Comparison of upper and lower airway expression of SARS-COV-2 receptors in mild allergic asthmatics

Background: SARS-CoV-2 virus infects host cells through ACE2 and TMPRSS2 receptors. Protein levels of ACE2 and TMPRSS2 have not been assessed in allergic airways. Method(s): We collected biopsies of endobronchial tissue from steroid-naive mild allergic asthmatics (AA n=23) and non-asthmatic controls (NA n=11), and inferior nasal turbinate tissue from AA with allergic rhinitis (AR n=8) and nonAA/AR controls (NR n=5). Tissue was immune-stained for SARS-CoV-2 receptor ACE2 and surface protein TMPRSS2. The number of immuno-positive cells in epithelium and laminae propria was expressed per mm2 of tissue. Result(s): The number of cells expressing ACE2 was higher in AA endobronchial tissue compared to NA control and AR nasal tissue. TMPRSS2 was higher in AR nasal tissue compared to NR control, and higher in control NA endobronchial tissue versus control NR nasal tissue. Co-expression of ACE2+TMPRSS2 was higher in AA endobronchial tissue versus NA control and trending higher in AR nasal tissue versus NR control (p=0.08). Conclusion(s): Overall, ACE2 is more highly expressed in endobronchial tissue versus nasal tissue, suggesting SARS-CoV-2 may more readily infect lower versus upper airways. It is unknown whether the higher expression of ACE2 and ACE2+TMPRSS2 observed in the airways of mild allergic asthmatic donors versus control donors translates to higher susceptibility to infection.

Reduced ACE2 and TMPRSS2 immunopositive bronchial cells in asthmatics after inhaled allergen challenge

Rationale: The incidence of SARS-CoV-2 infection and the impact of corticosteroid treatment in patients with symptomatic airway disease has been a concern. We examined airway expression of SARS-CoV-2 receptors following allergen challenge and steroid intervention in asthmatic patients. Method(s): From steroid-naive mild allergic asthmatic (AA n=23) we collected endobronchial biopsies pre and 24hr post allergen inhalation challenge (AIC). In a subset of AA with allergic rhinitis (AR n=8) we collected inferior nasal turbinate biopsies pre and 24hr post-nasal allergen challenges (NAC) after placebo treatment or after 21 days of 22 mg BID triamcinolone nasal spray. FEV1 and PNIF expressed as % fall from baseline quantified the early (ER, 0-2h) and late (LR, 3-7h) airway responses post challenge. Epithelium and laminae propria were immunostained for ACE2 and TMPRSS2 and expressed as # cells/mm2. Result(s): AIC reduced FEV1 (31% ER, 19% LR) and the number of bronchial cells immunopositive for ACE2, TMPRSS2 and double positive for ACE2/TMPRSS2 (P=0.0002, P=0.04, P=0.02, respectively). The PNIF reduction by NAC (69% ER, 49% LR) was attenuated by triamcinolone (31% ER, 18% LR), but without changes in ACE2 or TMPRSS2 in nasal tissue after NAC or steroid treatment (all P>0.05). In the nasal tissue, significantly fewer cells expressed ACE2 compared to bronchi (P=0.007). Conclusion(s): ACE2 and TMPRSS2 expression in bronchial tissue is reduced in the T2 microenvironment post allergen challenge, however it is unknown if this protects lower airways from SARS-CoV-2 infection. Low expression of ACE2 and TMPRSS2 in nasal tissue made it difficult to determine the effects of NAC or steroid.

Replication of SARS-CoV-2 Omicron BA.2 variant in ex vivo cultures of the human upper and lower respiratory tract.

BACKGROUND: The Omicron BA.2 sublineage has replaced BA.1 worldwide and has comparable levels of immune evasion to BA.1. These observations suggest that the increased transmissibility of BA.2 cannot be explained by the antibody evasion. METHODS: Here, we characterized the replication competence and respiratory tissue tropism of three Omicron variants (BA.1, BA.1.1, BA.2), and compared these with the wild-type virus and Delta variant, in human nasal, bronchial and lung tissues cultured ex vivo. FINDINGS: BA.2 replicated more efficiently in nasal and bronchial tissues at 33°C than wild-type, Delta and BA.1. Both BA.2 and BA.1 had higher replication competence than wild-type and Delta viruses in bronchial tissues at 37°C. BA.1, BA.1.1 and BA.2 replicated at a lower level in lung parenchymal tissues compared to wild-type and Delta viruses. INTERPRETATION: Higher replication competence of Omicron BA.2 in the human upper airway at 33°C than BA.1 may be one of the reasons to explain the current advantage of BA.2 over BA.1. A lower replication level of the tested Omicron variants in human lung tissues is in line with the clinical manifestations of decreased disease severity of patients infected with the Omicron strains compared with other ancestral strains. FUNDING: This work was supported by US National Institute of Allergy and Infectious Diseases and the Theme-Based Research Scheme under University Grants Committee of Hong Kong Special Administrative Region, China.

Cross-Species Translation of Correlates of Protection for COVID-19 Vaccine Candidates Using Quantitative Tools

Background. Several COVID-19 vaccines have been authorized, and the need for rapid, further modification is anticipated. This work uses a Model-Based Meta-Analysis (MBMA) to relate, across species, immunogenicity to peak viral load (VL) after challenge and to clinical efficacy. Together with non-clinical and/or early clinical immunogenicity data (ECID), this enables prediction of a candidate vaccine's clinical efficacy. The goal of this work was to enable the accelerated development of vaccine candidates by supporting Go/No-Go and study design decisions, and the resulting MBMA can be instrumental in decisions not to progress candidates to late stage development. Methods. A literature review with pre-specified inclusion/exclusion criteria enabled creation of a database including nonclinical serum neutralizing titers (SN), peak VL after challenge with SARS-CoV-2 (VL), along with data from several clinical vaccine candidates. Rhesus Macaque (RM) and golden hamster (GH) were selected (due to availability and consistency of data) for MBMA modeling. For both RM and GH, peak post-challenge VL in lung and nasal tissues were used as surrogates for clinical disease and were related to pre-challenge SN via the MBMA. The VL predictions from the RM MBMA were scaled to incidence rates in humans, with a scaling factor between RM and human SN estimated using early Phase 3 efficacy data. This enabled clinical efficacy predictions based on ECID. To qualify the model's predictive power, efficacies of COVID-19 vaccine candidates were compared to those predicted from the MBMA and their respective Ph1/2 SN data. More recently available clinical data enable building a clinical MBMA;comparing this to the RM MBMA further supports SN as predictive. Results. The MBMA analyses identified a sigmoidal decrease in VL (increasing protection) with increase in SN in all three species, with more SN needed (in both RM and GH) for protection in nasal swabs than in BAL (see figure). The comparison between predicted and reported clinical efficacies demonstrated the model's predictive power across vaccine platforms. RM and GH MBMA Protection Models and Translational Prediction with Observed Efficacies Sizes of circles indicate relative weight of the data in the respective quantitative model. Model and data visualizations have been harmonized (across tissue-types) separately for each of RM and GH using VACHER (Lommerse, et al., CPT:PSP, in press). Conclusion. By quantifying adjustments needed between species and assays, translational MBMA can inform development decisions by using nonclinical SN and VL, and ECID to predict protection from COVID-19.