Sublingual bivalent vaccination with PspA-C-CPE and Alcaligenes lipid A induces protective immunity against both Streptococcus pneumoniae and Clostridium perfringens

Streptococcus pneumoniae and Clostridium perfringens are major pathogens causing severe respiratory infections and foodborne illnesses, posing critical threats particularly in communal settings. Current countermeasures face significant limitations, including restricted serotype coverage for S. pneumoniae and the lack of approved vaccines for C. perfringens enterotoxin (CPE). Effective vaccines tailored to these pathogens are urgently needed. Promising candidates include pneumococcal surface protein A (PspA) for broad serotype coverage and the C-terminal receptor binding domain of CPE (C-CPE). The novel sublingual vaccine strategy we present here combines a recombinant bivalent fusion protein PspA-C-CPE with Alcaligenes lipid A, a potent mucosal adjuvant. Sublingual administration of this combination vaccine elicited robust and long-lasting protective immunity in mice. This vaccine effectively neutralized circulating CPE to prevent lethal hyperkalemia and promoted the rapid clearance of S. pneumoniae from the lungs after lethal challenge. Furthermore, Alcaligenes lipid A enhanced the production of IgG against both antigens for at least 49 weeks. These findings demonstrate that sublingual administration of PspA-C-CPE and Alcaligenes lipid A can orchestrate simultaneous defense in the mucosal and systemic compartments. This non-invasive vaccine offers immense public health potential for providing enduring comprehensive, concurrent protection against pneumococcal respiratory infections and CPE-associated foodborne illnesses.