Experimental immunization against Lyme borreliosis with recombinant Osp proteins: an overview

Interest in human and veterinary vaccines against Lyme borreliosis is growing. Both whole cell immunization and subunit vaccines can protect against infection with Borrelia burgdorferi. For development of a human vaccine the focus has been on a subunit vaccine. The most promising candidate is OspA, a major outer membrane lipoprotein of B. burgdorferi sensu lato. Of Osp proteins A through D, OspA shows the least variability between strains in its sequence and in the level of its expression. Borreliae in ticks express OspA. Antibodies to OspA kill borreliae in vitro and provide passive protection in mice. Active immunization of mice with OspA provides protection against challenge by syringe inoculation or tick bite. The lipid moiety of the OspA is necessary for immunogenicity in the absence of a potent adjuvant. A recombinant OspA-based vaccine is already in clinical trials. Although there is compelling evidence that immunization with OspA will provide protection, questions remain regarding the duration of protection from such immunization, the necessity to have a minimum level of neutralizing antibodies at all times for protection, and the relationship of an immune response to OspA and autoimmune features of Lyme borreliosis. The experimental aspects of immunization with Osp-A based constructs and other Lyme vaccine candidates are reviewed and discussed.