Role of the immune response in BCG for bladder cancer.

Intravesical bacillus Calmette-Guérin (BCG) has been shown in prospective, randomized clinical trials to be the treatment of choice for superficial bladder cancer. In this treatment regimen, viable bacteria are introduced into the bladder, provoking an infection which induces the immunological response that initiates antitumour activity. The role of T-lymphocytes and the T-lymphocyte subsets, helper T cells (Th) and cytotoxic T-cells (Tc) in the antitumour response has been evaluated. Depletion of total T, Th or Tc subsets in mice eliminated BCG-mediated antitumour activity. Delayed type hypersensitivity was abrogated only in Th-depleted mice, but the presence of Th-mediated delayed-type hypersensitivity (DTH) was not sufficient for expression of BCG-mediated antitumour activity. There was no evidence for the induction of protective immunity to the tumour after BCG therapy. These results show that T-lymphocytes are required for BCG-mediated antitumour activity and suggest that the antitumour activity mediated by BCG is of a nonspecific immunological type. No specific tumour cell immunity was detected.