ICAM-1 AND LFA-3 ENHANCE THE ABILITY OF ANTI-CD3 MAB TO STIMULATE INTERFERON-GAMMA PRODUCTION IN INTERLEUKIN-2-ACTIVATED T-CELLS

Interleukin-2 (IL-2)-activated killer cells, also referred to as lymph okine-activated killer (LAK) cells, are stimulated by tumor cells to e xpress cytotoxic activity and to also secrete cytokines such as interf eron gamma (IFN gamma) and tumor necrosis factor a (TNF alpha). We pre viously reported that secretion of cytokines by IL-2-activated T cells (LAK-T cells) is dependent on the initial cross-linking of the T cell receptor (TCR)-CD3-molecular complex, but the crosslinking of accesso ry molecules, such as LFA-1, CD2, CD44 and CD45, on LAK-T cells can en hance this cytokine production. We have developed an approach involvin g interspecific gene transfer to define further the contributions of L FA-1 and CD2 to the activation of LAK-T cells. The genes for huICAM-1 (a ligand for LFA-1) and huLFA-3 (a ligand for CD2) were transfected s ingly and in combination into a null mouse melanoma background, and cl onal populations of cells that stably express ICAM-1 and/ or LFA-3 wer e derived. Expression of the introduced ICAM-1 and/or LFA-3 by transfe cted cells enhanced their ability to bind LAK-T cells; the LFA-1/ICAM- 1-mediated binding was not further enhanced by activation with phorbol 12-myristate 13-acetate. ICAM-1- and/or LFA-3-transfected cells, in t he presence of immobilized anti-CD3, exhibited a greater ability to st imulate IFN gamma secretion by LAK-T cells compared to the untransfect ed parental lines. This experimental system, which allows ICAM-1/LFA-1 and CD2/LFA-3 interactions to occur on the LAK-T cell at a site dista l from the anti-CD3 signal, extends our under standing of LAK-T cell a ctivation by establishing that both LFA-1/ICAM-1 and CD2/LFA-3 can med iate co-stimulation via adhesion and signaling events.