Heat inactivation assay was performed essentially as described previously [19, 26, 30, 31] . Briefly, viruses were incubated at 45uC for 0, 5, 10, 20 or 40 min in either PBS (without Ca 2+ and Mg 2+ ) or growth medium containing 2% FBS. Then their infectious titers were re-determined by standard TCID 50 method (AdEasy vector system, Qbiogene Inc., Carlsbad, CA). One day before analysis 10 4 293 cells plus 100 ml of growth medium with 2% Fetal Bovine Serum (FBS) were added in 96-well flat bottom plates. Eight serial dilutions of the virus ranging from 10 23 to 10 210 or 10 26 to 10 213 were made in medium containing 2% FBS depending on the virus, and 100 ml of each dilution was added into 96-well plates, one row for each dilution. After incubation for 10 days at 37uC in 5% CO 2 humidified incubator the plates were examined for cytopathic effect (CPE) under microscope. Observable CPE containing wells were counted for each row in order to determine the ratio of positive wells per row in the 96-well plates. Titer was calculated by using TCID 50 .