Harnessing the power of morphological modulation: Peptidoglycan-based filamentous microparticles for prolonged immune response and oral vaccine efficacy

Peptidoglycan (PGN) plays a pivotal role in determining the diverse morphology of bacteria and enabling a range of surface biological functions. Inspired by the interesting phenomenon of bacterial morphological transformation under environmental stress, chemically enhancing the artificial adjustability of bacterial morphology opens a new approach for its use as a highly effective and versatile carrier. This study presents a novel approach using morphologically elongated purified probiotic PGN, presenting filamentous bacterium-like particles (fBLPs). By optimizing the conditions, bacterium-like particle (BLP) morphology was elongated 10- to 20-fold, and the antigenic loading was increased. Compared to traditional BLP, fBLP exhibited enhanced stability in gastric acid and a 4- to 6-fold higher uptake via Peyer's patches (PPs) (P ≤ 0.05). Furthermore, in vitro macrophage phagocytosis assays demonstrated that fBLP prolonged the phagocytosis process, leading to extended vaccine retention in vivo. In mice, a single dose of the fBLP-based vaccine provided 100% protection and prolonged the duration of immunity. Additionally, the co-administration of fBLP and Alum as oral adjuvants elicits a robust, synergistic immune response. This study presents a simple and cost-effective biochemical method that can generate advanced functions and therapeutic benefits by easily modulating bacterial morphology without complex genetic editing.