A peptide encoded by the human MAGE3 gene and presented by HLA-B44 induces cytolytic T lymphocytes that recognize tumor cells expressing MAGE3

Therapeutic Cancer Vaccines—Antigen Discovery and Adjuvant Delivery Platforms

For decades, vaccines have played a significant role in protecting public and personal health against infectious diseases and proved their great potential in battling cancers as well. This review focused on the current progress of therapeutic subunit vaccines for cancer immunotherapy. Antigens and adjuvants are key components of vaccine formulations. We summarized several classes of tumor antigens and bioinformatic approaches of identification of tumor neoantigens. Pattern recognition receptor (PRR)-targeting adjuvants and their targeted delivery platforms have been extensively discussed. In addition, we emphasized the interplay between multiple adjuvants and their combined delivery for cancer immunotherapy.

Immunotherapy of gastric cancer: Past, future perspective and challenges

Gastric cancer is considered as the third leading cause of deaths and the fifth most common cancers worldwide. Common treatment approaches include chemotherapy, radiation, gastric resection and targeted therapies. The emergence of gastric cancer immunotherapy has already shown some promising results and have altered the therapeutic procedures. Now, different combination therapies as well as novel immunotherapies targeting new molecules have been proposed. Despite ongoing investigations on the therapeutic options and significant advancements in this regard, the disease is poorly prognosed. In fact, limited therapeutic options and delayed diagnosis lead to the progression, dissemination and metastasis of the disease. Current immunotherapies are mostly based on cytotoxic immunocytes, monoclonal antibodies and gene transferred vaccines. The use of Immune checkpoint inhibitors (ICIs) have grown rapidly. In this review, we aimed to explore perspective and progression of different approaches of immunotherapy in the treatment of GC and the clinical outcomes reported so far. We also summarized the tumor immunosurveillance and tumor immunoescape.

Cellular immune responses against cancer-germline genes in cancers

BACKGROUND

Cancer-germline genes are a class of genes that are normally expressed in testis, trophoblast and few somatic tissues but abnormally expressed in tumor tissues. Their expression signature indicates that they can induce cellular immune responses, thus being applied as targets in cancer immunotherapy.

OBJECTIVES

To obtain the data of cellular immune responses against cancer-germline genes in cancer.

METHODS

We searched PubMed/Medline with the key words cancer-germline antigen, cancer-testis antigen, CD4+ T cell, CD8+ T cell and cancer.

RESULTS

About 40 cancer-germline genes have been shown to induce T cell specific responses in cancer patients. Melanoma, lung and breast cancer are among the mostly assessed cancer types. Several epitopes have been identified which can be used in immunotherapy of cancer.

CONCLUSION

Cellular immune responses against cancer-germline genes are indicative of appropriateness of these genes as therapeutic targets.

Patient HLA class I genotype influences cancer response to checkpoint blockade immunotherapy

CD8+ T cell-dependent killing of cancer cells requires efficient presentation of tumor antigens by human leukocyte antigen class I (HLA-I) molecules. However, the extent to which patient-specific HLA-I genotype influences response to anti-programmed cell death protein 1 or anti-cytotoxic T lymphocyte-associated protein 4 is currently unknown. We determined the HLA-I genotype of 1535 advanced cancer patients treated with immune checkpoint blockade (ICB). Maximal heterozygosity at HLA-I loci ("A," "B," and "C") improved overall survival after ICB compared with patients who were homozygous for at least one HLA locus. In two independent melanoma cohorts, patients with the HLA-B44 supertype had extended survival, whereas the HLA-B62 supertype (including HLA-B*15:01) or somatic loss of heterozygosity at HLA-I was associated with poor outcome. Molecular dynamics simulations of HLA-B*15:01 revealed different elements that may impair CD8+ T cell recognition of neoantigens. Our results have important implications for predicting response to ICB and for the design of neoantigen-based therapeutic vaccines.

Immune targets and neoantigens for cancer immunotherapy and precision medicine

Harnessing the immune system to eradicate malignant cells is becoming a most powerful new approach to cancer therapy. FDA approval of the immunotherapy-based drugs, sipuleucel-T (Provenge), ipilimumab (Yervoy, anti-CTLA-4), and more recently, the programmed cell death (PD)-1 antibody (pembrolizumab, Keytruda), for the treatment of multiple types of cancer has greatly advanced research and clinical studies in the field of cancer immunotherapy. Furthermore, recent clinical trials, using NY-ESO-1-specific T cell receptor (TCR) or CD19-chimeric antigen receptor (CAR), have shown promising clinical results for patients with metastatic cancer. Current success of cancer immunotherapy is built upon the work of cancer antigens and co-inhibitory signaling molecules identified 20 years ago. Among the large numbers of target antigens, CD19 is the best target for CAR T cell therapy for blood cancer, but CAR-engineered T cell immunotherapy does not yet work in solid cancer. NY-ESO-1 is one of the best targets for TCR-based immunotherapy in solid cancer. Despite the great success of checkpoint blockade therapy, more than 50% of cancer patients fail to respond to blockade therapy. The advent of new technologies such as next-generation sequencing has enhanced our ability to search for new immune targets in onco-immunology and accelerated the development of immunotherapy with potentially broader coverage of cancer patients. In this review, we will discuss the recent progresses of cancer immunotherapy and novel strategies in the identification of new immune targets and mutation-derived antigens (neoantigens) for cancer immunotherapy and immunoprecision medicine.

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.

Enhancing cancer immunotherapy by intracellular delivery of cell-penetrating peptides and stimulation of pattern-recognition receptor signaling

The importance of T-cell-mediated antitumor immunity has been demonstrated in both animal models and human cancer immunotherapy. In the past 30 years, T-cell-based immunotherapy has been improved with an objective clinical response rate of up to 72%. Identification of MHC class I- and II-restricted tumor antigens recognized by tumor-reactive T cells has generated a resurgence of interest in cancer vaccines. Although clinical trials with cancer peptide/protein vaccines have only met a limited success, several phase II/III clinical trials are either completed or ongoing with encouraging results. Recent advances in immunotherapy have led to the approval of two anticancer drugs (sipuleucel-T vaccine and anti-CTLA-4 antibody) by the US FDA for the treatment of metastatic castration-resistant prostate cancer and melanoma, respectively. Intracellular delivery of antigenic peptides into dendritic cells (DCs) prolongs antigen presentation of antigen-presenting cells to T cells, thus further improving clinical efficacy of peptide/protein cancer vaccines. Because innate immune responses are critically important to provide sensing and initiating of adaptive immunity, combined use of cell-penetrating peptide vaccines with stimulation of innate immune signaling may produce potent antitumor immune responses. We will discuss the recent progress and novel strategies in cancer immunotherapy.

Proteasome subtypes and the processing of tumor antigens: increasing antigenic diversity

Protein degradation by the proteasome releases peptides that can be loaded on MHC class I molecules and presented to cytolytic T lymphocytes. Several mechanisms were recently found to increase the diversity of antigenic peptides displayed at the cell surface, thereby maximizing the efficacy of immune responses. The proteasome was shown to produce spliced antigenic peptides, which are made of two fragments initially not contiguous in the parental protein. Different proteasome subtypes also produce distinct sets of antigenic peptides: the standard proteasome and the immunoproteasome, containing different catalytic subunits, have different cleavage specificities and produce different sets of peptides. Moreover, recent work confirmed the existence of two additional proteasome subtypes that are intermediate between the standard and the immunoproteasome, and each produce a unique peptide repertoire.

Novel immunotherapeutic agents and small molecule antagonists of signalling kinases for the treatment of metastatic melanoma

Melanoma incidence is increasing annually and over 40,000 die of this disease each year worldwide. In this review, we discuss the rationale and recent trial results of several novel immunotherapeutic approaches and small molecule inhibitors of signalling kinases. Ipilimumab is a humanized anti-CTLA4 antibody that has been proven to increase the median overall survival of large cohorts of patients with unresectable melanoma in two phase III trials. OncoVEX(GM-CSF) is an oncolytic herpes simplex virus-1 recombined with granulocyte-macrophage colony-stimulating factor that has demonstrated durable objective responses in a phase II trial. Tumour-infiltrating lymphocytes given after lymphocyte depletion and followed by high-dose interleukin (IL)-2 yield durable complete responses in a significant percentage of melanoma patients. Lastly, denileukin diftitox, a fusion of IL-2 and diphtheria toxin, was recently observed to deplete regulatory T cells and cause durable partial responses, particularly in chemo/immune-naïve patients. These agents are enabling the rational design of novel combination trials to simultaneously increase antigen presentation, deplete regulatory T cells and block immune check-points in order to activate melanoma antigen-specific immunity. Although melanoma metastases have been found to contain thousands of mutations, the V600E BRAF mutation is clearly a driver of the neoplastic phenotype and is present in 40-60% of melanomas. Two separate small molecule antagonists of B-Raf have been found to yield very high partial response rates in metastatic melanoma, and the B-Raf inhibitor, vemurafenib (PLX4032), was recently observed to increase median overall survival in an interim analysis. However, B-Raf inhibitor resistance through up-regulation or activating mutations of alternative oncogenic signalling receptors and enzymes is proving to be a major challenge. Inhibitors of c-Kit and mitogen-activated protein kinase (MEK) have also been found to have activity against melanomas and MEK inhibitors are now being examined as a strategy to overcome B-Raf inhibitor resistance. In summary, these studies reveal that, for the first time, several immunotherapeutic and targeted agents are yielding dramatic clinical responses and improvements in overall survival in patients with unresectable stage III and IV melanoma.

Insights into the processing of MHC class I ligands gained from the study of human tumor epitopes

The molecular definition of tumor antigens recognized by cytolytic T lymphocytes (CTL) started in the late 1980s, at a time when the MHC class I antigen processing field was in its infancy. Born together, these two fields of science evolved together and provided each other with critical insights. Over the years, stimulated by the potential interest of tumor antigens for cancer immunotherapy, scientists have identified and characterized numerous antigens recognized by CTL on human tumors. These studies have provided a wealth of information relevant to the mode of production of antigenic peptides presented by MHC class I molecules. A number of tumor antigenic peptides were found to result from unusual mechanisms occurring at the level of transcription, translation or processing. Although many of these mechanisms occur in the cell at very low level, they are relevant to the immune system as they determine the killing of tumor cells by CTL, which are sensitive to low levels of peptide/MHC complexes. Moreover, these unusual mechanisms were found to occur not only in tumor cells but also in normal cells. Thereby, the study of tumor antigens has illuminated many aspects of MHC class I processing. We review here those insights into the MHC I antigen processing pathway that result from the characterization of human tumor antigens recognized by CTL.

Prognostic value of MAGE-A and NY-ESO-1 expression in pharyngeal cancer

BACKGROUND

The prognostic value of cancer testis antigens in pharyngeal cancer is understudied.

METHODS

We recruited 90 patients who were treated for pharyngeal cancer. Monoclonal antibodies 57B and B9.8.1.1 were used for detection of MAGE-A and NY-ESO-1 genes.

RESULTS

MAGE-A and NY-ESO-1 gene products were detectable in 70.0% and 33.3% of pharyngeal tumors, respectively. No correlation was established between MAGE-A and NY-ESO-1 expression and TNM staging at presentation. Survival analysis showed a trend toward a shorter 5-year disease-free survival in the group of patients with MAGE-A-positive tumors (log-rank test, p = .122). In contrast, a trend toward a prolonged 5-year disease-free survival was observed in the group of patients with NY-ESO-1-positive tumors (log-rank test, p = .219).

CONCLUSION

In a large population of patients with pharyngeal cancer and available 5-year survival data, prognosis tended to be poorer with MAGE-A expression and better with NY-ESO-1 expression, but the correlations did not reach statistical significance.

Use of dentritic cells pulsed with HLA-A2-restricted MAGE-A1 peptide to generate cytotoxic T lymphocytes against malignant glioma

This study developed a novel approach of targeting malignant glioma with pMAGE-A1(278-286)-specific cytotoxic T lymphocytes (CTLs) induced from the peripheral blood mononuclear cells of healthy donors by multiple stimulations with human leukocyte antigen (HLA)-A2-restricted pMAGE-A1(278-286) peptide-pulsed dentritic cells. Cytotoxic assays were performed by the colorimetric CytoTox 96 assay to analyze cytotoxic activity of the induced CTLs against various target cells. The induced CTLs showed approximately 45% specific lysis against T2pMAGE-A1(278-286) (pMAGE-A1(278-286) peptide pulsed T2 cells) and U251 (HLA-A2(+), MAGE-A1(+)) at an effector:target ratio of 40:1, and approximately 5% cytolysis against T2pHIV, A172 (HLA-A2(-), MAGE-A1(+)), K562 and T2 cells without being pulsed with peptide at any effector:target ratio. The specific killing activity of the induced CTLs against T2pMAGE-A1(278-286) and U251 was much more obvious than in any other control group (P<0.05). The cytotoxic activity against the T2pMAGE-A1(278-286) and U251 was significantly eliminated by anti-HLA class I mAb W6/32. These results suggest that pMAGE-A1(278-286) epitope may serve as a surrogate tumor antigen target of specific immunotherapy for treating HLA-A2 patients with malignant glioma.

A review of vaccine clinical trials for non-small cell lung cancer

Recent evidence suggests that vaccines which enhance tumour antigen recognition may provide clinical benefit to subsets of non-small cell lung cancer patients. In this review, a variety of peptide-, gene- and cell-based clinical vaccine approaches targeting non-small cell lung cancer patients are reviewed. Results consistently demonstrate lack of toxicity. Examples of prolonged stable disease, tumour shrinkage response and survival benefit in comparison with historical and low-dose control groups have been demonstrated. Specific vaccines fulfilling justification for Phase III evaluation based on these results include LBLP25, TGF-beta2 antisense gene vaccine and GVAX.

Reverse immunology approach for the identification of CD8 T-cell-defined antigens: advantages and hurdles

One of the challenges of tumour immunology remains the identification of strongly immunogenic tumour antigens for vaccination. Reverse immunology, that is, the procedure to predict and identify immunogenic peptides from the sequence of a gene product of interest, has been postulated to be a particularly efficient, high-throughput approach for tumour antigen discovery. Over one decade after this concept was born, we discuss the reverse immunology approach in terms of costs and efficacy: data mining with bioinformatic algorithms, molecular methods to identify tumour-specific transcripts, prediction and determination of proteasomal cleavage sites, peptide-binding prediction to HLA molecules and experimental validation, assessment of the in vitro and in vivo immunogenic potential of selected peptide antigens, isolation of specific cytolytic T lymphocyte clones and final validation in functional assays of tumour cell recognition. We conclude that the overall low sensitivity and yield of every prediction step often requires a compensatory up-scaling of the initial number of candidate sequences to be screened, rendering reverse immunology an unexpectedly complex approach.

A new LAGE-1 peptide recognized by cytolytic T lymphocytes on HLA-A68 tumors

Antigens encoded by genes of the LAGE family, including LAGE-1 and NY-ESO-1, are of interest for cancer immunotherapy because they are tumor-specific and shared by tumors of different histological types. Several clinical trials are in progress with NY-ESO-1 peptides, protein, recombinant poxviruses, and dendritic cells pulsed with peptides. In this study, CD8 T lymphocytes from an individual without cancer were stimulated with dendritic cells infected with a recombinant avian poxvirus encoding a complete LAGE-1 protein. A CTL clone was isolated that recognized a new LAGE-1 peptide, ELVRRILSR, which corresponds to position 103-111 of the protein sequence. It is presented by HLA-A6801 molecules. When tumor cells expressing LAGE-1 were transfected with HLA-A68, they were lysed by the CTL clone, indicating that the peptide is processed in tumor cells. These results indicate that the LAGE-1.A68 peptide can be used for antitumoral vaccination. We observed also that specific T cells could be detected in a blood sample with a high sensitivity by using an A68/LAGE-1 fluorescent multimer.

HLA class I and class II frequencies in patients with cutaneous malignant melanoma from southeastern Spain: the role of HLA-C in disease prognosis

Available data have led to a controversy on the relationship between human leukocyte antigen (HLA) and cutaneous malignant melanoma susceptibility or prognosis. Moreover, the influence of HLA-C on melanoma has not yet been well established. Therefore, the aim of the current study was to analyze the possible influence of the HLA system on melanoma susceptibility and prognosis in the Spanish population. For this purpose, HLA-A and HLA-B serotyping and HLA-C, HLA-DRB1, and HLA-DQB1 genotyping by polymerase chain reactions using sequence-specific oligonucleotide (PCR-SSO) and sequence-specific primer (PCR-SSP) were performed in 174 melanoma patients and 227 ethnically matched controls. The number of controls was increased up to 356 for HLA-C typing. Patients were stratified according to the histological subtypes of melanoma, sentinel lymph node status, tumor thickness, and ulceration of primary lesion. No HLA-A, HLA-B, HLA-DRB1, or HLA-DQB1 relationship with melanoma was observed for susceptibility or disease prognosis. However, the analysis of HLA-C locus showed that individuals homozygous for HLA-C(Lys80) were significantly more frequent within the patient than the control group. Remarkably, individuals homozygous for group 2 HLA-C alleles (HLA-C(Lys80)) seem to be associated with metastatic progression of melanoma. In contrast, we found a negative association between group 1 HLA-C alleles (HLA-C(Asn80)) and disease susceptibility or metastasis development. In conclusion, although an association with HLA-A, HLA-B, HLA-DRB1, or HLA-DQB1 was not demonstrated, the study of the HLA-C locus revealed that the analysis of the dimorphism at position 80 in the alpha1 helix may help to evaluate the risk and prognosis of melanoma in our population.

Lessons to be learned from primary renal cell carcinomas: novel tumor antigens and HLA ligands for immunotherapy

The lack of sufficient well-defined tumor-associated antigens is still a drawback on the way to a cytotoxic T-lymphocyte-based immunotherapy of renal cell carcinoma (RCC). We are trying to define a larger number of such targets by a combined approach involving HLA ligand characterization by mass spectrometry and gene expression profiling by oligonucleotide microarrays. Here, we present the results of a large-scale analysis of 13 RCC specimens. We were able to identify more than 700 peptides, mostly from self-proteins without any evident tumor association. However, some HLA ligands derived from previously known tumor antigens in RCC. In addition, gene expression profiling of tumors and a set of healthy tissues revealed novel candidate RCC-associated antigens. For several of them, we were able to characterize HLA ligands after extraction from the tumor tissue. Apart from universal RCC antigens, some proteins seem to be appropriate candidates in individual patients only. This underlines the advantage of a personalized therapeutic approach. Further analyses will contribute additional HLA ligands to this repertoire of universal as well as patient-individual tumor antigens.

A listing of human tumor antigens recognized by T cells: March 2004 update

The technological advances occurred in the last few years have led to a great increase in the number of tumor associated antigens (TAA) that are currently available for clinical applications. In this review we provide a comprehensive list of human tumor antigens as reported in the literature updated at February 2004. The list includes all T cell-defined epitopes, while excluding analogs or artificially modified epitopes, as well as virus-encoded and antibodies-recognized antigens. TAAs are listed in alphabetical order along with the epitope sequence and the HLA allele which restricts recognition by T cells. Data on the tissue distribution of each antigen are also provided together with an extensive bibliography that allows a rapid search for any additional information may be needed on each single antigen or epitope. Overall, the updated list is a database tool for clinicians, scientists and students who have an interest in the field of tumor immunology and immunotherapy.

Vaccine-induced CD4+ T cell responses to MAGE-3 protein in lung cancer patients

MAGE-3 is the most commonly expressed cancer testis Ag and thus represents a prime target for cancer vaccines, despite infrequent natural occurrence of MAGE-3-specific immune responses in vivo. We report in this study the successful induction of Ab, CD8(+), and CD4(+) T cells in nonsmall cell lung cancer patients vaccinated with MAGE-3 recombinant protein. Two cohorts were analyzed: one receiving MAGE-3 protein alone, and one receiving MAGE-3 protein with adjuvant AS02B. Of nine patients in the first cohort, three developed marginal Ab titers and another one had a CD8(+) T cell response to HLA-A2-restricted peptide MAGE-3 271-279. In contrast, of eight patients from the second cohort vaccinated with MAGE-3 protein and adjuvant, seven developed high-titered Abs to MAGE-3, and four had a strong concomitant CD4(+) T cell response to HLA-DP4-restricted peptide 243-258. One patient simultaneously developed CD8(+) T cells to HLA-A1-restricted peptide 168-176. The novel monitoring methodology used in this MAGE-3 study establishes that protein vaccination induces clear CD4(+) T cell responses that correlate with Ab production. This development provides the framework for further evaluating integrated immune responses in vaccine settings and for optimizing these responses for clinical benefit.

Simultaneous prediction of binding capacity for multiple molecules of the HLA B44 supertype

We selected for study a set of B44-supertype molecules collectively represented in >40% of the individuals in all major ethnicities (B*1801, B*4001, B*4002, B*4402, B*4403, and B*4501). The peptide-binding specificity of each molecule was characterized using single amino acid substitution analogues and nonredundant peptide libraries. In all cases, only peptide ligands with glutamic acid in position 2 were preferred. At the C terminus, each allele was associated with a unique but broad pattern of preferences, but all molecules tolerated hydrophobic/aliphatic (leucine, isoleucine, valine, methionine), aromatic (tyrosine, phenylalanine, tryptophan), and small (alanine, glycine, threonine) residues. Secondary anchor motifs were also defined for all molecules. Together, these features were used to define a B44 supermotif and a novel algorithm for calculating degeneracy scores that can be used to predict B44-supertype degenerate binders. Approximately 90% of the peptides with a B44 supermotif degeneracy score of >10 bound at least three of the six B44-supertype molecules studied with high affinity. Finally, a number of peptides derived from hepatitis B and C viruses, HIV, and Plasmodium falciparum have been identified that have degenerate B44 supertype-binding capacity. Taken together, these findings have important implications for epitope-based approaches to vaccination, immunotherapy, and the monitoring of immune responses.

High frequency of HLA-B44 allelic losses in human solid tumors

Human leukocyte antigen (HLA) class I downregulation, a frequent phenomenon observed in a variety of human tumors, favors tumor immune escape from T-lymphocyte recognition. However, it is not known whether a particular HLA class I allele is lost more frequently than others. To address this question we analyzed HLA class I expression in tumor tissues derived from 300 patients diagnosed as having breast, colorectal, or laryngeal carcinomas. Cryostatic tumor sections and a broad panel of anti-HLA class I monoclonal antibodies were used. We found that the HLA-B44 allele was lost more frequently than other HLA class I alleles, and that the difference was not related with changes in HLA-B44 allele frequencies between patients and controls. In addition, we observed that 35% of the HLA-B44 negative tumors presented HLA haplotype loss associated with loss of heterozygosity. These tests were performed on DNA samples obtained from microdissected tumor tissues. The results seem to indicate that HLA class I allelic losses are not randomly distributed during tumor development but that some HLA class I alleles, and HLA-B44 in particular, are more frequently downregulated and may play an important role in immune escape mechanisms.

A naturally selected dimorphism within the HLA-B44 supertype alters class I structure, peptide repertoire, and T cell recognition

HLA-B*4402 and B*4403 are naturally occurring MHC class I alleles that are both found at a high frequency in all human populations, and yet they only differ by one residue on the alpha2 helix (B*4402 Asp156-->B*4403 Leu156). CTLs discriminate between HLA-B*4402 and B*4403, and these allotypes stimulate strong mutual allogeneic responses reflecting their known barrier to hemopoeitic stem cell transplantation. Although HLA-B*4402 and B*4403 share >95% of their peptide repertoire, B*4403 presents more unique peptides than B*4402, consistent with the stronger T cell alloreactivity observed toward B*4403 compared with B*4402. Crystal structures of B*4402 and B*4403 show how the polymorphism at position 156 is completely buried and yet alters both the peptide and the heavy chain conformation, relaxing ligand selection by B*4403 compared with B*4402. Thus, the polymorphism between HLA-B*4402 and B*4403 modifies both peptide repertoire and T cell recognition, and is reflected in the paradoxically powerful alloreactivity that occurs across this "minimal" mismatch. The findings suggest that these closely related class I genes are maintained in diverse human populations through their differential impact on the selection of peptide ligands and the T cell repertoire.

Identification of a polymorphic gene, BCL2A1, encoding two novel hematopoietic lineage-specific minor histocompatibility antigens

We report the identification of two novel minor histocompatibility antigens (mHAgs), encoded by two separate single nucleotide polymorphisms on a single gene, BCL2A1, and restricted by human histocompatibility leukocyte antigen (HLA)-A*2402 (the most common HLA-A allele in Japanese) and B*4403, respectively. Two cytotoxic T lymphocyte (CTL) clones specific for these mHAgs were first isolated from two distinct recipients after hematopoietic cell transplantation. Both clones lyse only normal and malignant cells within the hematopoietic lineage. To localize the gene encoding the mHAgs, two-point linkage analysis was performed on the CTL lytic patterns of restricting HLA-transfected B lymphoblastoid cell lines obtained from Centre d'Etude du Polymorphisme Humain. Both CTL clones showed a completely identical lytic pattern for 4 pedigrees and the gene was localized within a 3.6-cM interval of 15q24.3-25.1 region that encodes at least 46 genes. Of those, only BCL2A1 has been reported to be expressed in hematopoietic cells and possess three nonsynonymous nucleotide changes. Minigene transfection and epitope reconstitution assays with synthetic peptides identified both HLA-A*2402- and B*4403-restricted mHAg epitopes to be encoded by distinct polymorphisms within BCL2A1.

Tumor-specific shared antigenic peptides recognized by human T cells

The first tumor-specific shared antigens and the cancer-germline genes that code for these antigens were identified with antitumor cytolytic T lymphocytes obtained from cancer patients. A few HLA class I-restricted antigenic peptides were identified by this 'direct approach'. A large set of additional cancer-germline genes have now been identified by purely genetic approaches or by screening tumor cDNA expression libraries with the serum of cancer patients. As a result, a vast number of sequences are known that can code for tumor-specific shared antigens, but most of the encoded antigenic peptides have not yet been identified. We review here recent 'reverse immunology' approaches for the identification of new antigenic peptides. They are based on in vitro stimulation of naive T cells with dendritic cells that have either been loaded with a cancer-germline protein or that have been transduced with viruses carrying cancer-germline coding sequences. These approaches have led to the identification of many new antigenic peptides presented by class I or class II molecules. We also describe some aspects of the processing and presentation of these antigenic peptides.

Identification of a dominant self-ligand bound to three HLA B44 alleles and the preliminary crystallographic analysis of recombinant forms of each complex

A naturally processed and presented ligand that is shared by human leukocyte antigen (HLA) B*4402, B*4403 and B*4405 molecules has been identified in peptides isolated from immunoaffinity purified HLA B44 complexes. This peptide derived from HLA DPalpha residues 46-54, an endogenous product of HLA DP expressed in the cell line Hmy2.C1R, is a prominent peptide in the mass spectra of species isolated as bound peptides from each allele when the three HLA B44 subtypes were introduced as transfected gene products. Recombinant truncated forms of HLA B*4405(1-276), HLA B*4403(1-276), HLA B*4402(1-276) and beta(2)-microglobulin have been prepared as inclusion bodies in Escherichia coli and refolded in the presence of the DPalpha(46-54) peptide and purified by a combination of size exclusion and anion exchange chromatography. This material was determined to be correctly folded based on detection of a conformational epitope recognized by the W6/32 monoclonal antibody. Large, plate-like crystals of the three complexes were produced using polyethylene glycol as the precipitant. All the crystals belong to the space group P2(1)2(1)2(1) with unit cell dimensions of approximately a=51, b=82, c=110 A. The crystals of three B44/DPalpha complexes diffracted to a resolution of 1.9 A or better. For the first time, using this natural, high abundance ligand of the HLA B44 molecules we have successfully expressed and refolded the three HLA B44 molecules and produced crystals amenable to structural studies.

Antimelanoma activity of CTL generated from peripheral blood mononuclear cells after stimulation with autologous dendritic cells pulsed with melanoma gp100 peptide G209-2M is correlated to TCR avidity

Anchor residue-modified peptides derived from tumor-associated Ag have demonstrated success in engendering immune responses in clinical studies. However, tumor regression does not always correlate with immune responses. One hypothesis to explain this is that CTL resulting from such immunization approaches are variable in antitumor potency. In the present study, we evaluated this hypothesis by characterizing the activity of tumor-associated Ag-specific CTL. We chose an anchor residue-modified peptide from gp100, G209-2M, and used peptide-pulsed dendritic cells to generate CTL from PBMC of HLA-A2(+) normal donors. The specificities and avidities of the resulting CTL were evaluated. The results demonstrate that CTL generated by G209-2M can be classified into three categories: G209-2M-specific CTL which are cytotoxic only to G209-2M-pulsed targets; peptide-specific CTL which recognize both G209 and G209-2M peptides but not melanomas; and melanoma-reactive CTL which recognize peptide-pulsed targets as well as HLA-A2(+)gp100(+) melanomas. CTL that kill only peptide-pulsed targets require a higher peptide concentration to mediate target lysis, whereas CTL that lyse melanomas need a lower peptide concentration. Increasing peptide density on melanomas by loading exogenous G209 peptide enhances their sensitivity to peptide-specific CTL. High avidity CTL clones also demonstrate potent antimelanoma activity in melanoma model in nude mice. Injection of G209 peptide around transplanted tumors significantly enhances the antitumor activity of low avidity CTL. These results suggest that peptide stimulation causes expansion of T cell populations with a range of avidities. Successful immunotherapy may require selective expansion of the higher-avidity CTL and intratumor injection of the peptide may enhance the effect of peptide vaccines.

A MAGE-3 peptide presented by HLA-B44 is also recognized by cytolytic T lymphocytes on HLA-B18

Antigens encoded by MAGE genes are of particular interest for cancer immunotherapy because of their tumoral specificity and because they are shared by many tumors. Antigenic peptide MEVDPIGHLY, which is encoded by MAGE-3 and is known to be presented by human leukocyte antigen (HLA)-B44, is currently being used in therapeutic vaccination trials. We report here that a cytolytic T lymphocyte (CTL) clone, which is restricted by HLA-B*1801, recognizes the same peptide and, importantly, lyzes HLA-B18 tumor cells expressing MAGE-3. These results imply that the use of peptide MEVDPIGHLY can now be extended to HLA-B18 patients. We also provide evidence that, under limiting amounts of protein MAGE-3, HLA B*1801 and B*4403 compete for binding to the peptide.

Cancer/testis antigens: structural and immunobiological properties

Characterization of tumor-associated antigens recognized by cytotoxic T lymphocytes which has evolved during recent years opens new possibilities for specific anti-cancer immunotherapy. Among different groups of tumor-associated antigens, cancer/testis (CT) antigens (expressed in many tumors and among normal tissues only in testes) represent the most perspective antigens for immunotherapy because of their broad tumor-specific expression. More than 50 CT antigens have been described so far and, for many of them, epitopes recognized by T lymphocytes have been identified. The most studied group of CT antigens is the MAGE proteins, which form the so-called MAGE superfamily, together with some MAGE-like proteins that have a different distribution than classical CT antigens. The MAGE superfamily includes five families: MAGE-A, MAGE-B, MAGE-C, MAGE-D, and necdin. Comparison of the structure of members of MAGE superfamily points to the existence of a domain organization of these proteins. The central, core domain (second domain) is highly conservative. The first domain is homologous among MAGE family members with a CT expression, but unique for each member of the MAGE-D and necdin families. In addition to the homology of the central domain, the third domain is also homologous among all members of MAGE superfamily, but to a much lesser extent. The MAGE-D proteins contain an additional, fourth domain, which in the case of MAGE-D3 coincides with trophinin, a separate molecule described previously as an adhesion molecule that participates in embryo implantation. The structural classification of the members of MAGE superfamily might help in the future to understand the biological function of MAGE proteins. One important property of the CT antigens is the up-regulation of their expression by DNA demethylating agents, indicating a possible mechanism for their re-expression in tumors. One of the implications of this particular property could be that a combination of immunotherapy targeting CT antigens with chemotherapy inducing up-regulation of CT antigens might result in more efficient tumor eradication.

Adjuvant immunotherapy of resected, intermediate-thickness, node-negative melanoma with an allogeneic tumor vaccine: impact of HLA class I antigen expression on outcome

PURPOSE

An association between expression of > or = two of five HLA class I antigens (HLA-A2, HLA-A28, HLA-B44, HLA-B45, and HLA-C3; collectively called M5) and response to an allogeneic melanoma vaccine (Melacine; Corixa Corporation, Seattle, WA) has been described in stage IV melanoma. This study investigated whether class I antigen expression impacted relapse-free survival (RFS) after adjuvant therapy with this vaccine.

PATIENTS AND METHODS

We performed class I (HLA-A, HLA-B, and HLA-C) serotyping on patients enrolled onto Southwest Oncology Group Trial 9035, a randomized, observation-controlled, phase III trial of adjuvant Melacine. All patients had clinically node-negative cutaneous melanoma (1.5 to 4.0 mm). Interactions between treatment and class I antigen expression were tested. Analyses involved all serotyped patients and were adjusted for tumor thickness, method of nodal staging, sex, ulceration, and primary tumor site.

RESULTS

HLA typing was performed on 553 (80%) of the 689 enrolled patients (294 vaccinated and 259 observed). Expression of > or = two M5 antigens was associated with a superior vaccine treatment effect. Among patients who matched > or = two of the M5, the 97 vaccine-treated patients had improved RFS compared with the 78 observation patients (5-year relapse-free survival, 83% v 59%; P =.0002). The major components of this effect were contributed by HLA-A2 and HLA-C3. Among those who were HLA-A2-positive and/or HLA-C3-positive, the 5-year RFS for vaccinated patients was 77%, compared with 64% for observation (P =.004). There was no impact of HLA-A2 and/or HLA-C3 expression among observation patients.

CONCLUSION

This prospective analysis indicates a highly significant benefit of adjuvant therapy with Melacine among patients expressing > or = two of the M5 class I antigens, validating a prior observation in stage IV disease. HLA-A2 and HLA-C3 contributed most to this effect. Processed melanoma peptides found in Melacine may be presented by HLA-A2 and HLA-C3 and play a role in preventing relapse in vaccinated patients.

Immunotherapy for melanoma

BACKGROUND

Immunotherapy for cancers is based on the principle that the host's immune system is capable of generating immune responses against tumor cells. Currently available treatments for melanoma patients are limited by poor response rates. Interferon-a has been approved for adjuvant treatment of stage III melanoma with improved survival. New and more innovative approaches with improved efficacy are needed.

METHODS

We reviewed the various new approaches and strategies for immunotherapy for the treatment of melanoma.

RESULTS

Immunotherapy for melanoma includes a number of different strategies with vaccines utilizing whole cell tumors, peptides, cytokine-mediated dendritic cells, DNA and RNA, and antibodies.

CONCLUSIONS

A variety of approaches can be used to enhance immune reactivity in patients with melanoma. Preclinical studies and initial clinical trials have shown promising results. Additional clinical trials are currently ongoing to evaluate the clinical efficacy and the associated toxicities of these novel treatment strategies.

Unbalanced expression of HLA-A and -B antigens: a specific feature of cutaneous melanoma and other non-hemopoietic malignancies reverted by IFN-gamma

Conflicting evidences suggested that levels of HLA-A and -B antigens expressed on normal and neoplastic cells of given individuals are genetically predetermined, or, on the other hand, regulated by molecular mechanisms generating the down-regulated expression of HLA-B antigens frequently observed on melanoma cells. In our study, we quantitated, both at the protein and mRNA level, the amounts of HLA-A and -B antigens constitutively expressed on 23 primary cultures of metastatic melanomas and on autologous peripheral blood mononuclear cells (PBMC). Flow cytometric analyses identified a significantly (p < 0.01) lower expression of HLA-B antigens on melanoma cell cultures but not on autologous PBMC. Consistently, lower amounts of HLA-B antigens mRNA were detected by RNase protection assay exclusively in neoplastic cells. This unbalanced expression of HLA-A and -B antigens was readily reverted by interferon (IFN)-gamma but not by the DNA hypomethylating agent 5-aza-2'-deoxycytidine in 4 melanoma cell cultures investigated. Significantly (p < 0.05) lower levels of HLA-B antigens were also detected on cells from solid malignancies of different histotypes but not on neoplastic cells from hemopoietic neoplasms; levels of HLA-B antigens were rapidly up-regulated by IFN-gamma exclusively on non-hemopoietic transformed cells. Together, these data strongly argue against a genetic predetermination of the amounts of HLA-A and -B antigens expressed on normal and neoplastic cells of distinct melanoma patients and suggest that constitutively low levels of HLA-B antigens are a specific feature of non-hemopoietic transformed cells that is controlled by common regulatory mechanism(s) and that is possibly shared by non-hemopoietic normal cells.

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.

Efficient identification of novel HLA-A(*)0201-presented cytotoxic T lymphocyte epitopes in the widely expressed tumor antigen PRAME by proteasome-mediated digestion analysis

We report the efficient identification of four human histocompatibility leukocyte antigen (HLA)-A(*)0201-presented cytotoxic T lymphocyte (CTL) epitopes in the tumor-associated antigen PRAME using an improved "reverse immunology" strategy. Next to motif-based HLA-A(*)0201 binding prediction and actual binding and stability assays, analysis of in vitro proteasome-mediated digestions of polypeptides encompassing candidate epitopes was incorporated in the epitope prediction procedure. Proteasome cleavage pattern analysis, in particular determination of correct COOH-terminal cleavage of the putative epitope, allows a far more accurate and selective prediction of CTL epitopes. Only 4 of 19 high affinity HLA-A(*)0201 binding peptides (21%) were found to be efficiently generated by the proteasome in vitro. This approach avoids laborious CTL response inductions against high affinity binding peptides that are not processed and limits the number of peptides to be assayed for binding. CTL clones induced against the four identified epitopes (VLDGLDVLL, PRA(100-108); SLYSFPEPEA, PRA(142-151); ALYVDSLFFL, PRA(300-309); and SLLQHLIGL, PRA(425-433)) lysed melanoma, renal cell carcinoma, lung carcinoma, and mammary carcinoma cell lines expressing PRAME and HLA-A(*)0201. This indicates that these epitopes are expressed on cancer cells of diverse histologic origin, making them attractive targets for immunotherapy of cancer.

Monoclonal antibody 57B stains tumor tissues that express gene MAGE-A4

Monoclonal antibody (Mab) 57B, which was raised against a recombinant MAGE-A3 protein, was tested for its ability to stain cells expressing various members of the MAGE-A gene family. COS-7 cells transfected with cDNAs encoding MAGE-A1, A2, A3, A4, A6, or A12 were stained, whereas those transfected with MAGE-A8, A9, A10, or A11 cDNAs were not. However, in tissue sections, we observed a different pattern of staining: the antibody effectively stained the tumors that expressed MAGE-A4 and only these tumors, regardless of the expression of the other MAGE-A genes. It seems, therefore, that at the level of MAGE gene expression found in tumors, a level clearly lower than that observed in transfected COS cells, only the MAGE-A4 protein can be reliably detected. We conclude that the 57B Mab should be useful for tumor diagnosis related to therapeutic vaccination involving MAGE-A4.

b3a2 BCR-ABL fusion peptides as targets for cytotoxic T cells in chronic myeloid leukaemia

Peptide sequences spanning the BCR-ABL protein junction potentially constitute novel leukaemia-specific antigens. 9-mer b3a2 fusion peptides have been reported to bind with high affinity to HLA-A3, -A11 and -B8. We have studied the effect of b3a2 BCR-ABL junctional peptides on the cytotoxic T-cell (CTL) response against normal and chronic myeloid leukaemia (CML) cells. Antigen-presenting cells (APCs) were prepared from HLA-A3- or -B8-positive peripheral blood mononuclear cells (PBMCs) by incubation with phytohaemagglutinin (PHA) and interleukin (IL)-2 for 7 d. These APCs were pulsed with the respective b3a2 junctional peptide in the presence of beta2-microglobulin and were then used to challenge autologous PBMCs at 7-d intervals in the presence of IL-2, IL-6, IL-7 and IL-12. On subsequent exposure to target cells (either further pulsed normal APCs or unpulsed CML cells), specific HLA-restricted CTL responses were observed against all HLA-A3/-B8 matched normal target cells tested, but not to targets that were HLA mismatched. Cytotoxicity was also induced against HLA-A3/-B8 unpulsed CML cells, but not against unmatched CML cells. These data indicate (i) that endogenous BCR-ABL junctional peptides may be presented by CML cells and (ii) that exogenous peptides are potential stimulators of autologous antileukaemic CTLs.

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.

Melanoma vaccines

Remarkable advances in tumor vaccination have been made since Coley first deliberately infected cancer patients with both live and heat-killed bacteria. Melanoma is the most immunogenic solid tumor and, as such, has served as the major model for tumor vaccine investigation in both the laboratory and the clinic. Many advances in the field of melanoma vaccination have been based on an improved understanding of the cellular interaction required to induce a specific antitumor immune response. As a result of this new knowledge, many clinical trials of melanoma vaccines are now under way, and vaccines for metastatic melanoma have shown evidence of clinical effectiveness. This paper outlines the current status of melanoma vaccination.

A MAGE-A4 peptide presented by HLA-A2 is recognized by cytolytic T lymphocytes

The MAGE-encoded antigens that are recognized by cytolytic T lymphocytes (CTL) are shared by many tumors and are strictly tumor specific. Clinical trials involving therapeutic vaccination of cancer patients with MAGE antigenic peptides or proteins are in progress. To increase the range of patients eligible for therapy with peptides, it is important to identify additional MAGE epitopes. We have used a method to identify CTL epitopes, which selects naturally processed peptides. CD8(+) T cells, obtained from individuals without cancer, were stimulated with autologous dendritic cells infected with a recombinant adenovirus containing the MAGE-A4 coding sequence. Responder cell microcultures that specifically lysed autologous EBV-transformed B cells infected with vaccinia-MAGE-A4 were cloned using autologous stimulator cells infected with a Yersinia enterocolitica carrying the MAGE-A4 sequence. An anti-MAGE-A4 CTL clone was obtained and the epitope was found to be decapeptide GVYDGREHTV (amino acids 230-239) presented by HLA-A2 molecules. The CTL clone lysed HLA-A2 tumor cells expressing MAGE-A4. This is the first reported antigenic peptide encoded by MAGE-A4. It may be valuable for cancer immunotherapy because MAGE-A4 is expressed in 51% of lung carcinomas and 63% of esophageal carcinomas, whereas about 50% of Caucasians and Asians express HLA-A2.

Identification of Five MAGE-A1 Epitopes Recognized by Cytolytic T Lymphocytes Obtained by In Vitro Stimulation with Dendritic Cells Transduced with MAGE-A1

MAGE genes are expressed by many human tumors of different histological types but not by normal cells, except for male germline cells. The Ags encoded by MAGE genes and recognized by T cells are therefore strictly tumor-specific. Clinical trials involving therapeutic vaccination of cancer patients with MAGE antigenic peptides or proteins are in progress. To increase the range of patients eligible for therapy with peptides, it is important to identify additional MAGE epitopes recognized by CTL. Candidate peptides known to bind to a given HLA have been used to stimulate T lymphocytes in vitro. In some instances, CTL clones directed against these synthetic peptides have been obtained, but these clones often failed to recognize tumor cells expressing the relevant gene. Therefore, we designed a method to identify CTL epitopes that selects naturally processed peptides. Monocyte-derived dendritic cells infected with a recombinant canarypoxvirus (ALVAC) containing the entire MAGE-A1 gene were used to stimulate CD8+ T lymphocytes from the blood of individuals without cancer. Responder cell microcultures that specifically lysed autologous cells expressing MAGE-A1 were cloned using autologous stimulator cells either transduced with a retrovirus coding for MAGE-A1 or infected with recombinant Yersinia-MAGE-A1 bacteria. The CTL clones were tested for their ability to lyse autologous cells loaded with each of a set of overlapping MAGE-A1 peptides. This strategy led to the identification of five new MAGE-A1 epitopes recognized by CTL clones on HLA-A3, -A28, -B53, -Cw2, and -Cw3 molecules. All of these CTL clones recognized target cells expressing gene MAGE-A1.

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.

Antitumor immunity at work in a melanoma patient

This review covers the results obtained so far with a chronological analysis of the antitumor cytolytic T lymphocyte (CTL) cell response of a melanoma patient who enjoys an unusually favorable evolution. Two melanoma cell lines, MEL.A and MEL.B, were derived from metastases removed from the patient in 1988 and 1993, respectively. The patient developed a very strong CTL response against the MEL.A cells. Several antigens on these cells, presented by various HLA class I molecules, result from point mutations present in the genome of the tumor. The MEL.B cells, on the other hand, resist lysis by these CTLs because they have lost expression of most HLA class I molecules, suggesting that they were selected in vivo by the anti-MEL.A CTLs. New CTLs recognize MEL.B cells specifically, however. Analysis of their specificity indicates that they carry inhibitory receptors similar to those present on natural killer (NK) cells. These results illustrate the relationship between a tumor and the immune system in vivo over a period of several years. They are discussed in the context of the recent identification of many human tumor antigens recognized by CTLs, and the perspectives of specific immunotherapy opened up by these discoveries.

Modulation of proteasomal activity required for the generation of a cytotoxic T lymphocyte-defined peptide derived from the tumor antigen MAGE-3

We have analyzed the presentation of human histocompatability leukocyte antigen-A*0201-associated tumor peptide antigen MAGE-3271-279 by melanoma cells. We show that specific cytotoxic T lymphocyte (CTL)-recognizing cells transfected with a minigene encoding the preprocessed fragment MAGE-3271-279 failed to recognize cells expressing the full length MAGE-3 protein. Digestion of synthetic peptides extended at the NH2 or COOH terminus of MAGE-3271-279 with purified human proteasome revealed that the generation of the COOH terminus of the antigenic peptide was impaired. Surprisingly, addition of lactacystin to purified proteasome, though partially inhibitory, resulted in the generation of the antigenic peptide. Furthermore, treatment of melanoma cells expressing the MAGE-3 protein with lactacystin resulted in efficient lysis by MAGE-3271-279-specific CTL. We therefore postulate that the generation of antigenic peptides by the proteasome in cells can be modulated by the selective inhibition of certain of its enzymaticactivities.

Identification of MAGE-3 epitopes presented by HLA-DR molecules to CD4(+) T lymphocytes

MAGE-type genes are expressed by many tumors of different histological types and not by normal cells, except for male germline cells, which do not express major histocompatibility complex (MHC) molecules. Therefore, the antigens encoded by MAGE-type genes are strictly tumor specific and common to many tumors. We describe here the identification of the first MAGE-encoded epitopes presented by histocompatibility leukocyte antigen (HLA) class II molecules to CD4(+) T lymphocytes. Monocyte-derived dendritic cells were loaded with a MAGE-3 recombinant protein and used to stimulate autologous CD4(+) T cells. We isolated CD4(+) T cell clones that recognized two different MAGE-3 epitopes, MAGE-3114-127 and MAGE-3121-134, both presented by the HLA-DR13 molecule, which is expressed in 20% of Caucasians. The second epitope is also encoded by MAGE-1, -2, and -6. Our procedure should be applicable to other proteins for the identification of new tumor-specific antigens presented by HLA class II molecules. The knowledge of such antigens will be useful for evaluation of the immune response of cancer patients immunized with proteins or with recombinant viruses carrying entire genes coding for tumor antigens. The use of antigenic peptides presented by class II in addition to peptides presented by class I may also improve the efficacy of therapeutic antitumor vaccination.

A MAGE-6-encoded peptide is recognized by expanded lymphocytes infiltrating a spontaneously regressing human primary melanoma lesion

In recent years, experiments based on the in vitro stimulation of either autologous peripheral blood lymphocytes or tumor-infiltrating lymphocytes with melanoma cells have shown that distinct members of the large MAGE gene family encode tumor-associated antigenic peptides. However, little is still known about natural anti-MAGE responses in vivo. We have studied a case of spontaneously regressing human melanoma, hypothesizing that in this unique situation, the host immune system had developed an efficient cytotoxic T lymphocyte (CTL) response against the cancer cells. Amongst the dense tumor infiltrate, certain clonal populations of T cells were shown to be amplified, thereby suggesting that an antigen-driven selection had occurred at the tumor site. One of the expanded tumor-infiltrating lymphocytes was shown to be a Vbeta13+ CD8+ CTL displaying a strong and selective cytotoxic activity against the autologous melanoma cells. Here we show that this cytotoxic T cell clone recognizes a MAGE-6-encoded peptide. MAGE-6 is therefore the fourth gene of the MAGE family shown to encode antigenic peptide recognized by T cells. Together, these data provide further evidence that T cell responses against MAGE antigens may naturally develop in vivo.

Changes in the Fine Specificity of gp100(209–217)-Reactive T Cells in Patients Following Vaccination with a Peptide Modified at an HLA-A2.1 Anchor Residue

In a recent clinical trial, HLA-A2+ melanoma patients were vaccinated with a peptide derived from the melanoma Ag gp100, which had been modified at the second position (g9-209 2M) to enhance MHC binding affinity. Vaccination led to a significant increase in lymphocyte precursors in 10 of 11 patients but did not result in objective cancer responses. We observed that some postvaccination PBMC cultures were less reactive with tumor cells than they were with g9-209 peptide-pulsed T2 cells. In contrast, g9-209-reactive tumor-infiltrating lymphocyte cultures generally reacted equally with tumor cells and g9-209 peptide-pulsed T2 cells. To investigate this difference in T cell reactivity, T cell cloids derived from the PBMC of three patients vaccinated with g9-209 2M were compared with T cell cloids isolated from g9-209-reactive TIL cultures. All of the T cell cloids obtained from TIL reacted with HLA-A2+, gp100+ melanoma cell lines as well as with g9-209 and g9-209 2M peptide-pulsed targets. In contrast, only 3 of 20 PBMC-derived T cell cloids reacted with melanoma cell lines in addition to g9-209 and to g9-209 2M peptide-pulsed targets. Twelve of twenty PBMC-derived cloids reacted with g9-209 and g9-209 2M peptide-pulsed targets but not with melanoma cell lines. And 5 of 20 PBMC-derived cloids recognized only the g9-209 2M-modified peptide-pulsed targets. These results suggest that immunizing patients with the modified peptide affected the T cell repertoire by expanding an array of T cells with different fine specificities, only some of which recognized melanoma cells.

A MAGE-1-encoded HLA-A24-binding synthetic peptide induces specific anti-tumor cytotoxic T lymphocytes

Although several MAGE-1 peptides have already been identified, the MAGE-1-encoded peptide presented by HLA-A24, which is the most common allele in Japanese population and is also frequently present in Caucasians, might have a wide applicability for immunotherapy using these peptides. To identify this potential peptide, we examined the induction of specific cytotoxic T lymphocytes (CTL) from the peripheral-blood mononuclear cells (PBMC) in HLA-A24 healthy donors by in vitro stimulation with MAGE-1-encoded synthetic peptides with a binding affinity for HLA-A24, by a simplified method. Of the 5 peptides tested, the highest HLA binder (NYKHCFPEI) was able to elicit CTL from unseparated PBMC by stimulation with freshly isolated, peptide-pulsed PMBC as antigen-presenting cells (APC) and by also using interleukin 7 and keyhole-limpet hemocyanin for a primary culture. The induced CTL could thus lyse HLA-A24 tumor cells expressing MAGE-1, as well as the peptide-pulsed target cells, in an HLA-class-I-restricted manner. By using the MAGE-1/HLA-A24 peptide, NYKHCFPEI, we found it possible to immunize many more patients, especially Japanese patients, by means of such peptide-based immunotherapeutic approaches to MAGE-1-positive malignant tumors.

Higher frequency of selective losses of HLA-A and -B allospecificities in metastasis than in primary melanoma lesions

Expression of HLA class I molecules is essential for the recognition of tumor cells by CD8+ T cells. In this study, 48 bioptic samples of 42 patients in all stages of melanoma were investigated after short-time cultivation of tumor cells. To confirm melanocytic origin of cultured cells, samples were screened for mRNA expression of melanoma markers gp100, tyrosinase, MAGE-3, MelanA, and MUC18 by reverse transcriptase-polymerase chain reaction. Surface expression of specific HLA-A and -B allospecificities on melanoma cells were analyzed with a standard microcytotoxicity assay after stimulation with interferon (IFN)-alpha and compared with the background found in peripheral blood mononuclear cells from the corresponding patients. Immunohistochemistry and flow cytometry confirmed specific losses in cases where the appropriate monoclonal antibodies were available. The level of expression of HLA-I, HLA-II, and intercellular adhesion molecule 1 antigens on melanoma cells cultured in the presence or absence of IFN-alpha and IFN-gamma was determined cytofluorometrically. All cell cultures tested were found to be positive for one or more melanocytic markers by reverse transcriptase-polymerase chain reaction. The specific HLA-I alleles on the cultured cells were detectable in 45 of 48 samples. In 11 cases a specific loss of one HLA-I allele was observed (2 x A2, B7, B8, B18, 4XB44, B47, B49). Ten of these samples were derived from locoregional lymphnode metastases or from distant metastatic tumors. Only one sample from a primary melanoma showed a specific loss of HLA-I (B47). IFN-alpha upregulated expression of HLA-I up to 4-fold. IFN-gamma enhanced the appearance of HLA-II up to 35-fold and the expression of intercellular adhesion molecule 1 up to 40-fold. Selective loss of HLA-I allospecificities might be a major step in tumor progression.