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

Semliki forest virus vectors engineered to express higher IL-12 levels induce efficient elimination of murine colon adenocarcinomas

To evaluate the use of alphavirus vectors for tumor treatment we have constructed and compared two Semliki Forest virus (SFV) vectors expressing different levels of IL-12. SFV-IL-12 expresses both IL-12 subunits from a single subgenomic promoter, while in SFV-enhIL-12 each IL-12 subunit is expressed from an independent subgenomic promoter fused to the SFV capsid translation enhancer. This latter strategy provided an eightfold increase of IL-12 expression. We chose the poorly immunogenic MC38 colon adenocarcinoma model to evaluate the therapeutic potential of SFV vectors. A single intratumoral injection of 10(8) viral particles of SFV-IL-12 or SFV-enh-IL-12 induced>or=80% complete tumor regressions with long-term tumor-free survival. However, lower doses of SFV-enhIL-12 were more efficient than SFV-IL-12 in inducing antitumoral responses, indicating a positive correlation between the IL-12 expression level and the therapeutic effect. Moreover, repeated intratumoral injections of suboptimal doses of SFV-enhIL-12 increased the antitumoral response. In all cases SFV vectors were more efficient at eliminating tumors than a first-generation adenovirus vector expressing IL-12. In addition, the antitumoral effect of SFV vectors was only moderately affected by preimmunization of animals with high doses of SFV vectors. This antitumoral effect was produced, at least partially, by a potent CTL-mediated immune response.

Concurrent delivery of GM-CSF and B7-1 using an oncolytic adenovirus elicits potent antitumor effect

Oncolytic adenoviral vectors are currently being developed as biologic anticancer agents. Coupling the lytic function of an oncolytic adenovirus (Ad) with its ability as a transgene delivery system represents a powerful extension of this methodology. A clear advantage is the amplification of a therapeutic gene, as replicating vectors would be able to infect and deliver the gene of interest to neighboring cells. Granulocyte-macrophage colony-stimulating factor (GM-CSF) is one of the most potent stimulators of a specific and long-lasting antitumor immunity and its important role in the maturation of antigen-presenting cells to induce T-cell activation has been well documented. Similarly, the B7 family has also been shown to play an integral role in mediating an antitumor response. Most tumor cells, however, lack the expression of these costimulatory molecules on their surface, thus escaping immune system recognition. To increase the antitumor effect of an oncolytic Ad, we have generated an E1B 55 kDa-deleted oncolytic adenoviral vector, YKL-GB, that expresses both GM-CSF and B7-1. The therapeutic efficacy of YKL-GB Ad was evaluated in immunocompetent mice bearing murine melanoma B16-F10 tumors. Significant inhibition of tumor growth was seen in mice treated with YKL-GB compared to those treated with the analogous vector, YKL-1. Moreover, YKL-GB oncolytic Ad demonstrated enhanced antitumor activity and higher incidences of tumor regression compared to a replication-incompetent Ad, dl-GB, which coexpresses GM-CSF and B7-1. Localized GM-CSF and B7-1 gene transfer also conferred long-lasting immunity against a tumor re-challenge. To establish that the observed antitumor effect is associated with the generation of a tumor-specific immune response, we carried out interferon-gamma enzyme-linked immune spot assay. We observed that YKL-GB induced significantly higher immune cell activation than YKL-1. Furthermore, immunohistochemical studies demonstrated robust dendritic cells and CD4(+)/CD8(+) T-cell infiltration in these mice compared to the YKL-1-treated groups. In agreement with these results, splenocytes from tumor-bearing mice treated with YKL-GB expressed high levels of the costimulatory and activation molecules. These findings demonstrate the effectiveness of enhancing the immune response against tumors with an oncolytic Ad expressing both GM-CSF and B7-1 and provide a potential therapeutic strategy for the management of neoplasia.

Combined prophylactic and therapeutic cancer vaccine: Enhancing CTL responses to HPV16 E2 using a chimeric VLP in HLA-A2 mice

We identified the strategies to induce a CTL response to human papillomavirus (HPV) 16 E2 in HLA-A2 transgenic mice (AAD). A chimeric HPV16 virus-like particle (VLP) that includes full length HPV16 E7 and E2 (VLP-E7E2) was generated. The combination of E2 and E7 has the advantage that E2 is expressed in early dysplasia and neoplasia lesions, where E7 is expressed in more advance lesions. Since T cell response to E2 is less defined, we first evaluated the strategies to enhancing CD8(+) T cell responses to HPV E7, using different combinations of immune-modulators with VLP-E7E2. Data showed that the CTL response to E7 could be significantly enhanced by coinjection of GM-CSF and anti-CD40 antibodies with chimeric VLP-E7E2 without adjuvant. However, using the same combination, a low level of CD8(+) T cell response to E2 was detected. To enhance the CD8+ T cell response to E2, we analyzed T cell epitopes from E2 sequence. A heterogenous prime-boost with chimeric VLP-E7E2 and E2 peptides was performed. The data showed that the priming with chimeric VLP-E7E2, followed by boosting with E2 peptides, gave a better CTL response than 2 immunizations with E2 peptides. The enhanced immunity is due to the increase of CD11c(+) and CD11c(+) CD40(+) double positive dendritic cells in mice that received immune-modulators, GM-CSF and anti-CD40. Furthermore, the level of anti-L1 antibodies remains similar in mice immunized with chimeric VLP with/without immune-modulators. Thus, the data suggested that the chimeric VLP-E7E2 has a therapeutic potential for the treatment of HPV-associated CINs and cancer without diminishing VLPs potential as a prophylactic vaccine by inducing anti-L1 antibodies against free virus.

Tumor-Infiltrating Dendritic Cells Are Potent Antigen-Presenting Cells Able to Activate T Cells and Mediate Tumor Rejection

Dendritic cells (DC) are potent inducers of immune responses. DC have been shown to infiltrate tumors, but very little is known about the functional status of these naturally occurring tumor-infiltrating DC (TIDC). In this study, the status and function of TIDC from several types of mouse melanoma were investigated in detail. CD11c+/MHC II+ cells, consistent with a DC phenotype, were found in all of transplantable or spontaneous melanomas studied. These TIDC were predominantly myeloid (CD11c+/CD8alpha-/B220-) in nature with small numbers of plasmacytoid (CD11c+/B220+). TIDC had an intermediate maturation phenotype with some expression of costimulatory molecules and the capacity to take up particles. Upon culture overnight ex vivo, the TIDC markedly up-regulated the expression of costimulatory molecules and also increased IL-12 production. Importantly, such ex vivo-matured TIDC pulsed with OVA were able to migrate to lymph nodes, to activate naive OVA-specific CD4+ and CD8+ T cells, and to confer protection against a challenge with OVA-expressing tumor cells. In conclusion, melanomas are infiltrated by functional DC that can act as fully competent APC. These APC have the potential to be manipulated and may therefore represent a promising target for cancer immunotherapy.

Distinct and overlapping roles of interleukin-10 and CD25+ regulatory T cells in the inhibition of antitumor CD8 T-cell responses

Lack of antitumor immunity is often related to impaired CD8 T-cell responses that could result from a poor priming capacity by tumor-infiltrating dendritic cells (TIDC) and/or further inhibition by regulatory T cells (T(reg)). Interleukin-10 (IL-10) has been implicated in the inhibition of TIDC as well as in the generation and functions of T(reg). Here, we address some of the respective and possibly overlapping roles of IL-10 and CD25+ T(reg) in CD8 antitumor immunity. Whereas tumor antigen-specific CD8 T cells proliferated in vivo in the presence of IL-10 or T(reg), optimal effector functions were observed in mice lacking both IL-10 and T(reg). Indeed, tumors grown in normal but not in IL-10-deficient or CD25-depleted mice induced tumor antigen-specific CD8 suppressor T cells. Suppression involved transforming growth factor-beta. Similarly, both IL-10 and T(reg) were responsible for impaired CD8 T cell priming by TIDCs, but IL-12 production by TIDCs was prevented only by T(reg)-independent IL-10. Subsequently, IL-10 defect and T(reg) depletion were required to achieve optimal induction of CD8 T-cell effectors by TIDC following CpG activation. Our results point out major redundant and nonredundant roles for IL-10 and T(reg) in the inhibition of TIDC-mediated generation of antitumor CD8 T-cell response.

IL-4-transfected tumor cell vaccines activate tumor-infiltrating dendritic cells and promote type-1 immunity

We previously demonstrated that IL-4 gene-transfected glioma cell vaccines induce effective therapeutic immunity in preclinical glioma models, and have initiated phase I trials of these vaccines in patients with malignant gliomas. To gain additional mechanistic insight into the efficacy of this approach, we have treated mice bearing the MCA205 (H-2(b)) or CMS-4 (H-2(d)) sarcomas. IL-12/23 p40(-/-) and IFN-gamma(-/-) mice, which were able to reject the initial inoculation of IL-4 expressing tumors, failed to mount a sustained systemic response against parental (nontransfected) tumor cells. Paracrine production of IL-4 in vaccine sites promoted the accumulation and maturation of IL-12p70-secreting tumor-infiltrating dendritic cells (TIDCs). Adoptive transfer of TIDCs isolated from vaccinated wild-type, but not IL-12/23 p40(-/-), mice were capable of promoting tumor-specific CTL responses in syngeneic recipient animals. Interestingly, both STAT4(-/-) and STAT6(-/-) mice failed to reject IL-4-transfected tumors in concert with the reduced capacity of TIDCs to produce IL-12p70 and to promote specific antitumor CTL reactivity. These results suggest that vaccines consisting of tumor cells engineered to produce the type 2 cytokine, IL-4, critically depend on type 1 immunity for their observed therapeutic efficacy.

Redirecting in vivo elicited tumor infiltrating macrophages and dendritic cells towards tumor rejection

A hostile tumor microenvironment interferes with the development and function of the adaptive immune response. Here we report the mechanisms by which large numbers of tumor-infiltrating macrophages and dendritic cells (DC) can be redirected to become potent effectors and activators of the innate and adaptive immunity, respectively. We use adenoviral delivery of the CCL16 chemokine to promote accumulation of macrophages and DC at the site of preestablished tumor nodules, combined with the Toll-like receptor 9 ligand CpG and with anti-interleukin-10 receptor antibody. CpG plus anti-interleukin-10 receptor antibody promptly switched infiltrating macrophages infiltrate from M2 to M1 and triggered innate response debulking large tumors within 16 hours. Tumor-infiltrating DC matured and migrated in parallel with the onset of the innate response, allowing the triggering of adaptive immunity before the diffuse hemorrhagic necrosis halted the communication between tumor and draining lymph nodes. Treatment of B6>CXB6 chimeras implanted with BALB/c tumors with the above combination induced an efficient innate response but not CTL-mediated tumor lysis. In these mice, tumor rejection did not exceed 25%, similarly to that observed in CCR7-null mice that have DC unable to prime an adaptive response. The requirement of CD4 help was shown in CD40-KO, as well as in mice depleted of CD4 T cells, during the priming rather than the effector phase. Our data describe the critical requirements for the immunologic rejection of large tumors: a hemorrhagic necrosis initiated by activated M1 macrophages and a concomitant DC migration to draining lymph nodes for subsequent CTL priming and clearing of any tumor remnants.

Tumor-infiltrating dendritic cell subsets of progressive or regressive tumors induce suppressive or protective immune responses

Tumor-infiltrating dendritic cells (TID) have an ambivalent role in regulation of tumor regression or growth. However, their precise natures and molecular mechanisms have not been elucidated. In this study, we studied TIDs recruited in progressive P815 and regressive P198 tumors of the same origin. Our data showed that P815 tumors contained CD4+ 8+ and CD4- 8- TID815 subsets, whereas P198 tumors contained CD4+ 8+ and CD4+ 8- TID198 subsets. They similarly stimulate allogeneic T cell proliferation and have nitric oxide-mediated cytotoxicity to tumor cells with an exception of CD4- 8- TID815 with less efficiency. The newly identified fourth CD4+ 8+ TID815 or TID198 subset and the CD4+ 8- TID198 all express high levels of IFN-gamma and interleukin (IL)-6, whereas CD4- 8- TID815 secrete a marked level of transforming growth factor-beta. Vaccination of mice with P815 tumor lysate-pulsed CD4+ 8+ TID815 or TID198 and CD4+ 8- TID198 induced IFN-gamma-secreting Th1 and effective CTL responses leading to protective immunity against P815 tumor, whereas CD4- 8- TID815 stimulated IL-10-expressing Tr1 responses leading to immune suppression. Transfer of CD4+ Tr1 cells obtained from CD4- 8- TID815-immunized wild-type, but not IL-10(-/-) mice, into CD4+ 8+ TID815 immunized mice abolished otherwise inevitable development of antitumor immunity. Taken together, our findings provide an important insight into immunologic alterations in progressive and regressive tumors and an implication for dendritic cell-based approaches in the design of cancer vaccines.

A GM-CSF/CD40L Producing Cell Augments Anti-tumor T Cell Responses

BACKGROUND

Tumors evade T cell-mediated rejection despite the presence of tumor associated antigens (TAAs) and T cells specific for these TAAs in cancer patients. Therapeutic tumor vaccines are being developed to prevent this evasion. Previous reports revealed that anti-tumor T cell responses could be activated in mice when granulocyte macrophage-colony stimulating factor (GM-CSF) or CD40L are produced at tumor vaccine sites. We sought to test the hypothesis that production of GM-CSF and CD40L by a bystander cell line could induce an anti-tumor T cell response in an in vitro human model.

MATERIALS AND METHODS

The K562 cell line was stably transfected with the human GM-CSF and CD40L genes. The effect of this cell line on T cell responses was tested in a human autologous mixed tumor cell/lymph node cell model using tissue from a series of cancer patients.

RESULTS

There was no significant anti-tumor T cell response when human lymphocytes derived from tumor-draining lymph nodes were stimulated with autologous tumor cells in vitro. However, significant anti-tumor T cell responses were observed when bystander cells transfected with CD40L and GM-CSF were added to the cultures.

CONCLUSIONS

A fully autologous human model consisting of tumor cells as stimulator cells and tumor-draining lymph nodes as responder cells can be used to test immunotherapeutic strategies. T cells in these lymph nodes are unresponsive to autologous tumor cells, but this lack of responsiveness can be reversed in the presence of GM-CSF and CD40L. These data provide a rationale for testing tumor cell vaccines incorporating GM-CSF- and CD40L-expressing bystanders in clinical trials.

Homing phenotypes of tumor-specific CD8 T cells are predetermined at the tumor site by crosspresenting APCs

Expression of tissue-specific homing molecules directs antigen-experienced T cells to particular peripheral tissues. In studies using soluble antigens that focused on skin and gut, antigen-presenting cells (APCs) within regional lymphoid tissues were proposed to be responsible for imprinting homing phenotypes. Whether this occurs in other sites and after physiologic antigen processing and presentation is unknown. We define in vivo imprinting of distinct homing phenotypes on monospecific T cells responding to antigens expressed by tumors in intracerebral, subcutaneous, and intraperitoneal sites with efficient brain-tropism of CD8 T cells crossprimed in the cervical lymph nodes (LNs). Multiple imprinting programs could occur simultaneously in the same LN when tumors were present in more than one site. Thus, the identity of the LN is not paramount in determining the homing phenotype; this critical functional parameter is dictated upstream at the site of antigen capture by crosspresenting APCs.

Primary Antitumor Immune Response Mediated by CD4+ T Cells

Gene-targeted mice have recently revealed a role for lymphocytes and interferon-gamma (IFNgamma) in conferring protection against cancer, but the mechanisms remain unclear. Here, we have characterized a successful primary antitumor immune response initiated by naive CD4+ T cells. Major histocompatibility complex class II (MHC-II)-negative myeloma cells injected subcutaneously into syngeneic mice were surrounded within 3 days by macrophages that captured tumor antigens. Within 6 days, naive myeloma-specific CD4+ T cells became activated in draining lymph nodes and subsequently migrated to the incipient tumor site. Upon recognition of tumor-derived antigenic peptides presented on MHC-II by macrophages, the myeloma-specific CD4+ T cells were reactivated and started to secrete cytokines. T cell-derived IFNgamma activated macrophages in close proximity to the tumor cells. Tumor cell growth was completely inhibited by such locally activated macrophages. These data indicate a mechanism for immunosurveillance of MHC-II-negative cancer cells by tumor-specific CD4+ T cells through collaboration with macrophages.

Intratumoral immunotherapy: using the tumour against itself

Summary Diverse immunotherapy approaches have achieved success in controlling individual aspects of immune responses in animal models. Transfer of such immunotherapies to clinical trials has obtained some success in patients, with clinical responses observed or effective antigen specific immune responses achieved, but has had limited impact on patient survival. Key elements required to generate de novo cell-mediated antitumour immune responses in vivo include recruitment of antigen-presenting cells to the tumour site, loading these cells with antigen, and their migration and maturation to full antigen-presenting function. In addition, it is essential for antigen-specific T cells to locate the tumour to mediate cytotoxicity, emphasizing the need for local inflammation to target effector cell recruitment. We review those therapies that involve the tumour site as a target and source of antigen for the initiation of immune responses, and discuss strategies to generate and co-ordinate an optimal cell-mediated immune response to control tumours locally.

Both soluble and membrane-bound forms of Flt3 ligand enhance tumor immunity following "suicide" gene therapy in a murine colon carcinoma model

In prodrug-activated ("suicide") gene therapy, tumor cells are transfected with the gene for an enzyme that converts an inactive prodrug, such as ganciclovir (GCV), to a toxic compound. Transfected cells are killed on administration of GCV, as also are untransfected "bystander" cells. The ability of the dendritic cell stimulatory cytokine Flt3 ligand (Flt3-L) to modulate prodrug-activated gene therapy has been investigated. Transfectants of the murine colon carcinoma MC26 were generated expressing soluble (FLS) and membrane-bound forms of Flt3-L. They were inoculated together with wild-type MC26 cells and cells expressing herpes simplex virus-1 (HSV1) thymidine kinase into BALB/c mice, which were then administered GCV. Expression of Flt3-L or FLS prevented regrowth of tumor in most mice, which was comparable to the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF), while tumors recurred in all mice receiving "suicide" gene therapy alone. Recurring tumor cells were resistant to direct killing by GCV but sensitive to "bystander" killing in vitro. Mice without tumor recurrence were rechallenged with unmodified MC26 cells. Of those mice given transfectants expressing GM-CSF, Flt3-L, or FLS, approximately 50% were immune to rechallenge. These mice also showed cytotoxic and proliferative responses to MC26 cells. These experiments show that both soluble and membrane-bound forms of Flt3-L were able to induce a protective immune response to colon carcinoma cells in a fashion similar to GM-CSF.

Tumor-infiltrating dendritic cell precursors recruited by a beta-defensin contribute to vasculogenesis under the influence of Vegf-A

The involvement of immune mechanisms in tumor angiogenesis is unclear. Here we describe a new mechanism of tumor vasculogenesis mediated by dendritic cell (DC) precursors through the cooperation of beta-defensins and vascular endothelial growth factor-A (Vegf-A). Expression of mouse beta-defensin-29 recruited DC precursors to tumors and enhanced tumor vascularization and growth in the presence of increased Vegf-A expression. A new leukocyte population expressing DC and endothelial markers was uncovered in mouse and human ovarian carcinomas coexpressing Vegf-A and beta-defensins. Tumor-infiltrating DCs migrated to tumor vessels and independently assembled neovasculature in vivo. Bone marrow-derived DCs underwent endothelial-like differentiation ex vivo, migrated to blood vessels and promoted the growth of tumors expressing high levels of Vegf-A. We show that beta-defensins and Vegf-A cooperate to promote tumor vasculogenesis by carrying out distinct tasks: beta-defensins chemoattract DC precursors through CCR6, whereas Vegf-A primarily induces their endothelial-like specialization and migration to vessels, which is mediated by Vegf receptor-2.

Pilot study of treatment of biochemotherapy-refractory stage IV melanoma patients with autologous dendritic cells pulsed with a heterologous melanoma cell line lysate

Eleven AJCC stage IV melanoma patients with progressive disease after treatment with biochemotherapy were treated with autologous dendritic cells pulsed with heterologous tumor cell lysates. The vaccine used mature DCs (CD1a+++, CD40++, CD80++, CD83+, and CD86+++) generated from peripheral blood monocytes in the presence of GM-CSF and IL-4. After 7 days, DCs were matured with a defined cocktail of cytokines (IL-1+IL-6+TNF-alpha+PGE2) and simultaneously pulsed with lysates of heterologous melanoma cell lines, for 2 days. A total of 4 x 10(6) DCs was injected monthly under ultrasound control in an inguinal lymph node of normal appearance. The study was closed when all patients died as a consequence of tumor progression. No sign of toxicity was observed during the study. One patient experienced a partial response lasting 5 months, and two patients showed a mixed response which lasted 3 months. The median survival of the whole group was 7.3 months (range 3-14 months). This vaccination program had specific antitumoral activity in highly pretreated and large tumor burden stage IV melanoma patients and was well tolerated. The clinical responses and the median survival of the group of patients, together with the low toxicity of our DC vaccine, suggest that this approach could be applied to earlier AJCC stage IV melanoma patients.

Regulation of the trafficking of tumour-infiltrating dendritic cells by chemokines

To anticipate and initiate immune responses, dendritic cells follow a migratory route from their recruitment as sentinels into tissues, including solid tumors, then to secondary lymphoid organs where they profile the immune response. Migratory capacities--and especially chemokine responsiveness--are therefore key elements in dendritic cell biology. Here, we will review our current knowledge about tumour-infiltrating dendritic cells and the chemokine-driven migration flows in and out from tumors. Then we will discuss the consequences of the interactions between dendritic cells and tumors and the perspectives for translating our experimental knowledge of manipulating dendritic cell migratory flows into anti-cancer therapies.

Tolerance and cancer: mechanisms of tumor evasion and strategies for breaking tolerance

The development of malignant disease might be seen as a failure of immune surveillance. However, not all tumors are naturally immunogenic, and even among those that are immunogenic, the uncontrolled rapid growth of a tumor may sometimes out-run a robust immune response. Nevertheless, recent evidence suggests that mechanisms of tolerance that normally exist to prevent autoimmune disease may also preclude the development of an adequate antitumor response and that tumors themselves have the ability to thwart the development of effective immune responses against their antigens. A major challenge has been to develop approaches to breaking this tolerance in tumor-bearing hosts, and recent advances in our understanding of antigen presentation and tolerance have led to some promising strategies. An alternative approach is to use T cells from nontumor-bearing, allogeneic hosts in the form of lymphocyte infusions, with or without hematopoietic cell transplantation. Immunotherapy may occur in this setting via the response of nontolerant, tumor antigen-specific T cells from nontumor-bearing hosts or via the powerful destructive effect of an alloresponse directed against antigens shared by malignant cells in the recipient. Approaches to exploiting this beneficial effect without the deleterious consequence of graft-versus-host disease in allogeneic hematopoietic cell recipients are discussed.

Intralesional Injection of Adenovirus Encoding CC Chemokine Ligand 16 Inhibits Mammary Tumor Growth and Prevents Metastatic-Induced Death after Surgical Removal of the Treated Primary Tumor

The CC chemokine ligand (CCL)16 exerts chemotactic activity on human monocytes and lymphocytes. Although no murine homologous has been defined, the TSA mouse adenocarcinoma cells engineered to express human CCL16 are rapidly rejected by syngenic mice. An adenovirus encoding CCL16 (AdCCL16) was generated using a Cre-Lox-based system and was used to determine whether this chemokine might also block pre-existing tumors. Both recombinant and viral CCL16 showed in vitro chemotactic activity for murine CD4(+) and CD8(+) lymphocytes and dendritic cells (DC). AdCCL16, but not the control empty vector, when injected in established nodules significantly delayed tumor growth. Immunohistochemistry revealed accumulation of CD4(+) and CD8(+) T cells and DC in the treated tumors as well as in draining lymph nodes. DC from such lymph nodes stimulated IFN-gamma by a T cell clone specific for the known TSA tumor-associated Ag (TAA), suggesting the tumor origin of these cells. Lymphocytes from the same nodes showed specific CTL activity against TSA tumor cells and their immunodominant TAA peptide. Antitumor activity required CD4, CD8, and IFN-gamma production, as shown using subset-depleted and knockout mice. Despite the robust and rapid immune response triggered by intratumoral injection of AdCCL16, the lesions were not completely rejected; however, the same treatment given before surgical excision of primary lesions prevented metastatic spread and cured 63% of mice bearing the 4T1 mammary adenocarcinoma, which is perhaps the most compelling model of spontaneous metastasis.

Enhanced Efficacy of Tumor Cell Vaccines Transfected with Secretable hsp70

Tumor immunotherapy has exploited the ability of heat shock proteins to chaperone precursors of antigenic peptides to antigen-presenting cells and to activate efficiently an immune response against tumor-associated antigens. The most common strategy is based on the purification of heat shock protein-peptide complexes from tumor cell lines or from tumor surgical samples for in vivo administration. In this article, we have modified the murine-inducible hsp70 into a secreted protein and engineered tumor cells to secrete constitutively their antigenic repertoire associated with the hsp70 protein. In vitro studies showed that the relocalization of hsp70 from the cytoplasm to the secretory pathway did not modify the ability of hsp70 to interact with peptides derived either from natural tumor-associated antigens or model antigens, and that antigen-presenting cells specifically took up the secreted hsp70 and presented the chaperoned epitopes to T cells. In vivo studies showed that tumors secreting hsp70 displayed increased immunogenicity, with induction of a strong and specific CTL response. Mice injected with hsp70-secreting tumors showed increased survival and impaired tumor take compared with mice bearing parental tumors. More than 70% of mice rejected tumor cells secreting hsp70 through mechanisms that involve T lymphocytes and natural killer cells, with the induction of a memory response in the case of T lymphocytes. Moreover, hsp70 secretion increased the immunogenic potential of tumor cell vaccines.

Concurrent delivery of tumor antigens and activation signals to dendritic cells by irradiated CD40 ligand-transfected tumor cells resulted in efficient activation of specific CD8+ T cells

To improve the efficacy of tumor cell-based and dendritic cell (DC)-based cancer vaccines, this study explored the potential of a new cancer vaccine strategy, that is, the use of CD40 ligand-transfected tumor (CD40L-tumor) cells to simultaneously deliver both tumor-derived antigens (Ag) and maturation stimuli to DCs. Materials from frozen/thawed or irradiated human tumor cells, with or without surface CD40L, were internalized efficiently by immature DCs after coincubation. However, during the internalization process, only coculturing with irradiated CD40L-tumor cells resulted in concurrent, optimal DC maturation and production of proinflammatory chemokines and pro-Th1 cytokines, such as IL-6, IL-8, IL-12, IFN-gamma, and TNF-alpha. These activated DCs were the most potent cells to support the growth of CD8+, IFN-gamma-producing T cells, and to process tumor Ag for the generation of specific cytotoxic T cells in vitro. Animals vaccinated with irradiated CD40L-tumor cell-pulsed DCs were better protected against subsequent challenge of a weakly immunogenic tumor cell line than animals vaccinated with irradiated CD40L-tumor cells alone. Thus, our results strongly support the future clinical application of using DCs pulsed with irradiated CD40L-tumor cells as a cancer vaccine.

Role of immature myeloid Gr-1+ cells in the development of antitumor immunity

One of the mechanisms by which tumor cells evade the immune system is the lack of proper antigen-presenting cells. Improvement in host immunity against tumor cells can be achieved by promoting the differentiation of dendritic cells (DCs) from immature myeloid cells (Gr-1(+)Ly-6C(+)F4/80(+)) that accumulate in the bone marrow and lymphoid organs of mice with large tumor burdens. The enriched immature myeloid cells inhibit T-cell proliferation and tumor-specific T-cell response, which can be reversed by the differentiation of immature myeloid cells or depletion of F4/80(+) cells. Sorted Gr-1(+)/F4/80(+) immature myeloid cells differentiated into CD11c(+) cells that express CD80 and I-A/I-E (MHC class II) in the presence of recombinant murine granulocyte macrophage colony-stimulating factor (GM-CSF). Furthermore, intratumoral gene delivery of GM-CSF not only promoted the differentiation of carboxyfluoroscein succinimidyl ester-labeled immature myeloid cells into CD11c(+) cells with the characteristics of mature DCs (CD80(+), I-A/I-E(+)) but also enhanced innate natural killer and adaptive cytolytic T-cell activities in mice treated with interleukin (IL)-12 and anti-4-1BB combination therapy. More importantly, intratumoral delivery of GM-CSF and IL-12 genes in combination with 4-1BB costimulation greatly improved the long-term survival rate of mice bearing large tumors and eradicated the untreated existing hepatic tumor. The results suggest that inducing the maturation of immature myeloid cells, thus preventing their inhibitory activity and enhancing their antigen-presenting capability, by GM-CSF gene therapy is a critically important step in the development of effective antitumor responses in hosts with advanced tumors.

In situ recruitment of antigen-presenting cells by intratumoral GM-CSF gene delivery

Proper antigen presentation is paramount to the induction of effective and persistent antitumor immune responses. In a murine model of hepatic metastasis of colon cancer, we found that the numbers of in situ mature dendritic cells (DCs) and macrophages in tumor-infiltrating leukocytes (TILs) were significantly increased in mice treated with the combination therapy of herpes simplex virus thymidine kinase, interleukin 2, and GM-CSF genes when compared with control groups without GM-CSF treatment. Significantly higher levels of IFN-gamma, MIP-1 alpha, mIL-12, and GM-CSF were detected in the tumor after the combination therapy. T cells isolated from the combination therapy-treated mice exhibited higher ex vivo direct CTL activity than those from other treatment groups. Antigen-presenting cells (APCs) enriched from the TILs and liver of the combination therapy-treated mice induced higher levels of proliferation by the splenocytes from long-term surviving mice that had been cured of tumors at early time points (days 4 and 7) whereas significant APC activity was only observed in the spleen at the latter time point (day 7, 14) after the combination therapy. In contrast, APCs isolated from tk or tk + IL-2-treated mice did not induce any significant proliferation. Subcutaneous injection of fluorescence-labeled latex microspheres followed by the combination therapy showed a similar sequential trafficking of microspheres, day 4 after the combination therapy to tumor and day 14 to spleen. The results suggest that APCs recruited by intratumoral gene delivery of GM-CSF can capture antigens, mature to a stage suitable for antigen presentation, and subsequently migrate to the spleen where they can efficiently stimulate antigen-specific T cells.

Immunotherapeutic Approaches for Hematologic Malignancies

The immune system has two complementary arms: one is older and seemingly more primitive, called the innate immune system, found in both plants and animals. The second (already many millions of years old!) is the adaptive or antigen-specific immune system, limited to vertebrate animals. The human innate immune system has many cellular elements that include granulocytes, monocytes, macrophages, natural killer (NK) cells, mast cells, eosinophils, and basophils. Receptors for these cells are non-clonal, fixed in the genome, requiring no rearrangement, and recognize conserved molecular patterns that are specific to pathogens. The adaptive immune system (B cells and T cells) have receptors with great variation, able to recognize an almost an unlimited number of highly specific pathogens through rearrangement of receptor gene segments, and can also provide immunological memory so critical for vaccination. As the immune system has evolved to recognize non-self, malignant transformation of self can likely escape immune surveillance with relative ease. Contributors to this chapter are utilizing distinct components of either the innate or adaptive immune system that recognize non-self, in combination with what we know about differences between malignant and normal self, in an effort to develop novel and effective immunologic approaches against hematologic malignancies.

In Section I, Dr. Andrea Velardi reviews the benefits of NK cell alloreactivity in mismatched hematopoietic transplantation, provides updates on current clinical trials, and discusses further therapeutic perspectives emerging from murine bone marrow transplant models.

In Section II, Dr. David Scheinberg reviews novel leukemic antigens being targeted by humanized monoclonal antibodies as well as mechanisms by which antibody-mediated cytotoxicity occurs in vivo.

In Section III, Dr. Ivan Borrello reviews vaccine and adoptive T cell immunotherapy in the treatment of hematologic malignancies. Specifically, he discusses the various vaccine approaches used as well as strategies aimed at augmenting the tumor specificity of T cell therapies.

Granulocyte-Macrophage Colony-Stimulating Factor-Based Melanoma Cell Vaccines Immunize Syngeneic and Allogeneic Recipients via Host Dendritic Cells

Subcutaneous injection of GM-CSF-expressing cancer cells into experimental animals results in protective cancer immunity. To delineate the mode of action of such vaccines, we used trinitrophenyl, the antigenic moiety of the contact allergen trinitrochlorobenzene, as surrogate Ag. Trinitrophenyl-derivatized bone marrow-derived dendritic cells were found to elicit a contact hypersensitivity response in syngeneic, but not in allogeneic recipients, compatible with their expected mode of direct Ag presentation. When expressing GM-CSF, haptenized M3 melanoma cells were also able to induce a contact hypersensitivity response but, in contrast to bone marrow-derived dendritic cells, not only in syngeneic but also in allogeneic recipients. This argues for a critical role of host APC. To identify their nature, we introduced the beta-galactosidase (betagal) gene into M3-GM cells. Their administration activated betagal-specific, L(d)-restricted CTL in syngeneic BALB/c mice. Evaluation of lymph nodes draining M3-GM-betagal injection sites revealed the presence of cells presenting the respective L(d)-binding betagal peptide epitope. Based on their capacity to activate betagal-specific CTL, they were identified as being CD11c(+) dendritic cells. These experiments provide a rational basis for the use of GM-CSF-based melanoma cell vaccines in an allogeneic setting.

Myeloid cell expansion elicited by the progression of spontaneous mammary carcinomas in c-erbB-2 transgenic BALB/c mice suppresses immune reactivity

Transgenic female mice expressing the transforming rat oncogene c-erbB-2 (HER-2/neu) under the mouse mammary tumor virus (MMTV) promoter (BALB-neuT) spontaneously develop mammary carcinomas with a progression resembling that of human breast cancer. In these mice, activating antitumor immunotherapy fails to induce T cell-mediated cytotoxicity, suggesting a suppression of the immune response. We found a direct correlation between tumor multiplicity and an increased proportion of Gr-1+ (Ly6G)/Mac-1+(CD11b)/ER-MP12+(CD31) immature myeloid cells in the peripheral blood (PB) and spleen, suggesting that tumor load profoundly affects overall BALB-neuT hematopoiesis. In fact, myeloid colony formation was increased in bone marrow (BM) and spleen. The immature myeloid cells displayed suppressive activity on host T lymphocytes, which progressively failed to respond to alloantigens and CD3 triggering, while maintaining the ability to proliferate in response to nonspecific mitogens. Transplantation of normal BM into BALB-neuT mice readily resulted in hypertrophic hematopoiesis with myeloid cell expansion. This persistent influence of the tumor was mediated through the release of vascular endothelial growth factor (VEGF) but not granulocyte-macrophage colony-stimulating factor (GM-CSF), and was down-modulated when tumor load was reduced but not when BM was transplanted. Together, the data obtained in the BALB-neuT model of naturally occurring carcinogenesis show that tumor-associated immune suppression is secondary to a more general alteration of host hematopoiesis, conditioned by tumor-secreted soluble factors.

A controlled trial of granulocyte macrophage-colony stimulating factor during interruption of HAART

OBJECTIVES

To explore the effect of granulocyte macrophage colony stimulating factor (GM-CSF) on viral load and CD4 cell count during interruption of highly active antiretroviral therapy (HAART).

METHODS

Patients on effective HAART (CD4 cell count > 400 x 10(6)/l; viral load < 50 HIV RNA copies/ml) were randomized to one of two groups: 12 weeks' treatment interruption plus, during the first 4 weeks, 300 microg GM-CSF (Leucomax-Novartis) by subcutaneous injection three times weekly (GM-CSF group); 12 weeks' scheduled treatment interruption (STI-only group). Viral load, CD4 cell count, clinical events and side effects of treatment were monitored.

RESULTS

Thirty-three patients, 15 in the GM-CSF group and 18 in the STI-only group, were evaluated according to the intention-to-treat principle. The two groups were well matched with regard to pre-HAART viral loads and CD4 cell counts. During STI, viraemia was approximately two to three times lower in the group receiving GM-CSF (max 4.97 versus 5.45 in STI-only group; P = 0.03). Fifteen out of 17 patients in the STI-only group showed a decrease in their CD4 cell count between weeks 0 and 4 (median decrease 231 x 10(6) cells/l; P < 0.001); there was no such tendency in the GM-CSF group (P = non-significant when comparing CD4 cell counts at weeks 0 and 4). The median CD4 cell AUC (area under the curve) from week 0 to week 12 was higher in the GM-CSF group (9166 cells.week) than in patients without GM-CSF (7257), P = 0.02. GM-CSF produced local reactions in 88% of patients, and generalized symptoms such as fever, back pain or headache in 82% of patients. Seventy-six percent of patients completed the planned course of 12 injections.

CONCLUSIONS

The administration of GM-CSF blunted the viral rebound following interruption of HAART, and largely prevented a decrease of CD4 cell counts during a 12-weeks-treatment interruption. A better understanding of the underlying mechanism(s) may help to identify synergistic treatment targets and improved administration protocols to enhance control of chronic HIV infection.

Enhanced tumour growth after DNA vaccination against human papilloma virus E7 oncoprotein: evidence for tumour-induced immune deviation

We have examined the induction of anti-tumour immunity in a murine model using a gene vaccine approach to deliver a well defined tumour antigen. The vaccines expressed the human papilloma virus type 16 (HPV 16) E7 oncoprotein, and protection was measured against HPV 16-expressing C3R tumour cell line in vivo. In control mice injected with saline, C3R cells initially formed tumours but then regressed completely. As expected, animals injected with a peptide that represents the D(b)-presented CTL epitope from E7 (RAHYNIVTF) were completely protected from tumour growth. Contrary to expectation, however, we consistently saw enhanced tumour growth, delayed regression, or tumour outgrowth in mice vaccinated with two different E7-expressing DNA vaccines. We found no evidence for loss of D(b) or K(b) class I MHC molecules from C3R cells recovered from outgrown tumours, and fluorescent MHC/peptide tetramer staining revealed E7 gene vaccination did not delete RAHYNIVTF-specific CD8(+) T cells. However, we did observe an effect on cytokine production. Splenocytes from E7 gene vaccinated animals responded to re-stimulation in vitro with C3R cells by producing IL-4 but background levels of IFN-gamma. We also observed that cytokine production and E7 peptide-specific CTL were only detectable in vaccinated animals after C3R challenge, but not after DNA priming alone. We conclude that 'prime-boosting' is necessary to observe tumour-specific T cell responses with the gene vaccine approach, but that boosting with tumour cells causes skewing of the primed cells in a T2 direction that is incompatible with protective anti-tumour immunity.

Potential involvement of monocyte chemoattractant protein (MCP)-1/CCL2 in IL-4-mediated tumor immunity through inducing dendritic cell migration into the draining lymph nodes

We previously observed that IL-4 gene transduction into a mouse colon 26 adenocarcinoma cell line abrogated its tumorigenicity due to the generation of anti-tumor CTL. DEC-205- and CD11c-double positive cells were increased in the lymph nodes of mice injected with IL-4-transfected cells between 2 and 3 days after the tumor injection, compared with those injected with parental cells. Most of these double positive cells expressed CD86 antigen. Among the chemokines with chemotactic activities against dendritic cells, monocyte chemoattractant protein (MCP)-1/CCL2, ABCD-1/CCL22, and liver and activation-regulated chemokine (LARC)/CCL20 gene expression was enhanced no later than 3 days after the tumor injection, in the draining lymph nodes of IL-4-transfected cell bearing mice. Moreover, gene expression of the receptor for MCP-1/CCL2, CCR2, was enhanced in the draining lymph nodes of the mice injected with IL-4-transfected cells, and most DEC-205-positive cells in the lymph nodes expressed CCR2. Finally, the administration of anti-MCP-1/CCL2 antibodies retarded the rate of tumor regression in mice injected with IL-4-tranfected cells, concomitantly with a decrease in DEC-205- and CD11c-double positive cell number in the draining lymph nodes. Thus, locally produced MCP-1/CCL2 may be responsible for IL-4-mediated tumor rejection presumably based on the induction of dendritic cell migration into the draining lymph nodes.

Cutting edge: CD8+ effector T cells reject tumors by direct antigen recognition but indirect action on host cells

CD8(+) effector T cells recognize malignant cells by monitoring their surface for the presence of tumor-derived peptides bound to MHC class I molecules. In addition, tumor-derived Ags can be cross-presented to CD8(+) effector T cells by APCs. IFN-gamma production by CD8(+) T cells is often critical for tumor rejection. However, it remained unclear whether 1) CD8(+) T cells secrete IFN-gamma in response to Ag recognition on tumor cells or APCs and 2) whether IFN-gamma mediates its antitumor effect by acting on host or tumor cells. We show in this study that CD8(+) effector T cells can reject tumors in bone marrow-chimeric mice incapable of cross-presenting Ag by bone marrow-derived APCs and that tumor rejection required host cells to express IFN-gammaR. Together, CD8(+) effector T cells recognize Ag directly on tumor cells, and this recognition is sufficient to reject tumors by IFN-gamma acting on host cells.

Co-expression of bfl-1 enhances host response in the herpes simplex virus-thymidine kinase/ganciclovir gene therapy system

Anticancer suicide gene therapy using herpes simplex virus-thymidine kinase (HSV-tk) and ganciclovir (GCV) features the unique advantage of being able to elicit brisk host immune response against tumors and the host response reportedly can be potentiated with the co-expression of other appropriate immune- or apoptosis-related genes. We introduced a novel antiapoptotic gene, bfl-1, to test its applicability in the HSV-tk/GCV system. CT-26 murine colon cancer cells transfected with HSV-tk, alone or in combination with bcl-xL or bfl-1, were either grown in vitro or injected into syngeneic mice, followed by GCV administration. The co-expression of bfl-1 was associated with the upregulation of CD95 and CD40 ligand (CD40L) in vitro and with pronounced intratumoral T-lymphocyte infiltration in vivo. These results add to the previous findings that antiapoptotic genes can be used as an adjunctive component in the HSV-tk/GCV system to enhance host immune response against tumors.

Successful therapy of metastatic cancer using tumor vaccines in mixed allogeneic bone marrow chimeras

A frequent outcome of allogeneic stem cell transplantation (alloSCT) in the treatment of leukemia is the destruction of the host hematolymphoid compartment and, thus, the malignancy, through the combined action of high-dose chemoradiotherapy and a T-cell-mediated graft-versus-host effect. Unfortunately, alloSCT is frequently limited by toxicity, including graft-versus-host disease (GVHD), and has not been successful in the treatment of tumors derived from solid organs. Here we report a novel cooperation between host and donor T cells in the response to a tumor cell vaccine given after a nonmyeloablative allogeneic stem cell transplantation (NST) protocol that achieves stable mixed bone marrow chimerism. Treatment of animals with NST, posttransplantation donor lymphocyte infusions (DLIs), and a vaccine, comprising irradiated autologous tumor cells mixed with a granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing bystander line, results in potent and specific antitumor immunity. This combined modality immunotherapy, administered after surgical removal of the primary tumor, cured metastatic mammary cancer in most animals without inducing GVHD. Cured animals contained tumor-specific T cells of both host and donor origin, but immunodeficient hosts could not be cured by NST, DLI, and vaccine administration. Thus, transfer of allogeneic donor T cells may help break functional tolerance of a host immune system to a solid tumor, thereby providing a rationale for the generation of mixed hematopoietic chimerism by NST prior to tumor cell vaccination.

Broadening of epitope recognition during immune rejection of ErbB-2-positive tumor prevents growth of ErbB-2-negative tumor

Tumor heterogeneity is a limiting factor in Ag-specific vaccination. Ag-negative variants may arise after tumor cells bearing the immunizing Ags are destroyed. In situ priming to tumor-associated epitopes distinct from and not cross-reactive with the immunizing Ags may be crucial to the ultimate success of cancer vaccination. Immunization of BALB/c mice with DNA encoding wild-type human ErbB-2 (Her-2/neu, E2) or cytoplasmic ErbB-2 (cytE2), activated primarily CD4 or CD8 T cells, respectively, and both vaccines protected against ErbB-2-positive D2F2/E2 tumors. In > or =50% of protected mice, a second challenge of ErbB-2-negative D2F2 tumor cells was rejected. Recognition of non-ErbB-2, tumor-associated Ags was demonstrated by immune cell proliferation upon stimulation with irradiated D2F2 cells. This broadening of epitope recognition was abolished if CD4 T cells were depleted before D2F2/E2 tumor challenge, demonstrating their critical role in Ag priming. Similarly, mice that rejected D2F2/cytE2 tumor cells, which express only MHC I epitopes of ErbB-2, were not protected from a second challenge with D2F2 cells. Depletion of CD8 T cells abolished protection against D2F2, indicating the activation of D2F2-specific CTL. Therefore, long term protection may be achieved by immunization with dominant Ag(s), followed by a general enhancement of CD4 T cell activity to promote priming to multiple tumor-associated Ags.

OX40 ligand-transduced tumor cell vaccine synergizes with GM-CSF and requires CD40-Apc signaling to boost the host T cell antitumor response

Efficient T cell priming by GM-CSF and CD40 ligand double-transduced C26 murine colon carcinoma is not sufficient to cure metastases in a therapeutic setting. To determine whether a cellular vaccine that interacts directly with both APC and T cells in vivo might be superior, we generated C26 carcinoma cells transduced with the T cell costimulatory molecule OX40 ligand (OX40L) either alone (C26/OX40L) or together with GM-CSF (C26/GM/OX40L), which is known to activate APC. Mice injected with C26/OX40L cells displayed only a delay in tumor growth, while the C26/GM/OX40L tumor regressed in 85% of mice. Tumor rejection required granulocytes, CD4+, CD8+ T cells, and APC-mediated CD40-CD40 ligand cosignaling, but not IFN-gamma or IL-12 as shown using subset-depleted and knockout (KO) mice. CD40KO mice primed with C26/GM/OX40L cells failed to mount a CTL response, and T cells infiltrating the C26/GM/OX40L tumor were OX40 negative, suggesting an impairment in APC-T cell cross-talk in CD40KO mice. Indeed, CD4+ T cell-depleted mice failed to mount any CTL activity against the C26 tumor, while treatment with agonistic mAb to CD40, which acts on APC, bypassed the requirement for CD4+ T cells and restored CTL activation. C26/GM/OX40L cells cured 83% of mice bearing lung metastases, whereas C26/OX40L or C26/GM vaccination cured only 28 and 16% of mice, respectively. These results indicate the synergistic activity of OX40L and GM-CSF in a therapeutic setting.

IL-4-induced arginase 1 suppresses alloreactive T cells in tumor-bearing mice

We previously demonstrated that a specialized subset of immature myeloid cells migrate to lymphoid organs as a result of tumor growth or immune stress, where they suppress B and T cell responses to Ags. Although NO was required for suppression of mitogen activation of T cells by myeloid suppressor cells (MSC), it was not required for suppression of allogenic responses. In this study, we describe a novel mechanism used by MSC to block T cell proliferation and CTL generation in response to alloantigen, which is mediated by the enzyme arginase 1 (Arg1). We show that Arg1 increases superoxide production in myeloid cells through a pathway that likely utilizes the reductase domain of inducible NO synthase (iNOS), and that superoxide is required for Arg1-dependent suppression of T cell function. Arg1 is induced by IL-4 in freshly isolated MSC or cloned MSC lines, and is therefore up-regulated by activated Th2, but not Th1, cells. In contrast, iNOS is induced by IFN-gamma and Th1 cells. Because Arg1 and iNOS share L-arginine as a common substrate, our results indicate that L-arginine metabolism in myeloid cells is a potential target for selective intervention in reversing myeloid-induced dysfunction in tumor-bearing hosts.

Clinical implications of antigen transfer mechanisms from malignant to dendritic cells. exploiting cross-priming

Expansion and activation of cytolytic T lymphocytes bearing high-affinity T-cell receptors specific for tumor antigens is a major goal of active cancer immunotherapy. Physiologically, T cells receive promitotic and activating signals from endogenous professional antigen-presenting cells (APC) rather than directly from malignant cells. This phenomenon fits with the broader concept of cross-presentation that earlier was demonstrated for minor histocompatibility and viral antigens. Many mechanisms have been found to be capable of transferring antigenic material from malignant cells to APC so that it can be processed and subsequently presented by MHC class I molecules expressed on APC. Dendritic cells (DC) are believed to be the most relevant APC mediating cross-presentation because they can take up antigens from apoptotic, necrotic, and even intact tumor cells. There exist specific molecular mechanisms that ensure this transfer of antigenic material: 1) opsonization of apoptotic bodies; 2) receptors for released heat shock proteins carrying peptides processed intracellularly; 3) Fc receptors that uptake immunocomplexes and immunoglobulins; and 4) pinocytosis. DC have the peculiar capability of reentering the exogenously captured material into the MHC class I pathway. Exploitation of these pieces of knowledge is achieved by providing DC with complex mixtures of tumor antigens ex vivo and by agents and procedures that promote infiltration of malignant tissue by DC. The final outcome of DC cross-presentation could be T-cell activation (cross-priming) but also, and importantly, T-cell tolerance contingent upon the activation/maturation status of DC. Artificial enhancement of tumor antigen cross-presentation and control of the immune-promoting status of the antigen-presenting DC will have important therapeutic implications in the near future.

Dendritic cells: making progress with tumour regression?

Due to their potent ability to activate the immune system, dendritic cells (DC) are showing promise as potential adjuvants for tumour immunotherapy of cancer patients. However, little is known about the effect tumour cells can have on DC function. Indeed, the discovery of different DC subsets with different immunological functions indicates that the relationship between tumour cells and tumour-infiltrating DC subtypes is likely to be complex. There remains a lot to be understood about the effects of tumours on DC before we can expect to benefit from DC-based tumour immunotherapy of cancer patients. Here we review the recent advances being made in understanding DC phenotype and function in relation to interactions with different types of tumours.

4-1BB ligand stimulation enhances myeloid dendritic cell maturation from human umbilical cord blood CD34+ progenitor cells

In humans, at least two subsets of dendritic cells (DCs) are identified on the basis of differential surface expression of CD11c antigens. CD11c(+) and CD11c(-) cells are respectively of myeloid and lympholoid origin and functionally distinct, eliciting inflammatory and tolerant T cell responses. We investigated whether 4-1BB ligand (4-1BBL), a member of the tumor necrosis factor (TNF) family, is involved in the maturation process to mature myeloid DCs during in vitro DC differentiation from immature DCs derived from human umbilical cord blood (CB) CD34(+) progenitor cells. Enhanced levels of CD11c as well as immunostimulatory molecules such as CD86, MHC class II, and 4-1BBL were induced in response to 4-1BBL stimulation. These changes were accompanied by noticeable morphological transition from nonadherent to adherent myeloid-like DCs. Stimulation of 4-1BBL on DCs with 4-1BB-Fc or with 4-1BB-transfected Jurkat cells resulted in acquisition of capacity for the immature DCs to produce interleukin-12 (IL-12). This suggests that 4-1BBL may be an important mediator for maturation of CD11c(+) myeloid DCs, information of possible relevance for the design of DC-based vaccines with enhanced activity.

Induction of specific immune responses by polycation-based vaccines

The s.c injection of tumor Ag-derived, MHC class I-binding peptides together with cationic poly-amino acids (e.g., poly-L-arginine; pR) has been shown to protect animals against a challenge with tumor cells expressing the respective peptide(s). Given our only restricted knowledge about immunogenic tumor-associated peptides, we sought to determine whether this pR-based vaccination protocol would also induce protective cancer immunity if large proteins were used instead of peptide epitopes. We found that the intracutaneous administration of the model Ag beta-galactosidase (beta-gal) together with pR (referred to as pR-based protein vaccine; pR-PV) was significantly more potent in protecting mice against the growth of beta-gal-expressing RENCA cells than the protein alone. Coadministration of pR enhanced both the beta-gal-induced specific humoral and CD8 response. The protective effect required CD8(+), but neither CD4(+) T lymphocytes nor beta-gal-specific Abs. beta-Gal priming of protective CD8(+) T lymphocytes was found to be CD4(+) T cell-independent, to take place within the draining lymph nodes, and to be accomplished by day 5 after vaccination. Ablation of the injection sites as early as 1.5 h after pR-PV administration still led to protection in a large proportion of the animals, indicating that certain protein Ags administered intradermally in the context of polycations are quickly transported to the draining nodes, where they induce molecular and cellular events resulting in the helper-independent priming and expansion of Tc1 cells. However, optimal protection required the prolonged presence of the injection site, suggesting that pR-PV injection facilitates the formation of a cutaneous depot of Ag-charged cells capable of migration and T cell activation.

Prolonged maturation and enhanced transduction of dendritic cells migrated from human skin explants after in situ delivery of CD40-targeted adenoviral vectors

Therapeutic tumor vaccination with viral vectors or naked DNA, carrying the genetic code for tumor-associated Ags, critically depends on the in vivo transduction of dendritic cells (DC). Transfection of predominantly nonprofessional APC and only small numbers of DC may hamper proper T cell activation. Aim of this study was, therefore, the targeted, selective, and enhanced in situ transduction of DC. A human skin explant model was used to explore targeted transduction of cutaneous DC after intradermal injection of a bispecific Ab conjugate to link adenoviral (Ad) vectors directly to CD40 on the DC surface. A significantly enhanced transduction efficiency and selectivity, and an increased activation state of migrating DC were thus achieved. Moreover, DC transduced by CD40-targeted Ad maintained their Ag-specific CTL-stimulatory ability for up to 1 wk after the start of migration, in contrast to DC transduced by untargeted Ad, which had lost this capacity by that time. Because DC targeting in vivo might obviate the need for the in vitro culture of autologous DC for adoptive transfer, CD40-targeted Ad vectors constitute a promising new vaccine modality for tumor immunotherapy.

A push-pull approach to maximize vaccine efficacy: abrogating suppression with an IL-13 inhibitor while augmenting help with granulocyte/macrophage colony-stimulating factor and CD40L

Although a role for CD4(+) helper cells in CD8(+) cytotoxic T lymphocyte (CTL) induction by vaccines is widely recognized, much less is known about a counterbalancing role of CD4(+) T cells in down-modulating this response, or about ways to optimize vaccine responses through abrogation of this negative regulatory mechanism. Here, we discovered a synergistic enhancement of vaccine-mediated CTL induction and protection by the relief of suppression through depletion of regulatory CD4(+) cells, including CD4(+) NKT cells, or blockade of IL-13 made by these cells, combined with the cytokine granulocyte/macrophage colony-stimulating factor and the costimulatory molecule CD40L. Indeed, in the absence of helper epitopes, granulocyte/macrophage colony-stimulating factor and the helper-mimetic molecule CD40L are not sufficient to replace help to induce CTL without abrogation of CD4(+) T cell-mediated suppression, suggesting a role for T cell help in overcoming suppression. The increased CTL induction translated to striking protection against viral infection by a vaccine by using this synergistic combined approach. These results argue for a push-pull approach to maximize vaccine efficacy, especially for HIV and cancer.

In vitro activation of cancer patient-derived dendritic cells by tumor cells genetically modified to express CD154

PURPOSE

Triggering of CD40 on antigen-presenting cells via its ligand CD154 is an important event in the initial phase of an immune response against cancer cells. In this study, we investigated the effects of adenoviral CD154 immunomodulatory gene therapy on the activation of human dendritic cells (DCs) in a well-defined in vitro system.

EXPERIMENTAL DESIGN

Human bladder cancer cell lines and tumor cells from patients with renal cell carcinoma (RCC) were transduced with Ad-CD154 vectors or control vectors. Activation of human in vitro generated DCs after coculture with transduced tumor cells was analyzed. Therapeutic efficacy and cytotoxic T-lymphocyte (CTL) activity were assessed in a subcutaneous (s.c.) murine bladder cancer model.

RESULTS

Human bladder cancer cell lines expressing CD154 showed a decreased growth rate, increased apoptosis, and modulated expression of molecules important for recognition by cytotoxic lymphocytes. Further, CD154-expressing allogeneic bladder tumor cell lines and autologous tumor cells from patients with renal cell cancer induced maturation of DCs and stimulated IFN-gamma production from lymphocytes cocultured with mature DCs. In vivo studies showed that CD154 gene therapy was highly effective in wild-type mice but only minimally effective in nude mice. Consequently, strong tumor-specific CTL activity was detected in mice vaccinated with tumor cells expressing CD154.

CONCLUSIONS

Using tumor cell lines as well as patient-derived material, we could show that tumor cells expressing CD154 efficiently induce maturation and activation of DCs as well as activation of lymphocytes. Our murine in vivo studies demonstrate that lymphocytes contribute to the observed antitumor effect in a s.c. bladder tumor model. These studies should stimulate CD154 gene therapy approaches for the treatment of urologic malignancies.

Reversal of tumor-induced dendritic cell paralysis by CpG immunostimulatory oligonucleotide and anti-interleukin 10 receptor antibody

Progressing tumors in man and mouse are often infiltrated by dendritic cells (DCs). Deficient antitumor immunity could be related to a lack of tumor-associated antigen (TAA) presentation by tumor-infiltrating DCs (TIDCs) or to a functional defect of TIDCs. Here we investigated the phenotype and function of TIDCs in transplantable and transgenic mouse tumor models. Although TIDCs could encompass various known DC subsets, most had an immature phenotype. We observed that TIDCs were able to present TAA in the context of major histocompatibility complex class I but that they were refractory to stimulation with the combination of lipopolysaccharide, interferon gamma, and anti-CD40 antibody. We could revert TIDC paralysis, however, by in vitro or in vivo stimulation with the combination of a CpG immunostimulatory sequence and an anti-interleukin 10 receptor (IL-10R) antibody. CpG or anti-IL-10R alone were inactive in TIDCs, whereas CpG triggered activation in normal DCs. In particular, CpG plus anti-IL-10R enhanced the TAA-specific immune response and triggered de novo IL-12 production. Subsequently, CpG plus anti-IL-10R treatment showed robust antitumor therapeutic activity exceeding by far that of CpG alone, and elicited antitumor immune memory.

CD36 is differentially expressed by CD8+ splenic dendritic cells but is not required for cross-presentation in vivo

Cross-presentation allows the processing of Ags from donor cells into the MHC class I presentation pathway of dendritic cells (DCs). This is important for the generation of cytotoxic T cell immunity and for induction of self tolerance. Apoptotic cells are reported to be efficient targets for cross-presentation, and in vitro studies using human DCs have implicated CD36 in their capture. In support of a role for CD36 in cross-presentation, we show that this molecule is differentially expressed by CD8(+) splenic DCs, which previously have been identified as responsible for cross-presentation in the mouse. Three different cross-presentation models were examined for their dependence on CD36. These included cross-priming to OVA-coated spleen cells and cross-tolerance to OVA transgenically expressed in the pancreatic islet beta cells under constitutive conditions or during beta cell destruction. In these models, CD36 knockout DCs were equivalent to wild-type DCs in their capacity to cross-present either foreign or self Ags, indicating that CD36 is not essential for cross-presentation of cellular Ags in vivo.

Antigen presentation and T cell stimulation by dendritic cells

Dendritic cells take up antigens in peripheral tissues, process them into proteolytic peptides, and load these peptides onto major histocompatibility complex (MHC) class I and II molecules. Dendritic cells then migrate to secondary lymphoid organs and become competent to present antigens to T lymphocytes, thus initiating antigen-specific immune responses, or immunological tolerance. Antigen presentation in dendritic cells is finely regulated: antigen uptake, intracellular transport and degradation, and the traffic of MHC molecules are different in dendritic cells as compared to other antigen-presenting cells. These specializations account for dendritic cells' unique role in the initiation of immune responses and the induction of tolerance.

Spinning molecular immunology into successful immunotherapy

Until recently, immunotherapies have been of limited success, particularly against cancer. However, recent insights into the cells, molecules and signalling pathways that regulate immune responsiveness are providing new approaches for immunotherapy. In this article, I review some of the most promising molecular and cellular targets for immunotherapy and discuss approaches that use these targets to amplify immune responses and potentially break antigen-specific tolerance. These strategies provide a blueprint for the development of successful immunotherapy over the next decade.

GM-CSF-based cellular vaccines: a review of the clinical experience

Immunotherapy is playing an increasing role in the treatment of many cancers. The recent advances in antibody therapy gives much optimism that both passive (antibody therapy) as well as active (vaccine therapy) immunotherapeutic interventions will acquire an increasing presence in oncology. Granulocyte macrophage-colony stimulation factor (GM-CSF)-based vaccines have now been tested in several diseases in a variety of formulations. The success and broad applicability of such an approach rests on the development of an ideal vaccine formulation administered in the appropriate clinical context. This review summarizes the results from the clinical trials performed to date and discusses the future directions of GM-CSF-based cellular vaccine strategies aimed at maximizing the therapeutic benefit.

Interleukin-17 inhibits tumor cell growth by means of a T-cell-dependent mechanism

Interleukin 17 (IL-17) is a proinflammatory cytokine produced by activated CD4(+) memory T cells. We previously showed that IL-17 increased the growth rate of human cervical tumors transplanted into athymic nude mice. To address the possible role of T cells in the biologic activity of IL-17 for tumor control, we grafted 2 murine hematopoietic immunogenic tumors (P815 and J558L) transfected with a complementary DNA encoding murine IL-17 into syngeneic immunocompetent mice. We found that growth of the 2 IL-17-producing tumors was significantly inhibited compared with that of mock-transfected tumors. In contrast to the antitumor activity of IL-17 observed in immunocompetent mice, we observed no difference in the in vivo growth of IL-17-transfected or mock-transfected P815 cells (P815-IL-17 and P815-Neo, respectively) transplanted into nude mice. We then showed that IL-17 increased generation of specific cytolytic T lymphocytes (CTLs) directed against the immunodominant antigens from P815 called A, B, C, D, and E, since all mice injected with P815-IL-17 developed a P815-specific CTL response, whereas only 6 of 16 mice immunized with P815-Neo had a specific CTL response against the antigens. The induction of CTLs was associated with establishment of a tumor-protective immunity. These experiments suggest that T lymphocytes are involved in the antitumor activity of IL-17. Therefore, IL-17, like other cytokines, appears to be a pleiotropic cytokine with possible protumor or antitumor effects on tumor development, which often depends on the immunogenicity of tumor models.

GPI-anchoring of GM-CSF results in active membrane-bound and partially shed cytokine

Granulocyte-macrophage colony-stimulating factor (GM-CSF) can induce the generation and activation of dendritic cells (DCs), the most potent of antigen presenting cells (APCs). Tumors secreting GM-CSF have been shown to induce strong anti-tumor immune responses. In this report, we have constructed a glycosylphosphatidyl-inositol (GPI) anchored form of GM-CSF (GPI-GM-CSF). This protein subsequently was found expressed on the cell membrane and sensitive to phosphatidyl-inositol-specific phospholipase C (PIPLC), confirming that it is GPI-anchored. However, GM-CSF was also found in the culture supernatant of cells expressing GPI-GM-CSF. Inhibition studies using brefeldin A and para-formaldehyde fixation revealed that GM-CSF found in the supernatant was not secreted, but due to shedding or proteolytic cleavage. Accumulation of GM-CSF in the media from isolated membranes was time and temperature-dependent. The released portion represented 10-15% of all membrane-bound GM-CSF after 72h under culture conditions. GPI-GM-CSF retained functional activity to induce bone marrow cell proliferation and administration of GPI-GM-CSF expressing membranes induced the generation of DCs in vivo. These results demonstrate that GPI-anchored GM-CSF retains all functional activity of native GM-CSF while gaining the ability to attach to cell membranes. The ability of GPI-GM-CSF to be expressed on membranes and be partially released, can possibly lead to formation of a cytokine gradient, while retaining ability to target associated membrane antigens to DCs. This novel form of GM-CSF may have wide range of clinical applicability.

Cancer vaccines for hematologic malignancies

BACKGROUND

Improvements in the identification of tumor-associated antigens and in our understanding of the mechanisms regulating antitumor immune responses have revived interest in the use of therapeutic cancer vaccination. Due to their unique characteristics, hematologic malignancies represent an ideal target for vaccine-based therapeutic interventions.

METHODS

A review of published vaccine studies in experimental models as well as the results of clinical trials using vaccines for patients with hematologic tumors is presented.

RESULTS

Tumor vaccine strategies can be divided into two categories: antigen-specific strategies, in which the tumor antigens have been identified and can be isolated to develop a molecularly defined vaccine, and cellular or non-antigen-specific, in which the tumor-specific antigens are unknown but presumed to exist within the material used to generate the vaccine. Early clinical trials have shown not only the feasibility and safety of either approach but also the obstacles in therapeutic cancer vaccination as an effective treatment modality for hematologic malignancies.

CONCLUSIONS

Active immunization using current cancer vaccine approaches is feasible and safe. Although no major successes have been reported, the positive clinical results observed in some patients support the potential for therapeutic cancer vaccination in the management of hematologic malignancies. Results of studies that are testing vaccine formulations, targets, and settings (eg, bone marrow transplantation) may support the use of cancer vaccination as an efficient therapeutic strategy against tumors of hematologic origin.