PT  - JOURNAL ARTICLE
AU  - Huan Ma
AU  - Weihong Zeng
AU  - Xiangzhi Meng
AU  - Xiaoxue Huang
AU  - Yunru Yang
AU  - Dan Zhao
AU  - Peigen Zhou
AU  - Xiaofang Wang
AU  - Changcheng Zhao
AU  - Yong Sun
AU  - Peihui Wang
AU  - Huichao Ou
AU  - Xiaowen Hu
AU  - Yan Xiang
AU  - Tengchuan Jin
TI  - Potent in vitro Neutralization of SARS-CoV-2 by Hetero-bivalent Alpaca Nanobodies Targeting the Spike Receptor-Binding Domain
AID  - 10.1101/2021.02.02.429311
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.02.429311
4099  - http://biorxiv.org/content/early/2021/02/03/2021.02.02.429311.short
4100  - http://biorxiv.org/content/early/2021/02/03/2021.02.02.429311.full
AB  - Cell entry by SARS-CoV-2 requires the binding between the receptor-binding domain (RBD) of the viral Spike protein and the cellular angiotensin-converting enzyme 2 (ACE2). As such, RBD has become the major target for vaccine development, while RBD-specific antibodies are pursued as therapeutics. Here, we report the development and characterization of SARS-CoV-2 RBD-specific VHH/nanobody (Nb) from immunized alpacas. Seven RBD-specific Nbs with high stability were identified using phage display. They bind to SARS-CoV-2 RBD with affinity KD ranging from 2.6 to 113 nM, and six of them can block RBD-ACE2 interaction. The fusion of the Nbs with IgG1 Fc resulted in homodimers with greatly improved RBD-binding affinities (KD ranging from 72.7 pM to 4.5 nM) and nanomolar RBD-ACE2 blocking abilities. Furthermore, fusion of two Nbs with non-overlapping epitopes resulted in hetero-bivalent Nbs, namely aRBD-2-5 and aRBD-2-7, with significantly higher RBD binding affinities (KD of 59.2 pM and 0.25 nM) and greatly enhanced SARS-CoV-2 neutralizing potency. The 50% neutralization dose (ND50) of aRBD-2-5 and aRBD-2-7 was 1.22 ng/mL (∼0.043 nM) and 3.18 ng/mL (∼0.111 nM), respectively. These high-affinity SARS-CoV-2 blocking Nbs could be further developed into therapeutics as well as diagnosis reagents for COVID-19.Importance To date, SARS-CoV-2 has caused tremendous loss of human life and economic output worldwide. Although a few COVID-19 vaccines have been approved in several countries, the development of effective therapeutics including SARS-CoV-2 targeting antibodies remains critical. Due to their small size (13-15 kDa), highly solubility and stability, Nbs are particularly well suited for pulmonary delivery and more amenable to engineer into multi-valent formats, compared to the conventional antibody. Here, we report a serial of new anti-SARS-CoV-2 Nbs isolated from immunized alpaca and two engineered hetero-bivalent Nbs. These potent neutralizing Nbs showed promise as potential therapeutics against COVID-19.Competing Interest StatementThe authors have declared no competing interest.