Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2 + mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of patients with COVID-19. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression. RESULTS SARS-CoV-2 infects human intestinal enteroidsIn the intestine, ACE2 functions as a chaperone for the sodiumdependent neutral amino acid transporter B 0 AT1 (encoded by SLC6A19) on IECs and regulates microbial homeostasis (21,22). ACE2 expression is substantially higher in the small intestine than in all the other organs, including the lung, in both humans and mice (fig. S1, A and B). Given these data, we assessed whether SARS-CoV-2 can infect IECs as a first step for understanding its implications for fecal-oral transmission. We performed single-cell RNA sequencing (scRNA-seq) to capture the global transcriptomics in all IEC subsets in the mouse small intestinal epithelium (Fig. 1A, left). ACE2 mRNA was predominantly seen in Cd26 + Epcam + Cd44 − Cd45 − mature enterocytes (Fig. 1A, right) (23, 24). In addition, bulk RNA-seq revealed that primary human ileum enteroids had substantially higher mRNA levels of all known CoV receptors, including ACE2, than the of 10 that Ace2 high cells are also positive for Cd26 and Epcam but negative for Cd44 and Cd45. (B) Human duodenum enteroids were cultured in the Transwell monolayer system using maintenance (MAINT) or differentiation (DIFF) conditions for 3 days. Monolayers were stained for ACE2 (red) and actin (phalloidin, white). Scale bars, 32 m. (C) Human duodenum enteroids in monolayer, cultured in either maintenance (MAINT) or differentiation (DIFF) conditions, were apically infected with 1.5 × 10 5 plaque-forming units (PFU) of VSV-SARS-CoV-2 [multiplicity of infection (MOI) = 0.3] for 24 hours. The expression of VSV-N was measured by RT-qPCR and normalized to that of GAPDH. p.i., post-infection. (D) Human duodenum enteroids in 3D Matrigel were cultured in maintenance (MAINT) medium or differentiation (DIFF) medium for 3 days and infected with 2.2 × 10 5 PFU of VSV-SARS-CoV-2 for 18 hours. Enteroids were stained for virus (green), actin (phalloidin, white), and nucleus (DAPI, blue). Scale bars, 50 m. (E) Same as (C) except that virus titers were measured using a TCID 50 assay instead of viral RNA levels by qPCR. (F) Same as (D) except that human ileum enteroids were used instead. Scale bars, ...

Objective The technology for the growth of human intestinal epithelial cells is rapidly progressing. An exciting possibility is that this system could serve as a platform for individualized medicine and research. However, to achieve this goal, human epithelial culture must be enhanced so that biopsies from individuals can be used to reproducibly generate cell lines in a short time frame so that multiple, functional assays can be performed (i.e., barrier function and host-microbial interactions). Design We created a large panel of human gastrointestinal epithelial cell lines (n = 65) from patient biopsies taken during routine upper and lower endoscopy procedures. Proliferative stem/progenitor cells were rapidly expanded using a high concentration of conditioned media containing the factors critical for growth (Wnt3a, R-spondin and Noggin). A combination of lower conditioned media concentration and Notch inhibition was used to differentiate these cells for additional assays. Results We obtained epithelial lines from all accessible tissue sites within two weeks of culture. The intestinal cell lines were enriched for stem cell markers and rapidly grew as spheroids that required passage at 1:3–1:4 every 3 days. Under differentiation conditions, intestinal epithelial spheroids showed region-specific development of mature epithelial lineages. These cells formed functional, polarized monolayers covered by a secreted mucus layer when grown on Transwell membranes. Using two-dimensional culture, these cells also demonstrated novel adherence phenotypes with various strains of pathogenic Escherichia coli. Conclusion This culture system will facilitate the study of inter-individual, functional studies of human intestinal epithelial cells, including host-microbial interactions.

Evidence suggests that immunogenicity to mRNA-based SARS-CoV-2 vaccination in immunosuppressed patients may be reduced. This study assessed the response to 2 doses of mRNA-based SARS-CoV-2 vaccine among 133 participants with underlying chronic inflammatory disease, many of whom were receiving glucocorticoids, B-cell depletion therapy, or other immunosuppressant therapy.

BackgroundThe small intestinal epithelium is highly sensitive to radiation and is a major site of injury during radiation therapy and environmental overexposure.ObjectiveTo examine probiotic bacteria as potential radioprotective agents in the intestine.Methods8-week-old C57BL/6 wild-type or knockout mice were administered probiotic by gavage for 3 days before 12 Gy whole body radiation. The intestine was evaluated for cell-positional apoptosis (6 h) and crypt survival (84 h).ResultsGavage of 5×107 Lactobacillus rhamnosus GG (LGG) improved crypt survival about twofold (p<0.01); the effect was observed when administered before, but not after, radiation. Conditioned medium (CM) from LGG improved crypt survival (1.95-fold, p<0.01), and both LGG and LGG-CM reduced epithelial apoptosis particularly at the crypt base (33% to 18%, p<0.01). LGG was detected in the distal ileal contents after the gavage cycle, but did not lead to a detectable shift in bacterial family composition. The reduction in epithelial apoptosis and improved crypt survival offered by LGG was lost in MyD88−/−, TLR-2−/− and cyclo-oxygenase-2−/− (COX-2) mice but not TLR-4−/− mice. LGG administration did not lead to increased jejunal COX-2 mRNA or prostaglandin E2 levels or a change in number of COX-2-expressing cells. However, a location shift was observed in constitutively COX-2-expressing cells of the lamina propria from the villi to a position near the crypt base (villi to crypt ratio 80:20 for control and 62:38 for LGG; p<0.001). Co-staining revealed these COX-2-expressing small intestinal lamina propria cells to be mesenchymal stem cells.ConclusionsLGG or its CM reduce radiation-induced epithelial injury and improve crypt survival. A TLR-2/MyD88 signalling mechanism leading to repositioning of constitutive COX-2-expressing mesenchymal stem cells to the crypt base is invoked.

Oxidation of amino acid residues in proteins can be caused by a variety of oxidizing agents normally produced by cells. The oxidation of methionine in proteins to methionine sulfoxide is implicated in aging as well as in pathological conditions, and it is a reversible reaction mediated by a ubiquitous enzyme, peptide methionine sulfoxide reductase. The reversibility of methionine oxidation suggests that it could act as a cellular regulatory mechanism although no such in vivo activity has been demonstrated. We show here that oxidation of a methionine residue in a voltage-dependent potassium channel modulates its inactivation. When this methionine residue is oxidized to methionine sulfoxide, the inactivation is disrupted, and it is reversed by coexpression with peptide methionine sulfoxide reductase. The results suggest that oxidation and reduction of methionine could play a dynamic role in the cellular signal transduction process in a variety of systems.