Antiviral activities of live attenuated influenza virus vector-based vaccine against SARS-CoV-2 infection in lung epithelial cells

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Influenza A virus (IAV) are major causative agents of respiratory diseases that have led to global pandemics. In contrast to SARS-CoV-2 infections, which are characterized by a delayed host innate immune activation and viral clearance, IAV infections trigger a more robust and earlier innate antiviral response in the respiratory tract. Notably, IAV has been observed to induce viral interference with the replication of SARS-CoV-2 during co-infection. Therefore, we hypothesize that IAV-derived viral particles may represent a potential non-specific antiviral intervention against SARS-CoV-2 infections.

In this study, the antiviral activity of a live attenuated influenza virus (LAIV) vector-based COVID-19 vaccine, DelNS1-nCoV-RBD, was assessed against the infection of SARS-CoV-2 wild-type and Omicron BA.5.2 in lung epithelial cell-based models. These in vitro models included monoculture of human lung epithelial cell line Calu-3 and its co-culture with human peripheral blood mononuclear cells (PBMCs), as well as monocultures of primary mouse lung alveolar type 2 (AT2) cells and the co-culture with mouse airway immune cells. The viral replication and innate immune responses of both host cells and immune cells were monitored during SARS-CoV-2 infection and LAIV treatment, alongside a co-infection of SARS-CoV-2 with the competent IAV H1N1pdm09 for comparative analysis.

Our findings demonstrated that the introduction of LAIV vector-based vaccine conferred a more pronounced unilateral inhibitory effect on the replication of SARS-CoV-2, as well as a markedly diminished level of cell damage to Calu-3, compared to the outcome of H1N1pdm09 co-infection. The magnitude of the viral interference on SARS-CoV-2 particularly correlated with the early upregulation of type III interferon (IFN-lambda) and its corresponding signalling pathway stimulated by LAIV. Furthermore, the combination treatment of low-dose LAIV with exogenous IFN-lambda exhibited additive effect in suppressing the SARS-CoV-2 wild-type. Although the Omicron BA.5.2 displayed an increased resistance to exogenous IFN-lambda, it remained susceptible to the antiviral effects elicited by high-dose LAIV treatment.

The indirect crosstalk between SARS-CoV-2 infected Calu-3 cells and human PBMCs in the co-culture model revealed that the treatment with LAIV also promoted the innate immune responses of the immune cells. This was evidenced by the elevated gene expression levels of interferon-stimulated genes (ISGs) and the pro-inflammatory chemokine CXCL10 in PBMCs. However, the levels of other pro-inflammatory mediators such as IL-6, TNF, and NF-κB were not significantly altered following the addition of LAIV during SARS-CoV-2 infection. The murine cell-based co-culture model showed a similar enhancement of innate antiviral immune responses induced by LAIV in both lung AT2 cells and airway immune cells.

In conclusion, this study sheds a light in the potential application of intranasal administration of LAIV vector-based vaccine as an effective non-specific antiviral strategy for the early management of SARS-CoV-2 infections, through the stimulation of local innate antiviral immunity. This approach may provide a viable alternative strategy to protect individuals with high-risk exposure to SARS-CoV-2 from developing severe COVID-19. The LAIV-based platform also holds significant promise as a candidate for the development of future therapeutic vaccines against respiratory viral infections.