I am using the pSico based shRNA knockdown system to knock down my protein of interest in HT-29 cells. But the western results show lower or no expression of the protein for the vector only(pSico) infected as well, where as the control cell lysate and the other GFP control shows expression of the protein. This is very confusing.I have confirmed the DNA and repeated the experiment to avoid all possible mistakes. But getting the same results continuously. Any idea about what is going on?