CELL LINES AND CONSTRUCTS USEFUL IN PRODUCTION OF E1-DELETED ADENOVIRUSES IN ABSENCE OF REPLICATION COMPETENT ADENOVIRUS

Abstract: Cell lines useful for trans-complementing E1-deleted adenoviral vectors are described. The cell lines are capable of providing high yields of E1-deleted adenoviral vectors in the absence of replication-competent adenovirus over multiple passages.

Description: CELL LINES AND CONSTRUCTS USEFUL IN PRODUCTION OF El-DELETED ADENOVIRUSES IN ABSENCE OF REPLICATION COMPETENT ADENOVIRUS This work was supported by NIDDK (DK47757-06 & DK49136-05), NHLBI (HL49040-08) and NICHD (HD32649-05) of the National Institutes of Health The US government may have certain rights in this invention Field of the Invention This invention relates generally to the field of constructs and methods for producing viral vectors, and more particularly, for the production of adenoviruses Background of the Invention Recombinant adenoviruses have been described as useful for delivery of transgenes to cells for a variety of purposes, including both therapeutic and prophylactic (vaccine) uses However, successful commercialization of El -deleted adenoviruses will require suitable manufacturing processes, which have yet to be developed Infection of an E 1 trans-complementing cell line with the vector and purification of the resulting lysate is a simple and scalable process that yields sufficient quantities of product Unfortunately, production of El -deleted adenovirus vectors for gene therapy has been plagued by emergence of replication competent adenovirus (RCA) caused by homologous recombination between the vector and transfected El gene Several strategies have been described to avoid RCA However, to date none of these approaches has resulted in an El -complementing cell line which is stable and produces high yields of El -defective adenoviruses in the absence of detectable RCA J -L Imler et al , Gene Ther., 3 75-84 (1996) describes an A549 cell stably transfected with El a and Elb open reading frames (ORFs) and contiguous pIX gene The El a was driven by phosphoglycerate kinase promoter and RCA was reportedly eliminated However, more recent publications describing this system reveal that Imler was unable to detect Elb protein expression See, Introgene, WO 97/00326, published January 3, 1997 This Introgene application described an alternative system to that of Imler, cited above. This application describes cell lines derived from certain human diploid cells with Ela and Elb expressed, but no pIX (ECACC NO. 96022940). The cells were produced by transfection of human embryonic retinoblast (HER) cells with a vector containing nt 459 - 3510 of Ad, which corresponds to Ela, Elb, but excludes the Ela promoter, a portion of the Elb gene encoding the Elb 8.3 kb protein, and any pIX sequences. Another system for avoiding RCA is described in Massie, US 5,891,690. The patent describes an Ad El -complementing cell line having a stably integrated complementation element comprising a portion of the Ad El region covering the Ela gene and the Elb gene, but lacking the 5' ITR, the packaging sequence, and the Ela promoter. Further, the Ela gene is under control of a first promoter element and the E2b gene is under control of a second promoter. A specific cell line described and claimed by Massie contains nt 532 - 3525 of Ad5, which includes Ela, the Elb promoter, and a portion of the Elb gene. This cell line does not contain the carboxy terminus of the Elb gene, which encodes the 8.3 kb product, nor does it contain pIX gene sequences. What is needed in the art is a stable El -complementing cell line, which expresses all adenoviral Ela and Elb gene products, and which produces high yields of El -defective adenoviruses in the absence of detectable RCA. Summary of the Invention Advantageously, the present invention provides El expressing cell lines that are stable, can be adapted to suspension culture in serum free medium, and yields high quantity of vector. Significantly, the cell lines allow isolation and subculture of El- deleted recombinant adenoviruses in an environment free of replication competent adenovirus (RCA). Further, the cell lines of the invention effectively plaque vector to allow isolation and subculture of new recombinants in an environment free of RCA. Thus, in one aspect, the invention provides an El -complementing cell line useful for production of recombinant El -defective adenoviruses in the absence of detectable replication-competent adenovirus. The El -complementing cell line contains an aneuploid cell line stably transformed with a nucleic acid molecule comprising nucleic acid sequences encoding adenovirus Ela and adenovirus Elb under the control of a phosphoglycerate kinase (PGK) promoter. Suitably, the nucleic acid molecule lacks adenovirus sequences 5' to the sequences encoding adenovirus Ela. In another aspect, the invention provides a method for packaging of El- defective adenoviral particles in the absence of replication competent adenovirus. The method involves introducing a vector into cells from the El -complementing cell line of the invention, where the vector contains a defect in the adenovirus El region, adenovirus 5' and 3' cis-elements necessary for replication and packaging, adenovirus pIX, and regulatory sequences necessary for expression of the adenoviral genes and transgene. In another aspect, the invention provides a method of producing El -defective adenoviral particles in the absence of detectable replication competent adenovirus. The method involves infecting cells from the El -complementing cell line of the invention with an El -defective adenovirus and culturing under conditions which permit the cell to express the Ela and Elb proteins. Other aspects and advantages of the invention will be readily apparent from the following detailed description of the invention. Brief Description of the Drawings Fig. 1 is a schematic representation of the structures of the El -deleted recombinant adenoviral vector, Ad5 DNA sequence in 293 cells and PGK Ad5El fragment in the new El cell line. Fig. 2 A is a graph of the growth kinetics of an El -deleted recombinant adenovirus, H5.CBLαcZ, in 293 and new El cell lines. See Example 2C for details of the study. The yield of H5.CBLacZ virus in each cell line is shown on the v axis in a log scale. The time points are shown on the x axis. Fig 2B is a bar chart showing the relative plaquing efficiency (RPE) for H5 CBLacZ virus on new El cell lines which were compared with 293 cells See Example 2D for details of the study RPEs were computed as the percentage of the titer of H5 CBLαcZ virus Solid bars, the mean RPE of each cell line from three different experiments, error bars represent standard deviations. Detailed Description of the Invention The present invention provides a method of producing El -deleted adenoviruses in the absence of detectable replication-competent adenovirus (RCA), as well as cell lines and vectors useful in this method The resulting El -deleted adenoviruses are particularly well suited for use in delivering genes to a mammal, because these adenoviruses are substantially free of contaminating RCA In one desirable embodiment, the invention provides HeLa based cell lines that stably expresses the El locus from a promoter derived from the phosphoglycerate kinase (PGK) gene These cell lines have no adenoviral sequences 5' to the El open reading frame (ORF) and reduced (or no) homology 3' to El These cell line supports plaquing and amplification of El -deleted vectors at levels equal to or better than 293 cells without the emergence of RCA One example of such a cell line is the GH329 cell line, which has been deposited with the American Type Culture Collection (ATCC), 10801 University Boulevard, Manassas, NA 20110-2209, USA on September 29, 1999, and has been assigned accession number PTA-803 This deposit has been made pursuant to the provisions of the Budapest Treaty and in conformity with the requirements of 37 CFR §§1 801 et seq The GH329 cells been found to complement (and allow the replication of) El -deleted viral vectors in the absence of detectable replication competent adenoviruses (RCA) over at least 20 passages Currently, GH329 is believed to express a single copy of each the Ela and Elb proteins However, yields obtained using the GH329 cell line are at least equivalent to those obtained in 293 cells, in which RCA is observed following 5 to 10 passages Another suitable cell line is the GH364 cell line, which expresses between 5 to 10 copies of the Ela and Elb proteins Yet another cell line of the invention is the GH354 cell line The GH354 cells have been found to complement (and allow replication of) El -deleted viral vectors in the absence of detectable RCA over at least 20 passages Further, as with the GH329 cell line, yields obtained using the GH354 cell line are at least equivalent to those obtained in 293 cells The cell lines of the invention are particularly well suited for production of El- deleted adenovirus for preclinical and clinical use, as they are readily adapted to growth in serum free media The cell lines of the invention, e g , GH329, may be adapted to growth in serum-free media using techniques well known those of skill in the art These serum-free-media adapted cell lines are encompassed by the present invention Optionally, other useful cell lines may be derived from a cell line of the invention For example, the GH329 (or GH354 or GH364) cell line may be modified to stably express another desired protein(s) using the techniques described herein, as well as techniques known in the art In one desirable embodiment, a derivative of the GH329 cell line may be produced by stably transforming GH329 cells such that they contain one or more sequences expressing adenoviral proteins (or functional fragments thereof) required for replication of the El -deleted virus In addition to the adenoviral Ela and Elb functions provided by the cell line, the required adenoviral functions include E2a and E4 ORF6 Thus, in one embodiment, a GH329 derivative cell line may be produced which expresses the required functions of the E2 region or E4 region, or combinations thereof Suitably, the nucleic acid molecule(s) used to produce the GH329 derivative cell line contains no adenoviral sequences 5' to the El coding region and only the minimal adenoviral sequences required to express the desired functional proteins in the host cell Given this information, one of skill in the art may readily engineer other GH329 derivative cell lines I. El-Complementing Cell Line A. Target Cells The vector used to transform HeLa cells and produce the GH329 cell line of the invention may be used to develop other El -trans-complementing cell lines. Preferably, such other cell lines are derived from HeLa cells, an aneuploid epithelial- like cell derived from cervical carcinoma [ATCC CCL2]. However, using the vector described herein, another mammalian host cell may be selected from any mammalian species, such as human cell types, including without limitation, cells such as Vero cells, A549 and HKB cells. Other mammalian species cells are also useful, for example, primate cells, rodent cells or other cells commonly used in biological laboratories. The selection of the mammalian species providing the cells is not a limitation of this invention; nor is the type of mammalian cell, i.e., fibroblast, hepatocyte, tumor cell, etc. B. Transforming DNA Molecule Suitably, the target cells are transformed with a DNA molecule carrying, at a minimum, DNA sequences encoding adenovirus Ela and Elb under the control of a PGK promoter. This molecule lacks adenoviral sequences 5' of the El region, preferably excluding the native Ela promoter and contains minimal sequences 3' to the El region (i.e., optionally contains partial pIX sequences). The DNA sequences encoding the adenovirus Ela and Elb genes useful in this invention may be selected from among any known adenovirus type, including the presently identified 41 human types. Similarly, adenoviruses known to infect other animals may supply the gene sequences. The selection of the adenovirus type for each Ela and Elb gene sequence does not limit this invention. The sequences for a number of adenovirus serotypes, including that of serotype Ad5, are available from Genbank. A variety of adenovirus strains are available from the ATCC, or are available by request from a variety of commercial and institutional sources. In the following exemplary embodiment the Ela and Elb gene sequences are those from adenovirus serotype 5 (Ad5). By "adenoviral DNA which expresses the Ela gene product", it is meant any adenovirus gene encoding Ela or any functional Ela portion. Similarly included are any alleles or other modifications of the Ela gene or functional portion. Such modifications may be deliberately introduced by resort to conventional genetic engineering or mutagenic techniques to enhance the Ela expression or function in some manner, as well as naturally occurring allelic variants thereof. By "adenoviral DNA which expresses the Elb gene product", it is meant any adenovirus gene encoding Elb or any functional Elb portion. Similarly included are any alleles or other modifications of the Elb gene or functional portion. Such modifications may be deliberately introduced by resort to conventional genetic engineering or mutagenic techniques to enhance the Elb expression or function in some manner, as well as naturally occurring allelic variants thereof. The nucleic acid molecule carrying the Ad Ela and Ad Elb may be in any form which transfers these components to the host cell. Most suitably, these sequences are contained within a vector. A "vector" includes, without limitation, any genetic element, such as a plasmid, phage, transposon, cosmid, chromosome, virus, virion, etc.. In one particularly suitable embodiment, the nucleic acid molecule is a plasmid carrying Ad Ela, Ad Elb, partial pIX sequences, and the PGK promoter. The nucleic acid molecule may contain other non-viral sequences, such as those encoding certain selectable reporters or marker genes, e.g., sequences encoding hygromycin or purimycin, or the neomycin resistance gene for G418 selection, among others. The molecule may further contain other components. Conventional techniques may be utilized for construction of the nucleic acid molecules of the invention. See, generally, Sambrook et al, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratories, Cold Spring Harbor, New York. Once the desired nucleic acid molecule is engineered, it may be transferred to the target cell by any suitable method. Such methods include, for example, transfection, electroporation, liposome delivery, membrane fusion techniques, high velocity DNA-coated pellets, viral infection and protoplast fusion. Thereafter, cells are cultured according to standard methods and, optionally, seeded in media containing an antibiotic to select for cells containing the cells expressing the resistance gene After a period of selection, the resistant colonies are isolated, expanded, and screened for El expression See, Sambrook et al, cited above II Use of El-Complementing Cells in Production El-Deleted Adenovirus The El -complementing cells of the invention are useful for a variety of purposes Most suitably, the cells (e g , GH329) are used in packaging recombinant virus (i e , viral particles) from El -defective vectors and in high yield production of El -defective adenoviruses in the absence of detectable RCA The cells of the invention which express Ad5 Ela and Elb are suitable for use in packaging recombinant virus from El -defective vectors (e g , plasmids) containing sequences of Ad5 and Ad2 Further, these cells are anticipated to be useful in producing recombinant virus from other Ad serotypes, which are known to those of skill in the art A Packaging of El -Defective Vectors In a preferred embodiment, this method of the invention involves packaging of an El -deleted vector which contains a transgene into an El -deleted adenoviral particle useful for delivery of the transgene to a host cell In a preferred embodiment, the El -deleted vector contains all adenoviral genes necessary to produce and package an infectious adenoviral particle which replicates only in the presence of complementing El proteins, e g , such as are supplied by cell line of the invention The vector contains defects in both the Ela and Elb sequences, and most desirably, is deleted of all or most of the sequences encoding these proteins At a minimum, the El -deleted vector to be packaged contains adenoviral 5' and 3' cis-elements necessary for replication and packaging, a transgene, and a pIX gene or a functional fragment thereof The vector further contains regulatory sequences which permit expression of the encoded transgene product in a host cell, which regulatory sequences are operably linked to the transgene As used herein, "operably linked" sequences include both expression control sequences that are contiguous with the gene of interest and expression control sequences that act in trans or at a distance to control the gene of interest Also included in the vector are regulatory sequences operably linked to other gene products, e g , the pIX gene, carried by the vector 1 Adenoviral Elements The El -defective vector to be packaged includes, at a minimum, adenovirus cis-acting 5' and 3' inverted terminal repeat (ITR) sequences of an adenovirus (which function as origins of replication) and the native 5' packaging/enhancer domain These are 5' and 3' cis-elements necessary for packaging linear Ad genomes and further contain the enhancer elements for the El promoter The El -deleted vector to be packaged into a viral particle is further engineered so that it expresses the pIX gene product Most suitably, the pIX gene is intact, containing the native promoter and encoding the full length protein However, were desired, the native pIX promoter may be substituted by another desired promoter Alternatively, sequences encoding a functional fragment of pIX may be selected for use in the vector In yet another alternative, the native sequences encoding pIX or a functional fragment thereof may be modified to enhance expression For example, the native sequences may be modified, e g , by site-directed mutagenesis or another suitable technique, to insert preference codons to enhance expression in a selected host cell Optionally, the pIX may be supplied to the El - complementing cell line on a separate molecule An exemplary vector containing only the minimal adenoviral sequences is termed the AdΔEl-E4 vector, and lacks all functional adenoviral genes including El, E2, E3, E4, intermediate gene IXa and late genes LI, L2, L2, L4 and L5) with the exception of intermediate gene IX which is present However, in a preferred embodiment, the El -deleted vector contains, in addition to the minimal adenoviral sequences described above, functional adenoviral E2 and E4 regions In another suitable embodiment, the adenoviral sequences in the El -deleted vector include the 5' and 3' cis-elements, functional E2 and E4 regions, intermediate genes IX and IXa, and late genes LI through L5 However, the El -deleted vector may be readily engineered by one of skill in the art, taking into consideration the minimum sequences required, and is not limited to these exemplary embodiments. The vector is constructed such that the transgene and the sequences encoding pIX are located downstream of the 5' ITRs and upstream of the 3' ITRs. The transgene is a nucleic acid sequence, heterologous to the adenovirus sequence, which encodes a polypeptide, protein, or other product, of interest. The transgene is operatively linked to regulatory components in a manner which permits transgene transcription. 2. Transgene The composition of the transgene sequence will depend upon the use to which the resulting virus will be put. For example, one type of transgene sequence includes a reporter sequence, which upon expression produces a detectable signal. Such reporter sequences include without limitation, DNA sequences encoding β-lactamase, β-galactosidase (LacZ), alkaline phosphatase, thymidine kinase, green fluorescent protein (GFP), chloramphenicol acetyltransferase (CAT), luciferase, membrane bound proteins including, for example, CD2, CD4, CD8, the influenza hemagglutinin protein, and others well known in the art to which high affinity antibodies directed thereto exist or can be produced by conventional means, and fusion proteins comprising a membrane bound protein appropriately fused to an antigen tag domain from, among others, hemagglutinin or Myc. However, desirably, the transgene is a non-marker sequence encoding a product which is useful in biology and medicine, such as proteins, peptides, anti-sense nucleic acids (e.g., RNAs), enzymes, or catalytic RNAs. The transgene may be used to correct or ameliorate gene deficiencies, which may include deficiencies in which normal genes are expressed at less than normal levels or deficiencies in which the functional gene product is not expressed. One desirable type of transgene sequence encodes a therapeutic protein or polypeptide which is expressed in a host cell. The invention further includes using multiple transgenes, e.g., to correct or ameliorate a gene defect caused by a multi- subunit protein. In certain situations, a different transgene may be used to encode each subunit of a protein, or to encode different peptides or proteins. This is desirable when the size of the DNA encoding the protein subunit is large, e.g., for an immunoglobulin, the platelet-derived growth factor, or a dystrophin protein. In order for the cell to produce the multi- subunit protein, a cell is infected with the recombinant virus containing each of the different subunits. Alternatively, different subunits of a protein may be encoded by the same transgene. In this case, a single transgene includes the DNA encoding each of the subunits, with the DNA for each subunit separated by an internal ribozyme entry site (IRES). This is desirable when the size of the DNA encoding each of the subunits is small, e.g., total of the DNA encoding the subunits and the IRES is less than five kilobases. Other useful gene products include, molecules which induce an immune response, non-naturally occurring polypeptides, such as chimeric or hybrid polypeptides having a non-naturally occurring amino acid sequence containing insertions, deletions or amino acid substitutions. For example, single-chain engineered immunoglobulins could be useful in certain immunocompromised patients. Other types of non-naturally occurring gene sequences include antisense molecules and catalytic nucleic acids, such as ribozymes, which could be used to reduce overexpression of a gene. However, the selected transgene may encode any product desirable for delivery to a host or desirable for study. The selection of the transgene sequence is not a limitation of this invention. 3. Regulatory Sequences In addition to the major elements identified above for the vector, (e.g, the adenovirus sequences and the transgene), the vector also includes conventional control elements necessary to drive expression of the transgene in a host cell containing with the transgene. Thus the vector contains a selected promoter which is linked to the transgene and located, with the transgene, between the viral sequences of the vector. Suitable promoters may be readily selected from among constitutive and inducible promoters. Selection of these and other common vector elements are conventional and many such sequences are available [see, e.g., Sambrook et al, and references cited therein]. Examples of constitutive promoters include, without limitation, the retroviral Rous sarcoma virus (RSV) LTR promoter (optionally with the RSV enhancer), the cytomegalovirus (CMV) promoter (optionally with the CMV enhancer) [see, e g , Boshart et al, Cell, 41 521-530 (1985)], the SV40 promoter, the dihydrofolate reductase promoter, the β-actin promoter, the phosphoglycerol kinase (PGK) promoter, and the EFlα promoter [Invitrogen] Inducible promoters are regulated by exogenously supplied compounds, including, the zinc-inducible sheep metallothionine (MT) promoter, the dexamethasone (Dex)-inducible mouse mammary tumor virus (MMTV) promoter, the T7 polymerase promoter system [WO 98/10088], the ecdysone insect promoter [No et al, Proc. Natl. Acad. Sci. USA, 93 3346-3351 (1996)], the tetracycline-repressible system [Gossen et al, Proc. Natl. Acad. Sci. USA, 89 5547-5551 (1992)], the tetracycline-inducible system [Gossen et al, Science, 268 1766-1769 (1995), see also Harvey et al, Curr. Opin. Chem. Biol, 2 512-518 (1998)], the RU486-inducible system [Wang et al, Nat. Biotech, 15 239-243 (1997) and Wang et al, Gene Ther., 4 432-441 (1997)] and the rapamycin-inducible system [Magari et al, J. Clm. Invest, 100 2865-2872 (1997)] 4 Other Vector Elements The vector carrying the Ad ITRs flanking the transgene and regulatory sequences (e g , promoters, polyA sequences, etc ) may be in any form which transfers these components to the host cell Preferably, the vector is in the form of a plasmid Preferably to avoid homologous recombination, the plasmid does not contain any adenovirus sequences in the El region or the region 5' to the El region It may contain non-viral sequences, such as those encoding certain selectable reporters or marker genes, e g , sequences encoding hygromycin or purimycin, among others Other components of the plasmid may include an origin of replication and an amplicon, such as the amplicon system, employing the Epstein Barr virus nuclear antigen, for example, the vector components in pCEP4 (Invitrogen) See, also, J Horvath et al, Virology, 184 141-148 (1991) This amplicon system or similar amplicon components permit high copy episomal replication in the cells Other heterologous nucleic acid sequences optionally present in this vector include sequences providing signals required for efficient polyadenylation of the RNA transcript, and introns with functional splice donor and acceptor sites A common poly-A sequence which is employed in the vectors useful in this invention is that derived from the papovavirus SV-40 The poly-A sequence generally is inserted following the transgene sequences and before the 3' AAV ITR sequence A vector useful in the present invention may also contain an intron, desirably located between the promoter/enhancer sequence and the transgene One possible intron sequence is also derived from SV-40, and is referred to as the SV-40 T intron sequence Selection of these and other common vector elements are conventional and many such sequences are available [see, e g , Sambrook et al, and references cited therein at, for example, pages 3 18-3 26 and 16 17-16 27] 5 Co-Transfectwn of Adenoviral Sequences Preferably, the El -deleted vector contains all functional adenoviral sequences required for packaging and replication in the presence of the El- complementing cell line of the invention In addition to the Ela and Elb functions supplied by the trans-complementing cell line, functional adenoviral E2a and E4 ORF 6 region are required However, where the required functions are lacking from the El -deleted vector (i e , the El -deleted vector further contains functional deletions in E2a and/or E4 ORF6), these functions may be supplied by other sources In one embodiment, these functions may be supplied by co-transfection of the El- complementing cell line with one or more nucleic acid molecules capable of directing expression of the required adenoviral function Alternatively, a modified GH329 cell line of the invention which has been transformed to supply the required adenoviral functions may be utilized For example, a vector deleted of El and having a defective E2 region may be complemented in GH329 cells of the invention by transfecting the cells with a nucleic acid molecule (e g , a plasmid) expressing required E2 functions (e g , E2a) As another example, a vector lacking El through E4 functions may be complemented in GH329 cells by transfecting the cells with a nucleic acid molecule expressing functional E2, E3 and E4 (e g , E4 ORF6) Where a nucleic acid molecule is co-transfected into the cells of the invention, such a nucleic acid molecule contains no adenoviral El sequences, nor does it contain any sequences 5' to the El region Construction of these nucleic acid molecules is within the skill of those in the art Suitably, a selected recombinant vector, as described above, is introduced into El -complementing cells from a cell line of the invention using conventional techniques, such as the transfection techniques known in the art [see, K Kozarsky et al, Som. Cell andMolec. Genet., 19(5) 449-458 (1993)] Thereafter, recombinant El -deleted adenoviruses are isolated and purified following transfection Purification methods are well known to those of skill in the art and may be readily selected For example, the viruses may be subjected to plaque purification and the lysates subjected to cesium chloride centrifugation to obtain purified virus B Amplification of El -Deleted Adenoviruses The El -trans-complementing cell line of the invention (or a derivative thereof) may be used to amplify an El -defective adenovirus Suitably, the El - defective adenovirus will have been isolated and purified from cellular debris and other viral materials prior to use in this method This is particularly desirable where the El -defective adenovirus to be amplified is produced by methods other than those of the present invention Suitable purification methods, e g , plaque purification, are well known to those of skill in the art A culture, or preferably, a suspension of cells from an El -trans- complementing cell line of the invention, e g , GH329, are infected with the El- defective adenovirus using conventional methods A suitable multiplicity of infection (MOI) may be readily selected However, an MOI in the range of about 0 1 to about 100, about 0 5 to about 20, and/or about 1 to about 5, is desirable The cells are then cultured under conditions which permits cell growth and replication of the El- defective adenovirus in the presence of the El expressed by the cell line of the invention Suitably, the viruses are subjected to continuous passages for up to 5, 10, or 20 passages However, where desired, the viruses may be subjected to fewer, or more passages The cells are subjected to two to three rounds of freeze-thawing, the resulting lysate is then subjected to centrifugation for collection, and the supernatant is collected. Conventional purification techniques such as chloride gradient centrifugation or column chromatography are used to concentrate the rAd-ΔEl from the cellular proteins in the lysate. Advantageously, however, the method of the invention through use of the cell lines of the invention avoid the problems of contaminating RCA which plague conventional production techniques. III. El-Deleted Ad produced by method of invention The El -deleted adenoviruses produced according to the present invention are suitable for a variety of uses and are particularly suitable for in vivo uses, as the present invention permits these adenoviruses to be produced in serum-free media, and in the absence of detectable RCA. Thus, the El -deleted adenoviruses produced according to the invention are substantially free of contamination with RCA. In one embodiment, El -deleted viruses have been deemed suitable for applications in which transient transgene expression is therapeutic (e.g., p53 gene transfer in cancer and VEGF gene transfer in heart diseases). However, the El - deleted adenoviruses are not limited to use where transient transgene expression is desired. The El -deleted adenoviruses are useful for a variety of situations in which delivery and expression of a selected transgene is desired. Suitable doses of El -deleted adenoviruses may be readily determined by one of skill in the art, depending upon the condition being treated, the health, age and weight of the veterinary or human patient, and other related factors. However, generally, a suitable dose may be in the range of 10 10 to 10 18 , and preferably about 10 14 to 10 16 viral particles per dose, for an adult human having weight of about 80 kg. This dose may be suspended in about 0.01 mL to about 1 mL of a physiologically compatible carrier and delivered by any suitable means. The dose may be repeated, as needed or desired, daily, weekly, monthly, or at other selected intervals. The following examples are provided to illustrate the production of the exemplary cell lines of the invention and their use in producing El -deleted adenovirus which are free of detectable RCA over 20 passages These examples do not limit the scope of the invention One skilled in the art will appreciate that although specific reagents and conditions are outlined in the following examples, modifications can be made which are meant to be encompassed by the spirit and scope of the invention Example 1 - Production of El -complementing Cell Lines As described in this example, Vero, A549 and HeLa cells were stably transfected with plasmid constructs carrying a 3 4 kb DNA fragment of Ad 5 genome spanning 511 to 3924 bp (Ela and Elb open reading frames and part of the pIX gene) Fig 1 is provides a schematic representation of the relevant constructs In these constructs, the Ela native promoter was replaced with either sequences from the cytomegalovirus early gene (CMV) or human phosphoglycerate kinase gene (PGK) There is no overlap with the 5' region of the El -deleted vector (0-360 bp) described below and reduced overlap at the 3' region (vector begins at 3312 bp while the adenovirus sequence in 293 extends to 4300 bp) A Construction of PGKEl plasmids Ad5 El region (m u 1 42-10 9) was cloned into pBluescript SK(-) vector The 3 4 kb El fragment was further subcloned into a plasmid which allowed expression from promoters derived from the phosphoglycerate kinase gene [PGK] [Adra et al , Gene, 60 65-74 (1987)] or the immediate early gene of cytomegalovirus [CMV] [Thomsen et al , Proc. Natl. Acad. Sci. USA, 81 659-663 (1984)] Both contained the neomycin resistance gene for G418 selection B Transfections and selection of G418-resistant clone HeLa, A549 and Vero cells were obtained from ATCC and maintained as monolayers in Dulbecco modified Eagle's minimal essential medium (DMEM) supplemented with 10% fetal bovine serum Plasmids were transfected by calcium phosphate precipitation onto the cells seeded in 100 mm plates, using 10 μg of plasmid DNA for each plate Twenty-four hours post-transfection, cells were trypsinized and seeded in G418-containing media at various dilutions ranging from 1 5 to 1 40 After 2 weeks of selection, G418-resistant colonies were isolated, expanded and screened for El expression Only one stable clone formed from A549 transfectants, while over 70 clones from HeLa and 50 clones from Vero cell transfectants were isolated (data not shown) C Screening procedure for new El lines Stable G418-resistant clones were first screened with a blue comet formation assay in which 1 x 10 cells in 6 well plates were infected with 200 LacZ Forming Units (LFU) of H5 CBLαcZ [an El -deleted adenovirus expression LacZ from a β-actin promoter] [Gao et al , J. Virol, 70 8934-8943 (1996)] Six days post- infection cells were histochemically stained with 5-Bromo-4-chloro-3-indolyl-β-D- galactopyranoside (X-gal) and comets of blue cells in each well were scored Subsequently, the strongly positive clones were seeded into 4 well glass chamber slides for 24 hours Expression level of Ela and Elb proteins in the cells was assessed by immunofluorescent staining, using mouse monoclonal antibodies (Oncogene Science) G418 resistant clones were expanded and initially screened for their ability to support propagation of an El -deleted adenovirus vector harboring the LacZ transgene, the only clones capable of sustaining El -deleted adenovirus replication were HeLa derived Example 2 - Characterization of new El complementing cell lines A Genetic constitution Total genomic DNAs were isolated from each El complementing clone, digested with appropriate restriction endonucleases to release an internal El- containing plasmid fragment, and evaluated by DNA hybridization after electrophoresis More particularly, DNAs were fractionated on 1% agarose gels, transferred to nylon filters and hybridized with a 1 1 kb El Hind III/Sma I fragment All cell lines tested have at least one copy of the El gene integrated into HeLa genome One PGK-El clone (GH364) and one CMV-El cell line (GH414) harbor 5-10 copies of the El gene B Production of El proteins Cell pellets of each clone were harvested from 60 mm plates and resuspended in 200 μl of lysis buffer (20 mM Tris-Cl, pH 8 0, 140 mM NaCl, 1% NP- 40 v/v, 1 mM PMSF, 1 μg/ml each leupeptin, antipain, chymostatin, soybean trypsin inhibitor) Lysates were incubated on ice for one hour and spun in a microcentrifiige at o 14,000 rpm for 30 minutes at 4 C Supernatants were collected and total protein concentrations determined by Lowry's method Samples (50 μg) were fractionated on 10% SDS-PAGE gels and electrotransferred to nitrocellulose membranes Ela and Elb proteins were detected using the enhanced chemiluminescence (ECL) system (Amersham Life Science, Arlington Heights, JL) with a mouse polyclonal antibody (PharmMingen, San Diego, CA) and rat monoclonal antibodies (Oncogene Science) respectively Total cellular proteins from 293 cells were used as controls Western blot analysis revealed variable El protein expression profiles among different clones, in terms of total expression and the ratios of Ela and Elb proteins The anti-Ad5 antibody identified the Ela protein as a doublet at approximately 35 - 46 kDa C Growth kinetics of an El -deleted recombinant virus H5 CBLacZ on the novel El complementing cell lines HeLa, 293 and the cells of new El cell lines were infected with H5 CBLacZ at multiplicity of infection (MOI) equal to 0 5 Infected cells were harvested at 24, 48, 72, 96 and 120 hours post-infection Cells were lysed in the infection medium by 3 rounds of freeze/thaw and the titer of virus was determined by serial dilution infections on 293 cells followed by histochemical staining with X-gal Cells were histochemically stained with X-gal after 20 hours, and blue cells were counted Titers are expressed as LacZ forming units (LFU/ml) where one LFU is defined as the quantity of virus sufficient to cause visually detectable LacZ expression in one cell at 24 hour post-infection The yield of H5 CBLacZ virus in each cell line is shown on Fig 2 A, where the v axis is a log scale and the time points are shown on the x axis Two cell lines, GH329 and GH354, were equivalent if not better than 293 cells in terms of production (Fig 2 A) of El -deleted virus D Relative plaquing efficiencies (RPEs for H5 CBLacZ virus on new El cell lines The new El cell lines were compared with 293 cells in their abilities to support plaque formation of H5 CBLacZ virus Cells were infected with H5 CBEαcZ with a range of serial dilutions and overlaid with top agar after 20 hours Plaques were detected by staining with neutral red on day 10 post infection RPEs were computed as the percentage of the titer of H5 CBLacZ virus as compared to that on 293 cells Cells were infected with H5 CBLacZ over a range of serial dilutions and overlaid with top agar after 20 h Plaques were detected by staining with neutral red on day 10 post infection RPEs were computed as the percentage of the titer of H5 CBLacZ virus Solid bars, the mean RPE of each cell line from three different experiments, error bars, standard deviations Two cell lines, GH329 and GH354, were equivalent if not better than 293 cells in terms of plaquing efficacy (Fig 2B) of El -deleted virus Example 3 - Detection of RCAs in the El -deleted recombinant virus preps after multiple passages in either 293 or GH329 cells The propensity to generate RCA was studied by serially passaging an El- deleted LacZ virus (initially isolated on GH329) and both GH329 and 293 cells A portion of each lysate was used to infect a non-El expressing cell line (A549) to assess for RCA, which presented itself as cytopathology on serial passage and was confirmed by DNA hybridization analysis, as follows However, since crude Hirt DNAs were used for the Southern blot analysis, it would be difficult to use the assay to quantify the amount of RCAs in each sample H5 CBLacZ virus was plaque-purified twice on GH329 cells following the standard protocol (Gao et al , J. Virol, 70 8934-8943 1996)] The blue plaques identified by X-gal histochemical staining were selected, expanded to a large prep in GH329 cells and purified by CsCl gradient centrifugation The purified H5 CBEαcZ virus was designated as passage 0 (PO) and used for continuous passages on 293 and GH329 cells simultaneously for up to 20 passages Large-preparation viruses grown up in each cell line were CsCl gradient-purified from passages 5, 10, 15 and 20 A549 cells were obtained from ATCC and cultured in F-12K medium supplemented with 10% FBS For the RCA assay, cells were seeded at a density of lx 10 7 cells per an 150 mm plate 24 hours prior to the virus infection A total of 1 x 10 8 PFU each of testing viruses were diluted in 80 ml of F-12K medium with 2% fetal bovine serum (FBS) and 1% penicillin/streptomycin (P/S) and added to four 150 mm plates of A549 cells after removal of the growth medium from each plate At 24 hours post infection, 1 6 mis of FBS were added into each plate As a positive control, 1 PFU of Ad5 wild type virus was spiked into each of 1 x 10 8 PFU testing articles for the infection procedure described above Negative control plates were also analyzed in parallel Infected cells from each plate were harvested at 14 days later and lysed in infection medium by three rounds of freezing-thawing Twenty percent of total cell lysate from each plate were used to infect one plate of A549 cells following the protocol described above Seven days post infection, the plates were examined under a light microscope for cytopathic effects The RCA assay used in this study can detect 1 PFU of RCA in 10 8 PFUs of recombinant viruses The infected cells from each plate were harvested with the medium and spun down for collection of the cell pellet Each cell pellet was resuspended in 0 5 ml of 10 mM Tris-Cl, pH 8 0 and lysed by three cycles of freezing-thawing After centrifugation in a Sorvall-26 at 3,200 rpm for 15 min, the supernatant of each sample was collected One-third of each supernatant was mixed with an equal volume of 2x pronase solution (2mg/ml pronase, 100 mM Tris- Cl, pH 7 6, 2 mM EDTA, 1% SDS, incubate the solution at 37 C for 45 min), incubated at 37 °C for 4 hours, extracted with phenol-chloroform and ethanol precipitated The crude viral DNA samples were resuspended in equal volume of TE buffer and subjected to Nsi I endonuclease digestion and Southern blot analysis Blots were hybridized with a 420 bp El -Xba I/Cla I DNA probe The results showed that significant RCA emerged between passage 5 and 10 on 293 cells whereas no RCA was detected after 20 passages on GH329. The sensitivity of the RCA assay was confirmed by spiking a zero passage GH329 cells in the presence of vector with 1 pfu of wild type Ad. All publications cited in this specification are incorporated herein by reference. While the invention has been described with reference to a particularly preferred embodiment, it will be appreciated that modifications can be made without departing from the spirit of the invention. Such modifications are intended to fall within the scope of the appended claims.

Claims: What is claimed is 1. An El -complementing cell line useful for production of recombinant El- defective adenoviruses in the absence of detectable replication-competent adenovirus, said El -complementing cell line comprising an aneuploid cell line stably transformed with a nucleic acid molecule comprising nucleic acid sequences encoding adenovirus Ela and adenovirus Elb under the control of a phosphoglycerate kinase (PGK) promoter, and wherein the nucleic acid sequences further comprise a deletion of adenovirus sequences 5' to the sequences encoding adenovirus Ela. 2. The El -complementing cell line according to claim 1, wherein the aneuploid cell line is a HeLa cell line. 3. The El -complementing cell line according to claim 1 or claim 2, wherein the nucleic acid sequences further comprise nucleic acid sequences of the pIX gene region 4 The El -complementing cell line according to any of claims 1 to 3, wherein the nucleic acid molecule is a plasmid vector 5 The El -complementing cell line according to any of claims 1 to 4, wherein the nucleic acid molecule comprises multiple copies of the sequences encoding adenovirus Ela and adenovirus Elb 6 The El -complementing cell line according to any of claims 1 to 5, wherein the El -complementing cell line comprises multiple copies of said nucleic acid molecule 7 The El -complementing cell line according to any of claims 1 to 6, wherein the sequences encoding adenovirus Ela and the sequences encoding Elb are independently selected from adenovirus type 5 8 The El -complementing cell line according to claim 1, wherein the cell line is selected from the group consisting of GH364 and GH354 9 An adenovirus El -complementing cell line designated GH329, deposited with the ATCC under accession number PTA-803 10 A method for packaging of El -defective adenoviral particles in the absence of replication competent adenovirus, said method comprising the steps of (a) providing cells from an El -complementing cell line comprising an aneuploid cell line stably transformed with a nucleic acid molecule comprising nucleic acid sequences encoding adenovirus Ela and adenovirus Elb under the control of a phosphoglycerate kinase (PGK) promoter, wherein the nucleic acid sequences further comprise a deletion of adenovirus sequences 5' to the sequences encoding adenovirus Ela, (b) transfecting said cells with a recombinant vector comprising, from 5' to 3', adenovirus 5' inverted terminal repeat sequences (ITRs), nucleic acid sequences encoding adenovirus pIX under the control of sequences which direct expression of adenovirus pIX in said cells, and a defect in the adenovirus El region, and adenovirus 3' ITRs, and (c) culturing said transfected cells under conditions which permit packaging of the El -defective vector into a recombinant El -defective adenoviral particle 11 The method according to claim 10, wherein said recombinant vector further comprises a selected transgene 12 The method according to claim 11, wherein said transgene is located between the 5' and 3' ITRs 13 The method according to any of claims 10 to 12, further comprising the step of transfecting said cells with a second recombinant vector comprising adenovirus sequences encoding at least one adenoviral gene and a defect in the adenovirus El region 14 The method according to claim 13, wherein said second recombinant vector encodes adenovirus E2a 15 The method according to claim 13 or claim 14, wherein said second recombinant vector encodes adenovirus E4 or a functional fragment thereof 16 The method according to claim 15, wherein the functional fragment is E4 ORF6 17 The method according to claim 10, wherein the El -complementing cell line is selected from the group consisting of GH329, ATCC PTA-803, GH364 and GH354 18 A method of amplifying El -defective adenoviral particles in the absence of replication competent adenovirus, the method comprising the steps of (a) infecting an El -complementing cell line with El -defective adenoviruses, wherein said cell line comprises an aneuploid cell line stably transformed with a nucleic acid molecule comprising nucleic acid sequences encoding adenovirus Ela and adenovirus Elb under the control of a phosphoglycerate kinase (PGK) promoter, and wherein the nucleic acid sequences further comprise a deletion of adenovirus sequences 5' to the sequences encoding adenovirus Ela, (b) passaging the El -defective adenoviral particles on the El- complementing cell line for 2 to 20 passages, and (c) collecting the El -defective adenoviral particles 19 The method according to claim 18, wherein the El -defective adenoviruses of (a) are prepared by the steps comprising (i) providing cells from an El -complementing cell line comprising an aneuploid cell line stably transformed with a nucleic acid molecule comprising nucleic acid sequences encoding adenovirus Ela and adenovirus Elb under the control of a phosphoglycerate kinase (PGK) promoter, wherein the nucleic acid sequences further comprise a deletion of adenovirus sequences 5' to the sequences encoding adenovirus Ela, (ii) transfecting said cells with a recombinant vector comprising adenovirus 5' and 3' inverted terminal repeat sequences (ITRs), nucleic acid sequences encoding adenovirus pIX under the control of sequences which direct expression of adenovirus pIX in said cells, and a defect in the adenovirus El region, (iii) culturing said transfected cells under conditions which permit packaging of the El -defective vector into a recombinant El -defective adenoviral particle, and (iv) purifying the recombinant El -defective adenoviral particle from substantially all cellular debris

Inventors: GAO GUANGPING, WILSON JAMES M, GAO, GUANGPING, WILSON, JAMES, M.
Applicants: GAO GUANGPING, TRUSTEES OF THE UNIVERSITY OF, WILSON JAMES M, GAO, GUANGPING, THE TRUSTEES OF THE UNIVERSITY OF PENNSYLVANIA, WILSON, JAMES, M.
Application year: 2000
Main classification: C12N15
IPC codes: A61K39, A61K48, A61P31, C07K14, C12N5, C12N7, C12N15, C12R1