Dose-dependent immunogenicity of a soluble Neospora caninum tachyzoite-extract vaccine formulated with a soy lecithin/β-glucan adjuvant in cattle

Abstract

Mice immunized with a soluble extract of Neospora caninum tachyzoites (sNcAg) formulated with Providean-AVEC®, an aqueous soy-based adjuvant, are fully protected from N. caninum multiplication. Here we evaluated the dose-dependent immunogenicity of this vaccine formulation in cattle. Cattle (N=3 per group) were immunized with two applications (30 days apart) of formulations containing Providean-AVEC® and different payloads of sNcAg (100, 50 and 10μg), that were five to fifty times lower than the only reported study using this same antigen in cattle. Kinetics and magnitude of the vaccine-induced immune responses were dose-dependent. Cattle immunized with 100μg-sNcAg elicited high-avidity specific antibodies 3 weeks after the primary vaccination while those that received 50μg of antigen had maximum levels of specific high-avidity antibodies 5 days after the day 30 boost. Vaccination with 10μg of sNcAg induced comparable antibody responses after 2 weeks post re-vaccination. IgG1 was the predominant isotype in all vaccinated animals. Maximum systemic IFN-γ levels were measured in cattle immunized with 50 and 100μg-sNcAg (14±2.8ng/ml). CD4+-T cells from vaccinated animals proliferated after sNcAg stimulation in vitro, producing IFN-γ. Recall IFN-γ responses mediated by CD4+-T cells were detected up to 140 days post vaccination. Formulations containing Providean-AVEC® and 50μg of sNcAg stimulated broad cellular and humoral immune responses against N. caninum in cattle. The profile and magnitude of the immune response elicited by this vaccine can be modified by the antigen-dose and vaccination schedule. This is the first dose-response study performed in cattle using sNcAg as antigen.