CD58/LFA-3 and IL-12 provided by activated monocytes are critical in the in vitro expansion of CD56+ T cells

A small proportion of human CD3(+) T lymphocytes are known to co-express CD56, an antigen usually restricted in its expression to natural killer (NK) cells. Whereas the in vivo function of CD3 (+) CD56(+) T cells remains unknown. we and others have previously shown that both in vitro and in vivo, these cells can mediate a significantly greater degree of MHC-unrestricted cytotoxicity against a variety of human tumor cells when compared to either CD3(-) CD56(-) T cells or lymphokine activated killer (LAK) cells. While the mechanisms regulating the in vivo expansion of CD56(+) T cells are not known, here we demonstrate the importance of CD2-mediated IL-12-dependent signals in the in vitro expansion of CD56- T cells. Specifically, we show that activated monocytes provide a contact dependent factor (CD58/LFA-3) and a soluble factor (IL-12). both critical for the in vitro expansion of CD56(+) T cells. The biological and therapeutic implications of these findings are discussed.