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Nanoparticle formulations have long been proposed as subunit vaccine carriers owing to their ability to entrap proteins and co-deliver 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 as well as streptavidin-horse radish 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-1β, 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 pre-coated bNPs (but not with other proteins) suggesting that the pro-inflammatory response is specific 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.

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.

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in children worldwide, with the most severe disease occurring in very young infants. Despite half a century of research there still are no licensed RSV vaccines. Difficulties in RSV vaccine development stem from a number of factors, including: (a) a very short time frame between birth and first RSV exposure; (b) interfering effects of maternal antibodies; and (c) differentially regulated immune responses in infants causing a marked T helper 2 (Th2) immune bias. This review seeks to provide an age-specific understanding of RSV immunity critical to the development of a successful pediatric RSV vaccine. Historical and future approaches to the prevention of infant RSV are reviewed, including passive protection using monoclonal antibodies or maternal immunization strategies versus active infant immunization using pre-fusion forms of RSV F protein antigens formulated with novel adjuvants such as Advax that avoid excess Th2 immune polarization.

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.

Tissue resident memory T cells (TRMs) are an important yet incompletely understood cell population that enhance the clearance of respiratory syncytial virus (RSV) infection in both humans and animal models of disease. Limited data in an influenza model of disease suggests the establishment of TRMs in infants is impaired, but the establishment of TRMs during infant RSV infection is unknown. The purpose of this study was to characterize the quantity and function of infant TRM responses to RSV infection. To address this, BALB/c mice were infected with RSV as 10-day old mice or as 6–8-week-old adults. Peripheral T cells were then depleted using FTY720 at the time of an RSV re-challenge 4–5 weeks later. TRM response was evaluated using flow cytometry; viral titers and histological staining were used to assess disease outcomes. Mice infected as infants had significantly lower total numbers of CD4+ and CD8+ TRMs compared to those infected as adults. Furthermore, TRMs established in infancy showed a Th2-biased response, with increased production of IL-4 and IL-10 compared to adults, while adult TRMs produced more granzyme B from CD8+ cells and increased IFNγ from both CD4+ and CD8+ T cells. Mice infected in infancy also showed increased %PAS positive airways compared to those infected initially as adults, suggesting more severe RSV disease. In conclusion, infants have reduced ability to establish TRMs following RSV infection and their TRM population exhibits Th2 skewing. Further studies are needed to elucidate the mechanisms that prevent effective establishment of TRMs following infant pulmonary infections.

OBJECTIVES Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infections worldwide, causing disproportionate morbidity and mortality in infants and children. Infants with stronger Th1 responses have less severe disease, yet little is known about the infant T-cell response within the air space. Thus, we tested the hypothesis that RSV infected infant mice would have quantitative and qualitative deficiencies in CD4+ and CD8+ T-cell populations isolated from the bronchoalveolar lavage when compared to adults and that local delivery of IFN-γ would increase airway CD4+ Tbet+ and CD8+ Tbet+ T-cell responses. METHODS We compared the localization of T-cell responses in RSV-infected infant and adult mice and investigated the effects of local IFN-γ administration on infant cellular immunity. RESULTS Adult CD8+ CD44HI and CD4+ CD44HI Tbet+ T-cells accumulated in the alveolar space whereas CD4+ CD44HI Tbet+ T-cells were evenly distributed between the infant lung tissue and airway and infant lungs contained higher frequencies of CD8+ T-cells. Delivery of IFN-γ to the infant airway failed to increase the accumulation of T-cells in the airspace and unexpectedly reduced CD4+ CD44HI Tbet+ T-cells. However, intranasal IFN-γ increased RSV F protein-specific CD8+ T-cells in the alveolar space. CONCLUSION Together, these data suggest that quantitative and qualitative defects exist in the infant T-cell response to RSV but early, local IFN-γ exposure can increase the CD8+ RSV-specific T-cell response.

Respiratory syncytial virus (RSV) is recognized as a leading cause of acute viral illness in neonates worldwide. However, those with balanced Th1/Th2 responses, as a result of higher IFNγ concentrations, have milder disease and better clinical outcomes. The present study examined the effect of IFNγ administration during primary, neonatal RSV infection on innate and T cell responses during primary and secondary RSV exposure. During primary infection, neonates treated with IFNγ had increased alveolar macrophage (AM) expression of CD80, MHCII, and scavenger receptor A. Subsequent CD8 T cell recruitment and activation was reduced in this group compared to RSV controls, however the RSV-specific CD8 T cell response was enhanced. Upon secondary infection, neutrophil and monocyte recruitment was boosted and expression of CD86 and MHCII was significantly increased on AMs with a correlative decline in CD73 expression compared to primary infection controls. In mice previously infected with RSV, T cell recruitment and activation was significantly increased. However, only those mice that were treated with IFNγ during primary infection showed improved CD8 T cell specificity following secondary RSV exposure. Viral lung titers were also significantly reduced in groups previously exposed to RSV but only IFNγ treatment during primary infection demonstrated significant improvements in airway resistance following methacholine challenge. These results suggest that immunostimulation with IFNγ during primary neonatal RSV is associated with increased innate cell activation and improved CD8 T cell specificity. These cellular changes are associated with enhanced viral clearance and improved airway function.