SSX Expression Research Articles

A Role for SMARCB1 in Synovial Sarcomagenesis Reveals That SS18-SSX Induces Canonical BAF Destruction.

Reduced protein levels of SMARCB1 (also known as BAF47, INI1, SNF5) have long been observed in synovial sarcoma. Here, we show that combined Smarcb1 genetic loss with SS18-SSX expression in mice synergized to produce aggressive tumors with histomorphology, transcriptomes, and genome-wide BAF-family complex distributions distinct from SS18-SSX alone, indicating a defining role for SMARCB1 in synovial sarcoma. Smarcb1 silencing alone in mesenchyme modeled epithelioid sarcomagenesis. In mouse and human synovial sarcoma cells, SMARCB1 was identified within PBAF and canonical BAF (CBAF) complexes, coincorporated with SS18-SSX in the latter. Recombinant expression of CBAF components in human cells reconstituted CBAF subcomplexes that contained equal levels of SMARCB1 regardless of SS18 or SS18-SSX inclusion. In vivo, SS18-SSX expression led to whole-complex CBAF degradation, rendering increases in the relative prevalence of other BAF-family subtypes, PBAF and GBAF complexes, over time. Thus, SS18-SSX alters BAF subtypes levels/balance and genome distribution, driving synovial sarcomagenesis. SIGNIFICANCE: The protein level of BAF component SMARCB1 is reduced in synovial sarcoma but plays a defining role, incorporating into PBAF and SS18-SSX-containing canonical BAF complexes. Reduced levels of SMARCB1 derive from whole-complex degradation of canonical BAF driven by SS18-SSX, with relative increases in the abundance of other BAF-family subtypes.See related commentary by Maxwell and Hargreaves, p. 2375.This article is highlighted in the In This Issue feature, p. 2355.

Relationship between Cancer Stem Cell Marker CD133 and Cancer Germline Antigen Genes in NCI-H292 Lung Cancer Cells.

BackgroundPrevious studies have shown that lung cancer stem cells express CD133 and that certain cancer stem cells express cancer germline antigens (CGAs). The transcriptional regulation of CD133 is complicated and poorly understood. We investigated CD133 and CGA expression in a non-small cell lung cancer cell line.MethodsThe expression levels of CD133 and CGAs (MAGE-6, GAGE, SSX, and TRAG-3) were measured in an NCI-H292 lung cancer cell line. The methylation status of the CD133 gene promoter region was analyzed. The expression levels and promoter methylation statuses of CD133 and CGAs were confirmed by treatment with the demethylating agent 5-aza-2′-deoxycytidine (ADC).ResultsAfter treatment with ADC, CD133 expression was no longer detected. MAGE-6 and TRAG-3 were detected before ADC treatment, while GAGE and SSX were not detected. ADC treatment upregulated MAGE-6 and TRAG-3 expression, while GAGE expression was still undetected after treatment, and only weak SSX expression was observed. GAGE expression was not correlated with expression of CD133, while the levels of expression of MAGE-6, TRAG-3, and SSX were inversely correlated with CD133 expression.ConclusionThese results showed that CD133 expression can be regulated by methylation. Thus, the demethylation of the CD133 promoter may compromise the treatment of lung cancer by inactivating cancer stem cells and/or activating CGAs.

DrosophilaSister-of-Sex-lethal reinforces a male-specific gene expression pattern by controllingSex-lethalalternative splicing

In Drosophila, female development is governed by a single RNA-binding protein, Sex-lethal (Sxl), that controls the expression of key factors involved in dosage compensation, germline homeostasis and the establishment of female morphology and behaviour. Sxl expression in female flies is maintained by an auto-regulatory, positive feedback loop with Sxl controlling splicing of its own mRNA. Until now, it remained unclear how males prevent accidental triggering of the Sxl expression cascade and protect themselves against runaway protein production. Here, we identify the protein Sister-of-Sex-lethal (Ssx) as an inhibitor of Sxl auto-regulatory splicing. Sxl and Ssx have a comparable RNA-binding specificity and compete for binding to RNA regulatory elements present in the Sxl transcript. In cultured Drosophila cells, Sxl-induced changes to alternative splicing can be reverted by the expression of Ssx. Moreover, in adult male flies ablation of the ssx gene results in a low level of productive Sxl mRNA splicing and Sxl protein production in isolated, clonal cell populations. In sum, this demonstrates that Ssx safeguards male animals against Sxl protein production to reinforce a stable, male-specific gene expression pattern.

Abstract 1093: The melanoma-enriched microRNA miR-4731 regulates genes involved in cell cycle and the melanosome

Abstract We previously identified miR-4731-5p (miR-4731) as a melanoma-enriched microRNA following comparison of melanoma with other cell lines from solid malignancies. Additionally, miR-4731 has been found in serum from melanoma patients and expressed less abundantly in metastatic melanomas from stage IV patients relative to stage III patients. As miR-4731 has no known function, we used biotin-labelled miRNA duplex pull-down to identify binding targets of miR-4731 in three melanoma cell lines. Using the miRanda miRNA binding algorithm, all pulled-down transcripts common to the three cell lines (n = 1092) were predicted to be targets of miR-4731 and gene-set enrichment analysis of these (via STRING v9.1) highlighted significantly associated genes related to the ‘cell cycle’ and ‘melanosome’ pathways. Following miR-4731 overexpression, a selection (n = 81) of pull-down transcripts underwent validation using a custom qRT-PCR array. These data revealed that miR-4731 regulates multiple genes associated with the cell cycle (e.g. CCNA2, ORC5L, and PCNA) and melanosome (e.g. RAB7A, CTSD, and GNA13). Furthermore, members of the synovial sarcoma X breakpoint family (SSX) (melanoma growth promoters) were also down-regulated (e.g. SSX2, SSX4, and SSX4B) as result of miR-4731 overexpression. We therefore speculate that loss of miR-4731 expression supports melanoma growth by, in part; reducing its regulatory control of SSX expression levels together with members of the cell cycle pathway, which warrants further investigation. Citation Format: Mitchell S. Stark, Lisa Tom, Glen M. Boyle, Vanessa F. Bonazzi, Adrian C. Herington, Pamela M. Pollock, Nicholas K. Hayward. The melanoma-enriched microRNA miR-4731 regulates genes involved in cell cycle and the melanosome. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1093.

The ‘melanoma-enriched’ microRNA miR-4731-5p acts as a tumour suppressor

We previously identified miR-4731-5p (miR-4731) as a melanoma-enriched microRNA following comparison of melanoma with other cell lines from solid malignancies. Additionally, miR-4731 has been found in serum from melanoma patients and expressed less abundantly in metastatic melanoma tissues from stage IV patients relative to stage III patients. As miR-4731 has no known function, we used biotin-labelled miRNA duplex pull-down to identify binding targets of miR-4731 in three melanoma cell lines (HT144, MM96L and MM253). Using the miRanda miRNA binding algorithm, all pulled-down transcripts common to the three cell lines (n=1092) had potential to be targets of miR-4731 and gene-set enrichment analysis of these (via STRING v9.1) highlighted significantly associated genes related to the ‘cell cycle’ pathway and the ‘melanosome’. Following miR-4731 overexpression, a selection (n=81) of pull-down transcripts underwent validation using a custom qRT-PCR array. These data revealed that miR-4731 regulates multiple genes associated with the cell cycle (e.g. CCNA2, ORC5L, and PCNA) and the melanosome (e.g. RAB7A, CTSD, and GNA13). Furthermore, members of the synovial sarcoma X breakpoint family (SSX) (melanoma growth promoters) were also down-regulated (e.g. SSX2, SSX4, and SSX4B) as a result of miR-4731 overexpression. Moreover, this down-regulation of mRNA expression resulted in ablation or reduction of SSX4 protein, which, in keeping with previous studies, resulted in loss of 2D colony formation. We therefore speculate that loss of miR-4731 expression in stage IV patient tumours supports melanoma growth by, in part; reducing its regulatory control of SSX expression levels.

SSX2 regulates focal adhesion but does not drive the epithelial to mesenchymal transition in prostate cancer

Prostate cancer is the most commonly diagnosed malignancy for men in the United States. Metastatic prostate cancer, the lethal form of the disease, has a life expectancy of approximately five years. Identification of factors associated with this transition to metastatic disease is crucial for future therapies. One such factor is the SSX gene family, a family of cancer/testis antigens (CTA) transcription factors which have been shown to be aberrantly expressed in other cancers and associated with the epithelial to mesenchymal transition (EMT). We have previously shown that SSX expression in prostate cancers was restricted to metastatic tissue and not primary tumors. In this study, we have identified SSX2 as the predominant SSX family member expressed in prostate cancer, and found its expression in the peripheral blood of 19 of 54 (35%) prostate cancer patients, with expression restricted to circulating tumor cells, and in 7 of 15 (47%) metastatic cDNA samples. Further, we examined SSX2 function in prostate cancer through knockdown and overexpression in prostate cancer cell lines. While overexpression had little effect on morphology or gene transcript changes, knockdown of SSX2 resulted in an epithelial morphology, increased cell proliferation, increased expression of genes involved in focal adhesion, decreased anchorage independent growth, increased invasion, and increased tumorigenicity in vivo. We conclude from these findings that SSX2 expression in prostate cancer is not a driver of EMT, but is involved in processes associated with EMT including loss of focal adhesion that may be related to tumor cell dissemination.

Abstract 1423: SSX-2 expression and function in metastatic prostate cancer

Abstract Background: The SSX family of proteins, whose function and aberrant expression in prostate cancer isn't fully understood, may lead to disease progression from localized to metastatic disease. Cancer-testis antigens (CTAs) are a group of proteins whose expression is restricted to germline cells among normal somatic cells. CTAs have been found to be aberrantly expressed in many different cancers. Due to their restricted expression to tumor cells among MHC class I-expressing cells, there has been interest in CTAs as tumor-specific targets for CD8+ T cell-directed therapies. Amongst the CTA genes is the Synovial Sarcoma X chromosome breakpoint (SSX) gene family. The SSX family consists of ten highly homologous members, several of which have been detected in a wide variety of cancers. We have previously shown that SSX expression is confined to metastatic prostate tissue, and is not detected in primary prostate tumors. The function of the SSX family is largely unknown, and further insights into its function may reveal avenues for future directed therapies. Methods: We determined the identity and prevalence of SSX family members in metastatic prostate cancer tissues and in peripheral blood samples of patients with prostate cancer. Specifically, cDNA from metastatic prostate tissues was examined by PCR with primers specific for each SSX family member; SSX family member expression was detected in peripheral blood samples using rt-PCR. To further understand SSX-2 function, prostate cell lines with SSX-2 expression knocked down or overexpressed were evaluated in vitro for morphological changes, tumorigenicity (soft agar colony formation), proliferation, and invasion (scratch test). Finally using qPCR, expression levels of markers of the epithelial to mesenchymal transition (EMT) were examined in the knocked down and overexpressed cell lines. Results: SSX-2 was found to be the dominant family member expressed in prostate cancer, with 47% (7/15) of metastatic cDNA samples expressing SSX-2. SSX-1 was detected in one sample (1/15), and no additional family members were detected. SSX-2 mRNA was similarly detectable in the peripheral blood of 17 of 33 (51%) patients with recurrent prostate cancer and 0% (0 of 10) control blood donors without prostate cancer. In in vitro functional studies, SSX-2 knockdown of the 22Rv1 cell line led to cell morphology changes, increased cell proliferation, and a decrease in soft agar colony formation. Knockdown was also accompanied by altered expression of genes involved in EMT (Twist-1, ZEB1/2, Slug, vimentin). Complementary changes were observed in the RWPE-1 normal prostate epithelial cell line transfected to overexpress SSX-2. Conclusions: Due to the preferential expression of SSX-2 in disseminated prostate cancer, as well as the effects of SSX knockdown and overexpression on EMT-related genes, we believe that SSX-2 is involved in the EMT process, and potentially in the progression of prostate cancer to metastatic disease. Citation Format: Jordan E. Bloom, Douglas G. McNeel. SSX-2 expression and function in metastatic prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1423. doi:10.1158/1538-7445.AM2015-1423

Oncogenic Functions of the Cancer-Testis Antigen SSX on the Proliferation, Survival, and Signaling Pathways of Cancer Cells

SSX is a transcription factor with elusive oncogenic functions expressed in a variety of human tumors of epithelial and mesenchymal origin. It has raised substantial interest as a target for cancer therapy since it elicits humoral responses and displays restricted expression to cancer, spermatogonia and mesenchymal stem cells. Here, we investigated the oncogenic properties of SSX by employing a RNA interference to knock-down the endogenous expression of SSX in melanoma and osteosarcoma cell lines. Depletion of SSX expression resulted in reduced proliferation with cells accumulating in the G1 phase of the cell cycle. We found that the growth promoting and survival properties of SSX are mediated in part though modulation of MAPK/Erk and Wnt signaling pathways, since SSX silencing inhibited Erk-mediated signaling and transcription of cMYC and Akt-1. We also found that SSX forms a transient complex with β-catenin at the G1-S phase boundary resulting in the altered expression of β-catenin target genes such as E-cadherin, snail-2 and vimentin, involved in epithelial-mesenchymal transitions. Importantly the silencing of SSX expression in in vivo significantly impaired the growth of melanoma tumor xenografts. Tumor biopsies from SSX silenced tumors displayed reduced cyclin A staining, indicative of low proliferation and predominantly cycloplasmic β-catenin compared to SSX expressing tumors. The present study demonstrates a previously unknown function of SSX, that as an oncogene and as a tumor target for the development of novel anti-cancer drugs.

SSX expression and function in prostate cancer

Meeting abstracts Cancer-testis antigens (CTAs) are a group of proteins whose expression is essentially restricted to testis germline cells among normal somatic cells. CTAs also possess a heightened expression in many different types of cancer. Due to their restricted expression in tumor cells

Cancer/testis antigen SSX2 enhances invasiveness in MCF-7 cells by repressing ERα signaling

Cancer/testis antigen (CTA) SSX2, which is silent in most normal adult tissues and expressed in various malignant tumors, has been identified for decades. Expression of SSX in tumors has been associated with advanced stages and worse patient prognosis. However, little is known about its role in breast cancer. The SSX2 expression plasmid constructed was stably transfected into the breast cancer cell line MCF-7. The influence of SSX2 on MCF-7 cells was assessed using MTT assay, flow cytometry, transwell invasion assay and in vivo tumorigenicity assay. A comparative proteomic approach was performed to identify and clarify the underlying molecular mechanisms. SSX2 expression was more pronounced in ERα-negative breast cancer cells compared with the positive ones. Overexpression of SSX2 induced cell growth and prompted cell invasion. Both ERα and E-cadherin expression were suppressed in the SSX2 overexpressing MCF-7 cells. Eleven known proteins were identified with significant differential expression. Among these, five were decreased, while other six were increased in the SSX2 overexpressing MCF-7 cells. These results suggested SSX2 may enhance invasiveness in MCF-7 cells both in vivo and in vitro. The regulation of ERα signaling by target proteins of SSX2 may explain the metastatic potential of breast cancer cells.

Expression and Immunotherapeutic Targeting of the SSX Family of Cancer–Testis Antigens in Prostate Cancer

Recent U.S. Food and Drug Administration approval of the first immunotherapy for prostate cancer encourages efforts to improve immune targeting of this disease. The synovial sarcoma X chromosome breakpoint (SSX) proteins comprise a set of cancer-testis antigens that are upregulated in MHC class I-deficient germline cells and in various types of advanced cancers with a poor prognosis. Humoral and cell-mediated immune responses to the SSX family member SSX2 can arise spontaneously in prostate cancer patients. Thus, SSX2 and other proteins of the SSX family may offer useful targets for tumor immunotherapy. In this study, we evaluated the expression of SSX family members in prostate cancer cell lines and tumor biopsies to identify which members might be most appropriate for immune targeting. We found that SSX2 was expressed most frequently in prostate cell lines, but that SSX1 and SSX5 were also expressed after treatment with the DNA demethylating agent 5-aza-2'-deoxycytidine. Immunohistochemical analysis of microarrayed tissue biopsies confirmed a differential level of SSX protein expression in human prostate cancers. Notably, SSX expression in patient tumor samples was restricted to metastatic lesions (5/22; 23%) and no expression was detected in primary prostate tumors examined (0/73; P < 0.001). We determined that cross-reactive immune responses to a dominant HLA-A2-specific SSX epitope (p103-111) could be elicited by immunization of A2/DR1 transgenic mice with SSX vaccines. Our findings suggest that multiple SSX family members are expressed in metastatic prostate cancers which are amenable to simultaneous targeting.

Abstract A66: Expression and immunotherapeutic targeting of the SSX family of cancer-testis antigens in prostate cancer

Abstract Members of the SSX family of proteins were among the first cancer-testis antigens (CTA) identified. Characterized by tissue-restricted expression to MHC class l-deficient germline cells and frequent ectopic expression in tumors of various histological origin, CTA are highly tumor-specific antigens. SSX proteins comprise a family of ten members with mRNA expression often found in advanced-stage disease and associated with worse patient prognosis. We have previously shown that humoral and cell-mediated immune responses to SSX2 can arise spontaneously in patients with prostate cancer, which combined with the expression of these proteins in MHC class l-negative tissue, makes SSX proteins potentially attractive targets for tumor immunotherapy. In the current study, we evaluated SSX family member expression in prostate cancer cell lines and tumor biopsies to identify therapeutic targets for vaccine therapy in prostate cancer. We found by RT-PCR and qRT-PCR that SSX1, SSX2, and SSX5 were frequently expressed in prostate cancer cell lines and could be induced by treatment with epigenetic modifying agents (EMA) such as 5-aza-2′-deoxycytidine. Furthermore, we observed differential SSX protein expression in paraffin-embedded prostate cancer biopsies on tissue microarray by immunohistochemical staining. Interestingly, SSX expression in patient samples was restricted to metastatic prostate cancer lesions (5/22; 23%), while expression in primary prostate tumors was not observed (0/73). Finally, we determined that it is possible to elicit cross-reactive immune responses to a dominant SSX epitope p103–111 shared by the different SSX family members by immunization of A2/DR1 transgenic mice with SSX peptides or a plasmid DNA vaccine encoding SSX2. Overall, these results suggest that multiple SSX family members are expressed in prostate cancer and can be simultaneously targeted using immunotherapeutic vaccines. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A66.

Heterogeneous expression of GAGE, NY‐ESO‐1, MAGE‐A and SSX proteins in esophageal cancer: Implications for immunotherapy

Cancer/testis antigens (CTAs) elicit immune response in cancer patients and are therefore targets of immunotherapy. Current information on CTA expression is primarily based on mRNA assays and little is known about their expression at the protein level. The objectives of our study are to analyze GAGE, NY-ESO-1, MAGE-A and SSX protein expression in esophageal cancer and to correlate their expression patterns with clinicopathologic parameters and survival. We examined CTA protein expression in 213 patients with esophageal cancer by immunohistochemistry. Antigen-positive tumors were evaluated once and antigen-negative tumors were evaluated 3 times by examining different parts of the cancer specimen. GAGE, NY-ESO-1 and MAGE-A were heterogeneously expressed in 42 (20%), 44 (21%) and 111 (52%) tumors, respectively, whereas SSX expression was not detected. Of the 126 (59%) patients expressing CTAs, 70 (33%) expressed 1, 41 (19%) expressed 2 and 15 (7%) expressed 3 antigens. The expression of MAGE-A was correlated with those of GAGE (p = 0.001) and NY-ESO-1 (p = 0.002), and the expression of GAGE was correlated with that of NY-ESO-1 (p = 0.002). One hundred fifty-six (79%) sections were positively stained in the first evaluation, whereas 37 (19%) and 4 (2%) positive sections were identified in the second and third evaluations, respectively. Particularly, MAGE and GAGE expression showed overlaps. GAGE, NY-ESO-1 and MAGE-A protein expression was not correlated with the disease progression, TNM factors or survival. The detection of immunonegative cells in every specimen suggests addition of other drugs such as 5-aza-2'-deoxycytidine to increase the therapeutic effect of CTA-specific cancer vaccines.

Cancer/Testis Antigen Expression in Human Mesenchymal Stem Cells: Down-regulation of SSX Impairs Cell Migration and Matrix Metalloproteinase 2 Expression

Several families of genes by and large located on the X chromosome encode proteins of unspecified function. Commonly known as cancer/testis (CT) antigens, they are considered, under normal conditions, only to be expressed in cells of the germ line and placenta. CT genes are also often expressed in cancer cells, hence their classification. Here we report that their expression in normal cells is wider spread and can be observed in cells with the potential for self-renewal and pleuripotency, namely, stem cells. Several CT genes and their products, CT antigens, including SSX, NY-ESO-1, and N-RAGE, were expressed in undifferentiated mesenchymal stem cells (MSCs) and down-regulated after osteocyte and adipocyte differentiation. To elucidate the possible overlapping function played by these genes in cancer and stem cells, a comparative analysis of the localization of their proteins was made. In addition, localization relative to other MSC markers was examined. This revealed that SSX localizes in the cytoplasm and overlap occurs in regions where matrix metalloproteinase 2 (MMP2) and vimentin accumulate. Nevertheless, it was found that no protein interactions between these molecules occur. Further investigation revealed that the migration of a melanoma cell line (DFW), which expresses SSX, MMP2, and vimentin, decreases when SSX is down-regulated. This decrease in cell migration was paralleled by a reduction in MMP2 levels. Analogous to this, SSX expression is down-regulated in MSCs after differentiation; concomitantly a reduction in MMP2 levels occurs. In addition, E-cadherin expression increases, mimicking a mesenchymal epithelial transition. These results afford SSX a functional role in normal stem cell migration and suggest a potentially similar function in cancer cell metastases.

Expression of SSX-2 and SSX-4 genes in neuroblastoma.

The SSX genes are members of the family of cancer/testis antigens that encode tumor-associated antigens recognizable by autologous cytolytic T lymphocytes. Their expression is common in tumors of diverse lineages and absent in normal tissues except testis and thyroid. In this study, sixty-seven neuroblastomas (NB) (12 stage 1, 13 stage 2, 12 stage 3, 12 stage 4S and 13 stage 4) were examined by RT-PCR and a sensitive chemiluminescent detection method for SSX-2 and SSX-4 expression. Seventy-two percent (13/18) of stage 4 NB expressed SSX-2 and 67% (12/18) expressed SSX-4. SSX-2 and SSX-4 positivity correlated with metastatic NB stage 4 (p=0.02 and p=0.006, respectively). Sensitivity experiments showed SSX-2 detection was one tumor cell in 10(6) normal cells, and one in 10(4) for SSX-4. All normal tissues (n=6), with the exception of testis, normal bone marrow (BM, n=12) and normal peripheral blood (PBL, n=10) were negative for SSX-2 and SSX-4 expression. Thirty-two BM and 14 PBL obtained from 35 stage 4 NB patients at 24 months from their diagnosis were evaluated for SSX-2 expression. Unlike another cancer/testis antigen, GAGE, only one BM sample was positive, and no prognostic utility could be established. Further investigation of SSX expression at other relevant time points is warranted.

Expression of SSX genes in the neoplastic cells of Hodgkin's lymphoma

The cancer/testis antigen (CTA) group of tumor-associated proteins have been reported to be expressed in various cancers and in adult testis but they are essentially not found in any other normal adult nonneoplastic tissues. Prompted by the frequent detection of SSX1 in a previous comprehensive expression profile of the Hodgkin's lymphoma (HL) cell line L428, we analyzed SSX expression by nonnested reverse-transcription polymerase chain reaction (RT-PCR) in 4 HL cell lines (L428, L540, HD-MY-Z, and KM-H2) and 32 tumor samples of HL. The cellular localization of SSX expression in the tumor samples was further analyzed by in situ hybridization (ISH). All 4 HL cell lines were positive by RT-PCR using SSX consensus primers. Using primers specific to individual SSX genes, all 4 cell lines expressed multiple SSX family members. Five tumor samples (15.6%) were positive by RT-PCR using SSX consensus primers and direct sequencing of the RT-PCR products showed that 4 of 5 expressed more than 1 SSX family member. ISH confirmed that SSX expression originated in HL cells in all 5 RT-PCR–positive tumor samples. Furthermore, ISH demonstrated SSX-positive HL cells in 6 of 11 cases (55%) that were negative by RT-PCR. Our results suggest that members of the SSX family of CTA are expressed in most HL. This subset of HL may be a candidate for immunotherapy approaches directed at SSX proteins. HUM PATHOL 33:496-502. Copyright 2002, Elsevier Science (USA). All rights reserved.

Expression of SSX-2 and SSX-4 genes in neuroblastoma

The SSX genes are members of the family of cancer/testis antigens that encode tumor-associated antigens recognizable by autologous cytolytic T lymphocytes. Their expression is common in tumors of diverse lineages and absent in normal tissues except testis and thyroid. In this study, sixty-seven neuroblastomas (NB) (12 stage 1, 13 stage 2, 12 stage 3, 12 stage 4S and 13 stage 4) were examined by RT-PCR and a sensitive chemiluminescent detection method for SSX-2 and SSX-4 expression. Seventy-two percent (13/18) of stage 4 NB expressed SSX-2 and 67% (12/18) expressed SSX-4. SSX-2 and SSX-4 positivity correlated with metastatic NB stage 4 (p=0.02 and p=0.006, respectively). Sensitivity experiments showed SSX-2 detection was one tumor cell in 10(6) normal cells, and one in 10(4) for SSX-4. All normal tissues (n=6), with the exception of testis, normal bone marrow (BM, n=12) and normal peripheral blood (PBL, n=10) were negative for SSX-2 and SSX-4 expression. Thirty-two BM and 14 PBL obtained from 35 stage 4 NB patients at 24 months from their diagnosis were evaluated for SSX-2 expression. Unlike another cancer/testis antigen, GAGE, only one BM sample was positive, and no prognostic utility could be established. Further investigation of SSX expression at other relevant time points is warranted.