Genetic immunization with a melanocytic self-antigen linked to foreign helper sequences breaks tolerance and induces autoimmunity and tumor immunity

Quantification of B16 melanoma cells in lungs using triplex Q-PCR--a new approach to evaluate melanoma cell metastasis and tumor control

Skin cancer is the most common type of all cancers. However, it comprises several different types of cancers, one of which is malignant melanoma. Even though melanomas only make up about 5% of skin cancers, they are responsible for the majority of skin cancer deaths due to the poor chance of survival once the tumor has metastasized. In the present study, we have developed a new assay for quantitative analysis of B16 melanoma metastasis in the lungs. We have used a triplex Q-PCR to determine the expression of the melanoma genes GP100/Pmel and tyrosinase-related protein 2 (TRP-2), and found that B16.F10gp cells were detectable in the lungs as early as 2 hours after intravenous challenge with ≥10⁴ tumor cells. When investigating the gene expression as a function of time, we observed a gradual decrease from 2–24 hours post tumor challenge followed by an increase of approximately 2 log₁₀ on day 11. The early decrease was accelerated in the presence of activated NK cells. To further evaluate our assay, we also investigated the level of metastasis in the context of vaccination with replication defective adenoviral vectors, Ad-Ii-GP and Ad-GP, previously found to significantly delay the outgrowth of subcutaneous melanomas. Results obtained using Q-PCR were compared to conventional counting of metastatic foci under a dissection microscope. A marked reduction in gene expression was observed in the lungs after vaccination with both vectors; however, Ad-Ii-GP showed the highest protection, and matching results were obtained by enumeration of visible tumor nodules on the lung surfaces. Finally, we could show that inhibition of tumor metastasis required antigen-specific CD8 T cells and IFNγ, but not perforin. In conclusion, the presented results validate triplex Q-PCR as a fast, objective, and quantitative method for analysis of melanoma metastasis in the lungs.

T cell immunotherapy for melanoma from bedside to bench to barn and back: how conceptual advances in experimental mouse models can be translated into clinical benefit for patients

A solid scientific basis now supports the concept that cytotoxic T lymphocytes can specifically recognize and destroy melanoma cells. Over the last decades, clinicians and basic scientists have joined forces to advance our concepts of melanoma immunobiology. This has catalyzed the rational development of therapeutic approaches to enforce melanoma-specific T cell responses. Preclinical studies in experimental mouse models paved the way for their successful translation into clinical benefit for patients with metastatic melanoma. A more thorough understanding of how melanomas develop resistance to T cell immunotherapy is necessary to extend this success. This requires a continued interdisciplinary effort of melanoma biologists and immunologists that closely connects clinical observations with in vitro investigations and appropriate in vivo mouse models: From bedside to bench to barn and back.

Biolistic DNA vaccination against melanoma

We describe here the use of particle-mediated gene transfer for the induction of immune responses against melanoma antigens in murine tumor models using the melanocyte differentiation antigen tyrosinase-related protein 2 (TRP2) as an antigen in a murine B16 melanoma model. We have utilized marker genes such as β-galactosidase (βgal) and EGFP, which can be readily detected, as control antigens to establish the gene delivery and to detect antigen-specific humoral and cellular immune responses. After biolistic DNA vaccination with plasmids encoding the TRP2 gene we observed the induction of TRP2-specific T-cells and antibodies associated with vitiligo-like fur depigmentation and tumor immunity against B16 melanoma cells. Here we describe the preparation of cartridges with DNA-coated gold beads and the in vivo gene transfer into skin using the Helios Gene Gun system. We also describe protocols for the measurement of humoral and cellular immune responses against the melanocyte differentiation antigen TRP2. These protocols can subsequently be adapted to other antigens.

T-Cell Mediated Immune Responses Induced in ret Transgenic Mouse Model of Malignant Melanoma

Poor response of human malignant melanoma to currently available treatments requires a development of innovative therapeutic strategies. Their evaluation should be based on animal models that resemble human melanoma with respect to genetics, histopathology and clinical features. Here we used a transgenic mouse model of spontaneous skin melanoma, in which the ret transgene is expressed in melanocytes under the control of metallothionein-I promoter. After a short latency, around 25% mice develop macroscopic skin melanoma metastasizing to lymph nodes, bone marrow, lungs and brain, whereas other transgenic mice showed only metastatic lesions without visible skin tumors. We found that tumor lesions expressed melanoma associated antigens (MAA) tyrosinase, tyrosinase related protein (TRP)-1, TRP-2 and gp100, which could be applied as targets for the immunotherapy. Upon peptide vaccination, ret transgenic mice without macroscopic melanomas were able to generate T cell responses not only against a strong model antigen ovalbumin but also against typical MAA TRP-2. Although mice bearing macroscopic primary tumors could also display an antigen-specific T cell reactivity, it was significantly down-regulated as compared to tumor-free transgenic mice or non-transgenic littermates. We suggest that ret transgenic mice could be used as a pre-clinical model for the evaluation of novel strategies of melanoma immunotherapy.

Delivery route, MyD88 signaling and cross-priming events determine the anti-tumor efficacy of an adenovirus based melanoma vaccine

Adenovirus (Ad)-based vaccines are considered for cancer immunotherapy, yet, detailed knowledge on their mechanism of action and optimal delivery route for anti-tumor efficacy is lacking. Here, we compared the anti-tumor efficacy of an Ad-based melanoma vaccine after intradermal, intravenous, intranasal or intraperitoneal delivery in the B16F10 melanoma model. The intradermal route induced superior systemic anti-melanoma immunity which was MyD88 signaling-dependent. Predominant transduction of non-professional antigen-presenting cells at the dermal vaccination sites and draining lymph nodes, suggested a role for cross-presentation, which was confirmed in vitro. We conclude that the dermis provides an optimal route of entry for Ad-based vaccines for high-efficacy systemic anti-tumor immunization and that this immunization likely involves cross-priming events in the draining lymph nodes.

DNA vaccination with T-cell epitopes encoded within Ab molecules induces high-avidity anti-tumor CD8+ T cells

Stimulation of high-avidity CTL responses is essential for effective anti-tumor and anti-viral vaccines. In this study we have demonstrated that a DNA vaccine incorporating CTL epitopes within an Ab molecule results in high-avidity T-cell responses to both foreign and self epitopes. The avidity and frequency was superior to peptide, peptide-pulsed DC vaccines or a DNA vaccine incorporating the epitope within the native Ag. The DNA Ab vaccine was superior to an identical protein vaccine that can only cross-present, indicating a role for direct presentation by the DNA vaccine. However, the avidity of CTL responses was significantly reduced in Fc receptor gamma knockout mice or if the Fc region was removed suggesting that cross presentation of Ag via Fc receptor was also important in the induction of high-avidity CTL. These results suggest that generation of high-avidity CTL responses by the DNA vaccine is related to its ability to both directly present and cross-present the epitope. High-avidity responses were capable of efficient anti-tumor activity in vitro and in vivo. This study demonstrates a vaccine strategy to generate high-avidity CTL responses that can be used in anti-tumor and anti-viral vaccine settings.

Recombinant vesicular stomatitis virus transduction of dendritic cells enhances their ability to prime innate and adaptive antitumor immunity

Dendritic cell (DC)-based vaccines are a promising strategy for tumor immunotherapy due to their ability to activate both antigen-specific T-cell immunity and innate immune effector components, including natural killer (NK) cells. However, the optimal mode of antigen delivery and DC activation remains to be determined. Using M protein mutant vesicular stomatitis virus (DeltaM51-VSV) as a gene-delivery vector, we demonstrate that a high level of transgene expression could be achieved in approximately 70% of DCs without affecting cell viability. Furthermore, DeltaM51-VSV infection activated DCs to produce proinflammatory cytokines (interleukin-12, tumor necrosis factor-alpha, and interferon (IFN)alpha/beta), and to display a mature phenotype (CD40(high)CD86(high) major histocompatibility complex (MHC II)(high)). When delivered to mice bearing 10-day-old lung metastatic tumors, DCs infected with DeltaM51-VSV encoding a tumor-associated antigen mediated significant control of tumor growth by engaging both NK and CD8(+) T cells. Importantly, depletion of NK cells completely abrogated tumor destruction, indicating that NK cells play a critical role for this DC vaccine-induced therapeutic outcome. Our findings identify DeltaM51-VSV as both an efficient gene-delivery vector and a maturation agent allowing DC vaccines to overcome immunosuppression in the tumor-bearing host.

New T cell epitopes identified from an anti-idiotypic antibody mimicking ovarian cancer associated antigen

Anti-idiotype (Id) antibodies can be used to induce specific cellular immune responses against tumor antigens, but the mechanism of antigenicity is not always clear. We previously reported an anti-Id antibody, 6B11, which mimics human ovarian cancer associated antigen OC166-9. To explore the molecular basis of cellular immune response induced by 6B11, a panel of peptides derived from complementarity determining region (CDR) of 6B11 were synthesized. After a series of immunologic experiments, we found that the light chain CDR3 peptide and heavy chain CDR3 peptide were the MHC class I and class II epitopes of 6B11, respectively. The combination of MHC class I and class II epitopes is more effective than 6B11 in inducing specific cellular immune response against ovarian cancer. Our study provided the structural basis of antigenicity of 6B11. The identification of antigen-specific T cell eptitopes in 6B11 should facilitate the design of epitope-based vaccine against human ovarian cancer.

Critical contribution of immunoproteasomes in the induction of protective immunity against Trypanosoma cruzi in mice vaccinated with a plasmid encoding a CTL epitope fused to green fluorescence protein

Acquired immunity against infection with Trypanosoma cruzi is dependent on CD8(+)T cells. Here, to develop a vaccine strategy taking advantage of activated CD8(+)T cells, we constructed a DNA vaccine, designated pGFP-TSA1, encoding a fusion protein linking GFP to a single CTL epitope of TSA1, a leading candidate for vaccine against T. cruzi. C57BL/6 mice vaccinated with this plasmid showed suppressed parasitemia and prolonged survival. Vaccination with pGFP-TSA1 enhanced epitope-specific cytotoxicity and IFN-gamma secretion by CD8(+)T cells. Furthermore, the depletion of CD8(+)T cells prior to challenge infection with T. cruzi completely abolished this protection, indicating that CD8(+)T cells are the principal effector T cells involved. When mice deficient in the proteasome activator PA28alpha/beta or the immunoproteasome subunits LMP2 and LMP7 were used, the protective immunity against infection was profoundly attenuated. Our findings clearly demonstrate that vaccination with pGFP-TSA1 successfully induces protection dependent on CD8(+)T cell activation, in which immunoproteasomes play a crucial role. It is noteworthy to document that physical binding of the epitope and GFP is required for induction of this protection, since mice vaccinated with pTSA1-IRES-GFP failed to acquire resistance, probably because the epitope and GFP are separately expressed in the antigen-presenting cells.

A comparison and critical analysis of preclinical anticancer vaccination strategies

Anticancer vaccines have been extensively studied in animal models and in clinical trials. While vaccination can lead to tumor protection in numerous murine models, objective tumor regressions after anticancer vaccination in clinical trials have been rare. B16 is a poorly immunogenic murine melanoma that has been extensively used in anticancer vaccination experiments. Because B16 has been widely used, different vaccination strategies can be compared. We reviewed the results obtained when B16 was treated with five common vaccine types: recombinant viral vaccines, DNA vaccines, dendritic cell vaccines, whole-tumor vaccines, and peptide vaccines. We also reviewed the results obtained when B16 was treated with vaccines combined with adoptive transfer of tumor antigen-specific T cells. We found several characteristics of vaccination regimens that were associated with antitumor efficacy. Many vaccines that incorporated xenogeneic antigens exhibited more potent anticancer activity than vaccines that were identical except that they incorporated the syngeneic version of the same antigen. Interleukin-2 enhanced the antitumor efficacy of several vaccines. Finally, several effective regimens generated large numbers of tumor antigen-specific CD8(+) T cells. Identification of vaccine characteristics that are associated with antitumor efficacy may aid in the development of more effective anticancer vaccination strategies.

Vitiligo puzzle: the pieces fall in place

Over the years, the role of biochemical, immunological, genetic, and other biological aspects in the pathogenesis of vitiligo has been studied. So far, no convincing model describing the interplay of these contributing factors has been formulated. Based on existing research, we propose that vitiligo has a multi-factorial etiology, characterized by multiple steps, but always involving an increase of external or internal phenol/catechol concentration, serving as a preferred surrogate substrate of tyrosinase, competing with its physiological substrate tyrosine. The conversion of these substrates into reactive quinones is reinforced by a disturbed redox balance (increasing hydrogen peroxide). Such reactive quinones can be covalently bound to the catalytic centre of tyrosinase (haptenation). This could give rise to a new antigen, carried by Langerhans cells to the regional lymph node, stimulating the proliferation of cytotoxic T cells. However, the activation of such cytotoxic cells is only a first step in skin melanocyte killing, which also depends on a shift in the balance between immune defence and tolerance, e.g. resulting from a decrease in properly functioning T-regulatory cells. With this new model, based on a synthesis of several of the existing theories, in mind, the external and internal factors involved in the etiopathogenesis of vitiligo are reviewed, against the background of reported clinical data, experimental studies and existing and potential new therapies. A similar complex mechanism may also lead to some other autoimmune diseases.

Elevated frequencies of self-reactive CD8+ T cells following immunization with a xenoantigen are due to the presence of a heteroclitic CD4+ T-cell helper epitope

Immunization of mice with human dopachrome tautomerase (hDCT) provides greater protection against melanoma than immunization with the murine homologue (mDCT). We mapped the CD8(+) and CD4(+) T-cell epitopes in both proteins to better understand the mechanisms of the enhanced protection. The dominant CD8(+) T-cell epitopes were fully conserved between both proteins, yet immunization with hDCT produced frequencies of CD8(+) T cells that were 5- to 10-fold higher than immunization with mDCT. This difference was not intrinsic to the two proteins because comparable frequencies of CD8(+) T cells were elicited by both antigens in DCT-deficient mice. Strikingly, only hDCT elicited a significant level of specific CD4(+) T cells in wild-type (WT) mice. The murine protein was not devoid of CD4(+) T-cell epitopes because immunization of DCT-deficient mice with mDCT resulted in robust CD4(+) T-cell immunity directed against two epitopes that were not identified in WT mice. These results suggested that the reduced immunogenicity of mDCT in WT mice may be a function of insufficient CD4(+) T-cell help. To address this possibility, the dominant CD4(+) T-cell epitope from hDCT was introduced into mDCT. Immunization with the mutated mDCT evoked CD8(+) T-cell frequencies and protective immunity comparable with hDCT. These results reveal a novel mechanism by which xenoantigens overcome tolerance. Our data also suggest that immunologic tolerance is more stringent for CD4(+) T cells than CD8(+) T cells, providing a mechanism of peripheral tolerance where autoreactive CD8(+) T cells fail to be activated due to a lack of autoreactive CD4(+) T cells specific for the same antigen.

Control of human mesothelin-expressing tumors by DNA vaccines

Mesothelin has been implicated as a potential ideal target antigen for the development of antigen-specific cancer immunotherapy for the control of mesothelin-expressing cancers such as ovarian cancer, mesothelioma and pancreatic adenocarcinoma. In the current study, we utilized a DNA vaccine encoding human mesothelin (pcDNA3-Hmeso) to treat C57BL/6 mice challenged with luciferase-expressing, Hmeso-expressing ovarian cancer cell line, Defb29 Vegf-luc/Hmeso. The therapeutic effect of the tumor-challenged mice was followed by noninvasive bioluminescence imaging systems. The mechanism of the antitumor effect was characterized by depletion of subsets of lymphocytes as well as adopted transfer of serum from pcDNA3-Hmeso-vaccinated mice. We found that vaccination with pcDNA3-Hmeso DNA vaccine generates a significant antitumor effect and promotes survival in mice challenged with Defb29 Vegf-luc/Hmeso. Furthermore, we found CD4+ and CD8+ T-cell immune responses as well as the humoral immune responses are important for the observed antitumor effects in vaccinated mice. Our data indicated that vaccination with DNA vaccine targeting Hmeso could generate potent antitumor effects against mesothelin-expressing tumors through both T cell-mediated immunity as well as antibody-mediated immunity.

Rapid growth of invasive metastatic melanoma in carcinogen-treated hepatocyte growth factor/scatter factor-transgenic mice carrying an oncogenic CDK4 mutation

Currently, novel mouse models of melanoma are being generated that recapitulate the histopathology and molecular pathogenesis observed in human disease. Impaired cell-cycle control, which is a hallmark of both familial and sporadic melanoma, promotes slowly growing carcinogen-induced melanomas in the skin of mice carrying a mutated cyclin-dependent kinase 4 (CDK4(R24C)). Deregulated receptor tyrosine kinase signaling, which is another important feature of human melanoma, leads to spontaneous development of metastatic melanoma after a long latency period in mice overexpressing hepatocyte growth factor/scatter factor (HGF/SF mice). Here we report that treatment with 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate induced metastatic melanomas in all HGF/SF mice on the C57BL/6 background, which histologically resemble human melanoma. Importantly, mutant CDK4 dramatically increased the number and the growth kinetics of carcinogen-induced primary melanomas in the skin and promoted the growth of spontaneous metastases in lymph nodes and lungs in all HGF/SF mice within the first 3 months of life. Apart from very few skin papillomas, we did not observe tumors of other histology in carcinogen-treated HGF/SF x CDK4(R24C) mice. This new experimental mouse model can now be exploited to study further the biology of melanoma and evaluate new treatment modalities.

Therapeutic efficacy of antigen-specific vaccination and toll-like receptor stimulation against established transplanted and autochthonous melanoma in mice

Malignant melanoma is an attractive model disease for the development of antigen-specific immunotherapy because many antigens recognized by tumor-specific T cells have been identified. In C57BL/6 mice, genetic immunization with recombinant adenovirus encoding xenogeneic human tyrosinase-related protein 2 (Ad-hTRP2) induces protective but not therapeutic cellular immunity against growth of transplanted B16 melanoma cells. Here, we additionally applied CpG DNA and synthetic double-stranded RNA, which activate the innate immune system via Toll-like receptors (TLR). Both adenoviral vaccination and peritumoral injections of TLR ligands were required for rejection of established B16 melanoma in the skin. To more closely mimic the clinical situation in patients with melanoma, we evaluated this combined immunotherapeutic strategy in genetically modified mice, which overexpress hepatocyte growth factor (HGF) and carry an oncogenic mutation in the cyclin-dependent kinase 4 (CDK4)(R24C). HGF x CDK4(R24C) mice rapidly develop multiple invasive melanomas in the skin following neonatal carcinogen treatment, which spontaneously metastasize to lymph nodes and lungs. Vaccination with Ad-hTRP2 followed by injections of TLR ligands resulted in delayed growth of autochthonous primary melanomas in the skin and reduction in the number of spontaneous lung metastases but did not induce tumor regression. Carcinogen-treated HGF x CDK4(R24C) mice bearing multiple autochthonous melanomas did not reject transplanted B16 melanoma despite treatment with Ad-hTRP2 and TLR ligands, suggesting the development of tumor immunotolerance. Further investigations in our novel genetic melanoma model may help to better understand the role of the immune system in the pathogenesis and treatment of this life-threatening disease.

Comparison of recombinant adenovirus and synthetic peptide for DC-based melanoma vaccination

Optimal strategies for antigen-specific melanoma vaccination are currently being defined in experimental mouse models. Using a single H2-K(b)-binding peptide epitope derived from the melanosomal enzyme tyrosinase-related protein 2 (TRP2) in C57BL/6 mice, we show that adenovirus-transduced dendritic cells (DC) are clearly superior to peptide-pulsed DC for the induction of CD8+ T cells and antimelanoma immunity. Vaccine efficacy strictly depended on the presence of linked CD4+ T-cell help during the priming but not the effector phase of the immune response. These results provide important information for the translation of melanoma vaccine strategy in future clinical applications.

The ubiquitin-proteasome system plays essential roles in presenting an 8-mer CTL epitope expressed in APC to corresponding CD8+ T cells

MUT1 is an H-2Kb-restricted 8-mer CTL epitope expressed in Lewis lung carcinoma (3LL) tumor cells derived from C57BL/6 (B6) mice. We constructed a chimeric gene encoding ubiquitin-fused MUT1 (pUB-MUT1). By using a gene gun, B6 mice were immunized with the gene prior to challenge with 3LL tumor cells. Tumor growth and lung metastasis were prominently suppressed in mice immunized with pUB-MUT1 but only slightly in those immunized with the MUT1 gene (pMUT) alone. CD8+ T cells were confirmed to be the final effector by in vitro experiments and in vivo removal of the cells with a corresponding antibody. Anti-tumor immunity was profoundly suppressed in mice deficient in an immuno-subunit of proteasome, LMP7. Furthermore, mice deficient in a proteasome regulator, PA28alpha/beta, failed to acquire protective immunity. Thus, application of the ubiquitin-fusion degradation pathway was useful even in immunization with genes encoding a single CTL epitope for induction of specific and active CD8+ T cells.

Effective induction of anti-melanoma immunity following genetic vaccination with synthetic mRNA coding for the fusion protein EGFP.TRP2

RNA-based genetic immunization represents an alternative novel strategy for antigen-specific cancer vaccines. In the present paper we investigate the use of synthetic messenger RNA in an experimental melanoma model. We show that gene gun-based immunization using synthetic RNA mediates gene expression in the epidermis and effectively induces antigen-specific cellular and humoral immunity in mice in vivo. Importantly, bombardment of the skin with RNA coding for the melanocytic self-antigen TRP2 linked to the immunogenic protein EGFP was associated with protection against experimentally induced B16 melanoma lung metastases and vitiligo-like fur depigmentation. Our results provide a scientific basis for clinical trials using synthetic mRNA encoding melanocytic antigens linked to immunogenic helper proteins for vaccination of patients with melanoma.

Evaluation of genetic melanoma vaccines in cdk4-mutant mice provides evidence for immunological tolerance against authochthonous melanomas in the skin

We evaluated the efficacy of a candidate melanoma vaccine approach in mice genetically prone to develop melanoma due to the introduction of an oncogenic mutation (R24C) in the germline sequence of the cyclin-dependent kinase 4 (cdk4), a protein critically involved in cell cycle regulation. Melanomas were induced in cdk4-mutant mice by chemical carcinogenesis and UVB irradiation. A genetic prime-boost strategy targeting the clinically relevant differentiation antigen tyrosinase-related protein 2 (TRP2) was performed which was able to stimulate a melanocyte-specific cellular immune response associated with localized autoimmune vitiligo-like depigmentation. However, significant destruction of carcinogen-induced autochthonous melanocytic neoplasms in the skin was not observed following immunization. We provide evidence that autochthonous melanomas expressed TRP2 but not the MHC molecule H2-Kb and are immunologically tolerated in the skin. Our results highlight the importance of assessing melanoma vaccines in genetic mouse models that more adequately represent the expected clinical situation in order to identify strategies, which eventually may be of benefit for melanoma patients.

Unraveling the complex relationship between cancer immunity and autoimmunity: lessons from melanoma and vitiligo

A relationship between melanoma and vitiligo, a skin disorder characterized by the loss of melanocytes, has been postulated for many decades. In some cases, vitiligo is almost certainly a manifestation of autoimmune-mediated destruction of melanocytes. Melanocytes and melanoma cells share melanocyte differentiation antigens. Based on a number of observations, de novo vitiligo developing in patients with melanoma has been regarded as a sign of good prognosis. The immune system tolerates or ignores differentiation antigens because these antigens are self-derived. Therefore, immune tolerance or ignorance must be overcome to prime naive T and B cells to induce cancer immunity and autoimmunity against melanocyte differentiation antigens. Mouse models of concurrent melanoma and autoimmune vitiligo have revealed strategies to overcome immune ignorance or tolerance to melanocyte differentiation antigens: immunization with self-antigens as altered self (e.g., orthologues or mutated versions), expression in viral vectors, passive immunization with antibodies or T cells, incorporating potent adjuvants into active immunization, and blockade or removal of a downregulatory mechanism. Extensive investigations into the mechanisms that lead to tumor immunity and autoimmunity elicited by certain differentiation antigens have further revealed a variety of distinct cellular and molecular requirements, which are redundant and alternative.

A novel DNA vaccine based on ubiquitin-proteasome pathway targeting 'self'-antigens expressed in melanoma/melanocyte

Cancer vaccine that targets 'self'-antigens expressed at high levels in tumor cells is a potentially useful immunotherapy, but immunological tolerance often defeats this strategy. Here, we describe the use of a naked DNA vaccine encoding a self tumor antigen, tyrosinase-related protein 2, to whose N-terminus ubiquitin is fused in a 'nonremovable' fashion. Unlike conventional DNA vaccines, this vaccine broke the tolerance and induced protective immunity to melanoma in C57BL/6 mice, as evaluated by tumor growth, survival rate and lung metastasis. The protective immunity was cancelled in the proteasome activator PA28alpha/beta knockout mice. Moreover, this vaccination exhibited therapeutic effects on melanoma implanted before vaccination. Our findings provide evidence for the first time that naked DNA vaccines encoding a ubiquitin-fused self-antigen preferentially induce the main effector CD8+ T cells through efficient proteolysis mediated by the ubiquitin-proteasome pathway, and lead the way to strategies aimed at targeting tissue differentiation antigens expressed by tumors.

Targeting of Antigens to Activated Dendritic Cells In vivo Cures Metastatic Melanoma in Mice

Anti (alpha)-DEC-205 antibodies target to the DEC-205 receptor that mediates antigen presentation to T cells by dendritic cells. To exploit these properties for immunization purposes, we conjugated the melanoma antigen tyrosinase-related protein (TRP)-2 to alphaDEC-205 antibodies and immunized mice with these conjugates together with dendritic cell-activating oligonucleotides (CpG). Upon injection of the melanoma cell line B16, alphaDEC-TRP immunized mice were protected against tumor growth. Even more important for clinical applications, we were able to substantially slow the growth of implanted B16 cells by injection of alphaDEC-TRP2 conjugates into tumor bearing hosts. Approximately 70% of the animals were cured from existing tumors by treatment with alphaDEC conjugates carrying two different melanoma antigens (TRP-2 and gp100). This protection was due to induction of melanoma-specific CD4 and CD8 responses. Thus, these data show that targeting of dendritic cells in situ by the means of antibody-antigen conjugates may be a novel way to induce long-lasting antitumor immunity.

Initiation and regulation of CD8+T cells recognizing melanocytic antigens in the epidermis: implications for the pathophysiology of vitiligo

Antigen-specific CD8+T lymphocytes play an important role in defense against cutaneous microbial infection and skin cancer as well as in the pathophysiology of autoimmune skin disease such as lupus erythematodes and vitiligo. We have explored the role of CD8+ cytotoxic T lymphocytes (CTL) in an experimental mouse model of vitiligo, a pigmentation disorder characterized by focal loss of melanocytes in the skin. Using genetic immunization techniques we found that pigment cells in the epidermis can be destroyed by CD8+ T cells specifically recognizing a single H2-Kb-binding peptide derived from the model melanocytic self antigen tyrosinase-related protein 2 (TRP2), a melanosomal enzyme involved in pigment synthesis. Experimental evidence suggests that peripheral tolerance of pigment cell-specific cytotoxic CD8+T cells is regulated in two steps. In the induction phase, stimulation and expansion of these T cells in vivo strictly depends on CD4+ T cell help. In the effector phase, autoimmune destruction of melanocytes in the skin depends on local inflammation facilitating the migration of T cells into the epidermis and supporting effector functions. Our results suggest that accidental stimulation of CD8+ CTL recognizing MHC class I-binding peptides derived from melanocytic proteins in the context of an inflammatory skin disease may play an important role in the pathophysiology of vitiligo. Further investigations will address the role of chemokines, chemokine receptors and adhesion molecules in this experimental system and will reveal the role of keratinocytes and Langerhans cells in regulating cutaneous CD8+ T cell responses.

A phase I vaccination study with tyrosinase in patients with stage II melanoma using recombinant modified vaccinia virus Ankara (MVA-hTyr)

A significant percentage of patients with stage II melanomas suffer a relapse after surgery and therefore need the development of adjuvant therapies. In the study reported here, safety and immunological response were analyzed after vaccination in an adjuvant setting with recombinant modified vaccinia virus Ankara carrying the cDNA for human tyrosinase (MVA-hTyr). A total of 20 patients were included and vaccinated three times at 4-week intervals with 5x10(8) IU of MVA-hTyr each time. The responses to the viral vector, to known HLA class I-restricted tyrosinase peptides, and to dendritic cells transfected with tyrosinase mRNA, were investigated by ELISpot assay on both ex vivo T cells and on T cells stimulated in vitro prior to testing. The delivery of MVA-hTyr was safe and did not cause any side effects above grade 2. A strong response to the viral vector was achieved, indicated by an increase in the frequency of MVA-specific CD4+ and CD8+ T cells and an increase in virus-specific antibody titers. However, no tyrosinase-specific T-cell or antibody response was observed with MVA-hTyr in any of the vaccinated patients. Although MVA-hTyr provides a safe and effective antigen-delivery system, it does not elicit a measurable immune response to its transgene product in patients with stage II melanoma after repeated combined intradermal and subcutaneous vaccination. We presume that modification of the antigen and/or prime-boost vaccination applying different approaches to antigen delivery may be required to induce an effective tyrosinase-specific immune response.

Effective induction of antitumor immunity by immunization with plasmid DNA encoding TRP-2 plus neutralization of TGF-beta

Plasmid DNA vaccine is an appealing cancer immunotherapy. However, it is a weak immunogen and immunization with plasmid DNA encoding self-antigens, such as melanoma-associated antigens, could not induce antitumor immunity because of tolerance. In this study, we investigated the feasibility of using a plasmid DNA encoding Xenopus laevis transforming growth factor-beta 5 (aTGF-beta5) as an immunogen to induce neutralizing antibodies against murine TGF-beta1 (mTGF-beta1) and thus enhance the efficacy of plasmid DNA vaccine encoding murine tyrosinase-related protein 2 (mTRP-2) through neutralization of TGF-beta. The results showed that immunization with aTGF-beta5 resulted in the generation of mTGF-beta1-neutralizing antibodies, and immunization with a combination of aTGF-beta5 and mTRP-2 induced specific cytotoxic T lymphocytes (CTLs). On the contrary, immunization with mTRP-2 alone could not elicit the CTL response. Moreover, immunization of C57BL/6 wild-type mice with a combination of aTGF-beta5 and mTRP-2 induced the protective and therapeutic antitumor immunity to B16F10 melanoma, whereas the antitumor activity was abrogated in both CD4-deficient mice and CD8-deficient mice on the C57BL/6 background. Our results indicate that immunization with aTGF-beta5 is capable of breaking immune tolerance and induces mTGF-beta1-neutralizing antibodies. Neutralization of TGF-beta can enhance the efficacy of DNA vaccine encoding mTRP-2 and the induction of antitumor immunity by this immunization strategy is associated with CD4+ and CD8+ T cells.

In vivo manipulation of dendritic cells overcomes tolerance to unmodified tumor-associated self antigens and induces potent antitumor immunity

Most tumor-associated Ags are self proteins that fail to elicit a T cell response as a consequence of immune tolerance. Dendritic cells (DCs) generated ex vivo have been used to break tolerance against such self Ags; however, in vitro manipulation of DCs is cumbersome and difficult to control, resulting in vaccines of variable potency. To address this problem we developed a method for loading and activating DCs, in situ, by first directing sufficient numbers of DCs to peripheral tissues using Flt3 ligand and then delivering a tumor-associated Ag and oligonucleotide containing unmethylated CG motifs to these tissues. In this study, we show in three different tumor models that this method can overcome tolerance and induce effective antitumor immunity. Vaccination resulted in the generation of CD8(+) T and NK cell effectors that mediated durable tumor responses without attacking normal tissues. These findings demonstrate that unmodified tumor-associated self Ags can be targeted to DCs in vivo to induce potent systemic antitumor immunity.

Therapeutic effect of dendritic cells loaded with a fusion mRNA encoding tyrosinase-related protein 2 and enhanced green fluorescence protein on B16 melanoma

Dendritic cells (DCs) loaded with messenger RNA (mRNA) have been proposed to be useful for inducing specific cytotoxic T lymphocytes against tumor antigens. It is now also apparent that tumor antigen-specific T cell tolerance limits the efficacy of active immunotherapy. To improve the efficacy of mRNA-loaded DCs, we constructed a fusion mRNA encoding tyrosinase-related protein 2 (TRP2), which has a late endosomal/lysosomal sorting signal and enhanced green fluorescence protein (EGFP), and evaluated its effect in a murine melanoma model. C57BL/6 mice were challenged subcutaneously (s.c.) with 3 x 10(5) B16 tumor cells, and 3 and 10 days later, 3 x 10(5) DCs loaded with mRNA (DC/mRNA) were injected s.c. in the vicinity of the tumor site. Treatment with DC/TRP2 mRNA or DC/TRP2-EGFP mRNA significantly inhibited tumor growth compared to DC/PBS on day 17 after B16 challenge (DC/PBS vs. DC/TRP2 mRNA, p = 0.0411; DC/PBS vs.DC/TRP2-EGFP mRNA, p = 0.0253), whereas no antitumor effect was observed in mice treated with DC/EGFP mRNA or DC/TRP2 peptide. Moreover, the survival rate in mice immunized with DC/TRP2 mRNA or DC/TRP2-EGFP mRNA was significantly improved as compared with that in mice receiving DC/PBS (DC/PBS vs. DC/TRP2 mRNA, p = 0.0228; DC/PBS vs. DC/TRP2-EGFP mRNA, p = 0.0049). Depletion of CD4+ T cells or CD8+ T cells with antibody administration completely abrogated the therapeutic effectiveness of DC/TRP2-EGFP mRNA, suggesting the induction of a T cell immune response against the B16 tumor.

Peripheral CD8+ T Cell Tolerance Against Melanocytic Self-Antigens in the Skin Is Regulated in Two Steps by CD4+ T Cells and Local Inflammation: Implications for the Pathophysiology of Vitiligo

Experimental evidence has suggested a role for CD8+ cytotoxic T lymphocytes (CTL) in the pathophysiology of vitiligo, a pigmentation disorder with focal loss of melanocytes in the skin. The discovery of tyrosinase-related protein 2 (TRP2) as a model melanocytic self-antigen recognized by CD8+ CTL in C57BL/6 mice allowed us to analyze the requirements for CD8+ T cell-mediated autoimmune destruction of melanocytes in an experimental model. Using two different genetic methods for the induction of cellular immunity in vivo, gene gun bombardment of the skin and injection of recombinant adenovirus, we show that peripheral tolerance of CD8+ T cells recognizing a single TRP2-derived H2-Kb-binding peptide is regulated in two steps. In the induction phase, stimulation and expansion of TRP2-specific CD8+ T cells in vivo depend on CD4+ T cell help. In the effector phase, autoimmune destruction of melanocytes in the skin depends on local inflammation. Our results suggest that accidental stimulation of CD8+ CTL recognizing major histocompatibility complex class I-binding peptides derived from melanocytic proteins in the context of an inflammatory skin disease may play an important role in the pathophysiology of vitiligo.

Altered intracellular sorting signals do not influence the efficacy of genetic melanoma vaccines incorporating helper determinants in mice

BACKGROUND

A genetic melanoma vaccine consisting of cDNA encoding the model self-antigen tyrosinase-related protein 2 (TRP2) fused in-frame to the immunogenic enhanced green fluorescent protein (EGFP) was able to break immune tolerance and stimulate CD8+ T cells in vivo. In the present study we investigated whether alteration of the intracellular antigen localization as a result of the linkage with immune-enhancing helper proteins affects the resulting immune response.

METHODS

Expression plasmids and recombinant adenoviruses were constructed encoding various fusion proteins with different intracellular sorting signals which direct the antigen to the cytosol, the endoplasmic reticulum or the endosomal compartments. Genetic immunization of C57BL/6 mice was performed with all constructs using particle-bombardment of the skin and injection of recombinant adenoviruses. The resulting immune response was analyzed using ELISPOT and tumor rejection assays.

RESULTS

Induction of TRP2-specific CD8+ T cells in vivo and autoimmune-mediated destruction of melanocytes in the bombarded area of the skin were observed with all constructs expressing fusion proteins between TRP2 and EGFP. Importantly, injections of the different recombinant adenoviruses all mediated protective immunity against transplanted B16 melanoma cells.

CONCLUSIONS

Altered intracellular sorting signals do not significantly influence the efficacy of genetic melanoma vaccines incorporating helper determinants in our model system. These results further support the concept that linkage of immunogenic helper sequences can be successfully applied for antigen-specific immunotherapy of melanoma and provide a scientific basis for the translation of this strategy in future clinical applications.

Therapeutic effectiveness of recombinant cancer vaccines is associated with a prevalent T-cell receptor alpha usage by melanoma-specific CD8+ T lymphocytes

Definition of immune variables that correlate with the antitumor activity of cancer vaccines is critical for monitoring immunotherapy protocols. To define surrogate end points predictive of the therapeutic efficacy of recombinant vaccines based on melanoma antigen tyrosinase-related protein (TRP)-2, we evaluated several properties of antigen-specific CD8(+) T lymphocytes in single mice undergoing either prophylactic or therapeutic immunization. Predictive markers for the efficacy of genetic vaccination were identified in the prophylactic model used. Interestingly, the number of tetramer(+) CD8(+) T lymphocytes expanded in vitro after a single cycle of stimulation with the immunodominant TRP-2 peptide was of the highest predictive value. In the therapeutic model, no variable examined at a single mouse level predicted the long-term therapeutic effect. Mice that survived did not show the highest expansion of antigen-specific lymphocytes or the more functionally active effectors, ex vivo or after in vitro culture with the peptide antigen. Successful therapy correlated strictly with the skewing of the T-cell receptor repertoire of tetramer-sorted, TRP-2-specific CD8(+) T lymphocytes, which showed a preferential alpha chain usage with a common CDR3 region.

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.

Ubiquitin-fusion degradation pathway plays an indispensable role in naked DNA vaccination with a chimeric gene encoding a syngeneic cytotoxic T lymphocyte epitope of melanocyte and green fluorescent protein

Antitumour immunity against murine melanoma B16 was achieved by genetic immunization with a naked chimeric DNA encoding a fusion protein linking green fluorescent protein (GFP) to the N-terminus of a major CD8(+) cytotoxic T lymphocyte (CTL) epitope of tyrosinase-related protein 2 (TRP-2(181-188)) of murine melanoma, designated as pGFP-TRP-2. Tumour growth was profoundly suppressed in C57BL/6 mice immunized with pGFP-TRP-2, while mice vaccinated with pTRP-2 showed rapid tumour growth and died within 40 days after tumour challenge. Splenocytes of mice immunized with pGFP-TRP-2 showed high CTL activity specific for TRP-2(181-188). GFP-TRP-2 expressed in COS-7 cells was rapidly degradated in vitro and the degradation was almost completely prevented by adding a proteasome inhibitor, MG-132, in the culture. Furthermore, the antimelanoma immunity induced by genetic immunization with pGFP-TRP-2 was completely cancelled in mice deficient in proteasome activator PA28alpha/beta. Taken together, GFP-TRP-2 processed by cytosolic proteasome played a central role in breaking peripheral tolerance to a melanoma/melanocyte antigen, TRP-2(181-188), by activating CD8(+) CTL specific for TRP-2(181-188). TRP-2(181-188) fused to GFP may be readily cut off from GFP by the ubiquitin-fusion degradation (UFD) pathway and efficiently presented to major histocompatibility complex class I molecules, resulting in effective induction of CD8(+) T cells specific for the CTL epitope. Furthermore, CD4(+) T cells specific for GFP were shown to play a crucial role in the antimelanoma immunity, probably potentiating activity of TRP-2-specific CTL and/or the "ubiquitin-proteasome pathway". It is noteworthy to document that genetic immunization with pGFP plus pTRP-2(181-188) failed to exert the antitumour immunity.

Vaccination-induced autoimmune vitiligo is a consequence of secondary trauma to the skin

A major concern for cancer vaccines targeting self-tumor antigens is the risk of autoimmune sequelae. Although antitumor immunity correlates with autoimmune disease in some preclinical models, the mechanism(s) linking antitumor immunity and subsequent autoimmune pathology remain(s) to be determined. In the current study, we demonstrated that intradermal (i.d.) immunization with a recombinant adenovirus (Ad) expressing the murine melanoma antigen tyrosinase-related protein 2 (AdmTrp-2) results in a moderate level of tumor protection against the B16F10 murine melanoma without any vitiligo. Similar immunization with an Ad encoding human Trp-2 (AdhTrp-2) resulted in 50-fold greater protective immunity and produced vitiligo in all of the mice, suggesting that the development of autoimmunity may reflect the potency of the vaccine. Interestingly, delivery of AdhTrp-2 by i.m. injection generated protective immunity comparable with that seen in mice that received the vaccine by the i.d. route, but none of the recipients in the i.m. group developed vitiligo. The cellular and humoral responses in the i.m. immunized mice were greater than in the i.d. group; therefore, the lack of vitiligo was not caused by reduced efficacy of the vaccine. These results led us to hypothesize that vaccine-induced vitiligo was associated with local inflammatory responses. Mice immunized i.m. with AdhTrp-2 did develop vitiligo when they subsequently were injected i.d. with either a control Ad vector or complete Freund's adjuvant, suggesting that vitiligo is initiated by some form of trauma within the skin. Our data demonstrated that autoimmune pathology is not an unavoidable outcome of effective cancer vaccines directed against self-tumor antigens.

The inhibition of early N-glycan processing targets TRP-2 to degradation in B16 melanoma cells

Tyrosinase-related protein-2 (TRP-2) is a DOPAchrome tautomerase catalyzing a distal step in the melanin synthesis pathway. Similar to the other two melanogenic enzymes belonging to the TRP gene family, tyrosinase and TRP-1, TRP-2 is expressed in melanocytes and melanoma cells. Despite the increasing evidence of its efficiency as a melanoma antigen, little is known about the maturation and intracellular trafficking of TRP-2. Here we show that TRP-2 is mainly distributed in the TGN of melanoma cells instead of being confined solely to melanosomes. This, together with the plasma membrane occasional localization observed by immunofluorescence, suggest the TRP-2 participation in a recycling pathway, which could include or not the melanosomes. Using pulse-chase experiments we show that the TRP-2 polypeptide folds in the endoplasmic reticulum (ER) in the presence of calnexin, until it reaches a dithiothreitol-resistant conformation enabling its ER exit to the Golgi. If N-glycosylation inhibitors prevent the association with calnexin, the TRP-2 nascent chain undergoes an accelerated degradation process. This process is delayed in the presence of proteasomal inhibitors, indicating that the misfolded chain is retro-translocated from the ER into the cytosol and degraded in proteasomes. This is a rare example in which calnexin although indispensable for the nascent chain folding is not required for its targeting to degradation. Therefore TRP-2 may prove to be a good model to document the calnexin-independent retro-translocation process of proteasomally degraded proteins. Clearly, TRP-2 has a distinct maturation pathway from tyrosinase and TRP-1 and possibly a second regulatory function within the cell.

DNA vaccination breaks tolerance for a neo-self antigen in liver: a transgenic murine model of autoimmune hepatitis

Understanding the pathogenesis of autoimmune hepatitis requires an animal model in which chronic progressive immune injury develops spontaneously or with minimal manipulations. The new transgenic mouse model proposed in this study is based on the hypothesis that infectious agents have the potential to initiate autoreactivity through molecular mimicry. A transgenic mouse expressing lymphocytic choriomeningitis virus nucleoprotein (NP) in a H-2(b) background developed liver injury when vaccinated with plasmids expressing NP as an intracellular or a secretory protein. Coinjection of plasmids coding for NP and IL-12 facilitated the induction of a Th1 phenotype as detected by a specific B lymphocyte response characterized by a predominance of IgG2 subclass anti-NP Abs. CTLs activated in peripheral lymphoid organs by DNA vaccination migrated to the periportal and lobular areas of the liver. Their presence was associated with a significant degree of cytolysis, as evidenced by elevated transaminases several weeks after immunization. As activated specific T lymphocytes proliferated in the periphery and caused cytolysis of target cells, this study suggests that autoimmune hepatitis can be triggered by molecular mimicry, and that local injury may not be essential to initiate autoreactivity in the liver.

Emerging strategies in tumor vaccines

Reports of novel developments in tumor vaccines that have appeared in the year ending May 1, 2002 are reviewed here. Antigenic moieties were revealed for tumors previously considered nonimmunogenic. The use of peptides spanning mutations detected exclusively in tumor tissue avoids the common concern for autoimmune responses. Carbohydrate biology is revealing novel antigenic moieties. The search for helper epitopes from tumor antigens has come into full swing. Humoral immunity is regaining terrain, particularly through the development of antiidiotypic antibodies. Major steps forward have been made in optimizing modes and routes of antigen delivery and in the use of immune adjuvants. In the clinic, phase I/II trials support the notion that tumor vaccines are safe. Because these trials are conducted in patients in whom tumor remission is not a realistic endpoint, patient responses were established by immune monitoring strategies to detect subtle changes in antitumor reactivity. Both clinical and laboratory data stress the vast potential of tumor vaccines for the treatment of cancer.