All four cell lines were cryopreserved in liquid nitrogen freezer at À70 o C. For recovery of cryopreserved cells, the vials were transferred to a 37 o C water bath for 15-30 s, further thawed at room temperature and then transferred to a 15 ml polypropylene tube with a Pasteur pipette. An aliquot of 9 ml of RPMI-9% fetal bovine serum (FBS) was added in drops. The cells were allowed to settle for 5 min and then centrifuged at 4 o C for 10 min at 300 g. Supernatant was removed, and cells were suspended in fresh RPMI, gently tapped and vortexed. Cell viability was monitored by 0.2% trypan blue dye exclusion, and cell count was determined using a hemocytometer. Cells recovered from cryovials were grown in RPMI-1640 with glutamine (Invitrogen, Carlsbad, CA) supplemented with 9% FBS, HEPES buffer, gentamycin (5 mg%) and fungizone (0.5 mg%), at 37 C in a humidified atmosphere of 5% CO 2 . Upon confluency, cells were detached with sterile EDTA-dextrose (137 mM sodium chloride, 5.4 mM potassium chloride, 5.6 mM dextrose, 0.54 mM ethylene diamine tetra acetate (EDTA), 7.1 mM sodium bicarbonate) at 37 C for 5-15 min (or $45 min for HH639), recovered with cold RPMI-1640-9% FBS and resuspended in the same medium. Use of trypsin was avoided for harvesting the cells. Cell viability and cell count were reassessed before cells were seeded in culture flasks.