Graduation Year

2023

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Medicine

Major Professor

John H. Adams, Ph.D.

Committee Member

Andreas Seyfang, Ph.D.

Committee Member

Burt Anderson, Ph.D.

Committee Member

Liwang Cui, Ph.D.

Committee Member

Bala Chandran, Ph.D.

Keywords

Sporozoite, Recombinant antigen, Liver stage, Mouse model

Abstract

RTS,S/AS01, vaccine targeting malaria caused by Plasmodium falciparum, used in moderate to high malaria transmission, provides hope for pre-erythrocytic (PE) subunit malaria vaccine development. Despite this vaccine advance, efforts to develop an efficacious vaccine against the neglected parasite Plasmodium vivax have lagged. In addition, there exists a gap in our understanding of PE antigens that can induce broadly-neutralizing antibodies. In this dissertation, we provide the preliminary characterization of vaccine candidates targeting the PE of P. vivax. Through transcriptomic profiling data and a target product profile, we identified critical P. vivax antigens (SSP3, SPECT-1, and M2-MAEBL) that can potentially be targets of neutralizing antibodies. We recombinantly expressed P. vivax PE antigens and utilized them in immunogenicity and seroprevalence studies. Our data suggest that these candidates have little variation and are surface exposed on P. vivax sporozoites.

This dissertation also explores the predictive capability of PE in vitro assay outcomes to in vivo challenge outputs. As in vitro assays are used to screen therapeutic targets, we sought to validate these bioassays against a traditional transgenic mouse malaria in vivo challenge model. To answer this, we used two well-characterized species-specific monoclonal antibodies (mAbs) targeting circumsporozoite protein (CSP) along with two characterized transgenic P. berghei rodent lines (PbmCh-luc and Pb-PfCSP). Using the in vitro liver stage development assay (ILSDA), we generated a dose-response curve to determine the IC50 of anti-CSP mAbs. Next, we conducted an intravenous challenge of transgenic sporozoites after the passive transfer of mAbs in BALB/c mice. We report that antibody-mediated in vitro inhibition of characterized mAbs closely tracked a decrease in developing liver-stage schizonts in vivo.

This study validates an experimental in vitro platform to evaluate novel P. vivax PE vaccine candidates and predict relative in vivo outcomes as a selection tool in advancing the best PE candidates for future discovery research.

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