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.

Association between chronic lung allograft dysfunction and human Cytomegalovirus UL40 peptide variants in lung-transplant recipients.

Natural-Killer cells play an important role in the pathogenesis of chronic lung allograft dysfunction (CLAD) in lung-transplant recipients. Activating NKG2C+ and inhibitory NKG2A+ NK cells proliferate in response to human Cytomegalovirus (HCMV) infection via the presentation of virally encoded UL40 peptides on HLA-E molecules. We aimed to clarify whether infection with HCMV strains carrying different UL40 peptide variants is associated with the development of CLAD. We included 82 lung-transplant recipients, 18 patients developing CLAD and 64 matched control patients without CLAD. In all patients 1 episode of high-level HCMV-replication occurred. HCMV UL40 variants and Natural-Killer-cell proliferation with distinct UL40 peptides were assessed. The VMTPRTLIL variant was significantly overrepresented in patients developing CLAD (p < 0.0001) and lead to a significantly lower proliferation of inhibitory NKG2A+ cells, compared to the VMAPRTLIL, VMAPRTLVL and VMAPRTLLL variants (p < 0.0001). Thus, HCMV UL40 variants may contribute to development of CLAD over the NK cell response.

Extent of Cytomegalovirus Replication in the Human Host Depends on Variations of the HLA-E/UL40 Axis.

Human cytomegalovirus (HCMV) may cause severe infections in lung transplant recipients (LTRs). In response to HCMV infections, a subset of NKG2C+ NK cells expands, which limits HCMV replication and is characterized by high expression of the activating NKG2C/CD94 and absence of the inhibitory NKG2A/CD94 receptor. Both receptors bind to HLA-E, which is stabilized by HCMV-encoded UL40 peptides. HLA-E and UL40 occur as different genetic variants. In this study, we investigated the interplay between the human NK cell response and the infecting HCMV-UL40 strain, and we assessed the impact of HCMV-UL40 and of donor- and recipient-encoded HLA-E*0101/0103 variants on HCMV replication after lung transplantation. We included 137 LTRs displaying either no or low- or high-level (>1,000 copies/ml plasma) viremia. HCMV-UL40 and HLA-E*0101/0103 variants were determined. UL40 diversity was investigated by next-generation sequencing. UL40 peptide-dependent NK cell cytotoxicity was assessed by flow cytometry. Donor-encoded HLA-E*0101/0103 was significantly associated with development of high-level viremia after transplantation (P = 0.007). The HCMV-UL40 variant VMAPRTLIL occurred significantly more frequently in highly viremic LTRs, and the variant VMTPRTLIL occurred significantly more frequently in low-viremic LTRs (P = 0.004). This difference was associated with a better inhibition of NKG2A+ NKG2C- NK cells by VMAPRTLIL (P < 0.001). In LTRs with repeated high-level viremic episodes, HCMV strains with UL40 variants displaying low affinity to the patients' HLA-E variant emerged over time. The HLA-E-UL40 axis has a substantial impact on the level of HCMV replication in LTRs. The interplay between UL40 peptide variants, the recipient HLA-E status, and the activation of inhibitory NKG2A+ NKG2C- cells is of major importance for development of high-level viremia after lung transplantation.IMPORTANCE Infection with human cytomegalovirus (HCMV) is associated with substantial morbidity in immunosuppressed patients and after congenital infections. Therefore, development of a vaccine against HCMV is a main public health priority. Revealing the complex interaction between HCMV and host responses, is of utmost importance for understanding viral pathogenesis and for vaccine design. The present data contribute to the understanding of HCMV-specific host immune responses and reveal specifically the interaction between HLA-E and the virus-encoded UL40 peptide, which further leads to a potent NK cell response. We demonstrate that this interaction is a key factor for reduction of virus replication in immunosuppressed patients. We further show that distinct naturally occurring HCMV-UL40 variants reduce the activation of a specific subpopulation of host NK cells and thereby are associated with high-level viremia in the patients. These findings will allow the characterization of patients at risk for severe HCMV infection and contribute to strategies for HCMV vaccine development.

CDK6 Antagonizes p53-Induced Responses during Tumorigenesis.

Tumor formation is a multistep process during which cells acquire genetic and epigenetic changes until they reach a fully transformed state. We show that CDK6 contributes to tumor formation by regulating transcriptional responses in a stage-specific manner. In early stages, the CDK6 kinase induces a complex transcriptional program to block p53 in hematopoietic cells. Cells lacking CDK6 kinase function are required to mutate TP53 (encoding p53) to achieve a fully transformed immortalized state. CDK6 binds to the promoters of genes including the p53 antagonists Prmt5, Ppm1d, and Mdm4 The findings are relevant to human patients: Tumors with low levels of CDK6 have mutations in TP53 significantly more often than expected.Significance: CDK6 acts at the interface of p53 and RB by driving cell-cycle progression and antagonizing stress responses. While sensitizing cells to p53-induced cell death, specific inhibition of CDK6 kinase activity may provoke the outgrowth of p53-mutant clones from premalignant cells. Cancer Discov; 8(7); 884-97. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 781.