Genetically modified animals and immunodeficiency.

Mouse strains with defined genetic defects engineered by the method of targeted gene disruption and homologous recombination have furthered our understanding of immune functions at the single gene level. More importantly, these mutant 'gene knockout' mice are powerful in vivo tools to dissect the complex mechanisms of lymphocyte development and function, complementing our broadening knowledge of congenital and acquired human immunodeficiencies.