PROTECTION AGAINST LEISHMANIA-MAJOR INFECTION IN GENETICALLY SUSCEPTIBLE BALB C MICE BY GP63 DELIVERED ORALLY IN ATTENUATED SALMONELLA-TYPHIMURIUM (AROA(-) AROD(-))/

The gene encoding the Leishmania major (L. major) promastigote surface glycoprotein, gp63, was introduced into the Salmonella typhimurium (S . typhimurium) aroA(-) aroD(-) live oral vaccine strain BRD509 and exp ressed under the control of a constitutive tac promoter in plasmid pKK 233-2. This construct (GID101) expressed gp63 in vitro and was used to immunize highly susceptible BALB/c mice by the oral route. The plasmi d was relatively stably inherited by bacteria growing or persisting in the mesenteric lymph nodes of immunized mice. Mice immunized with GID 101 developed significant resistance against a challenge infection wit h L. major compared to controls immunized with BRD509 alone. Spleen an d lymph node cells from immunized mice developed a strong in vitro pro liferative T-cell response to killed or live L. major. The activated T cells secreted interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) which was abrogated by treatment with anti-CD4 but not with anti-CD8 a ntibody. The cells did not produce detectable levels of interleukin-4 (IL-4). The immunized mice also produced significant amounts of leishm anial specific IgG2a antibody but did not develop delayed-type hyperse nsitivity (DTH) to live parasites. No IgG1 antibody was detected. Thes e data therefore demonstrate that gp63 gene delivered orally by a vacc ine strain of S. typhimurium can preferentially induce the development of Th-l subset of CD4(+) T cells and protective immunity in the highl y susceptible BALB/c mice.