The stage‐specific in vitro efficacy of a malaria antigen cocktail provides valuable insights into the development of effective multi‐stage vaccines

Abstract

Multicomponent vaccines targeting different stages of Plasmodium falciparum represent a promising, holistic concept towards better malaria vaccines. Additionally, an effective vaccine candidate should demonstrate cross-strain specificity because many antigens are polymorphic, which can reduce vaccine efficacy. A cocktail of recombinant fusion proteins (VAMAX-Mix) featuring three diversity-covering variants of the blood-stage antigen PfAMA1, each combined with the conserved sexual-stage antigen Pfs25 and one of the pre-erythrocytic-stage antigens PfCSP_TSR or PfCelTOS, or the additional blood-stage antigen PfMSP1_19, was produced in Pichia pastoris and used to immunize rabbits. The immune sera and purified IgG were used to perform various assays determining antigen specific titers and in vitro efficacy against different parasite stages and strains. In functional in vitro assays we observed robust inhibition of blood-stage (up to 90%), and sexual-stage parasites (up to 100%) and biased inhibition of pre-erythrocytic parasites (0-40%). Cross-strain blood-stage efficacy was observed in erythrocyte invasion assays using four different P. falciparum strains. The quantification of antigen-specific IgGs allowed the determination of specific IC50 values. The significant difference in antigen-specific IC50 requirements, the direct correlation between antigen-specific IgG and the relative quantitative representation of antigens within the cocktail, provide valuable implementations for future multi-stage, multi-component vaccine designs.

Immunization with the Malaria Diversity-Covering Blood-Stage Vaccine Candidate Plasmodium falciparum Apical Membrane Antigen 1 DiCo in Complex with Its Natural Ligand PfRon2 Does Not Improve the In Vitro Efficacy

“…In agreement with our earlier DiCo-based studies (37, 44) and those reported by other groups (19, 45), we observed balanced IC 50 values (~150 μg/ml) against different strains. This is in contrast to using single alleles for immunization, where the IC 50 values in GIA are significantly higher (greater than twofold) for heterologous compared to homologous (vaccine-like) strains (18).…”

“…The DiCo1-3 sequences (Figure S1 in Supplementary Material) were amplified from their source constructs (37) and introduced into the plant expression vector pTRAkc-ERH (linearized with Nco I/ Not I) in-frame with an upstream signal peptide sequence and a downstream His 6 tag and SEKDEL signal for retention in the endoplasmic reticulum (38). Additionally, six different alleles of Pf AMA1 ( Pf AMA1-3D7, Pf AMA1-FCR3, Pf AMA1-HB3, Pf AMA1-Dd2, Pf AMA1-7G8, and Pf AMA1-RO33) were obtained as synthetic genes codon optimized for N. benthamiana from Geneart (Thermo Fisher Scientific, Waltham, MA, USA) and introduced into the plant expression vector pTRAkc-ERH using the cloning strategy mentioned above.…”

Biosensor binding data and its applicability to the determination of active concentration

“…CFCA data have been successfully correlated to growth inhibition in vaccine development (Spiegel et al 2015) and for the identification of biomarkers Shah et al 2015).…”

Characterization ofPlasmodium falciparumProteome at Asexual Blood Stages for Screening of Effective Vaccine Candidates: An Immunoinformatics Approach

“…29 Overall, our predicted data provide a strong rationale for developing asexual blood-stage vaccine component as part of a multivalent effective malaria vaccine that may need to incorporate antigens of several life-cycle stages including liver stage. [64][65][66][67] …”