Interleukin 2 is both necessary and sufficient for the growth and differentiation of lectin-stimulated cytolytic T lymphocyte precursors.

Minimal requirements for the growth and differentiation of lectin-stimulated cytolytic T lymphocyte precursors (CTL-P) have been investigated. CTL-P from murine spleen were purified by staining with monoclonal anti-Lyt-2 antibodies, followed by positive selection on a fluorescence-activated cell sorter. Microcultures containing 2000 purified Lyt-2+ cells were set up with optimal concentrations of lectin (leukoagglutinin or concanavalin A) and pure interleukin 2 (IL 2) obtained either by immunoaffinity chromatography or recombinant DNA technology. Proliferation and generation of CTL activity in lectin-stimulated Lyt-2+ cells were IL 2 dose-dependent. Furthermore, no increased response was observed when crude supernatants containing other putative CTL differentiation factors were added, even when IL 2 concentrations were suboptimal. When highly purified Lyt-2+ cells contaminated by 1% Lyt-2- cells and less than 0.1% macrophages were cultured at limiting dilution, as few as 20 responding cells proliferated and differentiated into CTL in the presence of leukoagglutinin and pure IL 2; in fact, CTL activity and proliferation were strongly correlated in individual microcultures. In addition, 10 to 30% of individual CTL-P were growth-inducible under these experimental conditions. Together, these data show that the proliferation and differentiation of lectin-stimulated CTL-P can occur in pure IL 2 without any demonstrable requirement for other differentiation factors or accessory cells.