The BNT162b2 mRNA COVID-19 Vaccine Increases the Contractile Sensitivity to Histamine and Parasympathetic Activation in a Human Ex Vivo Model of Severe Eosinophilic Asthma

Asthma is a heterogeneous inflammatory airway disease where severe patients exhibit airway hyperresponsiveness (AHR) often driven by activated tissue eosinophils, predisposing to bronchospasm and exacerbation-prone phenotypes. BNT162b2 (Pfizer-BioNTech) is an mRNA vaccine delivered in lipid nanoparticles (LNP) and widely used in Europe. Although generally recommended even in severe asthma, rare early bronchospasm and allergic reactions have been reported after COVID-19 mRNA vaccination, with most anaphylaxis cases occurring after the first dose. Data regarding direct effects of BNT162b2 on human airway smooth muscle (ASM) are lacking, and detailed safety profiles remain incompletely reported. The authors hypothesized that BNT162b2 may acutely worsen AHR in severe eosinophilic asthma. The study aimed to test the acute impact of BNT162b2 on contractile sensitivity to histamine and parasympathetic activation in a human ex vivo model of severe eosinophilic asthma.

Background data indicate higher rates of allergic reactions to mRNA COVID-19 vaccines among individuals with high-risk allergies; guidance recommends observation after vaccination in such patients. In severe asthmatics on biologics (e.g., benralizumab, mepolizumab, dupilumab), studies show mixed effects on vaccine-induced antibody levels, though overall humoral and cellular responses may be preserved. Reports exist of early-onset bronchospasm after first vaccine dose in asthmatics, and most anaphylaxis cases occur following dose one, suggesting a possible link in susceptible individuals. Detailed safety reporting for BNT162b2 in primary RCT publications and registries has been limited, and real-world safety data are relatively scarce. No prior data were available on BNT162b2 effects on human ASM ex vivo.

Design: Ex vivo, prospective, randomized, controlled, blinded, parallel-group study. Endpoint: Assess the impact of BNT162b2 on contractile sensitivity to histamine and parasympathetic activation in a human ex vivo model of severe eosinophilic asthma. Tissue source: Subsegmental bronchi obtained from uninvolved areas of lobectomy specimens from 10 non-asthmatic lung cancer patients; no chronic bronchodilator/corticosteroid use; normal IgE and lung function preoperatively. Model of severe eosinophilic asthma: Bronchi were passively sensitized overnight with 10% serum from a patient with atopic asthma during exacerbation (vs. non-sensitizing serum control), then challenged 45 min with platelet-activating factor (PAF, 100 nM) to activate resident eosinophils, reproducing ex vivo AHR of severe eosinophilic asthma. Organ bath setup: Rings (1–2 mm thick, 4–5 mm diameter) mounted in 10 mL Krebs-Henseleit buffer (37°C, aerated 95% O2/5% CO2) with indomethacin (5 µM); isometric force measured; passive tension 0.5–1.0 g; equilibration with washes. Interventions: - BNT162b2 (Pfizer-BioNTech) diluted per manufacturer; concentrations tested typically 1–1000 ng/mL; vehicle (0.9% NaCl) as control. Some experiments used denatured vaccine (mRNA heated 5 min at 70°C) to inactivate mRNA without altering PEG/LNP structure. - Histamine-induced tone: Histamine used to achieve EC20 partial precontraction; concentration-response curves (CRCs) to histamine constructed with/without 45 min pre-treatment with BNT162b2 1 ng/mL. - Resting tone: CRCs to BNT162b2 on resting tone. - Parasympathetic activation: Electrical field stimulation (EFS) with parameters 3–25 Hz, 10 V, 10 s, 0.5 ms biphasic pulses to stimulate parasympathetic ganglia and endogenous acetylcholine release. Groups: Non-sensitized (NS) bronchi and passively sensitized + PAF challenged (sens+PAF) bronchi. Outcomes and analysis: Responses expressed as %Emax to histamine (for resting/Hist tone) or %Emax at 25 Hz in control (for EFS). Sigmoidal fits used to estimate EC50 and pEC50. Data as mean ± SE; two-way ANOVA with multiple comparisons; significance p < 0.05. Sample size: n ≥ 5 per condition per pharmacological guidelines.

- Baseline hyperresponsiveness: Sens+PAF bronchi were significantly more responsive to histamine than NS (delta pEC50: 0.34 ± 0.08; p < 0.01) and to EFS (720 ± 140 mg vs. 410 ± 90 mg; p < 0.05). - Resting tone: In sens+PAF bronchi, BNT162b2 100–1000 ng/mL slightly but significantly increased resting tone (Emax +11.82 ± 2.27%; p < 0.001 vs. control); no effect in NS bronchi. - Histamine EC20 precontracted tissue: In sens+PAF bronchi, BNT162b2 1–1000 ng/mL significantly increased contractile response to histamine (Emax +42.97 ± 9.64%; p < 0.001 vs. control); no significant effect in NS. pEC50 of BNT162b2 on sens+PAF histamine-precontracted tissue: 0.52 ± 0.75. - CRC to histamine: In sens+PAF bronchi, BNT162b2 1 ng/mL shifted histamine CRC leftward by 0.76 ± 0.09 log units (p < 0.001); no significant shift in NS. - Parasympathetic EFS (3–25 Hz): In sens+PAF bronchi, BNT162b2 1–1000 ng/mL enhanced EFS-induced contraction (overall Emax +28.46 ± 4.40%; p < 0.001 vs. control); no significant effect in NS. pEC50 values not frequency-dependent: 1.19 ± 1.24 (3 Hz), 0.62 ± 0.34 (10 Hz), 1.83 ± 1.78 (25 Hz). - Denaturation: mRNA denaturation did not significantly alter BNT162b2 effects on histamine CRC or EFS (overall delta effect on EFS: −4.60 ± 4.45% vs. non-denatured; p > 0.05).

BNT162b2 acutely increases contractile sensitivity to both histamine and parasympathetic stimulation, but only in hyperresponsive airways modeled by passive sensitization and PAF challenge. No effects were observed in non-sensitized control bronchi, supporting a generally favorable respiratory safety profile in non-asthmatic airways. The persistence of effects after mRNA denaturation implies the active mRNA (tozinameran) is not responsible; excipients within the LNP formulation likely drive the response. Among excipients, ALC-0159 (containing polyethylene glycol, PEG) is proposed as a plausible candidate given known associations of PEG with hypersensitivity and allergic reactions. The facilitation of responses across EFS frequencies suggests potential enhancement of neurotransmitter release from parasympathetic postganglionic neurons, including C-fibers implicated in neurogenic inflammation, thereby increasing AHR through both direct ASM effects and neural pathways. Clinically, while general population safety appears consistent with trials, susceptible groups with severe eosinophilic asthma may experience bronchospasm even at very low LNP concentrations. Biodistribution data suggest airway exposure to PEG-containing LNP is plausible, warranting careful assessment of at-risk patients and further investigation of excipient-specific effects.

In a human ex vivo model of severe eosinophilic asthma, BNT162b2 increased airway contractile sensitivity to histamine and parasympathetic activation after a single exposure, indicating potential to elicit bronchospasm in hyperreactive airways. These effects are not due to the mRNA but are likely attributable to vaccine excipients, possibly PEG (ALC-0159). The findings support overall respiratory safety in non-hyperresponsive tissue but highlight potential risk for severe asthmatics, particularly children and adolescents. Preventive strategies such as pre-treatment with inhaled corticosteroid/formoterol before LNP-containing vaccinations may merit evaluation. Future research should include well-designed observational/clinical studies in asthmatic cohorts, detailed pharmacokinetics/biodistribution in the respiratory system, and targeted testing of individual LNP components to identify causative excipients.

- Ex vivo model: Findings require translation to clinical settings; in vivo confirmation is lacking. - Donor tissue from lung cancer surgeries may introduce bias versus non-cancer tissue donors. - Lack of posted detailed safety outcomes from key phase 3 RCTs limits direct clinical comparability. - Individual lipid excipients (ALC-0315, DSPC, cholesterol, ALC-0159) were not tested separately on ASM. - Official biodistribution data for respiratory tissues are limited; estimations rely on external studies and assumptions. - Potential contribution of LNP nanostructure to AHR cannot be excluded.