COVID-19-associated lung microvascular endotheliopathy: a "from the bench" perspective

Rationale: Autopsy and biomarker studies suggest that endotheliopathy contributes to coronavirus disease (COVID-19)-associated acute respiratory distress syndrome. However, the effects of COVID-19 on the lung endothelium are not well defined. We hypothesized that the lung endotheliopathy of COVID-19 is caused by circulating host factors and direct endothelial infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Objectives: We aimed to determine the effects of SARS-CoV-2 or sera from patients with COVID-19 on the permeability and inflammatory activation of lung microvascular endothelial cells. Methods: Human lung microvascular endothelial cells were treated with live SARS-CoV-2;inactivated viral particles;or sera from patients with COVID-19, patients without COVID-19, and healthy volunteers. Permeability was determined by measuring transendothelial resistance to electrical current flow, where decreased resistance signifies increased permeability. Inflammatory mediators were quantified in culture supernatants. Endothelial biomarkers were quantified in patient sera. Measurements and Main Results: Viral PCR confirmed that SARS-CoV-2 enters and replicates in endothelial cells. Live SARS-CoV-2, but not dead virus or spike protein, induces endothelial permeability and secretion of plasminogen activator inhibitor 1 and vascular endothelial growth factor. There was substantial variability in the effects of SARS-CoV-2 on endothelial cells from different donors. Sera from patients with COVID-19 induced endothelial permeability, which correlated with disease severity. Serum levels of endothelial activation and injury biomarkers were increased in patients with COVID-19 and correlated with severity of illness. Conclusions: SARS-CoV-2 infects and dysregulates endothelial cell functions. Circulating factors in patients with COVID-19 also induce endothelial cell dysfunction. Our data point to roles for both systemic factors acting on lung endothelial cells and viral infection of endothelial cells in COVID-19-associated endotheliopathy.

Baseline Plasma Viral Antigen Levels Are Associated with Clinical Deterioration in Hospitalized Covid-19: Potential Value for Stratifying Patients for Therapeutic Interventions

RATIONALE: Some biomarkers of host response to viral infection are associated with COVID-19 outcomes, but these biomarkers do not directly measure viral burden. The association between plasma viral antigen levels and clinical outcomes has not been previously studied. Our aim was to investigate the relationship between plasma SARS-CoV-2 viral antigen concentration and proximal clinical deterioration in hospitalized patients. METHODS: SARS-CoV-2 nucleocapsid antigen concentrations were measured using a validated microbead immunoassay (Quanterix, NIH/NIAID laboratory) in plasma collected at enrollment from 256 subjects in a prospective observational cohort of hospitalized patients with COVID-19 from 3 hospitals, admitted between March 2020 and August 2021. Relationships between viral antigen concentration and clinical status at 1 week as measured by the World Health Organization (WHO) ordinal scale as well as ICU admission were assessed. Models were adjusted for age and sex, baseline comorbidities including immunosuppression, endogenous neutralizing antibodies, baseline COVID-19 severity, smoking status, remdesivir therapy, steroid therapy, and vaccine status. Missing covariate data were imputed using multiple imputation by chained equations. RESULTS: The median viral antigen concentration for the 35 subjects who deteriorated by 1 week was 4507 (IQR 1225-9665) pg/mL compared to 494 (IQR 18-3882) pg/mL in the 212 subjects who did not (p = 0.0004 Figure a). Using ordinal regression, each doubling in viral antigen concentration was significantly associated with a worse WHO ordinal scale at 1 week (unadjusted OR 1.07, 95% CI 1.02-1.13;adjusted OR 1.10, 95% CI 1.02-1.18). Among 168 patients not in the ICU at baseline, the median viral antigen concentration for the 40 patients who progressed to the ICU was 4697 (IQR 482- 10410) pg/mL vs. 459 (IQR 15-3062) pg/mL in the 128 patients who did not progress to require ICU care (p = 0.0001 Figure b). Using logistic regression, each doubling in viral antigen concentration was significantly associated with ICU admission (unadjusted OR 1.18, 95% CI 1.06-1.32, adjusted OR 1.40, 95% CI 1.11-1.76). CONCLUSIONS: Higher plasma viral antigen concentration at hospital admission is independently associated with a significantly worse clinical status at 1 week and a higher odds of ICU admission among hospitalized patients with COVID-19. This novel finding indicates that plasma viral antigen concentration may identify hospitalized COVID-19 patients at highest risk of short-term clinical deterioration in both clinical practice and research. Results of plasma antigen tests are available within 2-3 hours and could be integrated for identifying hospitalized COVID-19 patients who might benefit from early intervention.

Hyperinflammatory ARDS Is Characterized by Interferon-High, Neutrophil-Predominant Inflammation in the Lower Respiratory Tract

Background: Latent class analyses in patients with acute respiratory distress syndrome (ARDS) have identified “hyper-inflammatory” and “hypo-inflammatory” phenotypes with divergent clinical outcomes and treatment responses. ARDS phenotypes are defined using plasma biomarkers and clinical variables. It is currently unknown if these phenotypes have distinct pulmonary biology and if pre-clinical models of disease replicate the biology of either phenotype. Methods: 45 subjects with ARDS (Berlin Definition) and 5 mechanically ventilated controls were selected from cohorts of mechanically ventilated patients at UCSF and ZSFG. Patients with COVID-19 were excluded from this analysis. A 3-variable classifier model (plasma IL-8, protein C, and bicarbonate;Sinha 2020) was used to assign ARDS phenotypes. Tracheal aspirate (TA) RNA was analyzed using established bulk and single-cell sequencing pipelines (Langelier 2018, Sarma 2021). Differentially expressed (DE) genes were analyzed using Ingenuity Pathway Analysis (IPA). Microbial community composition was analyzed with vegan. Fgsea was used to test for enrichment of gene sets from experimental ARDS models in genes that were differentially expressed between each phenotype and mechanically ventilated controls. Results: Bulk RNA sequencing (RNAseq) was available from 29 subjects with hypoinflammatory ARDS and 10 subjects with hyperinflammatory ARDS. 2,777 genes were differentially expressed between ARDS phenotypes. IPA identified several candidate upstream regulators of gene expression in hyperinflammatory ARDS including IL6, TNF, IL17C, and interferons (Figure 1A). 2,953 genes were differentially expressed between hyperinflammatory ARDS and 5 ventilated controls;in contrast, only 243 genes were differentially expressed between hypoinflammatory ARDS and controls, suggesting gene expression in the hypoinflammatory phenotype was more heterogeneous. Gene sets from experimental models of acute lung injury were enriched in hyperinflammatory ARDS but not in hypoinflammatory ARDS (Figure 1B). Single cell RNA sequencing (scRNAseq) was available from 6 additional subjects with ARDS, of whom 3 had hyperinflammatory ARDS. 14,843 cells passed quality control filters. Hyperinflammatory ARDS subjects had a markedly higher burden of neutrophils (Figure 1C), including a cluster of stressed neutrophils expressing heat shock protein RNA that was not present in hypoinflammatory ARDS. Expression of a Th1 signature was higher in T cells from hyperinflammatory ARDS. Differential expression analysis in macrophages identified increased expression of genes associated with mortality in a previous study of ARDS patients (Morell 2019). Conclusions: The respiratory tract biology of ARDS phenotypes is distinct. Hyperinflammatory ARDS is characterized by neutrophilic inflammation with distinct immune cell polarization. Transcriptomic profiling identifies candidate preclinical disease models that replicate gene expression observed in hyperinflammatory ARDS.

A Safety Monitoring Framework for Critical Care Trials of Agents with Potential to Lower Blood Pressure

RATIONALE: Based on encouraging preliminary data, we undertook a randomized, placebo-controlled trial of synthetic vasoactive intestinal peptide (aviptadil) for treatment of COVID-19 acute respiratory distress syndrome (ARDS). Aviptadil may cause vasodilation and resultant hypotension. Given the high background incidence of hypotension from many causes (e.g., sedatives, sepsis, positive pressure ventilation) in critically ill patients, an ascertainment and grading strategy for postrandomization hypotension capable of distinguishing “signal” from “noise” is essential to the trial's conduct and interpretation. METHODS: We evaluated whether existing adverse event (AE) severity frameworks were adequate to characterize hypotension occurring in critically ill patients. Based on these findings, we developed and implemented a customized framework for hypotension-related safety monitoring and outcome collection during the Therapeutics for Severely Ill Inpatients with COVID-19 (TESICO) trial of aviptadil for COVID-19 ARDS (NCT04843761). RESULTS: Hypotension severity assigned to COVID-19 ARDS patients by existing AE frameworks - largely developed for outpatients - appeared misaligned with the frameworks' own generic/conceptual severity criteria. Existing frameworks' hypotension-specific AE grading tables lacked necessary detail and reporting guidance, over-graded mild hypotension, and missed safety signals suggested by increasing vasopressor requirements. We therefore developed a novel hypotension AE grading table aligned with conceptual AE severity criteria for critically ill patients (Figure). In addition to general severity criteria, the table adds criteria specific to the investigational agent's peri-infusion period and provides guidance for evaluating the “seriousness” of a hypotensive event in the context of subjects' preexisting critical illness. In combination with detailed reporting on the components of AE events, the study's protocol committee, sponsor, and data safety monitoring board approved the customized table for use in outcome measurement as well as real-time safety monitoring and AE reporting. We implemented a strategy to efficiently collect the hypotension-related data required for safety monitoring and allow automated hypotension AE grading according to both the adopted schema and existing AE frameworks. CONCLUSIONS: We developed a framework acceptable to diverse stakeholders for hypotension safety monitoring in COVID-19 ARDS patients receiving aviptadil or placebo. The monitoring framework will be validated in the ongoing TESICO trial and could be adapted for other trials of vasoactive investigational agents targeting critically ill patients. Comprehensive AE grading criteria designed specifically for critically ill patients could improve trials' ability to meaningfully monitor and report safety outcomes in this population.

Revisiting the ROSE Trial - Why Did Participants with ARDS Identified as Hispanic/Latino Have Lower Mortality When Randomized to Receive Early Neuromuscular Blockade?

Rationale: The ROSE trial was a multicenter unblinded randomized clinical trial comparing early neuromuscular blockade (NMB) to usual care in patients with moderate to severe ARDS (NEJM 2019). This trial (n=1006) was stopped early for futility yet a subgroup analysis found that among Hispanic/Latino participants the NMB intervention group had a significantly lower mortality (32%) compared to those in the control group (53.7% p=0.02 for interaction). To evaluate potential contributors to these differences we compared baseline clinical and biological characteristics among Hispanic/Latino participants in the intervention vs control group. Methods: We compared demographics primary ARDS risk factor illness severity ventilatory parameters comorbidities and plasma biomarkers at baseline between the NMB intervention and control group for all 118 Hispanic/Latino patients recruited to the ROSE trial (11.6% of the trial population). We used multiple logistic regression to examine whether the mortality difference by treatment group would persist after controlling for the factors that differed significantly between groups. Results: At baseline Hispanic/Latino participants randomized to the control group had greater disease severity scores (APACHE III SOFA;p<0.05 for both) and a higher prevalence of shock (p=0.01) compared to those randomized to the intervention. There were no significant differences between groups in causes of lung injury or baseline ventilatory parameters. In an unadjusted logistic regression model the NMB intervention was significantly associated with mortality (OR 0.42;95%CI 0.20-0.89 p=0.02). The NMB intervention was no longer significantly associated with mortality when adjusting for severity of by illness by either SOFA score (OR 0.53;95%CI 0.24-1.20 p=0.13), APACHE III (OR 0.51, 95%CI 0.20- 1.30 p=0.16) or shock as defined by the need for vasopressors (OR 0.48, 95%CI 0.22-1.03, p=0.06). Hispanic/Latino participants in the control group had significantly higher interleukin-8 (p=0.02) and lower bicarbonate (p=0.045) than those in the intervention group. Conclusion: Together these clinical and biomarker data support the conclusion that the lower mortality associated with NMB in the Hispanic/Latino subgroup may have been partially due to baseline imbalances in systemic severity of illness. This finding underscores the need to cautiously interpret apparent treatment benefits within small subgroups. The COVID-19 pandemic has highlighted ethnic and racial disparities in ARDS. Future trials will benefit from increased representation of populations that are disproportionately affected to minimize the impact of spurious findings related to small sample sizes while creating more statistical power to prospectively address disparities.

Mesenchymal stem/stromal cell-based therapies for severe viral pneumonia: therapeutic potential and challenges.

Severe viral pneumonia is a significant cause of morbidity and mortality globally, whether due to outbreaks of endemic viruses, periodic viral epidemics, or the rarer but devastating global viral pandemics. While limited anti-viral therapies exist, there is a paucity of direct therapies to directly attenuate viral pneumonia-induced lung injury, and management therefore remains largely supportive. Mesenchymal stromal/stem cells (MSCs) are receiving considerable attention as a cytotherapeutic for viral pneumonia. Several properties of MSCs position them as a promising therapeutic strategy for viral pneumonia-induced lung injury as demonstrated in pre-clinical studies in relevant models. More recently, early phase clinical studies have demonstrated a reassuring safety profile of these cells. These investigations have taken on an added importance and urgency during the COVID-19 pandemic, with multiple trials in progress across the globe. In parallel with clinical translation, strategies are being investigated to enhance the therapeutic potential of these cells in vivo, with different MSC tissue sources, specific cellular products including cell-free options, and strategies to 'licence' or 'pre-activate' these cells, all being explored. This review will assess the therapeutic potential of MSC-based therapies for severe viral pneumonia. It will describe the aetiology and epidemiology of severe viral pneumonia, describe current therapeutic approaches, and examine the data suggesting therapeutic potential of MSCs for severe viral pneumonia in pre-clinical and clinical studies. The challenges and opportunities for MSC-based therapies will then be considered.

Tracheal aspirate sequencing identifies unique features of dysregulated host response in SARS-CoV 2 associated acute respiratory distress syndrome

Background: The coronavirus disease 2019 (COVID-19) pandemic has led to a rapid increase in the incidence of acute respiratory distress syndrome (ARDS). The distinct features of pulmonary biology in COVID-19 ARDS compared to other causes of ARDS, including other lower respiratory tract infections (LRTIs), are not well understood. Methods: Tracheal aspirates (TA) and plasma were collected within five days of intubation from mechanically ventilated adults admitted to one of two academic medical centers. ARDS and LRTI diagnoses and were verified by study physicians. Subjects were excluded if they received immunosuppression. TA from subjects with COVID-ARDS was compared to gene expression in TA from subjects with other causes of ARDS (OtherARDS) or mechanically ventilated control subjects without evidence of pulmonary pathology (NoARDS). Plasma concentrations of IL-6, IL-8, and protein C also were compared between these groups. Upstream regulator and pathway analysis was performed on significantly differentially expressed genes with Ingenuity Pathway Analysis (IPA). Subgroup analyses were performed to compare gene expression in COVID to ARDS associated with other viral LRTIs and bacterial LRTIs. The association of interferon-stimulated gene expression with SARS-CoV2 viral load was compared to the same association in nasopharyngeal swabs in a cohort of subjects with mild SARS-CoV2. Results: TA sequencing was available from 15 subjects with COVID, 32 subjects with other causes of ARDS (OtherARDS), and 5 mechanically ventilated subjects without evidence of pulmonary pathology (NoARDS). 696 genes were differentially expressed between COVID and OtherARDS (Figure 1A). IL-6, IL-8, B-cell receptor, and hypoxia inducible factor-1a signaling were attenuated in COVID compared to OtherARDS. Peroxisome proliferator-activated receptor (PPAR) and PTEN signaling were higher in COVID compared to OtherARDS (Figure 1B). Plasma levels of IL-6, IL-8, and protein C were not significantly different between COVID and OtherARDS. In subgroup analyses, IL-8 signaling was higher in COVID compared to viral LRTI, but lower than bacterial LRTI. Type I/III interferon was higher in COVID compared to bacterial ARDS, but lower compared to viral ARDS (Figure 1C). Compared to nasopharyngeal swabs from subjects with mild COVID-19, expression of several interferon stimulated genes was less strongly correlated with SARS-CoV2 viral load in TA (Figure 1D). IPA identified several candidate medications to treat COVID-19, including dexamethasone, G-CSF, and etanercept. Conclusions: TA sequencing identifies unique features of the host response in COVID-19. These differentially expressed pathways may represent potential therapeutic targets. An impaired interferon response in the lung may increase susceptibility to severe SARS-COV2.