RECOMBINANT PROTEINS OF A PAKISTANI STRAIN OF HEPATITIS E AND THEIR USE IN DIAGNOSTIC METHODS AND VACCINES

Abstract: A strain of hepatitis E virus from Pakistan (SAR-55) implicated in an epidemic of enterically transmitted non-A, non-B hepatitis, now called hepatitis E, is disclosed. The invention relates to the expression of the whole structural region of SAR-55, designated open reading frame 2 (ORF-2), in a eukaryotic expression system. The expressed protein is capable of forming HEV virus-like particles which can serve as an antigen in diagnostic immunoassays and as an immunogen or vaccine to protect against infection by hepatitis E.

Description: Title of the Invention RECOMBINANT PROTEINS OF A PAKISTANI STRAIN OF HEPATITIS E AND THEIR USE IN DIAGNOSTIC METHODS AND VACCINES The present application is a continuation-in- part of pending U.S. Application Serial No. 07/947,263 filed on September 18, 1992, now abandoned. Field Of Invention The invention is in the field of hepatitis virology. More specifically, this invention relates to recombinant proteins derived from an enterically transmitted strain of hepatitis E from Pakistan, SAR-55, and to diagnostic methods and vaccine applications which employ these proteins. Background of Invention Epidemics of hepatitis E, an enterically trans¬ mitted non-A/non-B hepatitis, have been reported in Asia, Africa and Central America (Balayan, M.S. (1987), Soviet Medical Reviews, Section E, Virology Reviews, Zhdanov, 0- V.M. (ed) , Chur, Switzerland: Harwood Academic Publishers, vol. 2, 235-261; Purcell, R.G., et al. (1988) in Zuckerman, A.J. (ed) , "Viral Hepatitis and Liver Disease", New York: Alan R. Liss, 131-137; Bradley, D.W. (1990), British Medical Bulletin. 46:442-461; Ticehurst, J-R. (1991) in Hollinger, F.B., Lemon, S.M., Margolis, H.S. (eds) : "Viral Hepatitis and Liver Disease", Williams and Wilkins, Baltimore, 501-513) . Cases of sporadic hepa¬ titis, presumed to be hepatitis E, account for up to 90% of reported hepatitis in countries where hepatitis E virus (HEV) is endemic. The need for development of a serological test for the detection of anti-HEV antibodies in the sera of infected individuals is widely recognized in the field, but the very low concentration of HEV excreted from infected humans or animals made it impos- sible to use such HEV as the source of antigen for serological tests and although limited success was reported in propagation of HEV in cell culture (Huang, R.T. et al. (1992), J. Gen. Virol.. 73:1143-1148), cell culture is currently too inefficient to produce the amounts of antigen required for serological tests. Recently, major efforts worldwide to identify viral genomic sequences associated with hepatitis E have resulted in the cloning of the genomes of a limited number of strains of HEV (Tarn, A.W. et al. (1991), Virology. 185:120-131; Tsarev, S.A. et al. (1992), Proc. Natl. Acad. Sci. USA. 89:559-563; Fry, K.E. et al. (1992), Virus Genes. 6:173-185). Analysis of the DNA sequences have led investigators to hypothesize that the HEV genome is organized into three open reading frames (ORFs) and to hypothesize that these ORFs encode intact HEV proteins. A partial DNA sequence of the genome of an HEV strain from Burma (Myanmar) is disclosed in Reyes et al., 1990, Science. 247:1335-1339. Tarn et al., 1991, and Reyes et al., PCT Patent Application WO91/15603 published October 17, 1991 disclose the complete nucleotide sequence and a deduced amino acid sequence of the Burma strain of HEV. These authors hypothesized that three forward open reading frames (ORFs) are contained within the sequence of this strain. Ichikawa et al., 1991, Microbiol. Immunol.. 35:535-543, discloses the isolation of a series of clones of 240-320 nucleotides in length upon the screening of a λgtll expression library with sera from HEV-infected cynomolgus monkeys. The recombinant protein expressed by one clone was expressed in E. coli. This fusion protein is encoded by the 3' region of ORF-2 of the Myanmar strain of HEV. The expression of additional proteins encoded within the 3' region of ORF-2 of a Mexican strain of HEV and of a Burmese strain of HEV is described in Yarbough et al., 1991 J. Virology. 65:5790-5797. This article describes the isolation of two cDNA clones derived from HEV. These clones encode the proteins in the 3' region of ORF-2. The clones were expressed in E. coli as fusion proteins. Purdy et al., 1992, Archives of Virology. 123:335-349, and Favorov et al. , 1992, J. of Medical Virology. 36:246-250, disclose the expression of a larger ORF-2 protein fragment from the Burma strain in E. coli. These references, as well as those previously discussed, only disclose the expression of a portion of the ORF-2 gene using bacterial expression systems. Successful expression of the full-length ORF-2 protein has not been disclosed until the present invention. Comparison of the genome organization and morphological structure of HEV to that of other viruses revealed that HEV is most closely related to the caliciviruses. Of interest, the structural proteins of caliciviruses are encoded by the 3' portion of their genome (Neil, J.D. et al. (1991) J. Virol.. 65:5440-5447; and Carter, M.J. et al. (1992), J. Arch. Virol.. 122:223- 235) and although there is no direct evidence that the 3' terminal part of the HEV genome also encodes the structural proteins, expression of certain small portions of the 3' genome region in bacterial cells resulted in production of proteins reactive with anti-HEV sera in ELISA and Western blots (Yarborough, et al., (1991); Ichikawa et al. (1991); Favorov et al. (1992) and Dawson, G.J. et al. (1992) J. Virol. Meth: 38:175-186). However, the function of ORF-2 protein as a structural protein was not proven until the present invention. The small proteins encoded by a portion of the ORF-2 gene have been used in immunoassay to detect antibodies to HEV in animal sera. The use of small bacterially expressed proteins as antigens in serological immunoassays has several potential drawbacks. First, the expression of these small proteins in bacterial cells often results in solubility problems and in non-specific cross-reactivity of patients' sera with .£. coli proteins when crude E. coli lysates are used as antigens in immunoassays (Purdy et al. (1992)). Second, the use of Western blots as a first-line serological test for anti- HEV antibodies in routine epidemiology is impractical due to time and cost constraints. An ELISA using small- peptides derived from the 3' -terminal part of the HEV genome resulted in the detection of only 41% positives from known HEV-infected patients. Third, it has been shown that for many viruses, including Picornaviridae which is the closest family to the Caliciviridae, important antigenic and immunogenic epitopes are highly conformational (Lemon, S.M. et al. (1991), in Hollinger, F.B., Lemon, S.M., Margolis, H.S. (eds) : "Viral Hepatitis and Liver Disease", Williams and Wilkins, Baltimore, 20- 24) . For this reason, it is believed that expression in a eukaryotic system of a complete ORF encoding an intact HEV gene would result in production of a protein which could form HEV-virus-like particles. Such a complete ORF protein would have an immunological structure closer to that of native capsid protein(s) than would the above- noted smaller proteins which represent only portions of the structural proteins of HEV. Therefore, these complete ORF proteins would likely serve as a more representative antigen and a more efficient immunogen than the currently- used smaller proteins. Summary Of Invention The present invention relates to an isolated and substantially pure preparation of a human hepatitis E viral strain SAR-55. The invention also relates to an isolated and substantially pure preparation of the genomic RNA of the human hepatitis E viral strain SAR-55. The invention further relates to the cDNA of the human hepatitis E viral strain SAR-55. It is an object of this invention to provide synthetic nucleic acid sequences capable of directing production of recombinant HEV proteins, as well as equivalent natural nucleic acid sequences. Such natural nucleic acid sequences may be isolated from a cDNA or genomic library from which the gene capable of directing synthesis of the HEV proteins may be identified and isolated. For purpose of this application, nucleic acid sequence refers to RNA, DNA, cDNA or any synthetic variant thereof which encodes for protein. The invention further relates to a method for detection of the hepatitis E virus in biological samples based on selective amplification of hepatitis E gene fragments utilizing primers derived from the SAR-55 cDNA. The invention also relates to the use of single- stranded antisense poly-or oligonucleotides derived from the SAR-55 cDNA to inhibit the expression of hepatitis E genes. The invention also relates to isolated and substantially purified HEV proteins and variants thereof encoded by the HEV genome of SAR-55 or encoded by synthetic nucleic acid sequences and in particular to recombinant proteins encoded by at least one complete open reading frame of HEV. The invention also relates to the method of pre¬ paring recombinant HEV proteins derived from an HEV genomic sequence by cloning the nucleic acid and inserting the cDNA into an expression vector and expressing the recombinant protein in a host cell. The invention also relates to the use of the resultant recombinant HEV proteins as diagnostic agents and as vaccines. The present invention also encompasses methods of detecting antibodies specific for hepatitis E virus in biological samples. Such methods are useful for diagnosis of infection and disease caused by HEV, and for monitoring the progression of such disease. Such methods are also useful for monitoring the efficacy of therapeutic agents during the course of treatment of HEV infection and disease in a mammal. This invention also relates to pharmaceutical compositions for use in prevention or treatment of Hepatitis E in a mammal. Description Of Figures Figure 1 shows the recombinant vector used to express the complete ORF-2 protein of the genome of HEV strain SAR-55. Figures 2A and 2B are sodium dodecyl sulfate- polyacrylamide gels (SDS-PAGE) in which cell lysates of insect cells infected with wild-type baculovirus or recombinant baculovirus (containing the gene encoding ORF- 2) were either stained with Coomassie blue (A) or subjected to Western blotting with serum of an HEV- infected chimp (B) . In both Figures 2A and 2B, lane 1 contains total cell lysate of noninfected SF-9 cells; lane 2 contains lysate of cells infected with wild-type baculovirus; lane 3 contains lysate of cells infected with recombinant baculovirus and lane 4 contains molecular weight markers. Figures 3A-3A' ' ' and 3B show immunoelectron micrographs (IEM) of 30 and 20 nm virus-like particles respectively, which are formed as a result of the expression of ORF-2 protein in recombinant infected insect cells. Figure 4 shows the results of an ELISA using as the antigen, recombinant ORF-2 which was expressed from insect cells containing the gene encoding the complete ORF-2. Serum anti-HEV antibody levels were determined at various times following inoculation of cynomolgus monkeys with either the Mexican (Cyno-80A82, Cyno-9A97 and Cyno 83) or Pakistani (Cyno-374) strains of HEV. Figures 5A-D show the results of an ELISA using RECTIFIED SHEET (RULE 91) as the antigen, recombinant ORF-2 which was expressed from insect cells containing the gene encoding the complete ORF-2. Serum IgG or IgM anti-HEV levels were determined over time following inoculation of two chimpanzees with HEV. Figures 6A-J show a comparison of ELISA data obtained using as the antigen the recombinant complete ORF-2 protein derived from SAR-55 as the antigen vs. a recombinant partial ORF-2 protein derived from the Burma strain of HEV (Genelabs) . Figures 7A-J show anti-HEV IgG ELISA and alanine aminotransferase (ALT) values for cynomolgus monkeys inoculated with ten-fold serial dilutions (indicated in parenthesis at the top of each panel) of a 10% fecal suspension of SAR-55 HEV. Recombinant antigens used in ELISA were: glutathione-S-transferase (GST); 3-2 (M), a fusion of the 3-2 epitope [Yarbough et al., (1991) J. Virol. 65:5790-5797] and GST; SG3 (B) , a fusion of 327 C- terminal amino acids of ORF-2 and GST [Yarbough et al., (1993) : Assay Development of diagnostic tests for Hepatitis E in "International Symposium on Viral Hepatitis and Liver Disease. Scientific Program and Abstract Volume." Tokyo:VHFL p. 87]; and a 55 kDa ORF-2 product directly expressed in insect cells. Figures 8A-E show anti-HEV IgM ELISA and ALT values for positive cynomolgus monkeys inoculated with ten-fold serial dilutions (indicated in parenthesis at the top of each panel) of the 10% fecal suspension of SAR-55 HEV. Recombinant antigens used in ELISA were: glutathione-S-transferase (GST); 3-2 (M), a fusion of the 3-2 epitope [Yarbough et al., 1991] and (GST); SG3 (B) , a fusion of 327 C-terminal amino acids of ORF-2 and GST [Yarbough et al., 1993]; and the 55 kDa ORF-2 product directly expressed in insect cells. Figure 9 shows an ethidium bromide stain of a 2% agarose gel on which PCR products produced from extracts of serial ten-fold dilutions (indicated at the top of each lane of the gel) of the 10% fecal suspension of the SAR-55 HEV were separated. The predicted length of the PCR products was about 640 base pairs and the column marked with an (M) contains DNA size markers. Figure 10 shows the pPIC9 vector used to express the complete ORF-2 protein or lower molecular weight fragments in yeast. Detailed Description of Invention The present invention relates to an isolated and substantially purified strain of hepatitis E virus (HEV) from Pakistan, SAR-55. The present invention also relates to the cloning of the viral genes encoding proteins of HEV and the expression of the recombinant proteins using an expression system. More specifically, the present invention relates to the cloning and expression of the open reading frames (ORF) of HEV derived from SAR-55. The present invention relates to isolated HEV proteins. Preferably, the HEV proteins of the present invention are substantially homologous to, and most preferably biologically equivalent to, the native HEV proteins. By "biologically equivalent" as used throughout the specification and claims, it is meant that the compositions are capable of forming viral-like particles and are immunogenic. The HEV proteins of the present invention may also stimulate the production of protective antibodies upon injection into a mammal that would serve to protect the mammal upon challenge with a wild-type HEV. By "substantially homologous" as used throughout the ensuing specification and claims, is meant a degree of homology in the amino acid sequence to the native HEV pro¬ teins. Preferably the degree of homology is in excess of 70%, preferably in excess of 90%, with a particularly preferred group of proteins being in excess of 99% homologous with the native HEV proteins. Preferred HEV proteins are those proteins that are encoded by the ORF genes. Of particular interest are proteins encoded by the ORF-2 gene of HEV and most particularly proteins encoded by the ORF-2 gene of the SAR-55 strain of HEV. The preferred proteins of the present invention, encoded by the ORF-2 gene, form virus- like particles. The amino acid sequences of the ORF-1, ORF-2 and ORF-3 proteins are shown below as SEQ ID NO. : 1, SEQ ID NO.: 2, and SEQ ID NO.: 3, respectively: (SEQ. ID NO. : 1) Met Glu Ala His Gin Phe lie Lys Ala Pro Gly lie Thr Thr Ala i 5 10 15 lie Glu Gin Ala Ala Leu Ala Ala Ala Asn Ser Ala Leu Ala Asn 20 25 30 Ala Val Val Val Arg Pro Phe Leu Ser His Gin Gin He Glu He 35 40 45 Leu He Asn Leu Met Gin Pro Arg Gin Leu Val Phe Arg Pro Glu 50 55 60 Val Phe Trp Asn His Pro He Gin Arg Val He His Asn Glu Leu 65 70 75 Glu Leu Tyr Cys Arg Ala Arg Ser Gly Arg Cys Leu Glu He Gly 80 85 90 Ala His Pro Arg Ser He Asn Asp Asn Pro Asn Val Val His Arg 95 100 105 Cys Phe Leu Arg Pro Ala Gly Arg Asp Val Gin Arg Trp Tyr Thr 110 115 120 Ala Pro Thr Arg Gly Pro Ala Ala Asn Cys Arg Arg Ser Ala Leu 125 130 135 Arg Gly Leu Pro Ala Ala Asp Arg Thr Tyr Cys Phe Asp Gly Phe 140 145 150 Ser Gly Cys Asn Phe Pro Ala Glu Thr Gly He Ala Leu Tyr Ser 155 160 165 Leu His Asp Met Ser Pro Ser Asp Val Ala Glu Ala Met Phe Arg 170 175 180 His Gly Met Thr Arg Leu Tyr Ala Ala Leu His Leu Pro Pro Glu 185 190 195 Val Leu Leu Pro Pro Gly Thr Tyr Arg Thr Ala Ser Tyr Leu Leu 200 205 210 He His Asp Gly Arg Arg Val Val Val Thr Tyr Glu Gly Asp Thr 215 220 225 Ser Ala Gly Tyr Asn His Asp Val Ser Asn Leu Arg Ser Trp He 230 235 240 Arg Thr Thr Lys Val Thr Gly Asp His Pro Leu Val He Glu Arg 245 250 255 Val Arg Ala He Gly Cys His Phe Val Leu Leu Leu Thr Ala Ala 260 265 270 Pro Glu Pro Ser Pro Met Pro Tyr Val Pro Tyr Pro Arg Ser Thr 275 280 285 Glu Val Tyr Val Arg Ser He Phe Gly Pro Gly Gly Thr Pro Ser 290 295 300 Ser Glu Val Asp Ala Val Pro Ser Pro Ala Gin Pro Asp Leu Gly 710 715 720 Phe Thr Ser Glu Pro Ser He Pro Ser Arg Ala Ala Thr Pro Thr 725 730 735 Pro Ala Ala Pro Leu Pro Pro Pro Ala Pro Asp Pro Ser Pro Thr 740 745 750 Leu Ser Ala Pro Ala Arg Gly Glu Pro Ala Pro Gly Ala Thr Ala 755 760 765 Arg Ala Pro Ala He Thr His Gin Thr Ala Arg His Arg Arg Leu 770 775 780 Leu Phe Thr Tyr Pro Asp Gly Ser Lys Val Phe Ala Gly Ser Leu 785 790 795 Phe Glu Ser Thr Cys Thr Trp Leu Val Asn Ala Ser Asn Val Asp 800 805 810 His Arg Pro Gly Gly Gly Leu Cys His Ala Phe Tyr Gin Arg Tyr 815 820 825 Pro Ala Ser Phe Asp Ala Ala Ser Phe Val Met Arg Asp Gly Ala 830 835 840 Ala Ala Tyr Thr Leu Thr Pro Arg Pro He He His Ala Val Ala 845 850 855 Pro Asp Tyr Arg Leu Glu His Asn Pro Lys Arg Leu Glu Ala Ala 860 865 870 Tyr Arg Glu Thr Cys Ser Arg Leu Gly Thr Ala Ala Tyr Pro Leu 875 880 885 Leu Gly Thr Gly He Tyr Gin Val Pro He Gly Pro Ser Phe Asp 890 895 900 Ala Trp Glu Arg Asn His Arg Pro Gly Asp Glu Leu Tyr Leu Pro 905 910 915 Glu Leu Ala Ala Arg Trp Phe Glu Ala Asn Arg Pro Thr Cys Pro 920 925 930 Thr Leu Thr He Thr Glu Asp Val Ala Arg Thr Ala Asn Leu Ala 935 940 945 He Glu Leu Asp Ser Ala Thr Asp Val Gly Arg Ala Cys Ala Gly 950 955 960 Cys Arg Val Thr Pro Gly Val Val Gin Tyr Gin Phe Thr Ala Gly 965 970 975 Val Pro Gly Ser Gly Lys Ser Arg Ser He Thr Gin Ala Asp Val 980 985 990 Asp Val Val Val Val Pro Thr Arg Glu Leu Arg Asn Ala Trp Arg 995 1000 1005 Arg Arg Gly Phe Ala Ala Phe Thr Pro His Thr Ala Ala Arg Val 1010 1015 1020 Thr Gin Gly Arg Arg Val Val He Asp Glu Ala Pro Ser Leu Pro 1025 1030 1035 Pro His Leu Leu Leu Leu His Met Gin Arg Ala Ala Thr Val His 1040 1045 1050 Leu Leu Gly Asp Pro Asn Gin He Pro Ala He Asp Phe Glu His 1055 1060 1065 Ala Gly Leu Val Pro Ala He Arg Pro Asp Leu Ala Pro Thr Ser 1070 1075 1080 Trp Trp His Val Thr His Arg Cys Pro Ala Asp Val Cys Glu Leu 1085 1090 1095 He Arg Gly Ala Tyr Pro Met He Gin Thr Thr Ser Arg Val Leu 1100 1105 1110 Arg Ser Leu Phe Trp Gly Glu Pro Ala Val Gly Gin Lys Leu Val 1115 1120 1125 Phe Thr Gin Ala Ala Lys Ala Ala Asn Pro Gly Ser Val Thr Val 1130 1135 1140 His Glu Ala Gin Gly Ala Thr Tyr Thr Glu Thr Thr He He Ala 1145 1150 1155 Thr Ala Asp Ala Arg Gly Leu He Gin Ser Ser Arg Ala His Ala 1160 1165 1170 He Val Ala Leu Thr Arg His Thr Glu Lys Cys Val He He Asp 1175 1180 1185 Ala Pro Gly Leu Leu Arg Glu Val Gly He Ser Asp Ala He Val 1190 1195 1200 Asn Asn Phe Phe Leu Ala Gly Gly Glu He Gly His Gin Arg Pro 1205 1210 1215 Ser Val He Pro Arg Gly Asn Pro Asp Ala Asn Val Asp Thr Leu 1220 1225 1230 Ala Ala Phe Pro Pro Ser Cys Glu He Ser Ala Phe His Glu Leu 1235 1240 1245 Ala Glu Glu Leu Gly His Arg Pro Ala Pro Val Ala Ala Val Leu 1250 1255 1260 Pro Pro Cys Pro Glu Leu Glu Gin Gly Leu Leu Tyr Leu Pro Gin 1265 1270 1275 Glu Leu Thr Thr Cys Asp Ser Val Val Thr Phe Glu Leu Thr Asp 1280 1285 1290 He Val His Cys Arg Met Ala Ala Pro Ser Gin Arg Lys Ala Val 1295 1300 1305 Leu Ser Thr Leu Val Gly Arg Tyr Gly Arg Arg Thr Lys Leu Tyr 1310 1315 1320 Asn Ala Ser His Ser Asp Val Arg Asp Ser Leu Ala Arg Phe He 1325 1330 1335 Pro Ala He Gly Pro Val Gin Val Thr Thr Cys Glu Leu Tyr Glu 1340 1345 1350 Leu Glu Glu Ala Met Val Glu Lys Gly Gin Asp Gly Ser Ala Val 1355 1360 1365 Leu Glu Leu Asp Leu Cys Ser Arg Asp Val Ser Arg He Thr Phe 1370 1375 1380 Phe Gin Lys Asp Cys Asn Lys Phe Thr Thr Gly Glu Thr He Ala 1385 1390 1395 His Gly Lys Val Gly Gin Gly He Ser Ala Trp Ser Lys Thr Phe 1400 1405 1410 Cys Ala Leu Phe Gly Pro Trp Phe Arg Ala He Glu Lys Ala He 1415 1420 1425 Leu Ala Leu Leu Pro Gin Gly Val Phe Tyr Gly Asp Ala Phe Asp 1430 1435 1440 Asp Thr Val Phe Ser Ala Ala Val Ala Ala Ala Lys Ala Ser Met 1445 1450 1455 Val Phe Glu Asn Asp Phe Ser Glu Phe Asp Ser Thr Gin Asn Asn 1460 1465 1470 Phe Ser Leu Gly Leu Glu Cys Ala He Met Glu Glu Cys Gly Met 1475 1480 1485 Pro Gin Trp Leu He Arg Leu Tyr His Leu He Arg Ser Ala Trp 1490 1495 1500 He Leu Gin Ala Pro Lys Glu Ser Leu Arg Gly Phe Trp Lys Lys 1505 1510 1515 His Ser Gly Glu Pro Gly Thr Leu Leu Trp Asn Thr Val Trp Asn 1520 1525 1530 Met Ala Val He Thr His Cys Tyr Asp Phe Arg Asp Leu Gin Val 1535 1540 1545 Ala Ala Phe Lys Gly Asp Asp Ser He Val Leu Cys Ser Glu Tyr 1550 1555 1560 Arg Gin Ser Pro Gly Ala Ala Val Leu He Ala Gly Cys Gly Leu 1565 1570 1575 Lys Leu Lys Val Asp Phe Arg Pro He Gly Leu Tyr Ala Gly Val 1580 1585 1590 Val Val Ala Pro Gly Leu Gly Ala Leu Pro Asp Val Val Arg Phe 1595 1600 1605 Ala Gly Arg Leu Thr Glu Lys Asn Trp Gly Pro Gly Pro Glu Arg 1610 1615 1620 Ala Glu Gin Leu Arg Leu Ala Val Ser Asp Phe Leu Arg Lys Leu 1625 1630 1635 Thr Asn Val Ala Gin Met Cys Val Asp Val Val Ser Arg Val Tyr 1640 1645 1650 Gly Val Ser Pro Gly Leu Val His Asn Leu He Glu Met Leu Gin 1655 1660 1665 Ala Val Ala Asp Gly Lys Ala His Phe Thr Glu Ser Val Lys Pro 1670 1675 1680 Val Leu Asp Leu Thr Asn Ser He Leu Cys Arg Val Glu 1685 1690 (SEQ. ID NO. 2) Met Arg Pro Arg Pro He Leu Leu Leu Leu Leu Met Phe Leu Pro 1 5 10 15 Met Leu Pro Ala Pro Pro Pro Gly Gin Pro Ser Gly Arg Arg Arg 20 25 30 Gly Arg Arg Ser Gly Gly Ser Gly Gly Gly Phe Trp Gly Asp Arg 35 40 45 Val Asp Ser Gin Pro Phe Ala He Pro Tyr He His Pro Thr Asn 50 55 60 Pro Phe Ala Pro Asp Val Thr Ala Ala Ala Gly Ala Gly Pro Arg 65 70 75 Val Arg Gin Pro Ala Arg Pro Leu Gly Ser Ala Trp Arg Asp Gin 80 85 90 Ala Gin Arg Pro Ala Ala Ala Ser Arg Arg Arg Pro Thr Thr Ala 95 100 105 Gly Ala Ala Pro Leu Thr Ala Val Ala Pro Ala His Asp Thr Pro 110 115 120 Pro Val Pro Asp Val Asp Ser Arg Gly Ala He Leu Arg Arg Gin 125 130 135 Tyr Asn Leu Ser Thr Ser Pro Leu Thr Ser Ser Val Ala Thr Gly 140 145 150 Thr Asn Leu Val Leu Tyr Ala Ala Pro Leu Ser Pro Leu Leu Pro 155 160 165 Leu Gin Asp Gly Thr Asn Thr His He Met Ala Thr Glu Ala Ser 170 175 180 Asn Tyr Ala Gin Tyr Arg Val Ala Arg Ala Thr He Arg Tyr Arg 185 190 195 Pro Leu Val Pro Asn Ala Val Gly Gly Tyr Ala He Ser He Ser 200 205 210 Phe Tyr Pro Gin Thr Thr Thr Thr Pro Thr Ser Val Asp Met Asn 215 220 225 Ser He Thr Ser Thr Asp Val Arg He Leu Val Gin Pro Gly He 230 235 240 Ala Ser Glu Leu Val He Pro Ser Glu Arg Leu His Tyr Arg Asn 245 250 255 Gin Gly Trp Arg Ser Val Glu Thr Ser Gly Val Ala Glu Glu Glu 260 265 270 Ala Thr Ser Gly Leu Val Met Leu Cys He His Gly Ser Pro Val 275 280 285 Asn Ser Tyr Thr Asn Thr Pro Tyr Thr Gly Ala Leu Gly Leu Leu 290 295 300 Asp Phe Ala Leu Glu Leu Glu Phe Arg Asn Leu Thr Pro Gly Asn 305 310 315 Thr Asn Thr Arg Val Ser Arg Tyr Ser Ser Thr Ala Arg His Arg 320 325 330 Leu Arg Arg Gly Ala Asp Gly Thr Ala Glu Leu Thr Thr Thr Ala 335 340 345 Ala Thr Arg Phe Met Lys Asp Leu Tyr Phe Thr Ser Thr Asn Gly 350 355 360 Val Gly Glu He Gly Arg Gly He Ala Leu Thr Leu Phe Asn Leu 365 370 375 Ala Asp Thr Leu Leu Gly Gly Leu Pro Thr Glu Leu He Ser Ser 380 385 390 Ala Gly Gly Gin Leu Phe Tyr Ser Arg Pro Val Val Ser Ala Asn 395 400 405 Gly Glu Pro Thr Val Lys Leu Tyr Thr Ser Val Glu Asn Ala Gin 410 415 420 Gin Asp Lys Gly He Ala He Pro His Asp He Asp Leu Gly Glu 425 430 435 Ser Arg Val Val He Gin Asp Tyr Asp Asn Gin His Glu Gin Asp 440 445 450 Arg Pro Thr Pro Ser Pro Ala Pro Ser Arg Pro Phe Ser Val Leu 455 460 465 Arg Ala Asn Asp Val Leu Trp Leu Ser Leu Thr Ala Ala Glu Tyr 470 475 480 Asp Gin Ser Thr Tyr Gly Ser Ser Thr Gly Pro Val Tyr Val Ser 485 490 495 Asp Ser Val Thr Leu Val Asn Val Ala Thr Gly Ala Gin Ala Val 500 505 510 Ala Arg Ser Leu Asp Trp Thr Lys Val Thr Leu Asp Gly Arg Pro 515 520 525 Leu Ser Thr He Gin Gin Tyr Ser Lys Thr Phe Phe Val Leu Pro 530 535 540 Leu Arg Gly Lys Leu Ser Phe Trp Glu Ala Gly Thr Thr Lys Ala 545 550 555 Gly Tyr Pro Tyr Asn Tyr Asn Thr Thr Ala Ser Asp Gin Leu Leu 560 565 570 Val Glu Asn Ala Ala Gly His Arg Val Ala He Ser Thr Tyr Thr 575 580 585 Thr Ser Leu Gly Ala Gly Pro Val Ser He Ser Ala Val Ala Val 590 595 600 Leu Ala Pro His Ser Val Leu Ala Leu Leu Glu Asp Thr Met Asp 605 610 615 Tyr Pro Ala Arg Ala His Thr Phe Asp Asp Phe Cys Pro Glu Cys 620 625 630 Arg Pro Leu Gly Leu Gin Gly Cys Ala Phe Gin Ser Thr Val Ala 635 640 645 Glu Leu Gin Arg Leu Lys Met Lys Val Gly Lys Thr Arg Glu Leu 650 655 660 (SEQ. ID NO. : 3) Met Asn Asn Met Ser Phe Ala Ala Pro Met Gly Ser Arg Pro Cys 1 5 10 15 Ala Leu Gly Leu Phe Cys Cys Cys Ser Ser Cys Phe Cys Leu Cys 20 25 30 Cys Pro Arg His Arg Pro Val Ser Arg Leu Ala Ala Val Val Gly 35 40 45 Gly Ala Ala Ala Val Pro Ala Val Val Ser Gly Val Thr Gly Leu 50 55 60 He Leu Ser Pro Ser Gin Ser Pro He Phe He Gin Pro Thr Pro 65 70 75 Ser Pro Pro Met Ser Pro Leu Arg Pro Gly Leu Asp Leu Val Phe 80 85 90 Ala Asn Pro Pro Asp His Ser Ala Pro Leu Gly Val Thr Arg Pro 95 100 105 Ser Ala Pro Pro Leu Pro His Val Val Asp Leu Pro Gin Leu Gly 110 115 120 Pro Arg Arg The three-letter abbreviations follow the conventional amino acid shorthand for the twenty naturally occurring amino acids. The preferred recombinant HEV proteins consist of at least one ORF protein. Other recombinant proteins made up of more than one of the same or different ORF proteins may be made to alter the biological properties of the protein. It is contemplated that additions, substitutions or deletions of discrete amino acids or of discrete sequences of amino acids may enhance the biological activity of the HEV proteins. The present invention is also a nucleic acid sequence which is capable of directing the production of the above-discussed HEV protein or proteins substantially homologous to the HEV proteins. This nucleic acid sequence, designated SAR-55, is set forth below as SEQ ID NO. : 4 and was deposited with the American Type Culture Collection (ATCC) on September 17, 1992 (ATCC accession number 75302) . AGGCAGACCA CATATGTGGT CGATGCCATG GAGGCCCATC 40 AGTTTATCAA GGCTCCTGGC ATCACTACTG CTATTGAGCA 80 GGCTGCTCTA GCAGCGGCCA ACTCTGCCCT TGCGAATGCT 120 GTGGTAGTTA GGCCTTTTCT CTCTCACCAG CAGATTGAGA 160 TCCTTATTAA CCTAATGCAA CCTCGCCAGC TTGTTTTCCG 200 CCCCGAGGTT TTCTGGAACC ATCCCATCCA GCGTGTTATC 240 CATAATGAGC TGGAGCTTTA CTGTCGCGCC CGCTCCGGCC 280 GCTGCCTCGA AATTGGTGCC CACCCCCGCT CAATAAATGA 320 CAATCCTAAT GTGGTCCACC GTTGCTTCCT CCGTCCTGCC 360 GGGCGTGATG TTCAGCGTTG GTATACTGCC CCTACCCGCG 400 GGCCGGCTGC TAATTGCCGG CGTTCCGCGC TGCGCGGGCT 440 CCCCGCTGCT GACCGCACTT ACTGCTTCGA CGGGTTTTCT 480 GGCTGTAACT TTCCCGCCGA GACGGGCATC GCCCTCTATT 520 CTCTCCATGA TATGTCACCA TCTGATGTCG CCGAGGCTAT 560 GTTCCGCCAT GGTATGACGC GGCTTTACGC TGCCCTCCAC 600 CTCCCGCCTG AGGTCCTGTT GCCCCCTGGC ACATACCGCA 640 CCGCGTCGTA CTTGCTGATC CATGACGGCA GGCGCGTTGT 680 GGTGACGTAT GAGGGTGACA CTAGTGCTGG TTATAACCAC 720 GATGTTTCCA ACCTGCGCTC CTGGATTAGA ACCACTAAGG 760 TTACCGGAGA CCACCCTCTC GTCATCGAGC GGGTTAGGGC 800 CATTGGCTGC CACTTTGTCC TTTTACTCAC GGCTGCTCCG 840 GAGCCATCAC CTATGCCCTA TGTCCCTTAC CCCCGGTCTA 880 CCGAGGTCTA TGTCCGATCG ATCTTCGGCC CGGGTGGCAC 920 CCCCTCCCTA TTTCCAACCT CATGCTCCAC CAAGTCGACC 960 TTCCATGCTG TCCCTGCCCA TATCTGGGAC CGTCTCATGT 1000 TGTTCGGGGC CACCCTAGAT GACCAAGCCT TTTGCTGCTC 1040 CCGCCTAATG ACTTACCTCC GCGGCATTAG CTACAAGGTT 1080 ACTGTGGGCA CCCTTGTTGC CAATGAAGGC TGGAACGCCT 1120 CTGAGGACGC TCTTACAGCT GTCATCACTG CCGCCTACCT 1160 TACCATCTGC CACCAGCGGT ACCTCCGCAC TCAGGCTATA 1200 TCTAAGGGGA TGCGTCGCCT GGAGCGGGAG CATGCTCAGA 1240 AGTTTATAAC ACGCCTCTAC AGTTGGCTCT TTGAGAAGTC 1280 CGGCCGTGAT TATATCCCCG GCCGTCAGTT GGAGTTCTAC 1320 GCTCAGTGTA GGCGCTGGCT CTCGGCCGGC TTTCATCTTG 1360 ACCCACGGGT GTTGGTTTTT GATGAGTCGG CCCCCTGCCA 1400 CTGTAGGACT GCGATTCGTA AGGCGGTCTC AAAGTTTTGC 1440 TGCTTTATGA AGTGGCTGGG CCAGGAGTGC ACCTGTTTTC 1480 TACAACCTGC AGAAGGCGTC GTTGGCGACC AGGGCCATGA 1520 CAACGAGGCC TATGAGGGGT CTGATGTTGA CCCTGCTGAA 1560 TCCGCTATTA GTGACATATC TGGGTCCTAC GTAGTCCCTG 1600 GCACTGCCCT CCAACCGCTT TACCAAGCCC TTGACCTCCC 1640 CGCTGAGATT GTGGCTCGTG CAGGCCGGCT GACCGCCACA 1680 GTAAAGGTCT CCCAGGTCGA CGGGCGGATC GATTGTGAGA 1720 CCCTTCTCGG TAATAAAACC TTCCGCACGT CGTTTGTTGA 1760 CGGGGCGGTT TTAGAGACTA ATGGCCCAGA GCGCCACAAT 1800 CTCTCTTTTG ATGCCAGTCA GAGCACTATG GCCGCCGGCC 1840 CTTTCAGTCT CACCTATGCC GCCTCTGCTG CTGGGCTGGA 1880 GGTGCGCTAT GTCGCCGCCG GGCTTGACCA CCGGGCGGTT 1920 TTTGCCCCCG GCGTTTCACC CCGGTCAGCC CCTGGCGAGG 1960 TCACCGCCTT CTGTTCTGCC CTATACAGGT TTAATCGCGA 2000 GGCCCAGCGC CTTTCGCTGA CCGGTAATTT TTGGTTCCAT 2040 CCTGAGGGGC TCCTTGGCCC CTTTGCCCCG TTTTCCCCCG 2080 GGCATGTTTG GGAGTCGGCT AATCCATTCT GTGGCGAGAG 2120 CACACTTTAC ACCCGCACTT GGTCGGAGGT TGATGCTGTT 2160 CCTAGTCCAG CCCAGCCCGA CTTAGGTTTT ACATCTGAGC 2200 CTTCTATACC TAGTAGGGCC GCCACACCTA CCCCGGCGGC 2240 CCCTCTACCC CCCCCTGCAC CGGATCCTTC CCCTACTCTC 2280 TCTGCTCCGG CGCGTGGTGA GCCGGCTCCT GGCGCTACCG 2320 CCAGGGCCCC AGCCATAACC CACCAGACGG CCCGGCATCG 2360 CCGCCTGCTC TTTACCTACC CGGATGGCTC TAAGGTGTTC 2400 GCCGGCTCGC TGTTTGAGTC GACATGTACC TGGCTCGTTA 2440 ACGCGTCTAA TGTTGACCAC CGCCCTGGCG GTGGGCTCTG 2480 TCATGCATTT TACCAGAGGT ACCCCGCCTC CTTTGATGCT 2520 GCCTCTTTTG TGATGCGCGA CGGCGCGGCC GCCTACACAT 2560 TAACCCCCCG GCCAATAATT CATGCCGTCG CTCCTGATTA 2600 TAGGTTGGAA CATAACCCAA AGAGGCTTGA GGCTGCCTAC 2640 CGGGAGACTT GCTCCCGCCT CGGTACCGCT GCATACCCAC 2680 TCCTCGGGAC CGGCATATAC CAGGTGCCGA TCGGTCCCAG 2720 TTTTGACGCC TGGGAGCGGA ATCACCGCCC CGGGGACGAG 2760 TTGTACCTTC CTGAGCTTGC TGCCAGATGG TTCGAGGCCA 2800 ATAGGCCGAC CTGCCCAACT CTCACTATAA CTGAGGATGT 2840 TGCGCGGACA GCAAATCTGG CTATCGAACT TGACTCAGCC 2880 ACAGACGTCG GCCGGGCCTG TGCCGGCTGT CGAGTCACCC 2920 CCGGCGTTGT GCAGTACCAG TTTACCGCAG GTGTGCCTGG 2960 ATCCGGCAAG TCCCGCTCTA TTACCCAAGC CGACGTGGAC 3000 GTTGTCGTGG TCCCGACCCG GGAGTTGCGT AATGCCTGGC 3040 GCCGCCGCGG CTTCGCTGCT TTCACCCCGC ACACTGCGGC 3080 TAGAGTCACC CAGGGGCGCC GGGTTGTCAT TGATGAGGCC 3120 CCGTCCCTTC CCCCTCATTT GCTGCTGCTC CACATGCAGC 3160 GGGCCGCCAC CGTCCACCTT CTTGGCGACC CGAATCAGAT 3200 CCCAGCCATC GATTTTGAGC ACGCCGGGCT CGTTCCCGCC 3240 ATCAGGCCCG ATTTGGCCCC CACCTCCTGG TGGCATGTTA 3280 CCCATCGCTG CCCTGCGGAT GTATGTGAGC TAATCCGCGG 3320 CGCATACCCT ATGATTCAGA CCACTAGTCG GGTCCTCCGG 3360 TCGTTGTTCT GGGGTGAGCC CGCCGTTGGG CAGAAGCTAG 3400 TGTTCACCCA GGCGGCTAAG GCCGCCAACC CCGGTTCAGT 3440 GACGGTCCAT GAGGCACAGG GCGCTACCTA CACAGAGACT 3480 ACCATCATTG CCACGGCAGA TGCTCGAGGC CTCATTCAGT 3520 CGTCCCGAGC TCATGCCATT GTTGCCTTGA CGCGCCACAC 3560 TGAGAAGTGC GTCATCATTG ACGCACCAGG CCTGCTTCGC 3600 GAGGTGGGCA TCTCCGATGC AATCGTTAAT AACTTTTTCC 3640 TTGCTGGTGG CGAAATTGGC CACCAGCGCC CATCTGTTAT 3680 CCCTCGCGGC AATCCTGACG CCAATGTTGA CACCTTGGCT 3720 GCCTTCCCGC CGTCTTGCCA GATTAGCGCC TTCCATCAGT 3760 TGGCTGAGGA GCTTGGCCAC AGACCTGCCC CTGTCGCGGC 3800 TGTTCTACCG CCCTGCCCTG AGCTTGAACA GGGCCTTCTC 3840 TACCTGCCCC AAGAACTCAC CACCTGTGAT AGTGTCGTAA 3880 CATTTGAATT AACAGATATT GTGCATTGTC GTATGGCCGC 3920 CCCGAGCCAG CGCAAGGCCG TGCTGTCCAC GCTCGTGGGC 3960 CGTTATGGCC GCCGCACAAA GCTCTACAAT GCCTCCCACT 4000 CTGATGTTCG CGACTCTCTC GCCCGTTTTA TCCCGGCCAT 4040 TGGCCCCGTA CAGGTTACAA CCTGTGAATT GTACGAGCTA 4080 GTGGAGGCCA TGGTCGAGAA GGGCCAGGAC GGCTCCGCCG 4120 TCCTTGAGCT CGACCTTTGT AGCCGCGACG TGTCCAGGAT 4160 CACCTTCTTC CAGAAAGATT GTAATAAATT CACCACGGGG 4200 GAGACCATCG CCCATGGTAA AGTGGGCCAG GGCATTTCGG 4240 CCTGGAGTAA GACCTTCTGT GCCCTTTTCG GCCCCTGGTT 4280 CCGTGCTATT GAGAAGGCTA TCCTGGCCCT GCTCCCTCAG 4320 GGTGTGTTTT ATGGGGATGC CTTTGATGAC ACCGTCTTCT 4360 CGGCGGCTGT GGCCGCAGCA AAGGCATCCA GAATGACTTT 4400 TCTGAGTTTG ATTCCACCCA GAATAATTTT TCCTTGGGCC 4440 TAGAGTGTGC TATTATGGAG GAGTGTGGGA TGCCGCAGTG 4480 GCTCATCCGC TTGTACCACC TTATAAGGTC TGCGTGGATT 4520 CTGCAGGCCC CGAAGGAGTC CCTGCGAGGG TTTTGGAAGA 4560 AACACTCCGG TGAGCCCGGC ACCCTTCTGT GGAATACTGT 4600 CTGGAACATG GCCGTTATCA CCCACTGTTA TGATTTCCGC 4640 GATCTGCAGG TGGCTGCCTT TAAAGGTGAT GATTCGATAG 4680 TGCTTTGCAG TGAGTACCGT CAGAGCCCAG GGGCTGCTGT 4720 CCTGATTGCT GGCTGTGGCC TAAAGTTGAA GGTGGATTTC 4760 CGTCCGATTG GTCTGTATGC AGGTGTTGTG GTGGCCCCCG 4800 GCCTTGGCGC GCTTCCTGAT GTCGTGCGCT TCGCCGGTCG 4840 GCTTACTGAG AAGAATTGGG GCCCTGGCCC CGAGCGGGCG 4880 GAGCAGCTCC GCCTCGCTGT GAGTGATTTT CTCCGCAAGC 4920 TCACGAATGT AGCTCAGATG TGTGTGGATG TTGTCTCTCG 4960 TGTTTATGGG GTTTCCCCTG GGCTCGTTCA TAACCTGATT 5000 GGCATGCTAC AGGCTGTTGC TGATGGCAAG GCTCATTTCA 5040 CTGAGTCAGT GAAGCCAGTG CTTGACCTGA CAAATTCAAT 5080 TCTGTGTCGG GTGGAATGAA TAACATGTCT TTTGCTGCGC 5120 CCATGGGTTC GCGACCATGC GCCCTCGGCC TATTTTGCTG 5160 TTGCTCCTCA TGTTTCTGCC TATGCTGCCC GCGCCACCGC 5200 CCGGTCAGCC GTCTGGCCGC CGTCGTGGGC GGCGCAGCGG 5240 CGGTTCCGGC GGTGGTTTCT GGGGTGACCG GGTTGATTCT 5280 CAGCCCTTCG CAATCCCCTA TATTCATCCA ACCAACCCCT 5320 TCGCCCCCGA TGTCACCGCT GCGGCCGGGG CTGGACCTCG 5360 TGTTCGCCAA CCCGCCCGAC CACTCGGCTC CGCTTGGCGT 5400 GACCAGGCCC AGCGCCCCGC CGCTGCCTCA CGTCGTAGAC 5440 CTACCACAGC TGGGGCCGCG CCGCTAACCG CGGTCGCTCC 5480 GGCCCATGAC ACCCCGCCAG TGCCTGATGT TGACTCCCGC 5520 GGCGCCATCC TGCGCCGGCA GTATAACCTA TCAACATCTC 5560 CCCTCACCTC TTCCGTGGCC ACCGGCACAA ATTTGGTTCT 5600 TTACGCCGCT CCTCTTAGCC CGCTTCTACC CCTCCAGGAC 5640 GGCACCAATA CTCATATAAT GGCTACAGAA GCTTCTAATT 5680 ATGCCCAGTA CCGGGTTGCT CGTGCCACAA TTCGCTACCG 5720 CCCGCTGGTC CCCAACGCTG TTGGTGGCTA CGCTATCTCC 5760 ATTTCGTTCT GGCCACAGAC CACCACCACC CCGACGTCCG 5800 TTGACATGAA TTCAATAACC TCGACGGATG TCCGTATTTT 5840 AGTCCAGCCC GGCATAGCCT CCGAGCTTGT TATTCCAAGT 5880 GAGCGCCTAC ACTATCGCAA CCAAGGTTGG CGCTCTGTTG 5920 AGACCTCCGG GGTGGCGGAG GAGGAGGCCA CCTCTGGTCT 5960 TGTCATGCTC TGCATACATG GCTCACCTGT AAATTCTTAT 6000 ACTAATACAC CCTATACCGG TGCCCTCGGG CTGTTGGACT 6040 TTGCCCTCGA ACTTGAGTTC CGCAACCTCA CCCCCGGTAA 6080 TACCAATACG CGGGTCTCGC GTTACTCCAG CACTGCCCGT 6120 CACCGCCTTC GTCGCGGTGC AGATGGGACT GCCGAGCTCA 6160 CCACCACGGC TGCTACTCGC TTCATGAAGG ACCTCTATTT 6200 TACTAGTACT AATGGTGTTG GTGAGATCGG CCGCGGGATA 6240 GCGCTTACCC TGTTTAACCT TGCTGACACC CTGCTTGGCG 6280 GTCTACCGAC AGAATTGATT TCGTCGGCTG GTGGCCAGCT 6320 GTTCTACTCT CGCCCCGTCG TCTCAGCCAA TGGCGAGCCG 6360 ACTGTTAAGC TGTATACATC TGTGGAGAAT GCTCAGCAGG 6 00 ATAAGGGTAT TGCAATCCCG CATGACATCG ACCTCGGGGA 6440 ATCCCGTGTA GTTATTCAGG ATTATGACAA CCAACATGAG 6480 CAGGACCGAC CGACACCTTC CCCAGCCCCA TCGCGTCCTT 6520 TTTCTGTCCT CCGAGCTAAC GATGTGCTTT GGCTTTCTCT 6560 CACCGCTGCC GAGTATGACC AGTCCACTTA CGGCTCTTCG 6600 ACCGGCCCAG TCTATGTCTC TGACTCTGTG ACCTTGGTTA 6640 ATGTTGCGAC CGGCGCGCAG GCCGTTGCCC GGTCACTCGA 6680 CTGGACCAAG GTCACACTTG ATGGTCGCCC CCTTTCCACC 6720 ATCCAGCAGT ATTCAAAGAC CTTCTTTGTC CTGCCGCTCC 6760 GCGGTAAGCT CTCCTTTTGG GAGGCAGGAA CTACTAAAGC 6800 CGGGTACCCT TATAATTATA ACACCACTGC TAGTGACCAA 6840 CTGCTCGTTG AGAATGCCGC TGGGCATCGG GTTGCTATTT 6880 CCACCTACAC TACTAGCCTG GGTGCTGGCC CCGTCTCTAT 6920 TTCCGCGGTT GCTGTTTTAG CCCCCCACTC TGTGCTAGCA 6960 TTGCTTGAGG ATACCATGGA CTACCCTGCC CGCGCCCATA 7000 CTTTCGATGA CTTCTGCCCG GAGTGCCGCC CCCTTGGCCT 7040 CCAGGGTTGT GCTTTTCAGT CTACTGTCGC TGAGCTTCAG 7080 CGCCTTAAGA TGAAGGTGGG TAAAACTCGG GAGTTATAGT 7120 TTATTTGCTT GTGCCCCCCT TCTTTCTGTT GCTTATTT 7168 The abbreviations used for the nucleotides are those standardly used in the art. The sequence in one direction has been designated by convention as the "plus" sequence since it is the protein-encoding strand of RNA viruses and this is the sequence shown above as SEQ ID. NO. :4. The deduced amino acid sequences of the open reading frames of SAR-55 have SEQ ID NO. 1, SEQ ID NO. 2, and SEQ ID NO. 3. ORF-1 starts at nucleotide 28 of SEQ. ID NO. 4 and extends 5078 nucleotides; ORF-2 starts at nucleotide 5147 of SEQ. ID NO. 4 and extends 1979 nucleo¬ tides; and ORF-3 starts at nucleotide 5106 of SEQ. ID NO. 4 and extends 368 nucleotides. Variations are contemplated in the DNA sequence which will result in a DNA sequence that is capable of directing production of analogs of the ORF-2 protein. By "analogs of the ORF-2 protein" as used throughout the specification and claims is meant a protein having an amino acid sequence substantially identical to a sequence specifically shown herein where one or more of the residues shown in the sequences presented herein have been substituted with a biologically equivalent residue such that the resultant protein (i.e. the "analog") is capable of forming viral particles and is immunogenic. It should be noted that the DNA sequence set forth above represents a preferred embodiment of the present invention. Due to the degeneracy of the genetic code, it is to be understood that numerous choices of nucleotides may be made that will lead to a DNA sequence capable of directing production of the instant ORF proteins or their analogs. As such, DNA sequences which are functionally equivalent to the sequences set forth above or which are functionally equivalent to sequences that would direct production of analogs of the ORF proteins produced pursuant to the amino acid sequence set forth above, are intended to be encompassed within the present invention. The present invention relates to a method for detecting the hepatitis E virus in biological samples based on selective amplification of hepatitis E gene fragments. Preferably, this method utilizes a pair of single-stranded primers derived from non-homologous regions of opposite strands of a DNA duplex fragment, which in turn is derived from a hepatitis E virus whose genome contains a region homologous to the SAR-55 sequence shown in SEQ ID No. : 4. These primers can be used in a method following the process for amplifying selected nucleic acid sequences as defined in U.S. Patent No. 4,683,202. The present invention also relates to the use of single-stranded antisense poly-or oligonucleotides derived from sequences homologous to the SAR-55 cDNA to inhibit the expression of hepatitis E genes. These anti-sense poly-or oligonucleotides can be either DNA or RNA. The targeted sequence is typically messenger RNA and more preferably, a signal sequence required for processing or translation of the RNA. The antisense poly-or oligonucleotides can be conjugated to a polycation such as polylysine as disclosed in Lemaitre, M. et al. (1989) Proc Natl Acad Sci USA 84:648-652; and this conjugate can be administered to a mammal in an amount sufficient to hybridize to and inhibit the function of the messenger RNA. The present invention includes a recombinant DNA method for the manufacture of HEV proteins, preferably a protein composed of at least one ORF protein, most preferably at least one ORF-2 protein. The recombinant ORF protein may be composed of one ORF protein or a combination of the same or different ORF proteins. A natural or synthetic nucleic acid sequence may be used to direct production of the HEV proteins. In one embodiment of the invention, the method comprises: (a) preparation of a nucleic acid sequence capable of directing a host organism to produce a protein Of HEV; (b) cloning the nucleic acid sequence into a vector capable of being transferred into and replicated in a host organism, such vector containing operational elements for the nucleic acid sequence; (c) transferring the vector containing the nucleic acid and operational elements into a host organism capable of expressing the protein; (d) culturing the host organism under condi¬ tions appropriate for amplification of the vector and expression of the protein; and (e) harvesting the protein. In another embodiment of the invention, the method for the recombinant DNA synthesis of a protein encoded by nucleic acids of HEV, preferably encoding by at least one ORF of HEV or a combination of the same or different ORF proteins, most preferably encoding at least one ORF-2 nucleic acid sequence, comprises: (a) culturing a transformed or transfected host organism containing a nucleic acid sequence capable of directing the host organism to produce a protein, under conditions such that the protein is produced, said protein exhibiting substantial homology to a native HEV protein isolated from HEV having the amino acid sequence according to SEQ ID NO. 1, SEQ ID NO. 2 or SEQ ID NO. 3, or combina¬ tions thereof. In one embodiment, the RNA sequence of the viral genome of HEV strain SAR-55 was isolated and cloned to cDNA as follows. Viral RNA is extracted from a biological sample collected from cynomolgus monkeys infected with SAR-55 and the viral RNA is then reverse transcribed and amplified by polymerase chain reaction using primers complementary to the plus or minus strands of the genome of a strain of HEV from Burma (Tarn et al. (1991)) or the SAR-55 genome. The PCR fragments are subcloned into pBR322 or pGEM-32 and the double-stranded PCR fragments were sequenced. The vectors contemplated for use in the present invention include any vectors into which a nucleic acid sequence as described above can be inserted, along with any preferred or required operational elements, and which vector can then be subsequently transferred into a host organism and replicated in such organism. Preferred vectors are those whose restriction sites have been well documented and which contain the operational elements pre¬ ferred or required for transcription of the nucleic acid sequence. The "operational elements" as discussed herein include at least one promoter, at least one operator, at least one leader sequence / at least one terminator codon, and any other DNA sequences necessary or preferred for appropriate transcription and subsequent translation of the vector nucleic acid. In particular, it is contemplated that such vectors will contain at least one origin of replication recognized by the host organism along with at least one selectable marker and at least one promoter sequence capable of initiating transcription of the nucleic acid sequence. In construction of the cloning vector of the present invention, it should additionally be noted that multiple copies of the nucleic acid sequence and its attendant operational elements may be inserted into each vector. In such an embodiment, the host organism would produce greater amounts per vector of the desired HEV protein. The number of multiple copies of the DNA sequence which may be inserted into the vector is limited only by the ability of the resultant vector due to its size, to be transferred into and replicated and transcribed in an appropriate host microorganism. In another embodiment, restriction digest frag¬ ments containing a coding sequence for HEV proteins can be inserted into a suitable expression vector that functions in prokaryotic or eukaryotic cells. By suitable is meant that the vector is capable of carrying and expressing a complete nucleic acid sequence coding for HEV proteins, preferably at least one complete ORF protein. In the case or ORF-2, the expressed protein should form viral-like particles. Preferred expression vectors are those that function in a eukaryotic cell. Examples of such vectors include but are not limited to vectors useful for expression in yeast (e.g. pPIC9 vector-Invitrogen) vaccinia virus vectors, adenovirus or herpesviruses, preferably the baculovirus transfer vector, pBlueBac. Preferred vectors are p63-2, which contains the complete ORF-2 gene, and P59-4, which contains the complete ORF-3 and ORF-2 genes. These vectors were deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, MD 20852 USA on September 10, 1992 and have accession numbers 75299 (P63-2) and 75300 (P59-4) . Example 1 illustrates the cloning of the ORF-2 gene into pBlueBac to produce p63-2. This method includes digesting the genome of HEV strain SAR-55 with the restriction enzymes Nrul and Bglll, inserting a polylinker containing Blnl and Bglll sites into the unique Nhel site of the vector and inserting the Nrul-Bglll ORF-2 fragment in Blnl-Bglll PBlueBac using an adapter. In yet another embodiment, the selected recombinant expression vector may then be transfected into a suitable eukaryotic cell system for purposes of expressing the recombinant protein. Such eukaryotic cell systems include, but are not limited to, yeast, and cell lines such as HeLa, MRC-5 or Cv-1. One preferred eukaryotic cell system is SF9 insect cells. One preferred method involves use of the pBlueBac expression vector where the insect cell line SF9 is cotransfected with recombinant pBlueBac and AcMNPV baculovirus DNA by the Ca precipitation method. The expressed recombinant protein may be detected by methods known in the art which include Coomassie blue staining and Western blotting using sera containing anti-HEV antibody as shown in Example 2. Another method is the detection of virus-like particles by immunoelectron microscopy as shown in Example 3. In a further embodiment, the recombinant protein expressed by the SF9 cells can be obtained as a crude lysate or it can be purified by standard protein purification procedures known in the art which may include differential precipitation, molecular sieve chromatography, ion-exchange chromatography, isoelectric focusing, gel electrophoresis, affinity, and immunoaffinity chromatography and the like. In the case of immunoaffinity chromatography, the recombinant protein may be purified by passage through a column containing a resin which has bound thereto antibodies specific for the ORF protein. An example of a protocol for the purification of a recombinantly expressed HEV ORF protein is provided in Example 10. In another embodiment, the expressed recombinant proteins of this invention can be used in immunoassays for diagnosing or prognosing hepatitis E in a mammal including but not limited to humans, chimpanzees, Old World monkeys, New World monkeys, other primates and the like. In a preferred embodiment, the immunoassay is useful in diag¬ nosing hepatitis E infection in humans. Immunoassays using the HEV proteins, particularly the ORF proteins, and especially ORF 2 proteins, provide a highly specific, sensitive and reproducible method for diagnosing HEV infections, in contrast to immunoassays which utilize partial ORF proteins. Immunoassays of the present invention may be a radioimmunoassay, Western blot assay, immunofluorescent assay, enzyme immunoassay, chemiluminescent assay, immunohistochemical assay and the like. Standard techniques known in the art for ELISA are described in Methods in Immunodiagnosis. 2nd Edition, Rose and Bigazzi, eds., John Wiley and Sons, 1980 and Campbell et al., Methods of Immunology. W.A. Benjamin, Inc., 1964, both of which are incorporated herein by reference. Such assays may be a direct, indirect, competitive, or noncompetitive immunoassay as described in the art. (Oellerich, M. 1984. J.Clin. Chem. Clin. BioChem. 22: 895-904) Biological samples appropriate for such detection assays include, but are not limited to, tissue biopsy extracts, whole blood, plasma, serum, cerebrospinal fluid, pleural fluid, urine and the like. In one embodiment, test serum is reacted with a solid phase reagent having surface-bound recombinant HEV protein as an antigen, preferably an ORF protein or combination of different ORF proteins such as ORF-2 and ORF-3, ORF-1 and ORF-3 and the like. More preferably, the HEV protein is an ORF-2 protein that forms virus-like particles. The solid surface reagent can be prepared by known techniques for attaching protein to solid support material. These attachment methods include non-specific adsorption of the protein to the support or covalent attachment of the protein to a reactive group on the support. After reaction of the antigen with anti-HEV antibody, unbound serum components are removed by washing and the antigen-antibody complex is reacted with a secondary antibody such as labelled anti-human antibody. The label may be an enzyme which is detected by incubating the solid support in the presence of a suitable fluorimetric or colorimetric reagent. Other detectable labels may also be used, such as radiolabels or colloidal gold, and the like. In a preferred embodiment, protein expressed by the recombinant vector pBlueBac containing the entire ORF- 2 sequence of SAR-55 is used as a specific binding agent to detect anti-HEV antibodies, preferably IgG or IgM antibodies. Examples 4 and 5 show the results of an ELISA in which the solid phase reagent has recombinant ORF-2 as the surface antigen. This protein, encoded by the entire ORF-2 nucleic acid sequence, is superior to the partial ORF-2 proteins, as it is reactive with more antisera from different primate species infected with HEV than are partial antigens of ORF-2. The protein of the present invention is also capable of detecting antibodies produced in response to different strains of HEV but does not detect antibodies produced in response to Hepatitis A, B, C or Hepatitis D. The HEV protein and analogs may be prepared in the form of a kit, alone, or in combinations with other reagents such as secondary antibodies, for use in immunoassays. The recombinant HEV proteins, preferably an ORF protein or combination of ORF proteins, more preferably an ORF-2 protein and substantially homologous proteins and analogs of the invention can be used as a vaccine to protect mammals against challenge with Hepatitis E. The vaccine, which acts as an immunogen, may be a cell, cell lysate from cells transfected with a recombinant expression vector or a culture supernatant containing the expressed protein. Alternatively, the immunogen is a partially or substantially purified recombinant protein. While it is possible for the immunogen to be administered in a pure or substantially pure form, it is preferable to present it as a pharmaceutical composition, formulation or preparation. The formulations of the present invention, both for veterinary and for human use, comprise an immunogen as described above, together with one or more pharmaceutically acceptable carriers and optionally other therapeutic ingredients. The carrier(s) must be "acceptable" in the sense of being compatible with the other ingredients of the formulation and not deleterious to the recipient thereof. The formulations may conveniently be presented in unit dosage form and may be prepared by any method well-known in the pharmaceutical art. All methods include the step of bringing into association the active ingredient with the carrier which 10 constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product into the 15 desired formulation. Formulations suitable for intravenous intramuscular, subcutaneous, or intraperitoneal administration conveniently comprise sterile aqueous solutions of the active ingredient with solutions which 20 are preferably isotonic with the blood of the recipient. Such formulations may be conveniently prepared by dissolving solid active ingredient in water containing physiologically compatible substances such as sodium chloride (e.g. 0.1-2.0M), glycine, and the like, and ^ having a buffered pH compatible with physiological conditions to produce an aqueous solution, and rendering said solution sterile. These may be present in unit or multi-dose containers, for example, sealed ampoules or vials. " The formulations of the present invention may incorporate a stabilizer. Illustrative stabilizers are polyethylene glycol, proteins, saccharides, amino acids, inorganic acids, and organic acids which may be used either on their own or as admixtures. These stabilizers 5 are preferably incorporated in an amount of 0.11-10,000 parts by weight per part by weight of immunogen. If two or more stabilizers are to be used, their total amount is preferably within the range specified above. These stabilizers are used in aqueous solutions at the appropriate concentration and pH. The specific osmotic pressure of such aqueous solutions is generally in the range of 0.1-3.0 osmoles, preferably in the range of 0.8- 1.2. The pH of the aqueous solution is adjusted to be within the range of 5.0-9.0, preferably within the range of 6-8. In formulating the immunogen of the present invention, anti-adsorption agent may be used. Additional pharmaceutical methods may be employed to control the duration of action. Controlled release preparations may be achieved through the use of polymer to complex or absorb the proteins or their derivatives. The controlled delivery may be exercised by selecting appropriate macromolecules (for example polyester, polyamino acids, polyvinyl, pyrrolidone, ethylenevinylacetate, methylcellulose, carboxymethylcellulose, or protamine sulfate) and the con¬ centration of macromolecules as well as the methods of incorporation in order to control release. Another possible method to control the duration of action by controlled-release preparations is to incorporate the proteins, protein analogs or their functional derivatives, into particles of a polymeric material such as polyesters, polyamino acids, hydrogels, poly(lactic acid) or ethylene vinylacetate copolymers. Alternatively, instead of incorporating these agents into polymeric particles, it is possible to entrap these materials in microcapsules prepared, for example, by coacervation techniques or by interfacial polymerization, for example, hydroxy- methylcellulose or gelatin-microcapsules and poly(methylmethacylate) microcapsules, respectively, or in colloidal drug delivery systems, for example, liposomes, albumin microspheres, microemulsions, nanopartides, and nanocapsules or in macroemulsions. When oral preparations are desired, the composi¬ tions may be combined with typical carriers, such as lactose, sucrose, starch, talc magnesium stearate, crystalline cellulose, methyl cellulose, carboxymethyl cellulose, glycerin, sodium alginate or gum arabic among others. The proteins of the present invention may be supplied in the form of a kit, alone, or in the form of a pharmaceutical composition as described above. Vaccination can be conducted by conventional methods. For example, the immunogen can be used in a suitable diluent such as saline or water, or complete or incomplete adjuvants. Further, the immunogen may or may not be bound to a carrier to make the protein immunogenic. Examples of such carrier molecules include but are not limited to bovine serum albumin (BSA) , keyhole limpet hemocyanin (KLH) , tetanus toxoid, and the like. The immunogen can be administered by any route appropriate for antibody production such as intravenous, intraperitoneal, intramuscular, subcutaneous, and the like. The immunogen may be administered once or at periodic intervals until a significant titer of anti-HEV antibody is produced. The antibody may be detected in the serum using an immunoassay. In yet another embodiment, the immunogen may be nucleic acid sequence capable of directing host organism synthesis of an HEV ORF protein. Such nucleic acid sequence may be inserted into a suitable expression vector by methods known to those skilled in the art. Expression vectors suitable for producing high efficiency gene transfer in vivo include, but are not limited to, retroviral, adenoviral and vaccinia viral vectors. Operational elements of such expression vectors are disclosed previously in the present specification and are known to one skilled in the art. Such expression vectors can be administered intravenously, intramuscularly, subcutaneously, intraperitoneally or orally. In an alternative embodiment, direct gene transfer may be accomplished via intramuscular injection of, for example, plasmid-based eukaryotic expression vectors containing a nucleic acid sequence capable of directing host organism synthesis HEC ORF protein(s) . Such an approach has previously been utilized to produce the hepatitis B surface antigen in vivo and resulted in an antibody response to the surface antigen (Davis, H.L. et 10 al. (1993) Human Molecular Genetics. 2:1847-1851; see also Davis et al. (1993) Human Gene Therapy. 4:151-159 and 733- 740) . When the immunogen is a partially or substantially purified recombinant HEV ORF protein, 15 dosages effective to elicit a protective antibody response against HEV range from about 2 μg to about 100 μg. A more preferred range is from about 5 μg to about 70 μg and a most preferred range is from about 10 μg to about 60 μg. Dosages of HEV-ORF protein - encoding nucleic 20 acid sequence effective to elicit a protective antibody response against HEV range from about 1 to about 5000 μg; a more preferred range being about 300 to about 1000 μg. The expression vectors containing a nucleic acid sequence capable of directing host organism synthesis of 25 an HEV ORF protein(s) may be supplied in the form of a kit, alone, or in the form of a pharmaceutical composition as described above. The administration of the immunogen of the present invention may be for either a prophylactic or 30 therapeutic purpose. When provided prophylactically, the immunogen is provided in advance of any exposure to HEV or in advance of any symptom due to HEV infection. The prophylactic administration of the immunogen serves to prevent or attenuate any subsequent infection of HEV in a " mammal. When provided therapeutically, the immunogen is provided at (or shortly after) the onset of the infection or at the onset of any symptom of infection or disease caused by HEV. The therapeutic administration of the immunogen serves to attenuate the infection or disease. A preferred embodiment is a vaccine prepared using recombinant ORF-2 protein expressed by the ORF-2 sequence of HEV strain SAR-55 and equivalents thereof. Since the recombinant ORF-2 protein has already been demonstrated to be reactive with a variety of HEV-positive sera, their utility in protecting against a variety of HEV strains is indicated. In addition to use as a vaccine, the composi¬ tions can be used to prepare antibodies to HEV virus-like particles. The antibodies can be used directly as antiviral agents. To prepare antibodies, a host animal is immunized using the virus particles or, as appropriate, non-particle antigens native to the virus particle are bound to a carrier as described above for vaccines. The host serum or plasma is collected following an appropriate time interval to provide a composition comprising antibodies reactive with the virus particle. The gamma globulin fraction or the IgG antibodies can be obtained, for example, by use of saturated ammonium sulfate or DEAE Sephadex, or other techniques known to those skilled in the art. The antibodies are substantially free of many of the adverse side effects which may be associated with other anti-viral agents such as drugs. The antibody compositions can be made even more compatible with the host system by minimizing potential adverse immune system responses. This is accomplished by removing all or a portion of the Fc portion of a foreign species antibody or using an antibody of the same species as the host animal, for example, the use of antibodies from human/human hybridomas. Humanized antibodies (i.e., nonimmunogenic in a human) may be produced, for example, by replacing an immunogenic portion of an antibody with a corresponding, but nonimmunogenic portion (i.e., chimeric antibodies) . Such chimeric antibodies may contain the reactive or antigen binding portion of an antibody from one species and the Fc portion of an antibody (nonimmunogenic) from a different species. Examples of chimeric antibodies, include but are not limited to, non- human mammal-human chimeras, rodent-human chimeras, murine-human and rat-human chimeras (Robinson et al., International Patent Application 184,187; Taniguchi M. , European Patent Application 171,496; Morrison et al. , European Patent Application 173,494; Neuberger et al., PCT Application WO 86/01533; Cabilly et al. , 1987 Proc. Natl. Acad. Sci. USA 84:3439; Nishimura et al. , 1987 Cane. Res. 47:999; Wood et al., 1985 Nature 314:446; Shaw et al. , 1988 J. Natl. Cancer Inst. 80: 15553, all incorporated herein by reference) . General reviews of "humanized" chimeric antibodies are provided by Morrison S., 1985 Science 229:1202 and by Oi et al., 1986 BioTechniques 4:214. Suitable "humanized" antibodies can be alternatively produced by CDR or CEA substitution (Jones et al., 1986 Nature 321:552; Verhoeyan et al. , 1988 Science 239:1534; Biedleret al. 1988 J. Immunol. 141:4053, all incorporated herein by reference) . The antibodies or antigen binding fragments may also be produced by genetic engineering. The technology for expression of both heavy and light cain genes in E. coli is the subject the PCT patent applications; publication number WO 901443, WO901443, and WO 9014424 and in Huse et al., 1989 Science 246:1275-1281. The antibodies can also be used as a means of enhancing the immune response. The antibodies can be administered in amounts similar to those used for other therapeutic administrations of antibody. For example, pooled gamma globulin is administered at 0.02-0.1 ml/lb body weight during the early incubation period of other viral diseases such as rabies, measles and hepatitis B to interfere with viral entry into cells. Thus, antibodies reactive with the HEV virus particle can be passively administered alone or in conjunction with another anti¬ viral agent to a host infected with an HEV to enhance the effectiveness of an antiviral drug. Alternatively, anti-HEV antibodies can be induced by administering anti-idiotype antibodies as immunogens. Conveniently, a purified anti-HEV antibody preparation prepared as described above is used to induce anti-idiotype antibody in a host animal. The composition is administered to the host animal in a suitable diluent. Following administration, usually repeated administration, the host produces anti-idiotype antibody. To eliminate an immunogenic response to the Fc region, antibodies produced by the same species as the host animal can be used or the FC region of the administered antibodies can be removed. Following induction of anti-idiotype antibody in the host animal, serum or plasma is removed to provide an antibody composition. The composition can be purified as described above for anti-HEV antibodies, or by affinity chroma¬ tography using anti-HEV antibodies bound to the affinity matrix. The anti-idiotype antibodies produced are similar in conformation to the authentic HEV-antigen and may be used to prepare an HEV vaccine rather than using an HEV particle antigen. When used as a means of inducing anti-HEV virus antibodies in an animal, the manner of injecting the anti¬ body is the same as for vaccination purposes, namely intramuscularly, intraperitoneally, subcutaneously or the like in an effective concentration in a physiologically suitable diluent with or without adjuvant. One or more booster injections may be desirable. The HEV derived proteins of the invention are also intended for use in producing antiserum designed for pre- or post-exposure prophylaxis. Here an HEV protein, or mixture of proteins is formulated with a suitable adjuvant and administered by injection to human volunteers, according to known methods for producing human antisera. Antibody response to the injected proteins is monitored, during a several-week period following immunization, by periodic serum sampling to detect the presence of anti-HEV serum antibodies, using an immunoassay as described herein. The antiserum from immunized individuals may be administered as a pre-exposure prophylactic measure for individuals who are at risk of contracting infection. The antiserum is also useful in treating an individual post- exposure, analogous to the use of high titer antiserum against hepatitis B virus for post-exposure prophylaxis. Of course, those of skill in the art would readily understand that immune globulin (HEV immune globulin) purified from the antiserum of immunized individuals using standard techniques may be used as a pre-exposure prophylactic measure or in treating individuals post- exposure. For both in vivo use of antibodies to HEV virus- like particles and proteins and anti-idiotype antibodies and diagnostic use, it may be preferable to use monoclonal antibodies. Monoclonal anti-virus particle antibodies or anti-idiotype antibodies can be produced as follows. The spleen or lymphocytes from an immunized animal are removed and immortalized or used to prepare hybridomas by methods known to those skilled in the art. (Goding, J.W. 1983. Monoclonal Antibodies: Principles and Practice, Pladermic Press, Inc., NY, NY, pp. 56-97). To produce a human-human hybridoma, a human lymphocyte donor is selected. A donor known to be infected with HEV (where infection has been shown for example by the presence of anti-virus antibodies in the blood or by virus culture) may serve as a suitable lymphocyte donor. Lymphocytes can be isolated from a peripheral blood sample or spleen cells may be used if the donor is subject to splenectomy. Epstein-Barr virus (EBV) can be used to immortalize human lymphocytes or a human fusion partner can be used to produce human-human hybridomas. Primary in vitro immunization with peptides can also be used in the generation of human monoclonal antibodies. Antibodies secreted by the immortalized cells are screened to determine the clones that secrete antibodies of the desired specificity. For monoclonal anti-virus particle antibodies, the antibodies must bind to HEV virus particles. For monoclonal anti-idiotype antibodies, the antibodies must bind to anti-virus particle antibodies. Cells producing antibodies of the desired specificity are selected. The above described antibodies and antigen binding fragments thereof may be supplied in kit form alone, or as a pharmaceutical composition for in vivo use. The antibodies may be used for therapeutic uses, diagnostic use in immunoassays or as an immunoaffinity agent to purify ORF proteins as described herein. Material The materials used in the Examples were as follows: Primates. Chimpanzee (Chimp) (Pan troglodytes) . Old world monkeys: cynomolgus monkeys (Cyno) (Macaca fascicularis) , rhesus monkeys (Rhesus) (Af. mulatta) , pigtail monkeys (PT) (M. nemestrina) , and African green monkeys (AGM) ( Cercopi thecus aethiops) . New World monkeys: mustached tamarins (Tarn) {Saguinus ystax) , squirrel monkeys (SQM) (Saimiri sciureus) and owl monkeys (OWL) (Aotus trivigatus) . Primates were housed singly under conditions of biohazard containment. The housing, maintenance and care of the animals met or exceeded all requirements for primate husbandry. Most animals were inoculated intravenously with HEV, strain SAR-55 contained in 0.5 ml of stool suspension diluted in fetal calf serum as described in Tsarev, S.A. et al. (1992), Proc. Natl. Acad. Sci USA. 89:559-563; and Tsarev, S.A. et al. (1993), J. Infect. Pis. (167:1302- 1306) . Chimp-1313 and 1310 were inoculated with a pool of stools collected from 7 Pakistani hepatitis E patients. Serum samples were collected approximately twice a week before and after inoculation. Levels of the liver enzymes serum alanine amino transferase (ALT) , isocitrate dehydrogenase (ICD) , and gamma glutamyl transferase (GGT) were assayed with commercially available tests (Medpath Inc., Rockville, MD) . Serologic tests were performed as described above. EXAMPLE 1 Identification of the DNA Sequence of the Genome of HEV Strain SAR-55. Preparation of Virus RNA Template for PCR. Bile from an HEV-infected cynomolgus monkey (10 μl) , 20% (wt/vol) SDS (to a final concentration of 1%) , proteinase K (10 mg/ml; to a final concentration of 1 mg/ml) , 1 μl of tRNA (10 mg/ml) , and 3 μl of 0.5 M EDTA were mixed in a final volume of 250 μl and incubated for 30 min. at 55°C. Total nucleic acids were extracted from bile twice with phenol/chloroform, 1:1 (vol/vol) , at 65°C and once with chloroform, then precipitated by ethanol, washed with 95% ethanol, and used for RT-PCR. RT-PCR amplification of HEV RNA from feces and especially from sera was more efficient when RNA was more extensively purified. Serum (100 μl) or a 10% fecal suspension (200 μl) was treated as above with proteinase K. After a 30-min incubation, 300 μl of CHAOS buffer (4.2 M guanidine thiocyanate/0.5 N- lauroylsarocosine/0.025 M Tris-HCL, pH 8.0) was added. Nucleic acids were extracted twice with phenol/chloroform at 65°C followed by chloroform extraction at room temperature. Then 7.5 M ammonium acetate (225 μl) was added to the upper phase and nucleic acids were precipitated with 0.68 ml of 2-propanol. The pellet was dissolved in 300 ul CHAOS buffer and 100 ul of H-O was added. Chloroform extraction and 2-propanol precipitation were repeated. Nucleic acids were dissolved in water, precipitated with ethanol, washed with 95% ethanol, and used for RT-PCR. Primers. Ninety-four primers, 21-40 nucleotides (nt) long, and complementary to plus or minus strands of the genome of a strain of HEV from Burma (BUR-121) (Tarn, A.W. et al. (1991), Virology. 185:120-131) or the SAR-55 genome were synthesized using an Applied Biosystems model 391 DNA synthesizer. The sequences of these 94 primers are shown below starting with SEQ. ID NO. 5 and continuing to SEQ. ID NO. 98: HEV Primer List ORF Primer Region Sequence D 3042 B 1 ACATTTGAATTCACAGACAT D 242 S 1 AATAATTCATGCCGTCGCTC C (SEQ. ID. NO. 14) R 241 S 1 AAGCTCAGGAAGGTACAACT C (SEQ. ID. NO. 15) R 231 S 1 AAATCGATGGCTGGGATCTG ATTC (SEQ. ID. NO. 16) R 230 S 1 GAGGCATTGTAGAGCTTTGT G (SEQ. ID. NO. 17) D 229 S 1 GATGTTGCACGGACAGCAAA TC (SEQ. ID. NO. 18) D 228 S 1 ATCTCCGATGCAATCGTTAA TAAC (SEQ. ID. NO. 19) (SEQ. ID. NO. 20) (SEQ. ID. NO. 21) (SEQ. ID. NO. 22) (SEQ. ID. NO. 23) (SEQ. ID. NO. 24) (SEQ. ID. NO. 25) (SEQ. ID. NO. 26) (SEQ. ID. NO. 27) (SEQ. ID. NO. 28) (SEQ. ID. NO. 29) (SEQ. ID. NO. 30) (SEQ. ID. NO. 31) (SEQ. ID. NO. 32) (SEQ. ID. NO. 33) (SEQ. ID. NO. 34) (SEQ. ID. NO. 35) (SEQ. ID. NO. 36) (SEQ. ID. NO. 37) (SEQ. ID. NO. 38) (SEQ. ID. NO. 39) (SEQ. ID. NO. 40) (SEQ. ID. NO. 41) (SEQ. ID. NO. 42) (SEQ. ID. NO. 43) (SEQ. ID. NO. 44) (SEQ. ID. NO. 45) (SEQ. ID. NO. 46) R 166 B 2 TATGGGAATTCGTGCCGTCC 0 TGAAG (EcoRI) (SEQ. ID. NO. 47) 143 B 1 AGTGGGAGCAGTATACCAGC (SEQ. ID. NO. 48) D 141 B 1 CTGCTATTGAGCAGGCTGCT (SEQ. ID. NO. 49) 5 ATAAAGAACCAGG (EcoRI) (SEQ. ID. NO. 62) R 111 B 2 GCGCTGAATTCGGATCACAA GCTCAGAGGCTATGCC (EcoRI) (SEQ. ID. NO. 63) D 110 B 2 GTATAACGGATCCACATCTC CCCTTACCTC (Bam HI) (SEQ. ID. NO. 64) D 109 B 2 TAACCTGGATCCTTATGCCG CCCCTCTTAG (Bam HI) (SEQ. ID. NO. 65) D 108 B 1 AAATTGGATCCTGTGTCGGG TGGAATGAATAACATGTC (BamHI) (SEQ. ID. NO. 66) R 107 B 1 ATCGGCAGATCTGATAGAGC GGGGACTTGCCGGATCC (SEQ. ID. NO. 67) D 101 B 2 TACCCTGCCCGCGCCCATAC TTTTGATG (SEQ. ID. NO. 68) R 100 B 1 GGCTGAGATCTGGTTCGGGT CGCCAAGAAGGTG (Bgl II) (SEQ. ID. NO. 69) R 99 B 2 TACAGATCTATACAACTTAA CAGTCGG (Bgl II) (SEQ. ID. NO. 70) R 98 B 2 GCGGCAGATCTCACCGACAC CATTAGTAC (Bgl II) (SEQ. ID. NO. 71) D 97 S 1 CCGTCGGATCCCAGGGGCTG CTGTCCTG (Bam HI) (SEQ. ID. NO. 72) R 96 B 2 AAAGGAATTCAAGACCAGAG GTAGCCTCCTC (EcoRI) (SEQ. ID. NO. 73) D 95 B 2 GTTGATATGAATTCAATAAC CTCGACGG (SEQ. ID. NO. 74) R 94 B 3'NC TTTGGATCCTCAGGGAGCGC GGAACGCAGAAATGAG (BamHI) (SEQ. ID. NO. 75) D 90 B 2 TCACTCGTGAATTCCTATAC TAATAC (EcoRI) (SEQ. ID. NO. 76) R 89 B 3'NC TTTGGATCCTCAGGGAGCGC GGAACGCAGAAATG (BamHI) (SEQ. ID. NO. 77) R 88 B 1 TGATAGAGCGGGACTTGCCG GATCC (BamHI) (SEQ. ID. NO. 78) R 87 B 1 TTGCATTAGGTTAATGAGGA TCTC (SEQ. ID. NO. 79) D 86 B 1 ACCTGCTTCCTTCAGCCTGC AGAAG (SEQ. ID. NO. 80) R 81 B 1 GCGGTGGATCCGCTCCCAGG CGTCAAAAC (BamHI) (SEQ. ID. NO. 81) D 80 B 1 GGGCGGATCGAATTCGAGAC CCTTCTTGG (EcoRI) (SEQ. ID. NO. 82) R 79 B 1 AGGATGGATCCATAAGTTAC CGATCAG (BamHI) (SEQ. ID. NO. 83) 78 B 1 GGCTGGAATTCCTCTGAGGA CGCCCTCAC (EcoRI) (SEQ. ID. NO. 84) 77 B 1 GCCGAAGATCTATCGGACAT AGACCTC (Bgl II) (SEQ. ID. NO. 85) 76 B 2 CAGACGACGGATCCCCTTGG ATATAGCCTG (BamHI) (SEQ. ID. NO. 86) D 75 B 5'NC GGCCGAATTCAGGCAGACCA CATATGTGGTCGATGCCATG (EcoRI) (SEQ. ID. NO. 87) D 72 B 1 GCAGGTGTGCCTGGATCCGG CAAGT (BamHI) (SEQ. ID. NO. 88) R 71 B 1 GTTAGAATTCCGGCCCAGCT GTGGTAGGTC (EcoRI) (SEQ. ID. NO. 89) D 63 B 1 CCGTCCGATTGGTCTGTATG CAGG (SEQ. ID. NO. 90) D 61 B 1 TACCAGTTTACTGCAGGTGT GC (SEQ. ID. NO. 91) D 60 B 1 CAAGCCGATGTGGACGTTGT CG (SEQ. ID. NO. 92) R 59 B 2,3 GGCGCTGGGCCTGGTCACGC CAAG (SEQ. ID. NO. 93) D 50 B 1 GCAGAAACTAGTGTTGACCC AG (SEQ. ID. NO. 94) R 49 B 2 TAGGTCTACGACGTGAGGCA AC (SEQ. ID. NO. 95) R 48 B 1 TACAATCTTTCAGGAAGAAG G (SEQ. ID. NO. 96) R 47 B 1 CCCACACTCCTCCATAATAG C (SEQ. ID. NO. 97) D 46 B 1 GATAGTGCTTTGCAGTGAGT ACCG (SEQ. ID. NO. 98) The abbreviations to the left of the sequences represent the following: R and D refer to reverse and forward primers, respectively; B and S refer to sequences derived from the Burma-121 Strain of Hepatitis E and the SAR-55 Strain of Hepatitis E, respectively; 5'NC and 3'NC refer to 5 prime and 3 prime non-coding regions of the HEV genome, respectively; and 1, 2 and 3 refer to sequence derived from open reading frames 1, 2 or 3, respectively. The symbol 0 to the right of some sequences shown indicates insertion of an artificial restriction site into these sequences. For cloning of PCR fragments, EcoRI, BamHI, or Bglll restriction sites preceded by 3-7 nt were added to the 5' end of primers. RT-PCR. The usual 100-μl RT-PCR mixture contained template, 10 mM Tris-HCL (ph 8.4), 50 mM KC1, 2.5 mM MgCl 2 , all four dNTPs (each at 0.2 mM) , 50 pmol of direct primer, 50 pmol of reverse primer, 40 units of RNasin (Promega) , 16 units of avian myeloblastosis virus reverse transcriptase (Promega) , 4 units of AmpliTaq (Cetus) , under 100 μl of light mineral oil. The mixture was incubated 1 h at 42°C and then amplified by 35 PCR cycles; 1 min at 94°C, 1 min at 45°C, and 1 min at 72°C. The PCR products were analyzed on 1% agarose gels. Cloning of PCR Fragments . PCR fragments containing restriction sites at the ends were digested with EcoRI and BajriHi or EcoRI and Bgrlll restriction enzymes and cloned in EcoRI/BairiHI-digested pBR322 or pGEM- 3Z (Promega) . Alternatively, PCR fragments were cloned into pCRlOOO (Invitrogen) using the TA cloning kit (Invitrogen) . Sequencing of PCR Fragments and Plasmids . PCR fragments were excised from 1% agarose gels and purified by Geneclean (Bio 101, La Jolla, CA) . Double-stranded PCR fragments were sequenced by using Sequenase (United States Biochemical) as described in Winship, P.R. (1984) , Nucleic Acids Rev.. 17:1266. Double-stranded plasmids purified through CsCl gradients were sequenced with a Sequenase kit (United States Biochemical) . Computer Analysis of Sequences. Nucleotide sequences of HEV strains were compared using the Genetics Computer Group (Madison, WI) software package (Devereaux, J. et al. (1984), Nucleic Acids Rev.. 12:387-395, version 7.5, on a VAX 8650 computer (at the National Cancer Insti¬ tute, Frederick, MD) ) . EXAMPLE 2 Construction of a Recombinant Expression Vector. P63 -2. A plasmid containing the complete ORF-2 of the genome of HEV strain SAR-55, Tsarev, S.A. et al. (1992), Proc. Natl. Acad. Sci. USA. 89:559-563), was used to obtain a restriction fragment Nrul-Bglll. Nrul cut the HEV cDNA five nucleotides upstream of the ATG initiation codon of ORF-2. An artificial Bgl II site previously had been placed at the 3' end of HEV genome just before the poly A sequence (Tsarev, S.A. et al. (1992), Proc. Natl. Acad. Sci. USA. 89:559-563). To insert this fragment into pBlueBac-Transfer vector (Invitrogen) a synthetic polylinker was introduced into the unique Nhel site in the vector. This polylinker contained Bin I and Bgl II sites which are absent in both HEV cDNA and pBlueBac sequences. The Nrul-BglII ORF-2 fragment was inserted in Bin I-Bglll pBlueBac using an adapter as shown in Fig. 1. EXAMPLE 3 Expression of P63 -2 in SF9 Insect Cells. p63-2 and AcMNPV baculovirus DNA (Invitrogen) were cotransfected into SF9 cells (Invitrogen) by the Ca precipitation method according to the Invitrogen protocol - By following this protocol; the AcMNPV baculovirus DNA can produce a live intact baculovirus which can package p63-2 to form a recombinant baculovirus. This recombinant baculovirus was plaque-purified 4 times. The resulting recombinant baculovirus 63-2-IV-2 was used to infect SF9 cells. SDS-PAGE and Western blot. Insect cells were resuspended in loading buffer (50 mM Tris-HCl, pH 6.8, 100 mM DTT, 2% SDS, 0.1% bromphenol blue and 10% glycerol) and SDS-polyacrylamide gel electrophoresis was performed as described, Laemmli, U.K. (1970), Nature. 227:680. Gels were stained with coomassie blue or proteins were electroblotted onto BA-85 nitrocellulose filters (Schleicher & Schuell) . After transfer, nitrocellulose membranes were blocked in PBS containing 10% fetal calf serum and 0.5% gelatin. As a primary antibody, hyperimmune serum of chimpanzee-1313 diluted 1:1000 was used. As a secondary antibody, phosphatase-labeled affinity-purified goat antibody to human IgG (Kirkegaard & Perry Laboratories, Inc.) diluted 1:2000 was used. Filters were developed in Western blue stabilized substrate for alkaline phosphatase (Promega) . All incuba¬ tions were performed in blocking solution, and washes were with PBS with 0.05% Tween-20 (Sigma). Expression of HEV ORF -2. The major protein synthesized in SF9 cells infected with recombinant baculo¬ virus 63-2-IV-2 was a protein with an apparent molecular weight of 74 KD (Fig. 2A, lane 3) . This size is a little larger than that predicted for the entire ORF-2 (71 KD) . The size difference could be due to glycosylation of the protein since there is at least one potential site of glycosylation (Asn-Leu-Ser) in the N-terminal part. This protein was not detected in noninfected cells (Figure 2A, lane 1) or in cells infected with wild-type nonrecombinant baculovirus (Figure 2A, lane 2) . In the latter case, the major protein detected was a polyhedron protein. When the same lysates were analyzed by Western blot (Figure 2B) with serum of chimp-1313 (hyperimmunized with HEV), only proteins in the recombinant cell lysate reacted (lane 3) and the major band was again represented by a 74 KD protein (Fig. 2B) . Minor bands of about,25, 29, 35, 40-45 and 55-70 kDa present in the Coomassie-stained gel (Fig. 2A, lane 3) also reacted with serum in the Western blot (Figure 2B, lane 3) . Some of the bands having molecular weights higher than 74 KD result from different extents of glycosylation while the lower molecular weight bands could reflect processing and/or degradation. Serum drawn from Chimp-1313 prior to inoculation with HEV did not react with any of the proteins by Western blot. EXAMPLE 4 Immunoelectron Microscopy of Recombinant Infected SF9 Cells. 5xl0 6 recombinant infected SF9 cells were sonicated in CsCl (1.30 g/ml) containing 10 mM Tris-HCl, pH 7.4, 0.3% sarcosyl and centrifuged 68 h, at 40,000 rpm (SW60Ti) . 50 ul of the fraction, which had the highest ELISA response and a buoyant density of 1.30 g/ml was diluted in 1 ml PBS and 5 ul of chimp-1313 hyperimmune serum was added. The hyperimmune serum was prepared by rechallenging a previously infected chimp with a second strain of hepatitis E (Mexican HEV) . Samples were incubated 1 h at room temperature and then overnight at 4 * C. Immune complexes were precipitated using a SW60Ti rotor at 30,000 rpm, 4 * C, 2 h. Pellets were resuspended in distilled water, negatively stained with 3% PTA. placed on carbon grids and examined at a magnification of 40,000 in an electron microscope EM-10, Carl Zeiss, Oberkochen, Germany. Detection of VLPs . Cell lysates from insect cells infected with wild-type or recombinant baculovirus 63-2-IV-2 were fractionated by CsCl density centrifugation. When fractions of the CsCl gradient from the recombinant infected insect cells were incubated with Chimp-1313 hyperimmune serum, two kinds of virus-like particles (VLP) covered with antibody were observed in the fraction with buoyant density of 1.30 g/ml: first (Fig. 3A-3A'''), antibody covered individual particles that had a size (30 nm) and morphological structure suggestive of HEV, second (Fig. 3B) , antibody-coated aggregates of particles smaller than HEV (about 20 nm) but which otherwise resembled HEV. Direct EM showed the presence of a very heterogenous population of objects including some of 30 and 20 nm in diameter respectively, which looked like virus particles but, in the absence of bound antibody, could not be confirmed as HEV. A number of IEM RECTIFIEDSHEET(RULE91) experiments suggested that at least some of the protein(s) synthesized from the ORF-2 region of the HEV genome, had assembled into a particulate structure. It was observed that insect cells at a later stage of infection, when the proportion of smaller proteins was higher, consistently gave better results in ELISA. Therefore, unfractionated lysates of recombinant insect cells from a later stage of infection were used as antigen in ELISA in subsequent tests. EXAMPLE 5 Detection by ELISA Based on Antigen from Insect Cells Expressing Complete ORF-2 of Anti -HEV Following Infection wi th Different Strains of HEV. 5xl0 6 SF9 cells infected with 63-2-IV-2 virus were resuspended in 1 ml of 10 mM Tris-HCl, pH 7.5, 0.15M NaCl then were frozen and thawed 3 times. 10 ul of this suspension was dissolved in 10 ml of carbonate buffer (pH 9.6) and used to cover one flexible microtiter assay plate (Falcon) . Serum samples were diluted 1:20, 1:400 and 1:8000, or 1:100, 1:1000 and 1:10000. The same blocking and washing solutions as described for the Western blot were used in ELISA. As a secondary antibody, peroxidase- conjugated goat IgG fraction to human IgG or horse radish peroxidase-labelled goat anti-Old or anti-New World monkey immunoglobulin was used. The results were determined by measuring the optical density (O.D.) at 405 nm. To determine if insect cell-derived antigen representing a Pakistani strain of HEV could detect anti- HEV antibody in cynomolgus monkeys infected with the Mexican strain of HEV, 3 monkeys were examined (Fig. 4) . Two monkeys cyno-80A82 and cyno-9A97, were infected with feces containing the Mexico '86 HEV strain (Ticehurst, J. et al. (1992), J. Infect. Pis.. 165:835-845) and the third monkey cyno-83 was infected with a second passage of the same strain. As a control, serum samples from cyno-374, infected with the Pakistani HEV strain SAR-55, were tested in the same experiment. All 3 monkeys infected with the Mexican strain seroconverted to anti-HEV. Animals from the first passage seroconverted by week 15 and from the second passage by week 5. Interestingly, the highest anti-HEV titer among the 4 animals, was found in cyno-83, inoculated with the second passage of the Mexican strain. Cynos inoculated with the first passage of the Mexican strain developed the lowest titers while those inoculated with the first passage of the Pakistani strain developed intermediate titers. EXAMPLE 6 Specifici ty of Anti -HEV ELISA Based on Antigen from Insect Cells Expressincr Complete ORF-2. To estimate if the ELISA described here specifically detected anti-HEV to the exclusion of any other type of hepatitis related antibody, serum samples of chimps were analyzed, in sets of four, infected with the other known hepatitis viruses (Garci, P. et al. (1992), J. Infect. Pis.. 165:1006-1011; Farci, P. et al. (1992), Science (in press); Ponzetto, A. et al. (1987) J Infect. Pis.. 155: 72-77; Rizzetto; m.et al. (1981) Hepatology 1: 567-574; reference for chimps - 1413, 1373, 1442, 1551 (HAV) ; and for chimps - 982, 1442, 1420, 1410 (HBV) ; is unpublished data from Purcell et al) (Table 1) . Samples of pre-inoculation and 5 week and 15 week post-inoculation sera were analyzed in HEV ELISA at serum dilutions of 1:100, 1:1000 and 1:10000. None of the sera from animals infected with HAV, HBV, HCV and HPV reacted in the ELISA for HEV antibody, but all 4 chimps inoculated with HEV developed the IgM and IgG classes of anti-HEV. IΛ © t_» o LΛ IΛ Table 1. Serological assay of anti-HEV antibody in chimpanzees infected with different hepatitis viruses (Hepatitis A, B, C, D, E) Chimp- 1413 HAV 5 Chimp- 1373 HAV 7 I Chimp- 1442 HAV 5 LΠ Chimp- 1451 HAV 5 Chimp- 982 HBV 3 Chimp- 1442 HBV 7 Chimp- 1420 HBV 9 Chimp- 1410 HBV 5 Chimp- 51 HCV 10 Chimp- 502 HCV 12 Chimp- 105 HCV 28 Chimp- 793 HCV 13 Chimp- 904 HDV 8 Chimp ■ 814 HDV 7 Chimp- 800 HDV 10 Chimp- 29 HDV 10 Chimp- 1310 HEV 5 1:10,000 1:100 1:10,000 Chimp- 1374 HEV 3 1:8000 - * 1:8000 - Chimp ■ 1375 HEV 3 1:8000 1:400 1:400 ) _- IΛ ro o _Λ o IΛ tΛ Table 1 (cont'd.) Chimp-1313 HEVlst 0 ** 5 - - 1:10,000 1:100 1:1000 - Chimp-1313 HEV2nd 0 ** 0.5 1:100 - 1:10,000 - 1:10,000 - Chimp-1374 was positive for IgM anti-HEV three and four weeks pos -inoculation (see Fig.5) ** Chimp-1313 was inoculated with HEV twice. 1st inoculation with pooled samples of 7 Pakistani patients. 2nd inoculation 45 months later with Mexican strain of HEV. _l t o EXAMPLE 7 Determination of the Host Range of the SAR-55 Strain of HEV in Non- Human Primates. Different primate species were inoculated 5 intravenously with a standard stool suspension of HEV and serial serum samples were collected to monitor for infection. Serum ALT levels were determined as an indicator of hepatitis while seroconversion was defined as a rise in anti-HEV. The results were compared with those Q obtained in cynomolgus monkeys and chimpanzees. Both rhesus monkeys inoculated with HEV (Table 2) demonstrated very prominent peaks of alanine aminotransferase activity as well as a strong anti-HEV response. The peak of alanine aminotransferase activity 5 was observed on day 35 for both animals, and seroconversion occurred on day 21. The maximum titer of anti-HEV was reached on day 29. Both African green monkeys used in this study (Table 2) developed increased alanine aminotransferase activity and anti-HEV. Although African green money 230 died 7 weeks after inoculation, proof of infection was obtained before that time. Peak alanine aminotransferase activity for monkey 74 exceeded the mean value of preinoculation sera by about three times and for monkey 230 by about five times. Peaks of alanine aminotransferase activity and seroconversion appeared simultaneously on days 28 and 21 in monkeys 74 and 230, respectively. Table 2. Biochemical and serologic profiles of HEV infection in eight primate species NOTE. -, no anti-HEV detected. * Previously studied using fragments of HEV proteins expressed in bacteria as antigen [18]. t BiomodaJ elevation of alanine aminotransferase. SD = standard deviation. Pigtail macaque 99 demonstrated an increase in alanine aminotransferase activity > 3 SD above the mean value of preinoculation sera, while pigtail macaque 98 did not. However, both monkeys seroconverted on day 21 and the anti-HEV titers were equivalent to those of the chimpanzees and Old World monkeys. Because of the low peak alanine aminotransferase values in the pigtail macaques, the possibility of immunization instead of infection with HEV cannot be completely ruled out. However, immunization is unlikely for several reasons. First, immunization in either of 2 tamarins, which are only one-fourth as large as the pigtail macaques but received the same amount of inoculum was not observed. Second, it is well known that the amount of HEV excreted in feces is usually very small, and 0.5 mL of the 10% suspension of feces used in this study is unlikely to contain an amount of antigen sufficient to immunize an animal, especially when inoculated intraveneously. Neither tamarin inoculated in this study had a significant rise in alanine aminotransferase activity or development of anti-HEV (Table 2) . Therefore, these animals did not appear to be infected. The squirrel monkeys did develop anti-HEV, but at significantly lower levels than chimpanzees or Old World monkeys (Table 2) . In addition, seroconversion occured later in other animals. Squirrel monkey 868 seroconverted on day 41 and 869 on day 35. The anti-HEV titer was not > 1:20 at any time during > 3 months of monitoring and clearly was waning in both animals after reaching a peak value on days 47-54. However, the increases in alanine aminotransferase activity were rather prominent in both animals and were temporally related to the time of seroconversion. The owl monkeys responded to HEV infection about as well as the Old World monkey species (Table 2) . Both owl monkeys seroconverted on day 21 and by day 28 the anti-HEV titer had reached a value of 1:8000. Alanine amino-transferase activity peaked on day 35 in owl monkey 924 but not until day 49 in monkey 925. EXAMPLE 8 Detection of IgM and IgG Anti-HEV in Chimps. In both chimps, the serum ALT levels increased about 4 weeks post-inoculation (Table 2, Fig. 5) . Both chimps seroconverted at the time of ALT enzyme elevation or earlier (Fig. 5A, 5C) . Levels of IgM anti-HEV also were determined for the chimps. In chimp-1374, the titer of IgM anti-HEV (Fig 5B) was not as high as the IgG titer (Fig 5A) and waned over two weeks. Although both IgG and IgM antibodies were first detected for this animal on day 20, the titer of IgM anti-HEV was the highest while the titer of IgG was the lowest on that day, but then rose and stayed approximately at the same level for more than three months. In chimp-1375, only IgM anti-HEV was detected on day 20 (Fig. 5D) . The titer was higher than in chimp-1374 and IgM anti-HEV was detected during the entire period of monitoring. IgG anti-HEV was first observed in this animal on day 27 (Fig. 5C) and remained at approximately the same level throughout the experiment. EXAMPLE 9 Comparison of ELISA Based on Complete ORF -2 Protein Expressed in Insect Cells Wi th That Based on Fragments of Structural Proteins Expressed in E. coli . To estimate if expression of the complete ORF-2 region of the HEV genome in eukaryotic cells had any advantage over expression of fragments of structural proteins in E. coli , we used the former antigen in ELISA to retest cynomolgus monkey sera that had been analyzed earlier (Tsarev, S.A. et al. (1992), Proc. Natl. Acad. Sci USA. 89:559-563; and Tsarev, S.A. et al. (1993) J. Infect. Pis. (167:1302-1306)), using the antigen fragments expressed in bacteria (Table 3) . Table 3. Comparison of ELISA based on antigen from insect cells expressing complete ORF-2 with that based on antigen from E.coli expressing fragments of structural proteins Cyno _ antigen derived from antigen derived from bacterial cells insect cells (Portion of ORF-2) * (Complete ORF-2) 1306) For 3 of the 6 monkeys examined by ELISA, the antigen expressed in insect cells detected seroconversion earlier than the antigen expressed in E. coli . Using the insect cell-derived antigen, we were able to detect anti-HEV antibody in sera from all six monkeys at the highest dilution tested (1:8000) . With E. coli-cell derived antigen (Burma Strain) no information about anti-HEV titers were obtained, since all sera were tested only at a dilution of 1:100 (Tsarev, SA et al (1992) Proc. Nat. Acad. Sci. USA: 89:559-563; Tsarev et al. (1993) J___ Infect. Pis. (167:1302-1306)). In another study, hepatitis E virus, strain SAR- 55 was serially diluted in 10-fold increments and the 10 "1 through 10 "5 dilutions were inoculated into pairs of cyno¬ molgus monkeys to titer the virus. The serum ALT levels were measured to determine hepatitis and serum antibody to HEV was determined by the ELISA method of the present invention (data in figures) or by Genelab's ELISA (three ELISAs, each based on one of the antigens designated 4-2, 3-2 and 612 in Yarbrough et al. (J. Virol.. (1991) 65:5790-5797) (data shown as positive (+) or negative (-) test at bottom of Figures 6 a-g) . All samples were tested under code. The ELISA method of the present invention detected seroconversion to IgG anti-HEV in all cynos inoculated and all dilutions of virus. In contrast, Genelab's results were strikingly variable, as summarized below. Table 4. ELISA of Oilution Present of Virus Genelab's ELISA Invention 10 "1 did not test positive 10 "2 positive for both animals, limited duration positive 10 "3 negative for both animals positive 10~* Cyno 389: positive for IgM and IgG positive Cyno 383: negative positive 10 "5 Cyno 386: negative positive Cyno 385: positive positive Since Cyno 385 (10 "s ) was positive in ELISA tests both by Genelabs and the present invention, the 10"* (ten times more virus inoculated) and 10 "3 (100 times more virus inoculated) would also have been expected to be positive. The present invention scored them as positive in contrast to Genelab's ELISA test which missed both positives at 10 ~3 and one at 10" 4 even though the ALT levels of Cyno 383 and 393 suggested active hepatitis. Therefore, the data support the advantages of the present ELISA method over the prior art methods of detecting antibodies to HEV. EXAMPLE 10 Comparison Of ELISAs Based On Recombinant ORF -2 Antigens Consisting Of Ei ther A 55 kDa Protein Expressed From The Complete ORF-2 Region Of The Pakistani SAR-55 Strain Of HEV Or Of Shorter Regions Of ORF-2 Expressed As Fusion Proteins In Bacteria . As described in Example 3 and as shown in Figures 2A and 2B, a number of proteins of varying molecular weights are expressed in insect cells infected with the recombinant baculovirus containing the complete ORF-2. A protein with a molecular weight of approximately 55 kPa was partially purified from 5xl0 8 SF-9 cells harvested seven days post-inoculation as follows: The infected cells were centrifuged, resuspended in 10 ml of 10 mM Tris-HCl (pH 8.0), 50 mM NaCl, containing 40 μg/ml of phenylmethylsulfonyl fluoride (Sigma, St. Louis, Missouri) , sonicated to disrupt the cells and the lysate was centrifuged at 90,000xg at 4°C for 30 min. The supernatant was loaded onto a PEAE-sepharose CL-6B (Pharmacia, Uppsala, Sweden) column equilibrated with 10 mM Tris-HCl (pH 8..0), 50 mM NaCl. The column was washed with loading buffer and the 55 kPa protein was eluted in 10 mM Tris-HCl (pH 8.0) 250 mM NaCl. Fractions containing the 55 kPa protein were combined and the protein was precipitated by addition of 3 g of (NH 4 ) 2 S0 4 to 10 ml of the protein solution. The protein pellet was dissolved in 10 mM Tris-HCl (pH 8.0), 50 mM NaCl. The 55 kDa protein was then used as the insect cell-expressed HEV antigen in ELISA in comparison testing against ELISAs based on either one of two HEV antigens expressed in bacteria, (3-2 (Mexico) (Goldsmith et al., (1992) Lancet. 339:328-331) or SG3 (Burma) (Yarbough et al., (1993) Assay development of diagnostics tests for hepatitis E. In "International Symposium on Viral Hepatitis and Liver Disease. Scientific program and abstract volume." Tokyo:VHFL, p 87, Abstract # 687) . These bacterial antigens were fusion proteins of the 26 kDa glutathione-S-transferase (GST) and either the antigenic sequence 3-2 (M) consisting of 42 amino acids located 6 amino acids upstream of the C- terminus of ORF-2 (Yarbough et al., (1991) J. Virol.. 65:5790-5797) or the 327 C-terminal amino acids of ORF-2 (Yarbough et al., (1993)). The ELISAs were carried out as follows. Sixty ng per well of the 55 kDa protein or 200 ng per well of the fusion antigens in carbonate buffer (pH 9.6) were incubated in wells of a polystyrene microtiter assay plate (Dynateck, S. Windham, ME) for 2 h at 37°C. Plates were blocked with PBS containing 10% fetal calf serum and 0.5% gelatin. Serum samples from cynomolgus monkeys inoculated intravenously (note: cynos 387 and 392 were inoculated orally) with a dilution of feces containing the SAR-55 strain of HEV ranging from 10 '1 through 10 "8 as indicated in Table 5 and Figures 7A-7J and 8A-8D were diluted 1:100 in blocking solution. Peroxidase-conjugated goat anti-human IgM (Zymed, San Francisco, CA) diluted 1:1000 or 1:2000, or peroxidase- labelled goat anti-human immunoglobulin diluted 1:1000 was used as the detector antibody. In all of the ELISA tests except those for the two orally inoculated monkeys, cyno-387 and cyno-392, the 55 kDa and the fusion antigens were tested concurrently in the same laboratory so that the only variable was the antigen used. Criteria for scoring positive reactions in anti-HEV ELISA with the 55 kDa antigen were an optical density value _ 0.2 and greater than twice that of a pre¬ inoculation serum sample for the same animal. In addition, since both antigens expressed in bacteria were fusion proteins with GST, the optical density of a sample tested with these antigens had to be 3 times higher than that obtained with non-fused GST in order to be considered positive (Goldsmith et al., (1992)). RESULTS Both cynomolgus monkeys (377, 378) inoculated with the 10 "1 dilution of the standard HEV fecal suspension had a pronounced increase in ALT activity at 4-5 weeks post-inoculation, indicative of hepatitis (Table 5, Figures 7A and 7B) . o_ > N) IΛ o IΛ o IΛ IΛ Table 5. Summaiy of biochemical and serological events occurring in cynomolgus monkeys after inoculation with 1 _ ' to 10 " * dilutions of the standard stock of the SAR-55 HEV inoculum. Cyno Dilution ALT weeks post-inocu- weeks post-inoculation anti-HEV of viral lation anti-HEV was detected with fusion antigen stock pre-inocu- peak peak was detected with inoculum lation week value 55 kDa antigen IgG IgM mean (SD) 1 (U/L) IgG IgM SG3 3-2(M) SG3 3-2(M) 76 (39) 5 264 4-15+ 3-7 4-10 4-5 3-4 3-5 50 (9) 4 285 4-15 62 (14) 4 89 3-15 3-10 4-6 121 (21) 15 314 5-15 89 (20) 1 135 5-15 * 6-15 _> 29 (8) 4 77 5-15 5-13 t 60 (7) 15 114 6-15 6-8 41 (4) 5 87 6-15 59 (32) 7 56 11-15 7-15 31 (4) 4 34 8-15 8-13 60 (4) 8 94 36 (3) 2 55 102 (16) 2 93 57 (4) 9 188 33 (3) 2-3 49 56 (4) 2 73 32 (4) 4 38 ND ND 49 (6) 3 70 ND ND ' ALT mean and standard deviation (SD) values of pre -inoculation sera. * The experiment was terminated after 15 weeks. > > ) tΛ o υ. o to tΛ tΛ Table 5 (cont'd.) * The OD values of pre -inoculation sera of Cyno-380, when tested by ELISA with 55 kDa antigen, were twice as high as the mean value of pre-inoculation sera for other cynomolgus monkeys. ' All ELISA tests except for Cyno-387 and Cyno-392 were performed in the same experiments. - not detected. ND - not done. All 3 antigens tested detected IgM anti-HEV in samples taken from cyno-377 3 weeks post-inoculation ( Table 5, Figure 8A) , but IgM anti-HEV was not detected in any samples from the second animal, cyno-378. IgG anti-HEV was detected in both animals with the 55 kDa-based ELISA, but only in cyno-377 with the ELISA based on fusion antigens. Values of OD for IgG anti-HEV were significantly higher than those for IgM anti-HEV. ELISA values obtained with the 55 kDa antigen were also significantly higher than those obtained with either of the two fusion antigens (Figures 7A and 7B) . The patterns of the OD values observed in ELISA with antigens from the two sources also differed significantly. In the case of ELISA based on the fusion antigens, positive signals reached a maximum shortly after seroconversion and then waned during the 15 weeks of the experiment. In ELISA based on the 55 kDa antigen, the positive signal reached a maximum shortly after seroconversion and remained at approximately the same high level throughout the experiment (15 weeks) . Elevation in ALT activities in both monkeys (394 and 395) inoculated with a 10 "2 dilution of the standard HEV stool suspension was significantly less pronounced at the expected time of hepatitis than in animals inoculated with the ten-fold higher dose ( Table 5, Figures 7C and 7D) . Cyno-395 actually had higher ALT activities prior to inoculation as well as at 15 weeks post-inoculation. The latter was probably not related to HEV infection. Weakly positive IgM anti-HEV was detected only in cyno-394 (Figure 8B) and only with ELISA based on the 55 kDa antigen. Both animals were infected, however, since IgG anti-HEV seroconversion was detected in both animals. In cyno-394, anti-HEV IgG was first detected by the 55 kDa antigen at week 3 and one week later with the 3-2 (M) antigen. The SG3 (B) antigen did not detect seroconversion in cyno-395 and anti-HEV IgG was detected only with the 55 kDa antigen. Anti-HEV tended to diminish in titer with time in this animal. Cyno-380 and cyno-383 were inoculated with a 10 "3 dilution of the standard HEV fecal suspension (Table 5, Figures 7E 7F, 8C) . Cyno-380 had fluctuating ALT activities before and after inoculation; therefore, ALT levels could not be used to document hepatitis E in this animal. In Cyno-383, a slight rise of ALT activities was observed (Figure 7F) , which was coincident with seroconversion and, therefore, might be due to mild hepatitis E. IgM Anti-HEV was not detected in sera from cyno-380 with any of the three antigens. Cyno-380 seroconverted for IgG anti-HEV when tested by ELISA with SG3 (B) but not with 3-2 (M) antigen. This animal had preexisting IgG anti-HEV when tested with the 55 kDa antigen, but there was a large increase in IgG anti-HEV starting at week 5 (Figure 7E) . Identification of preexisting antibody was reported earlier in sera from another cynomolgus monkey [Ticehurst et al., (1992) J. Infect Pis.. 165:835-845; Tsarev et al. , (1993) J. Infect. Pis.. 168:369-378]. Seroconversion occured at the expected time but the levels of IgG anti-HEV in samples from cyno-383 remained low and detectable only with the 55 kDa antigen. Cyno-389 and cyno-393 were inoculated with a 10" 4 dilution of the standard HEV fecal suspension (Figures 7G, 7H, 8D, Table 5) . Neither animal had a significant rise in ALT activities, although the timing of a small but distinct ALT peak in sera of cyno-393 at week 5 (Figure 7H) suggested borderline hepatitis. ELISA based on the SG3 (B) or 3-2 (M) antigens scored both animals as negative for HEV infection. In contrast, the 55 kDa antigen detected IgM anti-HEV in sera of cyno-389 at weeks 6-8 post-inoculation (Figure 8D) and IgG anti-HEV from week 6 through week 15 in both animals. Neither animal inoculated with the 10 "3 dilution of the standard fecal suspension developed a noticeable rise in ALT activities (Figure 71, 7J, Table 5) , but, in cyno-386, IgM and IgG anti-HEV were detected at weeks 8-13 and 8-15 respectively with the 55 kDa antigen (Figure 7J, 8E) . Cyno-385 anti-HEV IgG was detected with the 55 kDa and the 3-2 (M) antigen but not with SG3 (B) antigen. In contrast to previous patterns, IgG anti-HEV was detected with a fusion antigen four weeks earlier and at higher levels than with the 55 kDa antigen. None of the animals inoculated with dilutions of the standard HEV fecal suspension in the range of lO^-lO "8 developed antibody to any of the three HEV antigens. Increased ALT activities were not observed in those animals, except for one rather prominent peak of ALT activity at week 9 in cyno-400 (Table 5) . However, the absence of seroconversion in this animal indicated that this peak probably was not related to HEV infection. With respect to the two cynomolgus monkeys (387 and 392) inoculated orally with the 10 "1 dilution of the 10% fecal suspension, neither monkey was infected since ALT levels did not rise and ELISA performed with the 3- 2 (M) and 55 kDa antigens did not detect seroconversion to HEV (Table 5) . Finally, serological evidence for HEV infection was found in all animals inoculated with decimal dilutions of the fecal suspension through 10 "5 ; none of the animals receiving higher dilutions had such evidence. Prominent hepatitis, as defined by elevated ALT, was observed only in the two monkeys infected with the 10 "1 dilution. Significantly lower elevations of ALT activities were observed in some animals inoculated with higher dilutions of the fecal suspension while, in others, elevations were not found. Considered alone, these low ALT rises were not diagnostic of hepatitis. However, the coincidence of seroconversion and appearance of these ALT peaks suggests the presence of mild hepatitis in these animals. Anti-HEV IgG seroconversion was detected in all animals inoculated with dilutions of fecal suspension ranging from 10" 1 -10 "5 . A tendency toward lower levels of IgG anti-HEV and delayed seroconversion was observed in animals inoculated with higher dilutions of the stock. In sum, the 55 kDa Pakistani ORF-2 antigen was more efficient than either the 3-2 (M) or SG3 (B) antigen for detecting IgM and IgG anti-HEV in cynomolgus monkeys infected with the Pakistani strain of HEV. For example, for all animal sera except those from cyno-385, detection of IgG or IgM anti-HEV by ELISA was more efficient with the 55 kDa antigen than with either the 3-2 (M) or SG3 antigen. ELISA with the 55 kDa antigen produced internally consistent and reproducible results, detecting IgG anti-HEV in all ten animals inoculated with a fecal dilution of 10 "5 or lower. The magnitude of ELISA signals also decreased as the inoculum was diluted. The fusion antigens did not produce consistent results between the pairs of animals. Only one of each pair of animals inoculated with the 10 "1 , 10 "2 , 10 "3 , or 10 "5 dilution showed seroconversion to IgG anti-HEV, and only a single seroconversion for IgM anti-HEV was detected with these antigens. Neither of the animals inoculated with the 10"* dilution of the original inoculum seroconverted to either of the two fusion antigens even though sera from one animal (cyno-393) had sustained high levels of anti-HEV IgG when assayed with the 55 kDa antigen. Although, as discussed above, ELISA for IgM anti-HEV was significantly less sensitive than ELISA for cynomolgus IgG anti-HEV, the 55 kDa antigen was able to detect anti-HEV IgM in more animals than the 3-2 (M) or SG3 (B) antigen. In sum, a definitive conclusion about the infectious titer of the Pakistani viral inoculum used in this study could not be made with the combined data from the 3-2 (M) and SG3 (B) based ELISA but could be made with data obtained with the 55 kDa Pakistani ELISA alone. With respect to cyno-385, the difference in anti-HEV IgG detection between the two test results was four weeks. These data suggest the presence of a distinct epitope in the 3-2 (M) antigen recognized by this animal that is absent in the larger 55 kDa and SG3 (B) antigens. When total insect cell lysate, which contained both complete ORF-2 (75 kDa) and 55 kDa proteins, was used as antigen to retest these samples, the results were the same as when 55 kDa was used alone. This finding suggests that the 55 kDa protein may not lack 3-2 epitope amino acids but rather that the conformation of the 3-2 epitope sequence differed among all three antigens used in this study. Finally, it is interesting to note that despite the fact that antigen SG3 (B) contained a longer portion of ORF-2 and included the entire sequence of epitope 3-2, it did not detect more positive sera than the 3-2 (M) antigen. EXAMPLE 11 Determination of the Infectious Ti ter of the HEV SAR -55 Viral Stock BY RT-PCR Knowledge of the infectious titer of inocula is critical for interpretation of much of the data obtained in experimental infections of animal models. However, until now the infectious titer of an HEV viral stock has not been reported. Ten-fold dilutions of the fecal suspension containing the SAR-55 strain of HEV were extracted and RT-PCR amplification was performed as follows to determine the highest dilution in which HEV genomes could be detected. 200 ul of fecal suspension was mixed with 0.4 ml of 1.5M NaCl plus 15% polyethylene glycol (PEG) 8000 and kept overnite at 4°C. Pellets were collected by centrifugation for 3 minutes in a microcentrifuge (Beckman, Palo Alto, CA) at 16,000g and dissolved in 475 ul of solution containing 4.2M guanidine thiocyanate, 0.5% N-lauroylsarcosine, 0.25M TRIS-HC1 (pH 8.0). 0.15 M dithiothreitol (DTT), and l.Oμg of tRNA. Fifty microliters of 1M TRIS-HC1 (pH 8.0), 100 mM EDTA, and 10% SDS was then added. The RNA was extracted twice with phenol-chloroform (1:1) at 65°C, followed by chloroform extraction at room temperature. To the upper phase, 250 μL of 7.5 M ammonium acetate was added, and nucleic acids were precipitated with 0.6mL of 2-propanol, washed with 75% ethanol, washed with 100% ethanol, and used for reverse transcription (RT) PCR. For detection of the HEV genome, two sets of nested primers were used that represented sequences from the 3' region (ORF-2) of the SAR-55 genome. Primers for reverse transcription and the first PCR are shown as SEQ ID NO:99: GTATAACGGATCCACATCTCCCCTTACCTC and SEQ ID NO:100: TACAGATCTATACAACTTAACAGTCGG respectively. Primers for the second PCR are shown as SEQ ID NO: 101: GCGGCAGATCTCACCGACACCATTAGTAC and SEQ ID NO:102: TAACCTGGATCCTTATGCCGCCCCTCTTAG respectively. The RNA pellet was dissolved in 20 μL of 0.05 M TRIS-HCl (pH 7.6), 0.06 M KC1, 0.01 M MgCl 2 , 0.001 M DTT, 40 units of RNasin (Promega Biotec, Madison, WI) , 16 units of avian myeloblastosis virus reverse transcriptase (Promega Biotec) , and 10 pmol of reverse primer and incubated 1 hour at 42°C. To 20 μL of reverse transcriptase mixture was added 100 μL of 0.01 M TRIS-HCl (pH 8.4), 0.05 M KC1, 0.0025 M MgCl 2 , 0.0002 M each dNTP, 50 pmol of direct primer, 50 pmol of reverse primer, and 4 units of AmpliTaq (Perkin-Elmer Cetus, Norwalk, CT) under 100 μL of light mineral oil. The HEV cDNA was amplified by 35 cycles of PCR:1 min at 94°C, 1 min at 55°C, 1 min at 72°C. The products of PCR were analyzed on 1% agarose gels. Then 5 μL of this mixture was used for the second round of amplification under the same conditions, except the extension time was increased to 3 min. The RT-PCR products produced in all dilutions of the standard HEV feces in the range from 10 "1 to 10 "5 (Figure 9) were separated on a 2% agarose gel and were detected by ethiduim bromide staining of the gel. A decrease in the amount of the specific PCR product at higher dilutions was observed and the highest dilution of the 10% fecal suspension in which the HEV genome was detected was 10 '5 . Therefore, taking into account the dilution factor, the HEV genome titer was approximately lO 6,7 per gram of feces. In addition, only those dilutions that were shown by RT-PCR to contain the HEV genome were infectious for cynomolgus monkeys. Therefore, the infectivity titer of the standard fecal suspension and its genome titer as detected by RT-PCR were approximately the same. A similar correlation between RT-PCR and infectivity titer was found for one strain of hepatitis C virus [Cristiano et al., (1991) Hepatology. 14:51-55; Farci et al. , (1991) N. Engl. J. Med.. 25:98-104; Bukh et al. , (1992); Proc. Natl. Acad. Sci U.S.A.. 89:187-191) EXAMPLE 12 Acti e Jiraπuniza ion Using The ORF -2 Protein As A Vaccine And Passive Immunization Wi th Anti -HEV Posi tive Convalescent Plasma Cynomolgus monkeys {Macaca fascicularis) that were HEV antibody negative (<1:10) in an ELISA based on the 55 kDa ORF-2 protein were individually housed under BL-2 biohazard containment and a suspension (in fetal bovine serum) of feces containing the Pakistani HEV strain SAR-55, diluted to contain 10,000 or 1,000 CID J0 , was used for intravenous inoculation of animals. For active immunization studies, baculovirus recombinant-expressed 55 kDa ORF-2 protein was purified from 5xl0 8 SF-9 cells harvested 7 days post-inoculation as described in Example 10. Three mg of the purified 55 kDa protein were precipitated with alum and eight cynomolgus monkeys were immunized by intramuscular injection with 0.5 ml of vaccine containing 50 μg of the alum-precipitated 55 kDa protein. Four monkeys received a single dose and four monkeys received two doses separated by four weeks. Primates were challenged intravenously with 1,000 - 10,000 CID 50 of HEV four weeks after the last immunization. Four cynomolgus monkeys served as controls in the active immunization studies. Cyno-412 and 413 received one dose of placebo (0.5 ml of phosphate buffered saline) and cyno-397 and 849 received two doses of placebo. The control animals were challenged with 1,000 - 10,000 CID 50 of HEV. For passive immunity studies, cyno-384 was infected with 0.5 ml of a 10% pooled stool suspension containing two Chinese HEV isolates, KS1-1987 and KS2-1987 and plasma was repeatedly collected from the animal during convalesence. (Yin et al. (1993) J. Med. Virol.. 41:230- 241;). Approximately 1% of the blood of cyno-396 and cyno-399 and 10% of the blood of cyno-401 and cyno-402 was replaced with convalescent plasma from cyno-384 having an HEV antibody titer of 1:10,000. Animals were challenged with 1000 CID JO of HEV two days after infusion of the plasma. As a control, 10% of the blood of cyno-405 was replaced with anti-HEV negative plasma obtained from cyno- 384 prior to infection with HEV. Cyno-405 was then challenged with 1000 CID 50 of HEV. For both the passive and active immunization studies, percutaneous needle biopsies of the liver and samples of serum and feces were collected prior to inoculation and weekly for 15 weeks after inoculation. Sera were assayed for levels of alanine amino transferase (ALT) with commercially available tests (Metpath Inc., Rockville, MD) and biochemical evidence of hepatitis was defined as a two-fold or greater increase in ALT. Liver biopsies were examined under code and the anti-HEV ELISA utilized was described in Example 10. RNA extraction and RT-PCR were performed as in Example 11 except that RNA from 100 μl of serum or from 100 μl of 10% fecal suspension was extracted with TRIzol Reagent (Gibco BRL, Gaithersburg, Maryland) according to the manufacturer's protocol. For quantification, PCR positive serial sera or feces from each animal were combined and serially diluted in ten-fold increments in calf serum. One hundred μl of each dilution were used for RNA extraction and RT-PCR as described earlier in this Example. The PCR protocol used in this study could detect as few as 10 CID 50 of HEV per ml of serum and as few as 100 CID J0 per gram of feces. Peak ALT values of weekly serum samples for 5 weeks prior to inoculation and for 15 weeks post- inoculation were expressed as ratios (post/pre) for each animal. The geometric mean of the ratios from the control group of animals was compared with that from the passively or actively immunized animals using the Simes test (Simes, R.J. (1986) Biometrika. 73:751-754). The durations of viremia and virus shedding in feces and the HEV genome titers in the control group of animals were compared with those in passively or actively immunized animals using the Wilcoxon test [Noether, G. (1967) in Elements of nonparametric statistics (John Wiley & Sons Inc., New York), pp. 31-36.]. The same test was used to compare the above parameters between passively and actively immunized animals. For statistical analysis, serum samples that had _10 HEV genomes in 1 ml of serum were assigned a titer of 1:1 and fecal samples that had <100 HEV genomes in 1 g of feces were assigned a titer of 1:10. RESULTS Course of hepatitis E infection in nonimmunized animals. In 3 of 5 nonimmunized animals that were challenged with HEV, biochemical evidence of hepatitis was documented by at least a two-fold increase in serum ALT values. In two animals, significant increases in ALT activity were not found. However, histopathological data documented hepatitis in all 5 animals as shown in Table 6. U) tΛ o t VΛ o tΛ IΛ Table 6. Histopathological, biochemical, serological, and virological profiles of vaccinated and control animals challenged with HEV. Peak ALT value in U/L HEV HEV genome (week) antibody titer at the pre¬ post- time of serum feces inoculation inoculation challenge 67(0) 143 (9) 34(0) 45(3) 44(0) 261 (6) 79 (-2) 133 (2) 52 (-3) 139(7) 33(0) 53(6) 1:40 3-5 (3) 4 1-6 (6) 5.7 69(0) 63 (11) 1:40 2-4 (3) 3 1-4 (4) 4 *Necro-inflammatory changes rated 1 + were detected during two weeks in cyno-396, however, they were consistent with viral hepatitis only during one week. 'Cyno 013 died 9 weeks after challenge. Necro-inflammatory changes ranged between 1+ and 2+ on a scale of 1+ to 4+ and were temporally associated with elevations of ALT activities in those animals with such elevations. All control animals seroconverted to HEV 3-5 weeks post-challenge and developed maximum HEV antibody titers ranging from 1:1,000 to 1:32,000. There was a good correlation between the severity of infection, hepatitis, and the level of anti-HEV response. Cyno-405, which had the highest cumulative score for hepatitis, also had the longest period of viremia and viral excretion and the highest level of anti-HEV (Table 6) . The duration of viral shedding in feces was the same as, or longer than, that of the viremia. For all of the control animals, titers of the HEV genome in serum were lower (10 "3 - 10"* 7 ) than the titers in feces (10 "57 -10 "7 ) . In all five of these animals, viremia and virus shedding in feces were detected for 4-11 weeks and for an average of 4.2 weeks after seroconversion (range 2-9 weeks) . Passive immunization. Cyno-396 and 399, which had approximately 1% of their blood replaced with anti-HEV positive convalescent plasma, had an HEV antibody titer of 1:40 when it was determined two days post-transfusion (at the time of challenge) (Table 6) . A two-fold fall in HEV antibody titer was observed in both animals 1 week post- transfusion and HEV antibodies fell below the detectable level (<1:10) by 2 weeks post-transfusion. Anti-HEV was again detected 5 weeks post-challenge in cyno-396 and 4 weeks post-challenge in cyno-399, indicating that infection with HEV had occurred. The maximum HEV antibody titer (1:8,000) was reached 9-10 weeks post-challenge. Neither cynomolgus monkey demonstrated a significant elevation of ALT activity after challenge. However, histologic evidence of hepatitis was detected in cyno-396 and the HEV genome was detected in serum and feces from both animals (Table 6) . Cyno-401 and 402 had approximately 10% of their blood replaced with convalescent plasma. Two days post- transfusion, at the time of challenge, the HEV antibody titer in both cynomolgus monkeys was 1:200 (Table 7) . __ ro Ul ro o Uι o Ul Ul Table 7. HEV antibody profiles in control and immunized cynomolgus monkeys. the 15 weeks after challenge and reached a maximum titer of 1:4,000 in cyno-401 but only 1:80 in cyno-402. of 1:4,000 in cyno-401 but only 1:80 in cyno-402. Biochemical and histologic analyses did not reveal hepatitis in either animal. However, in both animals, HEV viremia and fecal shedding of virus were observed indicating that infection had occurred (Table 6) . Thus, passive immunoprophylaxis that achieved a higher titer of antibody protected cynomolgus monkeys against hepatitis after challenge with HEV. Active immunization. Four primates immunized with one 50 μg dose of the 55 kDa protein developed antibody to the recombinant protein ranging in titer from 1:100 to 1:10,000 (Table 7). One (cyno 013) died of an anesthesia accident 9 weeks after challenge and is included in the analyses (Table 6) . The four animals that received two doses of the antigen developed HEV antibodies with titers of 1:10,000. Two of the four monkeys died following intravenous challenge with HEV. This may have also been the result of an anesthesia accident but the exact etiology could not be determined. These two monkeys were deleted from further analyses. None of the 6 remaining animals developed abnormal ALT levels or histologic evidence of hepatitis following challenge (Table 6) . Cynomolgus monkeys immunized with either 1 or 2 doses of the 55 kDa protein did not develop viremia. However, 3 of 4 animals that received one dose of the immunogen excreted virus in their feces. In contrast, virus shedding was not observed in either of the two challenged animals that had received two doses of the vaccine. Most of the actively immunized animals developed higher HEV antibody titers than did passively immunized animals. However, cyno-013 had an HEV antibody titer of 1:100 at the time of challenge, compared with a titer of 1:200 in two animals immunized passively with anti-HEV plasma. Cyno-013, however, demonstrated greater protection against HEV infection than the passively immunized animals. Cyno-009, which had an HEV antibody titer of 1:1,000 at the time of challenge, was completely protected against hepatitis and HEV infection (Table 6) . In contrast, cyno-003 was infected and shed HEV in feces, even though it had an HEV antibody titer of 1:10,000 at the time of challenge. However, neither hepatitis nor viremia was detected in this animal or in other cynomolgus monkeys that received one dose of immunogen and had HEV antibody titers of 1:10,000 or greater. Comparison of course of HEV infection in control and immunized animals. As measured by histopathology, all immunized animals, with the exception of one of the passively immunized monkeys, were protected against hepatitis after intravenous challenge with HEV. Comparison of mean values for severity of hepatitis and level of viral replication between the control group and the passively and actively immunized animals indicated that, in general, the severity of infection was inversely related to the HEV antibody titer at the time of challenge and diminished in the order: unimmunized>passive immunization (1%) .passive immunization (10%)>active immunization (1 dose) >active immunization (2 doses) (Tables 6,8). However, the number of animals in each of the two subgroups of passively and actively immunized animals was not sufficient to permit statistical analysis. Therefore, statistical analysis was performed for combined passively immunized and combined actively immunized groups respectively in comparison with the combined control groups. The results of this analysis are presented in Table 8. __ υ_ ro Ul ro O Ut o Ul Ul 22 Table 3. Summaiy of mean values of HKV infection in control and immunized animals. CD O Passive and active imntunopmphylaxis α - P <0.0I and they show that the histopathology scores and duration of histologic changes in the control group were statistically different from those of passively or actively immunized animals. The higher post-/pre¬ inoculation ratios of peak ALT values in the control group were statistically significant when compared with those of the passively or actively immunized animals, indicating protection against biochemical manifestations of hepatitis in both groups of immunized animals. The duration of viremia and the titer of HEV in the feces were significantly lower in both groups of immunized animals than in the control group. Differences in the duration of virus shedding and titer of HEV in the serum, however, were not statistically different between the control group and the passively immunized group, although these parameters were significantly different when the control group was compared with the actively immunized group. Significant differences were also found between passively and actively immunized groups of animals for duration of viremia and fecal shedding as well as for HEV titers. In sum, the results presented in Tables 6-8 show that both passively and actively acquired HEV antibodies protected cynomolgus monkeys against hepatitis following challenge with virulent HEV. Although all 5 nonimmunized cynomolgus monkeys developed histologic evidence of hepatitis when challenged with 1,000 - 10,000 CID J0 of SAR- 55, both animals with passively acquired antibody titers of 1:200 were protected from hepatitis and one of two animals with an antibody titer as low as 1:40 also did not develop hepatitis. However, it should be noted that actively immunized animals demonstrated complete protection against hepatitis and more effective resistance to HEV infection than did passively immunized animals. For example, in contrast to results obtained from the passively immunized animals, viremia was not detected in actively immunized animals after challenge with HEV. An HEV antibody titer as high as 1:10,000 could be achieved in cynomolgus monkeys after one or two immunizations with the recombinant 55 kDa protein. Although one monkey (013) developed a titer of 1:100 after active immunization, this level still prevented hepatitis and viremia. The active immunization studies also demonstrated that while a single dose of vaccine prevented HEV viremia, viral shedding in feces was still detected. However, two doses of vaccine were observed to prevent all signs of hepatitis and HEV infection. These results thus suggest that a single dose of vaccine administered, for example, to individuals before foreign travel would protect them from hepatitis E in high risk environments. Finally, it is noted that the results presented are very similar to results reported previously for passive and active immunoprophylaxis of nonhuman primates against hepatitis A: passive immunoprophylaxis prevented hepatitis but not infection whereas vaccination prevented not only hepatitis but infection with HAV as well (Purcell, R.H. et al. (1992) Vaccine. 10:5148-5149). It is of interest that the study of immunoprophylaxis for HEV presented herein parallels the previous study of immunoprophylaxis against HAV, both in determination of the titer of antibody that protected (<1:100) and in outcome following intravenous challenge with virulent virus. Since other studies have demonstrated efficacy of comparable titers of passively and actively acquired anti- HAV in humans and have confirmed the predictive value of studies of primates in hepatitis research (Stapleton, J., et al. (1985) Ga s troen terol ogy 89:637-642; Innis, B.L., et al. (1992) Vaccine. 10: S159) , it is therefore highly likely that these results in cynomolgus monkeys will be predictive of protection in humans. EXAMPLE 13 Direct Expression In Yeast Of Complete ORF-2 Protein And Lower Molecular Weight Fragments Four cDNA ORF-2 fragments coding for: 1. complete ORF-2 protein (aa 1-660, MW 70979), fragment 1778-1703. (where the fragment numbers refer to the primer numbers given below) 2. ORF-2 protein starting from 34th aa (aa 34- 660, MW 67206), fragment 1779-1703. 3. ORF-2 protein starting from 96th aa (aa 96- 660, MW 60782), fragment 1780-1703. 4. ORF-2 protein starting from 124th aa (aa 124-660, MW 58050), fragment 1781-1703. were obtained using PCR by using plasmid P63-2 as template and the synthetic oligonucleotides shown below: SEQ ID N0.:103 (reverse primer #1703) GCACAACCTAGGTTACTATAACTCCCGAGTTTTACC, SEQ ID NO.:104 (direct primer #1778) GGGTTCCCTAGGATGCGCCCTCGGCCTATTTTG, SEQ ID N0.:105 (direct primer #1779) CGTGGGCCTAGGAGCGGCGGTTCCGGCGGTGGT, SEQ ID NO.:106 (direct primer #1780) GCTTGGCCTAGGCAGGCCCAGCGCCCCGCCGCT and SEQ ID NO.:107 (direct primer #1781) CCGCCACCTAGGGATGTTGACTCCCGCGGCGCC. All sequences shown in SEQ ID NOs: 103-107 contain artificial sequence CCTAGG at their 5' ends preceded by 4 nucleotides. The artificial sequence was a recognition site for Avr II (Bin I) restriction enzyme. Synthesized PCR fragments were cleaved with Blnl and cloned in the Avrll site of pPIC9 vector (Figure 10) ( Invi trogen) . Correct orientation of the fragments was confirmed by restriction analysis, using asymmetric EcoRI site present in ORF-2 sequences and in the vector. Purified recombinant plasmids pPIC9-1778 (containing fragment 1778-1703) ; pPIC9-1779 (containing fragment 1779- 1703); pPIC9-1780 (containing fragment 1780-1703) and pPIC9-1781 (containing fragment 1781-1730) were used for transformation of yeast spheroplast (Picha strain) according to Invitrogen protocol. Screening of recombinant clones and analysis of expression were performed using the same protocol. These expressed proteins may be used as immunogens in vaccines and as antigens in immunoassays as described in the present application. Finally, those of skill in the art would recognize that the vector and strain of yeast used in the above example could be replaced by other vectors (e.g. pHIL-Fl; Invitrogen) or strains of yeast (e.g. Saccharomyces Cerevisiae) . EXAMPLE 14 Purification and Amino Terminal Sequence Analysis of HEV ORF-2 Gene Products Synthesized in SF-9 Insect Cells JiLfected Wi th Recombinant Baculovirus 63 -2 -IV-2 As described in Example 10, SF-9 cells were infected with recombinant baculovirus 63-2-IV-2 and harvested seven days post-inoculation. The predominant protein band present on SDS-PAGE of the insect cell lysate was approximately 55 kDa in molecular weight. Further purification of this 55 kDa band was accomplished by ion- exchange column chromatography using DEAE-sepharose with a 150-450 mM NaCl gradient. DEAE fractions were assayed for the presence of the 55 kDa band by SDS-PAGE followed by Coomassie blue staining. The peak fraction was then resolved by polyacrylamide gel electrophoresis in the absence of SDS into three bands of 55 kDa, 61 kDa and a band of intermediate molecular weight. Analysis of each protein band from the polyacrylamide gel by amino-terminal microprotein sequencing revealed that the 55 and 61 kDa proteins shared a unique N-terminus at Ala-112 of SEQ ID N0:2. It is believed that the size differences in the two ORF-2 cleavage products may reflect either different glycosylation patterns or a COOH-terminal cleavage of the larger product. The third intermediate protein on the polyacrylamide gel was shown to be a baculovirus chitinase protein. The 55 and 61 kDa ORF-2 proteins were resolved into a single symmetrical peak fraction devoid of any chitinase by subjecting peak DEAE fractions to reverse phase HPLC using a micropore system with NaCl and acetonitrile solvents. EXAMPLE 15 Direct Expression of 55 and 61 kDa Cleavacre Products A cDNA ORF-2 fragment coding for ORF-2 protein starting from the 112th amino acid (amino acids 112-660 of ORF-2) was obtained by PCR using plasmid p63-2 as the template. The cDNA fragment was then inserted into a PBlueBac-3Transfer vector at the BamHI-PstI site in the vector. SF9 insect cells are infected with the recombinant baculovirus generated from this vector and insect cell lysates are analyzed for the presence of the 55 and 61 kDa ORF-2 proteins by Coomassie blue staining of polyacrylamide gels. The directly expressed protein(s) may be used as immunogens in vaccines and as antigens in immunoassays as described herein.

Claims: CLAIMS 1. An isolated and purified virus comprising hepatitis E strain SAR-55. 2. The cDNA of hepatitis E wherein the cDNA has a cDNA sequence according to SEQ ID No. 4. 3. A DNA sequence comprising a sequence capable of directing host organism synthesis of at least one complete open reading frame protein, said protein having substantial homology to a protein from HEV, or an analog of said protein. 4. A cDNA sequence of Claim 3, wherein said cDNA encodes a protein comprising the amino acid sequence of SEQ ID No. 2, or a variant thereof. 5. A recombinant protein encoded by a complete open reading frame 2 cDNA sequence of a hepatitis E virus where said protein is greater than about 50 kilodaltons. 6. The protein of claim 5, wherein the protein is encoded by a complete open reading frame 2 cDNA sequence according to SEQ ID NO: . 7. The protein of claim 6, wherein the protein is selected from one of the bands greater than 50 kilodaltons shown in lane 3 of Figure 2B. 8. The protein of claim 7, wherein the protein has a molecular weight of approximately 74 kilodaltons, said protein being antigenic. 9. The protein of claim 7, wherein the protein has a molecular weight of approximately 55 kilodaltons, said protein being antigenic. 10. A recombinant protein encoded by a CDNA sequence of an open reading frame 2 of hepatitis E where said protein is greater than about 50 kilodaltons. 11. A protein comprising the amino acid sequence of SEQ ID NO. 2. 12. A polypeptide fragment of the protein of claim 11, where said fragment is selected from a band greater than about 50 kilodaltons as shown in lane 3 of Figure 2B. 13. A method of producing a recombinant HEV protein, comprising: (a) culturing a host organism transformed with an HEV cDNA sequence, said sequence being capable of directing host organism synthesis of said recombinant protein, under conditions appropriate for amplification to cause expression of the protein; and (b) harvesting the protein. 14. The method of claim 13, wherein the expression vector is a eukaryotic expression vector. 15. The method of claim 13, wherein the cDNA sequence encodes a complete open-reading frame. 16. The method of claim 15, wherein the cPNA sequence encodes complete open-reading frame 2. 17. The method of claim 13, wherein the CPNA sequence encodes an open reading frame 2 protein of greater than about 50 kilodaltons. 18. A recombinant expression vector comprising a cPNA sequence encoding a complete open-reading frame of HEV. 19. The recombinant expression vector of claim 18, wherein the cPNA sequence encodes a complete open- reading frame 2. 20. The recombinant expression vector of claim 19, wherein the vector is p63-2 or pPIC9-1778. 21. A recombinant expression vector comprising a cPNA sequence encoding an HEV open reading frame 2 protein of greater than about 50 kilodaltons. 22. The recombinant expression vector of claim 21, wherein the vector is selected from the group consisting of pPIC9-1779, pPIC9-1780 or pPIC9-1781. 23. A host organism transformed or transfected with a recombinant expression vector according to claim 19. 24. A host organism transformed or transfected with a recombinant expression vector according to claim 21. 25. A method of detecting antibodies to Hepatitis E in a biological sample suspected of containing said antibodies comprising: (a) contacting the sample with a recombi¬ nant protein encoded by a cPNA sequence of an open reading frame 2 of a hepatitis E virus, where said protein is greater than about 50 kilodaltons, to form an immune complex with the antibodies; and (b) detecting the presence of the immune complex. 26. The method of claim 25, wherein the biological sample is selected from the group consisting of whole blood, plasma, serum, cerebrospinal fluid, tissue, urine and pleural fluid. 27. The method of claim 25, wherein IgM or IgG antibody is detected. 28. The method of claim 25, wherein the recom¬ binant HEV protein is bound to a solid support. 29. The method of claim 25, wherein the immune complex is detected using a labeled antibody. 30. A kit for use in a method of claim 25 comprising: a recombinant HEV protein encoded by a cPNA sequence of an open reading frame 2 of a hepatitis E virus, where said protein is greater than about 50 kilodaltons. 31. The kit of claim 30 further comprising a labeled secondary antibody. 32. A pharmaceutical composition comprising the protein of claim 5 and a suitable excipient, diluent or carrier. 33. A method of preventing hepatitis E, comprising administering the pharmaceutical composition of claim 32 to a mammal in an effective amount to stimulate the production of protective antibody. 34. A pharmaceutical composition comprising the protein of claim 10 and a suitable excipient, diluent or carrier. 35. A method of preventing hepatitis E, comprising administering the pharmaceutical composition of claim 34 to a mammal in an effective amount to stimulate the production of protective antibody. 36. A vaccine for immunizing a mammal against hepatitis E infection, comprising a recombinant protein according to claim 5 in a pharmacologically acceptable carrier. 37. A vaccine for immunizing a mammal against hepatitis E infection, comprising a recombinant protein according to claim 10 in a pharmacologically acceptable carrier. 38. A method for detecting hepatitis E virus comprising: (a) amplifying RNA via reverse transcription-polymerase chain reaction to produce amplification products; and (b) detecting said amplification products 39. A method for detecting hepatitis E virus comprising: (a) contacting a biological sample with anti-HEV antibody to form an immune complex with said hepatitis E virus; (b) detecting the presence of said immune complex. 40. Anti-HEV antibodies having specific binding affinity for HEV ORF-2 protein. 41. The antibodies of claim 40, wherein said antibodies are monoclonal antibodies. 42. A method of preventing hepatitis E comprising administering anti-HEV sera obtained from an HEV-infected subject to a mammal in an amount effective to protect said mammal from challenge with HEV. 43. A method of preventing hepatitis E comprising administering the antibodies of claim 40 to a mammal in an amount effective to protect said mammal from challenge with HEV.

Inventors: EMERSON SUZANNE U, PURCELL ROBERT H, TSAREV SERGEI A, EMERSON, SUZANNE, U., PURCELL, ROBERT, H., TSAREV, SERGEI, A.
Applicants: EMERSON SUZANNE U, PURCELL ROBERT H, TSAREV SERGEI A, US HEALTH, EMERSON, SUZANNE, U., PURCELL, ROBERT, H., THE GOVERNMENT OF THE UNITED STATES OF AMERICA, RE, TSAREV, SERGEI, A.
Application year: 1995
Main classification: C07K14
IPC codes: A61K35, A61K39, A61K48, A61P31, C07K14, C07K16, C12N1, C12N5, C12N7, C12N15, C12P21, C12R1, G01N33