A novel respiratory syncytial virus (RSV) F subunit vaccine adjuvanted with GLA-SE elicits robust protective TH1-type humoral and cellular immunity in rodent models

Longitudinal humoral analysis in RSV-infected infants identifies pre-existing RSV strain-specific G and evolving cross-reactive F antibodies

Respiratory syncytial virus (RSV) is among the most common causes of lower respiratory tract infection (LRTI) and hospitalization in infants. However, the mechanisms of immune control in infants remain incompletely understood. Antibody profiling against attachment (G) and fusion (F) proteins in children less than 2 years of age, with mild (outpatients) or severe (inpatients) RSV disease, indicated substantial age-dependent differences in RSV-specific immunity. Maternal antibodies were detectable for the first 3 months of life, followed by a long window of immune vulnerability between 3 and 6 months and a rapid evolution of FcγR-recruiting immunity after 6 months of age. Acutely ill hospitalized children exhibited lower G-specific antibodies compared with healthy controls. With disease resolution, RSV-infected infants generated broad functional RSV strain-specific G-responses and evolved cross-reactive F-responses, with minimal maternal imprinting. These data suggest an age-independent RSV G-specific functional humoral correlate of protection, and the evolution of RSV F-specific functional immunity with disease resolution.

Effects of adjuvants in a rabies-vectored Ebola virus vaccine on protection from surrogate challenge

Ebola virus is the primary contributor to the global threat of filovirus severe hemorrhagic fever, and Ebola virus disease has a case fatality rate of 50-90%. An inactivated, bivalent filovirus/rabies virus vaccine, FILORAB1, consists of recombinant rabies virus virions expressing the Ebola virus glycoprotein. FILORAB1 is immunogenic and protective from Ebola virus challenge in mice and non-human primates, and protection is enhanced when formulated with toll-like receptor 4 agonist Glucopyranosyl lipid adjuvant (GLA) in a squalene oil-in-water emulsion (SE). Through an adjuvant comparison in mice, we demonstrate that GLA-SE improves FILORAB1 efficacy by activating the innate immune system and shaping a Th1-biased adaptive immune response. GLA-SE adjuvanted mice and those adjuvanted with the SE component are better protected from surrogate challenge, while Th2 alum adjuvanted mice are not. Additionally, the immune response to FILORAB1 is long-lasting, as exhibited by highly-maintained serum antibody titers and long-lived cells in the spleen and bone marrow.

A prefusion-stabilized RSV F subunit vaccine elicits B cell responses with greater breadth and potency than a postfusion F vaccine

There is currently no licensed vaccine for respiratory syncytial virus (RSV). Here, we assess the effect of RSV fusion protein (F) conformation on B cell responses in a post hoc comparison of samples from the DS-Cav1 [prefusion (pre-F)] and MEDI7510 [postfusion (post-F)] vaccine clinical trials. We compared the magnitude and quality of the serological and B cell responses across time points and vaccines. We measured RSV A and B neutralization, F-binding immunoglobulin G titers, and competition assays at week 0 (before vaccination) and week 4 (after vaccination) to evaluate antibody specificity and potency. To compare B cell specificity and activation, we used pre-F and post-F probes in tandem with a 17-color immunophenotyping flow cytometry panel at week 0 (before vaccination) and week 1 (after vaccination). Our data demonstrate that both DS-Cav1 and MEDI7510 vaccination robustly elicit F-specific antibodies and B cells, but DS-Cav1 elicited antibodies that more potently neutralized both RSV A and B. The superior potency was mediated by antibodies that bind antigenic sites on the apex of pre-F that are not present on post-F. In the memory (CD27⁺) B cell compartment, vaccination with DS-Cav1 or MEDI7510 elicited B cells with different epitope specificities. B cells preferentially binding the pre-F probe were activated in DS-Cav1-vaccinated participants but not in MEDI7510-vaccinated participants. Our findings emphasize the importance of using pre-F as an immunogen in humans because of its deterministic role in eliciting highly potent neutralizing antibodies and memory B cells.

Using Dual Toll-like Receptor Agonism to Drive Th1-Biased Response in a Squalene- and α-Tocopherol-Containing Emulsion for a More Effective SARS-CoV-2 Vaccine

A diversity of vaccines is necessary to reduce the mortality and morbidity of SARS-CoV-2. Vaccines must be efficacious, easy to manufacture, and stable within the existing cold chain to improve their availability around the world. Recombinant protein subunit vaccines adjuvanted with squalene-based emulsions such as AS03™ and MF59™ have a long and robust history of safe, efficacious use with straightforward production and distribution. Here, subunit vaccines were made with squalene-based emulsions containing novel, synthetic toll-like receptor (TLR) agonists, INI-2002 (TLR4 agonist) and INI-4001 (TLR7/8 agonist), using the recombinant receptor-binding domain (RBD) of SARS-CoV-2 S protein as an antigen. The addition of the TLR4 and TLR7/8 agonists, alone or in combination, maintained the formulation characteristics of squalene-based emulsions, including a sterile filterable droplet size (<220 nm), high homogeneity, and colloidal stability after months of storage at 4, 25, and 40 °C. Furthermore, the addition of the TLR agonists skewed the immune response from Th2 towards Th1 in immunized C57BL/6 mice, resulting in an increased production of IgG2c antibodies and a lower antigen-specific production of IL-5 with a higher production of IFNγ by lymphocytes. As such, incorporating TLR4 and TLR7/8 agonists into emulsions leveraged the desirable formulation and stability characteristics of emulsions and can induce Th1-type humoral and cell-mediated immune responses to combat the continued threat of SARS-CoV-2.

HRSV prefusion-F protein with Adju-Phos adjuvant induces long-lasting Th2-biased immunity in mice

The development of human respiratory syncytial virus (hRSV) vaccine has been hampered by the risk of enhanced respiratory disease (ERD) which was induced by highly skewed toward Th2 immune response. In our previous study, we expressed the recombinant pre-F protein using Escherichia coli BL21, called RBF. To verify if the RBF protein could cause ERD, we tested the immunogenicity and safety of RBF with a commercial alum adjuvant (GMP-grade Adju-Phos). RBF alone and RBF/Adju-Phos elicited long-lasting protective antibodies and a cellular immune response in mice after three immunizations. Unfortunately, compared with the mice in RBF group, mice in RBF/Adju-Phos generated a serious Th2 humoral immune response that elicited Th2-mediated lung pathology. From the IL-4+:IFNγ+ ratio, there was also a robust Th2 cellullar immunologic response in the RBF/Adju-Phos group. This study demonstrates that it may not be enough for RBF to increase the titer of neutralizing antibodies. A balanced immune response must be induced for hRSV vaccine safety.

Intranasal vaccination with a recombinant protein CTA1-DD-RBF protects mice against hRSV infection

Human respiratory syncytial virus (hRSV) infection is a major pediatric health concern worldwide. Despite more than half a century of efforts, there is still no commercially available vaccine. In this study, we constructed and purified the recombinant protein CTA1-DD-RBF composed of a CTA1-DD mucosal adjuvant and prefusion F protein (RBF) using Escherichia coli BL21 cells. We studied the immunogenicity of CTA1-DD-RBF in mice. Intranasal immunization with CTA1-DD-RBF stimulated hRSV F-specific IgG1, IgG2a, sIgA, and neutralizing antibodies as well as T cell immunity without inducing lung immunopathology upon hRSV challenge. Moreover, the protective immunity of CTA1-DD-RBF was superior to that of the RBF protein, as confirmed by the assessment of serum-neutralizing activity and viral clearance after challenge. Compared to formalin-inactivated hRSV (FI-RSV), intranasal immunization with CTA1-DD-RBF induced a Th1 immune response. In summary, intranasal immunization with CTA1-DD-RBF is safe and effective in mice. Therefore, CTA1-DD-RBF represents a potential mucosal vaccine candidate for the prevention of human infection with hRSV.

Natural killer cells contribute to enhanced respiratory disease after oil-in-water emulsion adjuvanted vaccination against respiratory syncytial virus and infection

Respiratory syncytial virus (RSV) infection caused severe acute respiratory disease in children and the elderly. There is no licensed vaccine. It has been a challenging problem to avoid vaccine enhanced respiratory disease in developing a safe and effective RSV vaccine. Here, we investigated the impact of MF59-like oil-in-water emulsion adjuvant Addavax on the vaccine efficacy of inactivated split RSV (sRSV) and the roles of natural killer (NK) cells in enhanced respiratory disease in sRSV vaccinated mice after RSV infection. Addavax-adjuvanted sRSV vaccination induced higher levels of IgG1 isotype antibodies and more effective lung viral clearance upon RSV infection but promoted enhanced respiratory disease of weight loss, pulmonary inflammation, and NK and NK T (NKT) cell infiltrations in the lungs. Antibody treatment depleting NK cells prior to RSV infection resulted in preventing severe weight loss and histopathology, as well as attenuating infiltration of dendritic cell subsets and TNF-α⁺ T cells in the lungs. This study demonstrated the impacts of oil-in-water emulsion adjuvant on sRSV vaccination and the potential roles of NK and NKT cells in protection and respiratory disease after adjuvanted RSV vaccination and infection in a mouse model.

Respiratory Syncytial Virus (RSV) G Protein Vaccines With Central Conserved Domain Mutations Induce CX3C-CX3CR1 Blocking Antibodies

Respiratory syncytial virus (RSV) infection can cause bronchiolitis, pneumonia, morbidity, and some mortality, primarily in infants and the elderly, for which no vaccine is available. The RSV attachment (G) protein contains a central conserved domain (CCD) with a CX3C motif implicated in the induction of protective antibodies, thus vaccine candidates containing the G protein are of interest. This study determined if mutations in the G protein CCD would mediate immunogenicity while inducing G protein CX3C-CX3CR1 blocking antibodies. BALB/c mice were vaccinated with structurally-guided, rationally designed G proteins with CCD mutations. The results show that these G protein immunogens induce a substantial anti-G protein antibody response, and using serum IgG from the vaccinated mice, these antibodies are capable of blocking the RSV G protein CX3C-CX3CR1 binding while not interfering with CX3CL1, fractalkine.

Viral Emerging Diseases: Challenges in Developing Vaccination Strategies

In the last decades, a number of infectious viruses have emerged from wildlife or re-emerged, generating serious threats to the global health and to the economy worldwide. Ebola and Marburg hemorrhagic fevers, Lassa fever, Dengue fever, Yellow fever, West Nile fever, Zika, and Chikungunya vector-borne diseases, Swine flu, Severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and the recent Coronavirus disease 2019 (COVID-19) are examples of zoonoses that have spread throughout the globe with such a significant impact on public health that the scientific community has been called for a rapid intervention in preventing and treating emerging infections. Vaccination is probably the most effective tool in helping the immune system to activate protective responses against pathogens, reducing morbidity and mortality, as proven by historical records. Under health emergency conditions, new and alternative approaches in vaccine design and development are imperative for a rapid and massive vaccination coverage, to manage a disease outbreak and curtail the epidemic spread. This review gives an update on the current vaccination strategies for some of the emerging/re-emerging viruses, and discusses challenges and hurdles to overcome for developing efficacious vaccines against future pathogens.

Pharmacological management of human respiratory syncytial virus infection

INTRODUCTION

Human respiratory syncytial virus (hRSV) is the primary viral cause of respiratory diseases, leading to bronchiolitis and pneumonia in vulnerable populations. The only current treatment against this virus is palliative, and no efficient and specific vaccine against this pathogen is available.

AREAS COVERED

The authors describe the disease symptoms caused by hRSV, the economic and social impact of this infection worldwide, and how this infection can be modulated using pharmacological treatments, preventing and limiting its dissemination. The authors discuss the use of antibodies as prophylactic tools -such as palivizumab- and the use of nonspecific drugs to decrease the symptoms associated with the infection -such as bronchodilators, corticoids, and antivirals. They also discuss current vaccine candidates, new prophylactic treatments, and new antivirals options, which are currently being tested.

EXPERT OPINION

Today, many researchers are focused on developing different strategies to modulate the symptoms induced by hRSV. However, to achieve this, understanding how current treatments are working and their shortcomings needs to be further elucidated.

Human respiratory syncytial virus F protein expressed in Pichia pastoris or Escherichia coli induces protective immunity without inducing enhanced respiratory disease in mice

Human respiratory syncytial virus (hRSV) is the primary cause of severe respiratory tract disease in children and infants as well as in elderly and immunocompromised adults. The fusion protein (F) of hRSV is the major antigen eliciting a neutralizing antibody response and protective immunity in the host, especially those recognizing the prefusion F protein (pre-F). In this study, we made genetic constructs for expression of a recombinant prefusion F protein in Pichia pastoris GS115, called RGF. Using Escherichia coli BL21, we expressed the pre-F and postfusion F protein (Post-F), called RBF and Post-RBF, respectively. RGF and RBF showed high affinity for 5C4, a highly potent monoclonal antibody specific for pre-F. We studied the immunogenicity of RGF and RBF in mice. Compared to mice immunized with formalin-inactivated RSV (FI-RSV), mice immunized with RGF or RBF exhibited superior protective immunity, which was confirmed by serum neutralizing activity and viral clearance after challenge. As judged from the IgG1/IgG2a ratios and numbers of IFN-γ- and IL-4-secreting cells, RGF or RBF with alum adjuvant induced a balanced Th1-biased immune response and produced no signs of enhanced respiratory disease (ERD) upon hRSV challenge. In addition, the immunogenicity and protective efficacy of RGF were superior to those of RBF in mice. Therefore, RGF represents a potential vaccine candidate for the prevention of human infection with hRSV.

Therapeutic efficacy of PD1/PDL1 blockade in B16 melanoma is greatly enhanced by immunization with dendritic cell-targeting lentiviral vector and protein vaccine

While immune checkpoint inhibition is rapidly becoming standard of care in many solid tumors, immune checkpoint inhibitors (ICIs) fail to induce clinical responses in many patients, presumably due to insufficient numbers of tumor-specific T cells in the tumor milieu. To this end, immunization protocols using viral vectors expressing tumor-associated antigens are being explored to induce T cell responses that synergize with ICIs. However, the optimal combination of vaccine and immune checkpoint regimen remains undefined. Here, a dendritic cell-targeting lentiviral vector (ZVex®) expressing the endogenous murine tyrosinase-related protein 1 (mTRP1), or the human tumor antigen NY-ESO-1, was explored as monotherapy or heterologous prime-boost (HPB) vaccine regimen together with recombinant tumor antigen in the murine B16 melanoma model. PD1/PDL1 blockade significantly enhanced ZVex/mTRP1, but not ZVex/NY-ESO-1, induced immune responses in mice, whereas the opposite effect was observed with anti-CTLA4 antibody. Anti-tumor efficacy of anti-PD1, but not anti-PDL1 or anti-CTLA4, was significantly enhanced by ZVex/mTRP1 and HPB vaccination. These results suggest mechanistic differences in the effect of checkpoint blockade on vaccine-induced immune and anti-tumor responses against self versus non-self tumor antigens, possibly due to tolerance and state of exhaustion of anti-tumor T cells.

Preclinical Efficacy of a Lipooligosaccharide Peptide Mimic Candidate Gonococcal Vaccine

The global spread of multidrug-resistant strains of Neisseria gonorrhoeae constitutes a public health emergency. With limited antibiotic treatment options, there is an urgent need for development of a safe and effective vaccine against gonorrhea. Previously, we constructed a prototype vaccine candidate comprising a peptide mimic (mimitope) of a glycan epitope on gonococcal lipooligosaccharide (LOS), recognized by monoclonal antibody 2C7. The 2C7 epitope is (i) broadly expressed as a gonococcal antigenic target in human infection, (ii) a critical requirement for gonococcal colonization in the experimental setting, and (iii) a virulence determinant that is maintained and expressed by gonococci. Here, we have synthesized to >95% purity through a relatively facile and economical process a tetrapeptide derivative of the mimitope that was cyclized through a nonreducible thioether bond, thereby rendering the compound homogeneous and stable. This vaccine candidate, called TMCP2, when administered at 0, 3, and 6 weeks to BALB/c mice at either 50, 100 or 200 μg/dose in combination with glucopyranosyl lipid A-stable oil-in-water nanoemulsion (GLA-SE; a Toll-like receptor 4 and T_H1-promoting adjuvant), elicited bactericidal IgG and reduced colonization levels of gonococci in experimentally infected mice while accelerating clearance by each of two different gonococcal strains. Similarly, a 3-dose biweekly schedule (50 μg TMCP2/dose) was also effective in mice. We have developed a gonococcal vaccine candidate that can be scaled up and produced economically to a high degree of purity. The candidate elicits bactericidal antibodies and is efficacious in a preclinical experimental infection model.IMPORTANCE Neisseria gonorrhoeae has become resistant to most antibiotics. The incidence of gonorrhea is also sharply increasing. A safe and effective antigonococcal vaccine is urgently needed. Lipooligosaccharide (LOS), the most abundant outer membrane molecule, is indispensable for gonococcal pathogenesis. A glycan epitope on LOS that is recognized by monoclonal antibody (MAb) 2C7 (called the 2C7 epitope) is expressed almost universally by gonococci in vivo Previously, we identified a peptide mimic (mimitope) of the 2C7 epitope, which when configured as an octamer and used as an immunogen, attenuated colonization of mice by gonococci. Here, a homogenous, stable tetrameric derivative of the mimitope, when combined with a T_H1-promoting adjuvant and used as an immunogen, also effectively attenuates gonococcal colonization of mice. This candidate peptide vaccine can be produced economically, an important consideration for gonorrhea, which affects socioeconomically underprivileged populations disproportionately, and represents an important advance in the development of a gonorrhea vaccine.

First-in-human phase 1 dose-escalating trial of G305 in patients with advanced solid tumors expressing NY-ESO-1

Human tumor cells express antigens that serve as targets for the host cellular immune system. This phase 1 dose-escalating study was conducted to assess safety and tolerability of G305, a recombinant NY-ESO-1 protein vaccine mixed with glucopyranosyl lipid A (GLA), a synthetic TLR4 agonist adjuvant, in a stable emulsion (SE). Twelve patients with solid tumors expressing NY-ESO-1 were treated using a 3 + 3 design. The NY-ESO-1 dose was fixed at 250 µg, while GLA-SE was increased from 2 to 10 µg. Safety, immunogenicity, and clinical responses were assessed prior to, during, and at the end of therapy. G305 was safe and immunogenic at all doses. All related AEs were Grade 1 or 2, with injection site soreness as the most commonly reported event (100%). Overall, 75% of patients developed antibody response to NY-ESO-1, including six patients with increased antibody titer ( ≥ 4-fold rise) and three patients with seroconversion from negative (titer < 100) to positive (titer ≥ 100). CD4 T-cell responses were observed in 44.4% of patients; 33.3% were new responses and 1 was boosted ( ≥ 2-fold rise). Following treatment, 8 of 12 patients had stable disease for 3 months or more; at the end of 1 year, three patients had stable disease and nine patients were alive. G305 is a potent immunotherapeutic agent that can stimulate NY-ESO-1-specific antibody and T-cell responses. The vaccine was safe at all doses of GLA-SE (2-10 µg) and showed potential clinical benefit in this population of patients.

Cotton rat model for testing vaccines and antivirals against respiratory syncytial virus

Respiratory syncytial virus is the leading cause of pneumonia and bronchiolitis in infants and is a serious health risk for elderly and immunocompromised individuals. No vaccine has yet been approved to prevent respiratory syncytial virus infection and the only available treatment is immunoprophylaxis of severe respiratory syncytial virus disease in high-risk infants with Palivizumab (Synagis^®). The development of respiratory syncytial virus vaccine has been hampered by the phenomenon of enhanced respiratory syncytial virus disease observed during trials of a formalin-inactivated respiratory syncytial virus in 1960s. A search for effective respiratory syncytial virus therapeutics has been complicated by the fact that some of the most advanced respiratory syncytial virus antivirals, while highly effective in a prophylactic setting, had not demonstrated clinical efficacy when given after infection. A number of respiratory syncytial virus vaccines and antivirals are currently under development, including several vaccines proposed for maternal immunization. The cotton rat Sigmodon hispidus is an animal model of respiratory syncytial virus infection with demonstrated translational value. Special cohort scenarios, such as infection under conditions of immunosuppression and maternal immunization have been modeled in the cotton rat and are summarized here. In this review, we focus on the recent use of the cotton rat model for testing respiratory syncytial virus vaccine and therapeutic candidates in preclinical setting, including the use of special cohort models. An overview of published studies spanning the period of the last three years is provided. The emphasis, where possible, is made on candidates in the latest stages of preclinical development or currently in clinical trials.

A unique combination adjuvant modulates immune responses preventing vaccine-enhanced pulmonary histopathology after a single dose vaccination with fusion protein and challenge with respiratory syncytial virus

Alum adjuvanted formalin-inactivated respiratory syncytial virus (RSV) vaccination resulted in enhanced respiratory disease in young children upon natural infection. Here, we investigated the adjuvant effects of monophosphoryl lipid A (MPL) and oligodeoxynucleotide CpG (CpG) on vaccine-enhanced respiratory disease after fusion (F) protein prime vaccination and RSV challenge in infant and adult mouse models. Combination CpG + MPL adjuvant in RSV F protein single dose priming of infant and adult age mice was found to promote the induction of IgG2a isotype antibodies and neutralizing activity, and lung viral clearance after challenge. CpG + MPL adjuvanted F protein (Fp) priming of infant and adult age mice was effective in avoiding lung histopathology, in reducing interleukin-4⁺ CD4 T cells and cellular infiltration of monocytes and neutrophils after RSV challenge. This study suggests that combination CpG and MPL adjuvant in RSV subunit vaccination might contribute to priming protective immune responses and preventing inflammatory RSV disease after infection.

The efficacy of inactivated split respiratory syncytial virus as a vaccine candidate and the effects of novel combination adjuvants

Clinical trials with alum-adjuvanted formalin-inactivated human respiratory syncytial virus (FI-RSV) vaccine failed in children due to vaccine-enhanced disease upon RSV infection. In this study, we found that inactivated, detergent-split RSV vaccine (Split) displayed higher reactivity against neutralizing antibodies in vitro and less histopathology in primed adult mice after challenge, compared to FI-RSV. The immunogenicity and efficacy of FI-RSV and Split RSV vaccine were further determined in 2 weeks old mice after a single dose in the absence or presence of monophosphoryl lipid A (MPL) + CpG combination adjuvant. Split RSV with MPL + CpG adjuvant was effective in increasing T helper type 1 (Th1) immune responses and IgG2a isotype antibodies, neutralizing activity, and lung viral clearance as well as modulating immune responses to prevent pulmonary histopathology after RSV vaccination and challenge. This study demonstrates the efficacy of Split RSV as an effective vaccine candidate.

Prevention of Pediatric Respiratory Syncytial Virus Lower Respiratory Tract Illness: Perspectives for the Next Decade

The landscape of infant bronchiolitis and viral pneumonia may be altered by preventive interventions against respiratory syncytial virus under evaluation today. Pediatric wards in 2018 in developing countries may differ from those attended by future generation pediatricians who may not witness the packed emergency rooms, lack of available beds, or emergency situations that all physicians caring for children with RSV experience every year. In this review, we describe and discuss different prevention strategies under evaluation to protect pediatric patients. Then, we outline a number of potential challenges, benefits, and concerns that may result from successful interventions after licensure.

The long road to protect infants against severe RSV lower respiratory tract illness

Severe respiratory syncytial virus (RSV) lower respiratory tract illness (LRTI) in infants has proven challenging to prevent. In the last 50 years, conceptually different approaches failed to evolve into viable preventive alternatives for routine use. Inactivated RSV vaccine (that is, formalin-inactivated RSV) elicited severe LRTI in RSV-infected toddlers pre-immunized as infants; early purified F protein approaches in pregnant women failed to elicit sufficient immunity more than a decade ago; a second-generation monoclonal antibody (mAb) of high potency against the virus (that is, motavizumab) caused severe adverse reactions in the skin, and owing to lack of efficacy against RSV subgroup B, an extended half-life mAb targeting site V in the RSV fusion protein (that is, REG2222) did not meet its primary endpoint. In the meantime, two protein F vaccines failed to prevent medically attended LRTI in the elderly. However, palivizumab and the recent results of the Novavax maternal immunization trial with ResVax demonstrate that severe RSV LRTI can be prevented by mAb and by maternal immunization (at least to a certain extent). In fact, disease prevention may also decrease the rates of recurrent wheezing and all-cause pneumonia for at least 180 days. In this review, we discuss the history of RSV vaccine development, previous and current vaccine strategies undergoing evaluation, and recent information about disease burden and its implications for the effects of successful preventive strategies.

Antibody and B cell responses to an investigational adjuvanted RSV vaccine for older adults

Background: Infections with respiratory syncytial virus (RSV) cause significant morbidity and hospitalization in older adults. We studied the humoral, mucosal and B cell responses of an investigational adjuvanted RSV sF vaccine, MEDI7510, in older adults. Methods: In a substudy of a randomized (1:1), double-blind, placebo-controlled study of MEDI7510 in adults ≥60 years of age, we collected blood and nasal secretions at days 0, 8, 29, 91 and 180 post-vaccination to measure F-specific IgG and IgA antibodies by ELISA, and plasmablasts and memory B cells by IgA/IgG dual-color fluorospot. Results: The 27 vaccine- and 18 placebo-recipients had a mean age of 73 years and included 24 women. Among vaccinees, 93% had significant increases in F-specific plasma IgG 85% had increased plasma IgA; 74% had increased nasal IgG and 26% nasal IgA; 93% had IgG and 89% IgA plasmablasts on Day 8 post-immunization; and 82% had IgG and 7.4% IgA memory B cell responses to the vaccine. Vaccinees <70 years of age and women had the highest responses to the vaccine. Conclusions: This adjuvanted vaccine generated robust humoral immune responses in older adults, including RSV F-specific systemic and mucosal antibodies and memory B cells. Nevertheless, age ≥70 years was associated with decreased immunogenicity of the adjuvanted vaccine.

Viral-Induced Enhanced Disease Illness

Understanding immune responses to viral infections is crucial to progress in the quest for effective infection prevention and control. The host immunity involves various mechanisms to combat viral infections. Under certain circumstances, a viral infection or vaccination may result in a subverted immune system, which may lead to an exacerbated illness. Clinical evidence of enhanced illness by preexisting antibodies from vaccination, infection or maternal passive immunity is available for several viruses and is presumptively proposed for other viruses. Multiple mechanisms have been proposed to explain this phenomenon. It has been confirmed that certain infection- and/or vaccine-induced immunity could exacerbate viral infectivity in Fc receptor- or complement bearing cells- mediated mechanisms. Considering that antibody dependent enhancement (ADE) is a major obstacle in vaccine development, there are continues efforts to understand the underlying mechanisms through identification of the epitopes and antibodies responsible for disease enhancement or protection. This review discusses the recent findings on virally induced ADE, and highlights the potential mechanisms leading to this condition.

Soluble F proteins exacerbate pulmonary histopathology after vaccination upon respiratory syncytial virus challenge but not when presented on virus-like particles

Respiratory syncytial virus (RSV) fusion (F) protein is suggested to be a protective vaccine target although its efficacy and safety concerns remain not well understood. We investigated immunogenicity, efficacy, and safety of F proteins in a soluble form or on virus-like particle (F-VLP). F VLP preferentially elicited IgG2a antibody and T helper type 1 (Th1) immune responses whereas F protein induced IgG1 isotype and Th2 responses. Despite lung viral clearance after prime or prime-boost and then RSV challenge, F protein immune mice displayed weight loss and lung histopathology and high mucus production and eosinophils. In contrast, prime or prime-boost vaccination of F VLP induced effective protection, prevented infiltration of eosinophils and vaccine- enhanced disease after challenge. This study provides insight into developing an effective and safe RSV vaccine candidate.

A multifaceted approach to RSV vaccination

Respiratory Syncytial Virus (RSV) is the leading cause of pneumonia and bronchiolitis in infants, resulting in significant morbidity and mortality worldwide. In addition, RSV infections occur throughout different ages, thus, maintaining the virus in circulation, and increasing health risk to more susceptible populations such as infants, the elderly, and the immunocompromised. To date, there is no vaccine approved to prevent RSV infection or minimize symptoms of infection. Current clinical trials for vaccines against RSV are being carried out in four very different populations. There are vaccines that target two different pediatric populations, infants 2 to 6 month of age and seropositive children over 6 months of age, as well as women (non-pregnant or pregnant in their third trimester). There are vaccines that target adult and elderly populations. In this review, we will present and discuss RSV vaccine candidates currently in clinical trials. We will describe the preclinical studies instrumental for their advancement, with the goal of introducing new preclinical models that may more accurately predict the outcome of clinical vaccine studies.

Monoclonal antibody based in vitro potency assay as a predictor of antigenic integrity and in vivo immunogenicity of a Respiratory Syncytial Virus post-fusion F-protein based vaccine

The post-fusion form of Respiratory Syncytial Virus (RSV) fusion (F) protein has been used recently in clinical trials as a potential vaccine antigen with the objective of eliciting protective immune response against RSV. In this paper, in vitro antigenicity and in vivo immunogenicity of recombinant, soluble F protein of RSV (RSVsF) were evaluated by several assays. In Vitro Relative Potency (IVRP) of RSVsF was measured in a sandwich ELISA using two antibodies, each specific for epitope site A or C. Therefore, IVRP reflected the integrity of the antigen in terms of changes in antibody binding affinity of either or both of these sites. RSVsF samples with a wide range of IVRP values were generated by applying UV irradiation (photo) and high temperature (heat) induced stress for varying lengths of time. These samples were characterized in terms of stress induced modifications in primary and secondary structures as well as aggregation of RSVsF. Immunogenicity, also referred to as In vivo potency, was measured by induction of total F-protein specific IgG and RSV-neutralizing antibodies in mice dosed with these RSVsF samples. Comparison of results between IVRP and these immunogenicity assays revealed that IVRP provided a sensitive read-out of the integrity of epitope sites A and C, and a conservative and reliable evaluation of the potency of RSVsF as a vaccine antigen. This high throughput and fast turn-around assay allowed us to efficiently screen many different RSVsF antigen lots, thereby acting as an effective filter for ensuring high quality antigen that delivered in vivo potency. In vitro and in vivo potencies were further probed at the level of individual epitope sites, A and C. Results of these experiments indicated that site A was relatively resistant to stress induced loss of potency, in vitro or in vivo, compared to site C.

An Adjuvanted, Postfusion F Protein-Based Vaccine Did Not Prevent Respiratory Syncytial Virus Illness in Older Adults

Background

Respiratory syncytial virus (RSV) is an important cause of illness in older adults. This study assessed efficacy of a vaccine for prevention of RSV-associated acute respiratory illness (ARI), defined by specified symptoms with virologic confirmation.

Methods

This phase 2b study evaluated RSV postfusion F protein (120 µg) with glucopyranosyl lipid adjuvant (5 µg) in 2% stable emulsion. Subjects aged ≥60 years were randomly assigned at a ratio of 1:1 to receive vaccine or placebo (all received inactivated influenza vaccine). Ill subjects recorded symptoms and provided blood and nasal swab samples.

Results

In the per-protocol population (n = 1894), the incidence of RSV-associated ARI occurring ≥14 days after dosing was 1.7% and 1.6% in the vaccine and placebo groups, respectively, for a vaccine efficacy (VE) of –7.1% (90% confidence interval [CI], –106.9%–44.3%). Efficacy was not observed in secondary analyses that included seroresponse to nonvaccine RSV antigens (VE, 8.9%; 90% CI, –28.5%–35.4%) or symptoms combined with seroresponse (VE, 10.0%; 90% CI, –45.4%–44.4%). On day 29, 92.9% of vaccinees had an anti-F immunoglobulin G antibody seroresponse. Overall, 48.5% and 30.9% of RSV vaccine recipients reported local and systemic solicited symptoms, respectively.

Conclusion

The RSV vaccine was immunogenic but did not protect older adults from RSV illness.

Clinical Trials Registration

NCT02508194.

Development of a High-Throughput Respiratory Syncytial Virus Fluorescent Focus-Based Microneutralization Assay

Neutralizing antibodies specific for respiratory syncytial virus (RSV) represent a major protective mechanism against RSV infection, as demonstrated by the efficacy of the immune-prophylactic monoclonal antibody palivizumab in preventing RSV-associated lower respiratory tract infections in premature infants. Accordingly, the RSV neutralization assay has become a key functional method to assess the neutralizing activity of serum antibodies in preclinical animal models, epidemiology studies, and clinical trials. In this study, we qualified a 24-h, fluorescent focus-based microneutralization (RSVA FFA-MN) method that requires no medium exchange or pre- or postinfection processing to detect green fluorescent protein-expressing RSV strain A2 (RSVA-GFP)-infected cells, using a high-content imaging system for automated image acquisition and focus enumeration. The RSVA FFA-MN method was shown to be sensitive, with a limit of detection (LOD) and limit of quantitation (LOQ) of 1:10, or 3.32 log₂; linear over a range of 4.27 to 9.65 log₂ 50% inhibitory concentration (IC₅₀); and precise, with intra- and interassay coefficients of variation of <21%. This precision allowed the choice of a statistically justified 3-fold-rise seroresponse cutoff criterion. The repeatability and robustness of this method were demonstrated by including a pooled human serum sample in every assay as a positive control (PC). Over 3 years of testing between two laboratories, this PC generated data falling within 2.5 standard deviations of the mean 98.7% of the time (n = 1,720). This high-throughput and reliable RSV microneutralization assay has proven useful for testing sera from preclinical vaccine candidate evaluation studies, epidemiology studies, and both pediatric and adult vaccine clinical trials.

Intranasal immunization with a single dose of the fusion protein formulated with a combination adjuvant induces long-term protective immunity against respiratory syncytial virus

Respiratory syncytial virus (RSV) is the most common cause of respiratory tract infections in both children and elderly people. In this study we evaluated the short- and long-term protective efficacy of a single intranasal (IN) immunization with a RSV vaccine formulation consisting of a codon-optimized fusion (F) protein formulated with poly(I:C), an innate defense regulator peptide and a polyphosphazene (ΔF/TriAdj). This vaccine induced strong systemic and local immune responses, including RSV F-specific IgG1 and IgG2a, SIgA and virus neutralizing antibodies in mice. Furthermore, ΔF/TriAdj promoted production of IFN-γ-secreting T cells and RSV F85-93-specific CD8+ effector T cells. After RSV challenge, no virus was recovered from the lungs of the vaccinated mice. To evaluate the duration of immunity induced by a single IN vaccination, mice were again immunized once with ΔF/TriAdj and challenged with RSV five months later. High levels of IgG1, IgG2a and virus neutralizing antibodies were detected in the ΔF/TriAdj-vaccinated animals. Moreover, this vaccine formulation induced robust local SIgA production and IgA-secreting memory B cell development, and conferred complete protection against subsequent RSV challenge. In conclusion, a single IN vaccination with RSV ΔF protein formulated with TriAdj induced robust, long-term protective immune responses against RSV infection.

Inferior immunogenicity and efficacy of respiratory syncytial virus fusion protein-based subunit vaccine candidates in aged versus young mice

Respiratory syncytial virus (RSV) is recognized as an important cause of lower and upper respiratory tract infections in older adults, and a successful vaccine would substantially lower morbidity and mortality in this age group. Recently, two vaccine candidates based on soluble purified glycoprotein F (RSV F), either alone or adjuvanted with glucopyranosyl lipid A formulated in a stable emulsion (GLA-SE), failed to reach their primary endpoints in clinical efficacy studies, despite demonstrating the desired immunogenicity profile and efficacy in young rodent models. Here, one of the RSV F vaccine candidates (post-fusion conformation, RSV post-F), and a stabilized pre-fusion form of RSV F (RSV pre-F, DS-Cav1) were evaluated in aged BALB/c mice. Humoral and cellular immunogenicity elicited after immunization of naïve, aged mice was generally lower compared to young animals. In aged mice, RSV post-F vaccination without adjuvant poorly protected the respiratory tract from virus replication, and addition of GLA-SE only improved protection in the lungs, but not in nasal turbinates. RSV pre-F induced higher neutralizing antibody titers compared to RSV post-F (as previously reported) but interestingly, RSV F-specific CD8 T cell responses were lower compared to RSV post-F responses regardless of age. The vaccines were also tested in RSV seropositive aged mice, in which both antigen forms similarly boosted neutralizing antibody titers, although GLA-SE addition boosted neutralizing activity only in RSV pre-F immunized animals. Cell-mediated immune responses in the aged mice were only slightly boosted and well below levels induced in seronegative young mice. Taken together, the findings suggest that the vaccine candidates were not able to induce a strong anti-RSV immune response in recipient mice with an aged immune system, in agreement with recent human clinical trial results. Therefore, the aged mouse model could be a useful tool to evaluate improved vaccine candidates, targeted to prevent RSV disease in older adults.

Dose Selection for an Adjuvanted Respiratory Syncytial Virus F Protein Vaccine for Older Adults Based on Humoral and Cellular Immune Responses

This is the second phase 1 study of a respiratory syncytial virus (RSV) vaccine containing RSV fusion protein (sF) adjuvanted with glucopyranosyl lipid A (GLA) in a squalene-based 2% stable emulsion (GLA-SE). In this randomized, double-blind study, 261 subjects aged ≥60 years received inactivated influenza vaccine (IIV), a vaccine containing 120 μg sF with escalating doses of GLA (1, 2.5, or 5 μg) in SE, or a vaccine containing 80 μg sF with 2.5 μg GLA in SE. Subjects receiving 120 μg sF with 2.5 or 5 μg GLA were also randomized to receive IIV or placebo. Immunity to RSV was assessed by detection of microneutralizing, anti-F immunoglobulin G, and palivizumab-competitive antibodies and F-specific gamma interferon enzyme-linked immunosorbent spot assay T-cell responses. Higher adjuvant doses increased injection site discomfort, but at the highest dose, the reactogenicity was similar to that of IIV. Significant humoral and cellular immune responses were observed. The 120 μg sF plus 5.0 μg GLA formulation resulted in the highest responses in all subjects and in older subjects. These results confirm previous observations of vaccine tolerability, safety, and immunogenicity and were used to select the 120 μg sF plus 5.0 μg GLA formulation for phase 2 evaluation. (This study has been registered at ClinicalTrials.gov under registration no. NCT02289820.).

New Insights Contributing to the Development of Effective Vaccines and Therapies to Reduce the Pathology Caused by hRSV

Human Respiratory Syncytial Virus (hRSV) is one of the major causes of acute lower respiratory tract infections (ALRTI) worldwide, leading to significant levels of immunocompromisation as well as morbidity and mortality in infants. Its main target of infection is the ciliated epithelium of the lungs and the host immune responses elicited is ineffective at achieving viral clearance. It is thought that the lack of effective immunity against hRSV is due in part to the activity of several viral proteins that modulate the host immune response, enhancing a Th2-like pro-inflammatory state, with the secretion of cytokines that promote the infiltration of immune cells to the lungs, with consequent damage. Furthermore, the adaptive immunity triggered by hRSV infection is characterized by weak cytotoxic T cell responses and secretion of low affinity antibodies by B cells. These features of hRSV infection have meant that, to date, no effective and safe vaccines have been licensed. In this article, we will review in detail the information regarding hRSV characteristics, pathology, and host immune response, along with several prophylactic treatments and vaccine prototypes. We will also expose significant data regarding the newly developed BCG-based vaccine that promotes protective cellular and humoral response against hRSV infection, which is currently undergoing clinical evaluation.

Novel recombinant DNA vaccine candidates for human respiratory syncytial virus: Preclinical evaluation of immunogenicity and protection efficiency

The development of safe and potent vaccines for human respiratory syncytial virus (HRSV) is still a challenge for researchers worldwide. DNA-based immunization is currently a promising approach that has been used to generate human vaccines for different age groups. In this study, novel HRSV DNA vaccine candidates were generated and preclinically tested in BALB/c mice. Three different versions of the codon-optimized HRSV fusion (F) gene were individually cloned into the pPOE vector. The new recombinant vectors either express full-length (pPOE-F), secretory (pPOE-TF), or M2_82-90 linked (pPOE-FM2) forms of the F protein. Distinctive expression of the F protein was identified in HEp-2 cells transfected with the different recombinant vectors using ELISA and immunofluorescence. Mice immunization verified the potential for recombinant vectors to elicit significant levels of neutralizing antibodies and CD8⁺ T-cell lymphocytes. pPOE-TF showed higher levels of gene expression in cell culture and better induction of the humoral and cellular immune responses. Following virus challenge, mice that had been immunized with the recombinant vectors were able to control virus replication and displayed lower inflammation compared with mice immunized with empty pPOE vector or formalin-inactivated HRSV vaccine. Moreover, pulmonary cytokine profiles of mice immunized with the 3 recombinant vectors were similar to those of the mock infected group. In conclusion, recombinant pPOE vectors are promising HRSV vaccine candidates in terms of their safety, immunogenicity and protective efficiency. These data encourage further evaluation in phase I clinical trials.

Analytical Characterization of an Oil-in-Water Adjuvant Emulsion

Adjuvants are typically used in subunit vaccine formulations to enhance immune responses elicited by individual antigens. Physical chemical characterization of novel adjuvants is an important step in ensuring their effective use in vaccine formulations. This paper reports application of a panel of quantitative assays developed to analyze and characterize an oil-in-water adjuvant emulsion, which contains glucopyranosyl lipid A (GLA) and is a squalene-based emulsion. GLA is a fully synthetic analogue of monophosphoryl lipid A, which is a Toll-like receptor type 4 agonist and an FDA-approved adjuvant. The GLA-stable emulsion (GLA-SE) is currently being used for a respiratory syncytial virus vaccine in a phase 2 clinical trial. GLA was quantitated using reverse-phased high-performance liquid chromatography (RP-HPLC) coupled to a mass spectrometric detector, achieving higher assay sensitivity than the charged aerosol detection routinely used. Quantitation of the excipients of GLA-SE, including squalene, egg phosphatidyl choline, and Poloxamer 188, was achieved using a simple and rapid RP-HPLC method with evaporative light scattering detection, eliminating chemical derivatization typically required for these chromophore-lacking compounds. DL-α-tocopherol, the antioxidant of the GLA-SE, was quantitated using a RP-HPLC method with conventional UV detection. The experimental results compared well with values expected for these compounds based on targeted composition of the adjuvant. The assays were applied to identify degradation of individual components in a GLA-SE sample that degraded into distinct aqueous and oil phases. The methods developed and reported here are effective tools in monitoring physicochemical integrity of the adjuvant, as well as in formulation studies.

Passive and active immunization against respiratory syncytial virus for the young and old

INTRODUCTION

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants worldwide and also causes significant disease in the elderly. Despite 60 years of RSV research and vaccine development, there is only one approved medicine to prevent RSV infections. Palivizumab, a monoclonal antibody (mAb) against the RSV fusion (F) protein, is indicated for preterm infants and children at high-risk for RSV infections. It is an active time in RSV vaccine and mAb development with 14 vaccines and 2 mAbs currently being tested in clinical trials as of 13 February 2017. Active vaccination of women in the third trimester or passive immunization of infants with a mAb are particularly attractive approaches as the most severe disease occurs within the first 6 months of life. Areas covered: Here, we review current approaches for preventing RSV in the young and old, describe proposed clinical endpoints for studies in pediatric and adult clinical trials and highlight results from recent and ongoing clinical studies. Expert commentary: With 16 candidates in clinical development, approval of the first RSV vaccine or mAb for the prevention of RSV in all infants or the elderly is likely to occur in the next five years.

PCPP-Adjuvanted Respiratory Syncytial Virus (RSV) sF Subunit Vaccine: Self-Assembled Supramolecular Complexes Enable Enhanced Immunogenicity and Protection

PCPP, a well-defined polyphosphazene macromolecule, has been studied as an immunoadjuvant for a soluble form of the postfusion glycoprotein of respiratory syncytial virus (RSV sF), which is an attractive vaccine candidate for inducing RSV-specific immunity in mice and humans. We demonstrate that RSV sF-PCPP formulations induce high neutralization titers to RSV comparable to alum formulations even at a low PCPP dose and protect animals against viral challenge both in the lung and in the upper respiratory tract. PCPP formulations were also characterized by Th1-biased responses, compared to Th2-biased responses that are more typical for RSV sF alone or RSV sF-alum formulations, suggesting an inherent immunostimulating activity of the polyphosphazene adjuvant. We defined these immunologically active RSV sF-PCPP formulations as self-assembled water-soluble protein-polymer complexes with distinct physicochemical parameters. The secondary structure and antigenicity of the protein in the complex were fully preserved during the spontaneous aqueous self-assembly process. These findings further advance the concept of polyphosphazene immunoadjuvants as unique dual-functionality adjuvants integrating delivery and immunostimulating modalities in one water-soluble molecule.

Immunization with Low Doses of Recombinant Postfusion or Prefusion Respiratory Syncytial Virus F Primes for Vaccine-Enhanced Disease in the Cotton Rat Model Independently of the Presence of a Th1-Biasing (GLA-SE) or Th2-Biasing (Alum) Adjuvant

Respiratory syncytial virus (RSV) infection of children previously immunized with a nonlive, formalin-inactivated (FI)-RSV vaccine has been associated with serious enhanced respiratory disease (ERD). Consequently, detailed studies of potential ERD are a critical step in the development of nonlive RSV vaccines targeting RSV-naive children and infants. The fusion glycoprotein (F) of RSV in either its postfusion (post-F) or prefusion (pre-F) conformation is a target for neutralizing antibodies and therefore an attractive antigen candidate for a pediatric RSV subunit vaccine. Here, we report the evaluation of RSV post-F and pre-F in combination with glucopyranosyl lipid A (GLA) integrated into stable emulsion (SE) (GLA-SE) and alum adjuvants in the cotton rat model. Immunization with optimal doses of RSV F antigens in the presence of GLA-SE induced high titers of virus-neutralizing antibodies and conferred complete lung protection from virus challenge, with no ERD signs in the form of alveolitis. To mimic a waning immune response, and to assess priming for ERD under suboptimal conditions, an antigen dose de-escalation study was performed in the presence of either GLA-SE or alum. At low RSV F doses, alveolitis-associated histopathology was unexpectedly observed with either adjuvant at levels comparable to FI-RSV-immunized controls. This occurred despite neutralizing-antibody titers above the minimum levels required for protection and with no/low virus replication in the lungs. These results emphasize the need to investigate a pediatric RSV vaccine candidate carefully for priming of ERD over a wide dose range, even in the presence of strong neutralizing activity, Th1 bias-inducing adjuvant, and protection from virus replication in the lower respiratory tract.IMPORTANCE RSV disease is of great importance worldwide, with the highest burden of serious disease occurring upon primary infection in infants and children. FI-RSV-induced enhanced disease, observed in the 1960s, presented a major and ongoing obstacle for the development of nonlive RSV vaccine candidates. The findings presented here underscore the need to evaluate a nonlive RSV vaccine candidate during preclinical development over a wide dose range in the cotton rat RSV enhanced-disease model, as suboptimal dosing of several RSV F subunit vaccine candidates led to the priming for ERD. These observations are relevant to the validity of the cotton rat model itself and to safe development of nonlive RSV vaccines for seronegative infants and children.

Feasibility of Freeze-Drying Oil-in-Water Emulsion Adjuvants and Subunit Proteins to Enable Single-Vial Vaccine Drug Products

To generate potent vaccine responses, subunit protein antigens typically require coformulation with an adjuvant. Oil-in-water emulsions are among the most widely investigated adjuvants, based on their demonstrated ability to elicit robust antibody and cellular immune responses in the clinic. However, most emulsions cannot be readily frozen or lyophilized, on account of the risk of phase separation, and may have a deleterious effect on protein antigen stability when stored long term as a liquid coformulation. To circumvent this, current emulsion-formulated vaccines generally require a complex multivial presentation with obvious drawbacks, making a single-vial presentation for such products highly desirable. We describe the development of a stable, lyophilized squalene emulsion adjuvant through innovative formulation and process development approaches. On reconstitution, freeze-dried emulsion preparations were found to have a minimal increase in particle size of ∼20 nm and conferred immunogenicity in BALB/c mice similar in potency to freshly prepared emulsion coformulations in liquid form.

Thermoresponsive Polymer Nanoparticles Co-deliver RSV F Trimers with a TLR-7/8 Adjuvant

Structure-based vaccine design has been used to develop immunogens that display conserved neutralization sites on pathogens such as HIV-1, respiratory syncytial virus (RSV), and influenza. Improving the immunogenicity of these designed immunogens with adjuvants will require formulations that do not alter protein antigenicity. Here, we show that nanoparticle-forming thermoresponsive polymers (TRP) allow for co-delivery of RSV fusion (F) protein trimers with Toll-like receptor 7 and 8 agonists (TLR-7/8a) to enhance protective immunity. Although primary amine conjugation of TLR-7/8a to F trimers severely disrupted the recognition of critical neutralizing epitopes, F trimers site-selectively coupled to TRP nanoparticles retained appropriate antigenicity and elicited high titers of prefusion-specific, TH1 isotype anti-RSV F antibodies following vaccination. Moreover, coupling F trimers to TRP delivering TLR-7/8a resulted in ∼3-fold higher binding and neutralizing antibody titers than soluble F trimers admixed with TLR-7/8a and conferred protection from intranasal RSV challenge. Overall, these data show that TRP nanoparticles may provide a broadly applicable platform for eliciting neutralizing antibodies to structure-dependent epitopes on RSV, influenza, HIV-1, or other pathogens.

Respiratory syncytial virus vaccines: an update on those in the immediate pipeline

Respiratory syncytial virus (RSV) is among the most common causes of lower respiratory tract infection among infants and the elderly worldwide. Despite its long history, no licensed vaccine is available. Recently, advances in the knowledge of RSV biology and pathology as well as the development of new techniques to generate vaccine candidates have increased the number of promising vaccines. The aim of this review is to analyze RSV characteristics, to consider the history of RSV vaccines and to discuss RSV vaccines currently in development. Among the candidates in clinical trials, nanoparticle and subunit vaccines seem to be the most promising for pregnant women and the elderly, whereas live-attenuated or vector-based vaccines appear to be optimal for the pediatric population.

The science of vaccine adjuvants: advances in TLR4 ligand adjuvants

TLR ligands are used in modern vaccine adjuvants, TLR4 ligand-based adjuvants are the most advanced in commercial vaccines. Increased understanding of TLR4 receptor-ligand interactions enables chemical synthesis and modification of new leads and our understanding of the biological/immunological mechanisms of combination adjuvants enables formulation of potent and safe vaccine compositions. Characterization of non-glycolipid TLR4 ligands provided new mechanistic information that could lead to new formulations. This review discusses advances in TLR4 agonist design-both glycolipid and non-glycolipid based TLR4 ligands-as well as CD14 activation as options to activate or synergize with TLR4 signaling. Finally, we review the molecular and cellular mechanisms that are elicited by formulated TLR4 targeted combination adjuvants during the initiation of innate immune responses leading to quality adaptive responses.

Novel Respiratory Syncytial Virus-Like Particle Vaccine Composed of the Postfusion and Prefusion Conformations of the F Glycoprotein

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory disease in infants and children and represents an important global health burden for the elderly and the immunocompromised. Despite decades of research efforts, no licensed vaccine for RSV is available. We have developed virus-like particle (VLP)-based RSV vaccines assembled with the human metapneumovirus (hMPV) matrix protein (M) as the structural scaffold and the RSV fusion glycoprotein (F) in either the postfusion or prefusion conformation as its prime surface immunogen. Vaccines were composed of postfusion F, prefusion F, or a combination of the two conformations and formulated with a squalene-based oil emulsion as adjuvant. Immunization with these VLP vaccines afforded full protection against RSV infection and prevented detectable viral replication in the mouse lung after challenge. Analyses of lung cytokines and chemokines showed that VLP vaccination mostly induced the production of gamma interferon (IFN-γ), a marker of the Th1-mediated immune response, which is predominantly required for viral protection. Conversely, immunization with a formalin-inactivated RSV (FI-RSV) vaccine induced high levels of inflammatory chemokines and cytokines of the Th2- and Th17-mediated types of immune responses, as well as severe lung inflammation and histopathology. The VLP vaccines showed restricted production of these immune mediators and did not induce severe bronchiolitis or perivascular infiltration as seen with the FI-RSV vaccine. Remarkably, analysis of the serum from immunized mice showed that the VLP vaccine formulated using a combination of postfusion and prefusion F elicited the highest level of neutralizing antibody and enhanced the Th1-mediated immune response.

Brief History and Characterization of Enhanced Respiratory Syncytial Virus Disease

In 1967, infants and toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (RSV) experienced an enhanced form of RSV disease characterized by high fever, bronchopneumonia, and wheezing when they became infected with wild-type virus in the community. Hospitalizations were frequent, and two immunized toddlers died upon infection with wild-type RSV. The enhanced disease was initially characterized as a "peribronchiolar monocytic infiltration with some excess in eosinophils." Decades of research defined enhanced RSV disease (ERD) as the result of immunization with antigens not processed in the cytoplasm, resulting in a nonprotective antibody response and CD4(+) T helper priming in the absence of cytotoxic T lymphocytes. This response to vaccination led to a pathogenic Th2 memory response with eosinophil and immune complex deposition in the lungs after RSV infection. In recent years, the field of RSV experienced significant changes. Numerous vaccine candidates with novel designs and formulations are approaching clinical trials, defying our previous understanding of favorable parameters for ERD. This review provides a succinct analysis of these parameters and explores criteria for assessing the risk of ERD in new vaccine candidates.

Protection and Long-Lived Immunity Induced by the ID93/GLA-SE Vaccine Candidate against a Clinical Mycobacterium tuberculosis Isolate

Mycobacterium tuberculosis HN878 represents a virulent clinical strain from the W-Beijing family, which has been tested in small animal models in order to study its virulence and its induction of host immune responses following infection. This isolate causes death and extensive lung pathology in infected C57BL/6 mice, whereas lab-adapted strains, such as M. tuberculosis H37Rv, do not. The use of this clinically relevant isolate of M. tuberculosis increases the possibilities of assessing the long-lived efficacy of tuberculosis vaccines in a relatively inexpensive small animal model. This model will also allow for the use of knockout mouse strains to critically examine key immunological factors responsible for long-lived, vaccine-induced immunity in addition to vaccine-mediated prevention of pulmonary immunopathology. In this study, we show that the ID93/glucopyranosyl lipid adjuvant (GLA)-stable emulsion (SE) tuberculosis vaccine candidate, currently in human clinical trials, is able to elicit protection against M. tuberculosis HN878 by reducing the bacterial burden in the lung and spleen and by preventing the extensive lung pathology induced by this pathogen in C57BL/6 mice.

Understanding respiratory syncytial virus (RSV) vaccine development and aspects of disease pathogenesis

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infections causing bronchiolitis and some mortality in young children and the elderly. Despite decades of research there is no licensed RSV vaccine. Although significant advances have been made in understanding the immune factors responsible for inducing vaccine-enhanced disease in animal models, less information is available for humans. In this review, we discuss the different types of RSV vaccines and their target population, the need for establishing immune correlates for vaccine efficacy, and how the use of different animal models can help predict vaccine efficacy and clinical outcomes in humans.

Recent advances in the development of subunit-based RSV vaccines

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections causing pneumonia and bronchiolitis in infants. RSV also causes serious illness in elderly populations, immunocompromised patients and individuals with pulmonary or cardiac problems. The significant morbidity and mortality associated with RSV infection have prompted interest in RSV vaccine development. In the 1960s, a formalin-inactivated vaccine trial failed to protect children, and indeed enhanced pathology when naturally infected later with RSV. Hence, an alternative approach to traditional killed virus vaccines, which can induce protective immunity without serious adverse events, is desired. Several strategies have been explored in attempts to produce effective vaccine candidates including gene-based and subunit vaccines. Subunit-based vaccine approaches have shown promising efficacy in animal studies and several have reached clinical trials. The current stage of development of subunit-based vaccines against RSV is reviewed in this article.

The changing landscape of respiratory syncytial virus

Recognition of the acute and chronic burden of respiratory syncytial virus (RSV) lower respiratory tract infections (LRTI) sparked a wave of initiatives to develop preventive and therapeutic products against the pathogen in recent years. RSV is a leading cause of hospitalization in infants in industrialized and developing countries, has been causally linked to recurrent wheezing during childhood, associated with pediatric asthma, and is an important cause of mortality in the first months of life in the developing world. Significant changes in the epidemiology, clinical manifestations, and severe consequences of LRTI may emerge in the next decade with the advent of novel preventive strategies against RSV. This manuscript outlines some of these changes and discusses potential scenarios based on the current literature and experiences with other pathogens.

Inflammatory damage on respiratory and nervous systems due to hRSV infection

The exacerbated inflammatory response elicited by human Respiratory Syncytial Virus (hRSV) in the lungs of infected patients causes a major health burden in the pediatric and elderly population. Since the discovery of hRSV, the exacerbated host immune-inflammatory response triggered by this virus has been extensively studied. In this article, we review the effects on the airways caused by immune cells and cytokines/chemokines secreted during hRSV infection. While molecules such as interferons contribute at controlling viral infection, IL-17 and others produce damage to the hRSV-infected lung. In addition to affecting the airways, hRSV infection can cause significant neurologic abnormalities in the host, such as seizures and encephalopathy. Although the origin of these symptoms remains unclear, studies from patients suffering neurological alteration suggest an involvement of the inflammatory response against hRSV.