Biomedical subjects

A Knuth

Publications and source records attributed to A Knuth.

At least 55 records · Page 3Linked to original sources

PubMed1999

Cytotoxic T lymphocytes define multiple peptide isoforms derived from the melanoma-associated antigen MART-1/Melan-A.

Peptides derived from the melanoma-associated MART-1/Melan-A antigen are currently implemented in immunotherapy for inducing or augmenting T-cell responses directed against peptides expressed by autologous tumor cells in HLA-A2+ patients with melanoma. Here, we describe the specificity of the T-cell clone SK29-FFM1.1, which secretes GM-CSF in response to a panel of synthetic MART-1/Melan-A-derived peptides, including the naturally presented ILTVILGVL(32-40), but exhibits cytotoxicity and IFN-gamma secretion exclusively to the MART-1/Melan-A derived peptide AAGIGILTV(27-35). In addition, cytotoxic T-lymphocyte (CTL) clone SK29-FFM1.1 recognizes 3 different naturally processed and presented peptides on HLA-A2+ MART-1/Melan-A+ melanoma cells, as defined by cytotoxicity and IFN-gamma and GM-CSF secretion. Processing and presentation of MART-1/Melan-A peptides appears to be different in cells of non-melanocytic origin, as shown by the characterization of naturally presented peptides displayed by HLA-A2+ colorectal cancer cells transduced with a MART-1/Melan-A gene-containing retrovirus. Our data suggest that multiple epitopes, including ILTVILGVL and different isoforms of AAGIGILTV derived from MART-1/Melan-A may be naturally presented by melanoma cells to the immune system.

Amino Acid Sequence↗

PubMed1999

Induction of immunogenicity of a human renal-cell carcinoma cell line by TAP1-gene transfer.

Reduced expression of the major-histocompatibility-complex(MHC)-class-I antigens has been demonstrated in renal-cell carcinoma (RCC), and appeared to be associated with deficiencies in the expression and function of different components of the MHC-class-I-antigen-processing pathway and poor recognition by cytotoxic T-lymphocytes (CTL). In order to investigate the role of peptide transporters for the immunogenic phenotype of RCC, tumor cells were stably transfected with the human TAP1A gene. While the TAP1 transfectants showed heterogeneous TAP1-transgene expression pattern of mRNA and protein, high TAP1 expression and a TAP-controlled increase in MHC-class-I surface expression could be achieved in selected transfectants. IFN-gamma up-regulates the expression of MHC-class-I antigens and TAP1 both in control and in TAP1-transfected RCC cells to a similar level. No additive effect of TAP1 over-expression was observed in TAP1 transfectants. Although no enhanced CTL-mediated lysis was obtained, cytokine release was substantially increased in response to TAP1-transfected RCC cells, but not to control cells. Furthermore, TAP1 transfectants were able to stimulate the proliferation of allogeneic T cells. These studies suggest that abnormalities of MHC-class-I surface expression due to dysfunctional peptide transporters contribute to the immune escape phenotype of RCC cells and that the immune tolerance of RCC could be altered by TAP1-gene transfer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1999

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.

Cancer Vaccines↗

PubMed1999

Gene transfer of the Co-stimulatory molecules B7-1 and B7-2 enhances the immunogenicity of human renal cell carcinoma to a different extent.

Stimulation of a specific antitumour immune response with recruitment and induction of T-cell effector functions represents an attractive concept in human cancer therapy. Different cytokines and the B7 co-stimulatory molecules are both able to provide proliferation and activation signals for T cells. In the present study, we first demonstrated the absence of both B7-1 and B7-2 expression in human renal cell carcinoma (RCC) cell lines. The lack of B7 expression was associated with a low or absent proliferative response of allogeneic and autologous T cells upon stimulation with tumour cells. In order to investigate the role of B7-1 and B7-2, the human RCC cell line, MZ1257RC, which expresses normal levels of adhesion molecules and major histocompatibility complex (MHC) class I surface antigens, was transfected with B7-1 and B7-2 expression vectors, respectively. The B7-1- and B7-2-transduced MZ1257RC cells were potent stimulators of allogeneic and autologous T-cell proliferation. B7-2 transfectants were approximately two- to threefold more effective in the induction of primary T-cell activation than B7-1-transduced cells. Interleukin (IL)-12 synergized with the B7/CD28 interaction to enhance allogeneic T-cell proliferation, independently of the B7 molecule transduced. In contrast, IL-2 only co-operatively increased T-cell activation in the presence of B7-2. Our results suggest the following: first, that co-stimulatory molecules are required for efficient T-cell responses directed against RCC; second, that B7-2 appears to be a more potent stimulator of tumour immunity as compared to B7-1; and third, that B7 molecules selectively co-operate with different T-cell stimulatory cytokines. The different activity of B7-1 and B7-2 molecules on the immunogenicity of RCC will have implications for the development and optimization of RCC-specific cancer vaccines.

Antigens, CD↗

PubMed1998

Identification of multiple cancer/testis antigens by allogeneic antibody screening of a melanoma cell line library.

Cancer/testis (CT) antigens-immunogenic protein antigens that are expressed in testis and a proportion of diverse human cancer types-are promising targets for cancer vaccines. To identify new CT antigens, we constructed an expression cDNA library from a melanoma cell line that expresses a wide range of CT antigens and screened the library with an allogeneic melanoma patient serum known to contain antibodies against two CT antigens, MAGE-1 and NY-ESO-1. cDNA clones isolated from this library identified four CT antigen genes: MAGE-4a, NY-ESO-1, LAGE-1, and CT7. Of these four, only MAGE-4a and NY-ESO-1 proteins had been shown to be immunogenic. LAGE-1 is a member of the NY-ESO-1 gene family, and CT7 is a newly defined gene with partial sequence homology to the MAGE family at its carboxyl terminus. The predicted CT7 protein, however, contains a distinct repetitive sequence at the 5' end and is much larger than MAGE proteins. Our findings document the immunogenicity of LAGE-1 and CT7 and emphasize the power of serological analysis of cDNA expression libraries in identifying new human tumor antigens.

Amino Acid Sequence↗

PubMed1998

Molecular analysis of the HLA-A2 antigen loss by melanoma cells SK-MEL-29.1.22 and SK-MEL-29.1.29.

Due to the potential clinical relevance of HLA class I antigen losses in melanoma cells and the scanty information about the molecular mechanisms underlying these defects, we have characterized the cause of the HLA-A2 antigen loss by autologous melanoma cell lines SK-MEL-29.1.22 and SK-MEL-29.1.29. Both cell lines have structural defects of HLA-A2 genes, which cause lack of their transcription. In SK-MEL-29.1.22 cells the 5'-flanking region, exon 1, intron 1, and a region at the 5' end of exon 2 of the HLA-A2 gene are deleted. The breakpoint of the HLA-A2 gene, which is recombined with a DNA fragment of unknown origin, was localized between two GTTCG sequence repeats at position 101 of exon 2. These repeats may provide the sequence basis for misalignment in the process of DNA deletion. In SK-MEL-29.1.29 cells, loss of HLA-A2 antigens, as well as of HLA-B44 and HLA-Cw5 alleles, is caused by the loss of one copy of chromosome 6. Down-regulation of the expressed HLA class I alleles in the two HLA-A2 loss variants and in the parental cells was found to be associated with a low TAP1 expression and a reduced function of peptide transporters. Therefore, multiple defects result in loss or down-regulation of HLA class I alleles in SK-MEL-29.1.22 and SK-MEL-29.1.29 melanoma cells.

Antigens, Neoplasm↗

PubMed1998

A survey of the humoral immune response of cancer patients to a panel of human tumor antigens.

Evidence is growing for both humoral and cellular immune recognition of human tumor antigens. Antibodies with specificity for antigens initially recognized by cytotoxic T lymphocytes (CTLs), e.g., MAGE and tyrosinase, have been detected in melanoma patient sera, and CTLs with specificity for NY-ESO-1, a cancer-testis (CT) antigen initially identified by autologous antibody, have recently been identified. To establish a screening system for the humoral response to autoimmunogenic tumor antigens, an enzyme-linked immunosorbent assay (ELISA) was developed using recombinant NY-ESO-1, MAGE-1, MAGE-3, SSX2, Melan-A, and tyrosinase proteins. A survey of sera from 234 cancer patients showed antibodies to NY-ESO-1 in 19 patients, to MAGE-1 in 3, to MAGE-3 in 2, and to SSX2 in 1 patient. No reactivity to these antigens was found in sera from 70 normal individuals. The frequency of NY-ESO-1 antibody was 9.4% in melanoma patients and 12.5% in ovarian cancer patients. Comparison of tumor NY-ESO-1 phenotype and NY-ESO-1 antibody response in 62 stage IV melanoma patients showed that all patients with NY-ESO-1(+) antibody had NY-ESO-1(+) tumors, and no patients with NY-ESO-1(-) tumors had NY-ESO-1 antibody. As the proportion of melanomas expressing NY-ESO-1 is 20-40% and only patients with NY-ESO-1(+) tumors have antibody, this would suggest that a high percentage of patients with NY-ESO-1(+) tumors develop an antibody response to NY-ESO-1.

Antibodies, Neoplasm↗

PubMed1998

Simultaneous humoral and cellular immune response against cancer-testis antigen NY-ESO-1: definition of human histocompatibility leukocyte antigen (HLA)-A2-binding peptide epitopes.

A growing number of human tumor antigens have been described that can be recognized by cytotoxic T lymphocytes (CTLs) in a major histocompatibility complex (MHC) class I-restricted fashion. Serological screening of cDNA expression libraries, SEREX, has recently been shown to provide another route for defining immunogenic human tumor antigens. The detection of antibody responses against known CTL-defined tumor antigens, e.g., MAGE-1 and tyrosinase, raised the question whether antibody and CTL responses against a defined tumor antigen can occur simultaneously in a single patient. In this paper, we report on a melanoma patient with a high-titer antibody response against the "cancer-testis" antigen NY-ESO-1. Concurrently, a strong MHC class I-restricted CTL reactivity against the autologous NY-ESO-1-positive tumor cell line was found. A stable CTL line (NW38-IVS-1) was established from this patient that reacted with autologous melanoma cells and with allogeneic human histocompatibility leukocyte antigen (HLA)-A2(-), NY-ESO-1-positive, but not NY-ESO-1-negative, melanoma cells. Screening of NY-ESO-1 transfectants with NW38-IVS-1 revealed NY-ESO-1 as the relevant CTL target presented by HLA-A2. Computer calculation identified 26 peptides with HLA-A2-binding motifs encoded by NY-ESO-1. Of these, three peptides were efficiently recognized by NW38-IVS-1. Thus, we show that antigen-specific humoral and cellular immune responses against human tumor antigens may occur simultaneously. In addition, our analysis provides a general strategy for identifying the CTL-recognizing peptides of tumor antigens initially defined by autologous antibody.

Aged↗

PubMed1998

Strong immunogenic potential of a B7 retroviral expression vector: generation of HLA-B7-restricted CTL response against selectable marker genes.

The stimulation of a specific immune response is an attractive goal in cancer therapy. Gene transfer of co-stimulatory molecules and/or cytokine genes into tumor cells and the injection of these genetically modified cells leads to tumor rejection by syngeneic hosts and the induction of tumor immunity. However, the development of host immune response could be either due to the introduced immunomodulatory genes or due to vector components. In this study, human renal cell carcinoma cell lines were modified by a retrovirus to express the co-stimulatory molecule B7-1 together with the hygromycin/thymidine kinase fusion protein (HygTk) as positive and negative selection markers. These B7-1-transduced renal cell carcinoma cell lines were able significantly to activate allogeneic T cell proliferation. The cytolytic activity of these T cells was determined by employing several transduced and nontransduced renal cell carcinoma cell lines as targets. Evidence for a strong vector-specific T cell reactivity induced by the Hyg/Tk protein was obtained in autologous renal cell carcinoma systems. Antibody blocking experiments as well as peptide binding assays demonstrated an HLA-B7-restricted T cell response directed against both the Hyg and the Tk genes. Thus, the vector itself may mask the generation of immune reactivity against tumor antigens and may even detract from it. Vectors with immunogenic potential may be useful for tumor vaccination via cross priming in vivo, whereas antivector reactivities would be detrimental in situations where gene defects are being corrected and where long term expression of a therapeutic protein is required.

Antigens, Neoplasm↗

PubMed1998

Strategies for the development of vaccines to treat breast cancer.

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 (CTLs) in vitro and in vivo: "cancer-testis" (CT) antigens expressed in different tumors and normal testis, melanocyte differentiation antigens, point mutations of normal genes, antigens that are overexpressed in malignant tissues, and viral antigens. Clinical studies using 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 delayed-type hypersensitivity (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 proved to be effective in enhancing peptide-specific immune reactions by amplification of dermal peptide-presenting dendritic cells. Long-lasting complete tumor regressions have been observed after induction of CTLs by peptide immunization. However, in a few cases where there was disease progression after initial tumor response, loss of either the tumor antigen targeted by CTLs or of the presenting MHC class I molecule was detected as the mechanism 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, strong HLA-A2-restricted CTL reactivity against the same antigen was also found. Clinical studies involving tumor antigens that induce both antibody and CTL responses will show whether these are better candidates for immunotherapy of cancer.

Antigen-Antibody Reactions↗

PubMed1997

[Penetrating duodenal ulcer as a complication of a hepatic artery port catheter in hepatic metastasis of sigmoid carcinoma].

CASE REPORT: We report a typical complication of hepatic artery infusion therapy (HAI) in a patient with colon cancer metastatic to the liver. One year after the last HAI-therapy the patient presented with upper gastrointestinal bleeding. Endoscopy showed a large duodenic ulcer penetrating into an adjacent hepatic colon cancer metastasis. The hepatic artery catheter was visible at the ground of the duodenic ulcer. CONCLUSION: Thirty-five percent of patients under HAI-therapy develop gastric/duodenic ulcers. The severity of the HAI complication presented here, however, is quite uncommon.

Adenocarcinoma↗

PubMed1997

SSX: a multigene family with several members transcribed in normal testis and human cancer.

Analysis of t(X;18) translocation in synovial sarcoma had previously led to the definition of the SSX2 gene, the fusion partner on chromosome X. Subsequent screening of testicular cDNA libraries identified 2 highly homologous genes, SSX1 and SSX3. Among these 3 genes, SSX2 has been found to be identical to HOM-MEL-40, which codes for an immunogenic tumor antigen expressed in various human cancers. SSX2 thus belongs to the family of cancer/testis (CT) antigens, i.e., immunogenic protein antigens with characteristic mRNA expression in normal testis and in cancer. To define additional CT antigens, we have immuno-screened a testicular cDNA expression library with an allogeneic serum from a melanoma patient, and both SSX2 and SSX3 were isolated. Further studies using testicular cDNA and SSX probes defined 2 new members of this gene family, SSX4 and SSX5, while a shorter cDNA variant of SSX4 was also identified. All 5 members of the SSX family shared strong sequence homology, with nucleotide homology ranging from 88 to 95% and amino acid homology ranging from 77 to 91%. Genomic cloning of a prototype SSX gene (SSX2) showed that its coding region is encoded by 6 exons, and the shortened form of SSX4 cDNA represents an alternatively spliced product lacking the 5th exon. Analysis of SSX mRNA expression by gene-specific RT-PCR confirmed that all 5 SSX genes are expressed in testis. In addition, analysis of a panel of 12 melanoma cell lines showed strong mRNA expression of either SSX1 (3/12), SSX2 (3/12), SSX4 (1/12), or SSX5 (1/12), indicating variable activation of the genes in malignant cells.

Amino Acid Sequence↗

PubMed1997

Immunoselection in vivo: independent loss of MHC class I and melanocyte differentiation antigen expression in metastatic melanoma.

Peptides derived from melanocyte differentiation antigens have been identified as targets for MHC class I-restricted cytolytic T lymphocytes (CTLs) in human melanoma Regression of antigen-expressing tumors as well as selection of antigen-loss variants in the presence of antigen-specific CTLs have previously been reported. In the present study, we determined the expression of the melanocyte differentiation antigens Melan A/MART-1 and tyrosinase by mRNA analysis and by immunohistochemical staining with the monoclonal antibodies (MAbs) A103 and T311. Co-expression of Melan A/MART-1 and tyrosinase was detected by both methods in 18/20 melanomas tested. However, immunohistochemistry provided additional information on intensity and microheterogeneity of antigen expression that cannot be detected by mRNA analysis as a molecular basis for the escape from CTL recognition of antigen-negative tumor cells. Comparative analysis of repeated biopsies of metastatic lesions in 5 HLA-A2+ patients showed a gradual loss of Melan A/MART-1 expression in 4/5 and of tyrosinase in 2/5 samples in association with tumor progression. However, 3 of these patients had growing antigen-positive tumors in the presence of antigen-specific CTLs. This led us to assess the expression of MHC class I, the essential restriction element for CTL recognition, and of HLA-A2. We found an unexpectedly high frequency of MHC class I-negative tumors (9/20). Loss of MHC class I expression was detected in 3/5 progressive tumors and isolated loss of HLA-A2 in 1/5 tumors. Our results suggest that strategies enhancing the expression of MHC class I and tumor-associated antigens need to be considered in attempts at making vaccination more effective.

Adult↗

PubMed1997

Expression and function of the peptide transporters in escape variants of human renal cell carcinomas.

The transporter associated with antigen processing (TAP) complex is a heterodimeric transmembrane pump consisting of the TAP-1 and TAP-2 subunits; these subunits translocate peptides from the cytoplasm into the lumen of the endoplasmic reticulum, where they bind nascent major histocompatibility complex (MHC) class I molecules. Loss or reduced expression of the TAP genes results in the synthesis of unstable peptide free MHC class I molecules that are only weakly expressed on the cell surface. In a number of human tumor cell lines, downregulation of MHC class I expression has been found to be associated with reduced or absent TAP expression. To investigate whether alterations in MHC class I expression occur during transformation and subsequent progression and whether MHC class I suppression is caused by impaired TAP function, we analyzed the protein expression of MHC class I heavy and light chain and TAP-1 in three renal cell carcinoma (RCC) cell lines and short-term cultures from corresponding normal kidney tissue. In one case a cell line established from a metastatic lesion was also available. Compared with normal epithelial cells, suppression of TAP-1 and MHC class I molecules was detected in all three primary RCC cells and was even more pronounced in the metastatic cell line. In contrast to normal epithelial cells, MHC class I membrane expression of two RCC lines was enhanced by culture in the presence of MHC class I binding peptides or at low temperature (26 degrees C) instead of 37 degrees C. Unstable MHC class I surface expression is caused by dissociation of the MHC class I heavy and light chain molecules as a result of functional defects in the antigen processing machinery, e.g., impaired peptide transport. Attempts to counteract the reduced immunogenicity by transferring the TAP genes into these cells demonstrated that TAP-1-modified RCC cells expressed higher levels of MHC class I molecules. These data indicate that downregulation and instability of MHC class I surface expression in RCC cells is at least partially caused by deficient loading with endogenous peptides and can be restored by TAP gene transfer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1997

IFN-gamma-mediated coordinated transcriptional regulation of the human TAP-1 and LMP-2 genes in human renal cell carcinoma.

Some human tumor cells exhibit deficient expression of the peptide transporters TAP1 and TAP2 and of the proteasome subunits low molecular weight protein (LMP)-2 and LMP-7, which could be partially restored by cytokine treatment. Here, we show that IFN-gamma stimulation of human renal cell carcinoma lines increased the MHC class I, transporter associated with antigen processing (TAP), and LMP transcript and protein levels, but TAP and LMP expression are more rapidly induced by IFN-gamma than MHC class I molecules. No correlation between the level of induction of the MHC class I antigen presentation genes and IFN sensitivity/resistance was detected. The IFN-gamma-mediated increase of MHC class I, TAP-1, and LMP-2 expression was independent of de novo protein synthesis. Analysis of the dual TAP-1/LMP-2 promoter activity revealed that TAP-1 and LMP-2 expression are controlled by IFN-gamma at the transcriptional level. Site-specific mutations in the IFN-gamma-responsive element of the TAP-1/LMP-2 promoter blocked induction by IFN-gamma. Thus, the IFN-gamma-mediated coordinated transcriptional up-regulation of TAP-1 and LMP-2 expression occurs through the use of a common regulatory element, which might result in enhanced recognition of renal cell carcinoma cells by the immune system.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Granulocyte-macrophage-colony-stimulating factor enhances immune responses to melanoma-associated peptides in vivo.

Peptide epitopes derived from differentiation antigens of the melanocyte lineage were recently identified in human melanomas as targets for MHC-restricted cytotoxic T lymphocytes (CTL). The characterization of multiple CTL-defined antigenic determinants has opened possibilities of development of antigen-targeted vaccines. In the present study, we determined CTL reactivity against melanoma-associated peptides derived from Melan A/MART-1, tyrosinase, and gp100/Pmel17 in 3 HLA-A2+ melanoma patients. Then, we assessed the immune responses to synthetic melanoma-associated peptides injected intradermally. After 3 cycles of immunization with peptide alone, we used systemic GM-CSF as an adjuvant during the fourth cycle of immunization. Enhanced DTH reactions and CD8+ CTL responses were observed after treatment with systemic GM-CSF. Immunohistochemical characterization of DTH-constituting elements revealed infiltrates of CD4+ and CD8+ T lymphocytes and strong expression of IL-2 and gammaIFN, suggesting the activation of CD4+ ThI and CD8+ CTL by peptides presented by MHC-class-I molecules of dermal APC. Objective tumor regression was documented in all patients. We conclude that systemic GM-CSF enhances immune responses to melanoma-associated peptides and supports CTL-mediated tumor rejection in vivo.

Adjuvants, Immunologic↗

PubMed1996

Inverse relationship of melanocyte differentiation antigen expression in melanoma tissues and CD8+ cytotoxic-T-cell responses: evidence for immunoselection of antigen-loss variants in vivo.

Antigenic peptides derived from differentiation antigens of the melanocyte lineage were recently identified in human melanomas as targets for MHC-restricted cytotoxic T lymphocytes (CTL). CTL directed against peptides derived from the Melan A/MART-1, tyrosinase and gp100/Pmel17 antigens can be detected in melanoma patients and in healthy controls. The presence of defined antigenic peptides and corresponding precursor CTL in patients with metastatic melanoma opens perspectives for the development of antigen-specific tumor vaccines. In this study, we examined the expression of Melan A/MART-1, tyrosinase and gp100lPmel17 in fresh melanoma tissues of HLA-A2+ patients and the spontaneous CTL reactivity against antigenic peptides derived from these antigens. Our results demonstrate an inverse correlation of antigen expression and CTL response to Melan A/MART-1 and tyrosinase in patients with metastatic melanoma. In 2 patients with advanced disease, CTL responses against Melan A/MART-1 and tyrosinase were induced by intradermal immunization with synthetic nona- or deca-peptides derived from these antigens. Metastases increasing in size over time showed a loss of Melan A/MART-1 expression in the presence of CTL in one patient. The regression of a metastasis with persistent tyrosinase expression was observed in the other patient after the induction of CTL, reactive against tyrosinase. We conclude that CTL responses against melanocyte differentiation antigens may mediate regression of antigen-positive tumors and select for antigen-loss variants in vivo.

Amino Acid Sequence↗

PubMed1996

Analysis of the major histocompatibility complex class I antigen presentation machinery in normal and malignant renal cells: evidence for deficiencies associated with transformation and progression.

In some human tumors, reduced or defective MHC class I surface expression has been attributed to functional deficiencies of the genes of the antigen-processing machinery, the proteasome subunits low molecular weight (LMP)-2 and LMP-7, as well as the peptide transporters associated with antigen processing (TAP)-1 and TAP-2. Using normal epithelial kidney cells (MZ1851NN) and renal cell carcinoma cell lines established from the primary tumor (MZ1851RC) and a lymph node metastasis (MZ1851LN) of the same patient, we investigated whether the modulation of MHC class I antigens, TAP and LMP molecules, occurs during transformation and subsequent progression. The mRNA and protein expression of MHC class I heavy and light chain TAP and LMP was strongly reduced in MZ1851RC when compared to the corresponding normal kidney cells MZ1851NN, and this suppression was even more pronounced in the metastatic cell line MZ1851LN. In addition, the activity of the TAP molecules, as measured by peptide translocation assays, was also markedly diminished in MZ1851RC compared to MZ1851NN cells and was further down-regulated in cells of the metastatic lesion. MHC class I surface expression was enhanced by either culturing MZ1851RC and MZ1851LN cells at 26 degrees C instead of 37 degrees C or by incubation of both cell lines with class I-specific binding peptides, whereas MHC class I surface expression of MZ1851NN cells was not affected under these culture conditions. IFN-alpha and in particular IFN-gamma treatment enhances the steady-state mRNA and/or protein levels of TAP, LMP, and MHC class I genes of MZ1851 cell lines but had no additional effect on the stability of MCH class I surface expression. These data indicate that malignant transformation and subsequent in vivo selection of renal tubular cells can lead to the recovery of carcinoma cells that show stable expression of an immune escape phenotype. Deficiencies associated with this phenotype involve all levels of the MHC class I-restricted antigen presentation machinery, are at least partially reversible by IFN treatment, and are even more pronounced in cells that had acquired metastatic potential.

ATP Binding Cassette Transporter, Subfamily B, Mem↗