CD137 ligand-mediated reverse signaling inhibits proliferation and induces apoptosis in non-small cell lung cancer.

CD137 ligand (CD137L), a member of the tumor necrosis factor superfamily, is expressed on antigen-presenting cells and also on various tumor cells. Crosslinking of CD137L transmits signals that evoke different cellular responses in a variety of tumor cells. This study was designed to investigate signaling pathways activated by CD137L and its physiologic role in the progression of NSCLC. We investigated the expression of CD137L in tissues from 102 cases of human non-small cell lung cancer (NSCLC) using immunohistochemistry and analyzed the correlation with clinicopathological features using Fisher's exact test and overall survival using Kaplan-Meier curves and the log-rank test. The effect of CD137L reverse signaling induced by recombinant human CD137-Fc protein on NSCLC cell lines was assessed using proliferation and apoptosis assays, flow cytometry and Western blotting. Positive CD137L expression was observed in 53/102 (52.0%) of the NSCLC samples and correlated with early TNM stage (P = 0.046), well-differentiated tumors (P = 0.009) and better overall survival (P = 0.004). Moreover, induction of CD137L reverse signaling using CD137-Fc inhibited proliferation and induced apoptosis and cell cycle arrest in H1650 cells, which express high levels of CD137L; CD137L reverse signaling had no significant effects in PC9 cells, which express low levels of CD137L. In addition, CD137L reverse signaling-induced apoptosis occurred via activation of the intrinsic pathway and depended on phosphorylation of JNK. This study demonstrates a hitherto unrecognized role for CD137L reverse signaling in the development of NSCLC and indicates that CD137L has potential as a novel therapeutic target in NSCLC.

Recombinant soluble CD137 prevents type one diabetes in nonobese diabetic mice.

Nonobese diabetic (NOD) mice are genetically programmed to spontaneously develop type one diabetes (T1D). Multiple Insulin dependent diabetes (Idd) genetic loci have been identified but their functional effects are mostly poorly understood. TnfsfR9, expressing the protein product CD137, is a strong candidate gene in the Idd9.3 locus, and NOD.B10 Idd9.3 mice are significantly protected from type one diabetes (T1D). We previously showed that nonobese diabetic (NOD) mice have a deficiency in the numbers of CD137(pos) T regulatory cells, that CD137(pos) Tregs are the source of soluble CD137 (sCD137), and that NOD mice have low serum levels of sCD137. To test the hypothesis that correcting low levels of sCD137 could affect the disease, we constructed a lentiviral vector producing recombinant sCD137; this physiologic sCD137 is glycosylated and exists primarily as a dimer. NOD mice treated with the recombinant sCD137 are protected from developing T1D. Insulitis is significantly decreased, but not eliminated in the sCD137 treated mice, however insulin producing pancreatic beta cells are preserved despite residual insulitis. To begin to understand the protective immune mechanisms of sCD137, we tested sCD137 in vitro. It was previously suggested that sCD137 simply blocked the interaction between CD137 (on T cells) and CD137 ligand (on antigen presenting cells (APCs)). Here however, we use an APC independent assay and demonstrate that sCD137 can actively suppress highly purified CD4 T cells in a CD137L dependent fashion. These results support the hypothesis that sCD137 acts in a negative feedback loop to actively suppress over-zealous immune responses, and that it can be used clinically to suppress autoimmunity. sCD137 is an important Treg derived natural immunosuppressive molecule that regulates effector T cells to avert diabetes in vivo.

CD137 ligand signaling induces human monocyte to dendritic cell differentiation.

The ligand for CD137 (4-1BB) is expressed on peripheral human monocytes and delivers a potent activating signal via reverse signaling. Here we show that treatment of monocytes with a recombinant CD137 protein that induces reverse signaling through CD137 ligand reduces typical macrophage characteristics such as phagocytosis, oxidative burst and CD14 expression; however, typical DC characteristics including endocytosis, costimulatory molecule expression and the ability to stimulate proliferation of naïve T cells are induced. CD137-generated DC do not express DC-SIGN, CD1a or IL-12 and secrete less IL-10 than classical DC. CD137-generated DC are mature, and addition of LPS+IFN-gamma does not enhance their T-cell-stimulatory capacity. This indicates that CD137 as a sole factor is sufficient to induce development to mature DC, making stimulation of CD137 ligand the most simple protocol to generate mature DC. CD137-generated DC are more potent in inducing T-cell proliferation than classical DC. They inhibit development of Treg cells but induce T-cell expression of perforin, IFN-gamma, IL-13 and IL-17. These data demonstrate that CD137 as a single factor is sufficient to induce differentiation of peripheral monocytes to mature inflammatory DC that have a more potent T-cell-stimulatory capacity than classical DC.

[Antileukemic effects in vitro of new co-stimulatory molecule CD137].

This study was aimed to investigate the expression characteristics of new co-stimulatory molecule CD137 (4-1BB) on human T lymphocytes and antileukemic effects of monoclonal antibody hCD137mAb in stimulating the T lymphocyte proliferation, promoting the cytokine secretion, enhancing the cell killing effect and so on. The expression of CD137 on normal T lymphocytes treated with phytohemagglutinin (PHA) was detected by FACS and indirect immunofluorescence. In HL-60 and T lymphocyte system in vitro, the effect of hCD137mAb and PHA on T lymphocyte proliferation was tested by MTT colorimetric assay. The IFN-gamma and IL-4 expression levels on the surface of T cells were detected by FACS and indirect immunofluorescence. In vitro mixed lymphocyte tumor cell culture (MLTC) system, the function of hCD137mAb enhancing toxicity killing leukemic cells at different effect-target ratio were studied. The results showed that almost no expression of hCD137 was found in T cells without PHA stimulation, but after activation of T cells by PHA, the expression gradually increased with a peak at 7th day (FACS 56.4%+/-1.98%, indirect immunofluorescence 52.8%+/-2.01%). CD137mAb alone could not stimulate T cell proliferation (proliferation index 1.002+/-0.011), but could enhance PHA stimulating activity (proliferative index of 2.161+/-0.102) about 2-folds (proliferation index 4.705+/-0.133). Moreover, hCD137mAb increased expression of IFN-gamma high by about 3-fold in presence of PHA, but did not effect on IL-4. The hCD137mAb markedly enhanced T cell killing activity on HL-60 cell line and its co-stimulatory effect was best at the effect-target ratio of 40:1 with increasing of killing percentage by about 2-fold. It is concluded that the new co-stimulatory molecule CD137 has significant antileukemic effect, use of hCD137mAb is an effective, safe and simple immunization strategy for leukemia therapy, this study provides some experimental basis for clinical immunotherapy with CD137 mAb.

CD137 ligand-mediated reverse signals increase cell viability and cytokine expression in murine myeloid cells: involvement of mTOR/p70S6 kinase and Akt.

Cross-linking of CD137 ligand (CD137L), a member of the TNF family, with recombinant CD137-Fc (rCD137-Fc) protein enhanced adherence of bone marrow-derived macrophages, and increased the expression of ICAM-1, IL-1beta, IL-6, M-CSF and phosphotyrosine proteins. In RAW264.7 cells, a murine myeloid cell line, rCD137-Fc not only increased adherence but also cell multiplication, in a manner comparable to LPS or M-CSF. In addition, it up-regulated expression of IL-1beta, IL-1 receptor antagonist, IL-6, COX2, tenascin C, neuropeptide Y and M-CSF mRNA. Neutralization of M-CSF by incubating the RAW264.7 cells with anti-M-CSF mAb did not prevent the CD137L signal-induced viability. Viability was blocked by PP2, an Src tyrosine kinase inhibitor, rapamycin, an mTOR inhibitor and LY294002, a PI3K inhibitor, but not by Wortmannin, another PI3K inhibitor. Cross-linking of CD137L increased phosphorylation of Akt and p70S6 kinase. The latter was blocked by PP2, rapamycin or LY294002, but not by Wortmannin, whereas phosphorylation of Akt was blocked by LY294002 or Wortmannin. These findings demonstrate that reverse signals evoked by CD137L regulate immune functions in macrophages.