Robust Serum- and Feeder-Free Expansion of Mouse B Cells In Vitro

Abstract Mouse B cells are used in workflows to discover novel therapeutic antibodies or develop preclinical applications using genetically engineered B cells. In vitro expansion of B cells offers the opportunity to improve the recovery of antibody sequences and aids in the potential increase in the diversity of the B cell repertoire. Achieving robust expansion of B cells in culture can be challenging, as it typically requires the addition of serum, feeder cells, or specialized culture plates. The addition of serum can introduce unknown factors and result in lot-to-lot variability. Therefore, we have developed a first-to-market culture system that does not require the use of serum, feeder cells, or specialized culture plates to achieve robust in vitro expansion of mouse pan-B cells. Pan-B cells isolated from mouse splenocytes by immunomagnetic enrichment were cultured in serum-free ImmunoCultTM-XF B Cell Base Medium supplemented with ImmunoCultTM-ACF Mouse B Cell Expansion Supplement for > 9 days, starting with seeding densities of 100,000 cells/well and passaging every 3 days. Although pronounced donor variability was observed in the rate of expansion of viable cells, mean ~13-fold, ~150-fold, and ~200-fold rates were observed after 3, 6, and 9 days in culture, respectively (n=6 donors; range 94- to 328-fold at day 9). The expanded B cells also upregulated expression of activation and differentiation markers such as CD86 (mean 74%; n=6 donors; range 34 – 90%), CD138 (mean 68%; n=6 donors; range 57 – 73%), and CD267 (mean 79%; n=6 donors; range 49 – 91%) at day 9. The expansion supplement should facilitate mouse B cell studies for antibody discovery and diverse basic and translational applications.