Development and Characterization of Human Monoclonal Antibodies with Functional Activity against Plasmodium falciparum Merozoites

Ogwang, Rodney (2023). Development and Characterization of Human Monoclonal Antibodies with Functional Activity against Plasmodium falciparum Merozoites. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0001552c

Abstract

The development of highly effective interventions against malaria remains a research priority. Individuals in endemic areas develop a non-sterilizing form of immunity, and antibodies are thought to play a key role. However, it remains unclear which specific antibodies and antibody-mediated mechanisms underpin protective immunity. I hypothesized that malaria semi-immune individuals carry unique antibody signatures vital for immunity. My overall aim was to isolate a panel of Plasmodium-specific human monoclonal antibodies (mAbs) and characterise their functional activity (neutrophil activation, opsonic-phagocytosis and complement fixation) against merozoites.

To identify individuals making the kind of potent antibodies we can strive to emulate in vaccines and therapeutics, I conducted functional antibody screens in serum using established Fc-dependent effector functional assays. This enabled the selection of semi-immune individuals from different transmission settings with high levels of antibodies mediating opsonic-phagocytosis, neutrophil activation and complement fixation. Next, from these semi-immune individuals, I cloned the immunoglobulin variable genes from Plasmodium-specific B-cells into appropriate expression vectors and generated a panel of recombinant monoclonal antibodies (mAbs) with specificity to Plasmodium merozoites. To characterise these mAbs, I investigated the level of functional activity in vitro and evaluated Fc region modification for enhanced mAb potency. Finally, I identified the antibody cognate-interaction partners using a protein microarray approach.

I demonstrated the impact of malaria transmission intensity on the level of functional antibodies and suggest the use of an immune score accounting for all effector functions to select uniquely immune individuals. I generated a panel of mAbs targeting merozoites and show differing levels of function in vitro. I also show that a cross-isotype “IgG/A” antibody can enhance mAb neutrophil activation potency. Overall, this work shows that our understanding of blood-stage immunity to malaria may be improved through the agnostic isolation and characterisation of merozoite-specific mAbs. This may inform the design of effective vaccines and immunotherapies.