Imraan Ali BS, James P Chambers, Masarrat Ali and Richard C Tamfu
Background: Currently, neither vaccine nor drugs are available for treatment of Zika infection. Vaccines for Flaviviruses have been developed using whole inactivated Yellow Fever virus (YFV) as well as YFV-vectored constructs expressing Dengue Envelop-PrM protein. Thus, Flavivirus proteins show promise as vaccine candidates. Using a rabbit model, the aim of this work was to evaluate the response elicited to recombinant Zika Envelop and NS1 proteins.
Methods: His tagged (carboxy terminus) recombinant proteins were expressed in E. coli, purified using Ni-NTA Agarose and imidazole elution, and used to immunize adult New Zealand white male rabbits. Envelop and NS1 antibody ELISAs were developed, and levels of IgG and IgM assessed during the course of vaccination.
Results: Zika recombinant Envelop protein elicited a robust IgG response (4500 μg/ml serum) in contrast to the NS1 protein (~100 μg/ml serum). Both proteins elicited an IgM response; although, significantly lower, i.e., ~25-50 μg/ml serum. E. coli expressed Envelop and NS1 elicited IgG reacted robustly compared with sf9 cell expressed Envelop and NS1 glycosylated homologs. Zika Anti-Envelop IgG cross-reacted with E. coli expressed YFV and Dengue Type I Envelop homologs (approximately 20% control); whereas, Zika anti-NS1 IgG cross-reacted (approximately 20% control) with E. coli expressed WNV NS1 homolog.
Discussion and conclusion: Zika Envelop protein is unique among Flaviviruses; although, parts of it resemble West Nile, Japanese Encephalitis, and Dengue virus homologs. Although some cross-reactivity, i.e., ~25% A450 values was observed, and as with all animal model derived data there are limitations to human extrapolation, data presented here support the potential usefulness of 1) Zika recombinant Envelop protein as a vaccine candidate, and 2) Zika Envelop specific ELISA reagents.