GENERATION OF HYBRID GENES AND PROTEINS BY VIRUS-MEDIATED RECOMBINATION

Abstract: The ability of viruses to undergo recombination within tandemly arranged homologous sequences can be utilized to generate chimeric genes and proteins. Tandemly arranged homologous sequences will rapidly degenerate in a random fashion to yield a single copy comprised of portions of both original sequences. Therefore, a recombinant virus which contains two related but non-identical genes in tandem array yields a population of recombinant viruses which contain a spectrum of hybrid sequences derived from recombination between the original genes. The viruses, therefore, contain hybrid DNA sequences that encode proteins with new epitopes or different combinations of epitopes. Vaccines are derived which may afford protection against a broad spectrum of antigen types.

Description: Generation of Hybrid Genes and Proteins by Virus-Mediated Recombination Background Recombination involves the breakage and cross- wise reunion of nucleic acid strands within homolo¬ gous sequences. This phenomenon is a critical feature of evolution, particularly in eukaryotes; genetic exchange through recombinantion works constantly to blend and rearrange genomic sequences, creating genetic diversity by producing different combinations of genetic alleles. , Inter olecular recombination is the term used to describe recombination between two different nucleic acid molecules, for example, between two homologous chromosomes during meiosis, or between different viral genomes present in the same infected cell. Intermolecular recombination has been docu¬ mented in a number of different animal viruses, including RNA viruses such as picornaviruses (King et al. , 1982. Cell 29:921-928; Tolskaya et al. , 1983. Virology 124;121-132) and influenza virus (Fields and Winter. 1982. Cell ^8:303-313) as well as DNA viruses. The phenomenon of intermolecular recombination between viral genomes and exogenous DNA has been exploited for the development of certain viruses, including adenoviruses (Morin et al. 1987. Proc. Natl. Acad. Sci. USA 84:4626-4630), herpesviruses (Lowe et al. 1987. Proc. Natl. Acad. Sci. USA 4:3896-3900) and poxviruεes (Panicali and Paoletti. 1982. Proc. Natl. Acad. Sci. USA 79:4927-4931; Paoletti and Panicali, U.S. Patent No. 4,603,112) as live vectors for the cloning and expression of foreign DNA sequences. Vaccinia virus, an orthopox virus, has been most extensively characterized and developed as an infectious eukaryotic cloning vector (Paoletti and Panicali, U.S. Patent No. 4,603,112). Heterologous genes, including those encoding anti¬ gens from a variety of pathogens, have been ex¬ pressed in this vector system. In all cases, the foreign gene product expressed by the recombinant vaccinia virus was similar or identical to the gene product synthesized under native conditions. In some instances, vaccination of laboratory animals with ^recombinant vaccinia viruses has protected these animals against challenge with the correlate pathogens (Paoletti et al. 1984. Proc. Natl. Acad. Sci. USA £1:193-197; Kieny et al. 1984. Nature 212:163-166; Alizon et al. 1984. Nature 312:757-760; Boyle et al. 1985. Gene 2J_ : 169-177; Vil a et al. 1988. Science 242:1058-1061) . In addition to intermolecular recombination (recombination between different nucleic acid molecules) , intramolecular recombination (recom¬ bination between ho ologus sequences present on a single nucleic acid molecule) also has been docu¬ mented in a number of animal viruses, including picornaviruses, influenza virus, herpesviruses, and poxviruses. In vaccinia virus, for example, it has been shown that tandemly duplicated identical sequences are genetically unstable (Panicali and Paoletti. 1982. Proc. Natl. Acad. Sci. USA, 79:4927-4931; Ball. 1987. J. Virol. 61:1788-1795; Spyropoulos et al. 1988. J. Virol. 62:1046-1054) ; intramolecular recombination between these identical sequences results in a condensation of the dupli¬ cated structure to yield a single copy of the previously duplicated sequences. Recombinant vaccinia viruses that contain such tandem dupli- cations can be stably maintained only when a gene encoding a selectable marker (such as the thy idine kinase gene, or a gene encoding drug resistance) is placed between the duplicated sequences. The intramolecular recombination event that results in condensation of the duplicated structure also results in excision of the marker gene. Thus, selection for the function of the marker gene also selects for the presence of the duplication. Although intramolecular recombination between tandemly arranged, identical DNA sequences has been documented, there has thus far been no examination of _in vivo intramolecular recombination, between non-identical, but related (i.e., partially homolo¬ gous) DNA sequences. Different but related genes have been docu¬ mented in a variety of natural systems. One example may be found among certain pathogens that exhibit antigenic variation. For example, the occurrance of antigenic and genomic variation in human immuno¬ deficiency virus (HIV) , the causative agent of AIDS, has been demonstrated by a number of researchers (Starcich et aJL. 1986. Cell, 45:637-648; Hahn et al. 1986. Science, 232:1548-1553) . These studies have revealed that changes are found primarily in the viral envelope (env) gene, which encodes the antigens against which a major component of the antibody response is directed. The antigenic diversity exhibited by HIV and by other pathogenic organisms presents obstacles to the formulation of vaccines effective against these pathogens, as a vaccine effective against one variant or subtype may fail to protect against related strains. In order to develop successful vaccination protocols for these pathogens, it will be necessary to elicit immune responses capable of recognizing the many variant epitopes present in the family of diverse but, related proteins expressed by the p tiiogens. In order to achieve this, it may be necessary to immunize with a vaccine formulation in which many, if not all, of these variant epitopes are represented. ,Another example of different but related genes may be found among the interferons. The interferons (IFN) comprise a group of related proteins that are encoded by three distinct gene families, designated IFN-alpha, IFN-beta, and IFN-gam a. The 14 genes in the IFN-alpha family share approximately 80-90% homology. There is also limited homology (ap¬ proximately 30% between genes in the IFN-alpha and IFN-beta families (Joklik, W.K. 1985. Interferons. Pages 281-308 in Fields et al. , eds. Virology. Raven Press, N.Y., N.Y.) All interferons possess both antiviral and anticellular activity; all cause interference with multiplication of viruses and regulate a variety of cellular functions. However, they vary greatly in the relative extent to which they express these activities in various types of cells. Recently, recombinant DNA technologies have been used in an effort to produce hybrid interferons with altered biological and pharmacological properties. Several hybrid human IFN-alpha interferon species have been constructed (Streuli et al.. 1981. Proc. Natl. Acad. Sci. USA. 7^:2848-2852; Week et al. 1981. Nucleic Acids Res. :6153-6166) ; these were found to differ greatly in their ability to inhibit the multiplica¬ tion of various viruses in different mammalian cells and in infected animals (Week et al. 1982. Infect. Im un. 2iES:660-665) . Thus, it may be possible to improve upon the function of natural interferons by generating hybrid interferons with particular applications for clinical use in specific situa¬ tions, both in the antiviral area and the anticancer area. Summary of the Invention This invention pertains to methods of generat¬ ing, ijα vivo, hybrid DNA structures from two re¬ lated, but different, DNA sequences through a process of genetic recombination within or between viral genomes, and to the expression of the hybrid genes created by these methods in recombinant viruses. Methods of this invention exploit the phenomenon of intramolecular recombination (i.e., recombination between homologous DNA sequences present within a given viral genome) . The method is based upon the phenomenon of virus-mediated re¬ combination to generate, in a viral genome, hybrid genes from two related but nonidentical genes, provided that these genes share regions of homology. An example of related genes are genes encoding different variants of a given polypeptide. According to the methods of this invention, two related genes are introduced in tandem into a viral genome, preferably a poxviral genome. These tandem structures are genetically unstable in viruses. During replication of the viral genome, intra¬ molecular recombination between homologous regions shared by the related genes results in condensation of the duplicated structure to yield a single, hybrid sequence containing portions of the two original sequences. Nevertheless, it is possible to select for viruses that maintain a tandem duplica¬ tion in the genome if 1) a gene that encodes a selectable marker, under the control of a poxviral transcriptional promoter, is placed between the duplicated sequences and 2) the recombinant poxvirus is propagated under conditions that select for the function of the marker gene. Because recombination between the tandemly arranged genes results in the excision of the marker gene, only those viruses that retain the duplication, together with the intervening marker gene, will survive under selective growth conditions. A recombinant virus that contains in its genome two tandemly arranged, related genes (separated by an appropriate marker gene) can serve as the pro¬ genitor of a population of progeny viruses, each of which contains a different hybrid gene composed of portions of the two original genes. When the parental virus containing tandem DNA sequences separated by a marker gene is allowed to replicate under non-selective growth conditions, progeny viruses generated by intramolecular recombination between homologous sequences will be propagated. This intramolecular recombination event results in excision of the marker gene. Because the recom¬ bination event can occur between any homologous regions shared by the two genes, each of the progeny viruses will contain a different hybrid gene result¬ ing from the condensation of the original DNA sequences. Thus, a spectrum of hybrid genes can be generated from two related genes that contain regions of DNA sequence homology. The inclusion of appropriate transcriptional signals upstream of the first of the two duplicated DNA sequences will ultimately allow for the expression of the hybrid genes created by the intramolecular recombination events. The methods of this invention can be used to produce a mixture of live recombinant viral vectors capable of expressing hybrid genes derived from genes encoding antigenically distinct variants of a -8- given polypeptide. If this polypeptide represents an immunologically important antigen of a pathogenic organism, particularly an organism that exhibits antigenic and genomic variation, the viral vectors so produced may be used as live recombinant vac¬ cines; these vaccines may elicit immune responses to a broad range of serological types and subtypes of the pathogen, as the hybrid genes produced by this method may mimic the genetic changes that occur in the-pathogen in nature. In one embodiment of this invention, a recombinant vaccinia virus is con¬ structed to contain in tandem, envelope genes from two different strains of human immunodeficiency virus (HIV) , namely the RF and the BH10 strains of HIV-1. The progeny vaccinia viruses generated after intramolecular recombination between the two HIV envelope genes contain a spectrum of hybrid envelope genes derived from the original two genes of the different HIV-1 strains. This invention can also be used to generate chimeric proteins for other applications. For example, recombination between genes encoding related interferons will generate hybrid genes encoding chimeric proteins with novel pharmaco- logical properties. These chimeric interferons may exhibit improved function by comparison to natural interferons with regard to their applicability for therapeutic use in specific situations. In addition, vaccinia-mediated recombination between genes encoding related antigens can be used to map type-specific antigenic determinants. For example, a large number of vaccinia recombinants expressing novel hybrid antigens can be generated by recombination between genes encoding related anti¬ gens from two different serotypes of an organism. The ability of type-specific monoclonal antibodies to bind individual hybrid proteins in the vaccinia recombinants can be used to map specific epitopes. Brief Description of the Drawings Figure 1 illustrates a method of generating tandem DNA sequences and chimeric genes in vaccinia using a single-step approach. Figure 2 illustrates a step-wise method of generating tandem DNA sequences and chimeric genes in vaccinia. Figure 3 illustrates construction of a plasmid pABT4075 containing the HIV-1 strain BH10 env gene fused to the E_ ; _ coli lacZ gene. The gene is under the transcriptional control of the vaccinia 7.5K promotor. Figure 3A shows the intermediate step in creation of pAbT4075 which is constructed of pAbT167. Figure 3B shows construction of the vector pAbT4075. Figure 4 illustrates construction of a plasmid (pAbT8523) containing the HIV-1 strain RF env gene. Figure 4A shows construction of the plasmid pAbT4524B containing both Dral and NotI sites. Figure 4B shows construction of the plasmid pAbT4533, created by ligating together fragments of the plasmids pAbT4027 and pAbT4524B. Figure 4C showε construction of pAbT8523, created by ligating sections of two plasmids, pAbT4533 and pRF3HS. Figure 5 illustrates construction of plasmid pAbT4082 containing the HIV-l RF env gene modified at .the 5 1 end of the gp41-encoding region. Figure 5A shows creation of the plasmid pAbT8526, created by .ligating fragments of pAbT4533, pAbT8523 and pRF3HS. Figure 5B shows the creation of pAbT4082, derived from the partial digestion of the plasmid pAbT8526. Figure 6 iϊl " ustrates construction of a donor plasmid (pAbT4085) containing the vaccinia virus thymidine kinase gene flanked by two HIV-l env genes Figure 6A shows creation of the plasmid pAbT4083 derived from ligation of fragments from pAbT4075 and pAbT4082. Figure 6B shows creation of pAbT*€f85, derived from ligating segments of pAbT4083 and pAbT400. The donor plasmid also contains the RF env gene encoding gpl20 under the control of a vaccinia viral promotor and the lacZ gene fused in-frame to the BH10 env gene. Figure 7 is a schematic representation of the steps involved in generating a vaccinia virus containing related, but non-identical genes and steps involved in producing a recombinant virus which has undergone a condensation event to generate a fused HIV-l env gene. Figure 8 illustrates construction of plasmid pAbT4105 containing one particular condensed env gene derived from HIV-l strains BH10 and RF. Figure 8A shows creation of pAbT4105 derived from ligation of plasmid pAbT2009 to a 3 Kb vaccinia virus genomic fragment containing a condensed env gene. Figure 8B is a restriction map of plasmid pAbT4105 including sites which define the RF/BH10 junction. Figure 9 illustrates the construction and sequencing of a phage (pAbT4106) containing the junction between the HIV-l RF and BHIO env sequences in the hybrid gene from vAbT168-l. Figure 9A shows creation of pAbT4106 by ligation of a fragment from plasmid pAbT4105 with phage ml3mpl9. Figure 9B shows the partial nucleotide sequences of a portion of pAbT4106 containing the fused env gene, as well as regions of the parental RF and BHIO env genes from pAbT4085. Figure 10 illustrates the restriction map (Figure 10A) and nucleotide sequence (Figure 10B) of another condensed env gene from the recombinant virus vAbT168-2. Figure 11 shows the approach for generation of chimeric HIV env genes in vaccinia virus. Figure 12 shows the structure of hybrid env genes in intermediate recombinants. Figure 13 shows the structure of hybrid env genes in condensed recombinants. Detailed Description of the Invention The above and various other objects and ad¬ vantages of the present invention are achieved by methods for the generation, in vivo, of hybrid DNA structures from two related but different DNA sequences through various genetic recombination events within or between viral genomes, and the expression of the hybrid genes created by these methods in recombinant viruses. 1. DNA Sequences Useful for Generation of Hybrids DNA sequences suitable for use in methods of this invention can be any two or more DNA sequences that .share regions of homology (i.e., regions of similar DNA sequence) . They can include DNA se¬ quences encoding structural or functional components of various pathogens. The sequence homology that directs recombination between related DNA sequences may be localized to short regions of nucleotide identity. For example, the extent of nucleotide sequence identity necessary for intramolecular recombination in yeast can be as little as 10 nuσleotides (Mazzara and Green, 1983. Abstract 116. The Molecular Biology of Yeast, Cold Spring Harbor, New Y-pαrk) .. The minimum degree of homology required for intramolecular recombination between related DNA sequences can be determined experimentally for each set of related sequences. As a particular example, it is known that the env genes encoding the envelope glycoproteins of human immunodeficiency virus (HIV) , the causative agents of AIDS, vary widely among different isolates of HIV, and that each envelope glycoprotein variant elicits primarily type-specific neutralizing anti¬ bodies (i.e., antibodies capable of neutralizing only the cognate strain; Ho, D.D. et al. , 1988. Science, 239:1021-1023) . Although the nucleotide sequences of these HIV envelope genes are widely divergent, they nevertheless contain regions of DNA sequence homology suitable for the generation of hybrid genes by the methods of this invention. In a specific embodiment, hybrid genes are generated from the env gene of the RF strain of HIV-l and the env gene of the BHIO HIV-l strain. 2. Host Virus Hybrid DNA sequences can be generated in vivo in any virus (e.g., poxvirus) in which intramolecu¬ lar recombination can occur between duplicated sequences. The term "intramolecular recombination" refers to recombination within a single DNA molecule as opposed to recombination between DNA molecules. In particular, this term is used herein to mean recombination within the genomic DNA of a virus. The preferred virus used in the methods of this invention is the pox virus, vaccinia virus. The virus has been developed as an infectious eukaryotic cloning vector (Paoletti and Panicali, United States Patent No. 4,603,112) and recombinant vaccinia virus has been used successfully as a vaccine in several experimental systems. The virus is considered non-oncogenic, has a well-characterized genome, and can carry large amounts of foreign DNA without loss of infectivity (Mackett, M. and G.L. Smith. 1986. J. Gen. Virol., 67:2067-2082) . 3. Generation of Recombinant Viruses that Contain Tandemly Arranged, Related DNA Sequences Inserted in the Genome The generation of recombinant viruses (e.g., vaccinia viruses) that contain tandemly-arranged and related DNA elements inserted in the genome is based on the following methods. Briefly, to produce the recombinant viruses, donor plasmidε are constructed that contain elements to be inserted into the viral genome. These elements are flanked by DNA sequences homologous to DNA sequences present in the genome of the host virus; these sequences will serve to direct insertion of the elements to a particular region of the viral genome by i^ vivo recombination. Cells are infected with virus (e.g., vaccinia virus) and the infected cells are also transfected with the donor plasmids. Homologous recombination between plasmid DNA and virus DNA resultε in the formation of recombinant viruses that incorporate the desired elements from the donor plasmid. Various virus selection schemes (e.g., see Spyropoulos et al., 1988. J. Virol. 62 ^ :1046-1054; Falkner and Moss. 1988. J. Virol. 62:1849-1854; Franke et al., 1985. Mol. Cell Biol. 5_:1918-1924) can be incorporated into this general approach, in order to permit the identification and isolation of recombinant viruses. Specific details of two approaches used in this invention are described below. a. Donor plasmids for in vivo recombination with host virus In the first approach (Figure 1) , tandemly arranged related geneε are inserted into the genome of the virus (e.g. vaccinia virus) in a single recombination event by means of a specially designed donor vector. A preferred donor vector contains (in a 5' to 3 ' orientation) : i) a transcriptional promoter; ii) a first gene or gene fragment, encoding a polypeptide of interest, under the control of the transcriptional promoter; iii) a gene encoding a selectable marker, also under the control of a transcriptional promoter; iv) a second gene or gene fragment containing region(s) of DNA sequence homologous to the first gene, encoding a second poly- peptide of interest. The preferred donor vector also containε viral DNA sequences (labeled L and R in Figure 1) flanking the construct of elements i-iv, the flanking segments being homologous to a region of the viral genome into which the tandem genes are to be inserted. The transcriptional promoters in i and iii are required for the expression of the adjacent genes in vivo. For vaccinia virus, for example, these may include any of the well-characterized and isolated transcriptional promoters, such as the 7.5K promoter (Venkatesan et al. 1981 Cell 5:805-813) ; the Ba F promoter (Panicali et al. 1983 Proc. Natl. Acad. -16- Sci. USA 0:5364-5368); the 40K promoter (Rosel et al. 1986. J Virol. 0:436-449); the 30K promoter (Perkus et al. 1985 Science 229:981-984) ; the tk promoter (Hruby et al. 1983 Proc. Natl. Acad. Sci. 5 USA 80:3411-3415) and the UK promoter (Bertholet et al. 1985 Proc. Natl. Acad. Sci. USA 82:2096-2100) . The gene encoding the selectable marker (ele¬ ment iii) is required for the maintenance of the tandemly duplicated structure during viral replica- 10 tion.. Several types of marker genes can be used. A particularly preferred marker gene is the gene encoding thy idine kinase (t ) . Viruses that contain this gene can grow in the presence of the chemical methotrexate, while viruses lacking this 15 gene cannot (Complone-Piccardo et al., 1979. J. Virol. £1:281-287) . Thus, recombinants that contain the tk gene can be selected on the basis of their ability to grow in methotrexate. Other selectable markers include the vaccinia 20 virus host range (29K) gene (Gillard et al., Proc. Natl. Acad. Sci. USA. £2:5573-5577 1986), or genes that confer chemical or antibiotic resistance, such as the E. coli Neo or gpt genes (Franke et al. , Mol. Cell. Biol. 5:1918-1924 1985; Falkner and Mosε. 25 1988. J. Virol. 62:1849-1854 1988). In the second approach (Figure 2) , tandemly arranged related genes are inserted into the viral genome via two separate and sequential recombination events. A first gene, under the control of a 30 transcriptional promoter, is inserted into the viral genome using standard techniques of _in vivo recom¬ bination. The second related gene, together with a gene encoding a selectable marker (e.g., thymidine kinase) is then inserted into the virus containing the first gene. This insertion occurs via recom¬ bination between the first gene, contained on the viral genome, and the second gene, contained on a donor plasmid. This second recombination event generates a virus that contains two hybrid genes in tandem; these genes are separated by a gene encoding the selectable marker. In this second approach, the donor plasmid vector for inserting a second, related gene into a virus that already contains a first related gene has the following elements: i) a gene or gene fragment containing one or more regions homologous to a first gene already present in the genome of a recom¬ binant virus; and ii) a gene encoding a selectable marker, under the control of a transcriptional promoter. A preferred marker gene is the tk gene, as described previously. b. Integration of foreign DNA sequences into the viral genome and isolation of recombinants As described briefly above, homologous recom- bination between donor plasmid DNA and virus DNA in an infected cell results in the formation of recom¬ binant viruses that have incorporated the desired elements. Appropriate host cells for in vivo recombination are generally eukaryotic cells that can be infected by the virus (e.g., vaccinia virus) and transfected by the plasmid vector. Examples of -18- εuch cellε are chick embryo fibroblaεts, HuTK143 (human) cells, and CV-1 and BSC-40 (both monkey kidney) cells. Infection of cells with vaccinia virus and transfection of these cells with plasmid vectors is accomplished by techniques standard in the art such as Panicali and Paoletti, United States Patent No. 4,603,112, incorporated by reference herein. In both of the approaches deεcribed above, selection for function of the marker gene (e.g., the tk gene) following in vivo recombination permits isolation of recombinants that contain tandemly arranged and related genes (i.e., genes that share regions pf DNA homology) . Both approaches (Figures 1 and 2) will yield recombinant viruses in which the marker gene is positioned between the two tandemly arranged and related genes. 4. Intramolecular Recombination Methods of this invention for generating hybrid genes from two related genes in a recombinant virus are based upon the genetic instability of tandemly arranged non-identical DNA sequences that share regions of homology. Intramolecular recombination between regions of homology shared by the two related genes, which occurs during the course of normal viral replication, results in the formation of a single hybrid gene composed of portions of the two original genes. ~ Because the recombination events* can occur randomly between any homologous sequences contained on the two genes, these events will generate a spectrum of hybrid genes. In viruses generated by approach 1 or approach 2 (Figures 1 and 2, respectively), a gene encoding a selectable marker resides between the two tandemly arranged related genes. This arrangement permits isolation and propagation of viruses containing the genetically unstable tandem gene arrangement. Viruseε are propagated under conditions that permit growth of only those recombinants that contain the marker gene. Intramolecular recombination between homologous sequences on the two tandemly arranged, related genes results in the excision of the marker gene. Viruses that have undergone intramolecular recom¬ bination to generate a hybrid gene can be iden- tified, and in some cases, selected for, by virtue of the lack of the function encoded by the now- absent marker gene. For example, when the tk gene is used as the selectable marker, those progeny viruseε that have undergone intramolecular reco - bination, with the concomitant exciεion of the tk gene, can be selected in a medium containing 5- bromo-2'-deoxyuridine (BUdR) or trifluorothymidine. In this selective medium, only those viruses which lack tk gene function can survive. In viruses generated by approach 1, intra¬ molecular recombination between tandemly arranged, related genes will yield a final hybrid gene that contains a single fusion junction, i.e. , the 5 1 portion of the hybrid gene will be derived from the 5 1 region of one of the two original genes, while the 3 ' portion of the hybrid gene will be derived from the 3' region of the second of the two original genes. Each individual hybrid gene will contain a different fusion junction, generated by random recombination between the homologous regions shared by the two original genes (Figure 1) . Jn viruses generated by approach 2, each of the tandemly arranged genes is itself a hybrid gene, formed by recombination between a first gene located in the viral genome and a second, related gene contained on the donor plaεmid. Intramolecular recombination betwen this pair of hybrid genes results in the formation of a single hybrid gene that contains two separate fusion junctions. Thus, the inal hybrid gene will contain 5' and 3' seg- mentε from one of the two original geneε flanking a center segment derived from the second of the two original genes (Figure 2) . 5. Recombinant Virus aε Vaccines The methods of this invention can be exploited to produce a vaccine in the form of live, recom- binanfe viral vectors capable of expresεing a unique chimeric protein, or a population of related chi¬ meric proteins or protein segments, from a patho- • geni organism that exhibits antigenic variation. A recombinant- irus (e.g., poxvirus) that contains tandemly arranged genes encoding antigenically distinct forms of a chosen polypeptide can serve as the progenitor of a population of progeny viruseε. each of which contains a different hybrid gene composed of portions of the original tandemly arranged genes. These hybrid genes, created by intramolecular recombination events, can be ex- pressed by the recombinant poxviruseε aε chimeric polypeptides. If the chimeric polypeptides represent an immunologically important antigen of a pathogenic organism (e.g., the HIV env antigen), particularly an organism that exhibits antigenic and genomic variation, the population of viral vectors that express these polypeptides may be uεed aε live recombinant vaccineε; theεe vaccines may elicit immune responses to a broad range of serological types and subtypes of the pathogen. As an alternative to the uεe of the whole population of progeny viruses containing hybrid genes, it is also poεsible to isolate individual members of the population, each of which expresses a different and unique hybrid gene. The individual, plaque purified recombinants can be examined for their potential to elicit immune responεeε to the several variants of the cognate pathogen; appro¬ priate recombinants can then be used, individually or in combination, to formulate a live recombinant vaccine. An example of the use of the methods of this invention is the development of a vaccine effective againεt multiple strains of the human immuno- deficiency viruseε, HIV-l and HIV-2, the cauεative agents of AIDS. The genetic and antigenic variation among strains of HIV, which resideε primarily in the genes encoding the viral envelope proteins, presentε a major obstacle to the development of an HIV vaccine, as a vaccine effective against one variant may fail, to protect against related strains. To generate a vaccine with potential for eliciting an immune response against multiple HIV strainε, a parental poxviruε that contains, tandemly arranged in the genome, envelope genes from two widely divergent HIV-l strainε (e.g. , the RF and BHIO strains) can be constructed. Intramolecular re¬ combination between homologous regions of the two HIV envelope genes in the parental virus will give riεe to a population of progeny viruεeε, each of which containε a unique hybrid envelope gene generated from the random recombination between homologouε regionε shared by the two original genes. The chimeric envelope proteins encoded by these hybrid genes will contain both novel combinations of epitopes as well as new discontinuous epitopes. Either individual members of this population, a mixture of selected memberε of thiε population, or the entire population of progeny viruεeε can be uεed as a vaccine to immunize personε εuεceptible to HIV infection. During replication of the progeny viruεes in an immunized host, the chimeric antigens will be expresεed along with the normal complement of poxviral geneε. Theεe antigenε will εtimulate an immunological reεponεe directed againεt the variety of epitopes represented in the population; this immune response may be effective againεt a spectrum of HIV εtainε. A number of other pathogenε, in addition to HIV, exhibit genetic and antigenic variation which allowε them to eεcape hoεt immune surveillance. Theεe include variouε parasites, such as trypano- εomeε and malarial plaεmodia; and viruεeε, εuch aε influenza viruε (an orthomyxoviruε) , certain picornaviruses, and retroviruseε. The methods of this invention may be applied to the development of a vaccine for any of these pathogens. 6. The Generation of Chimeric Proteins for Pharmaceutical Useε Although the methodε of thiε invention are particularly suitable for developing vaccines against pathogens which exhibit antigenic diversity, they can also be used to generate hybrid genes encoding chimeric proteinε for other applicationε. For example, a recombinant virus that contains, tandemly arranged in the viral genome, genes en¬ coding related interferonε (or any two related genes encoding pharmacologically important polypeptideε) will, upon intramolecular recombination, give riεe to progeny viruses that contain hybrid genes. Individual progeny viruseε generated by the re¬ combination events could be isolated and the chi¬ meric proteins synthesized by these viruseε could be purified and examined for the deεired novel bio¬ logical properties. Alternatively, the novel hybrid geneε contained in the individual progeny viruseε _k could he isolated by standard recombinant DNA methodologieε and expressed in alternate recombinant organismε, including E. coli, yeast, baculovirus, or eukaryotic cells. 7. The Generation of Chimeric Proteins for Epitope Mapping Hybrid glycoprotein geneε have been uεed to map type-εpecific antigenic determinantε. For example, a large number of hybrid geneε containing portionε of the glycoprotein geneε from vesicular stomatitis virus serotypeε Indiana and New Jerεey were made by standard techniques of recombinant DNA. These hybrid geneε were individually expreεεed in vaccinia viruε and were uεed to map antigenic determinantε recognized by type-εpecific monoclonal antibodies (Keil and Wagner, 1989 Virology 170:392-407) . The methods of this invention can also be used to map type-specific antigenic determinants. For example,-given two related proteins and a collection of type-εpecific antibodieε which recognize only one (or the other) of the two proteins, the epitope recognized by each antibody can be mapped by con¬ structing a recombinant virus containing the two related geneε. The reεulting intramoleuclar recombin- ation eventε between the two related geneε will generate a population of viruεeε containing a spectrum of'hybrid genes. Antibody binding to individual hybrid proteins can then be asεayed (for example, by black plaque aεεay on the viral population) . The genes encoding individual hybrids of interest can then be mapped (for example, using the polymerase chain reaction technique to amplify the hybrid gene in the viral genome, followed by restriction mapping or sequence analysis) to localize the epitope. The invention is illustrated further by the following Exemplification. EXEMPLIFICATION Cells and Virus E. coli strains JM101 (Messing et al. , Nucl. Acids Reε. , £:309 (1981)) and MC1061 (Casadaban and Cohen, J. Mol. Biol., 138:179 (1980)) can be used as the host for the growth of all plaεmidε. The monkey kidney cell line BSC-40 is used for vaccinia virus infections. Vaccinia virus tk- mutant WR 417 (Spyropoulos et al. , J. Virol., ££:1046-1054 (1988)) is uεed as the parental virus for in vivo recombina¬ tion. Enzymes Restriction enzymeε are obtained from New England BioLabε or Boehringer-Mannheim. The large fragment of DNA polymerase (Klenow) is obtained from United States Biochemical Corp. calf intestinal phosphatase (CIP) and T4 DNA ligase is obtained from Boehringer-Mannheim. Molecular Cloning Procedures Restriction enzyme digeεtions, purification of DNA fragments and plasmidε, treatment of DNA with CIP, Klenow, ligaεe or linkers and tranεformation of 5 E_ ; _ coli are performed eεsentially as described (Maniatis et al. , Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1982), incorporated herein by refer¬ ence. 10 Preparation of Vaccinia Virus Recombinantε Viral infection, transfections, plaque purifi¬ cation and viruε amplification are performed essen¬ tially as described (Spyropoulos et al. , J. Virol. , £2.:1046-1054 (1988)). Infection and transfection 15 were performed in the presence of 5uM methotrexate (MTX) ; plaques were plated and purified in the absence of MTX. Vaccinia Virus Genomic Analyεiε DNA is extracted from vaccinia virus-infected 20 cells as described (Esposito et al. , J. Virol. Methods, _2:175 (1981)) and analyzed by restriction enzyme digestions and Southern hybridization as deεcribed (Maniatiε e al. , Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, 25 Cold Spring Harbor, N.Y., 1982). Vaccinia viruε recombinant DNA iε subcloned into phage ml3mpl8 (New England Biolabs) and sequenced by the chain-termina¬ tion method (Sanger et al. , Proc. National Acad. Sci. USA, 7_4:5463 (1977)). Polymerase chain reaction was performed using a kit (Perkin Elmer Cetus) according to manufacturer's inεtructionε. Productε and compoεitions described herein are hybrid proteins derived from the expresεion of condensed genes contained within viruses that have undergone intramolecular recombination according to the methods of the present invention. These pro¬ teins can have antigenic properties and, when suitably expressed, may serve a variety of purposes. One such use can be proteins that elicit immune responses to a broad range of HIV isolateε. Particular compoεitionε of thiε invention are chimeric env genes containing combined sequences of the RF and BHIO env genes of HIV-l. This invention will now be more specifically characterized through the use of the following examples, which are not construed to be limiting. EXAMPLE 1 Construction of a plasmid containing the HIV strain BHIO env gene fused to the E. coli lacZ gene, under the control of the vaccinia 7.5K promoter (Figure 3) The HIV-l strain BHIO env gene is located on plasmid pSV-Henv, obtained from Blair Ferguson (E.I. DuPont deNemourε and Co. ) . pSV-Henv was digested with Xbal and Xhol, treated with Klenow, and the 2700 bp fragment containing the eny-encoding se¬ quence was gel-purified. pAbT4007 (See U.S. patent application Serial No. 910,501, filed September 23, 1986) ' was digeεted with Smal, treated with CIP, and ligated to the 2700 bp fragment to create pAbT167, as shown in Figure 3A. pAbT167 was partially digested with Hindlll, and a 9500 bp partial digestion product, lacking both the 3 ' end of the env gene and the BamF pro¬ moter, was gel-purified and self-ligated to form pAbT4075 as shown in Figure 3B. pAbT4075 contains the BH10 env gene fused in-frame to lacZ at the Hindlll si"be at position 2000 in the BH10 env gene, encoding all of env protein gpl20 and approximately 300 bp of env protein gp41. EXAMPLE 2 Construction of a plasmid containing the HIV strain RF ertv gene modified at the 5' end of the gp41 - encoding portion.of the gene (Figures 4, 5) pAG3 (U.S. patent application Serial No. 910,501, εupra) waε digested with Ndel, treated with Klenow, and ligated to NotI linkers (dGCGGCCGC; New England BioLabs) . The resulting plasmid, pAbT4524A, waε digested with NotI, treated with Klenow and ligated to a εynthetic oligonucleotide (dGCTTTAAAGC; Biology Department, Brandeiε Univerεity) , containing a Dral site and restoring NotI sites flanking the Dral site in plaεmid pAbT4524B, aε εhown in Figure 4A. pAbT4027 (U.S. patent application Serial No. 910,501, εupra) was digested with Dral and a 5530 bp fragment was gel-purified. pAbT4524B was partially digested with Dral. A 2260 bp fragment was gel- purified, treated with CIP and ligated to the 5530 bp fragment to create pAbT4533, as shown in Figure 4B. The HIV-l strain RF env gene was obtained on plasmid pRF3HS from Blair Ferguson (E.I. DuPont deNemours and Co.). pRF3HS waε digested with Avail, treated with Klenow, digested with Spel and the resulting 500 bp fragment containing the 5' end of the RF env gene was gel-purified. pRF3HS was digested with EcoRI, treated with Klenow, digested with Spel and the resulting 2100 bp fragment con¬ taining the 3 ' end of the RF env gene waε gel- purified. pAbT4533 waε digested with Smal, treated with CIP and ligated to the 500 bp and 2100 bp fragmentε to create pAbT8523, as shown in Figure 4C. pAbT8523 was digested with EcoRI, treated with Klenow, ligated to an Xbal linker (New England BioLabs) , digested with Hindi, and a 900 bp frag- ment containing the 5' end of RF env was gel-puri¬ fied. pRF3HS was digested with Xhol, treated with Klenow, ligated to an SphI linker (New England BioLabε) , digested with Hindi and a 1700 bp frag¬ ment containing the 3 ' end of RF env was gel- purified. pAbT4533 was digeεted with Xbal and SphI and ligated to the 900 and 1700 bp fragments to form pAbT8526, as shown in Figure 5A. pAbT8526 was partially digested with Styl, treated with Klenow, and a 10,600 bp fragment was gel-purified and ligated to a BamHI linker (dCGGATCCG; New England BioLabs) to create pAbT4082 aε εhown in Figure 5B. pAbT4082 containε the HIV-l RF env gene with a Ba HI site inserted at the Styl site at position 1600, at the 5' end of the gp41- encoding region, 30 bp 3 1 to the gpl20-gp41 junc- tion. EXAMPLE 3 Conεtruction of an IVR vector containing the vac¬ cinia viruε thymidine kinaεe gene flanked by the gp!20 portion of the HIV-l εtrain RF env gene and the HIV-l εtrain BHIO env gene fuεed to lacZ (Figure §1 pAbT4082 was digested with Xbal and BamHI and the 1700 bp fragment containing the RF gpl20 gene was gel-purified. pAbT4075 waε digested with BamHI, partially digested with Xbal and treated with CIP, and a 9500 bp fragment was gel-purified and ligated to the 1700 bp fragment to create pAbT4083, as εhown in Figure 6A. pAbT400 (U.S. patent application Serial No. 910,501, supra) was digested with Sau3AI and the 900 bp fragment containing the vaccinia viruε thymidine kinase (tk) gene was gel-purified. pAbT4083 was digested with BamHI, treated with CIP and ligated to the 900 bp fragment to create pAbT4085, as shown in Figure 6B. pAbT4085 contains the RF gpl20, under the control of the 7.5K promoter, and the BH10 gpl60 geneε separated by the tk gene. In addition, the BH10 env gene is fused in-frame to the lacZ gene. EXAMPLE 4 Inεertion of tandem HIV-l env gene sequences into vaccinia virus and subsequent condensation of the tandem array to yield single-copy hybrid env genes (Figure 7) DNA sequences contained within pAbT4085 contain the tk gene flanked by two diverse env genes from HIV-l strainε BHIO and RF. Theεe env genes differ by 21% in the a ino acid sequence of their exterior envelope proteins (Starcich et al. , 1986, Cell 45:637). This vector is used to insert the desired structure into tk vaccinia by jln vivo recombination. Methotrexate is used to obtain and purify tk+ recom¬ binants away from the parental tk " virus, which cannot grow in the presence of methotrexate. A recombinant virus is therefore generated which contains both env genes as well as the tk gene (Figure 7) . Because recombination between conserved regions of the tandemly arrayed env genes results in dele¬ tion of the intervening sequences, including the tk gene, virus which have undergone condensation events can be selected using 5'-bromodeoxyuridine (BUdR) which permits growth of tk~,but not tk , virus. As a number of conserved regions spanning the env sequence are available for recombination, a vaccinia recombinant containing two different env genes in tandem will generate a diverse set of chimeric env genes. The E_ ; _ coli lacZ gene is included as a marker; plaques resulting from the growth of virus containing both env geneε will be colorleεs in the preεence of Xgal becauεe there is no tranεcriptional promoter to expreεε lacZ, whereaε virus containing a hybrid env gene fused in-frame to lacZ will give 5 rise to blue plaques. Plasmid pAbT4085 was transfected into BSC-40 cells which had previously been infected with the vaccinia tk~ strain WR 417 (Spyropoulos et al. , J. Virolj , 62:1046-1054 (1988 )) in the presence of 10 methotrexate. When the progeny viruε population waε plated in the presence of methotrexate and overlaid with Xgal only colorless (lacZ~) plaques were observed. When the same population was plated in the absence of methotrexate and overlaid with Xgal, 15 blue plaques were observed. Two blue recombinants, designated vAbT168-l and vAbT168-2, were plaque- purified in the absence of methotrexate and am¬ 4- plified. EXAMPLE 5 20 Analysis of the structures of two vaccinia-generated hy i€ epy-*genes fused to lacZ (Figures 7, 8, 9, 10) • -" ■ Vaccinia virus genomic DNA was prepared from the recombinant vAbT168-l derived from the previous Example. The D_{A was digested with Hindlll and the 25 resulting fragments separated by agarose gel elec- trophόresis. The restriction pattern observed was ** » consistent with that expected for a recombinant virus which had undergone a condensation event to generate a hybrid env gene, as shown in Figure 7. A 3 kb fragment containing the putative chimeric env gene was gel-purified and ligated to pAbT2009 (U.S. patent application Serial No. 910,501, supra) , previously digested with Hindlll and treated with CIP, to yield the plasmid pAbT4105, as shown in Figure 8A. The hybrid env gene in pAbT4105 was analyzed by restriction enzyme mapping; a restriction map is εhown in Figure 8B. The results indicate that the 5' end of the hybrid env gene is derived from the RF env gene and the 3' end from the BHIO env gene. The restriction analysis localized the RF/BH10 junction to a 118 bp region between a Styl and Hgal site, as indicated in Figure 8B. To further define the RF/BH10 junction, pAbT4105 was digeεted with Bglll and Hgal, treated with Klenow and a 200 bp fragment containing the hybrid junction waε gel-purified. Phage ml3mpl8 DNA (New England BioLabs) was digeεted with Hin i, treated with CIP and ligated to the 200 bp fragment to create pAbT4106, as shown in Figure 9A. Single-stranded preparations were made of pAbT4106 and the 200 bp insert sequenced by the chain-termination method. Sanger, Nicklen and Coulson, Proc. Natl. Acad. Sci. USA, 74, 5463 (1977) . The corresponding regions of the parental RF and BH10 env genes from pAbT4085 were also se¬ quenced. The relevant sequenceε of the RF, BH10 and vAbT168-l hybrid env geneε are shown in Figure 9B. Thus the RF/BH10 condensation event occurred within a conserved 22 bp region common to both the RF and -34- BH10 env genes, located 21-43 bp from the 3' end of the RF env fragment in pAbT4085 (Figure 9B) . Vaccinia virus genomic DNA was alεo prepared from recombinant vAbT168-2 and was analyzed by 5 Southern hybridization using HIV env DNA as a probe. The restriction map of the hybrid env gene from vAbT168-2 is shown in Figure 10A. The map indicates that the RF/BH10 junction in vAbT168-2 iε within a 360bp sequence between a Kpnl and a BsmI site in the 10 central region of gpl20, between hypervariable regions V and V„. This region of vAbT168-2 was sequenced and is shown in Figure 10B. In vAbT168-2, the RF/BH10 condensation event occurred within a conserved 23 bp sequence located between nucleotides 15 758 and 782. vAbT168-l and vAbT168-2 are thus two recombinantε containing different hybrid env-lacZ geneε derived by vaccinia viruε-mediated recombin¬ ation between adjacent RF and BHIO env geneε. EXAMPLE 6 2 0 Generation of hybrid env geneε (Figures 11, 12, 13) Having demonstrated the feasibility of using vaccinia virus-mediated recombination to derive hybrid env-lacZ genes, the generation of populations of recombinant vaccinia containing full-length, 25 chimeric env genes was undertaken. Approach 2 (Figure 11) was used in this εet of experiments. First, the HIV-l BHIO env gene (including 11 nucleo¬ tides of 5' proximal and 105 nucleotides of 3* proximal untranslated sequences) was inεerted, under the control of the vaccinia 4OK promoter (designated H6 in Rosel et al. , 1986 J. Virol. ££:436-449), into the Hindlll M region of the vaccinia genome uεing host-range selection (See Smith, International patent application PCT/US89/02486, filed June 7, 1989; this recombinant virus was designated vAbT271. Next, a plasmid vector, designated pAbT4120, was constructed containing the 5' portion of the HIV-l RF env gene fused at nucleotide 1449 (immediately following hypervariable region V_. in gpl20) to the lacZ gene. This vector also contained the gpt gene (Falkner and Mosε, 1988, J. Virol. 62:1849-1854) , under the control of the vaccinia Dl promoter (Lee-Chen et al. , 1988, Virology 163:64-79) , for selection of recombinants, and a bacterial replicon and ampicillin resistance gene for growth and selection in E. coli. Cells were infected with vAbT271 and then were transfected with pAbT4120. A single recombination event between homologous regions of the BHIO env gene in vAbT271 and the RF env gene in pAbT4120 would result in the genomic structure shown in Figure 11, containing two hybrid env genes. Nine different recombinantε, deεignated vAbT373I, were isolated and purified (uεing gpt and lacZ selection) to characterize these hybrid genes. The presence of a bacteri •al repli•con and ampr gene facilitated the subcloning of the vaccinia genomic region containing the 5'-proximal hybrid gene. Genomic DNA preparationε were digeεted with Hindlll, εelf-ligated and used to transform E. coli to ampicillin-resistance. Restriction mapping revealed a number of different hybrid junctions in these intermediate recombinants (Figure 12) . In four of theεe recombinantε (recombinants 1, 3, 5 and 6 as shown in Figure 12) , gpt-selective conditions were removed to allow the propagation of condensed virus containing a single, hybrid, full-length env gene. The lacZ gene served as a marker to distinguish condensed (colorlesε plaqueε) from uncondenεed (blue plaques) virus. After four serial passages of virus under non-selective conditions, approximately 90% of the progeny plaques from each of the four popula- tions " ,were colorless, indicating that nearly all the viral genomes had condensed to a single env gene. The two junction regions in each of the hybrid genes from eight individual recombinants (two from each population) designated vAbT373C were mapped by re&triction mapping of genomic DNA amplified by the polymerase chain reaction. Restriction mapping (Figure 13) showed that each of the eight vAbT373C viruses contain a unique, hybrid env gene; no two were identical chimeras. Deposit The plasmid pABT4085 was placed on deposit at the American Type Culture Collection in Rockville, Maryland on October 6, 1988 and assigned Accession No. 67818. Equivalents Those skilled in the art will recognize, or be able to ascertain using no more than routine ex¬ perimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompasεed by the following claims. PCT Applicant's Guide - Volume I - Annex M3 ANNEX M3 International Application No: PCT/

Claims: , 38 CLAIMS 1. A method of generating viruεes containing hybrid DNA sequences, comprising the steps of: a. providing a virus comprising at least two 5 tandemly arranged DNA sequences, the sequenceε being non-identical but sharing regions of homology; and b. allowing the virus to replicate under conditions which permit intramolecular 10 recombination between the homologous regions in the two tandemly arranged DNA sequences to produce a family of progeny viruses, each virus containing hybrid DNA sequences compriεing portions of the 15 original DNA sequences. 2. A method of Claim 1, wherein the virus is a pox virus. 3. A jmethod of Claim 2, wherein the pox virus is vaccinia virus. 20 4. A method of Claim 1, wherein a transcriptional promoter is located adjacent to the 5" end of the first of the tandemly arranged DNA se¬ quences. 5. A method of Claim 1, wherein the virus further 25 comprises a gene encoding a selectable marker under the control of a transcriptional promoter interposed between the tandemly arranged DNA εequenceε. 6. A method of Claim 5, wherein the selectable marker is selected from the group consisting of a thymidine kinase gene, E. coli Neo , E. coli gpt gene, and vaccinia 29K gene. 7. A method of Claim 1, wherein the tandemly arranged DNA sequences are selected from DNA sequences encoding structural or functional components of pathogenic organisms. 8. A method of Claim 7, wherein the pathogenic organism is an animal virus or a parasite. 9. A method of Claim 1, wherein the virus com¬ prising at least two tandemly arranged DNA sequences is provided by: a. providing a donor plasmid comprising: i) at least two tandemly arranged DNA sequences, the DNA sequences being non-identical but sharing regions of sequence homology; ϋ) DNA sequences flanking the tandemly arranged DNA sequences, the flanking sequences being homologous to a region of the viral genome where the tandemly arranged sequences are to be inserted; and b. introducing the donor plasmid and the virus into a host cell under conditions that permit recombination in vivo between the homologous DNA sequenceε of the viral genome and the donor plaεmid to produce a recombinant virus containing the tandemly arranged DNA sequences. 10. A method of Claim 9, wherein the donor plasmid further compriseε a tranεcriptional promoter adjacent to the 5* end of the firεt of the tandemly arranged DNA sequences. 11. A method of Claim 9, wherein the donor plasmid further compriseε a gene encoding a εelectable marker under the control of a tranεcriptional promoter interpoεed between the tandemly arranged DNA εequenceε. 12. A method of Claim 1, wherein the viruε com- prising at least two tandemly arranged DNA sequences is provided by: a. providing a virus comprising a first DNA sequence and a donor plasmid comprising a second DNA sequence, the second DNA , sequence being non-identical to, but con¬ taining regions homologous to, the first DNA sequence and a gene encoding a selec¬ table marker under control of a tranεcrip¬ tional promoter; and b. allowing in vivo recombination to occur between homologouε regions in the first DNA εequence, contained in the viruε, and the εecond DNA εequence, contained on the donor plaεmid, so that the elements of the donor plasmid are inserted into the viral genome to produce a recombinant virus con¬ taining the DNA sequences tandemly arranged in the genome. 13. A method of Claim 12, wherein the virus further comprises a tranεcriptional promoter adjacent to the 5 1 end of the DNA sequence. 14. A method of generating pox viruses containing hybrid DNA sequences, comprising the steps of: a. providing a pox virus comprising: i) at least two tandemly arranged DNA sequences, the sequences being non-identical but sharing regions of homology; ii) a transcriptional promoter adjacent to the 5' end of the first of the tandemly arranged DNA sequences; and iii) a gene encoding a selectable marker under the control of a transcrip- tional promoter located between the tandemly arranged DNA sequences; b. allowing the pox virus to replicate under conditions which permit intramolecular recombination between the homologous regions in the two tandemly arranged DNA sequences to produce a family of progeny pox viruses, each virus containing hybrid DNA sequences comprising portions of the original DNA sequenceε. 15. A method of Claim 14, wherein the pox viruε iε vaccinia virus. 16. A method of Claim 14, wherein the selectable marker is selected from the group consisting of ~~ . a thymidine kmase gene, E. coli Neo , E. coli gpt gene, and vaccinia 29K gene. 17. A method of Claim 14, wherein the transcrip¬ tional promoter is selected from the group consisting of the vaccinia virus 7.5K, 30K, OK, BamF, tk, and UK promoters. 18. A method of Claim 14, wherein the tandemly arranged DNA sequences are selected from DNA sequences encoding structural or functional components of pathogens. 19. A method of Claim 18, wherein the pathogen is an animal virus or a parasite. 20. A method of Claim 14, wherein the pox virus comprising at least two tandemly arranged DNA sequences is provided by: a. providing a donor plasmid comprising: i) at least two tandemly arranged DNA εequenceε, the DNA sequences being non-identical but sharing regions of sequence homology; ii) a transcriptional promoter adjacent to the 5 1 end of the first of the tandemly arranged DNA sequences; iii) a gene encoding a selectable marker under the control of a transcrip¬ tional promoter interposed between the tandemly arranged DNA sequenceε; and iv) DNA sequenceε flanking the elementε i-iii, the flanking sequences being homologous to a region of the pox viral genome where the tandemly arranged sequences are to be in¬ serted; and b. introducing the donor plasmid and a pox viral genome into a host cell under conditions that permit recombination in vivo between the homologous DNA sequences of the pox viral genome and the donor plasmid to produce a recombinant pox virus containing the tandemly arranged DNA sequences. 44 21. A method of Claim 14, wherein the pox virus comprising at least two tandemly arranged DNA sequenceε iε provided by: a. providing a first pox virus comprising a first DNA sequence under the control of a transcriptional promoter and a donor plasmid comprising i) a second DNA se¬ quence, the second DNA sequence being non-identical but sharing regions of homology to the first DNA sequence and ii) a gene encoding a selectable marker under the control of a transcriptional promoter; and b. _ allowing in vivo recombination to occur between homologous regions in the first DNA sequence, contained in the poxviral genome, and the second DNA sequence, contained on the donor plasmid, so that the elements of the donor plasmid are inserted into the pox viral genome to produce a recombinant pox virus containing the tandemly arranged DNA sequences separated by the gene encoding the selec¬ table marker. 22. A method of generating vaccinia viruses con¬ taining hybrid HIV DNA sequenceε, comprising the εtepε of: a. providing a donor plasmid comprising: i) at least two tandemly arranged HIV DNA sequenceε, the HIV DNA sequences being non-identical but sharing regions of homology; ii) a transcriptional promoter adjacent to the 5 1 end of the firεt of the tandemly arranged HIV DNA sequences; and iii) a gene encoding a selectable marker under the control of a transcrip- tional promoter interposed between the tandemly arranged HIV DNA se¬ quences; and iv) DNA sequences flanking the elements i-iii, the flanking εequenceε being homologouε to a region of the vac¬ cinia genome where the tandemly arranged εequenceε are to be in¬ serted; b. introducing the donor plasmid and a vaccinia viral genome into a hoεt cell under conditions that permit recombination in vivo between the homologous DNA se¬ quenceε of the vaccinia viral genome and the donor plasmid to produce a recombinant vaccinia viruε containing the tandemly arranged HIV DNA sequenceε; c. selecting for the recombinant viruses that contain tandemly arranged HIV DNA se¬ quences by propagating them under con¬ ditions that permit only those recombinant viruses containing the gene encoding the selectable marker to replicate; and d. propagating the recombinant vaccinia viruses which contain tandemly arranged HIV DNA sequenceε under conditionε that permit the replication of progeny viruses in which intramolecular recombination between homologous regions in the tandemly arranged HIV DNA sequences has occurred, to produce a family of progeny vaccinia viruses, each virus containing hybrid HIV DNA sequences comprising portions of the original two HIV DNA sequences. 23. A method of Claim 22, wherein the tandemly arranged HIV DNA sequences are env gene se- quences. 24. A method of Claim 23, wherein one of the HIV DNA sequences is from the env gene of HIV-l strain RF and a second HIV DNA sequence is from the env gene of HIV-l strain BHIO. 25. A method of Claim 22, wherein the selectable marker is selected from the group consisting of a thymidine kinase gene, E. coli Neo r , E. coli gpt gene, and vaccinia 29K gene. 26. A method of Claim 22, wherein the tranεcrip¬ tional promoter iε εelected from the group consisting of the vaccinia virus 7.5K, 3OK, 4OK, BamF, tk, and UK promoters. 27. A plasmid for recombination with a virus, comprising: a) at least two tandemly arranged DNA se¬ quences, the DNA sequences being non- identical but sharing regions of εequence homology; b) a transcriptional promoter adjacent to the 5 ' end of the first of the tandemly arranged DNA sequences; c) a gene encoding a selectable marker under the control of a tranεcriptional promoter interpoεed between the tandemly arranged DNA sequences; and d) DNA sequences flanking the elements i-iii, the flanking sequenceε being homologouε to a region of the viral genome where the tandemly arranged εequenceε are to be inεerted. 28. A plasmid of Claim 27, for recombination with a pox virus, wherein the promoters are pox viral promoters and the flanking sequences are pox viral sequenceε. 29. A plasmid of Claim 28, wherein the viruε iε a vaccinia virus. 30. A plasmid of Claim 30, wherein the tandemly arranged DNA sequences are HIV DNA sequenceε. 31. A plasmid of Claim 30, wherein the HIV DNA sequences are env gene sequenceε. 32. The plaεmid pAbT4085, ATCC designation 67818. 33. A combination of a plasmid and a virus for generating viruseε containing hybrid DNA sequences, comprising: a. a virus compriεing a firεt DNA sequence under the control of a transcriptional promoter; and b. a donor plasmid comprising a second DNA sequence, the second DNA sequence being non-identical, but sharing regions of homology to the first DNA sequence, and a gene encoding a selectable marker under the control of a transcriptional promoter. 34. The combination of Claim 33, wherein the virus is a pox virus. 35. The combination of Claim 34, wherein the pox virus is a vaccinia virus. 36. A family of recombinant viruseε containing hybrid DNA sequenceε derived from recombination between at leaεt two related but non-identical DNA εequences. 37. A family of recombinant viruses of Claim 36, wherein the viruses are pox viruses. 38. A family of recombinant viruseε of Claim 36, wherein the viruεeε are vaccinia viruses. 39. A family of recombinant viruses of Claim 36, wherein the recombination between the related but non-identical DNA sequences occurs intra- olecularly within a parental virus. 40. A family of recombinant viruses of Claim 36, wherein the DNA sequences are HIV DNA se¬ quenceε. 41. A family of recombinant viruεeε of Claim 40, wherein the HIV DNA sequences are env gene sequences. 42. A family of recombinant viruεeε produced by the method of Claim 1. 43. A family of recombinant viruεeε produced by the method of Claim 14. 44. A family of recombinant viruses produced by the method of Claim 22. 45. A method of vaccinating against a pathogenic organism that exhibitε antigenic variation, compriεing administering a family of recom¬ binant viruses containing and expresεing hybrid DNA sequences derived from recombination between at least two related but non-identical DNA εequenceε encoding an antigen of the organiεm. 46. A method of Claim 45, wherein the pathogenic organism is HIV. 47. A method of Claim 46, wherein the tandemly arranged HIV DNA sequences are env gene se¬ quences. 48. A method of Claim 47, wherein one of the HIV DNA sequences is from the env gene of HIV-l strain RF and a second HIV DNA εequence is from the env gene of HIV-l strain BHIO. 49. A method of mapping type-specific antigenic determinants, comprising a. preparing hybrid DNA sequences from sequences encoding two related polypep¬ tides according to the method of Claim 1; b. expressing hybrid polypeptide encoded by the hybrid sequences; c. testing for the presence of an antigenic determinant in the hybrid polypeptide; and d. mapping the determinant based upon the presence of type-specific sequenceε in the hybridε. 50. A method of generating hybrid polypeptideε with novel structural, functional or immunogenic propertieε, compriεing a. preparing hybrid DNA εequenceε from εequenceε encoding two related polypep¬ tideε according to the method of Claim 1; b. expreεεing hybrid polypeptideε encoded by the hybrid DNA εequences; and c. teεting for the presence of novel struc¬ tural, functional or immunogenic prop¬ erties of the hybrid polypeptides.

Inventors: GRITZ LINDA R, PANICALI DENNIS L, GRITZ, LINDA, R., PANICALI, DENNIS, L.
Applicants: APPLIED BIOTECHNOLOGY INC, APPLIED BIOTECHNOLOGY, INC.
Application year: 1990
Main classification: C12N7
IPC codes: A61K39, C07K14, C12N7, C12N15