Single-Cell Proteomics Study of Immune Cell Diversity by Quantitating 465 Proteins

The identification and characterization of T cell subpopulations is critical to reveal cell development throughout life and immune responses to environmental factors. Next-generation sequencing technologies have dramatically advanced the single-cell genomics and transcriptomics for T cell classification. However, gene expression is often not correlated with protein expression, and immunotyping is mostly accepted in the protein format. Current single-cell proteomics technologies are either limited in multiplex capacity or not sensitive enough to detect the critical functional proteins. Herein we present a cyclic multiplex in situ tagging (Cyclic MIST) technology to simultaneously measure 465 proteins, a scale of >10 times than similar technologies, in single cells. Such a high multiplexity is achieved by reiterative staining of the single cells coupled with a MIST array for detection. This technology has been thoroughly validated through comparison with flow cytometry and fluorescence immunostaining techniques. Both THP1 and CD4+ T cells are analyzed by the Cyclic MIST technology, and over 300 surface markers have been profiled to classify the subpopulations. This represents the most comprehensive mapping of the diversity of immune cells at the protein level. With additional information from intracellular proteins of the same single cells, our technology can potentially facilitate mechanistic studies of immune responses, particularly cytokine storm that results in sepsis.

From Cell States to Cell Fates: How Cell Proliferation and Neuronal Differentiation Are Coordinated During Embryonic Development

The central nervous system (CNS) exhibits an extraordinary diversity of neurons, with the right cell types and proportions at the appropriate sites. Thus, to produce brains with specific size and cell composition, the rates of proliferation and differentiation must be tightly coordinated and balanced during development. Early on, proliferation dominates; later on, the growth rate almost ceases as more cells differentiate and exit the cell cycle. Generation of cell diversity and morphogenesis takes place concomitantly. In the vertebrate brain, this results in dramatic changes in the position of progenitor cells and their neuronal derivatives, whereas in the spinal cord morphogenetic changes are not so important because the structure mainly grows by increasing its volume. Morphogenesis is under control of specific genetic programs that coordinately unfold over time; however, little is known about how they operate and impact in the pools of progenitor cells in the CNS. Thus, the spatiotemporal coordination of these processes is fundamental for generating functional neuronal networks. Some key aims in developmental neurobiology are to determine how cell diversity arises from pluripotent progenitor cells, and how the progenitor potential changes upon time. In this review, we will share our view on how the advance of new technologies provides novel data that challenge some of the current hypothesis. We will cover some of the latest studies on cell lineage tracing and clonal analyses addressing the role of distinct progenitor cell division modes in balancing the rate of proliferation and differentiation during brain morphogenesis. We will discuss different hypothesis proposed to explain how progenitor cell diversity is generated and how they challenged prevailing concepts and raised new questions.

Transcriptomic Crosstalk between Gliomas and Telencephalic Neural Stem and Progenitor Cells for Defining Heterogeneity and Targeted Signaling Pathways

Recent studies have begun to reveal surprising levels of cell diversity in the human brain, both in adults and during development. Distinctive cellular phenotypes point to complex molecular profiles, cellular hierarchies and signaling pathways in neural stem cells, progenitor cells, neuronal and glial cells. Several recent reports have suggested that neural stem and progenitor cell types found in the developing and adult brain share several properties and phenotypes with cells from brain primary tumors, such as gliomas. This transcriptomic crosstalk may help us to better understand the cell hierarchies and signaling pathways in both gliomas and the normal brain, and, by clarifying the phenotypes of cells at the origin of the tumor, to therapeutically address their most relevant signaling pathways.

Single-cell transcriptional profiling of splenic fibroblasts reveals subset-specific innate immune signatures in homeostasis and during viral infection

Our understanding of the composition and functions of splenic stromal cells remains incomplete. Here, based on analysis of over 20,000 single cell transcriptomes of splenic fibroblasts, we characterized the phenotypic and functional heterogeneity of these cells in healthy state and during virus infection. We describe eleven transcriptionally distinct fibroblastic cell clusters, reassuring known subsets and revealing yet unascertained heterogeneity amongst fibroblasts occupying diverse splenic niches. We further identify striking differences in innate immune signatures of distinct stromal compartments in vivo. Compared to other fibroblasts and to endothelial cells, Ly6C+ fibroblasts of the red pulp were selectively endowed with enhanced interferon-stimulated gene expression in homeostasis, upon systemic interferon stimulation and during virus infection in vivo. Collectively, we provide an updated map of fibroblastic cell diversity in the spleen that suggests a specialized innate immune function for splenic red pulp fibroblasts.

Single-nucleus transcriptomes reveal evolutionary and functional properties of cell types in the Drosophila accessory gland

Many traits responsible for male reproduction evolve quickly, including gene expression phenotypes in germline and somatic male reproductive tissues. Rapid male evolution in polyandrous species is thought to be driven by competition among males for fertilizations and conflicts between male and female fitness interests that manifest in post-copulatory phenotypes. In Drosophila, seminal fluid proteins secreted by three major cell types of the male accessory gland and ejaculatory duct are required for female sperm storage and use, and influence female post-copulatory traits. Recent work has shown that these cell types have overlapping but distinct effects on female post-copulatory biology, yet relatively little is known about their evolutionary properties. Here we use single-nucleus RNA-Seq of the accessory gland and ejaculatory duct from Drosophila melanogaster and two closely related species to comprehensively describe the cell diversity of these tissues and their transcriptome evolution for the first time. We find that seminal fluid transcripts are strongly partitioned across the major cell types, and expression of many other genes additionally define each cell type. We also report previously undocumented diversity in main cells. Transcriptome divergence was found to be heterogeneous across cell types and lineages, revealing a complex evolutionary process. Furthermore, protein adaptation varied across cell types, with potential consequences for our understanding of selection on male post-copulatory traits.

Single-Cell Transcriptional Profiling of Zebrafish Hematopoiesis Offers Insight into Early Lymphocyte Development and Reveals Novel Immune Cell Populations

The advent of single-cell RNA sequencing (scRNA-seq) has greatly expanded our appreciation for cell state diversity beyond classical developmental hierarchies and simple population subsets. In particular, rich transcriptional heterogeneity has been observed within immune cell populations leading to the identification of novel cell types. Except for a few notable exceptions, intensive work in this area has largely been confined to mammals. Much of the transcriptional profiling of blood cell development in zebrafish has failed to capture early stages of lymphocyte development as the majority of research has not included thymus datasets or captured sufficient marrow B cells to explore developmental trajectories. To gain insight into T and B cell development in the zebrafish and immune cell diversity more broadly, we performed scRNA-seq using 10x Genomics Next GEM technology on adult zebrafish kidney marrows (n = 5 biological replicates) in addition to whole juvenile thymi at 4 weeks post-fertilization (wpf) (n = 4 technical replicates) and whole adult thymi at 3-4 months post-fertilization (n = 4 biological replicates). After filtering out low quality cellular barcodes, 34,492 kidney marrow cells and 35,268 thymus cells remained for analysis. With respect to T cell development, we identified putative early thymic progenitors from their clustering with hematopoietic stem and progenitor cells and shared transcriptional signatures, including the enrichment of CD34, CSF1R, FLI1, and DNMT3B human orthologs. Multiple subsets of thymic and marrow T cells were characterized, including a subset of gamma delta T cells readily identified by their expression of T-cell receptor gamma and delta chain components and expression of a SOX13 ortholog in addition to a Th2-like population expressing IL4, IL13, and GATA3 orthologs. Among other immune cell populations, rich transcriptional diversity was present. Two distinct populations of B cells, largely mutually exclusive for ighd and ighz expression (dual detection <1%), were present across all datasets, including the 4 wpf thymi, a surprisingly early time point in zebrafish B cell ontogeny. A clustering of the adult datasets demonstrated ighz predominance in the thymus (63% of thymic B cells), whereas the majority of marrow B cells (85%) fell within the ighd cluster. Stages of B cell development were also clearly evident, with the earliest B cell progenitors expressing orthologs of human PAX5, DNTT, RAG1, and RAG2, in addition to sid1, an understudied gene proposed to be orthologous to VPREB1. The expression of dntt was notably absent from more mature subsets of rag1 and rag2+ B cell progenitors, analogous to its expression in mammals. Transcriptional signatures unique but reminiscent of mammalian dendritic cell subsets were identified: Plasmacytoid-like dendritic cells characterized by high expression of TLR7, TLR9, and IRF8 orthologs and conventional-like dendritic cells characterized by high expression of CKB, BATF3, and ZNF366 were present in both marrow and thymus datasets, suggestive of greater dendritic-like cell diversity in the zebrafish than previously appreciated. These findings illustrate the power of single-cell transcriptional profiling for illuminating immune cell development and heterogeneity in the zebrafish, demonstrating increasing parallels to the mammalian system. Disclosures Zon: Celularity: Consultancy; Branch Biosciences: Current holder of individual stocks in a privately-held company, Other: Founder; Scholar Rock: Current equity holder in publicly-traded company, Other: Founder; Amagma Therapeutics: Current holder of individual stocks in a privately-held company, Other: Founder; CAMP4 Therapeutics: Current holder of individual stocks in a privately-held company, Other: Founder; Fate Therapeutics: Current equity holder in publicly-traded company, Other: Founder; Cellarity: Consultancy.

Level of Unique T-Cell Clonotypes Are Associated with Clonal Hematopoiesis and Survival in Patients with Lymphoma Intended for Autologous Stem Cell Transplant

The advent of novel immunotherapy (CAR-T cell therapy, bispecific CD20×CD3 antibodies) have highlighted the importance of T-cells in the treatment of lymphoma. However, overall T-cell characteristics have not been properly examined in patients receiving conventional chemotherapy. Next-generation sequencing (NGS) of the T-cell receptor (TCR) has enabled the possibility of identifying hundred thousands of unique T-cell clones in a single patient sample. Here we analyzed the impact of systemic TCR diversity and T-cell clonotypes in patients with Non-Hodgkin lymphoma (NHL) and Hodgkin-lymphoma (HL) receiving high-dose chemotherapy with stem cell support (HDT/ASCT). Autologous peripheral blood stem cell harvest samples from patients with lymphoma (predominantly B-cell NHL) were collected as part of a national population-based study (Husby et al. - Leukemia 2020). We performed high-throughput RNA-based sequencing of the V, D and J segment of the TCR β-chain to identify unique clonal rearrangements. To ensure supreme quality for TCR repertoire calculations, samples with less than 100.000 aligned reads to the TCR β chain were omitted from further analysis. By using the MiXCR bioinformatic pipeline we analyzed the number of unique clonotypes and TCR repertoire diversity, as calculated by the Simpson index. T-cell clonotype and diversity were for categorical analyses split in two groups by the median, respectively. A total of 96 patients with lymphoma who were intended for HDT/ASCT were included and analyzed for TCR characteristics. In brief, median age was 56 years, 64% were male and major subtypes were diffuse large B-cell lymphoma (37%), follicular lymphoma (24%), Hodgkin lymphoma (16%), and mantle cell lymphoma (14%). Median follow-up time was 6.7 years. Number of unique T-cell clonotypes was not associated with age (Fig. 1A), but low levels were highly associated with inferior survival (Fig. 1B, p=0.008), especially in the first year of follow-up. In contrast, elderly patients had a trend toward lower TCR diversity (Fig. 1C, p=0.08), but this did not impact overall survival (Fig. 1D). Low T-cell clonotype levels was also significantly associated with presence of clonal hematopoiesis (Fig. 1E, p=0.033). No association with clonal hematopoiesis was found with regard to TCR diversity (Fig. 1F). Furthermore, we investigated TCR repertoire in relation to subsequent severe infections (defined as sepsis, pneumonia, or invasive fungal infection). Number of unique T-cell clonotypes did not have an impact (Fig. 1F), but remarkably patients with a high T-cell diversity had significant increased incidence of severe infections in the first 500 days after sampling (Fig. 1G, p=0.029). This implies that patients who have a high T-cell diversity before high-dose chemotherapy, are more capable of mounting an immune response against infectious pathogens. These findings should be validated in larger homogenous cohorts. However, they imply the importance of inherent immune characteristics in patients with lymphoma. Although the immune response is exceedingly complex, we have identified systemic T-cell characteristics that associate with several important clinical variables. Assessment of systemic immunological parameters in patients with aggressive lymphoma may in the future inform on choice of optimal personalized therapy. Figure 1 Figure 1. Disclosures El-Galaly: ROCHE Ltd: Ended employment in the past 24 months; Abbvie: Other: Speakers fee. Larsen: Odense University Hospital, Denmark: Current Employment; Celgene: Consultancy; BMS: Consultancy; Novartis: Consultancy; Gilead: Consultancy.

CA1 pyramidal cell diversity is rootedin the time of neurogenesis

Cellular diversity supports the computational capacity and flexibility of cortical circuits. Accordingly, principal neurons at the CA1 output node of the murine hippocampus are increasingly recognized as a heterogeneous population. Their genes, molecular content, intrinsic morphophysiology, connectivity, and function seem to segregate along the main anatomical axes of the hippocampus. Since these axes reflect the temporal order of principal cell neurogenesis, we directly examined the relationship between birthdate and CA1 pyramidal neuron diversity, focusing on the ventral hippocampus. We used a genetic fate-mapping approach that allowed tagging three groups of age-matched principal neurons: pioneer, early- and late-born. Using a combination of neuroanatomy, slice physiology, connectivity tracing and cFos staining in mice, we show that birthdate is a strong predictor of CA1 principal cell diversity. We unravel a subpopulation of pioneer neurons recruited in familiar environments with remarkable positioning, morpho-physiological features, and connectivity. Therefore, despite the expected plasticity of hippocampal circuits, given their role in learning and memory, the diversity of their main components is also partly determined at the earliest steps of development.