Vaccination for malignant melanoma: recent developments

The identification of tumor-associated antigens recognized by cellular or humoral effectors of the immune system has opened new perspectives for cancer immunotherapy. Different categories of cancer-associated antigens have been described as targets for CD8+ T cells in vitro and in vivo: (1) 'cancer-testis' (CT) antigens expressed in different tumors and normal testis; (2) melanocyte differentiation antigens; (3) point mutations of normal genes; (4) antigens that are overexpressed in malignant tissues, and (5) viral antigens. Clinical trials with antigenic peptides have been initiated to induce specific immunological responses in vivo. Immunological and clinical parameters for the assessment of peptide-specific reactions have been defined: DTH, CD8+ T cell, autoimmune and tumor regression responses. Preliminary results show that tumor-associated peptides alone elicit specific DTH and CD8+ T cell responses associated with tumor regression after intradermal vaccination. Granulocyte macrophage colony-stimulating factor has been shown to enhance peptide-specific immune reactions by amplification of dermal antigen-presenting dendritic cells. Complete tumor regressions have been observed after the induction of CD8+ T cell responses by peptide immunization. Based on these results, active immunotherapy with tumor-associated antigens may be a promising approach for patients in adjuvant treatment situations, who are at high risk for tumor recurrence. Recently, a strategy utilizing spontaneous antibody responses to tumor-associated antigens (SEREX) has led to the identification of a new CT antigen, NY-ESO-1. NY-ESO-1-specific spontaneous humoral and cellular immune responses were found in approximately 50% of patients with NY-ESO-1-positive tumors. Clinical studies have been initiated to evaluate the immunological effects of immunization with NY-ESO-1 peptides in cancer patients with detectable or absent immunity against NY-ESO-1.     

CTL-defined Cancer Vaccines: Perspectives for Active Immunotherapeutic Interventions in Minimal Residual Disease

The characterization of tumor-associated antigens recognized by cellular or humoral effectors of the immune system has opened new perspectives for cancer therapy. Several categories of cancer-associated antigens have been described as targets for cytotoxic T lymphocytes (CTL) in vitro and in vivo: (1) Cancer-Testis (CT) antigens expressed in different tumors and normal testis, (2) melanocyte differentiation antigens, (3) point mutations of normal genes, (4) antigens that are overexpressed in malignant tissues, and (5) viral antigens. Clinical studies with peptides derived from these antigens have been initiated to induce specific CTL responses in vivo. Immunological and clinical parameters for the assessment of peptide-specific reactions have been defined, i.e. induction of DTH-, CTL-, autoimmune-, and tumor-regression responses. Preliminary results demonstrate that tumor-associated peptides alone elicit specific DTH- and CTL-responses leading to tumor regression after intradermal injection. GM-CSF was proven effective to enhance peptide-specific immune reactions by amplification of dermal peptide-presenting dendritic cells. Long lasting complete tumor regressions have been observed after induction of CTL by peptide immunization. Based on these results, active immunotherapy with tumor-associated antigens may be a promising approach for patients with minimal residual disease, who are at high risk for tumor recurrence. However, in single cases with disease progression after an initial tumor response either a loss of the respective tumor antigen targeted by CTL or of the presenting MHC class I molecule was detected as mechanisms of immune escape under immunization in vivo. Based on these observations, cytokines to enhance antigen- and MHC-class I expression in vivo are being evaluated to prevent immunoselection. Recently, a strategy utilizing spontaneous antibody responses to tumor-associated antigens (SEREX) has led to the identification of a new CT antigen, NY-ESO-1. In a melanoma patient with high titer antibody against NY-ESO-1 also a strong HLA-A2 restricted CTL reactivity against the same antigen was found. Clinical studies involving tumor antigens that induce both antibody- and CTL-responses will show whether these are better candidates for immunotherapy of cancer.     

Identification of MHC class II-restricted T-cell epitopes in prostate-specific membrane antigen.

An effective tumor vaccine may be required to induce both CTLs and T-helper (Th) responses against tumor-associated antigens. CD4+ Th cells that recognize MHC class II-restricted epitopes play a central role in the initiation and maintenance of antitumor immune responses. Prostate-specific membrane antigen (PSMA) is highly expressed in prostate cancer and thus is a potential target for prostate cancer immunotherapy. In this study, we attempted to identify Th epitopes derived from PSMA for enhancing prostate cancer vaccine by eliciting PSMA-specific Th responses. We first screened a panel of six epitope peptide candidates selected with the TEPITOPE program and found that all six peptides induced peptide-specific T-cell proliferation from one or more donors with estimated T-cell precursor frequencies of 0-4.17 x 10(-6). We then established peptide-specific T-cell clones for five of these six peptides and demonstrated that the T-cell clone specific for the PSMA(459) epitope (NYTLRVDCTPLMYSL) can recognize processed antigens from recombinant PSMA proteins. The PSMA(459) peptide was found to induce CD4+ T-cell responses in healthy individuals and prostate cancer patients with different HLA-DR alleles. To test the potential clinical application, human HLA-DR4 transgenic mice were immunized with PSMA(459) peptide and we found that PSMA(459) peptide immunization activated T cells that specifically responded to antigenic peptides derived from PSMA proteins and PSMA-positive tumor. Thus, the naturally processed Th epitope PSMA(459) could be included in prostate tumor vaccines to enhance PSMA-specific CTL responses.     

Use of two predictive algorithms of the world wide web for the identification of tumor-reactive T-cell epitopes

Tumor cells can be effectively recognized and eliminated by CTLs. One approach for the development of CTL-based cancer immunotherapy for solid tumors requires the use of the appropriate immunogenic peptide epitopes that are derived from defined tumor-associated antigens. Because CTL peptide epitopes are restricted to specific MHC alleles, to design immune therapies for the general population it is necessary to identify epitopes for the most commonly found human MHC alleles. The identification of such epitopes has been based on MHC-peptide-binding assays that are costly and labor-intensive. We report here the use of two computer-based prediction algorithms, which are readily available in the public domain (Internet), to identify HL4-B7-restricted CTL epitopes for carcinoembryonic antigen (CEA). These algorithms identified three candidate peptides that we studied for their capacity to induce CTL responses in vitro using lymphocytes from HLA-B7+ normal blood donors. The results show that one of these peptides, CEA9(632) (IPQQHTQVL) was efficient in the induction of primary CTL responses when dendritic cells were used as antigen-presenting cells. These CTLs were efficient in killing tumor cells that express HLA-B7 and produce CEA. The identification of this HLA-B7-restricted CTL epitope will be useful for the design of ethnically unbiased, widely applicable immunotherapies for common solid epithelial tumors expressing CEA. Moreover, our strategy of identifying MHC class I-restricted CTL epitopes without the need of peptide/HLA-binding assays provides a convenient and cost-saving alternative approach to previous methods.     

Identification of a new MAGE-A10 antigenic peptide presented by HLA-A*0201 on tumor cells

MAGE-A antigens belong to cancer/testis (CT) antigens that are expressed in tumors but not in normal tissues with the exception of testis and placenta. Among MAGE-A antigens, MAGE-A10 is extensively expressed in various histological types of tumors, representing an attractive target for tumor immunotherapy. Cytotoxic T lymphocytes (CTLs) play a key role in anti-tumor immune responses, so the identification of CTL epitopes derived from MAGE-A10 would contribute a lot to the design of epitope-based vaccines for tumor patients. In this study, we predicted HLA-A*0201-restricted CTL epitope peptides of MAGE-A10, followed by peptide/HLA-A*0201 binding affinity and complex stability assays, and induced peptide-specific CTL immune responses. Of the selected three peptides (designated P1, P2 and P3), P1 (MAGE-A10310-318, SLLKFLAKV) could elicit peptide-specific CTLs both in vitro from HLA-A*0201-positive PBMCs and in HLA-A*0201/Kb transgenic mice. And, the induced CTLs could lyse MAGE-A10-expressing tumor cells in a HLA-A*0201-restricted fashion but not MAGE-A10-negative tumor cells. Our results demonstrate that the peptide MAGE-A10310-318 is a HLA-A*0201-restricted CTL epitope of MAGE-A10 and could serve as a target for therapeutic antitumoral vaccination.     

Identification of T helper epitopes from prostatic acid phosphatase.

Helper T cells (Th cells) play a central role in the initiation and maintenance of immune responses, including antitumor immunity. The ability of Th cells in murine models to maintain and enhance the cytolytic efficacy of CD8+ CTLs has led to a renewed interest in identifying human tumor antigens recognized by Th cells. Prostatic acid phosphatase (PAP) is a prostate cancer-associated tumor antigen. A rodent model has demonstrated that PAP-specific CTLs can induce destructive prostatitis. Human MHC class I epitopes derived from PAP have been identified previously, and peptide-specific CTLs have been shown to be able to lyse an MHC-restricted prostate cancer cell line. In the current study, we sought to identify Th epitopes derived from PAP that might be used to elicit PAP-specific Th responses, ultimately in the context of human vaccines targeting PAP. Using peripheral blood mononuclear cells (PBMCs) from subjects with and without PAP-specific Th responses, we screened a panel of 10 potential peptide epitopes for peptide-specific T-cell proliferation. Four peptides, p81-95, p199-213, p228-242, and p308-322, were identified for which peptide-specific T-cell proliferation occurred in the majority of patient PBMC samples that also exhibited PAP-specific T-cell proliferation. PBMCs from patients with prostate cancer and without PAP-specific Th immunity were then cultured in vitro with these four peptides. Peptide-specific T-cell lines could be generated from two of the four peptides, p199-213 and p228-242, that also proliferated in response to PAP protein stimulation. The ability of these two peptides to elicit PAP-specific Th responses suggests that they represent naturally processed PAP-specific MHC class II epitopes.     

Small cell lung carcinomas express shared and private tumor antigens presented by HLA-A1 or HLA-A2.

Tumor-derived peptides presented by MHC class I molecules are targets for tumor rejection by CD8+ CTLs. MHC-restricted CD8+ CTLs are required also for the identification and characterization of tumor antigens that will be useful for immune therapy. For many human solid tumors, however, tumor antigens remain undefined because of the difficulty of generating MHC-restricted, tumor-specific CTLs required for their analysis. CD8+ CTL responses are modulated by CD4+ helper T cells and by antigen-presenting cells. In this study, highly purified CD8+ T cells were mixed with tumor cells in primary cultures in the absence of any other cells to reduce the complexity of CTL generation. Tumor cells were transfected with HLA-A1 or HLA-A2 and used to stimulate partly matched HLA-A1- or HLA-A2-positive CD8+ T cells. Partial MHC class I matching of tumor and CD8+ T cells and omission of other cells in primary culture was highly effective in generating MHC class I-restricted CTL to poorly immunogenic small cell lung carcinomas (SCLCs). Cytotoxicity was further enhanced by cotransfection of tumor cells with B7.1 (CD80). ICAM-1 (CD54) was not as effective as costimulation. SCLC cells presented tumor-specific peptides with HLA-A1 and HLA-A2 and were lysed by A1- or A2-restricted CD8+ CTLs. A1- and A2-restricted CD8+ CTLs detected shared tumor antigens on unrelated SCLC tumor lines in addition to private antigens. The use of direct antigen presentation by MHC class I-transfected tumors to MHC class I-matched CD8+ T cells is an effective way to generate MHC class I-restricted CTLs toward poorly immunogenic tumors in vitro, permitting the molecular identification of their tumor antigens.     

Generation of cytotoxic T lymphocytes against native and altered peptides of human leukocyte antigen-A*0201 restricted epitopes from the human epithelial cell adhesion molecule.

A growing number of human tumor antigens have been described that can be recognized by CTLs in a MHC class I restricted fashion. The epithelial cell adhesion molecule (Ep-CAM) is expressed in a variety of human tumors and has attracted attention as a therapeutic target for monoclonal antibody serotherapy. We have identified immunogenic peptides derived from Ep-CAM, that bind to human leukocyte antigen-A*0201 and elicit strong peptide-specific human CTL responses, demonstrating that there is an effective T-cell repertoire against these Ep-CAM-derived peptides that can be recruited. Alterations to these peptides were made to increase their binding affinity to MHC class I molecules. The use of such "heteroclitic" peptides allowed generation of cytotoxic T cells that demonstrated increased killing of target cells pulsed not only with the heteroclitic but also with the native peptide. Most important, CTL cell lines that are generated against these peptides specifically lyse epithelial tumor cells expressing Ep-CAM but not normal hematopoietic or bronchial epithelial cells.     

Induction of antitumor immunity by proteasome-inhibited syngeneic fibroblasts pulsed with a modified TAA peptide

CTLs specific for tumor antigens play a major role in immunity against cancer. Improved binding affinity of putative TAA peptides could enhance the in vivo immunogenicity of these self-altered self- tumor antigens. We examined here the efficacy of tumor vaccines composed of an altered peptide ligand of MUT-1, designated MUT-D, which exhibited significantly higher class-I allele K(b) binding affinity than its native counterpart MUT-1. The peptide was loaded on antigen presenting cells composed of the C57BL/6-syngeneic fibroblast cell line BLK.CL4. These cells were treated with proteasome inhibitor in order to shut off the degradation of proteins and the subsequent loading of endogenous peptides onto MHC class-I molecules, thus allowing for the pulsing of these cells with the modified peptide MUT-D. Proteasome-inhibited and modified peptide-loaded fibroblasts induced a peptide-specific CTL that significantly delayed primary tumor progression and protected the pre-immunized mice against the development of lung metastasis following the surgical removal of the primary tumor. Genetic modification of the fibroblasts to express the immunostimulatory cytokine IL-2 did not improve the APC function of the modified cells, nor did it result in augmentation of the potency of the vaccine. Our results suggest that the proteasome-inhibited fibroblasts pulsed with modified, high binder tumor-associated antigen peptide are good antigen-presenting cells and represent an effective form of tumor vaccine.     

The anti-tumor immune response induced by a combination of MAGE-3/MAGE-n-derived peptides

Tumor antigen-derived peptides have been widely used to elicit tumor-specific cytotoxic T lymphocytes (CTLs). MAGE gene products are of particular interest owing to their wide expression in many tumors and their potential to induce tumor-specific CTL responses. Antigen-specific CTLs induced by MAGE gene-derived peptides have proven to be highly efficacious in the prevention and treatment of various types of tumors. MAGE-3 has been used as a target for tumor immunotherapy. MAGE-n is a new member of the MAGE gene family and has been shown to be closely associated with hepatocellular carcinoma (HCC). However, the majority of previous investigations focused on the single MAGE antigen-derived peptides as a cancer vaccine which has many limitations. The tumor antigen expression is known to be heterogeneous and tumor cells can express multiple tumor antigens. Thus, vaccines incorporating single antigen-derived epitopes may be inadequate in generating a complete immune response against the tumor. Instead, a polyvalent vaccine incorporating epitopes derived from several tumor antigens may be more effective. Our study combined the MAGE-3 and MAGE-n-derived peptides as a cancer vaccine. The results showed that the combination of MAGE-3 and MAGE-n epitopes induced more effective anti-tumor immune responses than either of the peptides alone. In addition, the peptide-specific activity was observed to be in an MHC-restricted manner. Our study indicated that the combination of several tumor antigen-derived peptides may present a better peptide-based cancer immunotherapy.     

Human CTL epitopes prostatic acid phosphatase-3 and six-transmembrane epithelial antigen of prostate-3 as candidates for prostate cancer immunotherapy

Specific immunotherapy of prostate cancer may be an alternative or be complementary to other approaches for treatment of recurrent or metastasized disease. This study aims at identifying and characterizing prostate cancer-associated peptides capable of eliciting specific CTL responses in vivo. Evaluation of peptide-induced CTL activity in vitro was done following immunization of HLA-A2 transgenic (HHD) mice. An in vivo tumor rejection was tested by adoptive transfer of HHD immune lymphocytes to nude mice bearing human tumors. To confirm the existence of peptide-specific CTL precursors in human, lymphocytes from healthy and prostate cancer individuals were stimulated in vitro in the presence of these peptides and CTL activities were assayed. Two novel immunogenic peptides derived from overexpressed prostate antigens, prostatic acid phosphatase (PAP) and six-transmembrane epithelial antigen of prostate (STEAP), were identified; these peptides were designated PAP-3 and STEAP-3. Peptide-specific CTLs lysed HLA-A2.1+ LNCaP cells and inhibited tumor growth on adoptive immunotherapy. Furthermore, peptide-primed human lymphocytes derived from healthy and prostate cancer individuals lysed peptide-pulsed T2 cells and HLA-A2.1+ LNCaP cells. Based on the results presented herein, PAP-3 and STEAP-3 are naturally processed CTL epitopes possessing anti-prostate cancer reactivity in vivo and therefore may constitute vaccine candidates to be investigated in clinical trials.     

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.     

Identification of HLA-A24-restricted CTL epitope from cancer-testis antigen, NY-ESO-1, and induction of a specific antitumor immune response.

PURPOSE: For the development of peptide-based, cancer-specific immunotherapy, the identification of CTL epitopes from additional tumor antigens is very important. NY-ESO-1, a cancer-testis antigen, is considered to be a promising target of tumor-specific immunotherapy. Because HLA-A24-expressing individuals cover >60% in the population of Japan, we aim at identifying NY-ESO-1-encoded peptide presented by HLA-A24. EXPERIMENTAL DESIGN: In our study, a HLA-A24-restricted CTL epitope was identified by using the following four-step procedure: (a) computer-based epitope prediction from the amino acid sequence of NY-ESO-1 antigen; (b) peptide-binding assay to determine the affinity of the predicted peptide with HLA-A24 molecule; (c) stimulation of primary T-cell response against the predicted peptides in vitro; and (d) testing of the induced CTLs toward various carcinoma cells expressing NY-ESO-1 antigen and HLA-A24. RESULTS: Of the tested peptides, effectors induced by a peptide of NY-ESO-1 at residue position 158-166 lysed three kinds of carcinoma cells expressing both NY-ESO-1 and HLA-A24. Our results indicate that peptide NY-ESO-1 (158-166) (LLMWITQCF) is a new HLA-A24-restricted CTL epitope capable of inducing NY-ESO-1-specific CTLs in vitro mediating HLA class I-restricted manner. CONCLUSIONS: We identified a novel HLA-A24-restricted NY-ESO-1-derived epitope peptide (LLMWITQCF) that could induce specific CTLs from the peripheral blood mononuclear cells of HLA-A24(+) healthy donors. This peptide would be useful in further evaluating the clinical utility of peptide-based, cancer-specific immunotherapy against various histological tumors.     

Induction of protective CTL immunity against peptide transporter TAP-deficient tumors through dendritic cell vaccination

A large proportion of human cancers show deficiencies in the MHC class I antigen-processing machinery. Such defects render tumors resistant to immune eradication by tumoricidal CTLs. We recently identified a unique population of CTL that selectively targets tumor immune-escape variants through recognition of MHC-presented peptides, termed TEIPP (T cell epitopes associated with impaired peptide processing), expressed on cells lacking functional TAP-peptide transporters. Previously, we showed that vaccination with TEIPP peptides mediates protection against TAP-deficient tumors. Here, we further explored the concept of TEIPP-targeted therapy using a dendritic cell (DC)-based cellular vaccine. Impairment of TAP function in DC induced the presentation of endogenous TEIPP antigens by MHC class I molecules, and immunization with these DCs protected mice against the outgrowth of TAP-deficient lymphomas and fibrosarcomas. Immune analysis of vaccinated mice revealed strong TEIPP-specific CTL responses, and a crucial role for CD8(+) cells in tumor resistance. Finally, we show that TEIPP antigens could be successfully induced in wild-type DC by introducing the viral TAP inhibitor UL49.5. Our results imply that immune intervention strategies with TAP-inhibited DC could be developed for the treatment of antigen processing-deficient cancers in humans.     

Antigen-specific immunotherapy and cancer vaccines

The specific activation of the immune system to control cancer growth in vivo has been a long-standing goal in cancer immunology and medical oncology. The identification of tumor-associated antigens has provided the basis for new concepts in antigen-specific immunotherapy. The first clinical trials on cancer vaccines were designed to evaluate the toxicity and objectively measurable immunologic effects in relation to clinical developments mostly in patients with metastatic disease. MHC class I- and II-restricted peptide epitopes, antigenic proteins, viral constructs, mini-genes and whole tumor cells have been used either alone or combined with different cytokines (i.e., IL-2, IL-12, GM-CSF), adjuvants (incomplete Freund's adjuvant, montanide, QS21) or with dendritic cells to induce specific immune responses in vivo. Standardized assay systems to evaluate the immunologic effects of cancer vaccines have been established. Clinical developments during and after vaccination were followed in relation to vaccine-induced immune responses. Prognostic tumor features, i.e., homogeneity of tumor antigen and MHC class I/II expression and intratumoral cellular infiltrates, have been identified that may help to select patients who are more likely to benefit from antigen-specific cancer vaccines in the future.     

Restoration of the expression of transporters associated with antigen processing in lung carcinoma increases tumor-specific immune responses and survival

A wide variety of human carcinomas have low expression of tumor-associated antigen presentation in the context of MHC class I antigens due to defects in the antigen presentation pathway. This immune evasion mechanism renders many tumors unrecognizable by host immune surveillance mechanisms. The present study examines the expression of HLA, tapasin, transporter associated with antigen processing 1 (TAP1), and beta2 microglobulin in human small cell lung carcinoma and non-small cell lung carcinoma. Immunohistochemical staining showed severe impairment of the antigen presentation pathway in all patients. In order to recover tumor immunogenicity, a nonreplicating adenovirus expressing human TAP1 (AdhTAP1) was used to restore the expression of TAP1 in the antigen presentation pathway-deficient mouse lung carcinoma cell line, CMT.64. Infection of CMT.64 cells with AdhTAP1 increased MHC class I antigen surface expression, antigen presentation, and susceptibility to antigen-specific CTLs. Fluorescence-activated cell sorting and ELISPOT analysis showed that AdhTAP1 treatment significantly increased dendritic cell cross-presentation and cross-priming of tumor antigens. Furthermore, ex vivo and in vivo AdhTAP1 treatment significantly retarded tumor growth and increased survival of mice bearing CMT.64 tumors. Fluorescence-activated cell sorting analysis and immunohistochemical staining showed a significant increase in CD8+ and CD4+ T cells and CD11c+ dendritic cells infiltrating the tumors. The results show that TAP should be considered as a part of the immunotherapies for various cancers because it is likely to provide a general method for increasing immune responses against tumors regardless of the antigenic composition of the tumor or the MHC haplotypes of the host.     

FBL-3肿瘤抗原的实验研究:Ⅰ.抗原的预测及合成多肽抗原性的验证

T细胞在肿瘤免疫中发挥着重要作用,它是通过T细胞抗原受体(TCR)识别肿瘤细胞表面由MHC分子呈递的肿瘤源性多肽,其中细胞毒T淋巴细胞(CTL)是通过识别肿瘤细胞MHC I类分子结合并呈递的多肽。研究表明:CTL识别的多肽常由8～9个氨基酸组成,多肽的呈递受MHC分子等位型的限制,不同的MHC分子具有不同的等位型特异的多肽结合基序(peptidebinding motif)。FBL-3是B6小鼠(H-2~b)源由Friend病毒诱导的小鼠白血病细胞,灭活FBL-3免疫B6小鼠可诱导FBL-3特异CTL产生,从而建立FBL-3特异的免疫应答,保护小鼠免受FBL-3的致瘤性。因此,实验中根据H-2D~b多肽结合基序和Friend病毒gag基因序列,预测出7个可能编码FBL-3抗原多肽的片段。根据预测的结果人工合成了7个九肽(gag1-gag7)。实验结果显示:合成多肽免疫B6小鼠可诱导多肽特异的CTL产生,但用体外实验方法不能诱导初次免疫应答;FBL-3特异CTL可以杀伤gag3,gag5致敏的靶细胞EL-4(H-2~b),但体内实验表明gag3,gag5不象FBL-3一样,它们体内免疫后不能建立有效的抗FBL-3肿瘤免疫效应。表明预测的7个多肽可能不是FBL-3的肿瘤抗原。文中讨论了多肽抗原性预测的复杂性和可能的对策。     

Equivalent induction of telomerase-specific cytotoxic T lymphocytes from tumor-bearing patients and healthy individuals.

Although high frequencies of T lymphocytes specific for certain tumor-associated antigens have been detected in some cancer patients, increasing evidence suggests that these T cells may be functionally defective in vivo and fail to induce meaningful clinical responses. One strategy to overcome this limitation is to target novel antigens that are ignored during the natural antitumor immune response but are nevertheless capable of triggering effector T-cell responses against tumors after optimal presentation by antigen-presenting cells. Here, we show that the telomerase catalytic subunit (hTERT)-a nearly universal tumor antigen identified by epitope deduction rather than from patient immune responses-is immunologically ignored by patients despite progressive tumor burden. Nevertheless, HLA-A2-restricted CTLs against hTERT are equivalently induced ex vivo from patients and healthy individuals and efficiently kill human tumor cell lines and primary tumors. Thus, telomerase-specific T cells from cancer patients are spared functional inactivation because of immunological ignorance. These findings support clinical efforts to target the hTERT as a tumor antigen with broad therapeutic potential.     

Thymus-leukemia antigen (TL) as a major histocompatibility complex (MHC) class Ib molecule and tumor-specific antigen

Mouse thymus-leukemia antigens (TL) belong to the family of major histocompatibility complex (MHC) class Ib antigens and have a unique mode of expression, i.e., in contrast to other MHC class Ib or Ia antigens, they are found restricted to the intestines in all mouse strains, but also in the thymus of certain strains (TL(+) strains). Nevertheless, a proportion of T lymphomas/leukemias in strains that do not express TL in the thymus (TL(-) strains) feature TL as a tumor antigen. TL was originally defined serologically, but subsequently we have succeeded in generating T cell receptor (TCR) and cytotoxic T lymphocytes (CTL) recognizing TL. By use of TL tetramers free from peptides and transfectants expressing various TL/H-2 chimeric molecules, we have been able to show that TL-specific CTL recognize the alpha1/alpha2 domain of TL without any additional antigen molecules. We previously reported that one of TL's functions in the thymus is positive selection of TCR CTL. Recent studies with TL tetramers revealed that they can bind to normal intestinal intraepithelial lymphocytes (iIEL) and thymocytes in a CD8-dependent, but TCR/CD3-independent manner, while their binding to TL-specific CTL is TCR/CD3- and CD8-dependent. The possible significance of these findings in relation to the roles of TL in the intestines is discussed. We have long been interested in TL as a model tumor antigen which shares characteristics with human differentiation tumor antigens, and we have demonstrated that growth of TL(+) lymphoma cells in vivo is suppressed by immunization with TL(+) skin or dendritic cells (DC) from TL transgenic mice. In addition, anti-tumor effects against TL(+) T lymphomas were obtained by adoptive transfer of TL tetramer strongly-positive TL-specific CTLs.