brane junctions between cells. Electrophysiologically,
these cells were shown to lack cAMP-dependent Cl
transport which is consistent with the presence of the
DF508 mutation [11]. The cells were plated on tissue
culture plasticware coated with ®bronectin, collagen and
bovine serum albumin and grown in MEM supplemented
with 10% FBS, L-glutamine and antibiotics according to
Kunzelmann et al. [11].
The immortalized human tracheal gland serous cell
line, CF-KM4, was from a CF patient homozygous for the
DF508 mutation and undergoing bipulmonary transplan-
tation [12]. In cell-attached patch-clamp experiments,
CF-KM4 cells do not express a cAMP-regulated chloride
channel. CF-KM4 cells retain the features of the native
gland serous cells, i.e. presence of cytokeratin and
constitutive secretion of secretory leucocyte proteinase
inhibitor (SLPI). In response to pharmacological stimula-
tions, CF-KM4 cells have CF-speci®c defective secretory
characteristics [12]. The cells were plated on tissue
culture plasticware coated with collagen I and grown in
DMEM/F12 medium supplemented with 1% Ultroser G,
glucose (10 g/L), sodium pyruvate (0.33 g/L) and
epinephrine (3 mM).
Gene transfer with His-pLK
1 day prior to transfection, SCFTE29o- or CF-KM4 cells
were seeded at 2r10
5
cells per 4 cm
2
well in a 12-well
plate (Falcon) and incubated at 37uC in a humidi®ed
atmosphere (5% CO
2
). At the time of the gene transfer
procedure, cell cultures were 70% con¯uent.
DNA/His-pLK complexes (His-polyplexes) were pre-
pared in serum-free medium with a potentially proton-
able imidazole per phosphate of 1.3: His-pLK (15 mgin
0.3 ml of serum-free medium) was mixed with a plasmid
(5 mg in 0.7 ml of serum-free medium) and held for
30 min at 37uC. Then, 1 ml of medium containing
complexes was supplemented with 1% heat-inactivated
FBS (SCFTE29o- cells) or 0.1% Ultroser G (CF-KM4
cells), unless otherwise speci®ed, and added to each
culture well after removal of the growth medium.
Gene transfer ef®ciency achieved with His-pLK was
compared to that obtained with unsubstituted pLK or with
glycosylated pLK previously shown to be ef®cient for gene
transfer into SCFTE29o- and CF-KM4 cells: pLK bearing
b-D-Lactosyl residues (Lac-pLK) and gluconoylated pLK
bearing N-Acetyl-b-D-Glucosaminyl residues (b-GlcNAc-,
GlcA-pLK) [6,13]. With complexes made of these
glycosylated pLK, chloroquine (100 mM) was added to
the transfection medium just before incubation with cells.
Polylysine and glycosylated pLK were ¯uoresceinylated
by using FITC as previously described [10,14±16].
Polyplex size measurements
The size of DNA/His-pLK complexes was determined by
quasi-elastic light scattering (QUELS) on a ZetaSizer 3000
(Malvern Instruments, Orsay, France). Polyplexes were
prepared as described above in MEM but also at low ionic
strength, either in H
2
OorinH
2
O containing 5% glucose
(H
2
O+G5%); His-pLK (15 mg in 0.03 ml in H
2
Oor
H
2
O+G5%) was mixed with a plasmid (5 mg in 0.07 ml of
H
2
OorH
2
O+G5%) and kept for 30 min at 37uC. Then,
the 100 ml containing the polyplexes were diluted in
900 mlH
2
O, H
2
O+G5% or MEM supplemented with
speci®ed amounts of heat-inactivated FBS. Polyplex size
measurements were performed 1 h after this preparation.
Gene transfer with polyethylenimine
To obtain various PEI : DNA charge ratios (net positive
nitrogen charges of the PEI divided by the net negative
phosphate charge of the DNA), a ®xed amount of plasmid
was complexed with different amounts of PEI, either
25 kDa or 800 kDa. Under physiological pH conditions,
PEI contains one positive charge among six nitrogen
atoms present in the molecule [17]. Therefore a PEI : DNA
charge ratio of 1.5 corresponds to nine nitrogen atoms per
phosphate. Plasmid (5 mg) and the required amount of
PEI 25 or 800 kDa (0.28 ml of 0.1 M PEI stock solution per
mg of plasmid for a +/x charge ratio of 1.5) were
separately diluted in 50 ml of 150 mM NaCl, mixed
together, maintained for 10 min at room temperature
and vortexed. Complexes were diluted into 1 ml of
culture medium containing 1% FBS or 0.1% Ultroser G,
unless otherwise speci®ed.
Lipofection
Similarly, to obtain various lipid : DNA charge ratios (net
positive charge of the cationic lipid divided by the net
negative charge of the DNA), a ®xed amount of plasmid
was complexed with different amounts of lipofectin or
lipofectAMINE in polystyrene tubes. Lipofectin contains
only one positive charge in the polar group and
lipofectAMINE contains ®ve positive charges per mole-
cule. Plasmid (5 mg) and the desired amount of lipofectin
(1.9 ml of a 1 mg/ml solution per mg of DNA for a +/x
charge ratio of 0.5) or lipofectAMINE (1.9 ml of a 2 mg/ml
solution per mg of DNA for a +/x charge ratio of 5) were
separately diluted into 50 ml of MEM, gently mixed
together and kept for 10 min at room temperature.
Lipid±DNA complexes (lipoplexes) were diluted into 1 ml
of culture medium containing 1% FBS or 0.1% Ultroser G,
unless otherwise speci®ed.
After incubation for 4 h, unless otherwise speci®ed, at
37uC, the transfection medium was removed and cells
were further incubated at 37uC in 1 ml of complete
growth medium until gene expression was measured.
Gene expression
Luciferase gene expression
Luciferase gene expression was measured by lumines-
cence according to De Wet et al. [18]. After 48 h or at
given intervals, cells from each well were harvested upon
trypsinization and lysed with 200 ml of homogenization
buffer (25 mM Tris, HCl pH 7.8, 8 mM MgCl
2
,1mM
370 I. Fajac et al.
Copyright # 2000 John Wiley & Sons, Ltd. J Gene Med 2000; 2: 368±378.