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Infection and Immunity, June 2000, p. 3097-3102, Vol. 68, No. 6
Laboratory of Mycobacteria, Center for
Biologics Evaluation and Research, Food and Drug Administration,
Bethesda, Maryland 20892
Received 24 September 1999/Returned for modification 14 February
2000/Accepted 25 February 2000
Genetic immunization is a promising new technology for developing
vaccines against tuberculosis that are more effective. In the present
study, we evaluated the effects of intracellular turnover of antigens
expressed by DNA vaccines on the immune response induced by these
vaccines in a mouse model of pulmonary tuberculosis. The mycobacterial
culture filtrate protein MPT64 was expressed as a chimeric protein
fused to one of three variants of the ubiquitin protein (UbG, UbA, and
UbGR) known to differentially affect the intracellular processing of
the coexpressed antigens. Immunoblot analysis of cell lysates of in
vitro-transfected cells showed substantial differences in the
degradation rate of ubiquinated MPT64 (i.e., UbG64 < UbA64 < UbGR64). The specific immune response generated in mice correlated
with the stability of the ubiquitin-conjugated antigen. The UbA64 DNA
vaccine induced a weak humoral response compared to UbG64, and a mixed
population of interleukin-4 (IL-4)- and gamma interferon
(IFN-
0019-9567/00/$04.00+0
DNA Vaccination against Tuberculosis: Expression of
a Ubiquitin-Conjugated Tuberculosis Protein Enhances
Antimycobacterial Immunity
)-secreting cells. Vaccination with the UbGR64 plasmid
generated a strong Th1 cell response (high IFN-
, low IL-4) in the
absence of a detectable humoral response. Aerogenic challenge of
vaccinated mice with Mycobacterium tuberculosis indicated
that immunization with both the UbA64- and UbGR64-expressing plasmids
evoked an enhanced protective response compared to the vector control.
The expression of mycobacterial antigens from DNA vaccines as fusion
proteins with a destabilizing ubiquitin molecule (UbA or UbGR) shifted
the host response toward a stronger Th1-type immunity which was
characterized by low specific antibody levels, high numbers of
IFN-
-secreting cells, and significant resistance to a tuberculous challenge.
*
Corresponding author. Mailing address: Laboratory of
Mycobacteria, OVRR/CBER/FDA, HFM-431, Bldg. 29, Rm. 502, 29 Lincoln
Dr., Bethesda, MD 20892. Phone: (301) 496-5978. Fax: (301) 402-2776. E-mail: morris{at}cber.fda.gov.
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