Conversion of tumor-specific CD4+ T-cell tolerance to T-cell priming through in vivo ligation of CD40.

Tumor antigen-specific T-cell tolerance limits the efficacy of therapeutic cancer vaccines. Antigen-presenting cells mediate the induction of T-cell tolerance to self-antigens. We therefore assessed the fate of tumor-specific CD4+ T cells in tumor-bearing recipients after in vivo activation of antigen-presenting cells with antibodies against CD40. Such treatment not only preserved the responsiveness of this population, but resulted in their endogenous activation. Established tumors regressed in vaccinated mice treated with antibody against CD40 at a time when no response was achieved with vaccination alone. These results indicate that modulation of antigen-presenting cells may be a useful strategy for enhancing responsiveness to immunization.

Isolation of a nitric oxide inhibitor from mammary tumor cells and its characterization as phosphatidyl serine.

Macrophages from mice bearing large D1-DMBA-3 mammary tumors have a decreased capacity to kill tumor targets. This effect is due to an impaired ability to produce nitric oxide (NO) in response to lipopolysaccharide (LPS) stimulation. Here we report that the DA-3 tumor cell line, derived from the in vivo adenocarcinoma D1-DMBA-3, produces a factor that inhibits both NO production/release and cytotoxicity of LPS-activated peritoneal exudate macrophages (PEM). However, other complex macrophage functions such as phagocytosis, superoxide production, mitochondrial dehydrogenase activity, and synthesis of proteins were not reduced by this factor. The NO inhibitor has been found to be lipid in nature. Lipid extracts from DA-3 cell culture supernatants were purified by repeated silica gel column chromatography. The active molecule was unambiguously characterized as phosphatidyl serine (PS) by fast atom bombardment tandem mass spectrometry. Preliminary results indicate a lack of induced NO synthase (iNOS) activity in the lysates of LPS-activated PEM pretreated with PS. The ubiquity of PS in the inner leaflet of biological membranes and its NO inhibitory property, suggest that this phospholipid may be one of the long elusive molecules responsible for regulating physiological levels of NO in the host and hence preventing cellular dysfunction and/or tissue damage. Furthermore, the possible overexpression and shedding of PS by DA-3 tumor cells may represent a novel mechanism to impair macrophage cytotoxicity, a host function that contributes to the protection against developing neoplasms.

[Expressions and prognostic significance of PTEN and PD-1 protein in patients with classical Hodgkin's lymphoma].

Objective: To elucidate the expression levels of key immune biomarkers, phosphate and tension homology deleted on chromosome ten (PTEN) and programmed cell death protein1(PD-1),of different immune tolerance pathway in classic Hodgkin's lymphoma (CHL) to further determine their clinical role and prognostic significance. Methods: The clinical features and prognostic factors of 56 CHL patients, who were admitted to the TianJin Medical University Cancer Institute from February 2003 to August 2013, were retrospectively analyzed. PTEN and PD-1 protein expression levels were analyzed by immunohistochemistry, Epstein-Barr virus encoded RNA (EBER) was performed by in situ hybridization assay. Correlations between the expression of biomarkers and clinicopathologic parameters were examined and survival analyses were performed. Results: This cohort of 56 CHL patients included 34 males and 22 females with a median age of 25 years (ranged from 7 to 71 years). In a univariate analysis, age≥45, IPS score >2, EBER positive, high expression of PTEN protein conferred inferior 5-year OS and 5-year PFS; In a multivariate model, age≥45, IPS score >2, EBER positive, high expression of PTEN protein were identified as the independent adverse prognostic factors for CHL. Conclusions: This study suggested for the first time that PTEN was independent prognostic immune biomarkers in CHL, which provided the novel therapeutic strategy of immune therapy for CHL.

Targeting histone deacetylase 6 mediates a dual anti-melanoma effect: Enhanced antitumor immunity and impaired cell proliferation.

The median survival for metastatic melanoma is in the realm of 8-16 months and there are few therapies that offer significant improvement in overall survival. One of the recent advances in cancer treatment focuses on epigenetic modifiers to alter the survivability and immunogenicity of cancer cells. Our group and others have previously demonstrated that pan-HDAC inhibitors induce apoptosis, cell cycle arrest and changes in the immunogenicity of melanoma cells. Here we interrogated specific HDACs which may be responsible for this effect. We found that both genetic abrogation and pharmacologic inhibition of HDAC6 decreases in vitro proliferation and induces G1 arrest of melanoma cell lines without inducing apoptosis. Moreover, targeting this molecule led to an important upregulation in the expression of tumor associated antigens and MHC class I, suggesting a potential improvement in the immunogenicity of these cells. Of note, this anti-melanoma activity was operative regardless of mutational status of the cells. These effects translated into a pronounced delay of in vivo melanoma tumor growth which was, at least in part, dependent on intact immunity as evidenced by the restoration of tumor growth after CD4+ and CD8+ depletion. Given our findings, we provide the initial rationale for the further development of selective HDAC6 inhibitors as potential therapeutic anti-melanoma agents.

A universal granulocyte-macrophage colony-stimulating factor-producing bystander cell line for use in the formulation of autologous tumor cell-based vaccines.

Irradiated tumor cells transduced with the gene encoding the cytokine GM-CSF have been extensively studied as a vaccine formulation capable of priming systemic antitumor immune responses in the tumor-bearing host. In spite of the therapeutic promise of this vaccine strategy demonstrated in both animal models and early-phase clinical trials, clinical development has been limited by difficulties pertaining to the need to establish in culture the tumor of each patient and to perform individualized gene transfer. To circumvent these issues, we generated an HLA-negative human cell line producing large quantities of human GM-CSF for use as a universal bystander cell to be mixed with unmodified autologous tumor cells in the formulation of a vaccine. This line is easily propagated as a suspension culture in defined, serum-free medium. In a mouse model, we find that vaccination with a mixture of autologous tumor cells and an MHC-negative allogeneic GM-CSF-producing bystander cell primes antitumor immune responses that are equivalent or better than those achieved using autologous tumor cells directly transduced to secrete GM-CSF. This strategy greatly simplifies further clinical development of autologous tumor cell-based vaccines.

Long-term follow-up of intensive ara-C-based chemotherapy followed by bone marrow transplantation for adult acute lymphoblastic leukemia: impact of induction Ara-C dose and post-remission therapy.

We report single institution outcome of brief, intensive ara-C-based chemotherapy using bone marrow transplantation as primary intensification for untreated adult patients with acute lymphoblastic leukemia (ALL). Overall disease-free and overall survival were inferior to those reported with prolonged chemotherapy modeled on pediatric protocols. Survival and disease-free survival were superior for patients receiving allogeneic BMT compared with chemopurged autologous transplant or maintenance chemotherapy (patients ineligible for or declining BMT). In multivariate analysis, non-L2-FAB, higher ara-C dose, absence of CNS disease, non-Ph1+ karyotype, allogeneic BMT, T cell phenotype, and younger age were associated with improved disease-free survival. Autologous BMT was not superior to chemotherapy, and appears unlikely to provide adequate curative treatment for most adult ALL patients if not followed by maintenance.

Enhancement of macrophage tumouricidal activity by the alkaloid derivative Ukrain. In vitro and in vivo studies.

Ukrain is a semisynthetic drug with immunomodulatory properties, derived from Chelidonium majus L. alkaloids and thiophosphoric acid. The effect of this compound on the growth of Balb/c syngenic mammary adenocarcinoma was assessed. Intravenous, but not subcutaneous or intraperitoneal, administration of this drug was found to be effective in delaying tumour growth in an actual therapeutic protocol initiated five days after tumour implantation. No untoward side-effects were observed using these in vivo treatment modalities. The role of macrophages in the observed retardation of tumour development was investigated using peritoneal exudate macrophages (PEM) in cytotoxicity assays. In previous studies, the authors have found that PEM of mammary tumour bearing mice lose their capacity to kill a variety of tumour target cells including the in vitro cultured homologous tumour cells (DA-3). Pretreatment of PEM from normal mice with 2.5 microM Ukrain for 24 h followed by stimulation with either IFN-gamma or with LPS+IFN-gamma enhanced their cytotoxic activity. Treatment of PEM from tumour bearing mice with 2.5 microM Ukrain and LPS results in a reversal of their defective cytotoxic response against the DA-3 target cells. Furthermore, Ukrain alone, in the absence of a secondary signal, induced the activation of tumouricidal function of PEM from tumour bearing but not from normal mice. These data indicate that Ukrain's in vivo effects against the development of mammary tumours may be due, at least in part, to its ability to restore macrophage cytolytic function.

Follicular dendritic cell-induced microRNA-mediated upregulation of PRDM1 and downregulation of BCL-6 in non-Hodgkin's B-cell lymphomas.

B-cell lymphoma 6 (BCL6) and PR domain containing 1 (PRDM1) are considered as master regulators for germinal center (GC) formation and terminal B-cell differentiation. Dysregulation of BCL6 and PRDM1 has been associated with lymphomagenesis. Here, we show for the first time that direct cell-cell contact between follicular dendritic cells (FDC) and B-lymphocytes, by influencing the expression of a set of microRNAs (miRNAs), regulates the expression of BCL6 and PRDM1. We identify that, on cell adhesion to FDC, FDC induces upregulation of PRDM1 expression through downregulation of miR-9 and let-7 families and induces downregulation of BCL-6 through upregulation of miR-30 family in B-lymphocytes and lymphoma cells. We further demonstrate that the miR-30 family directly controls BCL-6 expression and miR-9-1 and let-7a directly control PRDM-1 expression through targeting their 3'UTR, mediating the FDC effect. Our studies define a novel regulatory mechanism in which the FDC, through induction of miRNAs in B-lymphocytes, orchestrates the regulation of transcription factors, promotes germinal center B-cell survival and differentiation. Dysregulation of miRNAs may interfere with B-cell survival and maturation, thus representing a novel molecular mechanism, as well as a potential therapeutic target in B-cell lymphomas.

Histone deacetylases and the immunological network: implications in cancer and inflammation.

The initiation, magnitude and duration of an immune response against antigens are a tightly regulated process involving a dynamic, orchestrated balance of pro- and anti-inflammatory pathways in immune cells. Such a delicate balance is critical for allowing efficient immune response against foreign antigens while preventing autoimmune attack against self-antigens. In recent years, much effort has been devoted to understanding immune evasion by cancer cells. Also, significant advances have been made in mechanistically understanding the role of pro- and anti-inflammatory cytokines in the regulation of immune responses against antigens, including those expressed by tumors. However, we still know very little about the regulation of inflammatory/anti-inflammatory genes in their natural setting, the chromatin substrate. Several mechanisms have been identified to influence chromatin flexibility and allow dynamic changes in gene expression. Among those, chromatin modifications induced by acetylation and deacetylation of histone tails have gained wide attention. In this study, we discuss the role of histone deacetylases in the transcriptional regulation of genes involved in the inflammatory response and how these enzymes coordinate the dynamic expression of these genes during an immune response. This emerging knowledge is opening new avenues to better understand epigenetic regulation of inflammatory responses and providing new molecular targets for either amplifying or ameliorating immune responses.

Tolerance and cancer: a critical issue in tumor immunology.

Self-antigens are the most relevant and abundant antigens to which the host's immune system must be tolerant. Induction and maintenance of tolerance to self-antigens is mediated by several mechanisms that prevent inappropriate damage to normal tissues. However, these same mechanisms may impose potential barriers for the full development of effective immune responses against antigens expressed by tumors. A critical issue in tumor immunology is whether antigen presented by a progressively expanding tumor cell population results in T-cell tolerance. Utilizing a T cell receptor transgenic mice specific for a model tumor antigen expressed on a B-cell lymphoma, recently we have obtained direct evidence supporting the existence of tumor-induced antigen-specific tolerance. A better identification and understanding of the factor(s) involved in tumor-induced tolerance has clear implications for the development of novel cancer immunotherapies aimed at safely breaking tolerance, for example, releasing the brakes on antitumor immune responses while still limiting the induction of undesirable autoimmune responses.

In vivo blockade of CTLA-4 enhances the priming of responsive T cells but fails to prevent the induction of tumor antigen-specific tolerance.

The efficacy of therapeutic vaccination for the treatment of cancer is limited by peripheral tolerance to tumor antigens. In vivo blockade of CTLA-4, a negative regulator of T cell function, can induce the regression of established tumors and can augment the tumor rejection achieved through therapeutic vaccination. These outcomes may reflect enhanced tumor-specific T cell priming and/or interference with the development of tolerance to tumor antigens. We examined the effect of CTLA-4 blockade on the fate and function of T cells specific for a model tumor antigen in the tumor-bearing host. We found that while CTLA-4 blockade enhanced the priming of responsive T cells, it did not prevent the induction of tolerance to tumor antigens. These results demonstrate that there is a critical window in which the combination of CTLA-4 blockade and vaccination achieves an optimal response, and they point to mechanisms other than CTLA-4 engagement in mediating peripheral T cell tolerance to tumor antigens.

Mechanism of immune dysfunction in cancer mediated by immature Gr-1+ myeloid cells.

The mechanism of tumor-associated T cell dysfunction remains an unresolved problem of tumor immunology. Development of T cell defects in tumor-bearing hosts are often associated with increased production of immature myeloid cells. In tumor-bearing mice, these immature myeloid cells are represented by a population of Gr-1(+) cells. In this study we investigated an effect of these cells on T cell function. Gr-1(+) cells were isolated from MethA sarcoma or C3 tumor-bearing mice using cell sorting. These Gr-1(+) cells expressed myeloid cell marker CD11b and MHC class I molecules, but they lacked expression of MHC class II molecules. Tumor-induced Gr-1(+) cells did not affect T cell responses to Con A and to a peptide presented by MHC class II. In sharp contrast, Gr-1(+) cells completely blocked T cell response to a peptide presented by MHC class I in vitro and in vivo. Block of the specific MHC class I molecules on the surface of Gr-1(+) cells completely abrogated the observed effects of these cells. Thus, immature myeloid cells specifically inhibited CD8-mediated Ag-specific T cell response, but not CD4-mediated T cell response. Differentiation of Gr-1(+) cells in the presence of growth factors and all-trans retinoic acid completely eliminated inhibitory potential of these cells. This may suggest a new approach to cancer treatment.

Decreased macrophage-mediated cytotoxicity in mammary-tumor-bearing mice is related to alteration of nitric-oxide production and/or release.

Peritoneal-exudate macrophages (PEM) from mammary-tumor-bearing mice have impaired cytotoxic activity against syngeneic and allogeneic tumor targets. The ability of PEM from normal and tumor-bearing mice to bind tumor targets was found to be similar in the presence or the absence of surrogate receptors, which enhanced the binding but not the killing of tumor targets by PEM from tumor-bearing mice, suggesting that other mechanisms are involved in their impaired cytolytic activity. Soluble and membrane-bound TNF-alpha, as well as H2O2, were found in higher amounts in PEM from tumor bearers upon stimulation with LPS, as compared with PEM from normal mice. However, tumor-bearers' macrophages displayed decreased capacity to produce and/or release nitric oxide, which could be reversed by the addition of increasing levels of IFN-gamma. These results indicate that the lack of macrophage cytotoxicity in mammary-tumor-bearing mice is related to impaired production and/or release of NO by these effector cells, possibly aggravated by the insufficient IFN-gamma production previously reported in these animals. Moreover, mammary-tumor progression results in dis-regulation of synthesis of macrophage-mediators, with over-production of molecules to which mammary-tumor cells are insensitive and deficient production of NO, the crucial molecule to which these cells appear to be highly sensitive.

Sustaining the graft-versus-tumor effect through posttransplant immunization with granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing tumor vaccines.

For many cancers, autologous bone marrow transplantation (BMT) achieves a minimal residual disease state, yet relapse rates remain high. Using a syngeneic murine bone marrow transplant model, we demonstrate that vaccination with irradiated granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing autologous tumor cells is effective in the post-BMT period and actually results in a greater tumor-free survival than vaccination in the nontransplant setting. Employing T cells specific for a model tumor-antigen, we find that transplantation of the tumor-bearing host results in a massive expansion and activation of tumor-specific T cells in the early posttransplant period, but this response rapidly declines in association with tumor progression. Immunization with irradiated GM-CSF tumor cells during the period of immune reconstitution results in the sustained amplification and activation of this response that closely correlates with freedom from relapse. These results demonstrate the feasibility of integrating GM-CSF vaccines in the postautologous BMT setting and suggest mechanisms that may contribute to the observed efficacy of immunization during the critical period of immune reconstitution.

Role of tumor-derived cytokines on the immune system of mice bearing a mammary adenocarcinoma. II. Down-regulation of macrophage-mediated cytotoxicity by tumor-derived granulocyte-macrophage colony-stimulating factor.

Peritoneal elicited macrophages (PEM) from mammary tumor-bearing mice have a decreased capacity to become cytotoxic against syngeneic, allogeneic, and xenogeneic target cells upon in vitro stimulation with LPS, as compared with PEM of normal mice. A regulatory mechanism other than PG release is suggested because the addition of both indomethacin and LPS to macrophage cultures from tumor-bearing mice caused no changes in their cytotoxic capability. Because tumor products have been implicated in the down-regulation of immune responses, we investigated whether pretreatment with supernatants from the tumor cell line DA-3, derived from the in vivo mammary adenocarcinoma D1-DMBA-3, affects the cytolytic capacity of macrophages. This treatment inhibits, in a dose-dependent fashion, the ability of stimulated normal PEM to kill target cells. Partial purification of DA-3 cell line supernatant showed that most of the inhibitory activity was exerted by factors with a molecular mass greater than 10 kDa and less than 30 kDa. However, slight inhibition could also be observed with fractions containing molecules less than 10 kDa. The data suggest that more than one factor released by the mammary tumor cells may be involved in the down-regulation of macrophage-mediated cytotoxicity. Because the DA-3 cells constitutively produce granulocyte-macrophage CSF (GM-CSF), which has a molecular mass of 27 kDa, we pretreated PEM from normal mice in vitro with rGM-CSF for 24 h. This resulted in a dose-dependent decrease in their capacity to kill tumor target cells upon LPS stimulation. Furthermore, PEM from normal mice injected with rGM-CSF for 25 days displayed a profound decrease in their cytolytic ability against DA-3 targets upon in vitro stimulation with increasing amounts of LPS. The pretreatment of PEM from normal mice with a combination of DA-3 cell supernatants and specific anti-GM-CSF partially neutralized the inhibitory effect of the DA-3 supernatant on macrophage tumoricidal capability. These results indicate that tumor-derived GM-CSF is an important factor involved in the decreased macrophage cytotoxicity during mammary adenocarcinoma progression.

Cross-presentation of tumor antigens by bone marrow-derived antigen-presenting cells is the dominant mechanism in the induction of T-cell tolerance during B-cell lymphoma progression.

Tumor antigen-specific T-cell tolerance may limit the efficacy of therapeutic cancer vaccines. Direct presentation of antigens by tumor cells incapable of providing adequate costimulation to tumor-specific T cells has been suggested as the basis for this unresponsiveness. Using parent-into-F1 bone marrow (BM) chimeras, this study unambiguously demonstrates that the induction of this tolerant state requires T-cell recognition of tumor antigen presented by BM-derived antigen-presenting cells (APCs), not tumor cells themselves. In the absence of host APC presentation, tumor-specific T cells remained functional, even in the setting of antigen expressed by B-cell lymphomas residing in secondary lymphoid tissues. The intrinsic APC capacity of tumor cells has therefore little influence over T-cell priming versus tolerance, a decision that is regulated at the level of host APCs. (Blood. 2001;98:1070-1077)