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BackgroundPatients with immunocompromised disorders have mainly been excluded from clinical trials of vaccination against COVID-19. Thus, the aim of this prospective clinical trial was to investigate the safety and efficacy after two doses of BNT162b2 mRNA vaccination in five selected groups of immunocompromised patients and healthy controls.Methods539 study subjects (449 patients and 90 controls) were included in the clinical trial. The patients had either primary (n=90), or secondary immunodeficiency disorders due to human immunodeficiency virus infection (n=90), allogeneic hematopoietic stem cell transplantation/chimeric antigen receptor T cell therapy (n=90), solid organ transplantation (SOT) (n=89), or chronic lymphocytic leukemia (CLL) (n=90). The primary endpoint was seroconversion rate two weeks after the second dose. The secondary endpoints were safety and documented SARS-CoV-2 infection.FindingsAdverse events were generally mild, but one case of fatal suspected unexpected serious adverse reaction occurred. 72·2% of the immunocompromised patients seroconverted compared to 100% of the controls (p=0.004). Lowest seroconversion rates were found in the SOT (43·4%) and CLL (63·3%) patient groups with observed negative impact of treatment with mycophenolate mofetil and ibrutinib, respectively.InterpretationThe results showed that the mRNA BNT162b2 vaccine was safe in immunocompromised patients. The rate of seroconversion was substantially lower than in healthy controls, with a wide range of rates and antibody titres among predefined patient groups and subgroups. This clinical trial highlights the need for additional vaccine doses in certain immunocompromised patient groups and/or subgroups to improve immunity.FundingKnut and Alice Wallenberg Foundation, Nordstjernan AB, Region Stockholm, Swedish Research Council, Karolinska Institutet, and organizations for PID/CLL-patients in Sweden.

Background. COVID-19, caused by SARS-CoV-2, can involve sequelae and other medical complications that last weeks to months after initial recovery, which has come to be called Long-COVID or COVID long-haulers. This systematic review and meta-analysis aims to identify studies assessing long-term effects of COVID-19 and estimates the prevalence of each symptom, sign, or laboratory parameter of patients at a post-COVID-19 stage. Methods. LitCOVID (PubMed and Medline) and Embase were searched by two independent researchers. All articles with original data for detecting long-term COVID-19 published before 1st of January 2021 and with a minimum of 100 patients were included. For effects reported in two or more studies, meta-analyses using a random-effects model were performed using the MetaXL software to estimate the pooled prevalence with 95% CI. Heterogeneity was assessed using I2 statistics. This systematic review followed Preferred Reporting Items for Systematic Reviewers and Meta-analysis (PRISMA) guidelines, although the study protocol was not registered. Results. A total of 18,251 publications were identified, of which 15 met the inclusion criteria. The prevalence of 55 long-term effects was estimated, 21 meta-analyses were performed, and 47,910 patients were included. The follow-up time ranged from 14 to 110 days post-viral infection. The age of the study participants ranged between 17 and 87 years. It was estimated that 80% (95% CI 65-92) of the patients that were infected with SARS-CoV-2 developed one or more long-term symptoms. The five most common symptoms were fatigue (58%), headache (44%), attention disorder (27%), hair loss (25%), and dyspnea (24%). All meta-analyses showed medium (n=2) to high heterogeneity (n=13). Conclusions. In order to have a better understanding, future studies need to stratify by sex, age, previous comorbidities, the severity of COVID-19 (ranging from asymptomatic to severe), and duration of each symptom. From the clinical perspective, multi-disciplinary teams are crucial to developing preventive measures, rehabilitation techniques, and clinical management strategies with whole-patient perspectives designed to address long COVID-19 care.

The NK cell activation landscape in acute SARS-CoV-2 infection is associated with COVID-19 disease severity., Activated NK cells in severe COVID-19 Natural killer (NK) cells are cytotoxic lymphocytes that provide innate immune defense against viral infections and cancer, but little is known about their involvement in the host response to COVID-19. Maucourant et al. used high-dimensional flow cytometry to characterize NK cells in patients with moderate or severe COVID-19. SARS-CoV-2 infection was associated with fewer blood NK cells but a higher activation state in circulating NK cells. Severe COVID-19 resulted in an increase in “armed” NK cells containing high levels of cytotoxic proteins such as perforin. The adaptive NK subset was markedly expanded in a subset of severe patients. These findings lay the groundwork for future studies examining the mechanisms of NK cell activation in COVID-19 and their potential roles in host protection and immunopathology., Understanding innate immune responses in coronavirus disease 2019 (COVID-19) is important to decipher mechanisms of host responses and interpret disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections but might also contribute to immunopathology. Using 28-color flow cytometry, we here reveal strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients. This pattern was mirrored in single-cell RNA sequencing signatures of NK cells in bronchoalveolar lavage from COVID-19 patients. Unsupervised high-dimensional analysis of peripheral blood NK cells furthermore identified distinct NK cell immunotypes that were linked to disease severity. Hallmarks of these immunotypes were high expression of perforin, NKG2C, and Ksp37, reflecting increased presence of adaptive NK cells in circulation of patients with severe disease. Last, arming of CD56bright NK cells was observed across COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This study provides a detailed map of the NK cell activation landscape in COVID-19 disease.

Understanding innate immune responses in COVID-19 is important for deciphering mechanisms of host responses and interpreting disease pathogenesis. Natural killer (NK) cells are innate effector lymphocytes that respond to acute viral infections, but might also contribute to immune pathology. Here, using 28-color flow cytometry, we describe a state of strong NK cell activation across distinct subsets in peripheral blood of COVID-19 patients, a pattern mirrored in scRNA-seq signatures of lung NK cells. Unsupervised high-dimensional analysis identified distinct immunophenotypes that were linked to disease severity. Hallmarks of these immunophenotypes were high expression of perforin, NKG2C, and Ksp37, reflecting a high presence of adaptive NK cell expansions in circulation of patients with severe disease. Finally, arming of CD56bright NK cells was observed in course of COVID-19 disease states, driven by a defined protein-protein interaction network of inflammatory soluble factors. This provides a detailed map of the NK cell activation-landscape in COVID-19 disease.

Human NK cells can be subdivided into various subsets based on the relative expression of CD16 and CD56. In particular, CD56brightCD16−/dim NK cells are the focus of interest. They are considered efficient cytokine producers endowed with immunoregulatory properties, but they can also become cytotoxic upon appropriate activation. These cells were shown to play a role in different disease states, such as cancer, autoimmunity, neuroinflammation, and infection. Although their phenotype and functional properties are well known and have been extensively studied, their lineage relationship with other NK cell subsets is not fully defined, nor is their precise hematopoietic origin. In this article, we summarize recent studies about CD56bright NK cells in health and disease and briefly discuss the current controversies surrounding them.

Summary SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19. We here systematically mapped the functional and phenotypic landscape of SARS-CoV-2-specific T cell responses in unexposed individuals, exposed family members, and individuals with acute or convalescent COVID-19. Acute phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype that correlated with various clinical markers of disease severity, whereas convalescent phase SARS-CoV-2-specific T cells were polyfunctional and displayed a stem-like memory phenotype. Importantly, SARS-CoV-2-specific T cells were detectable in antibody-seronegative exposed family members and convalescent individuals with a history of asymptomatic and mild COVID-19. Our collective dataset shows that SARS-CoV-2 elicits robust, broad and highly functional memory T cell responses, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19., Highlights 1. Acute phase SARS-CoV-2-specific T cells display an activated cytotoxic phenotype 2. Broad and polyfunctional SARS-CoV-2-specific T cell responses in convalescent phase 3. Detection of SARS-CoV-2-specific T cell responses also in seronegative individuals

Regulatory T cells (Tregs) use different mechanisms to exert their suppressive function, among them the conversion of ATP to adenosine initiated by the ectonucleotidase CD39. In humans, the expression of CD39 on Tregs shows a high interindividual variation, and is especially high at sites of inflammation, like the synovia of patients with arthritis. How CD39 expression is regulated, and the functional consequences of different levels of CD39 expression is not known. We show here that stimulation of CD39 − Tregs results in a modest upregulation of CD39, which cannot explain the high levels observed in many donors. Moreover, CD39 + Tregs are present in naive compartments such as cord blood and thymus, and the individual frequency of CD39 + Tregs remains stable over time, suggesting inherent regulation of CD39 expression. Indeed, we show that a single nucleotide polymorphism in the CD39 gene determines expression levels in Tregs. CD39 + Tregs suppress T cell proliferation and inflammatory cytokine production more efficiently than CD39 − Tregs. Accordingly, Tregs from donors with the GG (high CD39) genotype have a higher capacity to suppress IFN-γ and IL-17 production by effector cells than Tregs from AA (low CD39) donors. Our study demonstrates that the expression of CD39 in Tregs is primarily genetically driven, and this may determine interindividual differences in the control of inflammatory responses.

SummaryBacteria, such as Fusobacterium nucleatum, are present in the tumor microenvironment. However, the immunological consequences of intra-tumoral bacteria remain unclear. Here, we have shown that natural killer (NK) cell killing of various tumors is inhibited in the presence of various F. nucleatum strains. Our data support that this F. nucleatum-mediated inhibition is mediated by human, but not by mouse TIGIT, an inhibitory receptor present on all human NK cells and on various T cells. Using a library of F. nucleatum mutants, we found that the Fap2 protein of F. nucleatum directly interacted with TIGIT, leading to the inhibition of NK cell cytotoxicity. We have further demonstrated that tumor-infiltrating lymphocytes expressed TIGIT and that T cell activities were also inhibited by F. nucleatum via Fap2. Our results identify a bacterium-dependent, tumor-immune evasion mechanism in which tumors exploit the Fap2 protein of F. nucleatum to inhibit immune cell activity via TIGIT.

Art. nº e62376; v. 8; issue 4, CD6 has recently been identified and validated as risk gene for multiple sclerosis (MS), based on the association of a single nucleotide polymorphism (SNP), rs17824933, located in intron 1. CD6 is a cell surface scavenger receptor involved in T-cell activation and proliferation, as well as in thymocyte differentiation. In this study, we performed a haptag SNP screen of the CD6 gene locus using a total of thirteen tagging SNPs, of which three were non-synonymous SNPs, and replicated the recently reported GWAS SNP rs650258 in a Spanish-Basque collection of 814 controls and 823 cases. Validation of the six most strongly associated SNPs was performed in an independent collection of 2265 MS patients and 2600 healthy controls. We identified association of haplotypes composed of two non-synonymous SNPs [rs11230563 (R225W) and rs2074225 (A257V)] in the 2nd SRCR domain with susceptibility to MS (Pmax(T) permutation=161024). The effect of these haplotypes on CD6 surface expression and cytokine secretion was also tested. The analysis showed significantly different CD6 expression patterns in the distinct cell subsets, i.e. – CD4+ naı¨ve cells, P = 0.0001; CD8+ naı¨ve cells, P,0.0001; CD4+ and CD8+ central memory cells, P = 0.01 and 0.05, respectively; and natural killer T (NKT) cells, P = 0.02; with the protective haplotype (RA) showing higher expression of CD6. However, no significant changes were observed in natural killer (NK) cells, effector memory and terminally differentiated effector memory T cells. Our findings reveal that this new MS-associated CD6 risk haplotype significantly modifies expression of CD6 on CD4+ and CD8+ T cells., doi:10.1371/journal.pone.0062376, European Community 212877; Gobierno Vasco (Grupos de Investigacion del Sistema Universitario Vasco) IT512-10;Ministerio de Ciencia e Innovacion - FEDER SAF2009-11491;FIS_FEDER CP10/00526 ;Junta de Andalucia-FEDER P07-CVI-02551

In acute myeloid leukemia (AML), residual leukemic (stem) cells that escape initial chemotherapy are considered a major source of relapse. Clinical trials have used IL-2 for AML patients with the aim to reduce relapse rates by eliminating residual leukemic cells through activation of NK and T cells. However, monotherapy with IL-2 has led to disappointing results. Nevertheless, recent clinical trials have shown that the co-administration of IL-2 and histamine dihydrochloride (HDC) provides maintenance of remission in AML. Histamine suppresses the formation of reactive oxygen species (ROS) thereby protecting NK and T cells from ROS-induced dysfunction and apoptosis. In addition, IL-2 is considered to maintain the anti-leukemic activity of NK cells. However, the direct effect of this treatment on NK cell numbers and anti-AML activity has not been studied in detail so far. In this study, we analyzed the immunophenotype and function of NK cells in a cohort of 7 AML patients (FAB M2, n=1; M4, n=2; M4-eo with inv 16, n=2; M5, n=2) treated with HDC plus IL-2. All patients had received induction chemotherapy with daunorubicin (45 mg/m² i.v. days 1-3), cytosine arabinoside, ARA-C (2 x 100 mg/m² i.v., days 1-7) and etoposide (100 mg/m² i.v., days 1-5) as well as at least 3 cycles of consolidation chemotherapy with high dose or intermediate dose ARA-C (Sperr et al, Clin Cancer Res 2004;10:3965-3971 and Krauth et al, J Immunol 2006;176:1759-1768). After having achieved a complete hematologic remission, patients were treated with HDC (0.5 mg) plus recombinant IL-2 (0.9 x 106 IU) twice daily s.c. for 21 days per cycle. Blood was drawn before and during treatment with HDC plus IL-2. We found that after one week of treatment with HDC plus IL-2, NK cell numbers increased in peripheral blood (from 101.8 ± 28.25 cells/µl before therapy to 208.2 ± 38.27 cells/µl after therapy, p In conclusion, treatment with HDC plus IL-2 causes a striking increase in CD56bright NK cells. These specifically expanded NK cells exhibit an activated phenotype with enhanced potential to kill leukemic cells. We propose that the maintenance of remission in AML patients treated with HDC plus IL-2 might, at least in part, be the result of an improved anti-leukemic NK cell function. Fig 1. Effect of HDC plus IL2 on NK cells of AML patients. A) Representative dot plots of the CD56bright and CD56dim NK cell subpopulations from an AML patient treated with histamine+IL2 before and after treatment. B) Absolute cell numbers of CD56bright NK cells of 7 AML patients before and after treatment, *** p Disclosures Sperr: MEDA Pharma GmbH & Co. KG: Speakers Bureau. Valent:MEDA Pharma GmbH & Co. KG: Speakers Bureau.

Tick-borne encephalitis virus (TBEV) is a flavivirus that belongs to the Flaviviridae family. TBEV is transmitted to humans primarily from infected ticks. The virus causes tick-borne encephalitis (TBE), an acute viral disease that affects the central nervous system (CNS). Infection can lead to acute neurological symptoms of significant severity due to meningitis or meningo(myelo)encephalitis. TBE can cause long-term suffering and has been recognized as an increasing public health problem. TBEV-affected areas currently include large parts of central and northern Europe as well as northern Asia. Infection with TBEV triggers a humoral as well as a cell-mediated immune response. In contrast to the well-characterized humoral antibody-mediated response, the cell-mediated immune responses elicited to natural TBEV-infection have been poorly characterized until recently. Here, we review recent progress in our understanding of the cell-mediated immune response to human TBEV-infection. A particular emphasis is devoted to studies of the response mediated by natural killer (NK) cells and CD8 T cells. The studies described include results revealing the temporal dynamics of the T cell- as well as NK cell-responses in relation to disease state and functional characterization of these cells. Additionally, we discuss specific immunopathological aspects of TBEV-infection in the CNS.