Investigating Interfacial Interactions between the Adjuvant and Antigens in Pneumococcal Conjugate Vaccine In Situ at the Molecular Level

Despite recent advances in prevention and treatment, pneumococcal disease is still a leading cause of serious illness and death among young children and elderly adults. Novel multivalent pneumococcal conjugate vaccines (PCVs) are under development against bacterial infections that cause pneumococcal disease. A PCV is a complex vaccine product consisting of polysaccharide antigens from multiserotypes. Each antigen is conjugated to a carrier protein, such as CRM197, to recruit long-lasting T-cell immune responses. In PCV, antigens are often formulated with an aluminum adjuvant to further enhance the efficacy of the vaccine. It is believed that antigen-aluminum adjuvant interactions play an important role in adjuvanticity and antigen potency, but detailed mechanisms have yet to be elucidated. In this research, a nonlinear optical spectroscopic technique, sum frequency generation (SFG) vibrational spectroscopy, was applied to study the interfacial conformations and orientations of the PCV antigen on the aluminum adjuvant surface, with the help of molecular dynamics simulations. Mechanisms of molecular interaction between the PCV antigens and the aluminum adjuvant are revealed in situ and in real time from the conformations and orientations acquired from SFG and simulations. The effects of the solution salt concentration and conjugation type on such interactions were studied. The findings obtained from this research provide design insights into the rational development of PCV formulations with improved performance.