Human CD4+ T cells specifically recognize a shared melanoma-associated antigen encoded by the tyrosinase gene

IL-12 directly up-regulates the expression of HLA class I, HLA class II and ICAM-1 on human melanoma cells: a mechanism for its antitumor activity?

IL-12 enhances cytolytic activity and proliferation of NK and T cells, and induces cytokines such as IFN-gamma. No direct effects on non-hematopoietic cells have been shown. This study investigates the effects of IL-12 on melanoma cells in vitro. We analyzed 15 melanoma cell cultures and 1 melanoma cell line. Out of 16 samples 13 expressed the beta chain of the IL-12 receptor (IL-12Rbeta). Preincubation with IL-12 increased the surface levels of human leukocyte antigen (HLA) class I, HLA class II and intercellular adhesion molecule (ICAM)-1 of those cultures with IL-12Rbeta expression. The effects of IL-12 on HLA class I could be blocked by an IL-12-neutralizing monoclonal antibody (mAb), but not by an mAb against IFN-gamma. Melanoma cells transduced with IL-12 expressed enhanced levels of HLA class I, HLA class II and ICAM-1 compared to controls. Co-incubation of the melanoma cells with allogeneic peripheral blood mononuclear cells (PBMC) resulted in enhanced proliferation and increased production of IL-2 and IFN-gamma after pretreatment with IL-12. IL-12 pretreatment increased the susceptibility of melanoma cells to lysis by prestimulated autologous PBMC. Since IL-12 induced immunocritical surface molecules on melanoma cells, it might be beneficial during immune interventions in melanoma patients.

Cloning genes encoding MHC class II-restricted antigens: mutated CDC27 as a tumor antigen

In an effort to identify tumor-specific antigens recognized by CD4(+) T cells, an approach was developed that allows the screening of an invariant chain-complementary DNA fusion library in a genetically engineered cell line expressing the essential components of the major histocompatibility complex (MHC) class II processing and presentation pathway. This led to the identification of a mutated form of human CDC27, which gave rise to an HLA-DR4-restricted melanoma antigen. A mutated form of triosephosphate isomerase, isolated by a biochemical method, was also identified as an HLA-DR1-restricted antigen. Thus, this approach may be generally applicable to the identification of antigens recognized by CD4(+) T cells, which could aid the development of strategies for the treatment of patients with cancer, autoimmune diseases, or infectious diseases.

Biochemical identification of a mutated human melanoma antigen recognized by CD4(+) T cells

CD4(+) T cells play a critical role in generating and maintaining immune responses against pathogens and alloantigens, and evidence suggests an important role for them in antitumor immunity as well. Although major histocompatibility complex class II-restricted human CD4(+) T cells with specific antitumor reactivities have been described, no standard method exists for cloning the recognized tumor-associated antigen (Ag). In this study, biochemical protein purification methods were used in conjunction with novel mass spectrometry sequencing techniques and molecular cloning to isolate a unique melanoma Ag recognized by a CD4(+) tumor-infiltrating lymphocyte (TIL) line. The HLA-DRbeta1*0101-restricted Ag was determined to be a mutated glycolytic enzyme, triosephosphate isomerase (TPI). A C to T mutation identified by cDNA sequencing caused a Thr to Ile conversion in TPI, which could be detected in a tryptic digest of tumor-derived TPI by mass spectrometry. The Thr to Ile conversion created a neoepitope whose T cell stimulatory activity was enhanced at least 5 logs compared with the wild-type peptide. Analysis of T cell recognition of serially truncated peptides suggested that the mutated amino acid residue was a T cell receptor contact. Defining human tumor Ag recognized by T helper cells may provide important clues to designing more effective immunotherapies for cancer.

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.

Cancer vaccines

It has been more than 100 years since the first reported attempts to activate a patient's immune system to eradicate developing cancers. Although a few of the subsequent vaccine studies demonstrated clinically significant treatment effects, active immunotherapy has not yet become an established cancer treatment modality. Two recent advances have allowed the design of more specific cancer vaccine approaches: improved molecular biology techniques and a greater understanding of the mechanisms involved in the activation of T cells. These advances have resulted in improved systemic antitumor immune responses in animal models. Because most tumor antigens recognized by T cells are still not known, the tumor cell itself is the best source of immunizing antigens. For this reason, most vaccine approaches currently being tested in the clinics use whole cancer cells that have been genetically modified to express genes that are now known to be critical mediators of immune system activation. In the future, the molecular definition of tumor-specific antigens that are recognized by activated T cells will allow the development of targeted antigen-specific vaccines for the treatment of patients with cancer.

Melanoma cells present a MAGE-3 epitope to CD4(+) cytotoxic T cells in association with histocompatibility leukocyte antigen DR11

In this study we used TEPITOPE, a new epitope prediction software, to identify sequence segments on the MAGE-3 protein with promiscuous binding to histocompatibility leukocyte antigen (HLA)-DR molecules. Synthetic peptides corresponding to the identified sequences were synthesized and used to propagate CD4(+) T cells from the blood of a healthy donor. CD4(+) T cells strongly recognized MAGE-3281-295 and, to a lesser extent, MAGE-3141-155 and MAGE-3146-160. Moreover, CD4(+) T cells proliferated in the presence of recombinant MAGE-3 after processing and presentation by autologous antigen presenting cells, demonstrating that the MAGE-3 epitopes recognized are naturally processed. CD4(+) T cells, mostly of the T helper 1 type, showed specific lytic activity against HLA-DR11/MAGE-3-positive melanoma cells. Cold target inhibition experiments demonstrated indeed that the CD4(+) T cells recognized MAGE-3281-295 in association with HLA-DR11 on melanoma cells. This is the first evidence that a tumor-specific shared antigen forms CD4(+) T cell epitopes. Furthermore, we validated the use of algorithms for the prediction of promiscuous CD4(+) T cell epitopes, thus opening the possibility of wide application to other tumor-associated antigens. These results have direct implications for cancer immunotherapy in the design of peptide-based vaccines with tumor-specific CD4(+) T cell epitopes.

Cancer vaccines: novel approaches and new promise

Cancer vaccines are a promising tool in the hands of the clinical oncologist. We have summarized the most recent findings and achievements in this exciting field. Tumor-associated antigens, as a basis for the new cancer vaccines, are reviewed. We emphasize novel approaches for the design of safe and more effective vaccines for cancer. We also discuss the possible clinical applications and the future prospects for vaccine development.

The role of CD4+ T cell responses in antitumor immunity

While most of the focus in cancer immunology is on CD8+ cytotoxic T lymphocyte responses, recent evidence indicates that CD4+ T cells are an equally critical component of the antitumor immune response. Successful immunity to cancer will therefore require activation of tumor-specific CD4+ T cells. Tumor antigens recognized by CD4+ T cells that are restricted by MHC class II are beginning to be defined in both murine and human tumors. These will provide the basis for new generations of antigen-specific tumor vaccines.

Tumor immunity and autoimmunity induced by immunization with homologous DNA

The immune system can recognize self antigens expressed by cancer cells. Differentiation antigens are prototypes of these self antigens, being expressed by cancer cells and their normal cell counterparts. The tyrosinase family proteins are well characterized differentiation antigens recognized by antibodies and T cells of patients with melanoma. However, immune tolerance may prevent immunity directed against these antigens. Immunity to the brown locus protein, gp75/ tyrosinase-related protein-1, was investigated in a syngeneic mouse model. C57BL/6 mice, which are tolerant to gp75, generated autoantibodies against gp75 after immunization with DNA encoding human gp75 but not syngeneic mouse gp75. Priming with human gp75 DNA broke tolerance to mouse gp75. Immunity against mouse gp75 provided significant tumor protection. Manifestations of autoimmunity were observed, characterized by coat depigmentation. Rejection of tumor challenge required CD4(+) and NK1.1(+) cells and Fc receptor gamma-chain, but depigmentation did not require these components. Thus, immunization with homologous DNA broke tolerance against mouse gp75, possibly by providing help from CD4(+) T cells. Mechanisms required for tumor protection were not necessary for autoimmunity, demonstrating that tumor immunity can be uncoupled from autoimmune manifestations.

Murine dendritic cells pulsed with whole tumor lysates mediate potent antitumor immune responses in vitro and in vivo

The highly efficient nature of dendritic cells (DC) as antigen-presenting cells raises the possibility of uncovering in tumor-bearing hosts very low levels of T cell reactivity to poorly immunogenic tumors that are virtually undetectable by other means. Here, we demonstrate the in vitro and in vivo capacities of murine bone marrow-derived, cytokine-driven DC to elicit potent and specific anti-tumor responses when pulsed with whole tumor lysates. Stimulation of naive spleen-derived T cells by tumor lysate-pulsed DC generated tumor-specific proliferative cytokine release and cytolytic reactivities in vitro. In addition, in two separate strains of mice with histologically distinct tumors, s.c. injections of DC pulsed with whole tumor lysates effectively primed these animals to reject subsequent lethal challenges with viable parental tumor cells and, important to note, also mediated significant reductions in the number of metastases established in the lungs. Tumor rejection depended on host-derived CD8(+) T cells and, to a lesser extent, CD4(+) T cells. Spleens from mice that had rejected their tumors contained specific precursor cytotoxic T lymphocytes. The use of whole tumor lysates as a source of tumor-associated antigen(s) for pulsing of DC circumvents several limitations encountered with other methods as well as provides certain distinct advantages, which are discussed. These data serve as rationale for our recent initiation of a phase I clinical trial of immunization with autologous tumor lysate-pulsed DC in adult and pediatric cancer patients.

Human Melanoma-Reactive CD4+ and CD8+ CTL Clones Resist Fas Ligand-Induced Apoptosis and Use Fas/Fas Ligand-Independent Mechanisms for Tumor Killing

Tumor cells have been shown recently to escape immune recognition by developing resistance to Fas-mediated apoptosis and acquiring expression of Fas ligand (FasL) molecule that they may use for eliminating activated Fas+ lymphocytes. In this study, we report that tumor-specific T lymphocytes isolated from tumor lesions by repeated in vitro TCR stimulation with relevant Ags (mostly represented by normal self proteins, such as MART-1/Melan A and gp100) can develop strategies for overcoming these escape mechanisms. Melanoma cells (and normal melanocytes) express heterogeneous levels of Fas molecule, but they result homogeneously resistant to Fas-induced apoptosis. However, CD4+ and CD8+ CTL clones kill melanoma cells through Fas/FasL-independent, granule-dependent lytic pathway. In these lymphocytes, Ag/MHC complex interaction with TCR does not lead to functional involvement of FasL, triggered, on the contrary, by T cell activation with nonspecific stimuli such as PMA/ionomycin. Additionally, melanoma cells express significant levels of FasL (detectable on the cell surface only after treatment with metalloprotease inhibitors), although to a lesser extent than professional immune cells such as Th1 clones. Nevertheless, antimelanoma CTL clones resist apoptosis mediated by FasL either in soluble form or expressed by Th1 lymphocytes or FasL+ melanoma cells. These results demonstrate that CD4+ and CD8+ antimelanoma T cell clones can be protected against Fas-dependent apoptosis, and thus be useful reagents of immunotherapeutic strategies aimed to potentiate tumor-specific T cell responses.

Pulsing of dendritic cells with cell lysates from either B16 melanoma or MCA-106 fibrosarcoma yields equally effective vaccines against B16 tumors in mice

BACKGROUND AND OBJECTIVES

Dendritic cells (DC) pulsed in vitro with a variety of antigens have proved effective in producing specific antitumor effects in vivo. Experimental evidence from other laboratories has confirmed that shared antigens can be encountered in histologically distinct tumors. In our experiments, we set out to evaluate the immunotherapeutic potential of vaccines consisting of DC pulsed with MCA-106 fibrosarcoma or B16 melanoma cell lysates and to determine whether a cross-reactivity exists between the two tumors.

METHODS

DC were prepared from the bone marrow of C57BL/6 (B6) mice by culturing progenitor cells in murine granulocyte-macrophage colony-stimulating factor (GM-CSF). They were separated into three equal groups and were either pulsed with B16 melanoma cell lysates (BDC), pulsed with tumor extract from the syngeneic fibrosarcoma MCA-106 (MDC), or left unpulsed (UDC). DC were then used to immunize three groups of mice, with all mice receiving two weekly intravenous (IV) doses of 1 x 10(6) DC from their respective preparations on days -14 and -7. A fourth group of control mice were left untreated. On day 0, all mice were challenged with subcutaneous injections of 1 x 10(5) B16 and 1 x 10(5) MCA tumor cells, administered in the left and right thighs, respectively. After the inoculations, the mice were monitored closely with respect to tumor growth and survival.

RESULTS

The MDC mice developed specific cellular immunity directed against not only MCA-106 tumor cells, but also against B16 melanoma, as measured through chromium-release assays of splenocyte preparations, while remaining ineffective at killing both L929 fibroblasts and CT26 tumor cells. By day 30 after tumor inoculations, control mice manifested the largest B16 tumor volumes at a mean of 2185 mm3, followed by the UDC, MDC, and BDC groups at 92 mm3 (P=0.00008), 3 mm3 (P=0.000002), and 2 mm3 (P=0.00004), respectively. The survival data mirrored this pattern, with control animals displaying the shortest mean survival time (37.1+/-4.0 days), followed by UDC (44.8+/-6.6), MDC (56.2 +/-14.7), and BDC (56.4+/-18.3) animals. No significant differences were noted between MCA-106 and B16 cell lysate-pulsed DC vaccines with respect to their abilities to inhibit B16 tumor growth and to prolong survival. These findings were confirmed using a B16 pulmonary metastasis model. Likewise, vaccination with interferon-gamma gene-modified MCA-106 tumor cells was shown to be effective at protecting against a subsequent subcutaneous B16 tumor challenge in 3 of 4 mice observed.

CONCLUSIONS

These results demonstrate that immunization with antigen-pulsed DC confers cellular immunity, retards tumor growth, and prolongs the survival of tumor-challenged mice. The ability of MCA-106 cell lysate-pulsed DC vaccines to inhibit the growth of subcutaneous B16 tumors also suggests the presence of shared tumor-associated antigens between these two histologically distinct tumors.

Gene therapy for melanoma in humans

As melanoma evolves, it interacts with the immune system. Based on this immunobiology, there are now a number of rationally designed attempts to develop genetically modified melanoma vaccines. This article outlines immunologic and other strategies in gene therapy for melanoma and provides an overview of current clinical trials.

The cytoplasmic tail of the mouse brown locus product determines intracellular stability and export from the endoplasmic reticulum

Several melanosome membrane proteins have been identified, forming a family of proteins known as tyrosinase related proteins. Human TRP-1/gp75 is sorted to melanosomes through the endoplasmic reticulum and Golgi complex to the endocytic pathway, directed by a sorting signal located in the cytoplasmic tail. This hexapeptide cytoplasmic sequence, which is conserved in the tyrosinase related protein family and through vertebrate evolution, was shown to act also as a sorting signal in mouse gp75, confirming that its sorting and cellular retention function is conserved between human and mouse. The cytoplasmic tail influenced the rate and efficiency of intracellular transport of gp75 from the endoplasmic reticulum to the cis-Golgi. Deletion of 33 or 27 amino acids from the carboxyl end of the 38 amino acid cytoplasmic tail of gp75 caused retention and rapid degradation of the truncated gp75 in the endoplasmic reticulum. This defective movement could be fully corrected by extending the truncated tail with the unrelated cytoplasmic tail of the low density lipoprotein receptor. Thus, the cytoplasmic tail of mouse gp75 not only determines sorting to the endocytic/melanosomal compartment, but also controls export from the endoplasmic reticulum to Golgi.

The role of the HLA-DQA1 gene in resistance to atrophic gastritis and gastric adenocarcinoma induced by Helicobacter pylori infection

BACKGROUND

It has been suggested that immunogenetic factors for susceptibility or resistance to disease caused by Helicobacter pylori exist in the host. To examine host genetic factors that increase the risk of gastric adenocarcinoma among H. pylori-infected persons, the HLA-DQA1 locus was examined in patients with gastric adenocarcinoma.

METHODS

Eighty-two gastric adenocarcinoma patients and 167 unrelated controls were examined for H. pylori infection and HLA-DQA1 genotyping. In addition, serum pepsinogen A (PGA) and pepsinogen C (PGC) values and the PGA/PGC ratio, which have been characterized as markers of gastric mucosal atrophy, also were analyzed.

RESULTS

Of the 167 controls, 121 were H. pylori positive (+) and 46 were H. pylori negative (-). All H. pylori (-) individuals had normal endoscopic and histologic findings. Among the 121 H. pylori (+) controls, 36 had superficial gastritis and 85 had atrophic gastritis. The allele frequency of DQA1*0102 was significantly lower in the H. pylori (+) atrophic gastritis group than in the H. pylori (+) superficial gastritis and H. pylori (-) normal control groups. In addition, the allele frequency of DQA1*0102 also was significantly lower in the H. pylori (+) intestinal type gastric adenocarcinoma group than in the H. pylori (-) normal control, H. pylori (+) superficial gastritis, and H. pylori (-) diffuse type gastric adenocarcinoma groups. Serum PGA and PGC values and the PGA/PGC ratio did not differ significantly among HLA-DQA1 genotypes; however, the PGA/PGC ratio was significantly lower in the H. pylori (+) atrophic gastritis and H. pylori (+) intestinal type gastric adenocarcinoma groups than in the H. pylori (-) normal control and H. pylori (+) superficial gastritis groups.

CONCLUSIONS

The DQA1*0102 allele may contribute to resistance against H. pylori-associated gastric atrophy and its association with intestinal type gastric adenocarcinoma, whereas the absence of DQA1*0102 may be a host genetic risk factor for H. pylori-associated atrophic gastritis and intestinal type gastric adenocarcinoma.

The role of the HLA-DQA1 gene in resistance to atrophic gastritis and gastric adenocarcinoma induced by Helicobacter pylori infection

BACKGROUND

It has been suggested that immunogenetic factors for susceptibility or resistance to disease caused by Helicobacter pylori exist in the host. To examine host genetic factors that increase the risk of gastric adenocarcinoma among H. pylori-infected persons, the HLA-DQA1 locus was examined in patients with gastric adenocarcinoma.

METHODS

Eighty-two gastric adenocarcinoma patients and 167 unrelated controls were examined for H. pylori infection and HLA-DQA1 genotyping. In addition, serum pepsinogen A (PGA) and pepsinogen C (PGC) values and the PGA/PGC ratio, which have been characterized as markers of gastric mucosal atrophy, also were analyzed.

RESULTS

Of the 167 controls, 121 were H. pylori positive (+) and 46 were H. pylori negative (-). All H. pylori (-) individuals had normal endoscopic and histologic findings. Among the 121 H. pylori (+) controls, 36 had superficial gastritis and 85 had atrophic gastritis. The allele frequency of DQA1*0102 was significantly lower in the H. pylori (+) atrophic gastritis group than in the H. pylori (+) superficial gastritis and H. pylori (-) normal control groups. In addition, the allele frequency of DQA1*0102 also was significantly lower in the H. pylori (+) intestinal type gastric adenocarcinoma group than in the H. pylori (-) normal control, H. pylori (+) superficial gastritis, and H. pylori (-) diffuse type gastric adenocarcinoma groups. Serum PGA and PGC values and the PGA/PGC ratio did not differ significantly among HLA-DQA1 genotypes; however, the PGA/PGC ratio was significantly lower in the H. pylori (+) atrophic gastritis and H. pylori (+) intestinal type gastric adenocarcinoma groups than in the H. pylori (-) normal control and H. pylori (+) superficial gastritis groups.

CONCLUSIONS

The DQA1*0102 allele may contribute to resistance against H. pylori-associated gastric atrophy and its association with intestinal type gastric adenocarcinoma, whereas the absence of DQA1*0102 may be a host genetic risk factor for H. pylori-associated atrophic gastritis and intestinal type gastric adenocarcinoma.

Human Melanoma Patients Recognize an HLA-A1-Restricted CTL Epitope from Tyrosinase Containing Two Cysteine Residues: Implications for Tumor Vaccine Development

To identify shared epitopes for melanoma-reactive CTL restricted by MHC molecules other than HLA-A*0201, six human melanoma patient CTL lines expressing HLA-A1 were screened for reactivity against the melanocyte differentiation proteins Pmel-17/gp100, MART-1/Melan-A, and tyrosinase, expressed via recombinant vaccinia virus vectors. CTL from five of the six patients recognized epitopes from tyrosinase, and recognition of HLA-A1+ target cells was strongly correlated with tyrosinase expression. Restriction by HLA-A1 was further demonstrated for two of those tyrosinase-reactive CTL lines. Screening of 119 synthetic tyrosinase peptides with the HLA-A1 binding motif demonstrated that nonamer, decamer, and dodecamer peptides containing the sequence KCDICTDEY (residues 243–251) all reconstituted the CTL epitope in vitro. Epitope reconstitution in vitro required high concentrations of these peptides, which was hypothesized to be a result of spontaneous modification of cysteine residues, interfering with MHC binding. Substitution of serine or alanine for the more N-terminal cysteine prevented modification at that residue and permitted target cell sensitization at peptide concentrations 2 to 3 orders of magnitude lower than that required for the wild-type peptide. Because spontaneous modification of sulfhydryl groups may also occur in vivo, tumor vaccines using this or other cysteine-containing peptides may be improved by amino acid substitutions at cysteine residues.

Protein sorting within the MHC class II antigen-processing pathway

Major histocompatibility complex (MHC) class II molecules are required for the presentation of antigenic peptides that are derived predominantly from internalized proteins. The assembly of MHC class II/peptide complexes occurs within endosomal compartments of antigen-presenting cells (APCs). Therefore, for assembly to occur, MHC class II molecules, foreign proteins, and accessory molecules must be sorted to appropriate intracellular sites. My laboratory is trying to understand how proteins are sorted to various antigen-processing compartments as well as to conventional endosomal organelles. Using chimeric marker proteins and a variety of biochemical and genetic approaches, we are addressing the specificity of protein sorting and the mechanisms by which sorting signals are deciphered. By using a similar chimeric protein approach to target endogenous proteins to distinct compartments, we hope to address the role of processing events in each compartment in the generation of MHC class II ligands.

Tumour surveillance: missing peptides and MHC molecules

Immunotherapy involving CTL is an attractive alternative for treatment of various malignancies. One of the approaches currently being explored for immune targeting of human cancers involves potentiation of immunogenicity of malignant cells by gene transduction. This strategy is undoubtedly influenced by the ability of the malignant cells to endogenously process and present target epitopes on their cell surface for immune recognition by CTL. However, there is increasing evidence to suggest that a large proportion of human cancers escape CTL-mediated immune surveillance by selectively down-regulating the expression of MHC class I molecules and peptide transporter genes. Understanding and molecular analysis of these immunologically relevant genetic defects in tumours is very important before translating preclinical studies of immunotherapy to rational clinical trials. Careful consideration of these potential limitations may lead to the development of novel immunotherapeutic strategies and, potentially, prevention of tumour progression or development.

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.

Specific T cell recognition of peptides derived from prostate-specific antigen in patients with prostate cancer

OBJECTIVES

To determine if proteins known to be expressed by both benign and malignant prostate epithelium can be recognized by T cells from patients with prostate cancer. We examined 7 HLA-A2 patients with prostate cancer for evidence of T cell reactivity with prostate-specific antigen (PSA).

METHODS

Four peptides derived from PSA were chemically synthesized and shown to bind to HLA-A2. As a control, we also examined the immunogenic influenza matrix peptide Flu58-66 that binds to HLA-A2. These peptides were used to stimulate peripheral blood lymphocytes by in vitro stimulation.

RESULTS

In 1 patient, specific recognition of peptide PSA141-150 was observed. The remaining 6 patients had no reactivity with any PSA-derived peptide. The T cell line with specific recognition of peptide PSA141-150 failed to recognize an autologous B cell blast line expressing endogenous PSA following infection with a recombinant PSA vaccinia virus construct. Three of the 7 patients demonstrated specific reactivity with Flu58-66.

CONCLUSIONS

We found specific recognition of one PSA-derived peptide in 1 patient of 7 with prostate cancer. The peptide-specific lymphocyte cell line did not recognize endogenous PSA, suggesting that the peptide may not be produced by prostate cancer cells producing PSA. Specific recognition of PSA peptides was not common in our patients with prostate cancer. Whether such activity can be induced by vaccination strategies or can be therapeutic in men with established prostate cancer remains to be demonstrated.

Tumor antigens discovery: perspectives for cancer therapy

The adoptive transfer of cytotoxic T lymphocytes (CTLs) derived from tumor-infiltrating lymphocytes (TIL) along with interleukin 2 (IL-2) into autologous patients with cancer resulted in the objective regression of tumor, indicating that these CTLs recognized cancer rejection antigens on tumor cells. To understand the molecular basis of T cell-mediated antitumor immunity, several groups started to search for such tumor antigens in melanoma as well as in other types of cancers. This led to the subject I will review in this article. A number of tumor antigens were isolated by the use of cDNA expression systems and biochemical approaches. These tumor antigens could be classified into several categories: tissue-specific differentiation antigens, tumor-specific shared antigens, and tumor-specific unique antigens. However, the majority of tumor antigens identified to date are nonmutated, self proteins. This raises important questions regarding the mechanism of antitumor activity and autoimmune disease. The identification of human tumor rejection antigens provides new opportunities for the development of therapeutic strategies against cancer. This review will summarize the current status and progress toward identifying human tumor antigens and their potential applications to cancer treatment.

Serological identification of human tumor antigens

Using the antibody repertoire of cancer patients for the systematic search for human tumor antigens, a plenitude of new human tumor antigens has been identified demonstrating that many human tumors elicit multiple immune responses in the autologous host. The abundance of serologically defined human tumor antigens facilitates the identification of T cell dependent antigens and provides a basis for peptide and gene therapy vaccine strategies in a wide variety of human cancers.

Nonreplicating recombinant vaccinia virus encoding human B-7 molecules elicits effective costimulation of naive and memory CD4+ T lymphocytes in vitro

We constructed recombinant vaccinia viruses (recVV) encoding the human T-cell costimulatory molecules B7-1 and B7-2. To abrogate the vaccinia virus transcription termination signal for early genes, the cDNA of B7-1 had to be modified by a T through C sense mutation at position 766. Upon infection with replication incompetent and noncytopathic recVV, several tumor cell lines as well as cultured human fibroblasts expressed the costimulatory molecules. All these cells were capable of providing effective costimulation for proliferation of resting CD4(+) T-cells after infection with recVV encoding B7 molecules. The costimulatory effect could be blocked with CTLA-4 IgG fusion protein, the soluble ligand for B7. RecVV-induced overexpression of B7 on syngeneic EBV-transformed lymphoblastoid B-cells was able to costimulate the proliferative response of CD4(+) memory cells against VV antigens. The possibility of easily engineering a variety of human cells using recVV encoding human B7 molecules holds implications for the future design of vaccination strategies.

Human minor histocompatibility antigens: new concepts for marrow transplantation and adoptive immunotherapy

Bone marrow transplantation (BMT) is the present treatment for hematological malignancies. Two major drawbacks of allogeneic BMT are graft-versus-host disease (GVHD) and leukemia relapse. The use of HLA-matched siblings as marrow donors results in the best transplant outcome. Nonetheless, the results of clinical BMT reveal that the selection of MHC-identical donors' bone marrow (BM) is no guarantee for avoiding GVHD or ensuring disease-free survival even when donor and recipient are closely related. It is believed that non-MHC-encoded so-called minor histocompatibility antigens (mHag) are involved in both graft-versus-host and graft-versus-leukemia activities. The recent new insights into the chemical nature of mHag not only reveal their physiological function but, more importantly, provide insights into their role in BMT. Together with the information on the human mHag genetics and tissue distribution gathered in the past, we may now apply this knowledge to the benefit of human BMT. Directly relevant is the utility of mHag molecular typing for diagnostics in BM donor selection. Most promising is the use of mHag-specific cytotoxic T cells for adoptive immunotherapy of leukemia.

Killing of rat adenocarcinoma 13762 in situ by adoptive transfer of CD4+ anti-tumor T cells requires tumor expression of cell surface MHC class II molecules

CD4+ anti-tumor T cells reactive with rat adenocarcinoma 13762 kill tumor in vitro and cause regression of tumor in vivo. The role of various host immune cells in CD4+ T-cell-mediated tumor elimination in vivo was investigated by adoptive transfer of anti-tumor T cell clones to recipients that were selectively depleted of individual immune cell types. By these means, macrophages and NK cells were found to be required for tumor killing. Depletion of host CD4+ T cells, CD8+ T cells, or neutrophils was without effect on tumor elimination by anti-tumor T cells. An essential role for antigen receptor-negative NK cells is likely dependent upon secretion of IFN-gamma from NK cells since treatment of tumor recipients with anti-IFN-gamma antibody prior to adoptive transfer and tumor challenge abrogated T cell killing, resulting in progressive tumor growth. Viability of adenocarcinoma 13762 or anti-tumor T cells was unaffected by treatment with either IFN-gamma or anti-IFN-gamma antibody in vitro, but cell surface MHC class II expression was induced in tumor cells by exposure to IFN-gamma. In addition, tumor cells were isolated from tumor-bearing animals by absorption using anti-MHC class II antibody, demonstrating that 13762 tumor expresses cell surface MHC class II antigens in situ. However, if hosts were depleted of NK cells before tumor challenge, MHC class II+ tumor was not recovered. Collectively these results suggest that adenocarcinoma 13762 is eliminated by MHC class II-restricted CD4+ T cells by direct tumor killing.

Engagement of the B lymphocyte antigen receptor induces presentation of intrinsic immunoglobulin peptides on major histocompatibility complex class II molecules

By means of the clonotypic variable region, the immunoglobulin (Ig) is a tumor-specific antigen on B cell neoplasms. We report that engagement of the B cell antigen receptor (BcR) promotes presentation of peptides derived from the B cell's intrinsic Ig to major histocompatibility complex (MHC) class II-restricted T cells. Thus, anti-Ig endowed normal, ex vivo B lymphocytes from H-2d, Ig constant heavy chain allotype b (IgCHb) mice with the capacity to stimulate an I-Ad-restricted T cell clone which recognizes the gamma 2ab 435-451 allopeptide. The corresponding self gamma 2aa peptide is cryptic and 6000-fold less antigenic than the gamma 2ab allopeptide. Even so, the syngeneic B cell lymphoma A20 which expresses surface(s) IgG2aa, was also recognized by the T cells after BcR ligation. Thus, anti-Ig triggered the disclosure of a cryptic tumor antigen determinant. We propose that autoantigens, by engaging the BcR of self-reactive B cells, induce presentation of intrinsic Ig peptides to which the T helper cell (Th) repertoire is not tolerant. In this way, B cells with anti-self potential may be activated without Th recognition of nominal autoantigen.

Interactions between autologous CD4+ and CD8+ T lymphocytes and human squamous cell carcinoma of the head and neck

The autotumor (AuTu)-specific cytolytic T lymphocyte (CTL) line established from the peripheral blood of a patient with oral squamous cell carcinoma (Cancer Res. 53, 1461, 1993) contained >95% of CD8+ and <5% of CD4+ T cells. This CTL line was infected with Herpesvirus saimiri to increase its life span in culture. Two transformed T cell sublines were obtained: the monoclonal CD4+ line (TCR Vbeta2+ V alpha15+) and the oligoclonal CD8+ line (TCR Vbeta6+, Vbeta7+ and Vbeta9+) both of which were maintained in culture for >6 months without AuTu restimulation and which did not produce any virus. The virus-transformed and untransformed T cell lines were compared for phenotypic and functional characteristics, including the ability to kill AuTu, induce expression of the major histocompatibility complex (MHC) antigens on AuTu, and respond to AuTu by cytokine production and/or proliferation. The H. saimiri-transformed CD4+ T cells expressed higher levels of surface adhesion molecules and CD45RO than untransformed cells and lysed AuTu by inducing DNA fragmentation as well as necrosis. This lysis was inhibited by antibodies to CD4 but not to class I or II MHC molecules. The CD4+ T cells produced IL2, TNF-alpha, and GM-CSF and proliferated in response to AuTu. They induced and sustained proliferation of CD8+ T cells in cocultures with AuTu. Supernatants obtained from cocultures of the CD4+ T cells with AuTu also induced proliferation of the CD8+ T cell line. In contrast, the H. saimiri-transformed CD8+ T cells did not kill AuTu or release cytokines in response to AuTu. However, upon pretreatment of AuTu with IFN-gamma to increase expression of MHC antigens, these T cells regained the ability to recognize and kill AuTu targets. Coincubation of AuTu with the CD4+ or CD8+ T cells significantly augmented expression of class I and II MHC antigens on AuTu. These data indicate that H. saimiri-transformed tumor-reactive T cell lines provide a useful model of interactions between immune effector cells and AuTu, and that CD4+ T cells play a critical role in the regulation of immune responses to squamous cell carcinoma of the head and neck.

Adoptive Transfer of Anti-CD3–Activated CD4+ T Cells Plus Cyclophosphamide and Liposome-Encapsulated Interleukin-2 Cure Murine MC-38 and 3LL Tumors and Establish Tumor-Specific Immunity

The infusion of anti-CD3–activated murine T cells plus interleukin-2 (IL-2) exerts antitumor effects against several tumors in murine immunotherapy models. This study compares the therapeutic efficacy of anti-CD3–activated CD4+ or CD8+ T-cell subsets, when given with cyclophosphamide (Cy) and liposome-encapsulated IL-2 (L-IL2) in a murine model. C57BL/6 mice bearing subcutaneous (SC) MC-38 colon adenocarcinoma, 3LL Lewis lung carcinoma, or 38C13 lymphoma for 7 to 14 days were pretreated with low-dose intraperitoneal (IP) Cy before intravenous (IV) injection of anti-CD3–activated T cells or T-cell subsets. Cell administration was followed by IP administration of L-IL2 for 5 days. Mice receiving activated CD4+ T cells showed significantly reduced tumor growth or complete remissions with prolonged disease-free survival in MC-38, 3LL, and 38C13. The timing of Cy doses in relation to adoptive transfer was critical in obtaining the optimal antitumor effect by CD4+ cells. Injecting Cy 4 days before the infusion of CD4+ cells greatly enhanced the antitumor effect of the CD4+ cells and improved survival of the mice compared with other Cy regimens. C57BL/6 mice cured of MC-38 after treatment with CD4+ T cells developed tumor-type immunologic memory as demonstrated by their ability to reject rechallenges with MC-38, but not 3LL. Similarly, mice cured of 3LL tumors rejected rechallenges of 3LL, but not MC-38. The immunologic memory could be transferred with an IV injection of splenocytes from mice cured of MC-38 or 3LL. No cytotoxic T-lymphocyte activity was detected in T cells or T-cell subsets from mice cured of MC-38 or 3LL. Increased IL-2 and interferon-γ (IFN-γ) production was observed from CD4+ subsets in cured animals when stimulated in vitro with the original tumor, but not with an unrelated syngeneic tumor. These results suggest that tumor-specific immunity can be achieved in vivo with anti-CD3–stimulated CD4+ T cells in this cellular therapy model.

Production of recombinant MART-1 proteins and specific antiMART-1 polyclonal and monoclonal antibodies: use in the characterization of the human melanoma antigen MART-1

Recombinant human MART-1 protein was produced by bacterial and baculoviral-insect cell expression systems. By immunization with bacterial MBP-MART-1 fusion protein or MBP cleaved MART-1 protein, a rabbit polyclonal and two murine monoclonal antibodies specific for MART-1 were produced. These antibodies specifically detected MART-1 in immuno-precipitation, Western blotting, flow cytometric assays and in immunohistochemical analysis of tissue sections. They also stained cytoplasmic components in melanocytes and most melanoma cells in frozen or paraffin embedded tissue sections, indicating that these antibodies may be useful for the diagnosis of melanoma. One of the monoclonal antibodies M2-7 C10 recognized only human MART-1, but the other monoclonal antibody M2-9 E3 recognized both human and murine MART-1. The size of the human MART-1 molecule detected by SDS-PAGE with these antibodies was approximately 18 kDa, suggesting possible posttranslational modifications in the MART-1 protein. Subcellular fractionation studies suggested that MART-1 was present in melanosomes and endoplasmic reticulum, although known melanogenic enzymatic activities were not detected in the MART-1 protein. These reagents may be useful for biological studies on melanocytes and melanoma cells as well as for the development and monitoring of immunotherapy for patients with melanoma.

Cytotoxicity of histocompatibility leukocyte antigen-DR8-restricted CD4 killer T cells against human autologous squamous cell carcinoma

Although CD8+ killer T cells reacting against human autologous tumor cells have recently been studied in detail, little is known about the cytotoxic mechanism of CD4+ T cells against such tumor cells. In order to investigate this, we have established CD4+ cytotoxic T lymphocyte TcOSC-20 lines. TcOSC-20 showed selective cytotoxic activity against autologous OSC-20 cells, derived from a cancer of the tongue, in an HLA-DR-restricted fashion. HLA-DR8 (DRB1*08032) is the only DR molecule expressed on OSC-20 cells, and anti-DR8 monoclonal antibody could inhibit the cytotoxicity, suggesting that HLA-DRB1*08032 is the tumor rejection antigen-presenting molecule to TcOSC-20. The Fas ligand was expressed on TcOSC-20 lines, and its expression was induced upon mixed lymphocyte-tumor cell culture of autologous peripheral blood lymphocytes. Furthermore, the cytotoxicity of TcOSC-20 was inhibited by anti-Fas ligand antibody. These data imply that TcOSC-20 lines recognize the tumor antigenic peptide presented by HLA-DR8, and exert cytotoxicity against autologous tumor cells via a Fas-mediated cytotoxic pathway.

Cloning and characterization of the genes encoding the murine homologues of the human melanoma antigens MART1 and gp100

The recent identification of genes encoding melanoma-associated antigens has opened new possibilities for the development of cancer vaccines designed to cause the rejection of established tumors. To develop a syngeneic animal model for evaluating antigen-specific vaccines in cancer therapy, the murine homologues of the human melanoma antigens MART1 and gp100, which were specifically recognized by tumor-infiltrating lymphocytes from patients with melanoma, were cloned and sequenced from a murine B16 melanoma cDNA library. The open reading frames of murine MART1 and gp100 encode proteins of 113- and 626-amino acids with 68.8 and 77% identity to the respective human proteins. Comparison of the DNA sequences of the murine MART1 genes, derived from normal melanocytes, the immortalized nontumorgenic melanocyte line Melan-a and the B16 melanoma, showed all to be identical. Northern and Western blot analyses confirmed that both genes encoded products that were melanocyte lineage proteins. Mice immunized with murine MART1 or gp100 using recombinant vaccinia virus failed to produce any detectable T-cell responses or protective immunity against B16 melanoma. In contrast, immunization of mice with human gp100 using recombinant adenoviruses elicited T cells specific for hgp100, but these T cells also cross reacted with B16 tumor in vitro and induced significant but weak protection against B16 challenge. Immunization with human and mouse gp100 together [adenovirus type 2 (Ad2)-hgp100 plus recombinant vaccinia virus (rVV)-mgp100], or immunization with human gp100 (Ad2-hgp100) and boosting with heterologous vector (rVV-hgp100 or rVV-mgp100) or homologous vector (Ad2-hgp100), did not significantly enhance the protective response against B16 melanoma. These results may suggest that immunization with heterologous tumor antigen, rather than self, may be more effective as an immunotherapeutic reagent in designing antigen-specific cancer vaccines.

T-cell recognition of melanoma antigens and its therapeutic applications

During the last few years, tumor immunology has gained impetus due to the molecular definition of T-cell-recognized antigens and the mechanisms of such recognition, antigen processing, and presentation. To date, the majority of the identified melanoma antigens are shared among different melanomas and some are also expressed in tumors of different histology. However, unique antigens expressed solely by the melanoma autologous to the T-cell used for their characterization were also found. The identification of the immunogenic peptides, the minimal target entity required for T-cell recognition, has provided novel reagents for the development of peptide-based immunotherapy. These findings, together with the understanding of requirements for T-lymphocyte recognition and activation, allow the design of new therapeutic protocols. In addition, the large body of data now available on the fine mechanism of antigen processing and presentation have revealed not only the role of the MHC molecules but also that of other intracellular proteins, such as transporter associated with antigen processing-1 and -2 and proteosome-related molecules. These findings suggest that, in order to select patients eligible for vaccination, the expression of the MHC allele involved in T-cell recognition, the profile of tumor antigens, and the status of the antigen-processing system should be carefully evaluated in tumors cells of prospective patients. In this review, some of the basic concepts of immune recognition and the current view of melanoma tumor antigens recognized by T-lymphocytes will be discussed along with the potential application of these findings in designing new therapeutic strategies.

Tumor antigens recognized by T lymphocytes

In the last five years, knowledge of human tumor antigens recognized by autologous cytolytic T lymphocytes (CTL) has increased considerably. So far, genetic and biochemical approaches have led to the molecular identification of three classes of antigens. Most of these antigens consist of peptides that are presented to T cells by HLA molecules. The first class comprises antigens encoded by genes such as MAGE, BAGE, and GAGE, which are expressed in various tumors of different histological origins, but not in normal tissues other than testis. The second class represents differentiation antigens encoded by genes that are only expressed in melanoma and normal melanocytes like tyrosinase, Melan-A/MART-1, gp100 and gp75. The third class includes antigens produced by unique point mutations in genes that are ubiquitously expressed. In most cases, the antigenic peptide is encoded by the mutated region of the gene. A number of these antigens provide promising targets for new protocols of specific cancer immunotherapy.

Immune response to a differentiation antigen induced by altered antigen: a study of tumor rejection and autoimmunity

Recognition of self is emerging as a theme for the immune recognition of human cancer. One question is whether the immune system can actively respond to normal tissue autoantigens expressed by cancer cells. A second but related question is whether immune recognition of tissue autoantigens can actually induce tumor rejection. To address these issues, a mouse model was developed to investigate immune responses to a melanocyte differentiation antigen, tyrosinase-related protein 1 (or gp75), which is the product of the brown locus. In mice, immunization with purified syngeneic gp75 or syngeneic cells expressing gp75 failed to elicit antibody or cytotoxic T-cell responses to gp75, even when different immune adjuvants and cytokines were included. However, immunization with altered sources of gp75 antigen, in the form of either syngeneic gp75 expressed in insect cells or human gp75, elicited autoantibodies to gp75. Immunized mice rejected metastatic melanomas and developed patchy depigmentation in their coats. These studies support a model of tolerance maintained to a melanocyte differentiation antigen where tolerance can be broken by presenting sources of altered antigen (e.g., homologous xenogeneic protein or protein expressed in insect cells). Immune responses induced with these sources of altered antigen reacted with various processed forms of native, syngeneic protein and could induce both tumor rejection and autoimmunity.

Factors associated with melanoma incidence and prognosis

Melanoma has a reputation as an unpredictable disease, but investigation has demonstrated a multiplicity of factors which are independently associated with melanoma incidence and prognosis. Major factors associated with melanoma incidence include those related to race and ethnicity, sunlight exposure, and genetic and familial predisposition. Major factors associated with melanoma prognosis include tumor thickness, ulceration, anatomic location, and patient's sex. These factors are clinically important in designing appropriate screening and prevention programs, as well as in selecting appropriate treatment and follow-up for the individual melanoma patient. There is an increasing need to identify the molecular mechanisms underlying these clinically defined etiologic and prognostic factors so that we may treat patients more effectively and more selectively. Available evidence indicates that the mechanisms of melanoma etiology include a loss of tumor suppressor genes. Mechanisms of melanoma progression include the accumulation of oncogene mutations, perhaps as a result of sun exposure, the development of autocrine and paracrine loops involving cytokines and growth factors, and alterations in cell-surface antigen expression. Finally, an antigen-specific immune response to melanoma appears to be important in the prognosis of some patients. Critical regulatory components of the melanoma immune response include antibodies, T-cells, and human leukocyte antigen (HLA) molecules.

Tumor antigens and tumor vaccines: peptides as immunogens

Tumor antigens recognized by human cytotoxic T lymphocytes (CTL) have been identified for multiple types of solid tumors. These include both shared and unique antigens. Unique antigens are those expressed uniquely by one patient's tumor, and shared antigens are those present on tumor cells from many different patients. Many of the shared antigens are derived from tissue-specific differentiation antigens, oncogenes, or a set of antigens expressed only in tumors or in testis. In addition to advances in understanding tumor antigens that stimulate CTL and T-helper cell responses, there have been advances in understanding immunity in general, including the characterization of cytokines, the recognition of the dendritic cell as an optimal antigen-presenting cell (APC), and the characterization of costimulatory molecules as critical components of antigen presentation. Together, these developments have breathed new life into tumor immunology, and they promise to lead to a new generation of peptide- and cell-based tumor vaccines.

Limited antitumor T cell response in melanoma patients vaccinated with interleukin-2 gene-transduced allogeneic melanoma cells

We have immunized advanced melanoma patients with a HLA-A2-compatible human melanoma line genetically modified to release interleukin-2 (IL-2), to elicit or increase a T cell-mediated anti-melanoma response that may affect distant lesions. Twelve stage-IV patients were injected subcutaneously at days 1, 13, 26, and 55 with IL-2 gene-transduced and irradiated melanoma cells at doses of 5 or 15 x 10(7) cells. Both local and systemic toxicities were mild, consisting of transient erythema at the vaccination site; fever occurred in a minority of patients. Three mixed responses were recorded. Seven patients were evaluable for immunological studies. Mixed tumor-lymphocyte cultures carried out with different allogeneic HLA-A2-matched melanoma lines as stimulators and targets revealed an increase in the MHC-unrestricted, but no changes in the MHC-restricted, cytotoxicity in peripheral blood lymphocytes (PBL) obtained after vaccination as compared with those obtained before vaccination. Increased recognition of the tyrosinase 368-376 peptide occurred in post-vaccination PBL of one patient, whereas a weak increase in recognition of the gp100 280-288 peptide was detectable in another patient; these 2 patients also recognized the gp100 457-466 peptide. After in vitro, stimulation with the only available autologous melanoma line, CD4+ cells with autologous tumor-specific cytotoxicity and ability to release interferon-gamma (IFN-gamma) were found in post- but not in pre-vaccination PBL. In the same patient, as well as in another patient, limiting dilution analysis showed that vaccination resulted in an increased frequency of melanoma-specific cytotoxic T lymphocyte (CTL) precursors. These results indicate that vaccination with cells releasing IL-2 locally can expand a T cell response against antigen(s) of autologous, untransduced tumor, although this response occurred in a minority of the melanoma patients studied.

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.

Melanoma-specific CD4+ T cells recognize nonmutated HLA-DR-restricted tyrosinase epitopes

Tyrosinase was the first melanoma-associated antigen shown to be recognized by CD4+ T cells. In this study, we have identified two HLA-DRB1*0401-restricted peptides recognized by these T cells: Ty 56-70 and Ty 448-462. As with many of the MHC class I-restricted melanoma epitopes, both are nonmutated self peptides that have intermediate and weak MHC binding affinities, respectively. Mutated and truncated versions of these peptides were used to define their MHC binding anchor residues. Anchor residues were then modified to derive peptides with increased MHC binding affinities and T cell stimulatory properties. Ty 56-70 and Ty 448-462 enhance the list of immunogenic HLA-A2-, A24-, and B44-restricted tyrosinase peptides already described. Thus, tyrosinase provides a model for anti-melanoma vaccines in which a single molecule can generate multivalent immunization incorporating both CD4+ and CD8+ T cell responses.