Methods: To develop a monoclonal antibody for pre-exposure prophylaxis (PrEP) of Lyme disease, we created a panel of borreliacidal human monoclonal antibodies (HuMabs) by immunizing mice that were transgenic for human immunoglobulin genes and inactivated mouse immunoglobulin genes with OspA protein of B. burgdorferi.
Results: Over 93 unique HuMabs bound to OspA and were tested in borreliacidal assays against Borrelia burgdorferi, B. afzelii and B. garini. Four HuMabs (221-7, 857-2, 319-44, and 212-55) were selected as lead candidates based on high borreliacidal activities (<10 nM of IC50). HuMab 319-44, 857-2 and 212-55 were borreliacidal against one or two species, whereas 221-7 was cidal (IC50 <10nM) against all three species. Partial epitope mapping for the four lead HuMabs was performed by ELISA reactivity with OspA truncations and competition with LA-2. HuMab 221-7 and 857-2 recognized a conformational epitope comprising a.a. 71-141, a relatively conserved region of OspA. HuMab 212-55 bound to an epitope within a.a. 142-273. HuMab 319-44 was found to bind within a.a. 178-273 and blocked LA-2 binding. Alanine scanning mutagenesis of the LA-2 binding site defined a.a. D249 and S250 to be within the 319-44 epitope. Surface plasmon resonance analysis revealed high affinity binding of all four HuMabs with OspA from B. burgdorferi. HuMab 221-7 bound strongly to OspA from all three Borrelia species with affinity of <10nM. Two HuMabs 319-44 and 221-7 were selected for further study in vivo and both prevented infection of mice challenged with B. burgdorferi-infected ticks.
Conclusion: These studies suggest that OspA-specific HuMabs could provide PrEP from Lyme disease caused by a broad range of Borrelia species.
A. Sadowski, None
W. Thomas Jr., None
M. S. Klempner, None