The S3Pvac synthetic vaccine, composed of three peptides (GK1, KETc1 and KETc12) effectively protects against cysticercosis under experimental and field conditions. Additionally, S3Pvac vaccine can effectively damage early-established cysticerci in experimentally lightly infected young pigs. This study was designed to explore if also fully-developed cysticerci that eluded immunity induced by the infection can be damaged by S3Pvac-induced immunity in naturally, heavily infected adult pigs. Fourteen pigs identified as cysticercotic by tongue inspection from rural communities were purchased and moved to controlled conditions in the Faculty of Veterinary Medicine. Half of these pigs were treated once a month three times with S3Pvac plus saponin, and the other half received only saponin (controls). Twelve months later pigs were euthanized, and the number of cysticerci, their macro and microscopic status and their capacity to transform into tapeworms were determined. S3Pvac failed to damage fully-developed muscle cysticerci of naturally, heavily infected adult pigs. To explore possible factors involved in the failure of the therapeutic capacity pooled sera from control and treated cysticercotic pigs were added to mice mononuclear peripheral cells. Pooled sera from non-infected pigs were also tested. Sera from control and treated infected pigs almost completely suppressed the T cell proliferative responses, pointing to the presence of suppressor factors. In conclusion, S3Pvac vaccine failed to damage fully-developed cysticerci in pigs in which a host parasite relationship had evolved after months of infection with immunological implications.
