A K-ras 13Gly-->Asp mutation is recognized by HLA-DQ7 restricted T cells in a patient with colorectal cancer. Modifying effect of DQ7 on established cancers harbouring this mutation?

Association of HLA-B*51:01 with papillary thyroid carcinoma in the Chinese Han population of the Shandong coastal areas

BACKGROUND

A lot of work has been done to study the association between human leukocyte antigen (HLA) and papillary thyroid carcinoma (PTC) in various populations. But the results of the currently available studies are not consistent. The aim of this study was to evaluate the association of HLA-A, -B, -C, -DRB1, and -DQB1 with PTC in the Chinese Han population of the coastal areas of Shandong Province with respect to age and sex.

METHODS

A total of 154 patients diagnosed with PTC were analyzed for HLA-A, -B, -C, -DRB1, and -DQB1 alleles by using a polymerase chain reaction sequence-based typing (PCR-SBT) method. Two hundred unrelated healthy individuals were typed as controls.

RESULTS

Compared with the controls, the HLA-B*51:01 (8.8% vs. 4.5%, p=0.029, OR 2.039 [CI 1.101-3.775]) and HLA-C*07:06 (2.6% vs. 0.5%, p=0.024, OR 5.307 [CI 1.119-25.171]) allele frequencies were higher in the PTC patients, while the HLA-C*07:01 (1.3% vs. 6.0%, p=0.001, OR 0.206 [CI 0.071-0.601]) allele frequency was lower in the PTC patients that did not persist after Bonferroni correction for multiple tests. This showed no statistically significant correlation of the HLA-A, -DRB1, and -DQB1 alleles and PTC. The incidence of PTC was more frequent in females between 30 and 60 years old. There were no significant differences in the age and sex distributions between the total and the HLA-B*51:01 positive PTC patients.

CONCLUSIONS

The HLA associations in this Chinese Han population differ markedly from studies done in Europeans and Caucasians. The results reveal that HLA-B*51:01 is more likely to be a susceptible allele for PTC in addition to age and sex in the coastal areas of Shandong Province.

Role of the HLA-DQ locus in the development of chronic gastritis and gastric carcinoma in Mexican patients

AIM: To determine the HLA-DQ locus in Mexican patients with Chronic gastritis and gastric adenocarcinoma.

METHODS: Oligotyping for HLA-DQ locus was performed in 45 Mexican patients with chronic gastritis and 13 Mexican patients with diffuse-type gastric adenocarcinoma, and was then compared with 99 clinically healthy unrelated individuals. H pylori infection and CagA status were assessed in patients by enzyme-linked immunosorbent assay (ELISA) method.

RESULTS: We found a significant increased frequency of HLA-DQB1*0401 allele in H pylori-positive patients with chronic gastritis when compared with healthy subjects [19 vs 0%, P = 1 × 10^-7, odds ratio (OR) = 4.96; 95% confidence interval (95% CI), 3.87-6.35]. We also found a significant increased frequency of HLA-DQB1*0501 in patients with diffuse-type gastric carcinoma in comparison with healthy individuals (P = 1 × 10^-6, OR = 13.07; 95% CI, 2.82-85.14).

CONCLUSION: HLA-DQ locus may play a different role in the development of H pylori-related chronic gastritis and diffuse-type gastric adenocarcinoma in the Mexican Mestizo population.

Specific T-cell immunity against Ki-ras peptides in patients with pancreatic and colorectal cancers

Mutations of codon 12 in the Ki-ras gene are frequently found in pancreatic and colorectal cancers. It has been demonstrated that human T-cells have the potential to recognise tumours expressing mutated ras-derived peptides. However, it remains unclear whether T-cells from a given individual can recognise the mutant peptides, which are expressed in that individual's tumour tissues. Mutations of the Ki-ras oncogene were analysed by the mutant-allele-specific amplification (MASA) method in pancreatic and colorectal tumour tissues, and T-cell responses against mutated Ki-ras-derived peptides were measured by [(3)H]thymidine incorporation and IFN-gamma production assays. Specific T-cell responses against Ki-ras-products were found in cancer patients, whereas no immune response was observed in normal individuals (P<0.01). Six of the eight pancreatic cancer patients (75%) and nine of 26 colorectal cancer patients (35%) had T-cell responses to mutated Ki-ras-derived-peptides. T-cell response in a given individual cannot recognise the same mutated ras peptide, which is expressed in that individual's tumour tissues. However, pancreatic and colorectal cancer patients have T-cell immunity against Ki-ras-peptides, and this provides potential target for cancer immunotherapy.

Spinning molecular immunology into successful immunotherapy

Until recently, immunotherapies have been of limited success, particularly against cancer. However, recent insights into the cells, molecules and signalling pathways that regulate immune responsiveness are providing new approaches for immunotherapy. In this article, I review some of the most promising molecular and cellular targets for immunotherapy and discuss approaches that use these targets to amplify immune responses and potentially break antigen-specific tolerance. These strategies provide a blueprint for the development of successful immunotherapy over the next decade.

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

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

Enhanced growth of primary tumors in cancer-prone mice after immunization against the mutant region of an inherited oncoprotein

One major objective of tumor immunologists is to prevent cancer development in individuals at high risk. (TG.AC x C57BL/6)F1 mice serve as a model for testing the feasibility of this objective. The mice carry in the germline a mutant ras oncogene that has an arginine at codon 12 instead of glycine present in the wild-type, and after physical (wounding) or chemical promotion, these mice have a high probability for developing papillomas that progress to cancer. Furthermore, F1 mice immunized with Arg(12) mutant ras peptide in complete Freund's adjuvant (CFA) develop T cells within 10 d that proliferate in vitro on stimulation with the Arg(12) mutant ras peptide. Within 14 d, these mice have delayed-type hypersensitivity to the peptide. Immunization with CFA alone or with a different Arg(12) mutant ras peptide in CFA induced neither response. To determine the effect of immunization on development of tumors, mice immunized 3 wk earlier were painted on the back with phorbol 12-myristate 13-acetate every 3 d for 8 wk. The time of appearance and the number of papillomas were about the same in immunized and control mice, but the tumors grew faster and became much larger in the mice immunized with the Arg(12) mutant ras peptide. Thus, the immunization failed to protect against growth of papillomas. The peptide-induced CD4(+) T cells preferentially recognized the peptide but not the native mutant ras protein. On the other hand, mice immunized with Arg(12) mutant ras peptide and bearing papillomas had serum antibodies that did bind native mutant ras protein. Together, these studies indicate that active immunization of cancer-prone individuals may result in immune responses that fail to eradicate mutant oncogene-expressing tumor cells, but rather induce a remarkable enhancement of tumor growth.

Tumor-specific CD4+ T lymphocytes from cancer patients are required for optimal induction of cytotoxic T cells against the autologous tumor

This study focuses on the specific CD4+ T cell requirement for optimal induction of cytotoxicity against MHC class II negative autologous tumors (AuTu) collected from patients with various types of cancer at advanced stages. CD4+ T cells were induced in cultures of cancer patients' malignant effusion-associated mononuclear cells with irradiated AuTu (mixed lymphocyte tumor cultures (MLTC)) in the presence of recombinant IL-2 and recombinant IL-7. Tumor-specific CD4+ T cells did not directly recognize the AuTu cells, but there was an MHC class II-restricted cross-priming by autologous dendritic cells (DCs), used as APC. CD8+ CTL, also induced during the MLTC, lysed specifically AuTu cells or DCs pulsed with AuTu peptide extracts (acid wash extracts (AWE)) in an MHC class I-restricted manner. Removal of CD4+ T cells or DCs from the MLTC drastically reduced the CD8+ CTL-mediated cytotoxic response against the AuTu. AWE-pulsed DCs preincubated with autologous CD4+ T cells were able, in the absence of CD4+ T cells, to stimulate CD8+ T cells to lyse autologous tumor targets. Such activated CD8+ T cells produced IL-2, IFN-gamma, TNF-alpha, and GM-CSF. The process of the activation of AWE-pulsed DCs by CD4+ T cells could be inhibited with anti-CD40 ligand mAb. Moreover, the role of CD4+ T cells in activating AWE-pulsed DCs was undertaken by anti-CD40 mAb. Our data demonstrate for the first time in patients with metastatic cancer the essential role of CD4+ Th cell-activated DCs for optimal CD8+ T cell-mediated killing of autologous tumors and provide the basis for the design of novel protocols in cellular adoptive immunotherapy of cancer, utilizing synthetic peptides capable of inducing T cell help in vivo.

Human leukocyte antigens and cancer: is it in our genes?

Human leukocyte antigens (HLAs) are widely expressed cell surface molecules which present antigenic peptides to T-lymphocytes, thus modulating the immune response. The efficiency of peptide presentation by HLAs is dependent on the extreme polymorphism in the HLA-encoding loci within the major histocompatibility complex (MHC). HLA polymorphism is known to alter disease susceptibility and progression in a range of predominantly inflammatory conditions, many of which are T-lymphocyte-mediated. More recently, the importance of alterations in HLA expression and polymorphisms within HLA-encoding loci has emerged in the development of malignancy. This review concentrates on the role of HLA polymorphism in malignant disease, with discussion of the major cancers in which HLA associations have become clear, as well as the potential mechanisms by which HLA polymorphisms may act as important factors, or cofactors, in the pathogenesis of malignant disease. In addition, the role of certain non-HLA genes within the MHC in the pathogenesis of malignancy is also considered briefly.

Identification of Peptide Superagonists for a Self-K-ras-Reactive CD4+ T Cell Clone Using Combinatorial Peptide Libraries and Mass Spectrometry

The proliferative responses of a human CD4+ T cell clone 29.15.2, reactive with a self-K-ras-derived peptide (3EYKLVVVGAGGVGKSALT20), were tested using a set of X9 combinatorial peptide libraries containing the flanking residues (EYKLVXXXXXXXXXSALT, where X indicates random amino acids). Certain peptide libraries, such as EYKLVXXXXXXMXXSALT and EYKLVXXXXXXXHXSALT, stimulated a marked proliferation of 29.15.2. However, no combinations of substitutions tested, such as EYKLVXXXXXXMHXSALT, exhibited additive effects. We subsequently synthesized peptides with degenerate sequences (a mixture of 480 species), where each position is composed of the wild-type (wt) residue or of amino acids that induced the proliferation of 29.15.2, in positional scanning. Interestingly, one fraction of degenerate peptides, separated by reverse-phase HPLC, stimulated much higher proliferation than did the wt; in addition, the retention time of this fraction was distinct from that of the wt. Mass spectrometry analysis of this fraction and flanking fractions identified five peptide species that exhibit strong signals in a manner that parallels the antigenic activity. Finally, 17 candidate peptide sequences were deduced from mass spectrometry and hydrophobicity scoring results, of which two peptides (EYKLVVVGAGGMLKSALT and EYKLVVVGAGGMIKSALT) did induce 52- and 61-fold stronger proliferation, respectively, compared with the wt. These findings indicate that: 1) synthetic peptides that carry “the best” residue substitution at each position of combinatorial peptide libraries do not always exhibit superagonism, and 2) such a drawback can be overcome with the use of mass spectrometry. This approach provides new perspectives for the accurate and efficient identification of peptide superagonists.

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.

Identification of a human CD8+ T lymphocyte neo-epitope created by a ras codon 12 mutation which is restricted by the HLA-A2 allele

Point mutations in the ras proto-oncogenes, notably at codon 12, are found in high frequency of human malignancies and, thus, may be appropriate targets for the induction of tumor-specific T cell responses in cancer immunotherapy. In this study, we examined the mutant ras protein sequence reflecting the substitution of Gly to Val at position 12 as a putative point-mutated determinant for potential induction of an HLA-A2-reactive, CD8+ cytotoxic T lymphocyte (CTL) response. We identified the ras 4-12(Val12) sequence as a minimal 9-mer peptide, which displayed specific binding to HLA-A2 by T2 bioassays. Peptide binding to HLA-A2 on T2 cells was weak and required coincubation with exogenous beta(2)-microglobulin to facilitate and enhance complex formation. In contrast, the wild-type ras 4-12(Gly12) peptide failed to bind to HLA-A2 even in the presence of beta(2)-microglobulin, consistent with the hypothesis that the point mutation creates a C-terminus anchor residue. A CD8+ CTL line against the ras 4-12(Val12) peptide was derived in vitro from a normal HLA-A2+ donor using a model culture system consisting of T2 cells as antigen presenting cells pulsed with exogenous mutant ras peptide and beta(2)-microglobulin plus cytokines (interleukin-2 and 12). Functional characterization of CD8+ CTL line revealed (1) peptide-specific and HLA-A2-restricted cytotoxicity against a panel of peptide-pulsed targets; (2) no specific lysis using the normal ras peptide sequence; (3) half-maximal lysis with exogenous peptide of approximately 0.3 microM; (4) lysis of HLA-A2+ B cell lines infected with a recombinant vaccinia virus construct encoding the point-mutated human K-ras gene; and (5) specific lysis of the HLA-A2+ SW480 colon carcinoma cell line expressing the naturally occurring K-ras Val12 mutation. Maximal lysis of SW480 cells occurred following interferon (IFN)-gamma pretreatment, which correlated with enhanced HLA-A2 and ICAM-1 (CD54) expression. Specificity of lysis was revealed by the absence of lysis against a HLA-A2+ melanoma cell line (+/- IFN-gamma), which lacked the mutant Val12 mutation, and the inability of an irrelevant CD8+ CTL line to lyse SW480 (+/- IFN-gamma) unless the appropriate exogenous peptide was added. These findings demonstrated that tumor cells may endogenously process and express mutant ras epitopes, such as the 4-12(Val12) sequence, albeit in limiting amounts that may be potentiated by IFN-gamma treatment. These data support the biological relevance of this sequence and, thus, may have important implications for the generation of ras oncogene-specific CTL responses in clinical situations.

Efficient induction of human CD4+ T cell lines reactive with a self-K-ras-derived peptide in vitro, using a mAb to CD29

In recent studies, we analyzed effects of a large series of mAbs submitted to T-cell and adhesion structure sections of 6th International Workshop on Human Leukocyte Differentiation Antigens, on proliferative responses of a human CD4+ T cell clone. We found that certain mAbs to CD27, CD28, CD29, CD43 and CD44 markedly restore T cell responsiveness, only in the presence of the natural peptide ligand at low concentrations and even in the absence IL-2. To set up efficient strategies for developing T cell lines and clones reactive with self-peptides in vitro, we stimulated PBMC with a K-ras-derived peptide in the presence of these mAbs and found that: (a) anti-CD29 mAb MAR4 is effective for in vitro expansion of K-ras (residue 3-20)-reactive T cells from PBMC; (b) indeed, DR8 (DRB*0802)-restricted and DR51 (DRB5*0102)-restricted CD4+ T cell clones were established from the T cell lines; (c) MAR4 inhibits anti-CD3-induced apoptosis of PBMC; and (d) MAR4 is effective in enhancing anti-CD3- and antigen-induced proliferative responses of PBMC. Therefore, mAb MAR4 increased efficiency in establishing T cell clones from PBMC, both by suppressing antigen-driven activation-induced cell death and by enhancing the T cell proliferation, only in the presence of TCR/CD3-mediated stimulation. Possible application of MAR4 for establishing self-reactive T cell lines and expanding T cells ex vivo for anti-cancer immunotherapy, is discussed.

Human tumor antigens recognized by T-cells

T-cells play an important role in in vivo tumor rejection in many animal tumor models and in human melanoma. Many human tumor antigens recognized by autologous T-cells have now been identified. These are found to be nonmutated and mutated peptides derived from various self proteins as well as viral proteins. A variety of mechanisms involved in generating these T-cell epitopes on growing cancers have also been identified. However, the role of these identified antigens remains to be evaluated. Passive or active immunotherapies using these identified tumor antigens are being conducted in many institutions. The results obtained from these clinical trials may give us better insight into the role of T-cell responses to each antigen in tumor rejection as well as the development of new antigen-specific immunotherapies for patients with cancer.

A newly identified pattern of K-ras mutations at codons 12 and 13 is associated with long-term survival in colorectal cancer

BACKGROUND

Although K-ras mutations reportedly occur in 40% to 60% of all colorectal carcinomas, the relationship between specific mutations and clinical outcome is unclear. The purpose of this study was to assess the frequency and types of K-ras mutations in 89 colorectal cancer patients, comparing groups with short-term (less than 5 years) and long-term (more than 10 years) survival.

METHODS

The group was divided into four cohorts by survival and modified Dukes classification (Dukes B2 and C2). DNA was extracted from formalin-fixed paraffin-embedded archival material. Mutational status was analyzed using a modification of allele-specific-polymerase chain reaction.

RESULTS

Mutations in codon 12 were found in 11.2% of tumors, and 83% of tumors had mutations in codon 13. Gly > Asp accounted for 85.2% of the mutations. Tumors with mutations in both codon 12 and codon 13 occurred significantly more frequently in the long-term (21.3%) versus the short-term (2.4%) survival group. Gly > Asp mutations in either codon were related to long-term survival, and 80% of long-term survivors with mutations in both codons had Gly > Asp mutations in both.

CONCLUSIONS

Simultaneous mutation in codons 12 and 13 of the K-ras gene appears to be a positive prognostic indicator in colorectal cancer.

A single residue polymorphism at DR beta 37 affects recognition of peptides by T cells

Single amino acid polymorphism at residue 37 of the HLA-DR beta chain (DR beta 37) between DRB1*0406 and 0403 markedly influences susceptibility to the insulin autoimmune syndrome. We investigated the effects of DR beta 37 polymorphism regarding recognition of nonself peptides by a T-cell clone, YN5-32, specific to a streptococcal peptide (M12p54-68) presented by the DRB1*0406 molecule. YN5-32 responded better to M12p54-68 presented by allogeneic DRB1*0403 with a single Tyr-substitution at DR beta 37-Ser of the DRB1*0406 molecule. One hundred and fifty-four peptides carrying single residue substitutions at each of the core residues 57-65 of M12p54-68, were tested for full agonistic and TCR antagonistic activities. Forty-six peptides showed full agonism, 34 analogues exhibited TCR antagonism, and 45 analogues exhibited neither full agonism nor TCR antagonism, irrespective of the presenting molecules (DRB1*0406 or 0403). On the other hand, 29 analogue peptides substituted at each of residues 57-63 of M12p54-68 were recognized differently by YN5-32, depending on the presenting molecules. These observations indicate that 1) single amino acid polymorphism (Ser-Tyr) at the DR beta 37 residue induced a conformational change distinguished by TCR in some but not all peptides; and 2) these conformational changes were observed even in analogue peptides carrying single residue substitutions at residues far from a putative DR beta 37 contact site. These findings provide further evidence for altered human T-cell responses induced by TCR ligands with minor modifications.

Augmentation of immune response by an analog of the antigenic peptide in a human T-cell clone recognizing mutated Ras-derived peptides

T-cells that recognize mutated p21 Ras are relevant to immune surveillance systems against cancer. We report here evidence that immune responses of a T-cell clone recognizing mutated p21 Ras can be augmented by an analog peptide. Using spleen cells from a gastric cancer patient, we established the CD4+ alpha beta Th1-like clone C27 that recognizes wild-type (3EYKLVVVGAGGVGKS17) and mutated p21 Ras protein molecules and peptides, in an HLA-DR1-restricted manner. C27 responded prominently to mutated Ras peptides carrying Val or Ala at position 12, as compared to wild-type and other mutated peptides. C27 also exhibited a much stronger response to a mutated p21 Ras whole-protein molecule-carrying Val at position 12, as compared with the wild-type protein. The proliferative response and production of GM-CSF, TNF-alpha, and IFN-gamma by C27 were further augmented by replacing the possible first DR anchor 4Tyr of the mutated Ras peptide with Trp, a more potent anchor residue for the DR1 molecule. Enhancement of peptide antigenicity by substituting the HLA anchor residue of an antigenic peptide recognized by tumor-reactive T-cells may prove to be a novel strategy for antigen-specific cancer immunotherapy.

Cytotoxic T-lymphocyte responses against mutated p21 ras peptides: an analysis of specific T-cell-receptor gene usage

Generation of cytotoxic-T-lymphocyte (CTL) responses against mutated ras peptides from peripheral-blood mononuclear cells (PBMC) was attempted in a group of HLA-A2.1+ healthy donors. Bulk PBMC cultures were stimulated in vitro with a mixture of peptides encompassing 12 Gly --> Val, 61 Gln --> Lys or 61 Gln --> Leu ras mutations and displaying HLA-A2.1 binding motifs, selected by a computer program. A promiscuous tetanus toxoid peptide was also added. Weekly thereafter, PBMC were re-stimulated with peptide pulsed autologous Epstein-Barr virus (EBV)-transformed B cells. After 8 rounds of re-stimulation, reproducible cytotoxic activity against peptide-pulsed target cells was detectable in one donor. The CTL line recognized 2 nonamers encompassing ras 61 Gln --> Leu mutation. Killing was mediated by CD8+ T cells displaying alphabeta TCR and was inhibited by anti-HLA-A2.1 monoclonal antibodies. No killing of tumor cells expressing the specific mutation could be observed. More than 60 CTL clones were generated. Fine specificity studies revealed effective, though differing cytotoxic activity against both 53-LDILDTAGL-61 and 55-ILDTAGLEE-63, but not against 54-DILDTAGLE-62 mutated peptides, in all but one of the clones. None was able to exert effective cytotoxic activity against tumor cells expressing the specific mutation. T-cell-receptor (TCR) usage was then analyzed phenotypically, by reverse-transcription-polymerase-chain-reaction (RT-PCR) and by sequence analysis. This study revealed the monoclonal nature of the CTL response against mutated nonamers, with TCR expressing Vbeta14 gene product in combination with, Jbeta2.7 and Cbeta2.

Malignant melanoma: relationship of the human leukocyte antigen class II gene DQB1*0301 to disease recurrence in American Joint Committee on Cancer Stage I or II

BACKGROUND

Melanoma patients who carry the human leukocyte antigen (HLA) Class II allele DQB1*0301 have an increased frequency of metastases at presentation compared with those lacking HLA-DQB1*0301. This study was designed to determine whether HLA-DQB1*0301 is associated with an increased risk of recurrence in melanoma patients presenting with American Joint Committee on Cancer (AJCC) Stage I or II (localized) disease.

METHODS

Molecular oligotyping of HLA-DQ genes was performed for 259 patients with AJCC Stage I or II melanoma. Rate of disease recurrence was determined by retrospective review and prospective follow-up. Kaplan-Meier analysis, log rank, and proportional hazard (Cox) comparison were performed.

RESULTS

Median follow-up was 24 months. Minimum follow-up was 6 months. Although HLA-DQB1*0301-positive and -negative patients were balanced with regard to standard melanoma prognostic factors (primary tumor thickness, level of invasion, presence of ulceration, anatomic location, and sex), HLA-DQB1*0301-positive patients were more likely to develop locally recurrent, regional, or distant metastatic melanoma during follow-up (actuarial median disease free survival 48 months [DQB1*0301-positive patients] vs. 97 months [DQB1*0301-negative patients]; log rank P = 0.0002). HLA-DQB1*0301 status, in addition to primary tumor thickness, was an independent prognostic indicator in these patients (Cox multivariate P = 0.02).

CONCLUSIONS

Patients presenting with localized melanoma who carry HLA-DQB1*0301 are at an increased risk of developing recurrent disease compared with stage-matched patients who lack this allele. HLA-DQB1*0301 is a genomic marker which independently identifies melanoma patients in whom recurrence is more likely, and is potentially useful in selecting those most likely to benefit from adjuvant therapy.

Binding of mutated Ras- and p53-derived peptides to HLA-DR molecules

We investigated binding of p53- and Ras-derived peptides with frequently observed missense mutations, to various L cell transfectants expressing a single species of HLA-DR complex, and found that: (i) all the synthetic peptides bound to various DR complexes with a variable affinity; (ii) some DR allelic products had a high affinity for both p53- and Ras-derived peptides (e.g., DRB1*1502), whereas others almost no affinity (e.g., DRB1*1101); and (iii) DR-binding motifs described in the literature can explain some of the allele-specific interactions between mutated peptides and DR complexes. Therefore, some mutated Ras- and p53-derived peptides could be tumor-specific antigens recognized by CD4+ T cells in an HLA-DR allele-specific manner.

New tumor antigens recognized by T cells

A series of tumor cell antigens that are recognized by cytolytic T lymphocytes has been characterized this year. Besides the antigens derived from proteins specifically expressed in tumors, many melanoma antigens derive from melanocytic differentiation proteins. In addition, antigens unique to individual tumors result from mutations in ubiquitously expressed genes.

CD8+ T cells from a patient with colon carcinoma, specific for a mutant p21-Ras-derived peptide (Gly13-->Asp), are cytotoxic towards a carcinoma cell line harbouring the same mutation

Several T lymphocyte clones (TLC), specific for a p21-Ras-derived peptide expressing a Gly13-->Asp mutation and of the CD8+ subtype, were generated from peripheral blood of a colon carcinoma patient. The TLC exerted cytotoxicity against an interferon-gamma (IFN gamma)-pretreated colon carcinoma cell line, HCT116, which harbours the Gly13-->Asp mutation and shares both HLA-A2 and HLA-B12(44) with the patient. This cytotoxic effect could be blocked by a monoclonal antibody (mAb) against CD8 molecules, as well as with a mAb against HLA class I molecules and a polyclonal antiserum against HLA-B12, identifying B12(44) as the antigen-presenting molecule. In growth-inhibition experiments, the growth of both IFN gamma-pretreated and untreated target cells were strongly inhibited by the presence of the CD8+ TLC. Together these data indicate that human cancer cells harbouring a spontaneous ras mutation can process aberrant p21 Ras and express peptide/HLA-class-I complexes on their surface in sufficient density to be recognized by Ras-specific cytotoxic T lymphocytes.