Cloning and characterization of the genes encoding the murine homologues of the human melanoma antigens MART1 and gp100

Immunosuppressive effects of interleukin-12 coexpression in melanoma antigen gene-modified dendritic cell vaccines

Genetic immunotherapy with tumor antigen gene-modified dendritic cells (DC) generates robust immunity, although antitumor protection is not complete in all models. Previous experience in a model in which C57BL/6 mice immunized with DC transduced with adenoviral vectors expressing MART-1 demonstrated a 20-40% complete protection to a tumor challenge with B16 melanoma cells. Tumors that did develop in immunized mice had slower growth kinetics compared to tumors implanted in naïve mice. In the present study, we wished to determine if the supraphysiological production of the Th1-skewing cytokine interleukin-12 (IL-12) could enhance immune activation and antitumor protection in this model. In a series of experiments immunizing mice with DC cotransduced with MART-1 and IL-12, antitumor protection and antigen-specific splenocyte cytotoxicity and interferon gamma production inversely correlated with the amount of IL-12 produced by DC. This adverse effect of IL-12 could not be explained by a direct cytotoxic effect of natural killer cells directed towards DC, nor the production of nitric oxide leading to down-regulation of the immune response - the two mechanisms previously recognized to explain immune-suppressive effects of IL-12-based vaccine therapy. In conclusion, in this animal model, IL-12 production by gene-modified DC leads to a cytokine-induced dose-dependent inhibition of antigen-specific antitumor protection.

Antigenicity and immunogenicity of Melan-A/MART-1 derived peptides as targets for tumor reactive CTL in human melanoma

Some cancer patients mount spontaneous T- and B-cell responses against their tumor cells. Autologous tumor reactive CD8 cytolytic T lymphocyte (CTL) and CD4 T-cell clones as well as antibodies from these patients have been used for the identification of genes encoding the target antigens. This knowledge opened the way for new approaches to the immunotherapy of cancer. In this review, we describe the characterization of the structure-function properties of the melanocyte/melanoma tumor antigen Melan-A/MART-1, the assessment of the T-cell repertoire available against this antigen in healthy individuals, and the analysis of naturally acquired and/or vaccine-induced CTL responses to this antigen in patients with metastatic melanoma.

Antigens derived from melanocyte differentiation proteins: self-tolerance, autoimmunity, and use for cancer immunotherapy

A large set of peptide antigens presented by class I major histocompatibility complex (MHC) molecules on human and murine melanomas and recognized by CD8+ T cells have been defined. These peptides represent attractive candidates for the development of therapeutic and/or prophylactic approaches to treat this cancer. However, the majority of the peptides that are presented by multiple tumors and recognized by T cells from multiple patients arise from proteins that are also expressed in normal melanocytes. It is expected that immune responses to such peptides will be compromised by self-tolerance or, alternatively, that stimulation of effective immune responses will be accompanied by autoimmune vitiligo. In this review, we describe a preclinical model to evaluate these issues and recent data to suggest that tolerance can be overcome to generate effective antitumor responses. This model also allows the rapid and systematic examination of parameters for the effective use of synthetic peptide vaccines.

The melanocytic protein Melan-A/MART-1 has a subcellular localization distinct from typical melanosomal proteins

To delineate the role of the melanocyte lineage-specific protein Melan-A/MART-1 in melanogenic functions, a set of biochemical and microscopical studies was performed. Biochemical analysis revealed that Melan-A/MART-1 is post-translationally acylated and undergoes a rapid turnover in a pigmented melanoma cell line. Immunofluorescence and immunoelectron microscopy analyses indicated that Melan-A/MART-1 is mainly located in the Golgi area and only partially colocalizes with melanosomal proteins. Quantitative immunoelectron microscopy showed that the highest proportion of the cellular content of Melan-A/MART-1 was found in small vesicles and tubules throughout the cell, whereas the concentration was maximal in the Golgi region, particularly the trans-Golgi network. Substantial labeling was also present on melanosomes, endosomes, ER, nuclear envelope, and plasma membrane. In early endosomes, Melan-A was enriched in areas of the limiting membrane covered by a bi-layered coat, a structural characteristic of melanosomal precursor compartments. Upon melanosome maturation, Melan-A concentration decreased and its predominant localization shifted from the limiting membrane to internal vesicle membranes. In conjunction with its acylation, the high expression levels of Melan-A in the trans-Golgi network, in dispersed vesicles, and on the limiting membrane of premelanosomes indicate that the protein may play a role during the early stage of melanosome biogenesis.

Lymphotactin cotransfection enhances the therapeutic efficacy of dendritic cells genetically modified with melanoma antigen gp100

Lymphotactin (Lptn) is a C chemokine that attracts T cells and NK cells. Dendritic cells (DC) are highly efficient, specialized antigen-presenting cells and antigen-pulsed DC has been regarded as promising vaccines in cancer immunotherapy. The aim of our present study is to improve the therapeutic efficacy of DC-based tumor vaccine by increasing the preferential chemotaxis of DC to T cells. In this study, Lptn and/or melanoma-associated antigen gp100 were transfected into mouse bone marrow-derived DC, which were used as vaccines in B16 melanoma model. Immunization of C57BL/6 mice with DC adenovirally cotransfected with Lptn and gp100 (Lptn/gp100-DC) could enhance the cytotoxicities of CTL and NK cells, increase the production of IL-2 and interferon-gamma significantly, as compared with immunization with gp100-DC, Lptn-DC, LacZ-DC, DC or PBS counterparts. The Lptn/gp100-DC immunized mice exhibited resistance to tumor challenge most effectively. It was found that the tumor mass of mice vaccinated by Lptn/gp100-DC showed obvious necrosis and inflammatory cell infiltration. In vivo depletion analysis demonstrated that CD8(+) T cells are the predominant T cell subset responsible for the antitumor effect of Lptn/gp100-DC and CD4(+) T cells were necessary in the induction phase of tumor rejection, while NK cells were less important although they participated in the antitumor response either in the induction phase or in the effector phase. In the murine model with the pre-established subcutaneous B16 melanoma, immunization with Lptn/gp100-DC inhibited the tumor growth most significantly when compared with other counterparts. These findings provide a potential strategy to improve the efficacy of DC-based tumor vaccines.

ik3-2, a relative to ik3-1/cables, is associated with cdk3, cdk5, and c-abl

A cDNA coding for ik3-2 (designated as ik3-2 from an interactor-2 with cdk3) was cloned by cross-hybridization with ik3-1 and RT-PCR. Analysis of amino acid sequence indicated that ik3-2 has the C-terminal cyclin-box-like region highly homologous to that of ik3-1 (identity in amino acids: 78%). On the other hand, the remainder of ik3-2 gene is not so similar to that of ik3-1. There are several regions other than the C-terminal cyclin-box-like region that are conserved between ik3-1 and ik3-2. In vivo binding assay indicated that like ik3-1, ik3-2 binds to cdk3, cdk5, and c-abl, although ik3-2 binds to cdk3 weakly as compared with ik3-1. The C-terminal cyclin-box-like region of ik3-2 (123 amino acids) is able to be associated with cdk5. Accordingly, ik3-2 is very similar to ik3-1 concerning its molecular interaction with other molecules, suggesting that ik3-2 function in the same biological field as ik3-1. Northern blot analysis indicated that ik3-2 is expressed ubiquitously all over tissues.

Lipopeptide-based melanoma cancer vaccine induced a strong MART-27-35-cytotoxic T lymphocyte response in a preclinal study

Identification of tumor antigens and their optimal antigenic peptides raised hopes for the development of peptide-based immunotherapeutic vaccine strategies for human melanoma, however. Synthetic peptides alone are not immunogenic enough, and adequate formulation is critical for elaboration of peptide vaccines. To improve formulation, we evaluated 2 lipopeptide constructs, both including HLA-A2-restricted MART 27-35-CD8+ T lymphocyte (CTL) epitope covalently linked to universal tetanus toxoid (TT) 830-843 helper T lymphocyte (HTL) epitope, in HLA-A2 transgenic mouse models that mimic human CTL responses in vivo. These 2 constructs only differed in the formulation of their lipid tail. We showed that lipopeptide constructs were strongly recognized, in vitro, by human MART 27-35 cytotoxic T cells derived from tumor-infiltrating lymphocytes. The transgenic Mice immunized with these 2 MART lipopeptide formulations containing covalently linked HTL-CTL epitopes induced strong MART 27-35 cytotoxic T cells. This CTL induction was critically dependent on the presence of the helper T lymphocyte epitope. These results also showed that a single palmitoyl-lysine chain is enough to assure immunogenicity of a given peptide and that the presence of a lipid tail bypass the need for adjuvant. These results support the selection of MART-lipopeptide melanoma vaccine for evaluation in a clinical trial.

CpG are efficient adjuvants for specific CTL induction against tumor antigen-derived peptide

The identification of CTL-defined tumor-associated Ags has allowed the development of new strategies for cancer immunotherapy. To potentiate the CTL responses, peptide-based vaccines require the coadministration of adjuvants. Because oligodeoxynucleotides (ODN) containing CpG motifs are strong immunostimulators, we analyzed the ability of CpG ODN to act as adjuvant of the CTL response against tumor-derived synthetic peptide in the absence or presence of IFA. Mice transgenic for a chimeric MHC class I molecule were immunized with a peptide analog of MART-1/Melan-A(26-35) in the presence of CpG ODN alone or CpG ODN emulsified in IFA. The CTL response was monitored ex vivo by tetramer staining of lymphocytes. In blood, spleen, and lymph nodes, peptide mixed with CpG ODN alone was able to elicit a stronger systemic CTL response as compared with peptide emulsified in IFA. Moreover, CpG ODN in combination with IFA further enhanced the CTL response in terms of the frequency of tetramer+CD8+ T cells ex vivo. The CTL induced in vivo against peptide analog in the presence of CpG ODN are functional, as they were able to recognize and kill melanoma cells in vitro. Overall, these results indicate that CpG ODN by itself is a good candidate adjuvant of CTL response and can also enhance the effect of classical adjuvant.

Assumptions of the tumor 'escape' hypothesis

The reasons why cancer cells are not destroyed by the immune system are likely to be similar, in most cases, to the reasons why normal cells are not destroyed by the immune system. Unfortunately for tumor immunologists, these reasons have not yet been fully elucidated. What is known, however, is that the lack of autoimmune destruction of normal tissue after immune activation is a finely regulated, highly orchestrated sequence of events. Viewed in this light, it is interesting to conceptualize the derangement of the tumor genome not merely as an engine that enables cancer cells to dodge immune recognition. The dysregulation characteristic of the transformed genome is also what makes tumor immunity, a specialized form of autoimmunity, possible.

Xenogeneic DNA immunization in melanoma models for minimal residual disease

INTRODUCTION

DNA immunization with xenogeneic genes encoding homologous antigens protects mice against tumor challenge with syngeneic melanoma in a lung metastasis model. The effect of xenogeneic human TRP-2 (hTRP2) DNA immunization on disease confined to an orthotopic site, the skin, and in a model of minimal residual disease that is relevant to a setting of adjuvant therapy for micrometastatic cancer is reported.

METHODS

Immunization and tumor challenge with B16F10LM3 melanoma were performed in C57BL/6 mice and in mice genetically deficient in MHC class I or II molecules. A melanoma variant of B16 with a predilection for lung metastasis was selected and used to challenge C57BL/6 mice. Tumor challenge in the footpad with the B16 variant was followed by local tumor growth and lung metastasis. The tumor-bearing distal extremities were surgically resected and mice were randomized to receive hTRP2 DNA immunization or no treatment. Approximately 3-5 weeks after surgical resection, lungs were harvested and metastases counted.

RESULTS

Xenogeneic DNA immunization with hTRP2 prevented tumor growth in the skin by a mechanism requiring CD4(+) and CD8(+) T cells but did not inhibit the growth of established tumors. Adjuvant immunization with hTRP2 DNA after resection significantly reduced lung metastases and decreased local recurrence rates after surgical resection.

CONCLUSIONS

Xenogeneic DNA immunization with hTRP2 was effective in protecting mice from intradermal tumor challenge. Immunization prevented local recurrence and the development of metastases in a mouse model of minimal residual disease, supporting a role for DNA immunization against melanosomal antigens as an adjuvant to surgery in high-risk primary melanomas.

Gene delivery by attenuated Salmonella typhimurium: comparing the efficacy of helper versus cytotoxic T cell priming in tumor vaccination

Using the murine B16F1 melanoma, we compared a CTL- versus helper T cell (TH)-directed vaccination approach. Mice were either orally vaccinated with attenuated Salmonella typhimurium (SL) or subcutaneously with dendritic cells (DCs) loaded with gp100 peptides predicted to bind to H2-Kb/H2-Db molecules. SL were transformed with the murine gp100 cDNA (SL-gp100) or with a fusion construct of gp100 and a fragment of invariant chain cDNA (SL-gp100/Ii). Transcription of these genes in vivo has been readily observed in monocytes and DC. Retardation of B16F1 growth was more efficiently achieved by vaccination with SL-gp100 than with DC. Vaccination with SL-gp100/Ii aiming at preferential presentation by MHC II molecules provided some further improvement due to a stronger expansion of TH and CTL. The importance of help was further sustained by a prolongation of the survival time when mice concomitantly received IL2. Notably, prophylactic, compared to therapeutic, vaccination had no additional impact on survival time/rate. This was due to a striking decrease in frequencies of gp100-specific TH, CTL, and cytokine-expressing cells during tumor growth. Thus, the efficacy of vaccination was limited by tumor-induced immunosuppression. Our data demonstrate the oral route of vaccination via Salmonella as a most convenient transfer regimen and confirm the superiority of protocols aiming at preferential activation of TH.

In situ cytokine therapy: redistribution of clonally expanded T cells

Immunity to tumors relies on recirculating antigen-specific T cells. Whilst induction of antigen-specific T cells by immunotherapy has been convincingly proven, direct evidence for recirculation of such cells is still lacking. Here, employing a recently established in situ immunotherapy model for murine melanoma we directly demonstrate the redistribution of clonally expanded T cells. In this model IL-2 is targeted to the tumor microenvironment by means of specific antibody-IL-2 fusion proteins resulting in the expansion of T cells. The therapeutic effect of the fusion protein is not restricted to tumors expressing the targeted antigen, but extends to antigen negative variants of the tumor if present in the same animal. Analysis of the T cell infiltrate by quantitative reverse transcription-PCR revealed the presence of highly expressed TCR BV regions in both tumor variants. TCR clonotype mapping revealed that the high expressions of these regions were caused by clonal expansions and, notably, that these specific clonotypic TCR transcripts were identical in both tumors. Thus, T cell clones activated locally by targeted IL-2 therapy recirculate and mediate eradication of distant tumor sites not subjected to in situ cytokine therapy.

Intracutaneous genetic immunization with autologous melanoma-associated antigen Pmel17/gp100 induces T cell-mediated tumor protection in vivo

Using the differentiation antigen Pmel17/gp100 to genetically immunize C57BL/6 mice (H-2(b)), we and colleagues noticed that only mice that had received the human homolog but not animals injected with the murine counterpart were protected against the growth of syngeneic B16 melanoma cells. The goal of this study was to determine whether the state of nonresponsiveness to the autoantigen Pmel17/gp100 can be broken by immunization with a plasmid DNA construct encoding the autologous form of the molecule. A construct containing the murine form of Pmel17 was administered intradermally to DBA/2 mice (H-2(d)), which were then investigated for the presence of Pmel17/gp100-specific immunity. We show that administration of plasmid DNA coding for the autologous melanoma-associated antigen Pmel17/gp100 protects DBA/2 mice against the growth of Pmel17-positive M3 melanoma cells but not against Pmel17-negative M3 melanoma cells or unrelated P815 mastocytoma cells. Cell depletion experiments demonstrated that this protective effect is mediated by T lymphocytes. The notion that Pmel17/gp100 represents the biologically relevant target in this system was supported by the observations (i) that recipients of Pmel17/gp100 DNA mount an antigen-specific cytotoxic T lymphocyte response and (ii) that M3 tumors growing in mice immunized with autologous Pmel17/gp100 had lost expression of this melanoma-associated antigen whereas M3 melanomas appearing in control-vector-treated animals were still Pmel17/gp100-positive. These results indicate that intracutaneous genetic immunization with autologous melanoma-associated antigen Pmel17/gp100 encoding plasmid DNA can lead to protection against melanoma cells as a result of the induction of a melanoma-associated antigen-specific and protective T-cell-mediated immune response. J Invest Dermatol 115:1082-1087 2000

Recombinant adenovirus-transduced dendritic cell immunization in a murine model of central nervous system tumor

Object

Dendritic cells (DCs) are potent antigen-presenting cells that have been shown to play a critical role in the initiation of host immune responses against tumor antigens. In this study, a recombinant adenovirus vector encoding the melanoma-associated antigen, MART-1, was used to transduce murine DCs, which were then tested for their ability to activate cytotoxic T lymphocytes (CTLs) and induce protective immunity against B16 melanoma tumor cells implanted intracranially.

Methods

Genetic modification of murine bone marrrow–derived DCs to express MART-1 was achieved through the use of an E1-deficient, recombinant adenovirus vector (AdVMART1). Sixty-two C57BL/6 mice were immunized by subcutaneous injection of AdVMART-1-transduced DCs (23 mice), untransduced DCs (17 mice), or sterile saline (22 mice). Using the B16 murine melanoma, which naturally expresses the MART-1 antigen, all the mice were then challenged intracranially with viable, unmodified syngeneic B16 tumor cells 7 days later. Splenocytes obtained from representative animals in each group were harvested for standard cytotoxicity and enzyme-linked immunospot assays. The remaining mice were followed for survival.

Immunization of C57BL/6 mice with DCs transduced with AdVMART1-DC elicited the development of antigen-specific CTL responses. As evidenced by a prolonged survival curve when compared with control-immunized mice harboring intracranial B16 tumors, AdMART1-DC vaccination was able to elicit partial protection against central nervous system (CNS) tumor challenge in vivo. However, this CNS antitumor immunity was weaker than that previously demonstrated against subcutaneous B16 tumors in which the same vaccination strategy was used.

Conclusions

These data suggest that immune responses generated against CNS tumors by DC-based vaccines may be different from those obtained against subcutaneous tumors.

HLA-A2.1/K(b) transgenic murine dendritic cells transduced with an adenovirus encoding human gp100 process the same A2.1-restricted peptide epitopes as human antigen-presenting cells and elicit A2.1-restricted peptide-specific CTL

HLA-A2.1/K(b) transgenic mice (A2.1/K(b) mice) were used to investigate the processing of human gp100 melanoma antigen by murine antigen presenting cells (APC). Bone marrow-derived dendritic cells (DC) from A2.1/K(b) mice were transduced with adenovirus encoding human gp100 (Ad2/hugp100v2). The Ad2/hugp100v2-transduced DC express human gp100, as documented by immunoperoxidase staining. Flow cytometric analysis demonstrates that Ad vector transduction does not downregulate expression of several markers, including MHC class I. We show that Ad2/hugp100v2-transduced DC are recognized by peptide-specific, A2.1-restricted CTL, suggesting correct processing and presentation of the hugp100 antigen by murine DC. To assess dominance among the various A2.1-restricted epitopes encoded by hugp100, A2.1/K(b) transgenic mice were immunized with Ad2/hugp100v2-transduced DC. Resulting effector cytotoxic T lymphocytes (CTL) were assayed for peptide specificity using a panel of six synthetic peptides known to encode A2.1-restricted epitopes of human gp100 (denoted G154, G177, G209, G280, G457, G476). CTL obtained from Ad2/hugp100v2-transduced DC immunized A2.1/K(b) mouse lysed target cells presenting five of the six epitopes, supporting the observation that murine cells correctly process the hugp100 antigen. The immunogenicity of individual gp100 epitopes correlates with their binding affinity to A2.1. CTL generated from A2.1/K(b) mice immunized with Ad2/hugp100v2-transduced DC also specifically recognize A2.1(+)/gp100(+) human melanoma cells. These data suggest that murine APC process and present the same set of HLA-restricted peptides, similar to human APC. HLA transgenic mice serve as a useful model system to study class I-restricted epitopes of human tumor-associated antigens.

Immunization with DNA coding for gp100 results in CD4 T-cell independent antitumor immunity

BACKGROUND

Xenogeneic DNA immunization can exploit small differences in expressed protein sequence resulting in immune recognition of self-molecules. We hypothesized that immunizing mice with xenogeneic DNA coding for the human melanosomal membrane glycoprotein gp100 would overcome immune ignorance or tolerance and result in tumor immunity. We also investigated the immunologic mechanisms of the antitumor immunity.

METHODS

C57BL/6 mice were immunized with DNA coding for human gp100, mouse gp100, or control vector by gene gun. After immunization, mice were challenged with a syngeneic melanoma expressing gp100, and tumor growth was analyzed. Mice deficient in major histocompatibility complex class I or class II molecules were similarly studied to assess the immunologic mechanism of the tumor protection.

RESULTS

There was significant tumor protection after vaccination with xenogeneic human gp100 DNA. Class I, but not class II, major histocompatibility complex molecules were required for tumor immunity. In addition, mice immunized with human gp100 demonstrated autoimmunity manifested as coat color depigmentation.

CONCLUSIONS

Immunization with xenogeneic DNA coding for the melanosomal glycoprotein gp100 results in tumor protection and autoimmune depigmentation. These results show that xenogeneic DNA vaccines can lead to cancer immunity without CD4(+) T-cell help with potential implications for rational vaccine design.

Development of a polynucleotide vaccine from melanoma antigen recognized by T cells-1 and recombinant protein from melanoma antigen recognized by T cells-1 for melanoma vaccine clinical trials

MART-1, a melanoma antigen recognized by T cells-1, is a melanocyte lineage-differentiation antigen expressed only in melanocytes and melanoma cells. This protein is recognized by many T-lymphocyte lines that are human leukocyte antigen (HLA)-A2 restricted and melanoma reactive. These observations have culminated in an array of clinical trials of MART-1 immunization using recombinant viruses or MART-1 immunodominant peptides. Polynucleotide immunization is a promising alternative to recombinant viral vaccines that allows delivery of the full-length cDNA encoding all potential peptide epitopes in a vector that is uncompromised by anti-viral immunity. In preparation for a phase I clinical trial of MART-1 polynucleotide immunization in patients with resected melanoma who were at significant risk for recurrence, the authors constructed a plasmid DNA encoding the MART-1 cDNA under transcriptional regulatory control of the cytomegalovirus immediate early promoter-enhancer and partially deleted intron A. This plasmid directs high-level MART-1 expression in transduced myoblasts and maturing myocytes diffusely throughout the cytoplasm. Immunization of mice with this construct by intramuscular injection elicited MART-1-specific immune responses in all animals. Previous trials of MART-1 immunization have been unable to examine the humoral immune response to MART-1 because of a lack of sufficient, highly purified protein. We have produced and purified Escherichia coli recombinant MART-1 protein using a glutathione-S-transferase fusion protein expression system. Protein staining of a sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a band of MART-1 protein at approximately 20 kD; and Western immunoblotting with an anti-MART-1 monoclonal antibody confirmed a doublet at approximately 20 kD. These findings are consistent with previous reports using different expression systems for recombinant MART-1. This protein preparation functioned well in enzyme-linked immunosorbent assays (ELISAs) to detect anti-MART-1 antibody responses in a mouse model; and a panel of healthy donor human sera showed minimal binding to ELISA plates coated with the protein, supporting its utility in monitoring human anti-MART-1 antibody responses. The glutathione-S-transferase fusion method yielded approximately 200 micrograms MART-1 per 2-L bacterial culture, enough to coat 100 ELISA plates.

Induction of potent antitumor CTL responses by recombinant vaccinia encoding a melan-A peptide analogue

There is considerable interest in the development of vaccination strategies that would elicit strong tumor-specific CTL responses in cancer patients. One strategy consists of using recombinant viruses encoding amino acid sequences corresponding to natural CTL-defined peptide from tumor Ags as immunogens. However, studies with synthetic tumor antigenic peptides have demonstrated that introduction of single amino acid substitutions may dramatically increase their immunogenicity. In this study we have used a well-defined human melanoma tumor Ag system to test the possibility of translating the immunological potency of synthetic tumor antigenic peptide analogues into recombinant vaccinia viruses carrying constructs with the appropriate nucleotide substitutions. Our results indicate that the use of a mutated minigene construct directing the expression of a modified melanoma tumor Ag leads to improved Ag recognition and, more importantly, to enhanced immunogenicity. Thus, recombinant vaccinia viruses containing mutated minigene sequences may lead to new strategies for the induction of strong tumor-specific CTL responses in cancer patients.

Generation of T-cell immunity to a murine melanoma using MART-1-engineered dendritic cells

The murine melanoma B16 expresses the murine counterpart of the human MART-1/Melan-A (MART-1) antigen, sharing a 68.6% amino acid sequence identity. In this study, mice were vaccinated with bone marrow-derived murine dendritic cells genetically modified with a replication-incompetent adenoviral vector to express the human MART-1 gene (AdVMART1). This treatment generated a protective response to a lethal tumor challenge of unmodified murine B16 melanoma cells. The response was mediated by major histocompatibility complex class I-restricted cytotoxic T lymphocytes specific for MART-1 antigen, which produced high levels of interferon-gamma when reexposed to MART-1 in vitro and lysed targets in a calcium-dependent mechanism suggestive of perforin/granzyme B lysis. MART-1 was presented by the dendritic cells used for vaccination and not by epitopes cross-presented by host antigen-presenting cells. In conclusion, dendritic cells genetically modified to express the human MART-1 antigen generate potent murine MART-1-specific protective responses to B16 melanoma.

Enhanced immune response to the melanoma antigen gp100 using recombinant adenovirus-transduced dendritic cells

Glycoprotein 100 (gp100) is one of a series of well-characterized human melanoma-associated antigens expressed by most melanoma cells. Immunization of C57BL/6 mice with an adenovirus (Ad) vector encoding human gp100 (Adhgp100) has been shown to induce limited protective immunity against challenge with murine melanoma B16 cells. In the current study we determined whether gp100-specific immunity can be enhanced using bone-marrow-derived dendritic cells (DCs) transduced with Adhgp100 ex vivo. Subcutaneous injection of Adhgp100-infected DCs resulted in potent T-cell-mediated protective immunity and a greater than 80% reduction of established tumors when administered to B16 tumor-bearing hosts. Compared to direct injection of Adhgp100 vector alone, immunization with Adhgp100-infected DCs induced markedly greater antitumor activity. In vitro CTL analysis demonstrated that DC-Adhgp100 immunization activated both CD4(+) and CD8(+) CTLs, while no lytic activity was generated by vaccination with Adhgp100 alone. In vivo depletion of CD4(+) T cells, but not CD8(+) T cells, completely abrogated CTL activity, suggesting that Adhgp100-transduced DCs result in activation of both CD4(+) and CD8(+) CTLs via a CD4(+)-dependent mechanism. We speculate that this improved efficacy of Adhgp100-transduced DCs compared to direct immunization with Adhgp100 may be the result of direct DC-mediated CD4(+) T cell activation. These results emphasize the importance of CD4(+) T cells in the development of therapeutic antigen-specific cancer vaccines.

DNA vaccines for cancer therapy

Vaccination with a tumour antigen-expressing plasmid DNA (pDNA) is a novel approach to human cancer immunotherapy. Initial results in preclinical rodent tumour models are promising, revealing that pDNA cancer vaccines can elicit both humoral, as well as cell-mediated immunity and, in some cases, protect against tumour growth. Compared to peptide, viral or dendritic cell vaccines, the delivery of tumour antigens using pDNA has the advantages of ease of manufacture, lack of toxicity and broad applicability to large populations. With advances in modern genomics strategies and the identification of an increasing number of tumour antigen genes, pDNA-based cancer vaccines may be used in the future to treat a wide variety of human cancers.

Protective immunization against melanoma by gp100 DNA-HVJ-liposome vaccine

DNA-based vaccine immunization effectively induces both humoral and cell-mediated immunity to antigens and can confer protection against numerous infectious diseases as well as some cancers. Human and mouse melanomas consistently express the tumor-associated antigen interacted with the melanogenesis pathway. Gp100 is immunogenic and has been shown to induce both antibody and cytotoxic T cell (CTL) responses in humans. To explore the potential use of DNA immunization to induce melanoma-specific immune responses, we assessed HVJ-AVE liposome incorporated with plasmid DNA encoding human gp100. The gp100 DNA vaccine was used in a mouse melanoma model to assess immunity against the B16 melanoma of C57BL/6 mice. Intramuscular injection of the DNA-HVJ-AVE liposomes induced both anti-gp100 antibody and CTL responses. Gp100 DNA-HVJ-AVE liposome immunization significantly delayed tumor development in mice challenged with B16 melanoma cells. Mice immunized with gp100 DNA-HVJ-AVE liposomes survived longer compared with control mice immunized with HVJ-AVE liposome alone. These results indicate that immunization with human gp100 DNA by HVJ-AVE liposomes can induce protective immunity against melanoma in this pre-clinical mouse model. This strategy may provide an effective approach for vaccine therapy with tumor-associated antigens against human melanoma.

Induction of Antitumor Immunity with Dendritic Cells Transduced with Adenovirus Vector-Encoding Endogenous Tumor-Associated Antigens

Dendritic cells (DCs) are professional Ag-presenting cells that are being considered as potential immunotherapeutic agents to promote host immune responses against tumor Ags. In this study, recombinant adenovirus (Ad) vectors encoding melanoma-associated Ags were used to transduce murine DCs, which were then tested for their ability to activate CTL and induce protective immunity against B16 melanoma tumor cells. Immunization of C57BL/6 mice with DCs transduced with Ad vector encoding the hugp100 melanoma Ag (Ad2/hugp100) elicited the development of gp100-specific CTLs capable of lysing syngeneic fibroblasts transduced with Ad2/hugp100, as well as B16 cells expressing endogenous murine gp100. The induction of gp100-specific CTLs was associated with long term protection against lethal s.c. challenge with B16 cells. It was also possible to induce effective immunity against a murine melanoma self Ag, tyrosinase-related protein-2, using DCs transduced with Ad vector encoding the Ag. The level of antitumor protection achieved was dependent on the dose of DCs and required CD4+ T cell activity. Importantly, immunization with Ad vector-transduced DCs was not impaired in mice that had been preimmunized against Ad to mimic the immune status of the general human population. Finally, DC-based immunization also afforded partial protection against established B16 tumor cells, and the inhibition of tumor growth was improved by simultaneous immunization against two melanoma-associated Ags as opposed to either one alone. Taken together, these results support the concept of cancer immunotherapy using DCs transduced with Ad vectors encoding tumor-associated Ags.

Recombinant virus vaccination against "self" antigens using anchor-fixed immunogens

To study the induction of anti-"self" CD8+ T-cell reactivity against the tumor antigen gp100, we used a mouse transgenic for a chimeric HLA-A*0201/H-2 Kb molecule (A2/Kb). We immunized the mice with a recombinant vaccinia virus encoding a form of gp100 that had been modified at position 210 (from a threonine to a methionine) to increase epitope binding to the restricting class I molecule. Immunogens containing the "anchor-fixed" modification elicited anti-self CD8+ T cells specific for the wild-type gp100(209-217) peptide pulsed onto target cells. More important, these cells specifically recognized the naturally presented epitope on the surface of an A2/Kb-expressing murine melanoma, B16. These data indicate that anchor-fixing epitopes could enhance the function of recombinant virus-based immunogens.

Vaccination with a recombinant vaccinia virus encoding a "self" antigen induces autoimmune vitiligo and tumor cell destruction in mice: requirement for CD4(+) T lymphocytes

Many human and mouse tumor antigens are normal, nonmutated tissue differentiation antigens. Consequently, immunization with these "self" antigens could induce autoimmunity. When we tried to induce immune responses to five mouse melanocyte differentiation antigens, gp100, MART-1, tyrosinase, and tyrosinase-related proteins (TRP) 1 and TRP-2, we observed striking depigmentation and melanocyte destruction only in the skin of mice inoculated with a vaccinia virus encoding mouse TRP-1. These mice rejected a lethal challenge of B16 melanoma, indicating the immune response against TRP-1 could destroy both normal and malignant melanocytes. Cytotoxic T lymphocytes specific for TRP-1 could not be detected in depigmented mice, but high titers of IgG anti-TRP-1 antibodies were present. Experiments with knockout mice revealed an absolute dependence on major histocompatibility complex class II, but not major histocompatibility complex class I, for the induction of both vitiligo and tumor protection. Together, these results suggest that the deliberate induction of self-reactivity using a recombinant viral vector can lead to tumor destruction, and that in this model, CD4(+) T lymphocytes are an integral part of this process. Vaccine strategies targeting tissue differentiation antigens may be valuable in cancers arising from nonessential cells and organs such as melanocytes, prostate, testis, breast, and ovary.

Assessment of Immunogenicity of Human Melan-A Peptide Analogues in HLA-A*0201/Kb Transgenic Mice

Previous studies have shown that substitution of single amino acid residues in human Melan-A immunodominant peptides Melan-A27–35 and Melan-A26–35 greatly improved their binding and the stability of peptide/HLA-A*0201 complexes. In particular, one Melan-A peptide analogue was more efficient in the generation of Melan-A peptide-specific and melanoma-reactive CTL than its parental peptide in vitro from human PBL. In this study, we analyzed the in vivo immunogenicity of Melan-A natural peptides and their analogues in HLA-A*0201/Kb transgenic mice. We found that two human Melan-A natural peptides, Melan-A26–35 and Melan-A27–35, were relatively weak immunogens, whereas several Melan-A peptide analogues were potent immunogens for in vivo CTL priming. In addition, induced Melan-A peptide-specific mouse CTL cross-recognized natural Melan-A peptides and their analogues. More interestingly, these mouse CTL were also able to lyse human melanoma cell lines in vitro in a HLA-A*0201-restricted, Melan-A-specific manner. Our results indicate that the HLA-A*0201/Kb transgenic mouse is a useful animal model to perform preclinical testing of potential cancer vaccines, and that Melan-A peptide analogues are attractive candidates for melanoma immunotherapy.

The use of combination vaccinia vaccines and dual-gene vaccinia vaccines to enhance antigen-specific T-cell immunity via T-cell costimulation

Several recombinant vaccinia viruses are currently being evaluated to induce antigen-specific immunity to a variety of infectious disease agents and tumor associated antigens. T-cell costimulation is extremely important in enhancing T-cell responses, and recombinant vaccines have now been shown to be effective vectors to express a range of these molecules. Both combination vaccines (an admixture of a recombinant vaccinia virus expressing a specific target antigen and a recombinant vaccinia virus expressing a costimulatory molecule) and dual-gene vaccines expressing both transgenes on the same vector have been shown capable of effectively enhancing antigen-specific responses via T-cell costimulation. In this report, we compare for the first time the use of both types of approaches to enhance antigen-specific T-cell responses, and we demonstrate the importance of route of vaccine administration and vaccine dose in attaining optimal T-cell responses. These studies should have direct bearing on the design of vaccine clinical trials for infectious agents and/or tumor associated antigens, in which T-cell costimulatory molecules will be employed to enhance antigen-specific T-cell responses via the use of either combination or dual-gene vaccinia vaccines.

Advances in cancer vaccine development

Traditionally, cancer vaccines have used whole tumour cells administered in adjuvant or infected with viruses to increase the immunogenicity of the cells. With the identification of tumour-associated and tumour-specific antigens (TAA, TSA), antigen and epitope-specific vaccines have been designed. Compared to tumour cell vaccines, antigen and epitope vaccines are more specific and easier to produce in large quantities but may display lower immunogenicity and lead to the in vivo selection of antigen or epitope-negative escape tumour variant cells. The optimal vaccine will elicit both humoral and cellular immunity in the patients as both parameters have been positively correlated with the induction of beneficial clinical responses. The choice of adjuvant, costimulation and delivery mode greatly determines the outcome of vaccinations and may favour the induction of T-cell responses of T helper (Th)1, Th2, or both Th1 and Th2 types. Animal models of TAA vaccines must take into account the normal tissue expression of TAA, which may induce immunological tolerance to TAA. With the identification of homologues of human TAA in animals, novel experimental models of cancer vaccines which mimic the condition in patients are now available. Several vaccines comprising tumour cells, TAA or anti-idiotypic antibodies mimicking TAA have recently entered phase III of clinical evaluation.

Developing recombinant and synthetic vaccines for the treatment of melanoma

To develop new vaccines for the treatment of patients with cancer, target antigens presented on tumor cell surfaces have been cloned. Many of these antigens are non-mutated differentiation antigens and are expressed by virtually all melanomas, making them attractive components for a widely efficacious melanoma vaccine. These antigens are also expressed by melanocytes, however, and are likely to be subject to immune tolerance. A central challenge for tumor immunologists has thus been the breaking of tolerance to cancer antigens. We review recent clinical trials using experimental cancer vaccines, including recent evidence that therapeutic vaccines can induce objective responses in patients with metastatic malignant melanoma. We focus on the foundations of these approaches in new experimental animal models designed to test novel vaccines and report on what these new models predict for the future development of therapeutic vaccines for cancer.

Activation of preexisting T cell clones by targeted interleukin 2 therapy

The induction of an immunological antitumor response capable of eradicating metastatic tumors is the ultimate goal of immunotherapy. We have recently shown that this can be achieved by interleukin 2 (IL-2) therapy directed to the tumor microenvironment by a recombinant antibody-IL-2 fusion protein. It is not known, however, whether this curative treatment is associated with a predominance of T cells carrying specific T cell receptor variable beta regions (TCRBV) or the presence of clonally expanded T cells. To address this question, we have used a quantitative reverse transcriptase-coupled PCR method to analyze the TCRBV region repertoire in tumor-infiltrating lymphocytes of treated and untreated animals. As controls the TCRBV region repertoire was analyzed in blood and skin from disease-free animals. The results indicate an overexpression of TCRBV5 in the tumors of all treated mice and an additional overexpression of individual regions in each tumor. Direct sequencing of these TCRBV regions did not reveal any evidence of clonal expansions. However, since clonal expansions could exist as subpopulations in highly expressed regions, not detectable by direct sequencing, a denaturing gradient gel electrophoresis assay was used for clonal analysis of TCRBV PCR products. Denaturing gradient gel electrophoresis analysis of selected TCRBV regions revealed the presence of clonotypic T cells in tumors from both treated and untreated animals. These data indicate that targeted IL-2 therapy in this model does not induce clonal T cell responses de novo, rather it acts as an activator for an already existing population of clonotypic T cells.

gp100/pmel 17 is a murine tumor rejection antigen: induction of "self"-reactive, tumoricidal T cells using high-affinity, altered peptide ligand

Many tumor-associated antigens are nonmutated, poorly immunogenic tissue differentiation antigens. Their weak immunogenicity may be due to "self"-tolerance. To induce autoreactive T cells, we studied immune responses to gp100/pmel 17, an antigen naturally expressed by both normal melanocytes and melanoma cells. Although a recombinant vaccinia virus (rVV) encoding the mouse homologue of gp100 was nonimmunogenic, immunization of normal C57BL/6 mice with the rVV encoding the human gp100 elicited a specific CD8(+) T cell response. These lymphocytes were cross-reactive with mgp100 in vitro and treated established B16 melanoma upon adoptive transfer. To understand the mechanism of the greater immunogenicity of the human version of gp100, we characterized a 9-amino acid (AA) epitope, restricted by H-2Db, that was recognized by the T cells. The ability to induce specific T cells with human but not mouse gp100 resulted from differences within the major histocompatibility complex (MHC) class I-restricted epitope and not from differences elsewhere in the molecule, as was evidenced by experiments in which mice were immunized with rVV containing minigenes encoding these epitopes. Although the human (hgp10025-33) and mouse (mgp10025-33) epitopes were homologous, differences in the three NH2-terminal AAs resulted in a 2-log increase in the ability of the human peptide to stabilize "empty" Db on RMA-S cells and a 3-log increase in its ability to trigger interferon gamma release by T cells. Thus, the fortuitous existence of a peptide homologue with significantly greater avidity for MHC class I resulted in the generation of self-reactive T cells. High-affinity, altered peptide ligands might be useful in the rational design of recombinant and synthetic vaccines that target tissue differentiation antigens expressed by tumors.

Generation of polyclonal rabbit antisera to mouse melanoma associated antigens using gene gun immunization

Lymphocytes from patients with melanoma have been used to clone melanoma associated antigens which are, for the most part, nonmutated melanocyte tissue differentiation antigens. To establish a mouse model for the use of these 'self' antigens as targets for anti-tumor immune responses, we have employed the mouse homologues of the human melanoma antigens Tyrosinase, Tyrosinase Related Protein-1 (TRP-1), gp100, and MART-1. We sought to generate antisera against these proteins for use in the construction of experimental recombinant and synthetic anti-cancer vaccines, and for use in biologic studies. Using genes cloned from the B16 mouse melanoma or from murine melanocytes, we immunized rabbits with plasmid DNAs coated onto microscopic gold beads that were then delivered using a hand-held, helium-driven 'gene gun'. This strategy enabled us to generate polyclonal rabbit sera containing antibodies that specifically recognized each antigen, as measured by immunostaining of vaccinia virus infected cells. The sera that we generated specifically for TRP-1, gp100, and MART-1 recognized extracts of the spontaneous murine melanoma, B16. The identities of the recognized proteins was confirmed by Western blot analysis. The titers and specificities of these antisera were determined using ELISA. Interestingly, serum samples generated against murine MART-1 and gp100 developed antibodies that were cross-reactive with the corresponding human homologues. Recognition of human gp100 and murine Tyrosinase appeared to be dependent upon conformational epitopes since specificity was lost upon denaturation of the antigens. These antisera may be useful in the detection, purification and characterization of the mouse homologues of recently cloned human tumor associated antigens and may enable the establishment of an animal model of the immune consequences of vaccination against 'self antigens.

Recombinant adenovirus encoding gp100 modulates experimental melanin-protein induced uveitis (EMIU)

Experimental melanin-protein induced uveitis (EMIU) is a T-cell mediated autoimmune uveitis induced by immunization with bovine uveal melanin protein. Gp100, a melanocyte lineage-specific protein, is identified as a human melanoma antigen. A recombinant adenovirus construct encoding gp100 (Ad2CMV-gp100) has been used as a vaccine for cancer therapy. This study examines the effect of Ad2CMV-gp100 on EMIU. To induce EMIU, rats were injected intraperitoneally on day 7 before immunization with ad2CMV-gp100, control adenovirus encoding LacZ (Ad2CMV-LacZ), or no virus. On day 21 after immunization, the right eye was processed for histology and the left eye was analysed for cytokines by quantitative reverse transcriptase-polymerase chain reaction. Western blot analysis showed that uveal melanin-protein contains gp100. In three independent experiments, ocular inflammation was significantly suppressed, and expression of ocular IL-12p40 mRNA was much lower in the rats which received Ad2CMV-gp100 before immunization than in those that received Ad2CMV-LacZ or no virus. No abnormalities developed in rats which received Ad2CMV-gp100 or Ad2CMV-LacZ alone. Therefore, Ad2CMV-gp100 injection prevents the development of EMIU, at least in part, through cytokine regulation.

The new vaccines: building viruses that elicit antitumor immunity

Whereas cancer cells are poor immunogens, some viruses are capable of eliciting powerful and lifelong immunity. Recombinant viruses and plasmid DNA encoding tumor-associated antigens can elicit powerful and specific immune responses that can be enhanced by the use of cytokines and costimulatory molecules. These immune responses have destroyed growing tumor cells in experimental animal models. For the first time, immunotherapeutic strategies that employ recombinant viruses are being tested in clinical trials with cancer patients.