Specific recruitment of γδ regulatory T cells in human breast cancer

Understanding the role of different subtypes of tumor-infiltrating lymphocytes (TIL) in the immunosuppressive tumor microenvironment is essential for improving cancer treatment. Enriched γδ1 T-cell populations in TILs suppress T-cell responses and dendritic cell maturation in breast cancer, where their presence is correlated negatively with clinical outcomes. However, mechanism(s) that explain the increase in this class of regulatory T cells (γδ Treg) in patients with breast cancer have yet to be elucidated. In this study, we show that IP-10 secreted by breast cancer cells attracted γδ Tregs. Using neutralizing antibodies against chemokines secreted by breast cancer cells, we found that IP-10 was the only functional chemokine that causes γδ Tregs to migrate toward breast cancer cells. In a humanized NOD-scid IL-2Rγ(null) (NSG) mouse model, human breast cancer cells attracted γδ Tregs as revealed by a live cell imaging system. IP-10 neutralization in vivo inhibited migration and trafficking of γδ Tregs into breast tumor sites, enhancing tumor immunity mediated by tumor-specific T cells. Together, our studies show how γδ Tregs accumulate in breast tumors, providing a rationale for their immunologic targeting to relieve immunosuppression in the tumor microenvironment.

A novel recombinant DNA vaccine encoding Mycobacterium tuberculosis ESAT-6 and FL protects against Mycobacterium tuberculosis challenge in mice

Mycobacterium tuberculosis 6-kDa early secretory antigenic target (ESAT-6) is a dominant target antigen for cell-mediated immunity in the early phase of tuberculosis. The fms-like tyrosine kinase 3 ligand (FL) that induces potent immune response has been used as an adjuvant in vaccine development. In this study, a new recombinant plasmid (pIRES-epitope-peptides-FL) encoding three T cell epitopes of ESAT-6 and FL was constructed, and the immunogenicity of the DNA vaccine was assessed in C57BL/6 mice immunized with the plasmid DNA vaccine. Additionally, a strategy of intramuscular injection with the DNA vaccine (prime) and intranasal administration of the epitope peptides (boost) was employed to induce higher immune reaction of the mice. The results showed that mice vaccinated with the recombinant plasmid DNA vaccine and boosted with the peptides not only increased the levels of Th1 cytokines (IFN-γ and IL-12), the number of IFN-γ⁺ T cells and activities of cytotoxic T lymphocytes as well as IgG, but also enhanced protection against Mycobacterium tuberculosis challenge. In conclusion, these data indicate that the novel recombinant pIRES-epitope-peptides-FL plasmid is a useful DNA vaccine for preventing Mycobacterium tuberculosis infection.

Molecular control of human regulatory T cell suppression for tumor immunotherapy (P2106)

Immunotherapy is a promising approach for treating patients with malignant tumor, but immunosuppressive microenvironments induced by regulatory T cells (Tregs) present a major barrier to successful anti-tumor immunotherapy. A better understanding of the suppressive mechanisms utilized by Tregs is essential for the development of novel strategies to treat human cancer. Here we report that human Tregs can induce senescence in responder naïve and effector T cells in vitro and in vivo. Senescent responder T cells induced by human Tregs changed their phenotypes and cytokine profiles, and possessed potent suppressive function. Furthermore, Treg-mediated molecular control of senescence in responder T cells was associated with selective modulation of p38 and ERK1/2 signaling and cell cycle regulatory molecules p16, p21 and p53. We further revealed that human Treg-induced senescence and suppressor function could be blocked by TLR8 signaling and/or by specific ERK1/2 and p38 inhibition in vitro and in vivo in animal models. Our studies identify a novel mechanism of human Treg cell suppression that induces targeted responder T cell senescence, and provide new insights relevant for the development of strategies capable of preventing and/or reversing Treg-induced immune suppression for tumor immunotherapy.

Enhanced immune response and protective effects of nano-chitosan-based DNA vaccine encoding T cell epitopes of Esat-6 and FL against Mycobacterium tuberculosis infection

Development of a novel and effective vaccine against Mycobacterium tuberculosis (M.tb) is a challenging for preventing TB infection. In this study, a novel nanoparticle-based recombinant DNA vaccine was developed, which contains Esat-6 three T cell epitopes (Esat-6/3e) and fms-like tyrosine kinase 3 ligand (FL) genes (termed Esat-6/3e-FL), and was enveloped with chitosan (CS) nanoparticles (nano-chitosan). The immunologic and protective efficacy of the nano-chitosan-based DNA vaccine (termed nano-Esat-6/3e-FL) was assessed in C57BL/6 mice after intramuscular prime vaccination with the plasmids DNA and nasal boost with the Esat-6/3e peptides. The results showed that the immunized mice remarkably elicited enhanced T cell responses and protection against M.tb H37Rv challenge. These findings indicate that the nano-chitosan can significantly elevate the immunologic and protective effects of the DNA vaccine, and the nano-Esat-6/3e-FL is a useful vaccine for preventing M.tb infection in mice.

Abstract 4995: Tumor-dervied gammadelta regulatory T cells suppress innate and adaptive immunity through the induction of immunosenescence

Fundamentally understanding the suppressive mechanisms utilized by different subsets of tumor-infiltrating regulatory T (Treg) cells is critical for the development of effective strategies for anti-tumor immunotherapy. Gammadelta Treg cells have recently been identified in human diseases including in cancer patients. However, the suppressive mechanisms and functional regulations of this new subset of unconventional Treg cells are largely unknown. In the current studies, we explored the suppressive mechanism(s) utilized by human breast tumor-derived gammadelta Treg cells on innate and adaptive immunity. We found that gammadelta Treg cells induced immunosenescence in targeted naïve and effector T cells, as well as dendritic cells (DCs). Furthermore, senescent T cells and DCs induced by gammadelta Treg cells had altered phenotypes and developed potent suppressive activities, further amplifying the immunosuppression mediated by gammadelta Treg cells. In addition, we demonstrated that manipulation of TLR8 signaling in gammadelta Treg cells can block gammadelta Treg-induced conversion of T cells and DCs into senescent cells in vitro and in vivo. Our studies identify the novel suppressive mechanism mediated by human tumor-derived gammadelta Treg cells on innate and adaptive immunity, which should be critical for development of strong and innovative approaches to reverse the tumor suppressive microenvironment and improve effects of immunotherapy. This work was supported by the grant from the American Cancer Society (RSG-10-160-01-LIB).

Key words: gammadelta T cells; Regulatory T cells; Dendritic cells; Senescence; Immune suppression

Citation Format: Jian Ye, Chunling Ma, Eddy C. Hsueh, Yanping Zhang, Mark A. Varvares, Daniel F. Hoft, Guangyong Peng. Tumor-dervied gammadelta regulatory T cells suppress innate and adaptive immunity through the induction of immunosenescence. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4995. doi:10.1158/1538-7445.AM2013-4995

Evidence that the biofungicide Serenade (Bacillus subtilis) suppresses clubroot on canola via antibiosis and induced host resistance

This study investigated how the timing of application of the biofungicide Serenade (Bacillus subtilis QST713) or it components (product filtrate and bacterial cell suspension) influenced infection of canola by Plasmodiophora brassicae under controlled conditions. The biofungicide and its components were applied as a soil drench at 5% concentration (vol/vol or equivalent CFU) to a planting mix infested with P. brassicae at seeding or at transplanting 7 or 14 days after seeding (DAS) to target primary and secondary zoospores of P. brassicae. Quantitative polymerase chain reaction (qPCR) was used to assess root colonization by B. subtilis as well as P. brassicae. The biofungicide was consistently more effective than the individual components in reducing infection by P. brassicae. Two applications were more effective than one, with the biofungicide suppressing infection completely and the individual components reducing clubroot severity by 62 to 83%. The biofungicide also reduced genomic DNA of P. brassicae in canola roots by 26 to 99% at 7 and 14 DAS, and the qPCR results were strongly correlated with root hair infection (%) assessed at the same time (r = 0.84 to 0.95). qPCR was also used to quantify the transcript activity of nine host-defense-related genes in inoculated plants treated with Serenade at 14 DAS for potential induced resistance. Genes encoding the jasmonic acid (BnOPR2), ethylene (BnACO), and phenylpropanoid (BnOPCL and BnCCR) pathways were upregulated by 2.2- to 23-fold in plants treated with the biofungicide relative to control plants. This induced defense response was translocated to the foliage (determined based on the inhibition of infection by Leptosphaeria maculans). It is possible that antibiosis and induced resistance are involved in clubroot suppression by Serenade. Activity against the infection from both primary and secondary zoospores of P. brassicae may be required for maximum efficacy against clubroot.

Tumor-derived γδ regulatory T cells suppress innate and adaptive immunity through the induction of immunosenescence

Fundamentally understanding the suppressive mechanisms used by different subsets of tumor-infiltrating regulatory T (Treg) cells is critical for the development of effective strategies for antitumor immunotherapy. γδ Treg cells have recently been identified in human diseases including cancer. However, the suppressive mechanisms and functional regulations of this new subset of unconventional Treg cells are largely unknown. In the current studies, we explored the suppressive mechanism(s) used by breast tumor-derived γδ Treg cells on innate and adaptive immunity. We found that γδ Treg cells induced immunosenescence in the targeted naive and effector T cells, as well as dendritic cells (DCs). Furthermore, senescent T cells and DCs induced by γδ Treg cells had altered phenotypes and impaired functions and developed potent suppressive activities, further amplifying the immunosuppression mediated by γδ Treg cells. In addition, we demonstrated that manipulation of TLR8 signaling in γδ Treg cells can block γδ Treg-induced conversion of T cells and DCs into senescent cells in vitro and in vivo. Our studies identify the novel suppressive mechanism mediated by tumor-derived γδ Treg cells on innate and adaptive immunity, which should be critical for the development of strong and innovative approaches to reverse the tumor-suppressive microenvironment and improve effects of immunotherapy.

Granzyme A produced by γ(9)δ(2) T cells induces human macrophages to inhibit growth of an intracellular pathogen

Human γ₉δ₂ T cells potently inhibit pathogenic microbes, including intracellular mycobacteria, but the key inhibitory mechanism(s) involved have not been identified. We report a novel mechanism involving the inhibition of intracellular mycobacteria by soluble granzyme A. γ₉δ₂ T cells produced soluble factors that could pass through 0.45 µm membranes and inhibit intracellular mycobacteria in human monocytes cultured below transwell inserts. Neutralization of TNF-α in co-cultures of infected monocytes and γ₉δ₂ T cells prevented inhibition, suggesting that TNF-α was the critical inhibitory factor produced by γ₉δ₂ T cells. However, only siRNA- mediated knockdown of TNF-α in infected monocytes, but not in γ₉δ₂ T cells, prevented mycobacterial growth inhibition. Investigations of other soluble factors produced by γ₉δ₂ T cells identified a highly significant correlation between the levels of granzyme A produced and intracellular mycobacterial growth inhibition. Furthermore, purified granzyme A alone induced inhibition of intracellular mycobacteria, while knockdown of granzyme A in γ₉δ₂ T cell clones blocked their inhibitory effects. The inhibitory mechanism was independent of autophagy, apoptosis, nitric oxide production, type I interferons, Fas/FasL and perforin. These results demonstrate a novel microbial defense mechanism involving granzyme A-mediated triggering of TNF-α production by monocytes leading to intracellular mycobacterial growth suppression. This pathway may provide a protective mechanism relevant for the development of new vaccines and/or immunotherapies for macrophage-resident chronic microbial infections.

A small subset of human T cells express γ₉δ₂ T cell receptors and recognize unique non-peptide phosphoantigens expressed by microbes and damaged cells, such as cancer. These cells are important because: 1) they reside within skin and mucosal surfaces at critical points of initial pathogen invasion, and 2) they are not restricted by polymorphic HLA types and thus can be activated by the same cognate antigens in highly diverse populations. Many important human pathogens such as the causes of AIDS, malaria, tuberculosis and others induce potent responses in γ₉δ₂ T cells that can be protective. However, the key mechanisms involved in γ₉δ₂ T cell-mediated protective immunity are not well defined. We have found that γ₉δ₂ T cells produce soluble granzyme A which correlates with their ability to protect against intracellular mycobacterial growth. We show directly that highly purified granzyme A alone can trigger human monocytes to control intracellular mycobacteria. We further show that the granzyme A-induced mycobacterial inhibition required production of TNF-α by infected monocytes. These studies may have important implications for future vaccine development and novel therapeutic strategies.

The role and regulation of human Th17 cells in tumor immunity

T helper 17 (Th17) cells play critical roles in the pathogenesis of inflammatory and autoimmune diseases, as well as in host protection against pathogens. The contribution of Th17 cells to human tumor immunity, however, remains largely unknown. Since their identification in 2005, Th17 cells have been extensively studied in mouse tumor models and human cancer patients. Although accumulating data suggest the importance of Th17 cells to tumor immunity, conclusions regarding the functional role of Th17 cells remain controversial. In this review, we summarize current knowledge regarding the regulation and functional role of Th17 cells in human cancers. In particular, we emphasize several recently identified characteristics of Th17 cells, including plasticity, their relationship with regulatory T cells, and Th17 cell heterogeneity in the tumor microenvironment. Improved understanding of these issues is critical to elucidating the role of Th17 cells in antitumor immunity and for the design of novel therapeutic approaches specifically targeting Th17 cells.

Tumor-infiltrating γδ T lymphocytes predict clinical outcome in human breast cancer

Understanding and dissecting the role of different subsets of regulatory tumor-infiltrating lymphocytes (TILs) in the immunopathogenesis of individual cancer is a challenge for anti-tumor immunotherapy. High levels of γδ regulatory T cells have been discovered in breast TILs. However, the clinical relevance of these intratumoral γδ T cells is unknown. In this study, γδ T cell populations were analyzed by performing immunohistochemical staining in primary breast cancer tissues from patients with different stages of cancer progression. Retrospective multivariate analyses of the correlations between γδ T cell levels and other prognostic factors and clinical outcomes were completed. We found that γδ T cell infiltration and accumulation in breast tumor sites was a general feature in breast cancer patients. Intratumoral γδ T cell numbers were positively correlated with advanced tumor stages, HER2 expression status, and high lymph node metastasis but inversely correlated with relapse-free survival and overall survival of breast cancer patients. Multivariate and univariate analyses of tumor-infiltrating γδ T cells and other prognostic factors further suggested that intratumoral γδ T cells represented the most significant independent prognostic factor for assessing severity of breast cancer compared with the other known factors. Intratumoral γδ T cells were positively correlated with FOXP3(+) cells and CD4(+) T cells but negatively correlated with CD8(+) T cells in breast cancer tissues. These findings suggest that intratumoral γδ T cells may serve as a valuable and independent prognostic biomarker, as well as a potential therapeutic target for human breast cancer.

Human herpesvirus 6 latent infection in patients with glioma

The etiology of glioma remains unclear so far. Human herpesvirus 6 (HHV-6) might be associated with glioma, but there is no direct evidence to support this. High percentages of HHV-6 DNA and protein were detected in tissue from gliomas, compared with normal brain tissue. In addition, a strain of HHV-6A was isolated from the fluid specimens from glioma cysts. High levels of interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor α, and transforming growth factor β (TGF-β) were detected in the cyst fluid specimens from HHV-6-positive patients with glioma. Furthermore, HHV-6A infection promoted IL-6, IL-8, and TGF-β production in astrocyte cultures. Our studies strongly suggest the involvement of HHV-6 infection in the pathogenesis of glioma.

Specific recruitment of gammadelta regulatory T cells by tumor cells in human breast cancer (127.38)

Understanding the role of different subtypes of tumor-infiltrating lymphocytes (TILs) in the tumor immunosuppressive microenvironment is essential to cancer treatment and elimination. We recently discovered that enriched gammadelta1 T cell populations in breast cancer TILs can suppress naïve and effector T cell responses and block the maturation and activities of dendritic cells. However, the mechanism(s) governing the gammadelta regulatory T (Treg) cell increase in breast cancer patients remains elusive. In this study, we showed that IP-10 secreted by breast cancer cells significantly attracted the migration of gammadelta Treg cells. Using the loss-of-function assay with neutralizing antibodies against the chemokines secreted by breast cancer cells, we demonstrated that IP-10 was the only functional chemokine that attracts the migration of gammadelta Treg cells by breast cancer cells. We further demonstrated that human breast tumor cells also can attract gammadelta Treg cells in vivo in NOD-SCID mice using live cell imaging systems. In addition, neutralization of IP-10 and CXCR3 significantly inhibited the migration and trafficking of gammadelta Treg cells to the breast tumor sites in vivo. These studies identify the mechanism responsible for the accumulation of gammadelta Treg cells in breast cancer patients and provide novel immunologic approaches capable of preventing the trafficking and generation of gammadelta Treg cells in breast tumor suppressive microenvironments.

Abstract 3544: Role of tumor-infiltrating gammadelta T lymphocytes in breast cancer

Breast cancer is the second leading cause of cancer-related deaths in women worldwide. Increasing evidence suggests that immunotherapy is a promising strategy for treating breast cancer, and understanding of the roles of different subtypes of tumor-infiltrating lymphocytes (TILs) in the tumor immunosuppressive microenvironment may be essential to cancer treatment and elimination. We recently discovered that enriched gammadelta1 T cell populations in the breast cancer TILs can suppress naïve and effector T cell responses and block the maturation and activities of dendritic cells (DC). In order to investigate the functional role of tumor-infiltrating gammadelta T cells in the immune pathogenesis of breast cancer, we further performed immunohistochemical staining to analyze gammadelta T cells, as well as CD4+, CD8+, IL-17-producing and FoxP3+ T cells in 50 freshly frozen tumor tissues from different stages of identified primary breast cancer and paired normal breast tissues. We found that the numbers of gammadelta T cells among tumor tissues were significantly increased compared with those in normal breast tissues in breast cancer patients. High numbers of gammadelta T cells were present in the patients with high tumor grades and lymph node metastases. Importantly, the patients with a high proportion of gammadelta T cells showed poorer survival rates in comparison to those with a low proportion of gammadelta T cells in breast cancer. These results indicate that gammadelta T cells constitute a dominant population existing in the breast tumor suppressive microenvironment that is negatively associated with clinical outcome, which may be an important cancer immunotherapeutic target for breast cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3544. doi:1538-7445.AM2012-3544

Differentiation of umbilical cord mesenchymal stem cells into steroidogenic cells in comparison to bone marrow mesenchymal stem cells

OBJECTIVES

Human umbilical cord can be obtained easily and it represents a non-controversial source of mesenchymal stem cells (MSCs) and umbilical cord Wharton's jelly-derived MSCs (UC-MSCs) have low immunogenicity. In this study, UC-MSCs were induced to become steroidogenic cells and compared to bone marrow-derived MSCs (BM-MSCs).

MATERIAL AND METHODS

UC-MSCs and BM-MSCs were induced to differentiate into steroidogenic cells by infection with adenovirus containing SF-1. Expression of steroidogenic mRNA was analysed by real-time RT-PCR and steroid secretion was detected by ELISA testing. Viability of differentiated cells was examined using cell counting kit-8 assay.

RESULTS

Both UC-MSCs and BM-MSCs expressed typical MSC markers and could differentiate into adipocytes, osteocytes and chondrocytes and both cell types had the potential to differentiate into steroidogenic cells after being infected with adenovirus containing SF-1 cDNA. However, UC-MSCs had significantly higher proliferative potential than BM-MSCs and differentiated UC-MSCs had significantly higher expression of all steroidogenic mRNAs tested over those of differentiated BM-MSCs; this included P450 side-chain cleavage enzyme, 3β-HSD, 17β-HSD type 3, LH-R, ACTH-R, P450c21 and CYP17. In addition, differentiated UC-MSCs secreted significantly more steroidogenic hormones than differentiated BM-MSCs, including testosterone and cortisol. Furthermore, differentiated UC-MSCs had significantly higher cell viability than differentiated BM-MSCs.

CONCLUSIONS

UC-MSCs had significantly higher potential of steroidogenic differentiation than BM-MSCs; thus, UC-MSCs could be favourable cells of choice for cell-based therapy for steroidogenic insufficiency compared to BM-MSCs.

Generating CTLs against the subdominant EBV LMP antigens by transient expression of an A20 inhibitor with EBV LMP proteins in human DCs

Epstein-Barr virus (EBV) infection leads to Hodgkin’s disease (HD) in some immunocompetent hosts. The malignant Reed-Sternberg cells of HD only express a limited array of subdominant EBV antigens to evade preexisting immune responses to EBV. The EBV-encoded latent membrane proteins (LMP1 and LMP2), which are expressed by HD and various EBV-associated malignancies, have been proposed as a potential target for CTL-based therapy. However, the precursor frequency for LMP-specific CTL is generally low in healthy EBV-infected hosts, and immunotherapy based on these antigens is often compromised by the poor immunogenicity and the oncogenic potential. In the present study, we report that transitively expressing an inhibitor of A20, a key negative regulator of inflammatory signaling pathways, together with the LMP antigens (truncated LMP1 and full-length LMP2) greatly enhances maturation and cytokine production of human (h) monocyte-derived dendritic cells (DCs). As a consequence, LMP1/2-expressed, A20-silenced hDCs have an enhanced potency to prime LMP-specific T cell response. When the in vitro primed T cells are adoptively transferred into tumor-xenografted, severe combined immunodeficient (SCID) mice, some of the xenografted tumors approach complete regression. Thus, the study may provide an available resource of LMP-specific T cells for T cell immunotherapy.

Diagnosis of head-and-neck cancer from exhaled breath

Background:

Head-and-neck cancer (HNC) is the eighth most common malignancy worldwide. It is often diagnosed late due to a lack of screening methods and overall cure is achieved in <50% of patients. Head-and-neck cancer sufferers often develop a second primary tumour that can affect the entire aero-digestive tract, mostly HNC or lung cancer (LC), making lifelong follow-up necessary.

Methods:

Alveolar breath was collected from 87 volunteers (HNC and LC patients and healthy controls) in a cross-sectional clinical trial. The discriminative power of a tailor-made Nanoscale Artificial Nose (NA-NOSE) based on an array of five gold nanoparticle sensors was tested, using 62 breath samples. The NA-NOSE signals were analysed to detect statistically significant differences between the sub-populations using (i) principal component analysis with ANOVA and Student's t-test and (ii) support vector machines and cross-validation. The identification of NA-NOSE patterns was supported by comparative analysis of the chemical composition of the breath through gas chromatography in conjunction with mass spectrometry (GC–MS), using 40 breath samples.

Results:

The NA-NOSE could clearly distinguish between (i) HNC patients and healthy controls, (ii) LC patients and healthy controls, and (iii) HNC and LC patients. The GC–MS analysis showed statistically significant differences in the chemical composition of the breath of the three groups.

Conclusion:

The presented results could lead to the development of a cost-effective, fast, and reliable method for the differential diagnosis of HNC that is based on breath testing with an NA-NOSE, with a future potential as screening tool.

Abstract 781: Plasticity of human tumor-infiltrating Th17 cells

Although Th17 cells play critical roles in the pathogenesis of many inflammatory and autoimmune diseases, their function in human tumor immunity remains largely unknown. We have recently identified Th17 cells as an important component of human tumor-infiltrating lymphocytes (TILs) obtained from melanoma, breast, colon and ovarian cancer patients, but their stability and plasticity in the tumor microenvironment is still unclear. In this study, we generated Th17 clones from TILs. We showed that Th17 clones can differentiate into IFN-gamma-producing and FoxP3+ cells after in vitro stimulation with OKT3 and allogeneic peripheral blood mononuclear cells (PBMCs). We further demonstrated that T cell receptor (TCR) engagement was responsible for this conversion, and that this differentiation was due to the epigenetic modification and reprogramming of gene expression profiles, including lineage-specific transcriptional factor and cytokine genes. In addition to expressing IFN-gamma and FoxP3, we showed that these differentiated Th17 clones mediated potent suppressive function after repetitive stimulation with OKT3, suggesting that these Th17 clones had differentiated into functional Treg cells. We further demonstrated that the Th17-derived Treg cells, unlike naturally occurring CD4+CD25+ Treg cells, did not reconvert back into Th17 cells even under Th17-biasing cytokine conditions. These results provide the critical evidence that human Th17 cells can differentiate into Treg cells and indicate the substantial developmental plasticity of Th17 cells, which may have clinical implications for the development of novel cancer immunotherapeutic approaches.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 781. doi:10.1158/1538-7445.AM2011-781

Abstract 4066: Combination metformin and ODC siRNA inhibit human melanoma proliferation and migration

Metformin can exert an antiproliferative effect on human tumor cells through the AMP-activated kinase (AMPK) pathway. Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis pathway in cancer cell proliferation and tumor progression. We hypothesized that the combination of Metformin and small interfering RNA (siRNA) against ODC could inhibit human melanoma cell growth and migration in vitro.

Human melanoma cell line cells (SK-MEL23, MEL1861, MEL938, MEL3910, and MEL888) were evaluated. ODC siRNA and contol siRNA were transfected into the human melanoma cells using lipofectamine per manufacturer's instructions (Santa CruZ. CA). Transfected cell were then treated with 1uM, 2uM, 5uM Metformin and assess for cell proliferation and migration assay at various time points up to 72 hours. Cell proliferation assay was performed in triplicates using Cell Titer Blue Assay system according to manufacturer's protocol (Promega). Migration was assessed by creating an artificial homogenous wound onto a cell culture monolayer with a sterile plastic 10µl micropipette tip. Migration of cells into the wound was observed and photographed up to 48 hours. A total of three areas were selected randomly from each well and the cells in three wells of each group were quantified. All Data were presented as means ± SD for the three separate experiments. For comparison between groups, the student's t test was used and p&lt; 0.05 was considered to be statically significant.

Human melanoma cells were infected with ODC siRNA or control siRNA. On quantitative RT-PCR and Western blot analysis, &gt;95% suppression of ODC expression was achieved. The siRNA-ODC significantly inhibited cells growth up to 50% at 72 hour (P&lt;0.01). Inhibition of melanoma cell proliferation was also observed with Metformin in a dose-dependent fashion in all 5 melanoma cell line cells. Combination of ODC siRNA and Metformin significantly inhibited cell growth compared to ODC siRNA or MF alone (P&lt;0.01) in all 5 melanoma cell line cells. The addition of Metformin to siRNA-ODC also significantly inhibited melanoma migration in the wounding assay model.

Metformin treatment and inhibition of ODC expression can have anti-proliferative effect on human melanoma cells. The combination also retard melanoma cell migration in a wounding model. The combination of Metformin and ODC inhibition may be a novel treatment strategy for human melanoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4066. doi:10.1158/1538-7445.AM2011-4066

Human tumor-infiltrating Th17 cells have the capacity to differentiate into IFN-gamma+ and FOXP3+ T cells with potent suppressive function (66.27)

Accumulating evidence suggests that T-helper 17 (Th17) cells and regulatory T (Treg) cells may exhibit development plasticity, and that CD4+ Tregs can differentiate into IL-17-producing T cells; however, whether Th17 cells can reciprocally convert into Tregs has not been described. In this study, we generated Th17 clones from tumor-infiltrating T lymphocytes (TILs). We showed that Th17 clones generated from TILs can differentiate into IFN-gamma-producing and FOXP3+ cells after in vitro stimulation with OKT3 and allogeneic peripheral blood mononuclear cells (PBMCs). We further demonstrated that T-cell receptor (TCR) engagement was responsible for this conversion, and that this differentiation was due to the epigenetic modification and reprogramming of gene expression profiles, including lineage-specific transcriptional factor and cytokine genes. In addition to expressing IFN-gamma and FOXP3, we showed that these differentiated Th17 clones mediated potent suppressive function after repetitive stimulation with OKT3, suggesting that these Th17 clones had differentiated into functional Tregs. We further demonstrated that the Th17-derived Tregs, unlike naturally occurring CD4+CD25+ Tregs, did not reconvert back into Th17 cells even under Th17-biasing cytokine conditions. These results provide the critical evidence that human tumor-infiltrating Th17 cells can differentiate into Tregs and indicate a substantial developmental plasticity of Th17 cells.

Human herpesvirus 6 suppresses T cell proliferation through the induction of infected cell cycle arrest in G2/M phase (154.38)

Human herpesvirus 6 is an important immunosuppressive and immunomodulatory virus which infects immune cells and strongly suppresses the proliferation of infected cells. However, the mechanisms responsible for the regulation and suppression mediated by HHV-6 are still unknown. In this study, we examined the ability of HHV-6A to manipulate cell cycle progression in the infected cells and explored the potential molecular mechanisms. We demonstrated that infection with HHV-6A imposed a growth-inhibitory effect on HSB-2 cells by inducing cell cycle arrest at G2/M phase. We then showed that the activity of Cdc2-cyclinB1 complex was significantly decreased in HHV-6A infected HSB-2 cells. Furthermore, we found that inactivation of Cdc2-cyclinB1 in infected cells was through the inhibitory Tyr15 phosphorylation resulting from the elevated Wee1 expression and inactivated Cdc25C; Meanwhile, the reduction of Cdc2-cyclinB1 activity in infected cells was also partly due to the increased expression of cell cycle regulatory molecule p21 in a p53-dependent manner. In addition, HHV-6A infection activated the DNA damage checkpoint kinases, Chk2 and Chk1. Our data suggest that HHV-6A infection induces G2/M arrest in infected T cells via various regulatory mechanisms. These results demonstrate potential mechanisms involved in immune suppression and modulation mediated by HHV-6 infection, and provide new insights relevant to the development of novel vaccines and immunotherapeutic approaches.

Human tumor-infiltrating Th17 cells have the capacity to differentiate into IFN-γ+ and FOXP3+ T cells with potent suppressive function

Accumulating evidence suggests that Th17 cells and Tregs may exhibit development plasticity and that CD4(+) Tregs can differentiate into IL-17-producing T cells; however, whether Th17 cells can reciprocally convert into Tregs has not been described. In this study, we generated Th17 clones from tumor-infiltrating T lymphocytes (TILs). We showed that Th17 clones generated from TILs can differentiate into IFN-γ-producing and FOXP3(+) cells after in vitro stimulation with OKT3 and allogeneic peripheral blood mononuclear cells. We further demonstrated that T-cell receptor (TCR) engagement was responsible for this conversion, and that this differentiation was due to the epigenetic modification and reprogramming of gene expression profiles, including lineage-specific transcriptional factor and cytokine genes. In addition to expressing IFN-γ and FOXP3, we showed that these differentiated Th17 clones mediated potent suppressive function after repetitive stimulation with OKT3, suggesting that these Th17 clones had differentiated into functional Tregs. We further demonstrated that the Th17-derived Tregs, unlike naturally occurring CD4(+) CD25(+) Tregs, did not reconvert back into Th17 cells even under Th17-biasing cytokine conditions. These results provide the critical evidence that human tumor-infiltrating Th17 cells can differentiate into Tregs and indicate a substantial developmental plasticity of Th17 cells.