Publications

The use of antibody-based therapy to treat a variety of diseases and conditions is well documented. The use of antibodies as an antidote to treat tetanus infections was one of the first examples of immunotherapy and remains the standard of care for cases involving potential infections. Plasma-derived immunoglobulins obtained from human or horse pose risks of infection from undetectable emergent viruses or may cause anaphylaxis. Further, there is a lack of consistency between lots. In the search for new formulations, we obtained a series of clonally related human monoclonal antibodies (mAbs) derived from B cells sorted from donors that presented anti-tetanus neutralizing titers. Donors were revaccinated prior to blood collection. Different strategies were used for single-cell sorting, since it was challenging to identify cells at a very low frequency: memory B cell sorting using fluorescent-labeled tetanus toxoid and toxin as baits, and plasmablast sorting done shortly after revaccination. Screening of the recombinant mAbs with the whole tetanus toxin allowed us to select candidates with therapeutic potential, since mAbs to different domains can contribute additively to the neutralizing effect. Because of selective binding to different domains, we tested mAbs individually, or in mixtures of two or three, in the neutralizing in vivo assay specified by Pharmacopeia for the determination of polyclonal hyperimmune sera potency. An oligoclonal mixture of three human mAbs completely neutralized the toxin injected in the animals, signaling an important step for clinical mAb development.

Infections with hepatitis C virus (HCV) represent a worldwide health burden and a prophylactic vaccine is still not available. Liver transplantation (LT) is often the only option for patients with HCV-induced end-stage liver disease. However, immediately after transplantation, the liver graft becomes infected by circulating virus, resulting in accelerated progression of liver disease. Although the efficacy of HCV treatment using direct-acting antivirals has improved significantly, immune compromised LT-patients and patients with advanced liver disease remain difficult to treat. As an alternative approach, interfering with viral entry could prevent infection of the donor liver. We generated a human monoclonal antibody (mAb), designated 2A5, which targets the HCV envelope. The neutralizing activity of mAb 2A5 was assessed using multiple prototype and patient-derived HCV pseudoparticles (HCVpp), cell culture produced HCV (HCVcc), and a human-liver chimeric mouse model. Neutralization levels observed for mAb 2A5 were generally high and mostly superior to those obtained with AP33, a well-characterized HCV-neutralizing monoclonal antibody. Using humanized mice, complete protection was observed after genotype 1a and 4a HCV challenge, while only partial protection was achieved using gt1b and 6a isolates. Epitope mapping revealed that mAb 2A5 binding is conformation-dependent and identified the E2-region spanning amino acids 434 to 446 (epitope II) as the predominant contact domain. Conclusion: mAb 2A5 shows potent anti-HCV neutralizing activity both in vitro and in vivo and could hence represent a valuable candidate to prevent HCV recurrence in LT-patients. In addition, the detailed identification of the neutralizing epitope can be applied for the design of prophylactic HCV vaccines.