New vaccines against tuberculosis are urgently required because of the impr
essive incidence of this disease worldwide and the highly variable protecti
ve efficacy of the current vaccine. The possibility of creating new live va
ccines by the rational attenuation of strains from the Mycobacterium tuberc
ulosis complex was investigated. Two auxotrophic mutants of M. tuberculosis
and M. bovis BCG were constructed by disruption of one of their purine bio
synthetic genes. These mutants appeared unable to multiply in vitro within
mouse bone-marrow derived macrophages. They were also attenuated in vivo in
the mouse and guinea pig animal models. In guinea pigs, the two mutants in
duced strong delayed-type hypersensitivity response to purified protein der
ivative. In a preliminary experiment, the two mutants were compared to the
BCG vaccine for their protective efficacy in a challenge against aerosolize
d virulent M. tuberculosis in the guinea pig model. Both mutants conferred
some level of protection. These experiments demonstrate that the rational a
ttenuation of M. tuberculosis could lead to the design of new candidate liv
e vaccines against tuberculosis.