Abstract LB-58: Spontaneous Epstein Barr virus-associated lymphomagenesis in primary human solid tumor xenografts

Abstract

Abstract Xenotransplantation of primary human solid tumors into immunodeficient mice is widely utilized as a tool for the study of human cancer biology. We have generated subcutaneous xenografts from a large number of human hepatocellular carcinoma (HCC) resection specimens, and have observed that subcutaneous implantation of tumor fragments or bulk cell suspensions results in a much higher rate of primary engraftment than implantation of cells sorted to exclude CD45+ leukocytes in non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. While the majority of xenografts arising from tumor fragments or bulk tumor cells retain typical characteristics of parent HCCs, we have noted the frequent development of very rapidly-growing tumors that do not share these attributes, and sought to further characterize these tumors. Histopathological analysis of these tumors revealed monomorphic populations of lymphoid cells demonstrating nuclear atypia, high mitotic index, and invasion into surrounding tissues. Flow cytometry and immunohistochemistry revealed that these tumors consisted almost completely of cells expressing the human leukocyte antigen CD45 and the human B-cell antigen CD20. In situ hybridization demonstrated strong expression of the Epstein-Barr virus (EBV)-encoded small RNA (EBER) in all tumors. Staining of tumors for mouse H2K expression was negative in all cases. These findings suggest that the originally implanted human HCC tumor fragments or bulk tumor cells were replaced by human B-cell lymphomas. No lymphomas arose from the implantation of human HCC cells that were sorted to exclude human CD45+ leukocytes. Histopathological re-examination of the parent tumors in all cases confirmed a diagnosis of HCC with no evidence of lymphoma. Analogous to post-transplant lymphoproliferative disorder (PTLD) in humans, our data suggest that these lymphomas spontaneously developed in xenografts through EBV-mediated transformation of EBV-infected passenger lymphocytes harbored in patient tumors in the permissive context of an immunodeficient host environment. Recognition of this phenomenon is important for those utilizing primary human tumor tissue in xenotransplantation assays, because the development of lymphomas may confound accurate analysis of tumor biology and may out-compete the tumor type of interest resulting in the loss of valuable experimental samples. Our observations highlight an important potential pitfall of human solid tumor xenotransplantation assays in models where primary engraftment requires the implantation of bulk cells or tumor fragments which may contain passenger lymphocytes. In such circumstances, our observations underscore the critical importance of routinely quantifying the degree of human lymphocyte “contamination” in xenograft-derived data and implementing strategies to deplete or eliminate human lymphocytes from these assays. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-58. doi:10.1158/1538-7445.AM2011-LB-58