ALTERNATIVELY TARGETED ADENOVIRUS

Abstract: The present invention provides a recombinant protein having an amino terminus of an adenoviral fiber protein and having a trimerization domain. A fiber incorporating such a protein exhibits reduced affinity for a native substrate than does a wild-type adenoviral fiber trimer. The present invention further provides an adenovirus incorporating the recombinant protein of the present invention.

Description: ALTERNATIVELY TARGETED ADENOVIRUS TECHNICAL FIELD OF THE INVENTION The present invention relates to an alternately targeted adenovirus and includes methods for producing and purifying such viruses as well as protein modifications mediating alternate targeting. BACKGROUND OF THE INVENTION The various physiological responses of a host animal to the presence of a virus depend on the different ways such viruses interact with the host animal, each of which is first mediated by the surface of the virus ("the virion"). The adenoviral virion is a non-enveloped icosahedron about 65-80 nm in diameter (Home et al. J. Mol. Biol. 1. 84-86 (1959)). It comprises 252 capsomeres -- 240 hexons and 12 pentons (Ginsberg et al. Virology, 28. 782-83 ( 1966)) — derived from three viral proteins (proteins II, III, and IV) (Maizel et al. Virology. 36, 1 15- 25 (1968); Weber et al. Virology, 76. 709-24 (1977)). Proteins IX. VI, and Ilia, also present, stabilize the virion (Stewart et al, Cell. 67. 145-54 (1991 ); Stewart et al. EMBO J., 12(7), 2589-99 (1993)). The hexon provides structure and form to the capsid (Pettersson. in The Adenoviruses, pp. 205-270. Ginsberg, ed., (Plenum Press. New York. NY. 1984)). and is a homotrimer of the protein II (Roberts et al . Science. 232. 1 148-1 151 (1986)). The hexon provides the main antigenic determinants of the virus, and it also contributes to the serotype specificity of the virus (Watson et al. J. Gen. Virol. 69, 525-35 (1988); Wolfort et al. J. Virol. 62. 2321 -28 (1988): Wolfort et al, J. Virol. 56, 896-903 (1985); Crawford-Miksza et al. J. Virol. 70. 1836-44 (1996)). The hexon trimer is comprised of a pseudohexagonal base and a triangular top formed of three towers (Roberts et al, supra; Athappilly et al. J. Mol. Biol. 242, 430-455 (1994)). The base pedestal consists of two tightly packed eight- stranded antiparallel beta barrels stabilized by an internal loop. The predominant antigenic and serotype-specific regions of the hexon appear to be in loops 1 and 2 (i.e., LI or 11. and LII or 12, respectively), within which are seven discrete hypervariable regions (HVR1 to HVR7) varying in length and sequence between adenoviral serotypes (Crawford-Miksza et al. supra). The penton contains a base, which is bound to the capsid. and a fiber, which is non-covalently bound to and projects from, the penton base. The penton base, consisting of protein III. is highly conserved among serotypes of adenovirus. and (except for the enteric adenovirus Ad40 and Ad41 ) it has five RGD tripeptide motifs (Neumann et al. Gene. 69. 153-57 ( 1988)). These RGD tripeptides apparently mediate adenoviral binding to α integrins. a family of a heterodimeric cell-surface receptors that also interact with the extracellular matrix and play important roles in cell signaling (Hynes. Cell. 69. 1 1-25 ( 1992)). These RGD tripeptides also play a role in endocytosis of the virion (Wickham et al. ( 1993). supra: Bai et al. J. Virol. 67, 5198-3205 (1993)). The adenoviral fiber is a homotrimer of the adenoviral polypeptide IV (Devaux et al. J. Molec. Biol. 215, 567-88 (1990)). which has three discrete domains. The amino-terminal "tail " domain attaches non-covalently to the penton base. A relatively long "shaft" domain, comprising a variable number of repeating 15 residue β-sheets motifs, extends outwardly from the vertices of the viral particle (Yeh et al. Virus Res.. 33. 179-98 (1991 )). Lastly, about 200 residues at the carboxy-terminus form the "knob " domain. Functionally, the knob mediates both primary viral binding to cellular proteins and fiber trimerization (Henry et al. J. Virol. 68(8), 5239-46 (1994)). Trimerization also appears necessary for the amino terminus of the fiber to properly associate with the penton base (Novelli et al. Virology. 185. 365-76 ( 1991 )). In addition to recognizing cell receptors and binding the penton base, the fiber contributes to serotype integrity and mediates nuclear localization. Moreover, adenoviral fibers from several serotypes are glycosylated (see, e.g., Mullis et α/.. J. Virol, 64( 1 1 ). 5317-23 ( 1990): Hong et al. J. Virol, 70( 10). 7071-78 ( 1996); Chroboczek et al. Adenovirus Fiber, p. 163-200 in "The Molecular Repertoire of Adenoviruses I. Virion Structure and Function. " W. Doerfler and P. Bδhm. eds. (Springer. NY 1995)). Fiber proteins from different adenoviral serotypes differ considerably. For example, the number of shaft repeats differs between adenoviral serotypes (Green et al, EMBO J.. 2, 1357-65 ( 1983)). Moreover, the knob regions from the closely related Ad2 and Ad5 serotypes are only 63% similar at the amino acid level (Chroboczek et al. Virology. 186. 280-85 (1992)). and Ad2 and Ad3 fiber knobs are only 20% identical (Signas et al. J. Virol. 53. 672-78 ( 1985)). In contrast, the penton base sequences of Ad5 and Ad2 are 99% identical. Despite these differences in the knob region, a sequence comparison of even the Ad2 and Ad3 fiber genes demonstrates distinct regions of conservation, most of which are also conserved among the other human adenoviral fibers (see, e.g.. Figures 1 A-2B) One interaction between the adenoviral virion and the host animal is the process of cellular infection, during which the wild-type virion first binds the cell surface by means of a cellular adenoviral receptor (AR) ( e.g.. the coxsackievirus and adenovirus receptor (CAR), the MHC class I receptor, etc. (Bergelson et al. Science. 275, 1320-23 ( 1997); Tanako et al. Proc. Nat. Acad. Sci. (USA), 94, 3352-56 (1997)). Uong et al. EMBO J.. 16(9). 2294-06 ( 1997)). After attachment to an AR, the virus binds α v integrins. Following attachment to these cell surface proteins, infection proceeds by receptor-mediated internalization of the virus into endocytotic vesicles (Svensson et al, J. Virol. 51. 687-94 (1984); Chardonnet et al. Virology, 40. 462-77 ( 1970)). Within the cell, virions are disassembled (Greber et al. Cell, 75, 477-86 (1993)). the endosome disrupted (Fitzgerald et al. Cell. 32. 607-17 (1983)). and the viral particles transported to the nucleus via the nuclear pore complex (Dales et al. Virology. 56. 465-83 ( 1973)). As most adenoviral serotypes interact with cells through broadly disseminated cell surface proteins, the natural range of host cells infected by adenovirus is broad. In addition to cellular infection, host animals react defensively to the presence of adenoviral virions through mechanisms that reduce the effective free titer of the virus. For example, host immune systems, upon exposure to a given adenoviral serotype. can efficiently develop neutralizing antibodies, greatly reducing the effective free titer of the virus upon repeat administration (see. e.g., Setoguchi et al, Am. J. Respir. Cell Mol. Biol. 10. 369-77 ( 1994); Kass-Eisler et al. Gene Ther., 1. 395-402 (1994): Kass-Eisler et al. Gene The/:, 3. 154-62 (1996)). Interestingly, such antibodies typically are directed against the same determinants of adenoviral serotype specificity, and are primarily directed to the hypervariable hexon regions and. to some extent, fiber and penton base domains (Watson et al, supra: Wolfort et al. ( 1988). supra: Wolfort et al. ( 1985). supra; Crawford-Miksza et al. supra). Of course, the presence of adenoviruses agglutinates red blood cells in humans in a serotype-dependent manner (Hierholzer, J. Infect. Diseases, 123(A), 541 -50 ( 1973)). Additionally, adenoviral virions are actively scavenged from the circulation by cells of the reticuloendothelial system (RES) (see, e.g.. Worgall et al. Hum Gene Ther., 8. 1675-84 (1997); Wolff et al. J. Virol, 77( 1 ), 624-29 (1997)). In such a response, Kupffer cells, endothelial liver cells, or other RES cells scavenge the virus from the circulation (see generally. Moghini et al. Crit. Rev. Ther. Drug Carrier Sys., 77(1), 31 -59 ( 1994); Van Rooijen et al. J. Le k. Biol, 62. 702-09 ( 1997)). For example, virions can become opsonized. possibly though interaction between collectins and glycocylated viral proteins, triggering recognition by such RES cells: alternatively, such cells may recognize charged amino acid residues on the virion surface (see Hansen et al. Immunobiol. 199(2). 165-89 (1998); Jahrling et al. J. Med. Virol. 72( 1 ). 1 - 16 ( 1983)). Based on the popularity of adenoviruses as gene transfer vectors, efforts have been made to increase the ability of adenovirus to enter certain cells, e.g.. those few cells it does not infect, an approach referred to as "targeting" (see. e.g.. International Patent Application WO 95/26412 (Curiel et al). International Patent Application WO 94/10323 (Spooner et al). U.S. Patent 5.543,328 (McClelland et al). International Patent Application WO 94/24299 (Cotten et al)). Of course, while the ability to target adenoviruses to certain cell types is an important goal, far more desirable is an adenovirus which infects only a desired cell type, an approach referred to as "alternative targeting." However, to exclusively target a virus, its native affinity for host cell ARs must first be abrogated, producing a recombinant adenovirus incapable of productively infecting the full set of natural adenoviral target cells. Efforts aimed at abrogating native adenoviral cell affinity have focused logically on changing the fiber knob. These efforts have proven disappointing, largely because they fail to preserve the important fiber protein functions of stable trimerization and penton base binding (Spooner et al, supra). Moreover, replacement of the fiber knob with a cell-surface ligand (McClelland et al. supra) produces a virus only suitable for infecting a cell type having that ligand. Such a strategy produces a virus having many of the same targeting problems associated with wild-type adenoviruses (in which fiber trimerization and cellular tropism are mediated by the same protein domain), thus decreasing the flexibility of the vector. Moreover, due to the necessity of having a propagating cell line, and the integral connection between the fiber trimerization and targeting functions, obtaining a mutant virus with substituted targeting is difficult. For example, removing the fiber knob and replacing it with a non-trimerizing ligand (e.g.. Spooner et al. McClelland et al, supra) results in a virus lacking appreciable fiber protein. Aside from the broad natural tropism of the virus noted above, the non- infectious interactions between adenovirus and the host also pose problems for using adenovirus as gene transfer vectors. Such interactions effectively reduce the free titer of a given dose of adenovirus beneath that which is clinically effective. As such, there is currently a need for an adenovirus exhibiting reduced affinity for such natural interactions with a host animal (e.g.. target cell affinity, innate or acquired immune survailence, etc). Moreover, there is a need for such a virus which is able to deliver and express a desired transgene within a predefined tissue - an alternatively targeted virus. BRIEF SUMMARY OF THE INVENTION The present invention provides a recombinant protein having an amino terminus of an adenoviral fiber protein and having a trimerization domain. A fiber incorporating such a protein exhibits reduced affinity for a native substrate than does a wild-type adenoviral fiber trimer. The present invention further provides an adenovirus incorporating the recombinant protein of the present invention. The present invention is useful in a variety of gene-transfer applications, in vitro and in vivo, as a vector for delivering a desired gene to a cell with minimal ectopic infection. Specifically, the present invention permits more efficient production and construction of safer vectors for gene transfer applications. The present invention is also useful as a research tool by providing methods and reagents for the study of adenoviral attachment and infection of cells and in a method of assaying receptor-ligand interaction. Similarly, the recombinant fiber protein can be used in receptor-ligand assays and as adhesion proteins in vitro or in vivo. Additionally, the present invention provides reagents and methods permitting biologists to investigate the cell biology of viral growth and infection. Thus, the vectors of the present invention are highly useful in biological research. DESCRIPTION OF THE DRAWINGS Figures 1 A and IB sets forth a comparison of the amino acid sequences of the non-group B serotype fiber knobs (SEQ ID NOs: 5-18) using the Clustal method with PAM100 residue weight table. The height of the bars at the top of each row of sequence comparison correlates to the degree of homology. Consensus and majority sequences are indicated as SEQ ID NOs: 29 and 30. respectively. Figures 2A and 2B sets forth a comparison of the amino acid sequences of the group B serotype fiber knobs (SEQ ID NOs: 19-25) using the J. Hein method with PAM250 residue weight The height of the bars at the top of each row of sequence comparison correlates to the degree of homology. Consensus and majority sequences are indicated as SEQ ID NOs: 31 and 32. respectively. DETAILED DESCRIPTION OF THE INVENTION Recombinant Protein The present invention provides a recombinant adenoviral fiber protein having an amino terminus derived from an adenoviral fiber protein and having a trimerization domain. A trimer including such a recombinant protein exhibits reduced affinity for a native substrate, such as an antibody, collectins. opsins. a cellular binding site. etc. (i.e.. native to the serotype from which the shaft, and particularly the amino-terminus. is drawn) as compared to a native adenoviral fiber trimer. The trimer can be a homotrimer or a heterotrimer of different fiber monomers. Any modification of the monomeric units reducing the affinity of the resulting trimer for its native cell surface binding site (i.e.. a native AR) is within the scope of the invention. Preferably, the reduction in affinity is a substantial reduction in affinity (such as at least an order of magnitude, and preferably more) relative to the unmodified corresponding fiber. As mentioned, where a trimerization domain is itself a ligand for a native cell surface binding site, fiber proteins possessing such trimerization domains present some of the same problems for targeting as native adenoviral fiber trimerization domains. Therefore, the trimerization domain of the inventive protein invention preferably is not a ligand for the CAR or MHC-1 cell surface proteins. Most preferably, the non-native trimerization domain is not a ligand for any native adenoviral cell-surface binding site, whether the site is an AR or other cell surface binding site. As is discussed herein, adenoviruses incorporating such proteins exhibit reduced ability to appreciably infect cells via native AR proteins, and can serve as efficient source vectors for engineering alternatively targeted vectors. Therefore, while the trimerization domain preferably is not a ligand for a cell surface binding site, the entire trimer can be such a ligand (e.g., by virtue of a non-native ligand as discussed herein). Moreover, the trimerization domain can be a ligand for a substrate other than a native cell surface binding site, as such trimerization-ligands do not present the same concern for cell targeting as do trimerization domains which are ligands for cell surface binding sites. Thus, for example, the non-native trimerization domain can be a ligand for a substrate on an affinity column, on a blood-borne molecule, or even on a cell surface when it is not a native cell-surface binding site (e.g.. on a cell engineered to express a substrate cell surface protein not native to the unmodified cell type). The recombinant fiber protein can lack a sizable number of residues, or even identifiable domains, as herein described. For example, the protein can lack the native knob domain; it can lack one or more native shaft β-sheet repeats, or it can be otherwise truncated. Thus, a recombinant fiber protein can have any desired modification so long as it trimerizes when produced by a eukaryotic cell. Furthermore, a recombinant fiber protein preferably is not modified appreciably at the amino terminus (e.g., the amino-terminus of a monomer preferably consists essentially of the native fiber amino-terminus) to ensure that a fiber incorporating the recombinant fiber protein interacts properly with the penton base. Hence, the present invention also provides a composition of matter comprising a recombinant fiber protein of the present invention and an adenoviral penton base. Preferably, the recombinant fiber protein and the penton base associate much in the same manner as wild-type fibers and penton bases. Of course, the penton base can also be modified, for example, to include a non-native ligand. for example as is described in U.S. Patent 5.559,099 (Wickham et al.). In one embodiment, the fiber is modified to render it less able to interact with the innate or acquired host immune system. For example, one or more amino acids of the native fiber protein can be mutated to render the recombinant fiber protein less able to be recognized by neutralizing antibodies than a wild-type fiber (see. e.g.. International Patent Application WO 98/40509 (Crystal et al). The fiber also can be modified to lack one or more amino acids mediating interaction with the RES. For example, the fiber can be mutated to lack one or more glycosylation or phosphorylation sites, or the fiber (or virus containing the fiber) can be produced in the presence of inhibitors of glycosylation or phosphorylation. Similarly, the fiber (or other protein within the virus) can be conjugated to a lipid derivative of polyethylene glycol (PEG) comprising a primary amine group, an epoxy group, or a diacylclycerol group (see, e.g.. Kilbanov et al, FEBS Lett., 268, 235 ( 1990); Senior et al, Biochem. Biophys. Acta., 1062, 1 1 (1991 ); Allen et al, Biochem. Biophys. Ada., 1066, 29 (1991): Mori et al. FEBS Lett, 284, 263 ( 1991 )) to avoid collectin and/or opsonin binding or scavenging by Kupffer (or other RES) cells. A recombinant fiber protein lacking one or more amino acids, as herein described, can optionally comprise a non-native residue (e.g.. several non-native amino acids) in addition to (i.e.. insertions) or in place of (i.e.. substitutions) the missing native amino acid(s); of course, alternatively, the native amino acid(s) can be deleted from the knob. Preferably, the amino-acid is substituted with another non-native amino acid to preserve topology and. especially, trimerization. Moreover, if substituted, the replacement amino acid preferably confers novel qualities to the recombinant fiber protein. For example, to maximally ablate binding to the native substrate, a native amino acid can be substituted with a residue (or a plurality of residues) having a different charge. Such a substitution maximally interferes with the electrostatic interaction between native adenoviral knob domains and cellular ARs or interferes with a conformational change required to efficiently bind an AR or elements of the RES. Similarly, a native amino acid can be substituted with a residue (or a plurality of residues) of differing weight, where possible. For example, substitution with a heavier residue maximally interferes with the steric interaction between adenoviral domains and native substrates, by virtue of the longer side-chains on such heavier residues. Any native amino-acid residue mediating or assisting in the interaction between the knob and a native cellular AR is a suitable amino acid for mutation or deletion from the recombinant fiber protein. Such amino acid need not itself be the site of contact between the fiber and the receptor. For example, the native amino acid might be involved in a conformational change associated with receptor binding. The inventive fiber protein can lack any number of such native amino acids, so long as. in the aggregate, the recombinant fiber protein can associate to form a trimer. The amino acid can be within a β-sheet of the knob or within a loop connecting two β-sheets (such as, for example, the AB. BC, CD. DE. EF. FG. GH. HI, or IJ loops). Indeed, the amino acid can be within 10 (e.g.. within 5) residues of a β sheet or a loop. In the mature, folded trimer of the present invention, the amino acid can be within about 10 nm (e.g.. within about 5 nm or even within about 2 nm) of a β sheet or a loop. Native amino acid residues for modification or deletion can be selected by any method. For example, the sequences from different adenoviral serotypes (which are known in the art) can be compared to deduce conserved residues likely to mediate AR-binding. Alternatively or in combination, the sequence can be mapped onto a three dimensional representation of the protein (such as the crystal structure) to deduce those residues most likely responsible for AR binding. These analyses can be aided by resorting to any common algorithm or program for deducing protein structural functional interaction. Alternatively, random mutations can be introduced into a cloned adenoviral fiber expression cassette. One method of introducing random mutations into a protein is via the Taq polymerase. For example, a clone encoding the fiber knob (see, e.g.. Roelvink et al, J. Virol, 70, 7614-21 (1996)) can serve as a template for PCR amplification of the adenoviral fiber knob, or a portion thereof. By varying the concentration of divalent cations in the PCR reaction, the error rate of the transcripts can be largely predetermined (see, e.g., Weiss et al, J. Virol, 71, 4385-94 ( 1997); Zhou et al. Niicl Acid. Res., 19. 6052 (1991)). The PCR products then can be subcloned back into the template vector to replace the sequence within the fiber coding sequence employed as a source for the PCR reaction, thus generating a library of fibers, some of which will harbor mutations which diminish native AR binding while retaining the ability to trimerize. The amino acids of knobs from strains other than Ad5 that correspond to these listed residues are apparent upon a comparison between the sequences of the fibers of different adenoviral strains, and any suitable method of determining such correspondence can be employed (e.g.. Clusal method with PAM 100 residue weight table. J. Hain method with PAM 250 residue weight table, etc.). Examples of such sequence comparison of the knobs of Ad fiber proteins (SEQ ID NOs:5- 25) are set forth in Figures 1 A-2B. By such comparison, residues (e.g., conserved) from other serotypes which, mutated as described, result in fiber trimers with reduced AR binding can be identified (see. e.g.. SEQ ID NOs: 29-32). Thus, for example, for CAR-binding fibers, preferably, the amino acid(s) to be mutated is within 10 (e.g.. within about 5) amino acids or within about 10 nm (e.g.. within about 5 nm) of an amino acid corresponding to residues 404-406. 408, 409. 412-417. 420, 439. 441. 442, 449-454. 456. 458. 460. 462. 466. 467, 469-472, 474.477. 482. 485. 487-492. 505-512. 515. 517. 519. 521-528. 533. 535. 537-549, 551. 553. 555. 559-568. 580. or 581 of the native Ad5 fiber protein (SEQ ID NO: 1 ). More preferably, the amino acid(s) to be mutated correspond to at least one of these residues, such as amino acid 189. 190. 198. 201. or 262 of the native Ad9 fiber protein (SEQ ID NO:3) or amino acid 395. 396, 404. 407, or 470 of the native Ad41 long fiber protein (SEQ ID NO:2). Even more preferably, the mutant fiber protein comprises at least one replacement mutation of a residue corresponding to residues 408. 409, 412-417. 420. 477. or 487-491 of the native Ad5 fiber protein or at least one deletion mutation of a residue corresponding to residues 474-477 or 489-492 of the native Ad5 fiber protein. Similarly, for group B fibers, the amino acid(s) to be mutated is within 10 (e.g.. within about 5) amino acids or within about 10 nm (e.g.. within about 5 nm) of an amino acid corresponding to residues 136. 155. 177. 181. 198. 210. 21 1. 215. 233. 234. 236. 238. 248. 257. 260. 261, 276, 284. 302. 303. 317. or 318 of the native Ad3 fiber protein (SEQ ID NO:4). The recombinant fiber protein of the present invention can be produced by any suitable method. For example, the mutant fiber protein can be synthesized using standard direct peptide synthesizing techniques (e.g.. as summarized in Bodanszky. Principles of Peptide Synthesis (Springer- Verlag. Heidelberg: 1984)), such as via solid-phase synthesis (see, e.g.. Merrifield. J. Am. Chem. Soc, 85, 2149-54 (1963); and Barany et al. Int. J. Peptide Protein Res.. 30. 705-739 (1987)). Alternatively, site-specific mutations can be introduced into the recombinant fiber protein by ligating into an expression vector a synthesized oligonucleotide comprising the modified site. Alternatively, a plasmid. oligonucleotide. or other vector encoding the desired mutation can be recombined with the adenoviral genome or with an expression vector encoding the recombinant fiber protein to introduce the desired mutation. Oligonucleotide- directed site-specific mutagenesis procedures also are appropriate (e.g.. Walder et al. Gene, 42, 133 (1986): Bauer et al. Gene. 37. 73 (1985); Craik. Biotechniques, 12-19 ( 1995); U.S. Patents 4,518,584 (Mark et al.) and 4,737.462 (Mark et al.)). However engineered, the DNA fragment encoding the recombinant fiber protein can be subcloned into an appropriate vector using well known molecular genetic techniques. The fragment is then transcribed and the peptide subsequently translated in vitro within a host cell. Any appropriate expression vector (e.g.. Pouwels et al. Cloning Vectors: A Laboratory Manual (Elsevior. NY: 1985)) and corresponding suitable host cells can be employed for production of recombinant peptides. Expression hosts include, but are not limited to, bacterial species, yeast, mammalian or insect host cell systems including baculovirus systems (e.g.. Luckow et al. Bio/Technology, 6, Al ( 1988)). and established cell lines such HEK-293. COS-7. C127. 3T3. CHO. HeLa. BHK. etc. An especially preferred expression system for preparing modified fibers of the invention is a baculovirus expression system (Wickham et al, J. Virol, 70. 6831-38 (1995)) as it allows the production of high levels of recombinant proteins. Of course, the choice of expression host has ramifications for the type of peptide produced, primarily due to post-translational modification. Once produced, the recombinant fiber proteins are assayed for fiber protein activity. Specifically, the ability of recombinant fiber protein to form trimers, interact with the penton base, and interact with native substrate's (e.g., antibodies. ARs, opsonins. collectins. RES cells, etc.) is assayed. Any suitable assay can be employed to measure these parameters. For example, as improperly folded monomers are generally insoluble (Scopes. "Protein Purification " (3d Ed.. 1994). Chapter 9, p. 270-82 (Springer- Verlag. New York)), one assay for trimerization is whether the recombinant fiber is soluble. Determining solubility of the fiber is aided if an amount of radioactive amino-acid is incoφorated into the protein during synthesis. Lysate from the host cell expressing the recombinant fiber protein can be centrifuged. and the supernatant and pellet can be assayed via a scintillation counter or by Western analysis. Subsequently, the proteins within the pellet and the supernatant are separated (e.g.. on an SDS-PAGE gel) to isolate the fiber protein for further assay. Comparison of the amount of fiber protein isolated from the pellet vis-a-vis the fiber protein isolated from the supernatant indicates whether the mutant protein is soluble. Alternatively, trimerization can be assayed by using a monoclonal antibody recognizing only the amino portion of the trimeric form of the fiber (e.g.. via immunoprecipitation. Western blotting, etc.). Another measure of trimerization is the ability of the recombinant fiber to form a complex with the penton base (Novelli and Boulanger. Virology. 185. 1 189 (1995)), as only fiber trimers can so interact. This propensity can be assayed by co- immunoprecipitation, gel mobility-shift assays, SDS-PAGE (boiled samples migrate as monomers, otherwise, they migrate as larger proteins), etc. Yet another measure of trimerization is to detect the difference in molecular weight of a trimer as opposed to a monomer. For example, a boiled and denatured trimer will run as a lower molecular weight than a non-denatured stable trimer (Hong and Angler, J. Virol, 70. 7071-78 ( 1996)). A trimeric recombinant fiber also can be assayed for its ability to bind native substrates. For example, modification of fiber to interfere with its interaction with the host innate or acquired immune system can be accomplished by measuring the free titer of the virus over time. This can be assessed by measuring serum half life, tropism to organs associated with the RES (e.g.. liver in mice and humans, lung in pigs. etc.). by agglutination of red blood cells, or by detection of adenoviral genetic material in cell samples. A trimeric recombinant fiber also can be assayed for its ability to bind native ARs. Any suitable assay that can detect this characteristic is sufficient for use in the present invention. A preferred assay involves exposing cells expressing a native AR (e.g., HEK-293 cells) to the recombinant fiber trimers under standard conditions of infection. Subsequently, the cells are exposed to native adenoviruses. and the ability of the viruses to bind the cells is monitored. Monitoring can be by autoradiography (e.g.. employing radioactive viruses), immunocytochemistry, or by measuring the level of infection or gene delivery (e.g.. using a reporter gene). In contrast with native trimers which reduce or substantially eliminate subsequent viral binding to the HEK-293 cells, those trimers not substantially reducing the ability of native adenoviruses to subsequently bind the cells are trimers of the present invention. The reduction of interference with subsequent viral binding indicates that the trimer is itself not a ligand for its native mammalian AR. or at least binds with reduced affinity. Alternatively, a vector including a sequence encoding a mutated fiber (or a library of putative mutated fibers, such as described herein) can be introduced into a suitable host cell strain to express the fiber protein, and. mutants can be identified by assaying the inability to bind the soluble CAR protein (e.g., by probing a replica lift with radiolabeled CAR or by other suitable method). Because a reduction in CAR-binding could be due to either selective ablation of the ligand or structural modification affecting trimerization. mutant fibers identified as non-CAR binding by such a library screen must be assayed for the ability to trimerize, as described above. Virion and Virus The present invention provides an adenoviral virion incoφorating the recombinant fiber protein of the present invention. The virion does not interact with native substrates (e.g., innate and acquired immune systems, cell-surface proteins, etc.) as readily as the wild-type serotype. due to the above-mentioned reduction in affinity of the fibers present in the virion. Moreover, the virion can be further modified to reduce interaction with native substrates through the inclusion of other recombinant proteins. Thus, for example, the virion can include one or more recombinant penton base proteins lacking a native RGD sequence to reduce cell binding via α, integrins (see. e.g.. U.S. patents 5.559.099 (Wickham et al.) and 5,731.190 (Wickham et al.)). Similarly, the virion can include one or more recombinant hexons lacking a native sequence (e.g.. HVR) to reduce its ability to be recognized by a neutralizing antibody (see, e.g.. International Patent Application WO 98/40509 (Crystal et al.)). Also, the virion can be modified to reduce its ability to interact with the RES. For example, the virion proteins can be mutated to lack one or more glycosylation or phosphorylation sites, or it can be produced in the presence of inhibitors of glycosylation or phosphorylation. Similarly, the virion proteins can be conjugated to a lipid derivative of PEG comprising a primary amine group, an epoxy group, or a diacylclycerol group, as discussed above, to reduce collectin and/or opsonin affinity or scavenging by Kupffer cells or other cells of the RES. Such modifications reduce the ability of host animals to develop neutralizing antibodies to the virions. thereby permitting repeat administration of the virions. While the virion exhibits reduced affinity for natural adenoviral substrates, it can include one or more non-adenoviral ligands, for example, to effect targeted infection of a population of cells other than that for which adenoviruses are naturally tropic. Additionally, the non-native ligand can be used to purify the virus, to inactivate the virus (e.g.. by adsorbing it to a substrate for the ligand), or to grow the virus on cell lines having receptors recognizing the non-native ligand. for example, as described in International Patent Application WO 98/54346 (Wickham et al). The virus can include any suitable ligand (e.g.. a peptide specifically binding to a substrate). For example, for targeting the adenovirus to a cell type other than that naturally infected (or a group of cell types other than the natural range or set of host cells), the ligand can bind a cell surface binding site (e.g., any site present on the surface of a cell with which the adenovirus can interact to bind the cell and thereby promote cell entry). A cell surface binding site can be any suitable type of molecule, but typically is a protein (including a modified protein such as a glycoprotein. a mucoprotein. etc.). a carbohydrate, a proteoglycan, a lipid, a mucin molecule, or other similar molecule. Examples of potential cell surface binding sites include, but are not limited to. heparin and chondroitin sulfate moieties found on glycosaminoglycans; sialic acid moieties found on mucins. glycoproteins, and gangliosides; common carbohydrate molecules found in membrane glycoproteins, including mannose. N-acetyl-galactosamine. N-acetyl-glucosamine, fucose. and galactose; glycoproteins such cell adhesion molecules (CAMs) (e.g.. ICAM-1. ICAM-2. ICAM-3. VCAM-1 , NCAM). selectins (e.g.. E-selectin, P-selectin. L-selectin. etc.). CD. cadherins. TNF family receptors. GPI-linked receptors, receptors that are efficiently internalized (e.g.. CD44, CD31 on endothelial cells. CD34 on high endo-venules). endoglin, growth factor receptors. PSA. androgen receptors, glucocorticoid receptors, prostate- specific membrane antigen (PSMA), MUC1. MUC234. MUC5AC. MUC5B, MUC7. KSA carcino-embryonic antigen (CEA). HER2 NEU (erbB2). folate receptor, corionic gonadotropin-β, (Zhang et al. Clin. Cancer Res., 4. 2669-76 (1998): Cancer Res., 58. 4055 (1998)), and others are known in the art. A particular cell surface binding site can be present on a narrow class of cell types (e.g.. cardiac muscle, skeletal muscle, smooth muscle, etc.) or a broader group encompassing several cell types. Through integration of an appropriate cell- specific ligand, the virion can be employed to target any desired cell type, such as. for example, neuronal, glial. endothelial (e.g., via tissue factor receptor. FLT-1 , CD31 ; CD36; CD34, CD105. CD13, ICAM-1 (McCormick et al. J. Biol Chem., 273, 26323-29 (1998)); thrombomodulin receptor (Lupus et al, Suppl, 2, SI 20 (1998)); VEGFR-3 (Lymboussaki et al, Am. J. Pathol, 153(2), 395-403 (1998); mannose receptor; VCAM-1 (Schwarzacher et al, Atherocsclerosis, 122, 59-67 (1996)). or other receptors); blood clots (e.g.. through fibrinogen or allbb3 peptide), epithelial (e.g.. inflamed tissue through selectins. VCAM-1. ICAM-1. etc.). keratinocytes. follicular cells, adipocytes. fibroblasts. hematopoietic or other stem cells, myoblasts, myofibers, cardiomyocytes. smooth muscle, somatic, osteoclasts. osteoblasts. tooth blasts, chondrocytes. melanocytes. hematopoietic cells, etc.. as well as cancer cells derived from any of the above cell types (e.g.. prostate (such as via PSMA receptor (see. e.g.. Schuur et al, J. Biol Chem., 271, 7043 ( 1998); Cancer Res., 58. 4055 (1998))). breast, lung, brain (e.g.. glioblastoma). leukemia/lymphoma, liver, sarcoma, bone, colon, testicular, ovarian, bladder, throat, stomach, pancreas, rectum, skin (e.g.. melanoma), kidney, etc.). Thus, the inventive virions can be targeted to cells within any organ or system, including, for example, respiratory system (e.g., trachea, upper airways, lower airways, alveoli), nervous system and sensory organs (e.g., skin, ear, nasal, tongue, eye), digestive system (e.g.. oral epithelium and sensory organs, salivary glands, stomach, small intestines/duodenum, colon, gall bladder, pancreas, rectum), muscular system (e.g.. skeletal muscle, connective tissue, tendons), skeletal system (e.g., joints (synovial cells), osteoclasts. osteoblasts. etc.). immune system (e.g.. bone marrow, stem cells, spleen, thymus. lymphatic system, etc.). circulatory system (e.g., muscles connective tissue, and/or endothelia of the arteries, veins, capillaries, etc.). reproductive system (e.g.. testis. prostrate, uterus, ovaries), urinary system (e.g.. bladder, kidney, urethra), endocrine or exocrine glands (e.g.. breasts, adrenal glands, pituitary glands), etc. In other embodiments (e.g., to facilitate purification or propagation within a specific engineered cell type), the non-native ligand can bind a compound other than a cell-surface protein. Thus, the ligand can bind blood- and/or lymph-borne proteins (e.g., albumin), synthetic peptide sequences such as polyamino acids (e.g., polylysine, polyhistidine. etc.), artificial peptide sequences (e.g., FLAG), and RGD peptide fragments (Pasqualini et al, J. Cell. Biol, 130, 1 189 (1995)). The ligand can even bind non-peptide substrates, such as plastic (e.g.. Adey et al. Gene, 156, 27 ( 1995)). biotin (Saggio et al. Biochem. J, 293. 613 ( 1993)), a DNA sequence (Cheng et al. Gene. 171, 1 ( 1996): Krook et al. Biochem. Biophys.. Res. Commun.. 204. 849 ( 1994)). streptavidin (Geibel et al. Biochemistry. 34. 15430 (1995): Katz. Biochemistry, 34. 15421 (1995)). nitrostreptavidin (Balass et al, Anal Biochem., 243, 264 (1996)), heparin (Wickham et al. Nature Biotechnol, 14, 1570-73 (1996)), canonic supports, metals such as nickel and zinc (e.g., Rebar et al. Science, 263, 671 (1994); Qui et al. Biochemistry, 33, 8319 (1994)), or other potential substrates. Examples of suitable ligands and their substrates for use in the method of the invention include, but are not limited to. CR2 receptor binding the amino acid residue attachment sequences. CD4 receptor recognizing the V3 loop of HIV gpl20. transferrin receptor and its ligand (transferrin). low density lipoprotein receptor and its ligand. the ICAM-1 receptor on epithelial and endothelial cells in lung and its ligand. linear or cyclic peptide ligands for streptavidin or nitrostreptavidin (Katz. Biochemistry, 34. 15421 (1995)). galactin sequences that bind lactose, galactose and other galactose-containing compounds, and asialoglycoproteins that recognize deglycosylated protein ligands. Moreover, additional ligands and their binding sites preferably include (but are not limited to) short (e.g., 6 amino acids or less) linear stretches of amino acids recognized by integrins. as well as polyamino acid sequences such as polylysine. polyarginine. etc. Inserting multiple lysines and/or arginines provides for recognition of heparin and DNA. Also, a ligand can comprise a commonly employed peptide tag (e.g., short amino acid sequences known to be recognized by available antisera) such as sequences from glutathione-S-transferase (GST) from Shistosoma manosi, thioredoxin β-galactosidase, or maltose binding protein (MPB) from E. coli., human alkaline phosphatase. the FLAG octapeptide. hemagluttinin (HA) (Wickham et al. (1996), supra), polyoma virus peptides. the SV40 large T antigen peptide. BPV peptides. the hepatitis C virus core and envelope Ε2 peptides and single chain antibodies recognizing them (Chan. J. Gen. Virol. 77. 2531 (1996)), the c-myc peptide. adenoviral penton base epitopes (Stuart et al. EMBO J, 16, 1 189-98 (1997)). epitopes present in the E2 envelope of the hepatitis C virus (see. e.g.. Chan et al. (1996), supra), and other commonly employed tags. A preferred substrate for a tag ligand is an antibody directed against it or a derivative of such an antibody (e.g.. a FAB fragment, single chain antibody (ScAb)). As mentioned, a suitable ligand can be specific for any desired substrate. such as those recited herein or otherwise known in the art. However, adenoviral vectors also can be engineered to include novel ligands (e.g., in protein II. Ill, Ilia. IV. IV. VI, and/or IX) by first assaying for the ability of a peptide to interact with a given substrate. Generally, a random or semirandom peptide library containing potential ligands can be produced, which is essentially a library within an expression vector system. Such a library can be screened by exposing the expressed proteins (i.e., the putative ligands) to a desired substrate. Positive selective binding of a species within the library to the substrate indicates a ligand for that substrate, at least under the conditions of the assay. For screening such a peptide library, any assay able to detect interactions between proteins and substrates is appropriate, and many are known in the art. However, one preferred assay for screening a protein library is a display system (e.g.. using an adenovirus or a bacteriophage). which employs a virus expressing the library (e.g.. Koivunen et al, Bio/Technology, 13. 265-70 (1995): Yanofsky et al. Proc. Nat. Acad. Sci. U.S.A., 93, 7381 -86 ( 1996); Barry et al. Nature Med., 2(3). 299-305 (1996)). Binding of the virus to the substrate is assayed by exposing the virus to the substrate, rinsing the substrate, and selecting for virus remaining bound to the substrate. Subsequently, limiting dilution can identify individual clones expressing the putative ligand. Thereafter, the insert present in such clones can be sequenced to determine the identity of the ligand. Once a given ligand is identified, it can be incoφorated into any location of the virus capable of interacting with a substrate (i.e.. the viral surface). For example, the ligand can be incoφorated into the fiber, the penton base, the hexon, protein IX. VI, or Ilia, or other suitable location. Where the ligand is attached to the fiber protein, preferably it does not disturb the interaction between viral proteins or monomers. Thus, the ligand preferably is not itself an oligomerization domain, as such can adversely interact with the trimerization domain as discussed above. Preferably the ligand is added to the virion protein, and is incoφorated in such a manner as to be readily exposed to the substrate (e.g.. at the terminus of the protein, attached to a residue facing the substrate, positioned on a peptide spacer to contact the substrate, etc.) to maximally present the ligand to the substrate. Where the ligand is attached to or replaces a portion of the penton base, preferably it is within the hypervariable regions to ensure that it contacts the substrate. Furthermore, where the ligand is attached to the penton base, preferably, the recombinant fiber is truncated or short (e.g., from 0 to about 10 shaft repeats) to maximally present the ligand to the substrate (see, e.g., U.S. Patent 5.559.099 (Wickham et al)). Where the ligand is attached to the hexon, preferably it is within a hypervariable region (Miksza et al. J. Virol. 70(3), 1836-44 (1996)). When engineered into an adenoviral protein, the ligand can comprise a portion of the native sequence in part and a portion of the non-native sequence in part. Similarly, the sequences (either native and/or nonnative) that comprise the ligand in the protein need not necessarily be contiguous in the chain of amino acids that comprise the protein. In other words, the ligand can be generated by the particular conformation of the protein, e.g.. through folding of the protein in such a way as to bring contiguous and/or noncontiguous sequences into mutual proximity. Of course an adenovirus of the present invention (or a blocking protein) can comprise multiple ligands. each binding to a different substrate. For example, a virus can comprise a first ligand permitting affinity purification as described herein, a second ligand that selectively binds a cell-surface site as described herein, and/or a third ligand for inactivating the virus, also as described herein. The protein including the ligand can include other non-native elements as well. For example, a non-native, unique protease site also can be inserted into the amino acid sequence. The protease site preferably does not affect fiber trimerization or substrate specificity of the fiber ligand. Many such protease sites are known in the art. For example, thrombin recognizes and cleaves at a known amino acid sequence (Stenflo et al. J. Biol. Chem., 257, 12280-90 ( 1982)). The presence of such a protease recognition sequence facilitates purification of the virus in some protocols. The protein can be engineered to include the ligand by any suitable method, such as those methods described above for introducing mutations into proteins. The virion can be used by itself, for example in studies of viral tropism or binding kinetics. In other embodiments, the virion can be used as a genetic vector. For example, the virion can be used in conjunction with lipids and/or liposomes to deliver exogenous genetic material to target cells, in accordance with well- documented methods. In other embodiments, the virion contains a genome derived from an adenovirus: thus, the invention provides an adenoviral vector including the inventive virion and an adenoviral genome. The adenoviral vector of the present invention can include one or more non-native amino acid sequences for expression (e.g.. "expression cassettes " or "genes") as well. Preferably, the non-native amino acid is capable of being transcribed in a cell into which the vector has been internalized. The non-native amino acid can encode a product that effects a biological (e.g.. therapeutic) response either at the cellular level or systemically) alternatively, the non-native nucleic acid sequence can encode a product that, in some fashion, can be detected in a cell (e.g.. a "reporter gene " ). The non-native amino acid can exert its effect at the level of RNA or protein. For instance, a protein encoded by the non-native amino acid can be employed in the treatment of an inherited disease, such as. e.g.. the cystic fibrosis transmembrane conductance regulator cDNA for the treatment of cystic fibrosis. Alternatively, the protein encoded by the non-native amino acid can exert its therapeutic effect by effecting cell death. For instance, expression of the non-native amino acid in itself can lead to cell killing, as with expression of the diphtheria toxin. Alternatively, the expression of the non-native amino acid, can render cells selectively sensitive to the action of certain drugs, e.g., expression of the HSV thymidine kinase gene renders cells sensitive to antiviral compounds including acyclovir, gancyclovir, and FIAU (l-(2-deoxy-2-fluoro-β-D- arabinofuranosil)-5-iodouracil). Moreover, the non-native amino acid can exert its effect at the level of RNA. for instance, by encoding an antisense message or ribozyme. a protein which affects splicing or 3 " processing (e.g.. polyadenylation). or a protein affecting the level of expression of another gene within the cell (i.e.. where gene expression is broadly considered to include all steps from initiation of transcription through production of a processed protein), perhaps, among other things, bv mediating an altered rate of mRNA accumulation, an alteration of mRNA transport, and/or a change in post-transcriptional regulation. Of course, where it is desired to employ gene transfer technology to deliver a given non- native amino acid, its sequence will be known in the art. Where the inventive adenoviral vector includes a non-native amino acid and a non-adenoviral ligand in its virion. the non-native amino acid can be operably linked to any suitable promoter, such as a promoter native to the adenoviral genome or a non- adenoviral promoter. Where the ligand is employed to deliver the vector to a desired cell type, preferably the non-adenoviral promoter is active within the cell type, and more preferably, the non-adenoviral promoter is a tissue-specific promoter (e.g.. specific for the cell type to which the ligand binds), such as those cell types discussed above. For example, expression in targeted endothelial cells can be mediated using the E-selectin promoter (see. e.g.. Whelan et al. TIBS, 21. 65-69 ( 1996)); passenger gene expression in targeted prostate cancer cells can be mediated using the PSA promoter (see. e.g.. Schuur et al. J. Cell Biol, 271, 7043 (1996). Pang et α/.. Cancer Res., 57. 495 ( 1997)) or the E2F promoter. Furthermore, the promoter can be that for a tissue-specific receptor, such as those receptors mentioned herein, still other tissue specific promoter systems are known in the art. Alternatively, the non-native amino acid can be placed under control of a regulable promoter (e.g.. metallothionein promoter, tetracycline-responsive promoter. RU486-responsive promoter, etc.). The altered protein (e.g.. the recombinant fiber protein or the coat protein having the ligand) and the non-native amino acid where present) can be incorporated into the adenovirus by any suitable method, many of which are known in the art. As mentioned herein, the protein is preferably identified assaying products produced in high volume from genes within expression vectors (e.g.. baculovirus vectors). The genes from the vectors harboring the desired mutation can be readily subcloned into plasmids, which are then transfected into suitable packaging cells (e.g., HEK-293 cells). Transfected cells are then incubated with adenoviruses under conditions suitable for infection. At some frequency within the cells, homologous recombination between the vector and the virus will produce an adenoviral genome harboring the desired mutation. Adenoviruses of the present invention can be either replication competent or replication deficient. Preferably, the adenoviral vector comprises a genome with at least one modification therein, rendering the virus replication deficient (see. e.g.. International Patent Application WO 95/34671 (Kovesdi et al)). The modification to the adenoviral genome includes, but is not limited to. addition of a DNA segment, rearrangement of a DNA segment, deletion of a DNA segment. replacement of a DNA segment, or introduction of a DNA lesion. A DNA segment can be as small as one nucleotide and as large as the adenoviral genome (e.g.. about 36 kb) or. alternately, can equal the maximum amount which can be packaged into an adenoviral virion (i.e.. about 38 kb). Preferred modifications to the adenoviral genome include modifications in the El . E2. E3. and/or E4 regions. An adenovirus also preferably can be a cointegrate. i.e., a ligation of adenoviral genomic sequences with other sequences, such as other virus, phage. or plasmid sequences. The virion and adenoviral vector of the present invention have many qualities which render them attractive choices for use in gene transfer, as well as other, applications. For example, in many embodiments, the adenovirus does not infect its native host cells as readily as does wild-type adenovirus. due to the recombinant fiber protein. Moreover, by virtue of additional modifications, such virions and vectors are less readily cleared from the host by the innate or acquired immune responses, thus boosting effective free titer and lengthening serum half- life. Furthermore, the virions and vectors have at least one non-native ligand specific for a substrate which facilitates viral propagation, targeting, purification, and/or inactivation as discussed herein. The presence of such ligands can effectively confine expression of non-native amino acids within a predefined cell type or tissue. Linking the non-native amino acid to a tissue-specific or regulable promoter further minimizes expression of the non-native amino acid outside of the targeted tissue. The ligands and the trimerization domains can be separate domains, thus permitting the virus to be easily be reengineered to incoφorate different ligands without perturbing fiber trimerization. Of course, for delivery into a host (such as an animal), a virus of the present invention can be incoφorated into a suitable carrier. As such, the present invention provides a composition comprising an adenovirus of the present invention and a pharmacologically acceptable carrier (e.g.. a pharmaceutically- acceptable carrier). Any suitable preparation is within the scope of the invention. The exact formulation, of course, depends on the nature of the desired application (e.g.. cell type, mode of administration, etc.). and many suitable preparations are set forth in U.S. Patent 5.559.099 (Wickham et al). Cell Line As mentioned herein, an adenovirus of the present invention does not readily infect its native host cell via the native AR because its ability to bind ARs is significantly attenuated (due to the incoφoration of the recombinant fiber protein of the present invention). Therefore, the invention provides a cell line able to propagate the inventive adenovirus. Preferably, the cell line can support viral growth for at least about 10 passages (e.g., about 15 passages), and more preferably for at least about 20 passages (e.g.. about 25 passages), or even 30 or more passages. For example, the adenoviruses can be first grown in a packaging cell line which expresses a native fiber protein gene. The resultant viral particles are therefore likely to contain both native fibers encoded by the complementing cell line and non-native fibers encoded by the adenoviral genome (such as those fibers described herein): hence a population of such resultant viruses will contain both fiber types. Such particles will be able to bind and enter packaging cell lines via the native fiber more efficiently than particles which lack native fiber molecules. Thus, the employment of such a fiber-encoding cell line permits adenovirus genomes encoding chimeric. targeted adenovirus fibers to be grown and amplified to suitably high titers. The resultant "mixed " stocks of adenovirus produced from the cell lines encoding the native fiber molecule will contain both native and chimeric adenovirus fiber molecules; however, the particles contain genomes encoding only the chimeric adenovirus fiber. Thus, to produce a pure stock of adenoviruses having only the chimeric adenovirus fiber molecules, the "mixed" stock is used to infect a packaging cell line which does not produce native fiber (such as HEK-293 for El -deleted non-group B viruses). The resultant adenoviruses contain only the fiber molecules encoded by the genomes (i.e., the chimeric fiber molecules). Similar fiber-complementing cell lines have been produced and used to grow mutant adenovirus lacking the fiber gene). However, the production rates of these cell lines have generally not been great enough to produce adenovirus titers of the fiber-deleted adenovirus comparable to those of fiber-expressing adenovirus particles. The lower titers produced by such mutants can be improved by temporally regulating the expression of the native fiber to more fully complement the mutant adenovirus genome. One strategy to produce such an improved cell line is to use of a regulable promoter to permit fiber production to be controlled and activated once the cells are infected with adenovirus. Alternatively, an efficient mRNA splice site introduced into the fiber gene in the complementing cell line improves the level of fiber protein production in the cell line. When the adenovirus is engineered to contain a ligand specific for a given cell surface binding site, any cell line expressing that receptor and capable of supporting adenoviral growth is a suitable host cell line. However, because many ligands do not bind cell surface binding sites (especially some of the novel ligands discussed herein), a cell line can be engineered to express the substrate for the ligand. The present invention provides a cell line expressing a non-native cell- surface receptor (a pseudo-receptor) to which a virus having a ligand for said receptor binds. Any cell line capable of supporting viral growth is a suitable cell line for use in the present invention. If the virus lacks genes essential for viral replication, preferably the cell line expresses complementing levels of such gene products (see, e.g., International Patent Application WO 95/34671 (Kovesdi et al.). U.S. Patents 5.658,724 (DeLuca) and 5.804,413 (DeLuca)). When the virus is an adenovirus, preferably the cell line of the present invention is derived from HEK- 293 cells. When the virus is a heφesvirus. preferably the cell line of the present invention is derived from VERO cells. The non-native cell surface binding site is a substrate molecule, such as described herein, to which an adenovirus having a ligand selectively binding that substrate can bind the cell and thereby promote cell entry. The binding site can recognize a non-native ligand incoφorated into the adenoviral coat or a ligand native to a virus. For example, when the non-native viral ligand is a tag peptide. the binding site can be a single chain antibody (ScAb) receptor recognizing the tag. Alternatively, the ScAb can recognize an epitope present in a region of a mutated fiber knob (if present), or even an epitope present on a native adenoviral coat protein, (e.g., on the fiber, penton. hexon. etc.). Alternatively, if the non- native ligand recognizes a cell-surface substrate (e.g.. membrane-bound protein), the binding site can comprise that substrate. If the substrate binding site is native to a cell-surface receptor, the cell line can express a mutant receptor with decreased ability to interact with the cellular signal transduction pathway (e.g.. a truncated receptor, such as NMDA (Li et al. Nat. Biotech.. 14, 989 ( 1996))). attenuated ability to act as an ion channel, or other modification. Infection via such modified proteins minimizes the secondary effects of viral infection on host- cell metabolism by reducing the activation of intracellular messaging pathways and their various response elements. The choice of binding site depends to a large extent on the nature of the adenovirus. However, to promote specificity of the virus for a particular cell type, the binding site preferably is not a native mammalian AR. Moreover, the binding site must be expressed on the surface of the cell to be accessible to the virus. Hence, where the binding site is a protein, it preferably has a leader sequence and a membrane tethering sequence to promote proper integration into the membrane (see. e.g.. Davitz et al, J. Exp. Med. 163, 1 150 (1986)). The cell line can be produced by any suitable method. For example, a vector (e.g.. an oligonucleotide, plasmid. viral, or other vector) containing a nucleic acid encoding the non-native receptor can be introduced into source cell line by conventional means. Preferably, the vector also encodes an agent permitting the cells harboring it to be selected (e.g.. the vector can encode resistance to antibiotics which kill cells not harboring the plasmid). At some frequency, the vector will recombine with the cell genome to produce a transformed cell line expressing the non-native receptor. EXAMPLES While it is believed that one of skill in the art is fully able to practice the invention after reading the foregoing description, the following examples further illustrate some of its features. In particular, the examples demonstrate the construction of several recombinant fiber proteins, each exhibiting reduced affinity for native adenoviral substrates. The examples further demonstrate the inclusion of such recombinant fiber proteins into adenoviral vectors, and the retargeting of such vectors using non-native ligands. The examples also demonstrate the successful construction of a pseudoreceptor cell line able to propagate the alternatively targeted viruses. As these examples are included for purely illustrative puφoses. they should not be construed to limit the scope of the invention in any respect. The procedures employed in these examples, such as affinity chromatography. Southern blots. PCR. DNA sequencing, vector construction (including DNA extraction, isolation, restriction digestion, ligation. etc.). cell culture (including antibiotic selection), transfection of cells, protein assays (Western blotting, immunoprecipitation, immunofluorescence). etc., are techniques routinely performed by those of skill in the art (see generally Sambrook et al. Molecular Cloning, A Laboratory Manual. Cold Spring Harbor Laboratory. Cold Spring Harbor. NY ( 1989)). Accordingly, in the interest of brevity, experimental protocols are not discussed in detail. EXAMPLE 1 This example describes mutant fiber trimers exhibiting reduced affinity for the CAR protein. Using standard site-directed mutagenesis. mutations were introduced into nearly every major sheet and loop in the native Ad5 fiber knob sequence (SEQ ID NO: l ). In a first series of mutagenesis, replacement mutations were designed in which between 3 and 6 contiguous amino acids within a loop were replaced by the same number of glycine residues. In a second series of mutagenesis. mutations were designed in which between 1 and 4 amino acids were deleted from the native sequence. Extensive point mutations also were conducted. One additional mutant was designed in which 12 amino acids were deleted and replaced with a tetrapeptide sequence. Respective baculovirus clones, each containing one of the recombinant mutant protein genes, were created and used to produce recombinant mutant knob proteins in insect cells. The baculovirus-infected insect cells were freeze-thawed at 3 days post-infection to release any soluble recombinant mutant protein (approximately 10 7 cells per ml of PBS). The freeze-thawed lysate was centrifuged and the soluble fraction and the insoluble pellet were collected. Western analysis of the soluble and insoluble fractions revealed that similar levels of the mutant and native fiber knobs were present in the soluble fraction. Mutants which retained solubility represent proteins which folded properly and trimerized. and these are set forth in Table 1. In the table, mutations are indicated by noting the location of the mutated residue or residues of the Ad5 fiber within parentheses. The identity of the native residue or residues is set forth to the left, and the identity of any substituting residue or residues is to the right of the parentheses. Deletions are further delineated using the "Δ " symbol. Table 1 Mutation Location Mutations AB Loop (403-418) T(404)G RLN(412-414)GGG P(405)G N(414)G A(406)K A(415)G S(408)E RLN AEK(415-417)SLNGGG S(408)G E(416)G P(409)A K(417)G R(412)G K(417)L B Sheet (419-428) K(420)A C Sheet (431 -440) L(439)S CD Loop (441 -453) V(441 )S SGTVQ(449-453)GSGSG ΔSG(449-450) D Sheet (454-461 ) S(454)N + R(460)Q 1(458)E + R(460)E H(456)E + R(460)E DE Loop (462-478 ) D(462)A DPE(474-476)GGG V(466)S DPEY(474-477)GGGG L(467)S Y(477)A NNS(469-471 )GGG Y(477)T ΔF(472) E Sheet (479-482) N(482)A F Sheet (485-486) L(485)G FG Loop (487-514) E(487)G P(505)G T(489)G ΔK(506) A(490)G H(506)A EGTAY(487-491 )GGGGG ΔKT(510-51 1 ) Y(491 )A SHGKTA(507-512)GSGSGS ΔTAYT(489-492) G Sheet (515-521 ) N(515)S + V(517)S Y(521 )H V(517)S + Q(519)S GH Loop (522-528) NGDKT(523-527)GSGSG K(526)E D(525)K K(528)S KTK(526-528)RSR H Sheet (528-536) T(535)E T(533)S + T(535)S HI Loop (537-549) N(537)E GTQETGDTTPSA(538- 549)GSGG I Sheet (550-557) S(551 )N + S(555)N S(553)E S(551 )E IJ Loop (558-572) SGHN(559-562)GSGS 1NE1(564-567)GSGS ΔHN(561 -562) E(566)K Y(563)H F(568)H C-Terminus (573-578) Q(580)G E(581 )G To determine whether a given mutant fiber had reduced affinity for CAR, competition experiments were performed by preincubating A549 cells with either the trimeric mutants or native fiber knobs followed by incubation with radiolabeled Ad5 virus. Either 1 or 10 μl volumes of the native knob preincubated with A549 cells blocked 90% or more of the labeled Ad5 binding to cells measured in the absence of a competitor. In this assay, any soluble, trimeric mutant less efficient in blocking fiber-mediated Ad5 cell binding or gene transduction than the native knob was considered to have reduced affinity for CAR. Those trimeric mutant fibers exhibiting reduced affinity for CAR in this assay are indicated in Table 2. The trimeric mutant fiber proteins were mass produced by infecting roughly 15 million insect cells each with the baculoviral vectors (MOI = 10) and culturing them for 3 days. The cells were harvested and freeze-thawed. and the cell debris was removed via centrifugation. NaCl was added to the supernatant to a final concentration of 750 ml. and then the supernatant was added to 500 μl TALON 7 " resin. After one hour at 25 °C. the resin was centrifuged at 2.500 for two minutes. The supernatant was removed, and the resin resuspended in 10 ml 750 mM NaCl. After 30 minutes incubation, the resin suspension was run through a column. The mutant protein was eluted using 2 ml of elution fluid (20 mM TRIS, pH 8.0, 100 mM NaCl, 150 mM imidazole). The eluate was dialized once against PBS with 750 mM NaCl. once against PBS with 500 mM NaCl. and once against PBS with 250 mM NaCl. Protein concentration was determined by standard methods and protein integrity verified by Western analysis. The purified proteins were subjected to a competition assay with Ad5 capsids to assess the degree to which each mutation decreased interaction with CAR. Serial dilutions of each mutant protein, as well as wild-type Ad5 fiber, were added to A549 cells (10 3 cells/well) in 24-well plates. Following this preincubation. an Ad5 vector containing the lacZ gene were added to each well (MOI = 10). After a one hour incubation at 37 °C. the inoculum was removed, the cells were washed with culture medium, and then and a culture medium (DMEM with 5 % FCS) added. The cells were incubated overnight, lysed 18 hours post infection, and assayed for β-galactosidase activity by standard methods. Plotting the degree of β-galactosidase activity against concentration of preincubation protein permitted assessment of each protein ' s IC, 0 value (the concentration of the competing protein at the 50% level). The degree to which each mutation reduced CAR-binding as calculated by this method is set forth in Table 2. Table 2 EXAMPLE 2 This example describes recombinant fiber proteins exhibiting reduced affinity for the CAR protein. The Ad9 and long Ad41 fiber proteins corresponding to mutations Ad5-1 , Ad5-2. Ad5-4, Ad5-5. and Ad5-9 (see Figures 1 A and IB) were generated. The resultant mutant proteins were soluble, and each was used in competition assays against wild type Ad5. as described in Example 1. to assess whether the mutations affected CAR binding. The results of these experiments (presented in Table 3) reveal that residues important for CAR binding are conserved among adenoviral serotypes. Table 3 EXAMPLE 3 This example describes the production of a pseudo-receptor for constructing a cell line able to replicate adenoviruses lacking native cell-binding function (but targeted for the pseudo-receptor). Specifically, the exemplary pseudo-receptor includes a binding domain from a single-chain antibody recognizing HA. Anti-HA ScFv was constructed as an N-l erm-VL-VH fusion protein. RT- PCR was performed on RNA obtained from hybridomas producing FIA antibodies using primers specific for K- or γ2β- and C-terminus of the VL and VH genes (see Gilliland et al, Tissue Antigens, 47, 1-20 (1996)). After sequencing the resulting PCR products, specific ohgonucleotides were designed to amplify the VL-VH fusion in a second round of PCR. The final PCR product was cloned to create a plasmid for production of anti-HA ScFv in E. coli. The expressed protein has a C- terminal E peptide for detection of binding to HA-tagged penton base via Western analysis of ELISA assay. Upon transformation of bacterial cells with the plasmid. Western analysis using an antibody recognizing the E peptide revealed a protein of the expected size. To determine whether the anti-HA ScFv was functional, it was used in protein A immunoprecipitation assays using adenoviral coat proteins (recombinant penton base) containing the HA epitope. The anti-HA ScFv was able to precipitate HA-containing penton base proteins. These results indicate the successful construction of the extracellular portion of a pseudo-receptor for binding an adenovirus having a non-native ligand (i.e.. HA). To create an entire anti-HA pseudo-receptor, the anti-HA ScFv was cloned in frame with sequences encoding a C-terminal pair of myc epitopes followed by the PDGF receptor transmembrane anchor. The entire sequence of this pseudo- receptor is indicated at SEQ ID NO:28. A eukaryotic expression plasmid containing this sequence, pSc(HA). was transfected into HEK-293 cells. The following day the pSc(HA)-transfected cells or cells transfected with a control ScFv construct were incubated for 30 min on ice with a fluoroscein-tagged HA peptide (HA*) or with a fluoroscein-tagged scrambled HA peptide (scrHA*). Following the incubation of HA* with the pSc(HA)-transfected cells, a discrete population of cells was found to brightly fluoresce specifically around the cell membrane. The pSc(HA)-transfected cells incubated with the scrHA* peptide did not display this fluorescent pattern, nor did the cells transfected with the control plasmid and then incubated with HA*. Enhanced fluorescence of the pSc(HA)- transfected cells incubated with HA* was also demonstrated by FACS analysis. Moreover, preincubation of the anti-HA pseudo-receptor cells with excess unlabelled HA peptide, but not unlabelled FLAG peptide, blocked the fluorescent pattern observed on cells incubated with HA* alone. These results demonstrate the successful construction and expression of a cell line consisting essentially of cells expressing a functional pseudo-receptor. EXAMPLE 4 This example describes an alternatively targeted adenovirus having recombinant fiber proteins exhibiting reduced affinity for the CAR protein and having a non-native ligand. The Ad5-10 mutant described in Example 1 was subjected to further site directed mutagenesis to introduce a polypeptide including the HA epitope into the HI loop of the fiber knob (between amino acids 543 and 544 of SEQ ID NO: l) . The resultant fiber has the TAYT deletion in the FG loop and an HA epitope sequence inserted into the HI loop. The gene encoding this mutant fiber was combined into a plasmid that contains a full length, El - and E3-deleted adenovirus genome carrying the above fiber mutation plus a CMV-driven LacZ reporter gene in the El region. This plasmid was then linearized and transfected into HEK-293 cells expressing the anti-HA pseudo-receptor described in Example 3. After 5 days the cells were freeze-thawed three times, and the virus-containing lysate was passaged onto fresh anti-HA-293 cells. The resultant adenoviruses were further amplified in the anti-HA-293 cells and then purified using standard methods. The vector (AdZ.F*fg(HA)hi) exhibits reduced binding capacity to CAR on standard HEK-293 cells due to the TAYT deletion; however, it binds with high affinity via its HA epitope to the anti-HA pseudoreceptor present on the anti-HA-293 cell line. EXAMPLE 5 This example describes an alternatively targeted adenovirus having recombinant fiber proteins exhibiting reduced affinity for the CAR protein and having more than one non-native ligand. The Ad5-10 mutant described in Example 1 was subjected to further site directed mutagenesis to introduce a polypeptide including the HA epitope and a high affinity RGD ligand into the HI loop of the fiber knob (between amino acids 543 and 544 of SEQ ID NO: 1 ) . The resultant plasmid encodes a fiber with the TAYT deletion in the FG loop and an RGD sequence inserted into the HI loop. The gene encoding this mutant fiber gene was then combined into a plasmid that contains a full length. El and E3-deleted adenovirus genome carrying the above fiber mutation plus a CMV-driven LacZ reporter gene in the El region. This plasmid was then linearized and transfected into HEK-293 cells expressing the anti-HA pseudo-receptor described in Example 2. After 5 days the cells are freeze-thawed three times and the virus-containing lysate is passaged onto fresh HEK-293 cells. The resultant adenoviruses were further amplified in the anti-HA-293 cells and then purified using standard methods. The vector exhibits reduced binding capacity to CAR on standard HEK-293 cells due to the TAYT deletion; however, it efficiently infects cells expressing α N integrins (such as tumor cells) via the RGD ligand present in the HI loop. EXAMPLE 6 This example describes an alternatively targeted adenovirus having recombinant fiber proteins exhibiting reduced affinity for the CAR protein and having a non-native ligand. The Ad5-3 mutant described in Example 1 was subjected to further site directed mutagenesis to introduce an 18 amino acid polypeptide including the HA epitope into the HI loop of the fiber knob (between amino acids 543 and 544 of SEQ ID NO: l ) . The resultant fiber has the RLNAEK mutation of the AB loop and an HA epitope sequence inserted into the HI loop. The gene encoding this mutant fiber was combined into a plasmid that contains a full length. El- and E3-deleted adenovirus genome carrying the above fiber mutation plus a CMV-driven LacZ reporter gene in the El region. This plasmid was then linearized and transfected into HEK-293 cells expressing the anti-HA pseudo-receptor described in Example 3. After 5 days the cells were freeze-thawed three times, and the virus-containing lysate was passaged onto fresh anti-HA 293 cells. The resultant adenoviruses were further amplified in the anti-HA 293 cells and then purified using standard methods. The vector (AdZ.F*ab(HA)hi) exhibits reduced binding capacity to CAR on standard HEK-293 cells due to the RLNAEK mutation: however, it binds with high affinity via its HA epitope to the anti-HA pseudoreceptor present on the anti-HA 293 cell line. EXAMPLE 7 This example describes an alternatively targeted adenovirus having recombinant fiber proteins exhibiting reduced affinity for the CAR protein and having more than one non-native ligand. The Ad5-3 mutant described in Example 1 was subjected to further site directed mutagenesis to introduce a polypeptide including the HA epitope and a high affinity RGD ligand into the HI loop of the fiber knob (between amino acids 543 and 544 of SEQ ID NO: 1 ) . The resultant plasmid encodes a fiber with the RLNAEK mutation of the AB loop and an HA epitope and RGD sequence inserted into the HI loop. The gene encoding this mutant fiber gene was then combined into a plasmid that contains a full length. El - and E3-deleted adenovirus genome carrying the above fiber mutation plus a CMV-driven LacZ reporter gene in the El region. This plasmid was then linearized and transfected into HEK-293 cells expressing the anti-HA pseudo-receptor described in Example 3. After 5 days the cells are freeze-thawed three times, and the virus-containing lysate was passaged onto fresh anti-HA 293 cells. The resultant adenoviruses were further amplified in the anti-HA 293 cells and then purified using standard methods. The vector exhibits reduced binding capacity to CAR on standard HEK-293 cells due to the RLNAEK mutation; however, it binds with high affinity via its HA epitope to the anti-HA pseudoreceptor present on the anti-HA 293 cell line. Moreover, the virus also efficiently infects cells expressing α, integrins (such as tumor cells) via the RGD ligand present in the HI loop. EXAMPLE 8 This example describes an alternatively targeted adenovirus having recombinant fiber proteins exhibiting reduced affinity for the CAR protein and having a non-native ligand. A mutation was introduced into the Ad2 fiber knob, deleting the Asn-Pro residues in the FG loop (residues 90 and 91 of SEQ ID NO:7). Additionally, the high-affinity RGD motif was introduced into the HI loop of this protein. The sequences encoding the knob domain were fused to sequences encoding the Ad5 shaft, resulting in a nucleic acid encoding a chimeric Ad5-Ad2 fiber. This construct was cloned into an Ad5 genome also containing the lacZ gene ( the Adz virus), replacing the native fiber sequence. The resultant viruses are termed AdZ.F*(RGD). Increasing particle doses of either AdZ or AdZ.F*(RGD) were incubated with either SKOV-3 cells (which express both CAR and α, integrins) or Ramos cells (which express CAR but not α x integrins) in suspension (10 6 cells/300 μl medium) for one hour at 36 °C, following which the cells were washed and incubated overnight. Following the incubation, the cells were assayed for lacZ activity using conventional methods. The SKOV-3 cells were transduced by both viruses, while the Ramos cells were transuded by AdZ. but only poorly transduced by AdZ.F*(RGD). These results demonstrate that the native CAR-binding ability of the vector can be blocked by mutating selective residues of the fiber knob and the virus retarded by the addition of a non-native ligand to the viral coat protein. EXAMPLE 9 This example demonstrated the reduced affinity for the CAR protein of recombinant fiber proteins. Various cell types (A172. HuVEC. HCAEC, A549. HeLa. HEK-293. and HS68) (10 6 cells/300 μl medium) were preincubated for 30 minutes at 37 °C with either soluble Ad5 fiber protein (3μg/ml) or penton base protein (100 μg/ml). Following this incubation, either AdZ. AdZ.F*ab(HA)hi or AdZ.F*fg(HA)hi ( 100 viral particles/cell) were added to the cells. After a one hour incubation at 37 °C. the cells were twice washed and incubated overnight, again at 37 °C. Following the incubation, the cells were assayed for lacZ activity using conventional methods. Except for the HS68 fibroblast cell line, the results indicate that preincubation with Ad5 fiber blocked AdZ transduction, but preincubation with penton base did not. In contrast, the viruses containing the mutant fibers were not blocked by preincubation with fiber, but were blocked by preincubation with penton base. These data are consistent with the ablation of native fiber-based infection through mutating the fibers as indicated. EXAMPLE 10 This example demonstrated the alteration of viral targeting in vivo, using an alternatively targeted adenovirus. The jugular veins of Balb/C mice were injected with either AdZ, AdZ.F*ab(HA)hi or AdZ.F*fg(HA)hi ( 10 10 particles/animal in 100 ml. eight animals each). The experiments were run in duplicate, and two animals served as a control ( 100 ml saline). At one day post inoculation, the animals were sacrificed and the liver of each was snap-frozen in liquid nitrogen. The livers were then pulverized, and lacZ activity was assayed by conventional methods to determine enzymatic activity/mass of tissue. The livers from the AdZ.F*ab(HA)hi- or AdZ.F*fg(FIA)hi-inoculated animals exhibited about 10% of the lacZ activity as those inoculated with AdZ, while control animals exhibited background levels of activity. These results indicate that fiber mutations ablating native cell-receptor binding are effective in greatly reducing native tropism in vivo. All references cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incoφorated by reference and were set forth in its entirety herein. While this invention has been described with an emphasis on preferred embodiments, it will be obvious to those of ordinary skill in the art that variations of the preferred embodiments can be used and that it is intended that the invention can be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the following claims.

Claims: WHAT IS CLAIMED IS: 1. A recombinant fiber protein comprising an amino terminus of an adenoviral fiber protein and a trimerization domain, wherein said trimerization domain comprises an adenoviral fiber knob domain having a mutation affecting at least one amino acid residue within the region corresponding to the AB loop. B sheet, DE loop, or FG loop of the wild-type Ad5 fiber protein, and wherein said recombinant fiber protein trimerizes when produced in a eukaryotic cell. 2. The recombinant fiber protein of claim 1. wherein said region is the AB loop. 3. The recombinant fiber protein of claim 1. wherein said region is the B sheet. 4. The recombinant fiber protein of claim 1. wherein said amino acid residue corresponds to a residue selected from the group of residues consisting of 408. 409. 412-417. 420. 474-477. and 487-492 of the wild-type Ad5 fiber protein. 5. A recombinant fiber protein comprising an amino terminus of an adenoviral fiber protein and a trimerization domain, wherein said trimerization domain comprises an adenoviral fiber knob having a mutation affecting at least one amino acid corresponding to residue 404-406. 408. 409, 412-417. 420. 439, 441. 442, 449-454, 456, 458. 460, 462, 466. 467, 469-472. 474-477. 482, 485, 487-492. 505-512, 515. 517, 519, 521 -528. 533. 535. 537-549, 551 , 553. 555, 559- 568, 580, or 581 of the wild-type Ad5 fiber protein, and wherein said recombinant fiber protein trimerizes when produced in a eukaryotic cell. 6. The recombinant fiber protein of claim 5. wherein said amino acid residue corresponds to residue 189. 190. 198. 201. or 262 of the native Ad9 fiber protein. 7. The recombinant fiber protein of claim 5. wherein said amino acid residue corresponds to residue 395, 396. 404, 407, or 470 of the native Ad41 long fiber protein. 8. The recombinant fiber protein of claim 5. wherein said amino acid residue corresponds to residue 136, 155, 177. 181 , 198, 210. 21 1. 215. 233, 234, 236. 238, 248, 257. 260. 261, 276. 284, 302. 303, 317. or 318 of the native Ad3 fiber protein. 9. The recombinant fiber protein of any of claims 1 -8. wherein said mutation alters the charge of said residue. 10. A trimer comprising the recombinant fiber protein of an\ of claims 1 - 8. wherein said trimer has an affinity for a native adenoviral cellular receptor of at least about an order of magnitude less than a wild-type adenoviral fiber trimer. 1 1. An adenoviral virion comprising the trimer of claim 10. 12. The adenoviral virion of claim 1 1. comprising a penton base having a mutation affecting at least one native RGD sequence. 13. The adenoviral virion of claim 1 1. comprising a hexon having a mutation affecting at least one native HVR sequence. 14. The adenoviral virion of claim 1 1. lacking a native glycosylation or phosphorylation site. 15. The adenoviral virion of claim 1 1. which is conjugated to a lipid derivative of polyethylene glycol comprising a primary amine group, an epoxy group, or a diacyl glycerol group. 16. The adenoviral virion of claim 1 1. which elicits less immunogenicity in a host animal than does a wild-type adenovirus. 17. The adenoviral virion of claim 1 1. comprising a non-adenoviral ligand. 18. The adenoviral virion of claim 17. wherein said non-adenoviral ligand is conjugated to a fiber. 19. The adenoviral virion of claim 17. wherein said non-adenoviral ligand is conjugated to a penton. 20. The adenoviral virion of claim 17. wherein said non-adenoviral ligand is conjugated to a hexon. 21. The adenoviral virion of claim 17, wherein said non-adenoviral ligand is conjugated to protein IX. VI. or Ilia. 22. The adenoviral virion of claim 17. wherein said non-adenoviral ligand binds a substrate other than a native mammalian adenoviral receptor. 23. The adenoviral virion of any of claim 17. wherein said non-adenoviral ligand binds a substrate other than a native cell-surface protein. 24. The adenoviral virion of claim 17. wherein said substrate is present on the surface of a cell. 25. An adenoviral vector comprising the adenoviral virion of claim 1 1 and an adenoviral genome. 26. The adenoviral vector of claim 25, which is replication incompetent. 27. The adenoviral vector of claim 25. which does not productively infect HEK-293 cells. 28. The adenoviral vector of claim 25. wherein said virion comprises a non-adenoviral ligand. and said adenoviral genome comprises a non-native nucleic acid for transcription. 29. The adenoviral vector of claim 25. wherein said non-native nucleic acid for transcription is operably linked to a non-adenoviral promoter. 30. The adenoviral vector of claim 25. wherein said ligand binds to a substrate present on the surface of a cell and wherein said non-adenoviral promoter is active within said cell. 31. The adenoviral vector of claim 29. wherein said non-adenoviral promoter is a tissue-specific promoter. 32. The adenoviral vector of claim 29, wherein said non-adenoviral promoter is a regulable promoter. 33. A method of infecting a cell, comprising contacting a cell with an adenoviral vector of claim 25. 34. The method of claim 33. wherein said adenoviral genome comprises a non-native nucleic acid encoding a protein, and wherein said nucleic acid is expressed within said cell to produce said protein.

Inventors: BRUDER JOSEPH T, KOVESDI IMRE, ROELVINK PETRUS W, WICKHAM THOMAS J, BRUDER, JOSEPH, T., KOVESDI, IMRE, ROELVINK, PETRUS, W., WICKHAM, THOMAS, J.
Applicants: GENVEC INC, GENVEC, INC.
Application year: 1999
Main classification: C12N15
IPC codes: A61K48, C07K14, C12N7, C12N15, C12P21, C12R1