Mapping interindividual dynamics of innate immune response at single-cell resolution (preprint)

Common genetic variants modulate the cellular response to viruses and are implicated in a range of immune pathologies, including infectious and autoimmune diseases. The transcriptional antiviral response is known to vary between infected cells from a single individual, yet how genetic variants across individuals modulate the antiviral response (and its cell-to-cell variability) is not well understood. Here, we triggered the antiviral response in human fibroblasts from 68 healthy donors, and profiled tens of thousands of cells using single-cell RNA-seq. We developed GASPACHO (GAuSsian Processes for Association mapping leveraging Cell HeterOgeneity), the first statistical approach designed to identify dynamic eQTLs across a transcriptional trajectory of cell populations, without aggregating single-cell data into pseudo-bulk. This allows us to uncover the underlying architecture and variability of antiviral response across responding cells, and to identify more than two thousands eQTLs modulating the dynamic changes during this response. Many of these eQTLs colocalise with risk loci identified in GWAS of infectious and autoimmune diseases. As a case study, we focus on a COVID-19 susceptibility locus, colocalised with the antiviral OAS1 splicing QTL. We validated it in blood cells from a patient cohort and in the infected nasal cells of a patient with the risk allele, demonstrating the utility of GASPACHO to fine-map and functionally characterise a genetic locus. In summary, our novel analytical approach provides a new framework for delineation of the genetic variants that shape a wide spectrum of transcriptional responses at single-cell resolution.

A proteome-wide genetic investigation identifies several SARS-CoV-2-exploited host targets of clinical relevance (preprint)

The virus SARS-CoV-2 can exploit biological vulnerabilities in susceptible hosts that predispose to development of severe COVID-19. Previous reports have identified several host proteins related to the interferon response (e.g. OAS1), interleukin-6 signalling (IL-6R), and the coagulation cascade (linked via ABO) that were associated with risk of COVID-19. In the present study, we performed proteome-wide genetic colocalisation tests leveraging publicly available protein and COVID-19 datasets, to identify additional proteins that may contribute to COVID-19 risk. Our analytic approach identified several known targets (e.g. ABO, OAS1), but also nominated new proteins such as soluble FAS (colocalisation probability > 0.9, p = 1 x 10-4), implicating FAS-mediated apoptosis as a potential target for COVID-19 risk. We also undertook polygenic (pan) and cis-Mendelian randomisation analyses that showed consistent associations of genetically predicted ABO protein with several COVID-19 phenotypes. The ABO signal was associated with plasma concentrations of several proteins, with the strongest association observed with CD209 in several proteomic datasets. We demonstrated experimentally that CD209 directly interacts with the spike protein of SARS-CoV-2, suggesting a mechanism that could explain the ABO association with COVID-19. Our work provides a prioritised list of host targets potentially exploited by SARS-CoV-2 and is a precursor for further research on CD209 and FAS as therapeutically tractable targets for COVID-19.