A mosaic RBD-nanoparticle pan-sarbecovirus vaccine elicits nanobodies that target highly conserved epitopes
- 1California Institute of Technology
Abstract
SARS-CoV-2, the virus that causes COVID-19, continually mutates, producing new variants of concern (VOCs). Substitutions in the SARS-CoV-2 spike protein receptor-binding domain (RBD) have resulted in reduced efficacies of vaccines and therapeutic monoclonal antibodies. Indeed, since the emergence of Omicron and earlier VOCs, most previously approved anti-RBD therapeutic monoclonal antibodies are no longer authorized as therapeutics. To address VOC substitutions effects on therapeutic antibody efficacy, we sought to identify single-domain nanobodies (VHHs) targeting RBD regions (class 4, class 1/4, portions of class 3 and class 5 RBD epitopes) that are more conserved across VOCs, reasoning that the smaller size of camelid nanobodies compared with conventional two-domain antibody combining sites would facilitate access to occluded RBD epitopes. We used a Beacon optofluidic platform to isolate and characterize single memory B cells from a llama immunized with a mosaic RBD-nanoparticle immunogen that elicits broad antibody responses across sarbecoviruses. Using multiplex binding assays, we identified nanobodies that bind to spike RBDs from diverse sarbecovirus strains. Competition ELISAs and crystal structures of VHH-RBD complexes showed that isolated nanobodies recognize broadly conserved epitopes, including those on the RBD that are inaccessible to analogous conventional two-domain antibodies. Promising VHH-Fcs neutralized SARS-CoV-2 variants of concern and zoonotic sarbecoviruses, demonstrating potential therapeutic utility for current and future outbreaks.
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BibTeX
@misc{malecek2026mosaic,
title = {{A mosaic RBD-nanoparticle pan-sarbecovirus vaccine elicits nanobodies that target highly conserved epitopes}},
author = {K. E. Malecek and J. R. Keeffe and C. Fan and J. Alvarez and A. Player and H. Gao and P. P. N. P. Gnanapragasam and S. Rho and L. Schimanski and L. N. Segovia and T. K. Tan and P. J. Bjorkman},
howpublished = {bioRxiv},
year = {2026},
month = oct,
doi = {10.64898/2026.10.13.758647},
url = {https://www.biorxiv.org/content/10.64898/2026.10.13.758647v1},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - A mosaic RBD-nanoparticle pan-sarbecovirus vaccine elicits nanobodies that target highly conserved epitopes
AU - K. E. Malecek
AU - J. R. Keeffe
AU - C. Fan
AU - J. Alvarez
AU - A. Player
AU - H. Gao
AU - P. P. N. P. Gnanapragasam
AU - S. Rho
AU - L. Schimanski
AU - L. N. Segovia
AU - T. K. Tan
AU - P. J. Bjorkman
PY - 2026
DA - 2026/10/13
PB - bioRxiv
DO - 10.64898/2026.10.13.758647
UR - https://www.biorxiv.org/content/10.64898/2026.10.13.758647v1
AB - SARS-CoV-2, the virus that causes COVID-19, continually mutates, producing new variants of concern (VOCs). Substitutions in the SARS-CoV-2 spike protein receptor-binding domain (RBD) have resulted in reduced efficacies of vaccines and therapeutic monoclonal antibodies. Indeed, since the emergence of Omicron and earlier VOCs, most previously approved anti-RBD therapeutic monoclonal antibodies are no longer authorized as therapeutics. To address VOC substitutions effects on therapeutic antibody efficacy, we sought to identify single-domain nanobodies (VHHs) targeting RBD regions (class 4, class 1/4, portions of class 3 and class 5 RBD epitopes) that are more conserved across VOCs, reasoning that the smaller size of camelid nanobodies compared with conventional two-domain antibody combining sites would facilitate access to occluded RBD epitopes. We used a Beacon optofluidic platform to isolate and characterize single memory B cells from a llama immunized with a mosaic RBD-nanoparticle immunogen that elicits broad antibody responses across sarbecoviruses. Using multiplex binding assays, we identified nanobodies that bind to spike RBDs from diverse sarbecovirus strains. Competition ELISAs and crystal structures of VHH-RBD complexes showed that isolated nanobodies recognize broadly conserved epitopes, including those on the RBD that are inaccessible to analogous conventional two-domain antibodies. Promising VHH-Fcs neutralized SARS-CoV-2 variants of concern and zoonotic sarbecoviruses, demonstrating potential therapeutic utility for current and future outbreaks.
ER -