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Review 1: "Intestinal organoids expose heterogeneity in SARS-CoV-2 susceptibility"

Published onMar 24, 2022
Review 1: "Intestinal organoids expose heterogeneity in SARS-CoV-2 susceptibility"
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key-enterThis Pub is a Review of
Variable susceptibility of intestinal organoid-derived monolayers to SARS-CoV-2 infection
Description

ABSTRACTGastrointestinal effects associated with COVID-19 are highly variable for reasons that are not understood. In this study, we used intestinal organoid-derived cultures differentiated from primary human specimens as a model to examine inter-individual variability. Infection of intestinal organoids derived from different donors with SARS-CoV-2 resulted in orders of magnitude differences in virus replication in small intestinal and colonic organoid-derived monolayers. Susceptibility to infection correlated with ACE2 expression level and was independent of donor demographic or clinical features. ACE2 transcript levels in cell culture matched the amount of ACE2 in primary tissue indicating this feature of the intestinal epithelium is retained in the organoids. Longitudinal transcriptomics of organoid-derived monolayers identified a delayed yet robust interferon signature, the magnitude of which corresponded to the degree of SARS-CoV-2 infection. Interestingly, virus with the Omicron variant spike protein infected the organoids with the highest infectivity, suggesting increased tropism of the virus for intestinal tissue. These results suggest that heterogeneity in SARS-CoV-2 replication in intestinal tissues results from differences in ACE2 levels, which may underlie variable patient outcomes.

RR:C19 Evidence Scale rating by reviewer:

  • Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review:

The article relies on the hypothesis of interindividual differences in responses to SARS-CoV-2 infection mainly based on differential ACE2 levels. The article provides relevant contributions to the field since the SARS-CoV-2 infection mechanism is still not fully understood, particularly in secondary site organs such as the intestine. To prove the hypothesis, human intestinal organoids were generated from human intestinal biopsies. The authors claim maintenance of ACE2 levels in intestinal organoids according to their corresponding biopsies. Molecular assays were performed to detect ACE2 levels in organoids in contrast with immunofluorescence for tissue biopsies. So, based on this comparison, it is hard to conclude that organoids retained ex vivo will have a differential ACE2 expression according to native tissue. Infection in vitro assays of intestinal tissue cells by SARS-CoV-2 showed the relationship with the expression of ACE-2, corroborating the hypothesis of this study. However, in our opinion, some details on performed assays need attention. According to the methods section, all assays, including the infection, were performed in monolayer cultures derived from intestinal organoids. Nevertheless, it is not clear in the main text, as the author refers to organoids in the results section. A few articles were published this year using the same approach of derived epithelial monolayers from intestinal organoids, however, they were performed directly into the intestinal organoids. We can conclude that there is an extrapolation in data interpretation since the authors refer to human organoids as a powerful platform to investigate interindividual differences in infectious disease susceptibility, however, experiments were carried out in monolayers instead of organoids.

In addition, images from organoids and monolayers derived from organoids are missing in the article, making it impossible to analyze the cellular morphologies during infection. In the figures section, some corrections need to be made regarding the numbering and missing information in graphics. Regarding the SARS-CoV-2 virus, the study used a recombinant and not the original virus. This information is restricted to the methods section and needs to be explicit throughout the text. In addition to this modification, a transmission electron microscopy image would be interesting and would show the viral particles infecting the organoids/monolayers, which would help us observe if it maintains the same morphology. The criticisms described here are intended to improve the quality of the article, which will further support the hypothesis of susceptibility of intestinal cells to the SARS-CoV-2 based on ACE-2 expression levels.

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