Which human tissue to use is perhaps a very important question. Each of our cells have undergone development and differentiation since we were first conceived. Each different cell type likely has a different set of changes that prevent it from reverting to it's original state, as a fertilized egg cell. Quiescence of a cell is when it is so deprived of nutrients that it will no longer divide, but it is not so starved that it dies.
Inducing quiescense may cause the cell to begin scavanging it's own protiens more rapidly than they can regenerate themselves. Steps of differentiation may have turned on certain cell functions and turned off others, but this starvation of the cell must reverse these steps of differentiation if cloning is going to work.
More information on Human Cell Cultures: