Mapping the epitopes of Schistosoma japonicum esophageal gland proteins for incorporation into vaccine constructs

Abstract

BackgroundThe development of a schistosome vaccine has proved challenging but we have suggested that characterisation of the self-cure mechanism in rhesus macaques might provide a route to an effective product. The schistosome esophagus is a complex structure where blood processing is initiated by secretions from anterior and posterior glands, achieved by a mixture of~40 unique proteins. The mechanism of self-cure in macaques involves cessation of feeding, after which worms slowly starve to death. Antibody coats the esophagus lumen and disrupts the secretory processes from the glands, potentially making their secretions ideal vaccine targets. Methodology/Principal findingsWe have designed three peptide arrays comprising overlapping 15-mer peptides encompassing 32 esophageal gland proteins, and screened them for reactivity against 22-week infection serum from macaques versus permissive rabbit and mouse hosts. There was considerable intra-and inter-species variation in response and no obvious unique target was associated with self-cure status, which suggests that self-cure is achieved by antibodies reacting with multiple targets. Some immuno-dominant sequences/regions were evident across species, notably including: MEGs 4.1C, 4.2, and 11 (Array 1); MEG-12 and Aspartyl protease (Array 2); a Tetraspanin 1 loop and MEG-n2 (Array 3). Responses to MEGs 8.1C and 8.2C were largely confined to macaques. As proof of principle, three synthetic genes were designed, comprising several key targets from each array. One of these was expressed as a recombinant protein and used to vaccinate rabbits. Higher antibody titres were obtained to the majority of reactive regions than those elicited after prolonged infection.

Epitope Mapping of Exposed Tegument and Alimentary Tract Proteins Identifies Putative Antigenic Targets of the Attenuated Schistosome Vaccine

“…Peptide Microarrays were screened exactly as described in Li et al ( 35 ); see Supplementary Figure 2 for a flow chart. Mouse primary antibodies were applied at a 1:200 dilution throughout.…”

“…Beginning in the 1980s, strenuous efforts were made to characterize the composition and antigenicity of the schistosome tegument, as a major parasite interface with the host, and potential target of immune attack. Techniques included biosynthetic labeling with 35 S methionine and iodination of surface proteins, linked to immunoprecipitation and separation of proteins on 1D and 2D gels (12). Isolated membranes of the adult worm tegument (13) were also used to probe both human (14) and rodent (15) responses to schistosome infection, using western blotting.…”

“…The approach has been used to identify epitopes in infectious agents as diverse as viruses, bacteria, protozoa and helminths (31)(32)(33)(34). Recently, the technology was applied to map the epitopes present in 32 S. japonicum esophageal gland proteins using macaque, rabbit and mouse sera, and identified a significant number of immunodominant sequences for incorporation into vaccine constructs (35). The current report is a companion study to the systems biology analysis (30) using sera generated from vaccinated and infected C57Bl/6 mice, supplemented by high titer serum from IFNgR KO mice (36), to screen peptide arrays for reactivity to 55 secreted and surfaceexposed proteins of S. mansoni.…”

The esophageal gland mediates host immune evasion by the human parasiteSchistosoma mansoni

“…Thus, schistosome FoxA likely regulates transcription of genes underlying differentiation and/or proper function of the esophageal gland. Identifying genes downstream of FoxA may reveal new targets to selectively disrupt esophageal gland function, facilitating schistosome killing by host immunity ( 57 ). Because the esophageal gland develops during larval stages, such targets also have the potential to act on immature worms, in contrast to praziquantel, which is only effective against adults ( 1 , 58 ).…”

Recent Progress in the Development of Liver Fluke and Blood Fluke Vaccines

“…In the past several decades, over 100 schistosome antigens have been advanced as possible vaccines [ 63 , 65 ], and recently developed approaches provide an avenue to identify and test additional candidate molecules for protective efficacy [ 66 , 67 , 68 ]. Indeed, many proteins are exposed at, or released from, the parasite–host interface so many other possibilities remain for potential vaccine exploitation.…”