New insights on the natural killer cell repertoire from a thorough analysis of cord blood cells

International audienceAlthough CB NK cells are characterized as immature lymphocytes, their impressive expansion and efficient graft-versus-leukemia response have been highlighted early after UCBT. To better evaluate their potential as source of effective NK cells, we revisited the study of NK cell repertoire from a large cohort of CB samples. Our study showed that the CB NK cell repertoire appears to be constructed early, depending on KIR gene content, but not on the autologous HLA environment. NKG2A was expressed on a large proportion of CB NK cells that inversely correlated with KIR + NK cell frequency. Self-HLA class I molecule-educated CB KIR + NK cells present a lower spontaneous lysis than do their adult counterparts, which is probably related to the low expression of activating NK receptors. We describe for the first time a proliferative and cytotoxic NKG2C + NK cell subset representing more than 10% of CB NK cells. NKG2A strongly inhibited CB NK cell degranulation, and its coexpression on NKG2C + NK cells may contribute to limiting their activation. Overall, the CB NK cell repertoire is constructed early and harbors numerous functional abilities shared by adult NK cells. In addition, their naïve viral status and fast expansion confer numerous advantages in immunotherapy on CB NK cells

Cytomegalovirus-Infected Primary Endothelial Cells Trigger NKG2C+ Natural Killer Cells

International audienceAmong innate cells, natural killer (NK) cells play a crucial role in the defense against cytomegalovirus (CMV). In some individuals, CMV infection induces the expansion of NKG2C+ NK cells that persist after control of the infection. We have previously shown that KIR2DL+ NK cells, in contrast to NKG2C+ NK cells, contribute to controlling CMV infection using a CMVinfected monocyte-derived dendritic cell (MDDC) model. However, the nature of CMV-infected cells contributing to the expansion of the NKG2C+ NK cell subset remains unclear. To gain more insight into this question, we investigated the contribution of NKG2C+ NK cell activation by CMV-infected primary human aortic endothelial cells (EC) isolated from kidney transplant donors, which constitutively express the human leukocyte antigen (HLA)-E molecule. Here, we show that, although classic HLA class I expression was drastically downregulated, nonclassic HLA-E expression was maintained in CMV-infected EC. By comparing HLA expression patterns in CMV-infected EC, fibroblasts and MDDC, we demonstrate a cell-dependent modulation of HLA-E expression by CMV infection. NKG2C+ NK cell degranulation was significantly triggered by CMV-infected EC regardless of the nature of the HLA-E allele product. EC, predominantly present in vessels, may constitute a privileged site for CMV infection that drives a ‘memory’ NKG2C+ NK cell subset

Severe Symptomatic Primary Human Cytomegalovirus Infection despite Effective Innate and Adaptive Immune Responses

International audiencePrimary human cytomegalovirus (HCMV) infection usually goes unnoticed, causing mild or no symptoms in immunocompetent individuals. However, some rare severe clinical cases have been reported without investigation of host immune responses or viral virulence. In the present study, we investigate for the first time phenotypic and functional features, together with gene expression profiles in immunocompetent adults experiencing a severe primary HCMV infection. Twenty primary HCMV-infected patients (PHIP) were enrolled, as well as 26 HCMV-seronegative and 39 HCMV-seropositive healthy controls. PHIP had extensive lymphocytosis marked by massive expansion of natural killer (NK) and T cell compartments. Interestingly, PHIP mounted efficient innate and adaptive immune responses with a deep HCMV imprint, revealed mainly by the expansion of NKG2C+ NK cells, CD16+ Vδ2(-) γδ T cells, and conventional HCMV-specific CD8+ T cells. The main effector lymphocytes were activated and displayed an early immune phenotype that developed toward a more mature differentiated status. We suggest that both massive lymphocytosis and excessive lymphocyte activation could contribute to massive cytokine production, known to mediate tissue damage observed in PHIP. Taken together, these findings bring new insights into the comprehensive understanding of immune mechanisms involved during primary HCMV infection in immunocompetent individuals.IMPORTANCE HCMV-specific immune responses have been extensively documented in immunocompromised patients and during in utero acquisition. While it usually goes unnoticed, some rare severe clinical cases of primary HCMV infection have been reported in immunocompetent patients. However, host immune responses or HCMV virulence in these patients has not so far been investigated. In the present study, we show massive expansion of NK and T cell compartments during the symptomatic stage of acute HCMV infection. The patients mounted efficient innate and adaptive immune responses with a deep HCMV imprint. The massive lymphocytosis could be the result of nonadapted or uncontrolled immune responses limiting the effectiveness of the specific responses mounted. Both massive lymphocytosis and excessive lymphocyte activation could contribute to massive cytokine production, known to mediate tissue damage. Furthermore, we cannot exclude a delayed immune response caused by immune escape established by HCMV strains

Derivation and validation of a risk-stratification model for patients with probable or proven COVID-19 in EDs: the revised HOME-CoV score

International audienceBackground The HOME-CoV (Hospitalisation or Outpatient ManagEment of patients with SARS-CoV-2 infection) score is a validated list of uniquely clinical criteria indicating which patients with probable or proven COVID-19 can be treated at home. The aim of this study was to optimise the score to improve its ability to discriminate between patients who do and do not need admission.Methods A revised HOME-CoV score was derived using data from a previous prospective multicentre study which evaluated the original Home-CoV score. Patients with proven or probable COVID-19 attending 34 EDs in France, Monaco and Belgium between April and May 2020 were included. The population was split into a derivation and validation sample corresponding to the observational and interventional phases of the original study. The main outcome was non-invasive or invasive ventilation or all-cause death within 7 days following inclusion. Two threshold values were defined using a sensitivity of >0.9 and a specificity of >0.9 to identify low-risk and high-risk patients, respectively. The revised HOME-CoV score was then validated by retrospectively applying it to patients in the same EDs with proven or probable COVID-19 during the interventional phase. The revised HOME-CoV score was also tested against original HOME-CoV, qCSI, qSOFA, CRB65 and SMART-COP in this validation cohort.Results There were 1696 patients in the derivation cohort, of whom 65 (3.8%) required non-invasive ventilation or mechanical ventilation or died within 7 days and 1304 patients in the validation cohort, of whom 22 (1.7%) had a progression of illness. The revised score included seven clinical criteria. The area under the curve (AUC) was 87.6 (95% CI 84.7 to 90.6). The cut-offs to define low-risk and high-risk patients were 3, respectively. In the validation cohort, the AUC was 85.8 (95% CI 80.6 to 91.0). A score of <2 qualified 73% of patients as low risk with a sensitivity of 0.77 (0.55–0.92) and a negative predictive value of 0.99 (0.99–1.00).Conclusion The revised HOME-CoV score, which does not require laboratory testing, may allow accurate risk stratification and safely qualify a significant proportion of patients with probable or proven COVID-19 for home treatment