Identification of a novel major histocompatibility complex class II-restricted tumor antigen resulting from a chromosomal rearrangement recognized by CD4(+) T cells

Granulocyte-macrophage-colony-stimulating factor added to a multipeptide vaccine for resected Stage II melanoma

BACKGROUND

Forty-eight patients with resected Stages IIA and IIB melanoma were immunized with two tumor antigen epitope peptides derived from gp100(209-217) (210M) (IMDQVPSFV) and tyrosinase(368-376) (370D) (YMDGTMSQV) emulsified with incomplete Freund's adjuvant (IFA). Patients were assigned randomly to receive either peptides/IFA alone or with 250 microm of granulocyte-macrophage-colony-stimulating factor (GM-CSF) subcutaneously daily for 5 days to evaluate the toxicities and immune responses in either arm. Time to recurrence and survival were secondary end points.

METHODS

Immunizations were administered every 2 weeks x 4, then every 4 weeks x 3, and once 8 weeks later. A leukapheresis to obtain peripheral blood mononuclear cells for immune analyses and skin testing with peptides and recall reagents was performed before and after eight vaccinations.

RESULTS

Local pain and granuloma formation, fever, and lethargy of Grade 1 or 2 were observed. Transient vaccine-related Grade III and no Grade IV toxicity was observed. Seventeen of the 40 patients for whom posttreatment skin tests were performed developed a positive skin test response to the gp100 peptide, but only 1 of the 40 patients developed a positive skin test response to tyrosinase. Immune responses were measured by release of interferon-gamma (IFN-gamma) in an enzyme-linked immunosorbent assay (ELISA) by effector cells in the presence of peptide-pulsed antigen-presenting cells, by cytokine release of IFN-gamma, GM-CSF, and tumor necrosis factor-alpha in a Luminex assay, or by an antigen-specific tetramer flow cytometry assay. Thirty-four of the 39 patients for whom the ELISA data were performed demonstrated an immune response after vaccination, as did 37 of 42 patients by tetramer assay. Enzyme-linked immunosorbent assay, Luminex, and tetramer responses in the GM-CSF/peptide/IFA group were higher than in the peptide/IFA group. Epitope spreading to the MART-1/MelanA 27-35 and 26-35 (27L) epitopes was detected by tetramer assay in 10 patients. Seven of 48 patients experienced disease recurrence with a median of 24 months of follow-up and 2 patients in this intermediate to high risk group have died.

CONCLUSION

These data suggest a significant number of patients with resected melanoma mount an antigen-specific immune response against a peptide vaccine. There is a trend for GM-CSF to modestly increase the immune response and support further development of GM-CSF as a vaccine adjuvant.

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.

Enhancing antitumor immune responses: intracellular peptide delivery and identification of MHC class II-restricted tumor antigens

The importance of T-cell-mediated antitumor immunity has been demonstrated in both animal models and human cancer therapy. The identification of major histocompatibility complex (MHC) class I-restricted tumor antigens has generated a resurgence of interest in immunotherapy for cancer. However, recent studies suggest that therapeutic strategies that have mainly focused on the use of CD8+ T cells (and MHC class I-restricted tumor antigens) may not be effective in eliminating cancer cells in patients. Novel strategies have been developed for enhancing T-cell responses against cancer by prolonging antigen presentation of dendritic cells to T cells and the inclusion of MHC class II-restricted tumor antigens. identification of MHC class II-restricted tumor antigens, which are capable of stimulating CD4+ T cells, not only aids our understanding of the host immune responses against cancer antigens, but also provides opportunities for developing effective cancer vaccines.

Natural antigenic peptides from squamous cell carcinoma recognized by autologous HLA-DR8-restricted CD4+ T cells

A large number of human tumor antigens recognized by CD8+ cytotoxic T lymphocytes (CTL) have been identified. Some of them have been employed in clinical trials and have achieved some objective responses. However, little is known about those that are recognized by CD4+ T cells, except for a very few that were identified from melanomas. Previously, we reported that an oral squamous cell carcinoma (SCC) cell line, OSC-20, was effectively lysed by HLA-DRB1*08032 (HLA-DR8)-restricted autologous CD4+ T cell line, TcOSC-20. In this study, we performed two steps of chromatographic purification of the tumor cell lysate in combination with mass spectrometry. We found one reverse-phase high-performance liquid chromatography (RP-HPLC) fraction that was effectively recognized by the T cells. We analyzed the fraction by nano-liquid chromatography/electrospray ionization ion trap mass spectrometry (LC/MS/MS) and found six representative ions. We could determine the primary amino acid sequence of each of the six ions. Three of them contained a potential HLA-DR8 binding motif, and TcOSC-20 showed a rather strong cytotoxic response to one of the synthetic peptides, namely, amino acid residues 321-336 of human alpha-enolase. Thus, several gene products of squamous cancer cells are endogenously processed and may be presented on HLA class II molecules, so that they could constitute target molecules for autologous CD4+ T cells.

Establishment of 15 cancer cell lines from patients with lung cancer and the potential tools for immunotherapy

BACKGROUND

Since lung cancer is the major cause of death not only in Japan but in many other industrialized countries, the development of new therapeutic modalities is quite important. In patients with melanoma, immunotherapy with some tumor antigens has been shown to result in tumor regression. However, little is known about specific immune responses and tumor antigens in lung cancer, due to difficulty in establishing appropriate lung cancer cell lines. In order to resolve these difficulties, we tried to establish and characterize lung cancer cell lines as useful tools for the analysis of tumor-specific immune responses in patients with lung cancer.

MATERIALS AND METHODS

We tried to establish lung cancer cell lines from 549 patients with resectable lung cancer and from 21 patients with pleural and pericardial effusions or lymph node metastasis. We characterized the established cell lines after the induction of tumor-specific cytotoxic T lymphocytes (CTLs), and analyzed both the major histocompatibility complex (MHC) class I and class II molecules on their surfaces.

RESULTS

We succeeded in establishing 15 lung cancer cell lines from 570 specimens (2.6%). The success rate of the establishment of lung cancer cell lines was significantly higher in patients at such advanced stages as MHC III and IV than in those at MHC stages I and II (p = 0.004). MHC class I molecules were expressed in 12 of 15 cell lines (80%), while MHC class II molecules were found in 3 of 15 cell lines (20%) on their cell surfaces by flow cytometry. A haplotype loss of MHC class I antigens was found in 6 of 15 cell lines (40%). Although CTLs were induced in only two of eight cell lines tried by stimulation with nontransduced autologous tumor cell lines, CTLs were successfully induced in all of eight cell lines tested by stimulation with CD80-transfected autologous tumor cells.

CONCLUSIONS

These results suggested that the tumor antigens recognized by CTLs could thus exist in the tumor cells derived from many lung cancer patients. It is, therefore, possible that antigen-specific immunotherapies may be potentially effective for patients with lung cancer by adoptive transfer of CTLs, as well as by vaccine therapy using tumor-specific antigens.

Cancer immunotherapy with peptide-based vaccines: what have we achieved? Where are we going?

Many human tumor-associated antigens (TAAs) have recently been identified and molecularly characterized. When bound to major histocompatibility complex molecules, TAA peptides are recognized by T cells. Clinical studies have therefore been initiated to assess the therapeutic potential of active immunization or vaccination with TAA peptides in patients with metastatic cancer. So far, only a limited number of TAA peptides, mostly those recognized by CD8(+) T cells in melanoma patients, have been clinically tested. In some clinical trials, partial or complete tumor regression was observed in approximately 10%-30% of patients. No serious side effects have been reported. The clinical responses, however, were often not associated with a detectable T-cell-specific antitumor immune response when patients' T cells were evaluated in ex vivo assays. In this review, we analyze the available human TAA peptides, the potential immunogenicity (i.e., the ability to trigger a tumor-specific T-cell response) of TAA peptides in vitro and ex vivo, and the potential to construct slightly modified forms of TAA peptides that have increased T-cell stimulatory activity. We discuss the available data from clinical trials of TAA peptide-based vaccination (including those that used dendritic cells to present TAA peptides), identify possible reasons for the limited clinical efficacy of these vaccines, and suggest ways to improve the clinical outcome of TAA peptide-based vaccination for cancer patients.

Identification of a mutated fibronectin as a tumor antigen recognized by CD4+ T cells: its role in extracellular matrix formation and tumor metastasis

CD4+ T cells play an important role in orchestrating host immune responses against cancer, particularly by providing critical help for priming and extending the survival of CD8+ T cells. However, relatively little is known about major histocompatibility complex class II-restricted human tumor antigens capable of activating CD4+ T cells. Here, we describe the identification of a mutated fibronectin (FN) as a tumor antigen recognized by human histocompatibility leukocyte antigen-DR2-restricted CD4+ T cells. Deoxyribonucleic acid (DNA) sequencing analysis indicated that this gene contains a mutation that results in the substitution of lysine for glutamic acid and gives rise to a new T cell epitope recognized by CD4+ T cells. Tumor cells harboring the mutant FN resulted in the loss of FN matrix formation and the gain of metastatic potential based on the migration pattern compared with that of tumor cells that express wild-type FN. Additional experiments using cell lines stably expressing the mutated FN cDNA demonstrated that the point mutation in FN was responsible for the loss of FN staining in extracellular matrices and the enhancement of tumor cell migration. These findings represent the first demonstration that a mutated gene product recognized by CD4+ T cells is directly involved in tumor metastasis, which indicates the importance of CD4+ T cells in controlling the spread of tumor cells to distant anatomic sites.

Assumptions of the tumor 'escape' hypothesis

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

Progress in the development of immunotherapy for the treatment of patients with cancer

Several recent developments have hallmarked progress in tumour immunology and immunotherapy. The use of interleukin-2 (IL-2) in cancer patients demonstrated that an immunological manipulation was capable of mediating the regression of established growing cancers in humans. The identification of the genes encoding cancer antigens and the development of means for effectively immunizing patients against these antigens has opened important new avenues of exploration for the development of effective active and cell-transfer immunotherapies for patients with cancer.

Histone deacetylase activity represses gamma interferon-inducible HLA-DR gene expression following the establishment of a DNase I-hypersensitive chromatin conformation

Expression of the retinoblastoma tumor suppressor protein (Rb) is required for gamma interferon (IFN-gamma)-inducible major histocompatibility complex class II gene expression and transcriptionally productive HLA-DRA promoter occupancy in several human tumor cell lines. Treatment of these Rb-defective tumor cell lines with histone deacetylase (HDAC) inhibitors rescued IFN-gamma-inducible HLA-DRA and -DRB mRNA and cell surface protein expression, demonstrating repression of these genes by endogenous cellular HDAC activity. Additionally, Rb-defective, transcriptionally incompetent tumor cells retained the HLA-DRA promoter DNase I-hypersensitive site. Thus, HDAC-mediated repression of the HLA-DRA promoter occurs following the establishment of an apparent nucleosome-free promoter region and before transcriptionally productive occupancy of the promoter by the required transactivators. Repression of HLA-DRA promoter activation by HDAC activity likely involves a YY1 binding element located in the first exon of the HLA-DRA gene. Chromatin immunoprecipitation experiments localized YY1 to the HLA-DRA gene in Rb-defective tumor cells. Additionally, mutation of the YY1 binding site prevented repression of the promoter by HDAC1 and partially prevented activation of the promoter by trichostatin A. Mutation of the octamer element also significantly reduced the ability of HDAC1 to confer repression of inducible HLA-DRA promoter activation. Treatment of Rb-defective tumor cells with HDAC inhibitors greatly reduced the DNA binding activity of Oct-1, a repressor of inducible HLA-DRA promoter activation. These findings represent the first evidence that HDAC activity can repress IFN-gamma-inducible HLA class II gene expression and also demonstrate that HDAC activity can contribute to promoter repression following the establishment of a DNase I-hypersensitive chromatin conformation.

Cancer vaccines

Attempts to generate an anticancer immune response in vivo in patients with cancer have taken several forms. Although to date there have been relatively few published studies describing the effects of the approach in hematologic malignancy, that circumstance is expected to change rapidly during the next few years. In solid tumors, it is not known which, if any, of the approaches being explored will be able to produce responses of sufficient effectiveness and duration to be of general clinical value. Despite the documented increase in survival of patients developing an immune response to tumor immunization, no randomized clinical trial has been entirely convincing. As knowledge of the molecular basis of the immune response and of the immune defenses used by cancer cells improves, it is reasonable to expect to see increasing benefits from tumor vaccines, which are likely to complement, long before they replace, conventional therapies.

Melanoma-Reactive CD8+ T cells recognize a novel tumor antigen expressed in a wide variety of tumor types

An autologous melanoma cell line selected for loss of expression of the immunodominant MART-1 and gp100 antigens was initially used to carry out a mixed lymphocyte tumor culture (MLTC) in a patient who expressed the human leukocyte antigen (HLA)-AI and HLA-A2 class I major histocompatibility complex alleles. Ten clones identified from this MLTC seemed to recognize melanoma in an HLA-A1-restricted manner but failed to recognize a panel of previously described melanoma antigens. The screening of an autologous melanoma cDNA library with one HLA-Al-restricted melanoma-reactive T-cell clone resulted in the isolation of a cDNA clone called AIM-2 (antigen isolated from immunoselected melanoma-2). The AIM-2 transcript seemed to have retained an intronic sequence based on its alignment with genomic sequences as well as expressed sequence tags. This transcript was not readily detected after Northern blot analysis of melanoma mRNA, indicating that only low levels of this product may be expressed in tumor cells. Quantitative reverse transcriptase-polymerase chain reaction analysis, however, demonstrated a correlation between T-cell recognition and expression in HLA-A1-expressing tumor cell lines. A peptide that was encoded within a short open reading frame of 23 amino acids and conformed to the HLA-A1 binding motif RSDSGQQARY was found to represent the T-cell epitope. The AIM-2-reactive T-cell clone recognized a number of neuroectodermal tumors as well as breast, ovarian, and colon carcinomas that expressed HLA-A1, indicating that this represents a widely expressed tumor antigen. Thus, AIM-2 may represent a potential target for the development of vaccines in patients bearing tumors of a variety of histologies.

Progress in human tumour immunology and immunotherapy

Studies of the administration of interleukin-2 to patients with metastatic melanoma or kidney cancer have shown that immunological manipulations can mediate the durable regression of metastatic cancer. The molecular identification of cancer antigens has opened new possibilities for the development of effective immunotherapies for patients with cancer. Clinical studies using immunization with peptides derived from cancer antigens have shown that high levels of lymphocytes with anti-tumour activity can be raised in cancer-bearing patients. Highly avid anti-tumour lymphocytes can be isolated from immunized patients and grown in vitro for use in cell-transfer therapies. Current studies are aimed at understanding the mechanisms that enable the cancer to escape from immune attack.

A MAGE-1 peptide recognized on HLA-DR15 by CD4(+) T cells

Antigens encoded by MAGE genes and recognized by T cells are of interest for cancer immunotherapy because of their strict tumoral specificity and because they are shared by many tumors. Several MAGE-1 peptide that are recognized by CD8(+) cytolytic T lymphocytes have been used in therapeutic vaccination trials. To obtain anti-tumor immune response, vaccines combining peptides recognized by CD8(+) and peptides recognized by CD4(+) T cells might be optimal. We focused therefore on the identification of MAGE peptides recognized by CD4(+) T cells. We report here the identification of MAGE-1 epitope EYVIKVSARVRF, which is presented to CD4(+) T lymphocytes by HLA-DR15. This HLA allele is present in 29 % of Asians and 17 % of Caucasians.

The role of MHC class II-restricted tumor antigens and CD4+ T cells in antitumor immunity

The identification of tumor antigens has generated a resurgence of interest in immunotherapy for cancer. However, both clinical and animal studies suggest that therapeutic strategies that have mainly focused on the use of CD8+ T cells (and MHC class I-restricted tumor antigens) are not effective in eliminating cancer cells. Recent interest has been directed towards the use of CD4+ T cells in generating antitumor immunity. To this end, the identification of MHC class II-restricted tumor antigens that can stimulate CD4+ T cells might provide opportunities for developing effective cancer vaccines.

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.

The immunoprotective MHC II epitope of a chemically induced tumor harbors a unique mutation in a ribosomal protein

CD4(+) T lymphocyte clones, generated from mice immunized with the methylcholanthrene-induced fibrosarcoma Meth A (H-2(d)), are restricted by I-E(d) and recognize a unique antigen on Meth A. The antigen has been purified and characterized as the ribosomal protein L11. The antigenic epitope is contained within the sequence EYELRKHNFSDTG and is generated by substitution of Asn by His (italic) caused by a single point mutation. The tumor contains the wild-type and the mutated alleles. Immunization of BALB/cJ mice with the mutated epitope but not with the wild-type epitope protects mice against a subsequent challenge with the Meth A sarcoma. Adoptive transfer of CD4(+) clones into BALB/c mice renders the mice specifically resistant to Meth A sarcoma. The mutated L11 epitope is thus shown to be an immunoprotective epitope in vivo by several criteria.

Identification of proacrosin binding protein sp32 precursor as a human cancer/testis antigen

Serological expression cloning of antigens eliciting a humoral immune response to a syngeneic mouse sarcoma identified pem (mouse placenta and embryonic expression gene) as a new member of the cancer/testis family. To identify the human homologue of pem, mouse pem sequences and pem-related expressed sequence tags from human testis were used as PCR primers for amplification using human testis cDNA. However, rather than pem, another gene, designated OY-TES-1, was isolated and found to be the human homologue of proacrosin binding protein sp32 precursor originally identified in mouse, guinea pig, and pig. OY-TES-1 maps to chromosome 12p12-p13 and contains 10 exons. Southern blot analysis suggests the presence of two OY-TES-1-related genes in the human genome. In normal tissues, OY-TES-1 mRNA was expressed only in testis, whereas in malignant tissues, a variable proportion of a wide array of cancers, including bladder, breast, lung, liver, and colon cancers, expressed OY-TES-1. Serological survey of 362 cancer patients with a range of different cancers showed antibody to OY-TES-1 in 25 patients. No OY-TES-1 sera reactivity was found in 20 normal individuals. These findings indicate that OY-TES-1 is an additional member of the cancer/testis family of antigens and that OY-TES-1 is immunogenic in humans.

Autologous dendritic cells for treatment of advanced cancer--an update

Dendritic cells (DC) are commonly viewed as the professional antigen-presenting cell. They capture antigens, migrate to appropriate lymphoid organs and initiate an antigen-specific CD4 and CD8 T cell response. Much is known about DC physiology, and it is now possible to culture, maintain and expand DC from different human sources, including hematopoietic progenitors in bone marrow and peripheral blood. Combined with the detection of an increasing number of tumor-associated antigens and T cell-recognized peptide epitopes, this has led to a new enthusiasm in the field of tumor immunotherapy and to various clinical applications in phase I/II studies on the treatment of different malignancies. This chapter will review the latest developments and give a brief update of the results obtained in studies of advanced melanoma, as well as provide a short overview of published results for other tumors.

Serological analysis of BALB/C methylcholanthrene sarcoma Meth A by SEREX: identification of a cancer/testis antigen

Antigens of BALB/c methylcholanthrene-induced fibrosarcoma Meth A recognized by the host humoral immune response were investigated by serological analysis of antigens by recombinant expression cloning (SEREX). Immunoscreening a cDNA library from Meth A (Kgamma) cells (Meth A retrovirally transfected with murine IFN-gamma cDNA) with sera from BALB/c mice growing parental Meth A transplants identified 10 antigens. One of them, OY-MS-4, showed characteristics of a cancer/testis (CT) antigen. Nucleotide sequence analysis revealed that OY-MS-4 was identical to a mouse placenta and embryonic expression gene (pem) known to be selectively expressed during embryogenesis and in transformed cell lines. In adult mice, expression of OY-MS-4 was restricted to testis and placenta. Four of 6 methylcholanthrene-induced fibrosarcomas in BALB/c mice showed strong expression of OY-MS-4. In 6 T-cell leukemias, only a dimethylbenzanthracene-induced leukemia, EL4 (C57BL), showed strong expression. Two other tumors, A20.2J and P815, induced by ethylnitrosourea and methylcholanthrene, respectively, also strongly expressed OY-MS-4. The other 9 gene products identified in Meth A by SEREX were expressed in all 15 tumors tested and in a range of normal tissues. Sequence analysis of cDNA inserts coding for the SEREX-defined antigens showed no evidence of mutation. Despite the expression of OY-MS-1-10 antigens in methylcholanthrene sarcomas other than Meth A, no antibody was detected in the sera of mice bearing these other sarcomas. The basis for the unique immunogenicity of OY-MS-1-10 presented by Meth A, but not by other syngeneic tumors expressing these gene products, is unknown.

Serological analysis of BALB/C methylcholanthrene sarcoma Meth A by SEREX: identification of a cancer/testis antigen

Antigens of BALB/c methylcholanthrene-induced fibrosarcoma Meth A recognized by the host humoral immune response were investigated by serological analysis of antigens by recombinant expression cloning (SEREX). Immunoscreening a cDNA library from Meth A (Kgamma) cells (Meth A retrovirally transfected with murine IFN-gamma cDNA) with sera from BALB/c mice growing parental Meth A transplants identified 10 antigens. One of them, OY-MS-4, showed characteristics of a cancer/testis (CT) antigen. Nucleotide sequence analysis revealed that OY-MS-4 was identical to a mouse placenta and embryonic expression gene (pem) known to be selectively expressed during embryogenesis and in transformed cell lines. In adult mice, expression of OY-MS-4 was restricted to testis and placenta. Four of 6 methylcholanthrene-induced fibrosarcomas in BALB/c mice showed strong expression of OY-MS-4. In 6 T-cell leukemias, only a dimethylbenzanthracene-induced leukemia, EL4 (C57BL), showed strong expression. Two other tumors, A20.2J and P815, induced by ethylnitrosourea and methylcholanthrene, respectively, also strongly expressed OY-MS-4. The other 9 gene products identified in Meth A by SEREX were expressed in all 15 tumors tested and in a range of normal tissues. Sequence analysis of cDNA inserts coding for the SEREX-defined antigens showed no evidence of mutation. Despite the expression of OY-MS-1-10 antigens in methylcholanthrene sarcomas other than Meth A, no antibody was detected in the sera of mice bearing these other sarcomas. The basis for the unique immunogenicity of OY-MS-1-10 presented by Meth A, but not by other syngeneic tumors expressing these gene products, is unknown.

Hijacking a chaperone: manipulation of the MHC class II presentation pathway

Novel antigen delivery systems are currently being developed by genetic manipulation of the MHC class II trafficking pathway. Specific targeting of endogenously synthesized antigens to the class II loading compartment can result in massively enhanced presentation of peptide epitopes. This emerging technology holds promise for a variety of clinical applications including vaccine development, cancer therapies and control of autoimmune diseases.

Detection of a potent humoral response associated with immune-induced remission of chronic myelogenous leukemia

The effectiveness of donor-lymphocyte infusion (DLI) for treatment of relapsed chronic myelogenous leukemia (CML) after allogeneic bone marrow transplantation is a clear demonstration of the graft-versus-leukemia (GVL) effect. T cells are critical mediators of GVL, but the antigenic targets of this response are unknown. To determine whether patients who respond to DLI also develop B-cell immunity to CML-associated antigens, we analyzed sera from three patients with relapsed CML who achieved a complete molecular remission after infusion of donor T cells. Sera from these individuals recognized 13 distinct gene products represented in a CML-derived cDNA library. Two proteins, Jkappa-recombination signal-binding protein (RBP-Jkappa) and related adhesion focal tyrosine kinase (RAFTK), were recognized by sera from three of 19 DLI responders. None of these antigens were recognized by sera from healthy donors or patients with chronic graft-versus-host disease. Four gene products were recognized by sera from CML patients treated with hydroxyurea and nine were detected by sera from CML patients who responded to IFN-alpha. Antibody titers specific for RAFTK, but not for RBP-Jkappa, were found to be temporally associated with the response to DLI. These results demonstrate that patients who respond to DLI generate potent antibody responses to CML-associated antigens, suggesting the development of coordinated T- and B-cell immunity. The characterization of B cell-defined antigens may help identify clinically relevant targets of the GVL response in vivo.

Antigen-processing machinery breakdown and tumor growth

Defects in the major histocompatibility complex (MHC) class I antigen-processing machinery (APM) have been described in tumors of different histology. Murine data suggest that defects in the MHC class II APM might also be associated with malignant transformation of human cells. This article describes the pathophysiology of the MHC class I and II APM, reviews APM abnormalities in tumor cells and discusses their role in the escape of tumor cells from in vitro recognition by T cells.

Identification of CD4+ T cell epitopes from NY-ESO-1 presented by HLA-DR molecules

In previous studies, the shared cancer-testis Ag, NY-ESO-1, was demonstrated to be recognized by both Abs and CD8+ T cells. Gene expression of NY-ESO-1 was detected in many tumor types, including melanoma, breast, and lung cancers, but was not found in normal tissues, with the exception of testis. In this study, we describe the identification of MHC class II-restricted T cell epitopes from NY-ESO-1. Candidate CD4+ T cell peptides were first identified using HLA-DR4 transgenic mice immunized with the NY-ESO-1 protein. NY-ESO-1-specific CD4+ T cells were then generated from PBMC of a patient with melanoma stimulated with the candidate peptides in vitro. These CD4+ T cells recognized NY-ESO-1 peptides or protein pulsed on HLA-DR4+ EBV B cells, and also recognized tumor cells expressing HLA-DR4 and NY-ESO-1. A 10-mer peptide (VLLKEFTVSG) was recognized by CD4+ T cells. These studies provide new opportunities for developing more effective vaccine strategies by using tumor-specific CD4+ T cells. This approach may be applicable to the identification of CD4+ T cell epitopes from many known tumor Ags recognized by CD8+ T cells.

Dendritic cells permit identification of genes encoding MHC class II-restricted epitopes of transplantation antigens

Minor or histocompatibility (H) antigens are recognized by CD4+ and CD8+ T lymphocytes as short polymorphic peptides associated with MHC molecules. They are the targets of graft versus host and graft versus leukemia responses following bone marrow transplantation between HLA-identical siblings. Several genes encoding class I-restricted minor H epitopes have been identified, but approaches used for these have proved difficult to adapt for cloning class II-restricted minor H genes. We have combined the unique antigen-presenting properties of dendritic cells and high levels of episomal expression following transfection of COS cells to identify a Y chromosome gene encoding two HY peptide epitopes, HYAb and HYEk.

Identification of a MHC class II-restricted human gp100 epitope using DR4-IE transgenic mice

CD4+ T cells play a central role in the induction and persistence of CD8+ T cells in several models of autoimmune and infectious disease. To improve the efficacy of a synthetic peptide vaccine based on the self-Ag, gp100, we sought to provide Ag-specific T cell help. To identify a gp100 epitope restricted by the MHC class II allele with the highest prevalence in patients with malignant melanoma (HLA-DRB1*0401), we immunized mice transgenic for a chimeric human-mouse class II molecule (DR4-IE) with recombinant human gp100 protein. We then searched for the induction of CD4+ T cell reactivity using candidate epitopes predicted to bind to DRB1*0401 by a computer-assisted algorithm. Of the 21 peptides forecasted to bind most avidly, murine CD4+ T cells recognized the epitope (human gp10044-59, WNRQLYPEWTEAQRLD) that was predicted to bind best. Interestingly, the mouse helper T cells also recognized human melanoma cells expressing DRB1*0401. To evaluate whether human CD4+ T cells could be generated from the peripheral blood of patients with melanoma, we used the synthetic peptide h-gp10044-59 to sensitize lymphocytes ex vivo. Resultant human CD4+ T cells specifically recognized melanoma, as measured by tumor cytolysis and the specific release of cytokines and chemokines. HLA class II transgenic mice may be useful in the identification of helper epitopes derived from Ags of potentially great clinical utility.

Immunologic approaches to antigen discovery for cancer vaccines

Since the early 1990s, scientists have identified an ever-expanding number of antigens to serve as targets for experimental cancer treatments, based on the stimulation of a patient's immune system. Using both immune cells and serum to screen potential candidates, several promising antigens are currently components of vaccines directed against a wide range of tumour types. These antigens vary in their tumour- and tissue-specificity. Their utility as a single reagent or as part of a multi-dimensional approach is as varied as the genes themselves. However, there are already reports indicating that the promise of evoking a clinically beneficial immune response, toward human tumours, is being fulfilled. In this review, we provide a summary of the current status of immunologic approaches to antigen discovery. We also discuss the need for additional, supportive data from non-immunologic techniques, as well as the progression of the preclinical process towards target validation.

Accessory molecules for MHC class II peptide loading

Accessory molecules, such as HLA-DM and invariant chain, modulate the ligands bound to MHC class II molecules in antigen-presenting cells. Recent investigations, including gene targeting experiments, have shed light on the functions of these molecules, their mechanisms of action, interactions with class II molecules, and the relationships with associated molecules such as tetraspanins and HLA-DO.

Melan-A/MART-1(51-73) represents an immunogenic HLA-DR4-restricted epitope recognized by melanoma-reactive CD4(+) T cells

The human Melan-A/MART-1 gene encodes an HLA-A2-restricted peptide epitope recognized by melanoma-reactive CD8(+) cytotoxic T lymphocytes. Here we report that this gene also encodes at least one HLA-DR4-presented peptide recognized by CD4(+) T cells. The Melan-A/MART-1(51-73) peptide was able to induce the in vitro expansion of specific CD4(+) T cells derived from normal DR4(+) donors or from DR4(+) patients with melanoma when pulsed onto autologous dendritic cells. CD4(+) responder T cells specifically produced IFN-gamma in response to, and also lysed, T2.DR4 cells pulsed with the Melan-A/MART-1(51-73) peptide and DR4(+) melanoma target cells naturally expressing the Melan-A/MART-1 gene product. Interestingly, CD4(+) T cell immunoreactivity against the Melan-A/MART-1(51-73) peptide typically coexisted with a high frequency of anti-Melan-A/MART-1(27-35) reactive CD8(+) T cells in freshly isolated blood harvested from HLA-A2(+)/DR4(+) patients with melanoma. Taken together, these data support the use of this Melan-A/MART-1 DR4-restricted melanoma epitope in future immunotherapeutic trials designed to generate, augment, and quantitate specific CD4(+) T cell responses against melanoma in vivo.

Cancer gene therapy: hard lessons and new courses

Gene therapy for the treatment of cancer was initiated with high levels of optimism and enthusiasm. Recently, this perception has had to be tempered by the realisation that efficiency and accuracy of gene delivery remain the most significant barriers to its success. So far, there has been a disappointing inability to reach target cells with sufficient efficacy to generate high enough levels of direct killing and this has necessitated the invocation of bystander effects in order for any potential strategy to be convincing. At least in the foreseeable future, clinical advance will come from co-operation with other more established disciplines - such as chemotherapy, radiotherapy and immunotherapy. This is inevitable - and necessary - in order to prove that gene therapy can have efficacy as part of a combinatorial therapy, before hoping to move clinical mountains alone. In addition, there will have to be a thorough understanding of the clinical situations in which gene therapy will be used in order both to understand its own limitations, and to exploit its full potential. This will enable it to find the appropriate clinical niche in which its abilities will be optimally useful. Finally, anyone wishing to practise clinical cancer gene therapy will rapidly have to learn the ways of the free market and be able to juggle commercial necessities with ideological purity. Gene Therapy (2000) 7, 2-8.

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.

Cancer immunotherapy: synthetic and natural peptides in the balance

The identification of human tumor-associated antigens has opened new avenues for immune intervention in cancer. Clinical trials using synthetic peptides that match segments of known tumor-associated proteins are ongoing. Alternatively, naturally processed peptides, obtained by acid treatment of tumor cells can be used. Here, Matteo Bellone and colleagues discuss the advantages and disadvantages of synthetic versus natural tumor peptides in cancer immunotherapy.

T cells work together to fight cancer

Recent studies have identified new melanoma antigens that are recognised by CD4(+) T cells. Analysis of tumour-specific CD4(+) T-cell responses may lead to the development of optimal anti-cancer vaccines that can induce an orchestrated effort of tumour-specific CD4(+) and CD8(+) T cells in the fight against cancer.

Human tumor antigens for cancer vaccine development

The adoptive transfer of tumor-infiltrating lymphocytes (TIL) along with interleukin (IL)-2 into autologous patients with cancer resulted in the objective regression of tumor, indicating that T cells play an important role in tumor regression. In the last few years, efforts have been made towards understanding the molecular basis of T-cell-mediated antitumor immunity and elucidating the molecular nature of tumor antigens recognized by T cells. Tumor antigens identified thus far could be classified into several categories: tissue-specific differentiation antigens, tumor-specific shared antigens and tumor-specific unique antigens. CD4+ T cells play a central role in orchestrating the host immune response against cancer, infectious diseases and autoimmune diseases, and we thus have attempted to identify major histocompatibility complex (MHC) class II-restricted tumor antigens as well. The identification of tumor rejection antigens provides new opportunities for the development of therapeutic strategies against cancer. This review will summarize the current status of MHC class I- and class II-restricted human tumor antigens, and their potential application to cancer treatment.