Epigenetic modulation of cancer-germline antigen gene expression in tumorigenic human mesenchymal stem cells: implications for cancer therapy

Cancer-germline antigens are promising targets for cancer immunotherapy, but whether such therapies will also eliminate the primary tumor stem cell population remains undetermined. We previously showed that long-term cultures of telomerized adult human bone marrow mesenchymal stem cells can spontaneously evolve into tumor-initiating, mesenchymal stem cells (hMSC-TERT20), which have characteristics of clinical sarcoma cells. In this study, we used the hMSC-TERT20 tumor stem cell model to investigate the potential of cancer-germline antigens to serve as tumor stem cell targets. We found that tumorigenic transformation of hMSC-TERT20 cells induced the expression of members of several cancer-germline antigen gene families (ie, GAGE, MAGE-A, and XAGE-1), with promoter hypomethylation and histone acetylation of the corresponding genes. Both in vitro cultures and tumor xenografts derived from tumorigenic hMSC-TERT20 single cell subclones exhibited heterogeneous expression of both GAGE and MAGE-A proteins, and similar patterns of expression were observed in clinical sarcomas. Importantly, histone deacetylase and DNA methyltransferase inhibitors were able to induce more ubiquitous expression levels of cancer-germline antigens in hMSC-TERT20 cells, while their expression levels in primary human mesenchymal stem cells remained unaffected. The expression pattern of cancer-germline antigens in tumorigenic mesenchymal stem cells and sarcomas, plus their susceptibility to enhancement by epigenetic modulators, makes them promising targets for immunotherapeutic approaches to cancer treatment.