The isolation of human monoclonal antibodies (mAbs) that neutralize a broad spectrum of primary HIV-1 isolates and the characterization of the human neutralizing antibody B cell response to HIV-1 infection are important goals that are central to the design of an effective antibody-based vaccine.

Antibodies targeting citrullinated proteins (ACPAs [anticitrullinated protein antibodies]) are commonly found in patients with rheumatoid arthritis (RA), strongly associate with distinct HLA-DR alleles, and predict a more aggressive disease course as compared with seronegative patients. Still, many features of these antibodies, including their site of production and the extent of MHC class II-driven T cell help, remain unclarified. To address these questions, we have used a single B cell-based cloning technology to isolate and express immunoglobulin (Ig) genes from joint-derived B cells of active RA patients. We found ∼25% of synovial IgG-expressing B cells to be specific for citrullinated autoantigens in the investigated ACPA(+) RA patients, whereas such antibodies were not found in ACPA(-) patients. The citrulline-reactive monoclonal antibodies did not react with the unmodified arginine peptides, yet several reacted with more than one citrullinated antigen. A role for active antigen selection of the citrulline-reactive synovial B cells was supported by the strong bias toward amino acid replacement mutations in ACPA(+) antibodies and by their loss of reactivity to citrullinated autoantigens when somatic mutations were reverted to the corresponding germline sequences.

Two validated assays, a bridging ELISA and a luciferase-based bioassay, were compared for detection of anti-drug antibodies (ADA) against interferon-beta (IFN-β) in patients with multiple sclerosis. Serum samples were tested from patients enrolled in a prospective study of 18 months. In contrast to the ELISA, when IFN-β-specific rabbit polyclonal and human monoclonal antibodies were tested, the bioassay was the more sensitive to detect IFN-β ADA in patients' sera. For clinical samples, selection of method of ELISA should be evaluated prior to the use of a multi-tiered approach. A titer threshold value is reported that may be used as a predictor for persistently positive neutralizing ADA.

The isolation of broadly neutralizing antibodies against influenza A viruses has been a long-sought goal for therapeutic approaches and vaccine design. Using a single-cell culture method for screening large numbers of human plasma cells, we isolated a neutralizing monoclonal antibody that recognized the hemagglutinin (HA) glycoprotein of all 16 subtypes and neutralized both group 1 and group 2 influenza A viruses. Passive transfer of this antibody conferred protection to mice and ferrets. Complexes with HAs from the group 1 H1 and the group 2 H3 subtypes analyzed by x-ray crystallography showed that the antibody bound to a conserved epitope in the F subdomain. This antibody may be used for passive protection and to inform vaccine design because of its broad specificity and neutralization potency.