The presence of neutralizing epitopes in human papillomavirus (HPV) L1 virus-like particles (VLPs) is the structural basis of prophylactic vaccines. An anti-HPV16 neutralizing monoclonal antibody (N-mAb) 26D1 was isolated from a memory B cell of a human vaccinee. The pre-binding of heparan sulfate to VLPs inhibited the binding of both N-mAbs to the antigen, indicating that the epitopes are critical for viral cell attachment/entry. Hybrid VLP binding with surface loop swapping between types indicated the essential roles of the DE and FG loops for both 26D1 (DEa in particular) and H16.V5 binding. Specifically, Tyr135 and Val141 on the DEa loop were shown to be critical residues for 26D1 binding via site-directed mutagenesis. Partially overlap between the epitopes between 26D1 and H16.V5 was shown using pairwise epitope mapping, and their binding difference is demonstrated to be predominantly in DE loop region. In addition, 26D1 epitope is immunodominant epitope recognized by both antibodies elicited by the authentic virus from infected individuals and polyclonal antibodies from vaccinees. Overall, a partially overlapping but distinct neutralizing epitope from that of H16.V5 was identified using a human N-mAb, shedding lights to the antibody arrays as part of human immune response to vaccination and infection.

Background We have previously obtained a mouse anti-hepatitis B surface antigen (HBsAg) antibody E6F6 with long-lasting serum HBsAg clearance effects. The E6F6 epitope-based protein CR-T3-SEQ13 (HBsAg aa 113–135) vaccination therapy in cynomolgus monkeys induced long-term polyclonal antibodies-mediated clearance of HBsAg in the HBV transgenic (HBV-Tg) mice. Methods We isolated monoclonal antibodies from CR-T3-SEQ13 vaccinated cynomolgus monkeys, compared their therapeutic effects with E6F6, identified their epitopes on HBsAg, determined the pharmacokinetics, and studied their physical property. Results A panel of anti-HBsAg mAbs was generated through memory B cell stimulatory culture. Two lead monkey-human chimeric antibodies, C1–23 and C3–23, effectively suppressed HBsAg and HBV DNA in HBV-Tg mice. The humanized antibodies and humanized-mouse reverse chimeric antibodies of two antibodies exhibited comparable HBsAg clearance and viral suppression efficacy as those versions of E6F6 in HBV-Tg mice. Humanized antibody hu1–23 exhibited more efficacy HBsAg-suppressing effects than huE6F6–1 and hu3–23 in HBV-Tg mice at dose levels of 10 mg/kg and 20 mg/kg. Evaluation of the binding sites indicates that the epitope recognized by hu1–23 is located in HBsAg aa 118–125 and 121–125 for hu3–23. Physical property study revealed that hu1–23 and hu3–23 are stable enough for further development as a drug candidate. Conclusions Our data suggest that the CR-T3-SEQ13 protein is a promising HBV therapeutic vaccine candidate; and hu1–23 and hu3–23 are therapeutic candidates for the treatment of CHB. Moreover, the generation of antibodies from the epitope-based vaccinated subjects may be an alternative approach for novel antibody drug discovery. Statement of Significance Cynomolgus monkey mAbs were generated from an HBsAg-epitope-based-protein vaccination through memory B cell stimulatory culture. The humanized antibodies can efficiently mediate HBsAg clearance in HBV-Tg mice and may serve as anti-HBsAg therapeutic candidates. Generation of mAbs from the epitope-based vaccinated subjects is an alternative approach for novel antibody discovery.