SummaryThe effects of purified recombinant interleukin 7 (IL7) on the generation of cytolytic T lymphocytes (CTL) in mixed lymphocyte culture (MLC) and on the induction oflymphokine-activated killer (LAK) cells in autologous cultures of human peripheral blood mononuclear cells were investigated . IL7 was found to induce the generation ofboth CTL and LAK cells in bulk cultures. The appearance of peak CTL activity in MLC established with exogenous IL-7 was delayed in comparison with replicate cultures containing exogenous IL2, but both cytokines stimulated quantitatively similar levels of antigen-specific lytic activity. An IL2-neutralizing antiserum inhibited substantially, but not completely, the effect of IL7 on CTL generation, implying the existence of both an indirect component of 11,7 activity via IL2 utilization, as well as an IL2-independent component. Cell surface phenotypic analysis of 11,2-or IL7-generated CTL effector cells revealed that CD8+ cells were responsible for the vast majority of lytic activity. Limiting dilution analysis (LDA) revealed that essentially identical frequencies of CTL precursors (CTLP) were capable of clonal expansion and/or differentiation in the presence of exogenous IL2, 114, or IL7, supporting the concept that all three of these cytokines are capable of exerting a major influence on T cell growth and differentiation . Approximately half of the CTLP that responded in IL7-supplemented LDA cultures did so in an IL2-independent manner. IL7 stimulated the development of LAK cells in autologous bulk cultures, but only weakly in comparison with IL2. In contrast to its effects on CTL generation, the induction of LAK cells by 11,7 was virtually independent of IL-2. LAK cells induced by IL7, like those induced by 11,2, were phenotypically heterogeneous and included CD8+, CD56+, and -y/S+ cells . Limiting dilution analysis indicated that 1172 stimulated fivefold more LAK-P than IL7 and 220-fold more than 1174. Collectively, these data suggest that 11,7 has potent regulatory effects on human cytolytic cell populations and, either alone or in combination with other cytokines, could be important for the in vitro expansion of cells for adoptive immunotherapy.Activation of resting T lymphocytes into cytolytic cells 1-1 normally requires both interaction with processed antigen through the TCR complex and the collaborative action of soluble cytokines (1) . Among the cytokines with reputed roles in T cell proliferation and/or differentiation are IL-1, -2, -4, -5, and -6, TNF, IFN-y, and granulocyte-macrophage CSF (2-8) . The most recent addition to the list of T cell-active cytokines was IL-7. IL-7 was originally purified and its cDNA cloned based upon the ability to cause the growth of pre-B cells (9) . More recently, it has been shown to be a potent costimulus for the proliferation of mitogenactivated murine and human T cells (10-13). Notably, IL7 has been shown to expand numerically both CD4+ and CD8+ T cells. The cytokine IL-2, in addition to promoting the growth and differentiation of T c...

In vitro studies have shown that cytokines are involved in the regulation of the immune response, but their role in vivo is less well defined. Specific cytokine antagonists enable the identification of particular cytokines involved in the response and offer a means for modifying it. Systemic administration of a soluble, extracellular portion of the receptor for interleukin-1 (sIL-1R) had profound inhibitory effects on the development of in vivo alloreactivity. Survival of heterotopic heart allografts was prolonged from 12 days in controls to 17 days in mice treated with sIL-1R. Lymph node hyperplasia in response to a localized injection of allogeneic cells was completely blocked by sIL-1R treatment. The inhibition was overcome by simultaneous administration of interleukin-1 (IL-1); thus, sIL-1R acts by neutralizing IL-1. These results implicate IL-1 as a regulator of allograft rejection and demonstrate the in vivo biological efficacy of a soluble cytokine receptor.

125I-labeled recombinant human B cell stimulatory factor 1 (BSF-1) was used to characterize receptors specific for this lymphokine on in vitro cell lines representing human B, T, and hematopoietic lineages, as well as on adherent cell lines of epithelial and endothelial origin, and on primary human gingival fibroblasts. BSF-1 binding was extremely rapid and saturable at both 4 and 37 degrees C, with a slow dissociation rate. On all human cell types examined, BSF-1 bound to a single class of high-affinity receptor (less than 3,000 receptors per cell) with a Ka of 0.5-1.0 X 10(10)/M. Human BSF-1 also bound to cell lines of simian but not murine origin. Comparison of kinetic characteristics obtained with a yeast-derived hyperglycosylated form of BSF-1 (Mr 60,000) and N-glycanase-treated, sugar-free BSF-1 (Mr 15,000) showed no significant differences. Among a panel of lymphokines and growth hormones, only unlabeled human BSF-1 was able to compete for the binding of 125I-labeled human BSF-1. Affinity crosslinking experiments resulted in the identification on both Raji cells and on primary human gingival fibroblasts of a receptor subunit with an average Mr of 139,000. These studies show that the BSF-1 receptor on human cells has an extremely broad cellular distribution, while further supporting the notion that the ability of BSF-1 to mediate a spectrum of biological activities cannot be accounted for by overt differences in the receptor for this lymphokine on different cell lineages.

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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