cells survived less toxicity so the percent transfected cells is not as high with the cos 7 cells 4 u00d7 10 4 5 u03bcl of lipofectamine u2122 was used in the absence of fbs and polybrene u2122 5 u03bcl of lipofectamine u2122 was used in the presence of fbs and the absence of polybrene u2122 and 12 u03bcl of lipofectamine u2122 was used in the presence of both fbs and polybrene u2122 polybrene u2122 was used at 80 u03bcg ml these cells showed less toxicity in response to serum free lipofectamine u2122 transfection once again the number of stained cells in the presence of serum and polybrene u2122 is nearly equivalent to that seen in the serum free transfection the activity of u03b2 galactosidase expression was determined from dose response transfection experiments as described in example 1 1 u00d7 10 5 bhk 21 cells were plated per 35 mm well 6 well plate the day after plating cells were rinsed with dmem and fed 0 8 ml of dmem with or without polybrene u2122 and 5 fbs the cells were transfected with 1 u03bcg pcmv u03b2 gal dna and lipofectamine u2122 reagent the day after transfection cells were rinsed with pbs harvested and assayed for u03b2 galactosidase activity peak activity points from the dose response were graphed as shown in fig1 the results at optimal conditions are as follows at optimal lipofectamine u2122 concentration in the presence of 5 fbs bhk 21 and cos 7 transfections showed a 20 30 fold increase in total activity of u03b2 galactosidase when polybrene u2122 was present in the transfection medium the amount of lipofectamine u2122 required for peak activity in serum and polybrene u2122 was higher than that required in.