**4.2.3 Cell line dependency**

Another factor, which may affect transfection efficiency of chitosan, is cell line dependency. Higher mitotic cell lines, such as cancer cells, usually have higher transfection efficiencies that lower proliferative rates of the cell line. This may be related to differences in cell physiology affecting the internalisation mechanism and subsequent internal trafficking of the vectors (Douglas et al., 2008). It has also been found that dividing cells have higher transfection ability compared to quiescent cells (Brunner et al., 2000) and higher levels of gene expression have been observed just before or during mitosis (Mortimer et al., 1999). This may explain why the immortalised cell line, with higher mitotic activity, has higher transfection ability than normal or primary cell lines. However, this factor requires further investigation.
