Hookworm is a blood feeding helminthes that infects more than 700 million people worldwide, predominantly in regions with low socioeconomic conditions.1 Hookworm moulds into 5 different stages in its life cycle. The different stages resulted in difficulties in selection of specific vaccine target against the parasite due its biological reformations. Thus, it is preferably to develop a vaccine that can target at least two of the five hookworm stages to combat the hematophagous parasite.
Two critical hookworm enzymes were found to be essential in feeding and growth. Hookworm larvae (L3) utilizes aspartic enzyme (ASP-2) during its growth into adult hookworm while adult hookworm exploits aspartic enzyme (APR-1) for haemoglobin digestion during feeding (Figure 1). Vaccine candidates based on these two proteins resulted in reduced faecal egg counts2,3 ; however, APR-1 autodegrades rapidly3 while ASP-2 vaccine trial to individuals previously infected by hookworm resulted in immediate-type hypersensitivity.4 To overcome these problems, subunit peptide based vaccine approach utilizing minimal peptide sequences from the proteins, showed promising results.5
With the aim to conserve the subunit peptides’ secondary structure, a series of subunit peptides vaccines based on APR-1 and ASP2 were designed. To enhance the antigen’s efficacy, peptide sequence modifications and conjugations to lipid core peptide (LCP) delivery system were performed. The peptide series were designed using Peptide Secondary Structure Prediction tools and homology test were performed using UniProt Blast software. LCPs and peptide epitopes were synthesized via solid phase peptide synthesis (SPPS). Products were analysed using transmission electron microscopy (TEM), dynamic light scattering (DLS), and circular dichroism (CD). We demonstrated that these vaccine candidates were able to self-assemble to form particles. The peptides were also verified to have the desired conformation upon conjugation to the LCP system.