The hookworm Ancylostoma ceylanicum intestinal transcriptome provides a platform for selecting drug and vaccine candidates.

Junfei Wei,Xin Gao,Ulrich Strych,Ashish Damania,Zhuyun Liu,Peter J Hotez,Makedonka Mitreva,Rojelio Mejia,Bin Zhan,Maria Elena Bottazzi

doi:10.1186/s13071-016-1795-8

Abstract

BackgroundThe intestine of hookworms contains enzymes and proteins involved in the blood-feeding process of the parasite and is therefore a promising source of possible vaccine antigens. One such antigen, the hemoglobin-digesting intestinal aspartic protease known as Na-APR-1 from the human hookworm Necator americanus, is currently a lead candidate antigen in clinical trials, as is Na-GST-1 a heme-detoxifying glutathione S-transferase.MethodsIn order to discover additional hookworm vaccine antigens, messenger RNA was obtained from the intestine of male hookworms, Ancylostoma ceylanicum, maintained in hamsters. RNA-seq was performed using Illumina high-throughput sequencing technology. The genes expressed in the hookworm intestine were compared with those expressed in the whole worm and those genes overexpressed in the parasite intestine transcriptome were further analyzed.ResultsAmong the lead transcripts identified were genes encoding for proteolytic enzymes including an A. ceylanicum APR-1, but the most common proteases were cysteine-, serine-, and metallo-proteases. Also in abundance were specific transporters of key breakdown metabolites, including amino acids, glucose, lipids, ions and water; detoxifying and heme-binding glutathione S-transferases; a family of cysteine-rich/antigen 5/pathogenesis-related 1 proteins (CAP) previously found in high abundance in parasitic nematodes; C-type lectins; and heat shock proteins. These candidates will be ranked for downstream antigen target selection based on key criteria including abundance, uniqueness in the parasite versus the vertebrate host, as well as solubility and yield of expression.ConclusionThe intestinal transcriptome of A. ceylanicum provides useful information for the identification of proteins involved in the blood-feeding process, representing a first step towards a reverse vaccinology approach to a human hookworm vaccine.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1795-8) contains supplementary material, which is available to authorized users.

Highlights

The intestine of hookworms contains enzymes and proteins involved in the blood-feeding process of the parasite and is a promising source of possible vaccine antigens
Among the lead candidate antigens are Na-APR-1, a cathepsin-D aspartic protease required for hemoglobin digestion and Na-Glutathione-S transferase (GST)-1, a glutathione-S transferase involved in detoxification of toxic heme derived from hemoglobin digestion – both molecules induce significant protective immunity in vaccinated animals against hookworm infection [16, 17]
Comparison of the FPKM value for the intestine expressed transcripts with the corresponding gene FPKM-derived from the transcriptome of the whole A. ceylanicum male worm, resulting in 964 genes being expressed at significantly higher level in the A. ceylanicum intestine than in the whole worm based on the Fisher’s exact test in Bioconductor package edgeR [32] (Table 1)

Summary

Introduction

The intestine of hookworms contains enzymes and proteins involved in the blood-feeding process of the parasite and is a promising source of possible vaccine antigens One such antigen, the hemoglobin-digesting intestinal aspartic protease known as Na-APR-1 from the human hookworm Necator americanus, is currently a lead candidate antigen in clinical trials, as is Na-GST-1 a heme-detoxifying glutathione S-transferase. Among the lead candidate antigens are Na-APR-1, a cathepsin-D aspartic protease required for hemoglobin digestion and Na-GST-1, a glutathione-S transferase involved in detoxification of toxic heme derived from hemoglobin digestion – both molecules induce significant protective immunity in vaccinated animals against hookworm infection [16, 17] These two antigens have been selected as the leading hookworm vaccine antigens for product development and are currently in phase 1 clinical trials [1, 8]. This issue had previously thwarted other vaccine development efforts for infective larval stage-derived antigens [19]

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Conclusion