Recognition of prostate and breast tumor cells by helper T lymphocytes specific for a prostate and breast tumor-associated antigen, TARP.

PURPOSE: T cell-based immunotherapy via the in vitro or in vivo expansion of prostate tumor-associated antigen (TAA)-specific T lymphocytes is one of the most promising therapeutic approaches to treat prostate cancer. T-cell alternate reading frame protein (TARP) is a mitochondrial protein that is specifically expressed in prostate epithelial cells. We have done experiments aimed at identifying helper T lymphocyte (HTL) epitopes for TARP for the design of T cell-based immunotherapy for prostate cancer. EXPERIMENTAL DESIGN: Dendritic cells from normal donors were pulsed with synthetic peptides derived from TARP, which were predicted to serve as HTL epitopes. These dendritic cells were used to stimulate CD4(+) T cells in vitro to trigger HTL responses against TARP. T-cell responses to these peptides were also studied with lymphocytes from prostate cancer patients. RESULTS: The two peptides, TARP(1-14) and TARP(14-27), were shown to elicit effective in vitro HTL responses using lymphocytes from both normal volunteers and prostate cancer patients. Peptide TARP(1-14)-reactive HTLs were found restricted by HLA-DR53 and could recognize naturally processed protein antigen derived from tumor cells, which was presented by autologous dendritic cells. Most significantly, stimulation with peptide TARP(14-27) generated four HTL lines restricted by HLA-DR1, HLA-DR9, HLA-DR13, and HLA-DR15, some of which capable of recognizing naturally processed antigens presented by dendritic cell or directly by TARP-positive tumor cells. CONCLUSIONS: Our results show that TARP constitutes a TAA that can be recognized by tumor-reactive HTL. The newly described TARP epitopes could be used to optimize and improve T-cell epitope-based immunotherapy against prostate and other tumors expressing TARP.     

Determination of cellularly processed HLA-A2402-restricted novel CTL epitopes derived from two cancer germ line genes, MAGE-A4 and SAGE.

PURPOSE: For identification of CTL epitopes useful for cancer vaccines, it is crucial to determine whether cognate epitopes are presented on the cell surface of target cancer cells through natural processing of endogenous proteins. For this purpose, we tried to use the cellular machinery of both mice and human to define naturally processed CTL epitopes derived from two "cancer germ line" genes, MAGE-A4 and SAGE. EXPERIMENTAL DESIGN: We vaccinated newly produced HLA-A2402 transgenic mice with DNA plasmids encoding target antigens. Following screening of synthesized peptides by splenic CD8(+) T cells of vaccinated mice, we selected candidate epitopes bound to HLA-A2402. We then examined whether human CD8(+) T cells sensitized with autologous CD4(+) PHA blasts transduced by mRNA for the cognate antigens could react with these selected peptides in an HLA-A2402-restricted manner. RESULTS: After DNA vaccination, murine CD8(+) T cells recognizing MAGE-A4(143-151) or SAGE(715-723) in an HLA-A2402-restricted manner became detectable. Human CTLs specific for these two peptides were generated after sensitization of HLA-A2402-positive CD8(+) T cells with autologous CD4(+) PHA blasts transduced with respective mRNA. CTL clones were cytotoxic toward tumor cell lines expressing HLA-A2402 and cognate genes. Taken together, these CTL epitopes defined in HLA-A24 transgenic mice are also processed and expressed with HLA-A2402 in human cells. The presence of SAGE(715-723)-specific precursors was observed in HLA-A2402-positive healthy individuals. CONCLUSIONS: Two novel HLA-A2402-restricted CTL epitopes, MAGE-A4(143-151) and SAGE(715-723), were identified. Our approach assisted by cellular machinery of both mice and human could be widely applicable to identify naturally processed CTL epitopes.     

The polycomb group proteins, BMI-1 and EZH2, are tumour-associated antigens

We used SEREX technology to identify novel tumour-associated antigens in patients with primary hepatocellular carcinoma and found serological responses to the polycomb group (PcG) protein BMI-1, which is overexpressed in a range of different tumour types. Further studies identified T-cell responses to both BMI-1 and another PcG protein, EZH2, in cancer patients and at relatively lower levels in some normal donors. We next identified several CD8+ T-cell epitopes derived from BMI-1 and EZH2 and demonstrated that EZH2-derived peptides elicited more significant interferon-gamma (IFN-gamma) release than BMI-1-derived peptides. That CD8(+) T cells were responsible for the observed responses was confirmed for EZH2 by both IFN-gamma capture assays and tetramer staining using an HLA-A0201-restricted, EZH2-derived YMSCSFLFNL (aa 666-674) epitope. The ability of YMSCSFLFNL (aa 666-674) to stimulate the in vitro expansion of specific T cells from peripheral blood lymphocytes was greatly enhanced when the CD25(+) T-cell population was depleted. EZH2-specific cytotoxic T lymphocyte clones specific for two HLA-A0201 epitopes were generated and found to recognise endogenously processed EZH2 in both HLA-matched fibroblasts and tumour cell lines. Given the widespread overexpression of PcG proteins in cancer and their critical role in oncogenesis, these data suggest that they may be useful targets for cancer immunotherapy.     

Characterization of the role of CD8+T cells in breast cancer immunity following mammaglobin-A DNA vaccination using HLA-class-I tetramers

INTRODUCTION: Mammaglobin-A(mam-A) is expressed in over 80% of human breast tumors. We recently reported that mam-A DNA vaccination resulted in breast cancer immunity in a preclinical model. Here we investigated whether mam-A HLA-class-I tetramers could be used to monitor and define the role of CD8(+)cytotoxic T-lymphocytes(CTL) in mediating breast cancer immunity following mam-A DNA vaccination. STUDY DESIGN: Mam-A DNA vaccination was performed in HLA-A2(+)huCD8(+ )transgenic mice. HLA-A2 tetramers carrying the immunodominant mamA2.1 peptide were used to monitor CD8(+)CTL. Human breast cancer colonies were developed in immunodeficient SCID-beige mice. ELISPOT was used to correlate frequency of mamA2.1 tetramer(+)CD8(+)T cells and IFN-gamma production [spots per million cells (spm)] in human subjects. RESULTS: Vaccination of HLA-A2(+)huCD8(+) mice with mam-A DNA vaccine, but not empty vector, led to the expansion of mamA2.1 tetramer(+)CD8(+)T-cells in peripheral blood (<0.5% pre-vaccination compared to >2.0% post-vaccination). CD8(+)T cells from vaccinated mice specifically lysed UACC-812(HLA-A2(+)/mam-A(+), 25% lysis) but not MDA-MB-415(HLA-A2(-)/mam-A(+)) or MCF-7(HLA-A2(+)/mam-A(-)) breast cancer cells. Adoptive transfer of purified CD8(+)T cells from vaccinated mice into immunodeficient SCID-beige mice with established human breast cancer colonies led to tetramer(+)CD8(+ )T-cell infiltration with regression of UACC-812 but not MCF-7 tumors. HLA-A2(+) breast cancer patients revealed increased frequency of mamA2.1 tetramer(+)CD8(+ )T-cells compared to normal controls (2.86 +/- 0.8% vs. 0.71 +/- 0.1%, P = 0.01) that correlated with the IFN-gamma response to mamA2.1 peptide (48.1 +/- 20.9 vs. 2.9 +/- 0.8 spm, P = 0.03). CONCLUSIONS: CD8(+ )T-cells are crucial in mediating breast cancer immunity following mam-A DNA vaccination. Mam-A HLA-class-I tetramers can be effectively used to monitor development of CD8(+ )T-cells following mam-A vaccination.     

Responses of human T cells to peptides flanking the tandem repeat and overlapping the signal sequence of MUC1

The epithelial mucin MUC1 is one of the few tumour-associated antigens identified for breast cancer. Several MUC1-derived peptides binding HLA-A*0201 molecules have been identified that correspond to sequences outside the tandem repeat. Immunisation with some of these peptides induces protective antitumour immunity in mice. Another HLA-A*0201-binding peptide has been identified in a human system. We have evaluated the CD8(+) T-cell responses to all these peptides using peripheral blood lymphocytes from breast cancer patients and normal donors. Specific CD8(+) T-cell responses could be generated in vitro against some of these peptides but only after several rounds of in vitro restimulation, and they did not recognise human cells endogenously expressing the antigen. Nevertheless, T cells recognised by HLA-A*0201 tetramers carrying a peptide from the signal sequence (LLLLTVLTV) could be detected in the peripheral blood of some HLA-A*0201(+) breast cancer patients but not in healthy adults. This peptide is the only one of those tested which was identified in the human system, and the results emphasize the potential problems involved in translation of data from laboratory animal models to the human system.     

Recognition of breast cancer cells by CD8+ cytotoxic T-cell clones specific for NY-BR-1

Immunotherapy for breast cancer using cytotoxic T cells (CTL) is hindered by the lack of well-characterized breast cancer antigens that are expressed in most breast tumor cells and recognized by CD8+ CTL. A recently described breast tissue differentiation antigen, NY-BR-1, is expressed in >80% breast tumors and elicits a humoral response in a subset of breast cancer patients. To identify potential NY-BR-1 epitopes that are recognized by CTL, CD8+ T cells were stimulated in vitro with autologous dendritic cells pulsed with NY-BR-1 peptides that were predicted to bind to HLA-A2. In multiple normal female donors and breast cancer patients, specific CD8+ CTL responses were detected by enzyme-linked immunospot assay against several NY-BR-1 peptides after two cycles of stimulation. CD8+ CTL clones against three NY-BR-1 epitopes were isolated and recognized peptide-pulsed target cells with high avidity. T-cell clones specific for one of the NY-BR-1 epitopes (p904) also recognized breast tumor cells expressing NY-BR-1, NY-BR-1(-) cells transfected with a cDNA encoding the NY-BR-1 protein, and autologous dendritic cells pulsed with opsonized NY-BR-1+ breast tumor cells. Taken together, these results show that the p904 epitope derived from NY-BR-1 is efficiently processed and presented endogenously and identify NY-BR-1 as a promising target for T-cell-based immunotherapy for breast cancer.     

Elevated frequencies of self-reactive CD8+ T cells following immunization with a xenoantigen are due to the presence of a heteroclitic CD4+ T-cell helper epitope

Immunization of mice with human dopachrome tautomerase (hDCT) provides greater protection against melanoma than immunization with the murine homologue (mDCT). We mapped the CD8(+) and CD4(+) T-cell epitopes in both proteins to better understand the mechanisms of the enhanced protection. The dominant CD8(+) T-cell epitopes were fully conserved between both proteins, yet immunization with hDCT produced frequencies of CD8(+) T cells that were 5- to 10-fold higher than immunization with mDCT. This difference was not intrinsic to the two proteins because comparable frequencies of CD8(+) T cells were elicited by both antigens in DCT-deficient mice. Strikingly, only hDCT elicited a significant level of specific CD4(+) T cells in wild-type (WT) mice. The murine protein was not devoid of CD4(+) T-cell epitopes because immunization of DCT-deficient mice with mDCT resulted in robust CD4(+) T-cell immunity directed against two epitopes that were not identified in WT mice. These results suggested that the reduced immunogenicity of mDCT in WT mice may be a function of insufficient CD4(+) T-cell help. To address this possibility, the dominant CD4(+) T-cell epitope from hDCT was introduced into mDCT. Immunization with the mutated mDCT evoked CD8(+) T-cell frequencies and protective immunity comparable with hDCT. These results reveal a novel mechanism by which xenoantigens overcome tolerance. Our data also suggest that immunologic tolerance is more stringent for CD4(+) T cells than CD8(+) T cells, providing a mechanism of peripheral tolerance where autoreactive CD8(+) T cells fail to be activated due to a lack of autoreactive CD4(+) T cells specific for the same antigen.     

Improved detection of melanoma antigen-specific T cells expressing low or high levels of CD8 by HLA-A2 tetramers presenting a Melan-A/Mart-1 peptide analogue.

MHC class I tetramers containing peptide epitopes are sensitive tools for detecting antigen-specific CD8(+) T-cell responses. We demonstrate here that binding of HLA-A2 tetramers to CD8(+) T cells specific for the melanoma-associated antigen Melan-A/MART-1 can be fine-tuned by altering either the bound peptide epitope or residues in the alpha 3 domain of HLA-A2, which is important for CD8 binding. Antigen-specific T cells expressing high levels of CD8 could be detected using HLA-A2 tetramers containing the peptide AAGIGILTV, an epitope which is naturally processed and presented from Melan-A/MART-1. In contrast, low CD8-expressing, antigen-specific T cells could be detected efficiently only by using a mutated HLA-A2 tetramer with an altered CD8 binding site or, less efficiently, using the wild-type HLA-A2 tetramer loaded with the peptide analogue ELAGIGILTV, which is superior in stimulating antigen-specific T-cell responses. Our results suggest ways to optimize the identification and expansion of antigen-specific T cells with different requirements for the costimulatory CD8 molecule in facilitating T-cell receptor binding to peptide variants.     

Naturally occurring T-cell response against mutated p21 ras oncoprotein in pancreatic cancer.

Mutated p21 ras proteins (muRas) are present in approximately 90% of pancreatic adenocarcinomas and express mutants which can function as cancer-specific antigens. To evaluate the frequency and magnitude of the natural T-cell response against muRas in 19 HLA-A2-positive patients with muRas-positive pancreatic carcinomas, antigen-experienced T lymphocytes in fresh peripheral blood mononuclear cells were shown by IFN-gamma enzyme-linked immunospot using muRas peptides (5-21) that encompass both HLA class I (HLA-A2)- and class II-restricted (HLA-DRB1) epitopes. Six of 19 patients (32%) were found to have a specific T-cell response against individual mutation-specific ras(5-21) but not against other ras mutations or wild-type ras. In contrast, none of 19 healthy subjects had T cells specifically secreting IFN-gamma (P = 0.004). The T-cell response consisted of both CD8(+) and CD4(+) T cells but was dominated by CD8 T cells in three of four patients. MuRas(5-14) and muRas(6-14) were shown to specifically induce CD8(+) T-cell mediated cytotoxicity against HLA-A2-positive, muRas-bearing pancreatic carcinoma cells. The T-cell response was not correlated with prognostic or clinical variables such as tumor-node-metastasis status, stage, or survival. In conclusion, a natural T-cell response against muRas proteins that could be exploited for immunostimulatory therapeutic approaches has been shown in a significant proportion of patients with pancreatic cancer.     

Simultaneous generation of CD8+ and CD4+ melanoma-reactive T cells by retroviral-mediated transfer of a single T-cell receptor

Adoptive immunotherapy of cancer requires the generation of large numbers of tumor antigen-reactive T cells for transfer into cancer patients. Genes encoding tumor antigen-specific T-cell receptors can be introduced into primary human T cells by retroviral mediated gene transfer as a potential method of providing any patient with a source of autologous tumor-reactive T cells. A T-cell receptor-specific for a class I MHC (HLA-A2)-restricted epitope of the melanoma antigen tyrosinase was isolated from a CD4(+) tumor-infiltrating lymphocyte (TIL 1383I) and introduced into normal human peripheral blood lymphocytes by retroviral transduction. T-cell receptor-transduced T cells secreted various cytokines when cocultured with tyrosinase peptide-loaded antigen-presenting cells as well as melanoma cells in an HLA-A2-restricted manner, and could also lyse target cells. Furthermore, T-cell clones isolated from these cultures showed both CD8(+) and CD4(+) transduced T cells could recognize HLA-A2(+) melanoma cells, giving us the possibility of engineering class I MHC-restricted effector and T helper cells against melanoma. The ability to confer class I MHC-restricted tumor cell recognition to CD4(+) T cells makes the TIL 1383I TCR an attractive candidate for T-cell receptor gene transfer-based immunotherapy.     

Prostate stem cell antigen: Identification of immunogenic peptides and assessment of reactive CD8+ T cells in prostate cancer patients

Identification of TAAs recognized by CD8(+) CTLs paved the way for new concepts in cancer therapy. In view of the heterogeneity of tumors and their diverse escape mechanisms, CTL-based cancer therapy largely depends on an appropriate number of TAAs. In prostate cancer, the number of antigens defined as suitable targets of CTLs remains rather limited. PSCA is widely distributed in prostate cancer. In this report, we define immunogenic peptides of PSCA which are recognized by circulating CD8(+) T cells from prostate cancer patients and able to activate CTLs in vitro. Screening the amino acid sequence of PSCA for peptides containing a binding motif for HLA-A*0201 resulted in 8 candidate peptides. Specificity and affinity of peptide binding were verified in a competition assay. Frequencies of CD8(+) T lymphocytes reactive against selected epitopes were determined in the blood of prostate cancer patients using the ELISPOT assay. Increased frequencies were revealed for CD8(+) T cells recognizing the peptides ALQPGTALL and AILALLPAL. CTLs from prostate cancer patients were raised against these 2 peptides in vitro when presented by autologous DCs. They specifically recognized peptide-pulsed T2 target cells and prostate cancer cells that were HLA-A*0201- and PSCA-positive, indicating that these peptides were naturally generated by tumor cells. These data suggest that PSCA is a promising target for the immunotherapy of prostate cancer.     

NY-ESO-1 protein formulated in ISCOMATRIX adjuvant is a potent anticancer vaccine inducing both humoral and CD8+ t-cell-mediated immunity and protection against NY-ESO-1+ tumors.

NY-ESO-1 is a 180 amino-acid human tumor antigen expressed by many different tumor types and belongs to the family of "cancer-testis" antigens. In humans, NY-ESO-1 is one of the most immunogenic tumor antigens and NY-ESO-1 peptides have been shown to induce NY-ESO-1-specific CD8(+) CTLs capable of altering the natural course of NY-ESO-1-expressing tumors in cancer patients. Here we describe the preclinical immunogenicity and efficacy of NY-ESO-1 protein formulated with the ISCOMATRIX adjuvant (NY-ESO-1 vaccine). In vitro, the NY-ESO-1 vaccine was readily taken up by human monocyte-derived dendritic cells, and on maturation, these human monocyte-derived dendritic cells efficiently cross-presented HLA-A2-restricted epitopes to NY-ESO-1-specific CD8(+) T cells. In addition, epitopes of NY-ESO-1 protein were also presented on MHC class II molecules to NY-ESO-1-specific CD4(+) T cells. The NY-ESO-1 vaccine induced strong NY-ESO-1-specific IFN-gamma and IgG2a responses in C57BL/6 mice. Furthermore, the NY-ESO-1 vaccine induced NY-ESO-1-specific CD8(+) CTLs in HLA-A2 transgenic mice that were capable of lysing human HLA-A2(+) NY-ESO-1(+) tumor cells. Finally, C57BL/6 mice, immunized with the NY-ESO-1 vaccine, were protected against challenge with a B16 melanoma cell line expressing NY-ESO-1. These data illustrate that the NY-ESO-1 vaccine represents a potent therapeutic anticancer vaccine.     

The spontaneous CD8+ T-cell response to HLA-A2-restricted NY-ESO-1b peptide in hepatocellular carcinoma patients.

PURPOSE: Hepatocellular carcinoma (HCC) can express various cancer-testis antigens including NY-ESO-1, members of the SSX family, members of the MAGE family, SCP-1, and CTP11. Immunotherapy directed against these antigens is a potential alternative treatment for HCC. To date, it remains unclear whether HCC patients have spontaneous immune responses to these tumor antigens. The objectives of this study were to measure immune responses to NY-ESO-1, a promising cancer vaccine candidate, in HCC patients using the HLA-A2-restricted NY-ESO-1b peptide (p157-165) to measure cellular responses and whole protein to measure antibody responses. EXPERIMENTAL DESIGN: In HLA-A2(+) patients with NY-ESO-1(+) HCC, we analyzed T-cell antigen-dependent interferon (IFN)-gamma and/or Granzyme B release by enzyme-linked immunospot (ELISPOT) assay and IFN-gamma-producing intracellular cytokine flow cytometry (CytoSpot). As an assay independent of T-cell function, we performed tetramer staining. Antibodies to whole NY-ESO-1 were assayed by enzyme-linked immunosorbent assay. RESULTS: The frequency of specific CD8(+) T-cell responses to NY-ESO-1b in 28 NY-ESO-1 mRNA(+)HLA-A2(+) HCC patients was 35.7% (10 of 28). The average magnitude of effector CD8(+) T cells was 0.3% (89 +/- 59 per 2.5 x 10(4) CD8(+) cells) and 1.2% as measured by IFN-gamma release ELISPOT and CytoSpot assays, respectively. These in vitro induced NY-ESO-1b-specific CD8(+) T cells can also recognize HepG2 cells transfected with pcDNA3.1-NY-ESO-1 in both IFN-gamma and Granzyme B ELISPOT assays. Frequencies of NY-ESO-1b-specific T cells in several patients were confirmed by tetramer staining. Nonfunctional tetramer(+)CD8(+) T cells were also present. The CD8(+) T-cell response was apparently increased in patients with late-stage HCC. A discordance between antibody and CD8(+) T-cell responses in HCC patients was observed. CONCLUSIONS: The elevated frequency of specific CD8(+) T-cell responses to NY-ESO-1b in NY-ESO-1 mRNA(+)HLA-A2(+) HCC patients suggests that NY-ESO-1 is appropriate for use in the immunotherapy of HCC patients.     

T cells reactive with HLA-A*0201 peptides from the histone demethylase JARID1B are found in the circulation of breast cancer patients

The nuclear protein PLU-1/JARID1B/KDM5 is widely expressed in breast cancers while showing highly restricted expression in normal adult tissues. To investigate whether JARID1B is a potential target antigen for immunotherapy of breast cancer, we have analyzed the responses of CD8(+) T cells to JARID1B HLA-A*0201 peptides in vitro and used peptide multimers to detect the presence of JARID1B reactive T cells in the circulation of breast cancer patients. Peptides were selected using two web-based algorithms: criteria for inclusion being a high score in both prediction algorithms, and nonhomology with retinoblastoma binding protein-2 (RBP2/JARID1A/KDM5A). A 65-peptide panel was selected and assayed for binding strength by competition assay to obtain the IC(50). The immunogenicity in vitro of these peptides was assessed by T cell stimulation experiments, using autologous dendritic cells as APCs in the first rounds followed by autologous lymphoblasts. Fourteen of the peptides assayed produced cultures having >2% of the CD8(+) cells being IFN-γ(+) after 3-6 rounds of stimulation. An HLA-A*0201 cell line could activate the specific T cells if pulsed with peptide, but endogenous peptide levels were insufficient for activation. Nevertheless, multimer staining of circulating T cells from breast cancer patients showed a significantly higher percentage of multimer positive CD8(+) T cells, as compared to healthy adults for two of three JARID1B epitopes tested. One of these, peptide 73 (QLYALPCVL), was analyzed for memory phenotype, and found to have a significantly higher proportion of central memory T cells than the control group, demonstrating a previous exposure to the peptide.     

Identification of known and novel immunogenic T-cell epitopes from tumor antigens recognized by peripheral blood T cells from patients responding to IL-2-based treatment

In previous studies CD8+ T cells specific for melanocyte antigens have been frequently found in melanoma patients responding to interleukin-2 (IL-2)-based therapies. In our study we analyzed the suitability of using circulating T cells from melanoma patients with clinical response after IL-2-based therapy to identify novel T-cell epitopes from defined tumor antigens. Using unstimulated peripheral blood mononuclear cells and the interferon-gamma (IFN-gamma) ELISPOT assay, we studied CD8(+) T-cell responses against 5 peptides from the tumor antigen tyrosinase (Tyr) selected by epitope prediction using an HLA-A1-binding computer algorithm. T cells specifically secreting IFN-gamma in response to 3 of these 5 peptides, namely, Tyr (454-463), Tyr (146-156) and Tyr (243-251), could be detected in 4 of 4 HLA-A1-positive patients with clinical response. In contrast, no T-cell responses against these peptides were seen in 6 HLA-A1-positive melanoma patients with progressive disease and in 8 healthy subjects. We could generate specific cytotoxic T lymphocytes (CTL) against Tyr (454-463) using peptide-pulsed autologous dendritic cells as antigen-presenting cells. The induced CTLs efficiently killed melanoma cells that express HLA-A1 and tyrosinase. The peptides Tyr (146-156) and Tyr (243-251) had recently been identified as CTL epitopes by other groups. Further ex vivo characterization of the T cells reactive against the novel epitope Tyr (454-463) in 1 patient by multicolor flow cytometry showed specific CD3+/CD8+/IFN-gamma+ T cells with frequencies of up to 0.41% of the CD3+/CD8+ T-cell population. Most of this T-cell population also expressed granzyme B. Our data confirm that in patients with tumor regressions induced by immunotherapy or chemoimmunotherapy circulating T cells reactive with tyrosinase epitopes can frequently be detected. Peripheral blood T cells from such patients are a valuable source for screening peptides selected by epitope prediction This strategy facilitates the rapid identification of immunogenic T-cell epitopes that are probable targets of immune-mediated tumor rejection.     

Identification of HLA-A3-restricted CD8+ T cell epitopes derived from mammaglobin-A,a tumor-associated antigen of human breast cancer

Mammaglobin-A is highly overexpressed in breast cancer cell lines and primary breast tumors. This pattern of expression is restricted to mammary epithelium and metastatic breast tumors. Thus, mammaglobin-A-specific T cell immune responses may provide an important approach for the design of breast cancer-specific immunotherapy. The purpose of our study was to define the T cell-mediated immune response to mammaglobin-A. We determined that the frequency of mammaglobin-A-reactive CD8+ and CD4+ T cells in breast cancer patients is significantly higher than that observed in healthy female controls using limiting dilution analyses (p = 0.026 and p = 0.02, respectively). We identified 8 mammaglobin-A-derived 9-mer peptides with the highest binding affinity for the HLA-A3 molecule (Mam-A3.1-8) using a computer-assisted analysis of the mammaglobin-A protein sequence. Subsequently, we determined that CD8+ T cells from breast cancer patients reacted to peptides Mam-A3.1 (23-31, PLLENVISK), Mam-A3.3 (2-10, KLLMVLMLA), Mam-A3.4 (55-63, TTNAIDELK) and Mam-A3.8 (58-66, AIDELKECF) using an IFN-gamma enzyme-linked immunospot assay. A CD8+ T cell line generated in vitro against HLA-A*0301-transfected TAP-deficient T2 cells loaded with these peptides showed significant cytotoxic activity against the Mam-A3.1 peptide. This CD8+ T cell line showed a significant HLA-A3-restricted cytotoxic activity against mammaglobin-A-positive but not mammaglobin-A-negative breast cancer cells. In summary, our study identified four HLA-A3-restricted mammaglobin-A-derived epitopes naturally expressed by breast cancer cells, indicating the immunotherapeutic potential of this novel antigen for the treatment and prevention of breast cancer.     

EphA2 as target of anticancer immunotherapy: identification of HLA-A*0201-restricted epitopes

EphA2 (Eck) is a tyrosine kinase receptor that is overexpressed in several human cancers such as breast, colon, lung, prostate, gastric carcinoma, and metastatic melanoma but not in nonmalignant counterparts. To validate EphA2 as a tumor antigen recognized by CD8+ T lymphocytes, we used reverse immunology approach to identify HLA-A*0201-restricted epitopes. Peptides bearing the HLA-A*0201-specific anchor motifs were analyzed for their capacity to bind and stabilize the HLA-A*0201 molecules. Two peptides, EphA2(58) and EphA2(550), with a high affinity for HLA-A*0201 were selected. Both peptides were immunogenic in the HLA-A*0201-transgenic HHD mice. Interestingly, peptide-specific murine CTLs cell lines responded to COS-7 cells coexpressing HLA-A*0201 and EphA2 and to EphA2-positive human tumor cells of various origin (renal cell, lung, and colon carcinoma and sarcoma). This demonstrates that EphA2(58) and EphA2(550) are naturally processed from endogenous EphA2. In addition, EphA2(58) and EphA2(550) stimulated specific CD8(+) T cells from healthy donor peripheral blood mononuclear cells. These T cells recognized EphA2-positive human tumor cells in an HLA-A*0201-restricted manner. Interestingly, EphA2-specific CD8+ T cells were detected in the peripheral blood mononuclear cells of prostate cancer patients. These results show for the first time that EphA2 is a tumor rejection antigen and lead us to propose EphA2(58) and EphA2(550) peptides for a broad-spectrum-tumor immunotherapy.     

Natural T-cell response against MHC class I epitopes of epithelial cell adhesion molecule, her-2/neu, and carcinoembryonic antigen in patients with colorectal cancer

The antigens epithelial cell adhesion molecule (Ep-CAM), her-2/neu, and carcinoembryonic antigen (CEA) are potential T-cell targets in antigen-specific vaccination-based cancer therapy. We performed this study to evaluate whether a natural specific T-cell response against these tumor-associated antigens (TAAs) already exists in patients with colorectal carcinoma (CRC). We used the IFN-gamma ELISPOT assay to detect circulating TAA-reactive T cells directly ex vivo in unstimulated peripheral blood mononuclear cells. We analyzed the T-cell response in peripheral blood mononuclear cells of 22 HLA-A2-positive patients with CRC and 8 HLA-A2-positive healthy subjects against 3 HLA A2-restricted peptide epitopes of the TAAs Ep-CAM (GLKAGVIAV), her-2/neu (IISAVVGIL), and CEA (YLSGANLNL). Seven of 22 patients but none of the 8 healthy subjects had T cells specifically secreting IFN-gamma in response to one to three of these antigens (n = 4, Ep-CAM; n = 5, her-2/neu; n = 6, CEA). In three of the seven responding patients, TAA-reactive T cells were further characterized by flow cytometry. In all three patients, the majority of these T cells have a CD3+CD8+IFN-gamma+CD69+CD45RA+ phenotype, resembling activated effector-type T cells. T-cell responses occurred only in patients with metastatic disease (Dukes' stages C and D). The results of this study indicate that natural T-cell responses against TAAs occur in approximately one-half of CRC patients with involvement of lymph nodes or distant metastases, but not in CRC patients with disease confined to the intestinum.     

Frequent cytolytic T-cell responses to peptide MAGE-A10(254-262) in melanoma

MAGE genes encode tumor-specific shared antigens that are among the most interesting candidates for cancer vaccines. Despite extensive studies, however, CD8+ T-cell responses to MAGE-derived epitopes have been detected only occasionally in cancer patients, even after vaccination. In contrast with these findings, we report here that HLA-A2 melanoma patients respond frequently to the recently identified peptide MAGE-A10(254-262). Indeed, as assessed by staining with fluorescent HLA-A2/peptide MAGE-A10(254-262) tetramers, CD8+ T cells directed against this peptide were readily detectable in a large proportion of HLA-A2+ melanoma patients. These results provide new insight into the immunogenicity of MAGE antigens and underline the potential usefulness of MAGE-A10 peptide-based cancer vaccines.