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.

Original languageEnglish
Pages (from-to)10267-10271
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number22
StatePublished - Oct 24 1995


  • auxotrophic mutant
  • dihydrofolate reductase-thymidylate synthase
  • macrophage
  • mouse
  • trypanosomatid protozoan parasite


Dive into the research topics of 'Development of a safe live Leishmania vaccine line by gene replacement'. Together they form a unique fingerprint.

Cite this