CELLULAR IMMUNE-RESPONSES TO 4 DOSES OF PERCUTANEOUS BACILLE CALMETTE-GUERIN IN HEALTHY-ADULTS

To explore the hypothesis that low-dose immunization might induce pref erential Th1 cell immunity, 76 adults were vaccinated with one of four doses of bacille Calmette-Guerin (BCG):The doses contained very low ( 1.6 X 10(5) cfu), low (3.2 x 10(6) cfu), standard (1.6 x 10(8) cfu), o r high (3.2 x 10(8) cfu) levels of BCG. Delayed-type hypersensitivity responses occurred 8 weeks after vaccination in 10% of persons given v ery low or low doses of BCG, compared with 95% and 100% of persons giv en standard or high doses, respectively. Lymphoproliferative responses , which were increased only for high-dose vaccinees, peaked 2 weeks af ter vaccination and were directed chiefly against Mycobacterium tuberc ulosis-secreted proteins, particularly the antigen 85 complex. Signifi cant increases in mycobacteria-specific interferon-gamma expression we re present 16 weeks after vaccination only for persons given standard or high doses of BCG. Percutaneous BCG appears capable of inducing a t emporary Th1-like immune response, but standard or higher dosages are required.