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Authors: Chuang Guo et al. Link to paper: https://www.biorxiv.org/content/10.1101/2020.04.08.029769v1

Journal/ Pre-Print: bioRxiv

Key Words: Tocilizumab, monocytes, single-cell RNA-seq, Patient samples

RESEARCH HIGHLIGHTS 

1. Identified CD14+ monocyte subset post treatment with Tocilizumab in severe stage

2. Assessment of transcription factor and cell-cell interactions (such as IL6/IL6R) potentially involved in regulation of immune regulation in the monocyte subset observed in the severe stage

3. Post treatment with Tocilizumab, high number of plasma B cells and effector CD8+ T cells present --> indicating that immune responses still present after treatment with Tocilizumab

SUMMARY 

Guo et al. performed single-cell RNA-seq of PBMCs in 2 patients at multiple timepoints after treatment with the IL-6-receptor blocker Tocilizumab. For controls, they used publicly available demo data from 10X rather than untreated patients, so disentangling effects of batch, disease and treatment was not possible. They identified a CD14+ monocyte subset almost exclusively from the severe stage, and describe upregulated genes in this population that might be involved in the cytokine storm. The authors also found high numbers of plasma B-cells and effector CD8+ T-cells post-treatment, indicating that these immune responses were still active 5 days after Tocilizumab treatment.

IMPACT FOR SARS-COV2/COVID19 RESEARCH EFFORTS

Understand the transcriptional response of immune cell populations against SARS-CoV2 at different stages of the disease although the data might be skewed due to Tocilizumab treatment.

Treatment option for SARS-CoV2/COVID19 positive individuals by alleviating cytokine storm with Tocilizumab treatment.

STUDY TYPE

· In silico study / bioinformatics study

· Patient Case study

STRENGTHS AND LIMITATIONS OF THE PAPER

Novelty:

· First scRNA-seq transcriptome of SARS-CoV2 infected patients treated with Tocilizmab

· Identify CD14+ monocyte population almost exclusively from severe stage after treatment which could be the major population responsible for the cytokine storm during the severe stage. Transcription factors identified that might regulate cytokine storm.

· Cell-cell interactions using an established method confirmed previously described interaction between monocytes and CD4 T-cells and plasma cells via IL6/IL6-R. This was lower in recovery stages. The effect of Tocilizumab is difficult to interpret as no untreated control patients are present.

· Post treatment with Tocilizumab, high number of plasma B cells and effector CD8+ T cells --> indicating that adaptive immune responses is not impaired after treatment with Tocilizumab

Standing in the field: Fits with previous reports of IL6-IL6R involvement in cytokine storm & sepsis on-set

Appropriate statistics: Some results are difficult to interpret as the control group without Tocilizumab treatment is missing, but other statistics and methods well described

Viral model used: SARS-CoV2 infected individuals

Translatability:

· Drug Tocilizumab used for treatment of patients, not control group as a comparison

· Immune cell interactions could be used for drug development (e.g. IL6/IL6R)

· Upregulated pro-inflammatory cytokines in severe-stage associated monocytes might be potential targets for inhibition to prevent cytokine storm

Main limitations:

· 2 patients only, non-consistent time point between patients

· No untreated controls present as a comparison (healthy control PBMC are not suitable control). The controls are demo samples from 10X, which do not seem to be

described (in terms of age, sex, ethnicity, etc) in either this paper or on the 10X website.

· Cell-cell interaction could have been assessed specifically between severe-stage specific CD14+ monocytes (cluster 9) and other cell types

· Potential follow-up: Absence of in vitro/in vivo experimental data on identified cell-populations and their function/behaviour in response to SARS-CoV2