Severe COVID-19 is associated with profound lymphopenia and an elevated neutrophil to lymphocyte ratio. We applied a novel dimer avoidance multiplexed polymerase chain reaction next-generation sequencing assay to analyze T (TCR) and B cell receptor (BCR) repertoires. Surprisingly, TCR repertoires were markedly diminished during the early onset of severe disease but recovered during the convalescent stage. Monitoring TCR repertoires could serve as an indicative biomarker to predict disease progression and recovery. Panoramic concurrent assessment of BCR repertoires demonstrated isotype switching and a transient but dramatic early IgA expansion. Dominant B cell clonal expansion with decreased diversity occurred following recovery from infection. Profound changes in T cell homeostasis raise critical questions about the early events in COVID-19 infection and demonstrate that immune repertoire analysis is a promising method for evaluating emergent host immunity to SARS-CoV-2 viral infection, with great implications for assessing vaccination and other immunological therapies.

Hepatocyte nuclear factor-4 alpha (HNF-4a) is an important transcription factor governing the expression of genes involved in multiple metabolic pathways. Secreted phospholipase A 2 GXIIB (PLA 2 GXIIB) is an atypical member of a class of secreted phospholipases A 2 . We establish in this study that PLA 2 GXIIB is an HNF-4a target gene. We demonstrate that HNF-4a binds to a response element on the PLA 2 GXIIB promoter. Moreover, HNF4a agonists induce PLA 2 GXIIB expression in human hepatocarcinoma cells. Importantly, PLA 2 GXIIB-null mice accumulate triglyceride, cholesterol, and fatty acids in the liver and develop severe hepatosteatosis resembling some of the phenotypes of liver-specific HNF4a-null mice. These defects are in part due to compromised hepatic very low-density lipoprotein secretion. Finally, adenovirus-mediated overexpression of HNF-4a elevates serum triglyceride level in wild-type but not PLA 2 GXIIB-null mice. Conclusion: Collectively, these evidences suggest that HNF-4a is a key physiological PLA 2 GXIIB transcriptional regulator and that PLA 2 GXIIB is a novel mediator of triglyceride metabolism in the liver. (HEPATOLOGY 2011;53:458-466)

Monoclonal antibodies (mAbs) encoded by targeting the spike receptor-binding domain (RBD) have been isolated from different COVID-19 patients. However, the existence and prevalence of shared VH3-53-encoded antibodies in the antibody repertoires is not clear. Using antibody repertoire sequencing, we found that the usage of VH3-53 increased after SARS-CoV-2 infection. A highly shared VH3-53-J6 clonotype was identified in 9 out of 13 COVID-19 patients. This clonotype was derived from convergent gene rearrangements with few somatic hypermutations and was evolutionary conserved. We synthesized 34 repertoire-deduced novel VH3-53-J6 heavy chains and paired with a common IGKV1-9 light chain to produce recombinant mAbs. Most of these recombinant mAbs (23/34) possess RBD binding and virus-neutralizing activities, and recognize ACE2 binding site via the same molecular interface. Our computational analysis, validated by laboratory experiments, revealed that VH3-53 antibodies targeting RBD are commonly present in COVID-19 patients' antibody repertoires, indicating many people have germline-like precursor sequences to rapidly generate SARS-CoV-2 neutralizing antibodies. Moreover, antigenspecific mAbs can be digitally obtained through antibody repertoire sequencing and computational analysis.