SphB1 export system for antigen presentation to the respiratory tract by a live pertussis vaccine

BPZE1 is a live attenuated vaccine currently in advanced clinical development for nasal immunization against pertussis. The ability of this vaccine to induce mucosal and systemic, humoral and cellular immunity make it an attractive mucosal delivery system for heterologous antigens to induce immunity especially in the respiratory tract. Here, we have developed a heterologous antigen expression system based on the pertactin-deficient BPZE1 derivative IB-V002 by using the SphB1 secretion system to present the SARS-CoV-2 nucleocapsid protein (N) as a model antigen to the respiratory mucosa. SphB1 is an autotransporter comprising a subtilisin-like passenger domain and a C-terminal ß-barrel domain. The passenger domain was replaced by the SARS-CoV-2 N protein. The recombinant gene was inserted into the urease locus of IB-V002 and placed under the control of the pertactin promoter and signal peptide. Immunoblot analyses indicated that the chimeric protein was produced and secreted by the recombinant strain named BT-V101. Mice intranasally immunized with BT-V101 induced N-specific IgG in serum and IFN-γ production by spleen cells. Importantly, a local N-specific CD8⁺ T cell response was observed in nose-associated lymphoid tissues by MHC class I tetramer staining. Additionally, immunization with BT-V101 efficiently primed mice to recombinant purified N protein given as a boost either intranasally or subcutaneously. These results demonstrate the suitability of the B. pertussis SphB1 secretion machinery to secret heterologous antigens for the development of a mucosal immunization vaccine platform with the induction of specific humoral and cellular, local, and systemic immune responses. KEY POINTS: • The SphB1 export system was used to secrete heterologous antigens by B. pertussis. • Recombinant B. pertussis induced systemic and local immunity to foreign antigens. • Recombinant B. pertussis efficiently primed immune responses to foreign antigens.