Microfluidic-Chip-Based Formulation and In Vivo Evaluations of Squalene Oil Emulsion Adjuvants for Subunit Vaccines

Background: Adjuvants play a crucial role in improving the immunogenicity of various antigens in vaccines. Squalene-in-water emulsions are clinically established vaccine adjuvants that improve immune responses, particularly during a pandemic. Current manufacturing processes for these emulsion adjuvants include microfluidizers and homogenizers and these processes have been used to produce emulsion adjuvants to meet global demands during a pandemic. These processes, however, are complex and expensive and may not meet the global needs based on the growing populations in low- and middle-income countries. At the forefront of adjuvant research, there is a pressing need to manufacture emulsion adjuvants using novel approaches that balance efficacy, scalability, speed of production, and cost-effectiveness.

Methods: In this study, we explored the feasibility of a microfluidic chip platform to address these challenges and evaluated the adjuvanticity of the emulsion adjuvant prepared using the microfluidic chip process in CB6F1 mice model, and compared it with a control formulation. We developed and optimized the process parameters to produce emulsion adjuvants with characteristics similar to SEA160 (control formulation).

Results: The resulting emulsion prepared using the microfluidic chip process (MC160) when mixed with ovalbumin, maintained antigen structural integrity. Immunogenicity studies in a CB6F1 mouse model, with the Cytomegalovirus glycoprotein B (CMV gB) antigen, resulted in humoral responses that were non-inferior between MC160 and SEA160, thereby validating the microfluidic chip approach for manufacturing emulsion adjuvants.

Conclusions: These findings demonstrate a proof of concept for using microfluidic chip platforms for formulating emulsion adjuvants, offering a simpler manufacturing platform that can be deployed to low- and middle-income countries for rapid production, improving adjuvant access and aiding in pandemic preparedness.