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.

Rat cells transformed by the highly oncogenic adenovirus 12 lack at least two cellular proteins which are present in cells transformed by the non-oncogenic adenovirus 5 and in untransformed cells. One protein has been identified as the heavy chain of the rat class I major histocompatibility complex. This finding may explain the difference in oncogenicity between adenoviral species.

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The hSNF5 chromatin-remodeling factor is a tumor suppressor that is inactivated in malignant rhabdoid tumors (MRTs). A number of studies have shown that hSNF5 re-expression blocks MRT cell proliferation. However, the pathway through which hSNF5 acts remains unknown. To address this question, we generated MRT-derived cell lines in which restoration of hSNF5 expression leads to an accumulation in G 0 /G 1 , induces cellular senescence and increased apoptosis.

Evidence is presented that cells transformed by adenovirus type 12 are oncogenic because they escape from T-cell immunity. This effect is brought about by reducing the expression of class I transplantation antigens and is a function of the protein translated from the 13S mRNA, transcribed from early region la. These findings establish a novel mechanism by which transformed cells can acquire an oncogenic phenotype.ADENOvIRUS-transformed rodent cells exhibit variable degrees of oncogenicity, depending on the adenovirus species used for transformation: rat cells transformed by the highly oncogenic adenovirus 12 (Ad12) are highly oncogenic in the syngeneic host', whereas rat cells transformed by the nononcogenic adenoviruses, for example Ad2 and Ad5, are rarely tumorigenic in immunocompetent syngeneic rats2. It has been proposed that cells transformed by the non-oncogenic adenoviruses fail to form tumours because they are more antigenic than are cells transformed by oncogenic adenoviruses and therefore are more readily eliminated by the immune system of the host3. The main evidence supporting this hypothesis is that rat cells transformed by the non-oncogenic Ad2, which are non-oncogenic in immunocompetent rats, do form tumours in immunosuppressed rate and in congenitally athymic nude mice.The adenovirus genes responsible for transformation in vitro are localized in a region near the left end of the viral genome, in a 4-kilobase (kb) DNA segment which comprises the first region of the genome to be expressed in lytic infection, and therefore designated early region I (El). This region consists of two transcriptional units, Ela and Elb (ref. 6). We have recently demonstrated that the difference in oncogenic potential between Ad5-and Ad12-transformed cells in nude mice is determined by the large tumour antigen specified by subregion E1b7'8. We show here that the identity of the Ela subregion determines the susceptibility of transformed cells to the cellular immune system, that is, rat cells expressing Ad5 Ela are highly susceptible to cytotoxic T cells and so are only oncogenic in immunodeficient animals, whereas cells expressing Ad12 Ela have a reduced susceptibility for T-killer cells and hence are oncogenic. By using a set of cell lines transformed by mutant El regions we show that the inactivation of major histocompatibility complex (MHC) class I gene expression is a function of the product of the Ad12 13S Ela mRNA. Oncogenicity of Ad-transformed cellsWe have recently reported the construction of two Ad5Ad12 hybrid early region 1 plasmids: one, pAd512, consisting of the Ela region of non-oncogenic Ad5 and the Elb region of highly oncogenic Ad12; and the other, pAd125, consisting of Ad12 Ela and Ad5 Elb. These plasmids were used to transform primary baby rat kidney (BRK) cells and the oncogenicity of the resulting transformed cell lines was tested in nude mice'. Comparison of the oncogenic potential of the various transformed cell lines in immunocompetent rats and in immunodeficient nude mice (Table 1) revealed a maj...