30 . an effective hbv dna vaccine provides advantages over a protein subunit vaccine because dna is stable under a variety of conditions . this allows for ease in storage and shipping , especially in lesser developed countries . because the vaccine need not contain an adjuvant ( see example i below ), raw material costs and manufacturing costs are lower . like hbv subunit vaccines , hbv dna vaccines are safer than vaccines based on live vectors such as viruses or bacteria . additional advantages include the production of a more native antigen conformation , ease of modifying the amino acid sequence of the antigen , and ability to co - deliver nucleic acids that can express other antigens or polypeptide adjuvants ( e . g ., cytokines ). 31 . the nucleic acid vaccines of the invention can be used as prophylactic vaccines in naive individuals , or as therapeutic vaccines in individuals already infected with hbv . 33 . an hbcag polypeptide encoded by a nucleic acid used in the methods or compositions of the invention is any protein or polypeptide sharing an epitope with a naturally occurring hbcag . such functionally related hbcag polypeptides can differ from the wild type hbcag sequence by additions or substitutions within the hbcag amino acid sequence . amino acid substitutions may be made on the basis of similarity in polarity , charge , solubility , hydrophobicity , hydrophilicity , and / or the amphipathic nature of the residues involved . 34 . nonpolar ( hydrophobic ) amino acids include alanine , leucine , isoleucine , valine , proline , phenylalanine , tryptophan , and methionine . polar neutral amino acids include glycine , serine , threonine , cysteine , tyrosine , asparagine , and glutamine . positively charged ( basic ) amino acids include arginine , lysine , and histidine . negatively charged ( acidic ) amino acids include aspartic acid and glutamic acid . 35 . hbcag variants with altered amino acid sequences can be obtained by random mutations to hbcag dna ( see u . s . pat . no . 5 , 620 , 896 ). this can be achieved by random mutagenesis techniques known in the art . following expression of the mutagenized dna , the encoded polypeptide can be isolated to yield highly antigenic hbcag . alternatively , site - directed mutations of the hbcag coding sequence can be engineered using techniques also well - known to those skilled in the art . 36 . in designing variant hbcag polypeptides , it is useful to distinguish between conserved positions and variable positions . to produce variants with increased antigenicity , conserved residues preferably are not altered . alteration of non - conserved residues are preferably conservative alterations , e . g ., a basic amino acid is replaced by a different basic amino acid . similar mutations to the hbcag coding sequence can be made to generate hbcag polypeptides that are better suited for expression in vivo . 37 . the nucleic acids useful in the methods and compositions of the invention include at least three components : ( 1 ) a hbcag coding sequence beginning with a start codon , ( 2 ) a mammalian transcriptional promoter operatively linked to the coding sequence for expression of the hbcag , and ( 3 ) a mammalian polyadenylation signal operably linked to the coding sequence to terminate transcription driven by the promoter . in this context , a “ mammalian ” promoter or polyadenylation signal is not necessarily a nucleic acid sequence derived from a mammal . for example , it is known that mammalian promoters and polyadenylation signals can be derived from viruses . 38 . in addition , complete hbcag nucleic acid sequences are known . see , e . g ., pasek et al ., nature 282 : 575 - 579 ( 1979 ), which discloses a sequence available under genbank accession no . j02202 . 39 . the nucleic acid vector can optionally include additional sequences such as enhancer elements , splicing signals , termination and polyadenylation signals , viral replicons , and bacterial plasmid sequences . such vectors can be produced by methods known in the art . for example , nucleic acid encoding the desired hbcag can be inserted into various commercially available expression vectors . see , e . g ., invitrogen catalog , 1998 . in addition , vectors specifically constructed for nucleic acid vaccines are described in yasutomi et al ., j virol 70 : 678 - 681 ( 1996 ). 41 . the nucleic acids of the invention can be administered to an individual , or inoculated , in the presence of substances that have the capability of promoting nucleic acid uptake or recruiting immune system cells to the site of the inoculation . for example , nucleic acid encapsulated in microparticles have been shown to promote expression of rotaviral proteins from nucleic acid vectors in viva ( u . s . pat . no . 5 , 620 , 896 ). 42 . a mammal can be inoculated with nucleic acid through any parenteral route , e . g ., intravenous , intraperitoneal , intradermal , subcutaneous , intrapulmonary , or intramuscular routes . it can also be administered , orally , or by particle bombardment using a gene gun . muscle is a useful tissue for the delivery and expression of hbcag - encoding nucleic acid because mammals have a proportionately large muscle mass which is conveniently accessed by direct injection through the skin . a comparatively large dose of nucleic acid can be deposited into muscle by multiple and / or repetitive injections . multiple injections can be used for therapy over extended periods of time . 43 . administration of nucleic acids by conventional particle bombardment can be used to deliver nucleic acid for expression of hbcag in skin or on an mucosal surface . particle bombardment can be carried out using commercial devices . for example , the accell iiυ ( powderject vaccines , inc ., middleton , wis .) particle bombardment device , one of several commercially available “ gene guns ”, can be employed to deliver nucleic acid - coated gold beads . a helios gene gun ( bio - rad ) can also be used to administer the dna particles . information on particle bombardment devices and methods can be found in sources including the following : yang et al ., proc natl acad sci usa 87 : 9568 [ 1990 ]; yang , crc crit rev biotechnol 12 : 335 [ 1992 ]; richmond et al ., virology 230 : 265 - 274 [ 1997 ]; mustafa et al ., virology 229 : 269 - 278 ( 1997 ); livingston et al ., infect immun 66 : 322 - 329 ( 1998 ) and cheng et al ., proc natl acad sci usa 90 : 4455 [ 1993 ]. 44 . in some embodiments of the invention , an individual is inoculated by a mucosal route . the hbcag - encoding nucleic acid can be administered to a mucosal surface by a variety of methods including nucleic acid - containing nose - drops , inhalants , suppositories , or microspheres . alternatively , a nucleic acid vector containing the hbcag gene can be encapsulated in poly ( lactide - co - glycolide ) ( plg ) microparticles by a solvent extraction technique , such as the ones described in jones et al ., infect immun 64 : 489 ( 1996 ); and jones et al ., vaccine 15 : 814 ( 1997 ). for example , the nucleic acid is emulsified with plg dissolved in dichloromethane , and this water - in - oil emulsion is emulsified with aqueous polyvinyl alcohol ( an emulsion stabilizer ) to form a ( water - in - oil )- in - water double emulsion . this double emulsion is added to a large quantity of water to dissipate the dichloromethane , which results in the microdroplets hardening to form microparticles . these microdroplets or microparticles are harvested by centrifugation , washed several times to remove the polyvinyl alcohol and residual solvent , and finally lyophilized . the microparticles containing nucleic acid have a mean diameter of 0 . 5 μm . to test for nucleic acid content , the microparticles are dissolved in 0 . 1 m naoh at 100 ° c . for 10 minutes . the a 260 is measured , and the amount of nucleic acid calculated from a standard curve . incorporation of nucleic acid into microparticles is in the range of 1 . 76 g to 2 . 7 g nucleic acid per milligram plg . 45 . microparticles containing about 1 to 100 μg of nucleic acid are suspended in about 0 . 1 to 1 ml of 0 . 1 m sodium bicarbonate , ph 8 . 5 , and orally administered to mice or humans , e . g ., by gavage . 46 . regardless of the route of administration , an adjuvant can be administered before , during , or after administration of the nucleic acid . an adjuvant can increase the uptake of the nucleic acid into the cells , increase the expression of the antigen from the nucleic acid within the cell , induce antigen presenting cells to infiltrate the region of tissue where the antigen is being expressed , or increase the antigen - specific response provided by lymphocytes . 48 . before administering the vaccines of this invention to humans , efficacy testing can be conducted using animals . in an example of efficacy testing , mice are vaccinated by intramuscular injection . after the initial vaccination or after optional booster vaccinations , the mice ( and negative controls ) are monitored for indications of vaccine - induced , hbcag - specific immune responses . methods of measuring hbcag - specific immune responses are described in the examples below and also in townsend et al ., j virol 71 : 3365 - 3374 ( 1997 ); kuhober et al ., j immunol 156 : 3687 - 3695 ( 1996 ); kuhrober et al ., int immunol 9 : 1203 - 1212 ( 1997 ); geissler et al ., gastroenterology 112 : 1307 - 1320 ( 1997 ); and sallberg et al ., j virol 71 : 5295 - 5303 ( 1997 ). 49 . anti - hbcag serum antibody levels in vaccinated animals can be determined using the core anti - hbc kit ( cat . no . 2259 - 20 , abbott gmbh , weisbaden , germany ). the concentrations of anti - hbcag antibodies are standardized against a readily available reference standard of the paul - ehrlich institute ( langen , germany ). 50 . cytotoxicity assays can be performed as follows . spleen cells from immunized mice are suspended in complete mem with 10 % fetal calf serum and 5 × 10 − 5 m 2 - mercapto - ethanol . cytotoxic effector lymphocyte populations are harvested after 5 days of culture , and a 5 - hour 51 cr release assay is performed in a 96 - well round - bottom plate using target cells . the effector to target cell ratio is varied . percent lysis is defined as ( experimental release minus spontaneous release ) / ( maximum release minus spontaneous release )× 100 . 51 . the invention is further illustrated by the following examples . the examples are provided for illustration only , and are not to be construed as limiting the scope or content of the invention in any way . example 1 : administration of hbcag nucleic acid by intramuscular injection into mice 52 . to construct an expression vector for use as the hbcag nucleic acid vaccine , two plasmids were used ( fig2 ). the pjw4303 plasmid containing a cytomegalovirus immediate - early promoter with intron a and a bovine growth hormone polyadenylation signal was described in yasutomi et al ., j virol 70 : 678 - 681 ( 1996 ). the fragment containing the hbcag - coding sequence was derived from plasmid pyta1 , which was described in yie et al ., chinese j virol 4 : 312 - 318 ( 1988 ). the hindiii - bamhi fragment of pyta1 included the full coding sequence of hbcag without any precore viral sequences upstream of the hbcag start codon . the hbcag nucleic acid vaccine vector was generated by inserting the hindiii - bamhi fragment of pyta1 into the hindiii and bamhi sites in the polylinker of pjw4303 , the polylinker being just downstream of the cytomegalovirus intron a in pjw4303 . the new vector was designated pjw4303 / hbc . 53 . to test for expression of hbcag from the new plasmid , pjw4303 / hbc was used to transfect 293t cells . 48 hours after transfection , the cell lysates were harvested and subjected to elisa and western blotting . transient expression of hbcag in 293t cells was clearly demonstrated by both methods . 54 . after confirming that the pjw4303 / hbc drove expression of hbcag in vitro , the plasmid was used to vaccinate mice by intramuscular injection . a total of 100 μg of pjw4303 / hbc in saline was bilaterally injected into the quadriceps muscles of a balb / c mouse and a c57bl / 6 mouse . a second balb / c mouse and c57bl / 6 mouse received 100 μg of pjw4303 in like fashion as controls . the mice were supplied by taconic farms , inc . and maintained in the animal colony facility of the university of massachusetts medical center . all mice were 6 - 8 weeks old females at the time of the first inoculation . the injections were repeated at 4 and 8 weeks after the first inoculation . 55 . at 0 , 4 , 8 , and 12 weeks after the initial immunization ( bleedings 1 - 4 , respectively ), serum samples were taken from all four mice . end - point titration of anti - hbc antibodies was performed by elisa using a microtiter plate coated with recombinant hbcag protein ( 0 . 1 μg / well ). three - fold serially diluted serum samples were incubated in the coated wells for 30 minutes . the liquid was then removed , and the wells washed . the wells were then incubated with biotinylated goat anti - mouse igg for 30 minutes , followed by washing . streptavidin - linked horseradish peroxidase ( hrp , vector laboratories , inc .) was then added and incubated for 30 minutes , followed by washing . hrp substrate 3 , 3 ′, 5 , 5 ′- tetramethylbenzidine ( tmb ) was then added to the wells to develop color , and the amount of converted substrate was read in a microplate reader . 56 . as shown in fig3 a , the anti - hbcag antibody levels in the balb / c mouse receiving pjw4303 / hbc ( hatched bars ) was above that of the balb / c mouse receiving the control plasmid ( solid bars ) by the third bleeding . as shown in fig3 b , the anti - hbcag antibody levels in the c57 / bl6 mouse receiving the pjw4303 / hbc plasmid was above that of the control mouse by the second bleeding . the titers determined by elisa were confirmed using the corezyme kit ( abbott ), which was standardized against the serum standard available from the paul - ehrlich institute . it was determined that the titer of about 150 , 000 by the fourth bleeding in hbcag immunized mice represented an unexpected titer of at least about 500 pei units / ml . previous publications have described anti - hbcag antibody responses of no more than 10 pei units / ml in animals receiving a hbcag nucleic acid vaccine ( kuhober et al ., j immunol 156 : 3687 - 3695 [ 1996 ] and kuhrober et al ., int immunol 9 : 1203 - 1212 [ 1997 ]). 57 . to determine if any cytotoxic t cell response against hbcag was generated in immunized mice , the mice were sacrificed at 12 weeks after the third inoculation . single spleen cell suspensions were prepared . cytotoxic effector lymphocyte populations were harvested after 6 days of culture and resuspended at 1 × 10 6 cells / ml . a 4 - hour 51 cr release assay was performed in a 96 - well round - bottom plate using p815 cells ( h - 2 d - restrictive , for balb / c mice ) or el - 4 cells ( h - 2 b restrictive , for c57 / bl6 mice ) as the target cells . the synthesized h - 2 d - restricted peptide syvntnmgl , ( seq id no : 2 ) was added to the balb / c spleen cell reaction at 10 μg / ml , and the synthesized h - 2 b - restricted peptide ( mglkfrql ; seq id no : 3 ) was added to the c57 / bl6 spleen cell reaction , also at 10 μg / ml . the effector cell to target cell ( e : t ) ratios used were 12 : 1 , 6 : 1 , 3 : 1 , 1 : 1 , and 0 . 5 : 1 . percent lysis was defined as ( experimental release - spontaneous release ) / ( maximum release - spontaneous release )× 100 . 58 . as shown in fig4 a , at least 50 % specific lysis could be achieved by an e : t ratio of above 6 : 1 in balb / c mice vaccinated with pjw4303 / hbc . a similar immune response was observed in the c57 / bl6 mice . as shown in fig4 b , at least 50 % specific lysis could be achieved by an e : t ratio of 12 : 1 in mice vaccinated with pjw4303 / hbc . thus , the pjw4303 / hbc nucleic acid vaccine , without adjuvants , elicited both significant antibody and cell - mediated immune responses in animals . 59 . to test another route of administration , the pjw4303 / hbc and the pjw4303 control dna was delivered intradermally by particle bombardment . the accell ii ™ particle bombardment device ( powderject vaccines , inc ., middleton , wis .) was employed to deliver dna - coated gold beads to the epidermis of two balb / c and two c57 / bl6 mice , one of each pair receiving the hbcag plasmid and the other of each pair receiving the control dna . 60 . for delivery by particle bombardment , dna was precipitated onto 0 . 95 or 1 - to 3 - μm gold beads ( degussa , south plainfield , n . j .) with 100 mm spermidine and 2 . 5 m cacl 2 at 1 μg of dna per 0 . 5 mg gold shot ( eisenbraun et al ., dna cell biol 12 : 791 - 797 [ 1993 ]). 61 . mice were anesthetized with 30 μl of ketaset / rompun ( 10 : 2 ). abdominal target areas were shaved and thoroughly rinsed with water prior to gene delivery . nucleic acid - coated gold particles were delivered into abdominal skin with the accell ii ™ gene gun , which employed a helium discharge as the motive force . each animal received six nonoverlapping deliveries per immunization , each delivery at 300 - 400 pounds per square inch . the immunization was repeated at 4 weeks and 8 weeks after the first immunization . 62 . antibody and cytotoxic t cell responses were determined as described in example 1 above . as shown in fig5 a , the immunization elicited an antibody titer of over 300 , 000 ( corresponding to at least about 1000 pei units / ml ) in a balb / c mouse by the third bleeding . again , like the intramuscular results in example 1 , this antibody response was unexpectedly high as compared to previous studies . the antibody response elicited in the c57 / bl6 mouse was comparable to that for the balb / c mice ( fig5 b ). as shown in fig6 a and 6b , the cytotoxic responses in the two strains of mice receiving pjw4303 / hbc were similar to that for the intramuscular results described in example 1 above . greater than 50 % specific lysis was observed at an e : t ratio of 12 for both strains of mice . 63 . these results indicated that the hbcag nucleic acid vaccine described herein produced humoral and cell - mediated immune responses by a variety administration methods . 64 . the expression vector ( pjw4303 / hbc ) described in examples 1 and 2 was also used as an hbcag nucleic acid vaccine to vaccinate monkeys . after confirming that the pjw4303 / hbc vector drove expression of hbcag in vitro , the plasmid was used to vaccinate monkeys by intramuscular injection . 65 . monkeys in group i ( animals # 1 and # 2 ) were immunized with hbcag nucleic acid vaccine while the other two monkeys in group ii (# 3 and # 4 ) received control plasmid dna vector without the hbc insert . each animal received 2 . 0 mg of dna plasmids intramuscularly ( im ) at each inoculation ( delivered equally as 500 μg shots at four muscle sites ). the dna inoculations were given every two months . animal sera were collected prior to each inoculation and elisa was done to detect anti - hbv antibody responses . 66 . table 1 below shows antibody responses induced by the hbcag nucleic acid vaccine in monkeys . monkeys immunized with the hbcag nucleic vaccine (# 1 and # 2 ) clearly had hepatitis b core specific antibody responses after one immunization ( animal # 1 ) or two immunizations ( animal # 2 ), respectively . two negative control monkeys ( animal # 3 and # 4 ) had no antibody responses against the hepatitis b core antigen . in table 1 (+) indicates a positive antibody response for hepatitis b core antigen , while (−) means a negative antibody response for hepatitis b core antigen . n / d indicates a test was not done . animal # 1 died of unrelated diseases before sample collection at the 4th month . 67 . because it is more difficult to induce immune response by im dna immunization in primates , the hbcag nucleic acid vaccine demonstrated its highly efficient potential to be developed as a clinical vaccine for human use .
hepatitis b virus core antigen nucleic acid vaccines and their use are disclosed . in the vaccines and methods of the invention , precore sequences in the 5 ′ untranslated region of the core antigen mrna are not present .