Cooperative supramolecular integration of QS-21 into polymeric micelles as a tunable nanoadjuvant platform for subunit vaccines

Abstract

Potent saponin adjuvants such as QS-21, used in clinically approved vaccine formulations, remain limited by intrinsic hemolytic activity and restricted aqueous stability, motivating biomaterials strategies aimed at regulating their interfacial behavior while preserving immunostimulatory function. Here, we show that when combined with amphiphilic PEO–PPO triblock copolymers (P123 and F127), QS-21 appears to participate in cooperative supramolecular integration into polymeric micelles rather than behaving as a passively encapsulated cargo. This architecture-dependent organization gives rise to structurally coherent nanosystems with enhanced dilution stability and controlled membrane activity. Comparative analysis revealed that P123/QS-21 assemblies form compact, monodisperse micelles (∼21 nm) with marked resistance to dilution, whereas F127-based systems display greater structural heterogeneity and reduced supramolecular robustness. Cooperative integration is associated with attenuation of hemolytic activity in a concentration-dependent manner relative to free QS-21 while preserving functional accessibility, consistent with controlled interfacial presentation of the saponin. These physicochemical features are supported by DLS, TEM, and NTA analyses. In vivo evaluation using a SARS-CoV-2 Spike subunit antigen indicates that P123/QS-21 is associated with enhanced systemic and mucosal antibody responses while inducing functional neutralizing activity. Together, these findings support cooperative supramolecular integration as a biomaterials design principle to modulate membrane activity and nanoadjuvant performance, providing a scalable and tunable framework for the development of subunit vaccine platforms.