Dendritic cells infiltrating tumors cotransduced with granulocyte/macrophage colony-stimulating factor (GM-CSF) and CD40 ligand genes take up and present endogenous tumor-associated antigens, and prime naive mice for a cytotoxic T lymphocyte response

Antitumor activities of human dendritic cells derived from peripheral and cord blood

AIM: To observe the biological specialization of human peripheral blood dendritic cells (DC) and cord blood derived DC and its effects on effector cells killing human hepatocarcinoma cell line BEL-7402 in vitro.

METHODS: The DC biological characteristics were detected with immunohistochemical and MTT assay. Two antitumor experimental groups are: peripheral blood DC and cord blood DC groups. Peripheral blood DC groups used LAK cells as the effector cells and BEL-7402 as target cells, while cord blood DC groups used CTL induced by tumor antigen twice pulsed DC as effector cells and BEL-7402 as target cells, additional peripheral blood DC and cord blood DC are added to observe its stimulating activities to effector cells. The effector¡äs cytotoxicity to tumor cells were detected with neutral red colorimetric assay at two effector/ target ratios of 5:1 and 10:1.

RESULTS: Peripheral blood DC and cord blood DC highly expressed HLA-ABC, HLA-DR, HLA-DQ, CD54 and S-100 protein. The stimulating activities to lymphocyte proliferation were compared between experimental groups (DC added) and control group (no DC added), in six experiment subgroups,the DC/lymphocyte ratio was sequentially 0.25:100, 0.5:100, 1:100, 2:100, 4:100 and 8:100, A values(^-x±s) were 0.75396 ± 0.009, 0.84916 ± 0.010, 0.90894 ± 0.012, 0.98371 ± 0.007, 1.01299 ± 0.006 and 1.20384 ± 0.006 in peripheral blood DC groups and 0.77650 ± 0.005, 0.83008 ± 0.007, 0. 92725 ± 0.007, 1.05990 ± 0.010, 1.15583 ± 0.011, 1. 22983 ± 0.011 in cord blood DC groups. A value was 0.59517 ± 0.005 in control group. The stimulating activities were higher in experimental groups than in control group (P < 0.01), which were increased when the DC concentration was enlarged (P < 0.01). Two differently derived DCs had the same phenotypes and similar stimulating activities (P > 0.05). In peripheral blood DC groups, the cytotoxicity (^-x±s) of the LD groups (experimental groups) and L groups (control group) was 58.16% ± 2.03% (5:1), 46c18% ± 2.25% (10:1) and 38c13% ± 1.29% (5:1) and 65.40% ± 1.56% (10:1) respectively; in cord blood DC groups, TD groups (experimental groups) and T groups (control groups) were 69.71% ± 2.33% (5:1), 77.64% ± 1.94% (10:1) and 56.89% ± 1.82% (5:1) and 60.99% ± 1.42% (10:1) respectively. The cytotoxicity activities were enhanced with increased effector/target ratio (P < 0.01). At the same effector/target ratio, the cytotoxicity of experimental groups were bigger than that of control groups (P < 0.01). The cytotoxicity activities of cord blood DC groups were higher than that of peripheral blood DC groups (P < 0.01).

CONCLUSION: Peripheral blood DC and cord blood DC are mature DC in morphology and function, both can enhance the effector cell killing activities to hepatocarcinoma cells. DC pulsed with tumor antigen can induce higher specific CTL activity than unpulsed DC.

Tumour escape from immune surveillance through dendritic cell inactivation

Dendritic cells (DC) are central to the initiation of immunity. To induce immune reactivity, DC are recruited at the site of antigen expression, uptake antigens and migrate to secondary lymphoid organs while receiving activation signals delivered by pathogens, dying cells, and/or T cells. Tumours can escape the immune system by interfering with the migration of DC or by not providing the necessary activation signals. Moreover, tumours promote the secretion of factors that inhibit DC differentiation and functions. We will review the current knowledge of the physiopathology of DC in cancer, which paves the way for novel strategies of therapeutic intervention.

Hyaluronic acid and chondroitin sulphate A rapidly promote differentiation of immature DC with upregulation of costimulatory and antigen-presenting molecules, and enhancement of NF-kappaB and protein kinase activity

Dendritic cells (DCs) have been identified as effective antigen-presenting cells (APCs). We demonstrate that extracellular matrix (ECM), hyaluronic acid (HA) and chondroitin sulphate A (CSA), in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), can rapidly promote the differentiation of monocyte-derived immature DCs, as characterized by the remarkable upregulation of human leucocyte antigen (HLA-DR), CD40, CD54, CD80 and CD86 expression to levels higher than those in the DCs generated by culturing with GM-CSF and interleukin (IL)-4 for 7 days and aggregation of the cells within 48 h. The upregulation of expression of HLA-DR, CD40, CD54, CD80 and CD86 was dose-dependent. Further studies showed that HA and CSA were able to augment nuclear factor (NF)-kappaB activity, as determined by gel mobility shift assay and promote protein phosphorylation. Inhibition of NF-kappaB by pyrolidine dithiocarbamate and sodium salicylate, and serine-threonine and tyrosine kinase by starosporine as well as phosphatidylinositide-3-kinase (PI-3-K) by wortmannin could prevent the effects of HA and CSA on the expression of HLA-DR, CD40, CD80 and CD86 in various degrees. Thus, our data demonstrate that HA or CSA can effectively and rapidly promote the differentiation of immature DC, suggesting that HA and CSA may possess a potential capacity in regulating immune responses.

Noncovalent association with stress protein facilitates cross-priming of CD8+ T cells to tumor cell antigens by dendritic cells

A viral oncogene carrying well-defined K(b)/D(b)-restricted epitopes was expressed in a heat shock protein (hsp)-associated or nonassociated form in the murine tumor cells P815 and Meth-A. Wild-type SV40 large T-Ag (wtT-Ag) is expressed without stable hsp association; mutant (cytoplasmic cT-Ag) or chimeric (cT272-green fluorescent fusion protein) T-Ag is expressed in stable association with the constitutively expressed, cytosolic hsp73 (hsc70) protein. In vitro, remnants from apoptotic wtT-Ag- or cT-Ag-expressing tumor cells are taken up and processed by immature dendritic cells (DC), and the K(b)/D(b)-binding epitopes T1, T2/3, and T4 of the T-Ag are cross-presented to CTL in a TAP-independent way. DC pulsed with remnants of transfected, apoptotic tumor cells cross-presented the three T-Ag epitopes more efficiently when they processed ATP-sensitive hsp73/cT-Ag complexes than when they processed hsp-nonassociated (native) T-Ag. In vivo, more IFN-gamma-producing CD8+ T cells were elicited by a DNA vaccine that encoded hsp73-binding mutant T-Ag than by a DNA vaccine that encoded native, non-hsp-binding T-Ag. Three- to 5-fold higher numbers of T-Ag (T1-, T2/3-, or T4-) specific, D(b)/K(b)-restricted IFN-gamma-producing CD8+ T cells were primed during the growth of transfected H-2(d) Meth-A/cT tumors than during the growth of transfected Meth-A/T tumors in F(1)(b x d) hosts. Hence, the association of an oncogene with constitutively expressed, cytosolic hsp73 facilitates cross-priming in vitro and in vivo of CTL by DC that process material from apoptotic cells.

Cross-presentation in viral immunity and self-tolerance

T lymphocytes recognize peptide antigens presented by class I and class II molecules encoded by the major histocompatibility complex (MHC). Classical antigen-presentation studies showed that MHC class I molecules present peptides derived from proteins synthesized within the cell, whereas MHC class II molecules present exogenous proteins captured from the environment. Emerging evidence indicates, however, that dendritic cells have a specialized capacity to process exogenous antigens into the MHC class I pathway. This function, known as cross-presentation, provides the immune system with an important mechanism for generating immunity to viruses and tolerance to self.

Effect of a cancer vaccine prepared by fusions of hepatocarcinoma cells with dendritic cells

AIM: To prepare a cancer vaccine (H₂₂-DC) expressing high levels of costimulatory molecules based on fusions of hepatocarcinoma cells (H₂₂) with dendritic cells (DC) of mice and to analyze the biological characteristics and induction of specific CTL activity of H₂₂-DC.

METHODS: DCs were isolated from murine spleen by metrizamide density gradient centrifugation, purified based on its characteristics of semi-adhesion to culture plates and FcR^-, and were cultured in the medium containing GM-CSF and IL-4. A large number of DC were harvested. DCs were then fused with H₂₂ cells by PEG and the fusion cells were marked with CD11c MicroBeads. The H₂₂-DC was sorted with Mimi MACS sorter. The techniques of cell culture, immunocytochemistry and light microscopy were also used to test the characteristics of growth and morphology of H₂₂-DC in vitro. As the immunogen, H₂₂-DC was inoculated subcutaneously into the right armpit of BALB/C mice, and their tumorigenicity in vivo was observed. MTT was used to test the CTL activity of murine spleen in vitro.

RESULTS: DC cells isolated and generated were CD11c+ cells with irregular shape, and highly expressed CD80, CD86 and CD54 molecules. H₂₂ cells were CD11c^- cells with spherical shape and bigger volume, and did not express CD80, CD86 and CD54 molecules. H₂₂-DC was CD11c⁺ cells with bigger volume, being spherical, flat or irregular in shape, and highly expressed CD80, CD86 and CD54 molecules, too. H₂₂-DC was able to divide and proliferate in vitro, but its activity of proliferation was significantly decreased as compared with H₂₂ cells and its growth curve was flatter than H₂₂ cells. After subcutaneous inoculation over 60 d, H₂₂-DC showed no tumorigenecity in mice, which was significantly different from control groups (P < 0.01). The spleen CTL activity against H₂₂ cells in mice implanted with fresh H₂₂-DC was significantly higher than control groups (P < 0.01).

CONCLUSION: H₂₂-DC could significantly stimulate the specific CTL activity of murine spleen, which suggests that the fusion cells have already obtained the function of antigen presenting of parental DC and could present H₂₂ specific antigen which has not been identified yet, and H₂₂-DC could induce antitumor immune response; although simply mixed H₂₂ cells with DC could stimulate the specific CTL activity which could inhibit the growth of tumor in some degree, it could not prevent the generation of tumor. It shows that the DC vaccine is likely to become a helpful approach in immunotherapy of hepatocarcinoma.

Adoptive tumor therapy with T lymphocytes enriched through an IFN-gamma capture assay

Successful adoptive T-cell therapy has been demonstrated in viral disease and selected forms of cancer. However, it is limited by the difficulty to efficiently isolate and amplify autologous tumor-reactive T-cell clones. Tetramers of major histocompatibility complex (MHC) class I and peptide have facilitated the characterization of CD8+ T cells specific for tumor-associated antigens. However, for adoptive T-cell therapy, MHC-tetramers have limitations: they require knowledge of tumor antigens, which is often not available; they select T cells with a single specificity, thereby posing risk for selection of tumor escape variants; they do not select for function, so that T cells may be anergic when isolated from cancer patients; and they do not allow the isolation of CD4+ T cells that can be essential for tumor rejection. Because interferon (IFN)-gamma is essential for tumor rejection, we isolated live T cells based on their IFN-gamma production. IFN-gamma secreted by previously activated T cells is retained on the cell surface, allowing their specific isolation and expansion. We show here that IFN-gamma+ but not IFN-gamma- T cells from tumor-immunized mice are cytolytic and mediate tumor rejection upon adoptive transfer. Importantly, tumor-specific T cells can be enriched from lymphocytes infiltrating human renal cell carcinoma by the IFN-gamma capture assay.

Dendritic cells and tumor immunity

Researchers and clinicians have tried for decades to use the mechanisms of immunity for the fight against cancer. Early attempts aimed at the instrumentation of soluble immune mediators such as antibodies or cytotoxic proteins for the therapy of malignancies. Major improvements in understanding the induction and regulation of cellular immunity have now made it possible to generate effector cells in cancer patients which are specific for the neoplastic disease. At the beginning of every cellular immune reaction against cancers tumor antigens have to be presented to T cells in order to activate them and drive them into clonal expansion. This is done by antigen presenting cells, the most powerful of which is the dendritic cell (DC). While DC were hard to isolate initially, they can be generated in large numbers in vitro today and manipulated in multiple ways before given back to a patient to induce tumor immunity. Thus, a great amount of hope lies in the use of DC as inducers of tumor immunity. However, the first clinical studies, which have now been completed with only limited success make clear, that still a lot of open questions remain to be answered. This review tries to give an overview of this rapidly developing field, mentioning the major conceptual approaches and techniques, but also discussing important caveats. The next years will show whether we can improve our understanding of DC biology and the mechanisms of immune induction strongly enough to effectively employ DC for immunotherapy of cancer.

Ex vivo host response to gastrointestinal cancer cells presented by autologous dendritic cells

BACKGROUND

Dendritic cells (DCs) capture apoptotic tumors and cross-present their antigens in the MHC class I and class II pathways for recognition by CD4+ and CD8+ T lymphocytes. Here we have tested the ability of fresh surgically resected colon and gastric cancer tumors to specifically activate host T lymphocytes when presented by autologous DCs.

METHODS

DCs derived from adherent blood mononuclear cells of five patients, after a 7-day culture with GM-CSF and IL-4, were exposed to apoptotic autologous tumor (AAT) or apoptotic autologous peritumor normal (AAN) cells and cultured 24 h with monocyte-conditioned medium to achieve full DC maturation. Tumor-specific response was evaluated as single-cell cytokine release in an enzyme-linked immunospot (ELISPOT) and as cytotoxicity in a cold target inhibition (51)Cr-release assay.

RESULTS

AAT-DCs induced specific IFN-gamma by T lymphocytes of two patients (rectal and gastric cancer), whereas in another two patients (rectal and gastric cancer) this response was depressed with a similar tumor-specific pattern and in one patient (rectal cancer) there was no response. Activation of IFN-gamma release was accompanied by tumor cytotoxicity and both responses were enhanced by IL-12, indicating the functional integrity of patients' lymphocytes.

CONCLUSION

These data show that T-cell memory against rectal/gastric carcinoma antigens can be triggered by tumor-loaded autologous DCs. However, escape mechanisms may exist among tumors of the same histological origin that can inhibit this host response. A DC-based antitumor immunological monitoring assay with autologous tumor biopsies may allow patients to be screened to determine those who are suitable candidates for immune-based immunotherapy.

Cross-presentation, dendritic cells, tolerance and immunity

This review examines the role of cross-presentation in tolerance and immunity. We discuss (a) the antigenic requirements for cross-presentation, (b) the phenotype of the antigen presenting cell (APC), (c) the cellular interactions and molecular signals involved in cross-priming, and (d) the factors that direct the immune system toward tolerance or immunity. A large part of this review is dedicated to summarizing our current knowledge of the cross-presenting APC.

Cross-presentation by dendritic cells of tumor antigen expressed in apoptotic recombinant canarypox virus-infected dendritic cells

We have investigated the possible usefulness of recombinant canarypox virus (ALVAC) encoding the melanoma-associated Ag, Melan-A/MART-1 (MART-1), in cancer immunotherapy, using a dendritic cell (DC)-based approach. ALVAC MART-1-infected DC express, and are able to process and present, the Ag coded by the viral vector. One consistent feature of infection by ALVAC is that these viruses induce apoptosis, and we show cross-presentation of Ag when uninfected DC are cocultured with ALVAC MART-1-infected DC. Uptake of apoptotic virally infected DC by uninfected DC and subsequent expression of tumor Ag in the latter were verified by flow cytometry analysis, image cytometry, and confocal microscopy. Functional activity was monitored in vitro by the stimulation of a MART-1-specific cytotoxic T cell clone. Heightened efficiency in Ag presentation is evidenced in the 2- to 3-fold increase in IFN-gamma production by the T cell clone, as compared with the ALVAC-infected DC alone. Cocultures of ALVAC MART-1-infected and uninfected DC are able to induce MART-1-specific T cell immune responses, as assessed by HLA class I/peptide tetramer binding, IFN-gamma ELISPOT assays, and cytotoxicity tests. Overall, our data indicate that DC infected with recombinant canarypox viruses may represent an efficient presentation platform for tumor Ags, which can be exploited in clinical studies.

Mechanisms of cytokine synergy essential for vaccine protection against viral challenge

The ability of cytokines to steer CD4(+) T(h) cell responses toward a T(h)1 or T(h)2 phenotype and enhance the magnitude of both CD8(+) cytotoxic T lymphocytes (CTL) and antibody responses has clearly been demonstrated by our lab and others, but the influence of cytokines on protective immune responses is much less clear. Here we show an essential role for CD4(+) T(h)1 helper cell induction and IFN-gamma production in protection from viral challenge with a recombinant vaccinia virus expressing HIV-1MN viral envelope glycoprotein gp160. Complete protection from viral challenge is achieved only when the triple combination of exogenous cytokines granulocyte macrophage colony stimulating factor (GM-CSF), IL-12 and tumor necrosis factor (TNF)-alpha are co-administered with the peptide vaccine. In vivo depletion of CD4(+) cells or immunization of IFN-gamma-deficient mice abrogates protection. GM-CSF, IL-12 and TNF-alpha also synergize for the enhanced induction of CTL; however, adoptive transfer of a CD8(+) CTL line afforded only partial protection in this viral challenge model. As a possible mechanism of in vivo protection we show that GM-CSF increases the percentage and activity of antigen-presenting dendritic cells in draining lymph nodes where the immune response is initiated. We further demonstrate synergy between IL-12 and the proinflammatory cytokine TNF-alpha in driving IFN-gamma production. Thus, a combination of IL-12 and TNF-alpha is essential for the optimal development of T(h)1 responses and help for CTL induction in BALB/c mice, and is complemented by a third cytokine, GM-CSF, which enhances antigen presentation.

Induction of antitumor immunity by transduction of CD40 ligand gene and interferon-gamma gene into lung cancer

CD40-CD40 ligand (CD40L) interaction is an important costimulatory signaling pathway in the crosstalk between T cells and antigen-presenting cells. This receptor-ligand system is known to be essential in eliciting strong cellular immunity. Here we demonstrate that murine lung cancer cells (3LLSA) transduced with the CD40L gene (3LLSA-CD40L) were rejected in syngeneic C57BL/6 mice, but grew in CD40-deficient mice to the same extent as control tumor cells. Immunohistochemical study showed that inflammatory cells, including CD4+, CD8+ T cells and NK cells, infiltrated into the inoculated 3LLSA-CD40L tumor tissue. Inoculation of 3LLSA-CD40L cells into mice resulted in the induction of 3LLSA-specific cytotoxic T-cell immunity, and the growth of parental 3LLSA tumors was inhibited when 3LLSA cells were inoculated into C57BL/6 mice mixed with 3LLSA-CD40L cells or when they were rechallenged 4 weeks after 3LLSA-CD40L cells were rejected. Furthermore, co-inoculation of interferon (IFN)-gamma-transduced cells (3LLSA-IFNgamma) with 3LLSA-CD40L cells enhanced the antitumor immunity efficiently in vivo. These results indicate that the in vivo priming with CD40L- and IFN-gamma gene-transduced lung cancer cells is a promising strategy for inducing antitumor immunity in the treatment of lung cancer.

Expression and release of stable and active forms of murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) targeted to different subcellular compartments

Cytokines have been used for several years as immunomodulators. However, one of the main drawbacks of systemically applied cytokines is their high toxicity. In addition, cytokines work in a paracrine form and frequently after cell-to-cell interaction. Therefore, a very restricted release of cytokines-in time and space-could be desired for most of their therapeutic applications. The murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) is one of the most promising cytokine candidates for cancer immunotherapy and as an adjuvant of DNA vaccines. With the aim of improving the administration and release of cytokines in a very restricted area, we have designed vectors expressing the mGM-CSF cDNA with different localization signals. Using this strategy we have shown that cytokines can be expressed and targeted to different subcellular compartments (i.e. the cytoplasm, the endoplasmic reticulum and the nucleus), stored inside the cells and released after cell lysis as stable active proteins. Moreover, a plasma membrane targeted form of mGM-CSF displayed substantial amount of biological activity. These vectors could have potential applications in immunotherapy for tumours and DNA vaccination protocols.

Phagocytic dendritic cells from myelomas activate tumor-specific T cells at a single cell level

Antigen-presenting cells (APCs) from subcutaneous mouse MOPC315 plasmacytoma phagocytosed immunoglobulin G-coated magnetic beads, enabling efficient isolation within 2 hours by magnetic separation (APC-MB). Cell morphology was heterogeneous, with some of the cells having dendrites. The surface phenotype of purified tumor APCs-MB was CD11b(+), CD11c(+), CD40(+), CD80(+), CD86(+), and MHC class II(+). Tumor APCs-MB expressed messenger RNA for fractalkine and ABCD-1 chemokines, and for CC-type chemokine receptors CCR5 and CCR7, indicating the presence of mature dendritic cells (DCs). Visualized at a single cell level within 4 hours after disruption of the tumor, APCs-MB induced rapid Ca(++) mobilization in MHC class II-restricted tumor idiotype (Id)-specific cloned CD4(+) T cells. In long-term assays, tumor APCs-MB induced proliferation of naive T cells from Id-specific T-cell receptor transgenic mice. The results suggest that tumor APCs-MB represent a heterogeneous cell population that includes myeloid-derived DCs of various stages of maturation. A considerable fraction (> or = 15%) of DCs is spontaneously primed with tumor-specific antigen.

A fresh look at tumor immunosurveillance and immunotherapy

Despite major advances in our understanding of adaptive immunity and dendritic cells, consistent and durable responses to cancer vaccines remain elusive and active immunotherapy is still not an established treatment modality. The key to developing an effective anti-tumor response is understanding why, initially, the immune system is unable to detect transformed cells and is subsequently tolerant of tumor growth and metastasis. Ineffective antigen presentation limits the adaptive immune response; however, we are now learning that the host's innate immune system may first fail to recognize the tumor as posing a danger. Recent descriptions of stress-induced ligands on tumor cells recognized by innate effector cells, new subsets of T cells that regulate tumor tolerance and the development of spontaneous tumors in mice that lack immune effector molecules, beckon a reflection on our current perspectives on the interaction of transformed cells with the immune system and offer new hope of stimulating therapeutic immunity to cancer.

Dendritic cells acquire antigens from live cells for cross-presentation to CTL

Dendritic cells (DC) can readily capture Ag from dead and dying cells for presentation to MHC class I-restricted CTL. We now show by using a primate model that DC also acquire Ag from healthy cells, including other DC. Coculture assays showed that fluorescently labeled plasma membrane was rapidly and efficiently transferred between DC, and transfer of intracellular proteins was observed to a lesser extent. Acquisition of labeled plasma membrane and intracellular protein was cell contact-dependent and was primarily a function of immature DC, whereas both immature and CD40L-matured DC could serve as donors. Moreover, immature DC could acquire labeled plasma membrane and intracellular proteins from a wide range of hemopoietic cells, including macrophages, B cells, and activated T cells. Notably, macrophages, which readily phagocytose apoptotic bodies, were very inefficient at acquiring labeled plasma membrane and intracellular proteins from other live macrophages or DC. With live-cell imaging techniques, we demonstrate that individual DC physically extract plasma membrane from other DC, generating endocytic vesicles of up to 1 microm in diameter. Finally, DC but not macrophages acquired an endogenous melanoma Ag expressed by live DC and cross-presented Ag to MHC class I-restricted CTL, demonstrating the immunological relevance of our finding. These data show for the first time that DC readily acquire Ag from other live cells. We suggest that Ag acquisition from live cells may provide a novel mechanism whereby DC can present Ag in the absence of direct infection, and may serve to expand and regulate the immune response in vivo.

Protective immunity to UV radiation-induced skin tumours induced by skin grafts and epidermal cells

There is little evidence that cutaneous dendritic cells (DC), including epidermal Langerhans cells (LC), can induce immunity to UV radiation (UVR)-induced skin tumours. Here, it is shown that cells within skin can induce protective antitumour immunity against a UVR-induced fibrosarcoma. Transplantation of the skin overlying subcutaneous tumours onto naïve recipients could induce protective antitumour immunity, probably because the grafting stimulated the tumour Ag-loaded DC to migrate to local lymph nodes. This suggests that cutaneous APC can present tumour Ag to induce protective antitumour immunity. Previously, it has been shown that immunization of mice with MHC class II+ epidermal cells (EC) pulsed with tumour extracts could induce delayed-type hypersensitivity against tumour cells. Here, this same immunization protocol could induce protective immunity against a minimum tumorigenic dose of UVR-induced fibrosarcoma cells, but not higher doses. Epidermal cells obtained from semiallogeneic donors and pulsed with tumour extract could also induce protective immunity. However, presentation of BSA Ag from the culture medium was found to contribute to this result using semiallogeneic EC. The results suggest that LC overlying skin tumours may be able to induce protective immunity to UVR-induced tumours if stimulated to migrate from the skin.

CD8(+) but not CD8(-) dendritic cells cross-prime cytotoxic T cells in vivo

Bone marrow-derived antigen-presenting cells (APCs) take up cell-associated antigens and present them in the context of major histocompatibility complex (MHC) class I molecules to CD8(+) T cells in a process referred to as cross-priming. Cross-priming is essential for the induction of CD8(+) T cell responses directed towards antigens not expressed in professional APCs. Although in vitro experiments have shown that dendritic cells (DCs) and macrophages are capable of presenting exogenous antigens in association with MHC class I, the cross-presenting cell in vivo has not been identified. We have isolated splenic DCs after in vivo priming with ovalbumin-loaded beta2-microglobulin-deficient splenocytes and show that they indeed present cell-associated antigens in the context of MHC class I molecules. This process is transporter associated with antigen presentation (TAP) dependent, suggesting an endosome to cytosol transport. To determine whether a specific subset of splenic DCs is involved in this cross-presentation, we negatively and positively selected for CD8(-) and CD8(+) DCs. Only the CD8(+), and not the CD8(-), DC subset demonstrates cross-priming ability. FACS((R)) studies after injection of splenocytes loaded with fluorescent beads showed that 1 and 0.6% of the CD8(+) and the CD8(-) DC subsets, respectively, had one or more associated beads. These results indicate that CD8(+) DCs play an important role in the generation of cytotoxic T lymphocyte responses specific for cell-associated antigens.

Immortalized myeloid suppressor cells trigger apoptosis in antigen-activated T lymphocytes

We described a generalized suppression of CTL anamnestic responses that occurred in mice bearing large tumor nodules or immunized with powerful recombinant viral immunogens. Immune suppression entirely depended on GM-CSF-driven accumulation of CD11b(+)/Gr-1(+) myeloid suppressor cells (MSC) in secondary lymphoid organs. To further investigate the nature and properties of MSC, we immortalized CD11b(+)/Gr-1(+) cells isolated from the spleens of immunosuppressed mice, using a retrovirus encoding the v-myc and v-raf oncogenes. Immortalized cells expressed monocyte/macrophage markers (CD11b, F4/80, CD86, CD11c), but they differed from previously characterized macrophage lines in their capacities to inhibit T lymphocyte activation. Two MSC lines, MSC-1 and MSC-2, were selected based upon their abilities to inhibit Ag-specific proliferative and functional CTL responses. MSC-1 line was constitutively inhibitory, while suppressive functions of MSC-2 line were stimulated by exposure to the cytokine IL-4. Both MSC lines triggered the apoptotic cascade in Ag-activated T lymphocytes by a mechanism requiring cell-cell contact. Some well-known membrane molecules involved in the activation of apoptotic pathways (e.g., TNF-related apoptosis-inducing ligand, Fas ligand, TNF-alpha) were ruled out as candidate effectors for the suppression mechanism. The immortalized myeloid lines represent a novel, useful tool to shed light on the molecules involved in the differentiation of myeloid-related suppressors as well as in the inhibitory pathway they use to control T lymphocyte activation.

Cytokine-secreting tumor cell vaccines

Modification of the tumor microenvironment with gene transfer techniques stimulates two immune mechanisms that effectuate tumor destruction. One involves improved tumor-antigen presentation for the development of specific cellular and humoral immunity. The second involves compromise of the tumor vasculature by soluble factors and leukocytes.

Management of malignant melanoma: new developments in immune and gene therapy

Thus far, the use of classical anti-cancer treatment modalities had only rarely a beneficial impact on the prognosis of patients with metastatic melanoma. We as physicians have therefore the obligation as well as the chance to develop and test new therapeutic strategies. Our growing knowledge about the genetic basis of melanoma provides one platform to fulfil this task. Another one comes from our increasing understanding of the molecular and cellular mechanisms involved in the induction/modulation of immune responses, as well as the progress made in the field of identification of melanoma antigens, and allows for the development of a new generation of vaccines. The aim of this article is to discuss several of these new concepts towards the use of immune and gene therapy of melanoma.

In vivo gene transfer of CD40 ligand into colon cancer cells induces local production of cytokines and chemokines, tumor eradication and protective antitumor immunity

The interaction between CD40 ligand (CD40L, CD154) and its receptor CD40 on antigen-presenting cells, is essential for the initiation of cell-mediated and humoral immune responses. In this study, we investigated the antitumor effect of in vivo gene transfer of CD40L to tumor cells using an adenoviral vector (AdCMVmCD40L) in a murine CT-26 colon cancer model. We found that injection of AdCMVmCD40L caused tumor regression in a dose-dependent manner. A complete regression of tumor was observed in 81% of mice treated with 10(9) p.f.u. of AdCMVmCD40L. The antitumor effect induced by CD40L was mediated by CD8+ T cells and was associated with the generation of tumor-specific cytolytic T lymphocytes (CTL). Animals that eradicated the tumor were protected against tumor cell rechallenge, and both CD4+ and CD8+ T cells were involved in specific protective immunity. Treatment with AdCMVmCD40L in one tumor nodule also caused complete regression of established tumors at distant sites. The antitumor effect elicited by AdCMVmCD40L was associated with the intratumoral production of IL-12 and IFN-gamma and with an increased intratumoral expression of chemokines such as MIP- 1alpha, MIP-1beta, MIP-2, RANTES, and eotaxin. These data demonstrate that intratumoral injection of AdCMVmCD40L induces a powerful cascade of chemokines and cytokines in the tumor mass and stimulates an efficient antitumor immunity leading to regression of established colon cancer and protection against tumor cell rechallenge.

Antitumor effects of the mouse chemokine 6Ckine/SLC through angiostatic and immunological mechanisms

Mouse 6Ckine/SLC (secondary lymphoid tissue chemokine) is a chemotactic factor for dendritic cells, T cells, and NK cells in vitro. In addition, mouse 6Ckine/SLC interacts with the chemokine receptor CXCR3, as do several chemokines with antiangiogenic properties. These dual properties of mouse 6Ckine/SLC were tested for the induction of an antitumor response by transducing the C26 colon carcinoma tumor cell line with a cDNA encoding mouse 6Ckine/SLC. The C26-6CK-transduced cells showed reduced tumorigenicity in immunocompetent or in nude mice. Part of this effect was likely due to angiostatic mechanisms as shown by immunohistochemistry and Matrigel assay. C26-6CK tumors were also heavily infiltrated with leukocytes, including granulocytes, dendritic cells, and CD8+ T cells. In vivo, anti-CD8 treatment increased the tumorigenicity of the C26-6CK tumor cells, and tumor-infiltrating CD8+ T cells had the phenotype of memory effector cells, suggesting the induction of cytotoxic tumor-specific T lymphocytes. On the other hand, anti-asialo-GM1 depletion also increased the tumorigenicity of C26-6CK cells, supporting the participation of NK cells. Finally, tumor-infiltrating dendritic cells had the phenotype and functional features of immature dendritic cells. Overall, these results suggest that mouse 6Ckine/SLC has strong antitumor effects by inducing both angiostatic, CD8+ T cell-mediated, and possibly NK-mediated tumor resistance mechanisms.

Requirement of mature dendritic cells for efficient activation of influenza A-specific memory CD8+ T cells

It is critical to identify the developmental stage of dendritic cells (DCs) that is most efficient at inducing CD8+ T cell responses. Immature DCs can be generated from monocytes with GM-CSF and IL-4, while maturation is accomplished by the addition of stimuli such as monocyte-conditioned medium, CD40 ligand, and LPS. We evaluated the ability of human monocytes and immature and mature DCs to induce CD8+ effector responses to influenza virus Ags from resting memory cells. We studied replicating virus, nonreplicating virus, and the HLA-A*0201-restricted influenza matrix protein peptide. Sensitive and quantitative assays were used to measure influenza A-specific immune responses, including MHC class I tetramer binding assays, enzyme-linked immunospot assays for IFN-gamma production, and generation of cytotoxic T cells. Mature DCs were demonstrated to be superior to immature DC in eliciting IFN-gamma production from CD8+ effector cells. Furthermore, only mature DCs, not immature DCs, could expand and differentiate CTL precursors into cytotoxic effector cells over 7 days. An exception to this was immature DCs infected with live influenza virus, because of the virus's known maturation effect. Finally, mature DCs pulsed with matrix peptide induced CTLs from highly purified CD8+ T cells without requiring CD4+ T cell help. These differences between DC stages were independent of Ag concentrations or the number of immature DCs. In contrast to DCs, monocytes were markedly inferior or completely ineffective stimulators of T cell immunity. Our data with several qualitatively different assays of the memory CD8+ T cell response suggest that mature cells should be considered as immunotherapeutic adjuvants for Ag delivery.

Polyethylene glycol-modified GM-CSF expands CD11b(high)CD11c(high) but notCD11b(low)CD11c(high) murine dendritic cells in vivo: a comparative analysis with Flt3 ligand

Dendritic cells (DC) are potent APCs that can be characterized in the murine spleen as CD11b(high)CD11c(high) or CD11b(low)CD11c(high). Daily injection of mice of Flt3 ligand (FL) into mice transiently expands both subsets of DC in vivo, but the effect of administration of GM-CSF on the expansion of DC in vivo is not well defined. To gain further insight into the role of GM-CSF in DC development and function in vivo, we treated mice with polyethylene glycol-modified GM-CSF (pGM-CSF) which has an increased half-life in vivo. Administration of pGM-CSF to mice for 5 days led to a 5- to 10-fold expansion of CD11b(high)CD11c(high) but not CD11b(low)CD11c(high) DC. DC from pGM-CSF-treated mice captured and processed Ag more efficiently than DC from FL-treated mice. Although both FL- and pGM-CSF-generated CD11b(high)CD11c(high) DC were CD8alpha-, a greater proportion of these DC from pGM-CSF-treated mice were 33D1+ than from FL-treated mice. CD11b(low)CD11c(high) DC from FL-treated mice expressed high levels of intracellular MHC class II. DC from both pGM-CSF- and FL-treated mice expressed high levels of surface class II, low levels of the costimulatory molecules CD40, CD80, and CD86 and were equally efficient at stimulating allogeneic and Ag-specific T cell proliferation in vitro. The data demonstrate that treatment with pGM-CSF in vivo preferentially expands CD11b(high)CD11c(high) DC that share phenotypic and functional characteristics with FL-generated CD11b(high)CD11c(high) DC but can be distinguished from FL-generated DC on the basis of Ag capture and surface expression of 33D1.

Feeding dendritic cells with tumor antigens: self-service buffet or à la carte?

Adoptive transfer of autologous dendritic cells (DC) presenting tumor-associated antigens initiate and sustain an immune response which eradicate murine malignancies. Based on these observations, several clinical trials are in progress testing safety and efficacy with encouraging preliminary reports. In these approaches, ex vivo incubation of DC with a source of tumor antigens is required to load the relevant antigenic epitopes on the adequate antigen presenting molecules. Recent data show that in some instances exogenous DC artificially injected into malignant tissue or endogenous DC attracted to the tumor nodule by means of gene transfer of GM-CSF and CD40L into malignant cells result in efficacious antitumor immunity. In the case of intratumoral injection of DC the procedure is curative only if DC had been genetically engineered to produce IL-12, IL-6 or to express CD40L. Evidence has been obtained showing that intratumoral DC can capture and process tumor antigens to be presented to T-lymphocytes. Although the exact mechanisms of tumor antigen acquisition by DC are still unclear, available data suggest a role for heat shock proteins released from dying malignant cells and for the internalization of tumor-derived apoptotic bodies. Roles for tumor necrosis versus apoptosis are discussed in light of the 'danger theory'. Gene Therapy (2000) 7, 1167-1170.

Chemokines and dendritic cell traffic

Localization in tissues and migration to lymphoid organs are essential steps in the immunobiology of dendritic cells (DC). Chemokines play an important role in guiding the traffic of DC. Receptor expression and responsiveness to constitutively made chemokines account for the presence of DC in normal tissues. Inflammatory chemokines and nonchemokine attractants promote recruitment and localization of DC at sites of inflammation and infection. Upon exposure to maturation signals, DC undergo a chemokine receptor switch, with down-regulation of inflammatory chemokine receptors followed by induction of CCR7. These temporally coordinated events allow DC to leave tissues and to localize in lymphoid organs by responding to CCR7 agonists. DC are also present in tumors that produce chemokines, but their significance remains to be defined. In addition to responding to chemokines, DC are a major source of certain chemokines such as macrophage-derived chemokine. The interaction of DC with chemokines is essential to the function of these cells in normal and pathological conditions and may provide tools for novel therapeutic strategies.

Dendritic cells purified from myeloma are primed with tumor-specific antigen (idiotype) and activate CD4+ T cells

Multiple myelomas produce tumor-specific antigen (TSA) in the form of idiotype (Id) on monoclonal Ig. CD4(+) T cells can recognize Id-peptide on MHC class II molecules and protect against challenges with MOPC315 cells, which are, as common for myelomas, class II-negative. The present study explains these previous results by demonstrating that Id can be transferred from myeloma cells to antigen-presenting cells (APC), which present processed Id-peptide on their class II molecules to Id-specific T cell receptor-transgenic (TCR-TG) CD4(+) T cells. Id-primed tumor APC were heterogeneous, the majority being dendritic cells with class II(+), CD11b(+) CD11c(+) CD40(+) CD80(+) CD86(+) markers. The APC were localized beneath CD31(+) endothelial cells of tumor microvessels, and their frequency declined with tumor progression. The APC could stimulate Id-specific naive TCR-TG, short-term polarized TCR-TG, and cloned CD4(+) T cells to proliferate and produce cytokines in vitro. Furthermore, small MOPC315 tumors established in Id-specific TCR-TG mice contained clusters of activated (CD69(+)CD25(+)) and proliferating (BrdUrd(+)) Id-specific transgenic CD4(+) blasts. The activated Id-specific T cells were located adjacent to Id-primed dendritic cells in the tumor. Thus, a TSA can be transferred in vivo from myeloma, and possibly other types of cancer cells to APC for MHC class II presentation to CD4(+) T cells.

Local and systemic effects after adenoviral transfer of the murine granulocyte-macrophage colony-stimulating factor gene into mice

Vectors encoding immunostimulatory genes are under investigation for their use as adjuvants for immunotherapy. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a prominent candidate gene for this approach because this cytokine can prime immune responses to 'self' tumour or other weak antigens. Prior studies suggested that GM-CSF induces accumulation and differentiation of antigen-presenting cells, particularly dendritic cells that can initiate immunity. To evaluate this model in vivo, we performed i.m. and i.p. injections of an adenovirus vector encoding murine GM-CSF (Ad-mGM-CSF) and evaluated local and systemic effects. After intramuscular injection, local changes were characterized by the accumulation of myeloid cells, a subsequent infiltration of lymphocytes and then myonecrosis. Intraperitoneal injection also induced an accumulation of myeloid cells, an increase in CD3-positive T and a decrease in B220-positive B lymphocytes. Expression of the dendritic cell marker CD11c on 48 +/- 9% of the peritoneal cells (n = 6) along with high levels of surface MHC class II, a characteristic morphology, and endocytosis of FITC-dextran suggested in vivo differentiation of dendritic cells after i.p. injection of Ad-mGM-CSF. Systemic effects were observed after i.m. and i.p. injection of Ad-mGM-CSF. All mice developed hepatosplenomegaly resulting from extramedullary haematopoiesis. These changes were specific to GM-CSF as they were not seen in mice injected with an adenovirus vector without a transgene. Our observations indicate that adenoviral transfer of GM-CSF is a powerful tool for inducing local and systemic expansion of haematopoietic cells. The local expansion of myeloid cells displaying signs of dendritic cell differentiation, as characterized for the peritoneal cell compartment, can explain the potency of GM-CSF when used as an adjuvant in genetic immunotherapy.

Dendritic cells acquire the MAGE-3 human tumor antigen from apoptotic cells and induce a class I-restricted T cell response

In an attempt to transduce monocyte-derived dendritic cells (DCs) with a retroviral vector coding for an intracytoplasmic tumor antigen (TAA), we were confronted by the evident dissociation between the ability of the treated DCs to induce a TAA-specific response, and the presence of integrated vector proviral DNA. The TAA, i.e., MAGE-3, was acquired by DCs and presented to immune effectors, thanks to the property of DCs to uptake the apoptotic bodies released by the irradiated vector-producing cells. Indeed, we observed that upon irradiation vector-producing cells underwent apoptotic cell death, monitored by annexin V and propidium iodide staining, and were phagocytosed by DCs. Lymphocytes obtained from a patient affected by a MAGE-3(+) melanoma, were stimulated in vitro with autologous DCs previously exposed to irradiated MAGE-3-expressing cells. This procedure led to the induction of MAGE-3-specific cytotoxic effectors, directed against a yet unknown MAGE-3 epitope presented by HLA-A*B5201 molecules. These data demonstrate that DCs can present engulfed human TAAs, thus providing strategies for cancer vaccination.

The control of T cell responses by dendritic cell subsets

Dendritic cells are known as the most efficient antigen-presenting cell type to activate naïve T cells; however, they are able to do more than just efficiently present antigen to T cells. They are key modulators of the immune response that can influence Th cell differentiation by preferentially inducing Th type 1 or 2 cell responses, and the differential polarisation of CD4(+) T cells appears to be mediated by discrete dendritic cell subsets.