DNA immunization with Onchocerca volvulus genes, Ov-tmy-1 and OvB20: serological and parasitological outcomes following intramuscular or GeneGun delivery in a mouse model of onchocerciasis.

The objective of this study was to evaluate whether the distinct immune responses invoked by epidermal and intramuscular DNA immunization could be harnessed to improve upon the levels of protection to Onchocerca volvulus infective larvae achieved previously by recombinant protein immunization. Intramuscular (IM) and epidermal (GeneGun) routes of DNA immunization generally drive T helper1 and Th2 dominant responses, respectively. This dichotomy was used in an attempt to further define the nature of host-protective immunity in a mouse model of onchocerciasis. Mice were immunized with DNA plasmids expressing the O. volvulus antigens, Ov-TMY-1 (tropomyosin) and OvB20 (a nematode specific gene product). While, IM and GeneGun immunization of mice with Ov-tmy-1 induced expected Th1/Th2-associated IgG isotype profiles, mice responded to OvB20 immunization with a Th2 dominant response, irrespective of the delivery route. Despite inducing potent serological responses, neither DNA construct promoted statistically significant levels of protection to L3 challenge infection. We conclude that DNA immunization has good potential for induction of humoral responses against nematode infections and that serological responses alone do not predict vaccination efficacy under the conditions used here to measure host resistance to parasite challenge.