Thymidine kinase obliteration: creation of transgenic mice with controlled immune deficiency.

The cell-specific expression of herpes simplex virus 1 thymidine kinase (HSV-1-tk) has provided a simple and highly efficient technique to achieve conditional ablation of targeted cell types in transgenic mice. The ablation is induced by treating transgenic animals expressing HSV-1-tk with the antiherpetic drug ganciclovir. In lymphoid tissues of mice expressing HSV-1-tk from an immunoglobulin promoter, administration of ganciclovir leads to massive destruction of B- and T-cell lineages. Tissues not expressing HSV-1-tk are insensitive to drug treatment. After depletion of greater than 99% of total thymocytes, a number of progenitor cells remain that are able to repopulate all T-cell lineages within 7 days. The ability to control and direct ablation allows for creation of conditional mutant phenotypes at precise periods of development. This technique also provides a potential means to enrich stem cell populations as well as permitting the creation of animal models for particular pathological conditions.