I am trying to transfect primary cells- mesenchymal stem cells using lipofectamine RNAiMAX. For its standardization I'm using a scrambled siRNA which is FITC tagged in order to come down to a set protocol which gives me a good transfection efficiency upto-10-15% atleast. I check the transfection efficiency via flow cytometry. However I'm just getting an efficiency of about 2-5%. I have tried both forward and reverse transfection.