The Ebola Virus (EBOV) outbreak of 2014/2015 has claimed more than 11000 lives. EBOV is an enveloped Filovirus with only one surface-exposed antigen, the receptor glycoprotein (GP). The experimental combination antibody therapy, ZMapp, contains three antibodies that target GP and has been used successfully to treat healthcare workers infected with EBOV in West Africa. ZMapp consists of two neutralising monoclonal antibodies (Mabs), 2G4 and 4G7, that share epitopes at the GP1/GP2 interface of the viral surface glycoprotein, and a third non-neutralising antibody (13C6) that binds to the glycan cap motif shared by all three of the transcriptionally edited glycoprotein gene products. However, a combination of yield limitations and the requirement for large doses when administering the treatment mean that the world’s supply is limited to a handful of doses. Currently, the primary source of ZMapp is from genetically modified tobacco plants, but production limitations have hampered the large scale treatment of infected individuals. Therefore we investigated the use of a mammalian expression system amenable to good manufacturing practice (GMP) production as an alternative source for ZMapp.
Recombinant, chimeric Mabs were cloned from synthetic sequences corresponding to the antibody variable domains into human IgG1 and IgK backbone expression plasmids. High yields of all three ZMapp antibodies were demonstrated in a transient Chinese hamster ovary (CHO) expression system. After protein-A purification the high affinity binding of all three antibodies to a recombinant GP was validated using ELISA. To generate high yield stable cells the constructs were transferred to a dual expression plasmid to enable expression of both heavy and light chains from a single vector incorporating puromycin and glutamine synthetase double selection. GMP compliant stable cell line production is now underway with the aim of producing yields in excess of 1g/L as an alternative source for this life-saving therapeutic of global importance.