Liat Izhak

Delicate Balance among Three Types of T Cells in Concurrent Regulation of Tumor Immunity

The nature of the regulatory cell types that dominate in any given tumor is not understood at present. Here, we addressed this question for regulatory T cells (Treg) and type II natural killer T (NKT) cells in syngeneic models of colorectal and renal cancer. In mice with both type I and II NKT cells, or in mice with neither type of NKT cell, Treg depletion was sufficient to protect against tumor outgrowth. Surprisingly, in mice lacking only type I NKT cells, Treg blockade was insufficient for protection. Thus, we hypothesized that type II NKT cells may be neutralized by type I NKT cells, leaving Tregs as the primary suppressor, whereas in mice lacking type I NKT cells, unopposed type II NKT cells could suppress tumor immunity even when Tregs were blocked. We confirmed this hypothesis in 3 ways by reconstituting type I NKT cells as well as selectively blocking or activating type II NKT cells with antibody or the agonist sulfatide, respectively. In this manner, we showed that blockade of both type II NKT cells and Tregs is necessary to abrogate suppression of tumor immunity, but a third cell, the type I NKT cell, determines the balance between these regulatory mechanisms. As patients with cancer often have deficient type I NKT cell function, managing this delicate balance among 3 T-cell subsets may be critical for the success of immunotherapy for human cancer.

Dissecting the Autocrine and Paracrine Roles of the CCR2-CCL2 Axis in Tumor Survival and Angiogenesis

The CCL2 CCR2 axis is likely to contributes to the development and progression of cancer diseases by two major mechanisms; autocrine effect of CCL2 as a survival/growth factor for CCR2+ cancer cells and, the attraction of CCR2+ CX3CR1+tumor associated macrophages that in the absence of CCR2 hardly migrate. Thus far no in vivo system has been set up to differentiate the selective contribution of each of these features to cancer development. Here we employed a chimera animal model in which all non-malignant cells are CCR2−/−, but all cancer cells are CCR2+, combined with an adoptive transfer system of bone marrow (BM) CX3CR1+ cells from CCR2+ mice harboring a targeted replacement of the CX3CR1gene by an enhanced green fluorescent protein (EGFP) reporter gene (cx3cr1 gfp), together with the CD45.1 congene. Using this system we dissected the selective contribution of CX3CR1+CCR2+ cells, which comprise only about 7% of CD11b+ BM cells, to tumor development and angiogenesis. Showing that aside for their direct pro-angiogenic effect they are essential for the recruitment of other CD11b+ cells to the tumor site. We further show that the administration of CCR2-Ig, that selectively and specifically neutralize CCL2, to mice in which CCR2 is expressed only on tumor cells, further suppressed tumor development, implicating for the key role of this chemokine supporting tumor survival in an autocrine manner. This further emphasizes the important role of CCL2 as a target for therapy of cancer diseases.

Predominant Expression of CCL2 at the Tumor Site of Prostate Cancer Patients Directs a Selective Loss of Immunological Tolerance to CCL2 That Could Be Amplified in a Beneficial Manner

We have previously shown that, during inflammatory autoimmune diseases in humans, the immune system develops a neutralizing auto-Ab–based response to a very limited number of inflammatory mediators, and that amplification of each response could be beneficial for the host. Our working hypothesis has been that this selective breakdown of immunological tolerance is due to a predominant expression of an inflammatory mediator at an immune-restricted site undergoing a destructive process. All three conditions also take place in cancer diseases. In this study, we delineate this hypothesis for the first time in a human cancer disease and then explore its clinical implications. We show that in primary tumor sections of prostate cancer subjects, CCL2 is predominantly expressed at the tumor site over other chemokines that have been associated with tumor development, including: CXCL12, CXCL10, CXCL8, CCL3, and CCL5. Subsequently, the immune response selectivity mounts an Ab-based response to CCL2. These Abs are neutralizing Abs. These findings hold diagnostic and therapeutic implications. The current diagnosis of prostate cancer is based on prostate-specific Ag measurements that do not distinguish benign hypertrophy from malignancy. We show in this study that development of anti-CCL2 Abs is selective to the malignant stage. From a clinically oriented perspective, we show, in an experimental model of the disease, that DNA-based amplification of this response suppresses disease, which has implications for a novel way of therapy in humans.

A Novel Recombinant Fusion Protein Encoding a 20-Amino Acid Residue of the Third Extracellular (E3) Domain of CCR2 Neutralizes the Biological Activity of CCL2

CCL2 is a key CC chemokine that has been implicated in a variety of inflammatory autoimmune diseases and in tumor progression and it is therefore an important target for therapeutic intervention in these diseases. Soluble receptor-based therapy is a known approach for neutralizing the in vivo functions of soluble mediators. Owing to the complexity of seven-transmembrane G protein-coupled receptors, efforts to generate neutralizing soluble chemokine receptors have so far failed. We developed a strategy that is based on the generation of short recombinant proteins encoding different segments of a G protein-coupled receptor, and tested the ability of each of them to bind and neutralize its target chemokine. We show that a fusion protein comprised of as few as 20 aa of the third extracellular (E3) domain of the CCL2 receptor, stabilized by the IgG H chain Fc domain (E3-IgG or BL-2030), selectively binds CCL2 and CCL16 and effectively neutralizes their biological activities. More importantly, E3-IgG (BL-2030) could effectively suppress the in vivo biological activity of CCL2, attenuating ongoing experimental autoimmune encephalomyelitis, as well as the development of human prostate tumor in SCID mice.

Abstract 3657: Cross-regulation between the two subsets of NKT cells is dependent on interferon-gamma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Overcoming the suppression of tumor immunity has been a major challenge in the fight against cancer. Suppression of tumor immunity is being regulated by different kinds of suppressor cells and depleting or blocking their function has been the target of immunotherapy development. One subset of immune suppressors is type II NKT cells. We have previously shown that, upon simultaneous stimulation, type I NKT cells that can promote tumor immunity and type II NKT cells cross regulate each other in vitro as well as in vivo. In some tumor models it was found that activation of type II NKT cells by sulfatide can completely abrogate the protective affect of type I NKT cell activation by alpha-galactosylceramide, leading to tumor progression and reduced survival. However the mechanism for this suppression has not been understood. By co-stimulating NKT cells in vitro, we found that type II NKT cells can inhibit the proliferation of type I NKT cells. By blocking a variety of immunregulators, we found that this suppression is dependent on interferon-gamma (IFNg). Blocking IFNg or its receptor reversed the suppression of type I NKT cell proliferation in vitro. In addition suppression was not observed in IFNgKO C57BL/6 NKT cells. It was also found that exogenous IFNg reduces the proliferation of type I NKT cells after stimulation, suggesting that IFNg is necessary for the suppression of type I NKT cells by type II NKT cells. This was unexpected as IFNg is also an effector cytokine secreted by type I NKT cells. The mechanism is under investigation. Blocking the ability of type II NKT cells to suppress type I NKT cells could shift the balance toward immune protection leading to a better tumor outcome. Citation Format: Liat Izhak, Shingo Kato, Stanley T. Parish, Masaki Terabe, Jay A. Berzofsky. Cross-regulation between the two subsets of NKT cells is dependent on interferon-gamma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3657. doi:10.1158/1538-7445.AM2014-3657