Advances in Clinical Mass Cytometry

The advent of high-dimensional single-cell technologies has enabled detection of cellular heterogeneity and functional diversity of immune cells during health and disease conditions. Because of its multiplexing capabilities and limited compensation requirements, mass cytometry or cytometry by time of flight (CyTOF) has played a superior role in immune monitoring compared with flow cytometry. Further, it has higher throughput and lower cost compared with other single-cell techniques. Several published articles have utilized CyTOF to identify cellular phenotypes and features associated with disease outcomes. This article introduces CyTOF-based assays to profile immune cell-types, cell-states, and their applications in clinical research.

Ly6C hi monocytes balance regulatory and cytotoxic CD4 T cell responses to control virus-induced immunopathology

Gammaherpesviruses (γHVs) have coevolved with their host, leading to a remarkably high infection prevalence and establishment of latency. The lifelong persistence of γHVs in hosts appears to broadly shape host immunity, and we show here that pulmonary infection with Murid herpesvirus 4 (MuHV-4), a mouse γHV, drives the recruitment of Ly6C hi monocytes (MOs) into the airway, thereby modulating the host immune response. The absence of Ly6C hi MOs is associated with severe virus-induced immunopathology and the systemic release of inflammatory mediators. Mechanistically, MuHV-4–imprinted MOs recruit CD4 T cells to the airways and trigger immunosuppressive signaling pathways through the PD-L1/PD-1 axis, thereby dampening the deleterious activation of cytotoxic CD4 T cells. These results uncover a role for Ly6C hi MOs in modulating CD4 T cell functions and reveal pathways that could be targeted therapeutically to reduce detrimental immunopathological responses associated with respiratory viral infections.

Conquering the Host: Determinants of Pathogenesis Learned from Murine Gammaherpesvirus 68

Gammaherpesviruses are an important class of oncogenic pathogens that are exquisitely evolved to their respective hosts. As such, the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi sarcoma herpesvirus (KSHV) do not naturally infect nonhuman primates or rodents. There is a clear need to fully explore mechanisms of gammaherpesvirus pathogenesis, host control, and immune evasion in the host. A gammaherpesvirus pathogen isolated from murid rodents was first reported in 1980; 40 years later, murine gammaherpesvirus 68 (MHV68, MuHV-4, γHV68) infection of laboratory mice is a well-established pathogenesis system recognized for its utility in applying state-of-the-art approaches to investigate virus-host interactions ranging from the whole host to the individual cell. Here, we highlight recent advancements in our understanding of the processes by which MHV68 colonizes the host and drives disease. Lessons that inform KSHV and EBV pathogenesis and provide future avenues for novel interventions against infection and virus-associated cancers are emphasized.

CyTOF: An Emerging Technology for Single-Cell Proteomics in the Mouse

The ability to analyze the proteome of single cells is critical for the advancement of studies of steady-state and pathological processes. Mass cytometry, or CyTOF, combines principles of mass spectrometry and flow cytometry to enable single-cell analysis of protein expression. CyTOF can simultaneously assess DNA content and proteins and has the capacity to measure 40 to 100 parameters in each cell. Applying this technology to tissues or cells on slides, termed imaging mass cytometry (IMC), allows for visualization of normal and diseased tissues in situ. The high-dimensional proteomic analysis that can be undertaken with CyTOF and IMC has the potential to enhance our understanding of complex and heterogeneous developmental and disease pathways. This article will describe the CyTOF experimental workflow, including reagent selection, sample preparation, and data analysis. CyTOF is compared to flow cytometry, focusing on the strengths and weaknesses of these powerful techniques. Importantly, we review key studies in mouse models of human disease that highlight the strength of CyTOF and IMC to drive discovery research and therapeutic advancement. © 2021 Wiley Periodicals LLC.

Progress and applications of mass cytometry in sketching immune landscapes

Recently emerged mass cytometry (cytometry by time-of-flight [CyTOF]) technology permits the identification and quantification of inherently diverse cellular systems, and the simultaneous measurement of functional attributes at the single-cell resolution. By virtue of its multiplex ability with limited need for compensation, CyTOF has led a critical role in immunological research fields. Here, we present an overview of CyTOF, including the introduction of CyTOF principle and advantages that make it a standalone tool in deciphering immune mysteries. We then discuss the functional assays, introduce the bioinformatics to interpret the data yield via CyTOF, and depict the emerging clinical and research applications of CyTOF technology in sketching immune landscape in a wide variety of diseases.

High-Dimensional Analysis of Postsplenectomy Peripheral Immune Cell Changes

Although the consequences of splenectomy are well understood in mice, much less is known about the immunologic changes that occur following splenectomy in humans. We sought to characterize the circulating immune cell populations of patients before and after elective splenectomy to determine if these changes are related to postsplenectomy survival outcomes. Retrospective clinical information was collected from 95 patients undergoing elective splenectomy compared with 91 patients undergoing pancreaticoduodenectomy (Whipple procedure). We further analyzed peripheral blood from five patients in the splenectomy group, collected before and after surgery, using single-cell cytometry by time-of-flight mass spectrometry. We compared pre- and postsplenectomy data to characterize both the major and minor immune cell populations in significantly greater detail. Compared with patients undergoing a Whipple procedure, splenectomized patients had significant and long-lasting elevated counts of lymphocytes, monocytes, and basophils. Cytometry by time-of-flight mass spectroscopy analysis demonstrated that the elevated lymphocytes primarily consisted of naive CD4⁺ T cells and a population of activated CD25⁺CD56⁺CD4⁺ T cells, whereas the elevated monocyte counts were mainly mature, activated monocytes. We also observed a significant increase in the expression of the chemokine receptors CCR6 and CCR4 on several cellular populations. Taken together, these data indicate that significant immunological changes take place following splenectomy. Whereas other groups have compared splenectomized patients to healthy controls, this study compared patients undergoing elective splenectomy to those undergoing a similar major abdominal surgery. Overall, we found that splenectomy results in significant long-lasting changes in circulating immune cell populations and function.