The human embryonic kidney cell line 293T (ATCC number CRL-11268) and the TE671 cell line were obtained from the American Type Culture Collection (ATCC, Manassas, VA) and maintained in Dulbbeco's modified eagle medium (DMEM) supplemented with 10% fetal calf serum (FCS) and 1% glutamine. All cell lines were grown at 37uC in a humidified atmosphere of 5% CO 2 .