Fusion of parvovirus B19 receptor-binding domain and pneumococcal surface protein A induces protective immunity against parvovirus B19 and Streptococcus pneumoniae.

BACKGROUND: Parvovirus B19 (B19) is a well-known cause of fifth disease in children, but infection during pregnancy may cause hydrops fetalis and stillbirth. The receptor-binding domain (RBD) of the VP1 unique capsid plays a pivotal role in infection. Here, we aimed to improve the immunogenicity of an RBD-based vaccine by genetically fusing it with Streptococcus pneumoniae surface protein A (PspA). METHODS: Mice were intramuscularly injected with RBD-based vaccines. Antigen-specific antibodies and neutralizing activity against B19 were measured. Protective immunity against S. pneumoniae was evaluated by monitoring the survival of mice nasally challenged with bacteria and determining antigen-specific T cell activation in splenic cells. RESULTS: RBD alone failed to generate neutralizing antibodies against B19, but fusion with PspA induced higher levels of neutralizing IgG compared to B19 virus-like particles. Furthermore, a comparable level of PspA-specific IgG was induced by RBD-PspA and PspA alone, which was sufficient to protect mice against pneumococcal infection. Stimulation with PspA, but not RBD, induced cytokine production in splenic cells from mice immunized with RBD-PspA, suggesting that PspA-specific T cells supported immunoglobulin class switching of both RBD- and PspA-specific B cells. CONCLUSIONS: RBD-PspA should be an effective bivalent vaccine against B19 and S. pneumoniae infections.