Abstract
Aims:To develop experimental bivalent vaccines against influenza and RSV using a cold-adapted LAIV backbone.Background:Respiratory syncytial virus (RSV) is a causative agent of bronchiolitis and pneumonia in young children, elderly and immunocompromised adults. No vaccine against RSV has been licensed to date for various reasons. One of the promising platforms for designing RSV vaccine is the use of live attenuated influenza vaccine (LAIV) viruses to deliver RSV epitopes to the respiratory mucosa.Objective:To generate recombinant LAIV viruses encoding a neutralizing epitope of the RSV fusion protein and assess their protective potential against both influenza and RSV infections in a mouse model.Methods:Reverse genetics methods were used to rescue recombinant LAIV+HA/RSV viruses expressing chimeric hemagglutinins encoding the RSV-F epitope at its N-terminus using two different flexible linkers. BALB/c mice were intranasally immunized with two doses of the recombinant viruses and then challenged with the influenza virus or RSV. The LAIV viral vector and formalin-inactivated RSV (FI-RSV) were included as control vaccines. Protection was assessed by the reduction of virus pulmonary titers. In addition, RSV-induced lung pathology was evaluated by histopathology studies.Results:Two rescued chimeric LAIV+HA/RSV viruses were identical to the LAIV vector in terms of replication capacityin vitroandin vivo. The RSV-F neutralizing epitope was successfully expressed only if inserted into the HA molecule via G-linker, but not A-linker. Both chimeric viruses induced high influenza-specific antibody levels and fully protected mice against a lethal influenza challenge virus. However, they induced weak anti-RSV antibody responses which did not prevent RS virus replication upon challenge, and only LAIV-HA+G-RSV variant protected mice against RSV-induced lung pathology.Conclusion:Although the designed LAIV-RSV chimeric viruses were unable to neutralize the RS virus pulmonary replication, the LAIV-HA+G-RSV reduced RSV-induced lung pathology and can be considered a promising bivalent vaccine against influenza and RSV infections and warrants its further development.
Highlights
Human Respiratory Syncytial Virus (RSV) is a causative agent of bronchiolitis and pneumonia responsible for fatalities among children under 5 years old and elderly worldwide [1]
The development of RSV vaccine has been challenging due to the failure of the alum-adjuvanted formalin-inactivated RSV (FIRSV) vaccine studied in infants and toddlers in the 1960s, which resulted in Enhanced Respiratory Disease (ERD) after subsequent exposure to a natural RSV infection: the majority of the vaccinees required hospitalization and two vaccinated children died [3, 4]
Two specific bands reacting with this antibody were detected only in the live attenuated influenza vaccine (LAIV)-HA+G-RSV virus and corresponded to the HA1 subunit (~55 kDa) and HA0 precursor (~75 kDa) influenza proteins, suggesting that the RSV epitope is expressed along with the influenza virus HA protein (Fig. 1B)
Summary
Human Respiratory Syncytial Virus (RSV) is a causative agent of bronchiolitis and pneumonia responsible for fatalities among children under 5 years old and elderly worldwide [1]. Since vaccination is the main strategy in the fight against infectious diseases, there are ongoing efforts to develop safe and effective RSV vaccines. The main reason vaccines have not been available for decades is limited knowledge of the complex interactions between the virus and the host, especially in humans. All potential RSV vaccines are being designed so as not to cause these ERD conditions, but such vaccine candidates cannot be generated by classical vaccine development methods, and new innovative strategies for RSV vaccine development are of high priority. Respiratory syncytial virus (RSV) is a causative agent of bronchiolitis and pneumonia in young children, elderly and immunocompromised adults. One of the promising platforms for designing RSV vaccine is the use of live attenuated influenza vaccine (LAIV) viruses to deliver RSV epitopes to the respiratory mucosa
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