The lack of therapeutic effects in mice of the combined gamma-irradiated Mycobacterium leprae and viable BCG against Mycobacterium leprae infection.

There are at least two approaches to antileprosy vaccines : One is the use of Mycobacterium leprae derived from M. leprae-infected armadillos (1) and the other is the use of mycobacteria other than M. leprae, which share the antigenic determinants with M. leprae such as M. nonchromogenicum (2), M. vaccae (2), M. simiae (3), M. tuberculosis H37Ra (3), and M, bovis BCG (3). Shepard et al. (3) reported that BCG could sensitize mice against M. leprae, on the basis of development of the delayed type hypersensitivity reactions as measured footpad swelling, and that the sensitizing efficacy of BCG was much more satisfactory than those of the other mycobacteria mentioned above. It was of interest to consider another observation (3) that BCG and M. leprae could provide the enhanced host with resistance against subsequent M. leprae infection. Shepard et al. (4) reported that a vaccine of viable BCG combined with heat-killed M. leprae exhibited a superior protective effect over M. leprae or BCG alone against M. leprae infection, particularly in low doses. The efficacy of the combined vaccine of BCG and killed M. leprae in clinical applications was reported by Convit et al. (5), who observed that the Mitsuda reactions converted to positive in patients administered a mixture of the two mycobacteria, but not of either alone. We gave mice a combined vaccine of gamma-irradiated M. leprae and BCG and the results are reported herein.