A double-blind, placebo-controlled study of Mycobacterium-specific human immune responses induced by intradermal bacille Calmette-Guérin vaccination.

Recent studies have indicated that type 1 T cell responses (potent interferon-gamma and cytolytic responses, with absence of interleukin-4 production) are important for protective immunity against mycobacteria. These observations suggest that assays of type 1 T cell responses may be useful as surrogate markers of protective immunity in the evaluation of new tuberculosis vaccines. To be useful as surrogate markers, immunologic assays must distinguish between vaccine recipients and control subjects in clinical trials. Previous studies have shown that bacille Calmette-Guérin (BCG) vaccination can induce human type 1 T cell responses, but randomized trials have not been done to determine whether measurement of these responses can distinguish between BCG recipients and control subjects. We have conducted a double-blind, placebo-controlled trial of intradermal vaccination with two different BCG strains. We compared the mean lymphoproliferative, cytotoxic, Th1 and Th2 cytokine, and antibody responses detected in BCG and placebo recipients. These studies demonstrated that significant increases in Mycobacterium-specific T cell proliferative responses and type 1 cytokine responses were induced by BCG when compared with results with a placebo. In addition, BCG induced significant increases in Mycobacterium-specific antibody responses with an isotype profile characteristic of a type 1 cytokine bias. T cell and antibody assays involving the use of mycobacterial whole cell lysates or live BCG were able to discriminate between BCG and placebo recipients better than were assays using mycobacterial culture filtrates. These studies provide important information for the development of immunologic assays that might be useful as surrogate markers of protective immunity in future trials of new tuberculosis vaccines.

Immune responses stimulated by percutaneous and intradermal bacille Calmette-Guérin.

Healthy volunteers were randomized to receive percutaneous or intradermal bacille Calmette-Guérin (BCG) vaccination. Delayed-type hypersensitivity (DTH) to tuberculin, as well as proliferative and interferon-gamma responses in peripheral blood mononuclear cells stimulated by whole cell lysates and culture filtrates of Mycobacterium tuberculosis and Mycobacterium avium-intracellulare, were compared before and after vaccination. Positive DTH reactions were detected in 83% of intradermal and 40% of percutaneous BCG recipients 3 months after vaccination (P < .004). M. tuberculosis-specific proliferation was increased after intradermal BCG (P < .01) but not after percutaneous BCG compared with prevaccination responses. In addition, M. tuberculosis-specific interferon-gamma production was increased after intradermal BCG compared with both prevaccination responses (P < .04) and those measured after percutaneous BCG (P < .05). Predominant immune responses stimulated by BCG were directed against antigens present in mycobacterial whole cell lysate. These results indicate that the BCG vaccination route can affect both in vivo and in vitro immune responses.