Differences in the expression of human class I MHC alleles and their associated peptides in the presence of proteasome inhibitors

We have studied the contributions of proteasome inhibitor-sensitive and -insensitive proteases to the generation of class I MHC-associated peptides. The cell surface expression of 13 different human class I MHC alleles was inhibited by as much as 90% or as little as 40% when cells were incubated with saturating concentrations of three different proteasome inhibitors. Inhibitor-resistant class I MHC expression was not due to TAP-independent expression or preexisting internal stores of peptides. Furthermore, it did not correlate with the amount or specificity of residual proteasome activity as determined in in vitro proteolysis assays and was not augmented by simultaneous incubation with multiple inhibitors. Mass spectrometry was used to directly characterize the peptides expressed in the presence and absence of proteasome inhibitors. The number of peptide species detected correlated with the levels of class I detected by flow cytometry. Thus, for many alleles, a significant proportion of associated peptide species continue to be generated in the presence of saturating levels of proteasome inhibitors. Comparison of the peptide-binding motifs of inhibitor-sensitive and -resistant class I alleles further suggested that inhibitor-resistant proteolytic activities display a wide diversity of cleavage specificities, including a trypsin-like activity. Sequence analysis demonstrated that inhibitor-resistant peptides contain diverse carboxyl termini and are derived from protein substrates dispersed throughout the cell. The possible contributions of inhibitor-resistant proteasome activities and nonproteasomal proteases residing in the cytosol to the peptide profiles associated with many class I MHC alleles are discussed.

Enhanced expression of HLA class I molecules in human hepatocellular carcinoma cells transduced with gamma-interferon gene

OBJECTIVE

To investigate the expression of exogenous gamma-interferon gene in human hepatocellular carcinoma cells following retroviral transduction and the effect on the expression of surface HLA class I molecules.

METHODS

Retroviral vector pLXSN was used to introduce human gamma-interferon (IFN-gamma) gene into four different human hepatocellular carcinoma cell lines (HCC). The G418-resistant colonies were isolated and cloned. The integration and expression of IFN-gamma gene were determined by PCR and RT-PCR analysis. A bioassay method was used to test the amount of IFN-gamma secreted by gene modified HCC cells. The expression of HLA class I molecules in HCC cells were analyzed by flow cytometry using indirect fluorescence staining.

RESULTS

Four different HCC cell lines were successfully transduced with human IFN-gamma gene using retroviral vector. The integration and expression of IFN-gamma gene were shown only in the transduced cells. All four genetically modified HCC cells can secrete varied amount of IFN-gamma and demonstrate a significant up-regulation of surface HLA class I antigens. One specific HLA class I antigen, HLA-A2, has almost the same degree of increase as that of the total HLA class I molecules after transduction with IFN-gamma gene.

CONCLUSIONS

Gene modification with IFN-gamma gene can significantly enhance the expression of HLA class I molecules in HCC cells and may increase its immunogenicity. These gene modified tumor vaccines can be helpful in tumor biotherapy.

A nucleotide insertion in exon 4 is responsible for the absence of expression of an HLA-A*01 allele

HLA class I typing performed in parallel by molecular biology and serology has revealed cases where an HLA class I allele was identified whereas the corresponding antigen was not detected on the cell surface. In the present report, we describe four members of a family in whom an HLA-A1 allele identified at the molecular level was typed as A "blank" by lymphocytotoxicity. This serologically blank antigen was undetectable by isoelectric focusing (IEF). Sequencing of the HLA-A*01 allele from the promoter region to the eighth exonic region revealed insertion of a "C" nucleotide at the beginning of the fourth exon as compared to the common HLA-A*0101 allele. This mutation causes a frame shift, giving rise to an early stop codon in the fourth exon.

Secretor status and human leucocyte antigens in coeliac disease

BACKGROUND

The ability to secrete blood group antigens into body fluids and secretions is controlled by a single gene on chromosome 19. By means of erythrocyte Lewis (Le) antigen phenotype secretor status can be inferred. An increase prevalence of non-secretors of blood group antigens among coeliac patients has recently been described.

METHODS

Blood was collected from 112 coeliac patients and 103 controls and tested for secretor status. Secretor status was correlated with human leucocyte antigens (HLA) in coeliac patients, thus evaluating a proposed interaction of susceptibility genes--that is, the secretor gene on chromosome 19 and HLA-linked genes on chromosome 6. Case notes for coeliacs were reviewed with regard to clinical outcome.

RESULTS

Of 112 coeliacs who had either Le(a) or Le(b) antigens, 36 (32%) were non-secretors Le(a+, b-), compared with 27% (28) of 103 disease-free controls (P = 0.313). Recessive Lewis phenotype Le(a-, b-) was found in 9% of coeliacs versus 2% of controls. Prevalence of HLA-A1, B8, DR3, and DQ2 was unrelated to secretor status in coeliac versus patients. An increased prevalence of complications and coeliac-associated abnormalities was found in the non-secreting and recessive coeliac groups.

CONCLUSIONS

This study shows no firm relationship between the non-secretor state and coeliac disease, nor any difference in the distribution of HLA markers among secretor and non-secretor coeliacs. It is unlikely, therefore, that the secretor gene is the much sought-after second coeliac gene.

Induction of antigen-specific cytolytic T cells in situ in human melanoma by immunization with synthetic peptide-pulsed autologous antigen presenting cells

Human melanoma cells can process the MAGE-1 gene product and present the processed nonapeptide EADPTGHSY on their major histocompatibility complex class I molecules, HLA-A1, as a determinant for cytolytic T lymphocytes (CTLs). Considering that autologous antigen presenting cells (APCs) pulsed with the synthetic nonapeptide might, therefore, be immunogenic, melanoma patients whose tumor cells express the MAGE-1 gene and who are HLA-A1+ were immunized with a vaccine made of cultured autologous APCs pulsed with the synthetic nonapeptide. Analyses of the nature of the in vivo host immune response to the vaccine revealed that the peptide-pulsed APCs are capable of inducing autologous melanoma-reactive and the nonapeptide-specific CTLs in situ at the immunization site and at distant metastatic disease sites.

Selective IgA deficiency, IgG subclass deficiency, and the major histocompatibility complex

Here we have examined the connection between IgA deficiency, IgG subclass deficiency, and the absence of alleles of complement C4, and show that IgA deficient subjects who have IgG subclass deficiencies may also have an increased frequency of C4 null alleles. In our group, we found an increased incidence of HLA B38 which might reflect the ethnic composition of the patients tested. While family studies are of primary importance to assess the relationships between histocompatibility antigens and immune deficiency, these studies are complicated by the observation that C4 null alleles are not always inherited with the humoral defect.