Over a year of the COVID-19 pandemic, distinct severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lineages have arisen in multiple geographic areas around the world. SARS-CoV-2 variants of concern (VOCs), i.e., B.1.1.7 (alpha), B.1.351 (beta), P.1 (gamma), and B.1.617.2 (delta), harboring mutations and/or deletions in spike protein N-terminal domain (NTD) or receptor-binding domain (RBD) regions showed evidence of increased transmissibility and disease severity and possible reduced vaccine efficacy.

SARS-CoV-2 Variants of Concerns (VOC), e.g., B.1.351 (20H/501Y.V2) and P1 (20J/501Y.V3), harboring N-terminal domain (NTD) or the receptor-binding domain (RBD) (e.g., E484K) mutations, exhibit reduced in vitro susceptibility to convalescent serum, commercial antibody cocktails, and vaccine neutralization, and have been associated with reinfection. The accumulation of these mutations could be the consequence of intra-host viral evolution due to prolonged infection in immunocompromised hosts. In this study, we document the microevolution of SARS-CoV-2 recovered from sequential tracheal aspirates from an immunosuppressed patient on tacrolimus, steroids and convalescent plasma therapy, and identify the emergence of multiple NTD and RBD mutations associated with reduced antibody neutralization as early as three weeks after infection. SARS-CoV-2 genomes from the first swab (Day 0) and three tracheal aspirates (Day 7, 21 and 27) were compared at the sequence level. We identified five different S protein mutations at the NTD or RBD regions from the second tracheal aspirate sample (21 Day). The S:Q493R substitution and S:243-244LA deletion had ~70% frequency, while ORF1a:A138T, S:141-144LGVY deletion, S:E484K and S:Q493K substitutions demonstrated ~30%, ~30%, ~20% and ~10% mutation frequency, respectively. However, the third tracheal aspirate sample collected one week later (Day 27) was predominated by the haplotype of ORF1a:A138T, S:141-144LGVY deletion and S:E484K (> 95% mutation frequency). Notably, S protein deletions (141-144LGVY and 243-244LA deletions in NTD region) and substitutions (Q493K/R and E484K in the RBD region) previously showed reduced susceptibly to monoclonal antibody or convalescent plasma. The observation supports the hypothesis that VOCs can independently arise and that immunocompromised patients on convalescent plasma therapy are potential breeding grounds for immune-escape mutants.

We utilized a CRISPR interference (CRISPRi) assay to control the gene expressions of two predicted essential peptidoglycan biosynthesis genes, pbpB and cwIM , in Mycobacterium abscessus and to evaluate their contribution to β-lactam susceptibility. Our results showed that CRISPR inhibition of each gene led to a significant 3-log 10 reduction in CFU in the presence of imipenem but not for cefoxitin.