Single cells from human primary colorectal tumors exhibit polyfunctional heterogeneity in secretions of ELR+ CXC chemokines

Single-Cell RNA Sequencing for Analyzing the Intestinal Tract in Healthy and Diseased Individuals

The intestinal tract is composed of different cell lineages with distinct functions and gene expression profiles, providing uptake of nutrients and protection against insults to the gut lumen. Changes in or damage to the cellulosity or local environment of the intestinal tract can cause various diseases. Single-cell RNA sequencing (scRNA-seq) is a powerful tool for profiling and analyzing individual cell data, making it possible to resolve rare and intermediate cell states that are hardly observed at the bulk level. In this review, we discuss the application of intestinal tract scRNA-seq in identifying novel cell subtypes and states, targets, and explaining the molecular mechanisms involved in intestinal diseases. Finally, we provide future perspectives on using single-cell techniques to discover molecular and cellular targets and biomarkers as a new approach for developing novel therapeutics for intestinal diseases.

A Portrait of Intratumoral Genomic and Transcriptomic Heterogeneity at Single-Cell Level in Colorectal Cancer

In the study of cancer, omics technologies are supporting the transition from traditional clinical approaches to precision medicine. Intra-tumoral heterogeneity (ITH) is detectable within a single tumor in which cancer cell subpopulations with different genome features coexist in a patient in different tumor areas or may evolve/differ over time. Colorectal carcinoma (CRC) is characterized by heterogeneous features involving genomic, epigenomic, and transcriptomic alterations. The study of ITH is a promising new frontier to lay the foundation towards successful CRC diagnosis and treatment. Genome and transcriptome sequencing together with editing technologies are revolutionizing biomedical research, representing the most promising tools for overcoming unmet clinical and research challenges. Rapid advances in both bulk and single-cell next-generation sequencing (NGS) are identifying primary and metastatic intratumoral genomic and transcriptional heterogeneity. They provide critical insight in the origin and spatiotemporal evolution of genomic clones responsible for early and late therapeutic resistance and relapse. Single-cell technologies can be used to define subpopulations within a known cell type by searching for differential gene expression within the cell population of interest and/or effectively isolating signal from rare cell populations that would not be detectable by other methods. Each single-cell sequencing analysis is driven by clustering of cells based on their differentially expressed genes. Genes that drive clustering can be used as unique markers for a specific cell population. In this review we analyzed, starting from published data, the possible achievement of a transition from clinical CRC research to precision medicine with an emphasis on new single-cell based techniques; at the same time, we focused on all approaches and issues related to this promising technology. This transition might enable noninvasive screening for early diagnosis, individualized prediction of therapeutic response, and discovery of additional novel drug targets.

Tuning the Surface Interactions between Single Cells and an OSTE+ Microwell Array for Enhanced Single Cell Manipulation

Retrieving single cells of interest from an array of microwells for further off-chip analysis is crucial in numerous biological applications. To this end, several single cell manipulation strategies have been developed, including optical tweezers (OT). OT represent a unique approach for contactless cell retrieval, but their performance is often suboptimal due to nonspecific cell adhesion to the microwell surface. In this study, we focused on improving the surface chemistry of microwell arrays to ensure efficient single cell manipulation using OT. For this purpose, the surface of an off-stoichiometry thiol-ene-epoxy (OSTE+) microwell array was grafted with polyethylene glycol (PEG) molecules with different molecular weights: PEG 360, PEG 500, PEG 2000, and a PEG Mix (an equimolar ratio of PEG 500 and PEG 2000). Contact angle measurements showed that the PEG grafting process resulted in an increased surface energy, which was stable for at least 16 weeks. Next, cell adhesion of two cell types, baker's yeast (Saccharomyces cerevisiae) and human B cells, to surfaces treated with different PEGs was evaluated by registering the presence of cellular motion inside microwells and the efficiency of optical lifting of cells that display motion. Optimal results were obtained for surfaces grafted with PEG 2000 and PEG Mix, reaching an average fraction of cells with motion of over 93% and an average lifting efficiency of over 96% for both cell types. Upon the integration of this microwell array with a polydimethylsiloxane (PDMS) microfluidic channel, PEG Mix resulted in proper washing of non-seeded cells. We further demonstrated the wide applicability of the platform by manipulating non-responding yeast cells to antifungal treatment and B cells expressing surface IgG antibodies. The combination of the optimized microwell surface with continuous microfluidics results in a powerful and versatile platform, allowing high-throughput single cell studies and retrieval of target cells for off-chip analysis.

Design of a Multiplexed Analyte Biosensor using Digital Barcoded Particles and Impedance Spectroscopy

Multiplexing allows quantifying multiple analytes in a single step, providing advantages over individual testing through shorter processing time, lower sample volume, and reduced cost per test. Currently, flow cytometry is the gold standard for biomedical multiplexing, but requires technical training, extensive data processing, and expensive operational and capital costs. To solve this challenge, we designed digital barcoded particles and a microfluidic architecture for multiplexed analyte quantification. In this work, we simulate and model non-fluorescence-based microfluidic impedance detection with a single excitation and detection scheme using barcoded polymer microparticles. Our barcoded particles can be designed with specific coding regions and generate numerous distinct patterns enabling digital barcoding. We found that signals based on adhered microsphere position and relative orientation were evaluated and separated based on their associated electrical signatures and had a 7 µm microsphere limit of detection. Our proposed microfluidic system can enumerate micron-sized spheres in a single assay using barcoded particles of various configurations. As representation of blood cells, the microsphere concentrations may provide useful information on disease onset and progression. Such sensors may be used for diagnostic and management of common critical care diseases like sepsis, acute kidney injury, urinary tract infections, and HIV/AIDS.

Dynamic secretome of bone marrow-derived stromal cells reveals a cardioprotective biochemical cocktail

Transplanted stromal cells have demonstrated considerable promise as therapeutic agents in diverse disease settings. Paracrine signaling can be an important mediator of these therapeutic effects at the sites of acute or persistent injury and inflammation. As many stromal cell types, including bone marrow-derived stromal cells (BMSCs), display tissue-specific responses, there is a need to explore their secretory dynamics in the context of tissue and injury type. Paracrine signals are not static, and could encode contextual dynamics in the kinetic changes of the concentrations of the secreted ligands. However, precise measurement of dynamic and context-specific cellular secretory signatures, particularly in adherent cells, remains challenging. Here, by creating an experimental and computational analysis platform, we reconstructed dynamic secretory signatures of cells based on a very limited number of time points. By using this approach, we demonstrate that the secretory signatures of CD133-positive BMSCs are uniquely defined by distinct biological contexts, including signals from injured cardiac cells undergoing oxidative stress, characteristic of cardiac infarction. Furthermore, we show that the mixture of recombinant factors reproducing the dynamics of BMSC-generated secretion can mediate a highly effective rescue of cells injured by oxidative stress and an improved cardiac output. These results support the importance of the dynamic multifactorial paracrine signals in mediating remedial effects of stromal stem cells, and pave the way for stem cell-inspired cell-free treatments of cardiac and other injuries.

Disrupting Inflammation-Associated CXCL8-CXCR1 Signaling Inhibits Tumorigenicity Initiated by Sporadic- and Colitis-Colon Cancer Stem Cells

Dysfunctional inflammatory pathways are associated with an increased risk of cancer, including colorectal cancer. We have previously identified and enriched for a self-renewing, colon cancer stem cell (CCSC) subpopulation in primary sporadic colorectal cancers (CRC) and a related subpopulation in ulcerative colitis (UC) patients defined by the stem cell marker, aldehyde dehydrogenase (ALDH). Subsequent work demonstrated that CCSC-initiated tumors are dependent on the inflammatory chemokine, CXCL8, a known inducer of tumor proliferation, angiogenesis and invasion. Here, we use RNA interference to target CXCL8 and its receptor, CXCR1, to establish the existence of a functional signaling pathway promoting tumor growth initiated by sporadic and colitis CCSCs. Knocking down either CXCL8 or CXCR1 had a dramatic effect on inhibiting both in vitro proliferation and angiogenesis. Likewise, tumorigenicity was significantly inhibited due to reduced levels of proliferation and angiogenesis. Decreased expression of cycle cell regulators cyclins D1 and B1 along with increased p21 levels suggested that the reduction in tumor growth is due to dysregulation of cell cycle progression. Therapeutically targeting the CXCL8-CXCR1 signaling pathway has the potential to block sustained tumorigenesis by inhibiting both CCSC- and pCCSC-induced proliferation and angiogenesis.

Pushing the limits of detection for proteins secreted from single cells using quantum dots

Single cell analysis methods are increasingly being utilized to investigate how individual cells process information and respond to diverse stimuli. Soluble proteins play a critical role in controlling cell populations and tissues, but directly monitoring secretion is technically challenging. Microfabricated well arrays have been developed to assess secretion at the single cell level, but these systems are limited by low detection sensitivity. Semiconductor quantum dots (QD) exhibit remarkably bright and photostable luminescence signal, but to date they have not been evaluated in single cell secretion studies using microfabricated well arrays. Here, we used QDs in a sandwich immunoassay to detect secretion of the soluble cytokine tumor necrosis factor-α (TNF-α) from single cells. To enhance detection sensitivity, we employed two different strategies. First, we used a unique single QD imaging approach, which provided a detection threshold (180 attomolar) that was >100-fold lower than previously reported results using QDs. We also amplified QD binding to each captured TNF-α molecule using the bioorthogonal cycloaddition reaction between trans-cyclooctene and tetrazine, which further lowered detection threshold to 60 attomolar. This is 6 orders of magnitude more sensitive than organic fluorophores that have been used for single cell secretion studies, and far surpasses single molecule resolution within sub-picoliter microwells that are used to assess single cell secretion. Finally, single cell secretion studies were performed using phorbol 12-myristate 13-acetate (PMA) differentiated and lipopolysaccharide (LPS) activated U-937 cells. TNF-α secretion was detected from 3-fold more single cells using the QD-based method in comparison to rhodamine, which was accomplished by extending sensitivity into the range of ∼2 to 10 000 molecules captured per microwell. In future work, we will apply this technique to assess immune cell secretion dynamics under diverse stimuli and disease settings. We will also incorporate multiplexing capabilities to evaluate the secretome at the resolution of single molecules.

Automated rare single cell picking with the ALS cellcelector™

Molecular analysis of rare single cells like circulating tumor cells (CTCs) from whole blood patient samples bears multiple challenges. One of those challenges is the efficient and ideally loss-free isolation of CTCs over contaminating white and red blood cells. While there is a multitude of commercial and non-commercial systems available for the enrichment of CTCs their cell output does not deliver the purity most molecular analysis methods require. Here we describe the ALS CellCelector™ which can solve this challenge allowing the retrieval of 100% pure single CTCs from blood processed by different upstream enrichment techniques. It is a multifunctional, extremely flexible system for automated screening of cell culture plates, Petri dishes, and microscope slides. Fixed or live single cells or multicellular clusters detected during screening can be picked out of those plates automatically. The complete scan and picking process is fully documented hence allowing highest standardization and reproducibility of all processes. Use of CellCelector allowed the isolation of pure single tumor cells or clusters from liquid biopsies of breast, prostate, ovarian, colorectal, lung, and brain cancers for their subsequent molecular analysis. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Targeting minimal residual disease: a path to cure?

Therapeutics that block kinases, transcriptional modifiers, immune checkpoints and other biological vulnerabilities are transforming cancer treatment. As a result, many patients achieve dramatic responses, including complete radiographical or pathological remission, yet retain minimal residual disease (MRD), which results in relapse. New functional approaches can characterize clonal heterogeneity and predict therapeutic sensitivity of MRD at a single-cell level. Preliminary evidence suggests that iterative detection, profiling and targeting of MRD would meaningfully improve outcomes and may even lead to cure.

Single-Cell Protein Assays: A Review

Quantification of single-cell proteomics provides key insights in the field of cellular heterogeneity. This chapter discusses the emerging techniques that are being used to measure the protein copy numbers at the single-cell level, which includes flow cytometry, mass cytometry, droplet cytometry, microengraving, and single-cell barcoding microchip. The advantages and limitations of each technique are compared, and future research opportunities are highlighted.

Microfluidic enrichment for the single cell analysis of circulating tumor cells

Resistance to drug therapy is a major concern in cancer treatment. To probe clones resistant to chemotherapy, the current approach is to conduct pooled cell analysis. However, this can yield false negative outcomes, especially when we are analyzing a rare number of circulating tumor cells (CTCs) among an abundance of other cell types. Here, we develop a microfluidic device that is able to perform high throughput, selective picking and isolation of single CTC to 100% purity from a larger population of other cells. This microfluidic device can effectively separate the very rare CTCs from blood samples from as few as 1 in 20,000 white blood cells. We first demonstrate isolation of pure tumor cells from a mixed population and track variations of acquired T790M mutations before and after drug treatment using a model PC9 cell line. With clinical CTC samples, we then show that the isolated single CTCs are representative of dominant EGFR mutations such as T790M and L858R found in the primary tumor. With this single cell recovery device, we can potentially implement personalized treatment not only through detecting genetic aberrations at the single cell level, but also through tracking such changes during an anticancer therapy.

Development of Microfluidic Systems Enabling High-Throughput Single-Cell Protein Characterization

This article reviews recent developments in microfluidic systems enabling high-throughput characterization of single-cell proteins. Four key perspectives of microfluidic platforms are included in this review: (1) microfluidic fluorescent flow cytometry; (2) droplet based microfluidic flow cytometry; (3) large-array micro wells (microengraving); and (4) large-array micro chambers (barcode microchips). We examine the advantages and limitations of each technique and discuss future research opportunities by focusing on three key performance parameters (absolute quantification, sensitivity, and throughput).

Frontier microfluidic techniques for short and long-term single cell analysis

Here, we review the frontier microfluidic techniques for single cell analysis (SCA), which is important for research of many biological systems. Microfluidics provides high-throughput, high-resolution experiments at low cost and reagent use, making it especially useful for single cell analysis. Recent advancements in the field have made SCA more feasible, improving device throughput and resolution, adding capabilities, and combining different functions to bring forth new assays. Developments in incubation have allowed for long-term cell tracking assays to be performed with single cell resolution. The ability of systems to provide chemical isolation or prolonged growth of adherent cells is also discussed.

Towards Engineered Processes for Sequencing-Based Analysis of Single Circulating Tumor Cells

Sequencing-based analysis of single circulating tumor cells (CTCs) has the potential to revolutionize our understanding of metastatic cancer and improve clinical care. Technologies exist to enrich, identify, recover, and sequence single cells, but to enable systematic routine analysis of single CTCs from a range of cancer patients, there is a need to establish processes that efficiently integrate these specific operations. Such engineered processes should address challenges associated with the yield and viability of enriched CTCs, the robust identification of candidate single CTCs with minimal degradation of DNA, the bias in whole-genome amplification, and the efficient handling of candidate single CTCs or their amplified DNA products. Advances in methods for single-cell analysis and nanoscale technologies suggest opportunities to overcome these challenges, and could create integrated platforms that perform several of the unit operations together. Ultimately, technologies should be selected or adapted for optimal performance and compatibility in an integrated process.