title: T cell epitope regions of the P. falciparum MSP1-33 critically influence immune responses and in vitro efficacy of MSP1-42 vaccines.
abstract: The C-terminal 42 kDa fragments of the P. falciparum Merozoite Surface Protein 1, MSP1-42 is a leading malaria vaccine candidate. MSP1-33, the N-terminal processed fragment of MSP1-42, is rich in T cell epitopes and it is hypothesized that they enhance antibody response toward MSP1-19. Here, we gave in vivo evidence that T cell epitope regions of MSP1-33 provide functional help in inducing anti-MSP1-19 antibodies. Eleven truncated MSP1-33 segments were expressed in tandem with MSP1-19, and immunogenicity was evaluated in Swiss Webster mice and New Zealand White rabbits. Analyses of anti-MSP1-19 antibody responses revealed striking differences in these segments' helper function despite that they all possess T cell epitopes. Only a few fragments induced a generalized response (100%) in outbred mice. These were comparable to or surpassed the responses observed with the full length MSP1-42. In rabbits, only a subset of truncated antigens induced potent parasite growth inhibitory antibodies. Notably, two constructs were more efficacious than MSP1-42, with one containing only conserved T cell epitopes. Moreover, another T cell epitope region induced high titers of non-inhibitory antibodies and they interfered with the inhibitory activities of anti-MSP1-42 antibodies. In mice, this region also induced a skewed TH2 cellular response. This is the first demonstration that T cell epitope regions of MSP1-33 positively or negatively influenced antibody responses. Differential recognition of these regions by humans may play critical roles in vaccine induced and/or natural immunity to MSP1-42. This study provides the rational basis to re-engineer more efficacious MSP1-42 vaccines by selective inclusion and exclusion of MSP1-33 specific T cell epitopes.
authors.affiliation: Department of Tropical Medicine, Medical Microbiology, and Pharmacology, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, United States of America. kae@hawaii.edu
authors.forename: Kae M
authors.initials: KM
authors.lastname: Pusic
authors.forename: Caryn N
authors.initials: CN
authors.lastname: Hashimoto
authors.forename: Axel
authors.initials: A
authors.lastname: Lehrer
authors.forename: Charmaine
authors.initials: C
authors.lastname: Aniya
authors.forename: David E
authors.initials: DE
authors.lastname: Clements
authors.forename: George S
authors.initials: GS
authors.lastname: Hui
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D005260:Female; D006801:Humans; D020066:Merozoite Surface Protein 1 / Q000276:immunology*; D051379:Mice; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000276:immunology*; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
chemical_list: D018984:Epitopes, T-Lymphocyte; D020066:Merozoite Surface Protein 1