Intramuscular administration of recombinant Newcastle disease virus expressing SARS-CoV-2 spike protein protects hACE-2 TG mice against SARS-CoV-2 infection

Abstract

Coronavirus disease 2019 (Covid-19) caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) became a pandemic, causing significant burden on public health worldwide. Although the timely development and production of mRNA and adenoviral vector vaccines against SARS-CoV-2 have been successful, issues still exist in vaccine platforms for wide use and production. With the potential for proliferative capability and heat stability, the Newcastle disease virus (NDV)-vectored vaccine is a highly economical and conceivable candidate for treating emerging diseases. In this study, a recombinant NDV-vectored vaccine expressing the spike (S) protein of SARS-CoV-2, rK148/beta-S, was developed and evaluated for its efficacy against SARS-CoV-2 in K18-hACE-2 transgenic mice. Intramuscular vaccination with low dose (10^6.0 EID₅₀) conferred a survival rate of 76 % after lethal challenge of a SARS-CoV-2 beta (B.1.351) variant. When administered with a high dose (10^7.0 EID₅₀), vaccinated mice exhibited 100 % survival rate and reduced lung viral load against both beta and delta variants (B.1.617.2). Together with the protective immunity, rK148/beta-S is an accessible and cost-effective SARS-CoV-2 vaccine.

Keywords: Intramuscular vaccine; K18-hACE-2 TG mice; Lung viral load; Newcastle disease virus-vectored vaccine; SARS-CoV-2.

Fig. 1

Construction and characterization of rK148/ beta-S. (A) Schematic description of the structure of the rK148/beta-S. The spike (S) gene of SARS-CoV-2 beta variant (B.1.351) was inserted between the phosphoprotein and matrix genes of K148/08. (B) After the rescue, the rK148/beta-S virus was checked for the insertion of the SARS-CoV-2 S gene. (C) S protein expression was verified using western blotting. The upper panel shows the expression of SARS-CoV-2 S protein, and the lower panel shows the expression of the NDV HN protein. Lane 1: rK148/beta-S, lane 2: K148. (D) Viral growth kinetics of rK148/08 and rK148/beta-S in 10-day-old specific pathogen-free chicken eggs. K148 and K148/beta-S (50 % egg infective dose of 10) were inoculated, and allantoic fluid was collected every 12 h for 4 d.

Fig. 2

Immunity and challenge in low-dose intramuscular vaccines of rK148/beta-S. (A) Low-dose vaccination and challenge schedule. (B) Change in body weight measured weekly until 8 weeks post vaccination (wpv). (C) Hemagglutination inhibition (HI) assay of a serum sample from vaccinated mice. Mouse with HI titer < 2 log₂ was regarded as seronegative. (D) Surrogate SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA) of a serum sample from vaccinated mice. Serum was used at 1/10 dilution. Mouse with surrogate SARS-CoV-2 titer < 30 was regarded as seronegative. (E,F) Body weight changes and survival rate at 14 day post challenge (dpc) with SARS-CoV-2. For the challenge, 50 μL each of beta variant (10^6.0EID₅₀/mL) were inoculated intranasally (n = 7).

Fig. 3

Animal experiment schedule and immunity in the high-dose intramuscular vaccine of rK148/beta-S. (A)High-dose vaccination and challenge schedule. (B) Change in body weight measured weekly until 8 wpv. (C) HI assay of a serum sample from vaccinated mice. Mouse with HI titer < 2 log₂ was regarded as seronegative. (D) Surrogate SARS-CoV-2 ELISA of a serum sample from vaccinated mice. Serum was used at 1/10 dilution. Mouse with surrogate SARS-CoV-2 titer < 30 was regarded as seronegative. (E) Splenocyte and IFN-γ enzyme-linked immunospot were performed using autopsy (n = 5 animals each) at 4 wpv of the secondary vaccine. PepTivator SARS-CoV-2 Prot_S1 was used as the antigen.

Fig. 4

Survival rate and lung viral load after challenge with two SARS-CoV-2 variants. (A, B) Body weight changes and survival rate at 14 dpc with SARS-CoV-2. For the challenge, 50 μL each of beta variant (10^6.0EID₅₀/mL) were inoculated intranasally (G1 = 13, G2 = 10, G3 = 13). (C, D) After the challenge with beta variant, autopsies were performed at 3 and 6 dpc (n = 3 animals each) to measure the viral load in the lungs. (E, F) Body weight changes and survival rate at 14 dpc with SARS-CoV-2. For the challenge, 50 μL each of delta variant (10^6.0EID₅₀/mL) were inoculated intranasally (G4 = 13, G5 = 13). (G, H) After the challenge with delta variant, autopsies were performed at 3 and 6 dpc (n = 3 animals each) to measure the viral load in the lungs.