Genetic Approaches to the Control of Mycobacterial Disease 
growing mycobacterium, M. smegmatis. These 
exhibit high plasmid transformation frequencies 
and thus provide a most useful surrogate host for 
analyzing the genes of slow-growing pathogenic 
mycobacteria. 
Genetic Analysis of Mycobacterial 
Virulence Determinants 
A major focus of this laboratory is to elucidate 
the causal mechanisms of mycobacterial diseases 
by identifying the genes responsible for specific 
virulence characteristics. The systems we have de- 
veloped allow us to introduce libraries of genes 
from virulent mycobacteria into avirulent strains 
with great efficiency. A complementary strategy 
is the generation of specific mutants that no 
longer are virulent in our animal models. The 
combination of these strategies has allowed us to 
identify a number of genes necessary for the bio- 
synthesis of amino acids, purines, and complex 
polysaccharides found on the surface of the 
pathogenic mycobacteria. By identifying the 
genes and their products responsible for viru- 
lence, we hope to be able to design approaches to 
the control of mycobacterial disease. In addition, 
the genetically engineered avirulent mutants 
should provide promising vaccine candidates. 
Genetic Analysis of Drug Targets of the 
Pathogenic Mycobacteria 
Although there are various efi'ective antibiotics 
for tuberculosis and leprosy, antibiotic-resistant 
bacteria are continually emerging as a major pub- 
lic health problem here and abroad. Moreover, 
there is no effective chemotherapy for M. avium 
infections. We are employing genetic approaches 
to identify the mechanisms of action of present 
anti-mycobacterial antibiotics and the mecha- 
nisms of resistances to these antibiotics. The ba- 
sic information so acquired should lead to the 
design of more effective drugs, strategies to over- 
come resistances, and diagnostic tests to detect 
mycobacterial strains containing resistance-con- 
ferring genes. We hope that improved strategies 
for treating leprosy, tuberculosis, and other myco- 
bacterial infections can be developed. 
Development of Recombinant BCG Vaccines 
By cloning and introducing foreign antigen 
genes into BCG, it may be possible to develop 
novel vaccines that would protect not only 
against tuberculosis but also against the pathogen 
from which the foreign gene was obtained. In col- 
laboration with Barry Bloom (HHMI, Albert Ein- 
stein College of Medicine) and colleagues at 
Medlmmune and the University of Pittsburgh, we 
are developing systems to express foreign anti- 
gens from a variety of parasitic, viral, and bacte- 
rial pathogens. We have devoted considerable ef- 
fort to elucidating the mycobacterial genetic 
signals necessary for expression and stable repli- 
cation of foreign genes. Preliminary results dem- 
onstrate that high levels of foreign proteins can 
be produced in BCG and that these recombinant 
vaccines can elicit both humoral and cellular im- 
mune responses in infected animals. It is our 
hope that recombinant BCG will not only yield 
effective vaccines but also provide a novel and 
useful tool for studying immune responses in 
mammalian hosts. 
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