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Imaging, Diagnosis, Prognosis |
Authors' Affiliations: 1 Department of Pathology, Brigham and Women's Hospital; 2 Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts; and 3 Laboratory of Immunopathology, Institute of Biology and Experimental Medicine (IBYME-CONICET), Buenos Aires, Argentina
Requests for reprints: Jeffery L. Kutok, Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115. Phone: 617-732-7510; Fax: 617-264-5169; E-mail: Jkutok{at}partners.org.
| Abstract |
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Experimental Design: We evaluated 225 cases of primary cHL and non–Hodgkin lymphoma for evidence of a functional AP1/Gal1 signature by immunohistochemical techniques.
Results: Gal1 is selectively expressed by malignant Reed-Sternberg cells in >90% of primary cHLs, and Gal1 expression is concordant with the activated AP1 component, c-Jun. In contrast, diffuse large B-cell lymphoma, primary mediastinal large B-cell lymphoma, and another Hodgkin-related entity, nodular lymphocyte–predominant Hodgkin lymphoma, do not express Gal1. However, anaplastic large cell lymphoma (ALCL), consistently expresses both Gal1 and its transcriptional regulator, c-Jun. The presence of activated c-Jun, indicative of functional AP1 activity, was confirmed by phospho-c-Jun immunostaining in cHL and ALCL.
Conclusions: These findings establish a functional AP1 signature that includes Gal1 expression in cHL and ALCL and suggests a common mechanism for tumor immunotolerance in these diseases. In addition, the combination of Gal1 and c-Jun serve as diagnostic biomarkers that delineate cHL and ALCL from other lymphomas with shared morphologic and/or molecular features.
Classical Hodgkin lymphomas (cHL; ref. 11) are unusual tumors with small numbers of malignant RS cells within an extensive inflammatory infiltrate, which includes abundant Th2 and T regulatory cells (12). Until recently, the factors that are responsible for creating and maintaining the Th2/T regulatory–skewed immunosuppressive microenvironment in cHL were undefined.
We recently reported that Hodgkin lymphoma cell lines selectively overexpress Gal1 via an AP1-dependent enhancer and constitutive activation of the AP1 transcription complex (13). In in vitro coculture assays, cHL Gal1 promoted the survival and expansion of Th2 cells at the expense of Th1 cells (13). In in vitro assays, Gal1 also favored the retention and/or expansion of T regulatory cells. In a pilot series of primary cHLs, Gal1 was selectively overexpressed by the malignant Reed-Sternberg cells (RS cells; ref. 13). Together, these observations indicate that the AP1-dependent production of Gal1 fosters the immunosuppressive microenvironment in cHL.
Herein, we ask whether the coordinate expression of activated AP1 pathway components and Gal-1 serves as a diagnostic signature of cHL. Because recent studies have revealed the unexpected presence of common signaling and survival pathways in cHL and additional non–Hodgkin lymphomas, we also sought to determine whether the AP1/Gal1 signature is shared by other molecularly or morphologically related lymphomas. In particular, we examined nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL), which exhibits morphologic similarities to cHL, including rare tumor cells within an abundant inflammatory infiltrate but has a distinct clinical course and therapeutic options (14). We also evaluated primary mediastinal large B-cell lymphoma (MLBCL), a B-cell tumor with molecular similarities to cHL including a dependence upon nuclear factor-
B signaling for growth and survival (15) and the more common diffuse large B-cell lymphoma (DLBCL). In addition, we evaluated anaplastic large cell lymphoma (ALCL), an aggressive T-cell tumor with certain morphologic similarities to cHL and a shared reliance upon AP1 signaling (16).
| Materials and Methods |
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Immunohistochemistry. Immunohistochemistry was performed using 5-µm-thick formalin- or B5-fixed, paraffin-embedded whole tissue sections on individual slides or tissue microarrays as previously described (17). Briefly, slides were soaked in xylene, passed through graded alcohols, and then pretreated with 10-mmol/L citrate (pH 6.0; Zymed) in a steam pressure cooker (Decloaking Chamber; BioCare Medical) as per manufacturer's instructions. All further steps were done at room temperature in a hydrated chamber. Slides were then treated with Peroxidase Block (DAKO USA) for 5 min to quench endogenous peroxidase activity. Unless otherwise stated, the Gal1 antibody used for all studies is a primary rabbit polyclonal anti-Gal1 antibody generated in the laboratory of G.A.R. and previously established to be specific for Gal1 (9, 13, 18–21). This antibody was applied at 1:10,000 dilution for 1 h in DAKO diluent. In a subset of cases, tumor staining for Gal1 was confirmed with both a distinct rabbit polyclonal antisera generated in the laboratory of M.A.S. against full-length recombinant Gal1, and a commercially available rabbit polyclonal antibody (PeproTech, Inc.) by the method previously described (ref. 22; data not shown). For detection of AP1 signaling, primary rabbit monoclonal anti–c-Jun (1:50 dilution; clone 60A8; Cell Signaling Technology), or primary rabbit monoclonal anti–phospho-c-Jun specific for phosphorylated serine at amino acid position 63 (1:50 dilution; clone 54B3; Cell Signaling Technology) was applied in DAKO diluent (DAKO) for 1 h at room temperature. Slides were washed in 50 mmol/L Tris-Cl (pH 7.4), and anti-rabbit or anti-murine horseradish peroxidase–conjugated antibody solution (Envision+ detection kit; DAKO) was applied for 30 min. After further washing, immunoperoxidase staining was developed using a 3,3'-diaminobenzidine chromogen kit (DAKO) per the manufacturer and counterstained with Harris hematoxylin (Polyscientific).
Immunohistochemical evaluation. Reactivity for Gal1, c-Jun, and phospho-c-Jun for all cases was determined and scored independently by two hematopathologists (S.J.R and J.L.K). Intensity of staining for Gal1 was scored as follows: 0, no staining detected; 1+, weak staining; 2+, moderate staining; 3+, strong staining of the tumor cells. Positive staining for a case was defined as 2+ or 3+ cytoplasmic staining in >50% of the tumor cells. A staining of 0 or 1+ in >50% of tumor cells, or focal reactivity of 2+ or 3+ in <50% of the tumor cells was considered negative. Positive staining of endothelial cells and macrophages served as positive internal controls. Staining for c-Jun and phospho-c-Jun was considered positive if nuclear staining for the antigen was observed >50% and >25% of interphase tumor nuclei, respectively. Staining of endothelial and dendritic cells served as internal positive controls for both antibodies. All cases were photographed at x1,000 original magnification with an Olympus BX41 microscope with the objective lens of x100/0.75 Olympus UPlanFL (Olympus). The pictures were taken using Olympus QColor3 and analyzed with acquisition software QCapture v2.60 (QImaging) and Adobe Photoshop 6.0 (Adobe). The differences in Gal1 expression in specific types of lymphoma were evaluated with a Fisher exact test.
| Results |
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Gal1 immunohistochemistry revealed robust cytoplasmic and weak cell membrane staining of RS cells in cHL (Fig. 1A , representative example). Intermixed macrophages, dendritic cells, and at least a subset of endothelial cells also showed expression of Gal1. In contrast, the preponderance of small lymphocytes and occasional granulocytes comprising the majority of the inflammatory infiltrate surrounding the RS cells were negative for Gal1 (Fig. 1A). The majority of primary cHLs (61%) exhibited very strong expression of Gal1 [3+ on a scale of 0 to 3 (no staining to very strong staining, respectively); Fig. 1A]; additional cases (31%) exhibited moderate staining scored as 2+ (Fig. 1B). In only rare cases were cHL RS cells negative for Gal1 expression (Table 1 ). Overall, 66 of 72 (92%) cases of cHL exhibited moderate to strong expression of Gal1 by the RS cells (Fig. 1A and B; Table 1). All of the examined subtypes of cHL were largely Gal1+; similarly, both EBV+ and EBV– tumors expressed this glycan-binding protein (Table 1).
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Gal1 expression in primary mediastinal and diffuse large B-cell lymphoma. With emerging data indicating that seemingly disparate tumors such as cHL and primary MLBCL share important molecular features and survival pathways (15), we evaluated the expression pattern of Gal1 in MLBCL (n = 17) and compared these findings to nonmediastinal forms of DLBCL (n = 102).
Expression of Gal1 was found in only 2 of 17 cases (12%) of MLBCL (Fig. 1D; Table 1). Similarly, only 7 of 102 cases of DLBCL (7%) exhibited Gal1 expression (Fig. 1E; Table 1). We found no distinguishing clinical, morphologic, or phenotypic features among the rare Gal1-positive MLBCLs or DLBCLs upon review. Positive Gal1 immunostaining is, thus, a powerful marker for distinguishing cHL from MLBCL (P < 0.000001, Fisher exact test) and delineating cHL from DLBCL (P < 0.000001, Fisher exact test).
Gal1 expression in ALCL. ALCLs are aggressive large cell lymphomas of T-cell origin with high levels of c-Jun and JunB expression and constitutive activation of AP1 (23). Given the role of the AP1 pathway in ALCL and the AP1-dependent Gal1 expression in cHL, we next asked whether ALCLs overexpressed Gal1. Ninety-five percent of primary ALCLs (18 of 19 cases) exhibited moderate to strong (2+ or 3+) diffuse cytoplasmic Gal1 staining (Fig. 1F); both ALK+ and ALK– tumors expressed this glycan-binding protein (Table 1).
The polyclonal Gal1 antiserum used for the above studies is well-characterized and known to be specific (13, 18). However, to validate our observations, we did immunostaining on a subset of cases with two additional polyclonal Gal1 antisera (one generated in the laboratory of M.A.S. and one commercially available reagent). There was a perfect correlation of staining patterns in Gal1-positive and Gal1-negative tumors with the two Gal1 antisera generated in the laboratories of our coauthors (data not shown). In this subset of cases, the commercially available antisera that recognizes Gal1 (22) was less sensitive than our polyclonal Gal1 antisera in detecting Gal1 expression in primary tumor cells (data not shown).
Association between Gal1 and c-Jun expression. Given the AP1 dependence of Gal1 in cHL (13) and the selective expression of Gal1 in another AP1-driven tumor, ALCL, we next assessed the coexpression of the AP1 component, c-Jun, and Gal1 in our series of primary lymphomas (Fig. 2 ).
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Association between Gal1 expression and phosphorylated (activated) c-Jun. The transcription factor, c-Jun, is constitutively expressed in Hodgkin cell lines and primary cHL tumors (13), and is a critical component of the AP1 transcriptional complex required for Gal1 expression (13). To confirm that the c-Jun protein detected by immunohistochemistry is functionally active, we did immunostaining on a subset of tumors with a monoclonal antibody that specifically recognizes the activated form of c-Jun (phospho Ser63 c-Jun; ref. 24). In all cases of Gal1+ cHL, there was corresponding expression of the activated phosphorylated form of c-Jun in RS cells (Supplementary Fig. S1; Fig. 2C). Similarly, all examined ALCLs expressed both Gal1 and phospho c-Jun (Fig. 2F). The rare cases of DLBCL and MLBCL that expressed Gal1 also exhibited nuclear c-Jun and phospho c-Jun staining (Supplementary Fig. S1).
| Discussion |
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Our observations have several implications for both the understanding of lymphoma cell biology and the practice of diagnostic pathology. We previously have shown that AP1-dependent production of Gal1 by Hodgkin cell lines promotes an immune privileged microenvironment by favoring the expansion of Th2 cells at the expense of Th1 cells and the retention and/or expression of T regulatory cells (13). These findings provide a mechanistic basis for the relative abundance of Th2 cells and Th2-associated cytokines that accompany malignant RS cells in primary biopsy samples of cHL (25). There are at least two consequences for the survival and expansion of RS cells in cHL. First, it is recognized that RS cells are dependent on the constitutive activation of the signaling molecule STAT6 for survival and growth. STAT6 activation, in turn, is triggered by cell surface receptors that recognize the Th2 associated cytokine, interleukin 13 (26). By skewing the T-cell population toward a Th2 phenotype, Gal1 likely promotes the survival and growth of RS cells. Second, in a recently described murine melanoma model, the expression of Gal1 by malignant cells directly suppressed T-cell–mediated tumor rejection in vivo (9). Similarly, abundant Gal1 expression by RS cells may promote a tolerant immunologic environment for malignant cells despite the magnitude of the inflammatory infiltrate (13). A recent report associating RS Gal1 expression and impaired EBV-specific immune responses is consistent with this hypothesis (22).
We find that 92% of examined primary cHL express high levels of Gal1 within the RS cells. This includes all subtypes of cHL (nodular sclerosis, mixed cellularity, lymphocyte rich and cHL not otherwise specified). The frequency of Gal1 expression in our series exceeds that recently reported by another group (62% of cases of EBV+ cHL; ref. 22). The lower reported incidence of Gal1 expression within the tumor cells in that study is likely due to the commercial Gal1 antibody used, which is less sensitive in detecting moderate levels of Gal1 than the two independent Gal1 antisera from our laboratories. We also find that Gal1 expression is not restricted to EBV+ cHL indicating that the protein likely plays an immunomodulatory role beyond the suppression of EBV-specific cytotoxic T cells.
Intriguingly, we also identified rare cases of cHL that do not express detectable levels of the protein within the RS cells. Review of these cases confirmed typical features of cHL and revealed no obvious morphologic variations in the degree of inflammatory infiltrate associated with the tumor cells. It will be of interest, however, to determine whether these rare tumors differ in the composition of their T-cell infiltrate or in their response to therapy.
Given that Hodgkin RS cell Gal1 expression is dependent on AP1 signaling in vitro, we examined c-Jun expression and activation in our primary cHL samples. In agreement with prior reports (23), we found that c-Jun is consistently expressed in the RS cells of cHL. Furthermore, using an antibody recognizing a serine phosphoepitope at amino acid position 63 that is specific for activated c-Jun, we find evidence for active AP1 signaling in every case of cHL. This finding is similar to that of a recent report that used an antibody that recognizes phosphorylated-c-Jun but cross-reacts with phospho-JunD (27).
In contrast to cHL, a distinctly different pattern of Gal1 expression and c-Jun activation was observed in NLPHL. In these tumors, moderate to strong Gal1 expression was not present and c-Jun staining was rarely detected. Interestingly, we found that a subset of cases of NLPHL exhibited weak Gal1 reactivity exclusively in a perinuclear pattern. We interpreted this staining as negative for Gal1 because the subcellular localization and magnitude of Gal1 staining greatly differ from that seen in other Gal1+ tumors.
Despite the recent observation that cHL and certain forms of DLBCL such as MLBCL possess similarities at the molecular level (15, 28), the tumor cells of MLBCL only rarely expresses Gal1 or c-Jun. Further, our examination of nonmediastinal DLBCLs indicates that Gal1 expression and AP1 activation is uncommon in the neoplastic B-cells of these tumors (7% cases). A minority of DLBCLs (18%) expressed c-Jun, and the coexpression of both Gal1 and c-Jun occurred in only 4% of cases of DLBCL. The presence of both Gal1 and c-Jun, therefore, is a discriminating characteristic of these tumor cells and is highly sensitive (92%) and specific (96%) for the diagnosis of cHL versus DLBCL.
Finally, we found that ALCL, an aggressive, large cell lymphoma of T-cell lineage, also expresses high levels of Gal1. In agreement with a prior report (27), we confirmed that c-Jun is expressed by the vast majority of ALCLs, and we found that all c-Jun+ cases also exhibit phospho-c-Jun immunostaining. These findings suggest that in ALCL, AP1 signaling likely drives Gal1 expression. Furthermore, Gal1 expression in ALCL may promote a more permissive microenvironment for tumor survival and growth. Although there are fewer infiltrating nonneoplastic T lymphocytes in ALCL compared with cHL, we did observe variable numbers of small, infiltrating lymphocytes in many of the primary ALCLs (29). With emerging interest in immunotherapy targeting ALK kinase in ALCL (30), understanding the mechanisms limiting effective antitumor responses will be important.
Recently, we showed that constitutive activation of the canonical nuclear factor-
B signaling pathway, as identified by the presence of nuclear c-REL containing heterodimers and increased expression of the nuclear factor-
B target and signaling molecule, TRAF1, is a common feature of both cHL and MLBCL that serves to distinguish these tumors from nonmediastinal DLBCL (17, 31). Here, we report that the majority of MLBCLs resemble nonmediastinal DLBCLs in failing to express Gal1 and c-Jun. Thus, immunostaining for the combination of the above-mentioned markers can be used to aid in distinguishing these entities when conventional morphology and immunophenotyping fail to establish a clear diagnosis (Fig. 3
).
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| Disclosure of Potential Conflicts of Interest |
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| Footnotes |
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Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/).
Received 10/23/07; revised 12/26/07; accepted 1/13/08.
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B. EMBO J 2002;21:4104–13.[CrossRef][Medline]
B activity, function, and target-gene signatures in primary mediastinal large B-cell lymphoma and diffuse large B-cell lymphoma subtypes. Blood 2005;106:1392–9.This article has been cited by other articles:
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H. D. Kopcow, F. Rosetti, Y. Leung, D. S. J. Allan, J. L. Kutok, and J. L. Strominger T cell apoptosis at the maternal-fetal interface in early human pregnancy, involvement of galectin-1 PNAS, November 25, 2008; 105(47): 18472 - 18477. [Abstract] [Full Text] [PDF] |
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