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 presence of replication-competent adenoviruses (RCAs) in batches of replication-defective adenovirus (Ad) vectors is a major problem for the application of these vectors in gene therapy. RCAs are generated by recombination between sequences in the Ad vector and homologous Ad sequences in the helper cells, resulting in the acquisition by the vector of early region 1. To prevent the formation of RCAs, we have developed helper cell lines, which we named PER, and matched Ad vectors that do not have sequence overlap. PER cells contain the Ad serotype 5 (Ad5) E1A- and E1B-encoding sequences (Ad5 nucleotides 459-3510) under the control of the human phosphoglycerate kinase (PGK) promoter. We demonstrate that PER cells synthesize high levels of the Ad5 E1A and E1B proteins. The yields from PER cells of E1-deleted Ads are similar to those obtained from earlier helper cells, such as 911 and 293 cells. Propagation of matched Ad vectors, which lack Ad5 nucleotides 459-3510, in one of the PER clones, PER.C6, does not result in the generation of RCAs, in contrast to propagation in 293 cells. We conclude that the combination of PER.C6 cells and nonoverlapping E1-deleted adenoviral vectors eliminates the problem of RCA generation by homologous recombination, and allows cost-effective production of safe, clinical-grade batches of recombinant Ad vectors.

It has recently been shown that an adenovirus mutant lacking expression of the large E1B protein (DE1B) selectively replicates in p53 de®cient cells. However, apart from the large E1B protein the adenovirus early region encodes the E1A and E4orf6 proteins which also have been reported to aect p53 expression as well as its functioning. After infection with wild-type adenovirus we observed a dramatic decrease in wild-type p53 expression while no down-regulation of p53 could be detected after infection with the DE1B virus. The dierent eects of the wild-type and DE1B adenovirus on p53 expression were not only found in cells expressing wild-type p53 but were also observed when tumor cells expressing highly stabilized mutant p53 were infected with these two viruses. Infection with dierent adenovirus mutants indicated the importance of a direct interaction between p53 and the large E1B protein for reduced p53 expression after infection. Moreover, coexpression of the E4orf6 protein was found to be required for this phenomenon, while expression of E1A is dispensable. In addition, we provide evidence that p53 is actively degraded in wild-type adenovirus-infected cells but not in DE1B-infected cells.

The efficiency and specificity of gene transfer with human adenovirus (hAd)-derived gene transfer vectors would be improved if the native viral tropism could be modified. Here, we demonstrate that the minor capsid protein IX (pIX), which is present in 240 copies in the Ad capsid, can be exploited as an anchor for heterologous polypeptides. Protein IX-deleted hAd5 vectors were propagated in hAd5 helper cells expressing pIX variants, with heterologous carboxyl-terminal extensions of up to 113 amino acids in length. The extensions evaluated consist of alpha-helical spacers up to 75 Å in length and to which peptide ligands were fused. The pIX variants were efficiently incorporated into the capsids of Ad particles. On intact particles, the MYC-tagged-pIX molecules were readily accessible to anti-MYC antibodies, as demonstrated by electron microscopic analyses of immunogold-labeled virus particles. The labeling efficiency improved with increasing spacer length, suggesting that the spacers lift and expose the ligand at the capsid surface. Furthermore, we found that the addition of an integrin-binding RGD motif to the pIX markedly stimulated the transduction of coxsackievirus group B and hAd receptor-deficient endothelioma cells, demonstrating the utility of pIX modification in gene transfer. Our data demonstrate that the minor capsid protein IX can be used as an anchor for the addition of polypeptide ligands to Ad particles.

Hemophilia A is caused by a deficiency of factor-VIII procoagulant (fVIII) activity. The current treatment by frequent infusions of plasma-derived fVIII concentrates is very effective but has the risk of transmittance of blood-borne viruses (human immunodeficiency virus [HIV], hepatitis viruses). Use of recombinant DNA-derived fVIII as well as gene therapy could make hemophilia treatment independent of blood-derived products. So far, the problematic production of the fVIII protein and the low titers of the fVIII retrovirus stocks have prevented preclinical trials of gene therapy for hemophilia A in large-animal models. We have initiated a study of the mechanisms that oppose efficient fVIII synthesis. We have established that fVIII cDNA contains sequences that dominantly inhibit its own expression from retroviral as well as from plasmid vectors. The inhibition is not caused by instability of the fVIII mRNA (t1/2, > or = 6 hours) but rather to repression at the level of transcription. A 305-bp fragment is identified that is involved in but not sufficient for repression. This fragment does not overlap the region recently identified by Lynch et al (Hum Gene Ther 4:259, 1993) as a dominant inhibitor of RNA accumulation. The repression is mediated by a cellular factor (or factors) and is independent of the orientation of the element in the transcription unit, giving the repressor element the hallmarks of a transcriptional silencer.