Resting (IL-2 non-responsive) precursors of human T cell receptor gamma delta-positive cells (TCR1 cells) are activated by a two signal process.

Precursors of T cells expressing the gamma delta-T cell receptor (TCR1 cells) have been identified in a resting (IL-2 non-responsive) subpopulation of human peripheral blood mononuclear cells (PBMC). Activation of the TCR1 precursor cells into proliferating and cytotoxic cells requires two signals, viz. IL-2 and either activated T cells (autologous or allogeneic) or malignant melanoma cells (MM-170). The activation process is inhibited by 0.1 microgram/ml cyclosporine. CD3 expression on TCR1 precursor cells was low, since the precursor cells were not always adequately depleted by OKT3 plus complement. Natural killer cells were generated from the same resting subpopulation of PBMC and by the same set of activation stimuli as were the TCR1 cells, suggesting a common pathway for activation of both cell types.