Melphalan and other anticancer modalities up-regulate B7-1 gene expression in tumor cells

Dying of Stress: Chemotherapy, Radiotherapy, and Small-Molecule Inhibitors in Immunogenic Cell Death and Immunogenic Modulation

Innovative strategies to re-establish the immune-mediated destruction of malignant cells is paramount to the success of anti-cancer therapy. Accumulating evidence suggests that radiotherapy and select chemotherapeutic drugs and small molecule inhibitors induce immunogenic cell stress on tumors that results in improved immune recognition and targeting of the malignant cells. Through immunogenic cell death, which entails the release of antigens and danger signals, and immunogenic modulation, wherein the phenotype of stressed cells is altered to become more susceptible to immune attack, radiotherapies, chemotherapies, and small-molecule inhibitors exert immune-mediated anti-tumor responses. In this review, we discuss the mechanisms of immunogenic cell death and immunogenic modulation and their relevance in the anti-tumor activity of radiotherapies, chemotherapies, and small-molecule inhibitors. Our aim is to feature the immunological aspects of conventional and targeted cancer therapies and highlight how these therapies may be compatible with emerging immunotherapy approaches.

An injectable thermosensitive hydrogel/nanomicelles composite for local chemo-immunotherapy in mouse model of melanoma

Recently, cancer immunotherapy and its combination with chemotherapy has been considered to improve therapeutic efficacy with lower systemic toxicity. Here, we prepared a thermosensitive hydrogel based hyaluronic acid (HA) encapsulated with macrophage colony-stimulating factor (GM-CSF) and paclitaxel (PTX) for chemoimmunotherapy of cancer. For this purpose, the micelles were prepared with the mixture of pluronic F127 (PF127) and tocopheryl polyethylene glycol (TPGS) and loaded with PTX. In the following step, thermosensitive hydrogel using PF127 and HA was prepared and co-encapsulated with the micelles and GM-CSF. Rheological performance, friability, release patterns for PTX and GM-CSF, and stability of GM-CSF in the hydrogel were evaluated in details. In-vitro and in vivo immunologic activities of GM-CSF in the hydrogel were also evaluated via numbering macrophages and recruited DCs in transwells and after subcutaneous injection of the GM-CSF-loaded hydrogel. Finally, mouse model of subcutaneous melanoma was induced in female C57 mice using B16 F10 cell line and the effect of optimized formulation was evaluated based on tumor volume and histological analysis. The hydrogel could maintain the biological activity of the incorporated drugs and exhibited a more prolonged release for PTX compared to GM-CSF. GM-CSF-releasing HA/PF127 hydrogel successfully recruited macrophages in vitro. Moreover, the most potent anti-tumor effect was observed following the intra-tumoral injection of the optimized formulation in melanoma bearing mice, compared to immunization by the GM-CSF and PTX alone. The current formulation shows a great promise to conquer resistant malignancies and provides a new approach for co-encapsulating of hydrophobic anticancer drugs and growth factor.

From Immunogenic Cell Death to Immunogenic Modulation: Select Chemotherapy Regimens Induce a Spectrum of Immune-Enhancing Activities in the Tumor Microenvironment

Cancer treatment has rapidly entered the age of immunotherapy, and it is becoming clear that the effective therapy of established tumors necessitates rational multi-combination immunotherapy strategies. But even in the advent of immunotherapy, the clinical role of standard-of-care chemotherapy regimens still remains significant and may be complementary to emerging immunotherapeutic approaches. Depending on dose, schedule, and agent, chemotherapy can induce immunogenic cell death, resulting in the release of tumor antigens to stimulate an immune response, or immunogenic modulation, sensitizing surviving tumor cells to immune cell killing. While these have been previously defined as distinct processes, in this review we examine the published mechanisms supporting both immunogenic cell death and immunogenic modulation and propose they be reclassified as similar effects termed "immunogenic cell stress." Treatment-induced immunogenic cell stress is an important result of cytotoxic chemotherapy and future research should consider immunogenic cell stress as a whole rather than just immunogenic cell death or immunogenic modulation. Cancer treatment strategies should be designed specifically to take advantage of these effects in combination immunotherapy, and novel chemotherapy regimens should be designed and investigated to potentially induce all aspects of immunogenic cell stress.

Immune recognition of irradiated cancer cells

Ionizing irradiation has been extensively employed for the clinical management of solid tumors, with therapeutic or palliative intents, for decades. Until recently, radiation therapy (RT) was believed to mediate antineoplastic activity mostly (if not only) as a consequence of cancer cell-intrinsic effects. Indeed, the macromolecular damage imposed to malignant cells by RT initiates one or multiple signal transduction cascades that drive a permanent proliferative arrest (cellular senescence) or regulated cell death. Both these phenomena show a rather linear dose-response correlation. However, RT also mediates consistent immunological activity, not only as an "on-target effect" originating within irradiated cancer cells, but also as an "off-target effect" depending on the interaction between RT and stromal, endothelial, and immune components of the tumor microenvironment. Interestingly, the immunological activity of RT does not exhibit linear dose-response correlation. Here, we discuss the mechanisms whereby RT alters the capacity of the immune system to recognize and eliminate irradiated cancer cells, either as an "on-target" or as on "off-target" effect. In particular, we discuss the antagonism between the immunostimulatory and immunosuppressive effects of RT as we delineate combinatorial strategies to boost the former at the expenses of the latter.

Immunostimulatory Effects of Melphalan and Usefulness in Adoptive Cell Therapy with Antitumor CD4+ T Cells

The alkylating agent melphalan is used in the treatment of hematological malignancies, especially multiple myeloma. In the past, the usefulness of melphalan has been solely attributed to its cytotoxicity on fastgrowing cancerous cells. Although the immunomodulatory effects of melphalan were suggested many years ago, only recently has this aspect of melphalan's activity begun to be elucidated at the molecular level. Emerging evidence indicates that melphalan can foster an immunogenic microenvironment by inducing immunogenic cell death (ICD) as characterized by membrane translocation of endoplasmic reticulum protein calreticulin (CRT) and by release of chromatin-binding protein high-mobility group box 1 (HMGB1). In addition, the lympho-depletive effect of melphalan can induce the release of pro-inflammatory cytokines and growth factors, deplete regulatory T cells, and create space to facilitate the expansion of infused tumor-reactive T cells. These features suggest that melphalan can be used as a preparative chemotherapy for adoptive T-cell therapy. This notion is supported by our recent work demonstrating that the combination of melphalan and adoptive transfer of tumor-reactive CD4+ T cells can mediate potent antitumor effects in animal models. This review summarizes the recent advances in understanding and utilizing the immunomodulatory effects of melphalan.

Impact of the immune cell population in peripheral blood on response and survival in patients receiving neoadjuvant chemotherapy for advanced gastric cancer

We aimed to investigate the prognostic value of the immune cells population in peripheral blood from patients with advanced gastric cancer treated with neoadjuvant chemotherapy. A total of 105 patients with advanced gastric cancer were evaluated in this study. Blood samples were collected before and 1 week after the last dose of chemotherapy. The percentage of CD3+, CD3+CD4+, CD3+CD8+, and CD4+CD25+Foxp3+ T cells was assessed using flow cytometry analysis. The relationship between T cell subsets and clinical outcome was evaluated. The percentage of CD3+CD8+ lymphocytes was significantly increased after chemotherapy and CD4+CD25+Foxp3+ regulatory T cells (Tregs) decreased ( p = 0.003 and p < 0.001, respectively). The percentage of CD3+CD8+ lymphocytes and Tregs was strongly associated with response to chemotherapy ( p = 0.017 and p < 0.030, respectively). Patients with high CD3+CD8+ T cells and low CD4+CD25+Foxp3+ Tregs had significantly increased overall survival ( p = 0.012 and p = 0.048, respectively). Neither CD3+ nor CD3+CD4+ T cells showed significant changes after chemotherapy or correlations with the clinical outcome. The positive correlation between a high CD3+CD8+ T cells or low CD4+CD25+Foxp3+ Tregs and clinical outcome indicates its key role in the prognosis of gastric cancer patients and may serve as a biomarker to identify patients likely to benefit from neoadjuvant chemotherapy.

Turning tumour cells into antigen presenting cells: The next step to improve cancer immunotherapy?

Downregulation/loss of the antigen presentation is a major immune escape mechanism in cancer. It allows tumour cells to become 'invisible' and avoid immune attack by antitumour T cells. In tumour harbouring properties of professional antigen presenting cells (i.e. tumour B cells in lymphoma), downregulation/loss of the antigen presentation may also prevent direct priming of naïve T cells by tumour cells. Here, we review treatments that may induce/restore antigen presentation by the tumour cells. These treatments may increase the generation of antitumour T cells and/or their capacity to recognise and eliminate tumour cells. By forcing tumour cells to present their antigens, these treatments may sensitise patients to T cell-based immunotherapies, including checkpoint inhibitors.

Alkylating agent melphalan augments the efficacy of adoptive immunotherapy using tumor-specific CD4+ T cells

In recent years, the immune-potentiating effects of some widely used chemotherapeutic agents have been increasingly appreciated. This provides a rationale for combining conventional chemotherapy with immunotherapy strategies to achieve durable therapeutic benefits. Previous studies have implicated the immunomodulatory effects of melphalan, an alkylating agent commonly used to treat multiple myeloma, but the underlying mechanisms remain obscure. In the present study, we investigated the impact of melphalan on endogenous immune cells as well as adoptively transferred tumor-specific CD4(+) T cells in tumor-bearing mice. We showed that melphalan treatment resulted in a rapid burst of inflammatory cytokines and chemokines during the cellular recovery phase after melphalan-induced myelodepletion and leukodepletion. After melphalan treatment, tumor cells exhibited characteristics of immunogenic cell death, including membrane translocation of the endoplasmic reticulum-resident calreticulin and extracellular release of high-mobility group box 1. Additionally, there was enhanced tumor Ag uptake by dendritic cells in the tumor-draining lymph node. Consistent with these immunomodulatory effects, melphalan treatment of tumor-bearing mice led to the activation of the endogenous CD8(+) T cells and, more importantly, effectively drove the clonal expansion and effector differentiation of adoptively transferred tumor-specific CD4(+) T cells. Notably, the combination of melphalan and CD4(+) T cell adoptive cell therapy was more efficacious than either treatment alone in prolonging the survival of mice with advanced B cell lymphomas or colorectal tumors. These findings provide mechanistic insights into melphalan's immunostimulatory effects and demonstrate the therapeutic potential of combining melphalan with adoptive cell therapy utilizing antitumor CD4(+) T cells.

Chemotherapy and Oncolytic Virotherapy: Advanced Tactics in the War against Cancer

Cancer is a traitorous archenemy that threatens our survival. Its ability to evade detection and adapt to various cancer therapies means that it is a moving target that becomes increasingly difficult to attack. Through technological advancements, we have developed sophisticated weapons to fight off tumor growth and invasion. However, if we are to stand a chance in this war against cancer, advanced tactics will be required to maximize the use of our available resources. Oncolytic viruses (OVs) are multi-functional cancer-fighters that can be engineered to suit many different strategies; in particular, their retooling can facilitate increased capacity for direct tumor killing (oncolytic virotherapy) and elicit adaptive antitumor immune responses (oncolytic immunotherapy). However, administration of these modified OVs alone, rarely induces successful regression of established tumors. This may be attributed to host antiviral immunity that acts to eliminate viral particles, as well as the capacity for tumors to adapt to therapeutic selective pressure. It has been shown that various chemotherapeutic drugs with distinct functional properties can potentiate the antitumor efficacy of OVs. In this review, we summarize the chemotherapeutic combinatorial strategies used to optimize virally induced destruction of tumors. With a particular focus on pharmaceutical immunomodulators, we discuss how specific therapeutic contexts may alter the effects of these synergistic combinations and their implications for future clinical use.

Immunological impact of neoadjuvant chemoradiotherapy in patients with borderline resectable pancreatic ductal adenocarcinoma

BACKGROUND

Little is known about the immunological effect of neoadjuvant chemoradiotherapy (NACRT) in the tumor microenvironment of pancreatic ductal adenocarcinoma. The objective of this study was to examine the immunological modifications induced by NACRT in patients with pancreatic cancer.

METHODS

Fifty-two patients with pancreatic cancer who underwent surgical resection were enrolled in this study. NACRT was administered to 22 patients, whereas the other 30 patients underwent surgical resection without NACRT. The resected tumor specimens were analyzed for the presence of tumor-infiltrating lymphocytes by using immunohistochemical staining for CD4, CD8, CD68, CD163, Foxp3, and major histocompatibility complex class I (MHC class I) antigen.

RESULTS

The number of CD4+ and CD8+ lymphocytes was significantly higher in patients who received NACRT than in those who did not receive NACRT. No significant difference in MHC class I expression was observed between the groups. In the NACRT group, patients with a high accumulation of CD8+ cells experienced longer overall survival than those with a low number of CD8+ cells.

CONCLUSIONS

NACRT may induce the accumulation of CD4+ and CD8+ cells in the tumor microenvironment and a high accumulation of CD8+ cells might be a good prognostic marker for pancreatic cancer treated with NACRT.

Changes in the immune cell population and cell proliferation in peripheral blood after gemcitabine-based chemotherapy for pancreatic cancer

PURPOSE

Regulatory T cells (Tregs) play a role in the immunosuppressive state in pancreatic cancer patients. We aimed to evaluate the changes of immune cells population including Tregs caused by gemcitabine (GEM)-based chemotherapy.

METHODS

Fifty-three patients with pancreatic cancer were enrolled in this study, of which 32 received GEM- based chemotherapy. Blood samples were collected before and at least 2 weeks after the last dose of chemotherapy. The peripheral blood mononuclear cells (PBMCs) were subjected to flow cytometry analysis after labeling with anti-CD4, anti-CD25, and anti-Foxp3 antibodies. Other lymphocytes and NK cell markers were also measured. The proliferative capacity of PBMCs stimulated with anti-CD3 was analyzed using H(3) thymidine.

RESULTS

The percentage and number of Tregs were significantly decreased after chemotherapy (p = 0.032, p = 0.003, respectively). The other immune cells and the proliferative capacity did not change.

CONCLUSION

This study showed that GEM-based chemotherapy produced an immunomodulatory effect via the depletion of Tregs.

Chemoimmunotherapy: reengineering tumor immunity

Cancer chemotherapy drugs have long been considered immune suppressive. However, more recent data indicate that some cytotoxic drugs effectively treat cancer in part by facilitating an immune response to the tumor when given at the standard dose and schedule. These drugs induce a form of tumor cell death that is immunologically active, thereby inducing an adaptive immune response specific for the tumor. In addition, cancer chemotherapy drugs can promote tumor immunity through ancillary and largely unappreciated immunologic effects on both the malignant and normal host cells present within the tumor microenvironment. These more subtle immunomodulatory effects are dependent on the drug itself, its dose, and its schedule in relation to an immune-based intervention. The recent approvals of two new immune-based therapies for prostate cancer and melanoma herald a new era in cancer treatment and have led to heightened interest in immunotherapy as a valid approach to cancer treatment. A detailed understanding of the cellular and molecular basis of interactions between chemotherapy drugs and the immune system is essential for devising the optimal strategy for integrating new immune-based therapies into the standard of care for various cancers, resulting in the greatest long-term clinical benefit for cancer patients.

Exploitation of the propulsive force of chemotherapy for improving the response to cancer immunotherapy

Since the early clinical studies of cancer immunotherapy, the question arose as to whether it was possible to combine it with standard cancer treatments, mostly chemotherapy. The answer, now, is past history. The combined use of immunotherapy and chemotherapy is not only possible but, in certain cases, can be advantageous, depending on the drug, the dose and the combination modalities. In order to find the best synergisms between the two treatments and to turn weak immunotherapeutic interventions into potent anticancer instruments, it is mandatory to understand the complex mechanisms responsible for the positive interactions between chemotherapy and immunotherapy. In this article, we review the current knowledge on mechanisms involved in the immunostimulating activity of chemotherapy and summarize the main studies in both mouse models and patients aimed at exploiting such mechanisms for enhancing the response to cancer immunotherapy.

Chemoimmunotherapy

Cancer chemotherapy drugs are historically regarded as detrimental to immunity because of their myelosuppressive effects. However, accumulating data suggest that the antitumor activity of conventional cancer chemotherapy results in part from its ability to harness the innate and adaptive immune systems by inducing immunologically active tumor cell death. Additional data broaden the immunologic effect of cancer chemotherapy drugs, demonstrating that some drugs have the ability to disrupt pathways of immune suppression and immune tolerance in a manner that depends on the drug dose, and the timing of its administration in relation to immunotherapy. Understanding the cellular and molecular basis of the interactions between chemotherapy drugs and the immune system will facilitate the strategic development of chemoimmunotherapy treatment regimens that both maximize tumor regression and the antitumor immune response for the long-term clinical benefit of cancer patients.

Paclitaxel enhances early dendritic cell maturation and function through TLR4 signaling in mice

Subclinical doses of Paclitaxel (PTX) given 1day prior to a HER-2/neu (neu)-targeted, granulocyte-macrophage colony stimulating factor (GM-CSF)-secreting whole-cell vaccine enhances neu-specific T cell responses and slows neu(+) tumor growth in tolerized HER-2/neu (neu-N) mice. We demonstrate that co-administration of PTX and Cyclophosphamide (CY) synergizes to slow tumor growth, and that in vitro, DC precursors exposed to PTX before LPS maturation results in greater co-stimulatory molecule expression, IL-12 production, and the ability to induce CD8(+) T cells with enhanced lytic activity against neu(+) tumors. PTX treatment also enhances maturation marker expression on CD11c(+) DCs isolated from vaccine-draining lymph nodes. Ex vivo, these DCs activate CD8(+) T cells with greater lytic capability than DC's from vaccine alone-treated neu-N mice. Finally, PTX treatment results in enhanced antigen-specific, IFN-gamma-secreting CD8(+) T cells in vivo. Thus, administration of PTX with a tumor vaccine improves T cell priming through enhanced maturation of DC.

Melanoma cells treated with GGTI and IFN-gamma allow murine vaccination and enhance cytotoxic response against human melanoma cells

Background

Suboptimal activation of T lymphocytes by melanoma cells is often due to the defective expression of class I major histocompatibility antigens (MHC-I) and costimulatory molecules. We have previously shown that geranylgeranyl transferase inhibition (done with GGTI-298) stimulates anti-melanoma immune response through MHC-I and costimulatory molecule expression in the B16F10 murine model [1].

Methodology/Principal Findings

In this study, it is shown that vaccination with mIFN-gand GGTI-298 pretreated B16F10 cells induces a protection against untreated tumor growth and pulmonary metastases implantation. Furthermore, using a human melanoma model (LB1319-MEL), we demonstrated that in vitro treatment with hIFN-γ and GGTI-298 led to the up regulation of MHC-I and a costimulatory molecule CD86 and down regulation of an inhibitory molecule PD-1L. Co-culture experiments with peripheral blood mononuclear cells (PBMC) revealed that modifications induced by hIFN-γ and GGTI-298 on the selected melanoma cells, enables the stimulation of lymphocytes from HLA compatible healthy donors. Indeed, as compared with untreated melanoma cells, pretreatment with hIFN-γ and GGTI-298 together rendered the melanoma cells more efficient at inducing the: i) activation of CD8 T lymphocytes (CD8+/CD69+); ii) proliferation of tumor-specific CD8 T cells (MelanA-MART1/TCR+); iii) secretion of hIFN-γ; and iv) anti-melanoma specific cytotoxic cells.

Conclusions/Significance

These data indicate that pharmacological treatment of melanoma cell lines with IFN-γ and GGTI-298 stimulates their immunogenicity and could be a novel approach to produce tumor cells suitable for vaccination and for stimulation of anti-melanoma effector cells.

Graft rejection occurring in post-liver transplant patients receiving cytotoxic chemotherapy: a case series

Liver transplant recipients are known to be at increased risk for the development of de novo neoplasms or the recurrence of preexisting malignancies, and this is possibly related to the use of immunosuppressive medication. Little is known about the effects of cytotoxic chemotherapy on graft function after transplantation. A retrospective chart and pathology database review was undertaken to identify post-liver transplant patients developing rejection during chemotherapy. All liver biopsies were reviewed by a hepatopathologist. Three patients were identified. All patients were diagnosed with cancer within 7 years of liver transplantation; two-thirds died soon after the diagnosis of malignancy. Rejection occurred soon after chemotherapy was started. All patients were receiving prednisone and tacrolimus (trough levels: 2.1-4.8 ng/mL). One patient developed plasma cell hepatitis (de novo autoimmune hepatitis). There was no histologic evidence of hepatotoxicity due to the chemotherapeutic agents. Cytotoxic chemotherapy should be used in liver transplant recipients with caution, and immunosuppressant doses should be maintained at therapeutic levels, as patients may be at risk for allograft rejection. Treatment of rejection or plasma cell hepatitis in this setting should be undertaken in a timely and aggressive fashion to prevent chronic ductopenic rejection.

Dormant tumor cells as a therapeutic target?

Tumor dormancy is characterised by the persistence of residual tumor cells for long periods. Recurrence from minimal residual disease is a major cause of cancer death. Thus, understanding how cancer cells become and remain dormant, may lead to new strategies to prevent relapse. Evidence has emerged that a balance exists between host and dormant tumor cells. Cross-talk between tumor cells and their micro-environment, angiogenesis, and anti-tumor immune response participate in the control of dormant tumor cells. Tumor cells have several mechanisms of maintaining equilibrium, and immune escape, including expression of immuno-regulatory molecules (e.g., increased expression of B7.1 and B7-H1); epigenetic modifications (e.g., silencing of the SOCS1 gene, de-regulating the JAK/STAT pathway); and autocrine loops. These new findings offer new opportunities to design specific treatments, to modify the balance in favor of the host immune response.

Chemotherapy and tumor immunity: an unexpected collaboration

Chemotherapy directly targets the transformed tumor cell, and has long been a key component of therapy for most early and advanced cancers. However, its utility is ultimately limited by unavoidable toxicity to normal tissues, and by drug resistance pathways deeply embedded within the biology of the tumor cell itself. These limitations strongly argue for innovative strategies to treat and manage cancer. Engaging the power of the patient's own immune system is a highly attractive way to complement the activity of standard cancer treatment. Tumor vaccines offer the potential for preventing cancer in those at high risk for disease development, preventing relapse in those diagnosed with early cancer, and treating advanced disease. Notably, the barriers to tumor vaccine efficacy are distinct from the limitations of combination chemotherapy. The ability of vaccines to induce a response robust enough to mediate tumor rejection is limited by the extent of disease burden, the suppressive effect of the local tumor micronenvironment, and multiple layers of systemic immune tolerance established to keep the immune response turned off. Chemotherapy can be used with tumor vaccines in unexpected ways, breaking down these barriers and unleashing the full potential of the antitumor immune response.

A vascular endothelial growth factor receptor-2 inhibitor enhances antitumor immunity through an immune-based mechanism

PURPOSE

Given the complex tumor microenvironment, targeting multiple cellular components may be the most effective cancer treatment strategy. Therefore, we tested whether antiangiogenic and immune-based therapy might synergize by characterizing the activity of DC101, an antiangiogenic monoclonal antibody specific for vascular endothelial growth factor receptor-2 (VEGF-R2), alone and with HER-2/neu (neu)-targeted vaccination.

EXPERIMENTAL DESIGN

Neu-expressing breast tumors were measured in treated nontolerant FVB mice and immune-tolerant neu transgenic (neu-N) mice. Neu-specific and tumor cell-specific immune responses were assessed by intracellular cytokine staining, ELISPOT, and CTL assays.

RESULTS

DC101 decreased angiogenesis and increased tumor cell apoptosis. Although DC101 increased serum levels of the immunosuppressive cytokine VEGF, no evidence of systemic immune inhibition was detected. Moreover, DC101 did not impede the influx of tumor-infiltrating lymphocytes. In FVB mice, DC101 inhibited tumor growth in part through a T cell-dependent mechanism, resulting in both increased tumor-specific CD8(+) T cells and tumor regression. Combining DC101 with neu-specific vaccination accelerated tumor regression, augmenting the lytic activity of CD8(+) cytotoxic T cells. In tolerant neu-N mice, DC101 only delayed tumor growth without inducing frank tumor regression or antigen-specific T-cell activation. Notably, mitigating immune tolerance by inhibiting regulatory T cell activity with cyclophosphamide revealed DC101-mediated augmentation of antitumor responses in vaccinated neu-N mice.

CONCLUSIONS

This is the first report of DC101-induced antitumor immune responses. It establishes the induction of tumor-specific T-cell responses as one consequence of VEGF-R2 targeting with DC101. These data support the development of multitargeted cancer therapy combining immune-based and antiangiogenic agents for clinical translation.

Low surface expression of B7-1 (CD80) is an immunoescape mechanism of colon carcinoma

Artificially enforced expression of CD80 (B7-1) and CD86 (B7-2) on tumor cells renders them more immunogenic by triggering the CD28 receptor on T cells. The enigma is that such B7s interact with much higher affinity with CTLA-4 (CD152), an inhibitory receptor expressed by activated T cells. We show that unmutated CD80 is spontaneously expressed at low levels by mouse colon carcinoma cell lines and other transplantable tumor cell lines of various tissue origins. Silencing of CD80 by interfering RNA led to loss of tumorigenicity of CT26 colon carcinoma in immunocompetent mice, but not in immunodeficient Rag-/- mice. CT26 tumor cells bind CTLA-4Ig, but much more faintly with a similar CD28Ig chimeric protein, thus providing an explanation for the dominant inhibitory effects on tumor immunity displayed by CD80 at that expression level. Interestingly, CD80-negative tumor cell lines such as MC38 colon carcinoma and B16 melanoma express CD80 at dim levels during in vivo growth in syngeneic mice. Therefore, low CD80 surface expression seems to give an advantage to cancer cells against the immune system. Our findings are similar with the inhibitory role described for the dim CD80 expression on immature dendritic cells, providing an explanation for the low levels of CD80 expression described in various human malignancies.

Serum alters the uptake and biologic activity of CpG oligodeoxynucleotides in B cell chronic lymphocytic leukemia

Immunostimulatory CpG-containing oligodeoxynucleotides (CpG ODN) have a number of effects on B cells, including upregulation of immunogenic molecules, and, therefore, appear attractive as potential components of immunotherapy for B cell chronic lymphocytic leukemia (B-CLL). Previous in vitro studies investigating the effect of CpG ODN on B-CLL cells used serum-low conditions and did not account for the longer-half life of CpG ODN in vitro. The present study was designed to explore how the presence of serum and exposure time affect CpG ODN-mediated changes on B-CLL cells. The optimal concentration for CpG ODN-mediated effects in the presence of 100% serum or plasma was higher (10-20 microg/ml) than for serum-low conditions. Maximal CpG ODN-mediated effects required the presence of ODN for no longer than 3 hours. The inhibition of CpG ODN-mediated effects by serum correlated with lower uptake of ODN into B-CLL cells in the presence of serum. A threshold effect on biologic response was observed, with a given amount of ODN internalized, resulting in phenotypic changes. In conclusion, systemic short-term application of CpG ODN appears to be sufficient to induce phenotypic changes, but higher doses of CpG ODN than previously thought may be necessary because of inhibition of their uptake by serum.

Clonal plasma cells from monoclonal gammopathy of undetermined significance, multiple myeloma and plasma cell leukemia show different expression profiles of molecules involved in the interaction with the immunological bone marrow microenvironment

The immunological bone marrow (BM) microenvironment plays a major role in controlling growth and survival of clonal plasma cells (PC); this might translate into different patterns of expression of molecules involved in immune responses on PC from different types of monoclonal gammopathies (MG). We have studied the expression of a group of nine such molecules on both BMPC and the plasma of 61 newly diagnosed MG patients (30 MG of undetermined significance (MGUS), 27 multiple myeloma (MM) and four plasma cell leukemia (PCL)) and five normal individuals. Clonal PC from all MG displayed significantly increased levels of CD56, CD86 and CD126, and decreased amounts of CD38 (P<0.001). Additionally, HLA-I and beta2-microglobulin were abnormally highly expressed in MGUS, while CD40 expression was decreased in MM and PCL (P<0.05). Interestingly, a progressive increase in the soluble levels of beta2-microglobulin was found from MGUS to MM and PCL patients (P=0.03). In contrast, all groups showed similar surface and soluble amounts of CD126, CD130 and CD95, except for increased soluble levels of CD95 observed in PCL. Overall, those phenotypic differences are consistent with increased antigen presentation and costimulatory capacities in MGUS, which progressively deteriorate in malignant MG (MM and PCL).

Apoptotic and necrotic cells induced by different agents vary in their expression of MHC and costimulatory genes

We have recently reported, in a murine tumor model, that apoptotic cells induced by different agents may vary in their ability to elicit host immunity. The basis for this observation is unclear but may involve varying efficiencies of cross-presentation and/or direct activation of immunity by different apoptotic preparations. As a first step in addressing this issue, we compared expression patterns of selected immune genes (MHC class I, class II, CD40, B7-1, B7-2) on viable and apoptotic populations induced by four different agents. The histone deacetylase inhibitor trichostatin A (TSA) induced MHC class II expression on viable and apoptotic cell populations, while LPAM, H2O2 and gamma-irradiation did not activate class II. Each agent employed elicited a different expression pattern of costimulatory molecules (CD40, B7-1, B7-2) on both apoptotic and 7-AAD+ 'necrotic' populations. In striking contrast to the TSA induction of MHC class II, class I cell surface protein was diminished on the apoptotic populations. These effects were not a result of changes in the cell cycle produced by the various treatments. The data demonstrate that distinctive gene expression patterns on viable and apoptotic cells are elicited by different apoptosis inducing agents. We discuss how expression patterns on dead or dying tumor cells could potentially affect the tumor's ability to elicit immunity.

Cytosine arabinoside induces costimulatory molecule expression in acute myeloid leukemia cells

Chemotherapeutic drugs kill cancer cells mainly by direct cytotoxicity, but they might also induce a stronger host immune response by causing the tumor to produce costimulatory cell surface molecules like CD80. We previously reported that in myeloid leukemic cells, gamma-irradiation induced CD80 expression. In this study, we show that cytosine arabinoside (Ara-C), even at low doses, induced CD80 expression in vitro in mouse DA1-3b leukemic cells, by a mechanism that involved reactive oxygen species. In vivo experiments in the mouse DA1-3b/C3H whole-animal acute myeloid leukemia (AML) model showed that injection of Ara-C induced expression of CD80 and CD86, and decreased expression of B7-H1, indicating that chemotherapy can modify costimulatory molecule expression in vivo, in a way not necessarily observed in vitro. Mouse leukemic cells exposed in vivo to Ara-C were more susceptible to specific cytotoxic lymphocyte (CTL)-mediated killing. Ara-C also induced CD80 or CD86 expression in 14 of 21 primary cultured human AML samples. In humans being treated for AML, induction chemotherapy increased CD86 expression in the leukemic cells. These findings indicate possible synergistic strategies between CTL-based immunotherapy and chemotherapy for treatment. They also suggest an additional mechanism by which chemotherapy can eradicate AML blasts.

Irradiation up-regulates CD80 expression through two different mechanisms in spleen B cells, B lymphoma cells, and dendritic cells

We have previously demonstrated irradiation-induced up-regulation of CD80 expression in A20-HL B lymphoma cells by inducing expression of tumour necrosis factor-alpha (TNF-alpha) and CD154. In the present study, we investigated whether irradiation also up-regulates CD80 expression in mouse spleen B cells. Because freshly prepared spleen B cells are highly sensitive to irradiation, we employed spleen B cells stimulated with lipopolysaccharide (LPS-B cells). X-irradiation (8 Gy) followed by incubation (9-12 hr) highly and selectively up-regulated CD80 expression in LPS-B cells, whereas the same treatment slightly increased expression of CD54 and did not affect expression of CD86, major histocompatibility complex class II, CD11a or surface immunoglobulin M. The irradiation-induced up-regulation of CD80 expression resulted in enhanced APC function of LPS-B cells. Up-regulation of CD80 expression on LPS-B cells was accompanied by an increase in CD80 mRNA accumulation and nuclear factor (NF)-kappaB activation. Activation of NF-kappaB was shown to be critical for up-regulation of CD80 expression as pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-kappaB, severely decreased the observed up-regulation. X-irradiation of LPS-B cells induced expression of TNF-alpha but not CD154. However, anti-TNF-alpha monoclonal antibody (mAb) with anti-CD154 mAb did not inhibit X-irradiation-induced up-regulation of CD80 expression in LPS-B cells, whereas these mAbs almost completely inhibited this up-regulation in A20-HL cells and bone marrow-derived dendritic cells (DCs). In contrast, a thiol antioxidant, N-acetyl-l-cysteine, completely blocked X-irradiation-induced up-regulation of CD80 expression in LPS-B cells, but not in A20-HL cells or in DCs. Based on these findings, we concluded that X-irradiation up-regulates CD80 expression not only in A20-HL cells and DCs but also in LPS-B cells, and that this up-regulation in LPS-B cells via NF-kappaB activation is dependent on the generation of reactive oxygen species, while that in A20-HL cells and DCs is not.

Neural stem/progenitor cells express costimulatory molecules that are differentially regulated by inflammatory and apoptotic stimuli

Increased expression of the costimulatory molecule CD80 (B7-1) was noted in the subventricular zone of the brain during the course of experimental autoimmune encephalomyelitis (EAE). This area of the brain is a neural stem cell (NSC) niche in the adult. We show that isolated NSCs from adult brain express CD80 and CD86 (B7-2) and this expression is increased after exposure to IFN-gamma or TNF-alpha, the prototypical Th1 cytokines expressed during EAE. CD80 and CD86 expressed by NSCs are functional and can costimulate allogeneic cells in a mixed lymphocyte reaction. Furthermore, cross-linking of CD80 on the surface of NSCs results in apoptosis of NSCs. In vitro, we show that T cells can interact with NSCs and form conjugates with redistribution of CD3 on the surface of T cells to the area of contact. These data raise the possibility that during CNS inflammatory diseases such as EAE, NSCs may express immune molecules and interact with the inflammatory environment potentially resulting in injury to the NSCs, which may have implications for repair mechanisms in the central nervous system.

Chemotherapy increases transgene expression in leukemic cells

BACKGROUND

Patients with acute myeloid leukemia (AML) often obtain complete remission with chemotherapy but the majority of patients relapse. Combining chemotherapy and gene therapy appears to be a promising approach; however, the effects of chemotherapy on transgene expression in leukemic cells have not yet been investigated.

METHODS

DA1-3b leukemic cells were transfected with pCDNA3 plasmids carrying GM-CSF or LacZ cDNA. The leukemic K562 cell line and primary cultured AML cells were transduced with an Ad5.CMV-LacZ adenoviral vector. Cells were then incubated with various concentrations of daunorubicin (DNR) and cytosine arabinoside (Ara-C), and expression of the transgene was measured. Murine DA1-3b-pCDNA3/LacZ leukemic cells were also injected into syngeneic C3H/Hej mice.

RESULTS

In the cells carrying pCDNA3, DNR and Ara-C dramatically increased expression of the LacZ and GM-CSF transgenes. Over-expression depended on drug dose and was due to increased transcription. Enhancement was also observed in K562 cells and in some primary cultured AML samples transduced with the Ad5.CMV-LacZ adenovirus. Addition of N-acetyl-L-cysteine inhibited the over-expression, suggesting that reactive oxygen species were involved in activating the CMV promoter. In the A549 lung carcinoma cell line transduced with Ad5.CMV-LacZ, Ara-C had only a minor effect, and DNR had a detrimental effect, suggesting that expression depends on cell type. In vivo experiments in which mice received DA1-3b-pCDNA3/LacZ leukemic cells, and were then treated with Ara-C, also showed increased transgene expression in these leukemic cells.

CONCLUSIONS

In leukemic cells, chemotherapeutic agents can induce over-expression of transgenes. This suggests a promising combined strategy for the treatment of acute leukemia.

B7-1 costimulatory molecule is critical for the development of experimental autoimmune myasthenia gravis

Following immunization with acetylcholine receptor (AChR), MHC class II-restricted, AChR-specific CD4 cell activation is critical for the development of experimental autoimmune myasthenia gravis (EAMG) in C57BL/6 mice. To study the contributions of B7-1 and B7-2 costimulatory molecules in EAMG, B7-1, B7-2, and B7-1/B7-2 gene knockout (KO) mice were immunized with Torpedo AChR in CFA. Compared with wild-type C57BL6 mice, B7-1 and B7-1/2 KO mice were resistant to EAMG development. B7-1 KO mice had reduced anti-AChR Ab compared with C57BL/6 mice. However, neither B7-1 nor B7-2 gene disruption impaired AChR-induced or dominant alpha(146-162) peptide-induced in vitro lymphoproliferative responses. Blocking of the B7-1 or B7-2 molecule by specific mAbs in vivo led to a reduction in the AChR-specific lymphocyte response, and the reduction was more pronounced in mice treated with anti-B7-2 Ab. The findings implicate B7-1 molecules as having a critical role in the induction of EAMG, and the resistance of B7-1 KO mice is associated with suppressed humoral, rather than suppressed AChR-specific, T cell responses. The data also point to B7-2 molecules as being the dominant costimulatory molecules required for AChR-induced lymphocyte proliferation.

Induction of 4-1BB (CD137) expression by DNA damaging agents in human T lymphocytes

4-1BB(CD137) is a member of the tumour necrosis factor receptor superfamily and is expressed on activated T cells, monocytes and natural killer (NK) cells. The interaction of 4-1BB and 4-1BB ligand provides a costimulatory signal leading to T-cell activation. The expression of 4-1BB has been known to be activation dependent. Interestingly, we found that expression of 4-1BB increased in human peripheral blood mononuclear cells after exposure to mitomycin C. Thus, we tested whether the treatment with other DNA-damaging agents, such as doxorubicin, bleomycin, and gamma-irradiation, could induce 4-1BB expression. The data indicated that 4-1BB expression increased dose-dependently by these agents reaching maximum at 2-3 days after the exposure. We found that the major 4-1BB-expressing population was CD3+ T cells, although a moderate number of CD14+ cells and a few NKB1+ cells also expressed 4-1BB. The levels of 4-1BB expression induced by anticancer drugs, were relatively lower than that induced by CD3 ligation. Interestingly, at subcytotoxic concentrations, doxorubicin and bleomycin considerably enhanced 4-1BB expression induced by CD3 ligation in CEM cells. The ligation of the damage-induced 4-1BB by monoclonal antibody enhanced the viability and proliferating capacity of the cells. In conclusion, the expression of 4-1BB might be one of the cellular responses of the immune cells against various genotoxic stresses.

DNA alkylating agents alleviate silencing of class II transactivator gene expression in L1210 lymphoma cells

MHC class II (Ia) Ag expression is inversely correlated with tumorigenicity and directly correlated with immunogenicity in clones of the mouse L1210 lymphoma (1 ). Understanding the mechanisms by which class II Ag expression is regulated in L1210 lymphoma may facilitate the development of immunotherapeutic approaches for the treatment of some types of lymphoma and leukemia. This study demonstrates that the variation in MHC class II Ag expression among clones of L1210 lymphoma is due to differences in the expression of the class II transactivator (CIITA). Analysis of stable hybrids suggests that CIITA expression is repressed by a dominant mechanism in class II-negative L1210 clones. DNA-alkylating agents such as ethyl methanesulfonate and the chemotherapeutic drug melphalan activate CIITA and class II expression in class II negative L1210 cells, and this effect appears to be restricted to transformed cell lines derived from the early stages of B cell ontogeny. Transient transfection assays demonstrated that the CIITA type III promoter is active in class II(-) L1210 cells, despite the fact that the endogenous gene is not expressed, which suggests that these cells have all of the transacting factors necessary for CIITA transcription. An inverse correlation between methylation of the CIITA transcriptional regulatory region and CIITA expression was observed among L1210 clones. Furthermore, 5-azacytidine treatment activated CIITA expression in class II-negative L1210 cells. Collectively, our results suggest that 1) CIITA gene expression is repressed in class II(-) L1210 cells by methylation of the CIITA upstream regulatory region, and 2) treatment with DNA-alkylating agents overcomes methylation-based silencing of the CIITA gene in L1210 cells.

4-1BB ligand-mediated costimulation of human T cells induces CD4 and CD8 T cell expansion, cytokine production, and the development of cytolytic effector function

4-1BB (CD137) is a costimulatory member of the TNFR family expressed on activated T cells. Its ligand, 4-1BBL, is expressed on activated APC. In the mouse, CD8 T cells are preferentially activated by agonistic anti-murine 4-1BB Abs. However, murine 4-1BBL can stimulate both CD4 and CD8 T cells. To date, there are only limited data on the effects of 4-1BBL on human T cell responses. To further understand the role of 4-1BBL in human T cell responses, we compared human CD4 and CD8 T cell responses to transfected human 4-1BBL plus TCR-mediated stimulation. Both human CD4 and CD8 T cells responded to 4-1BBL. The presence of 4-1BBL on the APC led to increased expansion, cytokine production, and the development of cytolytic effector function by human T cells. In unfractionated T cell cultures, CD4 and CD8 T cells could expand to a similar extent in response to signals through the TCR and 4-1BB, as measured by CFSE labeling and by quantitating T cell numbers in the cultures. In contrast to the results with total T cells, isolated CD8 T cells produced less IL-2 and expanded to a lesser extent than isolated CD4 T cells responding to 4-1BBL. Thus, 4-1BBL is most effective when both CD4 and CD8 T cells are included in the cultures. CD28 and 4-1BB were found to synergize in the induction of IL-2 by human T cells, and CTLA-Ig partially blocked 4-1BBL-dependent IL-2 production. However, a portion of the 4-1BBL-mediated effects were independent of CD28-B7 interaction.

Sub-lethal radiation enhances anti-tumor immunotherapy in a transgenic mouse model of pancreatic cancer

BACKGROUND

It is not uncommon to observe circulating tumor antigen-specific T lymphocytes in cancer patients despite a lack of significant infiltration and destruction of their tumors. Thus, an important goal for tumor immunotherapy is to identify ways to modulate in vivo anti-tumor immunity to achieve clinical efficacy. We investigate this proposition in a spontaneous mouse tumor model, Rip1-Tag2.

METHODS

Experimental therapies were carried out in two distinctive trial designs, intended to either intervene in the explosive growth of small tumors, or regress bulky end-stage tumors. Rip1-Tag2 mice received a single transfer of splenocytes from Tag-specific, CD4+ T cell receptor transgenic mice, a single sub-lethal radiation, or a combination therapy in which the lymphocyte transfer was preceded by the sub-lethal radiation. Tumor burden, the extent of lymphocyte infiltration into solid tumors and host survival were used to assess the efficacy of these therapeutic approaches.

RESULTS

In either intervention or regression, the transfer of Tag-specific T cells alone did not result in significant lymphocyte infiltration into solid tumors, not did it affect tumor growth or host survival. In contrast, the combination therapy resulted in significant reduction in tumor burden, increase in lymphocyte infiltration into solid tumors, and extension of survival.

CONCLUSIONS

The results indicate that certain types of solid tumors may be intrinsically resistant to infiltration and destruction by tumor-specific T lymphocytes. Our data suggest that such resistance can be disrupted by sub-lethal radiation. The combinatorial approach presented here merits consideration in the design of clinical trials aimed to achieve T cell-mediated anti-tumor immunity.

Melphalan-induced expression of IFN-beta in MOPC-315 tumor-bearing mice and its importance for the up-regulation of TNF-alpha expression

We have previously shown that administration of a low-dose of melphalan (L-phenylalanine mustard; L-PAM) to mice bearing a large s.c. MOPC-315 tumor leads to up-regulation of TNF-alpha expression, which is first evident at the mRNA level at 24 h after the chemotherapy. In this study, we show accumulation of IFN-beta mRNA in the spleen and tumor nodule of such mice as early as 1 h after the chemotherapy followed by elevated production of IFN-beta protein. IFN-beta protein in turn was found to be important for the L-PAM-induced up-regulation of TNF-alpha expression, as neutralization of IFN-beta inhibited the L-PAM-induced up-regulation of TNF-alpha mRNA expression in MOPC-315 tumor cells. In addition, L-PAM failed to up-regulate TNF-alpha expression in spleen cells from mice in which signaling by IFN-beta is deficient. Studies into the mechanism through which L-PAM leads to rapid accumulation of IFN-beta mRNA revealed that it requires de novo RNA synthesis, indicating that the regulation is at the transcriptional level. However, it did not require de novo protein synthesis, indicating that activation of pre-existing transcription factors is sufficient for IFN-beta gene expression. The L-PAM-induced accumulation of IFN-beta mRNA was mimicked with H(2)O(2) and was prevented with the antioxidant N-acetyl-L-cysteine, indicating that reactive oxygen species are involved in the transcriptional regulation of L-PAM-induced IFN-beta gene expression. Thus, the IFN-beta gene is an early response gene that is activated in response to L-PAM via a pathway that involves reactive oxygen species, and IFN-beta in turn plays an important role in L-PAM-induced TNF-alpha up-regulation.

Mechanism of melphalan-induced B7-1 gene expression in P815 tumor cells

We have previously shown that exposure of P815 tumor cells to melphalan (L-phenylalanine mustard; L-PAM) leads to up-regulation of B7-1 surface expression, and this L-PAM-induced up-regulation requires de novo RNA synthesis and is associated with accumulation of B7-1 mRNA. Here we show that the effect of L-PAM on B7-1 surface expression can be mimicked by exposing P815 tumor cells to oxidative stress but not to heat shock. Moreover, the antioxidant N-acetyl-L-cysteine prevented the L-PAM-induced accumulation of B7-1 mRNA in P815 tumor cells, suggesting that reactive oxygen species are involved in the transcriptional regulation of L-PAM-induced B7-1 gene expression. Although AP-1 and NF-kappaB are regarded as redox-sensitive transcription factors and the promoter/enhancer region of the B7-1 gene contains an AP-1 and an NF-kappaB binding site, exposure of P815 tumor cells to L-PAM led to rapid and transient activation only of NF-kappaB, but not AP-1, that bound specifically to a probe containing the respective binding site in the murine or human B7-1 gene. Moreover, exposure of P815 tumor cells to a cell-permeable peptide that selectively inhibits NF-kappaB activation by blocking the activation of the IkappaB-kinase complex was found to inhibit the L-PAM-induced B7-1 mRNA accumulation, indicating that NF-kappaB activation is essential for the L-PAM-induced B7-1 gene expression. Taken together, these results indicate that L-PAM leads to activation of B7-1 gene expression by activating NF-kappaB via a pathway that involves reactive oxygen species.

Complexities of CD28/B7: CTLA-4 costimulatory pathways in autoimmunity and transplantation

Recent advances in the understanding of T cell activation have led to new therapeutic approaches in the treatment of immunological disorders. One attractive target of intervention has been the blockade of T cell costimulatory pathways, which result in more selective effects on only those T cells that have encountered specific antigen. In fact, in some instances, costimulatory pathway antagonists can induce antigen-specific tolerance that prevents the progression of autoimmune diseases and organ graft rejection. In this review, we summarize the current understanding of these complex costimulatory pathways including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2 (CD86) molecules. We present evidence that suggests that multiple mechanisms contribute to CD28/B7-mediated T cell costimulation in disease settings that include expansion of activated pathogenic T cells, differentiation of Th1/Th2 cells, and the migration of T cells into target tissues. Additionally, the negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection supports a dynamic but complex process of immune regulation that is prominent in the control of self-reactivity. This is most apparent in regulation of the CD4(+)CD25(+)CTLA-4(+) immunoregulatory T cells that control multiple autoimmune diseases. The implications of these complexities and the potential for use of these therapies in clinical immune intervention are discussed.

Inhibition of effects of endogenously synthesized histamine disturbs in vitro human dendritic cell differentiation

Histamine, a principal mediator in various physiological and pathological cell functions is synthesized from L-histidine exclusively by histidine decarboxylase, an enzyme, which is expressed in many tissues of mammalian organism. Histamine plays a role in various cellular functions, including cell differentiation. The aim of this study was to determine the presence and to characterize the role of the endogenously produced histamine during in vitro dendritic cell (DC) differentiation induced by interleukin-4 (IL-4) and granulocyte-monocyte colony stimulating factor (GM-CSF). The changes in intracellular histamine content, biosynthesis and gene expression of histidine decarboxylase were investigated during this process. One also studied how histamine receptor antagonists and a histamine synthesis blocker influence the expression of differentiation antigens on the DC during in vitro maturation. During in vitro differentiation parallel culture incubations were performed by adding H1 receptor antagonist triprolidine, H2 receptor antagonist tiotidine, the tamoxifene derivate DPPE which blocks the intracellular binding of histamine, and an irreversible blocker of histidine decarboxylase, alpha-fluoromethyl histamine (alpha-FMH). The results show simultaneous increase in both histidine decarboxylase level and histamine content during differentiation of elutriated monocytes toward DC. Both blockade of de novo histamine production (by alpha-FMH) and inhibition of histamine binding (by H1 and H2 receptor antagonists, triprolidine and tiotidine, respectively) markedly decreased CD40 expression and that of CD45 from the 3rd day of treatment. DPPE by disturbing intracellular interaction of histamine with cytochrome P-450 moieties was able to decrease the expression of CD45, CD86, HLA-DR, CD33, CD40 and CD11c. Based on the data it is suggested that endogenous histamine is actively synthesized during cytokine-induced in vitro DC differentiation. The functional relevance and autocrine and paracrine action of endogenously produced histamine is supported by the data showing that inhibition of histamine synthesis by HDC, blocking of histamine binding by both 'extracellular' histamine receptors (by specific antagonists, triprolidine and tiotidine) and 'intracellular' antagonists (DPPE) disturb the differentiation of DC. This conclusion is supported by the fact, that by the inhibition of histamine acting in an autocrine/paracrine way, the expression pattern of differentiation markers on DC is markedly changed.

Costimulatory wars: the tumor menace

Advances in our understanding of T cell costimulatory molecules have provided a vast array of novel approaches to tumor immunotherapy. In the past year, combinatorial immunotherapy based on earlier studies of CTLA-4 blockade, the identification of novel B7-family members, the modulation of CD40 to reverse tolerance to tumor-associated antigens and the use of OX40 to enhance antitumor responses of CD4+ T cells have all contributed to the development of more-powerful immunomodulatory cancer therapies.