Two functionally distinct subsets of B cells that produce Th1- and Th2-like patterns of cytokines have recently been identified. Interleukin-12 (IL-12) is a critical immunoregulatory cytokine that promotes Th1 differentiation through activation of signal transducer and activator of transcription 4 (STAT4). IL-12 has been reported to induce interferon γ (IFN-γ) production in B cells, but the relevant signaling pathways are poorly documented. Here, in human primary B cells, we found a functional IL-12 receptor (IL-12R) that internalizes following IL-12 binding. IFN-γ and, to a lesser extent, IL-12 positively regulated the IL-12Rβ2 subunit but had no effect on IL-12Rβ1. On examining the effect of IL-12 on STAT4 and T-bet (2 key factors involved in IFN-γ promoter activation), we found that IL-12 induced the phosphorylation and nuclear translocation of STAT4. IL-12-dependent constitutive STAT4 activation was also observed in the Epstein-Barr virus (EBV)-transformed B-cell line RPMI 8866 that spontaneously produces IL-12. T-bet expression has been shown to be dependent on STAT1. IL-12 had no direct effect on STAT1 activation or T-bet expression in primary B cells. In contrast, IL-12-induced IFN-γ led to STAT1 activation, strong expression of T-bet, and IFN-γ expression. IL-12 therefore initiates a cascade of events in B cells, including STAT4 activation, IL-12Rβ2 up-regulation, IFN-γ production, and T-bet up-regulation, potentially leading to Th1-like differentiation. (Blood. 2003;102:4084-4089)

NK cells express receptors characterized by opposite functions that finely regulate their activities. Among inhibitory receptors, some are specific for different groups of MHC class I alleles, while others are still orphan receptors. On the contrary, various activating receptors are involved in the triggering of NK‐mediated natural cytotoxicity. In general, their engagement induces human NK cells to kill target cells that are either HLA class I‐negative or ‐deficient. Thus, the process of NK cell triggering mediated by Natural Cytotoxicity Receptors can be mainly considered as a non MHC‐restricted mechanism. Here, a brief description of the molecular nature of these receptors, as well as, of their 3D‐structures and of the implications for ligand recognition, is given.

Many renal cancer patients experience disease recurrence after immunotherapy or combined treatments due to persistence of cancer stem cells (CSCs). The identification of reliable inducers of CSC differentiation may facilitate the development of efficient strategies for eliminating CSCs. We investigated whether interleukin 15 (IL-15), a regulator of kidney homeostasis, induces the differentiation of CD105-positive (CD105⁺) CSCs from human renal cancers. CD105⁺ CSCs were cultured to preserve their stem cell properties and treated with recombinant human IL-15 (rhIL-15) to evaluate their ability to differentiate, to acquire sensitivity to chemotherapeutic drugs, and to form spheroids in vitro and tumors in vivo. Expression of stem cell and epithelial markers were studied by flow cytometry, immunocytochemistry, and immunoblotting. Identification of a CSC side population fraction and its sensitivity to chemotherapy drugs and expression of ATP-binding cassette (ABC) transporters and aldehyde dehydrogenase (ALDH) activities were determined by flow cytometry. Spheroid formation was determined in limiting dilution assay. Xenograft tumors were generated in severe combined immunodeficient mice (n = 12–18 mice per group). All statistical tests were two-sided. CD105⁺ CSCs treated with rhIL-15 at 10 pg/mL differentiated into cells expressing epithelial markers. rhIL-15 induced epithelial differentiation of all CD105⁺ CSCs subsets and blocked CSC self-renewal (sphere-forming ability) and their tumorigenic properties in severe combined immunodeficient mice. Vinblastine and paclitaxel induced statistically significant higher levels of apoptosis in rhIL-15-differentiated epithelial cells compared with CD105⁺ CSCs (mean percentage of apoptotic cells, vinblastine: 33% vs 16.5%, difference = 16.5%, 95% confidence interval = 12.25% to 20.74%, P = .0025; paclitaxel: 35% vs 11.6%, difference = 23.4%, 95% confidence interval = 22.5% to 24.24%, P = .0015). The higher sensitivity of rhIL-15-differentiated epithelial cells to chemotherapeutic drugs was associated with loss of detoxifying mechanisms such as ALDH and ABC transporter activities. IL-15 directs the epithelial differentiation of renal CSCs and meets the criteria for a treatment strategy: CSC pool depletion and generation of differentiated nontumorigenic cells that are sensitive to chemotherapeutic agents.

Membrane-bound and soluble interleukin-15 (IL-15)/IL-15 receptor α (Rα) complexes trigger differential transcription factor activation and functions on human hematopoietic progenitors. Indeed, human spleen myofibroblasts (SMFs) are characterized by a novel mechanism of IL-15 trans-presentation (SMFmb [membrane-bound]-IL-15), based on the association of an endogenous IL-15/IL-15Rα complex with the IL-15Rβγc chains. SMFmb-IL-15 (1) induces lineage-specific signaling pathways that differ from those controlled by soluble IL-15 in unprimed and committed normal progenitors; (2) triggers survival and proliferation of leukemic progenitors expressing low-affinity IL-15R (M07Sb cells); (3) causes only an antiapoptotic effect on leukemic cells expressing high-affinity receptors (TF1β cells). This behavior is likely due to the IL-15Rα chain present on these cells that interact with the SMFmb-IL-15, inhibiting signal transducer and transcriptional activator 5 (STAT5) activation. On the other hand, the soluble IL-15/IL-15Rα complex (hyper IL-15) displays a dominant pattern of action, activating only those cells expressing low-affinity IL-15R (IL-15Rβγc). Thus, hyper IL-15 induces antiapoptotic effects on M075b cells and the up-regulation of STAT6 activation on adult peripheral blood (PB) pre-natural killer (NK) committed progenitors. The latter effect using 100-fold concentrations of recombinant (r)-IL-15. In conclusion, SMFmb-IL-15 and soluble IL-15Rα/IL-15 complexes seem to play a pivotal role in the control of the survival, proliferation and differentiation of both normal and leukemic circulating progenitors, highlighting new functions of IL-15 and of IL-15Rα.