Genetically modified bone marrow-derived dendritic cells expressing tumor-associated viral or "self" antigens induce antitumor immunity in vivo

Dendritic Cell Vaccination in Non-Small Cell Lung Cancer: Remodeling the Tumor Immune Microenvironment

Non-small-cell lung cancer (NSCLC) remains one of the leading causes of death worldwide. While NSCLCs possess antigens that can potentially elicit T cell responses, defective tumor antigen presentation and T cell activation hinder host anti-tumor immune responses. The NSCLC tumor microenvironment (TME) is composed of cellular and soluble mediators that can promote or combat tumor growth. The composition of the TME plays a critical role in promoting tumorigenesis and dictating anti-tumor immune responses to immunotherapy. Dendritic cells (DCs) are critical immune cells that activate anti-tumor T cell responses and sustain effector responses. DC vaccination is a promising cellular immunotherapy that has the potential to facilitate anti-tumor immune responses and transform the composition of the NSCLC TME via tumor antigen presentation and cell-cell communication. Here, we will review the features of the NSCLC TME with an emphasis on the immune cell phenotypes that directly interact with DCs. Additionally, we will summarize the major preclinical and clinical approaches for DC vaccine generation and examine how effective DC vaccination can transform the NSCLC TME toward a state of sustained anti-tumor immune signaling.

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.

Cytotoxic Activity and Memory T Cell Subset Distribution of in vitro-Stimulated CD8+ T Cells Specific for HER2/neu Epitopes

Minimal residual disease remaining after resection of primary tumors can lead to tumor recurrence and metastasis, increasing mortality and morbidity rates among cancer patients. Thus, there is a need for new technologies for recognition and elimination of single cancer cells remaining in a patient's body after radiation therapy, chemotherapy, or surgical resection. Effector CD8⁺ T cells, also commonly known as cytotoxic T lymphocytes (CTLs), play a key role in antitumor cellular immunity and, when properly activated, are able to effectively destroy tumor cells. The aims of this study were to obtain CD8⁺ CTLs specific for the HER2/neu epitopes E75 and E88 and to assess the cytotoxic activity and composition of these cells in terms of the distribution of memory T-cell subsets. We obtained HER2-specific CD8⁺ T cells and assessed T cell subset distribution among them including naive T cells (T_N), central memory T cells (T_CM), effector memory T cells (T_EM), stem cell-like memory T cells (T_SCM) and terminally-differentiated T cells (T_EMRA) via eight-color flow cytometry. HER2-specific CTLs were largely (~40–50%) represented by T_SCM cells, a population capable of mounting pronounced antitumor immune responses due to a combination of effector function and self-maintenance. In comparison with activated peripheral blood mononuclear cells (PBMCs) and bulk CD8⁺ T cells, HER2-specific CTLs exhibited greater cytotoxicity against the HER2-expressing human breast adenocarcinoma cell line MCF-7 and produced higher levels of IFN-γ in response to tumor cells. We also showed the presence of HER2-specific CTLs in healthy individuals and increase in them in HER2-positive breast cancer patients. Collectively, our results suggest that HER2-specific CD8⁺ T cells isolated using this approach could be used for adoptive T-cell transfer to eliminate tumor cells and prevent metastasis and relapse in patients with HER2-overexpressing cancers.

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.

Development of HPV Vaccines for HPV-associated Head and Neck Squamous Cell Carcinoma

High-risk genotypes of the human papillomavirus (HPV), particularly HPV type 16, are found in a distinct subset of head and neck squamous cell carcinomas (HNSCC). Thus, these HPV-associated HNSCC may be prevented or treated by vaccines designed to induce appropriate HPV virus-specific immune responses. Infection by HPV may be prevented by neutralizing antibodies specific for the viral capsid proteins. In clinical trials, vaccines comprised of HPV virus-like particles (VLPs) have shown great promise as prophylactic HPV vaccines. However, given that capsid proteins are not expressed at detectable levels by infected basal keratinocytes, vaccines with therapeutic potential must target other non-structural viral antigens. Two HPV oncogenic proteins, E6 and E7, are important in the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Therefore, therapeutic vaccines targeting these proteins may have potential to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 is administered in live vectors, in peptides or protein, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should they fulfill their promise, these vaccines may prevent HPV infection or control its potentially life-threatening consequences in humans.

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.

The significance and regulatory mechanisms of innate immune cells in the development of sepsis

Sepsis with subsequent multiple organ dysfunction is a pronounced systemic inflammatory response to concealed or known infection and is a leading cause of death in intensive care units. The survival rate of severe sepsis and septic shock has not markedly improved in recent decades despite a great number of receptors and molecules involved in its pathogenesis have been found and taken as therapeutic targets. It is essential to thoroughly understand the host cell-mediated immunity involved in the development of sepsis and sepsis-related organ injury. Recent studies indicate that innate immune cells (such as neutrophils, macrophages, dendritic cells, T lymphocytes, regulatory T cells, and natural killer T cells) play pivotal roles in the maintenance of peripheral homeostasis and regulation of immune responses during sepsis. Therefore, an understanding of the biological significance and pathophysiological roles of different cell populations might gain novel insights into the immunoregulatory mechanisms of sepsis. In this review, we focus on major immune cells that may play potential roles in the contribution of new therapeutic approaches for sepsis.

Combined E7-dendritic cell-based immunotherapy and human sodium/iodide symporter radioiodine gene therapy with monitoring of antitumor effects by bioluminescent imaging in a mouse model of uterine cervical cancer

Using a uterine cervical cancer cell line expressing human papillomavirus (HPV) 16 E7 antigen and bioluminescent imaging (BLI), we evaluated the therapeutic potential of combined immunotherapy using transfected dendritic cells (DC-E7) and human sodium/iodide symporter (hNIS) radioiodine gene therapy in a xenograft animal cancer model. Dendritic cells expressing either E7 antigen (DC-E7) or no-insert (DC-no insert) were made for immunization materials, and murine uterine cervical cancer cell line coexpressing E7, firefly luciferase, hNIS, and EGFP genes (TC-1/FNG) were prepared for the animal tumor model. C57BL/6 mice were divided into five therapy groups (phosphate-buffered saline [PBS], DC-no insert, DC-E7, I-131, and DC-E7+I-131 groups). Single therapy with either DC-E7 or I-131 induced greater retardation in tumor growth compared with PBS or DC-no insert groups, and it resulted in some tumor-free mice (DC-E7 and I-131 groups, 40% and 20%, respectively). Combination therapy with DC-E7 and I-131 dramatically inhibited tumor growth, thus causing complete disappearance of tumors in all mice, and these effects were further confirmed by BLI in vivo. In conclusion, complete disappearance of the tumor was achieved with combined DC-E7 vaccination and hNIS radioiodine gene therapy in a mouse model with E7-expressing uterine cervical cancer, and serial BLIs successfully demonstrated antitumor effects in vivo.

Comparison of DNA- and mRNA-Transfected Mouse Dendritic Cells as Potential Vaccines against the Human Papillomavirus Type 16 associated Oncoprotein E7

Background

Dendritic cells (DCs) mediate the generation of strong cytotoxic T-lymphocyte (CTL) responses by functioning in antigen presentation and exerting adjuvant properties. We compared several activation markers and parameters of biological activity of DNA- and mRNA-transfected DCs in vitro and in vivo.

Methods

CpG-matured, bone marrow derived C57BL/6 mouse DCs were electroporated either with enhanced green fluorescence protein (EGFP) or human papillomavirus type 16 (HPV16) E7 expression plasmids or in vitro transcribed mRNAs encoding for the codon-optimized E7 or a shuffled version thereof. Activation marker expression and antigen presentation was analysed by fluorescence-activated cell sorting. The migratory behaviour of transfected DCs were investigated by in vitro chemotaxis experiments and cytokine expression by ELISA. CTL-priming capacity of transfected DCs were determined by vaccination of mice.

Results

mRNA transfection produced a two- to fourfold increase of the activation markers CD40, CD80, CD86 and MHC I and MHC II molecules. Predominately antigen-expressing DCs migrated after mRNA transfection. Furthermore, mRNA-transfected DCs were capable of inducing a chemokine gradient. After maturation, electroporation and activation with soluble CD40 ligand and interferon-γ, DCs displayed a T-helper cell type 2 cytokine expression pattern. Nevertheless, E7-transfected DCs were able to prime E7-specific CTL responses in vivo. The highest E7-specific CTL frequencies were found in mice immunized with mRNA-transfected DCs. The in vitro expanded CTLs exerted functional E7-specific cytotoxic activity.

Conclusions

Genetically modified DCs are suitable vehicles for the induction of E7-specific CTL responses in mice and hence could help to eradicate HPV-associated lesions in humans.

Mapping of cytotoxic T lymphocytes epitopes in E7 antigen of human papillomavirus type 11

One of the critical steps in the progression to condyloma acuminatum (CA) is the establishment of a persistent human papillomavirus (HPV) infection, majority of HPV type 6 and 11. Cytotoxic T lymphocytes (CTL), which can be induced by the epitope-based peptides in vitro, are thought to be able to recognize and destroy virus-infected cells. In order to screen and identify HLA-A*0201 restricted HPV-11E7 CTL epitopes, five epitope peptides and tetramers were selected including HPV-11E7 7-15 (TLKDIVLDL), 15-23 (LQPPDPVGL), 47-55 (PLTQHYQIL), 81-89 (DLLLGTLNI) and 82-90 (LLLGTLNIV). Human monocyte-derived dendritic cells (DCs) from HLA-A*0201 healthy individuals were pulsed with these peptides to assess the expression of CD83, CD86, HLA-DR and the secretion of IL-12. The ability of peptide-loaded mature DCs to activate autologous T cells was evaluated by analyzing the frequency of specific tetramer(+) CD8(+) T cells using flow cytometry, and the level of IFN-gamma secretion by ELISA. The ability of the epitope-specific CTLs to kill the target cells was also analysed. It was found that the immature DCs could be fully activated by all the five HPV-11E7 peptides and peptide-loaded mature DCs were able to stimulate the epitope-specific T cells in vitro. There was an increased frequency of CD8(+) T cells specific for the E7 7-15 epitope when compared to other four predicted epitopes of HPV-11E7 (P < 0.05). The epitope-specific CTLs for E7 7-15 induced the strongest cytotoxicity to HPV-11E7 expressing cell line at an E:T ratio of 50:1 (P < 0.05). Taken together, these findings demonstrate that E7 7-15 (TLKDIVLDL) is an HLA-A*0201-restricted CTL epitope of HPV type 11. We propose that this epitope could be more helpful in the characterization of HPV control mechanism and be useful for the development of immunotherapeutic approaches for low-risk HPV infectious diseases such as CA.

An MVA vaccine overcomes tolerance to human p53 in mice and humans

BACKGROUND

The cellular regulatory protein p53 is overexpressed by almost 50% of all malignancies making it an attractive target for a vaccine approach to cancer. A number of immunotherapy approaches targeting p53 have been evaluated successfully in murine models, but translation of these preclinical findings to the clinic has been unsuccessful. Prior studies in our laboratory employing murine models demonstrated that a modified vaccinia virus Ankara (MVA) vaccine expressing murine p53 could stimulate p53 specific immunity. Systemic administration of the MVA vaccine was able to effect the rejection of established tumors. To better understand the immunologic mechanisms that underlie the vaccine function of human p53, we utilized a murine model in which the murine germ line copy of p53 was replaced with a modified human one. These mice, referred to as Hupki, were evaluated as a tolerant model to explore the capacity of MVA expressing human p53 to overcome tolerance and reject human p53-expressing tumors.

RESULTS

MVAp53 immunization of Hupki mice resulted in the generation of p53-specific CD8(+) T cells and the rejection of a highly aggressive murine mammary carcinoma cell line 4T1(H-2d) transfected with human p53 (4T1p53). An immunologic correlate of tumor protection was evaluated utilizing an overlapping peptide library spanning the full length of human p53. This reagent was also used in combination with MVAp53 to stimulate p53-specific CD8(+) T cell responses in cancer patients.

CONCLUSION

These studies demonstrate the potential of MVAp53 to overcome tolerance to p53 for cancer immunotherapy.

Codon optimized expression of HPV 16 E6 renders target cells susceptible to E6-specific CTL recognition

The early proteins E6 and E7 of the cancer-related human papillomavirus type 16 (HPV 16) are constitutively expressed in cancer cells thus are targets for immune therapeutic approaches. Whereas previous studies have mainly focussed on the immunogenicity of E7 protein little is known about E6. In order to evaluate E6-specific DNA immunization strategies in a preclinical mouse model C57BL/6 mice were injected with plasmid pTHampE6 and analyzed for E6-specific CTL induction. CTL specific for the H2-K(b)-restricted E6-derived epitope E6 48-57, were readily detectable among splenocytes of immunized animals, however, these CTL showed a differential recognition pattern on various E6-expressing target cells. Using a newly generated E6-specific monoclonal antibody we found that most cell lines expressing E6 encoded by the natural gene showed undetectable protein amounts and were ignored by E6-specific CTL. However, transfection of a codon optimized version of the E6 gene (E6opt) strongly enhanced protein expression levels within these cells turning them into susceptible target cells. Surprisingly, we found that E6-positive TC-1 cells, although recognized by E6-specific CTL, were totally devoid of any detectable E6 protein. Inhibition of proteasomal function by lactacystin treatment diminished E6-specific CTL recognition of TC-1 cells and RMA/E6opt transfectants accompanied by intracellular accumulation of E6 protein as observed in RMA/E6opt transfectants, but not in TC-1 cells. These data suggest that in TC-1 cells rapid degradation processes might prevent stable expression of E6 protein yet generate precursor peptides in amounts sufficient for MHC class I restricted antigen presentation. Thus, the results presented in this paper show that: (i) use of optimized codons in transfection experiments can improve susceptibility of target cells to E6-specific CTL recognition and (ii) lack of detectable protein within a cell does not necessarily indicate the absence of epitope presentation. Both findings are of potential relevance for the design of tumor vaccines.

Adenoviral gene transfer of stromal cell-derived factor-1 to murine tumors induces the accumulation of dendritic cells and suppresses tumor growth

The human CXC chemokine, stromal cell-derived factor 1 (SDF-1alpha), is known to function in vitro as a chemotactic factor for lymphocytes, monocytes, and dendritic cells. In the context that dendritic cells are powerful antigen-presenting cells, we hypothesized that adenoviral gene transfer of SDF-1alpha to tumors might inhibit growth of preexisting tumors through attracting dendritic cells to the tumor. AdSDF-1alpha mediated the expression of SDF-1alpha mRNA and protein in A549 cells in vitro, and the supernatant of the AdSDF-1alpha-infected A549 cells showed chemotactic activity for dendritic cells. When syngeneic murine CT26 colon carcinoma tumors (BALB/c) and B16 melanoma and Lewis lung cell carcinoma (C57Bl/6) were injected with AdSDF-1alpha (5 x 10(8) plaque-forming units), there was an accumulation of dendritic cells and CD8(+) cells within the tumor and significant inhibition of tumor growth compared with tumors injected with PBS or AdNull (control vector). The injection of AdSDF-1alpha into tumors induced the inflammatory enlargement and the accumulation of dendritic cells in the draining lymph node. Intratumoral AdSDF-1alpha administration elicited tumor-specific CTLs and adoptive transfer of splenocytes from AdSDF-1alpha-treated mice resulted in the elongation of survival after tumor challenge. Interestingly, in wild-type and CD4(-/-) mice but not in CD8(-/-) mice, AdSDF-1alpha inhibited the growth of the tumor. These observations suggest that adenoviral gene transfer of SDF-1alpha may be a useful strategy to accumulate dendritic cells in tumors and evoke antitumor immune responses to inhibit tumor growth.

Recombinant cholera toxin B subunit activates dendritic cells and enhances antitumor immunity

Activation of dendritic cells (DC) is crucial for priming of cytotoxic T lymphocytes (CTL), which have a critical role in tumor immunity, and it is considered that adjuvants are necessary for activation of DC and for enhancement of cellular immunity. In this study, we examined an adjuvant capacity of recombinant cholera toxin B subunit (rCTB), which is non-toxic subunit of cholera toxin, on maturation of murine splenic DC. After the in vitro incubation of DC with rCTB, the expression of MHC class II and B7-2 on DC was upregulated and the secretion of IL-12 from DC was enhanced. In addition, larger DC with longer dendrites were observed. These data suggest that rCTB induced DC maturation. Subsequently, we examined the induction of tumor immunity by rCTB-treated DC by employing Meth A tumor cells in mice. Pretreatment with subcutaneous injection of rCTB-treated DC pulsed with Meth A tumor lysate inhibited the growth of the tumor cells depending on the number of DC. Moreover, intratumoral injection of rCTB-treated DC pulsed with tumor lysate had therapeutic effect against established Meth A tumor. Immunization with DC activated by rCTB and the tumor lysate increased number of CTL precursor recognizing Meth A tumor. The antitumor immune response was significantly inhibited in CD8+ T cell-depleted mice, although substantial antitumor effect was observed in CD4+ T cell-depleted mice. These results indicated that rCTB acts as an adjuvant to enhance antitumor immunity through DC maturation and that CD8+ T cells play a dominant role in the tumor immunity. Being considered to be safe, rCTB may be useful as an effective adjuvant to raise immunity for a tumor in clinical application.

Natural killer cells play a critical role in the immune response following immunization with melanoma-antigen-engineered dendritic cells

Tumor antigen gene-modified dendritic cells (DC) generates robust antigen-specific protective antitumor responses. Though the role of CD4 positive and CD8 positive cells in the immunological response to gene-modified DC has been well-characterized, the role of NK cells in this response has been somewhat less clear. Owing to the significant contribution of innate immunity in other model systems, we postulated that NK cells would hold a critical position in the generation of an immune response following immunization with tumor antigen-engineered DC. Immunization with MART-1 melanoma antigen-engineered DC in C57BL/6 mice resulted in the generation of antigen-specific cytotoxic T lymphocytes and in vivo protective responses to the murine B16 melanoma. These responses were dependent on the presence of functional NK cells, although NK cells alone were not sufficient in generating protective responses. Adoptive transfer of NK cells into an NK-deficient but T-cell-competent environment restored the protective response to gene-modified DC immunization. In conclusion, protective immunity after tumor antigen gene-modified DC immunization requires collaboration between CD4+ and CD8+ T cells and NK cells.

Immune characterization of clinical grade-dendritic cells generated from cancer patients and genetically modified by an ALVAC vector carrying MAGE minigenes

Gene delivery into dendritic cells (DC) is most efficiently achieved by viral vectors. Recombinant canarypox viruses (ALVAC) were validated safe and efficient in humans. We aimed firstly to evaluate DC transduction by ALVAC vectors, then to investigate if such infection induced or not the maturation of the DC, and finally to assess the efficiency of ALVAC-MAGE-transduced DC to activate specific CTL clones. Clinical grade DC from melanoma patients were generated from blood monocytes and infected with a recombinant ALVAC virus encoding either a marker gene (EGFP) or the MAGE-1-MAGE-3 minigenes. According to the patient-donor, 22+/-16% of immature DC were successfully transduced. Flow cytometry analysis of surface markers expressed on DC after ALVAC infection did not reveal a mature phenotype. Moreover, ALVAC transduction did not interfere with the capacity of the DC to further mature under poly:IC stimulation. But most importantly, our results demonstrated that DC from HLA-A1 patient-donors infected with the recombinant ALVAC MAGE-1-MAGE-3 minigenes virus were capable of activating a MAGE 3/A1 CTL clone more efficiently than same DC loaded with MAGE 3/A1 peptide, as shown by increased IFN-gamma secretion. These results could be the basis for the development of a new clinical strategy in melanoma patient's immunotherapy.

Vaccines for human papillomavirus-associated anogenital disease and cervical cancer: practical and theoretical approaches

The association of genital warts, cervical dysplasia and cervical cancer with certain human papillomavirus (HPV) types indicates that vaccine strategies that target the virus could be effective in controlling disease onset and progression. Three vaccine strategies are available. Firstly, a prophylactic approach of immunisation with HPV virus-like particles to elicit neutralising antibody would prevent infection. Secondly, vaccination targeting replicating virus in suprabasal cells of infected anogenital epithelium would be an effective therapy for infection and early dysplasias. Thirdly, immunotherapy directed to the oncoprotein products of the HPV E6 and E7 open reading frames would be effective in the control of cervical carcinoma. We examine how these strategies may be augmented by contemporary vaccine technologies, in particular through the use of live recombinant vaccine vectors, specific targeting of antigen processing pathways, dendritic cell and 'polytope' approaches, to produce 'designer' vaccines of maximum specificity and efficacy. How these approaches are being exploited by vaccine manufacturers and in clinical trials is discussed.

Multistep process through which adenoviral vector vaccine overcomes anergy to tumor-associated antigens

Our goal in the present work was to characterize the multiple steps involved in overcoming the anergy that exists in tumor hosts to tumor-associated antigen (TAA). Our studies showed that the subcutaneous injection of the Ad-sig-TAA/ecdCD40L vector resulted in secretion of the TAA/ecdCD40L protein for at least 10 days from infected cells. Binding of the TAA/ecdCD40L protein to dendritic cells (DCs) resulted in the induction of CCR-7 chemokine receptor expression and cytokine release. This was followed by migration of the DCs to regional lymph nodes. Tetramer staining, enzyme-linked immunospot (ELISPOT) assay, and cytotoxicity assay all showed that the Ad-sig-TAA/ecdCD40L vector increased the levels of splenic CD8+ T cells specific for the 2 TAAs (human MUC1 [hMUC1] and HPV E7) tested. Vaccination with the Ad-sighMUC1/ecdCD40L vector suppressed the growth of hMUC1 antigen-positive tumor cells in 100% of the test mice that were previously anergic to the hMUC1 antigen. These data suggest that Ad-sig-TAA-ecd/ecdCD40L vector injections may be of value in treating the many epithelial malignancies in which TAA-like hMUC1 is overexpressed. (Blood. 2004;104:2704-2713)

Novel approaches to therapeutic cancer vaccines

Although tumor vaccines have been studied for decades, there is no vaccine approved as a clinical product. Nevertheless, recent advances in immunology and tumor biology justify a renewed interest. First, cancer cells express many antigens that can be recognized by the immune system, some with high tumor selectivity. Second, knowledge about immune regulation, including the importance of costimulatory signals, has been successfully applied to the studies of tumors. Third, mechanisms of how tumors can escape from immunological control have been identified, setting the stage to discover agents to decrease their impact. Rejection of established mouse tumors has been accomplished as a result of therapeutic tumor vaccination and there are encouraging findings from vaccine trials in humans.

Preventative and therapeutic vaccines for cervical cancer

"High-risk" genotypes of the human papillomavirus (HPV), most commonly HPV genotype 16, are the primary etiologic agents of cervical cancer. Indeed HPV DNA is detected in 99% of cervical carcinomas. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by the induction of the appropriate viral-antigen-specific immune responses. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. HPV L1 virus-like particles (VLPs) show great promise as prophylactic HPV vaccines in ongoing clinical trials but L2-based preventative vaccines have yet to be tested in patients. Since the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target the nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Although other early viral antigens show promise for vaccination against papillomas, therapeutic vaccines targeting E6 and E7 may provide the best opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or proteins, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should this new generation of HPV preventative and therapeutic vaccines function in patients as demonstrated in animal models, oncogenic HPV infection and its associated malignancies could be controlled by vaccination. Importantly, recent advances in HPV detection and continued improvements in screening further enhance our opportunities to systematically eradicate HPV-associated malignancy.

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.

Vaccination to prevent and treat cervical cancer

Human papillomaviruses (HPVs) are the primary etiologic agents of cervical cancer. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by HPV vaccines. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. However, because the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Thus, therapeutic vaccines targeting E6 and E7 may provide the best option for controlling HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or protein, in nucleic acid form, as components of chimeric virus-like particles, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. If these preventive and therapeutic HPV vaccines prove successful in patients, as they have in animal models, then oncogenic HPV infection and its associated malignancies may be controllable by vaccination.

Increased Dendritic Cell Numbers Impair Protective Immunity to Intracellular Bacteria Despite Augmenting Antigen-Specific CD8+T Lymphocyte Responses

Dendritic cells (DCs) reside in tissues, where they function as sentinels, providing an essential link between innate and adaptive immunity. Increasing the numbers of DCs in vivo augments T cell responses, and can cause dramatic CTL-dependent tumor regression. To determine whether greater DC numbers promoted T cell-mediated protection in the context of host defense against intracellular bacteria, we treated mice with Flt3 ligand (Flt3-L) to increase DCs in vivo and challenged them with Listeria monocytogenes. Unexpectedly, after primary challenge with Listeria, the overall control of Listeria infection was impaired in Flt3-L-treated mice, which had greater bacterial burden and mortality than controls. Similar results were obtained when DC numbers were increased by treatment with polyethylene glycol-conjugated GM-CSF rather than Flt3-L and in mice infected with Mycobacterium tuberculosis. Impaired protection was not due to dysfunctional T cell responses, as Flt3-L-treated mice had a greater frequency and absolute number of Ag-specific CD8+ T cells, which produced IFN-gamma, exhibited cytolytic activity, and transferred protection. The increased Listeria burden in Flt3-L-treated mice was preferentially associated with DCs, which were unable to kill Listeria and more resistant to CTL lysis compared with macrophages in vitro. Although we cannot exclude the possibility that other potential effects, in addition to increased numbers of DCs, are shared by Flt3-L and polyethylene glycol-conjugated GM-CSF and contributed to the increase in susceptibility observed in treated mice, these results support the notion that DC numbers must be properly controlled within physiological limits to optimize host defense to intracellular bacterial pathogens.

Early Adenoviral Gene Expression Mediates Immunosuppression by Transduced Dendritic Cell (DC): Implications for Immunotherapy Using Genetically Modified DC

Long-lasting, high-level gene expression in the absence of a toxic or inflammatory response to viral Ags is necessary for the successful application of genetically modified dendritic cell (DC). We previously demonstrated that efficient transduction of mature DC using DeltaE1DeltaE3 adenoviruses suppressed their stimulatory capacity for T cells. The current study was designed to investigate in more detail the suppressive effect of Ad-DC. We demonstrate that immunosuppression is not mediated by alterations in the T cell phenotype or cytokine profiles released by stimulated T cells. Also DC phenotypes are not affected. However, we demonstrate a cell cycle arrest of the T cell population stimulated by adenovirally transduced DC. Surprisingly, only freshly transduced DC are perturbed in their stimulatory capacity. Experiments using cycloheximide to block early intracellular viral gene expression showed that viral genes expressed in DC are responsible for this transient immunosuppression. In agreement with these findings, high-capacity (gutless) Ad-vectors that differ in viral gene expression from conventional DeltaE1DeltaE3 adenovirus are suitable for an efficient transduction of human DC. DC transduced with gutless Ad-vectors showed a high allostimulatory capacity for CD4(+) and CD8(+) T cells. Thus, the immunosuppressive effect of DeltaE1DeltaE3 Ad-transduced mature DC seems to be the result of early viral gene expression in DC that can be prevented using gutless Ad-vectors for transduction. These results have important implications for the use of genetically modified DC for therapeutic application.

Transcriptional targeting of dendritic cells in gene gun-mediated DNA immunization favors the induction of type 1 immune responses

Cutaneous dendritic cells (DC) are pivotal for the elicitation of antigen-specific immune responses following gene gun-mediated biolistic transfection of the skin. We transcriptionally targeted transgene expression to DC using vectors containing the murine fascin promoter (pFascin) to control antigen production and compared the immune response elicited with conventional DNA immunization using plasmid constructs with the ubiquitously active CMV promoter (pCMV). Biolistic transfection with pFascin initiated a marked type 1 immune response characterized by the occurrence of a large population of IFN-gamma-producing T helper (Th) cells in spleen and draining lymph nodes. Consistently, immunoglobulin production was dominated by IgG2a antibodies. In contrast, the humoral response after repeated administration of pCMV was strongly enhanced and characterized by a type 2-like isotype pattern (IgG1 > IgG2a). Cytokine production analysis in vitro indicated compartmentalization of the immune response, revealing large numbers of IL-4-producing Th cells in the lymph nodes and dominant presence of IFN-gamma-producing Th cells in the spleen. Biolistic transfection with pFascin, like immunization with pCMV, led to potent induction of cytotoxic T cells as was assessed by JAM test. Thus gene gun immunization with plasmids that focus transgene expression and antigen production specifically to DC propagates type 1-biased cellular immune responses.

Interferon-alpha and interleukin-12 gene therapy of cancer: interferon-alpha induces tumor-specific immune responses while interleukin-12 stimulates non-specific killing

Cytokine gene therapy is applied in clinical studies of tumors, and IFN-alpha and IL-12 are widely used for cancer immunotherapy. Using a poorly immunogenic murine colorectal cancer cell line, MC38, we compared antitumor effects of IFN-alpha and IL-12. Transduced MC38 cell lines expressing IFN-alpha or IL-12 (MC38-IFNalpha or MC38-IL12, respectively) were established using retroviral vectors. Transduction of IFN-alpha or IL-12 gene to MC38 cells significantly reduced tumorigenicity in immunocompetent mice. When tumor-free mice initially injected with MC38-IFNalpha or MC38-IL12 cells were reinjected contralaterally with wild-type MC38 cells (MC38-WT) after 35 days, 7 of 12 or 2 of 12 mice rejected MC38-WT cells, respectively. In therapy-model mice with established tumor derived from MC38-WT cells, inoculation of gene-transduced cells significantly suppressed growth of the tumor in MC38-IFNalpha-inoculated groups, but not in the IL-12-inoculated group. Immunohistologic and flow cytometric analyses showed marked infiltration of CD8(+) cells in wild-type tumors of mice inoculated with IFN-alpha-expressing cells. Leukocyte-depletion experiments implicated CD8(+) T cells in tumor rejection induced by IFN-alpha-transduction; both CD8(+) T cells and natural killer cells were implicated in the more modest antitumor effect from IL-12 expression. To investigate induction of tumor-specific immune responses, we stimulated splenocytes from tumor-free mice twice in vitro with genetically modified MC38 cells. In vitro stimulations with MC38-IFNalpha cells induced definite MC38-specific lysis, but not stimulations with MC38-IL-12 cells. Injecting combination of MC38-IFNalpha and MC38-IL-12 cells caused an additive antitumor effect in the therapy model. These data suggested that IFN-alpha induces cytotoxic T lymphocytes and elicits long-lasting tumor-specific immunity, whereas IL-12 seems to stimulate non-specific killing. With additional refinements, combined IFN-alpha and IL-12 gene therapy might warrant clinical trials.

Transcriptional targeting of dendritic cells for gene therapy using the promoter of the cytoskeletal protein fascin

Strong cell-type-specific promoters are basic tools in gene therapy allowing for novel applications and focused strategies by transcriptionally targeting gene expression to selected cells. In immunotherapy, dendritic cells (DC) are of central importance, since they represent the principal inducers of immune responses. Here we describe isolation and use of the promoter of the murine actin-bundling protein fascin to target transcriptionally gene expression to cutaneous DC. Using the reporter gene enhanced green fluorescent protein (EGFP), we demonstrate that the fascin promoter mediates a strong antigen expression that is restricted to mature DC. DNA vaccination with antigen-encoding expression vectors under control of the fascin promoter using a gene gun resulted, consistently, in limited antigen expression by few directly transfected DC. Nevertheless, nearly as many antigen-specific CD8+ T cells directed against the encoded antigens EGFP and beta-galactosidase, respectively, were induced as with expression constructs under control of the ubiquitously expressed CMV promoter. This result impressively underlines the pivotal role of directly transfected DC in DNA vaccination. Immunization using the fascin promoter induced markedly lower levels of antigen-specific antibodies following single or repeated immunization. Thus, our DC-targeted DNA vaccination approach induces qualitatively distinct, predominantly cellular immune responses and provides new opportunities for immunotherapy.

CTLA-4 blockade enhances the therapeutic effect of an attenuated poxvirus vaccine targeting p53 in an established murine tumor model

p53 is overexpressed by half of all cancers, and is an attractive target for a vaccine approach to immunotherapy. p53 overexpression is frequently the result of point mutations, which leaves the majority of the protein in its wild-type form. Therefore, the majority of p53 sequence is wild type, making it a self-protein for which tolerance plays a role in limiting immune responses. To overcome tolerance to p53, we have expressed wild-type murine p53 in the nonpathogenic attenuated poxvirus, modified vaccinia virus Ankara (recombinant modified vaccinia virus Ankara expressing wild-type murine p53 (rMVAp53)). Mice immunized with rMVAp53 vaccine developed vigorous p53-specific CTL responses. rMVAp53 vaccine was evaluated for its ability to inhibit the outgrowth of the syngeneic murine sarcoma Meth A, which overexpresses mutant p53. Mice were inoculated with a lethal dose (5 x 10(5) cells injected s.c.) of Meth A tumor cells and vaccinated by i.p. injection 3 days later with 5 x 10(7) PFU of rMVAp53. The majority of mice remained tumor free and resistant to rechallenge with Meth A tumor cells. We wished to determine whether rMVAp53 immunization could effect the rejection of an established, palpable Meth A tumor. In subsequent experiments, mice were injected with 10(6) Meth A tumor cells, and treated 6 days later with anti-CTLA-4 Ab (9H10) and rMVAp53. The majority of treated mice had complete tumor regression along with lasting tumor immunity. In vivo Ab depletion confirmed that the antitumor effect was primarily CD8 and to a lesser extent CD4 dependent. These experiments demonstrate the potential of a novel cell-free vaccine targeting p53 in malignancy.

Priming of T cells with Ad-transduced DC followed by expansion with peptide-pulsed DC significantly enhances the induction of tumor-specific CD8+ T cells: implications for an efficient vaccination strategy

In recent years, vaccination strategies using antigen-presenting cells (APC) have been under investigation. Antigen delivery using genetic immunization through ex vivo transduction of dendritic cells (DC) is supposed to enhance the induction of antitumor responses in humans by activating a broad range of peptide-specific CD8+ T cells. In this study, we compared the potential of adenoviral (Ad)-transduced versus peptide-pulsed DC to induce melanoma-antigen (Ag)-specific T-cell responses in vitro. Whereas gp100-peptide-pulsed DC induced long-lasting specific CD8+ T-cell responses against single peptides, Ad-transduced DC induced broad and strong, specific immunity against various peptides of the gp100-Ag. Surprisingly, several restimulations led to decreasing gp100-specific and in parallel to increasing anti-adenoviral T-cell responses. Nevertheless, those anti-adenoviral T-cell responses provided an "adjuvant" effect by inducing an early release of high amounts of IL-2/IFN-gamma, therewith enhancing CTL induction in the initiation phase. Based on these data, we suggest a prime/boost vaccination strategy in melanoma patients--combining the use of Ad-DC and peptide-pulsed DC--to obtain efficient and long-term antitumor T-cell responses.

Oral vaccination with recombinant Listeria monocytogenes expressing human papillomavirus type 16 E7 can cause tumor growth in mice to regress

Listeria monocytogenes is a Gram-positive, facultative intracellular bacterium with the ability to present secreted proteins to the major histocompatibility complex class I pathway to stimulate cell-mediated immune response. In our study, we constructed the recombinant L. monocytogenes encoding human papillomavirus type 16 E7 gene (rLM-E7). When orally administered to syngeneic mice, rLM-E7 could induce a cytotoxic T-lymphocyte (CTL) response. Furthermore, in vitro flow cytometric assay and in vivo immune deficiency assays showed that rLM-E7 could prevent and eradicate tumor growth via CD8+-dependent CTLs. Hence, the potency of rLM-E7 as a therapeutic vaccine for cervical cancer is the result of the induction E7-specific cell-mediated immunity by L. monocytogenes. In addition to potency, this vaccine also offers ease of administration and reduced cost of production compared with other vaccines formulated for injection. Thus, L. monocytogenes encoding HPV-16 E7 may be a useful oral vaccine for cervical cancer treatment.

Fluorine-18 labeled mouse bone marrow-derived dendritic cells can be detected in vivo by high resolution projection imaging

Immunization with ex vivo generated dendritic cells has become a focus for many clinical applications. The optimal site of injection and the migration pattern of these cells remain to be elucidated. We therefore developed a novel method for labeling mouse bone marrow-derived dendritic cells (BMDC) with the positron emitting radioisotope F-18 using N-succinimidyl-4-[F-18]fluorobenzoate, which covalently binds to the lysine residues of cell surface proteins. When we determined the stability of F-18 labeled BMDC, we found that at 4 h only 44+/-10% of the initial cell-bound activity was retained at 37 degrees C, whereas considerably more (91+/-3%) was retained at 4 degrees C. Labeled cells did not exhibit any significant alteration in cell viability or phenotype as determined by trypan blue exclusion and FACS analysis 24 h after radiolabeling. Furthermore, F-18-labeled BMDC stimulated allogeneic T cells in a mixed leukocyte reaction as potently as did sham-treated BMDC and migrated towards secondary lymphoid tissue chemokine (SLC) in a chemotaxis assay in vitro with the same efficiency as sham-treated BMDC. Migration of F-18-labeled BMDC was studied after footpad injection by (1) ex vivo counting of dissected tissues using a gamma counter and (2) in vivo by imaging mice with PiPET, a 2-mm resolution positron projection imager. After 4 h, the ratio between measured activity in draining vs. contralateral (D/C) lymph nodes (LN) was 166+/-96 (n=7) in the case of live cell injections, whereas if we injected heat-killed F-18-labeled BMDC or F-18-labeled macrophages the D/C ratios were 17+/-2 (n=2) and 14+/-4 (n=2), respectively. Injection of cell-free activity in the form of F-18-labeled 4-fluorobenzoic acid resulted in a D/C ratio of 7+/-2 (n=3), suggesting that the activity measured in the draining lymph node was associated with migrated F-18-labeled BMDC. When F-18-labeled live cells were injected into the footpad, 0.18+/-0.04% (n=7) of footpad activity was found in the draining LN within 4 h, whereas none was found in the contralateral LN. Quantitative assessment of cell migration by PET projection imaging of mice confirmed the ex-vivo counting results. These studies indicate that PET imaging offers a new approach for in vivo studies of dendritic cell biodistribution and migration.

A modified DNA vaccine to p53 induces protective immunity to challenge with a chemically induced sarcoma cell line

Different vaccine constructs based on DNA vaccines and viral recombinant vaccines expressing mouse p53 were compared for induction of protective immune responses to challenge with a sarcoma cell line that expresses high levels of mutated p53 protein. Viral recombinant vaccines based on E1-deleted adenovirus or vaccinia virus recombinants expressing p53 with wild-type sequences in the mutational hotspot domain and a single mutation in the tetramerization domain (p53(mu338)) failed to induce protection against progression of this tumor cell line. A DNA vaccine expressing a form of p53 carrying the same point mutations as the tumor cell line showed low efficacy that was comparable to that of a DNA vaccine expressing p53(mu338). Efficacy of the DNA vaccine was augmented upon expressing p53(mu338) as a fusion protein linked to a viral leader sequence. Other modifications such as fusion to the signal sequence of the lysosome-associated membrane protein (LAMP) or ubiquitin failed to improve the efficacy of the vaccine to p53. Protection mediated by CD4(+) and CD8(+) T cells was specific for p53.

Adenovirus-transduced dendritic cells stimulate cellular immunity to melanoma via a CD4(+) T cell-dependent mechanism

We previously showed that genetic immunization of C57BL/6 mice with recombinant adenovirus encoding human TRP2 (Ad-hTRP2) was able to circumvent tolerance and induce cellular and humoral immune responses to murine TRP2 associated with protection against metastatic growth of B16 melanoma. In the present study we compared delivery of Ad-hTRP2 with cultured dendritic cells (DC) and direct injections of Ad-hTRP2. We show that application of Ad-hTRP2 with cultured DC enhanced protective immunity to B16 melanoma cells. Most importantly, delivery of recombinant adenovirus with DC alters the character of the immune response resulting in preferential stimulation of strong cellular immunity in the absence of significant humoral immunity to the encoded antigen. Adoptive transfer of lymphocytes from mice immunized with Ad-hTRP2-transduced DC confirmed that cellular components of the immune response were responsible for rejection of B16 melanoma. The protective efficacy of Ad-hTRP2-transduced DC clearly depended on the presence of CD4(+) T helper cells. Furthermore, AD-hTRP2-transduced DC, but not direct injection of Ad-hTRP2, were effective in the presence of neutralizing anti-adenoviral antibodies. These preclinical studies demonstrate the superiority of melanoma vaccines consisting of cultured DC transduced with recombinant adenoviruses encoding melanoma antigens.

A comparison of two types of dendritic cell as adjuvants for the induction of melanoma-specific T-cell responses in humans following intranodal injection

Dendritic cells (DCs) elicit potent anti-tumoral T-cell responses in vitro and in vivo. However, different types of DC have yet to be compared for their capacity to induce anti-tumor responses in vivo at different developmental stages. Herein, we correlated the efficiencies of different types of monocyte-derived DC as vaccines on the resulting anti-tumor immune responses in vivo. Immature and mature DCs were separately pulsed with a peptide derived from tyrosinase, MelanA/MART-1 or MAGE-1 and a recall antigen. Both DC populations were injected every 2 weeks in different lymph nodes of the same patient. Immune responses were monitored before, during and after vaccination. Mature DCs induced increased recall antigen-specific CD4(+) T-cell responses in 7/8 patients, while immature DCs did so in only 3/8. Expansion of peptide-specific IFN-gamma-producing CD8(+) T cells was observed in 5/7 patients vaccinated with mature DCs but in only 1/7 using immature DCs. However, these functional data did not correlate with the tetramer staining. Herein, immature DCs also showed expansion of peptide-specific T cells. In 2/4 patients vaccinated with mature DCs, we observed induction of peptide-specific cytotoxic T cells, as monitored by chromium-release assays, whereas immature DCs failed to induce peptide-specific cytotoxic T cells in the same patients. Instead, FCS-cultured immature DCs induced FCS-specific IgE responses in 1 patient. Our data demonstrate that this novel vaccination protocol is an efficient approach to compare different immunization strategies within the same patient. Thus, our data define FCS-free cultured mature DCs as superior inducers of T-cell responses in melanoma patients.

Gene-based cancer vaccines: an ex vivo approach

The application of gene transfer techniques to immunotherapy has animated the field of gene-based cancer vaccine research. Gene transfer strategies were developed to bring about active immunization against tumor-associated antigens (TAA) through gene transfer technology. A wide variety of viral and nonviral gene transfer methods have been investigated for immunotherapeutic purposes. Ex vivo strategies include gene delivery into tumor cells and into cellular components of the immune system, including cytotoxic T cells and dendritic cells (DC). The nature of the transferred genetic material as well as the gene transfer method has varied widely depending on the application. Several of these approaches have already been translated into clinical gene therapy trials. In this review, we will focus on the rationale and types of ex vivo gene-based immunotherapy of cancer. Critical areas for future development of gene-based cancer vaccines are addressed, with particular emphasis on use of DC and on the danger-tolerance hypothesis. Finally, the use of gene-modified DC for tumor vaccination and its prospects are discussed.

Safety and immunogenicity of ALVAC wild-type human p53 (vCP207) by the intravenous route in rhesus macaques

p53 is over-expressed in approximately 50% of human cancers, and transfer of cytotoxic T lymphocytes (CTL) against wild-type p53 protects mice against p53-over-expressing tumors, suggesting that p53 might be an attractive target for immunotherapy. Immunization of mice with a recombinant canarypox virus, ALVAC, expressing human wild-type p53 (vCP207) prevented growth of p53-over-expressing tumors. Since intravenous administration induced better immune responses in mice than other routes, we have proposed to use this route in cancer patients. However, because this vector has never been administered intravenously to humans, and because of the possibility of inducing auto-immunity to a self-antigen, we felt it was necessary to first evaluate safety in rhesus macaques. We found that three intravenous administrations of vCP207 at proportional doses up to 10x those proposed for humans produced no abnormalities in hematologic or clinical chemistry parameters. Serologic markers of autoimmunity and inflammation were unaffected, despite the >95% amino acid identity between human and rhesus p53. Pathological examination of numerous tissues yielded findings comparable to those in animals given placebo. Some animals showed anti-p53 antibody responses following vaccination, indicating that tolerance could be broken to some extent. However, with the exception of one animal with a possible delayed type hypersensitivity reaction to p53 protein, we did not see evidence for a cell-mediated response. The safety profile in monkeys with ALVAC-p53 provides encouragement for using such live, modified vectors via the intravenous route for human immunotherapy.

Cervical cancer vaccines: emerging concepts and developments

Certain human cancers are linked to infection by oncogenic viruses that are able to cause transformation of the normal host cell into a cancerous cell. Human papillomavirus (HPV) DNA and expression of viral transforming proteins are found in virtually all cervical cancer cells, indicating an important role of this virus in the pathogenesis of the disease. Evidence exists that the immune response to cancer cells can play a major role in determining the outcome of disease. The fact that HPV is a necessary cause for cervical cancer provides a clear opportunity to develop a therapeutic vaccine against the virus to treat patients with cervical cancer at its early and late stages. Development of a prophylactic vaccine for HPV would also reduce the incidence of cervical neoplasias by preventing virus infection. Various candidate HPV vaccines are being developed and tested in animal models and/or in human clinical trials. These HPV vaccines, both preventive and therapeutic, are the subjects of this review.

Immunogenicity of enhanced green fluorescent protein (EGFP) in BALB/c mice: identification of an H2-Kd-restricted CTL epitope

Enhanced green fluorescent protein (EGFP) is a novel marker gene product, which is readily detectable using techniques of fluorescence microscopy, flow cytometry, or macroscopic imaging. In the present studies, we have examined the immunogenicity of EGFP in murine models. A stable transfectant of the transplantable CMS4 sarcoma of BALB/c origin expressing EGFP, CMS4-EGFP-Zeo, was generated. Splenocytes harvested from mice immunized with a recombinant adenovirus expressing EGFP (Ad-EGFP) were restimulated in vitro with CMS4-EGFP-Zeo. Effector lymphocytes displayed strong cytotoxicity against CMS4-EGFP-Zeo, but not against mock-transfected CMS4-Zeo tumor cells. A number of candidate H2-Kd-binding peptides derived from the EGFP protein were chosen according to an epitope prediction program and synthesized. These peptides were tested for their ability to bind to H2-Kd molecules and stimulate IFNgamma-production by splenocytes harvested from Ad-EGFP-immunized mice. Using this methodology, the peptide, HYLSTQSAL (corresponding to EGFP200-208) which strongly binds to H2-Kd molecules, was identified as a naturally occurring epitope of EGFP. These results should facilitate the use of EGFP as a model tumor antigen in BALB/c mice.

Efficient nonviral transfection of dendritic cells and their use for in vivo immunization

Immunization with dendritic cells (DCs) transfected with genes encoding tumor-associated antigens (TAAs) is a highly promising approach to cancer immunotherapy. We have developed a system, using complexes of plasmid DNA expression constructs with the cationic peptide CL22, that transfects human monocyte-derived DCs much more efficiently than alternative nonviral agents. After CL22 transfection, DCs expressing antigens stimulated autologous T cells in vitro and elicited primary immune responses in syngeneic mice, in an antigen-specific manner. Injection of CL22-transfected DCs expressing a TAA, but not DCs pulsed with a TAA-derived peptide, protected mice from lethal challenge with tumor cells in an aggressive model of melanoma. The CL22 system is a fast and efficient alternative to viral vectors for engineering DCs for use in immunotherapy and research.