Immune response to a differentiation antigen induced by altered antigen: a study of tumor rejection and autoimmunity

Transduction of the gene coding for a human G-protein coupled receptor FPRL1 in mouse tumor cells increases host anti-tumor immunity

Low antigenicity or development of tolerance is believed to be a major contributor to the escape of malignant tumors from immune surveillance of the host. However, anti-tumor responses can be elicited by concomitant immunization of poorly antigenic tumor cells with homologous xenogeneic proteins as 'altered self' proteins. In our study, anti-tumor, but not anti-xenogeneic antigen, immune responses were generated after transduction of the gene coding for a G-protein coupled human formyl peptide receptor like-1 (FPRL1) into a mouse C26 colon cancer cell line. C26 cells transfected with FPRL1 gene exhibited markedly reduced tumorigenicity in syngeneic mice, in association with the appearance of high levels of antibody activity reacting with both FPRL1 containing and wild type C26 cells. The anti-tumor responses required the participation of CD4+ T lymphocytes, since no tumor rejection was observed in nude mice or in syngeneic mice depleted of CD4+ T cells. Furthermore, mice primed with FPRL1 transfected C26 cells were resistant to subsequent challenge by wild type C26 cells. These results indicate that the presence of human FPRL1 is capable of triggering specific anti-tumor host immune responses against poorly antigenic mouse tumor cells.

Human High Molecular Weight Melanoma-Associated Antigen Mimicry by Mouse Anti-Idiotypic Monoclonal Antibody MK2-23: Enhancement of Immunogenicity of Anti-Idiotypic Monoclonal Antibody MK2-23 by Fusion with Interleukin 2

To overcome unresponsiveness to the self-high molecular weight melanoma-associated antigen (HMW-MAA) in hosts with constitutive HMW-MAA expression, we have used as immunogen the anti-idiotypic monoclonal antibody (mAb) MK2-23, which mimics the antigenic determinant recognized by the anti-HMW-MAA mAb 763.74. In a phase I/II clinical trial, anti-idiotypic mAb MK2-23, conjugated to keyhole limpet hemocyanin (KLH) as a carrier and given with Bacillus Calmette-Guerin (BCG) as an adjuvant, elicited HMW-MAA-specific antibodies in about 60% of the immunized melanoma patients. The immune response was associated with survival prolongation. However, safety and standardization issues associated with the use of KLH and BCG in the clinical setting have prompted us to develop alternative immunization strategies. Conjugation of human interleukin 2 (IL-2) to mAb MK2-23 variable regions covalently linked to human immunoglobulin constant regions enhanced mAb MK2-23 immunogenicity in BALB/c mice to an extent similar to that induced by mAb MK2-23 conjugated to KLH and given with Freund's adjuvant. As determined by the level of serum antibodies and delayed-type hypersensitivity responses to HMW-MAA-bearing melanoma cells, immunization of mice with the MK2-23-IL-2 fusion protein elicited more robust humoral and cellular responses, respectively, than immunization with KLH-conjugated mAb MK2-23 and separate administration of IL-2. The immunogenicity of the fusion protein is dependent on IL-2 conjugation, because immunization of mice with either mAb MK2-23 or chimeric mAb MK2-23, in combination with IL-2, was not as effective in eliciting HMW-MAA-specific immune responses. These results suggest that the MK2-23-IL-2 fusion protein represents a useful immunogen to implement active specific immunotherapy in patients with melanoma, because it bypasses the requirement for KLH conjugation and adjuvant administration.

Differential Immunogenicity of Two Peptides Isolated by High Molecular Weight-Melanoma-Associated Antigen-Specific Monoclonal Antibodies with Different Affinities

Peptide mimics isolated from phage display peptide libraries by panning with self-tumor-associated Ag (TAA)-specific mAbs are being evaluated as immunogens to implement active specific immunotherapy. Although TAA-specific mAb are commonly used to isolate peptide mimics, no information is available regarding the Ab characteristics required to isolate immunogenic TAA peptide mimics. To address this question, we have used mAb 763.74 and mAb GH786, which recognize the same or spatially close antigenic determinant(s) of the human high m.w.-melanoma-associated Ag (HMW-MAA), although with different affinity. mAb 763.74 affinity is higher than that of mAb GH786. Panning of phage display peptide libraries with mAb 763.74 and mAb GH786 resulted in the isolation of peptides P763.74 and PGH786, respectively. When compared for their ability to induce HMW-MAA-specific immune responses in BALB/c mice, HMW-MAA-specific Ab titers were significantly higher in mice immunized with P763.74 than in those immunized with PGH786. The HMW-MAA-specific Ab titers were markedly increased by a booster with HMW-MAA-bearing melanoma cells, an effect that was significantly higher in mice primed with P763.74 than in those primed with PGH786. Lastly, P763.74, but not PGH786, induced a delayed-type hypersensitivity response to HMW-MAA-bearing melanoma cells. These findings suggest that affinity for TAA is a variable to take into account when selecting mAb to isolate peptide mimics from a phage display peptide library.

Improved approach to identify cancer-associated autoantigens

The failure to identify biomarkers of clinical significance for cancer diagnosis and prognosis generated a great deal of skepticism in regard to the usefulness of autoantibody-based methods. SEREX was a major advancement in immunoscreening that resulted in the identification of a large group of autoantigens recognized by cancer sera. However, few SEREX-defined autoantigens have proven to have definitive diagnostic value in clinical practice. Often, the identified antigens are patient-specific rather than tumor-specific and many tumor-associated antigens are rare in expression libraries made from non-autologous cells. Since autoantibodies are part of the normal immune response, it can be difficult to single out tumor-associated antibodies from the scores of irrelevant patient-specific responses. In our view, any practical approach for identifying cancer-related autoantigens must include an integral strategy for demonstrating tumor relevance early in the screening process. Care must also be taken not to exclude potentially important autoantibodies by pre-screening manipulations to patient sera. We have introduced substantial modifications in SEREX, designed to minimize confounding effects of unrelated autoantibodies and to eliminate steps that preclude the identification of cancer-related autoantigens commonly recognized by cancer sera. In addition, we incorporate methodology to identify candidate antigens that have potential diagnostic or prognostic value prior to their molecular cloning and characterization.

T-cell-based immunotherapy of melanoma: what have we learned and how can we improve?

The lack of effective treatment for advanced stage melanoma by conventional therapies, such as radiation and chemotherapy, has highlighted the need to develop alternative therapeutic strategies. Among them, immunotherapy has attracted much attention because of the potential role played by immunological events in the clinical course of melanoma and the availability of well-characterized melanoma antigens to target melanoma lesions with immunological effector mechanisms. In recent years, T-cell-based immunotherapy has been emphasized, in part because of the disappointing results of the antibody-based trials conducted in the early 1980s, and in part because of the postulated major role played by T-cells in tumor growth control. In this review, the characteristics of antibody and T-cell-defined melanoma antigens will first be described, with emphasis on those used in clinical trials. Following a review of the current immunization and immunomonitoring strategies, the results from the T-cell-based immunotherapy clinical trials conducted to date will be reviewed.

Immunoprevention of basal cell carcinomas with recombinant hedgehog-interacting protein

Basal cell carcinomas (BCCs) are driven by abnormal hedgehog signaling and highly overexpress several hedgehog target genes. We report here our use of one of these target genes, hedgehog-interacting protein (Hip1), as a tumor-associated antigen for immunoprevention of BCCs in Ptch1^+/− mice treated with ionizing radiation. Hip1 mRNA is expressed in adult mouse tissues at levels considerably lower than those in BCCs. Immunization with either of two large recombinant Hip1 polypeptides was well tolerated in Ptch1^+/− mice, induced B and T cell responses detectable by enzyme-linked immunosorbent assay, Western blot, delayed type hypersensitivity, and enzyme-linked immunospot assay, and reduced the number of BCCs by 42% (P < 0.001) and 32% (P < 0.01), respectively. We conclude that immunization with proteins specifically up-regulated by hedgehog signaling may hold promise as a preventive option for patients such as those with the basal cell nevus syndrome who are destined to develop large numbers of BCCs.

T Cell Immunity Induced by Live, Necrotic, and Apoptotic Tumor Cells

The rules that govern the engagement of antitumor immunity are not yet fully understood. Ags expressed by tumor cells are prone to induce T cell tolerance unless the innate immune system is activated. It is unclear to what extent tumors engage this second signal link by the innate immune system. Apoptotic and necrotic (tumor) cells are readily recognized and phagocytosed by the cells of the innate immune system. It is unknown how this affects the tumor's immunogenicity. Using a murine melanoma (B16m) and lymphoma (L5178Y-R) model, we studied the clonal sizes and cytokine signatures of the T cells induced by these tumors in syngeneic mice when injected as live, apoptotic, and necrotic cells. Both live tumors induced a type 2 CD4 cell response characterized by the prevalent production of IL-2, IL-4, and IL-5 over IFN-gamma. Live, apoptotic, and necrotic cells induced CD4 (but no CD8) T cells of comparable frequencies and cytokine profiles. Therefore, live tumors engaged the second signal link, and apoptotic or necrotic tumor cell death did not change the magnitude or quality of the antitumor response. A subclone of L5178Y-R, L5178Y-S cells, were found to induce a high-frequency type 1 response by CD4 and CD8 cells that conveyed immune protection. The data suggest that the immunogenicity of tumors, and their characteristics to induce type 1 or type 2, CD4 or CD8 cell immunity is not primarily governed by signals associated with apoptotic or necrotic cell death, but is an intrinsic feature of the tumor itself.

Shift from Systemic to Site-Specific Memory by Tumor-Targeted IL-2

IL-2 has been approved for treatment of patients with cancer. Moreover, it has been used as a component of vaccines against cancer. In this regard, we have recently demonstrated that dendritic cell-based peptide vaccination in mice required IL-2 to mount an effective immune response against established melanoma metastases. In this study, we confirm this observation by use of tumor-targeted IL-2. However, the development of a protective systemic memory was substantially impaired by this measure, i.e., mice, which successfully rejected s.c. tumors of B16 melanoma after vaccination with dendritic cells pulsed with tyrosinase-related protein 2-derived peptides plus a boost with targeted IL-2, failed to reject a rechallenge with experimental pulmonary metastases. Detailed analysis revealed a change in the distribution of the tumor-reactive T cell population: although targeted IL-2 expanded the local effector population, tyrosinase-related protein 2-reactive T cells were almost completely depleted from lymphatic tissues.

Tumor antigens for cancer immunotherapy: therapeutic potential of xenogeneic DNA vaccines

Preclinical animal studies have convincingly demonstrated that tumor immunity to self antigens can be actively induced and can translate into an effective anti-tumor response. Several of these observations are being tested in clinical trials. Immunization with xenogeneic DNA is an attractive approach to treat cancer since it generates T cell and antibody responses. When working in concert, these mechanisms may improve the efficacy of vaccines. The use of xenogeneic DNA in overcoming immune tolerance has been promising not only in inbred mice with transplanted tumors but also in outbred canines, which present with spontaneous tumors, as in the case of human. Use of this strategy also overcomes limitations seen in other types of cancer vaccines. Immunization against defined tumor antigens using a xenogeneic DNA vaccine is currently being tested in early phase clinical trials for the treatment of melanoma and prostate cancers, with proposed trials for breast cancer and Non-Hodgkin's Lymphoma.

CTLA-4 blockade in combination with xenogeneic DNA vaccines enhances T-cell responses, tumor immunity and autoimmunity to self antigens in animal and cellular model systems

Xenogeneic DNA vaccination can elicit tumor immunity through T cell and antibody-dependent effector mechanisms. Blockade of CTLA-4 engagement with B7 expressed on APCs has been shown to enhance T cell-dependent immunity. We investigated whether CTLA-4 blockade could increase T-cell responses and tumor immunity elicited by DNA vaccines. CTLA-4 blockade enhanced B16 tumor rejection in mice immunized against the melanoma differentiation antigens tyrosinase-related protein 2 and gp100, and this effect was stronger when anti-CTLA-4 was administered with booster vaccinations. CTLA-4 blockade also increased the T-cell responses to prostate-specific membrane antigen (PSMA) when given with the second or third vaccination. Based on these pre-clinical studies, we suggest that anti-CTLA-4 should be tested with xenogeneic DNA vaccines against cancer and that special attention should be given to sequence and schedule of administration.

Immunotherapy of malignant diseases. Challenges and strategies

In recent years, there has been growing interest in the application of immunotherapy as an alternative to chemotherapy and radiotherapy for the treatment of malignant diseases. This interest is due to a variety of factors, including revival of the immunosurveillance theory, availability of well-defined and structurally characterized human tumor-associated antigens (TAAs), progress in our understanding of the molecular pathways required for induction and maintenance of an immune response, and advances in methodologies to generate TAA-specific cytotoxic T lymphocytes (CTLs) and monoclonal antibodies (mAbs) as immunological probes. However, contrary to the positive results obtained with TAA-specific immunotherapy in animal model systems, the clinical response in patients has been disappointing. Frequently, the immune responses do not correlate with the clinical responses. Analysis of the underlying mechanisms of this dichotomy have identified the low immunogenicity of TAAs, the lack of immunological markers to predict clinical outcomes, and the ability of tumors to escape immune recognition and destruction as challenges to the development and application of immunotherapy. In this paper, we have reviewed the mechanisms underlying immune unresponsiveness to TAAs and strategies to overcome this unresponsiveness in the humoral and cellular immune responses, highlighting findings from different antigenic systems to prove the validity of these strategies. Additionally, we have addressed limitations to TAA-targeting immunotherapy as a result of the genetic instability of tumor cells, and have discussed strategies to overcome this limitation by targeting immunotherapy to molecules implicated in tumor-associated angiogenesis. Lastly, we have concluded by indicating the need to refine the implementation of clinical trials of immunotherapy, and to emphasize combination therapies to counteract the multiple tumor escape mechanisms.

Restraint stress and anti-tumor immune response in mice

Psychological stress modulates the immune system through the hypothalamic-pituitary-adrenal axis, the sympatho-adrenomedullary axis and the opioid system. According to literature data, restraint stress increases the immune cell apoptosis, decreases the spleen and thymus cell content, the natural killer (NK) activity in the spleen, and it compromises the anti-tumor immune response in mice. We immobilized mice in two consecutive nights, and then determined the cell number, apoptosis, NK cell content, NK activity and the level of cytokine mRNAs (TNF-beta, TNF-alpha, IL-4, IL-5, IL-1alpha, IFN-gamma, IL-2, IL-6, IL-1beta and IL-3) in the thymus and spleen. No consistent changes were detected in any of the immune parameters either in C57Bl/6 or in DBA/2 mice. Stressed or control B6 mice were injected with B16 melanoma cells immediately after the immobilization or one week later. No significant differences were found in the growth of primary tumors and lung metastases in stressed and control animals. Taken together, our mice, kept in a general-purpose non-SPF animal house, seemed to be refractory to the stress-induced immunomodulation. Our interpretation is that stress-induced immunomodulation can occur only in mice isolated from any background stressors, or rather natural stimuli, throughout their life.

Immunity to melanoma: unraveling the relation of tumor immunity and autoimmunity

Cancer cells express self-antigens that are weakly recognized by the immune system. Even though responses against autologous cells are difficult to induce, the immune system is still able to mount a response against cancer. The discovery of the molecular identity of antigens that are recognized by the immune system of melanoma patients has led to the elucidation of tumor immunity at a cellular and molecular level. Multiple pathways in both the priming and effector phases of melanoma rejection have been described. Animal models' active immunotherapies for melanoma show a requirement for the cellular compartment of the immune system in the priming phase, primarily CD4+T cells. More diverse elements are required for the effector phase, including components from the innate immune system (macrophages, complement and/or natural killer cells) and from the adaptive immune system (CD8+T cells and B cells). Minor differences in amino-acid sequences of antigens must determine the particular mechanisms involved in tumor rejection. Since the immune system contains T and B cells that recognize and reject autologous cells, a consequence of tumor immunity is potential autoimmunity. There are distinct pathways for tumor immunity and autoimmunity. The requirements for autoimmunity at the priming phase seem to be CD4+/IFN-gamma dependent while the effector mechanisms are alternative and redundant. Vitiligo (autoimmune hypopigmentation) can be mediated by T cells, FcgammaR+macrophages and/or complement.

A single heteroclitic epitope determines cancer immunity after xenogeneic DNA immunization against a tumor differentiation antigen

Successful active immunization against cancer requires induction of immunity against self or mutated self Ags. However, immunization against self Ags is difficult. Xenogeneic immunization with orthologous Ags induces cancer immunity. The present study evaluated the basis for immunity induced by active immunization against a melanoma differentiation Ag, gp100. Tumor rejection of melanoma was assessed after immunization with human gp100 (hgp100) DNA compared with mouse gp100 (mgp100). C57BL/6 mice immunized with xenogeneic full-length hgp100 DNA were protected against syngeneic melanoma challenge. In contrast, mice immunized with hgp100 DNA and given i.p. tolerizing doses of the hgp100 D(b)-restricted peptide, hgp100(25-33), were incapable of rejecting tumors. Furthermore, mice immunized with DNA constructs of hgp100 in which the hgp100(25-27) epitope was substituted with the weaker D(b)-binding epitope from mgp100 (mgp100(25-27)) or a mutated epitope unable to bind D(b) did not reject B16 melanoma. Mice immunized with a minigene construct of hgp100(25-33) rejected B16 melanoma, whereas mice immunized with the mgp100(25-33) minigene did not develop protective tumor immunity. In this model of xenogeneic DNA immunization, the presence of an hgp100 heteroclitic epitope with a higher affinity for MHC created by three amino acid (25 to 27) substitutions at predicted minor anchor residues was necessary and sufficient to induce protective tumor immunity in H-2(b) mice with melanoma.

Immunogene therapy of tumors with vaccine based on xenogeneic epidermal growth factor receptor

The breaking of immune tolerance against self epidermal growth factor receptor (EGFr) should be a useful approach for the treatment of receptor-positive tumors with active immunization. To test this concept, we constructed a plasmid DNA encoding extracellular domain of xenogeneic (human) EGFr (hEe-p) or corresponding control mouse EGFr (mEe-p) and empty vector (c-p). Mice immunized with hEe-p showed both protective and therapeutic antitumor activity against EGFr-positive tumor. Sera isolated from the hEe-p-immunized mice exhibited positive staining for EGFr-positive tumor cells in flow cytometric analysis and recognized a single 170-kDa band in Western blot analysis. Ig subclasses responded to rEGFr proteins were elevated in IgG1, Ig2a, and Ig2b. There was the deposition of IgG on the tumor cells. Adoptive transfer of the purified Igs showed the antitumor activity. The increased killing activity of CTL against EGFr-positive tumor cells could be blocked by anti-CD8 or anti-MHC class I mAb. In vivo depletion of CD4(+) T lymphocytes could completely abrogate the antitumor activity, whereas the depletion of CD8(+) cells showed partial abrogation. The adoptive transfer of CD4-depleted (CD8(+)) or CD8-depleted (CD4(+)) T lymphocytes isolated from mice immunized with hEe-p vaccine showed the antitumor activity. In addition, the increase in level of both IFN-gamma and IL-4 was found. Taken together, these findings may provide a new vaccine strategy for the treatment of EGFr-positive tumors through the induction of the autoimmune response against EGFr in a cross-reaction between the xenogeneic homologous and self EGFr.

A role for antibodies in tumor immunity

Recent advances have demonstrated the clinical utility of specific monoclonal antibodies that recognize tumor-associated antigens on the surface of the tumor cell in the treatment of breast cancer and B cell lymphoma in humans. In addition to these studies, an experimental tumor model, where antibodies that recognize a viral-encoded tumor-specific antigen play a major role in tumor immunity, will be discussed. Together, these studies implicate antibodies as a means of providing tumor immunity against some cancers. The necessity for designing cancer vaccines that induce antibodies with specificity for antigens on the tumor cell will be discussed.

Immunity to Cancer Through Immune Recognition of Altered Self: Studies with Melanoma

The adaptive immune system is capable of recognizing cancer through T- and B-cell receptors. However, priming adaptive immunity against self antigens is potentially a difficult task. Presentation of altered self to the immune system is a strategy to elicit immunity against poorly immunogenic antigens. We have shown that immunization with conserved paralogues of tumor antigens can induce adaptive immunity against self antigens expressed by cancer. Remarkably, cancer immunity elicited by closely related paralogues can generate distinct adaptive immune responses, either antibody or T-cell dependent. Cancer immunity induced by xenogeneic immunization follows multiple and alternative pathways. The effector phase of tumor immunity can be mediated by cytotoxic T cells or macrophages and perhaps natural killer cells for antibody-dependent immunity. Helper CD4+ T cells are typically, but not always, required to generate immunity. Autoimmunity is frequently observed following immunization. Cancer immunity and autoimmunity use overlapping mechanisms, and therefore they are difficult to uncouple, but distinct pathways can be discerned that open the eventual possibility of uncoupling tumor immunity from autoimmunity. Studies examining the molecular basis for immunogenicity of conserved paralogues are facilitating the development of new strategies to rationally design vaccines that trigger adaptive immune responses to cancer.

Synthetic and natural non-live vectors: rationale for their clinical development in cancer vaccine protocols

Different arguments suggest that cytotoxic CD8 T lymphocytes (CTL) play a key role in the protection against tumors and in the establishment of anti-tumor immunity. Unfortunately, administration of soluble proteins alone generally does not induce CD8+ T cells presumably because antigen derived peptides are not introduced into the major histocompatibility complex (MHC) class I antigen presentation pathway. Attenuated recombinant live vectors such as viruses or bacteria which have the ability to deliver antigen into the cytosol of cells have been shown to induce cytotoxic T cell response. However, there are safety concerns associated with these approaches especially in immunodeficient patients. Synthetic vectors such as heat shock proteins, virus like particles (VLP) and liposomes could deliver exogenous protein into the cytosol of cells associated with the induction of CTL and tumor immunity. We and other groups have successfully exploited the original intracellular traffic of toxins to use them as vectors for tumor antigens.

Multiple HLA class II-restricted melanocyte differentiation antigens are recognized by tumor-infiltrating lymphocytes from a patient with melanoma

Dramatic clinical responses were observed in patient 888 following the adoptive transfer of autologous tumor-infiltrating lymphocytes (TIL). Previously, extensive analysis of the specificity of class I-restricted T cells from patient 888 TIL has revealed that these T cells recognize a mutated, as well as several nonmutated tumor Ags. Additional studies that were conducted on TIL from patient 888 indicated that they contained CD4-positive T cells that recognized the autologous tumor that had been induced to express HLA class II molecules. Tumor-reactive CD4-positive T cell clones were isolated from TIL and tested for their ability to react with Ags that are recognized by HLA class I-restricted, melanoma-reactive T cells. Using this approach, T cell clones were identified that recognized an epitope expressed in both the tyrosinase-related protein 1 and tyrosinase-related protein 2 Ags in the context of the HLA-DRbeta1*1502 class II gene product. Additional clones were found to recognize an epitope of gp100 in the context of the same HLA-DR restriction element. These observations provide an impetus to develop strategies directed toward generating HLA class II-restricted tumor-reactive T cells.

Multiple pathways to tumor immunity and concomitant autoimmunity

The immune repertoire contains T cells and B cells that can recognize autologous cancer cells. This repertoire is directed against self, and in some cases altered self (mutations). Priming immune responses against self antigens can be difficult. Strategies are presented using altered self to elicit immunity against self in poorly immunogenic tumor models. Mechanisms underlying immunity to self antigens on cancer cells show that the immune system can use diverse strategies for cancer immunity, in both the immunization and the effector phases. CD4+ T cells are typically, but not always, required for immunization. The effector phase of tumor immunity can involve cytotoxic T cells, macrophages with activating Fc receptors, and/or killer domain molecules. This diversity in the effector phase is observed even when immunizing with conserved paralogs. A consequence of tumor immunity is potentially autoimmunity, which may be undesirable. Autoimmunity uses similar mechanisms as tumor immunity, but tumor immunity and autoimmunity can uncouple. These studies open up strategies for active immunization against cancer.

Fas ligand breaks tolerance to self-antigens and induces tumor immunity mediated by antibodies

The role of Fas ligand (FasL) in programmed cell death via interaction with its receptor Fas is well characterized. It has been proposed that expression of FasL can confer immune privilege to some organs, allowing them to kill infiltrating lymphocytes and inflammatory cells. However, a number of studies have shown that when tumors or transplants express FasL, rejection often occurs as a consequence of proinflammatory functions of FasL. Here we demonstrate that FasL elicits tumor immunity in a murine melanoma model with weak immunogenicity and low expression of major histocompatibility complex (MHC) class I. We show that protected mice recognize melanocyte differentiation self-antigens. Importantly, tumor immunity is mediated by antibodies, as it can be transferred by serum from protected mice.

Redundant and alternative roles for activating Fc receptors and complement in an antibody-dependent model of autoimmune vitiligo

Complement and Fc receptor (FcR)-positive cells mediate effector functions of antibodies. Antibody-dependent immunity against the melanosome membrane glycoprotein gp75/tyrosinase-related protein-1 (TYRP-1) of melanocytes leads to autoimmune hypopigmentation (vitiligo) in mice. Hypopigmentation occurred in mice deficient in activating FcR containing the common gamma subunit (Fc gamma R gamma(-/-)) and in mice deficient in the C3 complement component. Mice doubly deficient in both Fc gamma R gamma and C3 did not develop hypopigmentation, suggesting that complement and Fc gamma R formed redundant mechanisms. Following passive immunization with antibody, no further adaptive immune responses were required. Chimeric Fc gamma R gamma(-/-),C3(-/-) mice reconstituted with bone marrow from either Fc gamma R gamma(-/-) or C3(-/-) mice or adoptively transferred with Fc gamma R gamma(+/-) macrophages did develop antibody-mediated hypopigmentation. Thus, either complement or macrophages expressing activating Fc gamma R can independently and alternatively mediate disease in a model of autoimmune vitiligo.

ATP6S1 elicits potent humoral responses associated with immune-mediated tumor destruction

An important goal of cancer immunology is the identification of antigens associated with tumor destruction. Vaccination with irradiated tumor cells engineered to secrete granulocyte/macrophage colony-stimulating factor (GM-CSF) generates potent, specific, and long-lasting antitumor immunity in multiple murine tumor models. A phase I clinical trial of this vaccination strategy in patients with advanced melanoma demonstrated the consistent induction of dense CD4(+) and CD8(+) T lymphocyte and plasma cell infiltrates in distant metastases, resulting in extensive tumor destruction, fibrosis, and edema. Antimelanoma antibody and cytotoxic T cell responses were associated with tumor cell death. To characterize the targets of these responses, we screened an autologous cDNA expression library prepared from a densely infiltrated metastasis with postvaccination sera from a long-term responding patient. High-titer IgG antibodies detected ATP6S1, a putative accessory unit of the vacuolar H(+)-ATPase complex. A longitudinal analysis of this patient revealed an association between the vaccine-induced increase in antibodies to ATP6S1 and tumor destruction. Three additional vaccinated melanoma patients and three metastatic non-small cell lung carcinoma patients vaccinated with autologous GM-CSF-secreting tumor cells similarly showed a correlation between humoral responses to ATP6S1 and tumor destruction. Moreover, a chronic myelogenous leukemia patient who experienced a complete remission after CD4(+) donor lymphocyte infusions also developed high-titer antibodies to ATP6S1. Lastly, vaccination with GM-CSF-secreting B16 melanoma cells stimulated high-titer antibodies to ATPS1 in a murine model. Taken together, these findings demonstrate that potent humoral responses to ATP6S1 are associated with immune-mediated destruction of diverse tumors.

Strategies to overcome immune ignorance and tolerance

Cancer poses a difficult problem for immunotherapy because it arises from the host's own tissues. Many of the target antigens are tissue-specific molecules shared by cancer cells and normal cells. Thus, these are weak antigens that do not typically elicit immunity. In addition, tumors have several features that make their recognition and destruction by the immune system difficult. Despite these obstacles, several strategies for developing effective tumor immunity have been developed. Crucial to these approaches is the discovery and understanding of the molecular identity of antigens and the mechanisms involved in tumor immunity. In this review, strategies to overcome immune ignorance and tolerance are discussed.

Immunologic self tolerance maintained by T-cell-mediated control of self-reactive T cells: implications for autoimmunity and tumor immunity

T-cell-mediated dominant control of self-reactive T cells is one mechanism for maintaining immunologic self tolerance. It also hampers the generation of immunity to autologous tumor cells. Abrogation of the control can evoke potent tumor immunity as well as autoimmunity in normal animals. This common regulatory mechanism for autoimmunity and tumor immunity can be exploited to devise a novel immunotherapy against cancer.

B16 as a mouse model for human melanoma

This unit details protocols for in vivo models of subcutaneous growth and pulmonary metastases of B16 melanoma. Therapeutic approaches include the use of B16.GM-CSF and rVVmTRP-1 to induce autoimmune vitiligo and tumor protection. The induction and use of gp 100-specific therapeutic cytotoxic T lymphocytes (CTL) are discussed. Methods are also included for CTL induction, isolation and testing, CTL maintenance, and adoptive transfer. Support protocols detail the testing of mouse sera for presence of MDA-specific antibodies by immunoblotting and ELISA, respectively. Additional sections, including growing B16 melanoma, enumerating pulmonary metastases, and use of recombinant viruses for vaccination, are discussed together with safety concerns.

Epitope recognition by anti-cathepsin D autoantibodies in endometrial cancer patients

OBJECTIVE

This study analyzed a model for the identification of specific epitopes recognized by autologous tumor-reactive humoral responses of endometrial cancer patients as potential markers for the monitoring of cancer.

METHODS

The presence of circulating pro- and mature forms of cathepsin D and antibodies reactive with this enzyme were identified by Western immunoblot and quantitated by an enzyme immunoassay. Specific immunoreactivities with 34- and 52-kDa cathepsin D forms were analyzed by Western immunoblot using sera from endometrial cancer patients (n = 40) and normal volunteers (n = 15). Subsequently, reactivities with specific cathepsin D epitopes were defined by a peptide-specific ELISA.

RESULTS

Circulating pro-forms of cathepsin D were detected in 31 of 40 endometrial cancer patients tested and none of the control volunteers. Circulating IgG reactive with cathepsin D could be demonstrated in 29/31 patients with circulating procathepsin D, while an anti-cathepsin D response was not detectable in normal controls. This response appeared to be directed against the pro-peptide portion of cathepsin D. Using a peptide-specific ELISA, the frequencies of antibody production against specific epitopes within the pro-peptide were defined.

CONCLUSION

There is a demonstrable tumor-reactive immune response elicited in endometrial cancer patients, directed against specific antigenic epitopes, some of which are conserved among these patients. Since these proteins are recognized as non-self, due at least in part to posttranslational processing errors, defining these epitopes will be useful as a means of diagnosis, assessment of therapeutic success, and, ultimately, identification of immunotherapeutic targets.

Immunity against cancer: lessons learned from melanoma

Most major advances in human cancer immunology and immunotherapy have come from studies in melanoma. We are beginning to understand the immune repertoire of T cells and antibodies that are active against melanoma, with recent glimpses of the CD4(+) T cell repertoire. The view of what the immune system can see is extending to mutations and parts of the genome that are normally invisible.

Cancer vaccines

Cancer vaccines have been extensively tested in animal models, and in humans. Initial studies focused on first generation vaccines based on whole cell preparations or tumor lysates derived from autologous or allogeneic tumors. Clinical studies conducted with such candidate vaccines contributed to establish the feasibility of immunizing cancer patients against their own tumors. Significant clinical benefits were observed, both in terms of long term survival and recurrence rate, in some of these trials. More recently, however, cancer vaccines targeting well-characterized tumor-associated antigens, i.e. molecules selectively or preferentially expressed by cancer cells but not by normal cells, have been designed and tested in humans. Results obtained as of today with these second-generation vaccines suggest that they are safe and that they can elicit humoral and cellular responses against tumor-specific antigens, without inducing unacceptable clinical signs of autoimmunity. Advances in tumor biology and tumor immunity have helped to better understand the mechanisms displayed by a number of tumors to escape host immunity. This bulk of new knowledge will be used to design future cancer vaccines, which will likely target multiple TAAs, presented by different antigen presentation platforms, in association with synthetic adjuvants and/or immunostimulatory cytokines. Lastly, specific tools allowing to assess in a qualitative and quantitative manner immune responses are critically needed in order to establish correlates between clinical and immune responses in patients receiving experimental vaccines.

Divergent roles for CD4+ T cells in the priming and effector/memory phases of adoptive immunotherapy

The requirement for CD4(+) Th cells in the cross-priming of antitumor CTL is well accepted in tumor immunology. Here we report that the requirement for T cell help can be replaced by local production of GM-CSF at the vaccine site. Experiments using mice in which CD4(+) T cells were eliminated, either by Ab depletion or by gene knockout of the MHC class II beta-chain (MHC II KO), revealed that priming of therapeutic CD8(+) effector T cells following vaccination with a GM-CSF-transduced B16BL6-D5 tumor cell line occurred independently of CD4(+) T cell help. The adoptive transfer of CD8(+) effector T cells, but not CD4(+) effector T cells, led to complete regression of pulmonary metastases. Regression of pulmonary metastases did not require either host T cells or NK cells. Transfer of CD8(+) effector T cells alone could cure wild-type animals of systemic tumor; the majority of tumor-bearing mice survived long term after treatment (>100 days). In contrast, adoptive transfer of CD8(+) T cells to tumor-bearing MHC II KO mice improved survival, but eventually all MHC II KO mice succumbed to metastatic disease. WT mice cured by adoptive transfer of CD8(+) T cells were resistant to tumor challenge. Resistance was mediated by CD8(+) T cells in mice at 50 days, while both CD4(+) and CD8(+) T cells were important for protection in mice challenged 150 days following adoptive transfer. Thus, in this tumor model CD4(+) Th cells are not required for the priming phase of CD8(+) effector T cells; however, they are critical for both the complete elimination of tumor and the maintenance of a long term protective antitumor memory response in vivo.

Design and evaluation of antigen-specific vaccination strategies against cancer

After studies in preclinical mouse models, the efficacy and safety of tumor-specific vaccination strategies is currently being evaluated in cancer patients. The first wave of clinical trials has shown that in general such vaccination strategies are safe. However examples of clinical responses, especially in conjunction with vaccine-induced immune responses, are still scarce. The fact that most trials have so far been performed with end-stage cancer patients can largely account for this deficit. Greater efficacy of anticancer vaccines is expected in patients with less-progressed disease. In addition, the detection of both natural and vaccine-induced T cell immunity needs further improvement.

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.

Advances in specific immunotherapy of malignant melanoma

Management of malignant melanoma continues to present a challenge to dermatologists, particularly in advanced cases. In light of the steady increase in the worldwide incidence and mortality rates for melanoma, better understanding of the immune mechanisms regulating melanoma progression and interaction with the host's immune system seems eminently important. New studies on the role of immune mechanisms in the pathogenesis and clinical course of melanoma have recently been published. We review the immune mechanisms involved in tumor progression and ways in which these mechanisms may be applied toward immunotherapeutic management of malignant melanoma.

LEARNING OBJECTIVE

After the completion of this learning activity, participants should be familiar with (1) the immune mechanisms involved in host-tumor interaction and tumor rejection, (2) factors allowing the escape of melanoma cells from immune recognition, and (3) the current rationale for the different types of specific immunotherapy in melanoma. Better understanding of basic mechanisms in tumor immunology should raise awareness of future immunotherapeutic approaches in patients with melanoma, particularly in those who are at high risk of recurrence or who present with advanced disease.

Evaluation of CD8(+) T-cell frequencies by the Elispot assay in healthy individuals and in patients with metastatic melanoma immunized with tyrosinase peptide

The lack of reproducible, quantitative assays for T-cell responses has been a limitation in the development of cancer vaccines to elicit T-cell immunity. We utilized the Elispot assay, which allows a quantitative and functional assessment of T cells directed against specific peptides after only brief in vitro incubations. CD8(+) T-cell reactivity was determined with an interferon (IFN)-gamma Elispot assay detecting T cells at the single cell level that secrete IFN-gamma. We studied both healthy individuals and patients with melanoma. Healthy HLA-A*0201-positive individuals showed a similar mean frequency of CD8(+) cells recognizing a tyrosinase peptide, YMDGTMSQV, when compared with melanoma patients prior to immunization. The frequencies of CD8(+) cells recognizing the tyrosinase peptide remained relatively constant over time in healthy individuals. Nine HLA-A*0201-positive patients with stage IV metastatic melanoma were immunized intradermally with the tyrosinase peptide together with the immune adjuvant QS-21 in a peptide dose escalation study with 3 patients per dose group. Two patients demonstrated a significant increase in the frequency of CD8(+) cells recognizing the tyrosinase peptide during the course of immunization, from approx. 1/16,000 CD8(+) T cells to approx. 1/4,000 in the first patient and from approx. 1/14,000 to approx. 1/2,000 in the second patient. These results demonstrate that modest expansion of peptide-specific CD8(+) T cells can be generated in vivo by immunization with peptide plus QS-21 in at least a subset of patients with melanoma.

Self-tolerance to the murine homologue of a tyrosinase-derived melanoma antigen: implications for tumor immunotherapy

The human tyrosinase-derived peptide YMDGTMSQV is presented on the surface of human histocompatibility leukocyte antigen (HLA)-A*0201(+) melanomas and has been suggested to be a tumor antigen despite the fact that tyrosinase is also expressed in melanocytes. To gain information about immunoreactivity and self-tolerance to this antigen, we established a model using the murine tyrosinase-derived homologue of this peptide FMDGTMSQV, together with transgenic mice expressing the HLA-A*0201 recombinant molecule AAD. The murine peptide was processed and presented by AAD similarly to its human counterpart. After immunization with recombinant vaccinia virus encoding murine tyrosinase, we detected a robust AAD-restricted cytotoxic T lymphocyte (CTL) response to FMDGTMSQV in AAD transgenic mice in which the entire tyrosinase gene had been deleted by a radiation-induced mutation. A residual response was observed in the AAD(+)tyrosinase(+) mice after activation under certain conditions. At least some of these residual CTLs in AAD(+)tyrosinase(+) mice were of high avidity and induced vitiligo upon adoptive transfer into AAD(+)tyrosinase(+) hosts. Collectively, these data suggest that FMDGTMSQV is naturally processed and presented in vivo, and that this presentation leads to substantial but incomplete self-tolerance. The relevance of this model to an understanding of the human immune response to tyrosinase is discussed.

Tumor-specific immunotherapy based on dominant models of natural tolerance

The assumption that cancer immunotherapy may be based on the existence of autoreactive lymphocytes recognizing self-antigens on cancer cells, obviously opens a new opportunity. Nevertheless this analysis, relying on a recessive model of natural tolerance, limits the approach to try to activate peripheral lymphocytes, by increasing co-stimulatory signals or using modified self-antigens for immunization. Here we hypothesize that, based on emerging dominant tolerance notions in autoimmunity, it would be possible to induce a specific autoimmunity against tumor cells and arrest their growth following the removal of regulatory T cells. These immunoregulatory cells suppress available immunocompetent autoreactive cells capable of destroying tumor cells. Therefore, in order to reach a complete tumor-specific autoimmunity it is necessary to combine the T cell immunosuppression which abrogates the regulatory cells, with the cancer vaccines, which induces extensive proliferation of lymphoid cells directed towards specificities on tumor cells.

DNA vaccines

The premise that DNA coding for antigens produces proteins to stimulate the immune system when inoculated directly into muscle tissues, has the immense attractions of simplicity, versatility and economy. When other vaccination approaches are experiencing practical problems, meeting such challenges as AIDS and malaria, considerable attention has focused on DNA vaccines with entire conferences and a flood of commercial companies devoted to exploring the possibilities. A number of clinical trials for both infectious diseases and cancer have already commenced, even though a number of major issues have to be resolved.

Genetic vaccination with "self" tyrosinase-related protein 2 causes melanoma eradication but not vitiligo

"Self" melanocyte differentiation antigens are potential targets for specific melanoma immunotherapy. Vaccination against murine tyrosinase-related protein (TRP)-1/gp75 was shown recently to cause melanoma rejection, which was accompanied by autoimmune skin depigmentation (vitiligo). To further explore the linkage between immunotherapy and autoimmunity, we studied the response to vaccination with a related antigen, TRP-2. i.m. inoculation of plasmid DNA encoding murine trp-2 elicited antigen-specific CTLs that recognized the B16 mouse melanoma and protected the mice from challenge with tumor cells. Furthermore, mice bearing established s.c. B16 melanomas rejected the tumor upon vaccination with a recombinant vaccinia virus encoding trp-2. Depletion experiments showed that CD8+ lymphocytes and natural killer cells were crucial for the antitumor activity of the trp-2-encoding vaccines. Mice that rejected the tumor did not develop generalized vitiligo, indicating that protective immunity can be achieved in the absence of widespread autoimmune aggression.

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.

Autoimmunity and the immunotherapy of cancer: targeting the "self" to destroy the "other"

It is increasingly clear that immunity to "self"-antigens may result in tumor destruction in mouse and man. But which antigens should be targeted with therapeutic cancer vaccines? In the case of melanoma, recognition of melanocyte differentiation antigens (MDA) can be associated with autoimmune depigmentation (vitiligo). We propose that intersection of protein transport to melanosomes and endosomes allows for the loading of MDA-derived peptides on MHC class II molecules, resulting in the activation of MDA-specific CD4+ "helper" T cells that aid the induction of melanoma-specific CD8+ T cells. Thus, the immunogenicity of MDA may be a consequence of their unique cell biology. Studies of MDA-based vaccines can provide new insight into the development of more effective cancer vaccines.

Coupling and uncoupling of tumor immunity and autoimmunity

Self-antigens, in the form of differentiation antigens, are commonly recognized by the immune system on melanoma and other cancers. We have shown previously that active immunization of mice against the melanocyte differentiation antigen, a tyrosinase-related protein (TRP) gp75(TRP-1) (the brown locus protein) expressed by melanomas, could induce tumor immunity and autoimmunity manifested as depigmentation. In this system, tumor immunity and autoimmunity were mediated by autoantibodies. Here, we characterize immunity against another tyrosinase family glycoprotein TRP-2 (the slaty locus protein), using the same mouse model and method of immunization. As observed previously for gp75(TRP-1), immunity was induced by DNA immunization against a xenogeneic form of TRP-2, but not against the syngeneic gene, and depended on CD4(+) cells. Immunization against TRP-2 induced autoantibodies and autoreactive cytotoxic T cells. In contrast to immunization against gp75(TRP-1), both tumor immunity and autoimmunity required CD8(+) T cells, but not antibodies. Only autoimmunity required perforin, whereas tumor immunity proceeded in the absence of perforin. Thus, immunity induced against two closely related autoantigens that are highly conserved throughout vertebrate evolution involved qualitatively different mechanisms, i.e., antibody versus CD8(+) T cell. However, both pathways led to tumor immunity and identical phenotypic manifestations of autoimmunity.

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.

Taking lessons from dendritic cells: multiple xenogeneic ligands for leukocyte integrins have the potential to stimulate anti-tumor immunity

Expression of large numbers of different costimulatory integrin ligands (CILs) attributes dendritic cells with an ability to induce primary anti-tumor immune responses. Here, we show that optimized gene transfer of the xenogeneic (human) CILs VCAM-1, MAdCAM-1 and ICAM-1 causes rapid and complete rejection of established mouse EL-4 tumors, and generates prolonged systemic anti-tumor immunity; whereas human E-cadherin weakly slows tumor growth. In each case the immune response was mediated by CD8+ T cells and NK cells, accompanied by augmented tumor-specific cytolytic T cell (CTL) activity involving both the perforin and Fas-ligand pathways. Adoptive transfer of splenocytes from cured mice rapidly cleared established tumors in recipients. The mechanism for CIL-mediated immunity is unknown, but may involve CTL-facilitated tumor lysis, since CTLs were generally twice as efficient at killing CIL-transfected tumor cells than parental tumor cells. Optimized CIL-based gene therapy may provide an approach to complement or replace conventional DC adoptive cell therapy for suppressing tumor growth.

An HLA-A2 Polyepitope Vaccine for Melanoma Immunotherapy

Epitope-based vaccination strategies designed to induce tumor-specific CD8 CTL are being widely considered for cancer immunotherapy. Here we describe a recombinant poxvirus vaccine that codes for ten HLA-A2-restricted epitopes derived from five melanoma Ags conjoined in an artificial polyepitope or polytope construct. Target cells infected with the melanoma polytope vaccinia were recognized by three different epitope-specific CTL lines derived from HLA-A2 melanoma patients, and CTL responses to seven of the epitopes were generated in at least one of six HLA-A2-transgenic mice immunized with the construct. CTL lines derived from vaccinated transgenic mice were also able to kill melanoma cells in vitro. Multiple epitopes within the polytope construct were therefore shown to be individually immunogenic, illustrating the feasibility of the polytope approach for melanoma immunotherapy. Tumor escape from CTL surveillance, through down regulation of individual tumor Ags and MHC alleles, might be overcome by polytope vaccines, which simultaneously target multiple cancer Ags.