Multi-protein chimeric antigens, a novel combined approach for efficiently targeting and blocking the blood stage of Plasmodium falciparum

Abstract

Plasmodium falciparum-induced malaria remains a fatal disease affecting millions of people worldwide. Mainly, the blood stage of malaria is highly pathogenic and symptomatic, rapidly damaging the host organs and occasionally leading to death. Currently, no vaccines are approved for use against the blood stage of malaria. Canonical vaccines in the past have selected the most immunodominant or essential protein to block the growth of the parasite. This strategy works efficiently for low-complexity organisms such as viruses and a few bacteria but has not shown promising results for a malaria vaccine. Plasmodium has a complex life cycle and vaccine candidates especially during blood stage are ineffective due to multiple gene families showing redundancy, immune evasion, and insufficient antibody titer. Herein, we demonstrate a novel strategy of combining multiple antigens from the blood stage of Plasmodium falciparum using only the most immunodominant peptide sequences as a way of tackling polymorphism and redundancy. We created three chimeric antigens targeting eight PfEMP1 proteins (chimeric varB) and eight merozoite surface proteins (chimeric MSP and InvP) by selecting and stitching B-cell epitopes. Our chimeric constructs show naturally circulating antibodies against individual peptides using epitope-mapping microarray as well as entire proteins in malaria-infected patients. We demonstrate that anti-varB antibodies are neutralizing in nature and significantly reduce the cytoadhesion on an organ-on-chip system with a microfluidic device mimicking physiological conditions. We have applied a Deep Learning based method to quantify the number of adhered RBCs under fluidic conditions that is used to study cytoadhesion. Furthermore, the anti-MSP and InvP antibodies show complete growth inhibition in a single cycle at a combined concentration of 0.13 mg/ml. Overall, our results show that a combination of antigenic peptides from multiple antigens can function as a next-generation vaccine and effectively block the blood stage by reducing cytoadhesion and inhibiting the parasite growth.