Bystander effect between HSVtk positive cells and HSVtk nega

Bystander effect between HSVtk-positive cells and HSVtk-negative cells has been extensively studied especially from the aspect of cell-to-cell communication. Connexin43, a major molecule in the connexin family gene products, has been reported to be related to the bystander effect in suicide gene therapies (Dilber et al., 1997; Elshami et al., 1886; Mesnil et al., 1996; Vrionis et al., 1997; Ziu et al., 2006). We previously tested bystander effect between HSVtk-positive and HSVtk-negative tumor cells and found that the bystander effect was very potent in 9L cells with high connexin43 expression compared with in C6 cells with low connexin43 expression (Namba et al., 2001). However, we consequently found that the bystander effects between BMSCtk and C6 cells were very potent. In the present study, we examined bystander effect generated by human and rat BMSCtk cells on various kinds of human and rat buy URMC-099 tumor cells in both in vitro and in vivo conditions. The results have demonstrated that tumoricidal bystander effect in the suicide gene therapy using BMSCtk cells and GCV is not cell type- and species-specific, suggesting a possibility of “BMSCtk therapy” using pre-established BMSCtk cell.
Materials and methods
Results
Discussion We used commercially-available human BMSCs as the vector cells in the present study. Thus, a limitation of the present study is that the commercially-available BMSCs do not represent general BMSCs that are obtained from the patients. They may not behave as “stem cells” that have multipotent differentiation capacity, and therefore, more studies are obviously needed to establish ideal vector cells for clinical use. Induced pluripotent stem cells, recently established and vigorously examined in the field of reconstructive neurosciences, could be also suitable vehicles for gene therapy (Takahashi et al., 2007; Yu et al., 2007). We have recently confirmed that induced pluripotent stem cells have a potent migratory activity toward the conditioned medium of brain tumors and this activity is also not tumor cell type-specific, or dependent on the species as shown in the present migration assay (Koizumi et al., 2011). In the present study, we used the same number of BMSCtk cells as that of tumor cells (BMSCtk/tumor cell ratio of 1:1). The previous in vitro study testing the potency of the bystander effect, using rat BMSCtk or HSVtk-transduced neural stem cells and C6 cells at various ratios (BMSCtk/tumor cell ratio of 1:1 to 1:128) showed a very potent bystander effect up to BMSCtk/tumor cell ratio of 1:16 (Amano et al., 2009; Li et al., 2005b). Therefore, a dose response study at different BMSCtk/tumor cell ratios should be also performed between different BMSCtk/tumor cell combinations. In the present study, we only performed a co-implantation study, because the aim of the study was to test cell type- and species-specificity. We obviously have to test the effect on an established intracranial tumor as in our previous treatment studies (Amano et al., 2009; Li et al., 2005a). In vivo bystander effect between human BMSCtk and rat glioma cells was a little weaker than that between human BMSCtk and human glioma cells (Figs. 2 and 3), though the difference was not very obvious in in vitro conditions (Fig. 1). Precise mechanism is unknown but in vivo cell-to-cell communication, which is important for generation of bystander effect, may be different between human and rat cells. Bystander effect is still potent between cells of different species, but use of human BMSCs is recommended for treatment of human gliomas.
Conflict of interest The following are the supplementary related to this article.