convalescents, and to screen for broad-spectrum neutralizing antibodies against the SARS-CoV-2 RBD. Methods Using biotinylated RBD as a molecular probe, flow cytometry was employed to perform single-cell sorting of B cells from peripheral blood mononuclear cells (PBMCs) of convalescents. The obtained B cells were lysed and subjected to reverse transcription, followed by nested PCR amplification of the heavy and light chains of antibodies was conducted using random primers. The amplified products were cloned into corresponding expression vectors, and the respective matched heavy-light chain plasmids were co-transfected into 293F cells for expression. Monoclonal antibodies were then purified using Protein A column chromatography. Neutralization experiments were conducted with the wild-type (WT) pseudovirus, and antibodies with IC50<0.1 μg/mL were selected for further testing of neutralizing breadth and potency against the wild-type (WT), Beta variant (B.1.351), Delta variant (B.1.617.2), and currently prevalent pseudovirus strains (XBB, BA.5, BF.7). Results A total of 21 RBD-specific monoclonal B cells were obtained from two recovered patients, resulting in the isolation of 13 pairs of antibody light/heavy chains. Nine antibodies were successfully expressed, with P1-A1, P1-B6, and P1-B9 exhibiting IC50 values below 0.1 μg/mL against the pseudovirus of the wild-type strain (WT). Specifically, P1-B6 effectively neutralized the wild-type strain (WT), Beta variant (B.1.351), and Delta variant (B.1.617.2), with IC50 values reaching 0.01 μg/mL. P1-B9 demonstrated effective neutralization against the wild-type strain (WT), Beta variant (B.1.351), Delta variant (B.1.617.2), and Gamma variant (P.1) pseudoviruses, with IC50 values of 0.42 μg/mL, 0.63 μg/mL, 0.28 μg/mL, and 2.50 μg/mL, respectively. Additionally, P1-B6 exhibited good neutralization against BA.5 and BF.7 pseudoviruses, with IC50 values of 0.06 μg/mL and 0.09 μg/mL, respectively. Conclusions Infection with the SARS-CoV-2 WT strain can induce the generation of neutralizing antibodies with broad-spectrum activity. Generating these broadly neutralizing antibodies does not require an excessively high somatic hypermutation. The obtained antibodies can be used as candidates for SARS-CoV-2 diagnosis and prevention.

Objective:To investigate the correlation between the dynamic changes of the superior mesenteric artery (SMA) blood flow after umbilical cord milking (UCM)detected and feeding tolerance in premature infants.Methods:This was a prospective study a total of 88 premature infants delivered in Shanghai Jiading Maternal and Child Health Care Hospital from June 2018 to February 2020 were randomly divided into UCM group(45 cases) and early cord clamping group (ECC group, 43 cases). SMA blood flow indexes 15 min before the first feeding (prefeed) and 60 min after the first feeding (post-feed) were detected using the GE Voluson 730 Ultrasound Machine, including the peak systolic velocity (PSV), time-averaged mean velocity (TAMV), pulsatility index (PI) and resistance index (RI). The gestational age, birth weight, the weight at discharge, SMA blood flow indexes, time to achieve enteral nutrition, length of stay and incidence of complications between the two groups were analyzed using t test, Chi- square test or Fisher′ s exact test. Results:(1)There were no significant differences in the gestational age, birth weight, the mother′s hemoglobin before deliver, and the incidence of complications between UCM group and ECC group (all P>0.05). (2) Except for RI, all SMA blood flow indexes were higher in UCM group than those of ECC group.However, only prefeed TAMV[(24.74±11.47) cm/s vs.(20.24±7.71) cm/s], post-feed TAMV[(42.11±15.74 )cm/s vs.(28.31±9.99) cm/s] and TAMV change before and after feeding [(13.89-20.86) cm/s vs.(5.31-10.82) cm/s]were detected to be significantly higher in UCM group than those of ECC group (all P<0.05). (3) Multivariable linear regression analysis showed that the gestational age, birth weight, PSV elevation and PI reduction were negatively correlated with the length of adequate feeding (all P<0.05). (4) The time to achieve enteral nutrition[(11.75±7.36) d vs.(13.38±8.12) d] and the incidence of feeding intolerance [13.3% (6/45 cases) vs.20.9%(9/43 cases)] were lower in UCM group than those of ECC group, although no significant differences were detected (all P>0.05). Conclusions:UCM increases the hemoglobin level in premature infants, which is beneficial to feeding tolerance of premature infants by improving SMA blood flow.