Preclinical Evidence for the Protective Capacity of Antibodies Induced by Lyme Vaccine Candidate VLA15 in People

Abstract

Background Vaccine candidate VLA15 is designed to protect against the dominant Borrelia genospecies-causing Lyme disease in North America and Europe. Active immunization with VLA15 has protected in the mouse model of tick challenge. VLA15 is currently under evaluation in clinical studies for the prevention of Lyme borreliosis. Methods Mice were passively administered sera from clinical trial participants vaccinated with VLA15, or normal human serum from unvaccinated individuals as control. Post-transfer serum anti-OspA IgG titers were assessed by ELISA. Following passive transfer, mice were challenged with Ixodes ticks colonized with Borrelia burgdorferi (OspA serotype 1) or Borrelia afzelii (OspA serotype 2) and infection was determined by serology for VlsE C6 or by PCR and culture to assess the presence of Borrelia bacteria. Results Passive transfer of immune sera prevented transmission of Borrelia from the tick vector and protected mice against challenge. Post-transfer protective threshold IgG antibody titers were observed in this animal model of 131 U/mL for B. burgdorferi (OspA serotype 1) and 352 U/mL for B. afzelii (serotype 2). Conclusions Passive transfer of sera from trial participants immunized with VLA15 protected mice from borreliosis in a tick challenge model. This indicates that VLA15 induces functional immune responses in people that can be linked to efficacy in a stringent preclinical model.