Development of Plant-Based Multivalent Vaccine Candidates for SARS-CoV-2 and Influenza Virus Using Inactivated Lactococcus

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Background/Objectives: Since December 2019, the COVID-19 pandemic, driven by SARS-CoV-2, has caused ~690 million infections globally, manifesting with mild to severe symptoms, including pneumonia. After reduced activity, seasonal influenza re-emerged in winter 2022, creating a “twindemic” with SARS-CoV-2. Co-infections have been associated with higher risks, such as increased ventilator use and mortality, emphasizing the need for dual-target vaccines. This study investigates plant-based vaccines produced using a bacterium-like particle (BLP) system from Lactobacillus sakei to co-target SARS-CoV-2 and influenza. Methods: DNA fragments of the SARS-CoV-2 Omicron BA.1 variant spike (S) protein and H1N1 virus hemagglutinin (HA) ectodomain were synthesized and used to create recombinant constructs introduced into Agrobacterium. Protein expression was analyzed using Western blot and Bradford protein assays. Six-week-old K18-hACE2 mice were immunized with these antigens and challenged with influenza, SARS-CoV-2, or both to assess viral load and lung pathology at various times. Results: The SARS-CoV-2 S protein and influenza HA protein were successfully expressed in Nicotiana benthamiana and demonstrated strong binding to BLPs. In mouse models (BALB/c and K18-hACE2), these vaccines elicited potent humoral and cellular immune responses, with high neutralizing antibody titers and increased IFN-γ levels. Vaccinated mice demonstrated protection against viral challenges, reduced lung viral loads, and improved survival. In cases of co-infection, vaccinated mice showed rapid recovery and effective viral clearance, highlighting the potential of vaccines to combat simultaneous SARS-CoV-2 and influenza infections. Conclusions: Our findings highlight the potential of BLP-based multivalent vaccines for dual protection against major public health threats.

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