Identification of an immunodominant peptide of HER-2/neu protooncogene recognized by ovarian tumor-specific cytotoxic T lymphocyte lines

Induction of cytotoxic T-lymphocyte responses in vivo after vaccinations with peptide-pulsed dendritic cells

Vaccination of patients with cancer using dendritic cells (DCs) was shown to be effective for B-cell lymphoma and malignant melanoma. Here we provide evidence that patients with advanced breast and ovarian cancer can be efficiently vaccinated with autologous DCs pulsed with HER-2/neu– or MUC1-derived peptides. Ten patients were included in this pilot study. The DC vaccinations were well tolerated with no side effects. In 5 of 10 patients, peptide-specific cytotoxic T lymphocytes (CTLs) could be detected in the peripheral blood using both intracellular IFN-γ staining and 51Cr-release assays. The major CTL response in vivo was induced with the HER-2/neu–derived E75 and the MUC1-derived M1.2 peptide, which lasted for more than 6 months, suggesting that these peptides might be immunodominant. In addition, in one patient vaccinated with the MUC1-derived peptides, CEA- and MAGE-3 peptide-specific T-cell responses were detected after several vaccinations. In a second patient immunized with the HER-2/neu peptides, MUC1-specific T lymphocytes were induced after 7 immunizations, suggesting that antigen spreading in vivo might occur after successful immunization with a single tumor antigen. Our results show that vaccination of DCs pulsed with a single tumor antigen may induce immunologic responses in patients with breast and ovarian cancer. This study may be relevant to the design of future clinical trials of other peptide-based vaccines.

Induction of cytotoxic T-lymphocyte responses in vivo after vaccinations with peptide-pulsed dendritic cells

Vaccination of patients with cancer using dendritic cells (DCs) was shown to be effective for B-cell lymphoma and malignant melanoma. Here we provide evidence that patients with advanced breast and ovarian cancer can be efficiently vaccinated with autologous DCs pulsed with HER-2/neu– or MUC1-derived peptides. Ten patients were included in this pilot study. The DC vaccinations were well tolerated with no side effects. In 5 of 10 patients, peptide-specific cytotoxic T lymphocytes (CTLs) could be detected in the peripheral blood using both intracellular IFN-γ staining and 51Cr-release assays. The major CTL response in vivo was induced with the HER-2/neu–derived E75 and the MUC1-derived M1.2 peptide, which lasted for more than 6 months, suggesting that these peptides might be immunodominant. In addition, in one patient vaccinated with the MUC1-derived peptides, CEA- and MAGE-3 peptide-specific T-cell responses were detected after several vaccinations. In a second patient immunized with the HER-2/neu peptides, MUC1-specific T lymphocytes were induced after 7 immunizations, suggesting that antigen spreading in vivo might occur after successful immunization with a single tumor antigen. Our results show that vaccination of DCs pulsed with a single tumor antigen may induce immunologic responses in patients with breast and ovarian cancer. This study may be relevant to the design of future clinical trials of other peptide-based vaccines.

Generation of tumor-reactive CTL against the tumor-associated antigen HER2 using retrovirally transduced dendritic cells derived from CD34+ hemopoietic progenitor cells

Ag-specific CD8+ CTL are crucial for effective tumor rejection. Attempts to treat human malignancies by adoptive transfer of tumor-reactive CTL have been limited due to the difficulty of generating and expanding autologous CTL with defined Ag specificity. The current study examined whether human CTL can be generated against the tumor-associated Ag HER2 using autologous dendritic cells (DC) that had been genetically engineered to express HER2. DC progenitors were expanded by culturing CD34+ hemopoietic progenitor cells in the presence of the designer cytokine HyperIL-6. Proliferating precursor cells were infected by a retroviral vector encoding the HER2 Ag and further differentiated into CD83+ DC expressing high levels of MHC, adhesion, and costimulatory molecules. Retroviral transduction of DC resulted in the expression of the HER2 molecule with a transduction efficiency of 15%. HER2-transduced DC correctly processed and presented the Ag, because HLA-A*0201-positive DC served as targets for CTL recognizing the HLA-A*0201-binding immunodominant peptide HER2(369-377). HER2-transduced DC were used as professional APCs for stimulating autologous T lymphocytes. Following repetitive stimulation, a HER2-specific, HLA-A*0201-restricted CTL line was generated that was capable of lysing HLA-A*0201-matched tumor cells overexpressing HER2. A CD8+ T cell clone could be generated that displayed the same specificity pattern as the parenteral CTL line. The ability to generate and expand HER2-specific, MHC class I-restricted CTL clones using HER2-transduced autologous DC in vitro facilitates the development of adoptive T cell transfer for patients with HER2-overexpressing tumors without the requirement of defining immunogenic peptides.

A HER2/NEU-derived peptide, a K(d)-restricted murine tumor rejection antigen, induces HER2-specific HLA-A2402-restricted CD8(+) cytotoxic T lymphocytes

We have identified an H-2K(d)-binding peptide, HER2p780 (PYVSRLLGI), derived from murine HER2/neu (HER2), that can induce HER2-specific murine cytotoxic T lymphocytes (CTL). Weekly vaccination of BALB/c mice by syngeneic dendritic cells pulsed with HER2p780 peptide, entirely common to murine and human HER2, suppressed growth of pretransplanted HER2-expressing syngeneic tumors. A HER2-expressing human cancer cell line SKOV3 transfected with murine H-2K(d) cDNA could also be lysed by HER2p780-specific murine CTLs, indicating that human HER2-expressing cancer cells can process and present the cognate peptide in the context of H-2K(d). Since H-2K(d) and HLA-A2402 molecules have similar anchor motifs, the possibility of inducing HER2-specific CTL activity with HER2p780 in HLA-A2402 individuals was examined. CD8(+) CTL clones specific for HER2-expressing cancer cell lines were established from peripheral blood lymphocytes with HLA-A2402 by repeatedly sensitizing with peptide-pulsed autologous dendritic cells as well as peripheral blood mononuclear cells. Detailed analysis of their specificity revealed that the cytotoxicity of CTL clones is specific for the cognate peptide with HLA-A2402 restriction. The results suggest that HER2p780 is a unique peptide that may function as a tumor rejection antigen peptide in HLA-A2402 individuals, as it was directly proven here to function in a murine tumor system.

Pre-existent immunity to the HER-2/neu oncogenic protein in patients with HER-2/neu overexpressing breast and ovarian cancer

Immunomodulatory strategies, such as antibody therapy and cancer vaccines, are increasingly being considered as potential adjuvant therapies in patients with advanced stage breast cancer to either treat minimal residual disease or prevent relapse. However, little is known concerning the incidence and magnitude of the pre-existent breast cancer specific immune response in this patient population. Using the HER-2/neu oncogenic protein as a model, a well-defined tumor antigen in breast cancer, we questioned whether patients with advanced stage HER-2/neu overexpressing breast and ovarian cancers (III/IV) had evidence of pre-existent immunity to HER-2/neu. Forty-five patients with stage III or IV HER-2/neu overexpressing breast or ovarian cancer were evaluated for HER-2/neu specific T cell and antibody immunity. Patients enrolled had not received immunosuppressive chemotherapy for at least 30 days (median 5 months, range 1-75 months). All patients were documented to be immune competent prior to entry by DTH testing using a skin test anergy battery. Five of 45 patients (11%) were found to have a significant HER-2/neu specific T cell response as defined by a stimulation index > or = 2.0 (range 2.0-7.9). None of eight patients who were HLA-A2 had a detectable IFNgamma secreting T-cell precursor frequency to a well-defined HER-2/neu HLA-A2 T cell epitope, p369-377. Three of 45 patients (7%) had detectable HER-2/neu specific IgG antibodies, range 1.2-8.9 microg/ml. These findings suggest that patients with advanced stage HER-2/neu overexpressing breast and ovarian cancer can mount a T cell and/or antibody immune response to their tumor. However, in the case of the HER-2/neu antigen, the pre-existent tumor specific immune response is found only in a minority of patients.

Cytotoxic T-lymphocyte responses elicited to Wilms' tumor gene WT1 product by DNA vaccination

We recently have reported that Wilms' tumor gene WT1 is highly expressed not only in leukemias but also in various types of solid tumors and that WT1 protein is a novel tumor antigen against which cytotoxic T lymphocytes (CTLs) can be elicited by immunization with 9-mer WT1 peptides capable of binding to major histocompatibility complex (MHC) class I molecules. In the present study, plasmid DNA encoding murine full-length WT1 protein was injected intramuscularly into C57BL/6 mice. The mice vaccinated with the WT1 plasmid DNA elicited CTLs against the WT1 protein, and the CTLs specifically killed WT1-expressing tumor cells in a MHC class I-restricted manner. Furthermore, the vaccinated mice rejected the challenges of WT1-expressing tumor cells and survived with no signs of autoimmunity caused by the CTLs. These results demonstrated that vaccination with the WT1 plasmid DNA can elicit CTL responses specific for the WT1 protein, resulting in the acquisition of rejection activity against challenges of WT1-expressing tumor cells. This WT1 DNA vaccination may find clinical application for various types of solid tumors as well as leukemias.

Secretion of CXC chemokine IP-10 by peripheral blood mononuclear cells from healthy donors and breast cancer patients stimulated with HER-2 peptides

CXC chemokines play an important role in recruitment of T cells to the site of activation and regulation of angiogenesis. CXC chemokines are secreted by T cells stimulated with cytokines or by established cytotoxic T lymphocyte (CTL) lines at recognition of conventional antigen (Ag), but the activation requirements and the relationship of interferon-gamma (IFN-gamma) inducible protein (IP-10) secretion with IFN-gamma induction in lymphocytes are still unclear. We studied the induction of IP-10 from nonadherent peripheral blood mononuclear cells (PBMC) by IFN-gamma, interleukin-12 (IL-12), and the HER-2 peptide E75, which forms a CTL-defined antigen. We found that IFN-gamma alone was a weak inducer of IP-10 in these cells, whereas IL-12 was a significantly stronger inducer of IP-10. In the presence of IL-12, the tumor peptide E75 (HER-2, 369-377) was a stronger inducer of IP-10 than was IL-12 alone. E75 and its variants mutated at position 5 could also induce IP-10 in the absence of exogenous IL-12 or IFN-gamma. IP-10 induction by E75 required HLA-A2 presentation and B7-CD28 interactions and was partially inhibited by blocking of CD40-CD40L interactions. These results indicate that presentation of tumor peptides to peripheral T cells can induce a fast chemokine response, which in its early phase may be higher than the IFN-gamma response. This shows that the IP-10 response was independent of any early-phase IFN-gamma response in peripheral T cells. This may be important for understanding the regulation of the balance between chemoattractant chemokines (CC) and CXC chemokines by tumor Ag and may have implications for understanding the mechanisms of polarization of T cells and conditioning of antigen-presenting cells (APC) by tumor antigens.

Identification of genes differentially over-expressed in lung squamous cell carcinoma using combination of cDNA subtraction and microarray analysis

In order to develop effective vaccine products against human cancer, we are interested in identifying genes over-expressed in tumor cells. Through a combination of cDNA library subtraction and microarray technology, we identified seventeen genes preferentially expressed in lung squamous cell carcinoma, including four novel genes. To date, expression profiles of these genes were confirmed by Northern and/or real-time analysis, and several genes were also found to be expressed in head and neck squamous tumors. Thus, these combined methods represent a high throughput approach for identifying tumor specific genes. Furthermore, the report of characterization on these genes will allow them to be exploited for their diagnostic, prognostic, and therapeutic potentials including immunotherapy and antibody based anticancer therapy.

Melanoma vaccines

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

Cancer immunotherapy targeting Wilms' tumor gene WT1 product

The Wilms' tumor gene WT1 is expressed at high levels not only in acute myelocytic and lymphocytic leukemia and in chronic myelocytic leukemia but also in various types of solid tumors including lung cancers. To determine whether the WT1 protein can serve as a target Ag for tumor-specific immunity, three 9-mer WT1 peptides (Db126, Db221, and Db235), which contain H-2Db-binding anchor motifs and have a comparatively higher binding affinity for H-2Db molecules, were tested in mice (C57BL/6, H-2Db) for in vivo induction of CTLs directed against these WT1 peptides. Only one peptide, Db126, with the highest binding affinity for H-2Db molecules induced vigorous CTL responses. The CTLs specifically lysed not only Db126-pulsed target cells dependently upon Db126 concentrations but also WT1-expressing tumor cells in an H-2Db-restricted manner. The sensitizing activity to the Db126-specific CTLs was recovered from the cell extract of WT1-expressing tumor cells targeted by the CTLs in the same retention time as that needed for the synthetic Db126 peptide in RP-HPLC, indicating that the Db126-specific CTLs recognize the Db126 peptide to kill WT1-expressing target cells. Furthermore, mice immunized with the Db126 peptide rejected challenges by WT1-expressing tumor cells and survived for a long time with no signs of autoaggression by the CTLs. Thus, the WT1 protein was identified as a novel tumor Ag. Immunotherapy targeting the WT1 protein should find clinical application for various types of human cancers.

Role of HER2 gene overexpression in breast carcinoma

The HER2 proto-oncogene encodes a transmembrane glycoprotein of 185 kDa (p185(HER2)) with intrinsic tyrosine kinase activity. Amplification of the HER2 gene and overexpression of its product induce cell transformation. Numerous studies have demonstrated the prognostic relevance of p185(HER2), which is overexpressed in 10% to 40% of human breast tumors. Recent data suggest that p185(HER2) is a ligand orphan receptor that amplifies the signal provided by other receptors of the HER family by heterodimerizing with them. Ligand-dependent activation of HER1, HER3, and HER4 by EGF or heregulin results in heterodimerization and, thereby, HER2 activation. HER2 overexpression is associated with breast cancer patient responsiveness to doxorubicin, to cyclophosphamide, methotrexate, and fluorouracil (CMF), and to paclitaxel, whereas tamoxifen was found to be ineffective and even detrimental in patients with HER2-positive tumors. In vitro analyses have shown that the role of HER2 overexpression in determining the sensitivity of cancer cells to drugs is complex, and molecules involved in its signaling pathway are probably the actual protagonists of the sensitivity to drugs. The association of HER2 overexpression with human tumors, its extracellular accessibility, as well as its involvement in tumor aggressiveness are all factors that make this receptor an appropriate target for tumor-specific therapies. A number of approaches are being investigated as possible therapeutic strategies that target HER2: (1) growth inhibitory antibodies, which can be used alone or in combination with standard chemotherapeutics; (2) tyrosine kinase inhibitors (TKI), which have been developed in an effort to block receptor activity because phosphorylation is the key event leading to activation and initiation of the signaling pathway; and (3) active immunotherapy, because the HER2 oncoprotein is immunogenic in some breast carcinoma patients.

Reduced recognition of metastatic melanoma cells by autologous MART-1 specific CTL: relationship to TAP expression

Class I expression in context with T-cell receptor expression is crucial for peptide presentation and induction of CD8+ cytotoxic T lymphocytes (CTL). Presentation of class I bound peptides is dependent on transporter-associated proteins (TAP) expression and function. Tumor infiltrating lymphocytes from a patient with melanoma were isolated, expanded in vitro in the presence of interleukin-2, and tested for cytotoxicity against HLA-A2 positive, MART-1 positive autologous tumor cells, an HLA-A2-positive, MART-1 positive melanoma cell line (Mel-501), and HLA-A2-negative melanoma cells. Significant killing occurred against both A2-positive cell lines (63% and 65%, respectively), but not against the A2-negative line (18%) or A2-positive autologous tumor (1.5%). These CTL preferentially recognized the MART-1 peptide F119, 27-35, and gp100 peptide F125, 280-288, resulting in a 30% to 60% enhancement of lysis when autologous tumor or major histocompatibility complex class I "empty" T2 cells were pulsed with either peptide. To address whether the deficiency in autologous tumor recognition might be related to a deficiency in Ag presentation, we screened for the presence of TAP1 and TAP2 transcripts by polymerase chain reaction, Southern blotting, and scanning densitometry using sequence-specific primers and probes. Both TAP1 and TAP2 expression levels in the autologous tumor were minimal, yet were upregulated 7- to 18-fold, respectively, by interferon-gamma. Despite this increase, a similar increase in cytotoxicity did not occur. In short, deficiencies in TAP presentation may have functional significance for tumor escape from immunosurveillance and with respect to impending vaccine trials.

Poor binding of a HER-2/neu epitope (GP2) to HLA-A2.1 is due to a lack of interactions with the center of the peptide

Class I major histocompatibility complex (MHC) molecules bind short peptides derived from proteins synthesized within the cell. These complexes of peptide and class I MHC (pMHC) are transported from the endoplasmic reticulum to the cell surface. If a clonotypic T cell receptor expressed on a circulating T cell binds to the pMHC complex, the cell presenting the pMHC is killed. In this manner, some tumor cells expressing aberrant proteins are recognized and removed by the immune system. However, not all tumors are recognized efficiently. One reason hypothesized for poor T cell recognition of tumor-associated peptides is poor binding of those peptides to class I MHC molecules. Many peptides, derived from the proto-oncogene HER-2/neu have been shown to be recognized by cytotoxic T cells derived from HLA-A2(+) patients with breast cancer and other adenocarcinomas. Seven of these peptides were found to bind with intermediate to poor affinity. In particular, GP2 (HER-2/neu residues 654-662) binds very poorly even though it is predicted to bind well based upon the presence of the correct HLA-A2.1 peptide-binding motif. Altering the anchor residues to those most favored by HLA-A2.1 did not significantly improve binding affinity. The crystallographic structure shows that unlike other class I-peptide structures, the center of the peptide does not assume one specific conformation and does not make stabilizing contacts with the peptide-binding cleft.

Isolation of broadly reactive, tumor-specific, HLA Class-I restricted CTL from blood lymphocytes of a breast cancer patient

Blood lymphocytes of a HLA-A2 positive breast cancer patient were stimulated with either MCF-7 or MDA-MB-231, i.e., HLA-A2-matched allogeneic breast carcinoma cell lines. Several CD8+ CTL clones with reactivity against the stimulator cells but not against K562 were generated. Reactivity could be blocked with monoclonal antibody (mAb) W6/32, MA2.1, and/or BB7.2, indicating that the clones are HLA-class I and HLA-A2 restricted. The CTL clones generated following stimulation with MCF-7, recognized various other allogeneic HLA-A2+ tumor cell lines, including breast carcinoma, renal cell carcinoma, and melanoma cell lines, but not HLA-A2 tumor cell lines. The CTL clones did not recognize normal HLA-A2+ cells including breast epithelial cells, renal proximal tubular epithelial cells (PTEC), or EBV-transformed B cells including the autologous EBV cell line. In contrast to the CTL clones induced with MCF-7, the reactivity of the clones stimulated with MDA-MB-231, was limited to the stimulator cell MDA-MB-231. Cytotoxicity assays utilizing T2 cells loaded with peptides as target cells indicated that none of the examined CTL-epitopes derived from HER-2/neu, Muc-1, Ep-CAM-1, and p53 were recognized by the CTL clones generated. Our findings underscore that breast cancer is an immunogenic tumor and that HLA-class I-matched allogeneic tumor cells can be used as stimulator cells to generate tumor-specific CTL from peripheral blood of a breast cancer patient with specificity for an antigenic determinant that is broadly expressed on tumor cells from various origins or with specificity limited to the breast cancer stimulator cell.

A Cyclophilin B Gene Encodes Antigenic Epitopes Recognized by HLA-A24-Restricted and Tumor-Specific CTLs

We have studied Ags recognized by HLA class I-restricted CTLs established from tumor site to better understand the molecular basis of tumor immunology. HLA-A24-restricted and tumor-specific CTLs established from T cells infiltrating into lung adenocarcinoma recognized the two antigenic peptides encoded by a cyclophilin B gene, a family of genes for cyclophilins involved in T cell activation. These two cyclophilin B peptides at positions 84–92 and 91–99 induced HLA-A24-restricted CTL activity against tumor cells in PBMCs of leukemia patients, but not in epithelial cancer patients or in healthy donors. In contrast, the modified peptides at position 2 from phenylalanine to tyrosine, which had more than 10 times higher binding affinities to HLA-A24 molecules, could induce HLA-A24-restricted CTL activity against tumor cells in PBMCs from leukemia patients, epithelial cancer patients, or healthy donors. PHA-activated normal T cells were resistant to lysis by the CTL line or by these peptide-induced CTLs. These results indicate that a cyclophilin B gene encodes antigenic epitopes recognized by CTLs at the tumor site, although T cells in peripheral blood (except for those from leukemia patients) are immunologically tolerant to the cyclophilin B. These peptides might be applicable for use in specific immunotherapy of leukemia patients or that of epithelial cancer patients.

Humoral immune responses of cancer patients against "Cancer-Testis" antigen NY-ESO-1: correlation with clinical events

Humoral immune responses against the "Cancer-Testis" (CT) antigen NY-ESO-1 are frequently observed in patients with NY-ESO-1 expressing tumors. This is in contrast to other known tumor antigens (TA) defined by antibody or cytotoxic T cell (CTL) reactivity, i.e., MAGE-1, MAGE-3, SSX2, Melan A, and tyrosinase. No NY-ESO-1 antibody has been detected in healthy controls and patients with NY-ESO-1 negative tumors. In this study, we have assessed the NY-ESO-1 serum antibody response in patients with NY-ESO-1 positive tumors of different histological types and stages using Western blotting and an ELISA. Of the 12 patients analyzed, 10 had demonstrable NY-ESO-1 antibodies at the start of the study. All patients were followed for changes in NY-ESO-1 antibody titers during the course of tumor treatment and clinical evolution. In 4 patients, an increase of NY-ESO-1 antibody titer was observed with progression of disease or extensive tumor necrosis under treatment. One patient showed a stable NY-ESO-1 antibody titer over 3 years along with gradual regression of a large tumor mass. In 5 patients, a decrease of NY-ESO-1 antibody was detected: in 1 patient after curative tumor resection, in 3 patients with partial regression of metastatic disease under chemo- and immunotherapy, and in another patient with a NY-ESO-1 negative tumor relapse. Our results indicate that the induction and maintenance of NY-ESO-1 antibody is dependent on the presence of NY-ESO-1 expressing tumors. Furthermore, changes in NY-ESO-1 antibody titers correlate with the evolution of NY-ESO-1 positive disease.

Dendritic Cells Generated Either from CD34+ Progenitor Cells or from Monocytes Differ in Their Ability to Activate Antigen-Specific CD8+ T Cells

Dendritic cells (DC) can be generated in vitro from monocytes (M-DC) or from CD34+ hemopoietic progenitor cells (CD34-DC) but their precursors are not equivalent cells, prompting a comparison of the functional capacities of these APC. Both types of DCs established from the same individuals using the same cytokines displayed a comparable phenotype of mature DC (CD1a+, CD83+, CD86+, CD4+, HLA-DR++, CD14−, CD15− ) and were equally potent stimulators of allogeneic T cell proliferation, being both more powerful than immature M-DCs. An autologous panel of APCs produced in HLA-A2+ individuals, including CD34-DC, M-DC, monocytes, and EBV-lymphoid cell line was comparatively evaluated for presentation of the Erb-B2 peptide E75 to a CTL line. After short exposures (5 h) to E75-loaded APCs, similar levels of intracellular IFN-γ were induced in Ag-specific CD8+ T cells regardless of APC type. In sustained cultures (4–14 days), more Ag-specific T cells were obtained when peptide was presented on CD34-DC (p < 0.05) rather than on M-DC, EBV-lymphoid cell lines, or monocytes, and these effects were dose-dependent. Activated T cells expressed 4-1BB, and the presence of 4-1BB-Ig fusion protein partially blocked Ag-specific CD8+ cell activation after CD34-DC or M-DC presentation. Our results show that 34-DC have a preferential capacity to activate CD8+ T cells and that this property is not strictly correlated to their ability to induce allogeneic T cell proliferation but due to mechanisms that remain to be defined.

Human tumor antigens for cancer vaccine development

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

Identification of New HER2/neu-Derived Peptide Epitopes That Can Elicit Specific CTL Against Autologous and Allogeneic Carcinomas and Melanomas

Twenty-two new HLA-A2.1-binding peptides derived from the protooncogene HER2/neu were identified and analyzed for their capacity to elicit peptide and tumor-specific CTL responses. We used peptide-pulsed autologous DC from the ascites of patients with ovarian carcinomas to induce CTL. Of the 22 tested new HER2/neu-derived epitopes that could bind HLA-A2 with high (IC50 < 50 nM) or intermediate (50 nM < IC50 < 500 nM) affinity, we report the recognition by CTL of at least four novel epitopes, including HER2(9435), HER2(9665), HER2(9689), and HER2(10952), and confirm that of the known HER2 (9369) epitope. These epitopes were able to elicit CTL that specifically killed peptide-sensitized target cells and, most importantly, a HER2/neu-transfected cell line and the autologous tumor cells. We also confirm that HER2/neu is overexpressed in several melanoma lines, and as a new finding, report that some of these lines are sensitive to CTL induced by the HER2 (9369), HER2(9435), and HER2(9689) epitopes. Finally, CTL clones specific for HER2 (9369), HER2(9435), and HER2(9689) epitopes were isolated from tumor-specific CTL lines, further demonstrating the immunodominance of these epitopes. These findings broaden the potential application of HER2/neu-based immunotherapy.

Cancer gene and immunotherapy: recent developments

Gene and immunotherapeutic approaches to treat human malignant tumors are reviewed. Special attention is given to the different strategies of cancer gene therapy and to recent aspects of cytokine-supported tumor immunotherapy or tumor-specific vaccination. The limitations of these therapy approaches are critically discussed especially with respect to immune escape mechanisms.

Modification of cysteine residues in vitro and in vivo affects the immunogenicity and antigenicity of major histocompatibility complex class I-restricted viral determinants

In studying the subdominant status of two cysteine-containing influenza virus nuclear protein (NP) determinants (NP39-47 and NP218-226) restricted by H-2Kd, we found that the antigenicity of synthetic peptides was enhanced 10-100-fold by treatment with reducing agents, despite the fact that the affinity for Kd was not enhanced. Reducing agents also markedly enhanced the immunogenicity of cysteine-containing peptides, as measured by propagation of long-term T cell lines in vitro. Similar enhancing effects were obtained by substituting cysteine with alanine or serine in the synthetic peptides, demonstrating that sulfhydryl modification of cysteine is responsible for the impaired antigenicity and immunogenicity of NP39-47 and NP218-226. We found similar effects for two widely studied, cysteine-containing peptides from lymphocytic choriomeningitis virus. The major modifications of cysteine-containing synthetic peptides are cysteinylation and dimerization occurring through cysteine residues. We demonstrate that both of these modifications occur in cells synthesizing a cytosolic NP218-226 minigene product and, further, that T cells specific for cysteinylated NP218-226 are induced by influenza virus infection in mice, demonstrating that this modification occurs in vivo. These findings demonstrate that posttranslational modifications affect the immunogenicity and antigenicity of cysteine-containing viral peptides and that this must be considered in studying the status of such peptides in immunodominance hierarchies.

Antibody immunity to the HER-2/neu oncogenic protein in patients with colorectal cancer

The HER-2/neu protein is overexpressed in approximately 20% of human adenocarcinomas and is a defined tumor antigen in breast cancer. The purpose of this study was to evaluate the endogenous HER-2/neu specific antibody response in 57 patients with colorectal cancer. HER-2/neu specific antibodies, titer > or = 1:100, were detected in 14% (8/57) of patients with colorectal cancer compared to none of the normal control population (0/200). Furthermore, detection of HER-2/neu specific antibodies in the cancer population correlated significantly with HER-2/neu protein overexpression in the patients' tumor (p < 0.01). 46% of patients with HER-2/neu overexpressing tumors (6/13) and 5% of HER-2/neu negative tumors (2/44) had detectable HER-2/neu specific antibodies. The endogenous HER-2/neu antibody response in these patients was predominantly IgG or IgA.

Immune responses to all ErbB family receptors detectable in serum of cancer patients

Employing NIH3T3 transfectants with individual human ErbB receptor coding sequences as recombinant antigen sources, we detected by immunoblot analysis specific immunoreactivity against all four ErbB receptors among 13 of 41 sera obtained from patients with different types of epithelial malignancies. Overall, serum positivity was most frequently directed against ErbB2 followed by EGFR, ErbB3 and ErbB4. Specificity patterns comprised tumor patients with unique serum reactivity against ErbB2 or ErbB4. Moreover, approximately half of the positive sera exhibited concomitant reactivity with multiple ErbB receptors including EGFR and ErbB2, EGFR and ErbB4, ErbB2 and ErbB3 or EGFR, ErbB2 and ErbB3. Serum reactivity was confirmed for the respective ErbB receptors expressed by human tumor cells and corroborated on receptor-specific immunoprecipitates. Positive sera contained ErbB-specific antibodies of the IgG isotype. Representative immunohistochemical analysis of tumor tissues suggested overexpression of ErbB receptors for which serum antibodies were detectable in five of six patients. These findings implicate multiple ErbB receptors including ErbB3 and ErbB4 in addition to EGFR and ErbB2 in primary human cancer. Heterogeneity of natural ErbB-specific responses in cancer patients warrants their evaluation in light of immunotherapeutic approaches targeting these receptors.

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.

Identification of HLA-A24 epitope peptides of carcinoembryonic antigen which induce tumor-reactive cytotoxic T lymphocyte

Carcinoembryonic antigen (CEA), which is expressed in several cancer types, is a potential target for specific immunotherapy. HLA-A24 is the most frequent allele among Japanese and is also frequently present in Asians and Caucasians. We tested CEA-encoded HLA-A24 binding peptides for their capacity to elicit anti-tumor cytotoxic T lymphocytes (CTL) in vitro. For this purpose, we used CD8+ T lymphocytes from peripheral blood mononuclear cells (PBMC) of a healthy donor and autologous peptide-pulsed dendritic cells as antigen-presenting cells. This approach enabled us to identify 2 peptides, QYSWFVNGTF and TYACFVSNL, which were capable of eliciting CTL lines that lysed tumor cells expressing HLA-A24 and CEA. The cytotoxicity to tumor cells by the CTL lines was antigen-specific since it was inhibited by peptide-pulsed cold target cells as well as by anti-class I major histocompatibility complex (MHC) and anti-CD3 monoclonal antibodies (MAbs). The antigen specificity of the 2 CTL lines was examined using several tumor cell lines of various origins and for their peptide-dose responses. The identification of these novel CEA epitopes for CTL offers the opportunity to design and develop epitope-based immunotherapeutic approaches for treating HLA-A24+ patients with tumors that express CEA.

Ovarian and breast cytotoxic T lymphocytes can recognize peptides from the amino enhancer of split protein of the Notch complex

In this study we investigated recognition by ovarian tumor associated lymphocyte (OVTAL), and breast tumor associated lymphocytes (BRTAL), of peptides corresponding to the sequence 125-135 of the Aminoenhancer of split (AES) protein. Three of these peptides designated as G75:AES1/2 (128-135), G60: AES1/2 (127-137) and G61: AES1/2 (125-133) correspond to the wildtype AES sequence, while the fourth G76:GPLTPLPV, AES1/2 (128-135) corresponds to a variant sequence of the peptide G75 with the N-terminal Leu substituted to glycine. These sequences were chosen for study because mass-spectrometric analysis (MS) of a CTL active HPLC peptide fraction eluted from immunoaffinity precipitated HLA-A2 molecule, revealed: (a) the presence of an ion with a mass-to-charge ratio (m/z) of 793 which was more abundant than other ions of similar masses; (b) the tentatively reconstituted sequence of the ion 793 matched the sequence of peptide G76. We found that AES peptides G75 (128-135) and G76 (128-135) (L128G) reconstituted CTL recognition at concentrations ranging between 200-500 nM. These concentrations are lower than concentrations reported to activate effector function of CTL recognizing other epithelial tumor Ag. Furthermore, analysis with cloned CD8+ T cells indicated that G75 and G76 were not cross-reactive specificities, suggesting a key role for the N-terminal residues of the variant peptide in dictating specificities. Since the AES proteins are part of a set of transcriptional repressors encoded by the Enhancer of split [E(spl)] genes, and since these repressors are activated to suppress cell differentiation in response to Notch receptors signalling, the AES peptides may represent a novel class of self-antigens that deserve further consideration as tumor Ag in epithelial cancers.

Ovarian cancer-associated lymphocyte recognition of folate binding protein peptides

BACKGROUND

Tumor-associated lymphocytes (TAL) isolated from ovarian cancer patients contain cytotoxic T lymphocytes (CTL) capable of recognizing specific HLA/peptide complexes on tumor cells leading to tumor cell lysis. Currently, HER2/neu, overexpressed in only 30% of breast and ovarian cancers, is the only known source of CTL-recognized peptides in epithelial cancers. Therefore, we have investigated peptides derived from folate binding protein (FBP), which is over-expressed in more than 90% of ovarian cancers and in the majority of other epithelial tumors.

METHODS

TAL were isolated from the malignant ascites of four consecutive HLA-A2+ ovarian cancer patients and incubated in IL-2. Initial chromium-release assays were performed within 1 week. T2 cells, incubated with peptide, were used to reconstitute T cell epitopes. The FBP sequence was interrogated for HLA-A2 binding peptides, and five were synthesized (E37-41).

RESULTS

Freshly cultured, unstimulated ovarian TAL recognize peptides derived from FBP. These peptides are presented in the context of HLA-A2, and are specifically recognized in a HLA class I-restricted fashion. TAL recognition of these reconstituted T cell epitopes is concentration dependent. Furthermore, the FBP peptides are shown by cold target inhibition studies to be naturally processed and presented antigens.

CONCLUSIONS

FBP peptides are recognized by freshly isolated TAL from ovarian cancer patients, suggesting in vivo expression and sensitization. Because FBP is over-expressed 20-fold in most adenocarcinomas, these peptides may be used in a widely applicable peptide-based vaccine for epithelial tumors.

Bone marrow-derived dendritic cells pulsed with a tumor-specific peptide elicit effective anti-tumor immunity against intracranial neoplasms

Although the central nervous system (CNS) is often regarded as an immunologically privileged site, it is well established that specific CNS immunoreactivity can be generated through peripheral vaccination with CNS antigens. Dendritic cells (DC) are potent antigen presenting cells of hematopoietic origin that have emerged as a promising tool for cancer immunotherapy capable of evoking significant anti-tumor immunity when pulsed with tumor-associated peptides. To explore a role for DC-based immunization strategies for the treatment of CNS tumors, we developed a brain tumor model using the C3 sarcoma cell line which expresses the tumor-specific, major histocompatibility complex (MHC) class I-restricted peptide epitope E7(49-57). Syngeneic C57Bl/6 mice receiving intravenous (i.v.) injections of bone marrow-derived DCs pulsed with E7 peptide were effectively protected against a subsequent intracerebral challenge with C3 tumor cells. More importantly, this systemic immunization strategy was effective in a therapy model as 67% of animals (10 of 15) with established (day 7) intracerebral C3 tumors treated with 3 weekly injections of E7 peptide-pulsed DCs achieved a long-term survival (>90 days) while no control animals survived beyond day 41. In vivo depletion of CD8+ cells, but not CD4+ or asialo-GM1+ cells, abrogated the efficacy of E7 peptide-pulsed DC therapy of established tumors, indicating a pivotal role of specific CD8+ T-cell responses in mediating the anti-tumor effect. Our findings support the hypothesis that effective CNS anti-tumor immunoreactivity can be generated with DC-based tumor vaccines.

Identification of HER2/neu-derived peptide epitopes recognized by gastric cancer-specific cytotoxic T lymphocytes

We have derived HLA-A2.1-restricted, gastric cancer-specific cytotoxic T lymphocyte (CTL) lines by repetitive in vitro stimulation of tumor-associated lymphocytes (TAL) with autologous tumor cells. The HER2/neu specificity of these gastric cancer-specific CTLs was demonstrated using HER2/neu-transfected cell lines and HER2/neu-expressing tumors, and with a set of HER2/neu-derived peptide epitopes. Gastric cancer-specific CTLs specifically lysed autologous and allogeneic HLA-A2.1+, HER2/neu+ gastric cancer cells, HER2/neu-transfected C1R/A2 cell lines (HLA-A2.1+, HER2+) and HLA-A2.1-transfected SW626 tumor cell lines (HLA-A2.1+, HER2+). This recognition could be inhibited by anti-HLA-A2 antibody or by cold target HER2/neu-transfected C1R/A2 cells. Our results demonstrate that the HER2/neu-encoded HLA-A2.1-associated epitopes recognized by CTLs are presented as naturally processed peptides on gastric cancer lines. Furthermore, 3 of 19 tested HER2/neu-derived peptide epitopes [HER2(9(106)), HER2(9(369)), HER2(9(689))], which all bound HLA-A2.1 with high (IC50 < 50 nM) affinity, were able to sensitize HLA-A2+ C1R/A2 cells to be recognized by the gastric cancer-specific CTLs, demonstrating the immunodominance of these epitopes. In conclusion, our findings implicate HER2/neu-derived epitopes as potential candidates for novel immunotherapy and vaccine strategies against gastric cancer.

Generation of Human Cytolytic T Lymphocyte Lines Directed Against Prostate-Specific Antigen (PSA) Employing a PSA Oligoepitope Peptide

Prostate-specific Ag (PSA), which is expressed in a majority of prostate cancers, is a potential target for specific immunotherapy. Previous studies have shown that two 10-mer PSA peptides (designated PSA-1 and PSA-3) selected to conform to human HLA class I-A2 motifs can elicit CTL responses in vitro. A longer PSA peptide (30-mer) designated PSA-OP (oligoepitope peptide), which contains both the PSA-1 and PSA-3 HLA-A2 epitopes and an additional potential CTL epitope (designated PSA-9) for the HLA-class I-A3 allele, was investigated for the ability to induce cytotoxic T cell activity. T cell lines from different HLA-A2 and HLA-A3 donors were established by in vitro stimulation with PSA-OP; the CTL lines lysed PSA-OP as well as PSA-1- or PSA-3-pulsed C1R-A2 cells, and PSA-OP and PSA-9-pulsed C1R-A3 cells, respectively. The CTL lines derived from the PSA-OP peptide also lysed PSA-positive prostate cancer cells. PSA-OP-derived T cell lines also lysed recombinant vaccinia-PSA-infected targets but not targets infected with wild-type vaccinia. PSA-OP did not bind HLA-A2 and HLA-A3 molecules. The decrease in cytotoxicity in the presence of protease inhibitors suggests that the PSA-OP is cleaved into shorter peptides, which in turn can interact with HLA-class I molecules and, as a consequence, induce CTL-mediated lysis. We have also demonstrated that it is possible to induce CTL responses in HLA-A2.1/Kb transgenic mice by immunization with PSA-OP with adjuvant. These studies thus provide evidence that oligopeptides such as PSA-OP may be useful candidates for peptide-based cancer vaccines.

Growth and antigen recognition of tumor-infiltrating lymphocytes from human breast cancer

In the present study, we isolated tumor-infiltrating lymphocytes (TIL) from 21 primary solid tumors and tumor-associated lymphocytes (TAL) from 9 malignant effusions, respectively, of breast cancer patients. Significant proliferation and expansion of T cells was observed in 23 of 30 distinct samples. TIL were isolated from primary tumors by either enzymatic digestion or mechanical disruption. The TIL cultures were initiated using OKT3 mAb in the presence of moderate concentrations (25-50 U/ml) of IL-2, followed by 100 U/ml of tumor necrosis factor (TNF)-alpha. TAL were not stimulated with OKT3 mAb, but all were successfully expanded in culture in the presence of IL-2 alone or together with TNF-alpha. Seven of nine distinct TAL grew in culture as predominantly CD4+ lines. In contrast, only 14 of 21 (66%) of primary breast TIL expanded in culture and were predominantly of CD8+ phenotype. Autologous tumor lysis was observed in seven of eight cases tested. Only one of the four TIL tested and one of the four TAL tested preferentially lysed autologous tumor. HER-2 peptide E75 (369-377) was recognized by two TIL lines of the five primary TIL tested and three of the four TAL tested. This suggests that E75 may be recognized by primary breast tumors. This may be of interest in developing vaccine strategies for therapeutic management of breast cancer.

An Antigen Recognized by Autologous CTLs on a Human Bladder Carcinoma

By stimulating blood lymphocytes with autologous bladder carcinoma cells that had been transfected with B7-1, we obtained a panel of CTL clones which lyse specifically the bladder tumor cells in an MHC class I-restricted fashion. Based on inhibition with anti-HLA Abs and the recognition of allogeneic tumor cells, we could distribute our clones in three groups that recognized three distinct Ags. We characterized one of these Ags by screening a cDNA library prepared with the RNA from this bladder tumor line. This new tumor Ag is a peptide presented by HLA-B4403 molecules. It is produced by a point mutation in a gene that is recorded in databases under the name KIAA0205, is ubiquitously expressed, and whose function is unknown. We also found this mutation in the tumor sample that was originally resected from this patient, but the mutation was not found in the 100 or more independent tumors of various histologic types that were tested. This report is the first to describe the isolation of CTL clones directed against human bladder cancer and the molecular characterization of a bladder tumor Ag.

Use of cellular and cytokine adjuvants in the immunotherapy of cancer

Cellular and cytokine adjuvants, often immune effector cells and soluble factors, respectively, are supplemental and/or follow-up treatments of human origin for cancer patients who have unsatisfactory clinical responses to conventional chemotherapy, radiotherapy, and surgery. Since many human studies with these reagents are in their infancy, extensive data collection is only now being performed to determine which strategy provides the greatest therapeutic benefit. Research published in the literature since the genesis of this approach to cancer treatment is summarized in this report. Methodologies attempting to generate anticancer responses by provoking or enhancing the patient's own immune system are new compared with the other standard types of cancer treatment. Although a few encouraging human studies can be discussed, many of the most promising techniques are only now being transferred from the laboratory to the clinic. The administration of immune effector cells in combination with immunomodulators, such as interferons or interleukins, often enhances clinical outcome. The literature cited in this report indicate that immune-cell- and cytokine-based therapies hold promise in our attempts to improve the quality and duration of life in those with cancer. With each report reaching the literature, more effective clinical trials are being designed and implemented.

Identification of HLA-A2-restricted epitopes of the tumor-associated antigen MUC2 recognized by human cytotoxic T cells

Previous studies have shown that self-antigens overexpressed in malignant tissue can provide a basis for a tumor-specific immune response. The mucin MUC2 is strongly overexpressed in all mucinous tumors of colon, breast, ovary and pancreas. In the corresponding normal tissue it is either not expressed (breast, ovary, pancreas) or it is expressed at considerably lower levels than in the mucinous tumors (colon). We therefore investigated whether the MUC2 molecule comprises HLA-A2-binding epitopes recognized by human cytotoxic T cells. Four MUC2 peptides with high affinity and stable binding to HLA-A2 were identified. Those peptides and additionally 3 peptides with moderate binding to HLA-A2 were loaded onto dendritic cells, which were used for stimulation of autologous T cells from healthy donors. Two MUC2 peptides, which belonged to the group of stable binders, induced specific cytotoxic T-cell lines. Target cells loaded with these peptides were strongly lysed in a concentration-dependent and HLA-A2-restricted manner. Our data show that the tumor-associated mucin MUC2 has potential as a target antigen for cytotoxic T cells in patients with mucinous carcinomas.

Human HER-2/neu protein immunization circumvents tolerance to rat neu: a vaccine strategy for 'self' tumour antigens

Many newly defined tumour antigens are 'self' proteins. Immunizing cancer patients against these antigens may be difficult due to tolerance. The HER-2/neu oncogenic protein is such a 'self' tumour antigen. Rat neu is homologous with human HER-2/neu and provides a model system for studying vaccination strategies. Rats are tolerant to rat neu. Vaccination with this 'self' protein elicits no detectable immune response. The current studies evaluated whether tolerance to rat neu can be circumvented by immunizing with the highly homologous foreign human HER-2/neu protein. Rats were immunized with human HER-2/neu intracellular domain (hICD) protein that is 92% homologous to rat neu ICD. Animals immunized with hICD developed significant antibody and T-cell responses that were specific for both human HER-2/neu and rat neu. Neu-specific antibodies were present in titres of greater than 1:200,000. Analysis of the specificity of the antibody response using synthetic peptides demonstrated substantial reactivity to an epitope with 100% homology between rat and human protein. Significant T-cell responses (stimulation index > 10) to hICD and rat neu protein (stimulation index > 4) were detected. The T cells also responded to both human and rat ICD. The results imply that immunization with foreign proteins, which are highly homologous to 'self' tumour antigens, may be an effective vaccine strategy for 'self' tumour antigens.

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.

Growth stimulation of tumor-specific cytotoxic T lymphocytes on concanavalin a-immobilized carrier beads

Human tumor-specific CD4(+) cytotoxic T lymphocytes (CTL) were generated against duodenum papilloma cell line TGBC18TKB from HLA type-matched peripheral blood mononuclear cells. Concanavalin A (Con A) immobilized on carrier beads stimulated growth of the CTL in a long-term culture without repeated antigen stimulation, while soluble Con A induced death of the CTL. The CTL exhibited the target-specific cytotoxicity in a more potent manner than those before the long-term culture in the presence of the immobilized Con A. Enhanced expression of the adhesion molecule, CD11b, was observed on the CTL. These results suggest that immobilized Con A will be useful for continuous growth stimulation and large scale expansion of CTL without tumor antigen.

The multi-epitope approach for immunotherapy for cancer: identification of several CTL epitopes from various tumor-associated antigens expressed on solid epithelial tumors

One approach to development of specific cancer immunotherapy relies on the induction of cytotoxic T lymphocytes (CTL) specific for tumor-associated antigens (TAA). Induction of TAA-specific CTL could be used towards the eradication of established tumors, or to prevent their dissemination or recurrence after primary treatment. The present study identifies a set of CTL epitopes from TAA frequently found on solid epithelial tumors such as breast, lung and gastro-intestinal tumors. Specifically, HLA-A2.1 binding peptides from the MAGE2, MAGE3, HER-2/neu and CEA antigens were tested for their capacity to elicit in vitro anti-tumor CTL using lymphocytes from normal volunteers and autologous dendritic cells as antigen-presenting cells. A total of 6 new epitopes (MAGE2[10(157)], MAGE3[9(112)], CEA[9(691)], CEA[9(24)], HER2[9(435)] and HER2[9(5)]) were identified which were capable of specifically recognizing tumor cell lines lines expressing HLA-A2.1 and the corresponding TAA. In one case (CEA[9(24)]), induction of vigorous anti-tumor CTL responses required epitope engineering to increase HLA-A2.1 binding affinity. Finally, most of the newly identified epitopes (5 out of 6) were found to be highly crossreactive with other common HLA alleles of the A2 supertype (A2.2, A2.3, A2.6 and A6802), thus demonstrating their potential in providing broad and non-ethnically biased population coverage. The results are discussed in the context of the development of multi-epitope-based therapies with broad applicability for patients suffering from commonly found tumors.