection criterion for HCT donors. Nevertheless, post-transplant complications, in particular graft-versus-host disease (GvHD), relapse of disease and infectious complications, represent a major challenge and contribute significantly to morbidity and mortality. Recently, non-classical HLA class I molecules, especially HLA-E, have gained increasing attention in the context of allogeneic HCT. This review aims to summarize the latest findings on the immunomodulatory role of HLA-E, which serves as a ligand for receptors of the innate and adaptive immune system. In particular, we aim to elucidate how (i) polymorphisms within HLA-E, (ii) the NKG2A/C axis and (iii) the repertoire of peptides presented by HLA-E jointly influence the functionality of immune effector cells. Understanding this intricate network of interactions is crucial as it significantly affects NK and T cell responses and thus clinical outcomes after HCT.

Natural killer cell functional genetics and donor-specific antibody-triggered microvascular inflammation

Antibody-mediated rejection (ABMR) is a leading cause of graft failure. Emerging evidence suggests a significant contribution of natural killer (NK) cells to microvascular inflammation (MVI). We investigated the influence of genetically determined NK cell functionality on ABMR development and activity. The study included 86 kidney transplant recipients subjected to systematic biopsies triggered by donor-specific antibody detection. We performed killer immunoglobulin-like receptor typing to predict missing self and genotyped polymorphisms determining NK cell functionality (FCGR3AV/F158 [rs396991], KLRC2wt/del, KLRK1HNK/LNK [rs1049174], rs9916629-C/T). Fifty patients had ABMR with considerable MVI and elevated NK cell transcripts. Missing self was not related to MVI. Only KLRC2wt/wt showed an association (MVI score: 2 [median; interquartile range: 0-3] vs 0 [0-1] in KLRC2wt/del recipients; P = .001) and remained significant in a proportional odds multivariable model (odds ratio, 7.84; 95% confidence interval, 2.37-30.47; P = .001). A sum score incorporating all polymorphisms and missing self did not outperform a score including only KLRC2 and FCGR3A variants, which were predictive in univariable analysis. NK cell genetics did not affect graft functional decline and survival. In conclusion, a functional KLRC2 polymorphism emerged as an independent determinant of ABMR activity, without a considerable contribution of missing self and other NK cell gene polymorphisms.

Significance of HLA-E and its two NKG2 receptors in development of complications after allogeneic transplantation of hematopoietic stem cells

Transplantation of hematopoietic stem cells (HSCT) is a procedure commonly used in treatment of various haematological disorders which is associated with significantly improved survival rates. However, one of its drawbacks is the possibility of development of post-transplant complications, including acute and chronic graft-versus-host disease (GvHD) or CMV infection. Various studies suggested that NK cells and their receptors may affect the transplant outcome. In the present study, patients and donors were found to significantly differ in the distribution of the NKG2A rs7301582 genetic variants - recipients carried the C allele more often than their donors (0.975 vs 0.865, p<0.0001). Increased soluble HLA-E (sHLA-E) levels detected in recipients' serum 30 days after transplantation seemed to play a prognostic and protective role. It was observed that recipients with higher sHLA-E levels were less prone to chronic GvHD (11.65 vs 6.33 pg/mL, p=0.033) or more severe acute GvHD grades II-IV (11.07 vs 8.04 pg/mL, p=0.081). Our results also showed an unfavourable role of HLA-E donor-recipient genetic incompatibility in CMV infection development after transplantation (OR=5.92, p=0.014). Frequencies of NK cells (both CD56dim and CD56bright) expressing NKG2C were elevated in recipients who developed CMV, especially 30 and 90 days post-transplantation (p<0.03). Percentages of NKG2C+ NK cells lacking NKG2A expression were also increased in these patients. Moreover, recipients carrying a NKG2C deletion characterized with decreased frequency of NKG2C+ NK cells (p<0.05). Our study confirms the importance of NK cells in the development of post-transplant complications and highlights the effect of HLA-E and NKG2C genetic variants, sHLA-E serum concentration, as well as NKG2C surface expression on transplant outcome.

Inhibitory NKG2A+ and absent activating NKG2C+ NK cell responses are associated with the development of EBV+ lymphomas

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus, which infects over 90% of the adult human population worldwide. After primary infections, EBV is recurrently reactivating in most adult individuals. It is, however, unclear, why these EBV reactivations progress to EBV⁺ Hodgkin (EBV⁺HL) or non-Hodgkin lymphomas (EBV⁺nHL) only in a minority of EBV-infected individuals. The EBV LMP-1 protein encodes for a highly polymorphic peptide, which upregulates the immunomodulatory HLA-E in EBV-infected cells, thereby stimulating the inhibitory NKG2A-, but also the activating NKG2C-receptor on natural killer (NK) cells. Using a genetic-association approach and functional NK cell analyses, we now investigated, whether these HLA-E-restricted immune responses impact the development of EBV⁺HL and EBV⁺nHL. Therefore, we recruited a study cohort of 63 EBV⁺HL and EBV⁺nHL patients and 192 controls with confirmed EBV reactivations, but without lymphomas. Here, we demonstrate that in EBV⁺ lymphoma patients exclusively the high-affine LMP-1 GGDPHLPTL peptide variant-encoding EBV-strains reactivate. In EBV⁺HL and EBV⁺nHL patients, the high-expressing HLA-E*0103/0103 genetic variant was significantly overrepresented. Combined, the LMP-1 GGDPHLPTL and HLA-E*0103/0103 variants efficiently inhibited NKG2A+ NK cells, thereby facilitating the in vitro spread of EBV-infected tumor cells. In addition, EBV⁺HL and EBV⁺nHL patients, showed impaired pro-inflammatory NKG2C⁺ NK cell responses, which accelerated the in vitro EBV-infected tumor cells spread. In contrast, the blocking of NKG2A by monoclonal antibodies (Monalizumab) resulted in efficient control of EBV-infected tumor cell growth, especially by NKG2A⁺NKG2C⁺ NK cells. Thus, the HLA-E/LMP-1/NKG2A pathway and individual NKG2C⁺ NK cell responses are associated with the progression toward EBV⁺ lymphomas.

Activating NKG2C Receptor: Functional Characteristics and Current Strategies in Clinical Applications

The interest in NK cells and their cytotoxic activity against tumour, infected or transformed cells continuously increases as they become a new efficient and off-the-shelf agents in immunotherapies. Their actions are balanced by a wide set of activating and inhibitory receptors, recognizing their complementary ligands on target cells. One of the most studied receptors is the activating CD94/NKG2C molecule, which is a member of the C-type lectin-like family. This review is intended to summarise latest research findings on the clinical relevance of NKG2C receptor and to examine its contribution to current and potential therapeutic strategies. It outlines functional characteristics and molecular features of CD94/NKG2C, its interactions with HLA-E molecule and presented antigens, pointing out a key role of this receptor in immunosurveillance, especially in the human cytomegalovirus infection. Additionally, the authors attempt to shed some light on receptor's unique interaction with its ligand which is shared with another receptor (CD94/NKG2A) with rather opposite properties.

Adaptive NK cell response to human cytomegalovirus: Facts and open issues

Human cytomegalovirus (HCMV) infection exerts broad effects on the immune system. These include the differentiation and persistent expansion of a mature NK cell subset which displays a characteristic phenotypic and functional profile hallmarked by expression of the HLA-E-specific CD94/NKG2C activating receptor. Based on our experience and recent advances in the field, we overview the adaptive features of the NKG2C+ NK cell response, discussing observations and open questions on: (a) the mechanisms and influence of viral and host factors; (b) the existence of other NKG2C- NK cell subsets sharing adaptive features; (c) the development and role of adaptive NKG2C+ NK cells in the response to HCMV in hematopoietic and solid organ transplant patients; (d) their relation with other viral infections, mainly HIV-1; and (e) current perspectives for their use in adoptive immunotherapy of cancer.

High frequencies of adaptive NK cells are associated with absence of coronary plaque in cytomegalovirus infected people living with HIV

The objective of this study was to evaluate whether adaptive NKG2C+CD57+ natural killer (adapNK) cell frequencies are associated with pre-clinical coronary atherosclerosis in participants of the Canadian HIV and Aging Cohort Study. This cross-sectional study included 194 Canadian HIV and Aging Cohort Study participants aged ≥ 40 years of which 128 were cytomegalovirus (CMV)+ people living with HIV (PLWH), 8 were CMV-PLWH, 37 were CMV mono-infected individuals, and 21 were neither human immunodeficiency virus nor CMV infected. Participants were evaluated for the frequency of their adapNK cells and total plaque volume (TPV). TPV was assessed using cardiac computed tomography. Participants were classified as free of, or having, coronary atherosclerosis if their TPV was "0" and ">0," respectively. The frequency of adapNK cells was categorized as low, intermediate or high if they constituted <4.6%, between ≥4.6% and 20% and >20%, respectively, of the total frequency of CD3-CD56dim NK cells. The association between adapNK cell frequency and TPV was assessed using an adjusted Poisson regression analysis. A greater proportion of CMV+PLWH with TPV = 0 had high adapNK cell frequencies than those with TPV > 0 (61.90% vs 39.53%, P = .03) with a similar non-significant trend for CMV mono-infected participants (46.15% vs 34.78%). The frequency of adapNK cells was negatively correlated with TPV. A high frequency of adapNK cells was associated with a relative risk of 0.75 (95% confidence intervals 0.58, 0.97, P = .03) for presence of coronary atherosclerosis. This observation suggests that adapNK cells play a protective role in the development of coronary atherosclerotic plaques.

NK cell dysfunction is linked with disease severity in SARS-CoV-2 patients

SARS‐CoV‐2 first raised from Wuhan City, Hubei Province in November 2019. The respiratory disorder, cough, weakness, fever are the main clinical symptoms of coronavirus disease 2019 (COVID‐19) patients. Natural Killer (NK) cells as a first defense barrier of innate immune system have an essential role in early defense against pulmonary virus. They kill the infected cells by inducing apoptosis or the degranulation of perforin and granzymes. Collectively, NK cells function are coordinated by the transmitted signals from activating and inhibitory receptors. It is clear that the cytotoxic function of NK cells is disrupted in COVID‐19 patients due to the dysregulation of activating and inhibitory receptors. Therefore, better understanding of the activating and inhibitory receptors mechanism could facilitate the treatment strategy in clinic. To improve the efficacy of immunotherapy in COVID‐19 patients, the functional detail of NK cell and manipulation of their key checkpoints are gathered in current review.

Natural Killer (NK) cells as a major innate immunity compartment have a substantial role in the control of infection in coronavirus disease 2019 (COVID‐19) patients. Despite the important role of NK cells in viral diseases, the function of these cells is disrupted in COVID‐19 patients. Dysregulation of the activating and inhibitory receptors and cytokine storm in respiratory air‐way followed by accumulation of disarming NK cells, are major factors in disease severity in COVID‐19 patients. Therefore, it seems that the manipulating of immune checkpoints, the control of excessive secretion of cytokines (anticytokine therapy) and inhibitory receptors targeting by the monoclonal antibodies would be helpful to restore NK cell function

CXCR6+ and NKG2C+ Natural Killer Cells Are Distinct With Unique Phenotypic and Functional Attributes Following Bone Marrow Transplantation

Reactivation of human cytomegalovirus (HCMV) is a life-threatening complication in transplant patients. Natural Killer (NK) cells are the first lymphocyte lineage to reconstitute following an allogeneic hematopoietic stem cell transplant (HSCT). Amongst them, NK cell Group 2 isoform C/Killer cell lectin-like receptor subfamily C, member 2 (NKG2C)-expressing NK cells contribute significantly to patient protection upon HCMV reactivation. NKG2C⁺ NK cells are capable of immunological memory, albeit NK cell memory is not restricted to them. Hepatic C-X-C Motif Chemokine Receptor 6 (CXCR6)-expressing NK cells also mediate memory responses in mice and humans. Small numbers of them circulate and can thus be studied in peripheral blood samples. We hypothesize that NKG2C⁺ and CXCR6⁺ NK cell subsets are distinct. To test our hypothesis, we used multi-parametric flow cytometry to determine the phenotypes and effector functions of CD56^bright vs. CD56^dim and NKG2C⁺ vs. CXCR6⁺ human NK cell subsets in the peripheral blood (PB) of pediatric transplant recipients monthly while monitoring patients for HCMV reactivation. Interestingly, we did not find any NKG2C⁺CXCR6⁺ NK cells in the transplant recipients' peripheral blood, suggesting that NKG2C⁺ and CXCR6⁺ NK cells are distinct. Also, NKG2C-CXCR6- NK cells, rather than NKG2C⁺ NK cells, made up most NK cells post-transplant, even in transplant recipients with HCMV viremia. In contrast to NKG2C⁺ NK cells, CXCR6⁺ NK cells appeared phenotypically less differentiated but were highly proliferative and produced IFN-γ and TNF _α . Our findings contribute to our understanding of post-transplant NK cell development and its implications for human health.

Transcriptomic perspectives of memory-like NK cells and aging

A recent study highlights the presence of a unique memory-like natural killer (NK) cell subset, which accumulates with aging and appears to associate withdisease severity in COVID-19 patients. While the clinical relevance of memory in NK cells is being debated, the molecular identity of this subset in the form of a single-cell transcriptome is essential to define their origin, longevity, functions, and disease relevance.

Deletion of the Natural Killer Cell Receptor NKG2C Encoding KLR2C Gene and Kidney Transplant Outcome

Natural killer (NK) cells may contribute to antibody-mediated rejection (ABMR) of renal allografts. The role of distinct NK cell subsets in this specific context, such as NK cells expressing the activating receptor NKG2C, is unknown. Our aim was to investigate whether KLRC2 gene deletion variants which determine NKG2C expression affect the pathogenicity of donor-specific antibodies (DSA) and, if so, influence long-term graft survival. We genotyped the KLRC2^wt/del variants for two distinct kidney transplant cohorts, (i) a cross-sectional cohort of 86 recipients who, on the basis of a positive post-transplant DSA result, all underwent allograft biopsies, and (ii) 1,860 recipients of a deceased donor renal allograft randomly selected from the Collaborative Transplant Study (CTS) database. In the DSA+ patient cohort, KLRC2^wt/wt (80%) was associated with antibody-mediated rejection (ABMR; 65% versus 29% among KLRC2^wt/del subjects; P=0.012), microvascular inflammation [MVI; median g+ptc score: 2 (interquartile range: 0-4) versus 0 (0-1), P=0.002], a molecular classifier of ABMR [0.41 (0.14-0.72) versus 0.10 (0.07-0.27), P=0.001], and elevated NK cell-related transcripts (P=0.017). In combined analyses of KLRC2 variants and a functional polymorphism in the Fc gamma receptor IIIA gene (FCGR3A-V/F158), ABMR rates and activity gradually increased with the number of risk genotypes. In DSA+ and CTS cohorts, however, the KLRC2^wt/wt variant did not impact long-term death-censored graft survival, also when combined with the FCGR3A-V158 risk variant. KLRC2^wt/wt may be associated with DSA-triggered MVI and ABMR-associated gene expression patterns, but the findings observed in a highly selected cohort of DSA+ patients did not translate into meaningful graft survival differences in a large multicenter kidney transplant cohort not selected for HLA sensitization.

Assessment of NKG2C copy number variation in HIV-1 infection susceptibility, and considerations about the potential role of lacking receptors and virus infection

Human Immunodeficiency Virus (HIV) infection dynamics is strongly influenced by the host genetic background. NKG2C is an activating receptor expressed mainly on Natural Killer (NK) cells, and a polymorphism of copy number variation in the gene coding for this molecule has been pointed as a potential factor involved in HIV infection susceptibility. We evaluated the impact of the NKG2C deletion on HIV-1 susceptibility, with or without HBV/HCV co-infection, in a total of 780 individuals, including 385 HIV-infected patients and 395 healthy blood donors. NKG2C deletion genotyping was performed by standard PCR. To our knowledge, this is the first study to access the impact of complete NKG2C deletion among HIV-infected Brazilian individuals. The frequency of NKG2C deletion (range: 19–22%) was similar in cases and controls. No association of NKG2C deletion with HIV-1 susceptibility or influence on clinical features, HBV or HCV co-infection was observed in the evaluated population. Our findings suggest that NKG2C deletion, and the consequent absence of this receptor expression, does not directly impact HIV susceptibility, HBV/HCV-co-infection in the studied population, suggesting that other signaling pathways might be triggered and perform similar functions in cell activity in the absence of this specific receptor, preventing the development of disadvantageous phenotypes. Larger cohorts and studies involving protein expression are necessary to confirm our findings.

Donor NKG2C homozygosity contributes to CMV clearance after haploidentical transplantation

Cytomegalovirus (CMV) infection remains an important cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Several investigators have reported that adaptive NKG2C+ NK cells persistently expand during CMV reactivation. In our study, two cohorts were enrolled to explored the relationships among the NKG2C genotype, NKG2C+ NK cell reconstitution, and CMV infection. Multivariate analysis showed that donor NKG2C gene deletion was an independent prognostic factor for CMV reactivation and refractory CMV reactivation. Furthermore, the quantitative, qualitative reconstitution and anti-CMV function of adaptive NKG2C+ NK cells after transplantation was significantly lower in patients grafted with NKG2Cwt/del donor cells than in those grafted with NKG2Cwt/wt donor cells. The quantitative reconstitution of NKG2C+ NK cells at day 30 after transplantation was significantly lower in patients with treatment-refractory CMV reactivation than in those in the no-CMV-reactivation and CMV-reactivation groups. In humanized CMV-infected mice, we found that compared with those from NKG2Cwt/del donors, adaptive NKG2C+ NK cells from NKG2Cwt/wt donors induced earlier and stronger expansion of NKG2C+ NK cells and earlier and stronger CMV clearance in vivo. In conclusion, donor NKG2C homozygosity contributes to CMV clearance by promoting the quantitative and qualitative reconstruction of adaptive NKG2C+ NK cells after haploidentical allo-HSCT.

Dissection of the NKG2C NK cell response against Puumala Orthohantavirus

BACKGROUND

Infections with the Puumala orthohantavirus (PUUV) in humans may cause hemorrhagic fever with renal syndrome (HFRS), known as nephropathia epidemica (NE), which is associated with acute renal failure in severe cases. In response to PUUV-infections, a subset of potent antiviral NKG2C+ NK cells expand, whose role in virus defence and pathogenesis of NE is unclear. NKG2C+ NK cell proliferation is mediated by binding of NKG2C/CD94 to HLA-E on infected cells. The proliferation and activation of NKG2C+ NK cells via the NKG2C/HLA-E axis is affected by different NKG2C (NKG2Cwt/del) and HLA-E (HLA-E*0101/0103) alleles, which naturally occur in the human host. Homozygous (NKG2Cdel/del) and heterozygous (NKG2Cwt/del) deletions of the NKG2C receptor results in an impaired NKG2C/CD94 mediated proliferation and activation of NKG2C+ cells. We therefore analyzed the PUUV-mediated NKG2C+ NK cell responses and the impact of different NKG2C and HLA-E alleles in NE patients.

METHODOLOGY/PRINCIPAL FINDINGS

NKG2C+ NK cell expansion and effector functions in PUUV-infected cells were investigated using flow cytometry and it was shown that PUUV-infected endothelial cells led to a NKG2C/CD94 mediated NKG2C+ NK cell activation and expansion, dependent on the HLA-G-mediated upregulation of HLA-E. Furthermore, the NKG2Cdel and HLA-E*0101/0103 alleles were determined in 130 NE patients and 130 matched controls, and it was shown that in NE patients the NKG2Cwt/del allele was significantly overrepresented, compared to the NKG2Cwt/wt variant (p = 0.01). In addition, in vitro analysis revealed that NKG2Cwt/del NK cells exhibited on overall a lower proliferation (p = 0.002) and lower IFNγ expression (p = 0.004) than NKG2Cwt/wt NK cells.

CONCLUSIONS/SIGNIFICANCE

Our results corroborate the substantial impact of the NKG2C/HLA-E axis on PUUV-specific NK cell responses. A weak NKG2C+ NK cell response, as reflected by NKG2Cwt/del variant, may be associated with a higher risk for a severe hantavirus infections.

Characterization of Adaptive-like γδ T Cells in Ugandan Infants during Primary Cytomegalovirus Infection

Gamma-delta (γδ) T cells are unconventional T cells that help control cytomegalovirus (CMV) infection in adults. γδ T cells develop early in gestation, and a fetal public γδ T cell receptor (TCR) clonotype is detected in congenital CMV infections. However, age-dependent γδ T cell responses to primary CMV infection are not well-understood. Flow cytometry and TCR sequencing was used to comprehensively characterize γδ T cell responses to CMV infection in a cohort of 32 infants followed prospectively from birth. Peripheral blood γδ T cell frequencies increased during infancy, and were higher among CMV-infected infants relative to uninfected. Clustering analyses revealed associations between CMV infection and activation marker expression on adaptive-like Vδ1 and Vδ3, but not innate-like Vγ9Vδ2 γδ T cell subsets. Frequencies of NKG2C⁺CD57⁺ γδ T cells were temporally associated with the quantity of CMV shed in saliva by infants with primary infection. The public γδ TCR clonotype was only detected in CMV-infected infants <120 days old and at lower frequencies than previously described in fetal infections. Our findings support the notion that CMV infection drives age-dependent expansions of specific γδ T cell populations, and provide insight for novel strategies to prevent CMV transmission and disease.

Deletion of the NKG2C receptor encoding KLRC2 gene and HLA-E variants are risk factors for severe COVID-19

Purpose

Host genetic variants may contribute to severity of COVID-19. NKG2C⁺ NK cells are potent antiviral effector cells, potentially limiting the extent of SARS-CoV-2 infections. NKG2C is an activating NK cell receptor encoded by the KLRC2 gene, which binds to HLA-E on infected cells leading to NK cell activation. Heterozygous or homozygous KLRC2 deletion (KLRC2^del) may naturally occur and is associated with a significantly lower or absent NKG2C expression level. In addition, HLA-E*0101/0103 genetic variants occur, caused by a single-nucleotide polymorphism. We therefore investigated whether the severity of COVID-19 is associated with these genetic variants.

Methods

We investigated the distribution of KLRC2 deletion and HLA-E*0101/0103 allelic variants in a study cohort of 361 patients with either mild (N = 92) or severe (N = 269) COVID-19.

Results

Especially the KLRC2^del, and at a lower degree the HLA-E*0101, allele were significantly overrepresented in hospitalized patients (p = 0.0006 and p = 0.01), particularly in patients requiring intensive care (p < 0.0001 and p = 0.01), compared with patients with mild symptoms. Both genetic variants were independent risk factors for severe COVID-19.

Conclusion

Our data show that these genetic variants in the NKG2C/HLA-E axis have a significant impact on the development of severe SARS-CoV-2 infections, and may help to identify patients at high-risk for severe COVID-19.

Genetic Variants of the NKG2C/HLA-E Receptor-Ligand Axis Are Determinants of Progression-Free Survival and Therapy Outcome in Aggressive B-Cell Lymphoma

Simple Summary

NKG2C and its ligand HLA-E represent key molecules for NK cell-mediated immune responsiveness. However, the impact of genetic variants in NKG2C and HLA-E on clinical outcomes of aggressive B-cell non-Hodgkin lymphoma patients (B-NHL) has not been clarified. In this study, we analyzed the distribution of NKG2C deletion status and HLA-E variants in 441 patients and 192 healthy individuals. Homozygous deletion of NKG2C (NKG2C^−/−) was more often found in high-risk patients compared to patients with a lower risk and consequently was associated with reduced 2-year progression-free survival. The HLA-E*01:01 allele frequency was increased in B-NHL patients and was strongly related with complete remission. Our results show that absence of NKG2C and HLA-E allelic variations is predictive for B-NHL outcome; while carriers of HLA-E*01:01 are characterized by high, complete remission rates, NKG2C^−/− was rare, but associated with poorer outcome. Prospective validation of our results identifies patients that may benefit from risk-adapted therapy.

Abstract

Aggressive B-cell lymphomas account for the majority of non-Hodgkin lymphomas (B-NHL). NK cells govern the responses to anti-CD20 monoclonal antibodies and have emerged as attractive targets for immunotherapy in subtypes of B-NHL. NKG2C and its cognate ligand HLA-E represent key molecules for fine-tuning of NK cell-mediated immune responses. Here, we investigated the impact of genetic variants of NKG2C and HLA-E on clinical outcomes of 441 B-NHL patients. Homozygous deletion of NKG2C (NKG2C^−/−) was three-fold increased in patients compared to 192 healthy controls. Among studied patients, NKG2C^−/− was more abundant in International Prognostic Index (IPI) high-risk patients compared to patients with a lower IPI (p = 0.013). Strikingly, NKG2C^−/− was associated with a significantly reduced 2-year PFS (progression-free survival) (p = 0.0062) and represented an independent risk factor for 2-year PFS in multivariate analysis (p = 0.005). For HLA-E, the cognate ligand of NKG2C, the HLA-E*01:01 allele frequency was increased in B-NHL patients compared to controls (p = 0.033) and was associated with complete remission in univariate (p = 0.034) and multivariate (p = 0.018) analysis. Our data suggest that NKG2C and HLA-E genotyping is a promising tool for both defining risk groups of aggressive B-NHL and predicting response to immune therapeutic approaches.

Cytomegalovirus replication is associated with enrichment of distinct γδ T cell subsets following lung transplantation: A novel therapeutic approach?

BACKGROUND

Anti-viral treatments to control cytomegalovirus (CMV) after lung transplantation (LTx) are associated with toxicity and anti-viral resistance. Cellular immunotherapy with virus-specific cytotoxic T cells has yielded promising results but requires donor/recipient matching. γδ T cells are involved in anti-viral immunity and can recognize antigens independently of major histocompatibility complex molecules and may not require the same level of matching. We assessed the phenotype of circulating γδ T cells after LTx to identify the candidate populations for CMV immunotherapy.

METHODS

Peripheral blood mononuclear cells were isolated from lung transplant recipients before transplantation and at routine bronchoscopies after LTx. Patients were stratified by risk of CMV disease into moderate risk (recipient CMV seropositive, n = 15) or high risk (HR) (recipient CMV seronegative/donor CMV seropositive, n = 10). CMV replication was classified as polymerase chain reaction positive (>150 copies/ml) in blood and/or bronchoalveolar lavage within the first 18 months. The phenotype of γδ T cells was assessed by multicolor flow cytometry, and T-cell receptor (TCR) sequences were determined by deep sequencing.

RESULTS

In HR lung transplant recipients with CMV replication, we observed striking phenotypic changes in γδ T cells, marked by an increase in the proportion of effector Vδ1+ γδ T cells expressing the activating natural killer cell receptor NKG2C. Moreover, we observed a remarkable increase in TCR diversity.

CONCLUSIONS

NKG2C+ Vδ1+ γδ T cells were associated with CMV replication and may indicate their potential to control infection. As such, we propose that they could be a potential target for cellular therapy against CMV.

NKG2Cpos NK Cells Regulate the Expansion of Cytomegalovirus-Specific CD8 T Cells

Infection with the human CMV associates with phenotypic alterations in lymphocyte subsets. A highly reproducible finding in CMV-seropositive individuals is an expansion of NKG2Cpos NK cells. In this study, we analyzed if the altered NK cell compartment in CMV-seropositive human donors may affect CMV-specific CD8 T cells. Resting CMV-specific CD8 T cells were terminally differentiated and expressed high levels of the NKG2C ligand HLA-E. Activation of CMV-specific CD8 T cells with the cognate Ag further increased HLA-E expression. In line with a negative regulatory effect of NKG2Cpos NK cells on HLA-Ehigh CD8 T cells, depletion of NKG2Cpos NK cells enhanced Ag-specific expansion of CMV-specific CD8 T cells in vitro. In turn, the activation of NK cells in coculture with CMV-specific CD8 T cells promoted a selective loss of HLA-Ehigh CD8 T cells. To test if NKG2Cpos NK cells can target HLA-Ehigh CD8 T cells, Jurkat T cells with and without stabilized HLA-E on the surface were used. NKG2Cpos NK cells stimulated with HLA-Ehigh Jurkat cells released higher levels of Granzyme B compared with NKG2Cneg NK cells and NKG2Cpos NK cells stimulated with HLA-Elow Jurkat cells. Moreover, intracellular levels of caspase 3/7 were increased in HLA-Ehigh Jurkat cells compared with HLA-Elow Jurkat cells, consistent with higher rates of apoptosis in HLA-Ehigh T cells in the presence of NKG2Cpos NK cells. Our data show that NKG2Cpos NK cells interact with HLA-Ehigh CD8 T cells, which may negatively regulate the expansion of CMV-specific CD8 T cells upon activation.

Association of Severe Influenza Virus Infections With CD226 (DNAM-1) Variants

Natural killer (NK)-cell response against influenza viruses partly depends on expression of CD112, a ligand for NK-cell receptor CD226 (DNAM-1). We analyzed whether particular CD226 variants were associated with influenza disease severity. Comparison between 145 patients hospitalized with severe influenza at intensive care units (ICU) with 139 matched influenza-positive outpatients showed that presence of the rs763362 G allele (GG, AG) was associated with occurrence of severe influenza infections (P = .0076). Also, a higher frequency of rs727088 G and rs763361 T alleles was observed in the ICU group. Thus, CD226 variants may contribute to the severity of influenza virus disease.

NKG2C Natural Killer Cells in Bronchoalveolar Lavage Are Associated With Cytomegalovirus Viremia and Poor Outcomes in Lung Allograft Recipients

BACKGROUND

Cytomegalovirus (CMV) infection is a risk factor for chronic lung allograft dysfunction (CLAD), which limits survival in lung allograft recipients. Natural killer (NK) cells that express the NKG2C receptor mediate CMV-specific immune responses. We hypothesized that NKG2C NK cells responding to CMV in the lung allograft would reduce CMV-related inflammation and would improve CLAD-free survival.

METHODS

We prospectively followed 130 subjects who underwent lung transplantation from 2012 to 2016. Bronchoalveolar lavage (BAL) NK cells were immunophenotyped for NKG2C, maturation, and proliferation markers. CMV viral load, serologies, serial spirometry, and mortality were recorded from medical records. Natural killer cell subset association with CMV endpoints were made using generalized estimating equation-adjusted linear models. BAL NKG2C NK cell association with CLAD-free survival was assessed by Cox proportional hazards modeling.

RESULTS

NKG2C NK cells were more mature and proliferative than NKG2C NK cells and represented a median of 7.8% of BAL NK cells. The NKG2C NK cell proportion increased prior to the first detection of viremia and was nearly tripled in subjects with high level viremia (>1000 copies/mL) compared with no detected viremia. Subjects with increased BAL NKG2C NK cells, relative to the median, had a significantly increased risk for CLAD or death (hazard ratio, 4.2; 95% confidence interval, 1.2-13.3).

CONCLUSIONS

The BAL NKG2C NK cell proportion may be a relevant biomarker for assessing risk of CMV viremia and quantifying potential CMV-related graft injury that can lead to CLAD or death.

Natural killer cells in lung transplantation

Natural killer (NK) cells are innate lymphoid cells that have been increasingly recognised as important in lung allograft tolerance and immune defence. These cells evolved to recognise alterations in self through a diverse set of germline-encoded activating and inhibitory receptors and display a broad range of effector functions that play important roles in responding to infections, malignancies and allogeneic tissue. Here, we review NK cells, their diverse receptors and the mechanisms through which NK cells are postulated to mediate important lung transplant clinical outcomes. NK cells can promote tolerance, such as through the depletion of donor antigen-presenting cells. Alternatively, these cells can drive rejection through cytotoxic effects on allograft tissue recognised as 'non-self' or 'stressed', via killer cell immunoglobulin-like receptor (KIR) or NKG2D receptor ligation, respectively. NK cells likely mediate complement-independent antibody-mediated rejection of allografts though CD16A Fc receptor-dependent activation induced by graft-specific antibodies. Finally, NK cells play an important role in response to infections, particularly by mediating cytomegalovirus infection through the CD94/NKG2C receptor. Despite these sometimes-conflicting effects on allograft function, enumeration of NK cells may have an important role in diagnosing allograft dysfunction. While the effects of immunosuppression agents on NK cells may currently be largely unintentional, further understanding of NK cell biology in lung allograft recipients may allow these cells to serve as biomarkers of graft injury and as therapeutic targets.