PLGA-PEG Nano-Adjuvant-Delivered ClfA Vaccine Elicits IL-17A-Mediated Neutrophil Activation to Confer Complete Protection Against Methicillin-Resistant Staphylococcus aureus

Purpose: Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of severe, life-threatening infections worldwide, highlighting an urgent and unmet need for effective vaccines. Current Staphylococcus aureus ( S. aureus ) vaccine candidates predominantly employ aluminum-based adjuvants, which potently induce Th2-biased humoral immunity but fail to adequately elicit protective Th1/Th17 cellular responses. Given that Th1 and Th17 responses are critical for clearance of S. aureus infection, developing an adjuvant platform capable of redirecting immunity toward these pathways is urgently needed. To address this limitation, we aimed to develop a novel nano-vaccine and systematically evaluate its immunogenicity and protective efficacy. Methods: We constructed a nano-vaccine using PLGA 15k -PEG 5k -COOH nanoparticles (25%NPs) as the adjuvant and recombinant clumping factor A (rClfA) as the antigen. The immunogenicity of the 25%NPs-rClfA vaccine was compared with that of an aluminum-adjuvanted formulation. Specific antibody levels, neutralizing activity, and cytokine production (IFN-γ and IL-17A) were measured. Protective efficacy was assessed by challenging immunized subjects with a lethal dose of S. aureus strain ATCC25923. Mechanistic studies included evaluation of neutrophil phagocytosis and reactive oxygen species (ROS) release. The necessity of the Th17 pathway was confirmed via IL-17A blockade experiments. Results: Compared to the aluminum-adjuvanted vaccine, the 25%NPs-rClfA nano-vaccine elicited lower specific antibody titers but generated antibodies with superior neutralizing activity. It significantly enhanced the secretion of IFN-γ and IL-17A, with IL-17A sustaining elevated levels over an extended period. Crucially, the nano-vaccine conferred 100% protection against death following lethal S. aureus challenge. Mechanistically, it enhanced neutrophil phagocytosis and ROS production—key processes for bacterial clearance. Blockade of the Th17 pathway abrogated vaccine protection, demonstrating that IL-17A is essential for its efficacy. Conclusion: This study demonstrates that the PLGA-PEG nanoparticle-based rClfA nano-vaccine can effectively redirect immune responses toward protective Th1/Th17 immunity and robustly protect against lethal S. aureus infection, largely through an IL-17A-dependent mechanism. These findings provide important experimental and theoretical support for the translational development of S. aureus vaccines.