Long-term stability of the GMP-compliant recombinant BCG vaccine against human RSV under quality control analyses

The human respiratory syncytial virus (RSV) is a leading cause of severe respiratory infections in newborns, young children, immunocompromised patients, and older adults. The current landscape of approaches to preventing the RSV disease includes vaccines for older adults and pregnant women, as well as prophylactic monoclonal antibodies for newborns and infants, with positive results. To expand the availability of prophylactic options against the RSV disease for vulnerable individuals, including newborns and older adults, we developed a recombinant BCG-based vaccine expressing the RSV nucleoprotein (rBCG-N-RSV) and manufactured under Good Manufacturing Practice (GMP) conditions. This vaccine has previously been shown to be safe and immunogenic in murine models, in neonatal calves, and has completed a phase 1 clinical trial in human adults. This article aims to assess the quality control testing of a GMP lot of rBCG-N-RSV to ensure antigen expression, potency, safety, and efficacy, which are required to advance to further clinical trials. Notably, all these parameters complied with release requirements. Furthermore, vaccine safety and protection were evaluated in a murine model of RSV infection, demonstrating enhanced virus-specific CD4⁺ T cell activation and significant anti-N-RSV IgG levels in serum. Vaccination improved respiratory function after infection and increased viral clearance in the lungs of mice. Taken together, these data demonstrate long-term stability, safety, and protective capacity of a GMP lot of the rBCG-N-RSV vaccine in a preclinical model of RSV respiratory infection, highlighting the importance of rigorous control protocols for regulatory compliance of vaccine production.