Lineage-specific adjacent IFNG and IL26 genes share a common distal enhancer element.

Certain groups of physically linked genes remain linked over long periods of evolutionary time. The general view is that such evolutionary conservation confers 'fitness' to the species. Why gene order confers 'fitness' to the species is incompletely understood. For example, linkage of IL26 and IFNG is preserved over evolutionary time yet Th17 lineages express IL26 and Th1 lineages express IFNG. We considered the hypothesis that distal enhancer elements may be shared between adjacent genes, which would require linkage be maintained in evolution. We test this hypothesis using a bacterial artificial chromosome transgenic model with deletions of specific conserved non-coding sequences. We identify one enhancer element uniquely required for IL26 expression but not for IFNG expression. We identify a second enhancer element positioned between IL26 and IFNG required for both IL26 and IFNG expression. One function of this enhancer is to facilitate recruitment of RNA polymerase II to promoters of both genes. Thus, sharing of distal enhancers between adjacent genes may contribute to evolutionary preservation of gene order.

Virus replication in engineered human cells that do not respond to interferons.

The V protein of the paramyxovirus simian virus 5 blocks interferon (IFN) signaling by targeting STAT1 for proteasome-mediated degradation. Here we report on the isolation of human cell lines that express the V protein and can no longer respond to IFN. A variety of viruses, particularly slow-growing wild-type viruses and vaccine candidate viruses (which are attenuated due to mutations that affect virus replication, virus spread, or ability to circumvent the IFN response), form bigger plaques and grow to titers that are increased as much as 10- to 4,000-fold in these IFN-nonresponsive cells. We discuss the practical applications of using such cells in vaccine development and manufacture, virus diagnostics and isolation of newly emerging viruses, and studies on host cell tropism and pathogenesis.

Rescue of bovine respiratory syncytial virus from cloned cDNA: entire genome sequence of BRSV strain A51908.

Infectious bovine respiratory syncytial virus (BRSV) was produced by intracellular co-expression of five plasmid borne cDNAs, each under the control of a T7 RNA polymerase promoter. These separately encoded a full-length, genetically-marked copy of BRSV antigenome along with either BRSV or human respiratory syncytial virus (HRSV) support plasmids, which express N, P, L and M2-1 proteins. HEp2 cells were used in transfection and recombinant vaccinia virus (MVA-T7) provided T7 RNA polymerase to drive the transcription. The recovery of recombinant BRSV (rBRSV) was confirmed by immunological staining of plaques, restriction enzyme digestion and nucleotide sequencing of PCR fragments carrying the genetic markers from the rescued virus. The rBRSV was indistinguishable from its parental wild-type virus in its growth characteristics in cell culture. The present work has completed the entire genome sequence of BRSV strain A51908 (15,140 nt) and has also identified changes in sequence and growth characteristics in cell culture from the original BRSV strain A51908 laboratory isolate.

Contribution of the respiratory syncytial virus G glycoprotein and its secreted and membrane-bound forms to virus replication in vitro and in vivo.

The surface glycoproteins of viruses can play important roles in viral attachment, entry, and morphogenesis. Here, we investigated the role of the attachment G glycoprotein of human respiratory syncytial virus (RSV) in viral infection. RSV G is produced both as a complete, transmembrane form and as an N-terminally truncated form that is secreted. Using reverse genetics, we created mutant recombinant RSVs (rRSV) that do not express G (DeltaG) or express either the secreted or the membrane-bound form of G only (sG and mG, respectively). In Vero cells, the DeltaG virus formed plaques and grew as efficiently as wild-type rRSV and mG. In contrast, DeltaG replicated less efficiently and did not form distinct plaques in HEp-2 cells. This defect was primarily at the level of the initiation of infection, with only a minor additional effect at the level of packaging. Replication of DeltaG in the respiratory tract of mice was very highly restricted, indicating that G is important in vivo. Although the G protein expressed by the sG virus was confirmed to be secreted, this virus grew at least as efficiently as wild-type in HEp-2 cells and was only moderately attenuated in vivo. Thus, the G protein was important for efficient replication in HEp-2 cells and in vivo, but this function could be supplied in large part by the secreted form and thus does not require the cytoplasmic and transmembrane domains. Amino acids 184-198 have been identified as the major heparin-binding domain of the G protein and were implicated in mediating binding to cells [S. A. Feldman et al., 1999, J. Virol. 73, 6610-6617]. Heparin-like glycosaminoglycans also appeared to be important for infection in vitro by direct clinical isolates of RSV. Deletion of amino acids 187-197 from rRSV did not reduce its sensitivity to neutralization in vitro by incubation with soluble heparin, did not reduce its efficiency of growth in vitro, and resulted in only a modest reduction in vivo. Thus, the putative heparin-binding domain is not the sole determinant of heparin sensitivity and is not a critical functional domain.

Granulocyte-macrophage colony-stimulating factor expressed by recombinant respiratory syncytial virus attenuates viral replication and increases the level of pulmonary antigen-presenting cells.

An obstacle to developing a vaccine against human respiratory syncytial virus (RSV) is that natural infection typically does not confer solid immunity to reinfection. To investigate methods to augment the immune response, recombinant RSV (rRSV) was constructed that expresses murine granulocyte-macrophage colony-stimulating factor (mGM-CSF) from a transcription cassette inserted into the G-F intergenic region. Replication of rRSV/mGM-CSF in the upper and lower respiratory tracts of BALB/c mice was reduced 23- to 74- and 5- to 588-fold, respectively, compared to that of the parental rRSV. Despite this strong attenuation of replication, the level of RSV-specific serum antibodies induced by rRSV/mGM-CSF was comparable to, or marginally higher than, that of the parental rRSV. The induction of RSV-specific CD8(+) cytotoxic T cells was moderately reduced during the initial infection, which might be a consequence of reduced antigen expression. Mice infected with rRSV/mGM-CSF had elevated levels of pulmonary mRNA for gamma interferon (IFN-gamma) and interleukin 12 (IL-12) p40 compared to animals infected by wild-type rRSV. Elevated synthesis of IFN-gamma could account for the restriction of RSV replication, as was observed previously with an IFN-gamma-expressing rRSV. The accumulation of total pulmonary mononuclear cells and total CD4(+) T lymphocytes was accelerated in animals infected with rRSV/mGM-CSF compared to that in animals infected with the control virus, and the level of IFN-gamma-positive or IL-4-positive pulmonary CD4(+) cells was elevated approximately twofold. The number of pulmonary lymphoid and myeloid dendritic cells and macrophages was increased up to fourfold in mice infected with rRSV/mGM-CSF compared to those infected with the parental rRSV, and the mean expression of major histocompatibility complex class II molecules, a marker of activation, was significantly increased in the two subsets of dendritic cells. Enhanced antigen presentation likely accounts for the maintenance of a strong antibody response despite reduced viral replication and would be a desirable property for a live attenuated rRSV vaccine.

A chimeric human-bovine parainfluenza virus type 3 expressing measles virus hemagglutinin is attenuated for replication but is still immunogenic in rhesus monkeys.

The chimeric recombinant virus rHPIV3-N(B), a version of human parainfluenza virus type 3 (HPIV3) that is attenuated due to the presence of the bovine PIV3 nucleocapsid (N) protein open reading frame (ORF) in place of the HPIV3 ORF, was modified to encode the measles virus hemagglutinin (HA) inserted as an additional, supernumerary gene between the HPIV3 P and M genes. This recombinant, designated rHPIV3-N(B)HA, replicated like its attenuated rHPIV3-N(B) parent virus in vitro and in the upper and lower respiratory tracts of rhesus monkeys, indicating that the insertion of the measles virus HA did not further attenuate rHPIV3-N(B) in vitro or in vivo. Monkeys immunized with rHPIV3-N(B)HA developed a vigorous immune response to both measles virus and HPIV3, with serum antibody titers to both measles virus (neutralizing antibody) and HPIV3 (hemagglutination inhibiting antibody) of over 1:500. An attenuated HPIV3 expressing a major protective antigen of measles virus provides a method for immunization against measles by the intranasal route, a route that has been shown with HPIV3 and respiratory syncytial virus vaccines to be relatively refractory to the neutralizing and immunosuppressive effects of maternally derived virus-specific serum antibodies. It should now be possible to induce a protective immune response against measles virus in 6-month-old infants, an age group that in developing areas of the world is not responsive to the current measles virus vaccine.

Synergistic effects of gene-end signal mutations and the M2-1 protein on transcription termination by respiratory syncytial virus.

Individual mononegavirus genes terminate with a short cis-acting element, the gene-end (GE) signal, that directs polyadenylation and termination and might also influence the efficiency of reinitiation at the next downstream gene. The 12-13 nucleotide (nt) GE signals of human respiratory syncytial virus (RSV) consist of a conserved pentanucleotide (3'-UCAAU, negative sense), followed by a 3-nt middle region that is AU-rich but otherwise not conserved, followed by a 4- or 5-nt poly(U) region that is thought to generate the poly(A) tail of the encoded mRNA by reiterative copying. Most of the naturally occurring differences in the GE signals of the various RSV genes occur in the "middle" and "poly(U)" regions. We mutated a copy of the fusion protein (F) GE signal that was positioned at the end of the promoter-proximal gene of a tricistronic minigenome and evaluated the effect of these mutations on RSV transcription in a plasmid-initiated, intracellular assay. Mutations confirmed the importance of the middle region's AU-rich nature and 3-nt length, and the poly(U) tract's 4-nt minimum functional length, with maximal termination efficiency observed at five U residues. Nt assignments other than U at position 13 also affected the efficiency of termination, showing that this position is part of the functional 13-nt GE signal. These results indicate that differences in nt assignments in the middle and poly(U) regions of the GE signal, which occur frequently in nature, affect the efficiency of termination. Unexpectedly, the ability of certain mutations to inhibit termination was completely dependent on coexpression of the M2-1 protein, and in many other cases the inhibitory effect of the mutation was greatly enhanced in the presence of M2-1. Thus, M2-1 appears to have the effect of altering the polymerase such that it ignores suboptimal GE signals. Interestingly, certain mutations that greatly decreased the efficiency of termination in the absence of M2-1 did not have much effect on the expression of the second gene, implying that correct termination and/or polyadenylation at the upstream gene is not obligatory for reinitiation at the next downstream gene.

Deletion and substitution analysis defines regions and residues within the phosphoprotein of bovine respiratory syncytial virus that affect transcription, RNA replication, and interaction with the nucleoprotein.

The phosphoprotein (P) of bovine respiratory syncytial virus (BRSV) is a multifunctional protein that plays a central role in transcription and replication of the viral genomic RNA. To investigate the domains and specific residues involved in different activities of the P protein, we generated a total of 22 deletion and 17 point mutants of the P protein. These mutants were characterized using an intracellular BRSV-CAT minigenome replication system for the ability to (1) direct minigenome transcription, (2) direct minigenome replication, and (3) form complexes with nucleocapsid protein (N) and large polymerase protein (L). These studies revealed that all the regions of P protein except amino acids 41-80 are essential for minigenome transcription and replication. Interestingly, amino acids 41-60 appeared to contain sequences that negatively regulate transcription and replication. Analysis of the N- or C-terminal ends indicated that deletion of up to 3 amino acids from the N- or C-terminus completely ablated the replication, while leaving substantial residual transcription. Single amino acid substitutions within the N-terminal 4 or C-terminal 13 amino acids showed that substitution at position 2, 4, 234, 236, 238, 240, or 241 was highly inhibitory to both transcription and replication, whereas substitution at position 3 was highly inhibitory to replication while leaving substantial residual transcription. Substitution of serine residues at the C-terminus indicated that loss of phosphorylation sites did not appear to have any effect on transcription and replication. Coimmunoprecipitation of P-N and P-L complexes with P-specific antiserum revealed that substitution mutations at the N- or C-terminus did not affect binding to N and L proteins, except that substitution mutation at C-terminus position 234, 236, 238, 240, or 241 affected binding to N protein by 10-fold.

Construction of a live-attenuated bivalent vaccine virus against human parainfluenza virus (PIV) types 1 and 2 using a recombinant PIV3 backbone.

PIV1 and PIV2 are important agents of pediatric respiratory tract disease. We are developing live-attenuated vaccines against these viruses. We earlier constructed a PIV3/PIV1 antigenic chimeric virus, designated rPIV3-1, in which the hemagglutinin-neuraminidase (HN) and fusion (F) proteins of wild type rPIV3 were replaced by their PIV1 counterparts. In the present study, rPIV3-1 was used as a vector to express the HN protein of PIV2 to generate a single virus capable of inducing immunity to both PIV1 and PIV2. The PIV2 HN open reading frame was expressed from an extra gene cassette, under the control of PIV3 cis-acting transcription signals, inserted between the F and HN genes of rPIV3-1. The recombinant derivative, designated rPIV3-1.2HN, was readily recovered and exhibited a level of temperature sensitivity and in vitro growth similar to that of its parental virus. The rPIV3-1.2HN virus was restricted in replication in both the upper and lower respiratory tracts of hamsters compared with rPIV3-1, identifying an attenuating effect of the PIV2 HN insert in hamsters. rPIV3-1.2HN elicited serum antibodies to both PIV1 and PIV2 and induced resistance against challenge with wild type PIV1 or PIV2. Thus, rPIV3-1.2HN, a virus attenuated solely by the insertion of the PIV2 HN gene, functioned as a live attenuated bivalent vaccine candidate against both PIV1 and PIV2.

RhoA is activated during respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is an important human pathogen that can cause severe and life-threatening respiratory infections in infants and immunocompromised adults. We have recently shown the RSV F glycoprotein, which mediates viral fusion and entry, interacts with the cellular protein RhoA in two-hybrid and in vitro binding assays. Whether this interaction occurs in living cells remains an open question. However, because RhoA signaling is associated with many cellular functions relevant to RSV pathogenesis such as actin cytoskeleton organization, expression of proinflammatory cytokines, and smooth muscle contraction, we asked whether RhoA activation occurred during RSV infection of HEp-2 cells. We found that the amount of isoprenylated and membrane-bound RhoA in RSV-infected cultures was increased. Further evidence of RhoA activation was demonstrated by downstream signaling activity mediated by RhoA. There was an increase in p130(cas) phosphorylation during RSV infection, which was prevented by Y-27632, a specific inhibitor of Rho kinase, or lovastatin, an HMG-CoA reductase inhibitor that reduces the synthesis of groups needed for isoprenylation. In addition, RSV infection of HEp-2 cells resulted in an increase in the formation of actin stress fibers. Pretreatment of HEp-2 cells with Clostridium botulinum C3 exotoxin, an enzyme that specifically ADP-ribosylates and inactivates RhoA, prevented RSV-induced stress fiber formation. These observations indicate that RhoA and subsequent downstream signaling events are activated during RSV infection, which has implications for RSV pathogenesis.

Recombinant bovine/human parainfluenza virus type 3 (B/HPIV3) expressing the respiratory syncytial virus (RSV) G and F proteins can be used to achieve simultaneous mucosal immunization against RSV and HPIV3.

Recombinant bovine/human parainfluenza virus type 3 (rB/HPIV3), a recombinant bovine PIV3 (rBPIV3) in which the F and HN genes were replaced with their HPIV3 counterparts, was used to express the major protective antigens of respiratory syncytial virus (RSV) in order to create a bivalent mucosal vaccine against RSV and HPIV3. The attenuation of rB/HPIV3 is provided by the host range restriction of the BPIV3 backbone in primates. RSV G and F open reading frames (ORFs) were placed under the control of PIV3 transcription signals and inserted individually into the rB/HPIV3 genome in the promoter-proximal position preceding the nucleocapsid protein gene. The recombinant PIV3 expressing the RSV G ORF (rB/HPIV3-G1) was not restricted in its replication in vitro, whereas the virus expressing the RSV F ORF (rB/HPIV3-F1) was eightfold restricted compared to its rB/HPIV3 parent. Both viruses replicated efficiently in the respiratory tract of hamsters, and each induced RSV serum antibody titers similar to those induced by RSV infection and anti-HPIV3 titers similar to those induced by HPIV3 infection. Immunization of hamsters with rB/HPIV3-G1, rB/HPIV3-F1, or a combination of both viruses resulted in a high level of resistance to challenge with RSV or HPIV3 28 days later. These results describe a vaccine strategy that obviates the technical challenges associated with a live attenuated RSV vaccine, providing, against the two leading viral agents of pediatric respiratory tract disease, a bivalent vaccine whose attenuation phenotype is based on the extensive host range sequence differences of BPIV3.

Abnormality of calcium channel inhibitor released from fetal membranes in preterm labor.

OBJECTIVE: This study was undertaken to test the hypothesis that an inhibitor of uterine contractions acting at the level of the dihydropyridine receptor of the uterine L -type uterine calcium channel is released in greater amounts from fetal membranes before term than at term. STUDY DESIGN: Endogenous calcium channel inhibitor activity was generated with standardized 25-cm2 surface area fetal membrane samples from the following 4 categories of women: preterm in labor, preterm not in labor, term in labor, and term not in labor. The amount of inhibitor in each membrane category was quantified by means of a competitive binding assay. Inhibition of uterine contractions induced by Bay K 8644 (an L -type calcium channel agonist) was used as another test of endogenous calcium channel inhibitor activity released from fetal membranes of all 4 groups of patients. RESULTS: Endogenous calcium channel inhibitor activity was most variable but present in the greatest amount in fetal membranes of women who were preterm not in labor followed by those in women at term not in labor and at term in labor. Fetal membranes from women in preterm labor had the least amount of measured endogenous calcium channel inhibitor activity. Consistent with the competitive binding assay, endogenous calcium channel inhibitor activity from fetal membranes from women who were preterm not in labor, at term not in labor, and at term in labor inhibited Bay K 8644-induced uterine contractions. Fetal membranes from women in preterm labor did not inhibit Bay K 8644-induced contractions. Endogenous calcium channel inhibitor activity was present in the chorion, the decidua, and the placenta, with little activity in the amnion. CONCLUSION: The down-regulation of endogenous calcium channel inhibitor activity with advancing gestation is consistent with a potential role for this inhibitor in maintaining uterine quiescence and in regulating the transition into labor. One possible cause of idiopathic preterm labor may be an abnormally low amount of endogenous calcium channel inhibitor activity in fetal membranes.

Gestational changes in uterine L-type calcium channel function and expression in guinea pig.

Pregnancy can influence both the resting membrane potential and the ion channel composition of the uterine myometrium. Calcium flux is essential for excitation-contraction coupling in pregnant uterus. The uterine L-type calcium channel is an important component in mediating calcium flux and is purported to play a role in parturition. This study was undertaken to characterize gestational changes in 1) the uterine contractile response to the L-type calcium channel agonist, Bay K 8644; 2) the mRNA expression of channel subunits by semiquantitative reverse transcriptase-polymerase chain reaction; and 3) estimate channel protein levels by measuring (3)H-isradipine binding at the dihydropyridine binding site of the alpha(1c) subunit utilizing saturation binding methods. Sensitivity to Bay K 8644 increases beginning at 0.8 of gestation and persists through term. The change in sensitivity is coincident with an increased mRNA expression of the alpha(1c) and beta(2) subunits but with the least detectable amounts of isradipine binding. The expressed alpha(1c) transcript represents a novel structural variant with a 118-amino acid deletion in the III-IV linker and repeats IVS1-S3 of the protein sequence. The guinea pig uterine L-type calcium channel activity is highly regulated through gestation, but the regulation of mRNA expression may be different from regulation of protein levels, estimated by isradipine binding. The up-regulation of function, alpha(1c) subunit mRNA expression, and isradipine binding at term gestation are consistent with a role for this ion channel in parturition.

Respiratory syncytial virus can tolerate an intergenic sequence of at least 160 nucleotides with little effect on transcription or replication in vitro and in vivo.

The intergenic sequences (IGS) between the first nine genes of human respiratory syncytial virus (RSV) vary in length from 1 to 56 nucleotides and lack apparent conserved sequence motifs. To investigate their influence on sequential transcription and viral growth, recombinant RSV strain A2, from which the SH gene had been deleted to facilitate manipulation, was further modified to contain an M-G IGS of 16, 30, 44, 58, 65, 72, 86, 100, 120, 140, or 160 nucleotides. All of the viruses were viable. For viruses with an M-G IGS of 100 nucleotides or more, plaque size decreased with increasing IGS length. In this same length range, increasing IGS length was associated with modest attenuation during single-step, but not multistep, growth in HEp-2 cells. Surprisingly, Northern blot analysis of the accumulation of six different mRNAs indicated that there was little or no change in transcription with increasing IGS length. Thus, the RSV polymerase apparently can readily cross IGS of various lengths, including unnaturally long ones, with little or no effect on the efficiency of termination and reinitiation. This finding supports the view that the IGS do not have much effect on sequential transcription and provides evidence from infectious virus that IGS length is not an important regulatory feature. To evaluate replication in vivo, BALB/c mice were infected intranasally with RSV containing an M-G IGS of 65, 140, or 160 nucleotides. Replication of the latter two viruses was decreased up to 5- and 25-fold in the upper and lower respiratory tracts, respectively, on day 3 following infection. However, the level of replication at both sites on days 4 and 5 was very similar to that of the virus with an IGS of 65 nucleotides. Thus, the modest attenuation in vivo associated with the longer IGS was additive to that conferred by deletion of the SH gene and might be useful to incrementally increase the level of attenuation of a live-attenuated vaccine virus.

Glycosaminoglycan sulfation requirements for respiratory syncytial virus infection.

Glycosaminoglycans (GAGs) on the surface of cultured cells are important in the first step of efficient respiratory syncytial virus (RSV) infection. We evaluated the importance of sulfation, the major biosynthetic modification of GAGs, using an improved recombinant green fluorescent protein-expressing RSV (rgRSV) to assay infection. Pretreatment of HEp-2 cells with 50 mM sodium chlorate, a selective inhibitor of sulfation, for 48 h prior to inoculation reduced the efficiency of rgRSV infection to 40%. Infection of a CHO mutant cell line deficient in N-sulfation was three times less efficient than infection of the parental CHO cell line, indicating that N-sulfation is important. In contrast, infection of a cell line deficient in 2-O-sulfation was as efficient as infection of the parental cell line, indicating that 2-O-sulfation is not required for RSV infection. Incubating RSV with the purified soluble heparin, the prototype GAG, before inoculation had previously been shown to neutralize its infectivity. Here we tested chemically modified heparin chains that lack their N-, C6-O-, or C2-O-sulfate groups. Only heparin chains lacking the N-sulfate group lost the ability to neutralize infection, confirming that N-sulfation, but not C6-O- or C2-O-sulfation, is important for RSV infection. Analysis of heparin fragments identified the 10-saccharide chain as the minimum size that can neutralize RSV infectivity. Taken together, these results show that, while sulfate modification is important for the ability of GAGs to mediate RSV infection, only certain sulfate groups are required. This specificity indicates that the role of cell surface GAGs in RSV infection is not based on a simple charge interaction between the virus and sulfate groups but instead involves a specific GAG structural configuration that includes N-sulfate and a minimum of 10 saccharide subunits. These elements, in addition to iduronic acid demonstrated previously (L. K. Hallak, P. L. Collins, W. Knudson, and M. E. Peeples, Virology 271:264-275, 2000), partially define cell surface molecules important for RSV infection of cultured cells.

Bovine parainfluenza virus type 3 (BPIV3) fusion and hemagglutinin-neuraminidase glycoproteins make an important contribution to the restricted replication of BPIV3 in primates.

This study examines the contribution of the fusion (F) and hemagglutinin-neuraminidase (HN) glycoprotein genes of bovine parainfluenza virus type 3 (BPIV3) to its restricted replication in the respiratory tract of nonhuman primates. A chimeric recombinant human parainfluenza type 3 virus (HPIV3) containing BPIV3 F and HN glycoprotein genes in place of its own and the reciprocal recombinant consisting of BPIV3 bearing the HPIV3 F and HN genes (rBPIV3-F(H)HN(H)) were generated to assess the effect of glycoprotein substitution on replication of HPIV3 and BPIV3 in the upper and lower respiratory tract of rhesus monkeys. The chimeric viruses were readily recovered and replicated in simian LLC-MK2 cells to a level comparable to that of their parental viruses, suggesting that the heterologous glycoproteins were compatible with the PIV3 internal proteins. HPIV3 bearing the BPIV3 F and HN genes was restricted in replication in rhesus monkeys to a level similar to that of its BPIV3 parent virus, indicating that the glycoprotein genes of BPIV3 are major determinants of its host range restriction of replication in rhesus monkeys. rBPIV3-F(H)HN(H) replicated in rhesus monkeys to a level intermediate between that of HPIV3 and BPIV3. This observation indicates that the F and HN genes make a significant contribution to the overall attenuation of BPIV3 for rhesus monkeys. Furthermore, it shows that BPIV3 sequences outside the F and HN region also contribute to the attenuation phenotype in primates, a finding consistent with the previous demonstration that the nucleoprotein coding sequence of BPIV3 is a determinant of its attenuation for primates. Despite its restricted replication in the respiratory tract of rhesus monkeys, rBPIV3-F(H)HN(H) conferred a level of protection against challenge with HPIV3 that was indistinguishable from that induced by previous infection with wild-type HPIV3. The usefulness of rBPIV3-F(H)HN(H) as a vaccine candidate against HPIV3 and as a vector for other viral antigens is discussed.

Recombinant respiratory syncytial virus that does not express the NS1 or M2-2 protein is highly attenuated and immunogenic in chimpanzees.

Mutant recombinant respiratory syncytial viruses (RSV) which cannot express the NS1 and M2-2 proteins, designated rA2DeltaNS1 and rA2DeltaM2-2, respectively, were evaluated as live-attenuated RSV vaccines. The rA2DeltaNS1 virus contains a large deletion that should have the advantageous property of genetic stability during replication in vitro and in vivo. In vitro, rA2DeltaNS1 replicated approximately 10-fold less well than wild-type recombinant RSV (rA2), while rA2DeltaM2-2 had delayed growth kinetics but reached a final titer similar to that of rA2. Each virus was administered to the respiratory tracts of RSV-seronegative chimpanzees to assess replication, immunogenicity, and protective efficacy. The rA2DeltaNS1 and rA2DeltaM2-2 viruses were 2,200- to 55,000-fold restricted in replication in the upper and lower respiratory tracts but induced a level of RSV-neutralizing antibody in serum that was only slightly reduced compared to the level induced by wild-type RSV. The replication of wild-type RSV in immunized chimpanzees after challenge was reduced more than 10,000-fold at each site. Importantly, rA2DeltaNS1 and rA2DeltaM2-2 were 10-fold more restricted in replication in the upper respiratory tract than was the cpts248/404 virus, a vaccine candidate that retained mild reactogenicity in the upper respiratory tracts of 1-month-old infants. Thus, either rA2DeltaNS1 or rA2DeltaM2-2 might be appropriately attenuated for this age group, which is the major target population for an RSV vaccine. In addition, these results show that neither NS1 nor M2-2 is essential for RSV replication in vivo, although each is important for efficient replication.

Human parainfluenza virus type 3 (PIV3) expressing the hemagglutinin protein of measles virus provides a potential method for immunization against measles virus and PIV3 in early infancy.

Recombinant human parainfluenza virus type 3 (PIV3) was used as a vector to express the major protective antigen of measles virus, the hemagglutinin (HA) glycoprotein, in order to create a bivalent PIV3-measles virus that can be administered intranasally. The measles virus HA open reading frame (ORF) was inserted as an additional transcriptional unit into the N-P, P-M, or HA-neuraminidase (HN)-L gene junction of wild-type PIV3 or into the N-P or P-M gene junction of an attenuated derivative of PIV3, termed rcp45L. The recombinant PIV3 (rPIV3) viruses bearing the HA inserts replicated more slowly in vitro than their parental viruses but reached comparable peak titers of >/=10(7.5) 50% tissue culture infective doses per ml. Each of the wild-type or cold-passaged 45L (cp45L) PIV3(HA) chimeric viruses replicated 5- to 10-fold less well than its respective parent virus in the upper respiratory tract of hamsters. Thus, insertion of the approximately 2-kb ORF itself conferred attenuation, and this attenuation was additive to that conferred by the cp45L mutations. The attenuated cp45L PIV3(HA) recombinants induced a high level of resistance to replication of PIV3 challenge virus in hamsters and induced very high levels of measles virus neutralizing antibodies (>1:8,000) that are well in excess of those known to be protective in humans. rPIV3s expressing the HA gene in the N-P or P-M junction induced about 400-fold more measles virus-neutralizing antibody than did the rPIV3 with the HA gene in the HN-L junction, indicating that the N-P or P-M junction appears to be the preferred insertion site. Previous studies indicated that the PIV3 cp45 virus, a more attenuated version of rcp45L, replicates efficiently in the respiratory tract of monkeys and is immunogenic and protective even when administered in the presence of very high titers of passively transferred PIV3 antibodies (A. P. Durbin, C. J. Cho, W. R. Elkins, L. S. Wyatt, B. Moss, and B. R. Murphy, J. Infect. Dis. 179:1345-1351, 1999). This suggests that this intranasally administered PIV3(HA) chimeric virus can be used to immunize infants with maternally acquired measles virus antibodies in whom the current parenterally administered live measles virus vaccine is ineffective.

Effect of coexpression of interleukin-2 by recombinant respiratory syncytial virus on virus replication, immunogenicity, and production of other cytokines.

We constructed rRSV/mIL-2, a recombinant respiratory syncytial virus (rRSV) containing the coding sequence of murine interleukin-2 (mIL-2) in a transcription cassette inserted into the G-F intergenic region. The recovered virus (rRSV/mIL-2) expressed high levels (up to 2.8 microg/ml) of mIL-2 in cell culture. Replication of rRSV/mIL-2 in vitro was reduced up to 13.6-fold from that of wild-type (wt) rRSV, an effect that was due to the presence of the foreign insert but was not specific to mIL-2. Replication of the rRSV/mIL-2 virus in the upper and lower respiratory tracts of BALB/c mice was reduced up to 6.3-fold, an effect that was specific to mIL-2. The antibody response, including the levels of RSV-specific serum immunoglobulin G1 (IgG1), IgG2a, IgA, and total IgG, and the level of protective efficacy against wt RSV challenge were not significantly different from those of wt rRSV. Analysis of total pulmonary cytokine mRNA isolated 1 and 4 days following infection with rRSV/mIL-2 revealed elevated levels of mRNA for IL-2, gamma interferon (IFN-gamma), IL-4, IL-5, IL-6, IL-10, IL-13, and IL-12 p40 compared to those for wt rRSV. Flow cytometry of total pulmonary mononuclear cells isolated 10 days following infection with rRSV/mIL-2 revealed increased levels of CD4(+) T lymphocytes expressing either IFN-gamma or IL-4 compared to those of wt rRSV. These elevations in cytokine mRNA or cytokine-expressing CD4(+) cells relative to those of wt rRSV-primed animals were not observed following challenge with wt RSV on day 28. Thus, the expression of mIL-2 by rRSV was associated with a modest attenuation of virus growth in vivo, induction of serum antibodies at levels comparable to that of wt rRSV, and transient increases in both the Th1 and Th2 CD4(+) lymphocytes and cytokine mRNAs compared to those of wt rRSV.

Iduronic acid-containing glycosaminoglycans on target cells are required for efficient respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is an important human respiratory pathogen, particularly in infants. Glycosaminoglycans (GAGs) have been implicated in the initiation of RSV infection of cultured cells, but it is not clear what type of GAGs and GAG components are involved, whether the important GAGs are on the virus or the cell, or what the magnitude is of their contribution to infection. We constructed and rescued a recombinant green fluorescent protein (GFP)-expressing RSV (rgRSV) and used this virus to develop a sensitive system to assess and quantify infection by flow cytometry. Evaluation of a panel of mutant Chinese hamster ovary cell lines that are genetically deficient in various aspects of GAG synthesis showed that infection was reduced up to 80% depending on the type of GAG deficiency. Enzymatic removal of heparan sulfate and/or chondroitin sulfate from the surface of HEp-2 cells also reduced infection, and the removal of both reduced infection even further. Blocking experiments in which RSV was preincubated with various soluble GAGs revealed the relative blocking order of: heparin > heparan sulfate > chondroitin sulfate B. Iduronic acid is a component common to these GAGs. GAGs that do not contain iduronic acid, namely, chondroitin sulfate A and C and hyaluronic acid, did not inhibit infection. A role for iduronic acid-containing GAGs in RSV infection was confirmed by the ability of basic fibroblast growth factor to block infection, because basic fibroblast growth factor binds to GAGs containing iduronic acid. Pretreatment of cells with protamine sulfate, which binds and blocks GAGs, also reduced infection. In these examples, infection was reduced by pretreatment of the virus with soluble GAGs, pretreatment of the cells with GAG-binding molecules, pretreatment of the cells with GAG-destroying enzymes or in cells genetically deficient in GAGs. These results establish that the GAGs involved in RSV infection are present on the cell rather than on the virus particle. Thus, the presence of cell surface GAGs containing iduronic acid, like heparan sulfate and chondroitin sulfate B, is required for efficient RSV infection in cell culture.