Immune cell profiling in atherosclerosis: role in research and precision medicine

Abstract

Inflammation is intimately involved at all stages of atherosclerosis and remains a substantial residual cardiovascular risk factor in optimally treated patients. The proof of concept that targeting inflammation reduces cardiovascular events in patients with a history of myocardial infarction has highlighted the urgent need to identify new immunotherapies to treat patients with atherosclerotic cardiovascular disease. Importantly, emerging data from new clinical trials show that successful immunotherapies for atherosclerosis need to be tailored to the specific immune alterations in distinct groups of patients. In this Review, we discuss how single-cell technologies - such as single-cell mass cytometry, single-cell RNA sequencing and cellular indexing of transcriptomes and epitopes by sequencing - are ideal for mapping the cellular and molecular composition of human atherosclerotic plaques and how these data can aid in the discovery of new precise immunotherapies. We also argue that single-cell data from studies in humans need to be rigorously validated in relevant experimental models, including rapidly emerging single-cell CRISPR screening technologies and mouse models of atherosclerosis. Finally, we discuss the importance of implementing single-cell immune monitoring tools in early phases of drug development to aid in the precise selection of the target patient population for data-driven translation into randomized clinical trials and the successful translation of new immunotherapies into the clinic.

Conflict of interest statement

The authors declare no competing interests.

© 2021. Springer Nature Limited.

Figures

Fig. 1. Single-cell approaches to study human atherosclerosis.

a | After atherosclerotic tissue is dissociated into single cells, the sample is analysed using three approaches: cytometry by time of flight (CyTOF), cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) and single-cell RNA sequencing (scRNA-seq). b | CyTOF can be used to analyse the broad cell types and frequencies of immune cells across patients, with the use of unbiased approaches such as Louvain clustering. c | CITE-seq accurately integrates proteomics and gene expression signatures. d | scRNA-seq can be used to characterize phenotypically the immune cells from patients and to compare profiles of different cell types. pDCs, plasmacytoid dendritic cells.

Fig. 2. Single-cell approaches to study atherosclerotic tissue.

Tissue dissociation methods and in situ approaches are complementary systems to understand cell properties at the single-cell level. Several methods exist for each approach, and both approaches can be used for proteomics and transcriptomics analyses. The integration of the resulting data can be useful for the identification of molecular targets for disease therapies and subsequent drug discovery. FFPE, formalin-fixed paraffin-embedded; MIBI, multiplexed ion beam imaging.

Fig. 3. Integration of single-cell methods for the discovery and validation of drug targets.

a | Single-cell studies in humans and mice provide information about the disease. Whereas studies in humans define the actual disease state, mechanistic studies in mice can aid in the understanding of how perturbations affect the disease. Integration and cross-species validation of these studies can be used to identify novel molecular targets. Understanding these molecular pathways in large clinical cohorts can be used as validation and then secondarily validated in animal models with the use of pooled CRISPR screening. b | When new targets are identified and validated, candidate drugs can be assessed for their specific effect in modulating these pathways. One evaluation method is phosphoproteomics with cytometry by time of flight (phospho-CyTOF). In vivo testing in animals can be used to investigate further the efficacy of the drug and to evaluate the go/no-go decisions to enter clinical phases of drug development. The adoption of immune monitoring in the early phases of clinical trials can provide crucial information on patient selection and efficacy for the design of future end point-driven clinical trials.