Novel Virus-Like Particle Vaccine Encoding the Circumsporozoite Protein of Plasmodium falciparum Is Immunogenic and Induces Functional Antibody Responses in Mice.

Liriye Kurtovic,Jo-Anne Chan,Catherine Palmer,Betty Kouskousis,Linda Reiling,Eric Hanssen,David Wetzel,Bruce D Wines,Manfred Suckow,P Mark Hogarth,James G Beeson,Volker Jenzelewski,Damien R Drew,Michael Piontek

doi:10.3389/fimmu.2021.641421

Abstract

RTS,S is the leading malaria vaccine in development, but has demonstrated only moderate protective efficacy in clinical trials. RTS,S is a virus-like particle (VLP) that uses the human hepatitis B virus as scaffold to display the malaria sporozoite antigen, circumsporozoite protein (CSP). Particle formation requires four-fold excess scaffold antigen, and as a result, CSP represents only a small portion of the final vaccine construct. Alternative VLP or nanoparticle platforms that reduce the amount of scaffold antigen and increase the amount of the target CSP antigen present in particles may enhance vaccine immunogenicity and efficacy. Here, we describe the production and characterization of a novel VLP that uses the small surface antigen (dS) of duck hepatitis B virus to display CSP. The CSP-dS fusion protein successfully formed VLPs without the need for excess scaffold antigen, and thus CSP represented a larger portion of the vaccine construct. CSP-dS formed large particles approximately 31-74 nm in size and were confirmed to display CSP on the surface. CSP-dS VLPs were highly immunogenic in mice and induced antibodies to multiple regions of CSP, even when administered at a lower vaccine dosage. Vaccine-induced antibodies demonstrated relevant functional activities, including Fc-dependent interactions with complement and Fcγ-receptors, previously identified as important in malaria immunity. Further, vaccine-induced antibodies had similar properties (epitope-specificity and avidity) to monoclonal antibodies that are protective in mouse models. Our novel platform to produce VLPs without excess scaffold protein has wide implications for the future development of vaccines for malaria and other infectious diseases.

Highlights

There were an estimated 228 million cases of malaria and 405,000 deaths in 2018, largely attributed to infection with Plasmodium falciparum [1]
6 g dry cell weight (DCW) of yeast strain Der#949 were used to isolate 1.2 ± 0.1 mg product virus-like particle (VLP) containing the circumsporozoite protein (CSP)-dS fusion protein (YP/X = ~0.2 mg g-1) applying an analytical methodology based on two consecutive steps of ultracentrifugation
As a proof-ofconcept, we used the RTS,S vaccine construct of CSP as the model antigen since RTS,S has shown reproducible efficacy in human clinical trials, which is mediated by vaccine-induced antibodies

Summary

Introduction

There were an estimated 228 million cases of malaria and 405,000 deaths in 2018, largely attributed to infection with Plasmodium falciparum [1]. The most advanced malaria vaccine in development is RTS,S, which is based on the major surface antigen expressed by P. falciparum sporozoites, the circumsporozoite protein (CSP) This vaccine approach aims to prevent the initial asymptomatic stage of infection in the liver and to prevent subsequent parasite replication in the blood and development of clinical disease [5]. The RTS,S vaccine construct is a fusion protein of a truncated form of CSP (including the central-repeat and C-terminal regions of the protein) and the human hepatitis B surface antigen (HBsAg), which is co-expressed with excess HBsAg to self-assemble into virus-like particles (VLPs) [6]. These particles are ~20 nm in size and co-administered with the potent AS01 adjuvant to enhance vaccine immunogenicity [7]

Methods

Results

Conclusion