ABSTRACT
We describe therapeutic monoclonal antibodies isolated from human volunteers vaccinated with recombinant adenovirus expressing Ebola virus glycoprotein (EBOV GP) and boosted with modified vaccinia virus Ankara. Among 82 antibodies isolated from peripheral blood B cells, almost half neutralized GP pseudotyped influenza virus. The antibody response was diverse in gene usage and epitope recognition. Although close to germline in sequence, neutralizing antibodies with binding affinities in the nano- to pico-molar range, similar to "affinity matured" antibodies from convalescent donors, were found. They recognized the mucin-like domain, glycan cap, receptor binding region, and the base of the glycoprotein. A cross-reactive cocktail of four antibodies, targeting the latter three non-overlapping epitopes, given on day 3 of EBOV infection, completely protected guinea pigs. This study highlights the value of experimental vaccine trials as a rich source of therapeutic human monoclonal antibodies.
Subject(s)
Antibodies, Monoclonal/isolation & purification , Ebola Vaccines/isolation & purification , Ebola Vaccines/therapeutic use , Ebolavirus/immunology , Hemorrhagic Fever, Ebola/therapy , Vaccination , Adolescent , Adult , Animals , Antibodies, Monoclonal/blood , Antibodies, Monoclonal/therapeutic use , Antibodies, Neutralizing/blood , Antibodies, Neutralizing/isolation & purification , Antibodies, Neutralizing/therapeutic use , Antibodies, Viral/blood , Antibodies, Viral/isolation & purification , Antibodies, Viral/therapeutic use , Cells, Cultured , Dogs , Female , Guinea Pigs , HEK293 Cells , Hemorrhagic Fever, Ebola/blood , Hemorrhagic Fever, Ebola/immunology , Humans , Madin Darby Canine Kidney Cells , Male , Middle Aged , Vaccination/methods , Young AdultABSTRACT
The Plasmodium falciparum reticulocyte-binding protein homolog 5 (PfRH5) has recently emerged as a leading candidate antigen against the blood-stage human malaria parasite. However it has proved challenging to identify a heterologous expression platform that can produce a soluble protein-based vaccine in a manner compliant with current Good Manufacturing Practice (cGMP). Here we report the production of full-length PfRH5 protein using a cGMP-compliant platform called ExpreS(2), based on a Drosophila melanogaster Schneider 2 (S2) stable cell line system. Five sequence variants of PfRH5 were expressed that differed in terms of mutagenesis strategies to remove potential N-linked glycans. All variants bound the PfRH5 receptor basigin and were recognized by a panel of monoclonal antibodies. Analysis following immunization of rabbits identified quantitative and qualitative differences in terms of the functional IgG antibody response against the P. falciparum parasite. The antibodies induced by one protein variant were shown to be qualitatively similar to responses induced by other vaccine platforms. This work identifies Drosophila S2 cells as a clinically-relevant platform suited for the production of 'difficult-to-make' proteins from Plasmodium parasites, and identifies a PfRH5 sequence variant that can be used for clinical production of a non-glycosylated, soluble full-length protein vaccine immunogen.
