The mixed human umbilical cord blood-derived mesenchymal stem cells show higher antitumor effect against C6 cells than the single in vitro

Abstract

Objective: It is difficult for the treatment of neurologic tumors with current therapies, including glioma. Despite the advances in cancer therapeutics, the outcomes in these patients remain poor and, therefore, new modalities are required. Recent findings have demonstrated that human umbilical cord blood mesenchymal stem cells (UCB-MSCs) have the potential to inhibit glioma cell growth in vitro. Caspase-3 plays a critical role as an executioner of apoptosis and the level of caspase-3 expression determines the degree of apoptosis in cancer cell lines. CD133 (+) glioma displays a strong resistance to chemotherapy. Interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) are important cytokines in the generation of antitumor immunity.

Methods: UCB-MSCs were harvested by density gradient separation. Green fluorescence protein stable C6 cells were established. Cytotoxicity was detected by visual survival cell assay, and caspase-3 activity was assessed using immunohistochemistry staining and western blot. Flow cytometry was used to test CD133 positive C6 cells. The concentrations of IL-2 and IFN-gamma proteins secreted from UCB-MSCs were then quantified using enzyme-linked immunosorbent assay. The cytotoxicities of IL-2 alone, IFN-gamma alone, and combination of IL-2 and IFN-gamma were compared against malignant glioma cells.

Results: We noted a significant cytotoxicity of UCB-MSCs for malignant glioma cells. In addition, the toxicity of mixed UCB-MSCs was significantly higher than that of single UCB-MSCs for C6 glioma cells. Capase-3 levels in UCB-MSCs treatment at an effector/target (E/T) ratio of (5+5):1 were higher than those at an E/T ratio of 10:1. On the contrary, there was no change in the protein expression of capase-3 at an E/T ratio of 0:1. Immunohistochemistry staining and western blot revealed that the expression of capase-3 was higher in mixed UCB-MSCs treatment, when compared with single UCB-MSCs. We identified reductions of approximately 39 and 73% in the number of CD133 positive C6 cells treated with the single (10:1) and the mixed [(5+5):1] UCB-MSCs respectively as compared to the control group (0:1) in transwell inserts. However, the mixed UCB-MSCs secreted more immune response-related proteins (IL-2 and IFN-gamma) than the single UCB-MSCs. Combination of IL-2 and IFN-gamma might prove more cytotoxic on target cells than IL-2 alone and IFN-gamma alone.

Discussion: The data collected herein confirm for the first time that the mixed UCB-MSCs were shown to have more cytotoxic effects than the single UCB-MSCs through increasing the expression of caspase-3 and decreasing the expression of CD133 in C6 glioma cells. In addition, the mixed UCB-MSCs secrete more immune response-related proteins (IL-2 and IFN-gamma) than the single UCB-MSCs. Combination of IL-2 and IFN-gamma was shown to have more cytotoxic effects than IL-2 alone and IFN-gamma alone. These results demonstrate that the mixed UCB-MSCs are a potential new therapeutic agent for glioma.

Keywords:

• Umbilical cord blood
• Mesenchymal stem cells
• C6 cells