Role of beta-(1→3)(1→6)-D-glucan derived from yeast on natural killer (NK) cells and breast cancer cell lines in 2D and 3D cultures.

BACKGROUND: Beta-(1,3)(1,6)-D-glucan is a complex polysaccharide, which is found in the cell wall of various fungi, yeasts, bacteria, algae, barley, and oats and has immunomodulatory, anticancer and antiviral effects. In the present study, we investigated the effect of beta-(1,3)(1,6)-D-glucan derived from yeast on the proliferation of primary NK cells and breast cancer cell lines in 2D and 3D models, and on the cytotoxicity of primary NK cells against breast cancer cell lines in 2D and 3D models. METHODS: In this study, we investigated the effects of different concentrations of yeast-derived beta-(1→3)(1→6)-D-glucan on the proliferation and cytotoxicity of human NK cells and breast cancer cell lines in 2D and 3D models using the XTT cell proliferation assay and the CellTiter-Glo® 2.0 assay to determine the cytotoxicity of human NK cells on breast cancer cell lines in 2D and 3D models. RESULTS: We found that the co-incubation of NK cells with beta-glucan in the absence of IL2 at 48 h significantly increased the proliferation of NK cells, whereas the co-incubation of NK cells with beta-glucan in the presence of IL2 (70 U/ml) increased the proliferation of NK cells but not significantly. Moreover, beta-glucan significantly inhibited the proliferation of breast cancer cell lines in 2D model and induced a weak, non-significant growth inhibitory effect on breast cancer multicellular tumor spheroids (3D). In addition, the cytotoxicity of NK cells against breast cancer cell lines was examined in 2D and 3D models, and beta-glucan significantly increased the cytotoxicity of NK cells against MCF-7 (in 2D). CONCLUSIONS: Yeast derived beta-(1,3)(1,6)-D-glucan could contribute to the treatment of cancer by enhancing NK cell immune response as well as contributing to inhibition of breast cancer cell growth.

Next-Generation CEA-CAR-NK-92 Cells against Solid Tumors: Overcoming Tumor Microenvironment Challenges in Colorectal Cancer.

Colorectal carcinoma (CRC) presents a formidable medical challenge, demanding innovative therapeutic strategies. Chimeric antigen receptor (CAR) natural killer (NK) cell therapy has emerged as a promising alternative to CAR T-cell therapy for cancer. A suitable tumor antigen target on CRC is carcinoembryonic antigen (CEA), given its widespread expression and role in tumorigenesis and metastasis. CEA is known to be prolifically shed from tumor cells in a soluble form, thus hindering CAR recognition of tumors and migration through the TME. We have developed a next-generation CAR construct exclusively targeting cell-associated CEA, incorporating a PD1-checkpoint inhibitor and a CCR4 chemokine receptor to enhance homing and infiltration of the CAR-NK-92 cell line through the TME, and which does not induce fratricidal killing of CAR-NK-92-cells. To evaluate this therapeutic approach, we harnessed intricate 3D multicellular tumor spheroid models (MCTS), which emulate key elements of the TME. Our results demonstrate the effective cytotoxicity of CEA-CAR-NK-92 cells against CRC in colorectal cell lines and MCTS models. Importantly, minimal off-target activity against non-cancerous cell lines underscores the precision of this therapy. Furthermore, the integration of the CCR4 migration receptor augments homing by recognizing target ligands, CCL17 and CCL22. Notably, our CAR design results in no significant trogocytosis-induced fratricide. In summary, the proposed CEA-targeting CAR-NK cell therapy could offer a promising solution for CRC treatment, combining precision and efficacy in a tailored approach.

Symptom presentation and evolution in the first 48 hours after injury are associated with return to play after concussion in elite Rugby Union.

BACKGROUND: Return to play (RTP) in elite rugby is managed using a 6-stage graduated RTP protocol, which can result in clearance to play within 1 week of injury. We aimed to explore how symptom, cognitive, and balance presentation and evolution during concussion screens 2 h (head injury assessment (HIA) 2) and 48 h (HIA3) after injury were associated with time to RTP) to identify whether a more conservative graduated RTP may be appropriate. METHODS: A retrospective cohort study was conducted in 380 concussed rugby players from elite men's rugby over 3 consecutive seasons. Players were classified as shorter or longer returns, depending on whether RTP occurred within 7 days (allowing them to be considered to play the match 1 week after injury) or longer than 8 days, respectively. Symptom, cognitive, and balance performance during screens was assessed relative to baseline (normal or abnormal) and to the preceding screen (improving or worsening). Associations between sub-test abnormalities and RTP time were explored using odds ratios (OR, longer vs. shorter). Median day absence was compared between players with abnormal or worsening results and those whose results were normal or improving. RESULTS: Abnormal symptom results during screens 2 h and 48 h after concussion were associated with longer return time (HIA2: OR = 2.21, 95% confidence interval (95%CI): 1.39-3.50; HIA3: OR = 3.30, 95%CI: 1.89-5.75). Worsening symptom number or severity from the time of injury to 2 h and 48 h post-injury was associated with longer return (HIA2: OR = 2.49, 95%CI: 1.36-4.58; HIA3: OR = 3.34, 95%CI: 1.10-10.15. Median days absence was greater in players with abnormal symptom results at both HIA2 and HIA3. Cognitive and balance performance were not associated with longer return and did not affect median days absence. CONCLUSION: Symptom presentation and evolution within 48 h of concussion were associated with longer RTP times. This may guide a more conservative approach to RTP, while still adhering to individualized concussion management principles.

Cross-regulation of antibody responses against the SARS-CoV-2 Spike protein and commensal microbiota via molecular mimicry.

The commensal microflora provides a repertoire of antigens that illicit mucosal antibodies. In some cases, these antibodies can cross-react with host proteins, inducing autoimmunity, or with other microbial antigens. We demonstrate that the oral microbiota can induce salivary anti-SARS-CoV-2 Spike IgG antibodies via molecular mimicry. Anti-Spike IgG antibodies in the saliva correlated with enhanced abundance of Streptococcus salivarius 1 month after anti-SARS-CoV-2 vaccination. Several human commensal bacteria, including S. salivarius, were recognized by SARS-CoV-2-neutralizing monoclonal antibodies and induced cross-reactive anti-Spike antibodies in mice, facilitating SARS-CoV-2 clearance. A specific S. salivarius protein, RSSL-01370, contains regions with homology to the Spike receptor-binding domain, and immunization of mice with RSSL-01370 elicited anti-Spike IgG antibodies in the serum. Additionally, oral S. salivarius supplementation enhanced salivary anti-Spike antibodies in vaccinated individuals. Altogether, these data show that distinct species of the human microbiota can express molecular mimics of SARS-CoV-2 Spike protein, potentially enhancing protective immunity.

Early protective effect of a ("pan") coronavirus vaccine (PanCoVac) in Roborovski dwarf hamsters after single-low dose intranasal administration.

Introduction: The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted the danger posed by human coronaviruses. Rapid emergence of immunoevasive variants and waning antiviral immunity decrease the effect of the currently available vaccines, which aim at induction of neutralizing antibodies. In contrast, T cells are marginally affected by antigen evolution although they represent the major mediators of virus control and vaccine protection against virus-induced disease. Materials and methods: We generated a multi-epitope vaccine (PanCoVac) that encodes the conserved T cell epitopes from all structural proteins of coronaviruses. PanCoVac contains elements that facilitate efficient processing and presentation of PanCoVac-encoded T cell epitopes and can be uploaded to any available vaccine platform. For proof of principle, we cloned PanCoVac into a non-integrating lentivirus vector (NILV-PanCoVac). We chose Roborovski dwarf hamsters for a first step in evaluating PanCoVac in vivo. Unlike mice, they are naturally susceptible to SARS-CoV-2 infection. Moreover, Roborovski dwarf hamsters develop COVID-19-like disease after infection with SARS-CoV-2 enabling us to look at pathology and clinical symptoms. Results: Using HLA-A*0201-restricted reporter T cells and U251 cells expressing a tagged version of PanCoVac, we confirmed in vitro that PanCoVac is processed and presented by HLA-A*0201. As mucosal immunity in the respiratory tract is crucial for protection against respiratory viruses such as SARS-CoV-2, we tested the protective effect of single-low dose of NILV-PanCoVac administered via the intranasal (i.n.) route in the Roborovski dwarf hamster model of COVID-19. After infection with ancestral SARS-CoV-2, animals immunized with a single-low dose of NILV-PanCoVac i.n. did not show symptoms and had significantly decreased viral loads in the lung tissue. This protective effect was observed in the early phase (2 days post infection) after challenge and was not dependent on neutralizing antibodies. Conclusion: PanCoVac, a multi-epitope vaccine covering conserved T cell epitopes from all structural proteins of coronaviruses, might protect from severe disease caused by SARS-CoV-2 variants and future pathogenic coronaviruses. The use of (HLA-) humanized animal models will allow for further efficacy studies of PanCoVac-based vaccines in vivo.

Next Generation CD44v6-Specific CAR-NK Cells Effective against Triple Negative Breast Cancer.

There is a medical need to develop new and effective therapies against triple-negative breast cancer (TNBC). Chimeric antigen receptor (CAR) natural killer (NK) cells are a promising alternative to CAR-T cell therapy for cancer. A search for a suitable target in TNBC identified CD44v6, an adhesion molecule expressed in lymphomas, leukemias and solid tumors that is implicated in tumorigenesis and metastases. We have developed a next-generation CAR targeting CD44v6 that incorporates IL-15 superagonist and checkpoint inhibitor molecules. We could show that CD44v6 CAR-NK cells demonstrated effective cytotoxicity against TNBC in 3D spheroid models. The IL-15 superagonist was specifically released upon recognition of CD44v6 on TNBC and contributed to the cytotoxic attack. PD1 ligands are upregulated in TNBC and contribute to the immunosuppressive tumor microenvironment (TME). Competitive inhibition of PD1 neutralized inhibition by PD1 ligands expressed on TNBC. In total, CD44v6 CAR-NK cells are resistant to TME immunosuppression and offer a new therapeutic option for the treatment of BC, including TNBC.

Epstein-Barr virus, interleukin-10 and multiple sclerosis: A ménage à trois.

Multiple Sclerosis (MS) is an autoimmune disease that is characterized by inflammation and demyelination of nerve cells. There is strong evidence that Epstein-Barr virus (EBV), a human herpesvirus infecting B cells, greatly increases the risk of subsequent MS. Intriguingly, EBV not only induces human interleukin-10 but also encodes a homologue of this molecule, which is a key anti-inflammatory cytokine of the immune system. Although EBV-encoded IL-10 (ebvIL-10) has a high amino acid identity with its cellular counterpart (cIL-10), it shows more restricted and partially weaker functionality. We propose that both EBV-induced cIL-10 and ebvIL-10 act in a temporally and functionally coordinated manner helping the pathogen to establish latency in B cells and, at the same time, to balance the function of antiviral T cells. As a result, the EBV load persisting in the immune system is kept at a constant but individually different level (set point). During this immunological tug of war between virus and host, however, MS can be induced as collateral damage if the set point is too high. Here, we discuss a possible role of ebvIL-10 and EBV-induced cIL-10 in EBV-driven pathogenesis of MS.

Implications for Immunotherapy of Breast Cancer by Understanding the Microenvironment of a Solid Tumor.

Breast cancer is poorly immunogenic due to immunosuppressive mechanisms produced in part by the tumor microenvironment (TME). The TME is a peritumoral area containing significant quantities of (1) cancer-associated fibroblasts (CAF), (2) tumor-infiltrating lymphocytes (TIL) and (3) tumor-associated macrophages (TAM). This combination protects the tumor from effective immune responses. How these protective cell types are generated and how the changes in the developing tumor relate to these subsets is only partially understood. Immunotherapies targeting solid tumors have proven ineffective largely due to this protective TME barrier. Therefore, a better understanding of the interplay between the tumor, the tumor microenvironment and immune cells would both advance immunotherapeutic research and lead to more effective immunotherapies. This review will summarize the current understanding of the microenvironment of breast cancer giving implications for future immunotherapeutic strategies.

Expansion of cognitive testing for off-field concussion screening in elite rugby players: A cohort study.

OBJECTIVES: Current off-field concussion screening instruments have sub-optimal accuracy and additional testing domains may be necessary to detect the full spectrum of concussion presentations. This study aimed to determine if additional cognitive tests add utility to off-field screening for sport-related concussion. DESIGN: Reproducibility and diagnostic accuracy cohort studies were performed in the 2017 and 2018 seasons of the Super Rugby competition, conducted in Argentina, Australia, Japan, New Zealand, and South Africa. METHODS: Abridged versions of Stroop (score, time), Spatial Memory (score, failed trials), and Trail Making Trial-B (time, errors) cognitive tests, modified for off-field use, were examined. Players performed baseline testing prior to each season. Cases undergoing off-field screening as part of the World Rugby Head Injury Assessment Process underwent evaluation with the same cognitive tests during competition matches. Agreement between repeated pre-season baseline measurements, and the diagnostic accuracy of off-field testing against a clinical reference standard of concussion, was evaluated. RESULTS: Data were available for repeated preseason baseline testing in 644 players, and 100 cases undergoing off-field concussion screening. There was little individual agreement across pre-season baseline assessments for all tests (Lin's correlation and Gwets AC1 coefficients ranging between 0.2 and 0.3). There was significantly worse performance for the time taken to complete the modified Stroop Test in concussed players undergoing off-field screening, compared to non-concussed players (median time 21.1 v 18.4 s, p < 0.01; area under the receiver operating characteristic curve 0.7 (95% CI 0.5-0.8)). Other cognitive measures did not discriminate between injured and un-injured players, with no-statistically significant differences in distribution medians (p = 0.6-0.9) and AUROC values close to 0.5. CONCLUSIONS: The time taken to perform a modified Stroop Test may provide additional diagnostic accuracy if added to current off-field concussion screening tools. Abridged Spatial Memory and Trail Making Trial-B tests did not discriminate between concussed and non-concussed players.

Head injury assessment in rugby union: clinical judgement guidelines.

BACKGROUND/AIM: Clinical judgement is a recognised component of a complete off-field concussion assessment. This study identifies guidance criteria for team medical staff when using clinical judgement in their decision-making process during the World Rugby off-field concussion-assessment screen (HIA1). METHODS: Retrospective study of examining doctor clinical judgement in 1149 HIA1 assessments after a meaningful head impact event completed on rugby union players participating in elite-level international and national competitions between September 2015 and June 2018. We assessed (1) an abnormal subtest result as worse performance compared with preseason baseline values; (2) the proportion of cases where clinicians overruled abnormal HIA1 assessment subtest results and (3) made recommendations on how clinical judgement decisions may be made more safely based on the accuracy of clinical judgement decisions assessed against the final concussion diagnosis. RESULTS: One or more subtests were abnormal compared with baseline values in 857 of 1149 HIA1 assessments. Clinical judgement was used to return players to the game despite abnormal subtest results on 424 out of 857 occasions (49%). In a significant majority of cases 356/424 (84%), clinical judgement decisions were correct, with players later cleared of a concussion. An application of guided clinical judgement potentially decreased false negative assessments by 33% (21/63). CONCLUSIONS: Clinical judgement should be applied in the diagnosis of concussion but done so cautiously. We propose doctors should only use clinical judgement to overrule either one of; or a combination of (1) an abnormal tandem gait and (2) one abnormal cognitive test.

SARS-CoV-2 in severe COVID-19 induces a TGF-ß-dominated chronic immune response that does not target itself.

The pathogenesis of severe COVID-19 reflects an inefficient immune reaction to SARS-CoV-2. Here we analyze, at the single cell level, plasmablasts egressed into the blood to study the dynamics of adaptive immune response in COVID-19 patients requiring intensive care. Before seroconversion in response to SARS-CoV-2 spike protein, peripheral plasmablasts display a type 1 interferon-induced gene expression signature; however, following seroconversion, plasmablasts lose this signature, express instead gene signatures induced by IL-21 and TGF-ß, and produce mostly IgG1 and IgA1. In the sustained immune reaction from COVID-19 patients, plasmablasts shift to the expression of IgA2, thereby reflecting an instruction by TGF-ß. Despite their continued presence in the blood, plasmablasts are not found in the lungs of deceased COVID-19 patients, nor does patient IgA2 binds to the dominant antigens of SARS-CoV-2. Our results thus suggest that, in severe COVID-19, SARS-CoV-2 triggers a chronic immune reaction that is instructed by TGF-ß, and is distracted from itself.

Diagnostic Utility of New SCAT5 Neurological Screen Sub-tests.

BACKGROUND: The Sports Concussion Assessment Tool (SCAT) is recommended to screen for concussion following head impact events in elite sport. The most recent 5th edition (SCAT5) included a 'rapid neurological screen' which introduced new subtests examining comprehension, passive neck movement, and diplopia. This study evaluated the additional diagnostic value of these new subtests. METHODS: A prospective cohort study was performed in the Pro14 elite Rugby Union competition between September 2018 and January 2020. The SCAT5 was administered by the team doctor to players undergoing off-field screening for concussion during a medical room assessment. Sensitivity, specificity, false negatives, and positives were examined for SCAT5 comprehension, passive neck movement, and diplopia subtests. The reference standard was a final diagnosis of concussion, established by serial standardised clinical assessments over 48 h. RESULTS: Ninety-three players undergoing off-field screening for concussion were included. Sensitivity and specificity of the comprehension, passive neck movement, and diplopia subtests were 0, 8, 5% and 0, 91, 97%, respectively (concussion prevalence 63%). No players had any abnormality in comprehension. No players had abnormal passive neck movement or diplopia in the absence of abnormalities in other SCAT5 sub-components. CONCLUSIONS: The new SCAT5 neurological screen subtests are normal in the majority of players undergoing off-field concussion screening and appear to lack diagnostic utility over and above other SCAT5 subtests.

HCMV-Mediated Interference of Bortezomib-Induced Apoptosis in Colon Carcinoma Cell Line Caco-2.

Human cytomegalovirus (HCMV) has been implicated in the development of human malignancies, for instance in colon cancer. Proteasome inhibitors were developed for cancer therapy and have also been shown to influence HCMV infection. The aim of this study was to investigate if proteasome inhibitors have therapeutic potential for colon carcinoma and how this is influenced by HCMV infection. We show by immunofluorescence and flow cytometry that the colon carcinoma cell line Caco-2 is susceptible to HCMV infection. Growth curve analysis as well as protein expression kinetics and quantitative genome analysis further confirm these results. HCMV has an anti-apoptotic effect on Caco-2 cells by inhibiting very early events of the apoptosis cascade. Further investigations showed that HCMV stabilizes the membrane potential of the mitochondria, which is typically lost very early during apoptosis. This stabilization is resistant to proteasome inhibitor Bortezomib treatment, allowing HCMV-infected cells to survive apoptotic signals. Our findings indicate a possible role of proteasome inhibitors in colon carcinoma therapy.

Baseline SCAT Performance in Men and Women: Comparison of Baseline Concussion Screens Between 6288 Elite Men's and 764 Women's Rugby Players.

OBJECTIVE: This study compared Sports Concussion Assessment Tool (SCAT) performance in elite male (6288 players) and female (764 players) rugby players, to determine whether reference limits used for the management and diagnosis of concussion should differ between sexes. DESIGN: Cross-sectional census sample. SETTING: Data from World Rugby's Head Injury Assessment management system were analyzed. This data set covers global professional rugby. PARTICIPANTS: All professional players who underwent baseline SCAT testing as part of World Rugby's concussion management requirement formed the study cohort. Ten thousand seven hundred fifty-four SCAT assessments from 6288 elite male rugby players and 1071 assessments from 764 elite female players were analyzed. INTERVENTION: Elite men and women rugby players are independent variables. MAIN OUTCOME MEASURES: Sports Concussion Assessment Tool performance, including symptoms endorsed, cognitive submode performance, and balance performance. RESULTS: Women endorsed significantly more symptoms, with greater symptom severity, than men (relative ratio 1.34, 95% confidence interval, 1.25-1.45 women vs men). Women outperformed men in cognitive submodes with the exception of immediate memory and delayed recall and made fewer balance errors than men during the modified Balance Error Scoring System. Clinical reference limits, defined as submode score achieved by the worst-performing 50% of the cohort, did not differ between men and women. CONCLUSIONS: Women and men perform differently during SCAT baseline testing, although differences are small and do not affect either the baseline or clinical reference limits that identify abnormal test results for most submodes. The greater endorsement of symptoms by women suggests increased risk of adverse concussion outcomes and highlights the importance of accurate evaluation of any symptom endorsement at baseline.

Effect of a concussion on subsequent baseline SCAT performance in professional rugby players: a retrospective cohort study in global elite Rugby Union.

OBJECTIVES: This study assessed whether concussion affects subsequent baseline performance in professional rugby players. Annual baseline screening tests are used to guide return-to-play decisions and concussion diagnosis during subsequent screens. It is important that baseline performances are appropriate and valid for the duration of a season and unaffected by factors unrelated to the current head impact event. One such factor may be a concussion following baseline assessment. SETTING: The World Rugby concussion management database for global professional Rugby Union. PARTICIPANTS: 501 professional rugby players with two baseline Sports Concussion Assessment Tools (SCATs) and an intervening concussion (CONC) were compared with 1190 control players with successive annual SCAT5s and no diagnosed concussion (CONT). PRIMARY AND SECONDARY OUTCOME MEASURES: Symptom endorsement, cognitive and balance performance during annual SCAT baseline assessments. RESULTS: Players with a diagnosed concussion (CONC) endorsed fewer symptoms (change -0.42, 95% CI -0.75 to -0.09), and reported lower symptom severity scores during their second assessment (T2, p<0.001) than non-concussed players (CONT). Concussed players also improved Digits Backward and Final Concentration scores in T2 (p<0.001). Tandem gait time was improved during T2 in CONT. No other sub-mode differences were observed in either group. CONCLUSIONS: Reduced symptom endorsement and improved cognitive performance after concussion may be the result of differences in the motivation of previously concussed players to avoid exclusion from play, leading to under-reporting of symptoms and greater effort in cognitive tests. Improved cognitive performance may be the result of familiarity with the tests as a result of greater exposure to concussion screening. The changes are small and unlikely to have clinical significance in most cases, though clinicians should be mindful of possible reasons, possibly repeating sub-modes and investigating players whose baseline scores change significantly after concussion. The findings do not necessitate a change in the sport's concussion management policy.

The effect of exercise on baseline SCAT5 performance in male professional Rugby players.

BACKGROUND: Rugby Union requires annual baseline testing using the Sports Concussion Assessment Tool (SCAT5) as part of its head injury assessment protocols. Scores achieved during baseline testing are used to guide return-to-play decisions at the time of head impact events during matches, and concussion diagnosis during subsequent diagnostic screens. Baseline values must be valid, accurate representations of a player's capability in the various SCAT5 sub-modes, including symptom report, cognitive function and balance. The extent to which prior exercise may affect performance is an important consideration, and the present cross-sectional study aimed to explore how SCAT5 performance differs when assessed at rest (RSCAT) compared to after 30 min of exercise (EXSCAT) in 698 male professional rugby players for whom paired exercise and rest SCAT5 data were available. RESULTS: Symptom endorsement was greater when assessed after exercise than at rest. Fatigue/Low energy was 1.5 times more likely to be reported when assessed during EXSCAT. Orientation score was improved during SCAT5s performed after exercise, but only when rest and exercise SCAT5s were conducted on the same day, suggesting a learning effect. Concentration score was impaired during EXSCAT. No other cognitive sub-modes were affected by exercise. Total errors during Modified Balance Error Scoring System (MBESS) increased during EXSCAT, as a result of increased errors made during single leg balance, irrespective of testing sequence, with 42% of players making more errors in EXSCAT, compared to 28% making more errors in RSCAT. CONCLUSIONS: Symptoms, cognitive sub-modes and balance sub-modes are all affected by exercise. These may be the result of learning effects that improve cognitive performance, and the direct effects of exercise on sub-mode performance. The clinical implications of these changes may be assessed in the future through a study of diagnostic screens in players after head impact events, to confirm whether an exercise baseline screen is required annually, or whether specific sub-modes of the SCAT5 should be obtained at rest and after exercise.

Devilishly radical NETwork in COVID-19: Oxidative stress, neutrophil extracellular traps (NETs), and T cell suppression.

Pandemic coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and poses an unprecedented challenge to healthcare systems due to the lack of a vaccine and specific treatment options. Accordingly, there is an urgent need to understand precisely the pathogenic mechanisms underlying this multifaceted disease. There is increasing evidence that the immune system reacts insufficiently to SARS-CoV-2 and thus contributes to organ damage and to lethality. In this review, we suggest that the overwhelming production of reactive oxygen species (ROS) resulting in oxidative stress is a major cause of local or systemic tissue damage that leads to severe COVID-19. It increases the formation of neutrophil extracellular traps (NETs) and suppresses the adaptive arm of the immune system, i.e. T cells that are necessary to kill virus-infected cells. This creates a vicious cycle that prevents a specific immune response against SARS-CoV-2. The key role of oxidative stress in the pathogenesis of severe COVID-19 implies that therapeutic counterbalancing of ROS by antioxidants such as vitamin C or NAC and/or by antagonizing ROS production by cells of the mononuclear phagocyte system (MPS) and neutrophil granulocytes and/or by blocking of TNF-α can prevent COVID-19 from becoming severe. Controlled clinical trials and preclinical models of COVID-19 are needed to evaluate this hypothesis.

Replication in the Mononuclear Phagocyte System (MPS) as a Determinant of Hantavirus Pathogenicity.

Members of different virus families including Hantaviridae cause viral hemorrhagic fevers (VHFs). The decisive determinants of hantavirus-associated pathogenicity are still enigmatic. Pathogenic hantavirus species, such as Puumala virus (PUUV), Hantaan virus (HTNV), Dobrava-Belgrade virus (DOBV), and Sin Nombre virus (SNV), are associated with significant case fatality rates. In contrast, Tula virus (TULV) only sporadically causes mild disease in immunocompetent humans and Prospect Hill virus (PHV) so far has not been associated with any symptoms. They are thus defined here as low pathogenic/apathogenic hantavirus species. We found that productive infection of cells of the mononuclear phagocyte system (MPS), such as monocytes and dendritic cells (DCs), correlated well with the pathogenicity of hantavirus species tested. HTNV (intermediate case fatality rates) replicated more efficiently than PUUV (low case fatality rates) in myeloid cells, whereas low pathogenic/apathogenic hantavirus species did not produce any detectable virus titers. Analysis of PHPUV, a reassortant hantavirus derived from a pathogenic (PUUV) and an apathogenic (PHV) hantavirus species, indicated that the viral glycoproteins are not decisive for replication in MPS cells. Moreover, blocking acidification of endosomes with chloroquine decreased the number of TULV genomes in myeloid cells suggesting a post-entry block for low pathogenic/apathogenic hantavirus species in myeloid cells. Intriguingly, pathogenic but not low pathogenic/apathogenic hantavirus species induced conversion of monocytes into inflammatory DCs. The proinflammatory programming of MPS cells by pathogenic hantavirus species required integrin signaling and viral replication. Our findings indicate that the capacity to replicate in MPS cells is a prominent feature of hantaviral pathogenicity.