Abstract
Human mesenchymal stem cells (hMSCs) and mouse induced pluripotent stem cells (iPSCs) can be genetically modified with viral vectors and hold promise as a cell source for regenerative medicine, yet how hMSCs and iPSCs respond to viral vector transduction remains poorly understood, leaving the safety concerns unaddressed. Hereby we explored the responses of hMSCs and iPSCs against an emerging DNA viral vector, baculovirus (BV). First, we uncovered that BV transduction perturbed the transcription of 816 genes associated with 5 signaling pathways in hMSCs. Surprisingly, toll-like receptor-3 (TLR3), a receptor that generally recognizes double-stranded RNA, was apparently upregulated by BV transduction as confirmed by microarray, PCR array, flow cytometry and confocal microscopy. However, we can not find any TLRs activation after BV transduction in iPSCs. Cytokine array data showed that BV transduction triggered robust secretion of IL-6 and IL-8, but not of other inflammatory cytokines and IFN-b in hMSCs. BV transduction activated the signaling molecules (e.g. TRIF, NF-κB and IRF-3) downstream of TLR3, while silencing the TLR3 gene with small interfering RNA considerably abolished the cytokine expression and promoted cell migration. Surprisingly, our data indicated that BV tranduction of iPSCs only elicited mild immunse responses. These data demonstrate, for the first time, that a DNA viral vector can activate the TLR3 pathway in hMSCs but not in iPSCs, and lead to a cytokine expression profile distinct from that in immune cells. These findings underscore the importance of evaluating whether TLR3 signaling cascade plays roles in the immune response provoked by other DNA vectors (e.g. adenovirus). Nonetheless, BV transduction barely disturbed the surface marker expression and only induced transient and mild cytokine response, thereby easing the safety concerns of using BV for hMSCs and iPSCs engineering.