Previous Article | Next Article ![]()
Journal of Virology, June 2004, p. 6043-6047, Vol. 78, No. 11
0022-538X/04/$08.00+0 DOI: 10.1128/JVI.78.11.6043-6047.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Division of Virology,1 Department of Infectious Diseases,2 Department of Immunology,3 Animal Resources Center, St. Jude Children's Research Hospital,5 Departments of Pathology,4 Pediatrics, University of Tennessee, Memphis, Tennessee,7 Toyama Institute of Health, Toyama, Japan6
Received 13 August 2003/ Accepted 27 January 2004
|
|
|---|
|
|
|---|
The best known RSV vaccine was a formalin-inactivated (FI) vaccine tested in the 1960s. This vaccine failed to protect and resulted in enhanced disease upon natural infection (5), likely due to aberrant T-cell priming without effective neutralizing antibody priming (3, 14). Results of the FI-RSV vaccine contrast with the successful experience with live attenuated vaccines for paramyxoviruses (e.g., measles and mumps vaccines). However, the use of attenuated RSV vaccines has also been discouraging, with observed inadequate attenuation of viruses or reversion of genetic modifications (12, 4).
To safely elicit effective immune responses to RSV target antigens, we used a naturally attenuated xenotropic virus vector to express RSV G glycoprotein. In this study we examined the murine Sendai virus (SV) as the vaccine vector. We previously showed that SV is an effective, naturally attenuated live virus vaccine for its closely related (13, 20) human cognate, human parainfluenza virus type 1 (hPIV1) (8). Based on these preclinical findings and the known host-range restriction of SV (SV causes pneumonia in mice but no disease in humans [9]), we conducted a successful initial clinical study of intranasal SV as a vaccine for hPIV1 in human adults, demonstrating good tolerability (19). In this report we describe the use of reverse genetics to modify the SV cDNA backbone to express RSV G glycoprotein and our rescue of infectious recombinant SV (rSV RSVG). RSV G glycoprotein is a target of neutralizing antibody (24) and thus is a suitable vaccine candidate.
By using previously described methods (11), the full-length Z strain SV cDNA [pSeV(+)] from the nonsegmented, negative strand of SV was first modified to include a unique NotI site between the F and HN genes [pSV(+)N]. The RSV G gene was cloned from RNA extracted and amplified from RSV-infected HEp2 cells (RSV A2 strain) by using reverse transcription-PCR (Titan One Tube System; Roche). This RSV G PCR product was digested with NotI and cloned into the NotI site in pSV(+)N (Fig. 1). Successful recombinants were designated pSV(+)RSVG.
![]() View larger version (24K): [in a new window] |
FIG. 1. Design of pSV(+)RSVG and expression of RSV G target gene. (A) A unique NotI restriction enzyme site was created in the noncoding region of the HN gene to insert the RSV G glycoprotein gene. The NotI site was introduced into a subcloned ClaI-EcoRI fragment of pSeV(+) in pTF1 (21) by using a QuikChange Site-Directed Mutagenesis kit (Stratagene, La Jolla, Calif.). This modified fragment was then substituted for the wild-type fragment in pSeV(+) to create pSV(+)N. RSV G gene was cloned by using a forward primer which included a NotI site and a reverse primer which included an SV transcription termination signal and another transcription initiation signal (separated by an intergenic linker sequence [CTT]), followed by the NotI site. Thus, RSV G transcription initiated from the upstream SV HN transcription initiation sequence and terminated by using the new termination sequence. SV HN transcription initiated by using the newly introduced transcription initiation sequence. T7, T7 promoter; ribo, hepatitis delta virus ribozyme sequence. Black and gray boxes represent transcription initiation and termination sequences, respectively, of the nucleoprotein (NP), polymerase (P), matrix (M), fusion (F), hemagglutinin-neuraminidase (HN), and large (L) protein. (B) Western blot examination of lysates of HEp-2 cells (approximately 106 cells) infected with rSV RSVG (left lane) or wild-type RSV (right lane). Cells were lysed with 0.2 ml of TNE buffer (10 mM Tris [pH 7.4], 150 mM NaCl, 0.5% NP-40, and 1 mM EDTA) and were clarified (15,000 x g, 10 min). Supernatants were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in nonreducing conditions, transferred to Immobilon membrane (Millipore, Danvers, Mass.), and developed with RSV G-specific monoclonal antibody (clone 63-10F; Chemicon International Inc., Temecula, Calif.). Fully glycosylated RSV G protein (both N- and O-linked glycosylation) runs at approximately 90 kDa (G). Middle band likely represents partially glycosylated G protein, and the lower band represents unglycosylated G.
|
To confirm that the recombinant vector expressed glycosylated RSV G protein, lysates of rSV RSVG-infected HEp-2 cells (for 24 h at 34°C; MOI = 5) were examined by Western blot analysis. We observed a major band of fully glycosylated G protein as well as bands which likely represented partially glycosylated and unglycosylated G proteins (Fig. 1). Each of these bands were of the same size as bands produced by wild-type RSV. HEp-2 cells infected with SV alone were negative for RSV G expression.
To ensure that the host-range specificity of the parent SV was not altered, recombinant SV particles were examined for the absence of incorporated RSV G; we proposed that the absence of a cytoplasmic tail domain would preclude incorporation of G into the SV particles (23). Purified rSV RSVG viral particles were subjected to Western blot analysis for RSV G, using an assay with a sensitivity of 1 pg (Fig. 2). Whereas the presence of RSV G protein was obvious in a control preparation of RSV-infected HEp2 cell lysate, RSV G protein could not be identified from purified recombinant SV particles, even when abundant virus (e.g., 12 µg of purified virus) was examined (Fig. 2).
![]() View larger version (54K): [in a new window] |
FIG. 2. rSV RSVG particles do not contain G protein. rSV RSVG viral particles were first purified from infected cell supernatant (HEp-2 cells; MOI 5; 72 h at 34°C) by sucrose gradient centrifugation and then resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). RSV-infected HEp2 cell lysates (control) were also run on SDS-PAGE. (Left) Gels were transferred to a nitrocellulose sheet and were reacted with a monoclonal antibody directed against RSV G protein. The quantity of lysate run in each lane is indicated. RSV G detection assay (SuperSignal West Pico Chemiluminescent kit; Pierce Biotechnology, Rockland, Ill.) has a sensitivity of 1 pg. In contrast to the RSV G protein detected from all control preparations (RSV infected cell lysate), RSV G protein could not be detected from purified rSV RSVG, even with 12 µg of viral proteins. (Right) SDS-PAGE gels were also stained with GelCode Blue Stain Reagent (Pierce Biotechnology) to identify all proteins present in purified rSV RSVG particles. Arrow indicates the location of RSV G protein in the gel. SV protein abbreviations are the same as those described in the legend to Fig. 1.
|
![]() View larger version (35K): [in a new window] |
FIG. 3. rSV RSVG-primed cotton rats generate RSV-specific antibody. (A) Serial serum dilutions from immunized (gray bars) and control rats receiving PBS (black bars) were examined by enzyme-linked immunosorbent assay. RSV G-transfected 293T cells served as the source of antigen. 293T cells grown in polylysine-coated 24-well plates were transfected with pCAGGS (0.5 µg; in LipofectAMINE) for 24 h. After transfection, wells were washed and reacted with serial dilutions of cotton rat test serum (in PBS-0.1% bovine serum albumin [BSA]) for 30 min at room temperature (RT), washed again, and then reacted with rabbit anti-cotton rat IgG (1:3,000 in PBS-0.1% BSA; Virion Systems, Rockville, Md.) for 30 min at RT. Wells were washed and incubated with anti-rabbit immunoglobulin G-horseradish peroxidase conjugate (1:3,000 in PBS-0.1% BSA) for 30 min at RT. Wells were washed again and reacted with 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) substrate and measured by spectrophotometer. Results are reported as the absolute optical density at 405 nm (O.D. 405 nm) at each serum dilution. (B) RSV neutralizing activity was tested by plaque assay. Serum samples were mixed with RSV (100 to 500 PFU/well; 1 h at RT), and virus-serum mixtures were inoculated to HEp-2 cell monolayers (80 to 90% confluent) on 6-well plates, incubated for 1 h (37°C, 5% CO2), and then overlayed with medium containing methylcellulose. Plates were incubated for 7 days (37°C, 5% CO2), after which the methylcellulose was removed, the cells were fixed (formalin phosphate), and the plates were stained (hematoxylin and eosin) for plaque enumeration. Results are reported as the percent plaque reduction (y axis) observed at each serum dilution (x axis). (C) To measure protection from RSV challenge, sets of vaccinated (CR1 to CR6) and control (PBS recipients CR7 to CR12 and SV-inoculated CR13 to CR17, inset chart) were challenged with intranasal RSV (106 PFU) approximately 4 weeks after priming. Three days postchallenge animals were sacrificed, lungs were harvested, and lung tissue was cut into large fragments, mixed with PBS (1 ml), and processed with a mechanical Dounce homogenizer (PowerGen125 PCR Tissue Homogenizing kit; Fisher Scientific) over ice. Homogenates were then centrifuged and supernatants were collected and cryopreserved for virus quantitation (supernatant volume ranged between 4.0 to 6.5 ml/rat). RSV burden in lung supernatants was determined by plaque assay (see above) of serial dilutions of supernatants. Virus titers were determined by estimating the plaque number per volume plated, and the total virus burden per rat was calculated based on the total volume of supernatant obtained (reported along the y axis).
|
Five days after intranasal RSV challenge, sets of vaccinated and control rats were sacrificed, lungs were harvested and perfused with formalin, and sections were prepared for histologic analysis. Hematoxylin- and eosin-stained lungs were scored for inflammatory changes (bronchitis, peribronchiolitis, and alveolitis) in a blinded fashion and according to previously published criteria (16). Modest peribronchiolitis, alveolitis, and bronchitis were present in both control and vaccinated rats on the fifth day following RSV challenge (Table 1).
|
View this table: [in a new window] |
TABLE 1. Pulmonary histopathology following RSV challengea
|
We thank Greg Prince and Ray Langley for providing the anti-cotton rat antibody.
|
|
|---|
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»