Mouse efficacy model.

The mouse challenge model has been previously described (12). Briefly, infected ticks were prepared by placing Ixodes larva on B. burgdorferi strain N40–infected mice with severe combined immunodeficiency for a blood meal. Larvae were harvested and allowed to molt to the nymphal stage before use for challenge. Groups of 5 C3H/HeJ mice (The Jackson Laboratory, stock 00659) were i.p. injected with a HuMAbs at 10 mg/kg. The following day, mice were challenged by the placement of 6 infected tick nymphs behind the ear of each mouse. Three weeks after the tick placement, mice were euthanized, and tissue samples from an ear, the bladder, the heart, and a joint were harvested for culture. Tissue samples were monitored twice weekly for 4 weeks by dark-field microscopy for evidence of growth of spirochetes. Samples were also analyzed for B. burgdorferi DNA using OspA-specific PCR analysis. Serum samples were collected on day 21 to analyze the antibody concentration and for serological investigation by ELISA against lysate of B. burgdorferi. Animals were considered uninfected if results of all 3 tests were negative. Protocols were approved by the IACUC of Tufts University.