{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T21:13:32Z","timestamp":1792790012345,"version":"4.5.0"},"reference-count":39,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,21]],"date-time":"2026-09-21T00:00:00Z","timestamp":1789948800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"National Key Research and Development Program of China","award":["2023YFC2307800"],"award-info":[{"award-number":["2023YFC2307800"]}]},{"name":"Yunnan Key Research and Development Program","award":["202505AS350006"],"award-info":[{"award-number":["202505AS350006"]}]},{"name":"Yunnan Key Research and Development Program","award":["202303AC100026"],"award-info":[{"award-number":["202303AC100026"]}]},{"name":"National Natural Science Foundation of China","award":["82572575"],"award-info":[{"award-number":["82572575"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"crossref"}]},{"award":["82572575"],"award-info":[{"award-number":["82572575"]}],"id":[{"id":"https:\/\/ror.org\/01h0zpd94","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Background\/Objectives: Despite the gradual waning of global interest in SARS-CoV-2, the continued evolution and emergence of viral variants underscore the need for broadly protective vaccines. Vaccines targeting the highly mutable S1 subunit of the spike protein have shown limited breadth of protection, whereas conserved regions within the S2 fusion machinery remain critical targets for the development of vaccines effective against future variants. This study evaluated two mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding HR121, a conserved HR1-HR2-HR1 fusion-intermediate immunogen, in comparison with a recombinant HR121 protein vaccine. Methods: Two mRNA vaccine candidates, TM-HR121 and Fc-HR121, were designed to present HR121 through distinct antigen presentation strategies by incorporating a transmembrane anchor or an IgG Fc domain, respectively. Immunogenicity and protective efficacy were assessed in New Zealand White rabbits, BALB\/c mice, and Golden Syrian hamsters. Results: Both mRNA vaccines elicited robust HR121-specific binding antibody responses and broad neutralizing activity against seven SARS-CoV-2 pseudoviruses in rabbits. In mice, the mRNA vaccines induced higher peak IgG titers, a more balanced IgG1\/IgG2a profile, stronger antigen-specific IFN-\u03b3 responses, and enhanced T-cell responses compared with the recombinant protein vaccine, while maintaining detectable IL-4 responses. In hamsters, immunization with the HR121 mRNA vaccines significantly reduced lung viral RNA levels and attenuated pulmonary pathology and nucleocapsid antigen expression following authentic SARS-CoV-2 challenge. Conclusions: HR121-based mRNA-LNP vaccines successfully elicited cross-variant humoral and cellular immune responses and conferred protective efficacy in small-animal models. These findings support HR121 mRNA-LNP vaccines as a promising strategy for the development of broadly protective coronavirus vaccines targeting conserved S2 fusion epitopes.<\/jats:p>","DOI":"10.3390\/vaccines14090831","type":"journal-article","created":{"date-parts":[[2026,10,1]],"date-time":"2026-10-01T15:35:28Z","timestamp":1790868928000},"page":"831","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["mRNA Vaccines Targeting the Conserved SARS-CoV-2 Fusion Machinery Elicit Cross-Variant and Robust Immunity"],"prefix":"10.3390","volume":"14","author":[{"given":"Jun","family":"Li","sequence":"first","affiliation":[{"name":"Center for Life Sciences, School of Life Sciences, Yunnan University, Kunming 650091, China"},{"name":"Southwestern United Graduate School, Kunming 650500, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"given":"Ke-Meng","family":"Li","sequence":"additional","affiliation":[{"name":"Center for Life Sciences, School of Life Sciences, Yunnan University, Kunming 650091, China"},{"name":"State Key Laboratory of Vaccines for Infectious Diseases, Xiang An Biomedicine Laboratory, Department of Laboratory Medicine, School of Public Health, School of Life Sciences, Xiamen University, Xiamen 361102, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"}]},{"given":"Shu-Heng","family":"Yu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Genetic Evolution & Animal Models, Key Laboratory of Bioactive Peptides of Yunnan Province, KIZ-CUHK Joint Laboratory of Bioresources and Molecular Research in Common Diseases, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2330-3771","authenticated-orcid":false,"given":"Ming-Hua","family":"Li","sequence":"additional","affiliation":[{"name":"Kunming National High-Level Biosafety Research Center for Non-Human Primates, Center for Biosafety Mega-Science, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650107, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"investigation","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"}]},{"given":"Xiao-Li","family":"Feng","sequence":"additional","affiliation":[{"name":"Kunming National High-Level Biosafety Research Center for Non-Human Primates, Center for Biosafety Mega-Science, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650107, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"validation","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3784-8067","authenticated-orcid":false,"given":"Wei","family":"Pang","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Genetic Evolution & Animal Models, Key Laboratory of Bioactive Peptides of Yunnan Province, KIZ-CUHK Joint Laboratory of Bioresources and Molecular Research in Common Diseases, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China"},{"name":"Yunnan Provincial Key Laboratory of Cross-Border Infectious Diseases Control & Drug Innovation, Department of Pathogen Biology and Immunology, Faculty of Basic Medical Science, Kunming Medical University, Kunming 650118, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5469-0324","authenticated-orcid":false,"given":"Yong-Tang","family":"Zheng","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Genetic Evolution & Animal Models, Key Laboratory of Bioactive Peptides of Yunnan Province, KIZ-CUHK Joint Laboratory of Bioresources and Molecular Research in Common Diseases, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"given":"Jian","family":"Zhang","sequence":"additional","affiliation":[{"name":"Center for Life Sciences, School of Life Sciences, Yunnan University, Kunming 650091, China"},{"name":"Southwestern United Graduate School, Kunming 650500, China"},{"name":"School of Life Sciences and Obstetrics, Gynecology Hospital, Fudan University, Shanghai 200433, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"337","DOI":"10.1080\/22221751.2021.2022440","article-title":"Omicron Variant Showed Lower Neutralizing Sensitivity than Other SARS-CoV-2 Variants to Immune Sera Elicited by Vaccines after Boost","volume":"11","author":"Ai","year":"2022","journal-title":"Emerg. Microbes Infect."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"3491","DOI":"10.1080\/21645515.2021.1923350","article-title":"Emerging SARS-CoV-2 Variants: Impact on Vaccine Efficacy and Neutralizing Antibodies","volume":"17","author":"Sharun","year":"2021","journal-title":"Hum. Vaccines Immunother."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"265","DOI":"10.1038\/s41586-020-2008-3","article-title":"A New Coronavirus Associated with Human Respiratory Disease in China","volume":"579","author":"Wu","year":"2020","journal-title":"Nature"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"409","DOI":"10.1038\/s41579-021-00573-0","article-title":"SARS-CoV-2 Variants, Spike Mutations and Immune Escape","volume":"19","author":"Harvey","year":"2021","journal-title":"Nat. Rev. Microbiol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"657","DOI":"10.1038\/s41586-021-04385-3","article-title":"Omicron Escapes the Majority of Existing SARS-CoV-2 Neutralizing Antibodies","volume":"602","author":"Cao","year":"2022","journal-title":"Nature"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"676","DOI":"10.1038\/s41586-021-04388-0","article-title":"Striking Antibody Evasion Manifested by the Omicron Variant of SARS-CoV-2","volume":"602","author":"Liu","year":"2022","journal-title":"Nature"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"671","DOI":"10.1038\/s41586-021-04389-z","article-title":"Considerable Escape of SARS-CoV-2 Omicron to Antibody Neutralization","volume":"602","author":"Planas","year":"2022","journal-title":"Nature"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"386","DOI":"10.1038\/d41586-021-00340-4","article-title":"Variant-Proof Vaccines\u2014Invest Now for the next Pandemic","volume":"590","author":"Burton","year":"2021","journal-title":"Nature"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"281","DOI":"10.1016\/j.cell.2020.02.058","article-title":"Structure, Function, and Antigenicity of the SARS-CoV-2 Spike Glycoprotein","volume":"181","author":"Walls","year":"2020","journal-title":"Cell"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1260","DOI":"10.1126\/science.abb2507","article-title":"Cryo-EM Structure of the 2019-nCoV Spike in the Prefusion Conformation","volume":"367","author":"Wrapp","year":"2020","journal-title":"Science"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"343","DOI":"10.1038\/s41422-020-0305-x","article-title":"Inhibition of SARS-CoV-2 (Previously 2019-nCoV) Infection by a Highly Potent Pan-Coronavirus Fusion Inhibitor Targeting Its Spike Protein That Harbors a High Capacity to Mediate Membrane Fusion","volume":"30","author":"Xia","year":"2020","journal-title":"Cell Res."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"3067","DOI":"10.1038\/ncomms4067","article-title":"Structure-Based Discovery of Middle East Respiratory Syndrome Coronavirus Fusion Inhibitor","volume":"5","author":"Lu","year":"2014","journal-title":"Nat. Commun."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1068","DOI":"10.1038\/s41422-022-00746-3","article-title":"A Variant-Proof SARS-CoV-2 Vaccine Targeting HR1 Domain in S2 Subunit of Spike Protein","volume":"32","author":"Pang","year":"2022","journal-title":"Cell Res."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"e70088","DOI":"10.1002\/mco2.70088","article-title":"Recombinant Protein HR212 Targeting Heptad Repeat 2 Domain in Spike Protein S2 Subunit Elicits Broad-spectrum Neutralizing Antibodies against SARS-CoV-2 and Its Variants","volume":"6","author":"Lu","year":"2025","journal-title":"MedComm"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"261","DOI":"10.1038\/nrd.2017.243","article-title":"mRNA Vaccines \u2014 a New Era in Vaccinology","volume":"17","author":"Pardi","year":"2018","journal-title":"Nat. Rev. Drug Discov."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"594","DOI":"10.1038\/s41586-020-2814-7","article-title":"COVID-19 Vaccine BNT162b1 Elicits Human Antibody and TH1 T Cell Responses","volume":"586","author":"Sahin","year":"2020","journal-title":"Nature"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"9","DOI":"10.1038\/s41541-023-00783-y","article-title":"mRNA Vaccines Expressing Malaria Transmission-Blocking Antigens Pfs25 and Pfs230D1 Induce a Functional Immune Response","volume":"9","author":"Scaria","year":"2024","journal-title":"npj Vaccines"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Balinsky, C.A., Jiang, L., Jani, V., Cheng, Y., Zhang, Z., Belinskaya, T., Qiu, Q., Long, T.K., Schilling, M.A., and Jenkins, S.A. (2023). Antibodies to S2 Domain of SARS-CoV-2 Spike Protein in Moderna mRNA Vaccinated Subjects Sustain Antibody-Dependent NK Cell-Mediated Cell Cytotoxicity against Omicron BA.1. Front. Immunol., 14.","DOI":"10.3389\/fimmu.2023.1266829"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"54","DOI":"10.1007\/s00262-024-03888-y","article-title":"FcRn-Guided Antigen Trafficking Enhances Cancer Vaccine Efficacy","volume":"74","author":"Hong","year":"2025","journal-title":"Cancer Immunol. Immunother."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"112326","DOI":"10.1016\/j.celrep.2023.112326","article-title":"Fc-Mediated Pan-Sarbecovirus Protection after Alphavirus Vector Vaccination","volume":"42","author":"Adams","year":"2023","journal-title":"Cell Rep."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"626","DOI":"10.1038\/nri.2016.90","article-title":"Sex Differences in Immune Responses","volume":"16","author":"Klein","year":"2016","journal-title":"Nat. Rev. Immunol."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"e0097421","DOI":"10.1128\/mBio.00974-21","article-title":"Sex Differences in Lung Imaging and SARS-CoV-2 Antibody Responses in a COVID-19 Golden Syrian Hamster Model","volume":"12","author":"Dhakal","year":"2021","journal-title":"mBio"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"3699","DOI":"10.1038\/s41596-020-0394-5","article-title":"Quantification of SARS-CoV-2 Neutralizing Antibody by a Pseudotyped Virus-Based Assay","volume":"15","author":"Nie","year":"2020","journal-title":"Nat. Protoc."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1627","DOI":"10.1021\/acschembio.5c00208","article-title":"SARS-CoV-2 Omicron Variant Spike Glycoprotein Mutation Q954H Enhances Fusion Core Stability","volume":"20","author":"Vithanage","year":"2025","journal-title":"ACS Chem. Biol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"e2300360120","DOI":"10.1073\/pnas.2300360120","article-title":"Structure-Based Design of a SARS-CoV-2 Omicron-Specific Inhibitor","volume":"120","author":"Yang","year":"2023","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"7580","DOI":"10.1038\/s41467-025-63101-1","article-title":"A Broadly Neutralizing Antibody Recognizes a Unique Epitope with a Signature Motif Common across Coronaviruses","volume":"16","author":"Yan","year":"2025","journal-title":"Nat. Commun."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"4983","DOI":"10.1016\/j.ymthe.2026.05.012","article-title":"From Weak but Broad to Potent and Universal: A Trispecific Antibody against Conserved SARS-CoV-2 Spike Epitopes","volume":"34","author":"Tian","year":"2026","journal-title":"Mol. Ther."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Marcos-Villar, L., Perdiguero, B., Sin, L., \u00c1lvarez, E., Flores, S., Casasnovas, J.M., Pons, T., Sorzano, C.O.S., Del Hoyo, D., and Lapuhs, P. (2026). Preclinical Evaluation of a Multi-Epitope mRNA Vaccine Platform for Broad and Durable SARS-CoV-2 Protection. Front. Immunol., 17.","DOI":"10.3389\/fimmu.2026.1787877"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1113","DOI":"10.1126\/science.1234914","article-title":"Structure of RSV Fusion Glycoprotein Trimer Bound to a Prefusion-Specific Neutralizing Antibody","volume":"340","author":"McLellan","year":"2013","journal-title":"Science"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"e00176-17","DOI":"10.1128\/JVI.00176-17","article-title":"Discovery of a Prefusion Respiratory Syncytial Virus F-Specific Monoclonal Antibody That Provides Greater In Vivo Protection than the Murine Precursor of Palivizumab","volume":"91","author":"Zhao","year":"2017","journal-title":"J. Virol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"2439","DOI":"10.1056\/NEJMoa2027906","article-title":"Safety and Immunogenicity of Two RNA-Based Covid-19 Vaccine Candidates","volume":"383","author":"Walsh","year":"2020","journal-title":"N. Engl. J. Med."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"567","DOI":"10.1038\/s41586-020-2622-0","article-title":"SARS-CoV-2 mRNA Vaccine Design Enabled by Prototype Pathogen Preparedness","volume":"586","author":"Corbett","year":"2020","journal-title":"Nature"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"6863","DOI":"10.1016\/j.vaccine.2023.09.059","article-title":"SARS-CoV-2 mRNA Vaccine Requires Signal Peptide to Induce Antibody Responses","volume":"41","author":"Mo","year":"2023","journal-title":"Vaccine"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"2057832","DOI":"10.1080\/19420862.2022.2057832","article-title":"David versus Goliath: ACE2-Fc Receptor Traps as Potential SARS-CoV-2 Inhibitors","volume":"14","author":"Alfaleh","year":"2022","journal-title":"MAbs"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Wang, C., Tang, X., Jiang, C., Zhang, Y., Han, B., Sun, Y., Guo, J., Peng, H., Wang, Z., and Wang, Y. (2025). Intradermal Delivery of SARS-CoV-2 RBD3-Fc mRNA Vaccines via a Needle-Free Injection System Induces Robust Immune Responses in Rats. Front. Immunol., 16.","DOI":"10.3389\/fimmu.2025.1530736"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Xu, S., Li, J., Xu, M., Cai, Y., Qian, Y., Liu, R., He, Q., Fei, C., Wang, A., and Ruan, K. (2025). A Novel Trivalent BVDV mRNA Vaccine Displayed by Virus-like Particles Eliciting Potent and Broad-Spectrum Antibody Responses. Vaccines, 13.","DOI":"10.3390\/vaccines13070691"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"355","DOI":"10.1016\/j.immuni.2022.01.001","article-title":"mRNA-1273 Vaccine-Induced Antibodies Maintain Fc Effector Functions across SARS-CoV-2 Variants of Concern","volume":"55","author":"Kaplonek","year":"2022","journal-title":"Immunity"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"945","DOI":"10.1126\/science.abb8923","article-title":"Rapid COVID-19 Vaccine Development","volume":"368","author":"Graham","year":"2020","journal-title":"Science"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"114520","DOI":"10.1016\/j.celrep.2024.114520","article-title":"Neutralization Escape, Infectivity, and Membrane Fusion of JN.1-Derived SARS-CoV-2 SLip, FLiRT, and KP.2 Variants","volume":"43","author":"Li","year":"2024","journal-title":"Cell Rep."}],"container-title":["Vaccines"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2076-393X\/14\/9\/831\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,10,2]],"date-time":"2026-10-02T04:18:24Z","timestamp":1790914704000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2076-393X\/14\/9\/831"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,21]]},"references-count":39,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["vaccines14090831"],"URL":"https:\/\/doi.org\/10.3390\/vaccines14090831","relation":{},"ISSN":["2076-393X"],"issn-type":[{"value":"2076-393X","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,21]]}}}