Paramyxoviruses as Vaccine Vectors Against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

National Institute Of Allergy And Infectious Diseases

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Abstract

We are developing parainfluenza virus- and pneumovirus-vectored vaccines for intranasal immunization against SARS-CoV-2. These viral vectors are designed to be highly attenuated in humans. They replicate to low levels in the superficial layers of the respiratory epithelium, and are optimized to induce strong local mucosal and systemic immune responses to the SARS-CoV-2 spike protein S, the major protective antigen of SARS-CoV-2. Pediatric SARS-CoV-2 infections, though generally mild, are associated with substantial morbidity and contribute to transmission dynamics. A pediatric COVID vaccine for intranasal immunization would have the potential to reduce the burden of COVID illness while also restricting SARS-CoV-2 transmission. We developed bivalent vaccine candidates to protect infants and children against coronavirus disease-2019 (COVID-19) and parainfluenza virus type 3, another major cause of pediatric respiratory illness. These candidates are based on replication-competent chimeric bovine/human parainfluenza virus type 3 (B/HPIV3) expressing the prefusion-stabilized SARS-CoV-2 spike protein (S). Previously, we showed that prefusion stabilization increased S expression by B/HPIV3 in vitro. In hamsters, a single intranasal dose of B/HPIV3/S-2P (expressing the S-2P stabilized version of the S protein) induced high levels of serum SARS-CoV-2-neutralizing antibodies, as well as S-specific IgA and IgG. In FY 2023, we continued the development of these B/HPIV3 vectors. To further improve the immunogenicity, we generated B/HPIV3/S-6P, expressing a further-stabilized version of the S protein (S-6P, described by Hsieh et al., PMID 32703906). Indeed, intranasal immunization of hamsters with B/HPIV3/S-6P reproducibly elicited significantly higher levels of serum anti-S IgG and IgA to the receptor binding domain (RBD) than B/HPIV3/S-2P; hamster sera efficiently neutralized variants of concern (VoCs), including Omicron variants. B/HPIV3/S-2P and B/HPIV3/S-6P immunization protected hamsters against weight loss and lung inflammation following SARS-CoV-2 challenge with the vaccine-matched strain WA1/2020 or VoCs B.1.1.7/Alpha or B.1.351/Beta and induced near-sterilizing immunity. Three weeks post-challenge, B/HPIV3/S-2P and B/HPIV3/S-6P-immunized hamsters exhibited a robust anamnestic serum antibody response with increased neutralizing potency to VoCs, including Omicron sublineages. B/HPIV3/S-6P also primed for stronger anamnestic antibody responses after challenge with WA1/2020 than B/HPIV3/S-2P. (Liu X, Park HS, Matsuoka Y, Santos C, Yang L, Luongo C, Moore IN, Johnson RF, Garza NL, Zhang P, Lusso P, Best SM, Buchholz UJ, Le Nouen C. PLoS pathogens. 2023;19(6):e1011057. Epub 20230623. PMCID: PMC10325082.) B/HPIV3/S-6P was further evaluated in a preclinical study in rhesus macaques. We found that a single intranasal/intratracheal dose of B/HPIV3/S-6P induced strong S-specific airway mucosal IgA and IgG responses. High levels of S-specific antibodies were also induced in serum, which efficiently neutralized SARS-CoV-2 variants of concern of alpha, beta, and delta lineages, while their ability to neutralize Omicron sub-lineages was lower. Furthermore, B/HPIV3/S-6P induced robust systemic and pulmonary S-specific CD4+ and CD8+ T cell responses, including tissue-resident memory cells in the lungs. Following challenge, SARS-CoV-2 replication was undetectable in airways and lung tissues of immunized macaques. Based on these results, B/HPIV3/S-6P was selected for evaluation of safety and immunogenicity in a Phase 1 study. (Le Nouen C, Nelson CE, Liu X, Park HS, Matsuoka Y, Luongo C, Santos C, Yang L, Herbert R, Castens A, Moore IN, Wilder-Kofie T, Moore R, Walker A, Zhang P, Lusso P, Johnson RF, Garza NL, Via LE, Munir S, Barber DL, Buchholz UJ. Cell. 2022;185(25):4811-25 e17. Epub 20221110. PMCID: PMC9684001)