Metavac®-RSV mucosal bivalent vaccine candidate protects cotton rats against RSV and HMPV and its production process in serum-free Vero cells is scalable in a 2L bioreactor

Respiratory Syncytial Virus (RSV) and Human Metapneumovirus (HMPV) are the main etiologic agents of viral bronchiolitis and pneumonia in children and elderly. As Live-Attenuated Vaccines (LAV) can stimulate robust mucosal and cellular responses, we previously engineered an HMPV-based bivalent LAV Metavac®-RSV and reported its capacity to protect mice against HMPV and RSV challenges after intranasal delivery and to induce strong neutralizing antibody responses. To progress towards clinical development, we identified a GMP grade Vero cell platform as permissive and efficient to produce high yields of functional Metavac®-RSV. Deep sequencing and immunostaining analysis showed that Metavac®-RSV maintains genetic stability and RSV and HMPV F antigens expression after several passages in Vero cells. Furthermore, Metavac®-RSV produced in Vero cells protected cotton rats against both HMPV and RSV challenges, reducing significantly viral replication in the respiratory airways and inducing high titers of neutralizing antibodies production. Finally, we identified process parameters to scale-up the production process of infectious Metavac®-RSV using Vero cells cultivated on microcarriers in 2L single-use stirred-tank bioreactor. Altogether, these results underscore the potential of Metavac®-RSV as a promising LAV candidate for mucosal administration that could bring sterilizing immunity against pneumovirus infections, with a scalable upstream production process amenable to industrial manufacturing.