Uptake of Schistosoma mansoni extracellular vesicles by human endothelial and monocytic cell lines and impact on vascular endothelial cell gene expression.

The ability of the parasitic blood fluke Schistosoma mansoni and other parasitic helminths to manipulate host biology is well recognised, but the mechanisms that underpin these phenomena are not well understood. An emerging paradigm is that helminths transfer their biological cargo to host cells by secretion of extracellular vesicles (EVs). Herein, we show that two populations of S. mansoni secreted EVs - exosome-like vesicles (ELVs) and microvesicles (MVs) - are actively internalised in two distinct human cell lines that reflect the resident cell types encountered by the parasite in vivo: human umbilical vein endothelial cells (HUVECs) and THP-1 monocytes. RNA-sequencing of HUVECs co-cultured with S. mansoni ELVs compared with untreated HUVECs revealed differential expression of genes associated with intravascular parasitism, including vascular endothelial contraction, coagulation, arachidonic acid metabolism and immune cell trafficking and signalling. Finally, we show that antibodies raised against recombinant tetraspanin (TSP) proteins from the surface of S. mansoni EVs significantly blocked EV uptake by both HUVECs and THP-1 monocytes whereas pre-immunisation antibodies did not. To our knowledge, this is the first evidence demonstrating the internalisation of secreted EVs from any helminth into vascular endothelial cells, providing novel insight into the potential mechanisms underlying host-schistosome interactions. The ability of anti-TSP antibodies to block vesicle uptake by host target cells further supports the potential of TSPs as promising antigens for an anti-fluke vaccine. It also suggests a potential mechanism whereby the current candidate human schistosomiasis vaccine, Sm-TSP-2, exerts its protective effect in animal models.

Proteomic analysis of two populations of Schistosoma mansoni-derived extracellular vesicles: 15k pellet and 120k pellet vesicles.

Helminth parasites secrete extracellular vesicles (EVs) into their environment that have potential roles in host-parasite communication, and thus represent potentially useful targets for novel control strategies. Here, we carried out a comprehensive proteomic analysis of two different populations of EVs - 15k pellet and 120k pellet EVs - from Schistosoma mansoni adult worms. We characterised the proteins present in the membranes of the EVs (including external trypsin-liberated peptides, integral membrane proteins (IMPs) and peripheral membrane proteins (PMPs)), as well as cargo proteins, using LC-MS/MS. A total of 286 and 716 proteins were identified in 15k and 120k pellets, respectively. Some of the most abundant proteins identified from both 15k and 120k pellets include known vaccine candidates such as Sm-TSP-2, saponin B domain-containing proteins, calpain glutathione-S-transferase, Sm29 and cathepsin domain-containing proteins. Other abundant proteins that have not been tested as vaccines include DM9 domain-containing protein, 13 kDa tegumental antigen and histone H4-like protein. Sm23, a member of the tetraspanin family with known vaccine efficacy, was identified in the cargo and IMP compartments of only 15k pellet vesicles. Moreover, a collection of proteins with known or potential relevance in host-parasite communication including proteases, antioxidants and EV biogenesis/trafficking of both vesicle types were identified. Our results provide the first report of a comprehensive compartmental proteomic analysis of adult S. mansoni-derived EVs. Future research should investigate recombinant forms of these proteins as vaccine and serodiagnostic antigens as well as the roles of EV proteins in host-parasite communication.

Extracellular vesicles as a target for the development of anti-helminth vaccines.

There is a rapidly growing body of evidence that production of extracellular vesicles (EVs) is a universal feature of cellular life. More recently, EVs have been identified in a broad range of both unicellular and multicellular parasites where they play roles in parasite-parasite intercommunication as well as parasite-host interactions. Parasitic helminth-derived EVs traverse host target cell membranes whereupon they offload their molecular cargo - proteins, lipids, and genetic information such as mRNAs and miRNAs - which are thought to hijack the target cell and modulate its gene expression to promote parasite survival. As such, EVs represent a novel mechanism of intercellular communication that could be targeted for vaccine-mediated interruption, given the abundance of surface antigens expressed on helminth EVs, and the ability of antibodies to block their uptake by target cells. In this Perspective article, we review recent developments in the field of helminth-derived EVs and highlight their roles in helminth vaccine discovery and development.