Review 1: "Sofosbuvir protects human brain organoids against SARS-CoV-2"

Review:

The work “Sofosbuvir protects human brain organoids against SARS-CoV-2” provide insight on how the SARS-CoV-2 can affect the development of neuronal organoids, and demonstrates how Sofosbuvir, an antiviral drug, can protect the organoids against SARS-CoV-2. The work presented here was done by the group of Muorti, who published another work of using the brain organoids for identifying the effect of the Zika virus on brain development. Overall, I find the work novel, important and well performed. I believe that considering the accumulating evidence that SARS-CoV-2 has neurological effect, it is a significant work, which demonstrates the use of brain organoids for studying Cov-19, and to identify a potential prophylactic drug. While I think that this work is novel, and the experiment is a very well designed, there are some comments I would like to point out: 

- Can the authors explain the relatively low expression levels of ACE2 (compare to the neurons and astrocytes)? What is the percentage of the cellular population in the organoids? - It could be nice addition to do IHC to ACE2. - As the neurons and astrocytes exhibit higherACE2 expression compared to the brain organoids, do you see the same effect that was observed on the organoid in regular neuronal cultures? - The main advantage of the brain organoids, is the ability to observe the changes in the 3D structures and the organoid development due to the SARS-CoV-2. Do the authors see any of these changes? - What was the rationale for the virus dose of “750,000 PFU that corresponds to a MOI of 2.5 considering an average of 300,000 cells per organoid “. How much is expected to reach the brain or to the embryo based on the literature? 

Minor comments: On page 3 - Sars-CoV-2 should be in Capital letters. Page 13 at the bottom, there is too much space between the words. Some of the bars are bold and some are not (e.g. Fig 2. B, C, E, F). “Data and materials availability: All data is available in the main text or the supplementary materials.” – I didn’t see any link or reference to supplementary materials. 

Overall I find this work innovative, important, and good for publication.