Structural correlates of protection for antibodies targeting Marburg virus GP2

About This Grant

PROJECT SUMMARY Marburg viruses are highly lethal human pathogens with unpredictable patterns of emergence that have led to over 15 human outbreaks since their discovery in 1967, with average case fatality rates of ~50%. The natural target of neutralizing and protective antibodies in Marburg virus infection is the membrane-anchored surface glycoprotein (GP), but only four sites on Marburg virus GP have been identified as protective targets for such antibodies. As such, and in contrast to the numerous antibodies identified against the related Ebola viruses, the repertoire of effective monoclonal antibodies (mAbs) against Marburg viruses is severely limited in size and functional diversity, and no mAb countermeasures are currently approved for clinical use. Of the four known sites of vulnerability on Marburg virus GP one falls within the N-terminus of the GP2 subunit, referred to as the “wing”, that is targeted by protective but non-neutralizing antibodies. Such antibodies have been isolated both from a human survivor of infection and from animal immunizations. Limited structural information is currently available on the GP2 wing and its recognition by antibodies, which has hampered efforts to define underlying molecular determinants and correlates of protection for this region. We previously immunized a Rhesus macaque with repeated doses of diverse Marburg virus GP antigens and isolated a new panel of cross-Marburg virus GP- reactive monoclonal antibodies. Within this panel, we identified three antibody lineages, CM10, CM11, and CM12, that target the GP2 wing. Here, we will undertake in-depth biophysical and functional analyses of the CM10, CM11, and CM12 lineages, including assessment of binding affinities to GP, capacity to mediate Fc effector functions, and capacity to potentiate virus neutralization by receptor-binding region antibodies (Aim 1). To determine the structural basis for CM10, CM11, and CM12 recognition of the GP2 wing and to delineate structural correlates of protection, we will undertake a combined electron microscopic and crystallographic approach to determine their structures in complex with GP ectodomains and GP2 wing peptides, respectively (Aim 2). A selected subset of variants for will be tested for protective efficacy in a hamster model of Marburg Angola virus infection and disease under ABSL-4 containment (Aim 3), which will enable subsequent association with functional and structural attributes. Taken together, our proposed studies will advance the understanding of the GP2 wing as a target for protective mAbs and will expand the repertoire of candidate immunotherapeutics against Marburg viruses.