Dependency of human T lymphocyte colony formation on soluble factors produced by accessory or tumor cells.

When plated in agar, PHA-stimulated Ficoll-Hypaque separated human mononuclear cells readily form discrete T lymphocyte colonies. Separation of these mononuclear cells on Sephadex G-10 columns yields enriched populations of T lymphocytes (greater than 95% E rosette-positive); these purified cells do not respond to this nonspecific mitogen by undergoing clonal expansion. Colony growth, however, can be restored by the addition of irradiated adherent cells. T cell responses can also be reconstituted by incubating the Sephadex-nonadherent fraction with irradiated cultured human tumor cells of monocytic (U937 and HL60) and B lymphocytic (Raji and Daudi cells) lines, but not from a T cell clone (MOLT-4) or erythroleukemic (K562) cells. Growth can also be induced in cultures containing T cells by adding cells from patients with either acute myeloblastic or B cell chronic lymphocytic leukemia or by the addition of B cell-enriched, monocyte-depleted normal mononuclear cells. Soluble factors prepared from Sephadex-adherent cells or active tumor cell lines are effective in promoting T cell colony formation. These results indicate that accessory cells are required for PHA responses of cloned human T cells. This function can be supplied by both monocytic and B lymphocytic tumor cell lines and is due to the release of soluble factors that act, in conjunction with the mitogen, to activate responsive lymphocytes.