Adjuvant Effects of Tilorone Hydrochloride (Analog 11,567) with Inactivated Venezuelan Equine Encephalomyelitis Virus Vaccine 1 2

Abstract Tilorone analog 11,567 (BDD) was demonstrated to immunopotentiate Formalin-inactivated Venezuelan equine encephalomyelitis (VEE) TC-83 vaccine in mice and monkeys. The dosage of BDD required for adjuvant effects was different in mice and monkeys. In monkeys, primary and secondary antibody responses were increased (4- and 12-fold greater titers, respectively) when 10 mg/kg of BDD was given with VEE vaccine; however, 100 mg/kg of BDD had no adjuvant effect. Mice given 62 or 250 mg/kg of BDD with undiluted vaccine developed 3- and 4-fold greater antibody titers, respectively, than vaccine controls. The immunopotentiation effect of BDD was most dramatically demonstrated when graded doses (7 to 500 mg/kg) were given with a marginally antigenic dose of VEE vaccine (diluted 1:4). The BDD-vaccine combination induced antibody production, while vaccine administered without adjuvant did not. Antibody titers were significantly higher when 125 (P < 0.001) or 250 (P < 0.05) mg/kg of BDD were given with the diluted vaccine. Administration of 500 mg/kg of BDD did not increase antibody titers. Survival of mice challenged 14 days after vaccination was significantly greater (P < 0.05) in groups administered undiluted VEE vaccine containing BDD than in vaccine controls groups; although survival was not significantly greater than in vaccine groups given Freund's complete (FCA) or incomplete (FIA) adjuvant. However, when BDD was used with marginally antigenic doses of vaccine, survival was significantly greater (P < 0.05) than when FCA or FIA were used as adjuvants. The minimal dose of BDD (125 mg/kg) required to significantly potentiate antibody response to diluted vaccine was near the safety limits as ≥ 250 mg/kg induced skin lesions in mice.