Tom C. Tsang

Fusion of HepG2 cells with mesenchymal stem cells increases cancer-associated and malignant properties: An in vivo metastasis model

In the present study, we have tested the hypothesis that fusion between an altered cell and a mesenchymal stem cell produces a hybrid cell with enhanced characteristics associated with metastatic cancer cells, and we have developed a flexible model for investigating the mechanisms of metastasis. Human HepG2 cells with low metastatic potential were induced to fuse with rat bone marrow mesenchymal stem cells, and the progeny were compared with the parental cells for possession of enhanced in vitro and in vivo characteristics of malignant cells. Compared to the parental cells, the fused cells exhibited enhanced expression of E-cadherin, vimentin, Twist, Snail, matrix metalloproteinase 2 and 9 activities, aneuploidy and enhanced in vitro invasion and migration. In an in vivo xenograft assay, the fused cells generated increased numbers of metastatic liver and lung lesions. This model system is a flexible tool for investigation of the mechanisms of stem cell fusion in carcinogenesis and metastasis and for the discovery of new therapeutic targets to inhibit metastasis.

SING: a novel strategy for identifying tumor-specific, CTL-recognized tumor antigens

Traditional methods for identifying T cell‐recognized tumor antigens (Ags) are laborious and time‐consuming. In an attempt to simplify the procedure, a novel strategy, SING (SIgnal transduction molecule‐mediated, NFAT‐controlled, GFP expression) was established as a direct approach for cloning T cell‐recognized tumor Ags. In the SING system, a mouse T cell line (BW5147) was transduced with a chimeric H‐2Kb construct containing T cell‐signaling domains and a green fluorescent protein (GFP) reporter gene under the transcriptional control of nuclear factor of activated T cells (NFAT). The resultant BW5147 cells were named BS cells. This cell line could “sense” TCR stimulation through the T cell‐signaling domains after coculture with Ag‐specific T cells and then become fluorescent (expressing green fluorescence protein, GFP+) in the presence of Ag peptides. The interaction between BS cells and Ag‐specific T cells could be enhanced by addition of costimulatory signals. Currently, BS cells have been optimized to “sense” TCR stimulation after being pulsed with the relevant peptides at concentrations as low as 10‐9 M. Endogenous Ag‐expressing BS cells could also become fluorescent after coculture with Ag‐specific T cells. Our results provide a proof of principle for using the SING system to directly isolate Ag‐expressing BS cells from BS cell repertoires, which are retrovirally transduced with tumor‐derived cDNA libraries. Once tumor Ag‐marked BS cells are identified, the sequences encoding tumor Ags could be easily retrieved by PCR amplification of the genomic DNA using vector‐specific primers.