Purification of human respiratory syncytial virus fusion glycoprotein

Knockdown of the Autophagy Protein Beclin-1 Does Not Affect Innate Cytokine Production in Human Lung Epithelial Cells during Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is a major cause of respiratory tract infections in young children, globally. Autophagy is a cellular degradation process that mediates cell survival. Studies using mouse models have demonstrated that inhibiting autophagy affects the production of cytokines triggered by RSV. However, the effect of autophagy on RSV-induced cytokine production in human cells remains inadequately studied. Our previous research showed that inhibiting autophagy using pharmacological inhibitors did not affect the innate cytokine production in human lung epithelial cells (BEAS-2B) following RSV infection. In this study, we sought to validate these findings using a more specific approach, employing short-interfering RNA (siRNA) to target the important autophagy protein Beclin-1 (Bec-1). Prior to measuring cytokine production, we confirmed that silencing Bec-1 with siRNA effectively suppressed autophagy without affecting cell viability. Our results revealed that inhibiting autophagy through Bec-1 knockdown did not affect the production of innate cytokines CXCL8 and CCL5 in BEAS-2B cells during RSV infection, consistent with our previous findings using pharmacological inhibitors. Overall, our data suggest that targeting autophagy may not be an effective strategy for alleviating RSV-induced airway inflammation.

Inhibition of Autophagy Does Not Affect Innate Cytokine Production in Human Lung Epithelial Cells During Respiratory Syncytial Virus Infection

Human respiratory syncytial virus (RSV) is one of the major causes of childhood acute lower respiratory tract infection worldwide. Autophagy is an intracellular pathway involved in nutrient recycling. Recently, autophagy has been reported to play a role in regulating host cytokine response to several viruses, including vesicular stomatitis virus and human immunodeficiency virus. Previous in vivo studies using mouse model has shown that inhibition of autophagy reduces RSV-induced cytokine production. However, the role of autophagy in modulating RSV-induced cytokine response in human cells has not been reported. We investigated the role of autophagy in regulating the production of the cytokines C-X-C motif ligand 8 (CXCL8) and C-C motif ligand 5 (CCL5), in RSV-infected human bronchial epithelium BEAS-2B cells. Fluorescent microscopic analysis showed that RSV infection induced autophagosome formation in BEAS-2B cells. This autophagy inducing ability of RSV was further confirmed by flow cytometry. The effects of pharmacological inhibition of autophagy by SAR405 or chloroquine on cell death and cytokine release were quantified using lactate dehydrogenase assay and enzyme-linked immunosorbent assay (ELISA), respectively. We found that SAR405 or chloroquine did not cause cell death. Importantly, ELISA analysis showed that pharmacological inhibition of autophagy by SAR405 or chloroquine did not affect the productions of both CXCL5 and CXCL8. In contrast to the previous studies using mouse model, our data suggest that pharmacological inhibition of autophagy may not be a suitable strategy in controlling RSV-induced airway inflammation.

The Susceptibilities of Respiratory Syncytial Virus to Nucleolin Receptor Blocking and Antibody Neutralization are Dependent upon the Method of Virus Purification

Respiratory Syncytial Virus (RSV) that is propagated in cell culture is purified from cellular contaminants that can confound experimental results. A number of different purification methods have been described, including methods that utilize fast protein liquid chromatography (FPLC) and gradient ultracentrifugation. Thus, the constituents and experimental responses of RSV stocks purified by ultracentrifugation in sucrose and by FPLC were analyzed and compared by infectivity assay, Coomassie stain, Western blot, mass spectrometry, immuno-transmission electron microscopy (TEM), and ImageStream flow cytometry. The FPLC-purified RSV had more albumin contamination, but there was less evidence of host-derived exosomes when compared to ultracentrifugation-purified RSV as detected by Western blot and mass spectrometry for the exosome markers superoxide dismutase [Cu-Zn] (SOD1) and the tetraspanin CD63. Although the purified virus stocks were equally susceptible to nucleolin-receptor blocking by the DNA aptamer AS1411, the FPLC-purified RSV was significantly less susceptible to anti-RSV polyclonal antibody neutralization; there was 69% inhibition (p = 0.02) of the sucrose ultracentrifugation-purified RSV, 38% inhibition (p = 0.03) of the unpurified RSV, but statistically ineffective neutralization in the FPLC-purified RSV (22% inhibition; p = 0.30). The amount of RSV neutralization of the purified RSV stocks was correlated with anti-RSV antibody occupancy on RSV particles observed by immuno-TEM. RSV purified by different methods alters the stock composition and morphological characteristics of virions that can lead to different experimental responses.

A single intranasal administration of virus-like particle vaccine induces an efficient protection for mice against human respiratory syncytial virus

Human respiratory syncytial virus (RSV) is an important pediatric pathogen causing acute viral respiratory disease in infants and young children. However, no licensed vaccines are currently available. Virus-like particles (VLPs) may bring new hope to producing RSV VLP vaccine with high immunogenicity and safety. Here, we constructed the recombinants of matrix protein (M) and fusion glycoprotein (F) of RSV, respectively into a replication-deficient first-generation adenoviral vector (FGAd), which were used to co-infect Vero cells to assemble RSV VLPs successfully. The resulting VLPs showed similar immunoreactivity and function to RSV virion in vitro. Moreover, Th1 polarized response, and effective mucosal virus-neutralizing antibody and CD8⁺ T-cell responses were induced by a single intranasal (i.n.) administration of RSV VLPs rather than intramuscular (i.m.) inoculation, although the comparable RSV F-specific serum IgG and long-lasting RSV-specific neutralizing antibody were detected in the mice immunized by both routes. Upon RSV challenge, VLP-immunized mice showed increased viral clearance but decreased signs of enhanced lung pathology and fewer eosinophils compared to mice immunized with formalin-inactivated RSV (FI-RSV). In addition, a single i.n. RSV VLP vaccine has the capability to induce RSV-specific long-lasting neutralizing antibody responses observable up to 15 months. Our results demonstrate that the long-term and memory immune responses in mice against RSV were induced by a single i.n. administration of RSV VLP vaccine, suggesting a successful approach of RSV VLPs as an effective and safe mucosal vaccine against RSV infection, and an applicable and qualified platform of FGAd-infected Vero cells for VLP production.

Core bead chromatography for preparation of highly pure, infectious respiratory syncytial virus in the negative purification mode

Respiratory syncytial virus (RSV) is an important human pathogen, and is the most frequent viral cause of severe respiratory disease in infants. In addition, it is increasingly being recognized as an important cause of respiratory disease in the elderly and immunocompromised. Although a passive prophylactic treatment does exist for high-risk neonates and children, the overall disease burden warrants the development of a safe and effective prophylactic vaccine for use in otherwise healthy newborns and children. RSV is known to be an extremely labile virus, prone to aggregation and loss of infectious titer during virus handling and preparation procedures. To date infective RSV virions have been prepared by methods which are not readily scalable, such as density gradient ultracentrifugation. In this study we describe a scalable, chromatography-based purification procedure for preparation of highly pure, infectious RSV. The purification scheme is based on core bead technology and hollow fiber tangential flow filtration (TFF) and results in a ∼60% recovery of infectious virus titer. This method can be used to prepare highly purified wild type or live-attenuated vaccine strain viruses with titers as high as 1×10(8) plaque forming units per mL. A live-attenuated RSV vaccine prepared by this method was found to be immunogenic and protective in vivo, and its purity was 50-200-fold greater with respect to host cell dsDNA and Vero host cell proteins, than the raw feed stream. The results presented here can be considered a starting point for downstream process development of a live-attenuated vaccine approach for prevention of disease by RSV.

The respiratory syncytial virus G protein conserved domain induces a persistent and protective antibody response in rodents

Respiratory syncytial virus (RSV) is an important cause of severe upper and lower respiratory disease in infants and in the elderly. There are 2 main RSV subtypes A and B. A recombinant vaccine was designed based on the central domain of the RSV-A attachment G protein which we had previously named G2Na (aa130-230). Here we evaluated immunogenicity, persistence of antibody (Ab) response and protective efficacy induced in rodents by: (i) G2Na fused to DT (Diphtheria toxin) fragments in cotton rats. DT fusion did not potentiate neutralizing Ab responses against RSV-A or cross-reactivity to RSV-B. (ii) G2Nb (aa130-230 of the RSV-B G protein) either fused to, or admixed with G2Na. G2Nb did not induce RSV-B-reactive Ab responses. (iii) G2Na at low doses. Two injections of 3 µg G2Na in Alum were sufficient to induce protective immune responses in mouse lungs, preventing RSV-A and greatly reducing RSV-B infections. In cotton rats, G2Na-induced RSV-reactive Ab and protective immunity against RSV-A challenge that persisted for at least 24 weeks. (iv) injecting RSV primed mice with a single dose of G2Na/Alum or G2Na/PLGA [poly(D,L-lactide-co-glycolide]. Despite the presence of pre-existing RSV-specific Abs, these formulations effectively boosted anti-RSV Ab titres and increased Ab titres persisted for at least 21 weeks. Affinity maturation of these Abs increased from day 28 to day 148. These data indicate that G2Na has potential as a component of an RSV vaccine formulation.