Characterization of 911: A New Helper Cell Line for the Titration and Propagation of Early Region 1-Deleted Adenoviral Vectors

Currently, the preferred host for the production of early region-1 (E1)-deleted recombinant adenoviruses (rAdV) is cell line 293, which was generated by transformation of human embryonic kidney cells by sheared adenovirus 5 (Ad5) DNA. To develop alternative hosts for the production of rAdV, we generated adenovirus-transformed human cell lines by transformation of human embryonic retinoblasts (HER) with a plasmid containing base pairs 79–5789 of the Ad5 genome. One of the established HER cell lines, which we called 911, exhibited favorable growth characteristics and was chosen for further study. This cell line is demonstrated to have several characteristics in common with the well-known 293 cell line: The 911 cell line is highly transfectable, and exhibits similar frequencies of homologous recombination. However, it has additional characteristics that make it a useful alternative for 293. The 911 cells perform particularly well in plaque assays. Upon infection with E1-deleted adenoviruses, plaques become apparent in monolayers of 911 cells already after 3–4 days versus 4–10 days in monolayers of 293 cells, thereby reducing the time required for quantitative plaque assays. Furthermore, yields of E1-deleted adenovirus vectors up to three times as high as those achieved with 293 cells can be obtained with 911 cells. Finally, the Ad5-DNA content of the 911 cell line is completely known. These features make the 911 cell line a useful alternative for the construction, propagation, and titration of E1-deleted recombinant adenoviruses. The recombinant adenoviruses used today as gene transfer vectors for gene therapy purposes have a deletion in the E1 region of the viral genome. The defective gene products are provided in helper cells, thus allowing the defective viruses to be propagated. At the moment, there is only one widely available E1-expressing helper cell line, 293. This study describes the characterization of a new E1-complementing cell line 911 established by transformation of human embryonic retinoblasts with Ad5-E1. The authors demonstrate that 911 cells perform especially well in plaque assays and in small-scale production of adenovirus vectors.