Initial clinical trial of Mycobacterium tuberculosis antigen 5 in tuberculin-positive human subjects.

A single lot of Mycobacterium tuberculosis antigen 5 was used in graded doses to skin test 92 persons in a geographic area where nonspecific tuberculin reactivity is uncommon. In 47 tuberculin-positive subjects, antigen 5 was found to have a potency of 2.7 tuberculin units/micrograms. An intradermal dose of 0.50 microgram was found to give typical delayed skin test reactions in all of 15 tuberculin-positive subjects, with a mean reaction size of 15.17 mm. Some preparations of antigen 5 were found to be unstable during lyophilization and storage; solutions of antigen 5 in diluent containing Tween 80 were stable. Mycobacterium tuberculosis antigen 5 is a potent tuberculin skin test antigen deserving of further clinical evaluation.