) is a heterodimeric protein, first recovered from EBV-transformed B cell lines.It is a multifunctional cytokine, the properties of which bridge innate and adaptive immunity, acting as a key regulator of cell-mediated immune responses through the induction of T helper 1 differentiation. By promoting IFN-g production, proliferation, and cytolytic activity of natural killer and T cells, IL-12 induces cellular immunity. In addition, IL-12 induces an antiangiogenic program mediated by IFN-g^inducible genes and by lymphocyte-endothelial cell cross-talk. The immunomodulating and antiangiogenic functions of IL-12 have provided the rationale for exploiting this cytokine as an anticancer agent. In contrast with the significant antitumor and antimetastatic activity of IL-12, documented in several preclinical studies, clinical trials with IL-12, used as a single agent, or as a vaccine adjuvant, have shown limited efficacy in most instances. More effective application of this cytokine, and of newly identified IL-12 family members (IL-23 and IL-27), should be evaluated as therapeutic agents with considerable potential in cancer patients.Interleukin-12 (IL-12) is recognized as a master regulator of adaptive type 1, cell-mediated immunity, the critical pathway involved in protection against neoplasia and many viruses. This is supported by the analysis of numerous animal (1, 2) and human clinical studies that attribute improved clinical outcome (3) and mechanisms of IL-12 -based therapy (4) to strong type 1 responses in situ. Since the initial preclinical and clinical studies of IL-12, done over a decade ago, basic and translational science studies have contributed to the greater understanding of IL-12 immunobiology. In addition to its noted effects in the priming of T helper 1 (TH1) cell responses and IFN-g production by T and natural killer (NK) cells, more recent studies support its critical role as a third signal for CD8 + T cell differentiation (5, 6), and its ability to serve as an important factor in the reactivation and survival of memory CD4 + T cells (7). This is particularly relevant in the repolarization of CD4 + T cells from dysfunctional antitumor TH2 into TH1 cells in the cancer setting (8). Here, we review the immunomodulatory and antiangiogenic functions of IL-12, as well as the results of preclinical and clinical studies in which IL-12 was used as an anticancer agent.

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We describe a novel cytokine receptor named GP130 Like receptor, or GPL, that displays similarities with the interleukin-6 and interleukin-12 family of signaling receptors. Four different isoforms diverging in their carboxyl terminus were isolated, corresponding to proteins encompassing 560, 610, 626, and 745 amino acids. Sequences included a signal peptide of 32 amino acids, followed by a cytokine binding domain containing four conserved cysteines, a WSDWS motif, and a region consisting of three fibronectin type III domain repeats. No immunoglobulin-like module was identified in the GPL sequences. The intracellular part of longer isoforms contained a proline-rich region defining a box1 motif for interaction with the Janus kinases. The Gpl gene is organized in 15 exons and is located on 5q11.2 in tandem with the gp130 gene. Both genes were only separated by 24 kilobases, with opposite transcriptional orientations. The GPL receptor displayed a 28% identity with gp130. Specific GPL transcripts were observed in tissues involved in reproduction. Transcripts were also found in blood cells and in bone marrow, revealing expression of GPL in all of the myelomonocytic lineage, from hematopoietic stem cells to activated dendritic cells. In monocytes and dendritic cells, expression of GPL was strongly up-regulated by interferon-␥, indicating a possible involvement of GPL in Th1-type immune responses. The molecular basis of cell signaling mediated by GPL was studied using chimeric receptors where external portions of ␣ or ␤ interleukin-5 receptor subunits were fused to the internal portion of GPL or of related receptors. Results indicated that association of GPL to the intracellular portions of gp130, or LIF receptor, allowed the signaling cascade.

The cytokine IL-12, a product of dendritic cells (DC), plays a major role in cellular immunity, notably by inducing lymphocytes to produce IFN-gamma. Microbial products, T cell signals and cytokines induce the production of IL-12. Here, IL-1 beta is identified as a new IL-12-inducing agent, acting conjointly with CD40 ligand (CD40L) on human monocyte-derived DC in vitro. The effects of IL-1 beta were dose dependent, specifically blocked by neutralizing antibodies, and were observed both in immature and mature DC. Immature DC secreted more IL-12 than mature DC, but the effects of IL-1 beta were not due to a block of DC maturation as determined by analysis of DC surface markers. The mechanisms of action of IL-1 beta could be contrasted to that of other inducers of IL-12 such as IFN-gamma and lipopolysaccharide (LPS). Either IL-1 beta or IFN-gamma co-induced IL-12 with CD40L but conjointly, IL-1 beta, CD40L and IFN-gamma synergized, inducing very high levels of IL-12. The effects of IL-1 beta differed from those of LPS in that IL-1 beta, unlike LPS, could not induce IL-12 solely after IFN-gamma priming; and when combined with CD40L, IL-1 beta, unlike LPS, induced little IL-10. The mechanism of action of IL-1 beta involves IL-12 alpha mRNA up-regulation, and we show that the combination of CD40L and IL-1 beta induces high levels of IL-12 alpha and IL-12 beta mRNA in DC. Altogether, these results delineate a new mechanism linking adaptive and innate immune responses for the regulation of IL-12 production in DC and for the role of IL-1 beta in the development of cellular immunity.