Abstract: The present invention relates to a method for the controlled intracellular delivery of nucleic acid molecules into one or more target cells, in particular tumor cells, the method comprising: providing a polymeric complex formed between one or more nucleic acid molecules to be delivered and one or more cationic carrier molecules, wherein at least a part of the one or more carrier molecules in the polymeric complex are covalently attached to hydroxyalkyl starch, and wherein the hydroxyalkyl starch is shielding the polymeric complex; allowing the shielded polymeric complex to get into contact with the one or more target cells; deshielding the polymeric complex by removing the hydroxyalkyl starch; and allowing the deshielded polymeric complex to internalize into the one or more target cells. Removal of the hydroxyalkyl starch can be accomplished enzymatically by exposing the polymeric complex to amylase.