Ineffective control of Epstein-Barr-virus-induced autoimmunity increases the risk for multiple sclerosis.

Multiple sclerosis (MS) is a demyelinating disease of the CNS. Epstein-Barr virus (EBV) contributes to the MS pathogenesis because high levels of EBV EBNA386-405-specific antibodies cross react with the CNS-derived GlialCAM370-389. However, it is unclear why only some individuals with such high autoreactive antibody titers develop MS. Here, we show that autoreactive cells are eliminated by distinct immune responses, which are determined by genetic variations of the host, as well as of the infecting EBV and human cytomegalovirus (HCMV). We demonstrate that potent cytotoxic NKG2C+ and NKG2D+ natural killer (NK) cells and distinct EBV-specific T cell responses kill autoreactive GlialCAM370-389-specific cells. Furthermore, immune evasion of these autoreactive cells was induced by EBV-variant-specific upregulation of the immunomodulatory HLA-E. These defined virus and host genetic pre-dispositions are associated with an up to 260-fold increased risk of MS. Our findings thus allow the early identification of patients at risk for MS and suggest additional therapeutic options against MS.

HLA-E-restricted immune responses are crucial for the control of EBV infections and the prevention of PTLD.

Primary Epstein-Barr virus (EBV) infections may cause infectious mononucleosis (IM), whereas EBV reactivations in solid organ and hematopoietic stem cell transplant recipients are associated with posttransplantation lymphoproliferative disorders (PTLDs). It is still unclear why only a minority of primary EBV-infected individuals develop IM, and why only some patients progress to EBV+PTLD after transplantation. We now investigated whether nonclassic human leukocyte antigen E (HLA-E)-restricted immune responses have a significant impact on the development of EBV diseases in the individual host. On the basis of a large study cohort of 1404 patients and controls as well as on functional natural killer (NK) and CD8+ T-cell analyses, we could demonstrate that the highly expressed HLA-E∗0103/0103 genotype is protective against IM, due to the induction of potent EBV BZLF1-specific HLA-E-restricted CD8+ T-cell responses, which efficiently prevent the in vitro viral dissemination. Furthermore, we provide evidence that the risk of symptomatic EBV reactivations in immunocompetent individuals as well as in immunocompromised transplant recipients depends on variations in the inhibitory NKG2A/LMP-1/HLA-E axis. We show that EBV strains encoding for the specific LMP-1 peptide variants GGDPHLPTL or GGDPPLPTL, presented by HLA-E, elicit strong inhibitory NKG2A+ NK and CD8+ T-cell responses. The presence of EBV strains encoding for both peptides was highly associated with symptomatic EBV reactivations. The further progression to EBV+PTLD was highly associated with the presence of both peptide-encoding EBV strains and the expression of HLA-E∗0103/0103 in the host. Thus, HLA-E-restricted immune responses and the NKG2A/LMP-1/HLA-E axis are novel predictive markers for EBV+PTLD in transplant recipients and should be considered for future EBV vaccine design.

The natural killer cell-associated rs9916629-C allele is a novel genetic risk factor for fatal COVID-19.

The severity of COVID-19 is associated with individual genetic host factors. Among these, genetic polymorphisms affecting natural killer (NK) cell responses, as variations in the HLA-E- (HLA-E*0101/0103), FcγRIIIa- (FcγRIIIa-158-F/V), and NKG2C- (KLRC2wt/del ) receptor, were associated with severe COVID-19. Recently, the rs9916629-C/T genetic polymorphism was identified that indirectly shape the human NK cell repertoire towards highly pro-inflammatory CD56bright NK cells. We investigated whether the rs9916629-C/T variants alone and in comparison to the other risk factors are associated with a fatal course of COVID-19. We included 1042 hospitalized surviving and 159 nonsurviving COVID-19 patients as well as 1000 healthy controls. rs9916629-C/T variants were genotyped by TaqMan assays and were compared between the groups. The patients' age, comorbidities, HLA-E*0101/0103, FcγRIIIa-158-F/V, and KLRC2wt/del variants were also determined. The presence of the rs9916629-C allele was a risk factor for severe and fatal COVID-19 (p < 0.0001), independent of the patients' age or comorbidities. Fatal COVID-19 was more frequent in younger patients (<69.85 years) carrying the FcγRIIIa-158-V/V (p < 0.006) and in older patients expressing the KLRC2del variant (p < 0.003). Thus, patients with the rs9916629-C allele have a significantly increased risk for fatal COVID-19 and identification of the genetic variants may be used as prognostic marker for hospitalized COVID-19 patients.

Mechanistic Understanding of EBV+Lymphoproliferative Disease Development After Transplantation.

Posttransplant lymphoproliferative disorders (PTLDs) are among the most common malignant complications after transplantation, leading to a drastic reduction in patient survival rates. The majority of PTLDs are tightly linked to Epstein-Barr virus (EBV+PTLDs) and are the result of an uncontrolled proliferation of EBV-infected cells. However, although EBV infections are a common finding in transplant recipients, most patients with high EBV loads will never develop EBV+PTLD. Natural killer cells and EBV-specific CD8+ T lymphocytes are critical for controlling EBV-infected cells, and the impairment of these cytotoxic immune responses facilitates the unfettered proliferation of EBV-infected cells. Recent years have seen a considerable increase in available literature aiming to describe novel risk factors associated with the development of EBV+PTLD, which may critically relate to the strength of EBV-specific natural killer cell and EBV-CD8+ T lymphocyte responses. The accumulation of risk factors and the increased risk of developing EBV+PTLD go hand in hand. On the one hand, most of these risk factors, such as the level of immunosuppression or the EBV donor and recipient serologic mismatch, and distinct genetic risk factors are host related and affect cytotoxic EBV-specific immune responses. On the other hand, there is growing evidence that distinct EBV variants may have an increased malignant potential and are thus more likely to induce EBV+PTLD. Here, we aim to review, from a mechanistic point of view, the risk factors for EBV+PTLD in the host and the infecting EBV variants that may explain why only a minority of transplant recipients develop EBV+PTLD.

Immunomodulatory soluble HLA-G and HLA-E are associated with rapidly deteriorating CLAD and HCMV viremia after lung transplantation.

Plasma-soluble (s)HLA-G and sHLA-E are immunoregulatory proteins that balance the activation of NKG2A+ immune cells. In lung-transplant recipients (LTRs), dysregulated NKG2A+ natural killer cell responses may result in high-level human cytomegalovirus (HCMV) replication as well as chronic lung allograft dysfunction (CLAD), and especially the development of rapidly deteriorating CLAD is associated with high mortality. We thus analyzed the kinetics and function of sHLA-G and sHLA-E in follow-up samples of N = 76 LTRs to evaluate whether these immunoregulatory proteins are associated with the risk for CLAD and high-level HCMV replication. Here, we demonstrate that rapidly deteriorating CLAD LTRs are hallmarked by continually low (<107 ng/ml) sHLA-G levels. In contrast, high sHLA-E levels were associated with the following development of high-level (>1,000 copies/ml) HCMV episodes. Thus, sHLA-G and sHLA-E may serve as novel biomarkers for the development of rapidly deteriorating CLAD and high-level HCMV replication in LTRs.

Torque teno viruses exhaust and imprint the human immune system via the HLA-E/NKG2A axis.

The ubiquitous Torque teno virus (TTV) establishes a chronically persistent infection in the human host. TTV has not been associated with any apparent disease, but, as part of the human virome, it may confer a regulatory imprint on the human immune system with as yet unclear consequences. However, so far, only few studies have characterized the TTV-specific immune responses or the overall immunological imprints by TTV. Here, we reveal that TTV infection leads to a highly exhausted TTV-specific CD8+ T-cell response, hallmarked by decreased IFN-γ production and the expression of the inhibitory NKG2A-receptor. On a functional level, we identified a panel of highly polymorphic TTV-encoded peptides that lead to an expansion of regulatory NKG2A+ natural killer, NKG2A+CD4+, and NKG2A+CD8+ T cells via the stabilization of the non-classical HLA-E molecule. Our results thus demonstrate that TTV leads to a distinct imprint on the human immune system that may further regulate overall human immune responses in infectious, autoimmune, and malignant diseases.

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.