Immunization with a mucosal, post-fusion F/G protein-based polyanhydride nanovaccine protects neonatal calves against BRSV infection

Human respiratory syncytial virus (HRSV) is a leading cause of death in young children and there are no FDA approved vaccines. Bovine RSV (BRSV) is antigenically similar to HRSV, and the neonatal calf model is useful for evaluation of HRSV vaccines. Here, we determined the efficacy of a polyanhydride-based nanovaccine encapsulating the BRSV post-fusion F and G glycoproteins and CpG, delivered prime-boost via heterologous (intranasal/subcutaneous) or homologous (intranasal/intranasal) immunization in the calf model. We compared the performance of the nanovaccine regimens to a modified-live BRSV vaccine, and to non-vaccinated calves. Calves receiving nanovaccine via either prime-boost regimen exhibited clinical and virological protection compared to non-vaccinated calves. The heterologous nanovaccine regimen induced both virus-specific cellular immunity and mucosal IgA, and induced similar clinical, virological and pathological protection as the commercial modified-live vaccine. Principal component analysis identified BRSV-specific humoral and cellular responses as important correlates of protection. The BRSV-F/G CpG nanovaccine is a promising candidate vaccine to reduce RSV disease burden in humans and animals.

Mucosal delivery of a polyanhydride nanovaccine incorporating CpG and the post-fusion F/ G proteins induces protective immunity against BRSV infection in neonatal calves

Objective:

Previously, immunization with a single intranasal dose of a BRSV post-fusion F/G nanovaccine resulted in partial protection from a BRSV challenge (McGill et al. 2019, McGill et al. 2018). Knowledge gained from these previous studies was used to optimize the vaccine by incorporating CpG-ODN and to investigate the impact of mucosal vs. systemic vaccination routes. In this study a prime-boost immunization regimen was used.

Method:

36 neonatal, mixed-sex, Holstein calves were divided into 6 groups. Group 1 received a heterologous regime with saline and group 2 a homologous boost of the ‘empty’ nanovaccine CPG. Groups 3 and 4 received a homologous mucosal regime of the nanovaccine ± CpG, while groups 5 and 6 received a heterologous regime of the nanovaccine ± CpG. Vaccine-induced responses were monitored and 6 weeks after boost, all calves were challenged with BRSV. Nasopharyngeal swabs were collected for viral shedding and calves monitored for clinical signs and euthanized on day 7 after infection. Lungs were scored for gross pathology. Blood, nasal secretions and lung tissue samples were analyzed for BRSV specific immune responses.

Results:

Unvaccinated controls and CpG-only nanovaccine controls developed lung pathology consistent with a severe BRSV infection. We observed no evidence of vaccine enhanced disease in any vaccinated group. Calves that received the homologous vaccination of the nanovaccine + CPG had significantly less lung pathology and viral burden in the lungs compared to control calves.

Conclusions:

These results indicate that an intranasal homologous vaccination regimen with the post-fusion F/G + CpG nanovaccine has the capacity to reduce BRSV disease in neonatal calves with preexisting maternal antibodies.

Polymeric Nanoparticle-Based Vaccine Adjuvants and Delivery Vehicles

As vaccine formulations have progressed from including live or attenuated strains of pathogenic components for enhanced safety, developing new adjuvants to more effectively generate adaptive immune responses has become necessary. In this context, polymeric nanoparticles have emerged as a promising platform with multiple advantages, including the dual capability of adjuvant and delivery vehicle, administration via multiple routes, induction of rapid and long-lived immunity, greater shelf-life at elevated temperatures, and enhanced patient compliance. This comprehensive review describes advances in nanoparticle-based vaccines (i.e., nanovaccines) with a particular focus on polymeric particles as adjuvants and delivery vehicles. Examples of the nanovaccine approach in respiratory infections, biodefense, and cancer are discussed.

Applications of Nanovaccines for Disease Prevention in Cattle

Vaccines are one of the most important tools available to prevent and reduce the incidence of infectious diseases in cattle. Despite their availability and widespread use to combat many important pathogens impacting cattle, several of these products demonstrate variable efficacy and safety in the field, require multiple doses, or are unstable under field conditions. Recently, nanoparticle-based vaccine platforms (nanovaccines) have emerged as promising alternatives to more traditional vaccine platforms. In particular, polymer-based nanovaccines provide sustained release of antigen payloads, stabilize such payloads, and induce enhanced antibod- and cell-mediated immune responses, both systemically and locally. To improve vaccine administrative strategies and efficacy, they can be formulated to contain multiple antigenic payloads and have the ability to protect fragile proteins from degradation. Nanovaccines are also stable at room temperature, minimizing the need for cold chain storage. Nanoparticle platforms can be synthesized for targeted delivery through intranasal, aerosol, or oral administration to induce desired mucosal immunity. In recent years, several nanovaccine platforms have emerged, based on biodegradable and biocompatible polymers, liposomes, and virus-like particles. While most nanovaccine candidates have not yet advanced beyond testing in rodent models, a growing number have shown promise for use against cattle infectious diseases. This review will highlight recent advancements in polymeric nanovaccine development and the mechanisms by which nanovaccines may interact with the bovine immune system. We will also discuss the positive implications of nanovaccines use for combating several important viral and bacterial disease syndromes and consider important future directions for nanovaccine development in beef and dairy cattle.