COMPLEMENTING CELL LINES

Abstract: A packaging cell line capable of complementing recombinant adenoviruses based on serotypes from subgroup B, preferably adenovirus type 35. The cell line is preferably derived from primary, diploid human cells (e.g., primary human retinoblasts, primary human embryonic kidney cells and primary human amniocytes) which are transformed by adenovirus E1 sequences either operatively linked on one DNA molecule or located on two separate DNA molecules, the sequences being operatively linked to regulatory sequences enabling transcription and translation of encoded proteins. Also disclosed is a cell line derived from PER.C6 (ECACC deposit number 96022940), which cell expresses functional Ad35 E1B sequences. The Ad35-E1B sequences are driven by the E1B promoter or a heterologous promoter and terminated by a heterologous poly-adenylation signal. The new cell lines are useful for producing recombinant adenoviruses designed for gene therapy and vaccination. The cell lines can also be used for producing human recombinant therapeutic proteins such as human growth factors and human antibodies. In addition, the cell lines are useful for producing human viruses other than adenovirus such as influenza virus, herpes simplex virus, rotavirus, measles virus.

Description: COMPLEMENTING CELL LINES Technical field: The invention relates to the field of biotechnology generally, and more specifically to adenoviral-based complementing cell lines. Background: Typically, vector and packaging cells have to be adapted to one another so that they have all the necessary elements, but they do not have overlapping elements which lead to replication competent virus by recombination. Therefore, the sequences necessary for proper transcription of the packaging construct may be heterologous regulatory sequences derived from, for example, other human adenovirus (Ad) serotypes, non-human adenoviruses, other viruses like, but not limited to, SV40, hepatitis B virus (HBN), Rous Sarcoma Virus (RSV), cytomegalovirus (CMN), etc. or from higher eukaryotes such as mammals. In general, these sequences include a promoter, enhancer and poly-adenylation sequences. PER.C6 (ECACC deposit number 96022940) is an example of a cell line devoid of sequence overlap between the packaging construct and the adenoviral vector (Fallaux et al, 1998). Recombinant viruses based on subgroup C adenoviruses such as Ad5 and Ad2 can be propagated efficiently on these packaging cells. Generation and propagation of adenoviruses from other serotypes, like subgroup B viruses, has proven to be more difficult on PER.C6 cells. However, as described in European patent application 00201738.2, recombinant viruses based on subgroup B virus Ad35 can be made by co- transfection of an expression construct containing the Ad35 early region- 1 sequences (Ad35-El). Furthermore, Ad35-based viruses that are deleted for E1A sequences were shown to replicate efficiently on PER.C6 cells. Thus, the El A proteins of Ad5 complement Ad35-El A functions, whereas at least part of the EIB functions of Ad35 are necessary. This serotype specificity in EIB functions was recently also described for Ad7 recombinant viruses. In an attempt to generate recombinant adenoviruses derived from subgroup B virus Ad7, Abrahamsen et al. (1997) were not able to generate El -deleted viruses on 293 cells without contamination of wild-type (wt) Ad7. Viruses that were picked after plaque purification on 293-ORF6 cells (Brough et al, 1996) were shown to have incorporated Ad7 EIB sequences by non-homologous recombination. Thus, efficient propagation of Ad7 recombinant viruses proved possible only in the presence of Ad7-E1B expression and Ad5-E4-ORF6 expression. The EIB proteins are known to interact with cellular as well as viral proteins (Bridge et al, 1993; White, 1995). Possibly, the complex formed between the EIB 55K protein and E4-ORF6 which is necessary to increase mRNA export of viral proteins and to inhibit export of most cellular mRNAs, is critical and in some way serotype specific. Description of the Invention The present invention provides new packaging cell lines capable of complementing recombinant adenoviruses based on serotypes other than subgroup C viruses, such as serotypes from subgroup B, like adenovirus type 35. In one aspect the invention provides packaging cell lines capable of complementing recombinant adenovirus based on a serotype of subgroup B, preferably of serotype 35. With the terms "based on or derived from an adenovirus" is meant that it utilizes nucleic acid corresponding to nucleic acid found in said serotype. The utilized nucleic acid may be derived by PCR cloning or other methods known in the art. In one aspect of the invention, the new packaging cells are derived from primary, diploid human cells such as, but not limited to, primary human retinoblasts, primary human embryonic kidney cells or primary human amniocytes. Transfection of primary cells or derivatives thereof with the adenovirus El A gene alone can induce unlimited proliferation (immortalisation), but does not result in complete transformation. However, expression of E1A in most cases results in induction of programmed cell death (apoptosis), and occasionally immortalisation is obtained (Jochemsen et al, 1987). Co- expression of the EIB gene is required to prevent induction of apoptosis and for complete morphological transformation to occur (reviewed in White, 1995). Therefore, in one aspect of the invention, primary human cells or derivatives thereof are transformed by expression of adenovirus El proteins of a subgroup other than subgroup C, preferably subgroup B, more preferably adenovirus type 35. The combined activity of the El A and EIB proteins establishes indefinite growth of the cells and enables complementation of recombinant adenoviruses. The complete morphological transformation of primary cells by adenovirus El genes is the result of the combined activities of the proteins encoded by the El A and EIB regions. The roles of the different El proteins in lytic infection and in transformation have been studied extensively (reviewed in Zantema and van der Eb, 1995; White, 1995, 1996). The adenovirus El A proteins are essential for transformation of primary cells. The El A proteins exert this effect through direct interaction with a number of cellular proteins that are involved in regulation of transcription. These include the pRB family of proteins, p300/CBP and TATA binding protein. In addition to this E1A increases the level of p53 protein in the cells. In the absence of adenovirus EIB activity the rise in p53 levels leads to the induction of apoptosis. Both proteins encoded by the EIB region counteract the induction of apoptosis although by different mechanisms. E1B-21K seems to counteract apoptosis in a manner similar to Bcl-2 via interaction with the effector proteins downstream in the apoptosis pathway (Han et al, 1996), whereas E1B-55K functions through direct interaction with p53. Importantly, the molecular mechanism by which the E1B-55K proteins of Ad2 and 5 (subgroup C) and Adl2 (subgroup A) function in the ability to neutralise p53 may differ. Whereas Ad5 E1B-55 binds p53 strongly and the complex localises to the cytoplasm, Adl2 E1B-55K binds p53 weakly and both proteins are localised in the nucleus (Zantema et al, 1985; Grand et al, 1999). Both proteins, however, inhibit the transactivation of other genes by p53 (Yew and Berk, 1992). In rodent cells, the activity of E1A together with either E1B-21K or 55K is sufficient for full transformation although expression of both EIB proteins together is twice as efficient (Rao et al, 1992; ). In human cells however, the activity of the E1B- 55K protein seems to be more important given the observation that E1B-55K is indispensible for the establishment of transformed cells (Gallimore, 1986). Example 6 hereof describes the generation of pIG270. In this construct the Ad35-El genes are expressed from the hPGK promoter and transcription is terminated by the HBVpA. The hPGK promoter constitutes a HincII-EcoRI fragment of the promoter sequence described by Singer-Sam et al. (1984). The HBVpA is located in a BamHI- Bglll fragment of the Hepatitis B virus genome (Simonsen and Levinson, 1983; see also Genbank HBV-AF090841). As mentioned before, the promoter and polyadenylation sequences of the El expression constructs described in this invention may be derived from other somces whithout departing from the invention. Also, other functional fragments of the hPGK and HBVpA sequences mentioned above may be used. The functionality of pIG270 was shown by transformation of primary Baby Rat Kidney cells (BRK). Comparison with an equivalent Ad5-El expression construct learned that Ad35-El genes were less efficient in transforming these cells. The same has been found for the El genes of Adl2 (Bernards et al, 1982). It is unclear which El protein(s) determine(s) the difference in transformation efficiency of El sequences observed for adenoviruses from different subgroups. In the case of Adl2, transfection studies with chimeric E1A/E1B genes suggested that the efficiency of transformation of BRK cells was determined by the El A proteins (Bernards et al, 1982). The E1B-55K protein is shown infra to contain serotype-specifϊc functions necessary for complementation of El -deleted adenoviruses. If these functions are related to the regulation of mRNA distribution or another late viral function, it is unlikely that these are involved in the transformation efficiency. Analysis of functional domains in the Ad2 or Ad5 E1B-55K proteins using insertion mutants have revealed that functions related to viral replication, late protein synthesis and host protein shut-off are not confined to specific domains but are distributed along the protein (Yew et al, 1990). Using the same set of mutants, the domains important for interaction with p53 and E4-Orf6 were found to be more restricted. In addition to one common binding region (amino acids 262 to 326), p53 binding was affected by mutations at aa 180 and E4-Orf6 binding was affected by mutations at aa 143 (Yew and Berk, 1992; Rubenwolf et al, 1997). Altogether these results indicate that it is difficult to separate the E1B-55K functions related to transformation (p53 binding) and late protein synthesis (Orf6 binding). The invention discloses new El constructs that combine the high efficiency of transformation of one serotype with the serotype-specific complementation function of another serotype. These new constructs are used to transform primary human embryonic retinoblast cells and human amniocytes. In another aspect of the invention, the transforming El sequences are derived from different serotypes. As disclosed in European Patent application 00201738.2, Ad35 El sequences are capable of transforming Baby Rat Kidney (BRK) cells, albeit with a lower efficiency than that seen with Ad5 El sequences. This was also observed for El sequences from Adl2 (Bernards et al, 1982). Therefore, in this aspect of the invention, primary diploid human cells or derivatives thereof are transformed with chimeric El construct that consists of part of the El sequences of a serotype that enables efficient transformation of primary human cells or derivatives thereof and part of the El sequences of another serotype which El sequences provide the serotype-specific EIB function(s) that enable(s) efficient propagation of El -deleted viruses of that serotype. In a preferred embodiment of this aspect of the invention, the El A region is derived from a subgroup C adenovirus, like, but not limited to, Ad5, and the EIB coding sequences are derived from an alternative adenovirus more particularly from an adenovirus of subgroup B, more particularly from adenovirus type 35. E1B-21K coding sequences may also be chimeric comprising both subgroup C and subgroup B coding sequences. Preferably, all or most of E1B-21K comprises subgroup C coding sequences. In a more preferred embodiment, the E1A coding sequences and the E1B-21K coding sequences are derived from a subgroup C adenovirus, like, but not limited to, Ad5. In one embodiment the cell further comprises ElB-55k coding sequences that are, preferably, as far as not overlapping with the 21K coding sequences-derived from an adenovirus of subgroup B, more particular from adenovirus type 35. In an even more preferred embodiment, all El coding sequences are derived from a subgroup C adenovirus, like but not limited to Ad5, except for at least the part of the E1B-55K coding sequences that are necessary for serotype-specific complementation of an alternative adenovirus subgroup, more particular adenovirus subgroup B, more particular adenovirus type 35. The invention also provides a packaging cell line wherein the primary, diploid human cells or derivatives thereof have been transformed with a chimeric adenovirus El construct comprising part of a first adenovirus El coding sequence of a first adenovirus serotype that enables efficient transformation of primary human cells and derivatives thereof; and part of a second adenovirus El coding sequence of a second adenovirus serotype, wherein said second adenovirus El coding sequence provides the serotype-specific adenovirus EIB function(s) that enable(s) efficient propagation of recombinant adenovirus El -deleted viruses of said second adenovirus serotype. Preferably, said first adenovirus serotype is a subgroup C adenovirus and said second adenovirus serotype is a subgroup B adenovirus, more particular adenovirus type 35. In one embodiment the packing cell line of the invention comprises bovine adenovirus ElB-55k. Such a bovine ElB-55k expressing cell line is particularly suited for obtaining high yields of a complemented bovine recombinant adenovirus. The primary diploid human cells or derivatives thereof are transformed by adenovirus El sequences either operatively linked on one DNA molecule or located on two separate DNA molecules. In the latter case, one DNA molecule carries at least part of the El sequences of the serotype enabling efficient transformation and the second DNA molecule carries at least part of the sequences necessary for serotype-specific complementation. Provided is also a hybrid construct comprising El -sequences of the serotype enabling efficient transformation and El sequences of another serotype necessary for serotype-specific complementation. The sequences providing serotype specific complementation may ofcourse also contain further activities contributing to transformation. Preferably, said sequences enabling efficient transformation comprise El A. Preferably said sequences and said sequences necessary for serotype specific complementation preferably comprise EIB sequences. More preferably said sequences enabling efficient transforming comprise El A and E1B-21K sequences and said sequences necessary for serotype specific complementation comprise E1B-55K sequences. Provided also are cells transformed by such hybrid construct. Such cells can favorably be used for the propagation of recombinant El deleted adenovirus of said another serotype. Of co se it is also possible to provide both functions of El sequences on separate constructs. In all aspects, the sequences are operatively linked to regulatory sequences enabling transcription and translation of the encoded proteins. Preferably a packaging cell of the invention further comprises a DNA encoding at least E4-orf6 of an adenovirus of subgroup B, preferably adenovirus serotype 35. Preferably, said E4-orf6 is derived from said another serotype. Preferably said cell comprises E1B-55K and E4-orf6 of the same serotype as the recombinant vector to be propagated/complemented or otherwise produced. In another aspect of the invention, new packaging cells are described that are derived from PER.C6 (ECACC deposit number 96022940; Fallaux et al, 1998) and contain Ad35-El sequences integrated into their genome. These Ad35-El sequences are present in a functional expression cassette, but preferably do not contain sequences overlapping with sequences present in the recombinant viral vector. Preferably, the functional expression cassette consists of a heterologous promoter and poly-adenylation signal functionally linked to Ad35-El sequences. More specifically, the Ad35-El coding sequences are functionally linked to the human phosphoglycerate gene promoter (hPGK) and hepatitus B virus poly-adenylation signal (HBV-pA). Preferably, Ad35-El coding sequences comprise the coding regions of the El A proteins and the EIB promoter sequences linked to EIB coding sequences up to and including the stop codon of the EIB 55K protein. More preferably, the Ad35-El sequences comprise nucleotide 468 to nucleotide 3400 of the Ad35 wt sequence. To be able to select for transfected cells, a dominant selection marker like, but not limited to, the neo r gene has to be incorporated on the expression vector or the Ad35 expression vector is co-transfected with a separate expression vector mediating expression of the selection marker. In both cases, the selection marker becomes integrated in the cellular genome. Other Ad5-El transformed cell lines like 293 (Graham et al, 1977) and 911 (Fallaux et ah, 1996) or established human cell lines like A549 cells may be used without departing from the present invention. In another aspect of the invention, PER.C6-derived cells are described that express functional Ad35 EIB sequences. In one embodiment, the Ad35-E1B coding sequences are driven by the EIB promoter and terminated by a heterologous poly- adenylation signal like, but not limited to, the HBVpA. In a preferred embodiment, the Ad35-E1B coding sequences are driven by a heterologous promoter like, but not limited to, the hPGK promoter or Elongation Factor- 1 α ( E F - 1 α ) promoter and terminated by a heterologous pA signal like, but not limited to, the HBVpA. These Ad35-E1B sequences preferably comprise the coding regions of the EIB 2 IK and the EIB 55K proteins located between nucleotides 1611 and 3400 of the wild-type (wt) Ad35 sequence. More preferably, the Ad35-E1B sequences comprise nucleotides 1550 to 3400 of the wt Ad35 sequence. In an even more preferred embodiment, the EIB sequences comprise the coding sequences of the E1B-55K gene located between nucleotides 1916 and 3400 of the wt Ad35 sequence. In an even more preferred embodiment a packaging cell line or a cell line of the invention lacks a functional coding sequence for EIB 21k. Such cell lines in general produce significantly more recombinant adenovirus than EIB 2 IK positive cell lines. The invention further provides a method for complementing a recombinant adenovirus comprising providing a packaging cell line or a cell line according to the invention, with said recombinant adenovirus and culturing said cell to allow for complementation. In a preferred embodiment said method further comprises harvesting complemented recombinant adenovirus. Preferably said recombinant adenovirus is derived from adenovirus subgroup B. More preferably said recombinant adenovirus is derived from adenovirus serotype 35. In another aspect the invention provides a recombinant adenovirus obtained by a method of the invention or with a packaging cell of the invention. Such adenovirus can be obtained essentially free from contaminating wild type adenovirus, or replication competent adenovirus. Such recombinant adenovirus preparations are very suited for administration of therapeutic sequences to somatic tissues in vivo in for instance a gene therapeutic setting. Preferred are recombinant adenoviruses comprising a deletion of nucleic acid encoding at least one El -region protein. Preferably, such adenovirus further comprises a deletion of nucleic acid encoding at least one E3-region protein. Preferably, such adenovirus further comprises a deletion of nucleic acid encoding at least one E4- region protein. Preferably, such adenovirus further comprises a deletion of nucleic acid encoding at least E4-Orf6 protein. For this reason the invention also provides the use of a recombinant adenovirus of the invention for the preparation of a medicament. With the term E1B-55K protein as used herein, is meant the protein encoded by the E1B- region in an adenovirus serotype having a similar function in said serotype as provided by the E1B-55K protein Ad5. With the term E1B-2 IK protein as used herein, is meant the protein enclosed by the E1B- region in an adenovirus serotype having a similar function in said serotype as provided by the E1B-19K protein of Ad5. The same terminology applies for the sequences encoding these proteins. When referring to Ad35-El sequences from a specified nucleotide to nucleotide 3400 is meant 'up to and including nucleotide 3400'. Cell lines subject of this invention are useful for, among other things, the production of recombinant adenoviruses designed for gene therapy and vaccination. The cell lines, being derived from cells of human origin, are also useful for the production of human recombinant therapeutic proteins like, but not limited to human growth factors, human antibodies. In addition the cell lines are useful for the production of human viruses other than adenovirus like, but not limited to, influenza virus, heφes simplex virus, rotavirus, measles virus. A preferred derivative of primary, diploid human cells is the PER.C6 cell line (ECACC deposit number 960022940). It is within the skills of the artisan to provide for proteins having a similar function in kind as the adenovirus El protein referred to in this document. For instance a functional part may be provided and/or a derivative may be provided with a similar function in kind, not necessarily in amount. Such parts and derivatives are considered to be part of the invention, in as far as similar transforming complementing and/or serotype specificity function is provided in kind, not necessarily in amount. Brief Description of the Figures FIG. 1: Bar graph showing the percentage of serum samples positive for neutralization for each human wt adenovirus tested (see, Example 1 for description of the neutralization assay). FIG. 2: Graph showing absence of correlation between the VP/CCID50 ratio and the percentage of neutralization. FIG. 3: Bar graph presenting the percentage sera samples that show neutralizing activity to a selection of adenovirus serotypes. Sera were derived from healthy volunteers from Belgium and the UK. FIG. 4: Bar graph presenting the percentage sera samples that show neutralizing activity to adenovirus serotypes 5, 11, 26, 34, 35, 48 and 49. Sera were derived from five different locations in Europe and the United States. FIG. 5: Sequence of human adenovirus type 35. FIG. 6: Map of pAdApt35IPl. FIG. 7: Schematic representation of the steps undertaken to construct pWE.Ad35.pIX- rITR. FIG. 8: Map of pWE.Ad35.pIX-rITR. FIG. 9: Map of pRSV.Ad35-El. FIG. 10: Map of PGKneopA. FIG. 11: Map of pRSVpNeo. FIG. 12: Map of pRSVhbvNeo. FIG. 13: Map of pIG.ElA.ElB. FIG. 14: Map of pIGl 35. FIG. 15: Map ofpIG270. FIG. 16: Map of pBr.Ad35.1eftITR-pIX. FIG. 17: Map of pBr.Ad35.1eftITR-pIXΔElA FIG. 18: Map of pBr.Ad35.Δ21K FIG. 19: Map of pBr.Ad35.Δ55Kl FIG. 20: Map of pBrAd35ΔSM FIG. 21: Schematic representation of Ad35-E1A/E1B deletion constructs. FIG. 22: Map of pIG.35BL. FIG. 23 : Map of pRSVneo4. FIG. 24: Map of pIG35Bneo. FIG. 25: Map of pIG35.55K FIG. 26: Map of pIG535 FIG. 27: Map of pIG635 FIG. 28: Map of pIG735 FIG 29: Map of pCC271 FIG 30: Map of pCC535s FIG 31: Map of pCR535ElB FIG 32: Map of pCC2155s FIG 33: Map ofpCC536s FIG 34: Map of pIG536 FIG 35: Map of pBr.Ad35.PRn FIG 36: Map of pBr.Ad35.PRnΔE3 FIG 37: Map of pWE.Ad35.pIX-rITRΔE3 FIG 38: Alignment of E1B-21K (A) and E1B-55K (B) amino acid sequences in pCC536s with wtAd5 and wtAd35 sequences. Detailed Description of The Invention The invention is further explained by the use of the following illustrative examples. EXAMPLES Example 1 A high throughput assay for the detection of neutralizing activity in human serum To enable screening of a large amount of human sera for the presence of neutralizing antibodies against all adenovirus serotypes, an automated 96-wells assay was developed. Human sera A panel of 100 individuals was selected. Volunteers (50% male, 50% female) were healthy individuals between ages 20 and 60 years old with no restriction for race. All volunteers signed an informed consent form. People professionally involved in adenovirus research were excluded. Approximately 60 ml blood was drawn in dry tubes. Within two ho s after sampling, the blood was centrifuged at 2500 rpm for 10 minutes. Approximately 30 ml serum was transferred to polypropylene tubes and stored frozen at -20°C until further use. Serum was thawed and heat-inactivated at 56°C for 10 minutes and then aliquoted to prevent repeated cycles of freeze/thawing. Part was used to make five steps of twofold dilutions in medium (DMEM, Gibco BRL) in a quantity enough to fill out approximately 70 96-well plates. Aliquots of undiluted and diluted sera were pipetted in deep well plates (96-well format) and using a programmed platemate dispensed in 100 μl aliquots into 96- well plates. This way the plates were loaded with eight different sera in duplo (100 μl/well) according to the scheme below: Where Sl/2 to S8/2 in columns 1 and 6 represent 1 X diluted sera and Sx/4, Sx/8, Sx/16 and Sx/32 the twofold serial dilutions. The last plates also contained four wells filled with 100 μl fetal calf serum as a negative control. Plates were kept at -20°C until further use. Preparation of human adenovirus stocks Prototypes of all known human adenoviruses were inoculated on T25 flasks seeded with PER.C6 cells (Fallaux et al, 1998) and harvested upon full CPE. After freeze/thawing 1-2 ml of the crude lysates was used to inoculate a T80 flask with PER.C6 and virus was harvested at full CPE. The timeframe between inoculation and occurrence of CPE as well as the amount of virus needed to re-infect a new culture, differed between serotypes. Adenovirus stocks were prepared by freeze/thawing and used to inoculate 3-4 T175 cm 2 three-layer flasks with PER.C6 cells. Upon occurrence of CPE, cells were harvested by tapping the flask, pelleted and virus was isolated and purified by a two-step CsCl gradient as follows. Cell pellets were dissolved in 50 ml 10 mM NaPO 4 buffer (pH 7.2) and frozen at-20°C. After thawing at 37°C, 5.6 ml sodium deoxycholate (5% w/v) was added. The solution was mixed gently and incubated for 5-15 minutes at 37°C to completely lyse the cells. After homogenizing the solution, 1875 μl 1M MgCl 2 was added. After the addition of 375 μl DNAse (10 mg/ml) the solution was incubated for 30 minutes at 37°C. Cell debris was removed by centrifugation at 1880xg for 30 minutes at RT without brake. The supernatant was subsequently purified from proteins by extraction with FREON (3x). The cleared supernatant was loaded on a 1M Tris/HCl buffered cesium chloride block gradient (range: 1.2/1.4 g/ml) and centrifuged at 21000 rpm for 2.5 ho s at 10°C. The virus band is isolated after which a second purification using a 1M Tris/HCl buffered continues gradient of 1.33 g/ml of cesium chloride was performed. The virus was then centrifuged for 17 ho s at 55000 rpm at 10°C. The virus band is isolated and sucrose (50 % w/v) is added to a final concentration of 1%. Excess cesium chloride is removed by dialysis (three times 1 hr at RT) in dialysis slides (Slide-a-lizer, cut off 10000 kDa, Pierce, USA) against 1.5 liter PBS supplemented with CaCl 2 (0.9 mM), MgCl 2 (0.5mM) and an increasing concentration of sucrose (1, 2, 5%). After dialysis, the virus is removed from the slide-a-lizer after which it is aliquoted in portions of 25 and 100 μl upon which the virus is stored at -85°C. To determine the number of virus particles per milliliter, 50 μl of the virus batch is run on a high-pressure liquid chromatograph (HPLC) as described by Shabram et al (1997). Viruses were eluted using a NaCl gradient ranging from 0 to 600 mM. As depicted in table I, the NaCl concentration by which the viruses were eluted differed significantly among serotypes. Most human adenoviruses replicated well on PER.C6 cells with a few exceptions. Adenovirus type 8 and 40 were grown on 911-E4 cells (He et al, 1998). Purified stocks contained between 5x10 10 and 5x10 12 virus particles/ml (VP/ml; see table I). Titration of purified human adenovirus stocks Adenoviruses were titrated on PER.C6 cells to determine the amount of virus necessary to obtain full CPE in five days, the length of the neutralization assay. Hereto, lOOμl medium was dispensed into each well of 96-well plates. 25 μl of adenovirus stocks pre-diluted 10 4 , 10 5 , 10 6 or 10 7 times were added to column 2 of a 96-well plate and mixed by pipetting up and down 10 times. Then 25 μl was brought from column 2 to column 3 and again mixed. This was repeated until column 11 after which 25 μl from column 11 was discarded. This way, serial dilutions in steps of 5 were obtained starting off from a pre-diluted stock. Then 3xl0 4 PER.C6 cells (ECACC deposit number 96022940) were added in a 100 μl volume and the plates were incubated at 37 °C, 5% CO 2 for five or six days. CPE was monitored microscopically. The method of Reed and Muensch was used to calculate the cell culture-inhibiting dose 50% (CCID50). In parallel, identical plates were set up that were analyzed using the MTT assay (Promega). In this assay, living cells are quantified by colorimetric staining. Hereto, 20 μl MTT (7.5 mgr/ml in PBS) was added to the wells and incubated at 37 °C, 5% CO 2 for two ho s. The supernatant was removed and 100 μl of a 20:1 isopropanol/triton-XlOO solution was added to the wells. The plates were put on a 96-well shaker for 3-5 minutes to solubilize the precipitated staining. Absorbance was measured at 540 nm and at 690 nm (background). By this assay, wells with proceeding CPE or full CPE can be distinguished. Neutralization assay 96-well plates with diluted human serum samples were thawed at 37 °C, 5% CO 2 . Adenovirus stocks diluted to 200 CCID50 per 50 μl were prepared and 50 μl aliquots were added to columns 1-11 of the plates with serum. Plates were incubated for 1 horn at 37°C, 5% CO 2 . Then 50 μl PER.C6 cells at 6xl0 5 /ml were dispensed in all wells and incubated for 1 day at 37 °C, 5% CO 2 . Supernatant was removed using fresh pipette tips for each row and 200 μl fresh medimn was added to all wells to avoid toxic effects of the serum. Plates were incubated for another 4 days at 37 °C, 5% CO 2 . In addition, parallel control plates were set up in duplo with diluted positive control sera generated in rabbits and specific for each serotype to be tested in rows A and B and with negative control serum (FCS) in rows C and D. Also, in each of the rows E-H a titration was performed as described above with steps of five times dilutions starting with 200 CCID50 of each virus to be tested. On day 5, one of the control plates was analyzed microscopically and with the MTT assay. The experimental titer was calculated from the control titration plate observed microscopically. If CPE was found to be complete, i.e. the first dilution in the control titration experiment analyzed by MTT shows clear cell death, all assay plates were processed. If not, the assay was allowed to proceed for one or more days until full CPE was apparent after which all plates were processed. In most cases, the assay was terminated at day 5. For Adl, 5, 33, 39, 42 and 43 the assay was left for six days and for Ad2 for eight days. A serum sample is regarded as "non-neutralizing" when, at the highest serum concentration, a maximum protection of 40% is seen compared to controls without serum. The results of the analysis of 44 prototype adenoviruses against serum from 100 healthy volunteers are shown in FIG. 1. As expected, the percentage of serum samples that contained neutralizing antibodies to Ad2 and Ad5 was very high. This was also true for most of the lower numbered adenoviruses. Surprisingly, none of the serum samples contained neutralizing antibodies to Ad35. Also, the number of individuals with neutralizing antibody titers to the serotypes 26, 34 and 48 was very low. Therefore, recombinant El -deleted adenoviruses based on Ad35 or one of the other above mentioned serotypes have an important advantage compared to recombinant vectors based on Ad5 with respect to clearance of the viruses by neutralizing antibodies. Also, Ad5-based vectors that have (parts of) the capsid proteins involved in immunogenic response of the host replaced by the corresponding (parts of) the capsid proteins of Ad35 or one of the other serotypes will be less, or even not, neutralized by the vast majority of human sera. As can be seen in Table I, the VP/CCID50 ratio calculated from the virus particles per ml and the CCID50 obtained for each virus in the experiments was highly variable, and ranged from 0.4 to 5 log. This is probably caused by different infection efficiencies of PER.C6 cells and by differences in replication efficiency of the viruses. Furthermore, differences in batch qualities may play a role. A high VP/CCID50 ratio means that more viruses were put in the wells to obtain CPE in 5 days. As a consequence, the outcome of the neutralization study might be biased since more (inactive) virus particles could shield the antibodies. To check whether this phenomenon had taken place, the VP/CCID50 ratio was plotted against the percentage of serum samples found positive in the assay (FIG. 2). The graph clearly shows that there is no negative correlation between the amount of viruses in the assay and neutralization in serum. Example 2 Ebe prevalence of neutralizing activity (NA) to Ad35 is low in human sera from different geographic locations In Example 1 the analysis of neutralizing activity ("NA") in human sera from one location in Belgium was described. Strikingly, of a panel of 44 adenovirus serotypes tested, one serotype, Ad35, was not neutralized in any of the 100 sera assayed. In addition, a few serotypes, Ad26, Ad34 and Ad48 were found to be neutralized in 8%, or less, of the sera tested. This analysis was further extended to other serotypes of adenovirus not previously tested and, using a selection of serotypes from the first screen, was also extended to sera from different geographic locations. Hereto, adenoviruses were propagated, purified and tested for neutralization in the CPE-inhibition assay as described in Example 1. Using the sera from the same batch as in Example 1, adenovirus serotypes 7B, 11, 14, 18 and 44/1876 were tested for neutralization. These viruses were found to be neutralized in, respectively, 59, 13, 30, 98 and 54 % of the sera. Thus, of this series, Adl 1 is neutralized with a relatively low frequency. Since it is known that the frequency of isolation of adenovirus serotypes from human tissue as well as the prevalence of NA to adenovirus serotypes may differ on different geographic locations, we further tested a selection of the adenovirus serotypes against sera from different places. Human sera were obtained from two additional places in E ope (Bristol, UK and Leiden, NL) and from two places in the United States (Stanford, CA and Great Neck, NY). Adenoviruses that were found to be neutralized in 20% or less of the sera in the first screen, as well as Ad2, Ad5, Ad27, Ad30, Ad38, Ad43, were tested for neutralization in sera from the UK. The results of these experiments are presented in FIG. 3. Adenovirus serotypes 2 and 5 were again neutralized in a high percentage of human sera. Furthermore, some of the serotypes that were neutralized in a low percentage of sera in the first screen are neutralized in a higher percentage of sera from the UK, for example, Ad26 (7% vs. 30%), Ad28 (13% vs. 50%), Ad34 (5% vs. 27%) and Ad48 (8% vs. 32%). Neutralizing activity against Adl 1 and Ad49 that were found in a relatively low percentage of sera in the first screen, are found in an even lower percentage of sera in this second screen (13% vs. 5% and 20% vs. 11% respectively). Serotype Ad35 that was not neutralized in any of the sera in the first screen, was now found to be neutralized in a low percentage (8%) of sera from the UK. The prevalence of NA in human sera from the UK is the lowest to serotypes Adl 1 and Ad35. For further analysis, sera obtained from two locations in the US (Stanford, CA and Great Neck, NY) and from The Netherlands (Leiden). FIG. 4 presents an overview of data " obtained with these sera and the previous data. Not all viruses were tested in all sera, except for Ad5, Adl 1 and Ad35. The overall conclusion from this comprehensive screen of human sera is that the prevalence of neutralizing activity to Ad35 is the lowest of all serotypes throughout the western countries: on average 7% of the human sera contain neutralizing activity (5 different locations). Another B -group adenovirus, Adl 1 is also neutralized in a low percentage of human sera (average 11% in sera from 5 different locations). Adenovirus type 5 is neutralized in 56% of the human sera obtained from 5 different locations. Although not tested in all sera, D-group serotype 49 is also neutralized with relatively low frequency in samples from Emope and from one location of the US (average 14%). In the herein described neutralization experiments, a serum is judged non- neutralizing when, in the well with the highest serum concentration, the maximum protection of CPE is 40% compared to the controls without serum. The protection is calculated as follows: ^ protection s OD corresponding well - OD virus control x 100 % OD non-infected control - OD virus control As described in Example 1, the serum is plated in five different dilutions ranging from 4x to 64x diluted. Therefore, it is possible to distinguish between low titers (i.e., neutralization only in the highest serum concentrations) and high titers of NA (i.e., also neutralization in wells with the lowest serum concentration). Of the human sera used in o screen that were found to contain neutralizing activity to Ad5, 70% turned out to have high titers whereas of the sera that contained NA to Ad35, only 15% had high titers. Of the sera that were positive for NA to Adl 1 only 8% had high titers. For Ad49, this was 5%. Therefore, not only is the frequency of NA to Ad35, Adl 1 and Ad49 much lower as compared to Ad5, but of the sera that do contain A to these viruses, the vast majority has low titers. Adenoviral vectors based on Adl 1, Ad35 or Ad49 have therefore a clear advantage over Ad5 based vectors when used as gene therapy vehicles or vaccination vectors in vivo or in any application where infection efficiency is hampered by neutralizing activity. In the following examples, the construction of a vector system for the generation of safe, RCA-free Ad35-based vectors is described. Example 3 Sequence of the human adenovirus type 35 Ad35 viruses were propagated on PER. C6 cells and DNA was isolated as follows: To 100 μl of viras stock (Ad35: 3.26xl0 12 VP/ml), lOμl 10X DNAse buffer (130 mM Tris-HCl pH7.5; 1,2 M CaCl 2 ; 50mM MgCl 2 ) was added. After addition of 10 μl lOmgr/ml DNAse I (Roche Diagnostics), the mixture was incubated for 1 hr. at 37°C. Following addition of 2.5μl 0.5M EDTA, 3.2μl 20% SDS and 1.5μl ProteinaseK (Roche Diagnostics; 20mgr/ml), samples were incubated at 50°C for 1 hr. Next, the viral DNA was isolated using the GENECLEAN spin kit (Biol 01 Inc.) according to the manufacturer's instructions. DNA was eluted from the spin column with 25 μl sterile MilliQ water. The total sequence was generated by Qiagen Sequence Services (Qiagen GmbH, Germany). Total viral DNA was sheared by sonification and the ends of the DNA were made blunt by T4 DNA polymerase. Sheared blunt fragments were size fractionated on agarose gels and gel slices corresponding to DNA fragments of 1.8 to 2.2kb were obtained. DNA was purified from the gel slices by the QIAquick gel extraction protocol and subcloned into a shotgun library of pUC19 plasmid cloning vectors. An array of clones in 96-well plates covering the target DNA 8 (+/- 2) times was used to generate the total sequence. Sequencing was performed on Perkin-Elmer 9700 thermocyclers using Big Dye Terminator chemistry and AmpliTaq FS DNA polymerase followed by purification of sequencing reactions using QIAGEN DyeEx 96 technology. Sequencing reaction products were then subjected to automated separation and detection of fragments on ABI 377 XL 96 lane sequencers. Initial sequence results were used to generate a contiguous sequence and gaps were filled in by primer walking reads on the target DNA or by direct sequencing of PCR products. The ends of the virus turned out to be absent in the shotgun library, most probably due to cloning difficulties resulting from the amino acids of pTP that remain bound to the ITR sequences after proteinase K digestion of the viral DNA. Additional sequence runs on viral DNA solved most of the sequence in those regions, however it was difficult to obtain a clear sequence of the most terminal nucleotides. At the 5' end the sequence portion obtained was 5'-CCAATAATATACCT- 3' (SEQ. I.D. NO. ) while at the 3' end, the obtained sequence portion was 5'- AGGTATATTATTGATGATGGG-3' (SEQ. I.D. NO. __). Most human adenoviruses have a terminal sequence 5'-CATCATCAATAATATACC-3' (SEQ. I.D. NO. _ . In addition, a clone representing the 3' end of the Ad35 DNA obtained after cloning the terminal 7 kb Ad35 EcoRI fragment into pBr322 also turned out to have the typical CATCATCAATAAT... sequence. Therefore, Ad35 may have the typical end sequence and the differences obtained in sequencing directly on the viral DNA are due to artefacts correlated with run-off sequence runs and the presence of residual amino acids of pTP. The total sequence of Ad35 with corrected terminal sequences is given in FIG. 5. Based sequence homology with Ad5 (Genbank # M72360) and Ad7 (partial sequence Genbank # X03000) and on the location of open reading frames, the organization of the virus is identical to the general organization of most human adenoviruses, especially the subgroup B viruses. The total length of the genome is 34,794 basepairs. Example 4 Construction of a plasmid-based vector system to generate recombinant Ad35-based viruses. A functional plasmid-based vector system to generate recombinant adenoviral vectors comprises the following components: 1. An adapter plasmid comprising a left ITR and packaging sequences derived from Ad35 and at least one restriction site for insertion of an heterologous expression cassette and lacking El sequences. Furthermore, the adapter plasmid contains Ad35 sequences 3 ' from the EIB coding region including the pIX promoter and coding sequences enough to mediate homologous recombination of the adapter plasmid with a second nucleic acid molecule. 2. A second nucleic acid molecule, comprising sequences homologous to the adapter plasmid, and Ad35 sequences necessary for the replication and packaging of the recombinant virus, that is early, intermediate and late genes that are not present in the packaging cell. 3. A packaging cell providing at least functional El proteins capable of complementing the El function of Ad35. Other methods for generating recombinant adenoviruses on complementing packaging cells are known in the art, and may be applied to Ad35 viruses without departing from the invention. As an example, the construction of a plasmid-based system, as outlined above, is described in detail below. 1 Construction of Ad35 adapter plasmids. The adapter plasmid pAdApt (described in International Patent Application WO99/55132) was first modified to obtain adapter plasmids that contain extended polylinkers and that have convenient unique restriction sites flanking the left ITR and the adenovirus sequence at the 3' end to enable liberation of the adenovirus insert from plasmid vector sequences. Construction of these plasmids is described below in detail: Adapter plasmid pAdApt was digested with Sail and treated with Shrimp Alkaline Phosphatase to reduce religation. A linker, composed of the following two phosphorylated and annealed oligos: ExSalPacF 5' - TCG ATG GCA AAC AGC TAT TAT GGG TAT TAT GGG TTC GAA TTA ATT AA- 3' (SEQ. I.D. NO. __) and ExSalPacR 5' - TCG ATT AAT TAA TTC GAA CCC ATA ATA CCC ATA ATA GCT GTT TGC CA- 3' (SEQ. I.D. NO. _ was directly ligated into the digested construct, thereby replacing the Sail restriction site by Pi-Pspl, Swal and Pad. This construct was designated pADAPT+ExSalPac linker. Furthermore, part of the left ITR of pAdApt was amplified by PCR using the following primers: PCLIPMSF: 5'- CCC CAA TTG GTC GAC CAT CAT CAA TAA TAT ACC TTA TTT TGG -3' (SEQ. I.D. NO. _J and pCLIPBSRGI: 5'- GCG AAA ATT GTC ACT TCC TGT G - 3' (SEQ. I.D. NO. _). The amplified fragment was digested with Muni and BsrGI and cloned into pAd5/Clip (described in International Patent Application WO99/55132), which was partially digested with EcoRI and after purification digested with BsrGI, thereby re-inserting the left ITR and packaging signal. After restriction enzyme analysis, the construct was digested with Seal and SgrAI and an 800 bp fragment was isolated from gel and ligated into Scal/SgrAI digested pADAPT+ExSalPac linker. The resulting construct, designated pIPspSalAdapt, was digested with Sail, dephosphorylated, and ligated to the phosphorylated ExSalPacF/ExSalPacR double-stranded linker previously mentioned. A clone in which the Pad site was closest to the ITR was identified by restriction analysis and sequences were confirmed by sequence analysis. This novel pAdApt construct, termed pIPspAdapt thus harboms two ExSalPac linkers containing recognition sequences for Pad, PI-PspI and BstBL which surround the adenoviral part of the adenoviral adapter construct, and which can be used to linearize the plasmid DNA prior to cotransfection with adenoviral helper fragments. In order to further increase transgene cloning permutations, a number of polylinker variants were constructed based on pIPspAdapt. For this purpose, pIPspAdapt was first digested with EcoRI and dephosphorylated. A linker composed of the following two phosphorylated and annealed oligos: Ecolinker : 5' -AAT TCG GCG CGC CGT CGA CGA TAT CGA TAG CGG CCG C -3' (SEQ. I.D. NO. __) and Ecolinker-: 5' - AAT TGC GGC CGC TAT CGA TAT CGT CGA CGG CGC GCC G -3' (SEQ. I.D. NO. ) was ligated into this construct, thereby creating restriction sites for Ascl, Sail, EcoRV, Clal and Notl. Both orientations of this linker were obtained, and sequences were confirmed by restriction analysis and sequence analysis. The plasmid containing the polylinker in the order 5' Hindlll, Kpnl, Agel, EcoRI, Ascl, Sail, EcoRV, Clal, Notl, Nhel, Hpal, BamHI and Xbal was termed pIPspAdaptl while the plasmid containing the polylinker in the order Hindlll, Kpnl, Agel, Notl, Clal, EcoRV, Sail, Ascl, EcoRI, Nhel, Hpal, BamHI and Xbal was termed pIPspAdapt2. To facilitate the cloning of other sense or antisense constructs, a linker composed of the following two oligonucleotides was designed, to reverse the polylinker of pIPspAdapt: HindXba+ 5'-AGC TCT AGA GGA TCC GTT AAC GCT AGC GAA TTC ACC GGT ACC AAG CTT A-3' (SEQ. I.D. NO. _); HindXba- 5'-CTA GTA AGC TTG GTA CCGGTGAAT TCGCTAGCG TTAACG GATCCTCTA G-3' (SEQ. I.D. NO. ). This linker was ligated into Hindlll/Xbal digested pIPspAdapt and the correct construct was isolated. Confirmation was done by restriction enzyme analysis and sequencing. This new construct, pIPspAdaptA, was digested with EcoRI and the previously mentioned Ecolinker was ligated into this construct. Both orientations of this linker were obtained, resulting in pIPspAdapt3, which contains the polylinker in the order Xbal, BamHI, Hpal, Nhel, EcoRI, Ascl, Sail, EcoRV, Clal, Notl, Agel, Kpnl and Hindlll. All sequences were confirmed by restriction enzyme analysis and sequencing. Adapter plasmids based on Ad35 were then constructed as follows: The left ITR and packaging sequence corresponding to Ad35 wt sequences nucleotides 1 to 464 (FIG. 5) were amplified by PCR on wtAd35 DNA using the following primers: lPrimer 35Fl: 25'-CGG AAT TCT TAA TTA ATC GAC ATC ATC AAT AAT ATA CCT TAT AG-3 ' (SEQ. I.D. NO. Primer 35R2: 5'-GGT GGT CCT AGG CTG ACA CCT ACG TAA AAA CAG-3' (SEQ. I.D. NO. Amplification introduces a Pad site at the 5' end and an Avrll site at the 3' end of the sequence. For the amplification, Platinum Pfx DNA polymerase enzyme (LTI) was used according to manufacturer's instructions, but with primers at 0.6 μM and with DMSO added to a final concentration of 3%. Amplification program was as follows: 2 min. at 94°C, (30 sec. 94°C, 30 sec. at 56°C, 1 min. at 68°C) for 30 cycles, followed by 10 min. at 68°C. The PCR product was purified using a PCR purification kit (LTI) according to the manufacturer's instructions, and digested with Pad and Avrll. The digested fragment was then purified from gel using the GENECLEAN kit (Bio 101, Inc.). The Ad5-based adapter plasmid pIPspAdApt-3 was digested with Avrll and then partially with Pad and the 5762 bp fragment was isolated in an LMP agarose gel slice and ligated with the abovementioned PCR fragment digested with the same enzymes and transformed into electrocompetent DH10B cells (LTI). The resulting clone is designated ρIPspAdApt3- Ad351ITR. In parallel, a second piece of Ad35 DNA was amplified using the following priniers: 335F3: 5'- TGG TGG AGA TCT GGT GAG TAT TGG GAA AAC-3' (SEQ. I.D. NO. 435R4: 5'- CGG AAT TCT TAA TTA AGG GAA ATG CAA ATC TGT GAG G-3' (SEQ. I.D. NO. __) The sequence of this fragment corresponds to nucleotides 3401 to 4669 of wtAd35 (FIG. 5) and contains 1.3kb of sequences starting directly 3' from the EIB 55k coding sequence. Amplification and purification were done as previously described herein for the fragment containing the left ITR and packaging sequence. The PCR fragment was then digested with Pad and subcloned into pNEB193 vector (New England Biolabs) digested with Smal and Pad. The integrity of the sequence of the resulting clone was checked by sequence analysis. pNEB/Ad35pF3R4 was then digested with Bglll and Pad and the Ad35 insert was isolated from gel using the QIAExII kit (Qiagen). pIPspAdAρt3-Ad351ITR was digested with Bglll and then partially with Pad. The 3624 bp fragment (containing vector sequences, the Ad35 ITR and packaging sequences as well as the CMN promoter, multiple cloning region and polyA signal) was also isolated using the QIAExII kit (Qiagen). Both fragments were ligated and transformed into competent DH10B cells (LTI). The resulting clone, pAdApt35IP3, has the expression cassette from pIPspAdApt3 but contains the Ad35 left ITR and packaging sequences and a second fragment corresponding to nucleotides 3401 to 4669 from Ad35. A second version of the Ad35 adapter plasmid having the multiple cloning site in the opposite orientation was made as follows: pIPspAdaptl was digested with Ndel and Bglll and the 0.7 kbp band containing part of the CMN promoter, the MCS and SN40 polyA was isolated and inserted in the corresponding sites of pAdApt35IP3 generating ρAdApt35IPl (Fig. 6). pAdApt35.LacZ and pAdApt35.Luc adapter plasmids were then generated by inserting the transgenes from pcDΝA.LacZ (digested with Kpnl and BamHI) and pAdAp Luc (digested with Hindlll and BamHI) into the corresponding sites in pAdAρt35IPl. The generation of pcDΝA.LacZ and pAdApt.Luc is described in International Patent Application WO99/55132. 2) Construction of cosmid pWE. Ad35.pLX-rlTR FIG. 7 presents the various steps undertaken to construct the cosmid clone containing Ad35 sequences from bp 3401 to 34794 (end of the right ITR) that are described in detail below. A first PCR fragment (pIX-Νdel) was generated using the following primer set: 535F5: 5'-CGG AAT TCG CGG CCG CGG TGA GTA TTG GGAAAA C -3' (SEQ. I.D. NO. _ 635R6: 5'-CGC CAG ATC GTC TAC AGA ACA G-3' (SEQ. I.D. NO. _) DNA polymerase Pwo (Roche) was used according to manufacturer's instructions, however, with an end concentration of 0.6 μM of both primers and using 50 ngr wt Ad35 DNA as template. Amplification was done as follows: 2 min. at 94 °C, 30 cycles of 30 sec. at 94 °C, 30 sec. at 65 °C and 1 min. 45 sec. at 72 °C, followed by 8 min. at 68 °C. To enable cloning in the TA cloning vector PCR2.1, a last incubation with 1 unit superTaq polymerase (HT Biotechnology LTD) for 10 min. at 72 °C was performed. The 3370 bp amplified fragment contains Ad35 sequences from bp 3401 to 6772 with a Notl site added to the 5' end. Fragments were purified using the PCR purification kit (LTI). A second PCR fragment (Ndel-rlTR) was generated using the following primers: 735F7: 5'-GAA TGC TGG CTT CAG TTG TAA TC -3' (SEQ. I.D. NO. __) 835R8: 5'- CGG AAT TCG CGG CCG CAT TTAAAT CAT CAT CAA TAA TAT ACC-3' (SEQ. I.D. NO. _ Amplification was done with pfx DNA polymerase (LTD according to manufacturer's instructions but with 0.6 μM of both primers and 3% DMSO using 10 ngr. of wtAd35 DNA as template. The program was as follows: 3 min. at 94 °C and 5 cycles of 30 sec. at 94 °C, 45 sec. at 40 °C, 2 min.45 sec. at 68 °C followed by 25 cycles of 30 sec. at 94 °C, 30 sec. at 60 °C, 2 min.45 sec. at 68 °C. To enable cloning in the TA- cloning vector PCR2.1, a last incubation with 1 unit superTaq polymerase for 10 min. at 72 °C was performed. The 1.6 kb amplified fragment ranging from nucleotides 33178 to the end of the right ITR of Ad35, was purified using the PCR purification kit ( LTI). Both purified PCR fragments were ligated into the PCR2.1 vector of the TA- cloning kit (Invitrogen) and transformed into STBL-2 competent cells (LTI). Clones containing the expected insert were sequenced to confirm correct amplification. Next, both fragments were excised from the vector by digestion with Notl and Ndel and purified from gel using the GENECLEAN kit (BIO 101, Inc.). Cosmid vector pWE15 (Clontech) was digested with Notl, dephosphorylated and also purified from gel. These three fragments were ligated and transformed into STBL2 competent cells (LTI). One of the correct clones that contained both PCR fragments was then digested with Ndel, and the linear fragment was purified from gel using the GENECLEAN kit. Ad35 wt DNA was digested with Ndel and the 26.6 kb fragment was purified from LMP gel using agarase enzyme (Roche) according to the manufacturer's instructions. These fragments were ligated together and packaged using λl phage packaging extracts (Stratagene) according to the manufactmer's protocol. After infection into STBL-2 cells, colonies were grown on plates and analysed for presence of the complete insert. One clone with the large fragment inserted in the correct orientation and having the correct restriction patterns after independent digestions with three enzymes (Ncol, PvuII and Seal) was selected. This clone is designated pWE.Ad35.pIX-rITR. It contains the Ad35 sequences from bp 3401 to the end and is flanked by Notl sites (FIG. 8). 3) Generation of Ad35 based recombinant viruses on PER.C6. Wild type Ad35 virus can be grown on PER.C6 packaging cells to very high titers. However, whether the Ad5-El region that is present in PER.C6 is able to complement El -deleted Ad35 recombinant viruses is unknown. To test this, PER.C6 cells were cotransfected with the above described adapter plasmid pAdApt35.LacZ and the large backbone fragment pWE.Ad35.pIX-rITR. First, pAdApt35.LacZ was digested with Pad and pWE.Ad35.pIX-rITR was digested with Notl. Without further purification, 4 μgr of each construct was mixed with DMEM (LTI) and transfected into PER.C6 cells, seeded at a density of 5x10 cells in a T25 flask the day before, using Lipofectamin (LTI) according to the manufactmer's instructions. As a positive control, 6μgr of Pad digested pWE.Ad35.pIX-rITR DNA was cotransfected with a 6.7 kb Nhel fragment isolated from Ad35 wt DNA containing the left end of the viral genome including the El region. The next day, medium (DMEM with 10% FBS and lOmM MgCl 2 ) was refreshed and cells were further incubated. At day 2 following the transfection, cells were trypsinized and transferred to T80 flasks. The positive control flask showed CPE at five days following transfection, showing that the pWE.Ad35.pIX-rITR construct is functional at least in the presence of Ad35-El proteins. The transfection with the Ad35 LacZ adapter plasmid and pWE.Ad35.pIX-rITR did not give rise to CPE. These cells were harvested in the medium at day 10 and freeze/thawed once to release virus from the cells. 4 ml of the harvested material was added to a T80 flask with PER.C6 cells (at 80% confluency) and incubated for another five days. This harvest/re-infection was repeated for two times but there was no evidence for virus associated CPE. From this experiment, it seems that the Ad5-El proteins are not, or not well enough, capable of complementing Ad35 recombinant viruses, however, it may be that the sequence overlap of the adapter plasmid and the pWE.Ad35.pIX-rITR backbone plasmid is not large enough to efficiently recombine and give rise to a recombinant virus genome. The positive control transfection was done with a 6.7kb left end fragment and therefore the sequence overlap was about 3.5kb. The adapter plasmid and the pWE.Ad35.pIX-rITR fragment have a sequence overlap of 1.3kb. To check whether the sequence overlap of 1.3 kb is too small for efficient homologous recombination, a cotransfection was done with Pad digested pWE.Ad35.pIX-rITR and a PCR fragment of Ad35 wt DNA generated with the above mentioned 35F1 and 35R4 using the same procedures as previously described herein. The PCR fragment thus contains left end sequences up to bp 4669 and, therefore, has the same overlap sequences with pWE.Ad35.pIX-rITR as the adapter plasmid pAdApt35.LacZ, but has Ad35 El sequences. Following PCR column purification, the DNA was digested with Sail to remove possible intact template sequences. A transfection with the digested PCR product alone served as a negative control. Fo days after the transfection, CPE occurred in the cells transfected with the PCR product and the Ad35 pIX-rlTR fragment, and not in the negative control. This result shows that a 1.3kb overlapping sequence is sufficient to generate viruses in the presence of Ad35 El proteins. From these experiments, we conclude that the presence of at least one of the Ad35.El proteins is necessary to generate recombinant Ad35 based vectors from plasmid DNA on Ad5 complementing cell lines. 9 Example 5 1) Construction of Ad35.El expression plasmids Since Ad5-El proteins in PER.C6 are incapable of complementing Ad35 recombinant viruses efficiently, Ad35 El proteins have to be expressed in Ad5 complementing cells (e.g., PER.C6). Alternatively, a new packaging cell line expressing Ad35 El proteins has to be made, starting from either diploid primary human cells or established cell lines not expressing adenovirus El proteins. To address the first possibility, the Ad35 El region was cloned in expression plasmids as described below. First, the Ad35 El region from bp 468 to bp 3400 was amplified from wtAd35 DNA using the following primer set: 135F11: 5'-GGG GTA CCGAAT TCT CGC TAG GGTATT TATACC-3' (SEQ. I.D. NO._) 235F10: 5'-GCT CTA GAC CTG CAG GTTAGT CAG TTT CTT CTC CAC TG-3' (SEQ. I.D. NO. This PCR introduces a Kpnl and EcoRI site at the 5' end and an Sbfl and Xbal site at the 3' end. Amplification on 5 ngr. template DNA was done with Pwo DNA polymerase (Roche) using the manufacturer's instructions, however, with both primers at a final concentration of 0.6 μM. The program was as follows: 2 min. at 94 °C, 5 cycles of 30 sec. at 94 °C, 30 sec. at 56 °C and 2 min. at 72 °C, followed by 25 cycles of 30 sec. at 94°C, 30 sec. at 60 °C and 2 min. at 72 °C, followed by 10 min. at 72 °C. PCR product was purified by a PCR purification kit (LTI) and digested with Kpnl and Xbal. The digested PCR fragment was then ligated to the expression vector pRSVhbvNeo (see below) also digested with Kpnl and Xbal. Ligations were transformed into competent STBL-2 cells (LTI) according to manufacturer's instructions and colonies were analysed for the correct insertion of Ad35El sequences into the polylinker in between the RSV promoter and HBV polyA. The resulting clone was designated pRSV.Ad35-El (FIG. 9). The Ad35 sequences in pRSV.Ad35-El were checked by sequence analysis. pRSVhbvNeo was generated as follows: pRc-RSV (Invitrogen) was digested with PvuII, dephosphorylated with TSAP enzyme (LTI), and the 3kb vector fragment was isolated in low melting point agarose (LMP). Plasmid pPGKneopA (FIG. 10; described in International Patent Application WO96/35798) was digested with Sspl completely to linearize the plasmid and facilitate partial digestion with PvuII. Following the partial digestion with PvuII, the resulting fragments were separated on a LMP agarose gel and the 2245 bp PvuII fragment, containing the PGK promoter, neomycin-resistance gene and HBVpolyA, was isolated. Both isolated fragments were ligated to give the expression vector pRSV-pNeo that now has the original SV40prom-neo-SV40polyA expression cassette replaced by a PGKprom-neo-HBVpolyA cassette (FIG. 11). This plasmid was further modified to replace the BGHpA with the HBVpA as follows: pRSVpNeo was linearised with Seal and further digested with Xbal. The 1145 bp fragment, containing part of the Amp gene and the RSV promoter sequences and polylinker sequence, was isolated from gel using the GeneClean kit (Bio Inc. 101). Next, pRSVpNeo was linearised with Seal and further digested with EcoRI partially and the 3704 bp fragment containing the PGKneo cassette and the vector sequences were isolated from gel as above. A third fragment, containing the HBV polyA sequence flanked by Xbal and EcoRI at the 5' and 3' end respectively, was then generated by PCR amplification on pRSVpNeo using the following primer set: 3HBV-F: 5'- GGC TCTAGAGATCCTTCG CGGGAC GTC -3' (SEQ. I.D.NO. . and 4HBV-R: 5'- GGC GAA TTC ACT GCC TTC CAC CAA GC -3' (SEQ. I.D. NO. Amplification was done with Elongase enzyme (LTI) according to the manufactmer's instructions with the following conditions: 30 seconds at 94°C, then 5 cycles of 45 seconds at 94 °C, 1 minute at 42 °C and 1 minute 68 °C, followed by 30 cycles of 45 seconds at 94 °C, 1 minute at 65 °C and 1 minute at 68 °C, followed by 10 minutes at 68 °C. The 625 bp PCR fragment was then purified using the Qiaquick PCR purification kit, digested with EcoRI and Xbal and purified from gel using the GENECLEAN kit. The three isolated fragments were ligated and transformed into DH5 competent cells (LTI) to give the construct pRSVhbvNeo (FIG. 12). In this construct, the transcription regulatory regions of the RSV expression cassette and the neomycin selection marker are modified to reduce overlap with adenoviral vectors that often contain CMV and SV40 transcription regulatory sequences. 2) Generation of Ad35 recombinant viruses on PER.C6 cells cotransfected with an Ad35-El expression construct. PER.C6 cells were seeded at a density of 5 x 10 6 cells in a T25 flask and, the next day, transfected with a DNA mixture containing: 1 μg pAdApt35.LacZ digested with Pad 5 μg RSV.Ad35El undigested 2 μg pWE. Ad35.pIX-rlTR digested with Notl Transfection was done using Lipofectamine according to the manufacturer's instructions. Five ho s after addition of the transfection mixture to the cells, medium was removed and replaced by fresh medium. After two days, cells were transferred to T80 flasks and further cultured. One week post-transfection, 1 ml of the medium was added to A549 cells and, the following day, cells were stained for LacZ expression. Blue cells were clearly visible after two ho s of staining indicating that recombinant LacZ expressing viruses were produced. The cells were further cultured, but no clear appearance of CPE was noted. However, after 12 days, clumps of cells appeared in the monolayer and 18 days following transfection, cells were detached. Cells and medium were then harvested, freeze-thawed once, and 1 ml of the crude lysate was used to infect PER.C6 cells in a 6-well plate. Two days after infection, cells were stained for LacZ activity. After two ho s, 15% of the cells were stained blue. To test for the presence of wt and / or replicating competent viruses, A549 cells were infected with these viruses and further cultured. No signs of CPE were found indicating the absence of replication competent viruses. These experiments show that recombinant AdApt35.LacZ viruses were made on PER.C6 cells cotransfected with an Ad35-El expression construct. Ad35 recombinant viruses escape neutralization in human serum containing neutralizing activity to Ad5 viruses. The AdApt35.LacZ viruses were then used to investigate infection in the presence of serum that contains neutralizing activity to Ad5 viruses. Purified Ad5-based LacZ virus served as a positive control for NA. Hereto, PER.C6 cells were seeded in a 24-wells plate at a density of 2x10 5 cells/well. The next day, a human serum sample with high neutralizing activity to Ad5 was diluted in culture medium in five steps of five times dilutions. 0.5 ml of diluted serum was then mixed with 4x10 virus particles AdApt5.LacZ virus in 0.5 ml medium and after 30 minutes of incubation at 37 °C, 0.5 ml of the mixtme was added to PER.C6 cells in duplicate. For the AdApt35.LacZ viruses, 0.5 ml of the diluted serum samples were mixed with 0.5 ml crude lysate containing AdApt35.LacZ virus and after incubation 0.5 ml of this mixtme was added to PER.C6 cells in duplo. Virus samples incubated in medium without serum were used as positive controls for infection. After two homs of infection at 37 °C, medium was added to reach a final volume of 1 ml and cells were further incubated. Two days after infection, cells were stained for LacZ activity. The results are shown in Table II. From these results, it is clear that whereas AdApt5.LacZ viruses are efficiently neutralized, AdApt35.LacZ viruses remain infectious irrespective of the presence of human serum. This proves that recombinant Ad35-based viruses escape neutralization in human sera that contain NA to Ad5-based viruses. Example 6 Generation of cell lines capable of complementing El -deleted Ad35 viruses Generation ofpIG135 andpIG270 Construct pIG.El A.E1B (FIG. 13) contains El region sequences of Ad5 corresponding to nucleotides 459 to 3510 of the wt Ad5 sequence (Genbank accession number M72360) operatively linked to the human phosphoglycerate kinase promoter ("PGK") and the Hepatitis B Virus polyA sequences. The generation of this construct is described in International Patent Application No. WO97/00326. The El sequences of Ad5 were replaced by corresponding sequences of Ad35 as follows. pRSV.Ad35-El (described in Example 5) was digested with EcoRI and Sse8387I and the 3 kb fragment corresponding to the Ad35 El sequences was isolated from gel. Construct pIG.ElA.ElB was digested with Sse8387I completely and partially with EcoRI. The 4.2 kb fragment corresponding to vector sequences without the Ad5 El region but retaining the PGK promoter were separated from other fragments on LMP agarose gel and the correct band was excised from gel. Both obtained fragments were ligated resulting in pIG.Ad35-El. This vector was further modified to remove the LacZ sequences present in the pUCl 19 vector backbone. Hereto, the vector was digested with BsaAI and BstXI and the large fragment was isolated from gel. A double stranded oligo was prepared by annealing the following two oligos: 1BB1: 5'-GTG CCT AGG CCA CGG GG-3' (SEQ. I.D. NO. _ and 2BB2: 5'-GTG GCC TAG GCA C-3' (SEQ. I.D. NO. _). Ligation of the oligo and the vector fragment resulted in construct pIG135 (FIG. 14). Correct insertion of the oligo restores the BsaAI and BstXI sites and introduces a unique Avrll site. Next, we introduced a unique site at the 3' end of the Ad35-El expression cassette in pIG135. Hereto, the construct was digested with Sapl and the 3' protruding ends were made blunt by treatment with T4 DNA polymerase. The thus treated linear plasmid was further digested with BsrGI and the large vector-containing fragment was isolated from gel. To restore the 3' end of the HBVpolyA sequence and to introduce a unique site, a PCR fragment was generated using the following primers: 3270F: 5'- CAC CTC TGC CTAATC ATC TC -3' (SEQ. I.D. NO. _J and 4270R: 5'- GCT CTA GAAATT CCA CTG CCT TCC ACC -3' (SEQ. I.D. NO. _ . The PCR was performed on pIG.Ad35.El DNA using Pwo polymerase (Roche) according to the manufactmer's instructions. The obtained PCR product was digested with BsrGI and dephosphorylated using Tsap enzyme (LTI), the latter to prevent insert dimerization on the BsrGI site. The PCR fragment and the vector fragment were ligated to yield construct pIG270 (FIG. 15). Ad35 El sequences are capable of transforming rat primary cells New born WAG/RIJ rats were sacrificed at 1 week of gestation and kidneys were isolated. After careful removal of the capsule, kidneys were disintegrated into a single cell suspension by multiple rounds of incubation in trypsin/EDTA (LTI) at 37 °C and collection of floating cells in cold PBS containing 1% FBS. When most of the kidney was trypsinized all cells were re-suspended in DMEM supplemented with 10% FBS and filtered through a sterile cheesecloth. Baby Rat Kidney (BRK) cells obtained from one kidney were plated in 5 dishes (Greiner, 6 cm). When a confluency of 70-80% was reached, the cells were transfected with 1 or 5 μgr DNA/dish using the CaPO precipitation kit (LTI) according to the manufacturer's instructions. The following constructs were used in separate transfections: pIG.El A.E1B (expressing the Ad5-El region), pRSV.Ad35-El, pIG.Ad35-El and pIG270 (expressing the Ad35-El region). Cells were incubated at 37 °C, 5% CO 2 until foci of transformed cells appeared. Table III shows the number of foci that resulted from several transfection experiments using circular or linear DNA. As expected, the Ad5-El region efficiently transformed BRK cells. Foci also appeared in the Ad35-El transfected cell layer although with lower efficiency. The Ad35 transformed foci appeared at a later time point: ~2 weeks post transfection compared with 7-10 days for Ad5-El. These experiments clearly show that the El genes of the B group virus Ad35 are capable of transforming primary rodent cells. This proves the functionality of the Ad35-El expression constructs and confirms earlier findings of the fransforming capacity of the B-group viruses Ad3 and Ad7 (Dijkema, 1979). To test whether the cells in the foci were really transformed a few foci were picked and expanded. From the 7 picked foci at least 5 turned out to grow as established cell lines. Generation of new packaging cells derived from primary human amniocytes Amniotic fluid obtained after amniocentesis was centrifuged and cells were resuspended in AmnioMax medium (LTI) and cultured in tissue culture flasks at 37 °C and 10 % CO 2 . When cells were growing nicely (approximately one cell division/24 hrs.), the medium was replaced with a 1:1 mixture of AmnioMax complete medium and DMEM low glucose medium (LTI) supplemented with Glutamax I (end concentration 4mM, LTI) and glucose (end concentration 4.5 gr/L, LTI) and 10% FBS (LTI). For transfection ~ 5xl0 5 cells were plated in 10 cm tissue culture dishes. The day after, cells were transfected with 20 μgr of circular pIG270/dish using the CaPO 4 transfection kit (LTI) according to manufactmer's instructions and cells were incubated overnight with the DNA precipitate. The following day, cells were washed 4 times with PBS to remove the precipitate and further incubated for over three weeks until foci of transformed cells appeared. Once a week the medium was replaced by fresh medium. Other transfection agents like, but not limited to, LipofectAmine (LTI) or PEI (Polyethylemrnine, high molecular weight, water-free, Aldrich) were used. Of these three agents PEI reached the best transfection efficiency on primary human amniocytes: ~1% blue cells 48 hrs. Following transfection of pAdApt35. LacZ. Foci are isolated as follows. The medium is removed and replaced by PBS after which foci are isolated by gently scraping the cells using a 50-200 μl Gilson pipette with a disposable filter tip. Cells contained in -10 μml PBS were brought in a 96 well plate containing 15 μl trypsin/EDTA (LTI) and a single cell suspension was obtained by pipetting up and down and a short incubation at room temperature. After addition of 200 μl of the above described 1:1 mixtme of AmnioMax complete medium and DMEM with supplements and 10% FBS, cells were further incubated. Clones that continued to grow were expanded and analysed their ability to complement growth of El -deleted adenoviral vectors of different sub-groups, specifically ones derived from B-group viruses specifically from Ad35 or Adl 1. Generation of new packaging cell lines from HER cells HER cells are isolated and cultured in DMEM medium supplemented with 10% FBS (LTI). The day before transfection, ~5xl0 5 cells are plated in 6 cm dishes and cultured overnight at 37 °C and 10% CO 2 . Transfection is done using the CaPO precipitation kit (LTI) according to the manufacturer's instructions. Each dish is transfected with 8-10 μmgr pIG270 DNA, either as a circular plasmid or as a purified fragment. To obtain the purified fragment, pIG270 was digested with Avrll and Xbal and the 4 kb fragment corresponding to the Ad35 El expression cassette was isolated from gel by agarase treatment (Roche). The following day, the precipitate is washed away carefully by fom washes with sterile PBS. Then fresh medium is added and transfected cells are further cultured until foci of transformed cells appear. When large enough (>100 cells) foci are picked and brought into 96-wells as described above. Clones of transformed HER cells that continue to grow, are expanded and tested for their ability to complement growth of El -deleted adenoviral vectors of different sub-groups specifically ones derived from B-group viruses specifically from Ad35 or Adl 1. New packaging cell lines derived from PER. C6 As described in Example 5, it is possible to generate and grow Ad35 El -deleted viruses on PER.C6 cells with cotransfection of an Ad35-El expression construct, e.g. pRSV.Ad35.El. However, large-scale production of recombinant adenoviruses using this method is cumbersome because, for each amplification step, a transfection of the Ad35- El construct is needed. In addition, this method increases the risk of non-homologous recombination between the plasmid and the virus genome with high chances of generation of recombinant viruses that incorporate El sequences resulting in replication competent viruses. To avoid this, the expression of Ad35-El proteins in PER.C6 has to be mediated by integrated copies of the expression plasmid in the genome. Since PER.C6 cells are already transformed and express Ad5-El proteins, addition of extra Ad35-El expression may be toxic for the cells, however, it is not impossible to stably transfect transformed cells with El proteins since Ad5-El expressing A549 cells have been generated. In an attempt to generate recombinant adenoviruses derived from subgroup B virus Ad7, Abrahamsen et al. (1997) were not able to generate El -deleted viruses on 293 cells without contamination of wt Ad7. Viruses that were picked after plaque purification on 293-ORF6 cells (Brough et al, 1996) were shown to have incorporated Ad7 EIB sequences by non-homologous recombination. Thus, efficient propagation of Ad7 recombinant viruses proved possible only in the presence of Ad7-E1B expression and Ad5-E4-ORF6 expression. The EIB proteins are known to interact with cellular as well as viral proteins (Bridge et al, 1993; White, 1995). Possibly, the complex formed between the EIB 55K protein and E4-ORF6 which is necessary to increase mRNA export of viral proteins and to inhibit export of most cellular mRNAs, is critical and in some way serotype specific. The above experiments suggest that the El A proteins of Ad5 are capable of complementing an Ad7-E1A deletion and that Ad7-E1B expression in adenovirus packaging cells on itself is not enough to generate a stable complementing cell line. To test whether one or both of the Ad35-E1B proteins is/are the limiting factor in efficient Ad35 vector propagation on PER.C6 cells, we have generated an Ad35 adapter plasmid that does contain the EIB promoter and EIB sequences but lacks the promoter and the coding region for El A. Hereto, the left end of wtAd35 DNA was amplified using the primers 35F1 and 35R4 (both described in Example 4) with Pwo DNA polymerase (Roche) according to the manufacturer's instructions. The 4.6 kb PCR product was purified using the PCR purification kit (LTI) and digested with SnaBI and Apal enzymes. The resulting 4.2 kb fragment was then purified from gel using the QIAExII kit (Qiagen). Next, pAdApt35IPl (Example 4) was digested with SnaBI and Apal and the 2.6 kb vector-containing fragment was isolated from gel using the GeneClean kit (BIO 101, Inc). Both isolated fragments were ligated to give ρBr/Ad35.1eftITR-pIX (FIG.16). Correct amplification during PCR was verified by a functionality test as follows: The DNA was digested with BstBI to liberate the Ad35 insert from vector sequences and 4 μg of this DNA was co-transfected with 4 μg of Notl digested ρWE/Ad35.pIX-rlTR (Example 4) into PER.C6 cells. The transfected cells were passaged to T80 flasks at day 2 and again two days later CPE had formed showing that the new pBr/Ad35.1eftITR-pIX construct contains functional El sequences. The pBr/Ad35.1eftITR-pIX construct was then further modified as follows. The DNA was digested with SnaBI and Hindlll and the 5' Hindll overhang was filled in using Klenow enzyme. Religation of the digested DNA and transformation into competent cells (LTI) gave construct pBr/Ad351eftITR-pIXΔDElA (FIG. 17). This latter construct contains the left end 4.6 kb of Ad35 except for El A sequences between bp 450 and 1341 (numbering according to wtAd35, FIG. 5) and thus lacks the E1A promoter and most of the E1A coding sequences. pBr/Ad35.1eftITR-pIXΔDElA was then digested with BstBI and 2 μg of this construct was co-transfected with 6 μmgr of Notl digested p E /Ad35 . pIX-rlTR (Example 4) into PER.C6 cells. One week following transfection full CPE had formed in the transfected flasks. This experiment shows that the Ad35-E1A proteins are functionally complemented by Ad5-El A expression in PER.C6 cells and that at least one of the Ad35- EIB proteins cannot be complemented by Ad5-El expression in PER.C6. It further shows that it is possible to make a complementing cell line for Ad35 El-deleted viruses by expressing Ad35-E1B proteins in PER.C6. Stable expression of Ad35-E1B sequences from integrated copies in the genome of PER.C6 cells may be driven by the EIB promoter and terminated by a heterologous poly-adenylation signal like, but not limited to, the HBVpA. The heterologous pA signal is necessary to avoid overlap between the EIB insert and the recombinant vector, since the natural EIB termination is located in the pIX transcription unit that has to be present on the adenoviral vector. Alternatively, the EIB sequences may be driven by a heterologous promoter like, but not limited to the human PGK promoter or by an inducible promoter like, but not limited to the 7xtetO promoter (Gossen and Bujard, 1992). Also in these cases the transcription termination is mediated by a heterologous pA sequence, e.g. the HBV pA. The Ad35-E1B sequences at least comprise one of the coding regions of the EIB 21K and the EIB 55K proteins located between nucleotides 1611 and 3400 of the wt Ad35 sequence. The insert may also include (part of the) Ad35-E1B sequences between nucleotides 1550 and 1611 of the wt Ad35 sequence. Example 7 Ad35 -based viruses deleted for EIA and El B-2 IK genes efficiently propagate on Ad5 complementing cell lines. The generation of Ad35-based viruses that are deleted for EIA and retain the full EIB region is described in Example 6 of this application. Such viruses can be generated and propagated on the Ad5 complementing cell line PER.C6. The EIB region comprises partially overlapping coding sequences for the two major proteins 21K and 55K (Bos et al, 1981). Whereas dming productive wt adenoviral infection both 21K and 55K are involved in counteracting the apoptose-inducing effects of EIA proteins, the EIB 55K protein has been suggested to have additional functions during the late phase of virus infection. These include the accumulation of viral mRNAs, the control of late viral gene expression and the shutoff of most host mRNAs at the level of mRNA transport (Babiss et ah, 1984, 1985; Pilder et al, 1986). A complex formed between E1B-55K and the ORF6 protein encoded by the adenovirus early region 4 (Leppard and Shenk, 1989; Bridge and Ketner, 1990) exerts at least part of these functions. To analyze which of the EIB proteins is required for propagation of Ad35-E1A deleted recombinant viruses on PER.C6 packaging cells, the EIB region in construct pBr.Ad35.1eftITR-pIXΔElA (see Example 6 and FIG. 17) was further deleted. A first construct, pBr.Ad35Δ2 IK, retains the full E1B-55K sequence and is deleted for EIA and E1B-21K. Hereto, pBr.Ad35.1eftITR-pIXΔE 1A was digested with Ncol and BspEl and the 5 KB vector fragment was isolated from agarose gel using the geneclean kit (BIO 101, Inc.) according to the manufactmer's instructions. Then a PCR fragment was generated with pBr.Ad35.1eftITR-pLXΔE 1 A as template DNA using the following primers: 135D21 : 5'- TTA GAT CCA TGG ATC CCG CAG ACT C-3' (SEQ. I.D. NO. _J and 235B3: 5'- CCT CAG CCC CAT TTC CAG-3' (SEQ. I.D. NO. _). 3 Amplification was done using Pwo DNA polymerase (Roche) according to manufactmer's recommendations with the addition of DMSO (final concentration 3%) in the reaction mixture. The PCR program was as follows: 94°C for , then 30 cycles of 94°C for 30", 58°C for 30" and 72°C for 45" and a final step at 68°C for 8' to ens e blunt ends. This PCR amplifies Ad35-E1B sequences from nucl. 1908 to 2528 (sequence Ad35, FIG. 5) and introduces an Ncol site at the start codon of the E1B-55K coding sequence (bold in primer 35D21). The 620 bp PCR fragment was purified using the PCR purification kit (Qiagen) and then digested with Ncol and BspEI, purified from agarose gel as above and ligated to the above described NcoI/BspEl digested vector fragment to give pBr.Ad35Δ21K (FIG. 18). Since the coding regions of the 2 IK and 55K proteins overlap, it is only possible delete part of the 55K coding sequences while retaining 2 IK. Hereto, pBr.Ad35.1eftITR- pIXΔE 1 was digested with Bglll and the vector fragment was religated to give pBr.Ad35Δ55Kl (FIG. 19). This deletion removes EIB coding sequences from nucl. 2261 to 3330 (Ad35 sequence in FIG. 5). In this construct the N-terminal 115 amino acids are retained and become fused to 21 additional amino acids out of the proper reading frame before a stop codon is encountered. The 21K coding region is intact in construct pBr.Ad35Δ55 KI . A third construct that has a deletion of El A, 21K and most of the 55K sequences was generated as follows. pBr.Ad35.1eftITR-pIX (FIG. 16) was digested with SnaBI and Mfel (isoschizomer of Muni) and the 5' overhang resulting from the Mfel digestion was filled in using Klenow enzyme. The 4.4 kb vector fragment was isolated from gel using the geneclean kit (Bio 101, Inc.) according to the manufactmer's instructions and religated to give construct pBr.Ad35ΔSM (FIG. 20). In this construct, the Ad35 sequences between nucl. 453 and 2804 are deleted thus 596 nucl. of the 3' end of Elb- 55K are retained. A further deletion of 55K sequences was made in construct pBr.Ad35ΔElA. ΔE1B by digestion of ρBr.Ad35.1eftITR-pIX with SnaBI and Bglll, Klenow treatment to fill in the Bglll cohesive ends, and religation. FIG. 21 shows a schematic representation of the above mentioned constructs. To test whether Ad35-based viruses can be generated with these constructs, each of the constructs was cotransfected with Notl digested pWE.Ad35pIX-rITR (see Example 4) onto PER.C6 cells. Hereto, the respective fragments were PCR amplified using primers 35F1 and 35R4 (see, Example 4). This PCR amplification was done since some of the constructs were difficult to isolate in large enough quantities. In this way, equal quality of the different adapter fragments was ensured. For the amplification Pwo DNA polymerase (Roche) was used according to the manufactmer's instructions but with DMSO (3% final concentration)added to the PCR mixttire. Of each template ~ 50 ng DNA was used. The conditions for the PCR were as follows: 94°C for 2', then 5 cycles of 94°C for 30", 48°C for 45" and 72°C for 4' followed by 25 cycles of 94°C for 30", 60°C for 30" and 72°C for 4' and a final step at 68°C for 8'. 4PCR fragments were generated from pBr.Ad351eftITR-pIX, pBr.Ad35.1eftITR- pIXΔElA, pBr . Ad35Δ21K, pBr . Ad35Δ55Kl , pBr . Ad35ΔSM and p B r . Ad 35 ΔE 1 AΔE IB . All fragments were using the PCR purification kit (Qiagen) according to manufactmer's instractions and final concentrations were estimated on EtBr stained agarose gel using the Eagle Eye II Still Video system and EagleSight software (Stratagene) with the SmartLadder molecular weight marker (Emogentec) as reference. PER.C6 cells were seeded at a density of 2.5xl0 6 cells in a T25 culturing flask in DMEM containing 10% fetal calf serum (FCS) and lOmM MgSO 4 and cultured in a humidified stove at 37°C, 10% CO 2 . The next day, 3 mg of each of the PCR fragments was cotransfected with 5 μgr Notl digested pWE .Ad35pIX-rITR using LipofectAmine (GIBCO, Life Technologies Inc.) according to the manufactmer's instructions. Two days after the transfection, all cells were passed to a T80 flask and further cultured. Cultures were then monitored for the appearance of CPE. In line with the outcome of previous experiments described in Examples 4 and 6, pBr.Ad35.1eftITR- pIX and pBr.Ad35.1eftITR-pIXΔE!A showed almost full CPE within one week following transfection. Of the fragments with different EIB deletions only pBr.Ad35Δ2 IK showed CPE at the same time as the above two fragments. Constructs pBr.Ad35Δ55Kl , pBr .Ad35ΔSM and pBr .Ad35ΔElAΔElB did not give CPE at all, also not after harvesting by freeze-thawing and re-infection of the crude lysate onto fresh PER.C6 cells. From these experiments, it can be concluded that Ad35-E1B-55K, and not E1B- 2 IK, is necessary for generation and propagation of Ad35-based viruses on Ad5 complementing cell lines. Therefore, Ad35-based viruses having a deletion of the EIA and EIB 21K genes and having the E1B-55K gene or a functional fragment thereof, can be grown on Ad5 complementing cell lines. Alternatively, Ad35-based viruses can be grown on PER.C6 cells that stably express the full EIB region or the E1B-55K gene or a functional fragment thereof. The Ad35 E1B-55K gene or functional parts thereof may be expressed from a heterologous promoter, like, but not limited to, the human PGK promoter, the human cytomegalovirus immediate early promoter (CMV), Rous sarcoma virus promoter, etc. and terminated by a heterologous poly adenylation sequence (pA), like but not limited to the hepatitis B virus poly adenylation sequence (HBVpA), the Simian Virus 40 poly adenylation sequence (SV40pA), etc. As non-limiting examples PER.C6 cells that express the Ad35-E1B region driven by the EIB promoter and HBVpA, PER.C6 cells that express the Ad35-E1B region driven by the human PGK promoter and HBVpA and PER.C6 cells that express a functional fragment of Ad35 E1B- 55K driven by the human PGK promoter and HBVpA are described below. Generation ofpIG35BL andpIG35BS We describe the generation of two expression constructs, pIG.35BS and pIG.35BL, that both carry the Ad35-E1B genes and a neomycin selection marker. The two constructs differ in the length of the fragment containing the EIB promoter. In 35BL the promoter fragment is longer and includes the 3' end of the EIA region (103 nucl. coding sequence and pA). The EIB region is terminated by the HBVpolyA, the neo r gene is driven by a hPGKpromoter/HBVpA cassette. pIG.35BL was made as follows. Construct pRSN.Ad35El (described in Example 5, FIG. 9) was digested with Νrul and Hindlll and the protruding ends were filled in by Klenow treatment. The 7 kb vector fragment was separated from the smaller fragment on gel and isolated using the geneclean kit (BIO 101, Inc.). After religation of the DΝA and transformation into competent STBL2 cells (Gibco, LTI) correct clones were isolated. pIG.35BL (FIG. 22) contains 273 nucl. upstream of the start site of the E1B-21K coding region. pIG.35BS was made in the same way as pIG.35BL except that pRSN.Ad35El was digested with Νrul and Hpal (both enzymes leave blunt ends), resulting in a shorter fragment upstream of the coding region of E1B-21K: 97 nucleotides. To generate Ad35-E1B expressing cells, PER.C6 cells were seeded in 10 cm dishes at lxl 0 6 cells/dish. Two days later cells were transfected with Seal linearised constructs. Fom dishes were transfected with 1 and four with 2 μg DNA (total of 16 dishes; Lipofectamine (Gibco, LTI), no carrier DNA used) according to the manufactmer's instructions. The next day, transfected cells received G418-containing medium (0.75 mg/ml). Control transfections using LacZ expression constructs (2 μg ) were stained after 48 hrs and showed a transfection efficiency of ~25%. Four days following addition of selection medium untransfected cells started to die and again three days later clones were becoming visible. A week later, the first clones were picked. Transfection with 1 μg resulted in less and also initially smaller clones (total ~20 clones/dish against >50 clones/dish for the transfection with 2 μg DNA). The positive control transfection using 2 μg pcDNA3 (Invitrogen) resulted in ~ 50 clones. In total, 120 clones were picked and 107 were succesfully established (55 frompIG35BS and 52 frompIG35BL). Generation ofpIG35Bneo pIG35Bneo is an Ad35-E1B expression plasmid from which the EIB genes are expressed from a heterologous promoter (hPGK) and that also contains a neomycin resistance expression cassette. To avoid instability of the plasmid due to recombination events on homologous sequences, the RSV promoter drives the neo r gene. To achieve this, construct pRSVhbv.Neo (described in Example 5, FIG. 12) was digested with Seal and BamHI and protruding ends were filled in using Klenow enzyme. The 1070 bp fragment containing part of the Ampicilin gene and the RSV promoter was isolated from gel using the geneclean kit (BIO 101, Inc.). Next, pRSVhbvNeo was digested with Seal and EcoRI, blunted with Klenow and the 3.2 kb fragment containing the neo gene, HBVpA, vector and part of the Ampicilin gene was isolated as above. The two fragments were then ligated to give pRSVneo4 (FIG. 23). Construct ρIG270 (FIG. 15, described in Example 6) was then digested with EcoRI and Ncol and sticky ends were blunted with Klenow enzyme. The vector-containing fragment was isolated from gel as described above and religated to give pIG270delEl A. This construct was digested with Avrll and Xbal and protruding ends were filled in using Klenow enzyme. The 2.9 kb fragment containing the hPGK promoter and Ad35.ElB sequences was isolated from gel as above. Next, pRSVneo4 was digested with Bglll, blunted with Klenow enzyme, dephosphorylated and isolated from gel. The blunted Avrll/Xbal Ad35.ElB fragment was then ligated with the above prepared pRSVneo4 vector fragment and resulting clones were analysed. One clone that contained both expression cassettes in the same orientation was choosen and named pIG35Bneo (FIG. 24). Detailed analysis of this clone revealed that an extra Bglll site was present probably due to an incomplete Klenow reaction (Bglll site at nucl 2949 in FIG. 24). Generation ofpIG35.55K Construct pIG35.55K is similar to pIG35Bneo, however, it lacks the coding region of Ad35.ElB-21K. Hereto, both the EIA and E1B-21K sequences are first deleted from pIG270 as follows: Construct pIG270 is digested with EcoRI, treated with Klenow enzyme and purified using a PCR purification kit (Qiagen) according to the manufacturer's instructions. The recovered DNA is then digested with Agel and the ~5 kb vector fragment was isolated from gel as above. Next, Ad35 E1B-55K sequences sre amplified by PCR on pIG270 template DNA using the following primers: 535D21: 5'- TTA GAT CCA TGG ATC CCG CAG ACT C-3' (SEQ. I.D. NO. _ and 635B3: 5'- CCT CAG CCC CAT TTC CAG-3' (SEQ. I.D. NO. _). The conditions used for the amplification are as previously described. The PCR fragment is purified using the PCR purification kit (Qiagen) and digested with Ncol. Following Klenow treatment to fill in the protruding ends, the DNA is further digested with Agel and again column purified. The thus treated PCR fragment is then cloned into the above prepared EcoRI/ Agel digested vector fragment to give pIG270.ΔE 1 AΔ21 K . The last steps to obtain pIG35.55K (FIG. 25) are equivalent to the last steps described above for the generation of pIG35Bneo starting with pIG270.ΔElAΔ2 IK instead of pIG270.ΔElA . pIG35.55K is then linearized with Seal and used to transfect PER.C6 cells as described above. Clones that are resistent to G418 selection are picked and analysed for their ability to complement the propagation of E 1 -deleted Ad35 viruses . Example 8 New packaging cell lines for the generation and propagation of El-deleted Ad35- based vectors derived from primary human cells. The complete morphological transformation of primary cells by adenovirus El genes is the result of the combined activities of the proteins encoded by the EIA and EIB regions. The roles of the different El proteins in lytic infection and in transformation have been studied extensively (reviewed in Zantema and van der Eb, 1995; White, 1995, 1996). The adenovirus EIA proteins are essential for transformation of primary cells. The EIA proteins exert this effect through direct interaction with a number of cellular proteins that are involved in regulation of transcription. These include the pRB family of proteins, p300/CBP and TATA binding protein. In addition to this EIA increases the level of p53 protein in the cells. In the absence of adenovirus EIB activity the rise in p53 levels leads to the induction of apoptosis. Both proteins encoded by the EIB region counteract the induction of apoptosis although by different mechanisms. E1B-21K seems to counteract apoptosis in a manner similar to Bcl-2 via interaction with the effector proteins downstream in the apoptosis pathway (Han et al, 1996), whereas E1B-55K functions through direct interaction with p53. Importantly, the molecular mechanism by which the E1B-55K proteins of Ad2 and 5 (subgroup C) and Adl2 (subgroup A) function in the ability to neutralise p53 may differ. Whereas Ad5 E1B-55K binds p53 strongly and the complex localises to the cytoplasm, Adl2 E1B-55K binds p53 weakly and both proteins are localised in the nucleus (Zantema et al, 1985; Grand et al, 1999). Both proteins, however, inhibit the transactivation of other genes by p53 (Yew and Berk, 1992). In rodent cells, the activity of El A together with either E1B-21K or 55K is sufficient for full transformation although expression of both EIB proteins together is twice as efficient (Rao et al, 1992; ). In human cells however, the activity of the E1B- 55K protein seems to be more important given the observation that E1B-55K is indispensible for the establishment of transformed cells (Gallimore, 1986). Example 6 hereof describes the generation of pIG270. hi this construct the Ad35-El genes are expressed from the hPGK promoter and transcription is terminated by the HBVpA. The hPGK promoter constitutes a HincII-EcoRI fragment of the promoter sequence described by Singer-Sam et al. (1984). The HBVpA is located in a BarnHI- Bglll fragment of the Hepatitis B virus genome (Simonsen and Levinson, 1983; see also Genbank HBV-AF090841). As mentioned before, the promoter and polyadenylation sequences of the El expression constructs described in this invention may be derived from other somces whithout departing from the invention. Also, other functional fragments of the hPGK and HBVpA sequences mentioned above may be used. The functionality of pIG270 was shown by transformation of primary Baby Rat Kidney cells (BRK). Comparison with an equivalent Ad5-El expression construct learned that Ad35-El genes were less efficient in fr-msforming these cells. The same has been found for the El genes of Adl2 (Bernards et al, 1982). It is unclear which El protein(s) determine(s) the difference in transformation efficiency of El sequences observed for adenoviruses from different subgroups. In the case of Adl2, transfection studies with chimeric E1A E1B genes suggested that the efficiency of transfoπnation of BRK cells was determined by the E 1 A proteins (Bernards et ah, 1982). The E1B-55K protein is shown infra to contain serotype-specific functions necessary for complementation of El-deleted adenoviruses. If these functions are related to the regulation of mRNA distribution or another late viral function, it is unlikely that these are involved in the transformation efficiency. Analysis of functional domains in the Ad2 or Ad5 E1B-55K proteins using insertion mutants have revealed that functions related to viral replication, late protein synthesis and host protein shut-off are not confined to specific domains but are distributed along the protein (Yew et al, 1990). Using the same set of mutants, the domains important for interaction with p53 and E4-Orf6 were found to be more restricted. In addition to one common binding region (amino acids 262 to 326), p53 binding was affected by mutations at aa 180 and E4-Orf6 binding was affected by mutations at aa 143 (Yew and Berk, 1992; Rubenwolf et ah, 1997). Altogether these results indicate that it is difficult to separate the E1B-55K functions related to transformation (p53 binding) and late protein synthesis (Orf6 binding). The invention discloses new El constructs that combine the high efficiency of transformation of one serotype with the serotype-specific complementation function of another serotype. These new constructs are used to transform primary human embryonic retinoblast cells and human amniocytes. Ebe generation ofpIG535, pIG635 andpIG735 Construct pIG535 contains the Ad5 Εl A region and Ε1B promoter sequences linked to the Ad35 Ε1B sequences. Hereto, pIG270 (FIG. 15; see example 6) was digested with ΕcoRI and Ncol. The 5.3 kb vector fragment was then isolated from gel using the geneclean kit (BIO Inc. 101) according to the instructions of the manufacturer. Next, construct pIG.Εl A.Ε1B (FIG. 13; see example 6) was digested with ΕcoRI and Xbal and the resulting 890 bp fragment was isolated as above. A third fragment was generated by PCR amplification on pIG.Εl A.Ε1B using the following primers: 15Ε1A-F: 5'- GAG ACG CCC GAC ATC ACC TG -3' (SEQ. I.D. NO. _) and 25E1B-R: 5'- CAA GCC TCC ATG GGG TCA GAT GTA AC -3' (SEQ. I.D. NO. __). 3The following PCR program was used: 94°C for 2' followed by 30 cycles of 94°C for 30", 60 °C for 30" and 72 °C for 1', and a final step at 72°C for 10' to ensme blunt ends. The resulting 400 bp PCR fragment was digested with Xbal and Ncol. After gel isolation as above, the three fragments were ligated and transformed into STBL-2 bacteria. One colony containing all three fragments in the correct order was selected and designated pIG535 (FIG. 26). Construct pIG635 contains the Ad5 EIA and a chimeric Ad5-Ad35 EIB region such that the 21K sequence is essentially from Ad5 and linked to the Ad35 E1B-55K sequences as far as not overlapping with the 21K sequences. First, part of the Ad5 El sequences are amplified by PCR using pIG.El A.E1B as template and the following primers: 45 AK: 5'- GAG CGA AGA AAC CCA TCT GAG -3' (SEQ. I.D. NO. _ and 52155R: 5'- GGT CCA GGC CGG CTC TCG G -3' (SEQ. I.D. NO. _). Amplification is accomplished with Pwo DNA polymerase (Roche) according to manufacturer's instructions. The 210 bp fragments is then pmified from the primer sequences using the PCR purification kit (Qiagen). A second PCR fragment is amplified from pIG270 DNA as described above but with the following primers: 62155F: 5'- CCG AGA GCC GGC CTG GAC -3' (SEQ. I.D. NO. _) and 735F10: 5'- GCT CTA GAC CTG CAG GTT AGT CAG TTT CTT CTC CAC TG -3' (SEQ. I.D. NO. _). The 1.3 kb amplified fragment is purified as above and mixed in a 1 : 1 molar ratio with the first PCR fragment. The mixture is then first subjected to a PCR reaction without the addition of primers using Pwo DNA polymerase and the following program: 94 °C for 2' and then 5 cycles of 94°C for 30", 60 °C for 30", 72 °C for 90". Subsequently, primers 5AK and 35F10 are added at 0.6 μM concentration after which a last PCR amplifies a 1.5 kb fragment. Hereto, temperature was set as follows: 94 °C for 2', then 30 cycles of 94 °C for 30", 60°C for 30" and 72 °C for 90", followed by a final step at 72°C for 10' to ensme blunt ends. The resulting product is purified using the PCR purification kit (Qiagen) as above and digested with Kpnl and Sbfl (isoschizomer of Sse8387I). The digested DNA is then isolated from gel using the geneclean kit (BIO Inc., 101). Construct pIG.ElA.ElB is digested with Kpnl and Sbfl and the vector- containing fragment is isolated from gel as above. This fragment is ligated to the above prepared final PCR product and the ligation mixture is transformed into STBL-2 cells (Gibco, LTI) according to manufactmer's instructions. This gives construct pIG635 (Fig. 27). In construct pIG735, the border between Ad5 derived sequences and Ad35 derived sequences is located more 3' than in construct pIG635. First, a BspEI site is introduced in the Ad5 sequence of construct pIG.ElA.ElB without changing the amino acid sequence. Hereto, Ad5 sequences from pIG.ElA.ElB are amplified using the following PCR primers: 5AK: see above, and Bsp-R: 5'- GCT CTA GAC CTG CAG GGT AGC AAC AAT TCC GGA TAT TTA CAA G -3' (SEQ. I.D. NO. _). Amplification is accomplished using Pwo DNA polymerase (Roche) according to the manufacturer's instruction. The following PCR program is used: 94°C for 2' followed by 30 cycles of 94°C for 30", 60 °C for 30" and 72 °C for 30", and a final step at 72°C for 10' to ensme blunt ends. The resulting 0.6 kb fragment is purified as above and digested with Kpnl and Sbfl and ligated to the above described Kpnl/Sbfl digested pIG.ElA.ElB vector fragment. Selection of colonies after transformation of STBL-2 bacteria (Life Techn. Inc.) gives construct pIG.ElΔ55K . pIG . E 1Δ55K is then digested with Sbfl and partially with BspEI. The 6.4 kb Sbfl-partial BspEI digested vector fragment is then isolated from gel using the geneclean kit (BIO 101, Inc.). Next, pIG270 is digested with BspEI and Sbfl and the resulting 915 bp fragment is isolated from gel as above. This fragment is then ligated to the above prepared Sbfl/partial BspEI digested pIG.ElΔ55K vector fragment and transformed into STBL-2 competent cells. This gives construct pIG735 (FIG. 28). Clones are analysed by restriction enzyme digestion and sequencing to ensure correct ligation of the fragments. Constructs pIG535, pIG635 and pIG735 can be used to generate complementing cell lines from primary human cells as described in Example 6. Example 9 PER.C6-based complementing cell lines for El -deleted Ad35 viruses. PER.C6 cells were seeded in 10 cm culture dishes at a density of 3xl0 6 cells/dish in DMEM (Gibco BRL) complemented with FBS (Gibco BRL) up to 10% and lOmM MgCl 2 (4.9 M stock solution, Sigma). Two days later, 9 dishes were transfected with 1 μg Seal linearised pIG35.55K DNA (see example 7) and 9 dishes were transfected with 1.5 μg Seal linearised pIG35.55K DNA. Separate control dishes were transfected with 1 or 1.5 μg Seal linearised pAdApt35.LacZ to monitor transfection efficiency and with 1 or 1.5 μg Seal linearised pcDNA.nlsLacZ. pcDNA.nlsLacZ is a pcDNA3-based plasmid (Invitrogen) with the nlsLacZ gene (Bonnerot et al., 1987) driven by the CMN promoter. pcDNA.nlsLacZ also contains a neo r expression cassette. As a negative control one extra dish was transfected with linearised pAdApt35.LacZ, a construct that lacks the neo r selection gene. All transfections were performed with the LipofectAmine transfection kit (Invitrogen/Life Technologies) according to manufacturers instructions using 5 ml LipofectAmine reagent/μg DNA. Cells were incubated for 4 hrs with the transfection mixture after which the medium was replaced with PER.C6 culture medium. The next day medium was replaced with culture medium containing 0.5 mg/ml G418 (Gibco BRL) except in the two dishes that were transfected with 1 or 1.5 μg pAdApt35.LacZ. These latter dishes were used to monitor LacZ expression two days following transfection. After X-gal staining of these cultures transfection efficiency was estimated at approximately 40% with slightly more blue cells in the dish transfected with 1.5 μg DNA. Selection medium was refreshed twice weekly in the remaining transfected dishes. Within two weeks following first addition of selection medium most cells in the negative control dish (transfected with 1.5 μg pAdApt35.LacZ) were dead. In the dishes transfected with pcDNA.nlsLacZ cell clones were becoming visible. Since the cells transfected with pIG35.55K seemed to be more resistent to G418, the concentration was raised to 0.75 mg/ml 3 weeks following transfection. Three days and seven days later a total of 196 cell clones were picked from the dishes transfected with pIG35.55K and seeded in separate wells of 96-well plates. Cells remaining after colony picking of two 10 cm dishes of the transfection with 1 μg pIG35.55K DNA were trypsinised, pooled and expanded to give pool PER55K(1.0) The same was done for two dishes of the 1.5 μg transfection. The PER55K(1.0) cell pool was expanded and seeded in 4 T25 flasks at a density of 3.5x10 6 cells/flask for transfection to test virus generation. In addition, 3 T25 flasks with parental PER.C6 cells were seeded at the same density. pAdApt35.eGFP (an adapter plasmid containing the green fluorescent protein as marker gene; see example 4) was digested with Pad to liberate the adenoviral sequences from the plasmid backbone. pWE.Ad35.pIX-rITR (see example 4) was digested with Notl to liberate the adenoviral sequences from the cosmid backbone. 2 flasks with PER.C6 cells and 2 flasks with PER55K(1.0) cells were transfected with 2 μg digested pAdApt35.eGFP and 6 μg digested pWE.Ad35.pIX-rITR each. One flask of each cell line was transfected with 8 μg pAdApt35.LacZ to monitor transfection efficiency. The remaining flask with PER55K(1.0) cells served as a negative control and was treated as the others but did not receive the transfection mixture. All transfections were performed with LipofectAmine (Invitrogen/Life Techn.) according to manufacturers instructions using for each transfection a total of 8 μg DNA and 40 μl LipofectAmine reagent. The transfection mixture was removed after 4 hrs incubation and fresh culture medium was added. Transfections were done the day after seeding of the cells and again two days later cells in the T25 flasks were transfeπed to a T80 flask except for the LacZ control transfections. These were stained with X-gal solution after mild fixation. After five ho s incubation with staining solution, the percentage of blue cells was estimated at approximately 90% in both flasks showing that transfection went well for both cell lines. Fom days following the passage to the T80 flasks the transfected PER55K(1.0) cultures showed starting CPE (cytopatho genie effect, indicative of virus replication) with approximately 100 events/flask. The untransfected PER55K(1.0) cells were grown confluent with no evidence of CPE. In the transfected PER.C6 cultures only three CPE events were visible in the confluent monolayer of cells. Again three days later, the transfected PER55K(1.0) cultures showed full CPE, with all cells rounded and detached in clumbs. In contrast, in the PER.C6 cultures the few events of CPE had not progressed and cells were still in monolayer. This confirms earlier observations that generation of El-deleted Ad35-based viruses on PER.C6 is very inefficient. Also the untransfected PER55K(1.0) cultures showed, as expected, a confluent monolayer with no CPE. The cells and medium in the PER55K(1.0) flasks with full CPE were harvested and subjected to two freeze/thaw cycles after which the cell debris was removed by centrifugation at 3000 rpm for 10 minutes in a table centrifuge. One of the resulting crude lysates was used to infect a fresh culture of PER55K(1.0) cells in a T175 flask (1.5 ml/flask). Cells and medium were harvested at full CPE fom days later. This shows that infectious virus had formed in the initial transfections. GFP expression was confirmed by fluorescent microscopy of A549 cells infected with the crude lysate. The crude lysate was then used to analyse complementation of this El-deleted Ad35.AdApt.eGFP virus in the individual clones as described below. The above described clones that were picked from the pIG35.55K transfected PER.C6 cells were expanded and were functionally tested for the ability to sustain replication of Ad35.AdApt.eGFP. Hereto, the clones were seeded at two densities in 6-well plates and one day later infected with 15 ml of the above described crude lysate. CPE was monitored the day after. Of the 146 clones tested in this way 19 gave full CPE at day 2 or 3 and 68 gave full CPE at day 5 or 6. The remaining clones had only partial CPE or showed a few non-progressing events. The latter were indistinguishable from PER.C6 cells that were taken along as a negative control. Based on these results a selection of 24 clones was made that were further screened for the ability to generate recombinant El -deleted viruses following transfection of the pAdApt35.GFP adapter plasmid and the large pWE.Ad35.pIX-rITR cosmid clone. Hereto, clones were plated in T25 flasks and transfected with 2 μg of the adapter and 6 μg of the backbone plasmid using LipofectAmine as described above. Two days following the transfection, cells were transfeπed to T80 flasks to prevent overconfluency of the cultmes. Of the 24 clones 5 gave full CPE three days after passage to T80 and another 13 clones gave progressing to full CPE the day after. The remaining 6 clones showed no CPE or only starting. In comparison: routine generation of El -deleted Ad5 vectors on PER.C6 cells generally results in full CPE fom to six days after transfer to T80 flasks. This shows that the new clones efficiently complement El -deleted adenovirus vectors. One of the clones (clone #16) described above was used to generate and produce multiple batches of El and E1/E3 deleted Ad35 viruses containing different transgenes. Hereto, virus in crude lysates resulting from transfections as described above, but using different adapter plasmids, were plaque purified on the new cell line. Single plaques were tested for transgene activity and then amplified for medium scale production in 4-8 triple layer flasks (3x175 cm/flask). Cells were harvested at full CPE and the virus was released and purified as routinely done for adenoviruses and described in example 1. The extraction step with freon to remove cellular debris was, however, replaced by a centrifugation step. Thus after incubation with Dnasel, the cell debris was centrifugated in conical 50 ml tubes (Greiner) at 8000 rpm in a table top centrifuge (Beckman Coulter AUegra 21R with fixed angle rotor) for 30 minutes at 4°C. This step is repeated in a fresh 50 ml tube untill the supernatant was clear (usually one time). The amount of virus particles was determined by HPLC (Shabram et al., 1997). Table IN presents the yields after downstream processing of medium scale productions of El- and El/E3-deleted Ad35 viruses on triple layer flasks with PER55K clone #16 cells. The amount of purified viras particles is comparable with the yields of Ad5-based vectors on PER.C6 cells. We conclude that we have generated multiple cell lines that efficiently complement fully El-deleted Ad35-based vectors. Thus, Ad35 E1B-55K expression in an Ad5 complementing cell line facilitates replication of Ad35 vectors. Example 10 New complementing cell lines from primary cells Example 8 described the generation of construct pIG535, a hybrid Ad5El A-Ad35 EIB expression plasmid. pCC536s and pIG536 are also hybrid Ad5-Ad35 El constructs but with the EIA region, EIB promoter and most of the E1B-19K gene derived from Ad5 and most of the E1B-55K gene derived from Ad35. Constructs pCC536s and pIG536 differ only in the heterologous poly adenylation sequence that terminates the EIB transcript: pIG536 has the HBN pA sequence and pCC536s has a synthetic pA sequence (SpA). The SpA sequence consists of the upstream sequence element (USE) of the human C2 complement gene (Moreira et al, 1995) and the synthetic pA sequence (SPA) described by Levitt et al., 1989. The synthetic polyA sequence is build up using the following oligo 's: C2SPA-1: 5'- CCC TGC AGG GAC TTG ACT CAT GCT TGT TTC ACT TTC ACA TGG AAT TTC CCA GTT ATG AAA TTA ATA AAG -3 ' C2SPA-2: 5'- GTC TAG ACA CAC AAA AAA CCA ACA CAC TAT TGC AAT GAA AAT AAA TTT CCT TTA TTA ATT TCA TAA CTG -3 ' Oligonucleotides were mixed at lOμM concentration in lx annealing buffer (lOmM Tris HCl pH 7.5, lOOmM NaCl, ImM EDTA) and, using a PCR machine, the solution was heated to 94°C for 5 minutes and then cooled down to 65°C at 0.5°C / second and after incubation at 65 °C for 5 minutes further cooled down to 20°C at 0.05 °C / second. Subsequently, 10 μl 2mM dNTPs, 0.5 μl 1M MgC12 and 3 μl Klenow fragment (New England Biolabs) was added to 87 μl of the annealed sample and the mixture was incubated at room temperature for 30 minutes. 1 μl of the annealed and Klenow treated sample was then amplified using the following primers: C2for: 5'- CGG GAT CCC CTG CAG GGA CTT GAC -3' and SPArev: 5'- TTG CGA CTT AAG TCT AGA CAC ACA AAA AAC C -3' using Pwo DNA polymerase (Roche) according to manufacturers instructions but with addition of DMSO (Sigma) to a final concentration of 3%. The PCR program was set at 94°C for 2 minutes, followed by 30 cycles of (94 °C for 30", 55°C for 30" and 72°C for 20"). Where in this document PCR programs are described ' means time in minutes and ' ' means time in seconds. The amplified DNA was then purified using the QIAquick PCR purification kit (Qiagen) and digested with Xbal and Sbfl. The digested product was then again purified with the PCR purification kit to remove the small digested ends. Construct pIG270 was also digested with Xbal and Sbfl (isoschizomer of Sse8387I) and the resulting 5.9 kb vector containing fragment was isolated from gel using the GeneClean II kit (Biol 01, Lie). The treated vector and PCR insert were then ligated to give pCC271 (Fig e 29). pCC271 thus contains the PGK promoter, the Ad35 El region (nucl. 468 to and including 3400 from Ad35 sequence in example 3 and figme 5) and the synthetic pA (SpA). The synthetic pA sequence was then also cloned into the construct pIG535 as follows. pIG535 was digested with EcoRI, Pstl and Seal (All enzymes from New England Biolabs digested in NEB buffer 3) and the 3 kb insert coπesponding to chimeric Ad5-Ad35 El region was purified using the GeneClean II kit (Bio 101, Inc.). Construct pCC271 was digested with EcoRI and Pstl and the 3 kb vector fragment containing the SpA and PGK promoter was isolated as above. Both isolated fragments were ligated and transformed into STBL-2 competent cells (Invitrogen/LifeTechnologies) to give pCC535s (Figme 30). pCC535s contains the same Ad5-Ad35 El sequences as pIG535 however, a different pA sequence. For the construction of pCC536s, a subclone was made with the new hybrid EIB sequences. Hereto, Ad5 E1A/E1B21K sequences were amplified using the primers 5AK: 5'- GAG CGA AGA AAC CCA TCT GAG- 3' and 2155R: 5'- GGT CCA GGC CGG CTC TCG G-3' with pIG.ElA.ElB (see example 6 and Figme 13) as template DNA using Pwo DNA polymerase (Roche) according to manufactmers instructions and in addition a final concentration of 3% DMSO. The program was set at: 94°C for 2' followed by 30 cycles of (94°C for 30", 58°C for 30" and 72°C for 30") and ended with 68°C for 8'. This resulted in a 210 bp fragment coπesponding to nucl. 2022-2233 of the Ad5 sequence. A second PCR was performed on pCC271 with primers 2155F: 5'- CCG AGA GCC GGC CTG GAC C-3' and 35F10: 5'- GCT CTA GAC CTG CAG GTT AGT CAG TTT CTT CTC CAC TG-3'. The same PCR program was used but now with an elongation time of 90" . The resulting 1.3 kb fragment coπesponds to nucl. 2112 to 3400 of the Ad35 sequence with an Sbfl site at the 3'end. Note that primers 2155F and 2155R are fully complementary allowing assembly of the two fragments as follows: Both PCR fragments were purified from gel using the Qiagen gel extraction kit. Aliquots of the purified samples were then mixed in equimolar ratio and used as template for an assembly PCR amplification with primers 5AK and 35F10 with Pwo DNA polymerase as above using the program settings: 94°C for 2', and 5 cycles of (94°C for 30", 60°C for 30" and 72°C for 2') followed by 25 cycles of (94°C for 30", 58°C for 30" and 72 °C for 90"). The resulting 1.5 kb fragment was purified from gel using the QIAquick gel extraction kit (Qiagen), ligated to the pCR-Script/Amp cloning vector (Stratagene) and transformed into DH5a competent cells (Invitrogen/Life Technologies) resulting in pCR535ElB (Figme 31). This construct was checked by restriction analysis and sequencing to confirm coπect amplification of target sequences. pCR535ElB was then digested with Notl and protruding ends were made blunt with Klenow fragment. The DNA was then pmified using the QIAquick PCR purification kit (Qiagen) and eluted DNA was digested with Pstl. The 1.5 kb fragment containing the chimeric El sequences from the pCR535ElB vector was pmified from gel using the GeneClean II kit (BiolOl, Inc.). This fragment was ligated to vector pCC535s digested with PvuII and Pstl, and transformed into STBL-2 competent cells (Invitrogen/Life Technologies) to give pCC2155s (Figure 32). To complete the pCC536s construct Ad5- El sequences were then cloned into the pCC2155s subclone. Hereto, pIG.ElA.ElB was digested with EcoRI and Kpnl and the 1.6 kb fragment corresponding to Ad5 EIA and Ad5 EIB 21K (nucl. 459 to 2048 of the Ad5 sequence) was isolated from gel using the GeneClean kit. pCC2155s was digested with EcoRI and Kpnl and the vector containing fragment was also gel purified. Ligation of both isolated fragments and transformation into DH10B electrocompetent cells (Invitrogen/Life Technologies) resulted in pCC536s (Figme 33). The hybrid EIB sequences are shown in Figure 38 in more detail. FIG38A shows an alignment of protein sequences of E1B-21K in the pCC536s construct with wild type (wt) Ad35 and Ad5 sequences. As can be seen most of the E1B-2 IK protein in pCC536s is derived from Ad5 except for the C-terminal 6 amino acids that are identical to Ad35 E1B-21K. Figme 38B shows the same alignment for the E1B-55K proteins. In this case the N-terminal amino acids of pCC536s are identical to Ad5 upto aa 65. The remainder is identical to Ad35 E1B-55K. Obviously, different hybrid E1B-55K constructs can be designed using the general method oulined above whithout departing from the invention. Construct pIG536 was made by replacing a fragment with the SpA in pCC536s with the coπesponding fragment from pIG270 (example 6, Figme 15) containing the HBNpA. Hereto, pIG270 was digested with BamHI and Bgll and the 1.8 kb insert was isolated from gel using the GeneClean II kit (Bio 101, Inc.). pCC536s was digested with the same enzymes and the 4.8 kb vector containing fragment was purified from gel as above. Ligation of both isolated fragments and transformation into STBL-2 competent cells (Invitrogen/Life Technologies) gave construct pIG536 (Figme 34). The generated El constructs were tested in primary baby rat kidney (BRK) cells as described in example 6. The results (Table V) confirm earlier observations that Ad5-El genes more efficiently transform primary BRK cells than Ad35 El genes. The chimeric Ad5-Ad35 El expression constructs, pCC535s and pCC536s, produced more transformed colonies than the full Ad35 El constructs, pIG270 and pCC271. Furthermore, the use of a synthetic poly adenylation sequence in pCC535s resulted in slightly more foci compared to the HBVpA variant pIG535. Human embryonic retinoblast (HER) cells were isolated from the eyes of aborted fetuses of 18 and 21 weeks of age. The eyes were brought in a 6 cm dish with PBS and cleared from outside tissue. An incision was made to reach the inner side and the gray cell layer at the inner back of the eyes containing the retinoblasts, was scraped off. This layer was transfeπed to a 14 ml tube in 2ml of PBS and tissue was allowed to sediment after which the PBS was removed. 2 ml trypsin (0.25%, no EDTA, GibcoBRL) was added and incubated for 5 minutes at 37°C with occasional swirling. Tissue pieces were allowed to sediment and 1 ml trypsin with cells was transfeπed to a new tube. To this tube 4 ml culture medium (DMEM with 10% FCS) was added and the tube was stored on ice. The remaining tissue pieces in trypsin were brought in a 6 cm dish and cut into smaller pieces. These were, after addition of 2 ml fresh trypsin, again incubated in a 14 ml tube at 37°C with occasionally swirling. Then this mixture was added to the first isolated cells in culture medium and the total was centrifugated at 1000 rpm in a table top centrifuge. Supernatant was removed and cells were resuspended in 10 ml of culture medium. The isolated HER cells were plated in two 6 cm dishes and incubated at 37°C/ 10% CO2. Upon 90% confluency cultmes were split 1 :3 and further incubated. This procedure was repeated until enough dishes were obtained to be used for transfection and further culturing. Transfections were performed at different passage numbers using the CaPO cotransfection kit (Invitrogen/Life Technologies) according to manufactmers instructions. For each dish (50-70% confluency) 20 μg DNA was used. Initial transfections were performed with pIG.ElA.ElB, an Ad5-El expression construct, and with pIG535, the hybrid Ad5-E1A Ad35-E1B expression construct. 2-3 weeks following transfection transformed foci became visible in the pIG.ElA.ElB transfected dishes. On average 15- 20 foci/dish were found in the dishes that were transfected with pIG.ElA.ElB. Over 30 clones were picked and transfeπed to 96-well plates. Upon confluency cells were passaged to larger culture plates or flasks and finally viable frozen in ampoules in liqN 2 from a T175 flask. All picked clones were established in this way. Transformed foci appeared much later in the dishes that were transfected with pIG535, the first around five weeks following transfection. On average 3-4 clones were found per dish. A total of 46 clones were picked from 7 weeks to 3 months after transfections of which 14 were viable and could be passaged multiple times. Of these, 2 clones (clone #45 and #75) were grown up to a T175 flask and viable frozen in ampoules in liqN 2 . Primary HER cells were also transfected with constructs pCC535s andpCC536s. Transfection of pCC535s let to an average of 2 clones/dish and a total of 50 clones were picked. Of these picked clones 2 could be established. From the transfection with pCC536s, at least one clone could be established. The above described experiments show that primary HER cells can be transformed with hybrid Ad5-Ad35 El sequences. The efficiency of transformation was lower than obtained with the complete Ad5 El region. We then tested whether the new cell lines could complement recombinant Ad35-based El-deleted vectors. Hereto, the clone #45 that was obtained from the pIG535 transfection was seeded in T25 flasks at a density of 7x10 6 cells/flask and infected with Ad35.AdApt.eGFP virus (see example 9) at a multiplicity of infection (moi) of 5 and 25 viras particles/cell. Full CPE was seen at days 4 and 5 for the moi 25 and 5 respectively. As a comparison parallel cultures of clone #45 cells that were infected with Ad5.AdApt.eGFP viruses gave full CPE at days 7 and 8 for moi 25 and 5 respectively. The initial infection efficiency was comparable for Ad5 and Ad35 viruses, -80% (moi^S) and -95% (moi=25) of the cells were infected with GFP virus one day following infection as measured by fluorescence microscopy. Cells from clone #75 were seeded in a 6-well plate at a density of 2x10 6 cells/well and infected with Ad35.AdApt.eGFP or Ad5.AdApt.eGFP at moi 5 (VP/cell). Again initial infection efficiency was comparable for both viruses. Full CPE was observed at day 4 in case of Ad35.AdApt.eGFP infection whereas Ad5.AdApt.eGFP infected clone #75 cells gave full CPE on day 7. The difference in replication efficiency on Ad35 complementing cells between Ad35 and Ad5 recombinant vectors is even more clear when virus is generated by plasmid transfection. This is exemplified by the following transfection experiment. Clone #45 cells were seeded in T25 flasks at a density of 3.5x10 6 cells and transfected three days later using LipofectAmine reagent (Invitrogen Life Technologies) according to manufacturers instructions and described above. 2 μg pAdApt35.eGFP adapter plasmid digested with Pad was cotransfected with 6 μg pWE.Ad35.pIX-rITR or pWE.Ad35.pIX- rITRΔE3 backbone cosmid digested with Notl. 2 μg pAdApt.eGFP (Ad5 adapter plasmid, described in WO 00/70071) digested with Pad was cotransfected with 6 μg pWE.Ad5.AflII-rITRsp (Ad5 backbone plasmid, described in WO 00/70071) also digested with Pad. One T25 was not transfected and served as a negative control. One day later transfection efficiencies were monitored by fluorescent microscopy and estimated at 10-15% in all eGFP transfections. Three days following transfection cells were transfeπed to T80 flasks and further incubated at 37°C/10%CO 2 . Again three days later CPE events were becoming visible in the cultures transfected with the pAdApt35.eGFP and the pWE.Ad35pIX-rITR+ or - E3. The transfections with the E3- deleted backbone contained more green fluorescent cells and more CPE events. The transfection with Ad5 plasmids showed only around 20% green fluorescent cells, of which most were dying, and no CPE events. Two days later this difference had become bigger since cultures transfected with the pAdApt35.eGFP and the ρWE.Ad35pIX- rITRΔE3 clearly showed 80% CPE and cultmes transfected with the pAdApt35.eGFP and the pWE.Ad35pIX-rITR constructs showed progressing CPE events. The Ad5 transfected culture did not show any progression. Table VI summarizes these results. We conclude that the new complementing cell lines described above efficiently sustain replication of El deleted Ad35-based viruses and that the generation and replication of El deleted Ad5-based viruses is less efficient. Apparently, also Ad35-E1B55K proteins do not form a functional complex with Ad5-E4Orf6 proteins. Thus the serotype specificity for complementation is now also shown for recombinant Ad5 vectors on Ad35 packaging cells. Example 11 Generation of pWE.Ad.pIX-rITRΔE3 The early region-3 of human adenoviruses contains multiple coding regions for proteins that interfere with the host immune response to adenoviral infection. When adenoviral vectors are used as vaccine carrier such interference is unwanted. Therefore, we constructed an Ad35 backbone cosmid lacking the E3 region. Hereto, construct pBr.Ad35.PRn (Figure 35; described in example 13 in publication EP 1 054 064 Al) was digested with Stul and Mlul and the 17.3 kb vector fragment was purified from low melting point (LMP) gel using agarase enzyme (Roche) according to manufactmers instructions. Next, a PCR fragment was generated on pBr.Ad35.PRn using primers: 35E3for: 5'- AAT GAC TAA TGC AGG TGC GC-3' and 35E3rev: 5'- CGA CGC GTT GTA GTC GTT GAG CTT CTA G-3'. For the amplification Pwo DNA polymerase (Roche) was used according to manufactmers instructions and program set at: 94°C for 2', 30 cycles of (94°C for 30", 58°C for 30"'and 72°C for 1') and a final incubation at 68°C for 8'. The 833 bp PCR product was purified using the QIAquick PCR purification kit (Qiagen) and digested with Mlul and Stul. The digested DNA was purified from gel using the QIAquick gel extraction kit (Qiagen). Both isolated fragments were ligated and transformed into DH5a competent cells (Invitrogen/Life Technologies) to give pBr.Ad35.PRnΔE3 (Figme 36). The plasmid was checked by restriction analysis and sequencing of the PCR amplified insert. The E3 deletion was then cloned into the pWE.Ad35.pFX-rιTR cosmid backbone. Hereto, pWE.Ad35.pIX-rITR (see example 4 and Figme 8) was digested with Pad and the DNA was purified by precipitation with isopropanol and washing with 70% EtOH. Following resuspension in milliQ water, the DNA was digested with Swal and the 22.8 kb vector containing fragment was purified from LMP gel using agarase enzyme as above. Construct pBr.Ad35.PRnΔE3 was digested with Pad and Swal in the same manner and the 16.6 kb fragment was also isolated using agarase enzyme. Both isolated fragments were ligated using 0.5-0.6 μg of each fragment. Ligated fragments were then packaged using λ-phage packaging extracts (Stratagene) according to manufacturers instructions and mixed with STBL-2 cells. Bacteria were plated on LB+Amp plates and resulting colonies were analyzed for the presence of the coπect construct. This gave construct pWE.Ad35.pIX-rITRΔE3 (Figme 37). The E3 deletion extends from nucl. 27648 to 30320 of the Ad35 sequence (example 3) and thus spans a 2.6 kb region. Cotransfection of Notl digested pWE.Ad35.pIX-rITRΔE3 and IPsρ-1 digested pAdApt35.eGFP onto PER55-clone #16 cells (see example 9) as described above gave rise to GFP expressing Ad35-based viruses. Upon isolation of viral DNA from these viruses, PCR amplification of the E3 region showed that the viruses were deleted for 2.6 kb of E3 sequences as expected. Table I: Continued on next page. Legend to Table I: All human adenoviruses used in the neutralization experiments were produced on PER.C6 cells (Fallaux et ah, 1998) and purified on CsCl as described in example 1. The NaCl concentration at which the different serotypes eluted from the HPLC column is shown. Virus particles/ml (VP/ml) were calculated from an Ad5 standard. The titer in the experiment (CCID50) was determined on PER.C6 cells as described in Example 1 by tifrations performed in parallel with the neutralization experiment. The CCID50 is shown for the 44 virases used in this study and reflects the dilution of the virus needed to obtain CPE in 50% of the wells after 5 days. The ratio of VP/CCID50 is depicted in logio and is a measmement of the infectivity of the different batches on PER.C6 cells . Table II. AdApt35.LacZ viruses escape neutralization by human seram. Table III: The numbers of foci obtained with the different El expression constructs in BRK transformation experiments. Average # of foci/dish: Table TV: Yields of El- and E1/E3- deleted Ad35 viruses on clone #16 cells produced on triple layer flasks. Virus Scale(T175III flasks) Total # of Virus Particles after DSP VP/cell Ad35.AdApt.eGFP 4 7.5x10' ' 2500 Ad35.ΔE3.AdApt.empty 8 2xl0 12 3300 Ad35.ΔE3.AdApt.LacZ 8 3.8xl0 n 600 Ad35.ΔE3.AdApt.MV-F 4 8.8xl0 n 2900 Ad35.ΔE3.AdApt.MV-H 8 2.6xl0 12 4250 Table V: Transformation efficiencies on BRK cells with different Ad-El expression constructs. Construct Transfected DNA (μg) # foci per dish Experiment 1 pIG.ElA.ElB 5 44 pIG270 5 0 pCC271 5 0 pIG535 5 1 pCC535s 5 2.5 Experiment 2 pIG.ElA.ElB 4 15 pCC271 4 0 pCC535s 4 3 ρCC536s 4 3 Table VI: Generation of recombinant Ad35 viruses on the new established complementing cell line clone #45. GFP Expression X Transfected constructs Dayl Day3 Day 6 Day 8 pAdApt35.eGFP + pWE.Ad35.pIX-rITR 15% 20% 30% 50% pAdApt35.eGFP + pWE.Ad35.pIX-rITRΔE3 10% 25% 40-50% 100% pAdApt5.eGFP+ pWE.Ad5.AflII-rITR 15% 25% 20% 20% untransfected 0% 0% 0% 0% CPE events X Transfected constructs Dayl Day3 Day 6 Day 8 pAdApt35.eGFP +pWE.Ad35.pLX-rITR 0 0 1 several pAdApt35.eGFP + pWE.Ad35.pIX- rITRΔE3 0 0 several 80% pAdApt5.eGFP+ pWE.Ad5.AflII-rITR 0 0 0 0 untransfected 0 0 0 0 References: Abrahamsen, K., Kong, H-L., Mastrangeli, A., Brough, D., Lizonova, A., Crystal, R.G. and Falck-Pedersen, E. (1997). Construction of an adenooviras type 7a EIA " vector. J. Virol. 71, 11, p8946-8951. 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The 2.2 kb mRNA of the EIB region of human adenovirus type 12 and 5 directs the synthesis of two major tumor antigens from different AUG triplets. Cell 12, p721-732. Bridge, E. and Ketner, G. (1990). Interaction of adenoviral E4 and Elb products in late gene expression. Virology 174, p345-353. Bridge, E., Medghalchi, S., Ubol, S., Leesong, M. and Ketner, G. (1993). Adenovirus early region 4 and viral DNA synthesis. Virology 193, p794-801. Brough, D.E., Lizonova, A., Hsu, C, Kulesa, V.A. and Kovesdi, I. (1996). A gene transfer vector-cell line system for complete functional complementation of of adenovirus early regions 1 and 4. J. Virol. 70, p6497-6501. Fallaux, F.J., Kranenburg, O., Cramer, S.J., Houweling, A., van Ormondt, H., Hoeben, R.C. and van der Eb, A.J. (1996). Characterization of 911: a new helper cell line for the titration and propagation of early region 1-deleted adenoviral vectors. Hum. Gene Ther. 7 (2), p215-222. 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Definition of a major p53 binding site on Ad2ElB58K protein and a possible nuclear localization signal on the Adl2ElB54K protein. Oncogene 18, p955- 965. Han, J., Sabbatini, P., Perez, D., Rao, L., Modha, D. and White, E. (1996). The EIB 19K protein blocks apoptosis by interacting with and inhibiting the p53-inducible and death-promoting Bax protein. Genes Dev. 10 (4), p461-477. Jochemsen, A.G., Peltenburg L.T., te Pas, M.F., de Wit, CM., Bos, J.L. and van der Eb, A.J. (1987). Activation of adenovirus 5 EIA transcription by region EIB in transformed primary rat cells. EMBO J. 6 (11), p3399-3405. Moreira, A., Wollerton, M., Monks, J. and Proudfoot, NJ. (1995). Upstream sequence elements enhance poly(A) site efficiency of the C2 complement gene and are phylogenetically conserved. EMBO J., 14 (15), ρ3809-3819. Leppard, K.N. and Shenk, T. (1989). The adenovirus EIB 55kd protein influences mRNA franport via an intranuclear effect on RNA metabolism. EMBO J. 8, p2329-2336. 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Claims: Claims What is claimed is: 1. A packaging cell line capable of complementing recombinant adenovirus based on a serotype from subgroup B. 2. The packaging cell line of claim 1 wherein said serotype from subgroup B is adenoviras type 35. 3. The packaging cell line of claim 1 or 2, wherein said packaging cell line is derived from primary, diploid human cells, or derivatives thereof, said primary, diploid human cells or derivatives thereof having been transformed by adenovirus El coding sequences either operatively linked on one DNA molecule or located on two separate DNA molecules, said adenovirus El coding sequences being operatively linked to regulatory sequences enabling transcription and translation of encoded proteins. 4. The packaging cell line of claim 3 wherein the primary, diploid human cells, or derivatives thereof have been selected from the group consisting of primary human retinoblasts, primary human embryonic kidney cells and primary human amniocytes. 5. The packaging cell line of claim 3 or 4, wherein the primary, diploid human cells, or derivatives thereof have been transfected with an adenovirus EIA coding sequence to induce unlimited proliferation. 6. The packaging cell line of claim 5 wherein said packaging cell line further comprises an EIB coding sequence. 7. The packaging cell line of claim 3 or 4, wherein the primary, diploid human cells, or derivatives thereof have been transformed by expression of adenovirus El proteins of a subgroup other than subgroup C. 8. The packaging cell line of claim 7 wherein the subgroup other than subgroup C is subgroup B. 9. The packaging cell line of claim 8, wherein said adenovirus El proteins are derived from adenovirus type 35. 10. The packaging cell line of claim 3 or 4, wherein the primary, diploid human cells or derivatives thereof have been transformed with a chimeric adenovirus El construct comprising part of a first adenoviras El coding sequence of a first adenovirus serotype that enables efficient transformation of primary human cells or derivatives thereof; and part of a second adenovirus El coding sequence of a second adenovirus serotype, wherein said second adenovirus El coding sequence provides the serotype- specific adenoviras EIB function(s) that enable(s) efficient propagation of recombinant adenovirus El -deleted viruses of said second adenovirus serotype. 11. The packaging cell line of claim 10 wherein said first adenovirus serotype is a subgroup C adenovirus and said second adenovirus serotype is a subgroup B adenovirus, more particular adenoviras type 35. 12. The packaging cell line of claim 10 wherein EIA coding sequence and at least part of the E1B-21K coding sequence are derived from a subgroup C adenoviras, and the E1B-55K coding sequence as far as not overlapping with the 21 K coding sequence is derived from a subgroup B adenovirus. 13. The packaging cell line of claim 12 wherein said subgroup B adenoviras is adenovirus type 35. 14. The packaging cell line of claim 10 wherein all El coding sequences are derived from a subgroup C adenoviras, except for at least a part of the E1B-55K coding sequence that is necessary for serotype-specific complementation of an alternative adenovirus serotype, said EIB coding sequence being derived from said alternative adenovirus serotype. 15. The packaging cell line of any one of claims 6, 10 or 14, wherein said packaging cell line comprises bovine adenovirus E1B-55K. 16. The packaging cell line of claim 15, wherein said complementing recombinant adenoviras is derived from a bovine adenovirus. 17. The packaging cell line of claim 3 or 4, wherein the primary diploid human cells or derivatives thereof have been transformed by adenoviras El coding sequences located on two separate DNA molecules wherein the first DNA molecule carries at least part of the El coding sequences of the serotype enabling efficient transformation and the second DNA molecule caπies at least part of the sequences necessary for serotype-specific complementation. 18. The packaging cell line of claim 4 wherein said derivative cells are PER. C6 (ECACC deposit number 96022940) which further comprise an Ad35-El region integrated into their genome, and wherein said Ad35-El region is present in a functional expression cassette. 19. The packaging cell line of claim 18 wherein said Ad35-El region does not contain sequences overlapping with sequences present in an associated recombinant viral vector. 20. The packaging cell line of claim 18 or 19, wherein said functional expression cassette comprises a heterologous promoter and a poly-adenylation signal functionally linked to said Ad35-El region, wherein said heterologous promoter is a human phosphoglycerate gene promoter (hPGK) and wherein said poly-adenylation signal is a hepatitis B virus poly-adenylation signal (HBV-pA). 21. The packaging cell line of claim 20 wherein said Ad35-El region comprises the coding regions of the EIA proteins and the EIB promoter sequence linked to EIB coding sequences up to and including the stop codon of the EIB 55K protein. 22. The packaging cell line of claim 20 wherein said Ad35-El region comprises nucleotide 468 to and including nucleotide 3400 of the Ad35 wild-type sequence. 23. A cell line derived from PER.C6 (ECACC deposit number 96022940), which cell line comprises Ad35-E1B coding sequences. 24. The cell line of claim 23 wherein said Ad35-E1B coding sequences are driven by an EIB promoter and terminated by a heterologous poly-adenylation signal. 25. The cell line of claim 23, wherein said Ad35-E1B coding sequences are driven by a heterologous promoter. 26. The cell line of claim 25 wherein said Ad35-E1B coding sequences are driven by a hPGK promoter or an Elongation Factor- lα (EF-lα) promoter and terminated by a heterologous poly-adenylation signal. 27. The cell line of claim 24 or 26, wherein said heterologous poly- adenylation signal is a hepatitis B viras poly-adenylation signal (HBV-pA). 28. The cell line according to any one of claims 23-27, wherein said Ad35- E1B coding sequences comprise the coding sequences of the EIB 21K and the EIB 55K proteins located between nucleotides 1611 and 3400 of the wild-type Ad35 sequence. 29. The cell line of claim 28 wherein said Ad35-E1B coding sequences comprise nucleotides 1550 to and including nucleotide 3400 of the wild-type Ad35 sequence. 30. The cell line of claim 28 wherein said Ad35-E 1 B coding sequences comprise the coding sequences of the E1B-55K gene located between nucleotides 1916 and 3400 of the wild-type Ad35 sequence. 31. The cell line according to any one of claims 23-27, wherein said Ad35- E1B coding sequences comprise the coding sequences of the E1B-55K gene located between nucleotides 1916 and 3400 of the wild-type Ad35 sequence. 32. The cell line of claim 31, lacking a functional coding sequence for E1B- 21K. 33. The packaging cell line according to any one of claims 1-22, or a cell line according to any one of claims 23-32, further comprising a DNA encoding at least E4- orf6 of an adenoviras of subgroup B, preferably adenovirus serotype 35. 34. A method for complementing a recombinant adenovirus comprising providing a packaging cell line according to any one of claims 1-22, or a cell line according to any one of claims 23-33, with said recombinant adenovirus and culturing said cell to allow for complementation. 35. A method according to claim 34, further comprising harvesting complemented recombinant adenovirus. 36. A method according to claim 34, or claim 35, wherein said recombinant adenovirus is derived from [adenovirus] a subgroup B adenovirus. 37. A method according to claim 36, wherein said recombinant adenovirus is derived from adenovirus type 35. 38. A recombinant adenovirus obtained by a method according to any one of claims 34-37. 39. A recombinant adenovirus according to claim 38, comprising a deletion of nucleic acid encoding at least one El -region protein. 40. A recombinant adenovirus according to claim 38 or claim 39 comprising a deletion of nucleic acid encoding at least one E3 -region protein and/or at least one E4- region protein. 41. Use of a recombinant adenovirus according to any one of claims 38-40, for the preparation of a medicament. 42. Use of a packaging cell line according to any one of claims 1 -22, or a cell line according to any one of claims 23-33, for the complementation of a recombinant adenovirus.

Inventors: HAVENGA MENZO JANS EMCO, MEHTALI MAJID, VOGELS RONALD, HAVENGA, MENZO, JANS, EMCO, MEHTALI, MAJID, VOGELS, RONALD
Applicants: CRUCELL HOLLAND BV, HAVENGA MENZO JANS EMCO, MEHTALI MAJID, VOGELS RONALD, CRUCELL HOLLAND B.V., HAVENGA, MENZO, JANS, EMCO, MEHTALI, MAJID, VOGELS, RONALD
Application year: 2001
Main classification: C12N15
IPC codes: C12N5, C12N7, C12N15