Recombinant listeriolysin-O as a platform for next-generation vaccines: Mechanisms, immunological evidence, and translational applications in human and veterinary medicine.

Recombinant Listeriolysin O (rLLO), a cholesterol-dependent cytolysin (CDC) derived from Listeria monocytogenes, has gained increasing attention as a novel immunological adjuvant for next-generation vaccine development. rLLO enhances both innate and adaptive immune responses by facilitating controlled endosomal membrane permeabilization, promoting cytosolic antigen delivery, and enabling efficient antigen cross-presentation, leading to robust CD8⁺ T-cell activation. These immunological properties are particularly advantageous for vaccines targeting intracellular pathogens and malignancies. This narrative review synthesizes current experimental, preclinical, and translational evidence on the application of rLLO across diverse vaccine platforms in human and veterinary medicine, including DNA-, protein-, nanoparticle-, and vector-based formulations. Studies addressing infectious diseases, such as tuberculosis, HIV, dengue, and listeriosis, as well as cancer immunotherapy models, are critically examined. Emerging strategies involving fusion proteins, detoxified rLLO mutants, and recombinant delivery systems are highlighted to illustrate advances in formulation design and immunogenic optimization. Despite promising preclinical outcomes, several challenges remain, including the need for comprehensive safety evaluation, dosing and delivery strategy optimization, and regulatory pathway clarification. Addressing these limitations through standardized toxicological assessment and large-scale clinical and veterinary trials is essential for the successful translation of rLLO-based vaccine components. Overall, rLLO represents a versatile and potent immunological tool with significant potential to advance vaccine design in human and veterinary applications.