Recombinant RSV virus expression systems and vaccines Number:6,830,748 from the United States Patent and Trademark Office (PTO) owispatent

Title: Recombinant RSV virus expression systems and vaccines

Abstract: The present invention relates to genetically engineered recombinant respiratory syncytial viruses and viral vectors which contain deletions of various viral accessory gene(s) either singly or in combination. In accordance with the present invention, the recombinant respiratory syncytial viral vectors and viruses are engineered to contain complete deletions of the M2-2, NS1, NS2, or SH viral accessory genes or various combinations thereof. In addition, the present invention relates to the attenuation of respiratory syncytial virus by mutagenisis of the M2-1 gene.

Patent Number: 6,830,748 Issued on 12/14/2004 to Jin,   et al.

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Inventors:	Jin; Hong (Cupertino, CA); Tang; Roderick (San Carlos, CA); Li; Shengqiang (Palo Alto, CA); Bryant; Martin (Carlisle, MA)
Assignee:	MedImmune Vaccines, Inc. (Mountain View, CA)
Appl. No.:	368076
Filed:	August 3, 1999

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Current U.S. Class:	424/93.2 ; 424/204.1; 424/205.1; 424/211.1; 424/93.1; 435/235.1; 435/236; 435/239; 536/23.7; 536/23.72
Field of Search:	424/184.1,199.1,204.1,205.1,211.1,93.1,93.2,936 435/5,69.1,69.3,235.1,236,237,239,320.1,440,471,238,172.1,328.1,325 536/23.1,23.7,23.72

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References Cited [Referenced By]

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U.S. Patent Documents

	5166057		November 1992		Palese et al.
	5843451		December 1998		Compans et al.
	5993824		November 1999		Murphy et al.
	6033886		March 2000		Conzelmann
	6060308		May 2000		Parrington
	6168943		January 2001		Rose
	6376171		April 2002		Hardy et al.

Foreign Patent Documents

	0 440 219		Aug., 1991		EP
	WO 91/03552		Mar., 1991		WO
	WO 93/06218		Apr., 1993		WO
	WO 95/08634		Mar., 1995		WO
	WO 96/10632		Jan., 1996		WO
	WO 96/40945		Dec., 1996		WO
	WO97/12032		Apr., 1997		WO
	WO 97/12032		Apr., 1997		WO
	WO 98/02179		Jan., 1998		WO
	WO 98/02530		Jan., 1998		WO
	WO 98/50405		Nov., 1998		WO
	WO 98/53078		Nov., 1998		WO
	WO 99/57284		Nov., 1999		WO
	WO 99/63064		Dec., 1999		WO
	WO 00/18929		Apr., 2000		WO
	WO 00/53786		Sep., 2000		WO

Other References

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Replacement of the F and G proteins of respiratory syncytial virus (RSV) subgroup A with those of subgroup B generates chimeric live attenuated RSV subgroup B vaccine candidates. J Virol. Dec. 1999; 73(12):9773-80. . Lodish et al., Molecular Cell Biology, Third Edition, Scientific American Books, 1995. . Frillingos et al., "Cys-Scanning Mutageneis: A novel Approach to Structure-Function Reltionships in polytopic membrane proteins, FASEB," Journal, 12:1281-1299 (1998). . Collins et al., "Support Plasmids and Suppoet Proteins Required for Recovery of Recombinant REspiratory Syncytial Virus," Virology, vol. 259, pp. 251-255 (1999). . Hardy et al., The Cys3-His1 Motif of te REspiratory Syncytial Virus M2-1 Protein is Essential for Protein Function, Journal of Virology, vol. 74, 5880-5885 (2000). . Atreya, P. L. et et al., 1998, J. Virol. 72:1452-1461. . Baron & Barrett, 1997, J. virol. 71:1265-1271. . Beeler and Coelingh, 1988, J. Virol. 63:2941-2950. . Brown et al.,1967, J. 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Durbin et al.,1997, Virology 235:323-332. . Elango, N. et al.,1989, J Virol 63(3):1413-5. . Enami et al., 1990, Proc. Natl. Acad. Sci. USA 92:11563-11567. . Garcia et al., 1993, Virology 195:243-247. . Gharpure et al.,1969, J. Virol. 3: 414-421. . Gorman, et al.,(1982) Mol. Cell. Biol. 2:1044-1051. . Grosfeld, H. et al.,1995, J. Virol. 69:5677-5686. . Hardy, R. W. et al., 1998, J. Virol. 72, 520-526. . He et al.,1997, Virology 237:249-260. . Hiebert, S. W. et al.,1985, J Virol 55(3):744-51. . Hodes et al.,1974, Proc. Soc. Exp. Biol. Med. 145:1158-1164. . Hoffman & Banerjee, 1997, J. Virol. 71:4272-4277. . International Search Report PCT/US98/20230. . Jin, H. et al., 1997, Embo J. 16(6):1236-47. . Jin, H. et al., 1998, Virology 251:206-214. . Kapikian et al.,1969, Am. J. Epidemiol. 89:405-421. . Karron, R. A. et al.,1997, J. Infect. Dis. 176:1428-1436. . Kato et al., 1996, Genes to Cells 1:569-579. . Kim et al., 1973, Pediatrics 52:56-63. . Kingsbury et al.,1987, Virology 156:396-403. . Krystal et al.,1986, Proc. Natl. Acad. Sci. USA 83:2709-2713. . Kunkel, 1985, Proc. Natl. Acad. Sci. U.S.A. 82:488-492. . Lawson et al.,1995, Proc. Natl. Acad. Sci USA 92:4477-4481. . Luytjes et al., 1989, Cell 59:1107-1113. . McIntosh and Chanock. 1990 "Respiratory Syncytial Virus" 2nd ed. Virology (D. M. Knipe et al., Ed.) Raven Press. Ltd.. N.Y. 1045-1072. . Mink et al.,1991, Virology 185:615-624. . Nayak et al.,1983, Genetics of Influenza Viruses, P. Palese and D. W. Kingsbury, eds., Springer-Verlag, Vienna, pp. 255-279. . Olmsted et al., 1986, Proc. Natl. Acad. Sci. 83:7462-7466. . Park et al., 1991, Proc. Natl. Acad. Sci. USA 88:5537-5541. . Radecke et al., 1995, EMBO J. 14:5773-5784. . Sambrook et al.,Molecular Cloning--A Laboratory Manual, Cold Spring Harbor laboratory Press, Cold Spring Harbor, NY, 1989. . Schnell et al., 1994, EMBO J. 13:4195-4203. . Teng, M. N., et al., 1999, J Virol 73(1):466-473. . Wang et al., 1989, Proc. Natl. Acad. Sci. 88:9717-9721. . Worthington et et al., 1996, Proc. Natl. Acad. Sci. 93:13754-13759. . Wright et al., 1976, J. Pediatrics 88:931-936. . Yu et al., 1995 J. Virol. 69:2412-2419. . Howorka and Bayley, 1998, Improved protocol for high-throughput cysteine scanning mutagenesis. BioTechniques. 25(5):764-6, 768, 770 passim. . Teng and Collins, 1998, Identification of the respiratory syncytial virus proteins required for formation and passage of helper-dependent infectious particles. J. Virol. 72(7):5707-16. . Dudas RA, Karron RA. Respiratory syncytial virus vaccines. Clin Microbiol Rev. 1998 Jul;11(3):430-439. . Crowe et al. A further attenuated derivative of a cold-passaged temperature-sensitive mutant of human respiratory syncytial virus retains immunogenicity and protective efficacy against wild-type challenge in seronegative chimpanzees. Vaccine. Jul. 1994; 12(9):783-790. . Prince et al. Efficacy and safety studies of a recombinant chimeric respiratory syncytial virus FG glycoprotein vaccine in cotton rats. J Virol. Nov. 2000;74(22):10287-10292. . Tang et al. Effects of human metapneumovirus and respiratory syncytial virus antigen insertion in two 3' proximal genome positions of bovine/human parainfluenza virus type 3 on virus replication and immunogenicity. J Virol. Oct. 2003;77(20):10819-10828..

Primary Examiner: Housel; James
Assistant Examiner: Lucas; Zachariah
Attorney, Agent or Firm: Jones Day

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No. 09/161,122, filed Sep. 25, 1998 abandoned, which claims priority benefit under 35 U.S.C. .sctn.119(e) of provisional Application Nos. 60/060,153, filed Sep. 26, 1997, 60/084,133, filed May 1, 1998, and 60/089,207, filed Jun. 12, 1998, each of which is incorporated herein by reference in its entirety.

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Claims

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What is claimed is:

1. An isolated live-attenuated respiratory syncytial virus particle which comprises a respiratory syncitial virus antigenome or genome containing a C-terminal truncation of the M2-1 protein, wherein the virus exhibits a lower degree of virulence as compared to a wild type RSV, and wherein the truncation is less than 46 amino acids in length.

2. The isolated live-attenuated respiratory syncytial virus particle of claim 1, wherein a stop codon causing said C-terminal truncation is at a position selected from a group consisting of nucleotide position 8053-8055, 8137-8139, and 8140-8142.

3. The virus particle of claim 2, wherein the stop codon causing said C-terminal trunication is at nucleotide position 8137-8139.

4. An isolated live-attenuated respiratory syncytial virus particle which comprises a respiratory syncytial virus antigenome or genome containing at least one M2-1 gene mutation, wherein (i) one M2-1 gene mutation encodes an amino acid exchange from a cysteine to an amino acid selected from a group consisting of glycine, valine, aspartic acid, and alanine at amino acid position 96, (ii) wherein cysteine residues at positions 7, 15, and 21 are retained, and (iii) wherein the virus exhibits a lower degree of virulence as compared to a wild type RSV.

5. An isolated live-attenuated respiratory syncytial virus particle which comprises a respiratory syncytial virus antigenome or genome comprising an M2-1 gene mutation at amino acid position 96, wherein the virus exhibits a lower degree of virulence as compared to a wild type RSV, and wherein the Cys3His motif at the N-terminus of the M2-1 protein is maintained.

6. The isolated live-attenuated respiratory virus particle of claim 5, wherein the M2-1 gene mutation at amino acid position 96 encodes an amino acid exchange from a cysteine to an amino acid selected from a group consisting of glycine, valine, aspartic acid, and alanine.

7. The virus particle of claim 5, wherein the respiratory syncytial virus antigenome or genome further comprises a truncation of the M2-1 gene.

8. The virus particle of claim 6, wherein a stop codon causing said C-terminal truncation is at a position selected from a group consisting of nucleotide position 8053-8055, 8137-8139, and 8140-8142.

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Description

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1. INTRODUCTION

The present invention relates to recombinant negative strand virus RNA templates which may be used to express heterologous gene products in appropriate host cell systems and/or to construct recombinant viruses that express, package, and/or present the heterologous gene product. The expression products and chimeric viruses may advantageously be used in vaccine formulations. In particular, the present invention relates to methods of generating recombinant respiratory syncytial viruses and the use of these recombinant viruses as expression vectors and vaccines. The invention is described by way of examples in which recombinant respiratory syncytial viral genomes are used to generate infectious viral particles.

2. BACKGROUND OF THE INVENTION

A number of DNA viruses have been genetically engineered to direct the expression of heterologous proteins in host cell systems (e., vaccinia virus, baculovirus, etc.). Recently, similar advances have been made with positive-strand RNA viruses (e,g., poliovirus). The expression products of these constructs, i.e., the heterologous gene product or the chimeric virus which expresses the heterologous gene product, are thought to be potentially useful in vaccine formulations (either subunit or whole virus vaccines). One drawback to the use of viruses such as vaccinia for constructing recombinant or chimeric viruses for use in vaccines is the lack of variation in its major epitopes. This lack of variability in the viral strains places strict limitations on the repeated use of chimeric vaccinia, in that multiple vaccinations will generate host-resistance to the strain so that the inoculated virus cannot infect the host. Inoculation of a resistant individual with chimeric vaccinia will, therefore, not induce immune stimulation.

By contrast, negative-strand RNA viruses such as influenza virus and respiratory syncytial virus, demonstrate a wide variability of their major epitopes. Indeed, thousands of variants of influenza have been identified; each strain evolving by antigenic drift. The negative-strand viruses such as influenza and respiratory syncytial virus would be attractive candidates for constructing chimeric viruses for use in vaccines because its genetic variability allows for the construction of a vast repertoire of vaccine formulations which will stimulate immunity without risk of developing a tolerance.

2.1. RESPIRATORY SYNCYTIAL VIRUS

Virus families containing enveloped single-stranded RNA of the negative-sense genome are classified into groups having non-segmented genomes (Paramyxoviridae, Rhabdoviridae) or those having segmented genomes (Orthomyxoviridae, Bunyaviridae and Arenaviridae). Paramyxoviridae have been classified into three genera: pararnyxovirus (sendai virus, parainfluenza viruses types 1-4, mumps, newcastle disease virus); morbillivirus (measles virus, canine distemper virus and rinderpest virus); and pneumovirus (respiratory syncytial virus and bovine respiratory syncytial virus).

Human respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract disease in infants and young children and is responsible for considerable morbidity and mortality. Two antigenically diverse RSV subgroups A and B are present in human populations. RSV is also recognized as an important agent of disease in immuno-compromised adults and in the elderly. Due to the incomplete resistance to RSV reinfection induced by natural infection, RSV may infect multiple times during childhood and life. The goal of RSV immunoprophylaxis is to induce sufficient resistance to prevent the serious disease which may be associated with RSV infection. The current strategies for developing RSV vaccines principally revolve around the administration of purified viral antigen or the development of live attenuated RSV for intranasal administration. However, to date there have been no approved vaccines or highly effective antiviral therapy for RSV.

Infection with RSV can range from an unnoticeable infection to severe pneumonia and death. RSV possesses a single-stranded nonsegmented negative-sense RNA genome of 15,221 nucleotides (Collins, 1991, In The paramyxoviruses pp. 103-162, D. W. Kingsbury (ed.) Plenum Press, New York). The genome of RSV encodes 10 mRNAs (Collins et al., 1984, J. Virol. 49: 572-578). The genome contains a 44 nucleotide leader sequence at the 3' termini followed by the NS1-NS2-N-P-M-SH-G-F-M2-L and a 155 nucleotide trailer sequence at the 5' termini (Collins. 1991, supra). Each gene transcription unit contains a short stretch of conserved gene start (GS) sequence and a gene end (GE) sequences.

The viral genomic RNA is not infectious as naked RNA. The RNA genome of RSV is tightly encapsidated with the major nucleocapsid (N) protein and is associated with the phosphoprotein (P) and the large (L) polymerase subunit. These proteins form the nucleoprotein core, which is recognized as the minimum unit of infectivity (Brown et al., 1967, J. Virol. 1: 368-373). The RSV N, P, and L proteins form the viral RNA dependent RNA transcriptase for transcription and replication of the RSV genome (Yu et al., 1995, J. Virol. 69:2412-2419; Grosfeld et al., 1995, J. Virol. 69:5677-86). Recent studies indicate that the M2 gene products (M2-1 and M2-2) are involved and are required for transcription (Collins et al., 1996, Proc. Natl. Acad. Sci. 93:81-5).

The M protein is expressed as a peripheral membrane protein, whereas the F and G proteins are expressed as integral membrane proteins and are involved in virus attachment and viral entry into cells. The G and F proteins are the major antigens that elicit neutralizing antibodies in vivo (as reviewed in McIntosh and Chanock, 1990 "Respiratory Syncytial Virus" 2nd ed. Virology (D. M. Knipe et al., Ed.) Raven Press, Ltd., N.Y.). Antigenic dimorphism between the subgroups of RSV A and B is mainly linked to the G glycoprotein, whereas the F glycoprotein is more closely related between the subgroups.

Despite decades of research, no safe and effective RSV vaccine has been developed for the prevention of severe morbidity and mortality associated with RSV infection. A formalin-inactivated virus vaccine has failed to provide protection against RSV infection and its exacerbated symptoms during subsequent infection by the wild-type virus in infants (Kapikian et al., 1969, Am. J. Epidemiol. 89:405-21; Chin et al., 1969, Am. J. Epidemiol. 89:449-63) Efforts since have focused on developing live attenuated temperature-sensitive mutants by chemical mutagenesis or cold passage of the wild-type RSV (Gharpure et al., 1969, J. Virol. 3: 414-21; Crowe et al., 1994, Vaccine 12: 691-9). However, earlier trials yielded discouraging results with these live attenuated temperature sensitive mutants. Virus candidates were either underattenuated or overattenuated (Kim et al., 1973, Pediatrics 52:56-63; Wright et al., 1976, J. Pediatrics 88:931-6) and some of the vaccine candidates were genetically unstable which resulted in the loss of the attenuated phenotype (Hodes et al., 1974, Proc. Soc. Exp. Biol. Med. 145:1158-64).

Attempts have also been made to engineer recombinant vaccinia vectors which express RSV F or G envelope glycoproteins. However, the use of these vectors as vaccines to protect against RSV infection in animal studies has shown inconsistent results (Olmsted et al. 1986, Proc. Natl. Acad. Sci. 83:7462-7466; Collins et al., 1990, Vaccine 8:164-168).

Thus, efforts have turned to engineering recombinant RSV to generate vaccines. For a long time, negative-sense RNA viruses were refractory to study. Only recently has it been possible to recover negative strand RNA viruses using a recombinant reverse genetics approach (U.S. Pat. No. 5,166,057 to Palese et al.). Although this method was originally applied to engineer influenza viral genomes (Luytjes et al. 1989, Cell 59:1107-1113; Enami et al. 1990, Proc. Natl. Acad. Sci. USA 92: 11563-11567), it has been successfully applied to a wide variety of segmented and nonsegmented negative strand RNA viruses, including rabies (Schnell et al. 1994, EMBO J. 13: 4195-4203); VSV (Lawson et al., 1995, Proc. NatI. Acad. Sci USA 92: 4477-81); measles virus (Radecke et al., 1995, EMBO J. 14:5773-84); rinderpest virus (Baron & Barrett, 1997, J. Virol. 71: 1265-71); human parainfluenza virus (Hoffman & Baneree, 1997, J. Virol. 71:3272-7; Dubin et al., 1997, Virology 235:323-32); SV5 (He et al., 1997, Virology 237:249-60); respiratory syncytial virus (Collins et al. 1991, Proc. Nati. Acad. Sci. USA 88: 9663-9667) and Sendai virus (Park et al. 1991, Proc. Natl. Acad. Sci. USA 88:5537-5541; Kato et al. 1996, Genes to Cells 1:569-579). Although this approach has been used to successfully rescue RSV, a number of groups have reported that RSV is still refractory to study given several properties of RSV which distinguish it from the better characterized paramyxoviruses of the genera Paramyxovirus, Rubulavirus, and Morbillivirus. These differences include a greater number of RNAs, an unusual gene order at the 3' end of the genome, extensive strain-to-strain sequence diversity, several proteins not found in other nonsegmented negative strand RNA viruses and a requirement for the M2 protein (ORF1) to proceed with full processing of full length transcripts and rescue of a full length genome (Collins et al. PCT WO97/12032; Collins, P. L. et al. pp 1313-1357 of volume 1, Fields Virology, et al., Eds. (3rd ed., Raven Press, 1996).

3. SUMMARY OF THE INVENTION

The present invention relates to genetically engineered recombinant RS viruses and viral vectors which contain heterologous genes which for the use as vaccines. In accordance with the present invention, the recombinant RS viral vectors and viruses are engineered to contain heterologous genes, including genes of other viruses, pathogens, cellular genes, tumor antigens, or to encode combinations of genes from different strains of RSV.

Recombinant negative-strand viral RNA templates are described which may be used to transfect transformed cell that express the RNA dependent RNA polymerase and allow for complementation. Alternatively, a plasmid expressing the components of the RNA polymerase from an appropriate promoter can be used to transfect cells to allow for complementation of the negative-strand viral RNA templates. Complementation may also be achieved with the use of a helper virus or wild-type virus to provide the RNA dependent RNA polymerase. The RNA templates are prepared by transcription of appropriate DNA sequences with a DNA-directed RNA polymerase. The resulting RNA templates are of negative-or positive-polarity and contain appropriate terminal sequences which enable the viral RNA-synthesizing apparatus to recognize the template. Bicistronic mRNAs can be constructed to permit internal initiation of translation of viral sequences and allow for the expression of foreign protein coding sequences from the regular terminal initiation site, or vice versa.

As demonstrated by the examples described herein, recombinant RSV genome in the positive-sense or negative-sense orientation is co-transfected with expression vectors encoding the viral nucleocapsid (N) protein, the associated nucleocapsid phosphoprotein (P), the large (L) polymerase subunit protein, with or without the M2/ORF1 protein of RSV to generate infectious viral particles. Plasmids encoding RS virus polypeptides are used as the source of proteins which were able to replicate and transcribe synthetically derived RNPs. The minimum subset of RSV proteins needed for specific replication and expression of the viral RNP was found to be the three polymerase complex proteins (N, P and L). This suggests that the entire M2-1 gene function, supplied by a separate plasmid expressing M2-1, may not be absolutely required for the replication, expression and rescue of infectious RSV.

The expression products and/or chimeric virions obtained may advantageously be utilized in vaccine formulations. In particular, recombinant RSV genetically engineered to demonstrate an attenuated phenotype may be utilized as a live RSV vaccine. In another embodiment of the invention, recombinant RSV may be engineered to express the antigenic polypeptides of another strain of RSV (e.&., RSV G and F proteins) or another virus (e.g., an immunogenic peptide from gp120 of HIV) to generate a chimeric RSV to serve as a vaccine, that is able to elicit both vertebrate humoral and cell-mediated immune responses. The use of recombinant influenza or recombinant RSV for this purpose is especially attractive since these viruses demonstrate tremendous strain variability allowing for the construction of a vast repertoire of vaccine formulations. The ability to select from thousands of virus variants for constructing chimeric viruses obviates the problem of host resistance encountered when using other viruses such as vaccinia.

The present invention further relates to the attenuation of human respiratory syncytial virus by deletion of viral accessory gene(s) either singly or in combination.

The present invention further relates to the attenuation of human respiratory syncytial virus by mutagenesis of the viral M2-1 gene.

3.1. DEFINITIONS

As used herein, the following terms will have the meanings indicated: cRNA=anti-genomic RNA HA=hemagglutinin (envelope glycoprotein) HIV=human immunodeficiency virus L=large polymerase subunit M=matrix protein (lines inside of envelope) MDCK=Madin Darby canine kidney cells MDBK=Madin Darby bovine kidney cells moi=multiplicity of infection N=nucleocapsid protein NA=neuraminidase (envelope glycoprotein) NP=nucleoprotein (associated with RNA and required for polymerase activity) NS=nonstructural protein (function unknown) nt=nucleotide P=nucleocapsid phosphoprotein PA, PB1, PB2=RNA-directed RNA polymerase components RNP=ribonucleoprotein (RNA, PB2, PB1, PA and NP) rRNP=recombinant RNP RSV=respiratory syncytial virus vRNA=genomic virus RNA viral polymerase complex=PA, PB1, PB2 and NP WSN=influenza A/WSN/33 virus WSN-HK virus: reassortment virus containing seven genes from WSN virus and the NA gene from influenza A/HK/8/68 virus

4. DESCRIPTION OF THE FIGURES

FIG. 1. Schematic representation of the RSV/CAT construct (pRSVA2CAT) used in rescue experiments. The approximate 100 nt long leader and 200 nt long trailer regions of RSV were constructed by the controlled annealing of synthetic oligonucleotides containing partial overlapping complementarity. The overlapping leader oligonucleotides are indicated by the 1L-5L (SEQ ID NOs: 1-5) shown in the construct. The overlapping trailer nucleotides are indicated by the 1T-9T (SEQ ID NOs: 6-14) shown in the construct. The nucleotide sequences of the leader and trailer DNAs were ligated into purified CAT gene DNA at the indicate XbaI and PstI sites respectively. This entire construct was then ligated into KpnI/HindIII digested pUC19. The inclusion of a T7 promoter sequence and a HgaI site flanking the trailer and leader sequences, respectively, allowed in vitro synthesis of RSV/CAT RNA transcripts containing the precise genomic sequence 3' and 5' ends.

FIG. 2. Thin layer chromatogram (TLC) showing the CAT activity present in 293 cell extracts following infection and transfection with RNA transcribed from the RSV/CAT construct shown in FIG. 11 (SEQ ID NO:31). Confluent monolayers of 293 cells in six-well plates (-10.sup.6 cells) were infected with either RSV A2 or B9320 at an m.o.i. of 0.1-1.0 pfu cell. At 1 hour post infection cells were transfected with 5-10 .mu.g of CAT/RSV using the Transfect-Act.TM. protocol of Life Technologies. At 24 hours post infection the infected/transfected monolayers were harvested and processed for subsequence CAT assay according to Current Protocols in Molecular Biology, Vol. 1, Chapter 9.6.2; Gorman, et al., (1982) Mol. Cell. Biol. 2:1044-1051. Lanes 1, 2, 3 and 4 show the CAT activity present in (1) uninfected 293 cells, transfected with CAT/RSV-A2 infected 293 cells, co-infected with supernatant from (2) above. The CAT activity observed in each lane was produced from 1/5 of the total cellular extract from 10.sup.6 cells.

FIG. 3. Schematic representation of the RSV strain A2 genome showing the relative positions of the primer pairs used for the synthesis of cDNAs comprising the entire genome (SEQ ID NOs: 15-28). The endonuclease sites used to splice these clones together are indicated; these sites were present in the native RSV sequence and were included in the primers used for CDNA synthesis. Approximately 100 ng of viral genomic RNA was used in RT/PCR reactions for the separate synthesis of each of the seven cDNAs. The primers for the first and second strand CDNA synthesis from the genomic RNA template are also shown. For each cDNA, the primers for the first strand synthesis are nos. 1-7 and the primers for the second strand synthesis are nos. 1'-7'.

FIGS. 4A-C. Schematic representation of the RSV subgroup B strain B9320. BamHI sites were created in the oligonucleotide primers used for RT/PCR in order to clone the G and F genes from the B9320 strain into RSV subgroup A2 antigenomic CDNA (FIG. 4A). A cDNA fragment which contained G and F genes from 4326 nucleotides to 9387 nucleotides of A2 strain was first subcloned into pUC19 (pUCRVH). Bgl II sites were created at positions of 4630 (SH/G intergenic junction) (FIG. 4B) and 7554 (F/M2 intergenic junction (FIG. 4C). B93260 A-G and -F cDNA inserted into pUCR/H which is deleted of the A-G and F genes. The resulting antigenomic cDNA clone was termed as pRSVB-GF and was used to transfect Hep-2 cells to generate infectious RSVB-GF virus.

FIG. 5. Recombinant RSVB-GF virus was characterized by RT/PCR using RSV subgroup B specific primers. RSV subgroup B specific primers in the G region were incubated with aliquots of the recombinant RSV viral genomes and subjected to PCR. The PCR products were analyzed by electrophoresis on a 1% agarose gel and visualized by staining with ethidium bromide. As shown, no DNA product was produced in the RT/PCR reaction using RSV A2 as a template. However, a predicted product of 254 base pairs was seen in RT/PCR of RSVB-GF RNA and PCR control of plasmid pRSV-GF DNA as template, indicating the rescued virus contained G and F genes derived from B9320 virus.

FIGS. 6A-B. Identification of chimeric rRSVA2(B-G) by RT/PCR and Northern blot analysis of RNA expression. FIG. 6A. RT/PCT analysis of chimeric rRSV A2(B-G), in comparison with wild-type A2(A2). Virion RNA extracted from rRSVA2(B-G) (lanes 1, 2) and rRSVA2 (lanes 3,4) was reverse transcribed using a primer annealed to (-) sense vRNA in the RSV F gene in the presence (+) or absence (-) of reverse transcriptase (RT), followed by PCR with a primer fair flanking the B-G insertion site. No DNA was detected in RT/PCR when reverse transcriptase (RT) was absent (lanes 2,4). A cDNA fragment, which is about 1 kb bigger than the cDNA derived from A2, was produced from rRSVA(B-G). This longer PCR DNA product was digested by Stu I restriction enzyme unique to the inserted B-G gene (lane 5). 100 bp DNA size marker is indicated (M). FIG. 6B. Northern blot analysis of G mRNA expression. Hep2 cells were infected with RSV B9320, rRSVA2 and chimeric rRSVA2(B-G). At 48 hr postinfection, total cellular RNA was extracted and electrophoresed on a 1.2% agarose gel containing formaldehyde. RNA was transferred to Hybond Nylon membrane and the filter was hybridized with a .sup.32 P-labeled oligonucleotide probe specific for A2-G or specific for B9320-G mRNA. Both A2 G specific and B9320 G specific transcripts were detected in the rRSVA2 (B-G) infected cells. The run-off RNA transcript (G-M2) from rRSV A2 (B-G) infected cells is also indicated.

FIG. 7. Analysis of protein expression by rRSVA2 (B-G). Hep-2 cells were mock-infected (lanes 1, 5), infected with RSV B9320 (lanes 2, 6), rRSVA2 (lanes 3, 7) and rRSV A2 (B-G) (lanes 4, 8). At 14-18 hr postinfection, infected cells were labeled with .sup.35 S-promix and polypeptides were immunoprecipitated by goat polyclonal antiserum against RSV A2 strain (lanes 1-5) or by mouse polyclonal antiserum against RSV B9320 strain (lanes 5-8). Immunoprecipitated polypeptides were separated on a 10% polyacrylamide gel. Both RSV A2 specific G protein and RSV B9320 specific G protein were produced in rRSV A2 (B-G) infected cells. The G protein migration is indicated by *. Mobility of the F1 glycoprotein, and N, P, and M is indicated. Molecular sizes are shown on the left in kilodaltons.

FIG. 8. Plaque morphology of rRSV, rRSVC4G, rRSVA2(B-G) and wild-type A2 virus (wt A2). Hep-2 cells were infected with each virus and incubated at 35.degree. C. for six days. The cell monolayers were fixed, visualized by immunostaining, and photographed.

FIG. 9. Growth curve of rRSV, rRSVC4G, wild-type A2 RSV (wt A2) and chimeric rRSVA2(B-G). Hep-2 cells were infected with either virus at a moi of 0.5 and the medium was harvested at 24 hr intervals. The titer of each virus was determined in duplicate by plaque assay on Hep-2 cells and visualized by immunostaining.

FIG. 10. RSV L protein charged residue clusters targeted for site-directed mutagenesis (SEQ ID NO:29). Contiguous charged amino acid residues in clusters were converted to alanines by site-directed mutagenesis (SEQ ID NO:30) of the RSV L gene using the QuikChange site-directed mutagenesis kit (Stratagene).

FIG. 11. RSV L protein cysteine residues targeted for site-directed mutagenesis. Cysteine residues were converted to alanine-residues by site-directed mutagenesis of the RSV L gene using the QuikChange site-directed mutagenesis kit (Stratagene).

FIGS5. 12A-B. Identification RSV M2-2 and SH deletion mutants. Deletions in M2-2 were generated by Hind III digestion of pET(S/B) followed by recloning of a remaining Sac I to BamHI fragment into a full-length clone. Deletions in SH were generated by Sac I digestion of pET(A/S) followed by recloning of a remaining Avr II Sac I fragment into a full-length clone. FIG. 12A. Identification of the recovered rRSV.DELTA.SH and rRSVAM2-2 was performed by RT/PCR using primer pairs specific for the SH gene or M2-2 gene, respectively. FIG. 12B rRSV.DELTA.SH.DELTA.M2-2 was also detected by RT/PCR using primer pairs specific for the M2-2 and SH genes. RT/PCR products were run on an ethidium bromide agarose gel and bands were visualized by ultraviolet (UV) light.

FIGS. 13A-B. Structure of rA2.DELTA.M2-2 genome and recovery of rA2.DELTA.M2-2. (A). Sequences shown is the region of the M2 gene that M2-1 and M2-2 open reading frames overlap. Total of 234 nt that encode the C-terminal 78 amino acids of M2-2 was deleted through the introduced Hind III sites (underlined). The N-terminal 12 amino acid residues of the M2-2 open reading frame (SEQ ID NO:49) are maintained as it overlaps with the M2-1 gene (SEQ ID NO:48). (B). RT/PCR products of rA2.DELTA.M2-2 and rA2 viral RNA using primers V1948 and V1581 in the presence (+) or absence (-) of reverse transcriptase (RT). The size of the DNA product derived from rA2 or rA2.DELTA.M2-2 is indicated.

FIGS. 14A-B. Viral RNA expression by rA2.DELTA.M2-2 and rA2. (A). Total RNA was extracted from rA2 or rA2.DELTA.M2-2 infected Vero cells at 48 hr postinfection, separated by electrophoresis on 1.2% agarose/2.2 M formaldehyde gels and transferred to nylon membranes. Each blot was hybridized with a Dig-labeled riboprobe specific for the M2-2, M2-1, F, SH, G or N gene. The size of the RNA marker is indicated on the left. (B). Hep-2 and Vero cells were infected with rA2 or rA2.DELTA.M2-2 for 24 hr and total cellular RNA was extracted. RNA Northern blot was hybridized with a .sup.32 P-labeled riboprobe specific to the negative sense F gene to detect viral genomic RNA or a .sup.32 P-labeled riboprobe specific to the positive sense F gene to detect viral antigenomic RNA and F mRNA. The top panel of the Northern blot on the right was taken from the top portion of the gel shown in the lower panel and was exposed for 1 week to show antigenome. The lower panel of the Northern blot was exposed for 3 hr to show the F mRNA. The genome, antigenome, F mRNA and dicistronic F-M2 RNA are indicated.

FIGS. 15A-B. Viral protein expression in rA2 .DELTA.M2-2 and rA2 infected cells. (A). Mock-infected, rA2.DELTA.M2-2 and rA2 infected Vero cells were metabolically labeled with .sup.35 S-promix (100 .mu.Ci/ml) between 14 to 18 hr postinfection. Cell lysates were prepared for immunoprecipitation with goat polyclonal anti-RSV or rabbit polyclonal anti-M2-2 antisera Immunoprecipitated polypeptides were separated on a 17.5% polyacrylamide gel containing 4 M urea and processed for autoradiography. The positions of each viral protein are indicated on the right and the molecular weight size markers are indicated on the left. (B). Protein synthesis kinetics in Hep-2 and Vero cells by Western blotting. Hep-2 and Vero cells were infected with rA2 or rA2.DELTA.M2-2 and at 10 hr, 24 hr, or 48 hr postinfection, total infected cellular polypeptides were separated on a 17.5% polyacrylamide gel containing 4 M urea. Proteins were transferred to a nylon membrane and the blot probed with polyclonal antisera against M2-1, NS1 or SH as indicated.

FIG. 16. Plaque morphology of rA2.DELTA.M2-2 and rA2. Hep-2 or Vero cells were infected with rA2.DELTA.M2-2 or rA2 under semisolid overlay composed of 1% methylcellulose and 1.times.L15 medium containing 2% FBS for 5 days. Virus plaques were visualized by immunostaining with a goat polyclonal anti-RSV antiserum and photographed under microscope.

FIG. 17. Growth curves of rA2.DELTA.M2-2 in Hep-2 and Vero cells. Vero cells (A) or Hep-2 cells (B) were infected with rA2.DELTA.M2-2 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells. Virus titer at each time point is average of two experiments.

FIG. 18. Northern blot analysis of rA2.DELTA.NS1, rA2.DELTA.NS2 and rA2.DELTA.NS1.DELTA.NS2. Total cellular RNA was extracted from rA2, rA2.DELTA.NS1, rA2.DELTA.NS2 and rA2.DELTA.NS1.DELTA.NS2 infected Vero cells at 24 hr postinfection, separated by electrophoresis on 1.2% agarose/2.2 M formaldehyde gels and transferred to nylon membranes. Each blot was hybridized with a Dig-labeled riboprobe specific for the NS1, NS2, or M2-2 gene as indicated.

FIG. 19. Plaque morphology of deletion mutants. Hep-2 or Vero cells were infected with each deletion mutant as indicated under semisolid overlay composed of 1% methylcellulose and 1.times.L15 medium containing 2% FBS for 6 days. Virus plaques were visualized by immunostaining with a goat polyclonal anti-RSV antiserum and photographed under microscope.

FIG. 20. Growth curves of rA2.DELTA.NS1 in Vero cells. Vero cells were infected with rA2 .DELTA.NS1 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells.

FIG. 21. Growth curves of rA2.DELTA.NS2 in Vero cells. Vero cells were infected with rA2 .DELTA.NS2 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells.

FIG. 22. Growth curves of rA2.DELTA.SH.DELTA.M2-2 in Vero cells. Vero cells were infected with rA2.DELTA.SH.DELTA.M2-2 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells.

FIG. 23. Northern blot analysis of several deletion mutants. Total cellular RNA was extracted from Vero cells infected with each deletion mutant as indicated at 24 hr postinfection, separated by electrophoresis on 1.2% agarose/2.2 M formaldehyde gels and transferred to nylon membranes. Each blot was hybridized with a Dig-labeled riboprobe specific for the NS 1, NS2, SH or M2-2 gene as indicated.

FIG. 24. Growth curves of rA2.DELTA.NS2.DELTA.M2-2 in Vero cells. Vero cells were infected with rA2.DELTA.NS2.DELTA.M2-2 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells.

FIG. 25. Growth curves of rA2.DELTA.NS1.DELTA.NS2 in Vero cells. Vero cells were infected with rA2.DELTA.NS1.DELTA.NS2 or rA2 at m.o.i. of 0.5, and aliquots of medium were harvested at 24 hr intervals as indicated. The virus titers were determined by plaque assay in Vero cells.

5. DESCRIPTION OF THE INVENTION

The present invention relates to genetically engineered recombinant RS viruses and viral vectors which express heterologous genes or mutated RS viral genes or a combination of viral genes derived from different strains of RS virus. The invention relates to the construction and use of recombinant negative strand RS viral RNA templates which may be used with viral RNA-directed RNA polymerase to express heterologous gene products in appropriate host cells and/or to rescue the heterologous gene in virus particles. The RNA templates of the present invention may be prepared by transcription of appropriate DNA sequences using a DNA-directed RNA polymerase such as bacteriophage T7, T3 or Sp6 polymerase. The recombinant RNA templates may be used to transfect continuous/transfected cell lines that express the RNA-directed RNA polymerase proteins allowing for complementation.

The invention is demonstrated by way of working examples in which infectious RSV is rescued from CDNA containing the RSV genome in the genomic or antigenomic sense introduced into cells expressing the N, P, and L proteins of the RSV polyrnerase complex. The working examples further demonstrate that expression of M2-1 expression plasmid is not required for recovery of infectious RSV from cDNA which is contrary to what has been reported earlier (Collins et al., 1995, Proc. Natl. Acad. Sci. USA 92:11563-7). Furthermore, the deletion of the M2-ORF2 from recombinant RSV cDNA results in the rescue of attenuated RSV particles. M2-2-deleted-RSV is an excellent vehicle to generate chimeric RSV encoding heterologous gene products, these chimeric viral vectors and rescued virus particles have utility as expression vectors for the expression of heterologous gene products and as live attenuated RSV vaccines expressing either RSV antigenic polypeptides or antigenic polypeptides of other viruses.

The invention is further demonstrated by way of working examples in which a cDNA clone which contained the complete genome of RSV, in addition to a T7 promoter, a hepatitis delta virus ribozyme and a T7 terminator, is used to generate an infectious viral particle when co-transfected with expression vectors encoding the N, P, L proteins of RSV. In addition, the working examples describe RNA transcripts of cloned DNA containing the coding region--in negative sense orientation--of the chloramphenicol-acetyl-transferase (CAT) gene or the green fluorescent protein (GFP) gene flanked by the 5' terminal and 3' terminal nucleotides of the RSV genome. The working examples further demonstrate that an RSV promoter mutated to have increased activity resulted in rescue of infectious RSV particles from a full length RSV cDNA with high efficiency. These results demonstrate the successful use of recombinant viral negative strand templates and RSV polymerase with increased activity to rescue RSV. This system is an excellent tool to engineer RSV viruses with defined biological properties, e.g. live-attenuated vaccines against RSV, and to use recombinant RSV as an expression vector for the expression of heterologous gene products.

This invention relates to the construction and use of recombinant negative strand viral RNA templates which may be used with viral RNA-directed RNA polymerase to express heterologous gene products in appropriate host cells, to rescue the heterologous gene in virus particles and/or express mutated or chimeric recombinant negative strand viral RNA templates (see U.S. Pat. No. 5,166,057 to Palese et al., incorporated herein by reference in its entirety). In a specific embodiment of the invention, the heterologous gene product is a peptide or protein derived from another strain of the virus or another virus. The RNA templates may be in the positive or negative-sense orientation and are prepared by transcription of appropriate DNA sequences using a DNA-directed RNA polymerase such as bacteriophage T7, T3 or the Sp6 polymerase.

The ability to reconstitute RNP's in vitro allows the design of novel chimeric influenza and RSV viruses which express foreign genes. One way to achieve this goal involves modifying existing viral genes. For example, the G or F gene may be modified to contain foreign sequences, such as the HA gene of influenza in its external domains. Where the heterologous sequence are epitopes or antigens of pathogens, these chimeric viruses may be used to induce a protective immune response against the disease agent from which these determinants are derived. For example, a chimeric RNA may be constructed in which a coding sequence derived from the gp 120 coding region of human immunodeficiency virus was inserted into the coding sequence of RSV, and chimeric virus produced from transfection of this chimeric RNA segment into a host cell infected with wild-type RSV.

In addition to modifying genes coding for surface proteins, genes coding for nonsurface proteins may be altered. The latter genes have been shown to be associated with most of the important cellular immune responses in the RS virus system. Thus, the inclusion of a foreign determinant in the G or F gene of RSV may--following infection--induce an effective cellular immune response against this determinant. Such an approach may be particularly helpful in situations in which protective immunity heavily depends on the induction of cellular immune responses (e.g., malaria, etc.).

The present invention also relates to attenuated recombinant RSV produced by introducing specific mutations in the genome of RSV which results in an amino acid change in an RSV protein, such as a polymerase protein, which results in an attenuated phenotype.

The present invention also further relates to the generation of attenuated recombinant RSV produced by introducing specific deletions of viral accessory gene(s) either singly or in combination. Specifically, the present invention relates to the generation of attenuated recombinant RSV bearing a deletion of either the M2-2, SH, NS1, or NS2 viral accessory gene. Additionally, the present invention specifically relates to the generation of attenuated recombinant RSV bearing a combination deletion of either the M2-2/SH viral accessory genes, the M2-2/NS2 viral accessory genes, the NS1/NS2 viral accessory genes, the NS1/NS2 viral accessory genes, the SHNS1 viral accessory genes, the SH/NS2 viral accessory genes, or the SH/NS1/NS2 viral accessory genes.

The invention is demonstrated by way of the working examples presented herein in which infectious attenuated RSV is rescued from RSV cDNA bearing deletions in the M2-2, SH/NS2, or NS2 viral accessory gene(s) either singly or in combination. Such M2-2, SH, NS1, NS2, M2-2/SH, M2-2/NS2, NS1/NS2, SH/NS1, SH/NS2, or SH/NS1/NS2-deleted RSV represent excellent vehicles for the generation of live attenuated RSV vaccines. Additionally, such M2-2, SH, NS1, NS2, M2-2/SH, M2-2/NS2, NS/NS2, SH/NS1, SH/NS2, or SH/NS1/NS2-deleted RSV represent excellent vehicles for the generation of chimeric RSV encoding heterologous gene products in place of either the M2-2, SH, NS1, NS2, M2-2/SH, M2-NS2NS2, NS1/NS2, SH/NS1, SH/NS2, or SH/NS1/NS2 genes. These chimeric RSV-based viral vectors and rescued infectious attenuated viral particles thus have utility as expression vectors for the expression of heterologous gee products and as live attenuated RSV vaccines expressing either RSV antigenic polypeptides or antigenic polypeptides of heterologous viruses.

The present invention further relates to the generation of attenuated recombinant RSV produced by introducing specific mutations into the M2-1 gene. Specifically, the present invention relates to the generation of attenuated recombinant RSV bearing a mutation of the M2-1 gene introduced by one or more techniques, including, without limitation, cysteine scanning mutagenesis and C-terminal truncations of the M2-1 protein.

5.1. Construction of the Recombinant RNA Templates

Heterologous gene coding sequences flanked by the complement of the viral polymerase binding site/promoter, e.g. the complement of the 3'-RSV termini or the 3'- and 5'-RSV termini may be constructed using techniques known in the art. Heterologous gene coding sequences may also be flanked by the complement of the RSV polymerase binding site/promoter, e.g., the leader and trailer sequence of RSV using techniques known in the art. Recombinant DNA molecules containing these hybrid sequences can be cloned and transcribed by a DNA-directed RNA polymerase, such as bacteriophage T7, T3 or the Sp6 polymerase and the like, to produce the recombinant RNA templates which possess the appropriate viral sequences that allow for viral polymerase recognition and activity.

In a preferred embodiment of the present invention, the heterologous sequences are derived from the genome of another strain of RSV, e.g., the genome of RSV A strain is engineered to include the nucleotide sequences encoding the antigenic polypeptides G and F of RSV B strain, or fragments thereof. In such an embodiment of the invention, heterologous coding sequences from another strain of RSV can be used to substitute for nucleotide sequences encoding antigenic polypeptides of the starting strain, or be expressed in addition to the antigenic polypeptides of the parent strain, so that a recombinant RSV genome is engineered to express the antigenic polypeptides of one, two or more strains of RSV.

In yet another embodiment of the invention, the heterologous sequences are derived from the genome of any strain of influenza virus. In accordance with the present invention, the heterologous coding sequences of influenza may be inserted within a RSV coding sequence such that a chimeric gene product is expressed which contains the heterologous peptide sequence within the RSV viral protein. In either embodiment, the heterologous sequences derived from the genome of influenza may include, but are not limited to HA, NA, PB1, PB2, PA, NS1 or NS2.

In one specific embodiment of the invention, the heterologous sequences are derived from the genome of human immunodeficiency virus (HIV), preferably human immunodeficiency virus-1 or human immunodeficiency virus-2. In another embodiment of the invention, the heterologous coding sequences may be inserted within an RSV gene coding sequence such that a chimeric gene product is expressed which contains the heterologous peptide sequence within the influenza viral protein. In such an embodiment of the invention, the heterologous sequences may also be derived from the genome of a human immunodeficiency virus, preferably of human immunodeficiency virus-1 or human immunodeficiency virus-2.

In instances whereby the heterologous sequences are HIV-derived, such sequences may include, but are not limited to, sequences derived from the env gene (i.e., sequences encoding all or part of gp160, gp120, and/or gp41), the pol gene (i.e., sequences encoding all or part of reverse transcriptase, endonuclease, protease, and/or integrase), the gag gene (i.e., sequences encoding all or part of p7, p6, p55, p17/18, p24/25) tat, rev, nef, vif, vpu, vpr, and/or vpx.

One approach for constructing these hybrid molecules is to insert the heterologous coding sequence into a DNA complement of a RSV genomic RNA so that the heterologous sequence is flanked by the viral sequences required for viral polymerase activity; ie., the viral polymerase binding sitelpromoter, hereinafter referred to as the viral polymerase binding site. In an alternative approach, oligonuclcotides encoding the viral polymerase binding site, e.g., the complement of the 3'-terminus or both termini of the virus genomic segments can be ligated to the heterologous coding sequence to construct the hybrid molecule. The placement of a foreign gene or segment of a foreign gene within a target sequence was formerly dictated by the presence of appropriate restriction enzyme sites within the target sequence. However, recent advances in molecular biology have lessened this problem greatly. Restriction enzyme sites can readily be placed anywhere within a target sequence through the use of site-directed mutagenesis (eg., see, for example, the techniques described by Kunkel, 1985, Proc. Natl. Acad. Sci. U.S.A. 82;488). Variations in polymerase chain reaction (PCR) technology, described infra, also allow for the specific insertion of sequences (ie., restriction enzyme sites) and allow for the facile construction of hybrid molecules. Alternatively, PCR reactions could be used to prepare recombinant templates without the need of cloning. For example, PCR reactions could be used to prepare double-stranded DNA molecules containing a DNA-directed RNA polymerase promoter (e.g., bacteriophage T3, T7 or Sp6) and the hybrid sequence containing the heterologous gene and the influenza viral polymerase binding site. RNA templates could then be transcribed directly from this recombinant DNA. In yet another embodiment, the recombinant RNA templates may be prepared by ligating RNAs specifying the negative polarity of the heterologous gene and the viral polymerase binding site using an RNA ligase. Sequence requirements for viral polymerase activity and constructs which may be used in accordance with the invention are described in the subsections below.

5.1.1. Insertion of the Heterologous Genes

The gene coding for the L protein contains a single open reading frame. The genes coding for M2 contain two open reading frames for ORF1 and 2, respectively. NS1 and NS2 are coded for by two genes, NS1 and NS2. The G and F proteins, coded for by separate genes, are the major surface glycoproteins of the virus. Consequently, these proteins are the major targets for the humoral immune response after infection. Insertion of a foreign gene sequence into any of these coding regions could be accomplished by either an addition of the foreign sequences to be expressed or by a complete replacement of the viral coding region with the foreign gene or by a partial replacement. The heterologous sequences inserted into the RSV genome may be any length up to approximately 5 kilobases. Complete replacement would probably best be accomplished through the use of PCR-directed mutagenesis.

Alternatively, a bicistronic mRNA could be constructed to permit internal initiation of translation of viral sequences and allow for the expression of foreign protein coding sequences from the regular terminal initiation site. Alternatively, a bicistronic mRNA sequence may be constructed wherein the viral sequence is translated from the regular terminal open reading frame, while the foreign sequence is initiated from an internal site. Certain internal ribosome entry site (IRES) sequences may be utilized. The IRES sequences which are chosen should be short enough to not interfere with RS virus packaging limitations. Thus, it is preferable that the IRES chosen for such a bicistronic approach be no more than 500 nucleotides in length, with less than 250 nucleotides being preferred. Further, it is preferable that the IRES utilized not share sequence or structural homology with picornaviral elements. Preferred IRES elements include, but are not limited to the mammalian BiP IRES and the hepatitis C virus IRES.

5.2. Expression of Heterologous Gene Products Using Recombinant RNA Template

The recombinant templates prepared as described above can be used in a variety of ways to express the heterologous gene products in appropriate host cells or to create chimeric viruses that express the heterologous gene products. In one embodiment, the recombinant template can be combined with viral polymerase complex purified infra, to produce rRNPs which are infectious. To this end, the recombinant template can be transcribed in the presence of the viral polymerase complex. Alternatively, the recombinant template may be mixed with or transcribed in the presence of viral polymerase complex prepared using recombinant DNA methods (e.g. see Kingsbury et al., 1987, Virology 156:396-403). In yet another embodiment, the recombinant template can be used to transfect appropriate host cells to direct the expression of the heterologous gene product at high levels. Host cell systems which provide for high levels of expression include continuous cell lines that supply viral functions such as cell lines superinfected with RSV, cell lines engineered to complement RSV viral functions, etc. p 5.3. Preparation of Chimeric Negative Strand RNA Virus

In order to prepare chimeric virus, reconstituted RNPs containing modified RSV RNAs or RNA coding for foreign proteins may be used to transfect cells which are also infected with a "parent" RSV virus. Alternatively, the reconstituted RNP preparations may be mixed with the RNPs of wild type parent virus and used for transfection directly. Following transfection, the novel viruses may be isolated and their genomes identified through hybridization analysis. In additional approaches described herein for the production of infectious chimeric virus, rRNPs may be replicated in host cell systems that express the RSV or influenza viral polymerase proteins (es, in virus/host cell expression systems; transformed cell lines engineered to express the polymerase proteins, etc.), so that infectious chimeric virus are rescued; in this instance, helper virus need not be utilized since this function is provided by the viral polymerase proteins expressed. In a particularly desirable approach, cells infected with rRNPs engineered for all eight influenza virus segments may result in the production of infectious chimeric virus which contain the desired genotype; thus eliminating the need for a selection system.

Theoretically, one can replace any one of the genes of RSV, or part of any one of the RSV genes, with the foreign sequence. However, a necessary part of this equation is the ability to propagate the defective virus (defective because a normal viral gene product is missing or altered). A number of possible approaches exist to circumvent this problem.

A third approach to propagating the recombinant virus may involve co-cultivation with wild-type virus. This could be done by simply taking recombinant virus and co-infecting cells with this and another wild-type virus (preferably a vaccine strain). The wild-type virus should complement for the defective virus gene product and allow growth of both the wild-type and recombinant virus. This would be an analogous situation to the propagation of defective-interfering particles of influenza virus (Nayak et al., 1983, In: Genetics of Influenza Viruses, P. Palese and D. W. Kingsbury, eds., Springer-Verlag, Vienna, pp. 255-279). In the case of defective-interfering viruses, conditions can be modified such that the majority of the propagated virus is the defective particle rather than the wild-type virus. Therefore this approach may be useful in generating high titer stocks of recombinant virus. However, these stocks would necessarily c