Dorit Rennspiess

Early B-Cell Differentiation in Merkel Cell Carcinomas: Clues to Cellular Ancestry

Merkel cell carcinoma (MCC) is a highly malignant neuroendocrine nonmelanoma skin cancer, which is associated with the Merkel cell polyoma virus (MCPyV). Recently, expression of the terminal deoxynucleotidyl transferase (TdT) and the paired box gene 5 (PAX 5) has been consistently reported in the majority of MCCs. We tested 21 MCCs for the expression of MCPyV, TdT, PAX5, IgG, IgM, IgA, kappa, and lambda by immunohistochemistry and assessed IgH and Igk rearrangement in all 21 MCCs. All of the MCCs revealed specific expression of PAX5 and 72.8% of the MCCs expressed TdT. In addition, most of the MCCs revealed specific expression of one or more Ig subclasses and kappa or lambda. One MCC did reveal monoclonal IgH and Igk rearrangement next to two other MCCs showing Igk rearrangement. As coexpression of TdT and PAX5 under physiologic circumstances is restricted to pro/pre- and pre-B cells we propose, on the basis of our results, that the cell of origin of MCCs is a pro/pre- or pre-B cell rather than the postmitotic Merkel cells. MCPyV infection and transformation of pro-/pre-B cells are likely to induce the expression of simple cytokeratins as has been shown for SV40 in other nonepithelial cells. This model of cellular ancestry of MCCs might impact therapy and possibly helps to understand why approximately 20% of MCCs are MCPyV-negative.

Detection of Human Polyomavirus 7 in Human Thymic Epithelial Tumors

Introduction: Although the molecular genetics possibly underlying the pathogenesis of human thymoma have been extensively studied, its etiology remains poorly understood. Because murine polyomavirus consistently induces thymomas in mice, we assessed the presence of the novel human polyomavirus 7 (HPyV7) in human thymic epithelial tumors. Methods: HPyV7-DNA Fluorescence in situ hybridization (FISH), DNA-polymerase chain reaction (PCR), and immunohistochemistry (IHC) were performed in 37 thymomas. Of these, 26 were previously diagnosed with myasthenia gravis (MG). In addition, 20 thymic hyperplasias and 20 fetal thymic tissues were tested. Results: HPyV7-FISH revealed specific nuclear hybridization signals within the neoplastic epithelial cells of 23 thymomas (62.2%). With some exceptions, the HPyV7-FISH data correlated with the HPyV7-DNA PCR. By IHC, large T antigen expression of HPyV7 was detected, and double staining confirmed its expression in the neoplastic epithelial cells. Eighteen of the 26 MG-positive and 7 of the 11 MG-negative thymomas were HPyV7-positive. Of the 20 hyperplastic thymi, 40% were HPyV7-positive by PCR as confirmed by FISH and IHC in the follicular lymphocytes. All 20 fetal thymi tested HPyV7-negative. Conclusions: The presence of HPyV7-DNA and large T antigen expression in the majority of thymomas possibly link HPyV7 to human thymomagenesis. Further investigations are needed to elucidate the possible associations of HPyV7 and MG.

Reviewing the current evidence supporting early B-cells as the cellular origin of Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly malignant skin cancer characterized by early metastases and poor survival. Although MCC is a rare malignancy, its incidence is rapidly increasing in the U.S. and Europe. The discovery of the Merkel cell polyomavirus (MCPyV) has enormously impacted our understanding of its etiopathogenesis and biology. MCCs are characterized by trilinear differentiation, comprising the expression of neuroendocrine, epithelial and B-lymphoid lineage markers. To date, it is generally accepted that the initial assumption of MCC originating from Merkel cells (MCs) is unlikely. This is owed to their post-mitotic character, absence of MCPyV in MCs and discrepant protein expression pattern in comparison to MCC. Evidence from mouse models suggests that epidermal/dermal stem cells might be of cellular origin in MCC. The recently formulated hypothesis of MCC originating from early B-cells is based on morphology, the consistent expression of early B-cell lineage markers and the finding of clonal immunoglobulin chain rearrangement in MCC cells. In this review we elaborate on the cellular ancestry of MCC, the identification of which could pave the way for novel and more effective therapeutic regimens.

Fluorescence in situ hybridization and qPCR to detect Merkel cell polyomavirus physical status and load in Merkel cell carcinomas

The Merkel cell polyomavirus (MCPyV) is detected in 80% of Merkel cell carcinomas (MCC). Clonal integration and tumor‐specific mutations in the large T antigen are strong arguments that MCPyV is a human tumor virus. However, the relationship between viral presence and cancer induction remains discussed controversially. Since almost all studies on virus prevalence are based on PCR techniques, we performed MCPyV fluorescence in situ hybridization (FISH) on MCC to gain information about the quality of the viral presence on the single cell level. MCPyV‐FISH was performed on tissue microarrays containing 62 formalin‐fixed and paraffin‐embedded tissue samples including all tumor grades of 42 patients. The hybridization patterns were correlated to the qPCR data determined on corresponding whole tissue sections. Indeed, MCPyV‐FISH and qPCR data were highly correlated, i.e. 83% for FISH‐positive and 93% for FISH‐negative cores. Accordingly, the mean of the qPCR values of all MCPyV‐positive cores differed significantly from the mean of the negative cores (p = 0.0076). Importantly, two hybridization patterns were definable in the MCPyV‐FISH: a punctate pattern (85%) indicating viral integration, which correlated with a moderate viral abundance and a combination of the punctate with a diffuse pattern (15%), suggesting a possible coexistence of integrated and episomal virus which was associated with very high viral load and VP1 expression. Thus, MCPyV‐FISH adds important information on the single cell level within the histomorphological context and could therefore be an important tool to further elucidate MCPyV related carcinogenesis.

Phosphatidylinositol 3-kinase p110δ expression in Merkel cell carcinoma

The prognosis of stage III/IV Merkel cell carcinoma (MCC) is very poor. The Phosphatidylinositol 3-kinase p110δ specific inhibitor idelalisib has recently been reported to induce complete clinical remission in a stage IV MCC patient. Here we assessed the expression of p110δ in primary MCC and MCC cell lines including its functionality. Immunofluorescence microscopy revealed a specific cytoplasmic p110δ expression in 71.4% of the tested MCCs and in all tested MCC cell lines. Compared to the B cell leukemia cell line REH all MCC cell lines, except MKL-1, revealed a lower response towards the treatment with idelalisib. MKL-1 showed a 10-fold higher IC50 compared to REH which was accompanied by a significant decrease of Akt phosphorylation. However, treating the MCC cells with the specific PI3K p110α subunit inhibitor BYL719 led to a more effective decrease of the cell viability compared to idelalisib: WaGa cells 30-fold, PeTa cells 15-fold and all other MCC cell lines 3-fold. Although PI3K p110δ is expressed in the majority of MCCs and cell lines its inhibition by idelalisib alone does not suffice to effectively affect MCC cells viability.

Abstract 557: Fluorescence in situ hybridization versus qPCR as means to detect Merkel cell polyomavirus in Merkel cell carcinoma

Background: Merkel cell polyoma virus (MCPyV) is detected in 80% of Merkel cell carcinomas (MCC). The clonal integration and tumor specific mutations in the large T Antigen (LTAg) gene strongly implicate an oncogenic impact of the virus. To date the relationship between the viral presence and cancer induction, development or clinical prognosis is discussed controversial. Yet almost all studies are based on quantitative virus detection e.g. PCR or qPCR. Material and Method: In order to gain additional information about the quality of the viral presence on the single cell level we performed FISH analysis of formalin fixed and paraffin embedded (FFPE) MCCs (n= 62) on tissue micro arrays (TMA), determined the FISH pattern and correlated the results of the FISH analysis with the qPCR data. We grouped the MCCs according to different FISH evaluations and correlated them with the respective qPCR data on the basis of a determined cut-off. MCPyV FISH was established using the MKL-1 cell line which harbors integrated copies of MCPyV DNA. For MCPyV-qPCR the LT3 primer pair was used on whole tissue sections. Results: MCPyV-FISH on FFPE MKL-1 cells revealed punctate signals compatible with viral integration. The MCPyV FISH positive MCC cores (76%) mainly revealed two different signal patterns: a punctate pattern (85%) which correlated with a moderate relative viral presence and in some areas the punctate pattern was combined with a diffuse pattern (15%) indicating the episomal presence of the virus which is linked to viral replication. If a pattern mixture was seen this was associated with very high qPCR values. Comparing MCPyV FISH and qPCR data the results correlated highly with 83 % in the MCPyV positive evaluated group, whereas the negative group showed a concordance of 93 %. The mean of the qPCR values of all MCPyV positive cores differed significantly from the negative cores (p= 0.0076). The FISH signals were in some tumor areas from the same patient heterogenic in intensity, pattern and localization. Conclusion: While the qPCR using the LT3 primer pair was highly sensitive to detect MCPyV sequences in the respective MCC cases, the MCPyV FISH analysis highly concordantly revealed the quality of the viral presence, i.e. viral integration or episomal presence and morphological sublocalization in the tissues. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 557. doi:1538-7445.AM2012-557