The effects of B cell stimulatory factor 1 (BSF-1) on the generation of human CTL and lymphokine-activated killer (LAK) cells in vitro were investigated. Both L-2 and BSF-1 were potent helper factors for the generation of antigen-specific CTL in MLC; detection of optimal BSF-1-induced CTL activity in this system occurred when BSF-1 was added to cultures after an initial period of activation during which exogenous BSF-1 was not present. In contrast to IL-2, BSF-1 failed to induce an LAK cell population, as detected with Daudi tumor targets, in cultures that had not been allosensitized. Furthermore, when both lymphokines were added together at culture initiation, BSF-1 inhibited the IL-2-driven generation of cytolytic cells. The differential ability of BSF-1 to promote the generation of CTL but not LAK could have important implications for lymphokine-mediated immunotherapy.

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