Frequency and proportion of MBC responders induced by 4vHPV. (A) Frequency of HPV-16- (left panel) and HPV-18-specific (right panel) specific memory B cells (MBCs) per millions of total IgG-secreting B cells at Days 0, 365, 545 and 730 in the prospective cohort for all (solid blue line), HPV-naïve (dashed red line) and HPV-exposed (dashed green line) subjects; (B) proportion of MBC responders (defined as subjects with >455 L-16 B cell or >450 L-18 B cell per millions of total IgG-secreting B cells) to HPV-16- (left panel) and HPV-18- (right panel) in the prospective cohort at Days 365, 454 and 730 as indicated at x-axis for all (blue bar), HPV-naïve (red bar) and HPV-exposed (green bar) subjects.