Graduation Year

2015

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Public Health

Major Professor

John H. Adams, Ph.D.

Committee Member

Francis B. Ntumngia, Ph.D.

Committee Member

Ricardo Izurieta, Ph.D.

Committee Member

Wei Wang, Ph.D.

Keywords

Epitope mapping, malaria, phage display

Abstract

Plasmodium vivax Duffy binding protein (DBP) is an essential ligand for reticulocyte invasion making it a premier asexual blood stage vaccine candidate. However, strain-specific immunity due to DBPII allelic variation may complicate vaccine efficacy, suggesting that an effective DBPII vaccine needs to target immune responses to conserved epitopes that are potential targets of strain-transcending neutralizing immunity. Anti DBPII monoclonal antibodies, which were previously characterized by COS7 cell binding assay as inhibitory and non-inhibitory to DBPII-erythrocyte binding, were mapped to DBPII gene fragment libraries using phage display. Inhibitory mAb 3C9 binds to a conserved conformation-dependent epitope in subdomain 3 while non-inhibitory mAb 3D10 binds to a linear epitope in subdomain 1 of DBPII.

More definitive epitope mapping of mAb 3D10 was achieved using a random peptide library displayed on phage. Since DBP region II is mostly made up of alpha-helices, we used a randomized helical scaffold library, the Affibody library, displayed on phage, to determine epitope of conformation-dependent antibodies.

The immunogenicity of the identified epitopes was evaluated in mice and the immune sera evaluated for binding to DBPII by ELISA and inhibition of DBPII-erythrocyte binding by the COS7 cell assay. Immune serum from the mAb3C9 epitope blocked DBPII-erythrocyte, suggesting this epitope could be a good subunit vaccine target.

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