Two Recombinant Cytomegalovirus Antigens Formulated with the SPA14 Adjuvant System: Impact of Temperature, pH and Excipients on the Stability of each Antigen and Adjuvant Component

By evaluating the stability profiles of each component of a vaccine candidate (antigens, adjuvants), formulation conditions to mitigate vaccine instability can be identified. In this work, two recombinant Cytomegalovirus (CMV) glycoprotein antigens (gB, Pentamer) were formulated with SPA14, a novel liposome-based adjuvant system containing a synthetic TLR4 agonist (E6020) and a saponin (QS21). Analytical characterization and accelerated stability studies were performed with the two CMV antigens, formulated with and without SPA14, under various conditions (temperature, pH, excipients). For the antigens, the Pentamer was less stable than gB, and the addition of SPA14 adjuvant had negligible impact. For the SPA14 components, minor pH shifts (caused by the buffer's temperature dependent pKa shifts) destabilized the liposome (particle size by DLS) and QS21, but E6020 was unaffected (integrity by RP-UHPLC and LC-MS, respectively). The addition of chelators and free radical scavengers stabilized both the QS21 and E6020 components, consistent with oxidative degradation catalyzed by trace metal-ions. Interestingly, QS21 and E6020 also displayed improved storage stability in the presence of the protein antigens. These results are discussed in terms of developing key stability-indicating assays to optimize formulation conditions to stabilize the two CMV antigens and the three components of the SPA14 adjuvant system.