We have tried transfection of HMC3 with L3K several times, but not primary ones. L3K showed high toxic effect on HMC3, thus it would show higher on the primary ones. It is normal to get transfection efficiency of 10 to 25% with the use of L3K, I have not encountered with a higher one. If so I suggest to go on and apply a sorting or selection process to keep only the positive cells.