Aerosol Delivery of Palivizumab in a Neonatal Lamb Model of Respiratory Syncytial Virus Infection

Abstract

(1) Background: Palivizumab has been an approved preventative monoclonal antibody for respiratory syncytial virus (RSV) infection for over two decades. However, due to its high cost and requirement for multiple intramuscular injections, its use has been limited mostly to high-income countries. Following our previous study showing the successful lung deposition of aerosolised palivizumab in lambs, this current study evaluated the "proof-of-principle" effect of aerosolised palivizumab delivered as a therapeutic to neonatal lambs following RSV infection. (2) Methods: Neonatal lambs were intranasally inoculated with RSV-A2 on day 0 (day 3 post-birth) and treated with aerosolised palivizumab 3 days later (day 3 post-inoculation). Clinical symptoms, RSV viral load and inflammatory response were measured post-inoculation. (3) Results: Aerosolised therapeutic delivery of palivizumab did not reduce RSV viral loads in the nasopharynx nor the bronchoalveolar lavage fluid, but resulted in a modest reduction in inflammatory response at day 6 post-inoculation compared with untreated lambs. (4) Conclusions: This proof-of-principle study shows some evidence of aerosolised palivizumab reducing RSV inflammation, but further studies using optimized protocols are needed in order to validate these findings.

Keywords: aerosolisation; lamb model; lung; palivizumab; respiratory syncytial virus.

Figure 1

Study design and sampling timeline using an RSV lamb model. Neonatal lambs were infected with the RSV-A2 strain intranasally on day 0. Nasopharyngeal (NP) swabs, blood, and bronchoalveolar lavage fluid (BALF) were collected at baseline (day 0) and then on day 2, 4, 6, 8 and 10 post-inoculation. Lambs were euthanised either on day 6 (peak infection) or day 10 (recovery) post-inoculation according to the study group (refer to Table 1). Image was created using BioRender.com.

Figure 2

Clinical parameters of newborn lambs given aerosol treatment with palivizumab. (A) Nebuliser setup with face mask; (B) body weight; (C) body temperature; and (D) oxygen saturation for each group of lambs. The normal physiological range is shaded in (C,D). Red circles = control group 0 (n = 2); green squares = RSV/untreated group 1 (n = 6); blue triangles = RSV/palivizumab group 2 (n = 6). Data are presented as the mean ± SEM.

Figure 3

Comparison of RSV load in NP swabs and BALF samples on day 6 post-inoculation (time of peak-infection). (A) Nasopharyngeal (NP) and (B) bronchoalveolar lavage fluid (BALF) viral load are displayed as averages of all lambs in each group. Red circles = control group 0 (n = 2); green squares = RSV/untreated group 1 (n = 12); blue triangles = RSV/palivizumab group 2 (n = 11). Data are represented as the median ± IQR.

Figure 4

Comparison of inflammation/congestion scores in lambs. (A–C) Representative images (H&E stain, day 6 post-inoculation) in (A) control group lambs; (B) RSV/untreated group 1a lambs; and (C) RSV/palivizumab group 2a lambs. Scale bar = 100 μm. (D) Analysis of inflammation/congestion scores in each group at day 6 post-inoculation (H&E stain, median ± IQR). Red circles = control group 0 (n = 2); green squares = RSV/untreated group 1a (n = 6); blue triangles = RSV/palivizumab group 2 (n = 6).

Figure 5

Goblet cell (GC) counts in cartilaginous and non-cartilaginous airways of the lambs. Representative images (AB-PAS stain, day 6 post-inoculation) of cartilaginous airways and non- cartilaginous airways in (A) control group 0 lambs; (B) RSV/untreated group 1a lambs; and (C) RSV/palivizumab group 2a lambs. Scale bar = 100 μm. (D) Mean number of GC counts per 100 μm in each lamb from each group at day 6 post-inoculation (AB-Pas stain, median ± IQR). Red circles= control group 0 (n = 2); green squares = RSV/untreated group 1a (n = 6); blue triangles = RSV/palivizumab group 2a (n = 6).