Identification and optimization of critical process parameters for the production of NOMV vaccine against Neisseria meningitidis

Outer membrane vesicles (OMV) are used as a vaccine against Neisseria meningitidis serogroup B and are traditionally produced with detergent-extraction to remove toxic lipopolysaccharide. Engineered strains with attenuated lipopolysaccharide allowed the use of native vesicles (NOMV) with improved stability and immunogenicity. In the NOMV production process detergents are omitted and vesicle release is stimulated with EDTA extraction (a chelating agent) to enable a higher yield. Many process parameters may change the EDTA extraction efficiency, but it is unknown what the optimal ranges for these parameters are in terms of quality. The present study systematically optimized EDTA extraction and was representative for production at large-scale. Two critical process parameters were identified, harvest point of the cultivation (harvest) and pH of the extraction buffer (pH), which significantly affected yield (7-fold) and bacterial lysis (35-fold). The other quality attributes remained unchanged. Optimization of harvest and pH revealed that the desired low bacterial lysis coincided with intermediate but sufficient yield. High functional immunogenicity and low toxicity of the optimized vaccine were also confirmed. The EDTA extraction is therefore a robust process step which produces high quality OMV if harvest and pH are controlled accurately.