A single immunization of <i>Borreliella burgdorferi</i> -infected mice with Vanguard crLyme elicits robust antibody responses to diverse strains and variants of outer surface protein C

Lyme disease, caused by <i>Borreliella burgdorferi</i> and related species<i>,</i> is a growing health threat to companion animals across North America and Europe. Vaccination is an important preventive tool used widely in dogs living in, or near, endemic regions. In this report, we assessed anti-outer surface protein (Osp) A and anti-OspC antibody responses in <i>B. burgdorferi</i>-infected and -naïve mice (C3H/HeN) after immunization with a murine-optimized single dose of the Lyme disease subunit vaccine, Vanguard crLyme. crLyme is comprised of OspA and an OspC chimeritope-based immunogen designated as CH14. Mice that were infected and immunized developed higher levels of anti-OspC antibodies (Abs) than those infected only or that received one vaccine dose. The anti-OspC Abs that developed in the infected/immunized mice bound to all OspC variants tested (<i>n</i> = 22), whereas OspC Abs in serum from infected mice bound predominantly to the OspC variant (type A) produced by the infecting <i>B. burgdorferi</i> strain. Consistent with the absence of OspA expression in infected mammals, none of the infected mice developed Abs to OspA and did not develop anti-OspA Abs after single dose immunization. Lastly, serum from infected/immunized mice displayed significantly higher and broader killing activity than serum from non-immunized infected mice. The results of this study demonstrate that a single vaccination of actively infected mice results in strong anti-OspC Ab responses. This study contributes to our understanding of Ab responses to vaccination in actively infected mammals.