title: Vaccination against experimental cutaneous leishmaniasis using attenuated Salmonella typhimurium
Creators: name: McSorley, Stephen Joseph
Publisher: name: University of Glasgow
Year: 1995
Subjects: subject: Pharmacology, Parasitology.

description: The Salmonella typhimurium vaccine construct, GIDl0l, which constitutively expresses L. major gp63 was used as an oral vaccine against experimental cutaneous leishmaniasis in the susceptible BALB/c mouse. After 2 oral immunisations with GID101, lesion development was reduced following L. major infection. This vaccine therefore represents a considerable improvement over the previous attenuated S. typhimurium vaccine SL3261-gp63 which was unable to confer any protection to susceptible mice. After two oral doses of GIDl0l, spleen and mesenteric lymph node (MLN) cells from BALB/c mice were found to proliferate in vitro to parasite antigens and produce substantial amounts of IFN-gamma and IL-2 but no IL-4 or IL-5. The production of these cytokines was CD4+-cell dependant. Serum taken from immunised mice was found to contain parasite specific IgG2a but no parasite specific IgGl. In addition, no delayed type hypersensitivity (DTH) response to L. major was detected in vaccinated mice. These data are consistent with the notion that GID101 administration results in the induction of a protective Th1-like response to L. major. L. major gp63 was also expressed in the attenuated S. typhimurium strain, BRD509, under the control of either the nirB promoter which responds to anaerobic conditions (GID105) or the osmC promoter which is induced under high salt conditions (GID106). The construct GID105 displays more stable plasmid retention during colonisation in vivo when compared with the constitutive construct GID101. After oral administration, the construct GID106 does not colonise spleen or liver at all although it is found in the MLN. In addition, this construct loses plasmid more quickly m vivo compared to the GID101 strain. An antibody response to gp63 is generated in BALB/c mice after one oral dose of GID101, GID105 or GID106, while only the anaerobic construct GID105 is able to induce a significant cellular response to antigen. Spleen and MLN cells from mice administered GID105 respond in vitro to parasite antigen in a Thl-like manner. A single oral delivery of GID105 or GID106 is sufficient to reduce lesion swelling in susceptible mice after L. major infection, while a single dose of GID1041 does not confer any protection. Two doses of GID105 also reduces liver parasite burdens during L. donovani infection, while GID101 or GID106 provide no protection. Therefore construct GID105 can confer a degree of protection to L. major infection after a single oral dose and to L. donovani after two doses, representing a further improvement of the gp63 construct. A plasmid was generated which contains the cDNA for L. major p24/LACK under control of the inducable NirB promoter. This plasmid was introduced into the attenuated S. typhimurium strain BRD509. Expression of p24 by this construct (GID202) was demonstrated under anaerobic conditions by western blotting. After oral administration of GID202 to BALB/c mice bacteria were detected in the spleen, liver and MLN from around 3-7 days post administration until 21-28 days. Plasmid stability of the construct during colonisation was found be around 100% in all organs. BALB/c mice which were orally administered one or two doses of GID202 before L. major infection developed exacerbated disease. CBA mice given two oral doses of GID202 also generated an exacerbated infection although CBA mice which received a single dose were slightly protected. Spleen and MLN cells from mice administered GID202 responded in vitro in a Thl-like manner to both recombinant p24 and the immunodominant peptide of p24. These data demonstrate a disease-promoting effect of vaccination with p24 expressed in S. typhimurium correlating with a normally protective Th1 response in vitro.