A nonapeptide encoded by human gene MAGE-1 is recognized on HLA-A1 by cytolytic T lymphocytes directed against tumor antigen MZ2-E

MAGE-1 gene product is a cytoplasmic protein

MAGE-1 gene encodes a human melanoma antigen, recognized by syngeneic cytotoxic T lymphocytes (CTL). MAGE-1 transcripts are also detectable in breast cancers, in non-small-cell lung carcinomas and in central nervous system tumors. In order to identify, in cellular preparations, the protein encompassing the antigenic peptide, we generated a panel of monoclonal antibodies (MAbs) against the MAGE-1 gene product by using, as immunogen, a full-length recombinant preparation (rMAGE-1), obtained through expression cloning of the relevant gene in E. coli. Four reagents were obtained recognizing both rMAGE-1 and the 46-kDa native protein in cell lines expressing MAGE-1 mRNA. No positivity could be detected in MAGE-1-mRNA-negative melanoma lines. No surface labelling of MAGE-1-positive cell lines could be observed. In contrast, on permeabilization of MZ2 melanoma cells, all 4 MAbs induced efficient staining, as detected by cytofluorography. Fluorescence microscopy shows that MAGE-1 gene product is a cytoplasmic protein clustered in paranuclear organelle-like structures. Thus, MAGE-1 protein location closely resembles that of P91A and P198 murine-tumor antigens.

Direct analysis of tumor-associated peptide antigens

Adoptive immunotherapy with tumor-specific cytotoxic T lymphocytes (CTLs) can induce tumor regressions in animals and in human cancer patients. Antigens recognized by CTLs from cancer patients are being sought as possible immunogens, a number of which have been identified during the past year. The ultimate result may be the development of novel peptide-based immunotherapies and a new understanding of the T-cell response to human cancer.

Analysis of T cell receptor alpha beta variability in lymphocytes infiltrating melanoma primary tumours and metastatic lesions

The T cell receptor (TCR) alpha beta variable (V) gene family usage of tumour-infiltrating lymphocytes (TIL) in four different primary human malignant melanomas and their corresponding metastatic lesions was characterized using a recently developed method based on the reverse-transcription-coupled polymerase chain reaction (RT-PCR). All patients were typed for HLA-A1 and -A2, either serologically or by a newly developed RT-PCR method. Two of these patients expressed HLA-A2, one the HLA-A1 haplotype and one further patient was heterozygous HLA-A1/-A2. The prognostic parameters for all four patients indicated that rapid progression of the disease was to be expected. However, only two of the patients showed rapid progression, while the remaining two patients are still alive after more than 3 years. In TIL in primary melanomas, a possible correlation was suggested between HLA-A2 and the preferential usage of the TCR V gene families V alpha 4, V alpha 5, V alpha 22 and V beta 8, whereas the V beta 3 gene family appeared to be expressed together with HLA-A1. Other highly expressed V gene families, apparently not restricted to either HLA-A1 or -A2, were V alpha 1 (expressed in three of four primary tumours) and V alpha 21 (expressed in two of four tumours). We found no evidence suggesting any correlations between the haplotypes HLA-A1 and -A2 and preferential V gene family expression in the metastatic lesions, and the only common feature was V alpha 8, which was found to be highly expressed in two out of three subcutaneous metastases. The V gene families, which were highly expressed in the primary tumour were generally not, or only very weakly, expressed in metastases and vice versa, possibly reflecting a change in the phenotype of the metastatic melanoma target cells. With regards to patient 0368, it was possible to obtain and study material from two subcutaneous metastases. The first metastasis was excised more than a year after the primary tumour, showing a completely different V region repertoire. The second metastasis was excised at surgery 2 years after primary surgery and likewise showed a dramatic shift in comparison to the first subcutaneous metastasis. Although the present study only included a small number of patients, it suggests that the estimation of V gene expression, if applied to a larger amount of patient material, might make it possible to substantiate further the suggested correlations between the T cell response against the tumour, HLA and antigen expression.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure, chromosomal localization, and expression of 12 genes of the MAGE family

We reported previously that human gene MAGE-1 directs the expression of a tumor antigen recognized on a melanoma by autologous cytolytic T lymphocytes. Probing cosmid libraries with a MAGE-1 sequence, we identified 11 closely related genes. The analysis of hamster-human somatic cell hybrids indicated that the 12 MAGE genes are located in the q terminal region of chromosome X. Like MAGE-1, the 11 additional MAGE genes have their entire coding sequence located in the last exon, which shows 64%-85% identity with that of MAGE-1. The coding sequences of the MAGE genes predict the same main structural features for all MAGE proteins. In contrast, the promoters and first exons of the 12 MAGE genes show considerable variability, suggesting that the existence of this gene family enables the same function to be expressed under different transcriptional controls. The expression of each MAGE gene was evaluated by reverse transcription and polymerase chain reaction amplification. Six genes of the MAGE family including MAGE-1 were found to be expressed at a high level in a number of tumors of various histological types. None was expressed in a large panel of healthy tissues, with the exception of testis and placenta.

Autologous cytolytic T lymphocytes recognize a MAGE-1 nonapeptide on melanomas expressing HLA-Cw*1601

Human melanoma cell line MZ2-MEL expresses several antigens recognized by autologous cytolytic T lymphocyte (CTL) clones. We reported previously the identification of a gene, named MAGE-1, which codes for antigen MZ2-E which is presented by HLA-A1. Gene MAGE-1 is expressed in many tumors of several types but not in normal tissues except for testis. We show here that gene MAGE-1 directs the expression of another antigen recognized by CTL on the MZ2-MEL cells. This antigen, which was named MZ2-Bb, consists of MAGE-1-encoded peptide SAYGEPRKL bound to major histocompatibility molecule HLA-Cw*1601. The HLA-Cw*1601 allele was found to be expressed by 7 out of 99 individuals from a Caucasian population. Our results extend the range of tumor patients who could be eligible for immunization against MAGE antigens.

Defective lymphokine production by most CD8+ and CD4+ tumor-specific T cell clones derived from human melanoma-infiltrating lymphocytes in response to autologous tumor cells in vitro

Human melanomas are infiltrated by tumor-reactive T lymphocytes. However, the ability of these cells to elicit a specific anti-tumor response in vivo remains to be established. Because lymphokine production is critical for T cell functions, we have analyzed the capacity of melanoma-specific tumor-infiltrating lymphocyte (TIL) clones to produce major lymphokines: interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), as well as tumor necrosis factor (TNF), in response to direct antigen presentation by autologous and allogeneic tumor cells. We report here that, upon stimulation by autologous melanoma cells, all TIL clones secreted TNF but only a few of them produced significant amounts of IL-2, IL-4 or IFN-gamma. Nonetheless, all these clones consistently produced two or three of these last lymphokines upon stimulation with phorbol myristate acetate and calcium ionophore, as well as IL-2 upon CD3 stimulation, showing the existence of three lymphokine profiles among them: Th1, Th0 and a profile characterized by IL-2 and IL-4, but not IFN-gamma secretion. Stimulation of TIL clones by allogeneic melanoma lines sharing the appropriate HLA-peptide complexes revealed that defective IL-2 production seemed to be a constant feature for some clones, while it was, for other clones, dependent on the antigen-presenting tumor cells. For this last type of clone, we further showed that defective IL-2 induction resulted from an LFA-3 defect of some melanoma cells or from distinct yet undefined defects of other melanoma lines. Our data suggest that defective lymphokine secretion may be an essential component of the in vivo failure of melanoma-reactive TIL to control tumor development. Interestingly both CD4+ and CD8+ TIL clones from one patient were fully activated by the autologous melanoma cells in vitro, supporting a potential role of such TIL in spontaneous or induced tumor rejection.

Polyclonal uses of T-cell receptor (TCR)alpha and beta genes for cytotoxic T lymphocytes in human metastatic melanoma: possible involvement of TCR alpha in tumor-cell recognition

Identification of genetic structure and diversity of T-cell receptor (TCR)alpha and beta genes for cytotoxic T lymphocytes (CTLs) infiltrating human cancers is important for the better understanding of molecular mechanisms of host defense at tumor sites. cDNAs of TCR alpha and beta genes of 22 different melanoma-specific CTL clones established from the tumor-infiltrating lymphocytes of 2 patients were sequenced for analysis of their genetic structure and diversity. V alpha 7.2-J alpha 10-C alpha was found in 4 of 22 clones, 2 of which also used the same beta-chain. The other 20 clones showed different combinations of alpha and beta use. At deduced amino-acid levels, 7 of 9 clones from one patient used a threonine residue at the 26th position in the complementarity-determining region (CDR)1 of TCR alpha. Eight of 13 clones used a threonine at the 99th or a serine residue at the 100th position in CDR3 of TCR alpha CTL clones with the same or different TCR alpha showed the same or different patterns of cytotoxicity, respectively. These results suggest that CTLs usually do not demonstrate clonal expansion at tumor sites of metastatic melanoma's but rather that polyclonal T cells capable of binding to multiple melanoma determinants through CDR3 of TCR alpha accumulate in the tumor.

Generation of specific anti-melanoma reactivity by stimulation of human tumor-infiltrating lymphocytes with MAGE-1 synthetic peptide

The MAGE-1 gene encodes a tumor-specific antigen, MZ2-E, which is recognized by cloned, specific cytolytic T cells (CTL) derived from the peripheral blood of a patient with melanoma. We have produced a MAGE-1-specific CTL line derived from the tumor-infiltrating lymphocytes (TIL) of a melanoma patient by weekly restimulation with autologous EBV-B cells pulsed with the synthetic HLA-A1-restricted MAGE-1 epitope nonapeptide EADPTGHSY. The 1277.A TIL line grew in long-term culture in low-dose interleukin-2 (IL-2) and IL-4, and exhibited antigen-specific, MHC-class-I-restricted lysis of HLA-A1-bearing MAGE-1+ cell lines. Cytolysis of target cells pulsed with the synthetic MAGE-1 decapeptide KEADPTGHSY was superior to that of cells pulsed with the immunodominant nonapeptide. Single amino-acid or even side-chain substitutions in the immunodominant nonamer abrogated cytolysis. 1277.A TIL specifically secreted tumor necrosis factor alpha after co-incubation with HLA-A1-expressing MAGE-1+ cell lines or fresh tumor. These data suggest that tumor-antigen-specific, MHC-restricted CTL may be grown from TIL in the presence of synthetic epitope peptides and expanded for adoptive immunotherapy in melanoma patients.

Peptide binding to the most frequent HLA-A class I alleles measured by quantitative molecular binding assays

Quantitative assays to measure the binding of defined synthetic antigenic peptides and purified MHC class I molecules are described for several common human HLA-A alleles (A1, A2.1, A3, A11 and A24). Under appropriate conditions, the binding of radiolabeled peptides to purified MHC class I molecules is very effective, highly specific, and appears to be dependent on the specific sequence motif of the peptide as defined by critical anchor residue positions. Establishment and optimization of the assay reveals that a relatively high fraction of the MHC class I molecules isolated from EBV transformed B cell line sources is capable of binding exogenously added peptide. Scatchard analysis for all alleles yields 5-10% occupancy values. There is a stringent peptide size requirement that is reflected by the direct influence of peptide length on the binding affinity. The peptide-MHC class I interactions demonstrate remarkable similarity to peptide-MHC class II interactions, both in overall affinity and kinetic behavior. The immunological relevance of the peptide-MHC class I binding assay is also demonstrated by measuring the affinity of a panel of previously described HLA restricted peptides for their HLA restriction element. In 91% (10/11) of the cases, the peptides bound with affinities of 50 nM or less, and in the remaining 9% (1/11) of the cases, in the 50 to 500 nM range. Thus, these data provide the first quantitative estimate of what level of HLA-A binding affinity is associated with a diverse panel of immunodominant CTL epitopes in man.

Frequency of cytotoxic T lymphocyte precursors (CTLp) interacting with autologous tumor via the T-cell receptor: limiting dilution analysis of specific CTLp in peripheral blood and tumor-invaded lymph nodes of melanoma patients

The frequencies of cytotoxic T-lymphocyte precursors (CTLp) that lyse autologous tumor by a T-cell receptor (TCR)-dependent mechanism (specific CTLp) were evaluated by limiting dilution analysis (LDA) using lymphocytes from peripheral blood (PBL) and from surgically resected, tumor-invaded lymph nodes (LNL) in 9 melanoma patients. The frequency of specific CTLp was determined in PBLs and/or LNIs of all patients by a modified LDA assay, enabling us to measure lytic activity on the autologous tumor that could be significantly inhibited by an anti-CD3 monoclonal antibody (MAb). This assay allowed us to detect frequencies of specific CTLp ranging from 1/720 to 1/32,037 in peripheral blood and from 1/328 to 1/22,061 in tumor-invaded lymph nodes. These frequencies indicated that lymphoid populations from PBLs or LNLs of melanoma patients may contain as low as 30 to as much as 3,000 specific CTLp/10(6) lymphocytes. In addition, comparison of wells containing specific CTLp with those showing no inhibition by anti-CD3 MAb indicated that specific CTLp represent between 3 and 88% of all precursors with lytic activity on the tumor. In 6 of 9 patients, no marked differences between PBLs and LNIs in specific CTLp frequencies were found. A 10-fold increase of specific CTLp, in comparison to PBL and LNL, was found only in lymphocytes isolated from a subcutaneous metastasis of one patient. Our results indicate that CTLp interacting with autologous tumor by a TCR-dependent mechanism exist in PBL and LNL of most melanoma patients, although a wide variation in their absolute number is evident among different patients.

Identification of the immunodominant peptides of the MART-1 human melanoma antigen recognized by the majority of HLA-A2-restricted tumor infiltrating lymphocytes

Four melanoma proteins, MART-1, gp100, tyrosinase, and tyrosinase-related protein-1 (gp75) were evaluated for recognition by HLA-A2-restricted melanoma-specific cytotoxic T lymphocytes (CTLs) derived from the tumor-infiltrating lymphocytes (TIL) of 10 different patients. 9 of 10 TIL recognized MART-1, 4 recognized gp100 (including 3 that also recognized MART-1), but none of the TIL recognized tyrosinase or gp75. Based on the known HLA-A2.1 peptide binding motifs, 23 peptides from MART-1 were synthesized in an attempt to identify the epitopes recognized by TIL. Three peptides were recognized by TIL when pulsed on T2 target cells. One of the 9-mer peptides, AAGIGILTV, was most effective in sensitizing the T2 cells for TIL lysis. This peptide was recognized by 9 of 10 HLA-A2-restricted melanoma-specific CTLs. Therefore, this peptide appears to be a very common immunogenic epitope for HLA-A2-restricted melanoma-specific TIL and may be useful for the development of immunotherapeutic strategies.

Use of a skin test assay to determine tumor-specific CD8+ T cell reactivity

We have observed delayed-type hypersensitivity (DTH) reactions in immunized mice challenged subcutaneously with class I-binding peptides related to rejection antigens recognized by cytotoxic T lymphocytes on mutagenized (tum-) variants of mastocytoma P815. As observed by skin test in virally infected mice challenged with viral peptides, the intrafootpad injection of tum- peptides resulted in a dose-dependent DTH that peaked at approximately 24 h. The response was mediated by CD8+ cells and could be induced by previous vaccination of mice with live tumor cells, intrasplenic deposition of the eliciting peptide, or adoptive transfer with peptide-pulsed syngeneic dendritic cells. These sensitization procedures resulted in an immunologically specific footpad reaction detectable for up to 2-6 months after priming. The evaluation by DTH in cancer patients of long-lived CD8+ anti-tumor T cell responses following local challenge with tumor-specific peptides may be of great interest in human immunotherapy trials involving immunization against identified tumor antigens.

T cell recognition of melanoma antigens in association with HLA-A1 on allogeneic melanoma cells

Previous studies have shown that recognition of melanoma by cytotoxic T lymphocytes may be restricted by HLA-A1, A2 and other HLA antigens. The present study examined the cytotoxic specificity and major histocompatibility complex restriction of cloned cytotoxic T lymphocytes (CTL) isolated from a patient with the HLA phenotype A3,31 who had been immunized with a vaccine prepared from HLA-A1,3 melanoma cells. Cytotoxic assays against HLA-typed allogeneic melanoma cells indicated that cloned CTL from the patient were able to kill allogeneic melanoma cells expressing HLA-A1 but not other HLA-A1-positive cells. Studies on a representative clone indicated that proliferation and cytokine (tumour necrosis factor alpha) production in response to melanoma cells was also associated with HLA-A1 on melanoma cells. Response to the melanoma cells was associated with interleukin-4 (IL-4) rather than IL-2 production. The antigen recognized in the context of HLA-A1 on allogeneic melanoma cells was detected in cytotoxic assays on cells from 9 of 12 HLA-A1+ melanoma cell lines and did not appear to be the product of the MAGE-1 or -3 genes. These findings suggest that T cells can recognize melanoma antigens in the context of alloantigens and that allogeneic vaccines containing "immunodominant" alloantigens may generate CTL that are ineffective against autologous melanoma. The study does not, however, exclude the possibility that CTL with specificity to the latter may be activated by allogeneic vaccines, and further studies are needed to answer this question.

Generation of allo-reactive cytotoxic T lymphocytes by particle bombardment-mediated gene transfer

Mature T lymphocytes comprise functionally distinct subsets with discrete roles in the regulation of the immune response. The cellular basis of the anti-tumor effect is now understood to involve the activation and expansion of tumor-specific cytotoxic T lymphocytes (CTL). To immuno-potentiate the generation of CTL, we have employed the biolistic system for the genetic immunization of mice. Here, we report the efficient generation of anti-H-2Kb allo-reactive CTL by particle acceleration-mediated genetic immunization of mouse spleen cells with H-2Kb DNA. The insertion and expression of exogenous gene into host spleen cells following in situ genetic inoculation to effect the generation of a cellular immune response may permit novel alternative strategies for immunotherapy.

Isolation of naturally processed peptides recognized by cytolytic T lymphocytes (CTL) on human melanoma cells in association with HLA-A2.1

Cytolytic T lymphocyte (CTL) clones have previously been derived from peripheral blood of melanoma patient SK29(AV). They lyse autologous melanoma cells but not autologous Epstein-Barr virus (EBV)-transformed B lymphocytes. Immunoselection experiments indicate that these CTL clones recognize 4 different antigens (Aa, Ab, B, C) in association with a single HLA restriction element, HLA-A2.1. While the expression of antigens B and C appears to be confined to SK29-melanoma cells, antigens Aa and Ab are shared by a high proportion of allogeneic HLA-A2-positive melanoma lines. HLA-A2.1 and total HLA class I molecules have now been purified from SK29-melanoma cells using affinity chromatography and associated peptides have been eluted. Peptide pools eluted from HLA-A2.1 and total class I were separated by reversed phase high performance liquid chromatography (HPLC). Individual HPLC fractions were tested for their ability to sensitize target cells for recognition by SK29-CTL clones. The presence of antigens Aa, Ab, B and C was detected in distinct HPLC fractions that were identical for both peptide pools. As target for detection of peptide antigens in HPLC fractions, the use of the HLA-A2.1-positive antigen processing mutant cell line CEM x 721.174.T2 (T2), pre-incubated with anti-HLA-A2 monoclonal antibody (MAb) MA2.1, was shown to be essential. Single-peak target-sensitizing activity was found for antigens Ab and B, whereas multi-peak sensitizing activity was reproducibly detected for antigens Aa and C. We reason that at least some of these melanoma peptide antigens might occur in biochemically distinct isoforms.

p53, a potential target for tumor-directed T cells

Cell lineage-specific cellular proteins, oncogenes from viral or cellular origin and tumor suppressor genes encode tumor-specific/associated antigens. Such antigens can elicit an major compatibility complex (MHC) class I-restricted cytotoxic T lymphocyte (CTL) response, either naturally in cancer patients or following appropriate immunostimulation (in vitro or in vivo). The reported immune responses in humans to the melanoma-associated MAGE gene products, GP100 and tyrosinase, all self-proteins, support the idea to use wild-type p53 products as targets for T cells. An important step towards this goal is identification of potential p53 CTL epitopes. We identified the wild-type p53 peptides with the highest affinity to the HLA-A*0201 molecule using two assays: the previously described MHC peptide-binding assay and the peptide competition assay. We obtained CTL against four p53 peptides with a high affinity for the HLA-A*0201 molecule. These findings are discussed next to a short review concerning the p53 literature.

HLA restriction and T-cell-receptor V beta gene expression of cytotoxic T lymphocytes reactive with human squamous-cell carcinoma of the head and neck

A human cytotoxic-T-lymphocyte (CTL) line capable of killing autologous tumor (AuTu) cell targets was established from peripheral-blood lymphocytes of a patient with squamous-cell carcinoma of the tongue. The cultured CTL were CD3+CD8+CD11b-HLA-DR+T cell receptor (TCR) alpha/beta+. When tested in 4-hr 51Cr-release assays against various lines of squamous-cell carcinoma of the head and neck (SCCHN) and a variety of non-squamous human tumor and normal cell targets, the CTL were found to lyse the autologous SCCHN cell line (PCI-50) and 7 allogeneic SCCHN lines: PCI-1, -2, -4A, -4B, -13, -30 and -38. Of these tumor cell lines, PCI-13, -30 and -38 shared HLA-A2 locus with the AuTu, PCI-50, while PCI-4A and -4B shared HLA-B44 with AuTu. Lysis of AuTu (A2+B44+), PCI-13 (A2+B44-) and PCI-4B (A2- B44+) by the CTL was efficiently inhibited by monoclonal antibodies (MAbs) to CD3, CD8, TCR alpha/beta or the major-histocompatibility-complex (MHC)-class-I antigens. MAbs to HLA-A2 antigens inhibited lysis of PCI-50 or PCI-13 targets by the CTL. In cold-target inhibition assays, unlabeled PCI-4B or PCI-13 cells inhibited CTL lysis of AuTu targets. The CTL incubated in the presence of the HLA-A2+ SCCHN PCI-50 or -13, but not an HLA-A2+ gastric carcinoma, produced TNF-alpha, IFN-gamma and GM-CSF. The CTL were tested for their TCR V beta gene expression by polymerase chain reaction (PCR). At week 10 in culture, the time of the highest AuTu cytotoxicity mediated by the CTL line, V beta 6 was expressed by 26% of T cells. Three clones, obtained by limiting dilution from 10-week CTL and selected for high cytotoxicity against AuTu, were found to be V beta6+. Further analysis of the specificity of these clones indicated lytic activity against PCI-13 (A2+B44-), but not PCI-4B (A2-B44+) targets. In 16-week cultures, which retained AuTu cytotoxicity as well as V beta 6 expression, TCR V beta 2 was also expressed at high frequency (29%), and AuTu-reactive clones were found to be V beta 2+. Our results indicate that at least 2 different CTL populations (V beta 6+ and V beta 2+) are able to recognize SCCHN-associated antigen(s) and that the V beta 6+ T cells are HLA-A2 restricted, while V beta 2+ T cells may be HLA-B44 restricted.

Cloning of the gene coding for a shared human melanoma antigen recognized by autologous T cells infiltrating into tumor

By cDNA expression cloning we have isolated a gene encoding a shared human melanoma antigen recognized by HLA-A2 restricted autologous and allogenic tumor-infiltrating lymphocytes (TILs) from patients with metastatic melanoma. By using both transient and stable expression systems, transfection of this gene into non-antigen-expressing HLA-A2+ cell lines resulted in recognition by the antigen-specific TILs. The sequence of this cDNA revealed a previously undescribed putative transmembrane protein whose expression was restricted to melanoma and melanocyte cell lines and human retina but no other fresh or cultured normal tissues tested or other tumor histologies. Thus, we have identified a gene encoding a melanocyte lineage-specific protein (MART-1; melanoma antigen recognized by T cells 1) that is a widely shared melanoma antigen recognized by the T lymphocytes of patients with established malignancy. Identification of this gene opens possibilities for the development of immunotherapies for patients with melanoma.

Direct evidence to support the immunosurveillance concept in a human regressive melanoma

The concept of immunosurveillance against cancer has been an extensively debated question over the last decades. Multiple indirect arguments have supported the view that the immune system may control, at least in certain cases, malignant cell growth while direct demonstration is still lacking in the human. In an attempt to address this issue, we have selected a study model, namely spontaneously regressive melanoma. In previous series of experiments, the variability of T cell receptors (TCRs) in the lymphocytes infiltrating a regressive tumor lesion was investigated. Results demonstrated that clonal T cell populations, precisely defined through their V-D-J junctional sequences, were amplified in situ. One clone was predominant, expressing the V beta 16 variable gene segment. A specific anti-V beta 16 TCR mAb was generated here to purify and functionally characterize the corresponding cells. A tumor-infiltrating lymphocyte-derived V beta 16+ T cell line was developed using this reagent. These in vitro cultured cells were found to express the in vivo predominant TCR sequence exclusively and to display an HLA-B14-restricted cytotoxic activity against the autologous tumor cells. Immunohistochemical experiments, performed with the anti-V beta 16 mAb, showed that the corresponding CTLs are present in the tumor area, some of them being closely opposed to the melanoma cells. Together, these studies demonstrate the existence of a local adaptive immune response clinically associated to tumor regression, thus strongly supporting the validity of the immunosurveillance concept in certain human tumors.

Expression of mage genes by non-small-cell lung carcinomas

Human gene MAGE-I codes for an antigen that is recognized on melanoma cells by autologous cytolytic T lymphocytes (CTL). This antigen is potentially useful as a target for cancer immunotherapy because gene MAGE-I is not expressed in any normal tissues except the testis. We tested 46 surgical samples of non-small-cell lung carcinomas and observed MAGE-I expression in 16 of them (35%). Genes MAGE-2 and 3, which are closely related to MAGE-I, were expressed by a similar proportion of these tumors. Some small-cell lung tumors also express MAGE genes. The proportion of tumors expressing MAGE-I suggests that lung tumor patients may constitute the largest group of patients potentially eligible for pilot studies involving MAGE-I immunization.

Induction of anti-tumor cytotoxic T lymphocytes in normal humans using primary cultures and synthetic peptide epitopes

Cytotoxic T lymphocytes (CTLs) recognize peptide antigens associated with cell surface major histocompatibility complex (MHC) molecules. The identification of tumor cell-derived peptides capable of eliciting anti-tumor CTL responses would enable the design of antigen-specific immunotherapies. Our strategy to identify such potentially therapeutic peptides relies on selecting high-affinity MHC binders from known tumor-associated antigens. These peptides are subsequently tested for their ability to induce CTLs capable of killing tumor cells. With this strategy, we have identified a nine-residue epitope, derived from the product of the tumor-associated gene MAGE-3, which has the capacity to induce in vitro CTLs that kill melanoma and other tumor cell lines. These results show the primary in vitro induction of tumor-specific human CTLs and illustrate the feasibility of ex vivo antigen-specific approaches to the immunological therapy of cancer.

Long term response to chemotherapy in patients with visceral metastatic melanoma

PATIENTS AND METHODS

Eight patients who remain in long term remission 4 to 15 years after chemotherapy for visceral metastatic melanoma are described. These patients were observed among some 1100 patients with visceral melanoma seen at the Sydney Melanoma Unit between 1977 and 1989. Only about one-third of such patients received chemotherapy, almost always with single agent dacarbazine or a nitrosourea.

RESULTS

The apparently cured patients did not differ from the overall group of patients with visceral metastases in baseline characteristics, but 6 of the 8 had nodular lung metastases.

CONCLUSIONS

While the mechanism remains uncertain, one possibility could be that chemotherapeutic agents cause mutations which allow expression of antigenicity in tumour cells. In any case, the fact of occasional exceptionally good responses, perhaps amounting to cure, constitutes an argument for a trial of chemotherapy in patients with visceral metastatic melanoma.

Two tyrosinase nonapeptides recognized on HLA-A2 melanomas by autologous cytolytic T lymphocytes

A number of cytolytic T lymphocyte (CTL) clones derived from several melanoma patients have been found to recognize a majority of melanomas from HLA-A2 patients. We have reported previously that two such CTL clones recognize a product of the tyrosinase gene that is presented by HLA-A2. Here we show that one of these CTL clones recognizes a peptide encoded by the first nine amino acids of the putative signal sequence of tyrosinase. The other CTL clone recognizes a different tyrosinase peptide corresponding to amino acids 368-376. Both peptides contain consensus motifs of HLA-A2 binding peptides.

Human gene MAGE-3 codes for an antigen recognized on a melanoma by autologous cytolytic T lymphocytes

Human melanoma cell line MZ2-MEL expresses several antigens recognized by autologous cytolytic T lymphocyte (CTL) clones. We reported previously the identification of a gene, named MAGE-1, that codes for one of these antigens named MZ2-E. We show here that antigen MZ2-D, which is present on the same tumor, is encoded by another member of the MAGE gene family named MAGE-3. Like MAGE-1, MAGE-3 is composed of three exons and the large open reading frame is entirely located in the third exon. Its sequence shows 73% identity with MAGE-1. Like MZ2-E, antigen MZ2-D is presented by HLA-A1. The antigenic peptide of MZ2-D is a nonapeptide that is encoded by the sequence of MAGE-3 that is homologous to the MAGE-1 sequence coding for the MZ2-E peptide. Competition experiments using single Ala-substituted peptides indicated that amino acid residues Asp in position 3 and Tyr in position 9 were essential for binding of the MAGE-1 peptide to HLA-A1. Gene MAGE-3 is expressed in many tumors of several types, such as melanoma, head and neck squamous cell carcinoma, lung carcinoma and breast carcinoma, but not in normal tissues except for testes. It is expressed in a larger proportion of melanoma samples than MAGE-1. MAGE-3 encoded antigens may therefore have a wide applicability for specific immunotherapy of melanoma patients.

Identification of the MAGE-1 gene product by monoclonal and polyclonal antibodies

The human MAGE-1 gene encodes a melanoma peptide antigen recognized by autologous cytotoxic T lymphocytes. To produce antibodies against the MAGE-1 gene product, several approaches were taken. Three oligopeptides were synthesized based on predicted MAGE-1 amino acid sequences and were used to generate rabbit anti-peptide anti-sera. In addition, a truncated MAGE-1 cDNA was cloned into an Escherichia coli expression vector, and recombinant protein was produced and purified. All three rabbit anti-peptide antisera showed reactivity against the immunizing peptide, and one reacted with the recombinant MAGE-1 protein by immunoblotting, but none reacted with cell lysates from MAGE-1 mRNA-positive cells. The recombinant MAGE-1 protein was then used for the generation of mouse monoclonal and rabbit polyclonal antibodies. One IgG1 monoclonal antibody, MA454, as well as rabbit polyclonal antisera recognized a 46-kDa protein in extracts of MAGE-1 mRNA-positive melanoma cell lines. The antibodies showed no apparent cross-reactivity with products of the closely related MAGE-2 and MAGE-3 genes. Serological typing of normal and tumor cell lysates was in full agreement with mRNA analysis, showing expression of MAGE-1 protein in MAGE-1 mRNA-positive testis and a subset of melanomas but not in MAGE-1 mRNA-negative normal or tumor tissues. Transfection of the MAGE-1 gene into a MAGE-1 mRNA-negative melanoma cell line resulted in the expression of the 46-kDa protein, confirming the identity of this protein as the MAGE-1 gene product.

Structure of peptides associated with MHC class I molecules

Recent progress in understanding the structures of MHC class I molecules and the peptides that they bind has led to a generalized model for peptide binding, and an understanding of allelic specificity. Prediction on the basis of motifs and new techniques for peptide analysis have recently resulted in the identification of several peptides that comprise epitopes for antigen-specific T cells.

Growth inhibition of a colonic adenocarcinoma cell line (HT29) by T cells specific for mutant p21 ras

Mutations at codons 12, 13 or 61 of the ras proto-oncogenes are found in adenocarcinomas of the colon and rectum. Mutated ras encode tumor-specific proteins, and can elicit CD4+ HLA-class-II-restricted T cell responses both in mouse and man. The function of such T cells is, however, unclear. In a model system, we investigated whether HLA-class-II restricted CD4+ T cells, specific for a particular peptide derived from mutant p21 ras (Gln61-->Leu), might inhibit the growth of a colonic cancer cell line, when it was cultured in the presence of the corresponding peptide. We found in this case that the growth of the colonic adenocarcinoma cell line HT29, when also induced to express HLA class II molecules by interferon gamma treatment, was inhibited. The inhibition was peptide-specific and required the presence of HLA-DQ8 molecules on the target cell. However, HLA-DQ8-expressing HT29 cells functioned poorly as antigen-presenting cells and could only induce a weak proliferative T cell response in the presence of interleukin-2. The results suggest that colonic cancer cells expressing peptides derived from mutant p21 ras protein in a complex with HLA class II molecules may be a target for tumor-specific T cells. The results also indicate, however, that an initiation of the immune response will require "professional" antigen-presenting cells.

Methods to study peptides associated with MHC class I molecules

It is now an accepted fact that peptides of self or non-self origin form an essential component of the MHC class I structure. The peptide component of the heterotrimer contains the essential determinants recognized by the T-cell receptors of cytotoxic T lymphocytes, be it an antigen-specific, alloimmune or autoimmune response. Because of the importance of the recognition process, several methods have been developed to characterize naturally processed peptides presented by the class I molecules.

Recognition of HLA-A1 by murine monoclonal antibodies

Balb/c mice were immunized with cells from the mouse mastocytoma line P815 transfected with an HLA-A1 gene. The splenocytes of the immunized mice were fused with cells from the murine myeloma NS-1. In an initial screening, supernatants of growing cultures were tested for their binding capacity to the immunizing P815/A1+ cells as well as to P815/A2+ cells. Three out of 756 hybrids produced antibodies which bound to P815/A1+ cells only. They were cloned and further analyzed for their binding reactivity to reference B-lymphoblastoid cells from the Tenth International Histocompatibility Workshop. One monoclonal antibody, designated 6B11, reacted only with HLA-A1+ cells, while the two other antibodies, 3G3 and 7F10, appeared to detect antigenic determinants shared by HLA-A1, A3, A11, A26, and A30 (3G3) and by HLA-A1, A3, A11, A26, A28 and A30 (7F10). Flow cytometric studies on B-lymphoblastoid cell lines as well as on a series of tumor cell lines, including melanoma and colon carcinoma lines, confirmed the specificity of these antibodies. Monoclonal antibodies 7F10 and 6B11 were found to be of the IgM class and 3G3 of the IgG1 class. By complement-dependent 51Cr release experiments it was further shown that the two IgM antibodies 7F10 and 6B11 were able to lyse all cell lines of the HLA-A1 haplotype tested.

Flow-cytometric determination of peptide-class I complex formation. Identification of p53 peptides that bind to HLA-A2

A novel class I-peptide-binding assay was developed and used to identify a series of peptides derived from the human p53 tumor-suppressor gene product capable of binding the HLA-A2 class I allele. Brief pH 3.3 acid treatment of human cell lines rapidly denatures pre-existing class I complexes, as detected by loss of binding of conformation-dependent mAbs, leaving only free class I heavy chains associated with the viable cell surface. These heavy chains may be induced to refold and be recognized by antibodies (in 2-4 hours) when acid-treated cells are coincubated with exogenous beta 2-microglobulin and peptides capable of binding the relevant class I allele examined. This assay, with a detection limit of 1-10 nM peptide, was used to screen the capacity of a panel of nine peptides bearing HLA-A2-binding motifs and derived from the human p53 tumor-suppressor protein sequence. Eight of the nine peptides bound to, and reconstituted, HLA-A2 on acid-treated cells. This assay system will enable the rapid identification of peptides binding to any class I allele, which is the initial prerequisite for elucidating potential CD8+ T-cell epitopes.

Sequence and expression pattern of the human MAGE2 gene

We reported previously identification of the human MAGE1 gene, which encodes an antigen recognized on human melanoma MZ2-MEL by autologous cytolytic T lymphocytes. In addition to MAGE1, melanoma MZ2-MEL expresses several closely related genes, one of which has been named MAGE2. The complete MAGE2 sequence was obtained and it comprises 3 exons homologous to those of MAGE1 and an additional exon homologous to a region of the first MAGE1 intron. Like the open reading frame of MAGE1, that of MAGE2 is entirely encoded by the last exon. The MAGE1 and MAGE2 sequences of this exon show 82% identity and the putative proteins show 67% identity. The MAGE2 gene is expressed in a higher proportion of melanoma tumors than MAGE1. It is also expressed in many small-cell lung carcinomas and other lung tumors, laryngeal tumors, and sarcomas. No MAGE1 and MAGE2 gene expression was found in a large panel of healthy adult tissues, with the exception of testis.

Enhancing the recognition of tumour associated antigens

Activated CD8+ T cells (TCD8+) can directly recognize malignant cells because processed fragments of tumour associated antigens (TAA), 8-10 amino acids in length and complexed with MHC class I molecules, are displayed on tumour cell surfaces. Tumour cells have been genetically modified in a variety of ways in efforts to enhance the immune recognition of TAA. An alternative strategy is the expression of TAA in recombinant or synthetic form. This has been made possible by the recent cloning of TAA recognized by TCD8+. In this communication we review recent work in our own laboratory on the expression of TAA as synthetic peptide, by "naked" plasmid DNA injected intramuscularly or transdermally, and by recombinant viruses including vaccinia (rVV), fowlpox (rFV) and adenovirus (rAd). The expression of TAA in recombinant and synthetic forms allows increased control over the quantity, location, and kinetics of TAA presentation and can result in powerful, specific, anti-tumour immune responses.

Immunogenicity of fusion proteins. An example of tumor-specific/transformation-related antigens

Fusion proteins are generated in some solid tumors and hematological neoplasias by inter- or intrachromosome translocations. These proteins are believed to play a causal role in the pathogenesis of these diseases. Fusion proteins, therefore, can be considered tumor-specific/transformation-related molecules. The targeting of such structures could lead in the future to significant progress in the therapeutic index of anti-cancer treatment, by allowing the selective destruction of neoplastic cells. In this article, the author reviews the different oncogenic fusion molecules so far known, the mechanism(s) by which they are generated and the available information regarding their immunogenicity, and analyzes their potential use as future targets for a specific immune response.

T cell receptor (TCR) structure of autologous melanoma-reactive cytotoxic T lymphocyte (CTL) clones: tumor-infiltrating lymphocytes overexpress in vivo the TCR beta chain sequence used by an HLA-A2-restricted and melanocyte-lineage-specific CTL clone

HLA-A2+ melanomas express common melanoma-associated antigens (Ags) recognized in vitro by autologous cytotoxic T lymphocytes (CTL). However, it is not known whether tumor Ags can drive in vivo a selective accumulation/expansion of Ag-specific, tumor-infiltrating T lymphocytes (TIL). Therefore, to evaluate this possibility, 39 CTL clones isolated from several independent mixed lymphocyte tumor cultures (MLTC) of TIL and peripheral blood lymphocytes (PBL) of an HLA-A2+ melanoma patient and selected for T cell receptor (TCR)-dependent, HLA-restricted tumor lysis, were used for analysis of TCR alpha and beta chain structure by the cDNA polymerase chain reaction (PCR) technique with variable gene-specific primers followed by sequencing. Despite absence of oligoclonality in fresh TIL and PBL, as well as in T cells of day 28 MLTC (day of cloning), sequence analysis of TCR alpha and beta chains of TIL clones revealed a dominance of a major category of melanoma-specific, HLA-A2-restricted T cells expressing a V alpha 8.2/J alpha AP511/C alpha and V beta 2.1/D beta 1/J beta 1.1/C beta 1 TCR. The same TCR was also found in 2 out of 14 PBL clones. The other PBL clones employed a V alpha 2.1 gene segment associated with either V beta 13.2, 14, or w22. Clones A81 (V alpha 2.1/J alpha IGRJ alpha 04/C alpha and V beta 14/D beta 1/J beta 1.2/C beta 1) and A21 (V alpha 8.2/J alpha AP511/C alpha and V beta 2.1/D beta 1/J beta 1.1/C beta 1), representative of the two most frequent TCR of PBL and TIL, respectively, expressed different lytic patterns, but both were HLA-A2 restricted and lysed only HLA-A2+ melanomas and normal melanocytes, thus indicating recognition of two distinct HLA-A2-associated and tissue-related Ags. Finally, by the inverse PCR technique, the specific TCR beta chain (V beta 2.1/D beta 1/J beta 1.1/C beta 1) expressed by the dominant TIL clone was found to represent 19 and 18.4% of all V beta 2 sequences expressed in the fresh tumor sample and in the purified TIL, respectively, but < 0.19% of V beta 2+ sequences expressed in PBL. These results are consistent with the hypothesis that a clonal expansion/accumulation of a melanocyte-lineage-specific and HLA-A2-restricted T cell clone occurred in vivo at the site of tumor growth.

Tumor-rejection antigens recognized by T lymphocytes

Generations of immunologists have been searching for evidence to confirm the tantalizing notion that tumor-rejection antigens exist. If found, the ultimate reward was the possibility that these molecules might be used to induce tumor-specific immunity and effect tumor rejection. Until recently rewards have been few and far between. That is changing. The immediate rewards have become more satisfying and the ultimate reward almost palpable.

Analysis of antigens recognized on human melanoma cells by A2-restricted cytolytic T lymphocytes (CTL)

We have pursued our analysis of potential tumor-rejection antigens recognized on human melanoma by autologous cytolytic T lymphocytes (CTL). We reported previously that 3 distinct antigens (A,B,C) were recognized on melanoma cell line SK29-MEL in association with HLA-A2. Selection for melanoma-cell variants resistant to anti-A CTL revealed that antigen A consists of at least 2 determinants (Aa, Ab) which can be lost separately. Genetic linkage between Aa and Ab was suggested by concomitant loss of Aa and Ab in an immunoselected tumor-cell variant. This variant was also resistant to an autologous CTL clone restricted by HLA-B45, indicating that this CTL may also recognize a determinant of antigen A. Of 11 allogeneic HLA-A2 melanoma cell lines that were tested, 5 expressed both Aa and Ab, 1 expressed only Aa, and 1 only Ab. None of them was lysed by anti-B or anti-C CTL clones. A CTL clone derived from another HLA-A2-melanoma patient was found to have exactly the same lytic pattern as the anti-Ab CTL of the first patient. This suggested that it may be possible to elicit an anti-Ab response in many HLA-A2 patients. We conclude that there are at least 2 distinct antigens presented in association with HLA-A2 that are common to many melanomas and therefore constitute promising targets for specific immunotherapy.

The tyrosinase gene codes for an antigen recognized by autologous cytolytic T lymphocytes on HLA-A2 melanomas

Lymphocytes of melanoma patients can be restimulated in vitro with autologous tumor cells to generate antitumor cytolytic T lymphocytes (CTL). Previous reports have indicated that, when such CTL are obtained from HLA-A2 melanoma patients, they often display broad reactivity on A2 melanoma cell lines. Such antitumor CTL clones, which appeared to recognize the same antigen, were isolated from two patients. We report here the cloning of a cDNA that directs the expression of the antigen recognized by these CTL. This cDNA corresponds to the transcript of the tyrosinase gene. The gene was found to be active in all tested melanoma samples and in most melanoma cell lines. Among normal cells, only melanocytes appear to express the gene. The tyrosinase antigen presented by HLA-A2 may therefore constitute a useful target for specific immunotherapy of melanoma. But possible adverse effects of antityrosinase immunization, such as the destruction of normal melanocytes and its consequences, will have to be examined before clinical pilot studies can be undertaken.

A tumour-associated antigen expression in human haematological malignancies

Objective responses obtained with high-dose in vivo recombinant interleukin 2 (r-IL2) in some leukaemic patients suggest among other hypotheses that blasts might express tumour rejection antigens potentially recognized by cytolytic T lymphocytes. Such antigens have been described in human melanomas and the MAGE-1 gene, coding for a tumour rejection antigen was recently identified. This gene is expressed in various solid tumours, but not in normal cells. We have screened a panel of haematological malignancies by reverse transcription and PCR and we report that MAGE-1 is not expressed in the blasts from 48 patients whereas three cell lines derived from leukaemias express this gene.

Identifying strategies for immune intervention

In recent years the molecular basis of antigen recognition by T cells has been unraveled and the various pathways that control T cell activation and functional specialization have been defined. Consequently, it is now possible to delineate various strategies for intervention with the immune system to design protective vaccines, to induce an effective response to tumor antigens, and to control graft rejection and autoimmune diseases.