WO2011039612A1 - Detection and use of antiviral resistance mutations - Google Patents

Abstract

The present invention relates generally to viral variants exhibiting reduced sensitivity to anti-viral agents. More particularly, the present invention is directed to Hepatitis B virus (HBV) variants exhibiting complete or partial resistance to nucleoside or nucleotide analogs or other anti-viral agents and/or reduced interactivity with antibodies to viral surface components including reduced sensitivity to these antibodies or other anti -viral agents. Vaccines and diagnostic assays are also contemplated herein.

Description

DETECTION AND USE OF ANTIVIRAL RESISTANCE

MUTATIONS

FILING DATA

[0001] This application is associated with and claims priority from US Provisional Patent Application No. 61/247,867, filed on 1 October 2009, entitled "Detection and use of antiviral resistance mutations", the entire contents of which, are incorporated herein by reference.

FIELD

[0002] The present invention relates generally to viral variants exhibiting reduced sensitivity to anti-viral agents. More particularly, the present invention is directed to Hepatitis B virus (HBV) variants exhibiting complete or partial resistance to nucleoside or nucleotide analogs or other anti-viral agents and/or reduced interactivity with antibodies to viral surface components including reduced sensitivity to these antibodies or other antiviral agents. Vaccines and diagnostic assays are also contemplated herein.

BACKGROUND

[0003] Bibliographic details of the publications referred to in this specification are also collected at the end of the description.

[0004] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in any country.

[0005] Hepatitis B virus (HBV) can cause debilitating disease conditions and can lead to acute liver failure. HBV is a DNA virus which replicates via an NA intermediate and utilizes reverse transcription in its replication strategy (Summers and Mason, Cell 29:403- 415, 1982). The HBV genome is of a complex nature having a partially double-stranded DNA structure with overlapping open reading frames encoding surface, core, polymerase and X genes. The complex nature of the HBV genome is represented in Figure 1 . The polymerase consists of four functional regions, the terminal protein (TP), spacer, reverse transcriptase (rt) and ribonuclease (RNAse).

[0006] The polymerase gene of HBV overlaps the envelope gene, mutations in the catalytic domain of the polymerase gene can also affect the nucleotide and the deduced amino acid sequence of the envelope protein and vice versa. In particular, the genetic sequence for the neutralization domain of HBV known as the 'a' determinant, which is found within the HBsAg and located between amino acids 99 and 169, actually overlaps the major catalytic regions of the viral polymerase protein and in particular domains A and B.

[0007] The presence of an HBV DNA polymerase has led to the proposition that nucleoside or nucleotide analogs could act as effective anti-viral agents. Examples of nucleoside or nucleotide analogs currently being tested are penciclovir and its oral form (FCV) [Vere Hodge, Antiviral Chem Chemother 4: 67-84, 1993; Boyd et al. Antiviral Chem Chemother. 32:358-363, 1987; Kruger et al. Hepalology 22:219A, 1994; Main et al. J. Viral Hepatitis 3:21 1 -21 5, 1996], Lamivudine |(-)-P-2'-deoxy-3'-thiacytidine |; (3TC or LMV) [Severini et al, Antimicrobial Agents Chemother. 39:430-435, 1995; Dienstag el al. New England J Med 333: 1657- 1661 , 1995]. New nucleoside or nucleotide analogs which have already progressed to clinical trials include the pyrimidines Emtricitabine, ((-)-β-Ε- 2'-3 '-dideoxy-5-fluoro-3 '-thiacydidine; FTC), the 5-fluoro derivative of 3TC, and Clevudine (l -(2-fluoro-5-methyl-P-L-arabino-furanosyl) uracil; L-FMAU), a thymidine analog. The beta-L-thymidine analogue (LdT has recently been given FDA approval other similar compounds include beta-L-2'-deoxycytidine (LdC) and beta-L-2'-deoxyadenosine (LdA) [Standring et al , Anlivir Chem Chemother. 12 Suppl 7: 1 19-29, 2001 ]. Like 3TC, these are pyrimidine derivatives with an unnatural "L"- configuration. Several purine derivatives have also progressed to clinical trials; they include Entecavir ( BMS-200. 475 : ETV), a carbocyclic deoxyguanosine analog, diaminopurine dioxolane (DAPD), an oral pro-drug for dioxolane guanine ((-)-P-D-2-aminopurine dioxolane; DXG) and Adefovir dipivoxil, an oral prodrug for the acyclic deoxyadenosine monophosphate nucleoside or nucleotide analog Adefovir (9-[phosphonyl-methoxyethyl]-adenine; PMEA). Other drugs in pre-clinical and clinical trials include FLG [Medivir], ACH- 126,443 (L-d4C) [Archillion Pharmaceuticals], ICN 2001-3 (ICN) and Racivir (RCV) [Pharmassett].

[0008] Whilst these agents are highly effective in inhibiting HBV DNA synthesis, there is the potential for resistant mutants of HBV to emerge during long term antiviral chemotherapy. In patients on prolonged LMV therapy, key resistance mutations are selected in the rt domain within the polymerase at rtM204I/V +/- rtL180M as well as other mutations. The nomenclature used for the polymerase mutations is in accordance with that proposed by Stuyver et al, 2001 , supra. LMV is a nucleoside or a nucleotide analog that has been approved for use against chronic HBV infection. LMV is a particularly potent inhibitor of HBV replication and reduces HBV DNA litres in the sera of chronically infected patients after orthotopic liver transplantation (OLT) by inhibiting viral DNA : synthesis. LMV monotherapy seems unlikely to be able to control HBV replication in the longer term. This is because emergence of LMV-resistant strains of HBV seems almost inevitable during monotherapy.

[0009] Adefovir dipivoxil (ADV: formerly, bis-pom PMEA) is an orally available prodrug of the acyclic deoxyadenosine monophosphate analog adefovir (formerly, PMEA) (Figure 2). ADV is also a potent inhibitor of HBV replication and has been given FDA approval for use against chronic HBV infection. Adefovir dipivoxil differs from other agents in this class in that it is a nucleotide (vs. nucleoside) analog and as such bypasses the first phosphorylation reaction during drug activation. This step is often rate-limiting. Adefovir dipivoxil has demonstrated clinical activity against both wild-type and lamivudine-resistant strains of HBV and is currently in phase III clinical Testing (Gilson et al. J Viral Nepal 6:387-395, 1999; Perrillo el al, Hepalology 32. 129- 134, 2000; Peters el al. Transplantation 6S.T 912- 1914, 1999; Benhamou el al. Lancet 35^:718-723, 2001 ). During phase II studies a 30 mg daily dose of adefovir dipivoxil resulted in a mean 4 logio decrease in viremia over 12 weeks (Heathcote et al, Hepalology 28: A620, 1998). [0010] ADV is a substituted acyclic nucleoside phosphonate. This class of compounds also includes tenofovir disoproxil fumarate (also referred to as tenofovir DF, or tenofovir, or (TFV) or 9-R-(2-phosphonomethoxypropyl)adenine (PMPA) and is marketed as Viread by Gilead sciences).

[0011 ] Tenofovir (TFV) [Figure 3] has antiviral activity against both HBV and HIV (Ying et al, J Viral Hepat. 7(2): l 6 \ - \ 65, 2000; Ying et al, J. Viral liepat. 7(7J:79-83, 2000, Suo et al, J Biol Chem. 273 (42) .27250-27258. 1998).

[0012] FTC has activity against HBV and HIV (Frick et al, Antimicrob Agents Chemother 57:2285-2292, 1993).

[0013] LdT, LdC and LdA have activity against HBV (Standring et al 2001 supra).

[0014] Nucleoside or nucleotide analog therapy may be administered as monotherapy or combination therapy where two or more nucleoside or nucleotide analogs may be administered. The nucleoside or nucleotide analogs may also be administered in combination with other antiviral agents such as interferon or hepatitis B immunoglobulin (HBIG).

[0015] There is a need to monitor for the emergence of resistant strains of HBV to antiviral agents including nucleoside/nucleotide analogs and antibodies and to develop diagnostic protocols to detect these resistant viruses and/or to use them to screen for and/or develop or design agents having properties making them useful as anti-viral agents. Defective or attenuated forms of these resistant strains or antigenic components therefrom are also proposed to be useful in the development of therapeutic vaccine compositions as are antibodies directed to viral surface components. SUMMARY

[0016] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.

[0017] Nucleotide and amino acid sequences are referred to by a sequence identifier number (SEQ ID NO:). The SEQ ID NOs: correspond numerically to the sequence identifiers <400> 1 (SEQ ID NO: l ), <400>2 (SEQ ID NO:2), etc. A summary of the sequence identifiers is provided in Table 1 . A sequence listing is provided after the claims.

[0018] Specific mutations in an amino acid sequence are represented herein as "XaainXaa₂" where Xaai is the original amino acid residue before mutation, n is the residue number and Xaa₂ is the mutant amino acid. The abbreviation "Xaa" may be the three letter or single letter (i.e. "X") code. An "rt" before "XaainXaa₂" means "reverse transcriptase". An "s" means an envelope gene. The amino acid residues for HBV DNA polymerase are numbered with the residue methionine in the motif Tyr Met Asp Asp (YMDD) being residue number 204 (Stuyver et al, Hepatology 33:751 -757, 2001 ). The amino acid residues for HBV surface antigen are numbered according to Norder el al. J. Gen. Virol. 74. 341 - 1348, 1993. Both single and three letter abbreviations are used to define amino acid residues and these are summarized in Table 2.

[0019] In accordance with the present invention, HBV variants are selected in subjects with HBV infection treated with TFV and/or other antiviral agents including nucleoside and nucleotide analogs such as but not limited to ADV, LMV, FTC, ETV, FCV. L-FMAU, LdT, LdC and LdA. Consequently, HBV rt variants are identified which are resistant to. or which exhibit reduced sensitivity to, antiviral agents including nucleoside and nucleotide analogs such as TFV alone or in combination with ADV, LMV, F TC, E TV, FCV, L-FMAU, LdT, LdC and/or LdA. Corresponding mutations in the surface antigen also occur. The identification of these HBV variants is important for the development of assays to monitor TFV resistance alone or in combination with ADV, L V, FTC, BTV, FCV, L-FMAU, LdT, LdC and/or LdA and/or resistance to other nucleoside or nucleotide analogs or other anti-HBV agents or combinations thereof and to screen for agents which are useful as alternative therapeutic agents.

[0020] Reference herein to "anti-HBV agents" includes nucleoside and nucleotide analogs as well as immunological reagents (e.g. antibodies to HBV surface components) and chemical, proteinaceous and nucleic acid agents which inhibit or otherwise interfere with viral replication, maintenance, infection, assembly or release. An "anti-HBV agent" is an example of an "anti-viral agent".

[0021] The detection of such HBV variants is particularly important in the management of therapeutic protocols including the selection of appropriate agents for treating H BV infection. The method of this aspect of the present invention is predicated in part on monitoring the development in a subject of an increased HBV load in the presence of a nucleoside or nucleotide analog or other anti-HBV agents or combinations thereof. The clinician is then able to modify an existing treatment protocol or select an appropriate treatment protocol accordingly.

[0022] Accordingly, one aspect of the present invention is directed to an isolated Hepatitis B virus (HBV) variant wherein the variant comprises a nucleotide mutation in a gene encoding the rt component of the DNA polymerase or the envelope protein (surface antigenfs]) resulting in at least one amino acid addition, substitution and/or deletion to the rt component or envelope protein and wherein the variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0023] In particular, the present invention provides an isolated HBV strain which exhibits reduced sensitivity to TFV, the HBV strain comprising a mutation in the rt portion of its DNA polymerase selected from the list consisting of a mutation at codons 18 1 , 202, 249. 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141 . By "anti-viral agent" is meant TFV, ADV, LMV, FTC, ETV, FCV, L-FMAU, LdT, LdC and/or LdA as well as HBIG, I F y or any other agent which inhibits replication, maintenance, infection, assembly and/or release of HBV or ameliorates the symptoms of acute or chronic HBV infection. The variant HBV comprises a mutation in an overlapping open reading frame in its genome in a region defined by one or more of domains F and G and domain A through to E of HBV DNA polymerase.

[0024] Another aspect provides an isolated HBV variant comprising a nucleotide mutation in the S gene resulting in at least one amino acid addition, substitution and/or deletion to the surface antigen and which exhibits decreased sensitivity to TFV alone or in combination with one or more ADV, LMV, FTC, ETV, FCV, L-FMAU, LdT, LdC and/or LdA or other anti-viral agents. The surface antigen may also be referred to herein as "HBsAg", "s" and the "envelope protein".

[0025] Useful mutants in the rt region include, in an embodiment, rtS81 L, rtD83V rtV84L, rtS85P, rtRl l OK, rt L 146V, rtN139 , rt 168Stop, rtA 1 81 T, rtS202T, rtS202R, rt 241 R_; rt .141 N and rtF249L. The term "mutant" includes co-mutations such as at codons selected from the list: (i) 81 and 168; (ii) 1 10, 146, 202 and 241 ; and (iii) 84, 85 and 241 . Examples of co-mutations include (i) rtS81 L and rt 168Stop; (ii) rtR l l OK, rtL 1 46V, rtS202T and rt 241 R; (iii) rtV84L, rtS85P and rt 241 N; and (iv) an equivalent mutation or another substitution at these codon positions.

[0026] A particularly useful mutant comprises the co-mutations at codons 81 and 168 such as rtS81 L and rt 168Stop.

[0027] Useful mutants in the HBsAg region include mutants at codons 73, 75, 102, 1 22. 126, 137, 172 and 194 such as but not limited to sR73C, sM75I, sG102S, sR122 /I/T, sT126N, sC 137W, sW172Stop, sV 194L and sV 194D.

[0028] In a particular embodiment, an isolated HBV variant is provided wherein the variant comprises a nucleotide mutation in a gene encoding a DNA polymerase resulting in at least one amino acid addition, substitution and/or deletion to the rt component of the HBV DNA polymerase wherein the mutation is selected from the group consisting of rtS81 L, rtD83V rtV84L, rtS85P, rtRl l O , rt L I 46V, rtN 139K, rtK 168Stop, rtA 1 81 T. rtS202T, rtS202R, rtK241 R, ΠΚ141Ν, rtF249L, rtS81 L, rt 168Stop, rtRl l OK, HL 146V, rtS202T, rt 241 R, rtV84L, rtS85P and rtK241N; wherein the HBV variant exhibits decreased sensitivity to TFV alone or in combination with another anti -viral agent. This aspect includes co-mutations at two or more condons such as (i) rtS81 L and rt 168Stop; (ii) rtRl 10K, rtL 146V, rtS202T and H 241 R; (iii) rtV84L, rtS85P and rt 241 N.

[0029] The present invention further provides an isolated HBV variant is provided wherein the variant comprises a nucleotide mutation in the S gene resulting in at least one amino acid addition, substitution and/or deletion to the surface antigen wherein the mutation is selected from the group consisting of sR73C, SM75I, sG 102S, sR122 /I/T, sT 126N, sC 137W, sW 172Stop, sV 194L and sV 194D; wherein the HBV variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0030] A method is further contemplated for determining the potential for an HBV to exhibit reduced sensitivity to TFV alone or in combination with another anti-viral agent by screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase and associated with resistance or decreased sensitivity to TFV alone or in combination with the other anti-viral agent.

[0031] In a related embodiment, the present invention contemplates a method for identifying a human subject infected with a strain of HBV which exhibits reduced sensitivity to TFV, the method comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV. [0032] The present invention also contemplates a method for identifying a human subject infected with a strain of HBV which exhibits reduced sensitivity to TFV, the method comprising screening for a mutation in the nucleotide sequence encoding HBsAg which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV.

[0033] The present invention further provides a protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV.

[0034] The present invention also contemplates a protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV.

[0035] In an embodiment, the mutation is at a codon selected from the list consisting of codons 181 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141. In another embodiment, the mutation is a co-mutation at codons selected from the list consisting of (i) codons 81 and 168; (ii) codons 1 10, 146, 202 and 241 ; and (iii) codons 84, 85 241 . Particular mutations are selected from the list consisting of rtS81 L, rtD83V rtV84L, rtS85P, rtR l l OK, rt L 146V, rtN 139 , rt 168Stop, rtA 1 81 T, rtS202T, rtS202R, rtK241 R, rt 141 N and rtF249L. Particular co-mutations are selected from the list consisting of (i ) rtS81 L and rtF 168Stop; (ii) rtRl l OK, rtL146V, rtS202T and rtK241 R; and (iii) rtV84 L rtS85P and rtK241N.

[0036] The rt co-mutations rtS81 L and rtK168Stop are particularly useful in correlating to TFV resistance. [0037] Useful mutants in the HBsAg region contemplated herein include sR73C, sM75I, sG 102S, sR122K/I/T, sT126N, sC 137W, sW 1 72Stop, sV 194L and sV 1 94D.

[0038] The presence of such mutations is an indication of the likelihood of resistance to TFV alone or in combination with the other anti-viral agent.

[0039] As indicated above, anti-viral agents other than TFV include ADV, LMV, FTC, ETV, FCV, L-FMAU, LdT, LdC, LdA, HBIG, TNFy and any other agent which inhibits replication, maintenance, infection, assembly or release of HBV or ameliorates the symptoms of chronic or acute HBV infection.

[0040] Also provided is a composition comprising a variant HBV resistant to TFV alone or in combination with another anti-viral agent and one or more pharmaceutically acceptable carriers and/or diluents. In one embodiment, the variant HBV is "defective" meaning it can induce an immune response but substantially does not cause a disease condition. The term "attenuated" may also be used.

[0041 ] Yet another aspect provides a use of the aforementioned composition or a variant HBV comprising a nucleotide mutation in a gene encoding a DNA polymerase resulting in at least one amino acid addition, substitution and/or deletion to the DNA polymerase and a decreased sensitivity to TFV alone or in combination with another anti-viral agent in the manufacture of a medicament for the treatment and/or prophylaxis of HBV infection.

[0042] Also contemplated is a method for determining whether an HBV strain exhibits reduced sensitivity to a nucleoside or nucleotide analog or other anti-HBV agents by isolating DNA or corresponding mRNA from the HBV and screening for a mutation in the nucleotide sequence encoding the DNA polymerase wherein the presence of the following mutations in the rt region rtS81 L, rtD83V rtV84L, rtS85P, rtR l 1 0 , rt L I 46V, rtN 1 39K, rtK 168Stop, rtA 1 81 T, rtS202T, HS202R, rt 241 R, rtK 141 and rtF249L or the co- mutations selected from (i) rtS81 L and rt 168Stop; (ii) rtR l 1 OK, rtL 146V, rtS202T and rt 241 R; and (iii) rtV84L, rtS85P and rtK241N or an equivalent mutation or a mutation in the surface antigen selected from the list consisting of sR73C, sM75I, sG 102S, SR122K/I/T, sT126N, sC137W, sW172Stop, sV 194L and sV 194D is indicative of a variant which exhibits a decreased sensitivity to TFV alone or in combination with another antiviral agent.

[0043] In a particular embodiment, the variants are in an isolated form such that they have undergone at least one purification step away from naturally occurring body fluid. Alternatively, the variants may be maintained in isolated body fluid or may be in DNA form. The present invention also contemplates infectious molecular clones comprising the genome or parts thereof from a variant HBV. The detection of HBV or its components in cells, cell lysates, cultured supernatant fluid and bodily fluid may be by any convenient means including any nucleic acid-based detection means, for example, by nucleic acid hybridization techniques or via one or more polymerase chain reactions (PCRs). The term "bodily fluid" includes any fluid derived from the blood, lymph, tissue or organ systems including serum, whole blood, biopsy and biopsy fluid, organ explants and organ suspension such as liver suspensions.

[0044] Another aspect contemplates a method for detecting an agent which exhibits inhibitory activity to an HBV by generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in a plasmid vector and then transfecting the cells with the construct, contacting the cells, before, during and/or after transfection, with the agent to be tested, culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agents; and the subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral-component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent. In an embodiment, the plasmid vector is a baculovirus vector and the method comprises generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in or fused to an amount of a baculovirus genome effective to infect cells and then infecting the cells with the construct, contacting the cells, before, during and/or after infection, with the agent to be tested, culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent and then subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral-component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent.

[0045] In connection with these methods, the plasmid vector may include genes encoding part or all of other viral vectors such as baculovirus vectors or adenovirus vectors (see Ren and Nassal, J. Virol. 75(3): 1 104- 1 1 16, 2001 ).

[0046] In an alternative embodiment, the method comprises generating a continuous cell line comprising an infectious copy of the genome of the HBV in a replication competent effective amount such that the infectious HBV genome is stably integrated into the continuous cell line such as but not limited to the 2.2.15 or AD cell line, contacting the cells with the agent to be tested, culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent and then subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral-component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent.

[0047] In an alternative embodiment, a method is contemplated for detecting an agent which exhibits inhibitory activity to an HBV polymerase in an in vitro polymerase assay. The HBV polymerase activity can be examined using established assays (Gaillard el al, Antimicrob Agents Chemother. 4<5(¾): 1005- 1013, 2002; Xiong et al, Hepatology, 25^: 1669-73, 1998). The HBV polymerase may be a wild-type or reference HBV polymerase or mutant HBV polymerase. [0048] The identification of viral variants enables the production of vaccines comprising particular recombinant viral components such as polymerases or envelope genes PreS l , PreS2, S encoding for L, M, S proteins as well as therapeutic vaccines comprising defective HBV variants. Rational drug design may also be employed to identify or generate therapeutic molecules capable of interacting with a polymerase or envelope genes PreS l , PreS2, S encoding for L, M, S proteins or other component of the HBV. Such drugs may also have diagnostic potential. In addition, defective HBV variants may also be used as therapeutic compositions to generate an immune response against the same, similar or homologous viruses. Alternatively, antibodies generated to the HBV variants or surface components thereof may be used in passive immunization of subjects against infection by HBV variants or similar or homologous viruses. Furthermore, agents such as nucleoside or nucleotide analogs (e.g. TFV, ADV, L V, FTC, ETV, FCV, L-FMAU, LdT, LdC and LdA), RNAi or siRNA molecules (both DNA-derived or synthetic), antisense or sense oligonucleotides, chemical or proteinaceous molecules having an ability to down-regulate the activity of a component of HBV (e.g. a cytokine such as IFNy) and inhibit replication, maintenance, infection, assembly or release are contemplated by the present invention.

[0049] Also provided is a method for identifying an HBV strain which exhibits reduced sensitivity to TFV, the method comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase or screening for a corresponding mutation in the surface antigen which is associated with decreased sensitivity to TFV.

[0050] The present invention further contemplates a method of treatment of a subject infected with HBV, the method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV-resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount.

[0051] In a related embodiment, the present invention provides a method of treatment of a subject infected with HBV, the method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV-resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount.

[0052] Exemplary mutations including co-mutations include those listed above.

[0053] A summary of the abbreviations used throughout the subject specification are provided in Table 3.

[0054] A summary of sequence identifiers used throughout the subject specification is provided in Table 1 .

TABLE 1

Summary of sequence identifiers

SEQUENCE ID NO: DESCRIPTION

1 PCR and sequencing primer TN I

2 PCR and sequencing primer TN2

3 PCR and sequencing primer TN3

4 PCR and sequencing primer TN4

5 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 1

6 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 1

7 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 1

8 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 2

9 Deduced amino acid sequence of polymerase gene from resistant

HBV from Patient 2

10 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 3

1 1 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 3

12 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 3

13 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 4

14 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 4

15 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 4

16 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 5

17 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 5

18 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 5

19 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 6

20 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 6

21 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 6 SEQUENCE ID NO: DESCRIPTION

22 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 7

23 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 7

24 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 7

25 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 8

26 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 8

27 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 8

28 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 9

29 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 9

30 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 10

31 Deduced amino acid sequence of catalytic region of polymerase from resistant HBV Patient 10

32 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 10

33 Nucleotide sequence of catalytic region of polymerase from resistant HBV Patient 1 1

34 Deduced amino acid sequence of catalytic region of polymerase resistant HBV Patient 1 1

35 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 1 1

36 Deduced amino acid sequence of envelope gene from resistant

HBV from Patient 2

TABLE 2

Single and three letter amino acid abbreviations

Amino Acid Three-letter Abbreviation One-letter symbol

Alanine Ala A

Arginine Arg R

Asparagine Asn N

Aspartic acid Asp D

Cysteine Cys C

Glutamine Gin Q

Glutamic acid Glu E

Glycine Gly G

Histidine His H

Isoleucine He I

Leucine Leu L

Lysine Lys K

Methionine Met M

Phenylalanine Phe F

Proline Pro P

Serine Ser S

Threonine The T

Tryptophan Trp W

Tyrosine Tyr Y

Valine Val V

Any residue Xaa X TABLE 3

Abbreviations

ABBREVIATION DESCRIPTION

Xaai n Xaa₂ A substitution mutation from amino acid Xaai at codon n to amino acid Xaa₂

YMDD Tyr Met Asp Asp-a motif in the polymerase protein; where the Met residue is designated residue number 204 of the reverse transcriptase

BRIEF DESCRIPTION OF THE FIGURES

[0055] Figure 1 is a diagrammatic representation showing the partially double stranded DNA HBV genome showing the overlapping open reading frames encoding surface (S). core (C), polymerase (P) and X gene.

[0056] Figure 2 is a diagrammatic representation of the chemical structure of Adefovir (ADV).

[0057] Figure 3 is a diagrammatic representation of the chemical structure of Tenofovir (TFV).

[0058] Figure 4 is a diagrammatic representation of the HBV nucleotide sequence translated polymerase sequence, and deduced envelope sequence of HBV isolated from patient 1 after TFV treatment.

[0059] Figure 5 is a diagrammatic representation of the HBV nucleotide sequence translated polymerase sequence and deduced envelope sequence of HBV isolated from patient 2 after TFV treatment.

[0060] Figure 6 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 3 after TFV treatment.

[0061] Figure 7 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 4 after TFV treatment.

[0062] Figure 8 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 5 after TFV treatment. [0063] Figure 9 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 6 after TFV treatment.

[0064] Figure 10 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 7 after TFV treatment.

[0065] Figure 11 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 8 after TFV treatment.

[0066] Figure 12 is a diagrammatic representation of the HBV nucleotide sequence and translated polymerase sequence of HBV isolated from patient 9 after TFV treatment.

[0067] Figure 13 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 1 0 after TFV treatment.

[0068] Figure 14 is a diagrammatic representation of the HBV nucleotide sequence, translated polymerase sequence and HBsAg sequence of HBV isolated from patient 1 1 after TFV treatment.

DETAILED DESCRIPTION

[0069] The present invention is predicated in part on the identification of HBV variants which are resistant to or have decreased or reduced sensitivity to TFV alone or in combination with one or more anti-viral agents. The variants of HBV arise following treatment of patients with either TFV alone or in combination with ADV or LMV or ETV or FTC or FCV or L-FMAU or LdT or LdC or LdA or another agent such as 1 1BIG. Reference herein to "decreased" or "reduced" in relation to sensitivity to TFV and other anti-viral agents includes and encompasses a complete or substantial resistance to the nucleoside or nucleotide analog or other anti-HBV agents as well as partial resistance and includes a replication rate or replication efficiency which is more than a wild-type in the presence of a nucleoside or nucleotide analog or other anti-HBV agents. In one aspect, this is conveniently measured by an increase in viral load during treatment of a subject, or alternatively, there is no substantial decrease in HBV DNA viral load from pre-treatment HBV DNA levels during treatment (i.e., non-response to treatment).

[0070] Accordingly, one aspect of the present invention is directed to an isolated Hepatitis B virus (HBV) variant wherein the variant comprises a nucleotide mutation in a gene encoding the rt component of the DNA polymerase or the envelope protein (surface antigenfs]) resulting in at least one amino acid addition, substitution and/or deletion to the rt component or envelope protein and wherein the variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent. More particularly, the present invention provides an isolated HBV strain which exhibits reduced sensitivity to TFV, the HBV comprises a mutation in the rt portion of its DNA polymerase selected from the list- consisting of codons 181 , 202, 249, 81 , 83, 84, 85, 1 1 0, 146, 1 39, 1 68, 241 and 141 or in the surface antigen selected from the list consisting of codons 73, 75, 102, 1 22, 1 26, 1 37, 172 and 194.

[0071 ] Another aspect provides a method for determining the potential for an H BV to exhibit reduced sensitivity to TFV alone or in combination with another anti-viral agent the method comprising screening for a mutation in the nucleotide sequence encoding HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in any one or more of domains F and A through E or a region proximal thereto of the DNA polymerase and associated with resistance or decreases sensitivity to TFV alone or in combination with another anti-viral agent and wherein the presence of such a mutation is an indication of the likelihood of resistance to TFV alone or in combination with another anti-viral agent.

[0072] The present invention further provides a protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV.

[0073] Yet another aspect of the present invention contemplates a method for identifying a human subject infected with a strain of HBV which exhibits reduced sensitivity to T FV. the method comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV.

[0074] The present invention also contemplates a method for identifying a human subject infected with a strain of HBV which exhibits reduced sensitivity to TFV, the method comprising screening for a mutation in the nucleotide sequence encoding the surf ace antigen of HBV which results in an amino acid substitution, deletion and/or addition to HBsAg which is associated with decreased sensitivity to TFV.

[0075] The present invention also provides a protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the surface antigen of HBV which results in an amino acid substitution, deletion and/or addition in HBsAg which is associated with decreased sensitivity to TFV.

[0076] In an embodiment, the mutation in the rt component is at a codon selected from the list consisting of codons 181,202,249, 81, 83,84, 85, 110, 146, 139, 168,241 and 141. In another embodiment, the mutation in the rt is a co-mutation at codons selected from the list consisting of (i) codons 81 and 168; (ii) codons 110, 146, 202 and 241; and (iii) codons 84, 85 and 241. Particular mutations in the rt are selected from the list consisting of rtS81L, rtD83V rtV84L, rtS85P, rtRHO , rt L146V, rtN139K, rtK168Stop, rtA181T, rtS202T, rtS202R, rt 241R, rtK141N and rtF249L. Particular co-mutations in the rt are selected from the list consisting of (i) rtS81L and rtK168Stop; (ii) rtRl 10 , rtL146V, rtS202T and rtK241R; or (iii) rtV84L, rtS85P and rtK241N.

[0077] Useful mutants in the HBsAg region include mutations in a codon selected from 73, 75, 102, 122, 126, 137, 172 and 194 such as sR73C, sM75I, sG102S, sR122K/I/T, sT126N, sC137W, sW172Stop, sV194L and sV194D.

[0078] A further aspect provides an isolated HBV variant wherein the variant comprises a nucleotide mutation in a gene encoding a DNA polymerase resulting in at least one amino acid addition, substitution and/or deletion to the DNA polymerase wherein the mutation is selected from the group consisting of rtS81L, rtD83V rtV84L, rtS85P, rtRl 10 , rt LI 46V. rtN139K, rt 168Stop, rtA181T, HS202T, rtS202R, rt 241R, rtK141N and rtF249L; co- mutations of two or more substitutions selected from the list consisting of (i) rtS81L and rt 168Stop; (ii) rtRllOK, rtL146V, HS202T and rt 241R; or (iii) rtV84L, rtS85P and rt 241N; and co-mutations at the abovementioned codons resulting in a different amino acid substitution; wherein the HBV variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0079] Still another aspect provides an isolated HBV variant wherein the variant comprises a nucleotide mutation in the S gene resulting in at least one amino acid addition, substitution and/or deletion to the HBsAg wherein the mutation is selected from the group consisting of sR73C, sM75I, sG102S, sR122K/I/T, sT126N, sC 137W, sW 172Stop, sV194L and sV 194D wherein the HBV variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0080] As used in the subject specification, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. Thus, for example, reference to "a nucleoside or nucleotide analog" includes a single analog, as well as two or more analogs; reference to "an anti-viral agent" includes a single anti-viral agent as well as two or more anti-viral agents; reference to "the invention" includes reference to a single or multiple aspect of the invention; and so forth.

[0081] Reference to an "anti-viral agent" or an "anti-HBV agent" includes inter alia TFV, ADV, LMV, FTC, ETV, FCV, L-FMAU, LdT, LdC, LdA, HBIG and IFNy.

[0082] The terms "analog", "compound", "active agent", "pharmacologically active agent", "medicament", "active" and "drug" are used interchangeably herein to refer to a chemical compound that induces a desired effect such as inhibit viral replication, infection, maintenance, assembly and/or the function of an enzyme such as HBV DNA polymerase. The terms also encompass pharmaceutically acceptable and pharmacologically active ingredients of those active agents specifically mentioned herein including but not limited to salts, esters, amides, prodrugs, active metabolites, analogs and the like. When the terms "analog", "compound", "active agent", "pharmacologically active agent", "medicament", "active" and "drug" are used, then it is to be understood that this includes the active agent per se as well as pharmaceutically acceptable, pharmacologically active salts, esters, amides, prodrugs, metabolites, analogs, etc.

[0083] Therefore, compounds are contemplated which are useful in inhibiting H BV replication, infection, maintenance, assembly and/or the function of an enzyme such as HBV DNA polymerase. Reference to an "analog", "compound", "active agent", "pharmacologically active agent", "medicament", "active" and "drug" such as TFV, ADV, LMV, ETV, FTC, FCV, L-FMAU, LdT, LdC, LdA and/or optionally other nucleoside or nucleotide analogs or other anti-HBV agents or combinations thereof.

[0084] The present invention contemplates a method of treatment of a subject infected with HBV, the method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV-resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount.

|0085] In a related embodiment, the present invention provides a method of treatment of a subject infected with HBV, the method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV-resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount.

[0086] The term "effective amount" includes a "therapeutically effective amount".

[0087] The terms "effective amount" and "therapeutically effective amount" of an agent as used herein mean a sufficient amount of the agent to provide the desired therapeutic or physiological effect of inhibiting HBV replication, infection, maintenance, assembly and/or the function of an enzyme such as HBV DNA polymerase or surface antigen. Furthermore, an "effective HBV-inhibiting amount" or "effective symptom-ameliorating amount" of an agent is a sufficient amount of the agent to directly or indirectly inhibit replication, infection, maintenance, assembly and/or the function of an enzyme such as HBV DNA polymerase or surface antigen. Undesirable effects, e.g. side effects, are sometimes manifested along with the desired therapeutic effect; hence, a practitioner balances the potential benefits against the potential risks in determining what is an appropriate "effective amount". The exact amount required will vary from subject to subject, depending on the species, age and general condition of the subject, mode of administration and the like. Thus, it may not be possible to specify an exact "effective amount". However, an appropriate "effective amount" in any individual case may be determined by one of ordinary skill in the art using only routine experimentation.

[0088] By "pharmaceutically acceptable" carrier, excipient or diluent is meant a pharmaceutical vehicle comprised of a material that is not biologically or otherwise undesirable, i.e. the material may be administered to a subject along with the selected active agent without causing any or a substantial adverse reaction. Carriers may include excipients and other additives such as diluents, detergents, coloring agents, wetting or emulsifying agents, pH buffering agents, preservatives, and the like.

[0089] Similarly, a "pharmacologically acceptable" salt, ester, emide, prodrug or derivative of a compound as provided herein is a salt, ester, amide, prodrug or derivative that this not biologically or otherwise undesirable.

[0090] The terms "treating" and "treatment" as used herein refer to reduction in severity and/or frequency of symptoms, elimination of symptoms and/or underlying cause, prevention of the occurrence of symptoms and/or their underlying cause, and improvement or remediation of damage in relation to HBV infection. Thus, for example, "treating" a patient involves prevention of HBV infection as well as treatment of a clinically HBV symptomatic individual by inhibiting HBV replication, infection, maintenance, assembly and/or the function of an enzyme such as HBV DNA polymerase. Thus, for example, the present method of "treating" a patient with HBV infection or with a propensity for one to develop encompasses both prevention of HBV infection as well as treating HBV infection or symptoms thereof. In any event, the present invention contemplates the treatment or prophylaxis of HBV infection. [0091] "Patient" as used herein refers to an animal, preferably a mammal and more preferably a primate including a lower primate and even more preferably, a human who can benefit from the formulations and methods of the present invention. A patient regardless of whether a human or non-human animal may be referred to as an individual, subject, animal, host or recipient. The compounds and methods of the present invention have applications in human medicine, veterinary medicine as well as in general, domestic or wild animal husbandry. For convenience, an "animal" includes an avian species such as a poultry bird (including ducks, chicken, turkeys and geese), an aviary bird or game bird. The condition in a non-human animal may not be a naturally occurring HBV infection but HBV-like infection may be induced.

[0092] As indicated above, the preferred animals are humans, non-human primates such as marmosets, baboons, orangatangs, lower primates such as tupia, livestock animals, laboratory test animals, companion animals or captive wild animals. A human is the most preferred target. However, non-human animal models may be used.

[0093] Examples of laboratory test animals include mice, rats, rabbits, guinea pigs and hamsters. Rabbits and rodent animals, such as rats and mice, provide a convenient test system or animal model as do primates and lower primates. Livestock animals include sheep, cows, pigs, goats, horses and donkeys. Non-mammalian animals such as avian species, zebrafish, amphibians (including cane toads) and Drosophila species such as Drosophila melanogaster are also contemplated. Instead of a live animal model, a test system may also comprise a tissue culture system.

[0094] As indicated above, an "anti-HBV agent" includes a nucleoside or nucleotide analog, protein, chemical compound, RNA or DNA or RNAi or siRNA oligonucleotide (either DNA-derived or synthetic). Examples of nucleoside and nucleotide analogs include TFV, ADV, LMV, FTC, ETV, FCV, L-FMAU, LdT, LdC and LdA. [0095] In a particular embodiment, the decreased sensitivity is in respect of TFV. Alternatively, the decreased sensitivity is in respect of ADV, TFV and LMV. Alternatively, the decreased sensitivity is in respect of TFV and ETV. Alternatively, the decreased sensitivity is in respect of TFV and FTC. Alternatively, the decreased sensitivity is in respect of TFV and ETV and optionally ADV and LMV. Alternatively, the decreased sensitivity is in respect of TFV and ADV and optionally ETV. Alternatively, the decreased sensitivity is in respect of TFV and LMV and optionally ETV. Alternatively, the decreased sensitivity is in respect of TFV and ADV and FTC and optionally E TV. Alternatively, the decreased sensitivity is in respect to TFV and FTC and optionally ETV. Alternatively, the decreased sensitivity is in respect of TFV and FTC and LMV and optionally E TV. Alternatively, the decreased sensitivity is in respect of TFV and ADV and LMV and optionally ETV. Alternatively, the decreased sensitivity is in respect to TFV and ADV and FTC and optionally ETV or FCV. Alternatively, the decreased sensitivity is in respect to TFV and LMV and FTC and optionally ETV or FCV. Alternatively, the decrease sensitivity is in respect of TFV and ADV and LMV and FTC and optionally ETV or FC V. Alternatively, the decreased sensitivity is in respect of TFV and ADV and FTC and LMV and optionally ETV or FCV.

[0096] Reference herein to "anti-HBV agents" includes nucleoside and nucleotide analogs as well as immunological reagents (e.g. antibodies to HBV surface components) and chemical, proteinaceous and nucleic acid agents which inhibit or otherwise interfere with viral replication, maintenance, infection, assembly or release. Reference herein to "nucleic acid" includes reference to a sense or antisense molecule, RNA or DNA, oligonucleotides and RNAi and siRNA molecules and complexes containing same.

[0097] In addition to a mutation in the gene encoding DNA polymerase, due to the overlapping nature of the HBV genome (Figure 1 ), a corresponding mutation may also occur in the gene encoding the S gene encoding the surface antigen (FIBsAg) resulting in reduced interactivity of immunological reagents such as antibodies and immune cells to HBsAg. The reduction in the interactivity of immunological reagents to a viral surface component generally includes the absence of immunological memory to recognize or substantially recognize the viral surface component. The present invention extends, therefore, to an HBV variant exhibiting decreased sensitivity to TFV alone or in combination with another anti-viral agent or a reduced interactivity of an immunological reagent to HBsAg wherein the variant is selected following exposure to TFV alone or in combination with another anti-viral agent.

[0098] A viral variant may, therefore, carry a mutation only in the DNA polymerase gene or both in the DNA polymerase gene and the S gene. The term "mutation" is to be read in its broadest context and includes multiple mutations. Exemplary surface antigen mutations include a mutation in a codon selected from 73, 75, 102, 122, 126, 137, 172 and 194 such as sR73C, sM75I, sG 102S, sR122K/I/T, sT126N, sC 1 37W, sW 1 72Stop, sV 1 94L and sV 194D.

[0099] A mutation in any domain of the HBV DNA polymerase and in particular regions F and G, and domains A through to E is contemplated herein provided the mutation leads to decreased sensitivity to TFV alone or in combination with ADV and/or LMV and/or ETV and/or FTC and/or FCV and/or L-FMAU and/or LdT and/or LdC and/or LdA.

[0100] In this specification, reference is particularly made to the conserved regions of the DNA polymerase as defined by domains A to E. Regions A to E are defined by the amino acid sequence set forth in Formula II in Australian Patent No. 73483 1.

[0101 ] Particularly, the mutation results in an altered amino acid sequence in any one or more of domains F and G, and domains A through to E or regions proximal thereto of the HBV DNA polymerase.

[0102] Another aspect provides an FIBV variant comprising a mutation in an overlapping open reading frame in its genome wherein the mutation is in a region defined by one or more of domains F and G, and domains A through to E of HBV DNA polymerase and wherein the variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent. [0103] A further aspect contemplates an HBV variant comprising a mutation in the nucleotide sequence encoding HBsAg resulting in an amino acid addition, substitution and/or deletion in the HBsAg wherein the variant exhibits decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0104] More particularly, a variant HBV is provided comprising a surface antigen having an amino acid sequence with a single or multiple amino acid substitution, addition and/or deletion or a truncation compared to a surface antigen from a reference or wild-type HBV and wherein an antibody generated to the reference or wild-type surface antigen exhibits reduced capacity for neutralizing the HBV variant, the variant selected by exposure of a subject to TFV alone or in combination with another anti-viral agent.

[0105] The term "combination therapy" means that both combinations of TFV, ADV, LMV, FTC, FCV, L-FMAU, ETV, LdT, LdC, LdA and/or other anti-viral agent are co-administered in the same composition or simultaneously in separate compositions. The term "sequential therapy" means that the two agents are administered within seconds, minutes, hours, days or weeks of each other and in either order. Sequential therapy also encompasses completing a therapeutic course with one or more anti-viral agents and then completing a second or third or subsequent therapeutic courses with another anti-viral agent.

[0106] Accordingly, another aspect of contemplates an HBV variant comprising a surface antigen having an amino acid sequence with a single or multiple amino acid substitution, addition and/or deletion or truncation compared to the pretreatment HBV and wherein the surface antigen of the variant HBV exhibits an altered immunological profile compared to the pretreatment HBV where the variant HBV is selected for by exposure of a subject to TFV therapy or therapy by one or more other nucleoside or nucleotide analogs or other anti-HBV agents. [0107] Particularly, the variants are in isolated form such that they have undergone at least one purification step away from naturally occurring body fluid. Alternatively, the variants may be maintained in isolated body fluid or may be in DNA form. The present invention also contemplates infectious molecular clones comprising the genome or parts thereof from a variant HBV. Furthermore, the present invention provides isolated components from the variant HBVs such as but not limited to an isolated HBsAg. Accordingly, the present invention provides an isolated HBsAg or a recombinant form thereof or derivative or chemical equivalent thereof, the HBsAg being from a variant HBV selected by exposure of a subject to TFV alone or in combination with another anti-viral agent.

[0108] More particularly, an isolated variant HBsAg or a recombinant or derivative form thereof or a chemical equivalent thereof is provided wherein the HBsAg or its recombinant or derivative form or its chemical equivalent exhibits an altered immunological profile compared to an HBsAg from a reference HBV, the HBsAg being from a variant HBV selected by exposure of a subject to TFV alone or in combination with another anti-viral agent.

[0109] Even more particularly, an isolated variant HBsAg or a recombinant or derivative form thereof or a chemical equivalent thereof is provided wherein the HBsAg or its recombinant or derivative form or its chemical equivalent comprises an amino acid sequence with a single or multiple amino acid substitution, addition and/or deletion or a truncation compared to an HBsAg from a reference HBV and wherein a neutralizing antibody directed to a reference HBV exhibits no or reduced neutralising activity to an HBV carrying the variant HBsAg, the HBsAg being from a variant HBV selected by exposure of a subject to TFV alone or in combination with another anti-viral agent.

[0110] Particular mutations in the HBV DNA polymerase include variants selected from patients with HBV recurrence following exposure to TFV alone or in combination with another anti-viral agent. Nucleoside or nucleotide analogs or other anti-HBV agents may be indicated during , after or prior to a transplantation procedure (e.g. bone marrow transplantation (BMT) or OLT) or following treatment of patients diagnosed with hepatitis. Following selection of variants, viral loads are obtainable at levels similar to pre-treatment levels or increase while on therapy.

[0111 ] Useful mutants in the rt region include rtS81 L, rtD83V rtV84L, rtS85P, rtR l 1 0K, rtL 146V, rtN139K, rtK168Stop, rtA181 T, rtS202T, rtS202R, rt 241 R, rtK 141 N and rtF249L; as well as co-mutantions selected from (i) rtS81 L and rtK 168Stop; (ii) rtRl 1 OK, rtL 146V, rtS202T and rtK241 R; and (iii) rtV84L, rtS85P and HK241N; or an equivalent mutation or another substitution at the above-listed codons.

[01 12] Reference to "co-mutations" includes mutations at codons (i) 81 and 1 68; (ii) 1 10. 146, 202 and 241 ; and (iii) 84, 85 and 241 such as (i) rtSS I L and rtK 1 68Stop; (ii) rlR l l OK, rtL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and ΠΚ241 Ν. A "co- mutation" means that a variant will comprise mutations at all mentioned codons. The present invention is particularly directed to co-mutations at codons 81 and 168.

[0113] Such HBV variants and strains are proposed to exhibit a decreased sensitivity to TFV alone or in combination with another anti-viral agent. It should be noted that the nomenclature system for amino acid positions is based on the methionine residues in the YMDD motif being designated codon rtM204. This numbering system is different to that in Australian Patent No. 734831 where the methionine residue in the YMDD motif within the polymerase gene is designated codon 550. In this regard, rtL 1 80M and rtM204V correspond to L526M and M550V, respectively, in Australian Patent No. 73483 1 . Corresponding mutations may also occur in envelope genes such as in one or more of PreS l , PreS2 and S.

[01 14] The identification of the variants herein permits the generation of a range of assays to detect such variants. The detection of such variants may be important in identifying resistant variants to determine the appropriate form of chemotherapy and/or to monitor vaccination protocols, or develop new or modified vaccine preparations. (0115] Still another aspect contemplates a method for determining the potential for an HBV to exhibit reduced sensitivity to TFV alone or in combination with another anti-viral agent the method comprising isolating DNA or corresponding mRNA from the HBV and screening for a mutation in the nucleotide sequence encoding HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in any one or more of domains F and G, and A domains through to E or a region proximal thereto of the DNA polymerase and associated with resistance or decreased sensitivity to TFV alone or in combination with another anti-viral agent wherein the presence of such a mutation is an indication of the likelihood of resistance to TFV alone or in combination with another antiviral agent.

[0116] Another aspect provides a method for determining the potential for an HBV to exhibit reduced sensitivity to TFV alone or in combination with another anti-viral agent the method comprising isolating DNA or corresponding mRNA from the HBV and screenin for a mutation in the S gene in any one or more of domains F and G, and A domains through to E or a region proximal thereto of the DNA polymerase and the HBsAg associated with resistance or decreased sensitivity to TFV alone or in combination with another anti-viral agent wherein the presence of such a mutation is an indication of the likelihood of resistance to TFV alone or in combination with another anti-viral agent.

[0117] Particularly, the assay detects one or more of the following mutations in the rt. rtS81 L, rtD83V rtV84L, rtS85P, rtRl l OK, rtL146V, rtN139 , rt 168Stop, rtA 1 8 1 T. rtS202T, rtS202R, HK241 R, rt 141N and HF249L; or a co-mutation in the rt selected from (i) rtS81 L and rtK168Stop; (ii) rtRl l OK, rtL146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N; or in the surface antigen selected from sR73C, sM75I, sG 102S, SR122 /I/T, sT126N, sC 137W, sW172Stop, sV 194L and sV 194D wherein the variant exhibits a decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[01 18] Also contemplated is a method for determining whether an HBV strain exhibits reduced sensitivity to a nucleoside or nucleotide analog or other anti-HBV agents by isolating DNA or corresponding mRNA from the HBV and screening for a mutation in the nucleotide sequence encoding the DNA polymerase wherein the presence of the following mutations in the rt region rtS81 L, rtD83V rtV84L, rtS85P, rtRl l OK, rtL 146V, HN 1 39K, rt 168Stop, rtA 1 81 T, rtS202T, rtS202R, rt 241 R, rtK 141 N and rtF249L or the co- mutations selected from (i) rtS81 L and rt 168Stop; (ii) rtR l l OK, rtL 146V, rtS202T and rtK241 R; and (iii) rtV84L, rtS85P and rt 241 N or an equivalent mutation or a mutation in the surface antigen selected from the list consisting of sR73C, sM751, sG 1 02S, SR122K/I/T, sT126N, sC 137W, sW172Stop, sV 194L and sV 194D is indicative of a varian which exhibits a decreased sensitivity to TFV alone or in combination with another antiviral agent.

[0119] A further aspect produces a method for determining whether an HBV strain exhibits reduced sensitivity to a nucleoside or nucleotide analog or other anti-HBV agents, the method comprising isolating DNA or corresponding mRNA from the HBV and screening for a mutation in the nucleotide sequence encoding the DNA polymerase and/or a corresponding region of the S gene, wherein the presence of a mutation selected from sR73C, sM75I, sG 102S, sR122K/I/T, sT126N, sC 137W, sW 1 72Stop, sV 1 94L and sV 194D is indicative of a variant which exhibits a decreased sensitivity to TFV alone or in combination with another anti-viral agent.

[0120] The detection of HBV or its components in cells, cell lysates, cultured supernatant fluid and bodily fluid may be by any convenient means including any nucleic acid-based detection means, for example, by nucleic acid hybridization techniques or via one or more polymerase chain reactions (PCRs). The term "bodily fluid" includes any fluid derived from the blood, lymph, tissue or organ systems including serum, whole blood, biopsy and biopsy fluid, organ explants and organ suspension such as liver suspensions. The invention further encompasses the use of different assay formats of the nucleic acid-based detection means, including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), single-strand chain polymorphism (SSCP), amplification and mismatch detection (AMD), interspersed repetitive sequence polymerase chain reaction (IRS-PCR), inverse polymerase chain reaction (iPCR) and reverse transcription polymerase chain reaction (RT-PCR), amongst others. Other forms of detection include Northern blots, Southern blots, PCR sequencing, antibody procedures such as ELISA, Western blot and immunohistochemistry. A particularly useful assay includes the reagents and components required for immobilized oligonucleotide- or oligopeptide-mediated detection systems.

[0121 ] One particularly useful nucleic acid detection system is the reverse hybridization technique. In this technique, DNA from an HBV sample is amplified using a biotin or other ligand-labeled primer to generate a labeled ampliiicon. Oligonucleotides immobilized to a solid support such as a nitrocellulose film are then used to capture amplified DNA by hybridization. Specific nucleic acid fragments are identified via bioiin or the ligand. Generally, the labeled primer is specific for a particular nucleotide variation to be detected. Amplification occurs only if the variation to be detected is present. There are many forms of the reverse hybridization assay and all are encompassed by the present invention.

[0122] Another aspect contemplated herein provides a method for detecting a variant H BV exhibiting an altered immunological profile the method comprising isolating an HBV from a subject exposed to TFV alone or in combination with another anti-viral agent and then contacting the HBV with a panel of one or more antibodies to a surface antigen and screening for any change in binding affinity or binding spectrum.

[0123] In a related embodiment, a method is contemplated for detecting a variant H BV exhibiting an altered immunological profile, the method comprising isolating a serum sample from a subject exposed to TFV alone or in combination with another anti-viral agent and then contacting the serum with a panel of HBV surface antigens or antibody- binding fragments thereof and screening for any change in binding affinity or binding spectrum.

[0124] Detecting HBV replication in cell culture is particularly useful. [0125] This and other aspects are particularly amenable to microarray analysis such as to identify oligonucleotides including sense and antisense molecules, RNAi or siRNA molecules or DNA or RNA-binding molecules which down-regulate genomic sequences or transcripts of HBV. Microarray analysis may also be used to identify particular mutations in the HBV genome such as within the HBV DNA polymerase-coding region or the HBsAg-coding region.

[0126] Another aspect of contemplates a method for detecting an agent which exhibits inhibitory activity to an HBV by: generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in a plasmid vector and then transfecting the cells with the construct; contacting the cells, before, during and/or after transfection, with the agent to be tested; culturing the cells for a time and under conditions sufficient for the H B V to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agents; and then subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral-component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent.

[0127] In a particular embodiment, the plasmid vector may include genes encoding part or all of other viral vectors such as baculovirus or adenovirus (Ren and Nassal, 2001 , supra) and the method comprises: generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in or fused to an amount of a baculovirus genome or adenovirus genome effective to infect cells and then infecting the cells with the construct; contacting the cells, before, during and/or after infection, with the agent to be tested; culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent; and then subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral-component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent wherein the HBV is resistant or exhibits reduced sensitivity to TFV.

[0128] In an alternative embodiment, the method comprises: generating a continuous cell line comprising an infectious copy of the genome of the HBV in a replication competent effective amount such that the infectious HBV genome is stably integrated into the continuous cell line such as but not limited to 2.2.15 or AD; contacting the cells with the agent to be tested; culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent; and then subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral -component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent wherein the HBV exhibits resistance or reduced sensitivity to TFV.

[0129] The above-mentioned methods are particularly useful in identifying or developing agents against HBV variants such as those carrying rt mutations in codons 81 , 83, 84, 85, 1 10, 146, 1 39, 168, 1 81 , 202, 241 , 141 and/or 249 or surface antigen mutations in codons 73, 75, 102, 122, 126, 137, 172 and/or 194. In an embodiment, the rt mutations are rtS81 L, rtD83V rtV84L, rtS85P, rtR l l OK, rtL 146V, rtN 139 , rtK 168Stop, rtA 1 8 1 T, rtS202T, rtS202R, rt 241 R, H 141N and rtF249L. In another embodiment, the rt mutations are co-mutations (i) rtS81 L and rt 168Stop; (ii) rtR l l OK, HL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rt 241 N. In yet another embodiment, the surface antigen mutations are sR73C, sM75I, sG 102S, sR122 /I/T, sT126N, sC 137W, sW 172Stop, sV 194L and sV 194D.

[0130] The detection of amino acid variants of DNA polymerase or surface antigen is conveniently accomplished by a range of amino acid detection techniques. Where an HBV variant comprises an amino acid change, then such an isolate is considered a putative HBV variant having an altered DNA polymerase activity or HBsAg.

[0131 ] Further contemplated herein are agents which inhibit an HBV variant which is resistant to TFV alone or in combination with another anti-viral agent. Such agents are particularly useful if long term treatment by TFV alone or in combination with another anti-viral agent is contemplated by the clinician. The agents may be DNA or RNA or proteinaceous or non-proteinaceous chemical molecules. Natural product screening such as from plants, coral and microorganisms is also contemplated as a useful potential source of masking agents as is the screening of combinatorial or chemical libraries. The agents may be in isolated form or in the form of a pharmaceutical composition or formulation and may be administered in place of or sequentially or simultaneously with a nucleoside or nucleotide analog. Furthermore, rationale drug design is contemplated including solving the crystal or NMR structure of, for example, HBV DNA polymerase and designing agents which can bind to the enzyme's active site. This approach may also be adapted to other HBV components.

[0132] Accordingly, another aspect contemplates a method for detecting an agent which exhibits inhibitory activity to an HBV which exhibits resistance or decreased sensitivity TFV alone or in combination with another anti-viral agent, the method comprising: generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in a plasmid vector and then transfecting the cells with the construct; contacting the cells, before, during and/or after transfection, with the agent to be tested; culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent; and subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral- component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent.

[0133] Still another aspect provides a method for detecting an agent which exhibits inhibitory activity to an HBV which exhibits resistance or decreased sensitivity to TFV alone or in combination with another anti-viral agent, the method comprising: generating a genetic construct comprising a replication competent-effective amount of the genome from the HBV contained in or fused to an amount of a baculovirus genome effective to infect cells and then infecting the cells with the construct; contacting the cells, before, during and/or after infection, with the agent to be tested; culturing the cells for a time and under conditions sufficient for the HBV to replicate, express genetic sequences and/or assemble and/or release virus or virus-like particles if resistant to the agent; and subjecting the cells, cell lysates or culture supernatant fluid to viral- or viral- component-detection means to determine whether or not the virus has replicated, expressed genetic material and/or assembled and/or been released in the presence of the agent.

[0134] Particularly, the HBV genome is stably integrated into the cells' genome.

[0135] Generally, the HBV is resistant to or has reduce sensitivity to TFV. In an embodiment, the mutation is at a codon selected from the list consisting of rt codons 1 81 . 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141 . In another embodiment, the mutation is a co-mutation at rt codons selected from the list consisting of (i) 81 and 1 68: (ii) 1 10, 146, 202 and 241 ; and (iii) 84, 85 and 241 . Particular mutations are selected from the list consisting of rtS81 L, rtD83V rtV84L, rtS85P, rtRl l OK, HL 146V, ηΝΜ 39 , rtK 168Stop, rtA 181 T, rtS202T, rtS202R, rt 241 R, rt 141 N and rtF249L. Particular co- mutations are selected from the list consisting of (i) rtS81 L and rt 168Stop; (ii) rtR l 1 0K, rtL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rt 241N. Mutants contemplated in HBsAg include sR73C, sM75I, sG102S, sR122K/I/T, sT126N, sC 137W, sW172Stop, sV194L and sV194D.

[0136] Useful cells include 2.2.15 cells (Price el al, Proc. Nail. Acad. Sci. USA 86(21):8541 -8544, 1989 or AD cells (also known as HepAD32 cells or HepAD79 cells [Ying et al, 2000, supra ]. [0137] Whilst the baculovirus vector is a particularly useful in the practice of the instant method a range of other vectors may also be used such as but not limited to adenoviral vectors.

[0138] Cell lines (e.g. 2.2.15 or AD cells) carrying genetic constructs comprising all or a portion of an HBV genome or a gene or part of a gene therefrom are also contemplated herein.

[0139] Also provided is the use of the subject HBV variants to screen for anti-viral agents. These anti-viral agents inhibit the virus. The term "inhibit" includes antagonizing or otherwise preventing infection, replication, assembly and/or release or any intermediate step. Particular anti-viral agents include nucleoside or nucleotide analogs or anti-H V agents, as well as non-nucleoside molecules.

[0140] In addition, rational drug design is also contemplated to identify or generate chemical molecules which either mimic a nucleoside or which interact with a particular nucleotide sequence or a particular nucleotide. Combinatorial chemistry and two hybrid screening are some of a number of techniques which can be employed to identi fy potential therapeutic or diagnostic agents.

[0141 ] In one example, the crystal structure or the NMR structure of polymerase or the surface antigen is used to rationally design small chemical molecules likely to interact with key regions of the molecule required for function and/or antigenicity. Such agents may be useful as inhibitors of polymerase activity and/or may alter an epitope on the surface antigen.

[0142] Several models of the HBV polymerase have been prepared due to the similarity with reverse transcriptase from HIV (Das et al, J. Virol. 75(10) ΆΊΊ \ ΑΊΊ , 2001 ; Bartholomeusz et al, Intervirology 40(5-6) . 337 -342 1997; Allen et al, Hepalology 27^: 1670- 1677, 1998). The models of the HBV polymerase can be used for the rational drug design of new agents effective against HBV encoding the resistant mutations as well as wild type virus. The rational drug that is designed may be based on a modification of an existing antiviral agent such as the agent used in the selection of the HBV encoding the mutations associated with resistance. Viruses or clones expressing HBV genomic material encoding the mutations may also be used to screen for new antiviral agents.

[0143] In an alternative embodiment, a method is contemplated for detecting an agent which exhibits inhibitory activity to an HBV polymerase in an in vitro polymerase assay. The HBV polymerase activity can be examined using established assays (Gaillard el al, 2002, supra; Xiong et al, 1998, supra).

[0144] As indicated above, microarray technology is also a useful means of identi fying agents which are capable of interacting with defined HBV internal or external components. For example, arrays of HBV DNA polymerase or peptide fragments thereof carrying different amino acid variants may be used to screen for agents which are capable of binding or otherwise interacting with these molecules. This is a convenient way of determining the differential binding patterns of agents between HBV variants. Arrays of antibodies may also be used to screen for altered HBsAg molecules. Microarrays are also useful in proteomic analysis to identify molecules such as antibodies, interferons or cytokines which have an ability to interact with an HBV component. Microarrays of DNA and RNA molecules may also be employed to identify sense and antisense molecules for genetic regions on the HBV genome or transcripts thereof.

[0145] The above methods are particularly useful in identifying an inhibitor of an H BV resistant to or exhibiting reduced sensitivity to TFV alone or in combination with another anti-viral agent. The present invention extends, therefore, to compositions of the inhibitors. The inhibitors may also be in the form of antibodies or genetic molecules such as ribozymes, antisense molecules and/or sense molecules for co-suppression or the induction of RNAi or may be other nucleoside or nucleotide analogs or other anti-HBV agents or derivatives of known analogs. Reference to RNAi includes reference to short, interfering RNAs (siRNA) and all RNAi-type molecules may be DNA-derived or synthetic. [0146] The term "composition" includes a "pharmaceutical composition" or a formulation.

[0147] The inhibitor is referred to below as an "active ingredient" or "active compound" and may be selected from the list of inhibitors given above.

[0148] The composition may include an antigenic component of the HBV, a defective HBV variant or an agent identified through natural product screening or rational drug design (including combinatorial chemistry).

[0149] Pharmaceutically acceptable carriers and/or diluents include any and all solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents and the like. The use of such media and agents for pharmaceutical active substances is well known in the art. Except insofar as any conventional media or agent is incompatible with the active ingredient, use thereof in the therapeutic compositions is contemplated. Supplementary active ingredients can also be incorporated into the compositions.

[0150] The pharmaceutical composition may also comprise genetic molecules such as a vector capable of transfecting target cells where the vector carries a nucleic acid molecule capable of encoding an aspartyl protease inhibitor. The vector may, for example, be a viral vector.

[0151] Pharmaceutical forms suitable for injectable use include sterile aqueous solutions (where water soluble) and sterile powders for the extemporaneous preparation of sterile injectable solutions. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dilution medium comprising, for example, water, ethanol, polyol (for example, glycerol, propylene glycol and liquid polyethylene glycol, and the like), suitable mixtures thereof and vegetable oils. The proper fluidity can be maintained, for example, by the use of superfactants. The preventions of the action of microorganisms can be brought about by various anti-bacterial and anti-fungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thirmerosal and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminium monostearate and gelatin.

[0152] Sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with the active ingredient and optionally other active ingredients as required, followed by filtered sterilization or other appropriate means of sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, suitable methods of preparation include vacuum drying and the freeze-drying technique which yield a powder of active ingredient plus any additionally desired ingredient.

[0153] When the active ingredient is suitably protected, it may be orally administered, for example, with an inert diluent or with an assimilable edible carrier, or it may be enclosed in hard or soft shell gelatin capsule, or it may be compressed into tablets. For oral therapeutic administration, the active ingredient may be incorporated with excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers and the like. Such compositions and preparations should contain at least 1 % by weight of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 5 to about 80% of the weight of the unit. The amount of active compound in such therapeutically useful compositions is such that a suitable dosage will be obtained. Preferred compositions or preparations according to the present invention are prepared so that an oral dosage unit form contains between about 0.1 μg and 200 mg of active compound. Alternative dosage amounts include from about 1 g to about 1000 mg and from about 10 μg to about 500 mg. These dosages may be per individual or per kg body weight. Administration may be per hour, day, week, month or year. [0154] The tablets, troches, pills, capsules and the like may also contain the components as listed hereafter. A binder such as gum, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, lactose or saccharin may be added or a flavouring agent such as peppermint, oil of wintergreen or cherry flavouring. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier. Various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit. For instance, tablets, pills or capsules may be coated with shellac, sugar or both. A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propylparabens as preservatives, a dye and a flavouring. Of course, any material used in preparing any dosage unit form should be pharmaceutically pure and substantially nontoxic in the amounts employed. In addition, the active compound(s) may be incorporated into sustained-release preparations and formulations.

[0155] As stated above, the present invention further extends to an isolated HBsAg from the HBV variants herein described. More particularly, the present invention provides an HBsAg or a recombinant form thereof or derivative or chemical equivalent thereof. The isolated surface component and, more particularly, isolated surface antigen or its recombinant, derivative or chemical equivalents are useful in the development of biological compositions such as vaccine formulations.

[0156] Yet another aspect provides a composition comprising a variant HBV resistant to TFV alone or in combination with another anti-viral agent and one or more pharmaceutically acceptable carriers and/or diluents. Such a composition may be regarded as a therapeutic composition and is useful in generating an immune response including a humoral response. Generally, the HBV variants are "defective" and in themselves arc unable to cause a sustained infection in a subject.

[0157] As indicated above, antibodies may be generated to the mutant HBV agents and used for passive or direct vaccination against infection by these viruses. The antibodies may be generated in humans or non-human animals. In the case of the latter, the non- human antibodies may need to be deimmunized or more specifically humanized prior to use. Deimmunized may include, for example, grafting complimentarity determining regions (CDRs) from the variable region of a murine or non-human animal anti-HBV antibody onto a human consensus fragment antibody binding (Fab) polypeptide. Alternatively, amino acids defining epitopes in the variable region of the antibody may be mutated so that the epitopes are no longer recognized by the human MHC II complex.

[0158] Insofar as ribozyme, antisense or co-suppression (RNAi) or siRNA or complexes thereof repression is concerned, this is conveniently aimed at post-transcription gene silencing. DNA or RNA may be administered or a complex comprising RNAi or a chemical analog thereof specific for HBV mRNA may be employed.

[0159] All such molecules may be incorporated into pharmaceutical compositions.

[0160] In another embodiment, provided is a biological composition comprising a variant HBV or an HBsAg or L, M or S proteins from the variant HBV or a recombinant or derivative form thereof or its chemical equivalent.

[0161] Generally, if an HBV is used, it is first attenuated. The biological composition generally further comprises one or more pharmaceutically acceptable carriers and/or diluents.

[0162] The biological composition may comprise HBsAg or like molecule from one HBV variant or the composition may be a cocktail of HbsAgs or L, M or S proteins or like molecules from a range of TFV alone or in combination with another anti-viral agent HB V variants resistant to TFV alone or in combination with another anti-viral agent. Similar inclusions apply where the composition comprises an HBV.

[0163] Further provided is the use of defective HBV variants in the manufacture of therapeutic vaccines to vaccinate individuals against infection by HBV strains having a particular nucleotide sequence or encoding a particular polymerase or surface antigen or L, M or S proteins.

[0164] Examples of suitable vaccine candidates are defective forms of HBV variants which are resistant to TFV. In an embodiment, the mutation is at a codon selected from the list consisting of rt codons 181 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141 . In another embodiment, the mutation is a co-mutation at rt codons selected from the list consisting of (i) 81 and 168; (ii) 1 10, 146, 202 and 241 ; and (iii) 84, 85 and 241 . Particular rt mutations are selected from the list consisting of rtS81 L, rtD83V rtV84L, rtS85P, rtRU OK, rtL 146V, rtN139K, rt 168Stop, rtA181 T, rtS202T, rtS202R, rt 241 R, rtK141N and rtF249L. Particular rt co-mutations are selected from the list consisting of (i) rtS81 L and rt 168Stop; (ii) rtRU OK, rtL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N. Useful HBsAg mutations include those in HBsAg codons 73. 75. 102, 122, 126, 137, 1 72 and/or 194 such as sR73C, sM75I, sG 102S, sR122K/I/T, sT 1 26 , sC 1 37W, sW 1 72Stop, sV 194L and sV 194D.

[0165] In an embodiment, for example, an HBV variant may be identified having a particular mutation in its polymerase conferring resistance or decreased sensitivity to a nucleoside or nucleotide analog. This variant may then be mutated to render it defective, i.e. attenuated or unable to cause infection. Such a defective, nucleoside or nucleotide analog-resistant virus may then be used as a therapeutic vaccine against virulent viruses having the same mutation in its polymerase.

[0166] The subject invention extends to kits for assays for variant HBV resistant to TFV alone or in combination with another anti-viral agent. Such kits may, for example, contain the reagents from PCR or other nucleic acid hybridization technology or reagents for immunologically based detection techniques. A particularly useful assay includes the reagents and components required for immobilized oligonucleotide- or oligopeptide- mediated detection systems. [0167] Still another aspect of contemplates a method for determining the potential for an HBV to exhibit reduced sensitivity to TFV alone or in combination with another anti-viral agent, the method comprising isolating DNA or corresponding mRNA from the HBV and screening for a mutation in the nucleotide sequence encoding HBV DNA polymerase resulting in at least one amino acid substitution, deletion and/or addition in any one or more of domains F and G, and domains A through to E or a region proximal thereto of the DNA polymerase and associated with resistance or decreased sensitivity to TFV alone or in combination with another anti-viral agent, wherein the presence of such a mutation is an indication of the likelihood of resistance to TFV alone or in combination with another antiviral agent.

[0168] An assessment of a potential viral variant is important for selection of an appropriate therapeutic protocol. Such an assessment is suitably facilitated with the assistance of a computer programmed with software, which inter alia adds input codes for at least two features associated with the viral variants to provide a value corresponding to the resistance or sensitivity of a viral variant to a particular chemical compound or immunological agent. The value can be selected from (a) the ability to exhibit resistance for reduced sensitivity to a particular compound or immunological agent; (b) an altered DNA polymerase from wild-type HBV; (c) an altered surface antigen from wild-type HBV; or (d) morbidity or recovery potential of a patient. Thus, in accordance with the present invention, the values for such features are stored in a machine-readable storage medium, which is capable of processing the data to provide a value for a particular viral variant or a biological specimen comprising same.

[0169] Thus, in another aspect, a computer program product is contemplated for assessing the likely usefulness of a viral variant or biological sample comprising same for determining an appropriate therapeutic protocol in a subject the product comprising:

( 1 ) code that receives as input code for at least two features associated with the viral agents or biological sample comprising same, wherein the features are selected from: (a) the ability to exhibit resistance for reduced sensitivity to a particular compound or immunological agent;

(b) an altered DNA polymerase from wild-type HBV;

(c) an altered surface antigen from wild-type HBV; or

(d) morbidity or recovery potential of a patient;

(2) code that adds the input code to provide a sum corresponding to a value for the viral variants or biological samples; and

(3) a computer readable medium that stores the codes.

[0170] In a related aspect, a computer is provided for assessing the likely usefulness of a viral variant or biological sample comprising same in a subject, wherein the computer comprises:

(1 ) a machine-readable data storage medium comprising a data storage material encoded with machine-readable data, wherein the machine- readable data comprise input codes for at least two features associated with the viral variant or biological sample; wherein the features are selected from:-

(a) the ability to exhibit resistance for reduced sensitivity to a particular compound or immunological agent;

(b) an altered DNA polymerase from wild-type HBV;

(c) an altered surface antigen from wild-type HBV; or

(d) morbidity or recovery potential of a patient;

(2) a working memory for storing instructions for processing the machine- readable data; (3) a central-processing unit coupled to the working memory and to the machine-readable data storage medium, for processing the machine readable data to provide a sum of the input code corresponding to a value for the compound(s); and

(4) an output hardware coupled to the central processing unit, for receiving the value.

[0171] Any general or special purpose computer system is contemplated by the present invention and includes a processor in electrical communication with both a memory and at least one input/output device, such as a terminal. Figure 15 shows a generally suitable computer system. Such a system may include, but is not limited, to personal computers, workstations or mainframes. The processor may be a general purpose processor or microprocessor or a specialized processor executing programs located in RAM memory. The programs may be placed in RAM from a storage device, such as a disk or preprogrammed ROM memory. The RAM memory in one embodiment is used both for data storage and program execution. The computer system also embraces systems where the processor and memory reside in different physical entities but which are in electrical communication by means of a network.

[0172] In an alternative embodiment, the program screens for a mutation selected from, in one embodiment, rtS81L, rtD83V rtV84L, rtS85P, rtRl l OK, rtL 146V, HN 139 , rtK168Stop, HA181T, rtS202T, rtS202R, rtK241 R, rtK141N and rtF249L. In another embodiment (i) rtS81L and rt 168Stop; (ii) rtRl lOK, HL146V, HS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N.

[0173] Useful mutants in the HBsAg region include sR73C, sM75I, sG 102S, sR122K/l/T. ST126N, sC137W, sW172Stop, sV 194L and sV194D.

[0174] The present invention is further described by the following non-limiting Examples. EXAMPLE 1

Overlapping genome of HB V

[0175] The overlapping genome of HBV is represented in Figure 1. The gene encoding DNA polymerase (P), overlaps the viral envelope genes, Pre-S l and Pre-S2, and partially overlaps the X and core (C) genes. The HBV envelope comprises small, middle and large proteins HBV surface antigens. The large protein component is referred to as the HBV surface antigen (HBsAg) and is encoded by the S gene sequence. The Pre-S l and Pre-S2 gene sequences encode the other envelope components.

EXAMPLE 2

Patients on TFV and Analysis of HBV DNA

[0176] The mutation profile of TFV associated mutations in TFV patients were examined in patients that had no previous treatment and were previous treated ( Table 4).

[0177] Thirty-three histologically proven patients with chronic hepatitis B were prospectively treated with TFV 300mg daily for 6 or more months. Seven patients had prior exposure to 1MV and two had prior exposure to ADV.

[0178] Nested PCR was used to amplify the HBV rt polymerase region and the overlapping HBsAg genes.

[0179] Of the 33 patients, 20(60%) were HBeAg positive and 1 3 were HBeG negative. The baseline median DNA was I x l O⁷ (4.5 10" to 4.4 x l 0^K) copies/ml. and ALT was 65 (27-321 ).

[0180] The median duration of therapy was 12 months (6-24 months). Eight patients were found to select mutations. [0181 ] The mutations were rtS81 L, rtD83V rtV84L, HS85P, rtRl l O , rtL 146V, rtN 1 39 . rt 168Stop, rtA 181 T, rtS202T, HS202R, rt 241 R, rtK 141 N and rtF249L.

[0182] Two patients had virological breakthough while on TFV treatment. This include one patient that had previously ADV +LMV treatment (Patient 3, Table 4) that had novel TFV mutations rtL68P, rtS81 L and rtK168Stop. The second patient that had virological breakthough while on TFV treatment. This patient had no previous antiviral treatment and had selected HBV encoding the mutation rtA181 T.

EXAMPLE 3

Detection of Viral Markers

[0183] Hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), anti-HBe and hepatitis B core antigen (HBeAg) specific IgG and IgM were measured using commercially available immunoassays (Abbott Laboratories, North Chicago, 1 L, USA). Hepatitis B viral DNA levels were measured using a capture hybridization assay according to the manufacturer's directions (Digene Hybrid Capture II, Digene Diagnostics Inc.. Beltsville, MD). The manufacturers stated cut-off for detecting HBV viremia in clinical specimens was 0.7x 10⁶ copies/ml or 2.5 pg/ml [Hendricks el al, Am J Clin Pathol 704:537-46, 1995]. HBV DNA levels can also be quantitated using other commercial kits such as Cobas amplification HBV monitor kit (Roche).

EXAMPLE 4

HBV ON A

[0184] HBV DNA was extracted from 100 μΐ of serum as described previously by Aye el al, J. Hepatol. 26. 1 148-1 153, 1997.

[0185] Amplification conditions were denaturation at 95 C for 10 min then 40 cycles of 1 min at 94 C for denaturation, annealing at 55 C for 1 min and extension at 72 C for 2 min and final cycle of elongation step at 72 C for 10 min. Polymerase chain reaction was performed using outer primers (First Round)

TN I : (53-75) 5 '-CTYCCTGCTGGTGGCTCCAGTTC-3 ' (SEQ ID NO: l )

TN2: (1 175-1 192) 3'-CRTCAGCAAACACTTGRC-3' (SEQ ID NO:2)

The first round amplification was included in the second amplification step if detected negative or light band with the same reaction conditions.

Nested PCR was performed with following inner primers (Second Round)

TN3 : (253-272) 5'- CTCGTGGTGG ACTTCTCTC-3 ' (SEQ ID NO:3)

TN4: (1000-1019) 5'-GCAAARCCCMAAAGRCCCAC-3'(SEQ ID NO:4)

[0186] Obtained amplicon was purified by QIAGEN kit and was sequenced directly using an automated DNA sequencer (ABI Prism 310, Perkin Elmer, and USA) using TN3 and TN4 primers..

EXAMPLE 5

Adefovir Dipivoxil (ADV)

[0187] Adefovir dipivoxil (ADV) [formerly Bis-pom PMEA] is a potent inhibitor of HBV replication. The structure of ADV is shown in Figure 2 and its synthesis is described by Benzaria et al, J Med Chem. 39:4958-4965, 1996. EXAMPLE 6

Tenofovir (TFV)

[0188] Tenofovir (TFV) [formerly Bis-pom PMPA] is a potent inhibitor of HBV replication. The structure of tenofovir is shown in Figure 3 and its synthesis is described by Srinivas and Fridland, Antimicrob Agents Chemother. 42(6): 1484- 1487, 1998.

[0189] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of the steps or features.

TABLE 4

TFV mutation profile

BBTH-=Biochemical breakthrough vBTH= virological breakthrough

DNA- 1 =baseline DNA (log-copies/ml) DNA-2= DNA at 52 weeks (logcopies/ml ALT- 1 = baseline ALT

ALT-2= ALT at 52 weeks

0= Outside catalytic domains A-to E AWT= Awaited

2010/002467

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Claims

CLAIMS:

1. A method for identifying a human subject infected with a strain of Hepatitis B virus (HBV) which exhibits reduced sensitivity to tenofovir (TFV), said method comprising screening for a mutation in the nucleotide sequence encoding the reverse transcriptase (rt) component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through lo E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV wherein the mutation in the rt component is an amino acid substitution or stop mutation in a codon or two or more codons selected from the list consisting of codons 181 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141 .

2. The method of Claim 1 wherein the mutation in the rt component is a co-mutation at codons 81 and 168; or codons 1 10, 146, 202 and 241 ; or codons 84, 95 and 241 .

3. The method of Claim 1 wherein the mutations are selected from the list consisting of one or more of rtS81 L, rtD83V rtV84L, rtS85P, rtRl l O , rtL 146V, rtN 1 39 ₅ rt 168Stop, rtA181 T, rtS202T, rtS202R, rt 241 R, rtK 141 N and rtF249L.

4. The method of Claim 2 wherein the co-mutations are selected from the list consisting of (i) rtS81 L and rt 168Stop; (ii) rtRl 10 , rtL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N.

5. The method of Claim 2 wherein the co-mutations are rtS81 L and rt 168Stop.

6. The method of any one of Claims 1 to 5 wherein the HBV strain is also resistant to at least one other anti-viral agent.

7. The method of Claim 6 wherein the anti-viral agent is selected from the list consisting of Adefovir dipivoxil (ADV), Lamivudine (LMV), Emtricitabine (FTC), Entecavir (ETV), Famciclovir (FCV), Clevudine (L-FMAU), LdT, LdC, LdA, HB1G and cytokine.

8. A method for identifying a human subject infected with a strain of Hepatitis B virus (HBV) which exhibits reduced sensitivity to tenofovir (TFV), said method comprising screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV wherein the mutation is in a codon selected from one or more of 73, 75, 102, 122, 126, 137, 172 and 194.

9. The method of Claim 8 wherein the mutation is selected from sR73C, S.M75 L sG102S, SR122K/I/T, sT126N, sC 137W, sW172Stop, sV 194L and sV194D.

10. The method of Claim 8 or 9 wherein the HBV strain is also resistant to at least one other anti-viral agent.

1 1 . The method of Claim 1 0 wherein the anti-viral agent is selected from the list consisting of Adefovir dipivoxil (ADV), Lamivudine (LMV), Emtricitabine (FTC), Entecavir (ETV), Famciclovir (FCV), Clevudine (L-FMAU), LdT, LdC, LdA, HBIG and cytokine.

12 A method of treatment of a subject infected with HBV, said method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV-resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount wherein the mutation in the rt component is an amino acid substitution or stop mutation in a codon selected from the list consisting of one or more of codons 1 81 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141.

13. The method of Claim 12 wherein the mutation in the rt component is a co-mutation at codons 81 and 168; or at codons 1 10, 146, 202 and 241 ; or codons 84, 85 and 241 .

14. The method of Claim 12 wherein the mutations are selected from the list consisting of one or more of rtS81 L, rtD83V rtV84L, rtS85P, rtR l 1 OK, rtL 146V, rtN 1 39K, rtK 168Stop, HA 1 81 T, rtS202T, rtS202R, rtK241 R, HK 141 N and rtF249L.

15. The method of Claim 13 wherein the co-mutations are selected from the list consisting of (i) rtS81 L and rtK168Stop; (ii) rtRl 10K, rtL 146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N.

16. The method of Claim 15 wherein the co-mutations are rtS81 L and rtKl 68Stop.

17. The method of any one of Claims 12 to 16 wherein the HBV strain is also resistant to at least one other anti-viral agent.

18. A method of treatment of a subject infected with HBV, said method comprising determining if the subject is infected with a strain of HBV which is resistant to TFV by the method of screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV; and if the subject is infected with a TFV- resistant HBV, selecting an anti-viral agent which is active against the TFV-resistant HBV and administering the anti-viral agent in an effective amount wherein the mutation in the surface antigen is in a codon selected from one or more of 73, 75, 102, 122. 126, 1 37, 1 72 and 194.

19. The method of Claim 18 wherein the mutation is selected from sR73C, sM75 I , sG 102S, sR122K/I/T, sT126N, sC 137W, sW 1 72Stop, sV 194L and sV 194D.

20. A protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase which is associated with decreased sensitivity to TFV wherein the mutation in the rt component is an amino acid substitution or stop mutation in a codon selected from the list consisting of one or more of codons 181 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 139, 168, 241 and 141 .

21 . The protocol of Claim 20 wherein the mutation in the rt component is a co- mutation at codons 81 and 168; or at codons 1 10, 146, 202 and 241 ; or at codons 84. 85 and 241 .

22. The protocol of Claim 21 wherein the mutations are selected from the list consisting of one or more of rtS81 L, rtD83V rtV84L, rtS85P, rtRl 10K, HL 146V, rtN 1 39K, rt 168Stop, rtA 181 T, rtS202T, rtS202R, rtK241 R, rtK 141 N and rtF249L.

23. The protocol of Claim 22 wherein the co-mutations are selected from the list consisting of (i) rtS81L and rtK168Stop; (ii) rtRl l OK, rtL146V, rtS202T and rtK241 R; or (iii) rtV84L, rtS85P and rtK241N.

24. The protocol of Claim 22 wherein the co-mutations are rtS81 L and rt 1 68Stop.

25. The protocol of any one of Claims 20 to 24 wherein the HBV strain is also consistent to at least one other anti-viral agent.

26. The protocol of Claim 25 wherein the anti-viral agent is selected from the list consisting of Adefovir dipivoxil (ADV), Lamivudine (LMV), Emtricitabine (FTC), Entecavir (ETV), Famciclovir (FCV), Clevudine (L-FMAU), LdT, LdC, l .dA, H IG and cytokine.

27. A protocol for assessing whether a subject is infected by an HBV which is resistant to TFV, the protocol comprising screening for a mutation in the nucleotide sequence encoding the surface antigen which results in an amino acid substitution, deletion and/or addition which is associated with decreased sensitivity to TFV wherein the mutation in the surface antigen is in a codon selected from two or more of 73, 75, 102, 122, 126, 1 37, 1 72 and 194.

28. The protocol of Claim 27 wherein the mutation is selected from sR73C, sM751, sG 102S, sR122K/I/T, sT126N, sC 137W, sW172Stop, sV 194L and sV 194D.

29. A method for identifying an HBV strain which exhibits reduced sensitivity to TFV, said method comprising screening for a mutation in the nucleotide sequence encoding the rt component of the HBV DNA polymerase which results in an amino acid substitution, deletion and/or addition in any one or more of domains F and G and domains A through to E or a region proximal thereto of the DNA polymerase or screening for a corresponding mutation in the surface antigen which is associated with decreased sensitivity to TFV wherein the mutation in the rt component is an amino acid substitution or stop mutation in a codon selected from the list consisting of one or more of codons 1 81 , 202, 249, 81 , 83, 84, 85, 1 10, 146, 1 39, 168, 241 and 141 .

30. The method of Claim 29 wherein the mutation in the rt component is a co-mutation at codons 81 and 168; or at codons 1 10, 146, 202 and 241 ; or at codons 84, 85 and 241 .

31. The method of Claim 29 wherein the mutations are selected from the list consisting of one or more of rtS81 L, rtD83V rtV84L, rtS85P, rtRl l OK, HL 146V, HN 139 , rtK168Stop, rtA 1 81 T, rtS202T, rtS202R, rt 241 R, rt 141 N and HF249L.

32. The method of Claim 30 wherein the co-mutations are selected from the list consisting of (i) rtS81 L and rt 168Stop; (ii) rtRl l OK, rtL 146V, rtS202T and rt 241 R: or (iii) rtV84L, rtS85P and Π 241 Ν.

33. The method of Claim 32 wherein the co-mutations are rtS81 L and rt l 68Stop.

34. The method of Claim 29 wherein the mutation in the surface antigen is selected from sR73C, sM75I, sG102S, sR122 /I/T, sT126N, sC137W, sW172Stop, sV194L and sV194D.

35. The method of any one of Claims 29 to 34 wherein the HBV strain is also consistent to at least one other anti-viral agent.

36. The method of Claim 35 wherein the anti-viral agent is selected from the list consisting of Adefovir dipivoxil (ADV), Lamivudine (LMV), Emtricitabine (FTC), Entecavir (ETV), Famciclovir (FCV), Clevudine (L-FMAU), LdT, LdC, LdA, HBIG and cytokine.

37. An isolated HBV strain which exhibits reduced sensitivity to TFV, said HBV comprises a mutation in the rt portion of its DNA polymerase selected from the list consisting of one or more ofcodons 181,202, 249, 81, 83, 84, 85, 110.146, 139, 168, 241 and 141.

38. The isolated HBV of Claim 27 wherein the mutation in the rt component is a co-mutation at codons 81 and 168; or at codons 110, 146, 202 and 241; or at codons 84.85 and 241.

39. The isolated HBV of Claim 27 wherein the mutations are selected from the list consisting of one or more of rtS81L, rtD83V rtV84L, rtS85P, rtRl 1 OK, HL146V, HN139 , rtK168Stop, rtA181T, rtS202T, rtS202R, rtK241R, rtK141N and rtF249L.

40. The isolated HBV of Claim 39 wherein the co-mutations are selected from the list consisting of (i) rtS81L and rtK168Stop; (ii) rtRl 1 OK, rtL146V, rtS202T and rtK241R; or (iii) rtV84L, rtS85P and ΠΚ241Ν.

41 . The isolated HBV of Claim 38 wherein the co-mutations are rtS81 L and rtK168Stop.

42. The isolated HBV of Claim 37 further comprising a mutation in the surface antigen selected from one or more of sR73C, sM75I, sG102S, sR122 /I/T, sT126N, sC 1 37W, sW172Stop, sV 194L and sV 194D.

43. The isolated HBV of any one of Claims 37 to 42 wherein the HBV strain is also consistent to at least one other anti-viral agent.

44. The isolated HBV of Claim 43 wherein the anti-viral agent is selected from the list consisting of Adefovir dipivoxil (ADV), Lamivudine (LMV), Emtricitabine (F TC). Entecavir (ETV), Famciclovir (FCV), Clevudine (L-FMAU), LdT, LdC, LdA, H BIG and cytokine.

45. A composition comprising an anti-HBV agent, which HBV is as defined by any one of Claims 37 to 44.