SARS-CoV-2 remdesivir resistance mutations have been generated in vitro but have not been reported in patients receiving treatment with the antiviral agent. We present a case of an immunocompromised patient with acquired B-cell deficiency who developed an indolent, protracted course of SARS-CoV-2 infection. Remdesivir therapy alleviated symptoms and produced a transient virologic response, but her course was complicated by recrudescence of high-grade viral shedding. Whole genome sequencing identified a mutation, E802D, in the nsp12 RNA-dependent RNA polymerase, which was not present in pre-treatment specimens. In vitro experiments demonstrated that the mutation conferred a ~6-fold increase in remdesivir IC50 but resulted in a fitness cost in the absence of remdesivir. Sustained clinical and virologic response was achieved after treatment with casirivimab-imdevimab. Although the fitness cost observed in vitro may limit the risk posed by E802D, this case illustrates the importance of monitoring for remdesivir resistance and the potential benefit of combinatorial therapies in immunocompromised patients with SARS-CoV-2 infection.

One of the most important cellular defenses against RNA viruses is a large, multidomain protein known as RIG-I (Retinoic Acid Inducible Gene I), which functions as a pattern recognition receptor (PRR) that triggers early innate immune responses in vertebrate cells. 1-3 RIG-I is a member of a conserved family of double-stranded RNA (dsRNA) binding proteins that includes additional innate immune surveillance proteins MDA5 and LGP2. [3][4][5] By recognizing and responding to different types of viral RNA motifs, this family (known as the RIG-I-like receptors or RLRs) provides broad protection against viral infections. These proteins are, in turn, closely related to members of the broader Dicer family, such as DRH3 (Dicer related helicase 3), as all of these proteins share a distinctive set of dsRNA binding domains, and an ATPase core that is catalytically activated only upon binding of dsRNA. 6,7 This link between RLRs and Dicer-like proteins involved in miRNA processing suggests a shared evolutionary heritage and the possibility of cross-talk between these two systems. 5 The helicase core of the RLR/Dicer family proteins (previously termed DRAs) is distinct, 7 but identifiable as a member of Helicase Superfamily 2

TEA domain (TEAD) family transcription factors are key regulators in development, tissue homeostasis and cancer progression. TEAD4 acts as a critical downstream effector of the evolutionarily conserved Hippo signaling pathway. The well-studied oncogenic protein YAP forms a complex with TEAD4 to regulate gene transcription; so does the tumor suppressor VGLL4. Although it is known that TEAD proteins can bind promoter regions of target genes through the TEA domain, the specific and detailed mechanism of DNA recognition by the TEA domain remains partially understood. Here, we report the crystal structure of TEAD4 TEA domain in complex with a muscle-CAT DNA element. The structure revealed extensive interactions between the TEA domain and the DNA duplex involving both the major and minor grooves of DNA helix. The DNA recognition helix, α3 helix, determines the specificity of the TEA domain binding to DNA sequence. Structure-guided biochemical analysis identified two major binding sites on the interface of the TEA domain-DNA complex. Mutation of TEAD4 at either site substantially decreases its occupancy on the promoter region of target genes, and largely impaired YAP-induced TEAD4 transactivation and target gene transcription, leading to inhibition of growth and colony formation of gastric cancer cell HGC-27. Collectively, our work provides a structural basis for understanding the regulatory mechanism of TEAD-mediated gene transcription.