Structural and molecular analysis of a protective epitope of Lyme disease antigen OspA and antibody interactions.

The murine monoclonal antibody LA-2 recognizes a clinically protective epitope on outer surface protein (OspA) of Borrelia burgdorferi, the causative agent of Lyme disease in North America. Human antibody equivalence to LA-2 is the best serologic correlate of protective antibody responses following OspA vaccination. Understanding the structural and functional basis of the LA-2 protective epitope is important for developing OspA-based vaccines and discovering prophylactic antibodies against Lyme disease. Here, we present a detailed structure-based analysis of the LA-2/OspA interaction interface and identification of residues mediating antibody recognition. Mutations were introduced into both OspA and LA-2 on the basis of computational predictions on the crystal structure of the complex and experimentally tested for in vitro binding and borreliacidal activity. We find that Y32 and H49 on the LA-2 light chain, N52 on the LA-2 heavy chain and residues A208, N228 and N251 on OspA were the key constituents of OspA/LA-2 interface. These results reveal specific residues that may be exploited to modulate recognition of the protective epitope of OspA and have implications for developing prophylactic passive antibodies.

Pre-exposure Prophylaxis With OspA-Specific Human Monoclonal Antibodies Protects Mice Against Tick Transmission of Lyme Disease Spirochetes.

BACKGROUND: Tick transmission of Borrelia spirochetes to humans results in significant morbidity from Lyme disease worldwide. Serum concentrations of antibodies against outer surface protein A (OspA) were shown to correlate with protection from infection with Borrelia burgdorferi, the primary cause of Lyme disease in the United States. METHODS: Mice transgenic for human immunoglobulin genes were immunized with OspA from B. burgdorferi to generate human monoclonal antibodies (HuMabs) against OspA. HuMabs were generated and tested in in vitro borreliacidal assays and animal protection assays. RESULTS: Nearly 100 unique OspA-specific HuMabs were generated, and 4 HuMabs (221-7, 857-2, 319-44, and 212-55) were selected as lead candidates on the basis of borreliacidal activity. HuMabs 319-44, 857-2, and 212-55 were borreliacidal against 1 or 2 Borrelia genospecies, whereas 221-7 was borreliacidal (half maximal inhibitory concentration, < 1 nM) against B. burgdorferi, Borrelia afzelii, and Borrelia garinii, the 3 main genospecies endemic in the United States, Europe, and Asia. All 4 HuMabs completely protected mice from infection at 10 mg/kg in a murine model of tick-mediated transmission of B. burgdorferi CONCLUSIONS: Our study indicates that OspA-specific HuMabs can prevent the transmission of Borrelia and that administration of these antibodies could be employed as preexposure prophylaxis for Lyme disease.

Community-based intervention to increase HIV testing and case detection in people aged 16-32 years in Tanzania, Zimbabwe, and Thailand (NIMH Project Accept, HPTN 043): a randomised study.

BACKGROUND: In developing countries, most people infected with HIV do not know their infection status. We aimed to assess whether HIV testing could be increased by combination of community mobilisation, mobile community-based voluntary counselling and testing (VCT), and support after testing. METHODS: Project Accept is underway in ten communities in Tanzania, eight in Zimbabwe, and 14 in Thailand. Communities at each site were paired according to similar demographic and environmental characteristics, and one community from each pair was randomly assigned to receive standard clinic-based VCT (SVCT), and the other community was assigned to receive community-based VCT (CBVCT) plus access to SVCT. Randomisation and assignment of communities to intervention groups was done by the statistics centre by computer; no one was masked to treatment assignment because the interventions were community based. Intervention was provided for about 3 years (2006-09). The primary endpoint of HIV incidence is pending completion of assessments after the intervention. In this interim analysis, we examined the secondary endpoint of uptake in HIV testing, differences in characteristics of clients receiving their first HIV test, and repeat testing. Analyses were limited to clients aged 16-32 years. This study is registered with ClinicalTrials.gov, number NCT00203749. FINDINGS: The proportion of clients receiving their first HIV test during the study was higher in CBVCT communities than in SVCT communities in Tanzania (2341 [37%] of 6250 vs 579 [9%] of 6733), Zimbabwe (5437 [51%] of 10,700 vs 602 [5%] of 12,150), and Thailand (7802 [69%] of 11,290 vs 2319 [23%] 10,033). The mean difference in the proportion of clients receiving HIV testing between CBVCT and SVCT communities was 40·2% (95% CI 15·8-64·7; p=0·019) across three community pairs (one per country). HIV prevalence was higher in SVCT communities than in CBVCT communities, but CBVCT detected almost four times more HIV cases than did SVCT across the three study sites (952 vs 264; p=0·003). Repeat HIV testing in CBVCT communities increased in all sites to reach 28% of all those testing for HIV by the end of the intervention period. INTERPRETATION: CBVCT should be considered as a viable intervention to increase detection of HIV infection, especially in regions with restricted access to clinic-based VCT and support services after testing. FUNDING: US National Institute of Mental Health, HIV Prevention Trials Network (via US National Institute of Allergy and Infectious Diseases), and US National Institutes of Health.