Intranasal Administration of Recombinant Newcastle Disease Virus Expressing SARS-CoV-2 Spike Protein Protects hACE2 TG Mice against Lethal SARS-CoV-2 Infection

Abstract

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), emerged as a global outbreak in 2019, profoundly affecting both human health and the global economy. Various vaccine modalities were developed and commercialized to overcome this challenge, including inactivated vaccines, mRNA vaccines, adenovirus vector-based vaccines, and subunit vaccines. While intramuscular vaccines induce high IgG levels, they often fail to stimulate significant mucosal immunity in the respiratory system. We employed the Newcastle disease virus (NDV) vector expressing the spike protein of the SARS-CoV-2 Beta variant (rK148/beta-S), and evaluated the efficacy of intranasal vaccination with rK148/beta-S in K18-hACE2 transgenic mice. Intranasal vaccination with a low dose (10^6.0 EID₅₀) resulted in an 86% survival rate after challenge with the SARS-CoV-2 Beta variant. Administration at a high dose (10^7.0 EID₅₀) led to a reduction in lung viral load and 100% survival against the SARS-CoV-2 Beta and Delta variants. A high level of the SARS-CoV-2 spike-specific IgA was also induced in vaccinated mice lungs following the SARS-CoV-2 challenge. Our findings suggest that rK148/beta-S holds promise as an intranasal vaccine candidate that effectively induces mucosal immunity against SARS-CoV-2.

Keywords: Newcastle disease virus vector-based vaccine; SARS-CoV-2; SARS-CoV-2 spike-specific IgA; intranasal vaccine; lung viral load.

Figure 1

Immune response to intranasal vaccination of rK148/beta-S. (A) The schedule for vaccination, blood sampling, and euthanasia is outlined. (B) Body weight changes were recorded weekly up to eight weeks post-vaccination (wpv). (C) Hemagglutination inhibition (HI) assay was performed on serum samples from vaccinated mice; mice with HI titers < 2 log2 were considered seronegative. (D) Surrogate SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA) was conducted on serum samples from vaccinated mice, with serum diluted to 1/10. Mice with surrogate SARS-CoV-2 positivity index (PI) values < 30 were deemed seronegative. (E) Splenocyte analysis and IFN-γ enzyme-linked immunospot assays were performed on autopsied animals (n = 3 per group) at 4 weeks post-booster vaccination, using PepTivator SARS-CoV-2 Prot_S1 as the antigen. Groups with at least one shared letter superscript indicate no significant statistical differences were observed between pairwise comparisons within the same week (p > 0.05).

Figure 2

Survival rate, lung viral load, and SARS-CoV-2 spike-specific IgA following challenge with the SARS-CoV-2 Beta variant. (A) The schedule for SARS-CoV-2 Beta variant challenge and euthanasia is depicted. (B,C) Changes in body weight and survival rate were monitored at 14 days post-challenge (dpc) with the SARS-CoV-2 Beta variant. For the challenge, 50 μL of the Beta variant (10^6.0 EID₅₀/mL) was administered intranasally (n = 16). (D,E) Mice were euthanized at 3 and 6 dpc (n = 3 per group) to assess viral load in the lungs and measure SARS-CoV-2 spike-specific IgA levels. Groups sharing at least one letter superscript indicate no significant statistical differences between pairwise comparisons within the same week (p > 0.05).

Figure 2

Survival rate, lung viral load, and SARS-CoV-2 spike-specific IgA following challenge with the SARS-CoV-2 Beta variant. (A) The schedule for SARS-CoV-2 Beta variant challenge and euthanasia is depicted. (B,C) Changes in body weight and survival rate were monitored at 14 days post-challenge (dpc) with the SARS-CoV-2 Beta variant. For the challenge, 50 μL of the Beta variant (10^6.0 EID₅₀/mL) was administered intranasally (n = 16). (D,E) Mice were euthanized at 3 and 6 dpc (n = 3 per group) to assess viral load in the lungs and measure SARS-CoV-2 spike-specific IgA levels. Groups sharing at least one letter superscript indicate no significant statistical differences between pairwise comparisons within the same week (p > 0.05).

Figure 3

Survival rate and lung viral load following challenge with the SARS-CoV-2 Delta variant. (A) The schedule for SARS-CoV-2 Delta variant challenge and euthanasia is outlined. (B,C) Changes in body weight and survival rate were monitored after challenge with the SARS-CoV-2 Delta variant. For the challenge, 50 μL of the Delta variant (10^6.0 EID₅₀/mL) was administered intranasally (n = 13). (D) Following the challenge, mice were euthanized at 3 and 6 days post-challenge (dpc) (n = 3 per group) to assess viral load in the lungs. Groups with at least one shared letter superscript indicate no significant statistical differences between pairwise comparisons within the same week (p > 0.05).

Figure 4

Histopathological analysis of the lung, spleen, and small intestine after challenge with SARS-CoV-2 Beta variant. After the challenge with Beta variant, the mice were euthanized 5 dpc (n = 3) to perform histopathological analysis. Black arrows indicate perivascular edema; magnification ×100.