Nanoparticle-delivered TLR4 and RIG-I agonists enhance immune response to SARS-CoV-2 subunit vaccine

• Authors: Alexandra Atalis, Georgia Institute of Technology; Mark C. Keenum, Georgia Institute of Technology; Bhawana Pandey, Georgia Institute of Technology; Alexander Beach, Georgia Institute of Technology; Pallab Pradhan, Georgia Institute of Technology; Casey Vantucci, Georgia Institute of Technology; Laura O'Farrell, Georgia Institute of Technology; Richard Noel, Georgia Institute of Technology; Ritika Jain, Georgia Institute of Technology; Justin Hosten, Georgia Institute of Technology; Clinton Smith, Georgia Institute of Technology; Liana Kramer, Georgia Institute of Technology; Angela Jimenez, Georgia Institute of Technology; Miquel Ochoa, Georgia Institute of Technology; David Frey, Georgia Institute of Technology; Krishnendu Roy, Emory University
• Journal Title: Journal of Controlled Release
• Volume: Volume 347
• Publisher: Elsevier | 2022-07-01, Pages 476-488
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1016/j.jconrel.2022.05.023
• Subjects: Health Sciences, Epidemiology; Health Sciences, Immunology; Engineering, Biomedical; Biology, Cell; Health Sciences, Public Health
• Keywords: Science & Technology; Physical Sciences; Life Sciences & Biomedicine; Chemistry, Multidisciplinary; Pharmacology & Pharmacy; Chemistry; COVID-19 protein subunit vaccine; SARS-CoV-2 spike protein; Combination adjuvant; Monophosphoryl lipid A; Intranasal versus intramuscular vaccination; Adaptive immune response; RNA viruses; Signal transduction; Antibody response; Cell subsets; Stranded RNA; Recognition; Coronavirus; Activation; Adjuvants

Abstract

Despite success in vaccinating populations against SARS-CoV-2, concerns about immunity duration, continued efficacy against emerging variants, protection from infection and transmission, and worldwide vaccine availability remain. Molecular adjuvants targeting pattern recognition receptors (PRRs) on antigen-presenting cells (APCs) could improve and broaden the efficacy and durability of vaccine responses. Native SARS-CoV-2 infection stimulates various PRRs, including toll-like receptors (TLRs) and retinoic acid-inducible gene I (RIG-I)-like receptors. We hypothesized that targeting PRRs using molecular adjuvants on nanoparticles (NPs) along with a stabilized spike protein antigen could stimulate broad and efficient immune responses. Adjuvants targeting TLR4 (MPLA), TLR7/8 (R848), TLR9 (CpG), and RIG-I (PUUC) delivered on degradable polymer NPs were combined with the S1 subunit of spike protein and assessed in vitro with isogeneic mixed lymphocyte reactions (isoMLRs). For in vivo studies, the adjuvant-NPs were combined with stabilized spike protein or spike-conjugated NPs and assessed using a two-dose intranasal or intramuscular vaccination model in mice. Combination adjuvant-NPs simultaneously targeting TLR and RIG-I receptors (MPLA+PUUC, CpG+PUUC, and R848+PUUC) differentially induced T cell proliferation and increased proinflammatory cytokine secretion by APCs in vitro. When delivered intranasally, MPLA+PUUC NPs enhanced CD4+CD44+ activated memory T cell responses against spike protein in the lungs while MPLA NPs increased anti-spike IgA in the bronchoalveolar (BAL) fluid and IgG in the blood. Following intramuscular delivery, PUUC NPs induced strong humoral immune responses, characterized by increases in anti-spike IgG in the blood and germinal center B cell populations (GL7+ and BCL6+ B cells) in the draining lymph nodes (dLNs). MPLA+PUUC NPs further boosted spike protein-neutralizing antibody titers and T follicular helper cell populations in the dLNs. These results suggest that protein subunit vaccines with particle-delivered molecular adjuvants targeting TLR4 and RIG-I could lead to robust and unique route-specific adaptive immune responses against SARS-CoV-2.