Recent advances in the prevention of respiratory syncytial virus in pediatrics.

PURPOSE OF REVIEW: Respiratory syncytial virus (RSV) is a ubiquitous virus and the leading cause of pediatric hospitalization in the United States. Prevention strategies are key for reducing the burden of RSV. Several new agents aimed at preventing RSV in infants and children were FDA-approved in 2023, and many more are in the development pipeline. This review highlights new developments in RSV prevention in pediatric patients and the important safety considerations for clinical trials. RECENT FINDINGS: Two new preventive therapies were FDA approved in 2023; a maternal vaccine (Abrysvo) and a mAb (Beyfortus) have both demonstrated reduction in medically attended lower respiratory tract infections in infants and children. Evaluation of ongoing clinical trials demonstrates that the field is expanding further to include direct immunization of infants and children utilizing a variety of delivery modalities. While these developments present the optimistic prospect of RSV prevention in a range of ages, acute and long-term risks must be carefully evaluated. SUMMARY: Prevention of RSV is more accessible than ever, but careful consideration must be given to risks associated with new and developing prevention strategies. Rigor of clinical trials including longitudinal outcomes of agents in development and postmarketing surveillance of newly approved therapies will be of paramount importance to ensure long-term safety of new RSV prevention strategies.

Exacerbated lung inflammation following secondary RSV exposure is CD4+ T cell-dependent and is not mitigated in infant BALB/c mice born to PreF-vaccinated dams.

Respiratory syncytial virus (RSV) is the leading cause of childhood hospitalizations due to bronchiolitis in children under 5 years of age. Moreover, severe RSV disease requiring hospitalization is associated with the subsequent development of wheezing and asthma. Due to the young age in which viral protection is needed and risk of vaccine enhanced disease following direct infant vaccination, current approaches aim to protect young children through maternal immunization strategies that boost neutralizing maternal antibody (matAb) levels. However, there is a scarcity of studies investigating the influence of maternal immunization on secondary immune responses to RSV in the offspring or whether the subsequent development of wheezing and asthma is mitigated. Toward this goal, our lab developed a murine model of maternal RSV vaccination and repeat RSV exposure to evaluate the changes in immune response and development of exacerbated lung inflammation on secondary RSV exposure in mice born to immunized dams. Despite complete protection following primary RSV exposure, offspring born to pre-fusion F (PreF)-vaccinated dams had exaggerated secondary ILC2 and Th2 responses, characterized by enhanced production of IL-4, IL-5, and IL-13. These enhanced type 2 cellular responses were associated with exaggerated airway eosinophilia and mucus hyperproduction upon re-exposure to RSV. Importantly, depletion of CD4+ T cells led to complete amelioration of the observed type 2 pathology on secondary RSV exposure. These unanticipated results highlight the need for additional studies that look beyond primary protection to better understand how maternal immunization shapes subsequent immune responses to repeat RSV exposure.

Modeling the kinetics of lymph node retention and exposure of a cargo protein delivered by biotin-functionalized nanoparticles.

Generation of protective immunity through vaccination arises from the adaptive immune response developed primarily in the lymph nodes drained from the immunization site. Relative to the intramuscular route, subcutaneous administration allows for direct and rapid access to the lymphatics, but accumulation of soluble protein antigens within the lymph nodes is limited. Subunit vaccines also require immune stimulating adjuvants which may not accumulate in the same lymph nodes simultaneously with antigen. Herein we report the use of biotinylated poly (lactic-co-glycolic acid) nanoparticles (bNPs) to enhance delivery of a model protein antigen to the lymphatics. bNPs provide dual functionality as adjuvant and vehicle to localize antigens with stimulated immune cells in the same draining lymph node. Using streptavidin as a model antigen, which can be loaded directly onto the bNP surface, we evaluated the kinetics of lymph node occupancy and adaptive immune responses in wildtype C57BL/6 mice. Antigen exposure in vivo was significantly improved through surface loading onto bNPs, and we developed a working kinetic model to account for the retention of both particles and antigen in draining lymph nodes. We observed enhanced T cell responses and antigen-specific B cell response in vivo when antigen was delivered on the particle surface. This work highlights the advantage of combining intrinsic adjuvant and antigen loading in a single entity, and the utility of kinetic modeling in the understanding of particle-based vaccines. STATEMENT OF SIGNIFICANCE: Development of safe and effective subunit vaccines depends on effective formulations that render optimized exposure and colocalization of antigens and adjuvants. In this work, we utilize a nanoparticle system which features self-adjuvanting properties and allows for surface loading of recombinant protein antigens. Using in vivo imaging, we demonstrated prolonged co-localization of the antigen and adjuvant particles in draining lymph nodes and provided evidence of B cell activation for up to 21 days following subcutaneous injection. A pharmacokinetic model was developed as a step towards bridging the translational gap between particulate-based vaccines and observed outcomes. The results have implications for the rational design of particle-based vaccines.

RAGE contributes to allergen driven severe neutrophilic airway inflammation via NLRP3 inflammasome activation in mice.

Background: Asthma is a major public healthcare burden, affecting over 300 million people worldwide. While there has been great progress in the treatment of asthma, subsets of patients who present with airway neutrophilia, often have more severe disease, and tend to be resistant to conventional corticosteroid treatments. The receptor for advanced glycation endproducts (RAGE) plays a central role in the pathogenesis of eosinophilic asthma, however, it's role in neutrophilic asthma remains largely uninvestigated. Methods: A mouse model of severe steroid resistant neutrophilic airway disease (SSRNAD) using the common fungal allergen Alternaria alternata (AA) was employed to evaluate the effects of genetic ablation of RAGE and pharmacological inhibition of the NLRP3 inflammasome on neutrophilic airway inflammation. Results: AA exposure induced robust neutrophil-dominant airway inflammation and increased BALF levels of Th1/Th17 cytokines in wild-type mice, which was significantly reduced in RAGE-/- mice. Serum levels of IgE and IgG1 were increased similarly in both wild-type and RAGE-/- mice. Pharmacological inhibition of NLRP3 blocked the effects of AA exposure and NLRP3 inflammasome activation was RAGE-dependent. Neutrophil extracellular traps were elevated in the BALF of wild-type but not RAGE-/- mice and an atypical population of SiglecF+ neutrophils were identified in the BALF. Lastly, time-course studies found that RAGE expression promoted sustained neutrophil accumulation in the BALF of mice in response to AA.

Acute kidney injury in cystic fibrosis patients treated with intravenous colistimethate sodium or tobramycin.

OBJECTIVES: Colistimethate sodium and tobramycin are important systemic antibiotics for treatment of cystic fibrosis (CF) pulmonary exacerbations but can induce acute kidney injury (AKI). We characterize the rate of AKI in CF patients treated with systemic colistimethate sodium compared with tobramycin. METHODS: This single-centre, retrospective cohort study included hospitalized CF patients treated with IV colistimethate sodium or tobramycin. The primary outcome was AKI defined using the RIFLE criteria. Multivariate logistic regression using a mixed model was performed to identify variables that were independently associated with AKI. RESULTS: Overall, 156 patients representing 507 care encounters were included. The OR of AKI was not increased with IV colistimethate sodium relative to IV tobramycin after adjusting for other potential predictor variables (aOR 1.00; 95% CI 0.16-6.03). The frequency of AKI was 9.5% across all encounters, 6.9% with IV colistimethate sodium and 9.9% with IV tobramycin, with RIFLE category R (risk) being the most common stage, accounting for 4.2% of encounters with IV colistimethate sodium and 9.2% with IV tobramycin. The concomitant use of another nephrotoxin (aOR 2.51; 95% CI 1.27-4.95) or the combination of vancomycin and piperacillin/tazobactam (aOR 5.95; 95% CI 2.05-17.3) were both associated with increased odds of AKI. CONCLUSIONS: Systemic treatment with colistimethate sodium or tobramycin in the CF patient population is associated with a similar rate of nephrotoxicity. However, clinicians should be mindful of the increased risk for AKI in patients treated with either IV colistimethate sodium or IV tobramycin when used concurrently with other nephrotoxic agents, particularly the combination of vancomycin and piperacillin/tazobactam.

Immune Cells Activating Biotin-Decorated PLGA Protein Carrier.

Nanoparticle formulations have long been proposed as subunit vaccine carriers owing to their ability to entrap proteins and codeliver adjuvants. Poly(lactic-co-glycolic acid) (PLGA) remains one of the most studied polymers for controlled release and nanoparticle drug delivery, and numerous studies exist proposing PLGA particles as subunit vaccine carriers. In this work we report using PLGA nanoparticles modified with biotin (bNPs) to deliver proteins via adsorption and stimulate professional antigen-presenting cells (APCs). We present evidence showing bNPs are capable of retaining proteins through the biotin-avidin interaction. Surface accessible biotin bound both biotinylated catalase (bCAT) through avidin and streptavidin horseradish peroxidase (HRP). Analysis of the HRP found that activity on the bNPs was preserved once captured on the surface of bNP. Further, bNPs were found to have self-adjuvant properties, evidenced by bNP induced IL-1ß, IL-18, and IL-12 production in vitro in APCs, thereby licensing the cells to generate Th1-type helper T cell responses. Cytokine production was reduced in avidin precoated bNPs (but not with other proteins), suggesting that the proinflammatory response is due in part to exposed biotin on the surface of bNPs. bNPs injected subcutaneously were localized to draining lymph nodes detectable after 28 days and were internalized by bronchoalveolar lavage dendritic cells and macrophages in mice in a dose-dependent manner when delivered intranasally. Taken together, these data provide evidence that bNPs should be explored further as potential adjuvanting carriers for subunit vaccines.

Maternal immunization with adjuvanted RSV prefusion F protein effectively protects offspring from RSV challenge and alters innate and T cell immunity.

Respiratory syncytial virus (RSV) commonly causes severe respiratory tract infections in infants, peaking between 2 and 6 months of age; an age at which direct vaccination is unlikely to be effective. Maternal immunization can deliver high levels of antibodies to newborns, providing immediate protection. Following natural infection, antibodies targeting the prefusion conformation of RSV F protein (PreF) have the greatest neutralizing capacity and thus, may provide infants with a high degree of RSV protection when acquired through maternal vaccination. However, the influence of anti-PreF maternal antibodies on infant immunity following RSV exposure has not been elucidated. To address this knowledge gap, offspring born to dams immunized with a RSV PreF vaccine formulation were challenged with RSV and their immune responses were analyzed over time. These studies demonstrated safety and efficacy for RSV-challenged, maternally-immunized offspring but high and waning maternal antibody levels were associated with differential innate and T cell immunity.

Formulation of the prefusion RSV F protein with a Th1/Th2-balanced adjuvant provides complete protection without Th2-skewed immunity in RSV-experienced young mice.

Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections among infants with most infections occurring in the first year of life. Multiple RSV exposures are required for children to mount adult-like immune responses. Although adult RSV immunity is associated with less severe disease, the protection induced through natural infection is short-lived. Therefore, vaccination of RSV-experienced young children may accelerate immunity and provide long-term protection from RSV reinfection. However, the extent to which different Th-biased vaccine regimens influence pre-existing humoral and cellular immunity in RSV-experienced young children is unknown. To address this question, infant BALB/c mice were RSV-infected and subsequently immunized with the prefusion RSV F (PreF) antigen formulated with either a Th2-skewing (Alum) or Th1/Th2-balanced (Advax-SM) adjuvant. These studies show that both adjuvants boosted neutralizing antibody and protected from RSV reinfection, but Advax-SM adjuvant prevented the Th2-skewed immunity observed in RSV-experienced young mice immunized with PreF/Alum.

Prefusion RSV F Immunization Elicits Th2-Mediated Lung Pathology in Mice When Formulated With a Th2 (but Not a Th1/Th2-Balanced) Adjuvant Despite Complete Viral Protection.

Respiratory syncytial virus (RSV) remains the most common cause of lower respiratory tract infections in children worldwide. Development of a vaccine has been hindered by the risk of developing enhanced respiratory disease (ERD) upon natural exposure to the virus. Generation of higher quality neutralizing antibodies with stabilized pre-fusion F protein antigens has been proposed as a strategy to prevent ERD. We sought to test whether there was evidence of ERD in naïve BALB/c mice immunized with an unadjuvanted, stabilized pre-fusion F protein, and challenged with RSV line 19. We further sought to determine the extent to which formulation with a Th2-biased (alum) or a more Th1/Th2-balanced (Advax-SM) adjuvant influenced cellular responses and lung pathology. When exposed to RSV, mice immunized with pre-fusion F protein alone (PreF) exhibited increased airway eosinophilia and mucus accumulation. This was further exacerbated by formulation of PreF with Alum (aluminum hydroxide). Conversely, formulation of PreF with a Th1/Th2-balanced adjuvant, Advax-SM, not only suppressed RSV viral replication, but also inhibited airway eosinophilia and mucus accumulation. This was associated with lower numbers of lung innate lymphocyte cells (ILC2s) and CD4+ T cells producing IL-5+ or IL-13+ and increased IFNγ+ CD4+ and CD8+ T cells, in addition to RSV F-specific CD8+ T cells. These data suggest that in the absence of preimmunity, stabilized PreF antigens may still be associated with aberrant Th2 responses that induce lung pathology in response to RSV infection, and can be prevented by formulation with more Th1/Th2-balanced adjuvants that enhance CD4+ and CD8+ IFNγ+ T cell responses. This may support the use of stabilized PreF antigens with Th1/Th2-balanced adjuvants like, Advax-SM, as safer alternatives to alum in RSV vaccine candidates.