BCG induced CD4+ cytotoxic T cells from BCG vaccinated healthy subjects: relation between cytotoxicity and suppression in vitro.

Mycobacterial antigen specific cytotoxic T cells killing antigen-pulsed antigen presenting cells (APC) were induced from peripheral blood mononuclear cells (PBMC) of BCG-vaccinated healthy subjects after activation in vitro with BCG. CD8+ depleted cells were as effective as PBMC, indicating that CD4+ cells play a dominant role in this phenomenon. CD4+ T cell clones raised against BCG also exhibited mycobacterial antigen specific cytotoxicity and suppressed BCG-driven selfproliferation. However, the same clones could either suppress or enhance the proliferation of other T cell clones from the same subject. The possible function in vivo of the cytotoxicity mediated by CD4+ T cells is discussed.