Lack of HLA class I antigen expression by melanoma cells SK-MEL-33 caused by a reading frameshift in beta 2-microglobulin messenger RNA

Molecular and functional phenotypes of melanoma cells with abnormalities in HLA class I antigen expression

Analysis of melanoma cell lines with abnormalities in HLA Class I antigen expression has identified two serological phenotypes caused by distinct molecular defects. One is characterized by lack of HLA Class I antigen expression which is not induced by IFN-gamma or by incubation at 25 degrees C for 24 hrs. This phenotype reflects structural changes in the beta(2)m gene which interfere with its transcription and/or translation or result in the synthesis of a defective beta(2)-mu polypeptide unable to associate with HLA Class I heavy chains. The other phenotype manifests very low HLA Class I antigen expression which is enhanced by IFN-gamma or by incubation at 25 degrees C for 24 hrs. This phenotype reflects abnormalities in TAP heterodimer expression, which cause defects in stable assembly and intracellular transport of the HLA Class I antigen trimolecular complex. Loss of HLA Class I antigens renders melanoma cells resistant to lysis by HLA Class I antigen-restricted cytotoxic T cells which specifically recognize melanoma associated antigens. Therefore, abnormalities in HLA Class I antigen expression may have a negative impact on the outcome of T cell based immunotherapy. Characterization of the molecular defects underlying loss of HLA Class I antigens may suggest approaches to restore their expression. Inclusion of these approaches in the protocols of T cell based immunotherapy may improve its efficacy.

Loss of functional beta 2-microglobulin in metastatic melanomas from five patients receiving immunotherapy

BACKGROUND

In a subset of patients with metastatic melanoma, T lymphocytes bearing the cell-surface marker CD8 (CD8+ T cells) can cause the regression of even large tumors. These antitumor CD8+ T cells recognize peptide antigens presented on the surface of tumor cells by major histocompatibility complex (MHC) class I molecules. The MHC class I molecule is a heterodimer composed of an integral membrane glycoprotein designated the alpha chain and a noncovalently associated, soluble protein called beta2-microglobulin (beta 2m). Loss of beta 2m generally eliminates antigen recognition by antitumor CD8+ T cells.

PURPOSE

We studied the loss of beta 2m as a potential means of tumor escape from immune recognition in a cohort of patients receiving immunotherapy.

METHODS

We successfully grew 13 independent tumor cell cultures from tumor specimens obtained from 13 patients in a cohort of 40 consecutive patients undergoing immunotherapy for metastatic melanoma and for whom tumor specimens were available. These cell lines, as well as another melanoma cell line (called 1074mel) that had been derived from tumor obtained from a patient in a cytokine-gene therapy study, were characterized in vitro cytofluorometrically for MHC class I expression and by northern and western blot analyses for messenger RNA (mRNA) and protein expression, respectively, and ex vivo by immunohistochemistry.

RESULTS

After one melanoma cell line (1074mel) was found not to express functional beta 2m by cytofluorometric analysis, four (31%) of the 13 newly established melanoma cell lines were found to have an absolute lack of functional MHC class I expression. Northern blot analysis of RNA extracted from the five cell lines exhibiting no functional MHC class I expression showed that these cells contained normal levels of alpha-chain mRNA but variable levels of beta 2m mRNA. In addition, no immunoreactive beta 2m protein was detected by western blot analysis. When human beta 2m was transiently expressed with the use of a recombinant vaccinia virus, cell-surface MHC class I expression was reconstituted and the ability of these five cell lines to present endogenous antigens was restored. Immunohistochemical staining of tumor sections revealed a lack of immunoreactive MHC class I in vivo, supporting the notion that the in vitro observations were not artifactual. Furthermore, archival tumor sections obtained from patients prior to immunotherapy were available from three patients and were found to be beta 2m positive. This result was consistent with the hypothesis that loss of beta 2m resulted from immunotherapy.

CONCLUSIONS

These data suggest that the loss of beta 2m may be a mechanism whereby tumor cells can acquire immunoresistance. This study represents the first characterization of a molecular route of escape of tumors from immune recognition in a cohort of patients being treated with immunotherapy.

HLA associations in the antitumor response against malignant melanoma

In this study we analyzed the human leukocyte antigen (HLA) pattern of North American Caucasian patients with metastatic melanoma as compared with the North American Caucasian (NAC) population. We also investigated whether the HLA type of melanoma patients had an effect on their tolerance and response to interleukin-2 (IL-2)-based therapy. Four hundred twelve serologic phenotypes of Caucasian melanoma patients referred to the National Cancer Institute, National Institutes of Health, from February 1989 through December 1993 were collected by typing the patient's peripheral blood lymphocytes. Furthermore, 74 melanoma patients were typed for HLA class II by high-resolution sequence specific primer-polymerase chain reaction. Response rate and treatment-related toxicity in those patients receiving IL-2-based treatment (N = 272) were compared with HLA serologic types. The frequency of four HLA-B alleles was significantly different in the melanoma compared with the NAC population: of these, HLA-B5, -B8, and -B15 had a frequency falling between the NAC and the Northern European population. No other significant differences between melanoma patients and NAC population were noted for other HLA loci. A correlation was noted between HLA-DR3 and -DR4 alleles and decreased tolerance to IL-2, whereas homozygosity for HLA-DR decreased the chance of response. There were no significant associations between HLA type and response. It is unlikely that the associations noted between some HLA-B alleles and melanoma bear significantly on the etiology of the disease. The differences seen between American melanoma patients and the NAC population are probably best explained by geographical ancestry. The association between HLA-DR and tolerance to IL-2 therapy noted in this study may offer insight toward the understanding of mechanisms regulating the cascade of events after the systemic administration of IL-2.

Loss of HLA class I antigens by melanoma cells: molecular mechanisms, functional significance and clinical relevance

Malignant transformation of melanocytes may be associated with changes in the expression of major histocompatibility complex (MHC) HLA class I antigens. Interest in the characterization of abnormalities in the expression of MHC class I by melanoma cells has been rekindled by the current emphasis on the application of T-cell-based immunotherapy to melanoma. Here, Soldano Ferrone and Francesco Marincola review defects in class I expression as described in melanoma cells, as well as the molecular mechanisms, functional significance and clinical implications of such defects.

Quantitative correlation between HLA class I allele expression and recognition of melanoma cells by antigen-specific cytotoxic T lymphocytes

MHC class I antigen expression is necessary for CD8+ T-cell-mediated recognition of tumors. Recently, several mechanisms leading to loss or decreased expression of MHC antigens on the tumor cell surface have been described that may account for tumor escape from immune recognition. It is yet unknown whether tumor recognition by CTL occurs at a threshold amount of MHC molecules or correlates with the level of HLA-allele expression. In this study, a model was developed in which clones derived from the 624-MEL melanoma cell line and expressing varying amounts of HLA-A2 molecules were lysed in a standard 51Cr release assay by an HLA-A2-restricted CTL clone (A42) or a bulk culture of tumor-infiltrating lymphocytes. The A42 clone and the tumor-infiltrating lymphocyte culture were characterized previously as specifically recognizing the melanoma antigen MART-1(27-35) peptide. A marked heterogeneity in the susceptibility to lysis by A42 was observed in tumor clones and was not due to heterogeneous expression of MART-1 by the clones or loss of accessory molecules involved in the lymphocyte-target interaction. Lysis by A42 and by the tumor-infiltrating lymphocyte culture significantly correlated with the level of HLA-A2 expression, evaluated as mean channel number of fluorescence by flow cytometry (P < 0.001). Transfection of an HLA-A2-negative clone (624.28) with the HLA-A2.1 gene produced a panel of clones expressing different levels of HLA-A2, the lysis of which was highly correlated with the expression of HLA-A2 (P < 0.001). The addition of exogenous MART-1(27-35) peptide enhanced lysis of clones expressing intermediate amounts of HLA-A2 but did not affect clones with high expression. These data suggest that the number of HLA molecules present on the surface of tumor cells can quantitatively affect their lysis by CTL in situations with borderline amounts of peptide and/or MHC.

Defective major histocompatibility complex class I expression in a sarcomatoid renal cell carcinoma cell line

We studied major histocompatibility complex (MHC) class I expression in 12 tumor cell culture lines established from patients with metastatic renal cell carcinoma (RCC). In one of these cell culture lines, UOK 123, we found no surface expression of beta 2-microglobulin (beta 2m) and MHC class I by flow cytometry. Immunofluorescence staining using three different monoclonal antibodies to beta 2m revealed no detectable beta 2m in the endoplasmic reticulum (ER), Golgi apparatus, cytoplasm, or on the cell surface. There was no evidence of folded class I molecules inside or on the surface of the cells; however, the ER stained intensively for unfolded class I molecules. Transient expression of beta 2m by UOK 123 after infection with a recombinant vaccinia virus containing the gene for beta 2m resulted in normal expression of both beta 2m and class I (HLA-A, B, C) determinants assessed by flow cytometry analysis. No expression of class I or beta 2m was seen with the recombinant vaccinia vector carrying a control gene. The inability of class I molecules to reach the cell surface is due to the requirement of beta 2m for proper folding and presentation of the class I MHC complex. The failure to assemble and express MHC class I complex on the cell surface renders these cells incapable of antigen presentation to cytotoxic T cells and provides a mechanism for escape from immune recognition by the tumor.

The HLA-A,B,C genotype of the class I negative cell line Daudi reveals novel HLA-A and -B alleles

Daudi, a lymphoblastoid B cell line derived from an African Burkitt lymphoma does not express HLA-A,B,C antigens at the cell surface. Although HLA-A,B,C heavy chains are made normally they do not assemble into functional molecules because beta 2-microglobulin is absent. Previous serological analysis of somatic cell hybrids indicated that the HLA haplotypes of Daudi encoded HLA-A1, A10(A26), B17, and B16(38) antigens. Here we describe the application of molecular methods: ARMS-PCR, cDNA cloning and sequencing, immunoprecipitation and gel electrophoresis, to define the class I genotype of the Daudi cell line which is HLA-A*0102, A*6601, B*5801, B*5802, Cw*0302 and Cw*0602. With the exception of the B38 antigen, which is not a product of the alleles defined, the genotype is consistent with the serological description. Two previously undiscovered alleles emerged from this analysis: A*0102 and B*5802. The A*0102 allele differs from A*0101 by 5 nucleotide substitutions within exon 2 where it has a motif shared with A*30 alleles; the B*5802 allele differs from B*5801 by 3 substitutions in exon 3 where it has a motif shared with B*14 alleles. Subtyping HLA-A1 alleles showed A*0102 was well represented amongst individuals typed serologically as A1 in an African population but was absent from caucasoids. B*5802 has been found in a second individual. Thus the novel A and B alleles are not specific to the Daudi tumor. Overall, this analysis of a single East African cell illustrates the power of molecular methods to define new class I HLA alleles in non-caucasoid populations.

Lymphocyte-melanoma interaction: role of surface molecules

The coexistence of tumor-specific immunity with a progressing tumor is observed in most experimental systems and remains one of the major paradoxes of tumor immunology. Expression of several surface molecules on melanoma cells, e.g., intercellular adhesion molecule 1 (ICAM-1) or major histocompatibility complex (MHC) class II, has been associated with an aggressive tumor growth and an reduced host antitumor response. HLA class I expression is also frequently altered in melanoma compared to melanocytes. Given the central role of these molecules in the restriction of T cell recognition, regulation of tumor HLA class I expression might also be a strategy for the evasion of immune surveillance by the malignant cells. The fact that it is now possible to clone antigen-specific T cells from tumor patients, as well as the relevant autologous tumor cell lines, enabled us to establish a model system to investigate possible tumor escape mechanisms from immunosurveillance. Using this system, we were able to demonstrate that purified soluble ICAM-1 or 12-fold-concentrated cell-free melanoma supernatants, containing shed ICAM-1, were able to inhibit conjugate formation between T cell clones and the autologous melanoma cells as efficiently as monoclonal antibodies against CD11a, Soluble ICAM-1 also abrogated the MHC-restricted killing of the melanoma by T cell clones. We further observed that a number of CD4+ T cell clones and melanoma cell lines established from the same tumors form conjugates with each other, leading to an increase of [Ca2+]i in the T cell clone; however, this interaction failed to induce interleukin-2 production or proliferation of the T cell clone. Furthermore, this interaction rendered the T cell clone unresponsive to subsequent stimulation. All these effects were MHC class II restricted. Therefore, the melanoma was capable of delivering antigen-specific signals to the T cell clone, but did not deliver the costimulatory signals, e.g., a B7/CD28 interaction, necessary for full T cell activation. Transfection of the melanoma with an expression vector containing a B7 cDNA with subsequent B7 expression on its cell surface renders the melanoma a fully competent antigen-presenting cell which is able to induce a nuclear factor binding to the interleukin-2 promoter in the specific T cell clone, followed by enhanced interleukin-2 transcription, synthesis, and T cell proliferation.

Locus-specific analysis of human leukocyte antigen class I expression in melanoma cell lines

Surface expression of human leukocyte antigen (HLA) class I antigens on melanoma lines was evaluated by locus-specific monoclonal antibodies (mAbs) with three different techniques: Fluorescence-activated cell sorting (FACS), immunohistochemistry with cytospin preparation (ICP), and complement-mediated cytotoxicity (CMC). Eleven HLA class I-expressing cell lines developed from metastases were used. Specific expression of HLA loci was examined under routine culture conditions and after 48-h incubation in interferon-gamma (IFN-gamma; 500 U/ml). Loss of allelic expression was seen in one line (586-MEL): Products of genes coding for HLA-A29 and -B44, in strong linkage disequilibrium, were not detectable. HLA-A antigens were consistently detected by all methodologies and minimally affected by pretreatment with IFN-gamma. HLA-B antigens were detectable in 8 of 11 lines by ICP and 3 of 11 lines by CMC. By FACS the supratypic specificity HLA-Bw6 was expressed at low levels in most lines (mean fluorescence 47.2 +/- 13.4 and rose to 259.8 +/- 45.9 after incubation with IFN-gamma; p < 0.001). HLA-Cw antigen detection by CMC correlated with HLA-B (p < 0.01), suggesting that down-regulation and sensitivity to IFN-gamma are shared by the two loci. This low expression of the HLA-B antigens may play a role in the evasion of the host immune response and its up-regulation may be useful in allowing tumor antigen recognition.

Non-antibody immunotherapy of cancer

Immunotherapeutic agents have become important additions to the list of anti-cancer treatments; further progress will require more information about how the immune system can respond to tumor cells. Tumor cells can avoid eliciting an immune response through several mechanisms. Understanding these mechanisms may suggest strategies to manipulate tumor cells so that they trigger an effective immune response. Another strategy being developed is to improve the therapeutic index of cytokines so that better anti-tumor effects can be elicited with less toxicity.