Immunogenic variants obtained by mutagenesis of mouse mastocytoma P815. II. T lymphocyte-mediated cytolysis

Novel antibodies that selectively block mouse IL-12 enable the re-evaluation of the role of IL-12 in immune protection and pathology

The dimeric cytokine IL-12 is important in the control of various infections but also contributes to the pathology of certain diseases making it a potential target for therapy. However, its specific inhibition with antibodies is complicated by the fact that its two subunits are present in other cytokines: p40 in IL-23 and p35 in IL-35. This has led to erroneous conclusions like the alleged implication of IL-12 in experimental autoimmune encephalomyelitis (EAE). Here, we report the development of a mouse anti-mouse IL-12 vaccine and the production of monoclonal antibodies (mAbs) that do not react with p40 or p35 (in IL-35) but specifically recognize and functionally inhibit the IL-12 heterodimer. Using one of these mAbs, MM12A1.6, that strongly inhibited IFN-γ production and LPS-induced septic shock after viral infection, we demonstrate the critical role played by IL-12 in the rejection of male skin graft by female C57BL/6 syngeneic recipients and in the clearance of an immunogenic mastocytoma tumor variant by DBA/2 mice, but not in a parent to F1 immune aggression model nor in MOG-induced EAE, which was clearly prevented by anti-p40 mAb C17.8. Given this selective inhibition of IL-12, these mAbs provide new options for reassessing IL-12 function in vivo.

Identifying Antigens Recognized by Cytolytic T Lymphocytes on Tumors

Identification of antigenic peptides recognized by cytolytic T lymphocytes (CTL) is a prerequisite for the development of targeted cancer immunotherapy approaches. This chapter provides a global approach for the identification of peptides recognized by CTL. It implies the identification of the HLA molecule presenting the peptide as well as the design and screening of a cDNA library derived from the tumor cells. Methods used for the identification of spliced peptides on tumors are also described.

Cancer Immunosurveillance by T Cells

Cancer immunotherapy is based on the ability of the immune system to recognize tumors as foreign tissue. The idea of cancer immunosurveillance was first conceived over a century ago but remained controversial through much of the 20th century. In the past few decades, however, the field has progressed rapidly, and the concept of tumor immunosurveillance is now well established. With this chapter, we provide a historical background of immunosurveillance, the concept of immunoediting, and the role of different T-cell subsets in the tumor microenvironment. We also discuss the relationship between immune checkpoints, tumor antigens, T cell receptor repertoire, and immunosurveillance. Finally, we comment on the future of immunotherapy as it relates to T cell immunosurveillance.

Multiplex bead-based measurement of humoral immune responses against tumor-associated antigens in stage II melanoma patients of the EORTC18961 trial

Purpose: Determine the prognostic and predictive significance of tumor associated antigen (TAA)-specific serum antibodies in melanoma patients of a large adjuvant vaccination phase III trial. Patients and methods: Serum IgG antibodies were measured against a panel of 43 antigens by a bead-based multiplex assay in 970 stage II melanoma patients of the EORTC18961 trial, evaluating adjuvant ganglioside GM2-KLH/QS-21 vaccination versus observation. Primary end point was relapse-free survival (RFS). Patients' sera at baseline, after 12 and 48 weeks of study treatment and at the last available time point (at recurrence/remission) were evaluated. Results: Prognostic clinical variables are gender, surgical confirmation of lymph node-negative status, Breslow thickness and ulceration of the primary. Prognostic spontaneous antibody responses were associated with a significant dismal (GM2, Rhod_E2, SSX2) or good prognosis (CyclinB1, SCYE1v1) for RFS, distant metastasis-free (DMFS) or overall survival (OS). Predictive spontaneous antibody responses based on significant interaction with treatment were RhodN p = 0.02, Rab38 p = 0.04 for RFS, RhodE2 p = 0.006, Recoverin p = 0.04 for DMFS and RhodE2 p = 0.003; Recoverin p = 0.04, NA17.A p = 0.04, for OS respectively. The subgroups of patients according to antibody responses for RFS were determined for RhodN sero-negative (n = 849, HR = 1.07, p = 0.6); RhodN sero-positive (n = 121,HR = 0.42, p = 0.01) and Rab38 sero-negative (n = 682, HR = 1.12, p = 0.42), Rab38 sero-positive (n = 288, HR = 0.65, p = 0.04) patients respectively. Conclusion: We identified prognostic serum antibody responses against TAA in stage II melanoma patients. A set of antibody responses correlated with a beneficial outcome for GM2 vaccination.

Tum variants: immunogenic variants obtained by mutagen treatment of tumor cells

Mutagen treatment of mouse tumor cells produces at high frequency stable tumor cell variants that are rejected by syngeneic mice. As Thierry Boon discusses here, these 'tum-' variants express new surface antigens that can be recognized by cytolytic T lymphocytes. Tum- variants derived from spontaneous mouse tumors for which no immunogenicity had hitherto been demonstrated induce an immune protection against the parental tumor. Finally, he poses some interesting questions for future investigations.

Tumour antigens recognized by T lymphocytes: at the core of cancer immunotherapy

In this Timeline, we describe the characteristics of tumour antigens that are recognized by spontaneous T cell responses in cancer patients and the paths that led to their identification. We explain on what genetic basis most, but not all, of these antigens are tumour specific: that is, present on tumour cells but not on normal cells. We also discuss how strategies that target these tumour-specific antigens can lead either to tumour-specific or to crossreactive T cell responses, which is an issue that has important safety implications in immunotherapy. These safety issues are even more of a concern for strategies targeting antigens that are not known to induce spontaneous T cell responses in patients.

Identifying source proteins for MHC class I-presented peptides

Identification of antigenic peptides recognized by cytolytic T lymphocytes (CTL) is a prerequisite for the development of targeted cancer immunotherapy approaches. This chapter provides a global approach for the identification of peptides recognized by CTL. It implies the identification of the HLA molecule presenting the peptide as well as the design and screening of a cDNA library derived from the tumor cells.

Molecular cancer vaccines: Tumor therapy using antigen-specific immunizations

Vaccination against tumors promises selective destruction of malignant cells by the host's immune system. Molecular cancer vaccines rely on recently identified tumor antigens as immunogens. Tumor antigens can be applied in many forms, as genes in recombinant vectors, as proteins or peptides representing T cell epitopes.Analysis of various aspects indicates some advantage for peptide-based vaccines over the other modalities. Further refinements and extensively monitored clinical trials are necessary to advance molecular cancer vaccines from concepts into powerful therapy.

Promises and Limitations of Murine Models in the Development of Anticancer T-Cell Vaccines

Murine models have been instrumental in defining the basic mechanisms of antitumor immunity. Most of these mechanisms have since been shown to operate in humans as well. Based on these similarities, active vaccination strategies aimed at eliciting antitumor T-cell responses have been elaborated and successfully implemented in various mouse models. However, the results of human antitumor vaccination trials have been rather disappointing thus far. This review summarizes the different experimental approaches used in mice to induce antitumor T-cell responses and identifies some critical parameters that should be considered when evaluating results from murine models.

Termination of Systemic Immunity in the Presence of Intraocular Tumors: Influence of Ocular Immune Privilege on Tumor Vaccines

Ocular immune privilege preserves the visual axis by preventing the induction of sight-threatening nonspecific inflammation. Although privilege is essential for maintaining visual integrity, intraocular tumors exploit the privileged environment and grow progressively within the anterior chamber of the eye. Recently, a large number of laboratories have constructed genetically engineered tumor cell vaccines that express high levels of costimulatory signals. These vaccines are designed to bypass the normal pathways of T-cell activation and directly activate CD8+ tumor-specific T cells. In the following series of experiments, we determined whether a tumor cell vaccine that uses costimulatory signals (CD80 and IL-12) is capable of eliminating tumors within the immune-privileged anterior chamber. As expected, vaccine-immunized mice rejected subcutaneous flank tumors (a non-privileged site). However, the vaccine failed to protect mice from even a small number of tumor cells transplanted into the immune-privileged anterior chamber. Surprisingly, immunized mice that were simultaneously challenged with subcutaneous and anterior chamber tumors were unable to eliminate tumors at either site. The failure of systemic protective immunity coincided with the loss of tumor-specific delayed hypersensitivity and cytotoxic T cells. We conclude that tumor cell vaccines that induce complete protection against tumors in non-immune-privileged sites fail to protect against the same tumor within an ocular immune-privileged site. Moreover, a tumor that escapes elimination within the eye can terminate systemic protective immunity that is induced by the tumor cell vaccine.

Targets for active immunotherapy against pediatric solid tumors

The potential role of antibodies and T lymphocytes in the eradication of cancer has been demonstrated in numerous animal models and clinical trials. In the last decennia new strategies have been developed for the use of tumor-specific T cells and antibodies in cancer therapy. Effective anti-tumor immunotherapy requires the identification of suitable target antigens. The expression of tumor-specific antigens has been extensively studied for most types of adult tumors. Pediatric patients should be excellent candidates for immunotherapy since their immune system is more potent and flexible as compared to that of adults. So far, these patients do not benefit enough from the progresses in cancer immunotherapy, and one of the reasons is the paucity of tumor-specific antigens identified on pediatric tumors. In this review we discuss the current status of cancer immunotherapy in children, focusing on the identification of tumor-specific antigens on pediatric solid tumors.

Vaccination of a melanoma patient with mature dendritic cells pulsed with MAGE-3 peptides triggers the activity of nonvaccine anti-tumor cells

We previously characterized the CTL response of a melanoma patient who experienced tumor regression following vaccination with an ALVAC virus coding for a MAGE-A3 Ag. Whereas anti-vaccine CTL were rare in the blood and inside metastases of this patient, anti-tumor CTL recognizing other tumor Ags, mainly MAGE-C2, were 100 times more frequent in the blood and considerably enriched in metastases following vaccination. In this study we report the analysis of the CTL response of a second melanoma patient who showed a mixed tumor response after vaccination with dendritic cells pulsed with two MAGE-A3 antigenic peptides presented, respectively, by HLA-A1 and HLA-DP4. Anti-MAGE-3.A1 CD8 and anti-MAGE-3.DP4 CD4 T cells became detectable in the blood after vaccination at a frequency of approximately 10(-5) among the CD8 or CD4 T cells, respectively, and they were slightly enriched in slowly progressing metastases. Additional anti-tumor CTL were present in the blood at a frequency of 2x10(-4) among the CD8 T cells and, among these, an anti-MAGE-C2 CTL clone was detected only following vaccination and was enriched by >1,000-fold in metastases relative to the blood. The striking similarity of these results with our previous observations further supports the hypothesis that the induction of a few anti-vaccine T cells may prime or restimulate additional anti-tumor T cell clones that are mainly responsible for the tumor regression.

The functional significance of tumour-associated cell surface alterations of embryonic and unknown origin

The study of the phenotype of tumours aims to elucidate cell surface alterations that could be used for diagnostic, prognostic or therapeutic purposes. As tumours tend to escape the homeostatic growth control mechanisms of the host, it can be assumed that plasma membrane alterations are also responsible for the antisocial behaviour of tumour cells. Selected features of the transformed phenotype, of fetal or unknown origin, namely tumour-associated antigens, isozymes and growth factors, are discussed in relation to the altered growth pattern of the tumour cell. It is concluded that definitive structure-function relationships have not yet been established, but areas for future investigation are suggested.

A new tumor-specific antigen encoded by MAGE-C2 and presented to cytolytic T lymphocytes by HLA-B44

A panel of cytolytic T lymphocyte (CTL) clones was isolated from metastases and blood samples of a melanoma patient vaccinated with MAGE-3.A1-pulsed autologous dendritic cells. We report here the identification of a new antigen encoded by the MAGE-C2 cancer-germline gene. This antigen is recognized by some of these CTL on HLA-B*4403. The sequence of the peptide is SESIKKKVL. It is processed in various melanoma cell lines expressing MAGE-C2 and HLA-B*4403. Because of the expression pattern of gene MAGE-C2, this new antigen is strictly tumor-specific and could therefore be used for peptide-based antitumoral vaccination.

Identification of a new HLA-A*0201-restricted cytotoxic T lymphocyte epitope from CML28

Identification of cytotoxic T lymphocyte (CTL) epitopes from additional tumor antigens is essential for the development of specific immunotherapy of malignant tumors. CML28, a recently discovered cancer-testis (CT) antigen from chronic myelogenous leukemia, is considered to be a promising target of tumor-specific immunotherapy. Because HLA-A*0201 is one of the most common histocompatibility molecule in Chinese, we aim at identifying CML28 peptides presented by HLA-A*0201. A panel of CML28-derived antigenic peptides was predicted using a computer-based program. Four peptides with highest predicted score were synthesized and tested for their binding affinities to HLA-A*0201 molecule. Then these peptides were assessed for their immunogenicity to elicit specific immune responses mediated by CTLs both in vitro, from PBMCs sourced from four healthy HLA-A*0201(+) donors, and in vivo, in HLA-A*0201 transgenic mice. One of the tested peptides, CML28((173-181)), induced peptide-specific CTLs in vitro as well as in vivo, which could specifically secrete IFN-gamma and lyse major histocompatibility complex (MHC)-matched tumor cell lines endogenously expressing CML28 antigen and CML28((173-181) )pulsed Jurkat-A2/Kb cells, respectively. These results demonstrate that CML28((173-181) )is a naturally processed and presented CTL epitope with HLA-A*0201 motif and has a promising immunogenicity both in vitro and in vivo. As CML28 is expressed in a large variety of histological tumors besides chronic myelogenous leukemia, we propose that the newly identified epitope, CML28((173-181)), would be of potential use in peptide-based, cancer-specific immunotherapy against a broad spectrum of tumors.

Immunological aspects of head and neck cancer: biology, pathophysiology and therapeutic mechanisms

Advanced cancer and head and neck cancer, in particular, remains a major clinical challenge with its associated morbidity and inevitable mortality. Local control of early disease is achievable in many solid tumours with current surgical and radiotherapeutic techniques but metastatic disease is associated with poor outcome and prognosis. It is known that, by the time of presentation, many patients will already have occult microscopic metastatic disease, and surgery and radiotherapy will not result in long-term survival. What little effect modern chemotherapeutic agents have on microscopic disease is, however, limited by systemic toxicity and multi-drug resistance. Immune surveillance is postulated to be operative in man. There is evidence, however, that patients with progressive tumour growth have failure of host defences both locally and systemically. Various possible defects and tumour escape mechanisms are discussed in the review. Immunotherapy and, in particular adoptive T cell therapy and DC therapy, show promise as putative tumour-specific therapy with clinical benefits. These techniques are undergoing development and evaluation in phase 1 clinical trials. Preliminary data suggest that the treatments are well tolerated. Unfortunately, there is limited evidence of significant and prolonged improvements in clinical outcome. Further developments of beneficial protocols (adjuvants, mode and frequency of vaccination etc) and multicentre studies of the use of immunotherapy in cancer are now required.

Polyclonal CTL responses observed in melanoma patients vaccinated with dendritic cells pulsed with a MAGE-3.A1 peptide

Vaccination with mature, monocyte-derived dendritic cells (DC) pulsed with the MAGE-3(168-176) peptide, which is presented by HLA-A1, has been reported to induce tumor regressions and CTL in some advanced stage IV melanoma patients. We present here a precise evaluation of the level of some of these anti-MAGE-3.A1 CTL responses and an analysis of their clonal diversity. Blood lymphocytes were stimulated with the MAGE-3.A1 peptide under limiting dilution conditions and assayed with an A1/MAGE-3 tetramer. This was followed by the cloning of the tetramer-positive cells and by TCR sequence analysis of the CTL clones that lysed targets expressing MAGE-3.A1. We also used direct ex vivo tetramer staining of CD8 cells, sorting, and cloning of the positive cells. In three patients who showed regression of some of their metastases after vaccination, CTL responses were observed with frequencies ranging from 7 x 10(-6) to 9 x 10(-4) of CD8(+) blood T lymphocytes, representing an increase of 20- to 400-fold of the frequencies found before immunization. A fourth patient showed neither tumor regression nor an anti-MAGE-3.A1 CTL response. In each of the responses, several CTL clones were amplified. This polyclonality contrasts with the monoclonality of the CTL responses observed in patients vaccinated with MAGE-3.A1 peptide or with an ALVAC recombinant virus coding for this antigenic peptide.

Effective elicitation of anti-tumor immunity by collocation of antigen with encoding gene in the same vaccine

Peptide and naked DNA vaccines, aimed at generating strong cytotoxic T lymphocyte (CTL) responses capable of mediating tumor regression, have been considered of the most rapidly evolving technologies for tumor vaccination. Results from clinical trials of these strategies are encouraging, but unfortunately, most of those trials have been proved as partly successful. Given the distinct dynamics of antigen presentation for peptide and gene forms of antigens, we explored a novel concept that collocation of the antigen with the encoding gene in the same vaccine could effectively elicit anti-tumor immunity, and developed a novel peptide-DNA dual vaccine (PDDV), which combines the benefits of peptide and DNA vaccines and could induce tumor-specific CTL response. Furthermore, PDDV effectively protected mice against fatal P815 tumor challenge and cured tumor-bearing DBA/2 mice, suggesting PDDV as a potential formulation of tumor vaccine.

Inflammation and cancer, the mastocytoma P815 tumor model revisited: triggering of macrophage activation in vivo with pro-tumorigenic consequences

Subcutaneous in vivo injections of cells of the mastocytoma line P815 in syngenic DBA/2 mice induce locally fast growing solid tumors. These have been used extensively as a cancer model to analyze and manipulate the relationship between tumor cells and host's immune defenses. We report that progression of P815 tumors in vivo was accompanied by a burst (Days 5-7) of local inflammatory cells recruitment and angiogenesis observed histologically, corroborated in vivo by MRI with gadolinium, overtranscription of macrophage activation marker genes, secretion of TNF-alpha by regional lymph node cells and concomitant systemic inflammation. No substantial overtranscriptions of either VEGF or IL-10 or TGF-beta genes were observed. Induction of COX-2 gene was a late event. To establish a possible relationship between the tumor-induced local, regional and systemic increase of pro-inflammatory mediators and progression of tumors in vivo, we carried out experiments deliberately modulating the inflammatory status of the recipient animals. Pretreatment of recipient animals by i.p. injection of thioglycolate accelerated P815 tumor growth. At the opposite, treatment of mice with either a COX-1 + COX-2 inhibitor (aspirin, 1 mg/day/mouse) or a specific COX-2 inhibitor (celecoxib, 0.13 mg/day/mouse) for 2 weeks after injection of tumor cells, significantly reduced the size and growth rate of tumors compared to control mice. Experiments carried out in vitro indicated that peritoneal macrophages from untreated animals were strongly activated by live P815 cells and by P815 membrane preparations. The tumor-induced inflammatory reaction could establish a local micro environment favoring tumor progression. The P815 tumor model might be helpful to recognize important factors controlling host/tumor relationship.

Enhanced UVfemale1 tumor growth in CBF1 mice infected with Schistosoma mansoni due to modulation of Th1-like responses

Effects of Schistosoma mansoni infection on anti-tumor immunity were examined in CBF1 mice with ultraviolet-induced UVfemale1 fibrosarcoma cells. Although many laboratory established tumor cells had rejection mechanisms independent of CD4(+) T cells, we confirmed that CD4(+) cells had significant roles in rejection of UVfemale1 cells in the syngeneic CBF1 mice. When we prepared two CBF1 mouse groups, S. mansoni-infected and schistosome-free, the former group showed up-regulation of Th2-like response to UVfemale1 cells, whereas the latter group mice showed rather type 1-dominant patterns. Cytotoxic activity against UVfemale1 cells tested in vitro, which was attributed to CD8(+) cells, was significantly weaker in S. mansoni-infected mice compared with infection-free mice. In tumor challenge experiments in vivo, we observed that rapid and complete rejection of UVfemale1 cells required the presence of CD8(+) T cells. Under only CD4-depleted situation, survival of tumor cells in schistosome-free mice was prolonged up to 1 month or more. Under the presence of both CD4(+) and CD8(+) cells, S. mansoni infected mice rejected the challenged UVfemale1 cells as was seen in normal mice. However, when CD8(+) cells were depleted from S. mansoni-infected mice, inoculated UVfemale1 cells grew more rapidly than in infection-free mice. Our results suggest that functionally polarized cytokine patterns in schistosome-infected hosts promote rapid tumor growth.

Parameters involved in the recognition of fresh human leukemic blasts by tumor-specific cytolytic T cell clones: a model study

Although clinical experience and in vitro data provide evidence of an anti-leukemic activity of T cells, there are few examples of recognition of leukemic cells by tumor-specific T cells in vitro. Tumor antigens encoded by the MAGE genes are useful tools to study this recognition. We tested the sensitivity to recognition and lysis by anti-MAGE CTL clones of MAGE-A1 positive cell lines HL60 and K562, after transfection with an HLA-A1 construct, and of fresh leukemic blasts from 10 HLA-A2 patients, after incubation with a peptide encoded by gene MAGE-A3. The presentation of MAGE antigens by leukemic cell lines and fresh leukemic blasts induced TNF secretion and cytotoxicity by MAGE-specific CD8(+) CTL clones. The amount of peptide presented by the leukemic blasts, more than the level of expression of HLA class I, adhesion or costimulatory molecules, was the major limiting factor for recognition. These data indicate that leukemic cells may be targeted by T cells showing specificity for a leukemia antigen.

Cytolytic T lymphocytes raised against a human bladder carcinoma recognize an antigen encoded by gene MAGE-A12

Human bladder carcinoma line LB831-BLC expresses several distinct Ags that are recognized by different autologous CTL. Here, we show that one of these Ags is presented by HLA-Cw7 and encoded by gene MAGE-A12. This is the first time that CTL directed against a MAGE-encoded Ag have been derived from the lymphocytes of a patient with cancer other than melanoma. This new Ag was found to be nonapeptide VRIGHLYIL, corresponding to position 170-178 of the MAGE-A12 protein. Gene MAGE-A12 is silent in normal tissues except in male germline cells, which do not express HLA molecules. It is expressed in 26-62% of melanomas, infiltrating bladder carcinomas, lung carcinomas, esophageal carcinomas, and head and neck carcinomas. Because HLA-Cw7 is present in 43% of Caucasians, this new Ag is shared by many tumors and should be a useful target for cancer immunotherapy.

Processing of some antigens by the standard proteasome but not by the immunoproteasome results in poor presentation by dendritic cells

By stimulating human lymphocytes with an autologous renal carcinoma, we obtained CTL recognizing an antigen derived from a novel, ubiquitous protein. The CTL failed to lyse autologous EBV-transformed B cells, even though the latter express the protein. This is due to the presence in these cells of immunoproteasomes, which, unlike standard proteasomes, cannot produce the antigenic peptide. We show that dendritic cells also carry immunoproteasomes and fail to present this antigen. This may explain why the relevant CTL escape thymic deletion and are not regularly activated in the periphery. Lack of cleavage by the immunoproteasome was also observed for melanoma differentiation antigen Melan-A26-35/HLA-A2, currently used for antitumoral vaccination. For immunization with such antigens, proteins should be less suitable than peptides, which do not require proteasome digestion in dendritic cells.

Therapeutic Effects of Tumor-Reactive Type 1 and Type 2 CD8+ T Cell Subpopulations in Established Pulmonary Metastases

Cytolytic CD8+ T cells fall into two subpopulations based on cytokine-secretion. Type 1 CD8+ cells (Tc1) characteristically secrete IFN-γ, whereas type 2 CD8+ cells (Tc2) secrete IL-4 and IL-5. We assessed the relative therapeutic effects of adoptively transferred OVA-specific Tc1 and Tc2 CD8+ cells in mice bearing established OVA-transfected B16 melanoma lung metastases. Both Tc1 and Tc2 subpopulations mediated a reduction in lung tumor growth that subsequently prolonged survival times in mice with both early (day 7) and more advanced (day 14) levels of tumor development. CD8+ T cell populations recovered from spleens of tumor-bearing mice receiving Tc1 or Tc2 cells showed markedly enhanced tumor Ag-specific cytolytic and cytokine-releasing activities that correlated with delays in tumor cell growth and progression. Initially, both tumor-reactive Tc1 and Tc2 effector cells accumulated at the tumor site with nearly equal frequency. Tc1 cells persisted, whereas Tc2 cell numbers progressively diminished over time. Titration of Tc1 and Tc2 effector cells showed that protection was dose dependent with the former being 5-fold more effective. Tc2 cells achieved a comparable reduction in lung tumor cell growth at higher concentrations of cell transfer. Tc1 effectors from IFN-γ-deficient mice were less therapeutically effective than wild-type mice, but there was no significant reduction in activity between corresponding Tc2 populations. We speculate that the effectiveness of Tc1 and Tc2 cells may depend on different mechanisms. These studies suggest a potential role for Tc1 and Tc2 CD8+ subpopulations in tumor regression and immunotherapy.

Cytolytic T Lymphocytes Recognize an Antigen Encoded by MAGE-A10 on a Human Melanoma

From melanoma patient LB1751, cytolytic T lymphocytes (CTL) were generated that lysed specifically autologous tumor cells. To establish whether these CTL recognized one of the Ags that had previously been defined, a CTL clone was stimulated with cells expressing various MAGE genes. It produced TNF upon stimulation with target cells expressing MAGE-A10. The Ag was found to be nonapeptide GLYDGMEHL (codons 254–262), which is presented by HLA-A2.1. This is the first report on the generation of anti-MAGE CTL by autologous mixed lymphocyte-tumor cell culture (MLTC) from a melanoma patient other than patient MZ2, from whom the first MAGE gene was identified. MAGE genes are expressed in many tumors but not by normal tissues except male germline cells and placenta, which do not express HLA molecules. Therefore, the identification of an antigenic peptide derived from MAGE-A10 adds to the repertoire of tumor-specific shared Ags available for anti-tumoral vaccination trials.

Identification of a Second Major Tumor-Specific Antigen Recognized by CTLs on Mouse Mastocytoma P815

Murine mastocytoma P815 induces CTL responses against at least four distinct Ags (AB, C, D, and E). Recent studies have shown that the main component of the CTL response against the P815 tumor is targeted against Ags P815AB and P815E. The gene P1A has been well characterized. It encodes the P815AB Ag in the form of a nonameric peptide containing two epitopes, P815A and P815B, which are recognized by different CTLs. Here, we report the identification of the P815E Ag. Using a cDNA library derived from tumor P815, we identified the gene coding for P815E. We also characterized the antigenic peptide that anti-P815E CTLs recognize on the MHC class I molecule H-2Kd. The P815E Ag results from a mutation within an ubiquitously expressed gene encoding methionine sulfoxide reductase, an enzyme that is believed to be important in the protection of proteins against the by-products of aerobic metabolism. Surprisingly, immunizing mice i.p. with syngeneic tumor cells (L1210) that were constructed to express B7-1 and P815E did not induce resistance against live P815, even though a strong anti-P815E CTL response was observed with splenocytes from immunized animals.

The shared tumor-specific antigen encoded by mouse gene P1A is a target not only for cytolytic T lymphocytes but also for tumor rejection

A number of human tumor antigens have been characterized recently using cytolytic T lymphocytes (CTL) as screening tools. Some of them are encoded by MAGE-type genes, which are silent in normal tissues except in male germ cells, but are activated in a variety of tumors. These tumor-specific shared antigens appear to be promising targets for cancer immunotherapy. However, the choice of these antigens as targets has been questioned because of the lack of direct evidence that in vivo responses against such antigens can lead to tumor rejection. The antigen encoded by the mouse gene P1A represents the only available animal model system for MAGE-type tumor antigens. We show here that mice immunized by injection of L1210 leukemia cells expressing P1A and B7-1 (L1210.P1A.B7-1) are efficiently protected against a challenge with a lethal dose of mastocytoma P815 tumor cells, which express P1A. Mice immunized with L1210 cells expressing B7-1 but not P1A were not protected. Furthermore, we observed that P1A-transgenic mice, which are tolerant to P1A, were not protected after immunization with L1210.P1A.B7-1. These results demonstrate that the immune response to P1A is the major component of the tumor rejection response observed in normal mice, and support the use of tumor-specific shared antigens as targets for the immunotherapy of human cancer.

An Antigen Recognized by Autologous CTLs on a Human Bladder Carcinoma

By stimulating blood lymphocytes with autologous bladder carcinoma cells that had been transfected with B7-1, we obtained a panel of CTL clones which lyse specifically the bladder tumor cells in an MHC class I-restricted fashion. Based on inhibition with anti-HLA Abs and the recognition of allogeneic tumor cells, we could distribute our clones in three groups that recognized three distinct Ags. We characterized one of these Ags by screening a cDNA library prepared with the RNA from this bladder tumor line. This new tumor Ag is a peptide presented by HLA-B4403 molecules. It is produced by a point mutation in a gene that is recorded in databases under the name KIAA0205, is ubiquitously expressed, and whose function is unknown. We also found this mutation in the tumor sample that was originally resected from this patient, but the mutation was not found in the 100 or more independent tumors of various histologic types that were tested. This report is the first to describe the isolation of CTL clones directed against human bladder cancer and the molecular characterization of a bladder tumor Ag.

A CASP-8 mutation recognized by cytolytic T lymphocytes on a human head and neck carcinoma

Of the antigens recognized on human tumors by autologous cytolytic T lymphocytes, all those defined thus far have been identified on melanoma or renal cell carcinoma. We report here the identification of an antigen recognized by autologous cytolytic T lymphocytes on a human squamous cell carcinoma of the oral cavity. The antigen is encoded by a mutated form of the CASP-8 gene. This gene, also named FLICE or MACH, codes for protease caspase-8, which is required for induction of apoptosis through the Fas receptor and tumor necrosis factor receptor-1. The mutation, which was found in the tumor cells but not in the normal cells of the patient, modifies the stop codon and adds an Alu repeat to the coding region, thereby lengthening the protein by 88 amino acids. The ability of the altered protein to trigger apoptosis appears to be reduced relative to the normal caspase-8. The antigenic peptide is a nonamer presented by HLA-B*3503. The five last amino acids are encoded by the extension of the reading frame caused by the mutation. This, together with previous observations of CDK4 and beta-catenin mutations, suggests that a significant fraction of the point mutations generating a tumor antigen also play a role in the tumoral transformation or progression.

HLA and cancer: implications for cancer immunotherapy and vaccination

Both animal models and studies in humans indicate that the immune response has enormous potential for the treatment of cancer, and that HLA plays a central role in this. This role is likely to become increasingly important in years to come, as effective strategies for immunotherapy of cancer are developed. In the last few years, much of the focus of tumour immunology has been on the identification and characterization of tumour-associated antigens that represent HLA-restricted tumour-specific targets. In the next few years the emphasis is likely to change, such that the HLA type and antigen profile of an individual's tumour may define the most appropriate form of therapy for the patient. The ability of tumour cells to down-regulate or lose expression of some or all HLA molecules may prove to be a major barrier to the effectiveness of such treatments. The next few years should show whether the potential of the advances in tumour immunology made over the last decade can be realized, or whether the application of these advances as therapeutic strategies falls short of their promise.

Photodynamic effect on the specific antitumor immune activity

Photofrin is a potent sensitizer which localizes, among other sites in membranes of malignant cells. To evaluate the effect of photodymanic therapy (PDT) on specific antitumoral immunological response, we used a chromium release assay to compare the specific cytolytic activity (CLA) of primed mouse spleen T lymphocytes sensitized against syngeneic mastocytoma P511 cells. P511 cells or lymphocytes or both were treated or not with Photofrin and/or light (514 nm). Photofrin alone (1 microg/ml, 2 h) reduced CLA by 59% when P511 cells were treated although this decrease was not drug dose dependent. Photofrin (1 microg/ml, 2 h) followed by light (25 J/cm2) reduced CLA by 35% in a drug dose dependent manner. Longer incubation times led to reduced CLA inhibition (10% for 3 h incubation) after Photofrin followed by light. The light dose (25, 37, 50 J/cm2) did not influence CLA for a given Photofrin concentration. Photofrin alone (0.5 microg/ml, followed by light (25 J/cm2 for 2 h) reduced CLA respectively by 8 and 45% only when lymphocytes were treated. When lymphocytes and P511 cells were treated with Photofrin alone or followed by light (25 J/cm2), CLA was also reduced (by 19 and 41% respectively). This type of damage can be evaluated in terms of antigen expression on the target cells, on the lymphocyte T receptor, on H-2 (histocompatibility major complex), or on lymphocyte activity after PDT.

The expression of mouse gene P1A in testis does not prevent safe induction of cytolytic T cells against a P1A-encoded tumor antigen

Tumor antigen P815AB is recognized by cytolytic T lymphocytes (CTL) on mouse mastocytoma P815. This antigen is encoded by P1A, a gene activated in several tumors but silent in normal tissues except for testis and placenta. Notwithstanding the expression of P1A in testis, we found that male mice mounted P815AB-specific CTL responses as efficiently as females. The responding males remained fertile and no autoimmune lesions were observed in their testes. By immunohistochemistry with a rabbit antiserum directed against the P1A protein, we identified spermatogonia as the testicular cells expressing P1A. The absence of MHC class-I molecules on spermatogonia could be one of the mechanisms of protection against testicular autoimmunity, as the antigenic peptide should not be displayed at the cell surface. Human genes MAGE, BAGE and GAGE, which also code for tumor antigens recognized by autologous CTL, are not expressed in normal tissues other than testis. The results obtained in mice with antigen P815AB suggest that immunization of human males with such antigens will not generate autoimmune side-effects. Although P1A is strongly expressed in placenta, we also found that gestation did not prevent generation of CTL responses against antigen P815AB, and that such CTL responses did not affect gestation outcome. We identified labyrinthine trophoblasts as the placental cells expressing P1A. Again, the absence of MHC class-I molecules on these cells provides a plausible explanation for placental protection, although other mechanisms may also play a role.

A new gene coding for an antigen recognized by autologous cytolytic T lymphocytes on a human renal carcinoma

Previous reports have described antigens that are recognized on human melanoma cells by autologous cytolytic T lymphocytes (CTL). The genes coding for a number of these antigens have been identified. Here we report the cloning of a gene that codes for an antigen recognized by autologous CTL on a human renal carcinoma cell line. This antigen is presented by HLA-B7 and is encoded by a new gene that we have named RAGE1. No expression of RAGE1 was found in normal tissues other than retina. RAGE1 expression was found in only one of 57 renal cell carcinoma samples, and also in some sarcomas, infiltrating bladder carcinomas, and melanomas. This represents the first identification of an antigen recognized by autologous CTL on a renal tumor.

Induction of a cytolytic T-cell response in mice with a recombinant adenovirus coding for tumor antigen P815A

We investigated the efficacy of a recombinant adenovirus in inducing a cytolytic T-lymphocyte (CTL) response in mice against tumor antigen P815A, which is present on mouse mastocytoma P815. The recombinant adenoviral vector (Adeno.PIA) contained the sequence coding for the antigenic nonapeptide which binds to the H-2.Ld molecule to form antigen P815A. We verified that murine cells infected in vitro with Adeno. PIA were lysed by an anti-P815A CTL clone. Mice then received a single intradermal injection of Adeno. PIA, and after a few weeks their spleen cells were stimulated in vitro with tumor cells expressing antigen P815A. An anti-P815A CTL response was observed with the spleen lymphocytes of nearly all the mice, providing the lymphocytes were re-stimulated in vitro with cells expressing both P815A and co-stimulatory molecule B7.1. When the stimulatory cells did not express B7.1, a specific CTL response was observed in only 45% of the mice, and it was less intense. The Adeno. P1A viral vector was unable to raise an anti-P815A response in mice that had been previously infected with a recombinant adenovirus carrying the beta-galactosidase gene or with a defective adenovirus. We conclude that adenoviral vectors may be very useful for the priming of cytolytic T-cell responses directed against human tumor antigens. Other modes of immunization may be necessary to boost the responses induced with adenoviral vectors.

A mutated HLA-A2 molecule recognized by autologous cytotoxic T lymphocytes on a human renal cell carcinoma

Many human tumor cells have been shown to express antigens that are recognized by autologous cytotoxic T lymphocytes (CTL) and the molecular nature of a number of melanoma antigens has been defined recently. Here we describe the characterization of an antigen recognized on a renal cell carcinoma by autologous CTL clones. This antigen is encoded by the HLA-A2 gene present in the tumor cells. The sequence of this gene differs from the HLA-A2 sequence found in autologous peripheral blood lymphocytes by a point mutation that results in an arginine to isoleucine exchange at residue 170, which is located on the alpha-helix of the alpha 2 domain. Transfection experiments with the normal and mutated HLA-A2 cDNA demonstrated that this amino acid replacement was responsible for the recognition of the HLA-A2 molecule expressed on the tumor cells. The mutant HLA-A2 gene was also detected in the original tumor tissue from the patient, excluding the possibility that the mutation had appeared in vitro. Thus, HLA class I molecules carrying a tumor-specific mutation can be involved in the recognition of tumor cells by autologous CTL.

T cell tolerance and activation to a transgene-encoded tumor antigen

Much has been learned in recent years concerning the nature of tumor antigens recognized by T cells. To apply this knowledge clinically, the nature of the host response to individual and multiple tumor antigens has to be characterized. This will help to define the efficacy of immune surveillance and the immune status of the host following exposure to tumor antigens expressed on pre-neoplastic tissue. To approach these questions, we have developed a transgenic mouse which expresses the tumor-specific antigen P91A. The single amino acid substitution in P91A results in the expression of a new MHC class I (H-2Ld)-binding peptide. In transgenic tissue, the H-2Ld/P91A complex is expressed in isolation from other tumor-associated antigens, allowing definition of the immune response to a single defined tumor antigen, a situation closely analogous to events during tumorigenesis. We show that CD8+ T cell immune surveillance of P91A is ineffective without the introduction of a helper determinant operating through stimulation of CD4+ T cells. Recognition of the isolated P91A tumor antigen on normal tissue by CD8+ T cells is a tolerogenic process. Induction of T cell tolerance suggests tumor antigen-T cell interactions occurring during tumorigenesis may elicit T cell tolerance and hence confound some immunotherapeutic approaches.

A peptide recognized by human cytolytic T lymphocytes on HLA-A2 melanomas is encoded by an intron sequence of the N-acetylglucosaminyltransferase V gene

A cytolytic T lymphocyte (CTL) clone that lyses many HLA-A2 melanomas was derived from a population of tumor-infiltrating lymphocytes of an HLA-A2 melanoma patient. The gene coding for the antigen recognized by this CTL was identified by transfection of a cDNA library. It is the gene which has been reported to code for N-acetylglucosaminyltransferase V (GnT-V). Remarkably, the antigenic peptide recognized by the CTL is encoded by a sequence located in an intron. In contrast to the fully spliced GnT-V mRNA, which was found in a wide range of normal and tumoral tissues, the mRNA containing the intron region coding for the antigen was not found at a significant level in normal tissues. This mRNA was observed to be present in about 50% of melanomas. Our results suggest that a promoter located near the end of the relevant intron is activated in melanoma cells, resulting in the production of an mRNA coding for the antigen.

Regulatory mechanisms of antitumor T cell responses in the tumor-bearing state

Tumor-bearing hosts develop antitumor immune responses. However, a number of immunosuppressive mechanisms come into operation with the progression of tumor growth. This article will review the observations regarding the modulation of antitumor immune responses in the tumor-bearing state, and consider the mechanisms underlying tumor-induced immune defects, especially in the light of the induction of an abnormal cytokine network. We will also describe the restoration of suppressed antitumor immune responses by administration of a particular cytokine, interleukin-12.

A new family of genes coding for an antigen recognized by autologous cytolytic T lymphocytes on a human melanoma

Human melanoma MZ2-MEL expresses several distinct antigens that are recognized by autologous cytolytic T lymphocytes (CTL). Some of these antigens are encoded by genes MAGE-1, MAGE-3, and BAGE, which are expressed in a large fraction of tumors of various histological types but are silent in normal adult tissues with the exception of testis. We report here the identification of the gene coding for MZ2-F, another antigen recognized by autologous CTL on MZ2-MEL cells. This gene, which was named GAGE-1, is not related to any presently known gene. It belongs to a family of genes that are expressed in a variety of tumors but not in normal tissues, except for the testis. Antigenic peptide YRPRPRRY, which is encoded by GAGE-1, is recognized by anti-MZ2-F CTL on class I molecule HLA-Cw6. The two genes of the GAGE family that code for this peptide, namely GAGE-1 and GAGE-2, are expressed in a significant proportion of melanomas (24%), sarcomas (25%), non-small cell lung cancers (19%), head and neck tumors (19%), and bladder tumors (12%). About 50% of melanoma patients carry on their tumor at least one of the presently defined antigens encoded by the MAGE, BAGE, and GAGE genes.

Experimental gene therapy of cancer using tumor cells engineered to secrete interleukin-13

Cytokines locally delivered to the site of a tumor boost both specific and nonspecific host anti-tumor defenses. Interleukin (IL)-13 is a recently described cytokine produced by mouse type 2 helper T lymphocytes. The aim of this study was to evaluate the inhibition of tumor growth induced by IL-13 delivered locally within or around transplanted tumor cells in mice. We observed that local administration of IL-13 at the site of transplanted tumor cells in vivo had potent inhibitory effects on growth of both immunogenic (P815 mastocytoma, H-2d) or nonimmunogenic (3LL lung carcinoma, H-2b) tumor cells. Mice injected with transfected P815 cells secreting large amounts of IL-13 rejected the P815 tumor and developed systemic specific anti-tumor immunity leading to long-lasting specific anti-tumor protection. Less efficient anti-tumoral effects were obtained with the nonimmunogenic 3LL tumor model when local administration of IL-13 was achieved by co-inoculating xenogeneic chinese hamster ovary (CHO) IL-13 cells. Several local injections of CHO IL-13 cells were needed to obtain rejection of 3LL tumors and no induction of long-lasting anti-3LL memory was obtained. Several studies were performed to elucidate the IL-13 anti-tumoral effects. Experiments with nude mice indicated that Il-13 can also stimulate nonspecific anti-tumor defenses. The histological examination of P815 IL-13 cells undergoing rejection showed monocytic cells and neutrophils infiltrating the tumor. Studies indicated that IL-13 administered in vitro did not directly stimulate the cytotoxicity of peritoneal macrophages and natural killer cells. However, experiments with Boyden chemotaxis chambers indicated that IL-13 was chemotactic for macrophages. Finally, preliminary experiments in vitro suggest that IL-13 improved antigenic presentation of P815 membranes. Thus, anti-tumor effects of IL-13 in vivo most probably result from pleiotropic effects including recruitment of nonspecific cells and improved stimulation of immune-specific anti-tumor effectors.

Treatment with 8-MOP and UVA enhances MHC class I synthesis in RMA cells: preliminary results

The response of psoriasis and cutaneous T-cell lymphoma to treatment with 8-methoxypsoralen (8-MOP) and long wavelength ultraviolet light (UVA) is only partly understood. Psoralens form photoadducts within the DNA after activation by UVA and this damage leads to the inhibition of DNA synthesis. Additionally, it has been shown that different forms of DNA damage can induce a stress response, leading to upregulation of selected products. Among these are the major histocompatibility complex (MHC) class I genes. Thus the aim of the present study was to assess the rate of synthesis of MHC class I proteins in murine T-cell lymphoma cells (RMA) after treatment with 8-MOP and UVA. RMA cells were treated with 8-MOP (50-200 ng ml-1) and UVA (1 J.cm-2) and metabolically labelled with 35S-methionine 4 and 24 h after treatment. MHC class I synthesis was determined by immunoprecipitation of the cell lysates with an anti-Kb monoclonal antibody, Y3. After 4 h, treated and untreated cells demonstrated no differences in the rate of MHC class I synthesis. However, after 24 h a dose-dependent increase in MHC class I synthesis was observed. This increase in MHC class I expression could be responsible, at least partly, for the responses observed in patients treated with photopheresis.

Anti-leukocyte function-1 antibody treatment prevents the rejection of intraocular regressor tumors and their metastases

The role of the cell adhesion molecules, LFA-1 and ICAM-1, in intraocular tumor rejection was examined using four different syngeneic intraocular regressor tumors and four different inbred mouse strains. All four tumors undergo T cell-dependent immune rejection in the syngeneic host. Two of the tumors, D5.1G4 melanoma and P91 mastocytoma, undergo rejection by a cytotoxic T lymphocyte-like immune process. The other two tumors, UV5C25 fibrosarcoma and 124E2 melanoma, are rejected by a process that appears to be mediated by delayed-type hypersensitivity. Systemic administration of anti-LFA-1 prevented the rejection of all four categories of tumors. By contrast, similar in vivo treatment with anti-ICAM-1 antibody did not inhibit tumor rejection. The effect of anti-LFA-1 and anti-ICAM-1 antibody treatment on the rejection of metastases arising from intraocular P91 tumors was also examined and found to be highly dependent upon normal LFA-1 function since antibody treatment with anti-LFA-1 prevented the rejection of metastases. Treatment with anti-ICAM-1 antibody alone had no appreciable effect on the rejection of metastases. The results from this study indicate that the expression and function of LFA-1 is crucial for the generation of immune responses to tumor antigens originating within the eye and the expression of tumor immunity within the eye and at distant sites.

Increased surface expression of class I MHC molecules on immunogenic cells derived from the xenogenization of P815 mastocytoma cells with 8-methoxypsoralen and long-wavelength ultraviolet radiation

In a previous study we demonstrated that the treatment of the highly tumorigenic cell line, P815, with 8-methoxypsoralen and long-wavelength ultraviolet radiation resulted in the production of several immunogenic clones (tum-). Mice inoculated with the tum- cells survived much longer than mice inoculated with the original tumorigenic cells (tum+). It was suggested that the increased survival of mice treated with the tum- clones arose as a result of an increased antigenicity derived from the phototreatment. In this report we show that the tum- cells have a greater density of class I MHC molecules on their surface (50-157% compared to P815). Class I MHC density on the cell surface is required to elicit targeted cytotoxic responses. These results can be considered in terms of human class I MHC assays which show that many human tumor cells have a reduced expression of class I MHC. Because other DNA damaging agents have also been shown to enhance class I expression, it is suggested that in addition to the cytotoxic effects of these agents, other pleiotropic effects must be considered. Photochemotherapy may phenotypically alter cells so that the enhanced expression of class I MHC molecules on the surface of phototreated cells may be associated with the clinical responses observed in cutaneous T cell lymphoma patients.

p23 transplantation antigen mRNA is differentially expressed in human fetal brain

As gene expression governs development, we attempted to isolate differentially expressed genes in fetal and adult human brain. RNA samples extracted from adult and 18-24-week-old fetal human brain were reverse transcribed, amplified using twenty combinations of 3'-anchored primers and degenerate 5'-primers, and the resulting cDNA fragments separated on denaturing polyacrylamide gels. Thereafter, 45 (H1-H45) differentially displayed cDNA bands were extracted from the gels, amplified by polymerase chain reaction, and used as probes to detect their mRNA by northern blotting. One of these fragments, H8, confirmed on northern blotting to be highly expressed in fetal brain, was cloned and sequenced. This fragment was homologous to wild type p23 human transplantation antigen. This is phylogenetically a well conserved gene and appears to play an important role in cell growth. Even a single point mutation in the mouse gene results in cell destruction secondary to a cytotoxic T-lymphocyte response. Therefore, our finding that normal human fetal brain expresses high levels of wild type p23 transplantation antigen may have importance in maintaining cell growth during human brain development.

Individual differences in the orientation of the cytolytic T cell response against mouse tumor P815

We reported previously that the mouse tumor P815 expresses four distinct antigens (A, B, C, D) recognized by syngeneic cytolytic T lymphocytes (CTL). A fifth P815 antigen (E) was identified by means of a CTL clone derived from tumor-infiltrating lymphocytes. We compared a number of mice for the orientation of their CTL response with respect to the various P815 antigens. Lymphocytes from mice inoculated subcutaneously with living P815 cells were stimulated in vitro with tumor cells and the resulting CTL were tested against targets expressing either antigens A and B or antigens C, D and E. Many mice had an asymmetrical response, some producing CTL directed almost exclusively against antigens A, B and others producing CTL directed almost exclusively against C, D. E. When mice were inoculated into two separate sites, different orientations in the responses of the two local lymph nodes were often observed, suggesting that individual differences in the orientation of the anti-P815 CTL response do not result from preexisting differences between the animals. Asymmetrical CTL responses persisted in mice that were given a second injection of tumor cells. A possible interpretation of our results is that the major component of the CTL response is made of the progeny of a very small number of CTL precursors that happen to be the first to be stimulated by the tumor antigens.

BAGE: a new gene encoding an antigen recognized on human melanomas by cytolytic T lymphocytes

Several tumor antigens are recognized by autologous cytolytic T lymphocytes (CTL) on human melanoma MZ2-MEL. Some of them are encoded by genes MAGE-1 and MAGE-3, which are not expressed in normal tissues except in testis. Here, we report the identification of a new gene that codes for another of these antigens. This gene, named BAGE, codes for a putative protein of 43 aa and seems to belong to a family of several genes. The antigen recognized by the autologous CTL consists of BAGE-encoded peptide AARAVFLAL bound to an HLA-Cw 1601 molecule. Gene BAGE is expressed in 22% of melanomas, 30% of infiltrating bladder carcinomas, 10% of mammary carcinomas, 8% of head and neck squamous cell carcinomas, and 6% of non-small cell lung carcinomas. Like the MAGE genes, it is silent in normal tissues with the exception of testis. Because of its tumor-specific expression, the BAGE-encoded antigen may prove useful for cancer immunotherapy.

Localization of two cytotoxic T lymphocyte epitopes and three anchoring residues on a single nonameric peptide that binds to H-2Ld and is recognized by cytotoxic T lymphocytes against mouse tumor P815

Mouse mastocytoma P815 expresses tumor antigens P815A and P815B encoded by a single gene called P1A and carried by a single peptide named P1A 35-43 (NH2-Leu-Pro-Tyr-Leu-Gly-Trp-Leu-Val-Phe-COOH). P1A 35-43 is presented to anti-P815A and anti-P815B cytotoxic T lymphocytes (CTL) by major histocompatibility complex (MHC) H-2Ld molecules. In order to determine the individual role played by each amino acid residue of P1A 35-43 in binding to H-2Ld and in recognition by anti-A and anti-B T cell receptors (TcR), a series of P1A35-43 peptides substituted by alanine at single positions was synthesized and tested for binding to H-2Ld and for CTL recognition. Binding to H-2Ld was estimated by measuring the ability of the peptide to up-regulate cell surface expression of H-2Ld. We found that three residues were important for interaction of P1A 35-43 with H-2Ld. Two of them, Pro at position 2 and Phe at position 9 were consistent with the described H-2Ld binding motif. A third residue, Trp at position 6, was also required for effective MHC binding of the tumor antigen. CTL sensitization assays showed that alanine substitution at position 7 (Leu) or at position 8 (Val) dramatically affected peptide recognition by anti-A CTL while positions 3 (Tyr) and 4 (Leu) were critical for recognition by anti-B CTL. We conclude that Pro2, Trp6 and Phe9 constitute the anchor residues of P1A 35-43 to H-2Ld, whereas the dipeptidyl sequences Tyr3-Leu4 and Leu7-Val8 form the core epitopes recognized by the TcR of anti-P815B and anti-P815A CTL, respectively.

An intracisternal A-particle sequence codes for an antigen recognized by syngeneic cytolytic T lymphocytes on a mouse spontaneous leukemia

Cytolytic T lymphocyte (CTL) clones directed against spontaneous mouse leukemia LEC have been obtained. By transfecting a cosmid library into cells which were then tested for their ability to stimulate the CTL, we identified the gene coding for the antigen recognized by one of these CTL clones. It is the gag gene of an endogenous defective retrovirus that belongs to the intracisternal A particle (IAP) family. A gag-encoded nonapeptide presented by the H-2 Dk molecule caused recognition by the anti-LEC CTL clone. Southern blot and polymerase chain reaction analyses indicated that the expression of the antigen by the LEC tumor cell line resulted from the transposition of an IAP sequence into a new genomic location.