Addition of Lauryldimethylamine N-Oxide (LDAO) to a Copper-Free Click Chemistry Reaction Improves the Conjugation Efficiency of a Cell-Free Generated CRM197 Variant to Clinically Important Streptococcus pneumoniae Serotypes.

Strain-promoted azide-alkyne cycloaddition (SPAAC) reactions like click chemistry have the potential to be highly scalable, robust, and cost-effective methods for generating small- and large-molecule conjugates for a variety of applications. However, despite method improvements, the rates of copper-based click chemistry reactions continue to be much faster than the rates of copper-free click chemistry reactions, which makes broader deployment of click chemistry challenging from a safety and compatibility standpoint. In this study, we used a zwitterionic detergent, namely, lauryldimethylamine N-oxide (LDAO), in a copper-free click chemistry reaction to investigate its impact on the generation of conjugate vaccines (CVs). For this, we utilized an Xpress cell-free protein synthesis (CFPS) platform to generate a proprietary variant of CRM197 (eCRM) containing non-native amino acids (nnAA) with azide-containing side chains as a carrier protein for conjugation to several clinically relevant dibenzocyclooctyne (DBCO)-derivatized S. pneumoniae serotypes (types 3, 5, 18C, and 19A). For conjugation, we performed copper-free click chemistry in the presence and absence of LDAO. Our results show that the addition of LDAO significantly enhanced the reaction kinetics to generate larger conjugates, which were similarly immunogenic and equally stable to conjugates generated without LDAO. Most importantly, the addition of LDAO substantially improved the efficiency of the conjugation process. Thus, our results for the first time show that the addition of a zwitterionic surfactant to a copper-free click chemistry reaction can significantly accelerate the reaction kinetics along with improving the efficiency of the conjugation process.

Non-clinical immunological comparison of a Next-Generation 24-valent pneumococcal conjugate vaccine (VAX-24) using site-specific carrier protein conjugation to the current standard of care (PCV13 and PPV23).

Despite widespread utilization of pneumococcal conjugate vaccines (PCVs) and the resultant disease reduction, the development of PCVs containing additional serotypes remains a public health priority due to serotype replacement and the resultant shift to non-vaccine containing serotypes. However, incorporating additional serotypes to existing PCVs using conventional technologies has proven problematic. Immune responses to individual serotypes have consistently decreased as more polysaccharide-conjugates are added due to carrier suppression. Using our proprietary cell-free protein synthesis (CFPS) platform, we have successfully produced eCRM® based on the CRM197 sequence for use as an enhanced carrier protein to develop a 24-valent PCV. The eCRM carrier protein contains multiple non-native amino acids (nnAAs) located outside of the primary T-cell epitope regions, thereby enabling site-specific covalent conjugation of the pneumococcal polysaccharides to the nnAAs to consistently expose the critical T-cell epitopes. eCRM also serves to reduce structural heterogeneity associated with classic reductive-amination conjugation while promoting formation of the conjugate matrix structures, the hallmark of PCVs. This process serves to increase the overall polysaccharide:protein ratio, enabling the inclusion of more serotypes while minimizing carrier-mediated immunological interference. The aim of this non-clinical study was to construct a 24-valent PCV and evaluate its immunogenicity. Using the XPressCF® CFPS platform, the eCRM carrier protein was separately conjugated through nnAAs to each of the 24 pneumococcal polysaccharides through click chemistry and mixed with aluminum phosphate to produce VAX-24, Vaxcyte's proprietary PCV preclinical candidate. VAX-24, Prevnar13® and Pneumovax®23 were administered to New Zealand White rabbits to compare the resulting opsonophagocytic activity (OPA) and anti-capsular IgG antibodies. VAX-24 showed conjugate-like immune responses to all 24 serotypes based on comparable OPA and IgG responses to Prevnar13 and higher responses than Pneumovax 23. This study demonstrates the utility of site-specific conjugation technology in a preclinical setting and the potential for a PCV with improved serotype coverage.

Evaluation of Heavy-Chain C-Terminal Deletion on Product Quality and Pharmacokinetics of Monoclonal Antibodies.

Due to their potential influence on stability, pharmacokinetics, and product consistency, antibody charge variants have attracted considerable attention in the biotechnology industry. Subtle to significant differences in the level of charge variants and new charge variants under various cell culture conditions are often observed during routine manufacturing or process changes and pose a challenge when demonstrating product comparability. To explore potential solutions to control charge heterogeneity, monoclonal antibodies (mAbs) with native, wild-type C-termini, and mutants with C-terminal deletions of either lysine or lysine and glycine were constructed, expressed, purified, and characterized in vitro and in vivo. Analytical and physiological characterization demonstrated that the mAb mutants had greatly reduced levels of basic variants without decreasing antibody biologic activity, structural stability, pharmacokinetics, or subcutaneous bioavailability in rats. This study provides a possible solution to mitigate mAb heterogeneity in C-terminal processing, improve batch-to-batch consistency, and facilitate the comparability study during process changes.