Regulation Of Tumor Immunity Research Articles

The Impact of Estrogen in the Tumor Microenvironment.

Tumor immune escape is now a hallmark of cancer development, and therapies targeting these pathways have emerged as standard of care. Specifically, immune checkpoint signal blockade offers durable responses and increased overall survival. However, the majority of cancer patients still do not respond to checkpoint blockade immune therapy leading to an unmet need in tumor immunology research. Sex-based differences have been noted in the use of cancer immunotherapy suggesting that sex hormones such as estrogen may play an important role in tumor immune regulation. Estrogen signaling already has a known role in autoimmunity, and the estrogen receptor can be expressed across multiple immune cell populations and effect their regulation. While it has been well established that tumor cells such as ovarian carcinoma, breast carcinoma, and even lung carcinoma can be regulated by estrogen, research into the role of estrogen in the regulation of tumor-associated immune cells is still emerging. In this chapter, we discuss the role of estrogen in the tumor immune microenvironment and the possible immunotherapeutic implications of targeting estrogen in cancer patients.

Regulation of Cancer Immune Checkpoint: Mono- and Poly-Ubiquitination: Tags for Fate.

The antagonism, stalemate and compromise between the immune system and tumor cells is closely associated with tumor development and progression. In recent years, tumor immunotherapy has made continuous breakthroughs. It has become an important approach for cancer treatment, improving the survival and prognosis of more and more tumor patients. Further investigating the mechanism of tumor immune regulation, and exploring tumor immunotherapy targets with high specificity and wide applicability will provide researchers and clinicians with favorable weapons towards cancer. Ubiquitination affects protein fate through influencing the activity, stability and location of target protein. The regulation of substrate protein fate by ubiquitination is involved in cell cycle, apoptosis, transcriptional regulation, DNA repair, immune response, protein degradation and quality control. E3 ubiquitin ligase selectively recruits specific protein substrates through specific protein-protein interactions to determine the specificity of the overall ubiquitin modification reaction. Immune-checkpoint inhibitory pathway is an important mechanism for tumor cells to evade immune killing, which can inhibit T cell activity. Blocking the immune checkpoints and activating T cells through targeting the negative regulatory factors of T cell activation and removing the "brake" of T lymphocytes can enhance T cells immune response against tumors. Therefore, blocking the immune checkpoint is one of the methods to enhance the activity of T cells, and it is also a hot target for the development of anti-tumor drugs in recent years, whose inhibitors have shown good effect in specific tumor treatment. Ubiquitination, as one of the most important posttranslational modification of proteins, also modulates the expression, intracellular trafficking, subcellular and membranous location of immune checkpoints, regulating the immune surveillance of T cells to tumors.

Inhibition of DCLK1 down-regulates PD-L1 expression through Hippo pathway in human pancreatic cancer

Immunotherapy is one of the most promising strategies for cancer, compared with traditional treatments. As one of the key emerging immunotherapies, anti-PD-1/PD-L1 treatment has brought survival benefits to many advanced cancer patients. However, in pancreatic cancer, immunotherapy-based approaches have not achieved a favorable clinical effect because of mismatch repair deficiencies. Therefore, the majority of pancreatic tumors are regarded as immune-quiescent tumors and non-responsive to single-checkpoint blockade therapies. Many preclinical and clinical studies suggest that it is still important to clarify the regulatory mechanism of the PD-1/PD-L1 pathway in pancreatic cancer. As a marker of cancer stem cells, DCLK1 has been found to play an important role in the occurrence and development of a plethora of human cancers. Recent researches have revealed that DCLK1 is closely related to EMT process of tumor cells, meanwhile, it could also be used as a biomarker in gastrointestinal tumors to predict the prognoses of patients. However, the role that DCLK1 plays in the immune regulation of tumor microenvironments remains unknown. Therefore, we sought to understand if DCLK1 could positively regulate the expression of PD-L1 in pancreatic cancer cells. Furthermore, we examined if DCLK1 highly correlated with the Hippo pathway through TCGA database analysis. We found that DCLK1 helped regulate the level of PD-L1 expression by affecting the corresponding expression level of yes-associated protein in the Hippo pathway. Collectively, our study identifies DCLK1 as an important regulator of PD-L1 expression in pancreatic tumor and highlights a central role of DCLK1 in the regulation of tumor immunity.

Noncoding RNAs as potential mediators of resistance to cancer immunotherapy.

Substantial evolution in cancer therapy has been witnessed lately, steering mainly towards immunotherapeutic approaches, replacing or in combination with classical therapies. Whereas the use of various immunotherapy approaches, such as adoptive T cell therapy, genetically-modified T cells, or immune checkpoint inhibitors, has been a triumph for cancer immunotherapy, the great challenge is the ability of the immune system to sustain long lasting anti-tumor response. Additionally, epigenetic changes in a suppressive tumor microenvironment can pertain to T cell exhaustion, limiting their functionality. Noncoding RNAs (ncRNAs) have emerged over the last years as key players in epigenetic regulation. Among those, microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) have been studied extensively for their potential role in regulating tumor immunity through direct regulation of genes involved in immune activation or suppression. In this review, we will provide an overview of contemporary approaches for cancer immunotherapy and will present the current state of knowledge implicating miRNAs and lncRNAs in regulating immune response against human cancer and their potential implications in resistance to cancer immunotherapy, with main emphasis on immune checkpoints regulation.

The Role of Tumor-Infiltrating B Cells in Tumor Immunity.

Earlier studies on elucidating the role of lymphocytes in tumor immunity predominantly focused on T cells. However, the role of B cells in tumor immunity has increasingly received better attention in recent studies. The B cells that infiltrate tumor tissues are called tumor-infiltrating B cells (TIBs). It is found that TIBs play a multifaceted dual role in regulating tumor immunity rather than just tumor inhibition or promotion. In this article, latest research advances focusing on the relationship between TIBs and tumor complexity are reviewed, and light is shed on some novel ideas for exploiting TIBs as a possible tumor biomarker and potential therapeutic target against tumors.

Exosome DNA: Critical regulator of tumor immunity and a diagnostic biomarker.

Nanosized cellular vesicles "exosome" contains a variety of biological cargo including DNA fragments from cell-of-origin. Despite its biological stability and clinical utility in tumor diagnosis, exosome DNA (ExoDNA) is very little studied as compare with exosome RNA. Cytoplasmic accumulation of damaged DNA from nucleus and mitochondria often leads to its packaging in exosomes by yet unknown pathways. ExoDNA modulates tumor immunity via paracrine interactions and activation of cytosolic DNA sensor pathways, for example, STING, cGAS, and so forth in specific immune cell subsets. In addition to priming tumor immunity, ExoDNA is also emerging as a critical regulator of check-point immunotherapy. As a useful diagnostic biomaterial, ExoDNA contains a variety of clinically relevant tumor-specific mutations representing multiple genes (e.g., EGFR, BRAF, RAS, IDH, and HER2), thus making it a promising "liquid biopsy" material for therapy recommendations. Hence, ExoDNA in addition to tumor immunity modulation, is also emerging as a suitable diagnostic material for personalized therapy in cancer. Here, we review the current status of ExoDNA research and its potential uses in tumor biology.

Innate αβ T Cells Mediate Antitumor Immunity by Orchestrating Immunogenic Macrophage Programming.

Unconventional T-lymphocyte populations are emerging as important regulators of tumor immunity. Despite this, the role of TCRαβ+CD4-CD8-NK1.1- innate αβ T cells (iαβT) in pancreatic ductal adenocarcinoma (PDA) has not been explored. We found that iαβTs represent ∼10% of T lymphocytes infiltrating PDA in mice and humans. Intratumoral iαβTs express a distinct T-cell receptor repertoire and profoundly immunogenic phenotype compared with their peripheral counterparts and conventional lymphocytes. iαβTs comprised ∼75% of the total intratumoral IL17+ cells. Moreover, iαβT-cell adoptive transfer is protective in both murine models of PDA and human organotypic systems. We show that iαβT cells induce a CCR5-dependent immunogenic macrophage reprogramming, thereby enabling marked CD4+ and CD8+ T-cell expansion/activation and tumor protection. Collectively, iαβTs govern fundamental intratumoral cross-talk between innate and adaptive immune populations and are attractive therapeutic targets. SIGNIFICANCE: We found that iαβTs are a profoundly activated T-cell subset in PDA that slow tumor growth in murine and human models of disease. iαβTs induce a CCR5-dependent immunogenic tumor-associated macrophage program, T-cell activation and expansion, and should be considered as novel targets for immunotherapy.See related commentary by Banerjee et al., p. 1164.This article is highlighted in the In This Issue feature, p. 1143.

CD73: an emerging checkpoint for cancer immunotherapy.

CD73 is a novel immune checkpoint associated with adenosine metabolism that promotes tumor progression by suppressing antitumor immune response and promoting angiogenesis. The inhibition of CD73, in combination with immune checkpoint blockade, targeted therapy or conventional therapy, improves antitumor effects in numerous preclinical mouse models of cancer. Emerging evidence suggests that the combination of anti-CD73 and immune checkpoint blockade has promising clinical activity in patients with advanced solid tumors. In this review, we will discuss the specific role of CD73 on both tumor cells and nontumor cells in regulating tumor immunity and tumorigenesis and provide an update on the current view of the antitumor activity of targeting CD73 by mAb or small molecule selective inhibitors in preclinical and clinical settings.

Clinical significance of soluble forms of immune checkpoint molecules in advanced esophageal cancer.

Immune checkpoint molecules are expressed on cancer cells and regulate tumor immunity by binding to ligands on immune cells. Although soluble forms of immune checkpoint molecules have been detected in the blood of patients with some types of tumors, their roles have not been fully elucidated. Soluble PD-L1, PD-1, CD155, LAG3, and CD226 (sPD-L1, sPD-1, sCD155, sLAG3, and sCD226, respectively) were measured in the sera of 47 patients with advanced esophageal cancer and compared with those of 24 control subjects. Pretreatment levels of sPD-1 and sCD155 were significantly higher in the patients with cancer than in the control subjects (P = 0.023, P = 0.001). The sPD-1 levels tended to be higher in the patients with lymph node metastasis, a large tumor diameter, and higher levels of serum SCC antigen (P = 0.150, P = 0.189, and P = 0.078, respectively). However, higher levels of sCD155 were associated with a better response to chemotherapy and favorable overall survival (P = 0.111 and P = 0.068, respectively). After 2 courses of chemotherapy, the levels of sCD155 and sCD226 were significantly increased (P < 0.001 and P = 0.002, respectively). Moreover, the increase in sCD226 during chemotherapy was associated with poor treatment response (P = 0.019). sPD-1 levels are possibly dependent on the tumor aggressiveness of the esophageal cancer. Furthermore, the pretreatment levels of sCD155 and kinetic change of sCD226 after chemotherapy may be used as biomarkers of the treatment response and prognosis in patients with esophageal cancer.

MiR-217 Inhibits M2-Like Macrophage Polarization by Suppressing Secretion of Interleukin-6 in Ovarian Cancer

Ovarian cancer is one of the most deadly cancers with rapid proliferation and poor prognosis among patients. Therapies focusing on regulation of tumor immunity and microenvironments are developing. MiR-217 was dysregulated in cancer progress and plays important roles in tumorigenesis and metastasis. However, the role of miR-217 in regulation of macrophage polarization and its underlying molecular mechanism remain unclear. The expression of miR-217 in ovarian cancerous tissues and cell lines were assessed by qRT-PCR. And we detected the staining of CD86 and CD206 via flow-cytometry and the levels of Arg-1 and CCR2 by western-blot in order to evaluate M2 macrophage polarization. The targeting regulation of miR-217 on pro-inflammatory factor IL-6 was assessed by dual-luciferase reporter assay and western-blot. ELISA assay was used to evaluate the secretion of IL-6 and IL-10 of cells. MiR-217 was found to be downregulated in ovarian cancerous tissues and cell lines. This downregulation correlated with an increased expression of the IL-6, Arg-1, CCR2, and CD206 gene. The overexpression of miR-217 in SKOV3 cells can inhibit the polarization of macrophages towards an M2-like phenotype. We also found that IL-6 was validated to induce M2 macrophage polarization and its secretion in SKOV-3 cells was inhibited by miR-217 directly. Moreover, we revealed that miR-217 suppressed M2 macrophage polarization partly thought JAK/STAT3 signal pathway. Taken together, these findings indicate that miR-217 inhibits tumor-induced M2 macrophage polarization through targeting of IL-6 and regulation JAK3/STAT3 signaling pathway, which may provide a potential therapeutic target for treating ovarian cancer.

Advances in the role of exosome-derived long non-coding RNAs in hepatocellular carcinoma

Exosomes are one kind of microvesicles secreted by living cells. It contains some small non-coding RNAs (microRNA, lncRNA, circRNA, etc.) which play an important role in signal transduction. In addition, they transfer information through circulating small vesicles, regulate epithelial-mesenchymal transition, tumor microenvironment, promote microangiogenesis, regulate tumor immunity, chemoradiation resistance, and regulate cellular energy metabolism pathways, thereby promoting the occurrence, development and metastasis of hepatocellular carcinoma. This article reviews the mechanism of lncRNA in exogenous and in vivo in relation to the occurrence, development and metastasis of hepatocellular carcinoma.

The complex entanglement of Hippo-Yap/Taz signaling in tumor immunity.

The Hippo-Yap/Taz pathway, originally identified as a central developmental regulator of organ size, has been found perturbed in many types of human tumors, and linked to tumor growth, survival, evasion, metastasis, stemness, and drug resistance. Beside these tumor-cell-intrinsic functions, Hippo signaling also plays important immune-regulatory roles. In this review, we will summarize and discuss recent breakthroughs in our understanding of how various components of the Hippo-Yap/Taz pathway influence the tumor immune microenvironment, including their effects on the tumor secretome and immune infiltrates, their roles in regulating crosstalk between tumor cells and T cells, and finally their intrinsic functions in various types of innate and adaptive immune cells. While further research is needed to integrate and reconcile existing findings and to discern the overall effects of Hippo signaling on tumor immunity, it is clear that Hippo signaling functions as a key bridge connecting tumor cells with both the adaptive and innate immune systems. Thus, all future therapeutic development against the Hippo-Yap/Taz pathway should take into account their multi-faceted roles in regulating tumor immunity in addition to their growth-regulatory functions. Given that immune therapies have become the mainstay of cancer treatment, it is also important to pursue how to manipulate Hippo signaling to boost response or overcome resistance to existing immune therapies.

The Role of Yes-Associated Protein (YAP) in Regulating Programmed Death-Ligand 1 (PD-L1) in Thoracic Cancer.

The programmed death-ligand 1(PD-L1)/PD-1 pathway is an immunological checkpoint in cancer cells. The binding of PD-L1 and PD-1 promotes T-cell tolerance and helps tumor cells escape from host immunity. Immunotherapy targeting the PD-L1/PD-1 axis has been developed as an anti-cancer therapy and used in treating advanced human non-small cell lung cancer (NSCLC) and malignant pleural mesothelioma (MPM). Yes-associated protein (YAP) is a key mediator of the Hippo/YAP signaling pathway, and plays important roles in promoting cancer development, drug resistance and metastasis in human NSCLC and MPM. YAP has been suggested as a new therapeutic target in NSCLC and MPM. The role of YAP in regulating tumor immunity such as PD-L1 expression has just begun to be explored, and the correlation between YAP-induced tumorigenesis and host anti-tumor immune responses is not well known. Here, we review recent studies investigating the correlation between YAP and PD-L1 and demonstrating the mechanism by which YAP regulates PD-L1 expression in human NSCLC and MPM. Future work should focus on the interactions between Hippo/YAP signaling pathways and the immune checkpoint PD-L1/PD-1 pathway. The development of new synergistic drugs for immune checkpoint PD-L1/PD-1 blockade in NSCLC and MPM is warranted.

FOXP3 and CD25 double staining antibody cocktails identify regulatory T cells in different types of tumor tissues using tissue microarrays

Regulatory T cells (Tregs) are CD4+ T cells that express CD25 and transcription factor Forkhead box P3 (FOXP3), and Tregs play a central role in regulation of tumor immunity. FOXP3 immunohistochemistry has been widely used to study Tregs in paraffin embedded tissue, and flow cytometry using fresh tissue has been used to identify FOXP3+/CD25+ double positive Tregs. In our study, we validated the FOXP3/CD25 double staining antibody cocktails for detecting Tregs in paraffin-embedded tissue. Tissue microarrays (TMA) included 115 malignant tumors, 3 ovarian mucinous borderline tumors and 15 benign tissues. Digital image analysis was performed using ImageJ software. Our results showed that FOXP3/CD25 double positive lymphocytes, a subset of FOXP3+ lymphocytes, accounted for variable percentage of the total FOXP3+ lymphocytes and they were positively correlated with FOXP3+ cell counts. Tumors from different sites had variable FOXP3+/CD25+ and FOXP3+ lymphocyte counts. Tumors from lung, head & neck and colon had more and renal cell carcinoma had minimal FOXP3+/CD25+ and FOXP3+ lymphocytes. In conclusion, FOXP3/CD25 double staining antibody cocktails can be easily applied to paraffin-embedded tissue, and FOXP3+/CD25+ Tregs count was positively correlated with FOPX3+ Tregs count but they were not interchangeable. We recommend using CD25/FOXP3 double staining for studying Tregs in tumor tissue.

Loss of VGLL4 suppresses tumor PD-L1 expression and immune evasion.

Targeting immune checkpoints, such as PD-L1 and its receptor PD-1, has opened a new avenue for treating cancers. Understanding the regulatory mechanism of PD-L1 and PD-1 will improve the clinical response rate and efficacy of PD-1/PD-L1 blockade in cancer patients and the development of combinatorial strategies. VGLL4 inhibits YAP-induced cell proliferation and tumorigenesis through competition with YAP for binding to TEADs. However, whether VGLL4 has a role in anti-tumor immunity is largely unknown. Here, we found that disruption of Vgll4 results in potent T cell-mediated tumor regression in murine syngeneic models. VGLL4 deficiency reduces PD-L1 expression in tumor cells. VGLL4 interacts with IRF2BP2 and promotes its protein stability through inhibiting proteasome-mediated protein degradation. Loss of IRF2BP2 results in persistent binding of IRF2, a transcriptional repressor, to PD-L1 promoter. In addition, YAP inhibits IFNγ-inducible PD-L1 expression partially through suppressing the expression of VGLL4 and IRF1 by YAP target gene miR-130a. Our study identifies VGLL4 as an important regulator of PD-L1 expression and highlights a central role of VGLL4 and YAP in the regulation of tumor immunity.

Expression of B7 Homolog 1 (B7H1) Is Associated with Clinicopathologic Features in Urothelial Bladder Cancer

BackgroundB7 homolog 1 (B7H1) plays an important role in regulating tumor immunity. The purpose of this study was to probe the relationship between B7H1 expression and clinical outcomes in urothelial bladder cancer.Material/MethodsWe investigated 110 urothelial bladder cancer cases. The expressions of B7H1 in tumors were analyzed by immunohistochemistry and RT-PCR. The correlation between B7H1 expression and survival rate was analyzed by log-rank test.ResultsB7H1 expression was significantly increased in cancerous tissues compared to normal tissues (p<0.05). B7H1 expression was not associated with sex, age, diameter, or the combination of these factors (p>0.05). The positive expression of B7-H1 was positively correlated with grade, stage, recurrence, and metastasis (p<0.05). The RT-PCR results were consistent with the immunohistochemistry outcomes. Furthermore, the expression of B7H1 in tumors was highly correlated with the survival rate (p<0.05).ConclusionsExpression of B7H1 is correlated with clinicopathologic features in bladder cancer. Up-regulation of B7H1 can result in progression and recurrence of urothelial bladder cancer.

A RIPK3-PGE2 Circuit Mediates Myeloid-Derived Suppressor Cell-Potentiated Colorectal Carcinogenesis.

Receptor-interacting protein kinase 3 (RIPK3) is essential for mucosal repair in inflammatory bowel diseases (IBD) and colorectal cancer. However, its role in tumor immunity is unknown. Here, we report that decreased RIPK3 in colorectal cancer correlates with the accumulation of myeloid-derived suppressor cells (MDSC). Deficiency of RIPK3 boosted tumorigenesis via accumulation and immunosuppressive activity of MDSCs. Reduction of RIPK3 in MDSC and colorectal cancer cells elicited NFκB-transcribed COX-2, which catalyzed the synthesis of prostaglandin E2 (PGE2). PGE2 exacerbated the immunosuppressive activity of MDSCs and accelerated tumor growth. Moreover, PGE2 suppressed RIPK3 expression while enhancing expression of NFκB and COX-2 in MDSCs and colorectal cancer cells. Inhibition of COX-2 or PGE2 receptors reversed the immunosuppressive activity of MDSCs and dampened tumorigenesis. Patient databases also delineated the correlation of RIPK3 and COX-2 expression with colorectal cancer survival. Our findings demonstrate a novel signaling circuit by which RIPK3 and PGE2 regulate tumor immunity, providing potential ideas for immunotherapy against colorectal cancer.Significance: A novel signaling circuit involving RIPK3 and PGE2 enhances accumulation and immunosuppressive activity of MDSCs, implicating its potential as a therapeutic target in anticancer immunotherapy.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/19/5586/F1.large.jpg Cancer Res; 78(19); 5586-99. ©2018 AACR.

Checkpoint Inhibition in Myeloma: Opportunities and Challenges.

Despite major improvements in the treatment landscape, most multiple myeloma (MM) patients eventually succumb to the underlying malignancy. Immunotherapy represents an attractive strategy to achieve durable remissions due to its specificity and capacity for long term memory. Activation of immune cells is controlled by a balance of agonistic and inhibitory signals via surface and intracellular receptors. Blockade of such inhibitory immune receptors (termed as “immune checkpoints”) including PD-1/PD-L1 has led to impressive tumor regressions in several cancers. Preclinical studies suggest that these immune checkpoints may also play a role in regulating tumor immunity in MM. Indeed, myeloma was among the first tumors wherein therapeutic efficacy of blockade of PD-1 axis was demonstrated in preclinical models. Expression of PD-L1 on tumor and immune cells also correlates with the risk of malignant transformation. However, early clinical studies of single agent PD-1 blockade have not led to meaningful tumor regressions. Immune modulatory drugs (IMiDs) are now the mainstay of most MM therapies. Interestingly, the mechanism of immune activation by IMiDs also involves release of inhibitory checkpoints, such as Ikaros-mediated suppression of IL-2. Combination of PD-1 targeted agents with IMiDs led to promising clinical activity, including objective responses in some patients refractory to IMiD therapy. However, some of these studies were transiently halted in 2017 due to concern for a possible safety signal with IMiD-PD1 combination. The capacity of the immune system to control MM has been further reinforced by recent success of adoptive cell therapies, such as T cells redirected by chimeric-antigen receptors (CAR-Ts). There remains an unmet need to better understand the immunologic effects of checkpoint blockade, delineate mechanisms of resistance to these therapies and identify optimal combination of agonistic signaling, checkpoint inhibitors as well as other therapies including CAR-Ts, to realize the potential of the immune system to control and prevent MM.

Abstract B44: Regulation of macrophage activation by vascular niche in glioblastoma

Abstract Spatiotemporal regulation of tumor immunity remains largely unexplored. Here we identify a vascular niche that controls alternative macrophage activation in glioblastoma (GBM). We show that tumor-promoting macrophages are spatially proximate to GBM-associated endothelial cells (ECs), permissive for angiocrine-induced macrophage polarization. We identify ECs as a major source for interleukin (IL)-6 expression in GBM microenvironment. Furthermore, we reveal that colony stimulating factor-1 (CSF-1) and angiocrine IL-6 induce robust arginase-1 expression and macrophage alternative activation, mediated through peroxisome proliferator-activated receptor (PPAR)-γ-dependent transcriptional activation of hypoxia-inducible factor (HIF)-2α. Finally, utilizing a genetic murine GBM model, we show that EC-specific knockout of IL-6 inhibits macrophage alternative activation and improves survival in the GBM-bearing mice. These findings illustrate a vascular niche-dependent mechanism for alternative macrophage activation and cancer progression, and suggest that targeting endothelial IL-6 may offer a selective and efficient therapeutic strategy for GBM, and possibly other solid malignant tumors. Note: This abstract was not presented at the conference. Citation Format: Qirui Wang, Yanqing Anna Gong, Yi Fan. Regulation of macrophage activation by vascular niche in glioblastoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B44.

Tissue-Specific Roles of NKT Cells in Tumor Immunity.

NKT cells are an unusual population of T cells recognizing lipids presented by CD1d, a non-classical class-I-like molecule, rather than peptides presented by conventional MHC molecules. Type I NKT cells use a semi-invariant T cell receptor and almost all recognize a common prototype lipid, α-galactosylceramide (α-GalCer). Type II NKT cells are any lipid-specific CD1d-restricted T cells that use other receptors and generally don’t recognize α-GalCer. They play important regulatory roles in immunity, including tumor immunity. In contrast to type I NKT cells that most have found to promote antitumor immunity, type II NKT cells suppress tumor immunity and the two subsets cross-regulate each other, forming an immunoregulatory axis. They also can promote other regulatory cells including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs), and can induce MDSCs to secrete TGF-β, one of the most immunosuppressive cytokines known. In some tumors, both Tregs and type II NKT cells can suppress immunosurveillance, and the balance between these is determined by a type I NKT cell. We have also seen that regulation of tumor immunity can depend on the tissue microenvironment, so the same tumor in the same animal in different tissues may be regulated by different cells, such as type II NKT cells in the lung vs Tregs in the skin. Also, the effector T cells that protect those sites when Tregs are removed do not always act between tissues even in the same animal. Thus, metastases may require different immunotherapy from primary tumors. Newly improved sulfatide-CD1d tetramers are starting to allow better characterization of the elusive type II NKT cells to better understand their function and control it to overcome immunosuppression.