Modified OspA Delivered Via Distinct Vehicles and Routes Confers Equivalent Protection Against Tick-Transmitted Borrelia burgdorferi

Abstract Vaccines targeting outer surface protein A (OspA) of Borrelia burgdorferi protect against Lyme disease by eliciting antibodies that neutralize spirochetes in the Ixodes scapularis tick midgut during engorgement before transmission occurs. We evaluated whether different delivery vehicles and administration routes for a modified OspA construct (OspA BPBPk ) differed in protective efficacy. Four groups of nine C3H-HeN mice were immunized with OspA BPBPk delivered intranasally by live parainfluenza virus 5 (PIV5- OspA BPBPk ) or by subcutaneous administration of recombinant protein adjuvanted with aluminum hydroxide (rOspA BPBPk ) using three prime-boost regimens and a vector/adjuvant control: homologous intranasal PIV5-OspA BPBPk (IN/IN), homologous subcutaneous rOspA BPBPk (SC/SC), and heterologous intranasal PIV5-OspA BPBPk prime/subcutaneous rOspA BPBPk boost (IN/SC). Mice were challenged on day 90, approximately 2 months after the boost, with nymphal ticks infected with 19 strains of B. burgdorferi . All OspA BPBPk -containing vaccines elicited high antigen-specific IgG antibody titers (geometric mean titers of 10⁴–10⁶, approximately 4 log₁₀ higher than the control group), reduced B. burgdorferi loads in engorged nymphal ticks by 1.7-2 Log 10 , neutralized B. burgdorferi motility in multi-strain cultures, and prevented recovery of viable spirochetes from tissues after tick challenge. While one mouse (1/9, 11%) in the heterologous IN/SC vaccinated group had detectable flaB DNA in tissues and seroreactivity to B. burgdorferi PepVF, culture of spirochetes from heart and bladder showed no evidence of active infection. Although homologous immunization produced the most consistent results in mice, different delivery vehicles and routes of immunization with OspA BPBPk vaccines did not affect overall efficacy as assessed by recovery of viable B. burgdorferi from tissues.