Immunogenicity of single versus mixed allele vaccines of Plasmodium vivax Duffy binding protein region II

Abstract

The Duffy Binding protein (DBP) of Plasmodium vivax is vital for host erythrocyte invasion. DBP region II (DBPII) contains critical residues for receptor recognition and anti-DBPII antibodies have been shown to inhibit erythrocyte binding and invasion, thereby making the molecule an attractive vaccine candidate against P. vivax blood stages. Similar to other blood-stage antigens, allelic variation within the DBPII and associated strain-specific immunity is a major challenge for development of a broadly effective vaccine against P. vivax malaria. We hypothesized that immunization with a vaccine composed of multiple DBP alleles or a modified epitope DBP (DEKnull) will be more effective in producing a broadly reactive and inhibitory antibody response to diverse DBPII alleles than a single allele vaccine. In this study, we compared single, naturally occurring DBPII allele immunizations (Sal1, 7.18, P) and DEKnull with a combination of (Sal1, 7.18, P) alleles. Quantitative analysis by ELISA demonstrated that the multiple allele vaccine tend to be more immunogenic than any of the single allele vaccines when tested for reactivity against a panel of DBPII allelic variants whereas DEKnull was less immunogenic than the mixed-allele vaccine but similar in reactivity to the single allele vaccines. Further analysis for functional efficacy by in vitro erythrocyte-binding inhibition assays demonstrated that the multiple allele immunization produced a stronger strain-neutralizing response than the other vaccination strategies even though inhibition remained biased toward some alleles. Overall, there was no correlation between antibody titer and functional inhibition. These data suggest that a multiple allele vaccine may enhance immunogenicity of a DBPII vaccine but further investigation is required to optimize this vaccine strategy to achieve broader coverage against global P. vivax strains.

Broadly neutralizing epitopes in the Plasmodium vivax vaccine candidate Duffy Binding Protein

“…These polymorphisms result in strain-specific immune responses that render individuals susceptible to future infections by alternate strains and require vaccine efforts to preemptively account for this vulnerability (50). Two approaches to overcoming this variability involve multiallele vaccines and artificially engineered synthetic immunogens (8,37,38,47). Both approaches require the identification of broadly neutralizing epitopes as described here.…”

“…There are currently two strategies for vaccine development to counteract this variation: (i) creation of a multiallele vaccine encompassing all variants encountered in endemic regions, and (ii) engineering of a single synthetic antigen lacking highly immunogenic polymorphic sites (8,37,38). Both approaches necessitate the identification of globally conserved epitopes that elicit broadly neutralizing antibodies (bnAbs).…”

Immunogenicity of a Synthetic Vaccine Based on Plasmodium vivax Duffy Binding Protein Region II

“…Recombinant DBPII antigens from three naturally occurring alleles (Sal1, 7.18, and P), the synthetic DBPII allele (DEKnull) (36), and rPvMSP1-19 were expressed and purified as described previously (37,48). Briefly, the genes coding for the various antigens were synthesized, codon optimized for expression in Escherichia coli, and cloned into expression vector pET21aϩ (Novagen) with a C-terminal 6ϫHis tag to facilitate purification by affinity chromatography.…”

“…Immunized mice were evaluated for allele-specific anti-DBPII antibody titers by ELISA as previously reported (37,48). Briefly, ELISA plates (Nunc) were precoated with 0.2 g of rDEKnull, Sal1, P, 7.18, or PvMSP1-19 per well, and unbound surfaces were blocked with 5% (wt/vol) skim milk in phosphate-buffered saline-0.05% Tween 20 for 2 h at room temperature.…”

“…We demonstrated that removal of this dominant variant epitope lowered DBP immunogenicity, but importantly, inhibitory anti-DBPII antibodies were elicited against conserved neutralizing epitopes on the native Sal1 strain, which was used as the template and shared with other DBP allelic variants. Therefore, recombinant DEKnull (rDEKnull) was able to produce inhibitory anti-DBP antibodies against diverse DBPII alleles (37). Previous studies have demonstrated that naturally acquired immunity to the erythrocytic stages of malaria parasites is strongly dependent on antibodies (38)(39)(40).…”