Vaccination with dendritic cells inhibits the growth of hepatic metastases in B6 mice

Trial watch: dendritic cell vaccination for cancer immunotherapy

Dendritic- cells (DCs) have received considerable attention as potential targets for the development of anticancer vaccines. DC-based anticancer vaccination relies on patient-derived DCs pulsed with a source of tumor-associated antigens (TAAs) in the context of standardized maturation-cocktails, followed by their reinfusion. Extensive evidence has confirmed that DC-based vaccines can generate TAA-specific, cytotoxic T cells. Nonetheless, clinical efficacy of DC-based vaccines remains suboptimal, reflecting the widespread immunosuppression within tumors. Thus, clinical interest is being refocused on DC-based vaccines as combinatorial partners for T cell-targeting immunotherapies. Here, we summarize the most recent preclinical/clinical development of anticancer DC vaccination and discuss future perspectives for DC-based vaccines in immuno-oncology.

Trial watch: Dendritic cell-based anticancer immunotherapy

Dendritic cell (DC)-based vaccines against cancer have been extensively developed over the past two decades. Typically DC-based cancer immunotherapy entails loading patient-derived DCs with an appropriate source of tumor-associated antigens (TAAs) and efficient DC stimulation through a so-called "maturation cocktail" (typically a combination of pro-inflammatory cytokines and Toll-like receptor agonists), followed by DC reintroduction into patients. DC vaccines have been documented to (re)activate tumor-specific T cells in both preclinical and clinical settings. There is considerable clinical interest in combining DC-based anticancer vaccines with T cell-targeting immunotherapies. This reflects the established capacity of DC-based vaccines to generate a pool of TAA-specific effector T cells and facilitate their infiltration into the tumor bed. In this Trial Watch, we survey the latest trends in the preclinical and clinical development of DC-based anticancer therapeutics. We also highlight how the emergence of immune checkpoint blockers and adoptive T-cell transfer-based approaches has modified the clinical niche for DC-based vaccines within the wide cancer immunotherapy landscape.

Trial watch: Dendritic cell-based anticancer therapy

The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a privileged position at the interface between innate and adaptive immunity, orchestrating a large panel of responses to both physiological and pathological cues. In particular, whereas the presentation of antigens by immature DCs generally results in the development of immunological tolerance, mature DCs are capable of priming robust, and hence therapeutically relevant, adaptive immune responses. In line with this notion, functional defects in the DC compartment have been shown to etiologically contribute to pathological conditions including (but perhaps not limited to) infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. Thus, the possibility of harnessing the elevated immunological potential of DCs for anticancer therapy has attracted considerable interest from both researchers and clinicians over the last decade. Alongside, several methods have been developed not only to isolate DCs from cancer patients, expand them, load them with tumor-associated antigens and hence generate highly immunogenic clinical grade infusion products, but also to directly target DCs in vivo. This intense experimental effort has culminated in 2010 with the approval by the US FDA of a DC-based preparation (sipuleucel-T, Provenge®) for the treatment of asymptomatic or minimally symptomatic metastatic castration-refractory prostate cancer. As an update to the latest Trial Watch dealing with this exciting field of research (October 2012), here we summarize recent advances in DC-based anticancer regimens, covering both high-impact studies that have been published during the last 13 mo and clinical trials that have been launched in the same period to assess the antineoplastic potential of this variant of cellular immunotherapy.

Conditioning vaccination site with irradiated MIP-3alpha-transfected tumor cells enhances efficacy of dendritic cell-based cancer vaccine

Macrophage inflammation protein-3alpha (MIP-3alpha) is a chemokine expressed in inflamed tissue and capable of inducing migration of immature dendritic cells (DCs) or Langerhans cells. We postulated that conditioning vaccination sites with MIP-3alpha might enhance the efficacy of subsequently administered DC-based cancer vaccines. Our results demonstrate that subcutaneously injection of irradiated tumor cells expressing MIP-3alpha induces substantial cell infiltration to the injection site. Vaccination of irradiated tumor cells expressing MIP-3alpha followed by DCs pulsed with irradiated tumor cells can effectively suppress tumor growth in animals, which is significantly better than vaccination with irradiated MIP-3alpha-producing tumor cells or DCs pulsed with tumor cells alone. The protective effect was most evident when the MIP-3alpha-producing tumor cells and DC-based vaccines were injected at the same site. These results support the notion that this combination vaccination strategy might generate a more effective immune response to suppress the growth of tumor cells in animals.

The importance of the age factor in cancer vaccination at older age

Cancer is an age-related disease, and with the graying of the society there is an increasing need to optimize cancer management and therapy to elderly patients. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Therefore, research is needed to establish whether age-specific tumor-immunological variables permit optimal use of cancer vaccines and therapy in the elderly. This review summarizes the current knowledge of T cell unresponsiveness in cancer patients and elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, new directions that may lead to effective cancer vaccination at older age will be proposed.

Immunisation with 'naïve' syngeneic dendritic cells protects mice from tumour challenge

Dendritic cells (DCs) ‘pulsed’ with an appropriate antigen may elicit an antitumour immune response in mouse models. However, while attempting to develop a DC immunotherapy protocol for the treatment of breast cancer based on the tumour-associated MUC1 glycoforms, we found that unpulsed DCs can affect tumour growth. Protection from RMA-MUC1 tumour challenge was achieved in C57Bl/6 MUC1 transgenic mice by immunising with syngeneic DCs pulsed with a MUC1 peptide. However, unpulsed DCs gave a similar level of protection, making it impossible to evaluate the effect of immunisation of mice with DCs pulsed with the specific peptide. Balb/C mice could also be protected from tumour challenge by immunisation with unpulsed DCs prior to challenge with murine mammary tumour cells (410.4) or these cells transfected with MUC1 (E3). Protection was achieved with as few as three injections of 50 000 naïve DCs per mouse per week, was not dependent on injection route, and was not specific to cell lines expressing human MUC1. However, the use of Rag2-knockout mice demonstrated that the adaptive immune response was required for tumour rejection. Injection of unpulsed DCs into mice bearing the E3 tumour slowed tumour growth. In vitro, production of IFN-γ and IL-4 was increased in splenic cells isolated from mice immunised with DCs. Depleting CD4 T cells in vitro partially decreased cytokine production by splenocytes, but CD8 depletion had no effect. This paper shows that naïve syngeneic DCs may induce an antitumour immune response and has implications for DC immunotherapy preclinical and clinical trials.

Antitumor activity of a fusion of esophageal carcinoma cells with dendritic cells derived from cord blood

The aim of this experiment was to develop a cytotoxic cancer vaccine (EC109-DC) prepared by fusions of esophageal carcinoma cells with dendritic cells derived from cord blood and to study the biological characteristics and resultant induction of antitumor immunity. CD34+ hematopoietic stem cells were isolated from cord blood using a CD34+ Progenitor Cell Isolation Kit by magnetic cell sorting system (MACS). CD34+ cells were incubated with rhGM-CSF, rhTNF-alpha and rhSCF for 2 weeks as DC (dendritic cells), and then by PEG-3600 to fuse with an esophageal carcinoma cell line. Selection with MACS marked with HLA-DR MicroBeads generated EC109-DC. Phenotypes and proliferation were analyzed by flow cytometry and cell culture in vitro. The lymphocyte proliferation reaction and CTL cytotoxicity were examined by MTT assay. The EC109-DC cells could proliferate slowly in vitro and highly expressed CD80, CD83 and CD86. The lymphocyte proliferation reaction and specific cytotoxicity against EC109 induced by EC109-DC cells were significantly higher than in control groups (p < 0.05). EC109-DC cells obtained by PEG fusion acquired the immuno-stimulating phenotype and could significantly stimulate the lymphocyte proliferation reaction and CTL activity. The results of this research provide the basis for materials to develop the DC-based vaccine against esophageal carcinoma.

A pilot clinical trial of vaccination with dendritic cells pulsed with autologous tumor cells derived from malignant pleural effusion in patients with late-stage lung carcinoma

BACKGROUND

The authors conducted a pilot clinical trial to explore the vaccination of patients with late-stage lung carcinoma with dendritic cells (DCs) pulsed with necrotic tumor cells derived from malignant pleural effusion specimens, and to evaluate the antitumor immune response induced by this therapy.

METHODS

Autologous DCs were generated by culturing adherent mononuclear cells with interleukin-4 and granulocyte-macrophage-colony-stimulating factor for 7 days. Day-7 DCs were cocultured overnight with autologous necrotic tumor cells derived from pleural effusion specimens to allow internalization of tumor antigens. DCs were then treated with tumor necrosis factor-alpha for 16 hours. The antigen-loaded DCs were injected into each patient's inguinal lymph nodes under sonographic guidance. Eight patients with late-stage nonsmall cell lung carcinoma were treated in this manner. Patients were vaccinated once weekly for 4 weeks and then boosted twice biweekly.

RESULTS

The authors found that there was no Grade II/III toxicity and autoimmune response in all patients after intranodal injection of the DC vaccine. Minor to moderate increases in T-cell responses against tumor antigens were observed after DC vaccination in six of eight patients. Five patients had progressive disease. One patient had minor tumor response and two patients had stable disease. The two patients who had longer disease control also had better T-cell responses.

CONCLUSIONS

The results indicated that it was feasible to immunize patients with lung carcinoma intranodally with DCs pulsed with necrotic tumor cells enriched from pleural effusion specimens, and this approach may generate T-cell responses and provide clinical benefit in some patients.

Generation of carcinoembryonic antigen (CEA)-specific T-cell responses in HLA-A*0201 and HLA-A*2402 late-stage colorectal cancer patients after vaccination with dendritic cells loaded with CEA peptides

PURPOSE

We intranodally immunized metastatic colorectal carcinoma patients, who had failed standard chemotherapy, with dendritic cells (DCs) pulsed with HLA-A*0201- or HLA-A*2402-restricted carcinoembryonic antigen (CEA) peptides to evaluate the safety of this treatment and the immune response against CEA peptides before and after the treatment.

EXPERIMENTAL DESIGN

Six patients with the HLA-A*2402 genotype and 4 patients with the HLA-A*0201 genotype were enrolled. A single CEA peptide (YLSGANLNL) or two CEA peptides (QYSWFVNGTF and TYACFVSNL) were used for patients with the HLA-A*0201 or HLA-A*2402 genotype, respectively. Autologous DCs were generated by culturing adherent mononuclear cells with interleukin 4 and granulocyte macrophage colony-stimulating factor for 6 days. Maturation of DCs was then induced with tumor necrosis factor alpha for 40 h. Mature DCs were pulsed with appropriate CEA peptides for 2 h. After washing, 1 million peptide-pulsed DCs were injected into one inguinal lymph node under sonographic guidance. Each patient received four injections.

RESULTS

No grade II/III toxicity or autoimmunity was observed. An increase in the number of CEA-specific T cells after DC vaccination could be detected in 7 of 10 (70%) patients. Two (20%) patients had stable disease for at least 12 weeks. One of these 2 patients experienced a transient decrease in CEA levels during the treatment period and also had the most significant T-cell response against the immunizing CEA peptides.

CONCLUSIONS

These results suggest that our vaccination procedure can generate or boost specific T-cell responses and may provide clinical benefit in certain cancer patients.

Current Status of Clinical Studies for Colorectal Cancer in Taiwan

The incidence and age-adjusted mortality of colorectal cancer (CRC) has drastically increased in the past 2 decades in Taiwan. Fortunately, chemotherapy for metastatic CRC also showed improvement in terms of tumor response rate and survival in the corresponding time period. For its low toxicity profile and high objective response rate (17.5%-31.9% in patients who received low-dose 5-fluorouracil [5-FU] that failed and 53.3%-61.5% in patients who were chemotherapy-naive), weekly 24-hour infusion of high-dose 5-FU and leucovorin (LV) has been a favorable regimen for advanced CRC for medical oncologists in Taiwan. Investigators also put their effort in exploring the mechanisms of high efficacy and low toxicity profile of this regimen, as well as the prognostic factors in predicting tumor response to this regimen. With the emergence of new, active compounds for metastatic CRC, a simple 2-hour infusion of oxaliplatin plus 46-hour infusion of 5-FU/LV every 2 weeks has become a favorable regimen, with an overall response rate (ORR) of 40%-50% and overall survival of 18.2 months in chemotherapy-naive patients. Conversely, there were also studies to suggest that biweekly oxaliplatin plus weekly or biweekly bolus 5-FU/LV was shown to achieve a comparable tumor response and survival in 5-FU-refractory metastatic CRC. In patients who had been treated with oxaliplatin plus infusional 5-FU/LV that failed, salvage biweekly irinotecan plus bolus and infusional 5-FU/LV could achieve an ORR of 22.2% with a median duration of response of 8 months. As for oral fluoropyrimidine analogues, oral tegafur/uracil and capecitabine are available in Taiwan. In addition, a clinical trial of dendritic cell-based immunotherapy for chemotherapy-refractory metastatic CRC has also been initiated and is in progress.

Progress in the Development of Immunotherapy of Cancer Using Ex Vivo-Generated Dendritic Cells Expressing Multiple Tumor Antigen Epitopes

Immunotherapy with tumor-associated antigen-pulsed, ex vivo-generated dendritic cells (DCs) is a promising approach for the treatment of cancer that has shown efficacy in animal models and is now being tested in the clinic. The majority of studies performed to date make use of a single tumor-associated epitope. However, because of the high rate of mutation in tumor cells allowing for loss of expression of a single antigen, it is likely that use of multiple antigenic epitopes will induce a broader, longer-lasting, and effective tumor-specific immune response. Multiple vehicles for loading DCs with multiple antigenic epitopes are under investigation to determine the most effective method for vaccination, with many of these methods showing promise. These loading methods, as well as other critical considerations for making DC vaccination as efficacious as possible, are discussed in this article.

Dendritic cell-induced activation of adaptive and innate antitumor immunity

While studying Ag-pulsed syngeneic dendritic cell (DC) immunization, we discovered that surprisingly, unpulsed DCs induced protection against tumor lung metastases resulting from i.v. injection of a syngeneic BALB/c colon carcinoma CT26 or a syngeneic C57BL/6 lung carcinoma LL/2. Splenocytes or immature splenic DCs did not protect. The protection was mediated by NK cells, in that it was abrogated by treatment with anti-asialo-GM1 but not anti-CD8, and was induced by CD1(-/-) DCs unable to stimulate NKT cells, but did not occur in beige mice lacking NK cells. Protection correlated with increased NK activity, and increased infiltration of NK but not CD8(+) cells in lungs of tumor-bearing mice. Protection depended on the presence of costimulatory molecules CD80, CD86, and CD40 on the DCs, but surprisingly did not require DCs that could make IL-12 or IL-15. Unexpectedly, protection sensitive to anti-asialo-GM1 and increased NK activity were still present 14 mo after DC injection. As NK cells lack memory, we found by depletion that CD4(+) not CD8(+) T cells were required for induction of the NK antitumor response. The role of DCs and CD4(+) T cells provides a novel mechanism for NK cell induction and innate immunity against cancer that may have potential in preventing clinical metastases.

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.

Treatment of non-resectable hepatocellular carcinoma with autologous tumor-pulsed dendritic cells

BACKGROUND

The response of hepatocellular carcinoma (HCC) to therapy is often disappointing and new modalities of treatment are clearly needed. Active immunotherapy based on the injection of autologous dendritic cells (DC) co-cultured ex vivo with tumor antigens has been used in pilot studies in various malignancies such as melanoma and lymphoma with encouraging results.

METHODS

In the present paper, the preparation and exposure of patient DC to autologous HCC antigens and re-injection in an attempt to elicit antitumor immune responses are described.

RESULTS

Therapy was given to two patients, one with hepatitis C and one with hepatitis B, who had large, multiple HCC and for whom no other therapy was available. No significant side-effects were observed. The clinical course was unchanged in one patient, who died a few months later. The other patient, whose initial prognosis was considered poor, is still alive and well more than 3 years later with evidence of slowing of tumor growth based on organ imaging.

CONCLUSIONS

It is concluded that HCC may be a malignancy worthy of DC trials and sufficient details in the present paper are given for the protocol to be copied or modified.

Specific immunotherapy of cancer in elderly patients

The concept of immunotherapy of cancer is more than a century old, but only recently have molecularly defined therapeutic approaches been developed. In this review, we focus on the most promising approach, active therapeutic vaccination. The identification of tumour antigens can now be accelerated by methods allowing the amplification of gene products selectively or preferentially transcribed in the tumour. However, determining the potential immunogenicity of such gene products remains a demanding task, since major histocompatibility complex (MHC) restriction of T cells implies that for any newly defined antigen, immunogenicity will have to be defined for any individual MHC haplotype. Tumour-derived peptides eluted from MHC molecules of tumour tissue are also a promising source of antigen. Tumour antigens are mostly of weak immunogenicity, because the vast majority are tumour-associated differentiation antigens already 'seen' by the patient's immune system. Effective therapeutic vaccination will thus require adjuvant support, possibly by new approaches to immunomodulation such as bispecific antibodies or antibody-cytokine fusion proteins. Tumour-specific antigens, which could be a more potent target for immunotherapy, mostly arise by point mutations and have the disadvantage of being not only tumour-specific, but also individual-specific. Therapeutic vaccination will probably focus on defined antigens offered as protein, peptide or nucleic acid. Irrespective of the form in which the antigen is applied, emphasis will be given to the activation of dendritic cells as professional antigen presenters. Dendritic cells may be loaded in vitro with antigen, or, alternatively, initiation of an immune response may be approached in vivo by vaccination with RNA or DNA, given as such or packed into attenuated bacteria. The importance of activation of T helper cells has only recently been taken into account in cancer vaccination. Activation of cytotoxic T cells is facilitated by the provision of T helper cell-derived cytokines. T helper cell-dependent recruitment of elements of non-adaptive defence, such as leucocytes, natural killer cells and monocytes, is of particular importance when the tumour has lost MHC class I expression. Barriers to successful therapeutic vaccination include: (i) the escape mechanisms developed by tumour cells in response to immune attack; (ii) tolerance or anergy of the evoked immune response; (iii) the theoretical possibility of provoking an autoimmune reaction by vaccination against tumour-associated antigens; and (iv) the advanced age of many patients, implying reduced responsiveness of the senescent immune system.

Hepatocellular carcinoma--cause, treatment and metastasis

In the recent decades, the incidence of hepatocellular carcinoma (HCC) has been found to be increasing in males in some countries. In China, HCC ranked second of cancer mortality since 1990s. Hepatitis B and C viruses (HBV and HCV) and dietary aflatoxin intake remain the major causative factors of HCC. Surgery plays a major role in the treatment of HCC, particularly for small HCC. Down-staging unresectable huge HCC to smaller HCC and followed by resection will probably be a new approach for further study. Liver transplantation is indicated for small HCC, however, some issues remain to be solved. Different modes of regional cancer therapy for HCC have been tried. Systemic chemotherapy has been disappointing in the past but the future can be promising. Biotherapy, such as cytokines, differentiation inducers, anti-angiogenic agents, gene therapy and tumor vaccine will probably play a role, particularly in the prevention of tumor recurrence. HCC invasiveness is currently the major target of study. Tremendous works have been done at the molecular level, which will provide clues for biomarker of HCC progression as well as targets for intervention.

Induction and clonal expansion of tumor-specific cytotoxic T lymphocytes from renal cell carcinoma patients after stimulation with autologous dendritic cells loaded with tumor cells

Melanoma and renal cell carcinoma (RCC) are considered to be the most immunogenic tumors in humans. To generate conditions to induce primary T-cell responses against RCC and to allow further expansion of tumor-specific cytotoxic T lymphocytes (CTL) for adoptive transfer, peripheral blood mononuclear cells from RCC patients were stimulated with primary autologous tumor cells or monocyte-derived dendritic cells (DC) loaded with either tumor lysate (TU-LY) or apoptotic tumor cells (TU-AP). Whereas repetitive stimulation (4x) with tumor cells alone induced a predominant population of CD3(-) natural killer cells, 4 weeks of stimulation with tumor-loaded DC favored induction and expansion of CD4+ T cells (>80%). However, 2 weekly stimulation cycles with tumor-loaded DC followed by restimulation with autologous irradiated tumor cells alone were optimal for induction of tumor-specific CTL responses in vitro. Using these culture conditions a marked increase of CD4+ T cells was observed during the first 2 weeks of stimulation with tumor-loaded DC. Subsequent restimulation with autologous tumor cells alone gave rise to 500-fold expansion of CD8+ T cells. These CD8+ T cells were shown to exhibit strong major histocompatibility complex class I-restricted cytotoxic activity against the autologous tumor. Comparison of TU-LY and TU-AP as a source of tumor antigen for loading DC did not show any difference in stimulating tumor-specific CTL. Length pattern analysis of the complementary determining region 3 (CDR3) of the T-cell receptor Vbeta chain revealed expansion of oligoclonal CTL populations with outgrowth of 1 or 2 clones after prolonged stimulation with autologous tumor cells. Our study demonstrated an efficient method for generating tumor-specific CTL in vitro that may be used to identify tumor cell antigens or that can be expanded for adoptive T-cell transfer in tumor immunotherapy.

Antigen-specific immunotherapy for human papillomavirus 16 E7-expressing tumors grown in the liver

BACKGROUND/AIMS

We have previously reported a recombinant vaccinia-based vaccine (vac-Sig/E7/LAMP-1) that demonstrated a significant anti-tumor effect in a subcutaneous tumor challenge model. Since the liver is one of the most common sites for tumor metastasis and organ microenvironments may modulate tumor cell responses to therapies, the aim of the present study was to evaluate the potency of vac-Sig/E7/LAMP-1 in treating E7-expressing tumors grown in the liver.

METHODS

For in vivo tumor prevention experiments, mice were vaccinated intraperitoneally with vac-Sig/E7/LAMP-1 followed by intrahepatic tumor challenge. For in vivo tumor regression experiments, mice were first challenged with tumor cells and then vaccinated with vac-Sig/E7/LAMP-1 intraperitoneally. In addition, enzyme-linked immunospot assays were used to determine the frequency of E7-specific T cell precursors.

RESULTS

For in vivo tumor protection experiments, tumor growth was observed in all of the mice vaccinated with wild-type vaccinia and 60% of the mice vaccinated with wild-type E7 vaccinia. All of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after tumor challenge. For the tumor regression assays, all of the mice vaccinated with vac-Sig/E7/LAMP-1 remained tumor-free 30 days after vaccination. In contrast, all of those mice receiving culture medium, wild-type vaccinia, or wild-type E7 vaccinia developed tumors in the liver. In addition, mice vaccinated with vac-Sig/E7/LAMP-1 had the highest E7-specific CD8+ T cell precursors.

CONCLUSIONS

Our data suggest that vac-Sig/E7/LAMP-1 is an effective vaccine for controlling E7-expressing tumors grown in the liver and our model suggests that antigen-specific immunotherapy may represent a powerful tool for treating liver tumors with characterized tumor-specific antigens. In addition, our data indicate that the number of E7-specific CD8+ T cell precursors directly correlated with the anti-tumor effect generated by Sig/E7/LAMP-1 vaccinia.

Vaccination for melanoma

Our knowledge of the immune system has grown tremendously in the 50 years since Coley used bacteria in an attempt to create a vaccine for cancer. The strategy for cancer vaccines has developed in that time as well. Both clinical and laboratory evidence suggests that melanoma is the more immunogenic of solid tumors. If treated early, melanoma can be controlled with surgery, but many patients continue to die from it. With our increased understanding of the immune system's interaction with melanoma, many clinical trials of melanoma vaccines are now underway. Vaccines designed to treat metastatic melanoma have shown some evidence of clinical effectiveness. This article outlines the current status of melanoma vaccination.

Dendritic cells: immunological sentinels with a central role in health and disease

Immunological effector cells must be sensitive to the antigens or environmental signals that indicate that a pathogen is present. To this end, a group of cells known as the professional antigen-presenting cells have the ability to educate T, B and NK cells as to the fingerprints of specific infections. The most adept of these cells are a closely related family termed dendritic cells (DC). A subset of these act as peripheral sentinels, specializing in the uptake, processing and presentation of antigenic material combined with an ability to detect a wide variety of 'danger' signals. These 'danger' or activation signals induce profound changes in dendritic cell physiology, facilitating the efficient stimulation of both adaptive and innate immunity. In the present review, a number of recent advances in the understanding of DC biology are discussed. These advances offer insights into the pathogenesis of a wide variety of diseases and point towards future strategies for immunotherapy.

Melanoma vaccines

Remarkable advances in tumor vaccination have been made since Coley first deliberately infected cancer patients with both live and heat-killed bacteria. Melanoma is the most immunogenic solid tumor and, as such, has served as the major model for tumor vaccine investigation in both the laboratory and the clinic. Many advances in the field of melanoma vaccination have been based on an improved understanding of the cellular interaction required to induce a specific antitumor immune response. As a result of this new knowledge, many clinical trials of melanoma vaccines are now under way, and vaccines for metastatic melanoma have shown evidence of clinical effectiveness. This paper outlines the current status of melanoma vaccination.

Cancer therapy: new concepts on active immunization

There is increasing evidence that tumors express putative target molecules for a therapeutic immune reaction. Yet, tumor cells lack the prerequisites for appropriate antigen presentation and--hence--the immune system does not respond. This difficulty can probably be circumvented when tumor antigens are processed by conventional antigen presenting cells. Thus, the identification of immunogenic tumor-associated antigens may allow new modes of vaccination with the hope of adding a fourth and hopefully powerful weapon to surgery, radiation and chemotherapy in the fight against cancer.

Induction of Epstein-Barr Virus-Specific Cytotoxic T-Lymphocyte Responses Using Dendritic Cells Pulsed With EBNA-3A Peptides or UV-Inactivated, Recombinant EBNA-3A Vaccinia Virus

Cell-mediated immunity, especially the cytotoxic T lymphocyte (CTL), provides resistance to Epstein-Barr virus (EBV), as is demonstrated by the occurrence of posttransplant lymphoproliferative disease in immunosuppressed patients. We set out to use dendritic cells (DCs) to elicit anti–EBV-specific CTLs in culture. In unselected, HLA-B8+ donors, monocyte-derived mature DCs were pulsed with the HLA-B8–restricted EBNA-3A peptide, FLRGRAYGL, and added to autologous T cells for 7 days at a DC:T ratio of 1:5 to 1:60. The cultured cells specifically lysed EBNA-3A peptide-pulsed, HLA-B8+, B-lymphoblastoid cell lines in a 5-hour51Cr-release assay. The generation of CTLs did not require the addition of interleukin-2. In comparison, monocytes were weak antigen-presenting cells. DCs were then infected with recombinant vaccinia-EBNA-3A. Vaccinia infection significantly decreased the viability of immature DCs after 3 days of culture (to 25% to 45%) but had a smaller effect on mature DC recovery (40% to 70%). To decrease these cytopathic effects and to expand the potential use of vaccinia vectors for DC therapy in immunocompromised patients, we successfully used psoralen and UV-inactivated virus. Mature DCs pulsed with either live or inactivated vaccinia EBNA-3A virus could elicit strong EBNA-3A–specific CTLs. Therefore, mature DCs are powerful stimulators of EBV-specific CTLs and their major histocompatibility complex class I products can even be charged with UV-inactivated recombinant vaccinia.

Induction of Epstein-Barr Virus-Specific Cytotoxic T-Lymphocyte Responses Using Dendritic Cells Pulsed With EBNA-3A Peptides or UV-Inactivated, Recombinant EBNA-3A Vaccinia Virus

Cell-mediated immunity, especially the cytotoxic T lymphocyte (CTL), provides resistance to Epstein-Barr virus (EBV), as is demonstrated by the occurrence of posttransplant lymphoproliferative disease in immunosuppressed patients. We set out to use dendritic cells (DCs) to elicit anti–EBV-specific CTLs in culture. In unselected, HLA-B8+ donors, monocyte-derived mature DCs were pulsed with the HLA-B8–restricted EBNA-3A peptide, FLRGRAYGL, and added to autologous T cells for 7 days at a DC:T ratio of 1:5 to 1:60. The cultured cells specifically lysed EBNA-3A peptide-pulsed, HLA-B8+, B-lymphoblastoid cell lines in a 5-hour51Cr-release assay. The generation of CTLs did not require the addition of interleukin-2. In comparison, monocytes were weak antigen-presenting cells. DCs were then infected with recombinant vaccinia-EBNA-3A. Vaccinia infection significantly decreased the viability of immature DCs after 3 days of culture (to 25% to 45%) but had a smaller effect on mature DC recovery (40% to 70%). To decrease these cytopathic effects and to expand the potential use of vaccinia vectors for DC therapy in immunocompromised patients, we successfully used psoralen and UV-inactivated virus. Mature DCs pulsed with either live or inactivated vaccinia EBNA-3A virus could elicit strong EBNA-3A–specific CTLs. Therefore, mature DCs are powerful stimulators of EBV-specific CTLs and their major histocompatibility complex class I products can even be charged with UV-inactivated recombinant vaccinia.

Immunotherapeutic potential of dendritic cells generated in long-term stroma-dependent cultures

Long term cultures (LTC) producing dendritic cells (DC) have been established from spleen. A well developed stromal cell layer supported production of DC in numbers suitable for experimentation. Cells had obvious membrane pseudopodia and could be collected from culture every 2-3 days. Large cells produced in LTC stained with fluorescently labelled monoclonal antibodies specific for DC such as 33D1, and M1/70 which is specific for DC and myeloid cells. These staining patterns confirmed the presence of DC within the LTC population. LTC-DC were tested and shown capable of migration in vivo in B10.A(2R) mice following footpad inoculation. Most cells entered the spleen and a small number entered popliteal lymph node. LTC-DC have migratory capacity comparable with control spleen lymphocytes. LTC-DC were tested for capacity to induce an anti-tumour immune response after exposing cells to tumour cell membranes. LTC-DC pulsed with BL/VL3 tumour antigens were able to induce a BL/VL3-specific primary cytotoxic T lymphocyte (CTL) response detectable in popliteal lymph nodes and spleen of C57BL/6J mice within 6 days of priming. BL/VL3 tumour cells grew in sublethally irradiated C57BL/6J mice giving 100% mortality. Adoptive transfer of spleen cells from mice given BL/VL3 antigen-pulsed LTC-DC, two weeks previously, significantly slowed the growth of BL/VL3 tumour cells in mice. DC produced in LTC can function as antigen presenting cells (APC) when adoptively transferred into animals. Their capacity to migrate effectively, to induce a CTL response and to reduce tumour load suggests that DC grown using this in vitro system may have valuable clinical potential in humans.