Here, we report that our previously identified antibodies, RBD-chAb-45 and -51, retain high binding ability for all tested SARS-CoV-2 variant pseudoviruses, including four VOCs (Fig.?1). RBD-chAb-45, and -51 showed PRNT50 values 4.93C37.54?ng/ml when used as single treatments or in combination with RBD-chAb-15 or -28, according to plaque assays with authentic Alpha, Gamma and Delta SARS-CoV-2 variants. Furthermore, the antibody cocktail of RBD-chAb-15 and -45 exhibited potent prophylactic and therapeutic effects in Delta SARS-CoV-2 variant-infected hamsters. Conclusions The cocktail of RBD-chAbs exhibited potent neutralizing activities against SARS-CoV-2 variants. These antibody cocktails are highly promising candidate tools for controlling new SARS-CoV-2 variants, including Delta. non-neutralizing Neutralizing abilities of anti-RBD chAbs in combination Previously, we found that RBD-chAb-45 and -51 share overlapping epitopes according to an ELISA-based competition-binding assay . In addition, RBD-chAb-15 and -28 have highly comparable epitopes, and RBD-chAb-25 has an epitope that partially overlaps with those Rabbit Polyclonal to Cytochrome P450 1B1 of RBD-chAb-15 and -28. However, only RBD-chAb-25 loses its neutralizing ability against SARS-CoV-2 variant pseudoviruses with the N501Y mutation . To evaluate the neutralizing abilities of cocktails made up of RBD-chAbs with different epitopes, we performed neutralization assessments using SARS-CoV-2 variant pseudoviruses. Combinations of RBD-chAb-15 or -28 with RBD-chAb-45 or -51 exhibited high neutralizing activities toward different SARS-CoV-2 pseudoviruses, including Alpha, Beta, Gamma, Epsilon, Iota, Kappa and Delta variants (Fig.?2A). The RBD-chAb cocktails showed low IC50 values ranging from 3 to 27?ng/ml (Table ?(Table2).2). To evaluate the RBD-chAbs cocktail neutralization potential against CX-4945 sodium salt the authentic SARS-CoV-2 Alpha, Gamma and Delta variants, we performed the PRNT and showed that RBD-chAb-15 or -28 combined with RBD-chAb-45 or -51 displayed the high potencies against the authentic computer virus; the PRNT50 values were less than 38?ng/ml (Fig.?2B). Open in a separate windows Fig. 2 Neutralization of SARS-CoV-2 variants by RBD-chAb combinations. A Neutralization assays testing RBD-chAb-15 or -28 combined with -45 or -51 against SARS-CoV-2 variant pseudoviruses. Each assay was performed in triplicate; data points represent the mean. Data for each RBD-chAb are representative of at least two impartial neutralization experiments. B Neutralizing RBD-chAb-15 or -28 combined with -45 or -51 inhibits SARS-CoV-2 variants, Alpha, Gamma and Delta; contamination was assessed by PRNT. The PRNT50 value was calculated with Prism software. Each assay was performed in triplicate, and all data points are shown, along with the mean??SD Table 2 Half-maximal inhibitory concentrations (IC50) values for RBD-chAb combinations against pseudoviruses of SARS-CoV-2 variants test. ***test. * em P /em ? ?0.05, *** em P /em ? CX-4945 sodium salt ?0.001 Discussion SARS-CoV-2 is an RNA virus with a high mutation rate, which results in the rapid emergence of variants. Identified variants with high transmissibility or that cause increased rates of severe disease or death are classified as VOCs and include: B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma) and B.1.617.2 (Delta) . A major public health concern is usually that new SARS-CoV-2 variants may be resistant to neutralizing antibodies induced by contamination or vaccination, as well as therapeutic antibodies developed against initial SARS-CoV-2. Here, we report that our previously identified antibodies, RBD-chAb-45 and -51, retain high binding ability for all tested SARS-CoV-2 variant pseudoviruses, including four VOCs (Fig.?1). Because the epitope for RBD-chAb-25 includes N501 in the S protein, the antibody had reduced binding ability toward variants with the N501Y mutation [including CX-4945 sodium salt B.1.1.7 (Alpha), B.1.351 (Beta) and P1 (Gamma)] (Fig.?1). However, RBD-chAb-25 still retained the ability to recognize other variants (Fig.?1). Combinations of RBD-chAbs showed neutralization ability for all those tested SARS-CoV-2 variants in the pseudovirus neutralization assay (Fig.?2). Therefore, our six.