Vaccine efficacy of a lysine auxotroph of Mycobacterium tuberculosis

Abstract

The in vivo growth phenotype and vaccine efficacy of a lysine auxotrophic mutant of Mycobacterium tuberculosis strain H37Rv are described. An immunization experiment using a mouse model with an aerosol challenge showed that two doses of the M. tuberculosis mutant were required to generate protection equivalent to that of the Mycobacterium bovis BCG vaccine.

FIG. 1.

Vaccine efficacy of the M. tuberculosis lysine auxotroph mc²3026. C57BL/6 mice were injected intravenously with 10⁶ CFU of the M. tuberculosis lysine auxotroph mc²3026, followed by one or two additional injections at 4-week intervals. Five mice were sacrificed weekly after each immunization, and the viable bacteria counts of the auxotroph were determined for the lungs and spleens. Control mice were given a similar amount of BCG-Pasteur or PBST only. (A) Clearance of the auxotroph from the lungs of mice after each immunization period. Closed squares, one injection; closed diamonds, two injections; closed circles, three injections. Three months after the initial immunization the vaccinated and control mice were challenged with virulent M. tuberculosis Erdman by the aerosol route. Five mice were sacrificed following the challenge period, and the lung homogenates were plated to check the viable counts of the challenge inoculum. Groups of vaccinated and control mice were sacrificed 14, 28, and 42 days later, and the lung and spleen homogenates were plated to determine viable CFU. (B) Viable challenge bacteria per lung in mice given one dose of the M. tuberculosis lysine auxotroph. (C) Viable challenge bacteria per lung in mice given two doses of the auxotroph. Closed squares, viable challenge bacteria per lung in mice given the M. tuberculosis lysine auxotroph mc²3026; open diamonds, viable challenge bacteria per lung in mice given BCG-Pasteur; open circles, viable challenge bacteria per lung in mice given PBST. P values are indicated in the figure. Note that the results shown here are for the lungs. Similar results (not shown) were obtained for the spleens in all the experiments.

FIG. 2.

Survival curves for mice immunized three times with the M. tuberculosis lysine auxotroph mc²3026. C57BL/6 mice were injected intravenously with 10⁶ CFU of the M. tuberculosis lysine auxotroph mc²3026, followed by two more injections at 4-week intervals, and challenged as described in the text. The percent survival is shown for mice immunized thrice with the M. tuberculosis lysine auxotroph mc²3026 (closed squares; 5 mice total), mice immunized once with BCG-Pasteur (closed diamonds; 5 mice), and PBST controls (closed circles; 10 mice).