WO2007010398A2

WO2007010398A2 - Caveolin-3 and in vitro culture of hepatitis c virus

Info

Publication number: WO2007010398A2
Application number: PCT/IB2006/002565
Authority: WO
Inventors: Marcello Merola; Stefania Crotta; Alessia Bianchi
Original assignee: Novartis Vaccines And Diagnostics Srl
Priority date: 2005-07-18
Filing date: 2006-07-18
Publication date: 2007-01-25
Also published as: CA2615558A1; JP2009513109A; WO2007010398A3; EP1910522A2

Abstract

Caveolin-3 has been identified as a cellular factor that associates with HCV protein El and E2, and is proposed as a cellular limiting factor. As an alternative possibility, caveolin-3 may act as a cellular receptor for HCV, acting alongside CD81. In either scenario, cells with increased expression of caveolin-3 will be better suited to the in vitro culture of HCV, and blocking the interaction between caveolin-3 and HCV proteins has therapeutic potential.

Description

CAVEOLIN-3 AKD JDV VITRO CULTURE OF HEPATITIS C VIRUS

AU documents cited herein are incorporated by reference in their entirety.

TECHNICAL FEELD

This invention is in the field of hepatitis C virus (HCV) culture and its in vitro culture. BACKGROUND ART

One problem in HCV research has been the lack of an efficient in vitro culture system.

A sub-genomic replicon containing most of the non-structural proteins of HCV has been shown to replicate in a hepatoma cell line [1] and a further subgenomic replicon with improved transfection efficiency has also been disclosed [2,3]. These. systems have allowed detailed studies on the HCV replication mechanism, but the absence of structural genes in the replicons means that virion assembly is not possible. Reference 4 describes a method for persistent and transient replication of a . full-length HCV genome in cell culture, in which mutant "selectable full-length" (sfl) genomes could stably replicate in 21-5 cells (derived from the Huh-7 cell line) and express all viral proteins. These 21-5 cells were found not to produce viral particles. Because of the lack of particle assembly within cells, it has been proposed that there is a cellular factor which limits HCV maturation and assembly. If this limiting factor could be identified then its intracellular levels could artificially be increased, thereby permitting in vitro virion assembly. Furthermore, if the factor is critical to virion assembly then preventing or disrupting its interaction with HCV proteins has therapeutic potential. DISCLOSURE OF THE INVENTION -

Caveolin-3 has been identified as a cellular factor that associates with HCV protein El and E2, and is proposed as a cellular limiting factor. As an alternative possibility, caveolin-3 may act as a cellular receptor for HCV, acting alongside CD81. In either scenario, cells with increased expression of caveolin-3 will be better suited to the in vitro culture of HCV, and blocking the interaction between caveolin-3 and HCV proteins has therapeutic potential. Moreover, animal models of HCV infection may be improved by providing increased caveolin-3 expression.

HCV has previously been associated with caveolin-1 and caveolin-2. For example, references 5-7 report that caveόlin-1 was over-expressed in HCV-related cirrhotic liver. Moreover, HCV RNA has previously been found to were co-fractionate with caveolin-2 [8]. There have not, however, been any previous reports that HCV associated with caveolin-3. Whereas caveolins 1 and 2 are both ubiquitously expressed [9], caveolin-3 expression has been reported to be muscle-specific (with some evidence also suggesting expression in astrocytes [10]). This expression pattern does not match the tissue trophism of HCV, and so the association between HCV and caveolin-3 is surprising.

Thus the invention provides a cell, wherein (i) the cell includes a hepatitis C virus genome, and/or nucleic acid encoding a hepatitis C virus genome; and (ii) the cell expresses caveolin-3. The invention also provides a cell that includes (i) a hepatitis C virus genome, and/or nucleic acid encoding a hepatitis C virus genome, and (ii) nucleic acid encoding caveolin-3. The nucleic acid is preferably a mKNA transcript encoding caveolin-3 i.e. the nucleic acid is being expressed.

The invention also provides an in vitro cell culture comprising a cell of the invention. The invention provides a process for growing hepatitis C virus, comprising the steps of: (a) providing a cell that expresses caveolin-3 and that includes a hepatitis C virus genome and/or nucleic acid • encoding a hepatitis C virus genome; and (b) culturing the cell. A process for producing HCV can then comprise the step: (c) purifying HCV virions.

The invention also provides a process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with (ϊj nucleic acid encoding caveolin-3 and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) culturing the cell. A process for producing HCV can then comprise the step: (c) purifying HCV virions.

The invention also provides a process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with a vector encoding caveolin-3, wherein the cell includes a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) culturing the cell. A process for producing HCV can then comprise the step: (c) purifying HCV virions.

The invention also provides a process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with nucleic acid encoding caveolin-3; (b) infecting the cell with a hepatitis C virus; and (c) culturing the cell. Steps (a) and (b) can be performed in either order. A process for producing HCV can then comprise the step: (d) purifying HCV virions.

The invention also provides a process for growing hepatitis C virus, comprising the step of culturing a cell comprising (i) an endogenous caveolin-3 gene, and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome, under conditions where the caveolin-3 gene is expressed. A process for producing HCV can then comprise the step of purifying HCV virions. The invention also provides a process for modifying a cell that does not express caveolin-3, comprising a step of turning on caveolin-3 expression in the cell by a method selected from: (i) transfecting the cell with a vector encoding caveolin-3; or (ii) modifying the regulatory components of an endogenous caveolin-3 gene in the cell in order to turn on expression of the endogenous gene. The modified cell can then be used for HCV growth. The invention provides a process for growing hepatitis C virus, comprising the steps of: (a) providing a cell comprising (i) a caveolin-3 gene, and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) maintaining the cell under conditions of serum deprivation, A process for producing HCV can then comprise the step of (c) purifying HCV virions. The caveolin-3 gene is preferably endogenous. The invention also provides an animal comprising a cell of the invention. The cell may have been implanted into the animal, or may be endogenous. The invention provides a proteinaceous complex comprising: (i) CD81; (ii) a HCV protein; and (iii) caveolin-3. The complex may also include cholesterol.

The invention provides a method of screening for compounds that inhibit the interaction between caveolin-3 and a HCV protein, said method comprising assessing inhibition of the interaction

5 between caveolin-3 and a HCV protein in the presence of a candidate compound. Candidate compounds that inhibit the interaction may have antiviral activity. This method of screening may comprise the steps of: (i) mixing caveolin-3 and a HCV protein and one or more candidate compound(s); (ii) incubating the mixture to permit any interaction caveolin-3, the HCV protein and the candidate compound(s); and (iii) assessing whether an interaction between caveolin-3 and the

10 HCV protein is inhibited. The mixing of caveolin-3, the HCV protein and. candidate compound(s) in step (i) may be done in any order.

The invention also provides a compound that inhibits the interaction between caveolin-3 and a HCV protein, wherein the compound is obtained or obtainable by a screening method of the invention. .

The invention also provides an antibody that can specifically bind to caveolin-3. "

15 The invention also provides a compound that can downregulate expression of caveolin-3 in a target cell. This will typically be a nucleic acid that can act in a sequence-specific manner in relation to caveoliή-3, such as an antisense nucleic acid, a ribozyme, a locked nucleic acid, or a siRNA.

Hepatitis C virus genomes

Cells of the invention include a HCV genome and/or nucleic acid encoding a HCV genome. Thus the 20 cells may include a + strand single-stranded RNA genome, or they may include nucleic acid that can be transcribed to give, either directly or indirectly, a + strand KNA genome. For instance, transcription of a DNA copy of the genome in the correct orientation (even though the natural HCV life cycle does not include a DNA stage) gives a RNA that can act as a HCV genome i.e. it can direct expression of the HCV polyprotein, which is then processed as seen in the normal HCV life cycle.

25 The HCV genomic RNA naturally includes a 5' cap (m⁷G5'ppp5¹A) and no poly-A tail, with both 5^? and 3' noncoding regions (NCRs). These elements will typically be present in HCV genomes used according to the invention, but the HCV genome and/or the nucleic acid encoding the genome may include one or more elements not seen in native genomes. For instance, it is normal for HCV genomes used in in vitro replication systems to include one or more of the following: a sequence

30 encoding a selection marker (such as a neomycin resistance marker) e.g. near the 5' end of the genome, upstream of the polyprotein; an internal ribosome entry site (IRES) such as from EMCV or poliovirus e.g. upstream of the polyprotein coding sequence, to permit translation of the polyprotein even though there may be other upstream coding sequences. A construct with a 5' T7 promoter at the 5' end of the genome has been described [11], but this is not preferred.

35. The HCV genome can be of any type (e.g. 1, 2, 3, 4, 5, 6) or subtype (e.g. Ia, Ib, Ic, Id, Ie, If, Ig, Ih, Ii, Ij, Ik, 11, Im, 2a, 2b, 2c, 2d, 2e, 2f, 2g, 2h, 2i, 2k, 21, 2m, 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3k, 4a, 4c, 4d, 4e, 4f, 4g, 4h, 4k, 41, 4m, 4n, 4o, 4p, 4q, 4r, 4s, 4t, 5a, 6a, 6b, 6d, 6f, 6g, 6h, 6i, 6j, 6k, 61, 6m, 6n). This nomenclature is the current standard, as set out by the MAID Hepatitis C Virus (HCV) Sequence Database [12] in which previous genotypes 7-9 have been reclassified as subtypes of type 6, based on reference 13. Thus the new classification includes previous classifications I, II, DI, IV, V, VI, 4α, 4β, 7a, 7b, 7c/NGπMI, 7d, NGI₅ 8a, 8b, 9a, 9b, 9c, 10a/TD3 and 11a. One suitable HCV strain for use with the invention is the genotype 2a strain JFHl [14].

The HCV genome may include one or more mutations (including insertions, deletions and/or substitutions) relative to a wild-type genome, or may be a hybrid of more than one wild-type genome e.g. a chimera of a subtype 2a strain {e.g. J6) and a subtype Ia strain {e.g. WIl). Mutations in the genome are frequent, as the viral RNA replicase lacks proof-reading activity, and resulting mutant genomes (or 'quasi-species') can readily be obtained and analysed. Some mutations have been reported to improve the ability of a genome to be replicated in particular cells. Reference 4 describes mutants for cell-adaptation, including El 202G, T1280I, K1846T and S2197P. Reference 3 describes HCV variants that include mutations {e.g. R1164G, S1172C, S1172P, A1174S, Sl 1791) that increase transfection efficiency and the ability to survive subpassages. Other known mutations include, but are not limited to, L1757I, N2109D, P2327S and K2350E. Particular mutations may be preferred for use with particular host cells, and vice versa. Although the polyprotein of the HCV preferably includes all of C, El, E2, p7, NS2, NS3, NS4A, NS4B, NS5A and NS5B, larger deletions and insertions are also possible {e.g. deletion of mature coding regions, such as of non-structural proteins, or insertion of non-HCV sequences). The invention can also be used with subgenomic HCVs {i.e. including less than a full genome, typically including non-structural proteins but not structural proteins e.g. lacking full C, El, E2), but a key advantage of the invention is that it permits the replication of full-length genomes.

These and other mutations can be present in the HCV genome used according to the invention, but these mutants will generally not remove the ability of the genome to direct expression of a HCV polyprotein that can then replicate the HCV genome from which it was expressed.

The HCV RNA or the nucleic acid encoding the HCV RNA may be introduced into a cell as part of a process of the invention, or it may already be part of the cell e.g. the 21-5 cell line [4] is already infected with HCV. Where the cell includes nucleic acid that encodes a HCV genome, this can take the form of DNA or RNA, and can either be chromosomal or extra-chromosomal {e.g. episomal). A DNA plasmid that encodes the HCV genome can conveniently be used.

DNA encoding both the HCV genome and the caveolin-3 protein can be used. This DNA will usually have two separate transcriptions: (i) the HCV genome (or possibly the anti-genome), and (ii) mRNA encoding caveolin-3, but it is also possible to have a single transcript including: (i) the HCV genome (or anti-genome) and coding sequences for caveolin-3, with an IRES to control translation of the downstream sequence.

-A- A HCV genome will typically be included in the form of a replicon i.e. a nucleic acid that is capable of directing the generation of copies of itself. Cell-based HCV replication systems that use a genomic or subgenomic replicon system are well known. Replicons are based on the sense strand of the viral RNA, but the invention can also utilise a complementary sequence that can be converted into the sense strand to provide a replicon. Replicons may also contain non-HCV genes e.g. reporter genes.

Caveolin-3

Caveolins are the defining protein components of caveolae [9]. Caveolae were classically defined as plasma membrane invaginations with a characteristic diameter of ~50 to 100 nm, but this morphological description is now known to be inadequate. Caveolae can be invaginated, flat within the plane of the plasma membrane, or detached vesicles. In addition, caveolae can fuse to form grape-like structures and tubules with sizes significantly larger than 100 nm. Morphologically, they are abundant in endothelia, muscle cell types, adipocytes, and lung epithelial cells. Caveola-like structures are also present within the nervous system.

Caveolae have a unique lipid composition. They are mainly composed of cholesterol and sphingolipids. In contrast, noncaveolar regions of the plasma membrane are composed mainly of phospholipids. The caveolins are a family of 21- to 25-kDa integral membrane proteins that have been implicated in a variety of cellular functions. At least three caveolin genes are known to exist.

They are thought to facilitate the formation of invaginated caveolae through their interactions with cholesterol. Caveolins are thought to associate with membranes via a central 33-amino-acid hydrophobic domain, allowing both the N- and C-terminal domains to remain entirely cytosolic.

Caveolins bind cholesterol directly.

Three important related functional roles have been described for caveolins: (i) the main structural protein components of caveolae membranes; (ii) shuttle proteins in the biosynthetic trafficking of cholesterol from the ER to the plasma membrane, and (iii) scaffolding proteins to organize and inactivate signalling molecules that are concentrated on the cytoplasmic surface of caveolar membranes.

Caveolins have been functionally implicated in a wide variety of signal transduction processes. In general, caveolin- 1 and caveolin-3 repress the enzymatic activity of a wide variety of signal transducing molecules, while caveolin-2 has little or no effect. One notable exception is the insulin receptor tyrosine kinase; caveolin- 1 and -3 augment the ability of the insulin receptor to phosphorylate IRS-I, one of its major substrates.

Caveolin-3 is localized to the sarcolemma (muscle cell plasma membrane) and coincides with the distribution of another muscle-specific plasma membrane marker protein, dystrophin. Caveolin-3 cofractionates with cytoplasmic signalling molecules (G proteins and Src-like kinases) and members of the dystrophin complex (dystrophin, α-sarcoglycan, and β-dystroglycan).

-^. It has also been shown that caveolin-3 forms a physical complex with dystrophin, suggesting an essential role for caveolin-3 in muscle biology. Caveolin-3 protein expression is dramatically induced during the differentiation of C2C12 skeletal myoblasts in culture. In addition, caveolin-3 is transiently associated with T-tubules during muscle development and may be involved in the early development of the T-tubule system.

Caveolin-3 also interacts with phosphofructokinase-M in muscle. This interaction is (i) highly regulated by the extracellular concentration of glucose and (ii) can be stabilized by a number of relevant intracellular metabolites, such as fructose 1,6-bisphosphate and fructose 2,6-bisphosphate, which are known allosteric activators of phosphofructokinase-M. Glucose-dependent plasma membrane recruitment of activated phosphofructokinase-M by caveolin-3 may play a key role in regulating energy metabolism in skeletal muscle fibres.

Genetic evidence highlights the importance of caveolin-3 in muscle function. A form of autosomal dominant limb girdle- muscular dystrophy (LGMD) associated with a severe deficiency of caveolin-3 in muscle fibers has been reported. The human caveolin-3 gene was mapped to chromosome 3p25, and two mutations in the gene were identified, a missense mutation in the membrane-spanning region (P→L) and a microdeletion in the scaffolding domain (ΔTFT) . These mutations may interfere with caveolin-3 oligomerization and possibly disrupt caveolar formation at the muscle cell plasma membrane. However, the molecular mechanisms by which these two mutations cause muscular dystrophy remain unknown. The phenotypic behavior of these caveolin-3 mutations was investigated by using heterologous expression. Wild-type caveolin-3 or caveolin-3 mutants were transiently expressed in NIH 3T3 cells. LGMD-IC mutations led to formation of unstable high-molecular-mass aggregates of caveolin-3 that were retained within the Gόlgi complex and not targeted to the plasma membrane. Consistent with its autosomal dominant form of genetic transmission, LGMD-IC mutants of caveolin-3 behaved in a dominant-negative fashion, causing the retention of wild-type caveolin-3 at the level of the Golgi complex. These data provide a molecular explanation for why caveolin-3 levels are downregulated in patients with LGMD-IC.

Caveolin-3 has been reported to be a chaperonin [16].

It has now been found that caveolin-3 expression is seen not only in muscle. Surprisingly, it has been detected in the Huh-7 cell line [15] that carries a HCV replicon, and has moreover been found ^"to co-localise in the cell with particulate HCV protein structures. Expression seems not to be induced by HCV infection, but to exist at a low endogenous level.

The GeneCard entry for caveolin-3 can be found using code CAV3. The GeneCard reveals that the protein has also been referred to as LGMDlC, M-caveolin and VIP -21. Ten SNPs have been described so far. The reference human CAV3 sequence is a 151-mer having GI number GL4502589 and accession number NPJ)01225 (SEQ ID NO: 1):

-f.. 2565

MMAEEHTDLE AQIVKDIHCK EIDLVNRDPK NINEDIVKVD FEDVIAEPVG TYSFDGVWKV SYTTFTVSKY WCYRLLSTLL GVPLALLWGF LFACISFCHI WAVVPCIKSY LIEIQCISHI YSLCIRTFCN PLFAALGQVC SSIKVVLRKE V

Disease-related single amino acid variations have been disclosed at residues 27 (R/Q), 29 (DfB), 33 (N/K), 44 (YfE), 46 (A/T and A/V), 56 (G/S), 64 (TYP), 72 (C/W), 87 (L/P), 93 (A/T), and 105 (P/L). Deletion of residues 64-66 has also been reported. Truncated forms of caveolin-3 have also been reported e.g. the cavDGV truncation in reference 16.

Further human CAV3 sequences in the databases include entries AF043101, AAC14931.1, Y14747, CAA75042.1, AF036367, AAC39758.1, AF036366, AAC39758.1, AP036365, AAC39756.1, BC069368, AAH69368.1, etc. Human caveolin-3 is 95% identical to the mouse and rat caveolin-3 protein sequences. Human caveolin-3 shows 82% and 58% similarity with human caveolin-1 and -2.

With this background of functional characterisation and sequence information, a skilled person can readily identify whether a given sequence is a caveolin-3 sequence. Preferred caveolin-3 proteins of the invention have at least 50% sequence identity (e.g. 60%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more) to SEQ ID NO: 1. Other preferred caveolin-3 proteins comprise a fragment of at least n consecutive amino acids of SEQ ID NO: 1, where n is 7 or more (e.g. 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 or more). The fragment may omit signal peptides, etc. The fragment may be due to truncations of a caveolin-3 at the C-terminus and/or N-terminus. Preferred fragments include the central region of amino acids 84-104, which represents the transmembrane domain. Another preferred fragment includes the caveolin-scaffolding domain of caveolin-3 e.g. at least amino acids 55-73.

These polypeptide may, compared to SEQ ID NO: 1, include one or more (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.) conservative amino acid replacements i.e. replacements of one amino acid with another which has a related side chain. Genetically-encoded amino acids are generally divided into four families: (1) acidic i.e. aspartate, glutamate; (2) basic i.e. lysine, arginine, histidine; (3) non-polar i.e. alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan; and (4) uncharged polar i.e. glycine, asparagine, glutamine, cysteine, serine, threonine, tyrosine. Phenylalanine, tryptophan, and tyrosine are sometimes classified jointly as aromatic amino acids. In general, substitution of single amino acids within these families does not have a major effect on the biological activity. The polypeptides may have one or more (e.g. 1, 2, 3. 4, 5, 6, 7, 8, 9, 10, etc.) single amino acid deletions relative to SEQ ID NO: 1. The polypeptides may also include one or more (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.) insertions (e.g. each of 1, 2, 3, 4 or 5 amino acids) relative to SEQ ID NO: 1.

Cell types Cells of the invention have two essential features: (1) they can express the HCV genome, in order to support the HCV life cycle and its replication; and (2) they can express caveolin-3. The cells can already have both of these features, or one or both of them can be introduced. Thus, for example, a cell can be infected with HCV, or with nucleic acid encoding HCV, and can also (either before, after, or at the same time as introduction of HCV) be transfected with a vector encoding caveolin-3.

As all wild-type human cells include a gene encoding caveolin-3 then the cell may already express this protein e.g. a muscle cell. Where a cell does not naturally express caveolin-3 from the endogenous gene then the ability to express this protein can be achieved by activating expression of the endogenous gene (e.g. by promoter replacement) and/or by providing a further copy that is expressed. The further copy may be episomal or chromosomal.

Expression of endogenous caveolin-3 can also be achieved by stimulating the cell to express the endogenous gene. One known way of stimulating caveolin-3 expression uses serum deprivation. This treatment typically involves substituting a 'high mitogen' growth medium (e.g. containing 10% fetal bovine serum) with a 'low mitogen' growth medium containing low or no serum (e.g. containing 2% horse serum). It has been described in reference 17 for use in differentiating muscle cells.

In addition to including a HCV genome, a cell may include nucleic acid encoding one or both of hepatitis C virus proteins El and E2. As disclosed in reference 18, the ability to express El and/or E2 protein(s) separately from the El and E2 proteins that are produced during the HCV life cycle promotes virion assembly. The nucleic acid encoding El and/or E2 may be DNA or RNA. DNA vectors are preferred. The nucleic acid can either be chromosomal or extra-chromosomal (e.g. episomal). A preferred nucleic acid vector for introducing El and E2 to a cell is a retroviral vector, which may be an integrating vector. The El and E2 sequences may therefore be introduced as inserts in the RNA genome of a retrovirus. After reverse transcription (and, where applicable, integration) the El and E2 sequences will be in DNA form within the cell. Other suitable vectors include DNA plasmids. In addition to expressing El and E2, the nucleic acid(s) may express p7.

As HCV naturally infects eukaryotic cells, the invention will generally use a eukaryotic cell. It is preferred to use a mammalian cell, such as a primate cell, including a human cell. Other animals whose cells can be used for HCV study include, but are not limited to: a mouse; a rat; a woodchuck; a shrew, such as a tree shrew; a chimpanzee; a gibbon; a tamarin; and a marmoset.

As HCV naturally infects liver cells then it is convenient to use a cell derived from liver (e.g. hepatocytes), although any suitable caveolin-3 -expressing cells can be used instead, including muscle cells. Muscle cells (including myocytes) are a convenient cell type because caveolin-3 expression can be up-regulated by the simple step of serum deprivation. However, the invention can use a cell that is not a muscle cell, particularly a non-muscle cell that expresses caveolin-3.

Typically, the cells used in the invention will be cell lines, and preferably packaging cell lines. A preferred cell line for use with the invention is derived from a hepatocellular carcinoma, namely the human hepatoma cell line known as Ηuh7' [15]. A particularly preferred cell line is the Huh7-derived cell line known as '21-5', which supports a full length HCV replicon. Other preferred cell lines are Huh-7.5 and Huh-7.8, which are sub-lines of Huh-7 that can support complete HCV replication in cell culture [19,20], with Huh-7.5 being preferred. Cells derived by passaging of Huh7 cells (and their derivatives) can also be used, as well as cells derived by treating Huh7 cells with α-interferon and/or γ-interferon. As disclosed in reference 20, cell lines permissive for HCV can be prepared by a process comprising (a) culturing cells infected with HCV; (b) curing the cells of HCV; and (c) identifying a sub-line of the cured cells that is permissive for HCV replication.

Other established human hepatoma and hepatoblastoma cell lines include HuH-6 cl-5, PLC/PRF/5, huH-1, and huH-4. Huh7 cells can be grown as monolayers in media such complete DMEM {e.g. Dulbecco's modified minimal essential medium supplemented with 2 mM L-glutamine, nonessential amino acids, 100 U/ml penicillin, 100 μg/ml streptomycin, 10% fetal calf serum). Particular cell types may be preferred for use with particular viral strains, and vice versa.

Cells of the invention express polyprotein from the HCV genome. As a result, the cells include the protein building blocks for expressing HCV particles, including virions and virus-like particles (VLPs). Virions and VLPs can thus be prepared from the cells of the invention. These may or may not include a RNA genome. The cells can also express complexes of El and E2. The cells may also express complexes of El, E2, NS3 and NS5a.

As described above in more detail, cells of the invention include a HCV genome and/or nucleic acid encoding a HCV genome. A HCV genome can be introduced into a cell by viral infection, or can be produced in situ either after viral infection (real or artificial) or after transcription from a DNA copy of the genome. Methods for introducing HCV genomes or DNA encoding a HCV genome into a cell are routine in the art. HCV genomes that have been transcribed in vitro can be introduced into Huh7 cells using electroporation, as disclosed in reference 4 (4xlO⁶ Huh-7 cells electroporated with lμg of purified in vitro transcripts, or 2.4xlO⁷ Huh-7 cells electroporated with 60μg of HCV RNA).

Cells of the invention can grow in an in vitro culture. Details for culturing these cells under conditions where HCV replication occurs are known in the art. Methods for purifying HCV virions after viral growth are also known in the art.

When the HCV genome is expressed according to the invention, dot-like particles can be seen if immunofluorescent staining is used. If desired, release of these particles from the cells can be facilitated by treating them with suitable release agents e.g. to cause the release of exosomes, etc. Such agents include alcohol, stress conditions, etc. Non-covalent E1/E2 heterodimers have been detected in the endoplasmic reticulum, and can be recovered from this cellular compartment.

Animal models

A number of animal models for HCV infection have been described e.g. references 21 to 29.

Where the efficiency of HCV infection is lower than desired, it can be increased by up-regulating caveolin-3 expression in the animal. This can be achieved in various ways. For example, a cell of the invention can be implanted or injected into a host animal, where the exogenous cell can express caveolin-3 and facilitate HCV growth. As an alternative, genetic changes can be introduced into the endogenous cells of the animal e.g. using gene therapy techniques. As a further alternative, such genetic changes can be introduced into a cell from which animals are generated {e.g. into an embryonic cell, a stem cell, an embryonic stem cell, a nuclear transfer donor cell, etc.), thereby providing homogeneity throughout the animal. As a further alternative, the animal may be subjected to a treatment that stimulates expression of its endogenous caveolin-3 genes.

Thus expression of endogenous caveolin-3 genes can be up-regulated, and/or exogenous caveolin-3 genes can be introduced. Where exogenous caveolin-3 genes are introduced, the gene may be from the same organism as the animal {e.g. introduce a murine caveolin-3 gene into a mouse), or may be from a different organism {e.g. introduce a human caveolin-3 gene into a mouse). The animal of the invention preferably has a liver in which a cell has been modified in this way. More preferably, all of its liver cells are modified in this way.

The animal of the invention may be free from HCV infection, in which case it can subsequently be exposed to HCV infection for study purposes; or it may be infected with HCV, in which case it is useful for the virological study of HCV e.g. cell entry, infection progress, replication, viral assembly, efficacy of antiviral compounds, etc.

The animal may be immunodeficient e.g. a SCID animal, or an irradiated animal. Irradiated SCID mice are particularly useful.

Any suitable animal can be used, but typical models are based on a mammal selected from the group consisting of: a mouse; a rat; a woodchuck; a shrew, such as a tree shrew {Tupαiα belαngeri); a chimpanzee; a gibbon; a tamarin; and a marmoset.

Cells of one organism can be introduced into a different organism for the production of animal models. For instance, it is known to engraft human hepatocytes into the liver of a mouse host [30,31].

Screening methods

As described above, the invention provides screening methods for identifying compounds that can inhibit the interaction between caveolin-3 and a HCV protein. The HCV protein will typically be El, E2, or an oligomer comprising El &/or E2, or may be a core or non-strucutral protein. The screening methods involve assessing the interaction of the HCV protein with caveolin-3, and the ability of a test compound to disrupt this interaction is indicative of potential therapeutic activity to prevent HCV maturation. Direct screening

Inhibition of the HCV/caveolin-3 interaction in the presence of candidate compounds may be assessed directly. Various methods for direct detection of protein/protein interactions are available.

For example, one or both of HCV and caveolin-3 may be labelled with a fluorescent label such that the interaction between HCV and caveolin-3 may be detected by an intrinsic fluorescence change which occurs when an HCV/caveolin-3 complex is formed or disrupted. For example, the HCV protein may be joined to a fluorescence resonance energy transfer (FRET) donor and caveolin-3 to a FRET acceptor (or vice versa) such that, when HCV and caveolin-3 interact, stimulation of the FRET donor excites the FRET acceptor causing it to emit photons. Interaction may be also be detected by fluorescent labelling of the HCV protein and/or caveolin-3 such that fluorescence is quenched when they form a complex.

Another method for assessing interaction between HCV and caveolin-3 proteins is co-immuno- precipitation. For example, an anti-HCV antibody can be used to immunoprecipitate the relevant HCV protein from a mixture, and the precipitated material can be tested {e.g. by western blot, or by detecting the presence of a tag in the target protein) for the presence of caveolin-3. The reverse can also be used i.e. immunoprecipitation with an anti-caveolin-3 antibody followed by checking for co-precipitated HCV protein.

Other methods for assessing interaction between HCV and caveolin-3 may include using NMR to determine whether a complex is present when a candidate compound is present.

The presence of a HCV/caveolin-3 complex may also be detected as a band at a particular position when run on a gel. Disruption of the complex by addition of a candidate compound may be detected by the presence of bands at different positions on the gel.

Interaction of HCV and caveolin-3 proteins may also be assessed by detecting the accessibility of peptide sequences {e.g. epitopes) on HCV and/or caveolin-3 proteins that are masked when they form a complex. Indirect screening for inhibitors using two-hybrid systems

Whether the interaction between HCV and caveolin-3 proteins is inhibited in the presence of a candidate compound may also be assessed indirectly. One indirect method of screening for inhibition of the interaction between HCV and caveolin-3 proteins in the presence of a candidate compound involves using a two-hybrid system. A HCV protein may be fused to an activation domain of a transcription factor and caveolin-3 to a DNA-binding domain of a transcription factor (or vice versa), such that their interaction promotes the transcription of a reporter gene in a cell.

The invention thus provides a method of screening for compounds that inhibit the interaction between HCV and caveolin-3 proteins, said method comprising the steps of: (i) contacting a cell containing a nucleic acid molecule comprising a promoter operatively linked to a reporter gene with: (a) a first fusion protein comprising one of a HCV protein and caveolin-3 fused to the activation domain of a transcription factor, (b) a second fusion protein comprising the other of a HCV protein and caveolin-3 fused to the DNA-binding domain of a transcription factor; and (iii) a candidate compound; and (ii) assessing the level of expression of the reporter gene, wherein interaction between HCV and caveolin-3 proteins promotes transcription of the reporter gene by activating said promoter.

-II- This method may be used to assess interaction between HCV and caveolin-3 proteins in any eukaryotic cell. Preferably, the method is used to assess the interaction between HCV and caveolin-3 proteins in a yeast cell or a mammalian cell. Where the candidate compound is an organic compound and a yeast two-hybrid system is being used, the permeability of the yeast cell wall is preferably enhanced e.g. by using chemicals such as polymyxin B.

The level of expression of a reporter gene in the two-hybrid system is indicative of the level of interaction between HCV and caveolin-3 proteins. A candidate compound that inhibits the interaction decreases or abolishes the level of expression of the reporter gene.

Preferably, the reporter gene is easily assayed. For example, the reporter gene may give a detectable signal, such as a visible signal. The reporter gene may encode a protein which gives a visible signal itself, or which catalyses a reaction which gives a visible change e.g. a fluorescent protein or an enzyme. The reporter gene may encode an enzyme such as a beta-galactosidase or a peroxidase, both of which are commonly used with coloured substrates and/or products. The reporter gene may encode a fluorescent protein, such as green fluorescent protein (GFP) or a fluorescent derivative thereof such as YFP or CFP [32]. The reporter gene may encode a luminescent protein, such as luciferase. The reporter gene may drive DNA replication [33] in the cell or may encode a drug resistance marker [34].

The reporter gene may encode a protein that enables positive selection of cells in which the interaction between HCV and caveolin-3 proteins is inhibited. For example, the reporter gene may encode a protein that is toxic or cytostatic so that only cells that do not express the protein are able to survive or grow ('reverse two hybrid' or 'MAPPIT' assays [35-37]). As a result, the only cells to survive are those in which the candidate compound inhibits the interaction between HCV and caveolin-3 proteins so that the reporter gene is not expressed. Examples of reporter genes of this type that may be used in yeast include URA3, LYS2 and CYH2 [38]. The protein encoded by the reporter gene may also prevent cell growth in the absence or presence of a particular amino acid or other component in cell media. For example, the reporter gene may encode a DNA-binding protein, TnIO tetracycline, which represses transcription of a TetRop-HIS3 gene so that yeast cells in which the reporter gene is expressed do not grow in the absence of histidine [39]. In contrast, yeast cells in which the interaction between HCV and caveolin-3 proteins has been disrupted do not express TNlO tetracycline and are consequently able to grow in the absence of histidine.

The proteins encoded by the reporter genes may be in the form of fusion proteins. Methods for the generation of fusion proteins are standard in the art and will be known to the skilled reader.

The level of expression of the reporter gene may also be assessed by measuring the level of a mRNA transcribed from the reporter gene or the level of protein translated after its transcription. Systems for carrying out screening methods

The screening methods of the invention may be carried out in cell-free systems or in cells or tissues. In particular, the indirect screening methods described above may be carried out in a cell-free system, in a cell or in a tissue. The cell-free system must contain all the necessary components for transcription of the reporter gene where the level of expression is detected by measuring mRNA levels, and all the necessary components for transcription and translation of the reporter gene where the level of expression is assessed by measuring protein levels.

It is preferred that the methods of screening of the invention be conducted in cell-free systems since this facilitates high-throughput screening of candidate compounds. Indirect screening methods of the invention are preferably carried out in eukaryotic cells, such as mammalian (e.g. human) or yeast cells. They may also be performed in mammalian (e.g human) tissues. A typical cell is a liver cell.

Reference standards

A reference standard (e.g. a control), is typically needed in order to detect whether the interaction between HCV and caveolin-3 proteins is inhibited. In order to detect whether a candidate compound inhibits the interaction between HCV and caveolin-3 proteins, the interaction between HCV and caveolin-3 proteins in the presence of a candidate compound may be compared with the interaction between HCV and caveolin-3 proteins in the absence of a candidate compound.

The reference may have been determined before performing the method of the invention, or may be determined during (e.g. in parallel) or after the method has been performed. It may be an absolute standard derived from previous work.

Candidate compounds

Typical candidate compounds for use in all the screening methods of the invention include, but are not restricted to, peptides, peptoids, proteins, lipids, metals, small organic molecules, RNA aptamers, antibiotics and other known pharmaceuticals, polyamines, antibodies or antibody derivatives (e.g. antigen-binding fragments, single chain antibodies including scFvs, etc.), and combinations or derivatives thereof. Small organic molecules have a molecular weight of about more than 50 and less than about 2,500 daltons, and most preferably between about 300 and about 800 daltons. Candidate compounds may be derived from large libraries of synthetic or natural compounds. For instance, synthetic compound libraries are commercially available from MayBridge Chemical Co. (Revillet, Cornwall, UK) or Aldrich (Milwaukee, WI). Alternatively, libraries of natural compounds in the form of bacterial, fungal, plant and animal extracts may be used. Additionally, candidate compounds may be synthetically produced using combinatorial chemistry either as individual compounds or as mixtures. In some instances, it may be desirable to conduct a preliminary screening step to reduce the number of candidate compounds used in the methods of the invention. Compounds that bind to HCV and

-I J- caveolin-3 proteins individually are inherently more likely to inhibit interaction between HCV and caveolin-3 proteins than those that do not.

The invention therefore provides a method of screening for compounds that inhibit the interaction between HCV and caveolin-3 proteins further comprising the preliminary step of screening for candidate compounds by identifying compounds that bind to either HCV and caveolin-3 proteins.

In vivo confirmation of function of compounds identified

Once a compound has been identified as an inhibitor of the interaction between HCV and caveolin-3 proteins, it may be desirable to perform further experiments to confirm the in vivo antiviral function of the compound. The invention therefore provides a method of assessing the in vivo antiviral effect of a compound obtained or obtainable by any of the methods described above comprising administering the compound to a test animal and assessing the effect on the HCV life cycle. Tests in non-humans may be used.

Compounds identified by screening methods The invention provides a compound that inhibits the interaction between HCV and caveolin-3 proteins, obtained or obtainable by any of the methods described above. Preferably, the compounds of the invention are organic compounds.

There is also provided a composition comprising a compound that inhibits the, interaction between HCV and caveolin-3 proteins, obtained or obtainable by any of the methods described above. Compounds that are found to inhibit HCV activity may be useful antiviral in their own right or may be lead compounds for the development of new contraceptives. They may also be useful in antiviral research.

Pharmaceutical uses of compounds identified

Once a compound has been identified using one of the methods of the invention, it may be necessary to conduct further work on its pharmaceutical properties. For example, it may be necessary to alter the compound to improve its pharmacokinetic properties or bioavailability. The invention extends to any compounds identified by the methods of the invention which have been altered to improve their pharmacokinetic properties, and to composition comprising those compounds.

The invention further provides compounds obtained or obtainable using the methods of the invention, and compositions comprising those compounds, for use as antivirals. The invention also provides the use of a compounds obtained or obtainable using the methods of the invention, or compositions comprising those compounds in the manufacture of an antiviral medicament. An antiviral method comprising administering a compound obtained or obtainable by any one of the methods of the invention, or a composition comprising such a compound, to a mammal, preferably a human, is also provided. Therapeutic antibodies

As mentioned above, the invention provides an antibody that can specifically bind to caveolin-3. Reference 40 describes a murine monoclonal antibody that recognises the N-terminal region of caveolin-3, but not other members of the caveolin family. Murine and rabbit anti-caveolin-3 antibodies are available for in vitro research use from Research Diagnostics Inc. under catalog numbers RDI-CAVEO3abm and RDI-C AVEOL3abrX. AbCam rabbit polyclonal antibody ab2912 is also available. Anti-caveolin-3 antibodies have previously been injected into a cell's cytoplasm via pipette for investigation of sodium channels [41].

Antibodies of the invention preferably bind to an epitope located in caveolin-3 such that the binding prevents caveolin-3 from interacting with a HCV protein. Thus these antibodies can be used in therapeutic methods to prevent HCV maturation. It has been reported [42,43] that some caveolin-3 epitopes can be masked unless associated cholesterol is depleted. Thus some antibodies recognise caveolin-3 in the plasma membrane, some recognise caveolin-3 in the Golgi, and some recognise both. Appropriately-reactive antibodies can be selected by routine testing. Antibodies of the invention may be polyclonal or monoclonal and may be produced by any suitable means {e.g. by recombinant expression). To increase compatibility with the human immune system, the antibodies may be chimeric or humanised [e.g. refs. 44 & 45], or fully human antibodies may be used. Antibodies of the invention preferably are not native murine or rabbit antibodies.

Soluble antibodies that retain binding activity in an intracellular environment are preferred. Antibodies of the invention are preferably provided in purified or substantially purified form. Typically, the antibody will be present in a composition that is substantially free of other polypeptides e.g. where less than 90% (by weight), usually less than 60% and more usually less than 50% of the composition is made up of other polypeptides.

Antibodies of the invention can be of any isotype (e.g. IgA, IgG, IgM i.e. an α, γ or μ heavy chain), but will generally be IgG. Within the IgG isotype, antibodies may be IgGl, IgG2, IgG3 or IgG4 subclass.^" Antibodies of the invention may have a K or a λ light chain.

Antibodies of the invention can take various forms, including whole antibodies, antibody fragments such as F(ab')₂ and F(ab) fragments, Fv fragments (non-covalent heterodimers), single-chain antibodies such as single chain Fv molecules (scFv), minibodies, oligobodies, etc. The term "antibody" does not imply any particular origin, and includes antibodies obtained through non-conventional processes, such as phage display.

Therapeutic nucleic acids

As an alternative to blocking caveolin-3 activity post-translationally (e.g. by using antibodies), expression of the protein can be blocked at an earlier stage, either by preventing transcription or by preventing translation of a transcribed mRNA. Techniques for achieving this effect include antisense, ribozymes and gene silencing.

45- Thus the invention provides a nucleic acid that can inhibit the expression of caveolin-3 in a cell, wherein the nucleic acid is selected from: an antisense nucleic acid; a ribozyme; a locked nucleic acid; and a gene silencing nucleic acid. These nucleic acids are particularly useful for therapeutic purposes. They may be administered directly, or they may be generated in situ from expression in the cell. Thus the invention also provides nucleic acids that can be transcribed in a cell to provide the active molecules.

Antisense techniques generally involve the use of a nucleic acid sequence that is complementary to the transcribed (sense) mRNA sequence of a gene. The antisense molecule may be targeted to the control, 5' or regulatory regions (signal sequence, promoters, enhancers and introns) of the target. Inhibition can also be achieved using "triple helix" methodology, which can inhibit the ability of a double helix to open sufficiently for the binding of polymerases, transcription factors, or regulatory molecules. Inhibition can also be achieved by hybridisation of the antisense molecule to a hybridised mKNA, thereby preventing the transcript from binding to ribosomes etc.

Ribozymes (enzymatic RNA molecules) may also be used to catalyze the specific cleavage of RNA. They can be natural or synthetic. Synthetic ribozymes can be designed to specifically cleave mRNAs at selected positions thereby preventing translation of the mRNAs into functional polypeptide. The mechanism of ribozyme action involves sequence-specific hybridization of the ribozyme molecule to complementary target RNA, followed by endonucleolytic cleavage. Examples which may be used include engineered hammerhead motif ribozyme molecules that can specifically and efficiently catalyze endonucleolytic cleavage of target sequences. Specific ribozyme cleavage sites within any potential RNA target are initially identified by scanning the target molecule for ribozyme cleavage sites e.g. which include GUA, GUU, or GUC trinucleotides. Once identified, short RNA sequences of between 15 and 20 ribonucleotides corresponding to the region of the target gene containing the cleavage site may be evaluated for secondary structural features which may render the oligonucleotide inoperable. The suitability of candidate targets may also be evaluated by testing accessibility to hybridization with complementary oligonucleotides using ribonuclease protection assays.

Locked nucleic acids (LNAs) are described in more detail in reference 46. They have high binding affinity toward complementary DNA and RNA. Modified and chimeric LNA oligonucleotides have been applied. LNA oligonucleotides are commercially available, can be transfected using standard techniques, are non-toxic, lead to increased target accessibility, can be designed to activate RNase H, and function in steric block approaches. LNA-Antisense, including gapmer LNA containing a central DNA or phosphorothioate-DNA segment flanked by LNA gaps, is particularly useful.

Various gene silencing techniques are available. The most commonly used involves RNA interference (RNAi), which is mediated by double-stranded RNA (dsRNA) molecules. An appropriately-sized dsRNA molecule (e.g. siRNAs, or small interfering RNAs, having 21-23 nucleotides per strand) that is homologous to a target transcript will cause rapid degradation of that transcript by a RISC, thereby resulting in gene silencing. In addition to siRNAs, stRNAs can be used to slice genes by suppressing translation, and μRNAs can also cause gene silencing. Preferred target sites for siKNAs start at a AA dinucleotide sequences downstream of the start codon, and continue for the next 19 3' nucleotides. Kits and algorithms for siKNA design and delivery are readily available e.g. see references 47, 48, etc.

As RNA molecules can be degraded in vivo then, where a technique will tolerate it, it is possible to replace natural R]SfA nucleotides with artificial nucleotides. For example, RNA molecules may be modified by the use of phosphorothioate or 2' O-methyl rather than phosphodiesterase linkages within the backbone of the molecule, or by the inclusion of non-traditional bases such as inosine, queosine, and wybutosine, as well as acetyl-, methyl-, thio-, and similarly modified forms of adenine, cytidine, guanine, thymine, and uridine. Nucleotide analogs such as peptide nucleic acids (PNAs) can also be used.

Pharmaceutical compositions

Antibodies and nucleic acids of the invention may be provided as pharmaceutical compositions that additionally include a pharmaceutically acceptable carrier. Such compositions can be prepared using a process comprising the step of admixing the active ingredient with the pharmaceutically acceptable carrier.

Typical 'pharmaceutically acceptable carriers' include any carrier that does not itself induce the production of antibodies harmful to the individual receiving the composition. Suitable carriers are typically large, slowly metabolised macromolecules such as proteins, polysaccharides, polylactic acids, polyglycolic acids, polymeric amino acids, amino acid copolymers, and lipid aggregates (such as oil droplets or liposomes). Such carriers are well known to those of ordinary skill in the art. The vaccines may also contain diluents, such as water, saline, glycerol, etc. Additionally, auxiliary substances, such as wetting or emulsifying agents, pH buffering substances, sucrose, and the like, may be present. Sterile pyrogen-free, phosphate-buffered physiologic saline is a typical carrier {e.g. based on water for injection). A thorough discussion of pharmaceutically acceptable excipients is available in reference 49.

Compositions of the invention will typically be in aqueous form {e.g. solutions or suspensions) rather than in a dried form {e.g. lyophilised). Aqueous compositions are also suitable for reconstituting other materials from a iyophilised form. Where a composition of the invention is to be used for such extemporaneous reconstitution, the invention also provides a kit, which may comprise two vials, or may comprise one ready-filled syringe and one vial, with the aqueous contents of the syringe being used to reactivate the dried contents of the vial prior to injection.

Compositions of the invention may be presented in vials, or they may be presented in ready-filled syringes. The syringes may be supplied with or without needles. Compositions may be packaged in unit dose form or in multiple dose form. A syringe will generally include a single dose of the composition, whereas a vial may include a single dose or multiple doses. For multiple dose forms, therefore, vials are preferred to pre-filled syringes.

Effective dosage volumes can be routinely established, but a typical human dose of the composition has a volume of about 0.5ml e.g. for intramuscular injection. The pH of the composition is preferably between 6 and 8, and more preferably between 6.5 and 7.5 (e.g. about T). Stable pH may be maintained by the use of a buffer e.g. a Tris buffer, a phosphate buffer, or a histidine buffer. Compositions of the invention will generally include a buffer. If a composition comprises an aluminium hydroxide salt, it is preferred to use a histidine buffer [50] e.g. at between 1-1OmM, preferably about 5mM. The composition may be sterile and/or pyro gen-free. Compositions of the invention may be isotonic with respect to humans.

Compositions may be prepared as injectables, either as liquid solutions or suspensions. The composition may be prepared for pulmonary administration e.g. as an inhaler, using a fine powder or a spray. The composition may be prepared as a suppository or pessary. The composition may be prepared for nasal, aural or ocular administration e.g. as spray, drops, gel or powder [e.g. refs 51 & 52]. Injectables for intramuscular administration are typical.

Compositions of the invention may include an antimicrobial, particularly when packaged in multiple dose format. Antimicrobials such as thiomersal and 2-phenoxyethanol are commonly found in vaccines, but it is preferred to use either a mercury-free preservative or no preservative at all.

Compositions of the invention may comprise detergent e.g. a Tween (polysorbate), such as Tween 80. Detergents are generally present at low levels e.g. <0.01%.

Compositions of the invention may include sodium salts {e.g. sodium chloride) to give tonicity. A concentration of 10+2 mg/ml NaCl is typical. The concentration of sodium chloride is preferably about 9 mg/ml.

Methods of treatment The invention also provides a method for treating a mammal, comprising administering a pharmaceutical composition of the invention to the mammal. The mammal is preferably a human.

The invention also provides the antibodies and nucleic acids of the invention for use as a medicament. The invention also provides the use of antibodies or nucleic acids of the invention in the manufacture of a medicament for raising an immune response in a mammal. These uses and methods are preferably for the prevention and/or treatment of a disease caused by HCV e.g. hepatitis. Methods for checking efficacy of therapeutic hepatitis treatments are known in the art.

Compositions of the invention will generally be administered directly to a patient. Direct delivery may be accomplished by parenteral injection {e.g. subcutaneously, intraperitoneally, intravenously, intramuscularly, or to the interstitial space of a tissue), or by rectal, oral, vaginal, topical,

-l δ- transdermal, intranasal, ocular, aural, pulmonary or other mucosal administration. Intramuscular administration to the thigh or the upper arm is preferred. Injection may be via a needle {e.g. a hypodermic needle), but needle-free injection may alternatively be used. A typical intramuscular dose is 0.5 ml. Dosage treatment can be a single dose schedule or a multiple dose schedule. General

The term "comprising" encompasses "including" as well as "consisting" e.g. a composition "comprising" X may consist exclusively of X or may include something additional e.g. X + Y.

The term "about" in relation to a numerical value x means, for example, x+10%.

The word "substantially" does not exclude "completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Identity between polypeptide sequences is preferably determined by the Smith- Waterman homology search algorithm as implemented in the MPSRCH program (Oxford Molecular), using an affme gap search with parameters gap openpenalty=12 and gap extension penalty=l . Detailed information about hepatitis C virus, including its life cycle, replication, culture conditions, genome, polyprotein, proteolytic processing, etc., can be found in chapters 32 to 34 of reference 53.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 shows immunofluorescence results using naϊve 21-5 cells (Figures IA, IB, 1C) and R809-infected 21-5 cells (Figures ID, IE, IF). The staining antibody is either anti-El/E2 (Figures 1C, IF) or anti-caveolin-3 (Figures IB, IE). Figure IA is an overlay of Figures IB and 1C. Figure ID is an overlay of Figures IE and IF.

Figure 2 is similar to Figure 1, but shows cells after 72 hours of serum deprivation.

Figure 3 is a western blot of cellular extracts. The markers in lane 13 are 193, 102.9, 59.9, 41.2, 27.6, 20.7 and 15.4 kDa. MODES FOR CARRYING OUT THE INVENTION

Reference 18 describes an improved method for HCV replicon expression, wherein El and E2 proteins are expressed separately and in addition to the El and E2 that arises from translation of the HCV genome. The El and E2 were provided to 21-5 cells [4], together with p7 protein (ElE2p7 protein), by a lentiviral vector, which integrates into the chromosome to give the 21-5_R809 cells. Confocal microscopy shows that the Core, El, E2, NS3, NS5a proteins co-localise with the HCV genome in these cells, to form dot-like structures.

Further work on the co-localising material has now been performed and, surprisingly, caveolin-3 has also been found to be present. Nothing iri the prior art suggests that caveolin-3 is expressed in liver cells. Confocal microscopy was performed on Huh-7 and 21-5 cells, and anti-caveolin-3 antibodies showed only dim labelling, with no defined pattern. By western blot, however, the protein could be seen in naϊve Huh-7 cells, in Huh-7 cells transfected with the HCV replicon, and in Huh-7 cells transfected with both the replicon and the lentiviral vector. These results suggest that caveolin-3 is expressed at low levels in Huh-7 cells and that, rather than being induced by HCV infection, is accumulated inside the El/E2-containing dots.

Figure 1 shows immunofluorescence microscopy of 21-5 cells and 21-5_R809 cells. HCV E1/E2 proteins are not seen in naϊve 21-5 cells (Figure 1C), but are seen after the R809 lentiviral vector is introduced (Figure IF). Caveolin-3 is diffusely detected in naϊve 21-5 cells (Figure IB), but bright spots can be seen in the R809-infected cells (Figure IE). The overlay of Figures IE and IF (Figure IB) shows that the E1/E2 and the caveolin-3 are co-localised. NS3, NS5a and viral RNA are also seen in these spots.

The usual stimulus for caveolin-3 induction in muscle cells is serum deprivation. This technique was thus used on 21-5 cells and 21-5JR.809 cells, both of which have a full-length HCV replicon. It was also used on these cells with transfection by the lentiviral vector.

Figure 2 shows immunofluorescence of 21-5 cells, with and without R809 infection, after 72 hours of serum deprivation. In comparison to Figure 1, E1/E2 expression can be seen, and caveolin-3 shows expression in dots. The E1/E2 and caveolin-3 co-localise.

Figure 3 is a western blot of various Triton X-IOO cellular extracts, stained with anti-caveolin-3 serum. Mouse muscle cells (lanes 1-4) show caveolin-3 expression. Resting cells (lanes 1 & 2) show expression, and after 48 hours (lane 3) or 96 hours (lane 4) of serum deprivation then expression is increased. Huh-7 cells without (lane 5) or with (lane 6) horse serum (2%) show no detectable caveolin-3 expression. Huh-7 cells after R809 infection show similar results (lanes 7 & 8). 21-5 cells with (lanes 9 & 10) or without (lanes 11 & 12) R809 infection also show no detectable caveolin-3. As described in reference 18, expression of El and E2 is not seen in native 21-5 cells. After serum deprivation, however, El and E2 expression could be seen by immunofluorescence, which also showed caveolin-3 -associated dot-like structures. Western blot analysis showed that overall caveolin-3 expression levels in 21-5 cells did not increase during serum deprivation (unlike the effect seen in muscle cells), and so it seems that instead the diffuse protein is being concentrated into specific structures which are then visible by immunofluorescence.

Overall, these results suggest that caveolin-3 appears to play a role in HCV maturation.

It will be understood that the invention has been described by way of example only and modifications may be made whilst remaining within the scope and spirit of the invention. REFERENCES (the contents of which are hereby incorporated by reference)

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Claims

1. A cell, wherein (i) the cell includes a hepatitis C virus genome, and/or nucleic acid encoding a hepatitis C virus genome; and (ii) the cell expresses caveoIin-3.

2. A cell that includes (i) a hepatitis C virus genome, and/or nucleic acid encoding a hepatitis C virus genome, and (ii) nucleic acid encoding caveolin-3.

3. The cell of claim 2, wherein the nucleic acid is a mRN A transcript encoding caveolin-3.

4. An in vitro cell culture comprising a cell of any preceding claim.

5. A process for growing hepatitis C virus, comprising the steps of: (a) providing a cell that expresses caveolin-3 and that includes a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) culturing the cell.

6. .A process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with (i) nucleic acid encoding caveolin-3 and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) culturing the cell.

7. A process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with a vector encoding caveolin-3, wherein the cell includes a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome; and (b) culturing the cell.

8. The process of claims 5-7, further comprising the step: (c) purifying HCV virions.

9. A process for growing hepatitis C virus, comprising the steps of: (a) transfecting a cell with nucleic acid encoding caveolin-3; (b) infecting the cell with a hepatitis C virus; and (c) culturing the cell.

10. A process for growing hepatitis C virus, comprising the step of culturing a cell comprising (i) an endogenous caveolin-3 gene, and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis C virus genome, under conditions where the caveolin-3 gene is expressed.

11. A process for growing hepatitis C virus, comprising the steps of: (a) providing a cell comprising (i) a caveolin-3 gene, and (ii) a hepatitis C virus genome and/or nucleic acid encoding a hepatitis

C virus genome; and (b) maintaining the cell under conditions of serum deprivation.

12. The process of claims 9-11, further comprising a step of purifying HCV virions.

13. A process for modifying a cell that does not express caveolin-3, comprising a step of turning on caveolin-3 expression in the cell by a method selected from: (i) transfecting the cell with a vector encoding caveolin-3; or (ii) modifying the regulatory components of an endogenous caveolin-3 gene in the cell in order to turn on expression of the endogenous gene.

14. An animal comprising a cell of the invention.

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15. The animal of claim 15, where the animal is a mouse.

16. A proteinaceous complex comprising: (i) CD81; (ii) a HCV protein; and (iii) caveolin-3.

17. A process for screening for compounds that inhibit the interaction between caveolin-3 and a HCV protein, said method comprising assessing inhibition of the interaction between caveolin-3 and a HCV protein in the presence of a candidate compound.

18. The process of claim 17, comprising the steps of: (i) mixing caveolin-3 and a HCV protein and one or more candidate compound(s); (ii) incubating the mixture to permit any interaction caveolin-3, the HCV protein and the candidate compound(s); and (iii) assessing whether an interaction between caveolin-3 and the HCV protein is inhibited.

19. The cell, process, culture, animal or complex of any preceding claim, wherein the cell includes nucleic acid that encodes a HCV genome, in the form of DNA or RNA.

20. The cell, process, culture, animal or complex of any preceding claim, wherein the caveolin-3 comprises amino acid sequence GL4502589.

21. The cell, process or culture of any one of claims 1 to 13, wherein the cells are mammalian cells.

22. The cell, process or culture of claim 21, wherein the cells are human cells.

23. The cell, process or culture of claim 21 or claim 22, wherein the cells are derived from liver.

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