Immunotherapeutic strategies targeting natural killer T cell responses in cancer.

Natural killer T (NKT) cells are a unique subset of lymphocytes that bridge the innate and adaptive immune system. NKT cells possess a classic αß T cell receptor (TCR) that is able to recognize self and foreign glycolipid antigens presented by the nonclassical class I major histocompatibility complex (MHC) molecule, CD1d. Type I NKT cells (referred to as invariant NKT cells) express a semi-invariant Vα14Jα18 TCR in mice and Vα24Jα18 TCR in humans. Type II NKT cells are CD1d-restricted T cells that express a more diverse set of TCR α chains. The two types of NKT cells often exert opposing effects especially in tumor immunity, where type II cells generally suppress tumor immunity while type I NKT cells can enhance anti-tumor immune responses. In this review, we focus on the role of NKT cells in cancer. We discuss their effector and suppressive functions, as well as describe preclinical and clinical studies utilizing therapeutic strategies focused on harnessing their potent anti-tumor effector functions, and conclude with a discussion on potential next steps for the utilization of NKT cell-targeted therapies for the treatment of cancer.

Histone deacetylase inhibitors enhance CD1d-dependent NKT cell responses to lymphoma.

Histone deacetylases (HDACs) are a family of enzymes that influence expression of genes implicated in tumor initiation, progression, and anti-tumor responses. In addition to their canonical role in deacetylation of histones, HDACs regulate many non-canonical targets, such as Signal Transducer and Activator of Transcription 3 (STAT3). We hypothesize that tumors use epigenetic mechanisms to dysregulate CD1d-mediated antigen presentation, thereby impairing the ability of natural killer T (NKT) cells to recognize and destroy malignant cells. In this study, we pre-treated CD1d-expressing tumor cells with HDAC inhibitors (HDACi) and assessed CD1d-dependent NKT cell responses to mantle cell lymphoma (MCL). Pre-treatment with Trichostatin-A, a pan-HDACi, rapidly enhanced both CD1d- and MHC class II-mediated antigen presentation. Similarly, treatment of MCL cells with other HDACi resulted in enhanced CD1d-dependent NKT cell responses. The observed changes are due, at least in part, to an increase in both CD1D mRNA and CD1d cell surface expression. Mechanistically, we found that HDAC2 binds to the CD1D promoter. Knockdown of HDAC2 in tumor cells resulted in a significant increase in CD1d-mediated antigen presentation. In addition, treatment with HDACi inhibited STAT3 and STAT3-regulated inflammatory cytokine secretion by MCL cells. We demonstrated that MCL-secreted IL-10 inhibits CD1d-mediated antigen presentation and pre-treatment with TSA abrogates secretion of IL-10 by MCL. Taken together, our studies demonstrate the efficacy of HDACi in restoring anti-tumor responses to MCL through both cell-intrinsic and cell-extrinsic mechanisms and strongly implicate a role for HDACi in enhancing immune responses to cancer.

Sphingosine 1-phosphate signaling impacts lymphocyte migration, inflammation and infection.

Sphingosine 1-phosphate (S1P) is a sphingosine containing lipid intermediate obtained from ceramide. S1P is known to be an important signaling molecule and plays multiple roles in the context of immunity. This lysophospholipid binds and activates G-protein-coupled receptors (GPCRs) known as S1P receptors 1-5 (S1P1-5). Once activated, these GPCRs mediate signaling that can lead to alterations in cell proliferation, survival or migration, and can also have other effects such as promoting angiogenesis. In this review, we will present evidence demonstrating a role for S1P in lymphocyte migration, inflammation and infection, as well as in cancer. The therapeutic potential of targeting S1P receptors, kinases and lyase will also be discussed.

VEGF Potentiates GD3-Mediated Immunosuppression by Human Ovarian Cancer Cells.

PURPOSE: Natural killer T (NKT) cells are important mediators of antitumor immune responses. We have previously shown that ovarian cancers shed the ganglioside GD3, which inhibits NKT-cell activation. Ovarian cancers also secrete high levels of VEGF. In this study, we sought to test the hypothesis that VEGF production by ovarian cancers suppresses NKT-cell-mediated antitumor responses. EXPERIMENTAL DESIGN: To investigate the effects of VEGF on CD1d-mediated NKT-cell activation, a conditioned media model was established, wherein the supernatants from ovarian cancer cell lines (OV-CAR-3 and SK-OV-3) were used to treat CD1d-expressing antigen-presenting cells (APC) and cocultured with NKT hybridomas. Ovarian cancer-associated VEGF was inhibited by treatment with bevacizumab and genistein; conditioned medium was collected, and CD1d-mediated NKT-cell responses were assayed by ELISA. RESULTS: Ovarian cancer tissue and ascites contain lymphocytic infiltrates, suggesting that immune cells traffic to tumors, but are then inhibited by immunosuppressive molecules within the tumor microenvironment. OV-CAR-3 and SK-OV-3 cell lines produce high levels of VEGF and GD3. Pretreatment of APCs with ascites or conditioned medium from OV-CAR-3 and SK-OV-3 blocked CD1d-mediated NKT-cell activation. Inhibition of VEGF resulted in a concomitant reduction in GD3 levels and restoration of NKT-cell responses. CONCLUSIONS: We found that VEGF inhibition restores NKT-cell function in an in vitro ovarian cancer model. These studies suggest that the combination of immune modulation with antiangiogenic treatment has therapeutic potential in ovarian cancer. Clin Cancer Res; 22(16); 4249-58. ©2016 AACR.

NKT Cell Responses to B Cell Lymphoma.

Natural killer T (NKT) cells are a unique subset of CD1d-restricted T lymphocytes that express characteristics of both T cells and natural killer cells. NKT cells mediate tumor immune-surveillance; however, NKT cells are numerically reduced and functionally impaired in lymphoma patients. Many hematologic malignancies express CD1d molecules and co-stimulatory proteins needed to induce anti-tumor immunity by NKT cells, yet most tumors are poorly immunogenic. In this study, we sought to investigate NKT cell responses to B cell lymphoma. In the presence of exogenous antigen, both mouse and human NKT cell lines produce cytokines following stimulation by B cell lymphoma lines. NKT cell populations were examined ex vivo in mouse models of spontaneous B cell lymphoma, and it was found that during early stages, NKT cell responses were enhanced in lymphoma-bearing animals compared to disease-free animals. In contrast, in lymphoma-bearing animals with splenomegaly and lymphadenopathy, NKT cells were functionally impaired. In a mouse model of blastoid variant mantle cell lymphoma, treatment of tumor-bearing mice with a potent NKT cell agonist, α-galactosylceramide (α-GalCer), resulted in a significant decrease in disease pathology. Ex vivo studies demonstrated that NKT cells from α-GalCer treated mice produced IFN-γ following α-GalCer restimulation, unlike NKT cells from vehicle-control treated mice. These data demonstrate an important role for NKT cells in the immune response to an aggressive hematologic malignancy like mantle cell lymphoma.