title: Development of a safe live Leishmania vaccine line by gene replacement.
abstract: Vaccination with live Leishmania major has been shown to yield effective immunization in humans; however, this has been discontinued because of problems associated with virulence of the available vaccine lines. To circumvent this, we tested the ability of a dhfr-ts- null mutant of L. major, obtained by gene targeting, to infect and then to vaccinate mice against challenge with virulent L. major. Survival and replication of dhfr-ts- in macrophages in vitro were dependent upon thymidine, with parasites differentiating into amastigotes prior to destruction. dhfr-ts- parasites persisted in BALB/c mice for up to 2 months, declining with a half-life of 2-3 days. Nonetheless, dhfr-ts- was incapable of causing disease in both susceptible and immunodeficient (nu/nu) BALB/c mice. Animal infectivity could be partially restored by thymidine supplementation. When inoculated by the i.v., s.c., or i.m. routes into mice, dhfr-ts- could elicit substantial resistance to a subsequent challenge with virulent L. major. Thus, Leishmania bearing auxotrophic gene knockouts can be safe and induce protective immunity. Potentially, dhfr-ts- could be used as a platform for delivery of immunogens relevant to other diseases.
mesh_terms: D000818:Animals; D018390:Gene Targeting; D006801:Humans; D018320:Leishmania major / Q000254:growth & development* / Q000276:immunology*; D016773:Leishmaniasis, Cutaneous / Q000276:immunology* / Q000517:prevention & control; D008264:Macrophages / Q000469:parasitology; D051379:Mice; D008807:Mice, Inbred BALB C; D008808:Mice, Inbred CBA; D008819:Mice, Nude; D016052:Protozoan Vaccines / Q000276:immunology*; D013045:Species Specificity; D013936:Thymidine / Q000494:pharmacology; D013997:Time Factors; D014613:Vaccines, Attenuated / Q000276:immunology*
chemical_list: D016052:Protozoan Vaccines; D014613:Vaccines, Attenuated; D013936:Thymidine