DNA vaccine encoding the moonlighting protein Onchocerca volvulus glyceraldehyde-3-phosphate dehydrogenase (Ov-GAPDH) leads to partial protection in a mouse model of human filariasis.

River blindness, caused by the filarial parasite Onchocerca volvulus, is a major socio-economic and public health problem in Sub-Saharan Africa. In January 2015, The Onchocerciasis Vaccine for Africa (TOVA) Initiative has been launched with the aim of providing new tools to complement mass drug administration (MDA) of ivermectin, thereby promoting elimination of onchocerciasis in Africa. In this context we here present Onchocerca volvulus glyceraldehyde-3-phosphate dehydrogenase (Ov-GAPDH) as a possible DNA vaccine candidate. We report that in a laboratory model for filariasis, immunization with Ov-GAPDH led to a significant reduction of adult worm load and microfilaraemia in BALB/c mice after challenge infection with the filarial parasite Litomosoides sigmodontis. Mice were either vaccinated with Ov-GAPDH.DNA plasmid (Ov-pGAPDH.DNA) alone or in combination with recombinantly expressed Ov-GAPDH protein (Ov-rGAPDH). During the following challenge infection of immunized and control mice with L. sigmodontis, those formulations which included the DNA plasmid, led to a significant reduction of adult worm loads (up to 57% median reduction) and microfilaraemia (up to 94% reduction) in immunized animals. In a further experiment, immunization with a mixture of four overlapping, synthetic Ov-GAPDH peptides (Ov-GAPDHpept), with alum as adjuvant, did not significantly reduce worm loads. Our results indicate that DNA vaccination with Ov-GAPDH has protective potential against filarial challenge infection in the mouse model. This suggests a transfer of the approach into the cattle Onchocerca ochengi model, where it is possible to investigate the effects of this vaccination in the context of a natural host-parasite relationship.

Molecular and functional characterisation of the heat shock protein 10 of Strongyloides ratti.

Strongyloides stercoralis and S. ratti are intestinal parasitic nematodes infecting rats and humans, respectively. Both present extraordinary life cycles comprising a free-living generation in addition to parasitic stages. In search of molecules possibly involved in parasite-host interaction, we performed mass spectrometry to identify excretory/secretory products of S. ratti. Amongst others we detected homologs of the heat shock proteins HSP10 and HSP60 (Sr-HSP10 and Sr-HSP60). HSPs are well known as chaperones involved in stress responses of cells, but recent studies suggest additional roles of small HSPs for parasite biology including immune modulation. To characterise Sr-HSP10, we cloned its full-length cDNA, analysed the genomic organisation, tested its presumptive role as an interaction partner of Sr-HSP60, studied its transcription in the parasite, and expressed the protein to test its immune responses. The cDNA contains an open reading frame of 330bp encoding a polypeptide of 110 amino acids with an approximate molecular weight of 10kDa. The Sr-HSP10 protein is highly homologous to that of the human pathogen S. stercoralis with only eight amino acid substitutions. Analysis of the genomic organisation of the Sr-HSP10 locus revealed that the gene is linked head-to-head to the gene encoding Sr-HSP60, and both share a bidirectional promoter. RT-PCR experiments indicated potential independent expression of the Sr-HSPs genes. In situ hybridisation results demonstrate Sr-HSP10 transcription in the gut area. Mammalian and yeast two-hybrid assays show dimerisation of Sr-HSP10, but no binding to recombinant Sr-HSP60. Immunisation experiments finally revealed a strong immunogenicity of Sr-HSP10 and provided evidence for a role in regulating the host-parasite interaction.