Live Respiratory Syncytial Virus Research Articles

Cold-adapted influenza vaccine carrying three repeats of a respiratory syncytial virus (RSV) fusion glycoprotein epitope site protects BALB/c mice and cotton rats against RSV infection

Respiratory syncytial virus is the major cause of respiratory viral infections, particularly in infants, immunocompromised populations, and the elderly (over 65 years old), the prevention of RSV infection has become a priority. In this study, we generated a chimeric influenza virus, termed LAIV/RSV/HA-3F, using reverse genetics technology which contained three repeats of the RSV fusion protein neutralizing epitope site II to the N terminal in the background of the hemagglutinin (HA) gene of cold adapted influenza vaccine A/California/7/2009 ca. LAIV/RSV/HA-3F exhibited cold-adapted (ca) and attenuated (att) phenotype. BALB/c mice immunized intranasally with LAIV/RSV/HA-3F showed robust immunogenicity, inducing viral-specific antibody responses against both influenza and RSV, eliciting RSV-specific humoral, cellular and mucosal immune responses. LAIV/RSV/HA-3F also conferred protection as indicated by reduced viral titers and improved lung histopathological alterations against live RSV virus challenge. Mechanismly, single-cell RNA sequencing (scRNA-seq) and single-cell T cell antigen receptor (TCR) sequencing were employed to characterize the immune responses triggered by chimeric RSV vaccine, displaying that LAIV/RSV/HA-3F provided protection mainly via interferon-γ (IFN-γ). Moreover, we found that LAIV/RSV/HA-3F significantly inhibited viral replication in the challenged lung and protected against subsequent RSV challenge in cotton rats without causing lung disease. Taken together, our findings demonstrated that LAIV/RSV/HA-3F has potential as a promising bivalent vaccine with dual purpose candidate for the prevention of influenza and RSV, and preclinical and clinical studies warrant further investigations.

Early life respiratory syncytial virus disease—a preventable burden

Early life respiratory syncytial virus disease—a preventable burden

Design of hepadnavirus core protein-based chimeric virus-like particles carrying epitopes from respiratory syncytial virus

Respiratory syncytial virus (RSV) is one of the most important pathogens causing respiratory tract infection in humans, especially in infants and the elderly. The identification and structural resolution of the potent neutralizing epitopes on RSV fusion (F) protein enable an “epitope-focused” vaccine design. However, the display of RSV F epitope II on the surface of the widely-used human hepatitis B virus core antigen (HBcAg) has failed to induce neutralizing antibody response in mice. Here, we used the hepadnavirus core protein (HcAg) from different mammalian hosts as scaffolds to construct chimeric virus-like particles (VLPs) presenting the RSV F epitope II. Mouse immunization showed that different HcAg-based chimeric VLPs elicited significantly different neutralizing antibody responses, among which the HcAg derived from roundleaf bat (RBHcAg) is the most immunogenic. Furthermore, RBHcAg was used as the scaffold platform to present multiple RSV F epitopes, and the immunogenicity was further improved in comparison to that displaying a single epitope II. The designed RBHcAg-based multiple-epitope-presenting VLP formulated with MF59-like adjuvant elicited a potent and balanced Th1/Th2 immune response, and offered substantial protection in mice against the challenge of live RSV A2 virus. The designed chimeric VLPs may serve as the potential starting point for developing epitope-focused vaccines against RSV. Our study also demonstrated that RBHcAg is an effective VLP carrier for presenting foreign epitopes, providing a promising platform for epitope-focused vaccine design.

Azithromycin therapy in infants hospitalized for respiratory syncytial virus bronchiolitis: Airway matrix metalloproteinase-9 levels and subsequent recurrent wheeze

BackgroundEarly life respiratory syncytial virus (RSV) bronchiolitis is a significant risk factor for childhood asthma. In vitro and in vivo studies suggested that decreasing levels of airway matrix metalloproteinase (MMP)-9 during RSV bronchiolitis may be associated with clinical benefits. ObjectiveTo investigate whether azithromycin therapy during severe RSV bronchiolitis reduces upper airway MMP-9 levels, whether upper airway MMP-9 levels correlate with upper airway interleukin IL-8 levels, and whether MMP-9 level reduction is associated with reduced post-RSV recurrent wheeze (RW). MethodsA total of 200 otherwise healthy 1- to 18-month-old infants hospitalized with RSV bronchiolitis were randomized into a double-blind, placebo-controlled trial of oral azithromycin (10 mg/kg daily for 7 days followed by 5 mg/kg daily for 7 days) or placebo. Infants were followed for 2 to 4 years for the outcome of RW (3 or more wheezing episodes). Nasal lavage samples for MMP-9 levels were obtained at baseline, day 14 (end of the study treatment), and after 6 months. ResultsUpper airway MMP-9 levels were highly correlated with IL-8 levels at all 3 time points: randomization, day 14, and 6 months (r = 0.80; P < .0001 for all time points). MMP-9 levels were similar between treatment groups at randomization, were lower on day 14 among children treated with azithromycin (P = .0085), but no longer different after 6 months. MMP-9 levels at baseline and change from baseline to day 14 were not associated with the development of RW (P = .49, .39, respectively). ConclusionAzithromycin therapy in children hospitalized with RSV bronchiolitis had a short-term anti-inflammatory effect in reducing upper airway MMP-9 levels. However, the reduction in MMP-9 levels did not relate to subsequent RW post-RSV. Trial RegistrationThis study is a secondary analysis of the Azithromycin to Prevent Wheezing following severe RSV bronchiolitis-II clinical trial registered at Clinicaltrials.gov (NCT02911935).

Lactobacillus johnsoniisupplementation modulates functional response of bone-marrow derived dendritic cells in respiratory allergy and viral infection

Abstract The immunomodulatory properties of probiotics are particularly important at the establishment of Th 1-Th 2immune balance early in life. A skewing to Th 2immune response driven by dendritic cell regulation can lead to airway alteration during respiratory allergy and respiratory virus infection. Previous work from our lab have determined that oral supplementation of mice with Lactobacillus johnsonii (Lj) resulted to be protective against viral and allergen airway exposure. In order to further analyze whether Lj supplementation of moms could alter offspring responses to allergic disease, female mice were supplemented daily with Lj for a week before mating. Allergen-sensitized offspring from Lj supplemented-mothers were protected from airway hyperreactivity, had a diminished mucus production and shown a reduced allergen-restimulated Th 2cytokine response upon later life allergen-induced responses. Maternal Lj supplementation changed the functional response of bone-marrow derived dendritic cells (BMDC) activated in vitro with respiratory syncytial virus (RSV), decreased expression of pathological cytokines and chemokines in non-sensitized pups, but increased protective innate cytokines expression in allergic offspring. Neonates supplemented directly with Lj before early life RSV infection altered long term inflammatory activity of BMDC by reducing expression of proinflammatory innate cytokines. These results have shown the immunomodulatory potential of Lj supplementation during pre- and post-natal periods to protect from allergic and viral immune responses in distal mucosal surfaces by altering systemic immune cell responses. RO1HL144858

A live single-cycle RSV vaccine expressing prefusion F protein

Live-attenuated Respiratory syncytial virus (RSV) vaccines given intranasally have potential to provide comprehensive protection, including lung-resident immunity. It has however proven challenging to impart both sufficient safety and efficacy in a vaccine. To achieve the latter, we used a trans-complementing approach to generate live single-cycle RSV vaccines expressing the prefusion form (preF) of the viral fusion protein (F), either membrane-anchored or secreted. Both viruses were tested for their ability to induce a protective immune response in mice after intranasal prime-boost vaccination. The secreted preF vaccine failed to induce a protective response. The anchored preF vaccine induced anti-preF antibodies and antiviral T cells, and protected mice from lung pathology and viral shedding after challenge. Neither vaccine induced anti-G antibodies, for reasons unknown. In spite of the latter and single-cycle replication, the membrane-anchored preF vaccine was protective and demonstrates potential for development of an efficacious live vaccine with a stable safety phenotype.

LUNG AND GUT MICROBIOME DURING EARLY-LIFE RESPIRATORY SYNCYTIAL VIRUS INFECTION

LUNG AND GUT MICROBIOME DURING EARLY-LIFE RESPIRATORY SYNCYTIAL VIRUS INFECTION

Maternal gut microbiome regulates immunity to RSV infection in offspring.

Development of the immune system can be influenced by diverse extrinsic and intrinsic factors that influence the risk of disease. Severe early life respiratory syncytial virus (RSV) infection is associated with persistent immune alterations. Previously, our group had shown that adult mice orally supplemented with Lactobacillus johnsonii exhibited decreased airway immunopathology following RSV infection. Here, we demonstrate that offspring of mice supplemented with L. johnsonii exhibit reduced airway mucus and Th2 cell-mediated response to RSV infection. Maternal supplementation resulted in a consistent gut microbiome in mothers and their offspring. Importantly, supplemented maternal plasma and breastmilk, and offspring plasma, exhibited decreased inflammatory metabolites. Cross-fostering studies showed that prenatal Lactobacillus exposure led to decreased Th2 cytokines and lung inflammation following RSV infection, while postnatal Lactobacillus exposure diminished goblet cell hypertrophy and mucus production in the lung in response to airway infection. These studies demonstrate that Lactobacillus modulation of the maternal microbiome and associated metabolic reprogramming enhance airway protection against RSV in neonates.

Presence of maternal antibody at initial respiratory syncytial virus (RSV) infection shapes innate and adaptive responses following repeat RSV exposure

Abstract RSV is the leading cause of childhood hospitalization due to bronchiolitis and a significant risk factor for the development of allergic airway responses. Maternal vaccination has emerged as a promising strategy to protect infants against severe disease. However, the presence of maternal antibody (matAb) at primary RSV infection has been linked to development of wheeze later in life. Therefore, we sought to understand how high levels of matAb during early life RSV infection shapes innate and adaptive immune responses on repeat RSV exposure. Using a murine model of maternal vaccination, we assessed immune responses following adult RSV re-challenge of infants born to unvaccinated and RSV preF-vaccinated dams. Presence of matAb at primary RSV infection resulted in differential activation of resident lung populations at 4 days post-secondary infection (DPSI). Specifically, proliferation of IL-5+ and IL-13+ type 2 innate lymphoid cells were increased in association with elevated numbers of eosinophils in the alveolar space. At 8 DPSI, IL-4-, IL-5-, and IL-13-producing, but not IFNγ-producing, CD4+ T cells were significantly increased, indicating a dominant Th2 response in mice born to vaccinated dams. Importantly, lung inflammation and mucus production were similarly elevated in mice born to immunized and unimmunized dams, suggesting that maternal vaccination did not prevent pathology on repeat infection. Taken together, these data demonstrate that the presence of matAb at primary RSV infection differentially alters innate and adaptive immune responses on secondary RSV exposure. Understanding the mechanisms that drive differential cell activation in the presence of matAb will guide future maternal immunization strategies.

Leveraging Health Administrative Data to Investigate Maternal Vulnerabilities in Early Life Respiratory Syncytial Virus (RSV) Hospitalizations in Ontario, Canada

IntroductionRespiratory syncytial virus (RSV) is the leading cause of hospitalization among infants globally. Several RSV vaccine candidates are currently in trial and the severity of RSV-related illness can be reduced with prophylaxis. To optimize delivery of these programs and reduce inequities, a comprehensive understanding of risk factors for severe RSV-related illness is required.&#x0D; Objectives and ApproachThe objective of this study was to quantify the risks of severe, early life RSV-related illness in terms of medical conditions, birth characteristics and novel socio-economic factors. We used linked population-based health and socio-demographic administrative data for all children born in Ontario (Apr 1st, 2012-March 31st, 2018), including laboratory viral testing data for a subset of children, to identify all RSV-related hospitalizations occurring in Ontario before a child’s third birthday or end of follow-up (March 31st, 2019). We calculated the relative risk of RSV-related admission, adjusted for several medical complexity and transmission factors. Critically, we leveraged these routinely collected health administrative data to determine the admission risks associated with various novel measures indicative of maternal social vulnerability, such as homelessness and involvement with the criminal justice system.&#x0D; Results11,279 RSV-related hospitalizations were identified among 789,484 children; 57% of admissions occurred before 6 months of age. We identified several socio-economic factors independently associated with increased risk of severe RSV-related illness, including several maternal factors: young age at first delivery (Relative risk (RR) &lt;20 vs 40+ years: 2.27, 95%CI:(1.89,2.73)), involvement with the criminal justice system [RR:1.34 (1.16,1.55)], social assistance use (RR:1.53 (1.45,1.62)), homelessness [RR:1.69 (1.01,2.83)], mental health/addictions concerns [RR:1.51 (1.36,1.67)] and child apprehension [RR:1.59 (1.29,1.96)].&#x0D; Conclusion / ImplicationsWe identified several socio-economic factors independently associated with increased risk of severe RSV-related illness, including several novel factors related to maternal vulnerability. This information could inform the selection of high-risk groups for RSV prophylaxis or immunization programs.

Juvenile, but Not Adult, Mice Display Increased Myeloid Recruitment and Extracellular Matrix Remodeling during Respiratory Syncytial Virus Infection.

Early life respiratory syncytial virus (RSV) infection has been linked to the onset of asthma. Despite this association, our knowledge of the progression of the initial viral infection is limited, and no safe or effective vaccine currently exists. Bronchioalveolar lavage, whole-lung cellular isolation, and gene expression analysis were performed on 3-wk- (juvenile) and 8-wk-old (adult) RSV-infected C57BL/6 mice to investigate age-related differences in immunologic responses; juvenile mice displayed a sustained myeloid infiltrate (including monocytes and neutrophils) with increased RNA expression of Ccl2, Ccl3, and Ccl4, when compared with adult mice, at 72 h postinfection. Juvenile mice demonstrated αSma expression (indicative of myofibroblast activity), increased hyaluronan deposition in the lung parenchyma (attributed to asthma progression), and a lack of CD64 upregulation on the surface of monocytes (which, in conjunction with serum amyloid P, is responsible for clearing residual hyaluronan and cellular debris). RSV infection of human airway epithelial cell, human lung fibroblast, and U937 monocyte cocultures (at air-liquid interface) displayed similar CCL expression and suggested matrix metalloproteinase-7 and MMP9 as possible extracellular matrix modifiers. These mouse data, in conjunction with our findings in human monocytes, suggest that the sustained influx of myeloid cells in the lungs of juvenile mice during acute RSV infection could potentiate extracellular matrix remodeling, facilitating conditions that support the development of asthma.

STAT1 participates in the induction of substance P expression in airway epithelial cells by respiratory syncytial virus

Purpose The regulation effect and mechanism of respiratory syncytial virus (RSV) infection on the expression of tachykinin substance P (SP) in airway epithelial cells was investigated. Methods The regulation of SP expression by RSV was investigated in the BEAS-2B airway epithelial cell line. RT-qPCR, immunofluorescence, and ELISA assay were used to examine the expression of the SP encoding gene TAC1, the intracellular SP protein expression, and the extracellular SP secretion. Results The mRNA expression of TAC1 and the intracellular SP protein level in BEAS-2B cells were significantly enhanced by RSV infection with multiplicity of infection (MOI) values of both 1 and 0.1 at 48 hours post infection. Heat-inactivated and UV-inactivated RSV, but not live RSV, significantly induced SP secretion in both control BEAS-2B cells and CX3CR1 receptor knockout cells without affecting the TAC1 gene expression or cell viability. RSV G protein (2–10 μg/ml) and fractalkine (10–50 ng/ml), both CX3CR1 receptor ligands, did not affect SP secretion in BEAS-2B cells. Inhibition of STAT1 phosphorylation by fludarabine (1 μM) markedly reduced the RSV-induced TAC1 gene expression and antagonized the inhibition of RSV replication by interferon-α in BEAS-2B cells. Conclusions STAT1 participates in RSV infection-induced SP expression in airway epithelial cells.

Live Respiratory Syncytial Virus Attenuated by M2-2 Deletion and Stabilized Temperature Sensitivity Mutation 1030s Is a Promising Vaccine Candidate in Children.

The safety and immunogenicity of live respiratory syncytial virus (RSV) candidate vaccine, LID/ΔM2-2/1030s, with deletion of RSV ribonucleic acid synthesis regulatory protein M2-2 and genetically stabilized temperature-sensitivity mutation 1030s in the RSV polymerase protein was evaluated in RSV-seronegative children. Respiratory syncytial virus-seronegative children ages 6-24 months received 1 intranasal dose of 105 plaque-forming units (PFU) of LID/ΔM2-2/1030s (n = 21) or placebo (n = 11). The RSV serum antibodies, vaccine shedding, and reactogenicity were assessed. During the following RSV season, medically attended acute respiratory illness (MAARI) and pre- and postsurveillance serum antibody titers were monitored. Eighty-five percent of vaccinees shed LID/ΔM2-2/1030s vaccine (median peak nasal wash titers: 3.1 log10 PFU/mL by immunoplaque assay; 5.1 log10 copies/mL by reverse-transcription quantitative polymerase chain reaction) and had ≥4-fold rise in serum-neutralizing antibodies. Respiratory symptoms and fever were common (60% vaccinees and 27% placebo recipients). One vaccinee had grade 2 wheezing with rhinovirus but without concurrent LID/ΔM2-2/1030s shedding. Five of 19 vaccinees had ≥4-fold increases in antibody titers postsurveillance without RSV-MAARI, indicating anamnestic responses without significant illness after infection with community-acquired RSV. LID/ΔM2-2/1030s had excellent infectivity without evidence of genetic instability, induced durable immunity, and primed for anamnestic antibody responses, making it an attractive candidate for further evaluation.

Association Between Respiratory Syncytial Virus-Associated Acute Lower Respiratory Infection in Early Life and Recurrent Wheeze and Asthma in Later Childhood.

Recurrent wheeze and asthma in childhood are commons causes of chronic respiratory morbidity globally. We aimed to explore the association between respiratory syncytial virus (RSV) infection in early life and subsequent respiratory sequelae up to age 12 years. We estimated the strength of association by 3 control groups and 3 follow-up age groups, with data from studies published between January 1995 and May 2018. We also estimated associations by diagnostic criteria, age at infection, and high-risk population. Overall, we included 41 studies. A statistically significant association was observed between early life RSV infection and subsequent childhood recurrent wheeze, in comparison to those who were healthy or those without respiratory symptoms: OR 3.05 (95% confidence interval [CI], 2.50-3.71) for 0 to <36 months follow-up age; OR 2.60 (95% CI, 1.67-4.04) for 36-72 months; and OR 2.14 (95% CI, 1.33-3.45) for 73-144 months. For the subsequent development of asthma, a statistically significant association was observed only in relation to those aged 73-144 months at follow-up: OR 2.95 (95% CI, 1.96-4.46). Further studies using standardized definitions and from diverse settings are needed to elucidate the role of confounders and provide more robust estimates.

Live-Attenuated Respiratory Syncytial Virus Vaccine With Deletion of RNA Synthesis Regulatory Protein M2-2 and Cold Passage Mutations Is Overattenuated.

BackgroundThe live respiratory syncytial virus (RSV) candidate vaccine LIDcpΔM2-2 is attenuated through deletion of M2-2 and 5 cold-passage mutations.MethodsRSV-seronegative children aged 6–24 months received a single intranasal dose of 105 plaque-forming units (PFU) of LIDcpΔM2-2 or placebo. RSV serum antibodies, vaccine infectivity, and reactogenicity were assessed.ResultsFour of 11 (36%) vaccinees shed vaccine virus with median peak titers of 1.6 log10 PFU/mL by quantitative culture and 4.5 log10 copies/mL by polymerase chain reaction; 45% had ≥4-fold rise in serum-neutralizing antibodies. Respiratory symptoms or fever were common in vaccinees (64%) and placebo recipients (6/6, 100%).ConclusionsRSV LIDcpΔM2-2 is overattenuated. Clinical Trial Numbers. NCT02890381, NCT02948127.

Chitinase 3-like 1 protein plays a critical role in respiratory syncytial virus-induced airway inflammation.

BackgroundChitinase 3‐like 1 protein (CHI3L1) (YKL‐40 in humans and breast regression protein [BRP]‐39 in mice) is required for optimal allergen sensitization and Th2 inflammation in various chronic inflammatory diseases including asthma. However, the role of CHI3L1 in airway inflammation induced by respiratory viruses has not been investigated. The aim of this study was to investigate the relationship between CHI3L1 and airway inflammation caused by respiratory syncytial virus (RSV) infection.MethodsWe measured YKL‐40 levels in human nasopharyngeal aspirate (NPA) from hospitalized children presenting with acute respiratory symptoms. Wild‐type (WT) and BRP‐39 knockout (KO) C57BL/6 mice were inoculated with live RSV (A2 strain). Bronchoalveolar lavage fluid and lung tissue samples were obtained on day 7 after inoculation to assess lung inflammation, airway reactivity, and expression of cytokines and BRP‐39.ResultsIn human subjects, YKL‐40 and IL‐13 levels in NPA were higher in children with RSV infection than in control subjects. Expression of BRP‐39 and Th2 cytokines, IL‐13 in particular, was increased following RSV infection in mice. Airway inflammation caused by RSV infection was reduced in BRP‐39 KO mice as compared to WT mice. Th2 cytokine levels were not increased in the lungs of RSV‐infected BRP‐39 KO mice. BRP‐39 regulated M2 macrophage activation in RSV‐infected mice. Additionally, treatment with anti‐CHI3L1 antibody attenuated airway inflammation and Th2 cytokine production in RSV‐infected WT mice.ConclusionThese findings suggest that CHI3L1 could contribute to airway inflammation induced by RSV infection. CHI3L1 could be a potential therapeutic candidate for attenuating Th2‐associated immunopathology during RSV infection.

Respiratory syncytial virus F and G protein core fragments fused to HBsAg-binding protein (SBP) induce a Th1-dominant immune response without vaccine-enhanced disease.

The induction of a dominant Th2-type response is the main cause of harmful inflammation in respiratory syncytial virus (RSV) vaccine trials. A balanced Th1 versus Th2 immune response is needed for a safe and effective RSV vaccine. In this study, we evaluated the potential of a recombinant protein SBP-FG as a vaccine candidate with the main focus on shifting the harmful Th2 response to a Th1 response. SBP-FG consists of epitopes from RSV fusion (F) and attachment (G) proteins conjugated to the N-terminus of HBsAg-binding protein (SBP). SBP-FG induced significantly stronger immune responses assessed at the level of total IgG, IgA and neutralizing antibodies as compared with formalin-inactivated RSV (FI-RSV) and live RSV. Analysis of IgG isotypes, lung cytokines and T helper cells showed that SBP-FG induced a dominant Th1-type response. Further, SBP-FG immunized mice showed significantly reduced lung eosinophilia, reduced viral multiplication in lungs after challenge infection and provided protection against RSV infection. These results suggest that SBP-FG can be developed into a safe and effective vaccine against RSV. However, more studies are required to further evaluate SBP-FG as a potent vaccine candidate against RSV.

T-Cell Responses in Adults During Natural Respiratory Syncytial Virus Infection.

The pathogenesis of respiratory syncytial virus (RSV) in older adults may be due to age-related T-cell immunosenescence. Thus, we evaluated CD4 and CD8 T-cell responses during RSV infection in adults across the age spectrum. Peripheral blood mononuclear cells collected during RSV infection in adults, age 26-96 years, were stimulated with live RSV and peptide pools representing F, M, NP, and G proteins and analyzed by flow cytometry. There were no significant age-related differences in frequency of CD4+ T cells synthesizing interferon (IFN)γ, interleukin (IL)2, IL4, IL10, or tumor necrosis factor (TNF)α or in CD8+IFNγ+ T cells. IL4+CD4+ T-cell numbers were low, as were IL13 and IL17 responses. However, in univariate analysis, CD4 T-cell IFNγ, IL2, IL4, IL10, and TNFα responses and CD8+IFNγ+ T cells were significantly increased with more severe illness requiring hospitalization. In multivariate analysis, viral load was also associated with increased T-cell responses. We found no evidence of diminished RSV-specific CD4 or CD8 T-cell responses in adults infected with RSV. However, adults with severe disease seemed to have more robust CD4 and CD8 T-cell responses during infection, suggesting that disease severity may have a greater association with T-cell responses than age.

Live-Attenuated Respiratory Syncytial Virus Vaccine Candidate With Deletion of RNA Synthesis Regulatory Protein M2-2 is Highly Immunogenic in Children.

Live respiratory syncytial virus (RSV) candidate vaccine LIDΔM2-2 is attenuated by deletion of the RSV RNA regulatory protein M2-2, resulting in upregulated viral gene transcription and antigen expression but reduced RNA replication. RSV-seronegative children ages 6-24 months received a single intranasal dose of 105 plaque forming units (PFU) of LIDΔM2-2 (n = 20) or placebo (n = 9) (NCT02237209, NCT02040831). RSV serum antibodies, vaccine infectivity, and reactogenicity were assessed. During the following RSV season, participants were monitored for respiratory illness and pre- and post-RSV season serum antibodies. Vaccine virus was shed by 95% of vaccinees (median peak titers of 3.8 log10 PFU/mL by quantitative culture and 6.3 log10 copies/mL by PCR); 90% had ≥4-fold rise in serum neutralizing antibodies. Respiratory symptoms and fever were common in vaccine (95%) and placebo (78%). One vaccinee had grade 2 rhonchi concurrent with vaccine shedding, rhinovirus, and enterovirus. Eight of 19 vaccinees versus 2 of 9 placebo recipients had substantially increased RSV antibody titers after the RSV season without medically attended RSV disease, indicating anamnestic vaccine responses to wild-type RSV without significant illness. LIDΔM2-2 had excellent infectivity and immunogenicity, encouraging further study of vaccine candidates attenuated by M2-2 deletion. NCT02237209, NCT02040831.

Preclinical assessment of safety of maternal vaccination against respiratory syncytial virus (RSV) in cotton rats

Maternal immunization directed to control RSV infection in newborns and infants is an appealing vaccination strategy currently under development. In this work we have modeled maternal vaccination against RSV in cotton rats (CR) to answer two fundamental questions on maternal vaccine safety. We tested (i), whether a known, unsafe RSV vaccine (i.e., FI-RSV Lot 100 vaccine) induces vaccine enhanced disease in the presence of passively transferred, RSV maternal immunity, and (ii) whether the same FI-RSV vaccine could induce vaccine enhanced disease in CR litters when used to immunize their RSV-primed mothers. Our data show that FI-RSV immunization of pups with subsequent RSV infection results in vaccine-enhanced disease independent of whether the pups were born to RSV-seropositive or RSV-seronegative mothers, and that FI-RSV immunization of RSV-seropositive mothers does not present a health risk to either the mother or the infant. Our study also raises a novel concern regarding infant immunization, namely that “safe” RSV vaccines (e.g., live RSV administered intramuscularly) may induce vaccine-enhanced disease in RSV-infected pups born to seropositive mothers. Finally, we describe for the first time a sharp decrease in RSV neutralizing antibody titers in immunized seropositive CR at the time of delivery. This decline may reflect maternal immune suppression, potentially pinpointing a window of increased vulnerability to RSV infection that could be alleviated by effective immunization of expectant mothers.