Respiratory Syncytial Virus Neutralizing Research Articles

RSV neutralizing antibodies in dried blood.

The key correlate of protection of respiratory syncytial virus (RSV) vaccines and monoclonal antibodies (mAb) is virus neutralization, measured using sera obtained through venipuncture. Dried blood obtained with a finger prick can simplify acquisition, processing, storage, and transport in trials, and thereby reduce costs. In this study we validate an assay to measure RSV neutralization in dried capillary blood. Functional antibodies were compared between matched serum and dried blood samples from a phase I trial with RSM01, an investigational anti-RSV Prefusion F mAb. Hep-2 cells were infected with a serial dilution of sample-virus mixture using RSV-A2-mKate to determine half-maximal inhibitory concentration. Stability of dried blood was evaluated over time and during temperature stress. Functional antibodies in dried blood were highly correlated with serum (R2 = 0.98, p < 0.0001). The precision of the assay for dried blood was similar to serum. The function of mAb remained stable for 9 months at room temperature and frozen dried blood samples. We demonstrated the feasibility of measuring RSV neutralization using dried blood as a patient-centered solution that may replace serology testing in trials against RSV or other viruses, such as influenza and SARS-CoV-2.

2712. Respiratory syncytial virus (RSV) pre-fusion F antibody titers in hematopoietic cell transplant recipients with upper versus lower respiratory tract infections

Abstract Background Humoral immune responses to respiratory syncytial virus (RSV) infection in hematopoietic cell transplant (HCT) recipients have not been well characterized. We measured RSV pre-fusion F antibody (RSVpreF) titers in HCT recipients in 3 groups: upper respiratory tract infections (URTI) only, lower respiratory tract infections (LRTI) only, and those who progressed from URTI to LRTIs (progressors). Methods We evaluated adult and pediatric allogeneic HCT recipients who acquired RSV from 12/2011 to 12/2019. Prospective and leftover clinical serum specimens were collected from the Fred Hutchinson Cancer Center. Samples included baseline prior to infection, at RSV URTI or LRTI diagnosis, and after infection (both 4-6 and &amp;gt;8 weeks). Quantitative RSVpreF titers were determined using the MesoScale Discovery electrochemiluminescence assay. We compared longitudinal log10 RSVpreF titers among groups using linear mixed effect models with restricted cubic splines. Results A total of 129 samples from 39 patients were analyzed; 24 with URTI only, 8 progressors, and 7 with LRTI only. The median age at infection was 45 years, but HCT recipients with LRTI only had an overall higher median age of 54 (range 23-63) (Table 1). Most had acute leukemia (n=18, 46%) and received peripheral blood stem cells (n=27, 69%) as their cell source (Table 1). Median RSVpreF values were similar across the 3 different groups at each timepoint (Table 2). Trajectories of RSVpreF titers over time for each patient trended towards an increase following RSV diagnosis in all groups (Figure 1a). Predicted curves in RSVpreF titers over time did not differ significantly by group (Figure 1b, p=0.38).Table 2.Summary of RSVpreF titers among allogeneic transplant recipients before and after a post-HCT RSV infection. RSVpreF titers were obtained utilizing Meso Scale Discovery chemiluminescence assays. (A) RSVpreF titers for allogeneic HCT recipients with RSV infection. Each line represents a patient. The top panel shows patients with RSV URTI only, the middle panel shows patients who progressed from URTI to LRTI, and the bottom panel shows patients who presented with RSV LRTI. Open circles represent time points prior to RSV diagnosis, filled circles represent time points just prior to, on or after URTI, and asterisks represent time points just prior to, on, or after LRTI. (B) RSVpreF titers plotted by days from RSV diagnosis. Open circles represent observed values and lines represent model predicted trajectories. Black circles and lines correspond to patients with RSV URTI only, blue corresponds to patients who progressed from RSV URTI to LRTI, and dark orange represents patient who presented with RSV LRTI at diagnosis. An outlying observation at day -53 was excluded. Conclusion Among allogeneic HCT recipients with RSV infection, RSVpreF titers increased in response to RSV infection, but did not differ among patients with URTI only, progressors, or those with LRTI only across pre and post infection time points. Our novel immunoassay results are similar to those from previously described RSV neutralization assays, but extended the observation period beyond 4 weeks after infection, revealing a modest increase in RSVpreF titers. Further characterization of RSV humoral immunity, including mucosal immunity, is needed. Disclosures chikara Ogimi, MD, bioMerieux Japan Ltd.: Honoraria|Horiba: Honoraria|Pfizer: Honoraria Janet A. Englund, MD, Ark Biopharma: Advisor/Consultant|AstraZeneca: Advisor/Consultant|AstraZeneca: Grant/Research Support|GlaxoSmithKline: Grant/Research Support|Meissa Vaccines: Advisor/Consultant|Merck: Grant/Research Support|Moderna: Advisor/Consultant|Moderna: Grant/Research Support|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Sanofi Pasteur: Advisor/Consultant Emily T. Martin, PhD, MPH, Merck: Grant/Research Support Michael J. Boeckh, MD PhD, Allovir: Advisor/Consultant|Amazon: Grant/Research Support|Ansun: Grant/Research Support|Merck: Advisor/Consultant|Merck: Grant/Research Support|Moderna: Advisor/Consultant|Symbio: Advisor/Consultant Alpana Waghmare, MD, Allovir: Grant/Research Support|Amazon: Grant/Research Support|Ansun Biopharma: Grant/Research Support|GlaxoKlineSmith/Vir: Grant/Research Support|Kyorin Pharmaceuticals: Advisor/Consultant|Pfizer: Grant/Research Support|Vir Biotechnology: Advisor/Consultant

Fc-mediated functions of nirsevimab complement direct respiratory syncytial virus neutralization but are not required for optimal prophylactic protection.

Nirsevimab is an extended half-life (M252Y/S254T/T256E [YTE]-modified) monoclonal antibody to the pre-fusion conformation of the respiratory syncytial virus (RSV) Fusion protein, with established efficacy in preventing RSV-associated lower respiratory tract infection in infants for the duration of a typical RSV season. Previous studies suggest that nirsevimab confers protection via direct virus neutralization. Here we use preclinical models to explore whether fragment crystallizable (Fc)-mediated effector functions contribute to nirsevimab-mediated protection. Nirsevimab, MEDI8897* (i.e., nirsevimab without the YTE modification), and MEDI8897*-TM (i.e., MEDI8897* without Fc effector functions) binding to Fc γ receptors (FcγRs) was evaluated using surface plasmon resonance. Antibody-dependent neutrophil phagocytosis (ADNP), antibody-dependent cellular phagocytosis (ADCP), antibody-dependent complement deposition (ADCD), and antibody-dependent cellular cytotoxicity (ADCC) were assessed through in vitro and ex vivo serological analyses. A cotton rat challenge study was performed with MEDI8897* and MEDI8897*-TM to explore whether Fc effector functions contribute to protection from RSV. Nirsevimab and MEDI8897* exhibited binding to a range of FcγRs, with expected reductions in FcγR binding affinities observed for MEDI8897*-TM. Nirsevimab exhibited in vitro ADNP, ADCP, ADCD, and ADCC activity above background levels, and similar ADNP, ADCP, and ADCD activity to palivizumab. Nirsevimab administration increased ex vivo ADNP, ADCP, and ADCD activity in participant serum from the MELODY study (NCT03979313). However, ADCC levels remained similar between nirsevimab and placebo. MEDI8897* and MEDI8897*-TM exhibited similar dose-dependent reduction in lung and nasal turbinate RSV titers in the cotton rat model. Nirsevimab possesses Fc effector activity comparable with the current standard of care, palivizumab. However, despite possessing the capacity for Fc effector activity, data from RSV challenge experiments illustrate that nirsevimab-mediated protection is primarily dependent on direct virus neutralization.

Evaluation of a stabilized RSV pre-fusion F mRNA vaccine: Preclinical studies and Phase 1 clinical testing in healthy adults

Human respiratory syncytial virus (RSV) causes a substantial proportion of respiratory tract infections worldwide. Although RSV reinfections occur throughout life, older adults, particularly those with underlying comorbidities, are at risk for severe complications from RSV. There is no RSV vaccine available to date, and treatment of RSV in adults is largely supportive. A correlate of protection for RSV has not yet been established, but antibodies targeting the pre-fusion conformation of the RSV F glycoprotein play an important role in RSV neutralization. We previously reported a Phase 1 study of an mRNA-based vaccine (V171) expressing a pre-fusion-stabilized RSV F protein (mDS-Cav1) in healthy adults. Here, we evaluated an mRNA-based vaccine (V172) expressing a further stabilized RSV pre-fusion F protein (mVRC1). mVRC1 is a single chain version of RSV F with interprotomer disulfides in addition to the stabilizing mutations present in the mDS-Cav1 antigen. The immunogenicity of the two mRNA-based vaccines encoding mVRC1 (V172) or a sequence-optimized version of mDS-Cav1 to improve transcriptional fidelity (V171.2) were compared in RSV-naïve and RSV-experienced African green monkeys (AGMs). V172 induced higher neutralizing antibody titers than V171.2 and demonstrated protection in the AGM challenge model. We conducted a Phase 1, randomized, placebo-controlled, clinical trial of 25 μg, 100 μg, 200 μg, or 300 μg of V172 in healthy older adults (60–79 years old; N = 112) and 100 μg, 200 μg, or 300 μg of V172 in healthy younger adults (18–49 years old; N = 48). The primary clinical objectives were to evaluate the safety and tolerability of V172, and the secondary objective was to evaluate RSV serum neutralization titers. The most commonly reported solicited adverse events were injection-site pain, injection-site swelling, headache, and tiredness. V172 was generally well tolerated in older and younger adults and increased serum neutralizing antibody titers, pre-fusion F-specific competing antibody titers, and RSV F-specific T-cell responses.

In-vivo and human evidence for potential efficacy of therapeutic polyclonal RSV neutralizing antibodies for palivizumab-resistant RSV infections

BackgroundMonoclonal antibody (palivizumab), intravenous immune globulin (IGIV), or respiratory syncytial virus (RSV)-polyclonal-hyperimmune-globulin (RSV-IG as Respigam®, RI-001, RI-002) are used with ribavirin in RSV-infected immunocompromised patients, with debated efficacy. Palivizumab-resistance (PR) can arise during treatment of persistent infections in this population. RSV-IG may confer benefit in PR-RSV infection. MethodsRSV-IG [RI-001] was provided for an immunocompromised infant with RSV-pneumonitis refractory to ribavirin and palivizumab. RSV-neutralizing antibody, respiratory RSV load (qPCR), and F-gene-sequence-detection of PR was determined. Prophylactic RSV-IG [RI-002] or palivizumab was administered in a cotton-rat model infected with wild-type and PR-RSV. Lung RSV load and neutralizing antibody were measured. ResultsAs protective RI-001-neutralizing antibody titers waned in the infant, a subpopulation of PR-escape mutants were detected with a fatal RSV-burden in the lungs. In PR-RSV-infected cotton rats, prophylactic RI-002 reduced RSV-load in the lungs (2.45 vs 0.28 log10 PFU/g lung-tissue reduction, respectively, p < 0.05) and provided protective RSV-neutralizing antibody. ConclusionsRSV-IG and ribavirin use in immunocompromised patients requires further study.

Tryptophan-like side chain holding aptamers inhibit respiratory syncytial virus infection of lung epithelial cells

Respiratory syncytial virus (RSV) is a leading cause of serious and even fatal acute lower respiratory tract infections in infants and in the elderly. Potent RSV neutralization has been achieved by antibodies that selectively bind the prefusion form of the viral fusion (F) protein. We hypothesised that similar potent neutralization could be achieved using F protein targeting aptamers. Aptamers have yet to reach their translational potential for therapeutics or diagnostics due to their short half-life and limited range of target-aptamer interactions; these shortcomings can, however, be ameliorated by application of amino acid-like side chain holding nucleotides. In this study, a stabilized version of the prefusion RSV F protein was targeted by aptamer selection using an oligonucleotide library holding a tryptophan-like side chain. This process resulted in aptamers that bound the F protein with high affinity and differentiated between its pre- and postfusion conformation. Identified aptamers inhibited viral infection of lung epithelial cells. Moreover, introduction of modified nucleotides extended aptamer half-lives. Our results suggest that targeting aptamers to the surface of viruses could yield effective drug candidates, which could keep pace with the continuously evolving pathogens.

Virus-like particles containing a prefusion-stabilized F protein induce a balanced immune response and confer protection against respiratory syncytial virus infection in mice.

Respiratory syncytial virus (RSV) is a serious respiratory pathogen in infants and young children worldwide. Currently, no licensed RSV vaccines are available. In this study, we explored stable prefusion conformation virus-like particles (Pre-F VLPs) as RSV vaccine candidates. RSV fusion (F) protein mutants were constructed to form stabilized Pre-F or postfusion (Post-F) configurations. VLPs containing Pre-F or Post-F protein were generated using a recombinant baculovirus (rBV)-insect cell expression system. The assembly and immunological properties of Pre-F or Post-F VLPs were investigated. Pre-F and Post-F VLPs contained antigenic sites Ø and I of pre- and postfusion conformations, respectively. Compared with Post-F VLPs, immunization with Pre-F VLPs elicited upregulation of IFN-γ, IL-2 and IL-10 and downregulation of IL-4 and IL-5 cytokine production in mice. A high percentage of CD25+ Foxp3+ cells or a low percentage of IL-17A-producing cells among CD4+ T cells was observed in the lungs of mice vaccinated with Pre-F VLPs. Importantly, immunization with Pre-F VLPs induced a high level of RSV neutralizing antibody and a balanced immune response, which protected mice against RSV infection without evidence of immunopathology. Our results suggested that Pre-F VLPs generated from rBV-insect cells represent promising RSV vaccine candidates.

Virus reduction neutralization test and LI-CORmicroneutralization assaybridging and WHO international standard calibration studies for respiratory syncytial virus.

Background: Respiratory syncytial virus (RSV) vaccine is an unmet medical need. The virus reduction neutralization test (VRNT) was developed to replace the LI-CORmicroneutralization assay to measure RSV neutralization titers. Methods: A bridging study using selected V171 phase I samples and calibration studies using the WHO international standard antiserum to RSV were performed to compare VRNT and LI-COR. Results: From the bridging study, we showed good concordance between VRNT and LI-COR titers, and similar post-/prevaccination titer ratios. From the calibration studies, we can convert VRNT and LI-COR titers into similar IU/ml. Conclusion: The VRNT and LI-COR microneutralization assay correlate well and the titers can be standardized as similar IU/ml, enabling direct comparison of titers from different assays.

Development and comparison of three cell-based potency assays for anti-respiratory syncytial virus monoclonal antibody

There is an increasing demand for monoclonal antibody (mAb) therapies to confer passive immunity against viral diseases. Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis, lower respiratory tract infections, and hospitalization in infants. Currently, there is no RSV vaccine but a humanized mAb available for high risk infants. MK-1654 is a fully human mAb with YTE mutation in the fragment crystallizable (Fc) region to extend the half-life in circulation. It binds to a highly conserved epitope of RSV Fusion protein with high affinity and neutralizes RSV infection. A functional cell-based assay is a regulatory requirement for clinical development, commercial release, and stability testing of MK-1654. In this study, we have evaluated three RSV neutralization assays to test the potency of MK-1654, including an imaging-based virus reduction neutralization test (VRNT) and two reporter virus-based assays (RSV-GFP and RSV-NLucP). All three methods showed good dose response curves of MK-1654 with similar EC50 values. RSV-NLucP method was chosen for further development because it is simple and can be easily adapted to quality control testing laboratories. After optimization, the RSV-NLucP assay was pre-qualified with good linearity, relative accuracy, intermediate precision, and specificity, therefore suitable for a cell-based potency assay.

Intranasal and intrapulmonary vaccination with an M protein-deficient respiratory syncytial virus (RSV) vaccine improves clinical signs and reduces viral replication in infant baboons after an RSV challenge infection

Respiratory syncytial virus (RSV) is the major viral respiratory pathogen for human infants and children. Despite a severe global burden incurred by annual RSV epidemics, there is no licensed RSV vaccine. We have developed an RSV vaccine from a human RSV strain from which the gene for the viral M protein has been deleted (“Mnull RSV”). RSV infects airway cells and produces each of its proteins. The M protein is responsible for reassembling the various other synthesized viral proteins into new, intact virus. In the absence of the M protein, therefore, reassembly does not occur, and the Mnull RSV does not replicate.We vaccinated 2-week old infant baboons with Mnull RSV either intranasally (IN) or directly into the lung (intratracheal, or IT), then infected these animals by inoculating human RSV directly into the lung. IN vaccination induced inconsistent serum RSV neutralizing antibody (NA) responses, but provided moderate reductions in respiratory rates, overall signs of illness and viral replication in bronchoalveolar lavage (BAL) fluid following infection. Intratracheal vaccination induced much stronger RSV NA responses, which persisted for at least 4–6 months. Following RSV infection, animals vaccinated by the IT route had much greater reductions in tachypnea and work of breathing than animals vaccinated IN, and had undetectable amounts of virus in BAL fluids. These results support the further development of IT Mnull RSV vaccination to reduce the impact of RSV infection in humans.

A phase 1, randomized, placebo-controlled study to evaluate the safety and immunogenicity of an mRNA-based RSV prefusion F protein vaccine in healthy younger and older adults

ABSTRACT Respiratory Syncytial Virus (RSV) causes lower respiratory tract infections that can be severe and sometimes fatal. The risk for severe RSV infection is highest in infants and older adults. A safe and effective RSV vaccine for older adults represents a serious unmet medical need due to higher morbidity and mortality in this age group. In this randomized, partially double-blind, placebo-controlled, phase 1 dose-escalation study, we evaluated the safety, tolerability and immunogenicity of an investigational messenger ribonucleic acid (mRNA) vaccine encoding the RSV fusion protein (F) stabilized in the prefusion conformation. The study was conducted in healthy younger adults (ages ≥18 and ≤49 years) and healthy older adults (ages ≥60 and ≤79 years). Participants received mRNA-1777 (V171) or placebo as a single intramuscular dose. For each dose level, three sentinel participants were administered open-label mRNA-1777 (V171). Seventy-two younger adults were randomized and administered 25, 100, or 200 µg mRNA-1777 (V171) or placebo, and 107 older adults were randomized and administered 25, 100, 200 or 300 µg mRNA-1777 (V171) or placebo. Primary objectives were safety and tolerability and secondary objectives included humoral and cell-mediated immunogenicity. All dose levels of mRNA-1777 (V171) were generally well tolerated and no serious adverse events related to the vaccine were reported. Immunization with mRNA-1777 (V171) elicited a humoral immune response as measured by increases in RSV neutralizing antibody titers, serum antibody titers to RSV prefusion F protein, D25 competing antibody titers to RSV prefusion F protein, and cell-mediated immune responses to RSV-F peptides.

Purification of Antibodies From Human Milk and Infant Digestates for Viral Inhibition Assays.

Oral administration of enteric pathogen-specific immunoglobulins may be an ideal approach for preventing infectious diarrhea in infants and children. For oral administration to be effective, antibodies must survive functionally intact within the highly proteolytic digestive tract. As an initial step toward assessing the viability of this approach, we examined the survival of palivizumab, a recombinant monoclonal antibody (IgG1κ), across infant digestion and its ability to neutralize respiratory syncytial virus (RSV). Human milk and infant digestive samples contain substances known to interfere with the RSV neutralization assay (our selected functional test for antibody survival through digestion), therefore, antibody extraction from the matrix was required prior to performing the assay. The efficacy of various approaches for palivizumab purification from human milk, infant's gastric and intestinal digestates, including casein precipitation, salting out, molecular weight cut-off, and affinity chromatography (protein A and G) were compared. Affinity chromatography using protein G with high-salt elution followed by 30-kDa molecular weight cut-off centrifugal filtration was the most effective technique for purifying palivizumab from human milk and infant digestates with a high yield and reduced background interference for the viral neutralization assay. This work is broadly applicable to the optimal isolation of antibodies from human milk and infant digesta for viral neutralization assays, enables the examination of how digestion affects the viral neutralization capacity of antibodies within milk and digestive samples, and paves the way for assessment of the viability of oral administration of recombinant antibodies as a therapeutic approach to prevent enteric pathogen-induced infectious diarrhea in infants.

Evaluation of the respiratory syncytial virus G-directed neutralizing antibody response in the human airway epithelial cell model

Human respiratory syncytial virus (RSV) is a major cause of serious respiratory tract infections in infants and the elderly. Recently it was shown that the RSV G glycoprotein mediates attachment to cells using CX3CR1 as a receptor, and that G-specific neutralizing antibodies can be detected using human airway epithelial (HAE) cell cultures. To investigate the contributions of G-specific antibodies to RSV neutralization, we performed HAE neutralization assays on sera from RSV G-immunized mice or RSV-infected infants. We confirmed that G-specific neutralization using serum from mice or humans could only be detected on HAE cultures. We also found that RSV G-specific antibodies in infants were either subgroup specific or cross-neutralizing. Altogether, our results suggest that G is an important target for generating neutralizing antibodies and would be beneficial to include in an RSV vaccine. Further, inclusion of G antigens from both RSV subgroups may enhance the vaccine cross protection potency.

Partial Degradation of Recombinant Antibody Functional Activity During Infant Gastrointestinal Digestion: Implications for Oral Antibody Supplementation.

Oral administration of engineered immunoglobulins has the potential to prevent enteric pathogen-induced diarrhea in infants. To prevent infection, these antibodies need to survive functionally intact in the proteolytic environment of the gastrointestinal tract. This research examined both ex vivo and in vivo the functional survival across infant digestion of palivizumab, a model FDA-approved recombinant antibody against respiratory syncytial virus (RSV) F protein. Palivizumab-fortified feed (formula or human milk), infant gastric, and intestinal samples were incubated to simulate in vivo digestion (ex vivo digestion). Palivizumab-fortified human milk was also fed to infants, followed by collection of gastric and intestinal samples (in vivo digestion). Palivizumab was purified from the samples of digestate using protein G spin columns followed by filtration through molecular weight cut-off membranes (30 kDa). Palivizumab functional survival across ex vivo and in vivo digestion was determined via an anti-idiotype ELISA and an RSV plaque reduction neutralization test. Palivizumab concentration and RSV neutralization capacity both decreased when incubated in intestinal samples (ex vivo study). The concentration and neutralization activity of orally-supplemented palivizumab also decreased across infant digestion (in vivo study). These results indicate that if recombinant IgGs were selected for oral supplementation to prevent enteric infections, appropriate dosing would need to account for degradation occurring in the digestive system. Other antibody formats, structural changes, or encapsulation could enhance survival in the infant gastrointestinal tract.

Bovine IgG Prevents Experimental Infection With RSV and Facilitates Human T Cell Responses to RSV

Respiratory syncytial virus (RSV) infections represent a major burden of disease in infants and are the second most prevalent cause of death worldwide. Human milk immunoglobulins provide protection against RSV. However, many infants depend on processed bovine milk-based nutrition, which lacks intact immunoglobulins. We investigated the potential of bovine antibodies to neutralize human RSV and facilitate-cell immune activation. We show cow's milk IgG (bIgG) and Intravenous Immunoglobulin (IVIG) have a similar RSV neutralization capacity, even though bIgG has a lower pre-F to post-F binding ratio compared to human IVIG, with the majority of bIgG binding to pre-F. RSV is better neutralized with human IVIG. Consequently, we enriched RSV specific T cells by culturing human PBMC with a mixture of RSV peptides, and used these T cells to study the effect of bIgG and IVIG on the activation of pre-F-pecific T cells. bIgG facilitated in vitro T cell activation in a similar manner as IVIG. Moreover, bIgG was able to mediate T cell activation and internalization of pathogens, which are prerequisites for inducing an adaptive viral response. Using in vivo mouse experiments, we showed that bIgG is able to bind the murine activating IgG Fc Receptors (FcγR), but not the inhibiting FcγRII. Intranasal administration of the monoclonal antibody palivizumab, but also of bIgG and IVIG prevented RSV infection in mice. The concentration of bIgG needed to prevent infection was ~5-fold higher compared to IVIG. In conclusion, the data presented here indicate that functionally active bIgG facilitates adaptive antiviral T cell responses and prevents RSV infection in vitro and in vivo.

First-in-human administration of a live-attenuated RSV vaccine lacking the G-protein assessing safety, tolerability, shedding and immunogenicity: a randomized controlled trial

BackgroundHuman respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in early infancy and in elderly. A pediatric vaccine against RSV would not only prevent morbidity and mortality amongst infants and young children but could also reduce transmission to elderly. The RSVΔG vaccine consists of a live-attenuated RSV that lacks the G attachment protein. RSVΔG is severely impaired in binding to host cells and exhibits reduced infectivity in preclinical studies. Intranasal immunization of cotton rats with RSVΔG vaccine protected against replication of wildtype RSV, without inducing enhanced disease. MethodsWe performed a first-in-human trial with primary objective to evaluate safety and shedding of RSVΔG (6.5 log10 CCID50) after intranasal administration. Healthy adults aged between 18 and 50, with RSV neutralizing serum titers below 9.6 log2, received a single dose of either vaccine or placebo (n = 48, ratio 3:1). In addition to safety and tolerability, nasal viral load, and systemic and humoral immune responses were assessed at selected time points until 4 weeks after immunization. ResultsIntranasal administration of RSVΔG was well tolerated with no findings of clinical concern. No infectious virus was detected in nasal wash samples. Similar to other live-attenuated RSV vaccines, neutralizing antibody response following inoculation was limited in seropositive adults. ConclusionsA single dose of 6.5 log10 CCID50 of RSVΔG was safe and well-tolerated in seropositive healthy adults. RSVΔG was sufficiently attenuated but there were no signs of induction of antibodies. Safety and immunogenicity can now be explored in children and eventually in seronegative infants.Clinical trial register: NTR7173/EudraCT number 2016‐002437‐30.

Human parainfluenza virus type 3 expressing the respiratory syncytial virus pre-fusion F protein modified for virion packaging yields protective intranasal vaccine candidates.

Human respiratory syncytial virus (RSV) and parainfluenza virus type 3 (HPIV3) are among the most common viral causes of childhood bronchiolitis and pneumonia worldwide, and lack effective antiviral drugs or vaccines. Recombinant (r) HPIV3 was modified to express the RSV fusion (F) glycoprotein, the major RSV neutralization and protective antigen, providing a live intranasal bivalent HPIV3/RSV vaccine candidate. This extends previous studies using a chimeric bovine-human PIV3 vector (rB/HPIV3). One advantage is that rHPIV3 expresses all of the HPIV3 antigens compared to only two for rB/HPIV3. In addition, the use of rHPIV3 as vector should avoid excessive attenuation following addition of the modified RSV F gene, which may occur with rB/HPIV3. To enhance its immunogenicity, RSV F was modified (i) to increase the stability of the prefusion (pre-F) conformation and (ii) by replacement of its transmembrane (TM) and cytoplasmic tail (CT) domains with those of HPIV3 F (H3TMCT) to increase incorporation in the vector virion. RSV F (+/- H3TMCT) was expressed from the first (F/preN) or the second (F/N-P) gene position of rHPIV3. The H3TMCT modification dramatically increased packaging of RSV F into the vector virion and, in hamsters, resulted in significant increases in the titer of high-quality serum RSV-neutralizing antibodies, in addition to the increase conferred by pre-F stabilization. Only F-H3TMCT/preN replication was significantly attenuated in the nasal turbinates by the RSV F insert. F-H3TMCT/preN, F/N-P, and F-H3TMCT/N-P provided complete protection against wt RSV challenge. F-H3TMCT/N-P exhibited the most stable and highest expression of RSV F, providing impetus for its further development.

2781. Statistical Modeling to Predict Maternal RSV Vaccine Efficacy from Neutralizing Titers

BackgroundIn the United States, respiratory syncytial virus (RSV) is the leading cause of respiratory-related hospitalization in infants. The well-studied efficacy of the prophylactic monoclonal antibody, palivizumab, at preventing RSV disease in the highest risk infants provides proof of mechanism that serum neutralizing antibody protects against RSV. The expense and burden of monthly antibody injections limit the utility of palivizumab, leaving a large unmet medical need. Maternal immunization, with transplacental transfer of antibodies to the fetus, is an alternative, highly practical approach to protect many more infants.MethodsLevels of protection by known palivizumab serum concentrations provide a basis for predicting maternal RSV vaccine efficacy in infants based on serum neutralizing antibody titers elicited in vaccine clinical trials, using statistical modeling to compensate for differences between palivizumab prophylaxis and maternal immunization. The model adjusts for the dependency of maternal vaccine responses on pre-immunization RSV neutralizing titers, exponential decay of maternal antibodies in infants, and exponentially decreasing airway resistance (reducing RSV disease risk) as infants grow.ResultsThe rates of severe RSV disease by age projected from the model match the pattern of US infant hospitalization for RSV, with a peak at 1.5 months of age. The model relates vaccine-elicited increases in maternal RSV neutralizing titers to predicted reductions in severe RSV disease in infants from 0 to 6 months of age.ConclusionStatistical modeling of maternal RSV vaccine efficacy based on elicited RSV neutralizing titers provides a rational basis for decision-making during RSV vaccine development.Disclosures All authors: No reported disclosures.

Antigenicity and immunogenicity of unique prefusion-mimic F proteins presented on enveloped virus-like particles

Pre-fusion stabilizing mutations (DS-Cav1) in soluble fusion (F) proteins of human respiratory syncytial virus (RSV) were previously reported. Here we investigated the antigenic and immunogenic properties of pre-fusion like RSV F proteins on enveloped virus-like particles (VLP). Additional mutations were introduced to DS-Cav1 (F-dcmTM VLP); fusion peptide deletion and cleavage mutation site 1 (F1d-dcmTM VLP) or both sites (F12d-dcmTM VLP). F1d-dcmTM VLP and F12d-dcmTM VLP displayed higher reactivity against pre-fusion specific site Ø and antigenic site I and II specific monoclonal antibodies, compared to F-dcmTM VLP with DS-Cav1 only. Mice immunized with F1d-dcmTM VLP and F12d-dcmTM VLP induced higher levels of DS-Cav1 pre-fusion specific IgG antibodies, RSV neutralizing activity titers, and effective lung viral clearance after challenge. These results suggest that cleavage site mutations and fusion peptide deletion in addition to DS-Cav1 mutations have contributed to structural stabilization of pre-fusion like F conformation on enveloped VLP, capable of inducing high levels of pre-fusion F specific and RSV neutralizing antibodies.

Hypergammaglobulinemia and Impaired Transplacental Transfer of Respiratory Syncytial Virus Antibody in Papua New Guinea.

Passively-acquired respiratory syncytial virus (RSV) neutralizing antibody (Ab) can protect against RSV-associated lower respiratory tract illness. Maternal RSV immunization is, therefore, an attractive strategy for protection of very young infants. Vaccines for this purpose are currently being evaluated in clinical trials, but conditions such as preterm birth, placental malaria, maternal hypergammaglobulinemia and HIV infection might threaten this strategy. Each has been shown to impair transplacental Ab transfer for a variety of pathogens, but RSV-specific data are limited. Work in The Gambia demonstrated that placental malaria impaired transplacental transfer of RSV Ab, but a subsequent study in malaria-endemic Papua New Guinea (PNG) indicated that such associations may have been confounded by hypergammaglobulinemia (IgG > 1700 mg/dL). Here we confirm and extend those findings by measuring RSV neutralizing Ab and maternal IgG in sera from a larger cohort of 325 mother/infant pairs in PNG, and demonstrate the applicability of a high-throughput assay for assessment of neutralizing Ab. One-third of mother-infant pairs demonstrated impaired RSV Ab transfer. Infants of hypergammaglobulinemic women were more likely to have both impaired transfer [cord-to-maternal titer ratio <1.0, adjusted odds ratio (OR): 3.36 (95% confidence interval: 1.81-6.30)] and the lowest RSV cord titers [adjusted OR: 5.09 (95% confidence interval: 1.95-13.32, P < 0.001)], but neither outcome was associated with placental malaria. Once maternal RSV vaccines become available, successful implementation will require clear understanding and mitigation of factors that can impair passive protection, necessitating epidemiologic studies of such relationships ahead of vaccine availability. This study underscores the need to focus on hypergammaglobulinemia as a condition of importance.