Functional deficiencies of components of the MHC class I antigen pathway in human tumors of epithelial origin.

An association between oncogenic transformation and repression of different components of the MHC class I antigen processing machinery (APM) have been described in murine model systems. In order to discover whether a similar correlation exists, human tumor cell lines of distinct histology with altered ras protein were analyzed for the expression of APM components utilizing RT-PCR and Western blot analyses. A heterogeneous expression pattern of MHC class I antigens, TAP peptide transporter, proteasome subunits, proteasome activator PA28 and the chaperones calnexin, calreticulin as well as tapasin was displayed by these tumor cell lines. Single or combined deficiencies in the expression and/or function of TAP, LMP2, LMP10 and tapasin were demonstrated in 11 of 12 cell lines studied, whereas the expression of calnexin, calreticulin, beta2-microglobulin, LMP7 and PA28alpha was unaltered or only weakly decreased. The impaired expression of TAP, LMP subunits and tapasin was not associated with altered ras, but resulted in reduced MHC class I surface expression. In particular, a significant allele- and locus-specific downregulation of the HLA-A and HLA-B haplotypes was found. IFN-gamma treatment corrected the TAP, LMP and tapasin deficiencies and enhanced the constitutive PA28alpha, LMP7, calnexin and calreticulin expression which was accompanied with increased levels of MHC class I antigens. Thus, dysregulation rather than structural alterations of different APM components might be one mechanism of colon carcinoma, small cell lung carcinoma and pancreatic carcinoma cell lines to evade immune recognition.

CD4+ tumor-infiltrating lymphocytes in cervical cancer recognize HLA-DR-restricted peptides provided by human papillomavirus-E7.

Human papillomavirus (HPV)-encoded proteins may provide targets for CD8+ or CD4+ T lymphocytes infiltrating into cervical cancer. We established an MHC class II-restricted CD4+ T cell line from a patient with cervical cancer that recognizes autologous (HPV35+, HPV59+) cervical cancer cells and the HLA-DR4-matched cervical cancer cell line Me180 (HPV68+) as determined by TNF-alpha secretion. Expression of different HPV-E7 genes in autologous B cells revealed that this T cell line defines a DR4-presented T cell epitope that is shared among the E7 genes of HPV59 and HPV68. MHC class II-presented peptides may be implemented to augment T cell responses directed against autologous tumor cells, particularly if cancer cells lack MHC class I expression, which is a frequent event in the evolution of cervical cancer.

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.

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.

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.

Inhibitory effect of sulfur-containing amino acids on burnt off-flavours in canned liver sausages.

The sensory quality of canned liver sausages is limited by a negative burnt high-temperature-heated flavour, caused by Maillard reaction products between amino acids and sugars. In experiments with liver sausage, reduced glutathione in concentrations of 0.01-0.30% had no positive effect on taste and color. N-acetyl-L-cysteine, an acylated derivative of the amino acid L-cysteine, was tested in concentrations between 0.03-0.50%; a concentration of 0.15% was optimal for the inhibition of the burnt flavour. An acid taste caused by lower pH was corrected by the addition of 0.25% diphosphate. When 0.15% N-acetyl-L-cysteine and 0.25% diphosphate were added to the sausage preparations, the heat-induced changes in amino acids and glucose were the same as in the control. Moreover, under different sterilization conditions, the additive mixture was shown to be an excellent inhibitor of the burnt flavour.

Role of amino acids and glucose in development of burnt off-flavours in liver sausage during heat processing.

The effect of amino acids and glucose on the development of burnt off-flavours was investigated in meat model systems for liver sausage. At a constant glucose concentration, the burnt flavour was intensified by addition of an amino acid mixture. In a batter without liver, the development of burnt off-flavours, similar to those in liver sausage, could be induced through addition of exogenous amino acids and glucose. The endogenous amino acids from liver reacted more intensely than the exogenous amino acids in the formation of the burnt flavour components. After heating batches with added exogenous amino acids and glucose the free amino acid contents (73-89% of initial content) were higher than in batches to which liver was added (42-53% of initial content). The differences in the free amino acid content of glycine, glutamic acid and threonine were linearly related to the intensity of burnt flavour. Results indicate that burnt flavour is due to the Maillard reaction.