Live-Attenuated Respiratory Syncytial Virus Vaccine With M2-2 Deletion and With Small Hydrophobic Noncoding Region Is Highly Immunogenic in Children

Abstract

Background: Respiratory syncytial virus (RSV) is the leading viral cause of severe pediatric respiratory illness, and vaccines are needed. Live RSV vaccine D46/NS2/N/ΔM2-2-HindIII, attenuated by deletion of the RSV RNA regulatory protein M2-2, is based on previous candidate LID/ΔM2-2 but incorporates prominent differences from MEDI/ΔM2-2, which was more restricted in replication in phase 1.

Methods: RSV-seronegative children aged 6-24 months received 1 intranasal dose (105 plaque-forming units [PFUs] of D46/NS2/N/ΔM2-2-HindIII [n = 21] or placebo [n = 11]) and were monitored for vaccine shedding, reactogenicity, RSV-antibody responses and RSV-associated medically attended acute respiratory illness (RSV-MAARI) and antibody responses during the following RSV season.

Results: All 21 vaccinees were infected with vaccine; 20 (95%) shed vaccine (median peak titer, 3.5 log10 PFUs/mL with immunoplaque assay and 6.1 log10 copies/mL with polymerase chain reaction). Serum RSV-neutralizing antibodies and anti-RSV fusion immunoglobulin G increased ≥4-fold in 95% and 100% of vaccines, respectively. Mild upper respiratory tract symptoms and/or fever occurred in vaccinees (76%) and placebo recipients (18%). Over the RSV season, RSV-MAARI occurred in 2 vaccinees and 4 placebo recipients. Three vaccinees had ≥4-fold increases in serum RSV-neutralizing antibody titers after the RSV season without RSV-MAARI.

Conclusions: D46/NS2/N/ΔM2-2-HindIII had excellent infectivity and immunogenicity and primed vaccine recipients for anamnestic responses, encouraging further evaluation of this attenuation strategy.

Clinical trials registration: NCT03102034 and NCT03099291.

Keywords: RNA regulatory protein M2-2; immunogenicity; live-attenuated viral vaccine; neutralizing antibodies; pediatric RSV vaccine; respiratory syncytial virus.

© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.

Figures

Figure 1.

Vaccine virus shed in nasal wash (NW) specimens from vaccinees. Titers (closed circles) and peak titers (open diamonds) for individual participants are shown along with median titers (solid line). NW specimens were collected from vaccinees during acute-phase study visits (window: indicated study day ± 1 d) after inoculation on day 0, and titers were determined by immunoplaque assay (A) and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) (B). The lower limits of detection (dashed lines) were 0.5 log10 plaque-forming units (PFUs)/mL and 1.7 log10 copies/mL for immunoplaque assay and RT-qPCR, respectively.

Figure 2.

Serum respiratory syncytial virus (RSV) antibody titers in vaccine and placebo recipients. Serum RSV 60% plaque reduction neutralizing titers (PRNT60) (A) and anti-RSV fusion (F) immunoglobulin G (IgG) titers (B) were determined by means of complement-enhanced 60% plaque reduction neutralization assay and IgG-specific enzyme-linked immunosorbent assay against purified RSV F protein, respectively, for vaccine (open circles) and placebo (x’s) recipients in serum samples collected before inoculation (screening), after inoculation (study day 56), before surveillance (October of the enrollment year), and after surveillance (usually April after the RSV season). Titers are expressed as the reciprocal log2 values. Lines indicate median (solid lines) and mean (dashed lines) values. P values were determined by means of Wilcoxon rank sum test. Data for the presurveillance and postsurveillance visits are missing for 2 vaccine recipients.

Figure 3.

Serum respiratory syncytial virus (RSV)–neutralizing antibody titers among participants with wild-type RSV during RSV surveillance. Serum RSV 60% plaque reduction neutralizing titers (PRNT60) in serum samples collected before and after RSV surveillance are shown for vaccine and placebo recipients who had RSV-associated medically attended respiratory illness (MAARI) or had a ≥4-fold increase in either serum RSV PRNT60 or anti-RSV fusion (F) immunoglobulin G (IgG) titer. Dashed and solid lines indicate subjects with or without RSV-associated MAARI during surveillance. Note that 1 vaccine recipient with a ≥4-fold increase in anti-RSV F IgG titer had a smaller increase in serum neutralizing antibody titer, and 1 vaccine recipient with RSV-associated MAARI did not have a 4-fold increase in either antibody titer. Titers are expressed as reciprocal log2 values, but for ease of interpretation, some arithmetic values are indicated.