Monolithic Chip for High-throughput Blood Cell Depletion to Sort Rare Circulating Tumor Cells

A comparative study of circulating tumor cell isolation and enumeration technologies in lung cancer

Circulating tumor cells (CTCs) have potential as diagnostic, prognostic, and predictive biomarkers in solid tumors. Despite Food and Drug Administration (FDA) approval of CTC devices in various cancers, the rarity and heterogeneity of CTCs in lung cancer make them technically challenging to isolate and analyze, hindering their clinical integration. Establishing a consensus through comparative analysis of different CTC systems is warranted. This study aimed to evaluate seven different CTC enrichment methods across five technologies using a standardized spike-in protocol: the CellMag™ (EpCAM-dependent enrichment), EasySep™ and RosetteSep™ (blood cell depletion), and the Parsortix® PR1 and the new design Parsortix® Prototype (PP) (size- and deformability-based enrichment). The Parsortix® systems were also evaluated for any differences in recovery rates between cell harvest versus in-cassette staining. Healthy donor blood (5 mL) was spiked with 100 fluorescently labeled EpCAMhigh H1975 cells, processed through each system, and the isolation efficiency was calculated. The CellMag™ had the highest recovery rate (70 ± 14%), followed by Parsortix® PR1 in-cassette staining, while the EasySep™ had the lowest recovery (18 ± 8%). Additional spike-in experiments were performed with EpCAMmoderate A549 and EpCAMlow H1299 cells using the CellMag™ and Parsortix® PR1 in-cassette staining. The recovery rate of CellMag™ significantly reduced to 35 ± 14% with A549 cells and 1 ± 1% with H1299 cells. However, the Parsortix® PR1 in-cassette staining showed cell phenotype-independent and consistent recovery rates among all lung cancer cell lines: H1975 (49 ± 2%), A549 (47 ± 10%), and H1299 (52 ± 10%). Furthermore, we demonstrated that the Parsortix® PR1 in-cassette staining method is capable of isolating heterogeneous single CTCs and cell clusters from patient samples. The Parsortix® PR1 in-cassette staining, capable of isolating different phenotypes of CTCs as either single cells or cell clusters with consistent recovery rates, is considered optimal for CTC enrichment for lung cancer, albeit needing further optimization and validation.

Laser-Patterning of Micromagnets for Immuno-Magnetophoretic Exosome Capture

Efficient isolation and patterning of biomolecules is a vital step within sample preparation for biomolecular analysis, with numerous diagnostic and therapeutic applications. For exosomes, nanoscale lipid-bound biomolecules, efficient isolation is challenging due to their minute size and resultant behavior within biofluids. This study presents a method for the rapid isolation and patterning of magnetically tagged exosomes via rationally designed micromagnets. Micromagnet fabrication utilizes a novel, scalable, and high-throughput laser-based fabrication approach that enables patterning at microscale lateral resolution (<50 µm) without lithographic processing and is agnostic to micromagnet geometry. Laser-based processing allows for flexible and tunable device configurations, and herein magnetophoretic capture within both an open-air microwell and an enclosed microfluidic system is demonstrated. Patterned micromagnets enhance localized gradient fields throughout the fluid medium, resulting in rapid and high efficiency magnetophoretic separation, with capture efficiencies nearing 70% after just 1s within open-air microwells, and throughputs upward of 3 mL h-1 within enclosed microfluidic systems. Using this microchip architecture, immunomagnetic exosome isolation and patterning directly from undiluted plasma samples is further achieved. Lastly, a FEA-based modeling workflow is introduced to characterize and optimize micromagnet unit cells, simulating magnetophoretic capture zones for a given micromagnet geometry.

Exploiting the metabolic vulnerability of circulating tumour cells

Metastasis has a major part in the severity of disease and lethality of cancer. Circulating tumour cells (CTCs) represent a reservoir of metastatic precursors in circulation, most of which cannot survive due to hostile conditions in the bloodstream. Surviving cells colonise a secondary site based on a combination of physical, metabolic, and oxidative stress protection states required for that environment. Recent advances in CTC isolation methods and high-resolution 'omics technologies are revealing specific metabolic pathways that support this selection of CTCs. In this review, we discuss recent advances in our understanding of CTC biology and discoveries of adaptations in metabolic pathways during their selection. Understanding these traits and delineating mechanisms by which they confer acquired resistance or vulnerability in CTCs is crucial for developing successful prognostic and therapeutic strategies in cancer.

Novel Isolating Approaches to Circulating Tumor Cell Enrichment Based on Microfluidics: A Review

Circulating tumor cells (CTCs), derived from the primary tumor and carrying genetic information, contribute significantly to the process of tumor metastasis. The analysis and detection of CTCs can be used to assess the prognosis and treatment response in patients with tumors, as well as to help study the metastatic mechanisms of tumors and the development of new drugs. Since CTCs are very rare in the blood, it is a challenging problem to enrich CTCs efficiently. In this paper, we provide a comprehensive overview of microfluidics-based enrichment devices for CTCs in recent years. We explore in detail the methods of enrichment based on the physical or biological properties of CTCs; among them, physical properties cover factors such as size, density, and dielectric properties, while biological properties are mainly related to tumor-specific markers on the surface of CTCs. In addition, we provide an in-depth description of the methods for enrichment of single CTCs and illustrate the importance of single CTCs for performing tumor analyses. Future research will focus on aspects such as improving the separation efficiency, reducing costs, and increasing the detection sensitivity and accuracy.

Live cell pool and rare cell isolation using Enrich TROVO system

Although several technologies have been developed to isolate cells of interest from a heterogenous sample, clogging and impaired cell viability limit such isolation. We have developed the Enrich TROVO system as a novel, nonfluidic technology to sort live cells. The TROVO system combines imaging-based cell selection and photo-crosslinking of (gelatin methacrylate) gelMA-hydrogel to capture cells. After capture, cells are released by enzymatic digestion of the hydrogel and then retrieved for downstream analysis or further cell culturing. The system can capture cells with a recovery rate of 48% while maintaining 90% viability. Moreover, TROVO can enrich rare cells 506-fold with 93% efficiency using single step isolation from a 1:104 cell mixture, and can also capture one target cell from 1 million cells, reaching an enrichment ratio of 9128. In addition, 100% purity and 49% recovery rate can be achieved by a following negative isolation process. Compared to existing technologies, the TROVO system is clog-resistant, highly biocompatible, and can process a wide range of sample sizes.

Microfluidic-SERS Technologies for CTC: A Perspective on Clinical Translation

Enumeration and phenotypic profiling of circulating tumor cells (CTCs) provide critical information for clinical diagnosis and treatment monitoring in cancer. To achieve this goal, an integrated system is needed to efficiently isolate CTCs from patient samples and sensitively evaluate their phenotypes. Such integration would comprise a high-throughput single-cell processing unit for the isolation and manipulation of CTCs and a sensitive and multiplexed quantitation unit to detect clinically relevant signals from these cells. Surface-enhanced Raman scattering (SERS) has been used as an analytical method for molecular profiling and in vitro cancer diagnosis. More recently, its multiplexing capability and power to create distinct molecular signatures against their targets have garnered attention. Here, we share our insights into the combined power of microfluidics and SERS in realizing CTC isolation, enumeration, and detection from a clinical translation perspective. We highlight the key operational factors in CTC microfluidic processing and SERS detection from patient samples. We further discuss microfluidic-SERS integration and its clinical utility as a paradigm shift in clinical CTC-based cancer diagnosis and prognostication. Finally, we summarize the challenges and attempt to look forward to what lies ahead of us in potentially translating the technique into real clinical applications.

Precision Phenotypic Profiling and Capture of Circulating Tumor Cells via a Vertical Laminar Flow-Stacked Microfluidic Chip

The heterogeneity of circulating tumor cells has a significant impact on the diagnosis, treatment, and monitoring of cancer. Research on the subtypes of circulating tumor cells can bring better treatment outcomes for cancer patients. Here, we proposed a microfluidic chip for the magnetic capture of subtypes of circulating tumor cells from the whole blood and phenotypic profiling by stacking laminar flow vertically. Circulating tumor cells were sorted and captured by the three-dimensional regulation of both magnetic fields in the vertical direction and flow fields in the lateral direction. Using EpCAM-magnetic beads, we achieved sorting and sectional capture of target cells in whole blood and analyzed the surface expression levels of the captured cells, confirming the functionality of the microfluidic chip in sorting and capturing subtypes of circulating tumor cells. This microfluidic chip can also aid in the subsequent subtype analysis of other rare cells.

On reactive Ion Etching of Parylene-C with Simple Photoresist Mask for Fabrication of High Porosity Membranes to Capture Circulating and Exfoliated Tumor Cells

A high porosity micropore arrayed parylene membrane is a promising device that is used to capture circulating and exfoliated tumor cells (CTCs and ETCs) for liquid biopsy applications. However, its fabrication still requires either expensive equipment or an expensive process. Here, we report on the fabrication of high porosity (>40%) micropore arrayed parylene membranes through a simple reactive ion etching (RIE) that uses photoresist as the etching mask. Vertical sidewalls were observed in etched parylene pores despite the sloped photoresist mask sidewalls, which was found to be due to the simultaneous high DC-bias RIE induced photoresist melting and substrate pedestal formation. A theoretical model has been derived to illustrate the dependence of the maximum membrane thickness on the final pore-to-pore spacing, and it is consistent with the experimental data. A simple, yet accurate, low number (<50) cell counting method was demonstrated through counting cells directly inside a pipette tip under phase-contrast microscope. Membranes as thin as 3 μm showed utility for low number tumor cell capture, with an efficiency of 87-92%.

Tumor cell-based liquid biopsy using high-throughput microfluidic enrichment of entire leukapheresis product

Circulating Tumor Cells (CTCs), interrogated by sampling blood from patients with cancer, contain multiple analytes, including intact RNA, high molecular weight DNA, proteins, and metabolic markers. However, the clinical utility of tumor cell-based liquid biopsy has been limited since CTCs are very rare, and current technologies cannot process the blood volumes required to isolate a sufficient number of tumor cells for in-depth assays. We previously described a high-throughput microfluidic prototype utilizing high-flow channels and amplification of cell sorting forces through magnetic lenses. Here, we apply this technology to analyze patient-derived leukapheresis products, interrogating a mean blood volume of 5.83 liters from patients with metastatic cancer, with a median of 2,799 CTCs purified per patient. Isolation of many CTCs from individual patients enables characterization of their morphological and molecular heterogeneity, including cell and nuclear size and RNA expression. It also allows robust detection of gene copy number variation, a definitive cancer marker with potential diagnostic applications. High-volume microfluidic enrichment of CTCs constitutes a new dimension in liquid biopsies.

A novel method for the isolation of single cells mimicking circulating tumour cells adhered on Smart Bio Surface slides by Laser Capture Microdissection

In recent years, the importance of isolating single cells from blood circulation for several applications, such as non-invasive tumour diagnosis, the monitoring of minimal residual disease, and the analysis of circulating fetal cells for prenatal diagnosis, urged the need to set up innovative methods. For such applications, different methods were developed. All show some weaknesses, especially a limited sensitivity, and specificity. Here we present a new method for isolating a single or a limited number of cells adhered to SBS slides (Tethis S.p.a.) (a glass slide coated with Nanostructured Titanium Dioxide) by Laser Capture Microdissection (LCM) and subsequent Whole Genome Amplification. SBS slides have been shown to have an optimal performance in immobilizing circulating tumour cells (CTCs) from early breast cancer patients. In this work, we spiked cancer cells in blood samples to mimic CTCs. By defining laser parameters to cut intact samples, we were able to isolate genetically intact single cells. We demonstrate that SBS slides are optimally suited for isolating cells using LCM and that this method provides high-quality DNA, ideal for gene-specific assays such as PCR and Sanger sequencing for mutation analysis.

In vivo photoacoustic flow cytometry-based study of the effect of melanin content on melanoma metastasis

A major cause of death in cancer patients is distant metastasis of tumors, in which circulating tumor cells (CTCs) are an important marker. Photoacoustic flow cytometry (PAFC) can monitor CTCs in real time, non-invasively, and label-free; we built a PAFC system and validated the feasibility of PAFC for monitoring CTCs using in vivo animal experiments. By cultivating heavily-pigmented and moderately-pigmented melanoma cells, more CTCs were detected in mice inoculated with moderately-pigmented tumor cells, resulting in more distant metastases and poorer survival status. Tumor cells with lower melanin content may produce more CTCs, increasing the risk of metastasis. CTC melanin content may be down-regulated during the metastatic which may be a potential indicator for assessing the risk of melanoma metastasis. In conclusion, PAFC can be used to assess the risk of melanoma metastasis by dynamically monitoring the number of CTCs and the CTC melanin content in future clinical diagnoses.

An integrated centrifugal microfluidic strategy for point-of-care complete blood counting

Centrifugal microfluidics holds the potential to revolutionize point-of-care (POC) testing by simplifying laboratory tests through automating fluid and cell manipulation within microfluidic channels. This technology can facilitate blood testing, the most frequent clinical test, at the POC. However, an integrated centrifugal microfluidic device for complete blood counting (CBC) has not yet been fully realized. To address this, we propose an integrated portable system comprising a centrifuge and a hybrid microfluidic disc specifically designed for CBC analysis at the POC. The disc enables the implementation of various spin profiles in different stages of CBC to facilitate in-situ cell separation, solution metering and mixing, and differential cell counting. Furthermore, our system is coupled with a custom script that automates the process and ensures precise quantification of cells using light and fluorescent images captured from the detection chamber of the disc. We demonstrate a close correlation between the proposed method and the hematology analyzer, considered the gold standard, for quantifying hematocrit (R2 = 0.99), white blood cell count (R2 = 0.98), white blood cell differential count (granulocyte/agranulocyte; R2 = 0.89), red blood cell count (R2 = 0.97), and mean corpuscular volume (R2 = 0.94). The integration of our portable system offers significant advantages, enabling more accessible and affordable CBC testing at the POC. Considering the simplicity, affordability (∼$250 capital cost and <$2 operational cost per test), as well as low power consumption (>100 tests using a typical 24 V/10 Ah battery), this system has the potential to enhance healthcare delivery, particularly in resource-limited settings and remote areas where access to traditional laboratory facilities is limited.

Establishing Single-Cell Clones from In Vitro-Cultured Circulating Tumor Cells

Cancer is a common health problem with more than 90% of deaths due to metastases. Circulating tumor cells (CTCs) contain precursors that can initiate metastases. However, CTCs are rare, heterogeneous, and difficult to expand in culture. We have previously created CTC-derived cell lines from stage IV breast cancer patients. These CTC lines were used to establish single-cell CTC clones using flow cytometry cell sorting.

Label-free microfluidic chip for segregation and recovery of circulating leukemia cells: clinical applications in acute myeloid leukemia

We present a label-free microfluidic chip for the segregation of circulating leukemia cells (CLCs) from blood samples, with a focus on its clinical applications in Acute Myeloid Leukemia (AML). The microfluidic chip achieved an approximate capture efficiency of 92%. The study analyzed a comprehensive set of 66 blood specimens from AML patients in different disease stages, including newly diagnosed and relapsing cases, patients in complete remission, and those in partial remission. The results showed a significant difference in CLC counts between active disease stages and remission stages (p < 0.0001), with a proposed threshold of 5 CLCs to differentiate between the two. The microfluidic chip exhibited a sensitivity of 95.4% and specificity of 100% in predicting disease recurrence. Additionally, the captured CLCs were subjected to downstream molecular analysis using droplet digital PCR, allowing for the identification of genetic mutations associated with AML. Comparative analysis with bone marrow aspirate processing by FACS demonstrated the reliability and accuracy of the microfluidic chip in tracking disease burden, with highly agreement results obtained between the two methods. The non-invasive nature of the microfluidic chip and its ability to provide real-time insights into disease progression make it a promising tool for the proactive monitoring and personalized patient care of AML.

Precision Isolation of Circulating Leukemia Cells in Chronic Myelogenous Leukemia Patients Using a Novel Microfluidic Device and Its Clinical Applications

Chronic Myelogenous Leukemia (CML) is a prevalent hematologic malignancy characterized by the malignant transformation of myeloid cells and their proliferation in the peripheral blood. The management of CML poses significant challenges, particularly in detecting and eradicating minimal residual disease, which is crucial for preventing relapse and improving survival outcomes. Traditional minimal residual disease detection methods, such as bone marrow aspiration, are invasive and have limitations which include the potential for sampling errors and false negatives. This study introduces a novel label-free microfluidic chip designed for the segregation and recovery of circulating leukemia cells, offering a non-invasive liquid biopsy approach with potential applications in precision medicine. Over July 2021 to October 2023, we recruited 56 CML patients across various disease stages and collected blood samples for analysis using our microfluidic device. The device demonstrated high efficacy in isolating circulating leukemia cells, with an optimal capture efficiency of 78% at a sample flow rate of 3 mL/h. Our results indicate that the microfluidic device can efficiently segregate and quantify circulating leukemia cells, providing a detailed understanding of CML progression and treatment response. The significant reduction in circulating leukemia cell counts in patients in complete remission highlights the device's potential in monitoring treatment efficacy. Furthermore, the device's sensitivity in detecting minimal residual disease could offer a more reliable prognostic tool for therapeutic decision-making in CML management.

The Evolution of Affordable Technologies in Liquid Biopsy Diagnostics: The Key to Clinical Implementation

Cancer remains a leading cause of death worldwide, despite many advances in diagnosis and treatment. Precision medicine has been a key area of focus, with research providing insights and progress in helping to lower cancer mortality through better patient stratification for therapies and more precise diagnostic techniques. However, unequal access to cancer care is still a global concern, with many patients having limited access to diagnostic tests and treatment regimens. Noninvasive liquid biopsy (LB) technology can determine tumour-specific molecular alterations in peripheral samples. This allows clinicians to infer knowledge at a DNA or cellular level, which can be used to screen individuals with high cancer risk, personalize treatments, monitor treatment response, and detect metastasis early. As scientific understanding of cancer pathology increases, LB technologies that utilize circulating tumour DNA (ctDNA) and circulating tumour cells (CTCs) have evolved over the course of research. These technologies incorporate tumour-specific markers into molecular testing platforms. For clinical translation and maximum patient benefit at a wider scale, the accuracy, accessibility, and affordability of LB tests need to be prioritized and compared with gold standard methodologies in current use. In this review, we highlight the range of technologies in LB diagnostics and discuss the future prospects of LB through the anticipated evolution of current technologies and the integration of emerging and novel ones. This could potentially allow a more cost-effective model of cancer care to be widely adopted.

Recent Progress in Enhanced Cancer Diagnosis, Prognosis, and Monitoring Using a Combined Analysis of the Number of Circulating Tumor Cells (CTCs) and Other Clinical Parameters

Analysis of circulating tumor cells (CTCs) holds promise to diagnose cancer or monitor its development. Among the methods, counting CTC numbers in blood samples could be the simplest way to implement it. Nevertheless, its clinical utility has not yet been fully accepted. The reasons could be due to the rarity and heterogeneity of CTCs in blood samples that could lead to misleading results from assays only based on single CTC counts. To address this issue, a feasible direction is to combine the CTC counts with other clinical data for analysis. Recent studies have demonstrated the use of this new strategy for early detection and prognosis evaluation of cancers, or even for the distinguishment of cancers with different stages. Overall, this approach could pave a new path to improve the technical problems in the clinical applications of CTC counting techniques. In this review, the information relevant to CTCs, including their characteristics, clinical use of CTC counting, and technologies for CTC enrichment, were first introduced. This was followed by discussing the challenges and new perspectives of CTC counting techniques for clinical applications. Finally, the advantages and the recent progress in combining CTC counts with other clinical parameters for clinical applications have been discussed.

Analytical Validation of a Spiral Microfluidic Chip with Hydrofoil-Shaped Pillars for the Enrichment of Circulating Tumor Cells

The isolation of circulating tumor cells (CTCs) from peripheral blood with high efficiency remains a challenge hindering the utilization of CTC enrichment methods in clinical practice. Here, we propose a microfluidic channel design for the size-based hydrodynamic enrichment of CTCs from blood in an epitope-independent and high-throughput manner. The microfluidic channel comprises a spiral-shaped part followed by a widening part, incorporating successive streamlined pillars, that improves the enrichment efficiency. The design was tested against two benchmark designs, a spiral microfluidic channel and a spiral microfluidic channel followed by a widening channel without the hydrofoils, by processing 5 mL of healthy blood samples spiked with 100 MCF-7 cells. The results proved that the design with hydrofoil-shaped pillars perform significantly better in terms of recovery (recovery rate of 67.9% compared to 23.6% in spiral and 56.7% in spiral with widening section), at a cost of slightly lower white blood cell (WBC) depletion (depletion rate of 94.2% compared to 98.6% in spiral and 94.2% in spiral with widening section), at 1500 µL/min flow rate. For analytical validation, the design was further tested with A549, SKOV-3, and BT-474 cell lines, yielding recovery rates of 62.3 ± 8.4%, 71.0 ± 6.5%, and 82.9 ± 9.9%, respectively. The results are consistent with the size and deformability variation in the respective cell lines, where the increasing size and decreasing deformability affect the recovery rate in a positive manner. The analysis before and after the microfluidic chip process showed that the process does not affect cell viability.

Scalable mesenchymal stem cell enrichment from bone marrow aspirate using deterministic lateral displacement (DLD) microfluidic sorting

The growing interest in regenerative medicine has opened new avenues for novel cell therapies using stem cells. Bone marrow aspirate (BMA) is an important source of stromal mesenchymal stem cells (MSCs). Conventional MSC harvesting from BMA relies on archaic centrifugation methods, often leading to poor yield due to osmotic stress, high centrifugation force, convoluted workflow, and long experimental time (∼2-3 hours). To address these issues, we have developed a scalable microfluidic technology based on deterministic lateral displacement (DLD) for MSC isolation. This passive, label-free cell sorting method capitalizes on the morphological differences between MSCs and blood cells (platelets and RBCs) for effective separation using an inverted L-shaped pillar array. To improve throughput, we developed a novel multi-chip DLD system that can process 2.5 mL of raw BMA in 20 ± 5 minutes, achieving a 2-fold increase in MSC recovery compared to centrifugation methods. Taken together, we envision that the developed DLD platform will enable fast and efficient isolation of MSCs from BMA for effective downstream cell therapy in clinical settings.

Blood component separation in straight microfluidic channels

Separation of blood components is required in many diagnostic applications and blood processes. In laboratories, blood is usually fractionated by manual operation involving a bulk centrifugation equipment, which significantly increases logistic burden. Blood sample processing in the field and resource-limited settings cannot be readily implemented without the use of microfluidic technology. In this study, we developed a small footprint, rapid, and passive microfluidic channel device that relied on margination and inertial focusing effects for blood component separation. No blood dilution, lysis, or labeling step was needed as to preserve sample integrity. One main innovation of this work was the insertion of fluidic restrictors at outlet ports to divert the separation interface into designated outlet channels. Thus, separation efficiency was significantly improved in comparison to previous works. We demonstrated different operation modes ranging from platelet or plasma extraction from human whole blood to platelet concentration from platelet-rich plasma through the manipulation of outlet port fluidic resistance. Using straight microfluidic channels with a high aspect ratio rectangular cross section, we demonstrated 95.4% platelet purity extracted from human whole blood. In plasma extraction, 99.9% RBC removal rate was achieved. We also demonstrated 2.6× concentration of platelet-rich plasma solution to produce platelet concentrate. The extraction efficiency and throughput rate are scalable with continuous and clog-free recirculation operation, in contrast to other blood fractionation approaches using filtration membranes or affinity-based purification methods. Our microfluidic blood separation method is highly tunable and versatile, and easy to be integrated into multi-step blood processing and advanced sample preparation workflows.

Circulating tumor cells in cancer-risk populations as a cancer interception tool

Cancer interception (CI) is a new approach to cancer prevention and treatment in a cancer-risk population that aims to detect and treat pre-tumoral stages. It has several potential advantages over traditional cancer diagnosis and monitoring methods because it is non-invasive, making it less painful and risky than conventional biopsy procedures. The circulating tumor cells (CTCs), liquid biopsy family members, are essential for the CI approach; then, the liquid biopsy (LB) is used as a CI tool. LB can be performed frequently because of its easy sampling and early pathological stages, which allow repeated non-invasive monitoring of cancer progression and response to treatment. CTCs have been found in the bloodstream of several types of cancer patients, including in early-stage cancer and premalignant lesions, suggesting a tumor development role in cancer's early stages. This chapter will present foundational scientific studies addressing CI and the clinical impact of CTC screening in a population at risk for cancer.

Quantification of capture efficiency, purity, and single-cell isolation in the recovery of circulating melanoma cells from peripheral blood by dielectrophoresis

This paper describes a dielectrophoretic method for selection of circulating melanoma cells (CMCs), which lack reliable identifying surface antigens and are extremely rare in blood. This platform captures CMCs individually by dielectrophoresis (DEP) at an array of wireless bipolar electrodes (BPEs) aligned to overlying nanoliter-scale chambers, which isolate each cell for subsequent on-chip single-cell analysis. To determine the best conditions to employ for CMC isolation in this DEP-BPE platform, the static and dynamic dielectrophoretic response of established melanoma cell lines, melanoma cells from patient-derived xenografts (PDX) and peripheral blood mononuclear cells (PBMCs) were evaluated as a function of frequency using two established DEP platforms. Further, PBMCs derived from patients with advanced melanoma were compared with those from healthy controls. The results of this evaluation reveal that each DEP method requires a distinct frequency to achieve capture of melanoma cells and that the distribution of dielectric properties of PBMCs is more broadly varied in and among patients versus healthy controls. Based on this evaluation, we conclude that 50 kHz provides the highest capture efficiency on our DEP-BPE platform while maintaining a low rate of capture of unwanted PBMCs. We further quantified the efficiency of single-cell capture on the DEP-BPE platform and found that the efficiency diminished beyond around 25% chamber occupancy, thereby informing the minimum array size that is required. Importantly, the capture efficiency of the DEP-BPE platform for melanoma cells when using optimized conditions matched the performance predicted by our analysis. Finally, isolation of melanoma cells from contrived (spike-in) and clinical samples on our platform using optimized conditions was demonstrated. The capture and individual isolation of CMCs, confirmed by post-capture labeling, from patient-derived samples suggests the potential of this platform for clinical application.

Biosensors for the Isolation and Detection of Circulating Tumor Cells (CTCs) in Point-of-Care Settings

Circulating tumor cells (CTCs) are cells that have been shed from tumors and circulate in the bloodstream. These cells can also be responsible for further metastases and the spread of cancer. Taking a closer look and analyzing CTCs through what has come to be known as "liquid biopsy" has immense potential to further researchers' understanding of cancer biology. However, CTCs are very sparse and are therefore difficult to detect and capture. To combat this issue, researchers have attempted to create devices, assays, and further techniques to successfully isolate CTCs for analysis. In this work, new and existing biosensing techniques for CTC isolation, detection, and release/detachment are discussed and compared to evaluate their efficacy, specificity, and cost. Here, we specifically aim to evaluate and identify the potential success of these techniques and devices in point-of-care (POC) settings.

Multichannel impedance cytometry downstream of cell separation by deterministic lateral displacement to quantify macrophage enrichment in heterogeneous samples

The integration of on-chip biophysical cytometry downstream of microfluidic enrichment for inline monitoring of phenotypic and separation metrics at single-cell sensitivity can allow for active control of separation and its application to versatile sample sets. We present integration of impedance cytometry downstream of cell separation by deterministic lateral displacement (DLD) for enrichment of activated macrophages from a heterogeneous sample, without the problems of biased sample loss and sample dilution caused by off-chip analysis. This required designs to match cell/particle flow rates from DLD separation into the confined single-cell impedance cytometry stage, the balancing of flow resistances across the separation array width to maintain unidirectionality, and the utilization of co-flowing beads as calibrated internal standards for inline assessment of DLD separation and for impedance data normalization. Using a heterogeneous sample with un-activated and activated macrophages, wherein macrophage polarization during activation causes cell size enlargement, on-chip impedance cytometry is used to validate DLD enrichment of the activated subpopulation at the displaced outlet, based on the multiparametric characteristics of cell size distribution and impedance phase metrics. This hybrid platform can monitor separation of specific subpopulations from cellular samples with wide size distributions, for active operational control and enhanced sample versatility.

Label-free enrichment of human adipose-derived stem cells using a continuous microfluidic sorting cascade

Human adipose tissue is a rich source of mesenchymal stem cells (MSCs). Human adipose-derived stem cells (ADSCs) are first prepared by tissue digestion of lipoaspirate. The remaining constituent contains a mixture of ADSCs, other cell types and lysed fragments. We have developed a scalable microfluidic sorter cascade which enabled high-throughput and label-free enrichment of ADSCs prepared from tissue-digested human adipose samples to improve the quality of purified stem cell product. The continuous microfluidic sorter cascade was composed of spiral-shaped inertial and deterministic lateral displacement (DLD) sorters which separated cells based on size difference. The cell count characterization results showed >90% separation efficiency. We also demonstrated that the enriched ADSC sub-population by the microfluidic sorter cascade yielded 6× enhancement of expansion capacity in tissue culture. The incorporation of this microfluidic sorter cascade into ADSC preparation workflow facilitates the generation of transplantation-scale stem cell product. We anticipate our stem cell microfluidic sorter cascade will find a variety of research and clinical applications in tissue engineering and regeneration medicine.

Lossless Immunocytochemistry Based on Large-Scale Porous Hydrogel Pellicle for Accurate Rare Cell Analysis

Rare cells, such as circulating tumor cells or circulating fetal cells, provide important information for the diagnosis and prognosis of cancer and prenatal diagnosis. Since undercounting only a few cells can lead to significant misdiagnosis and incorrect decisions in subsequent treatment, it is crucial to minimize cell loss, particularly for rare cells. Moreover, the morphological and genetic information on cells should be preserved as intact as possible for downstream analysis. The conventional immunocytochemistry (ICC), however, fails to meet these requirements, causing unexpected cell loss and deformation of the cell organelles which may mislead the classification of benign and malignant cells. In this study, a novel ICC technique for preparing lossless cellular specimens was developed to improve the diagnostic accuracy of rare cell analysis and analyze intact cellular morphology. To this end, a robust and reproducible porous hydrogel pellicle was developed. This hydrogel encapsulates cells to minimize cell loss from the repeated exchange of reagents and prevent cell deformation. The soft hydrogel pellicle allows stable and intact cell picking for further downstream analysis, which is difficult with conventional ICC methods that permanently immobilize cells. The lossless ICC platform will pave the way for robust and precise rare cell analysis toward clinical practice.

Rapid metabolomic screening of cancer cells via high-throughput static droplet microfluidics

Effective isolation and in-depth analysis of Circulating Tumour Cells (CTCs) are greatly needed in diagnosis, prognosis and monitoring of the therapeutic response of cancer patients but have not been completely fulfilled by conventional approaches. The rarity of CTCs and the lack of reliable biomarkers to distinguish them from peripheral blood cells have remained outstanding challenges for their clinical implementation. Herein, we developed a high throughput Static Droplet Microfluidic (SDM) device with 38,400 chambers, capable of isolating and classifying the number of metabolically active CTCs in peripheral blood at single-cell resolution. Owing to the miniaturisation and compartmentalisation capability of our device, we first demonstrated the ability to precisely measure the lactate production of different types of cancer cells inside 125 pL droplets at single-cell resolution. Furthermore, we compared the metabolomic activity of leukocytes from healthy donors to cancer cells and showed the ability to differentiate them. To further prove the clinical relevance, we spiked cancer cell lines in human healthy blood and showed the possibility to detect the cancer cells from leukocytes. Lastly, we tested the workflow on 8 preclinical mammary mouse models including syngeneic 67NR (non-metastatic) and 4T1.2 (metastatic) models with Triple-Negative Breast Cancer (TNBC) as well as transgenic mouses (12-week-old MMTV-PyMT). The results have shown the ability to precisely distinguish metabolically active CTCs from the blood using the proposed SDM device. The workflow is simple and robust which can eliminate the need for specialised equipment and expertise required for single-cell analysis of CTCs and facilitate on-site metabolic screening of cancer cells.

Recent Advances in Methods for Circulating Tumor Cell Detection

Circulating tumor cells (CTCs) are released from primary tumors and transported through the body via blood or lymphatic vessels before settling to form micrometastases under suitable conditions. Accordingly, several studies have identified CTCs as a negative prognostic factor for survival in many types of cancer. CTCs also reflect the current heterogeneity and genetic and biological state of tumors; so, their study can provide valuable insights into tumor progression, cell senescence, and cancer dormancy. Diverse methods with differing specificity, utility, costs, and sensitivity have been developed for isolating and characterizing CTCs. Additionally, novel techniques with the potential to overcome the limitations of existing ones are being developed. This primary literature review describes the current and emerging methods for enriching, detecting, isolating, and characterizing CTCs.

Isolation of Cancer Cells from Liquid Biopsies Using 3D-Printed Affinity Devices

Liquid biopsies are examination procedures for deciding the grouping of malignant growth cells tracked down in samples of blood and other body fluids. Liquid biopsies are likewise significantly less intrusive than tissue biopsies as they just require small amount of blood or body fluids from the patient. With the utilization of microfluidics, cancer cells can be isolated from the fluid biopsy and achieve early diagnosis. 3D printing is turning out to be progressively well known for microfluidic devices creation. 3D printing has shown multiple advantages compared to traditional microfluidic devices production, including effortless large-scale manufacturing of precise copies, the fuse of new materials, and execution of additional complicated or drawn-out plans that are hard to execute in conventional microfluidic devices. Combining 3D printing with microfluidics makes for a relatively inexpensive analysis of liquid biopsies with a chip that can be more advantageous to use over traditional microfluidic chips. In this chapter, a method for affinity-based separation of cancer cells in a liquid biopsy using a 3D microfluidic chip will be discussed, along with the rationale behind the method.

Technologies for Viable Circulating Tumor Cell Isolation

The spread of tumor cells throughout the body by traveling through the bloodstream is a critical step in metastasis, which continues to be the main cause of cancer-related death. The detection and analysis of circulating tumor cells (CTCs) is important for understanding the biology of metastasis and the development of antimetastatic therapy. However, the isolation of CTCs is challenging due to their high heterogeneity and low representation in the bloodstream. Different isolation methods have been suggested, but most of them lead to CTC damage. However, viable CTCs are an effective source for developing preclinical models to perform drug screening and model the metastatic cascade. In this review, we summarize the available literature on methods for isolating viable CTCs based on different properties of cells. Particular attention is paid to the importance of in vitro and in vivo models obtained from CTCs. Finally, we emphasize the current limitations in CTC isolation and suggest potential solutions to overcome them.

Biomedical Applications of Microfluidic Devices: A Review

Both passive and active microfluidic chips are used in many biomedical and chemical applications to support fluid mixing, particle manipulations, and signal detection. Passive microfluidic devices are geometry-dependent, and their uses are rather limited. Active microfluidic devices include sensors or detectors that transduce chemical, biological, and physical changes into electrical or optical signals. Also, they are transduction devices that detect biological and chemical changes in biomedical applications, and they are highly versatile microfluidic tools for disease diagnosis and organ modeling. This review provides a comprehensive overview of the significant advances that have been made in the development of microfluidics devices. We will discuss the function of microfluidic devices as micromixers or as sorters of cells and substances (e.g., microfiltration, flow or displacement, and trapping). Microfluidic devices are fabricated using a range of techniques, including molding, etching, three-dimensional printing, and nanofabrication. Their broad utility lies in the detection of diagnostic biomarkers and organ-on-chip approaches that permit disease modeling in cancer, as well as uses in neurological, cardiovascular, hepatic, and pulmonary diseases. Biosensor applications allow for point-of-care testing, using assays based on enzymes, nanozymes, antibodies, or nucleic acids (DNA or RNA). An anticipated development in the field includes the optimization of techniques for the fabrication of microfluidic devices using biocompatible materials. These developments will increase biomedical versatility, reduce diagnostic costs, and accelerate diagnosis time of microfluidics technology.

Technological and computational advances driving high-throughput oncology

Engineering and computational advances have opened many new avenues in cancer research, particularly when being exploited in interdisciplinary approaches. For example, the combination of microfluidics, novel sequencing technologies, and computational analyses has been crucial to enable single-cell assays, giving a detailed picture of tumor heterogeneity for the very first time. In a similar way, these 'tech' disciplines have been elementary for generating large data sets in multidimensional cancer 'omics' approaches, cell-cell interaction screens, 3D tumor models, and tissue level analyses. In this review we summarize the most important technology and computational developments that have been or will be instrumental for transitioning classical cancer research to a large data-driven, high-throughput, high-content discipline across all biological scales.

MagPure chip: an immunomagnetic-based microfluidic device for high purification of circulating tumor cells from liquid biopsies

The isolation of circulating tumor cells (CTCs) directly from blood, as a liquid biopsy, could lead to a paradigm shift in cancer clinical care by providing an earlier diagnosis, a more accurate prognosis, and personalized treatment. Nevertheless, CTC-specific challenges, including their rarity and heterogeneity, have hampered the wider use of CTCs in clinical studies. Microfluidic-based isolation technologies have emerged as promising tools to circumvent these limitations but still fail to meet the constraints of high purity and short processing time required to ensure compatibility with clinical follow-up. In this study, we developed an immunomagnetic-based microfluidic device, the MagPure chip, to achieve the negative selection of CTCs through the depletion of white blood cells (WBCs) and provide highly purified samples for subsequent analysis. We demonstrate that the MagPure chip depletes all magnetically labeled WBCs (85% of WBCs were successfully labeled) and ensures a CTC recovery rate of 81%. In addition, we show its compatibility with conventional biological studies, including 2D and 3D cell culture, as well as phenotypic and genotypic analyses. Finally, we successfully implemented a two-step separation workflow for whole blood processing by combining a size-based pre-enrichment system (ClearCell FX1®) with the MagPure chip as a subsequent purification step. The total workflow led to high throughput (7.5 mL blood in less than 4 h) and high purity (947 WBCs per mL remaining, 99.99% depletion rate), thus enabling us to quantify CTC heterogeneity in size and tumor marker expression level. This tumor-marker-free liquid biopsy workflow could be used in a clinical context to assess phenotype aggressiveness and the prognosis rate.

The Discovery of Novel Circulating Cancer-Related Cells in Circulation Poses New Challenges to Microfluidic Devices for Enrichment and Detection

Circulating tumor cells (CTCs) enumeration has been widely used as a surrogate predictive marker for early diagnoses, the evaluation of chemotherapy efficacy, and cancer prognosis. Microfluidic technologies for CTCs enrichment and detection have been developed and commercialized as automation platforms. Currently, in addition to CTCs, some new types of circulating cancer-related cells (e.g., CCSCs, CTECs, CAMLs, and heterotypic CTC clusters) in circulation are also reported to be correlated to cancer diagnosis, metastasis, or prognosis. And they widely differ from the conventional CTCs in positive markers, cellular morphology, or size, which presents a new technological challenge to microfluidic devices that use affinity-based capture methods or size-based filtration methods for CTCs detection. This review focuses on the biological and physical properties as well as clinical significance of the novel circulating cancer-related cells, and discusses the challenges of their discovery to microfluidic chip for enrichment. Finally, the current challenges of CTCs detection in clinical application and future opportunities are also discussed.

Isolation of Circulating Tumor Cells

Circulating tumor cells (CTCs) enter the vasculature from solid tumors and disseminate widely to initiate metastases. Mining the metastatic-enriched molecular signatures of CTCs before, during, and after treatment holds unique potential in personalized oncology. Their extreme rarity, however, requires isolation from large blood volumes at high yield and purity, yet they overlap leukocytes in size and other biophysical properties. Additionally, many CTCs lack EpCAM that underlies much of affinity-based capture, complicating their separation from blood. Here, we provide a comprehensive introduction of CTC isolation technology, by analyzing key separation modes and integrated isolation strategies. Attention is focused on recent progress in microfluidics, where an accelerating evolution is occurring in high-throughput sorting of cells along multiple dimensions.

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Circulating tumor cells (CTCs) spread cancer through the bloodstream (metastasis)

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CTC-based liquid biopsy enables minimally invasive sampling of cancer cells in blood

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Their extreme rarity requires all CTC types to be enriched from large blood volumes

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CTC isolation technology is analyzed, with a focus on high-throughput microfluidics

Microfluidic flow cytometry for blood-based biomarker analysis

Flow cytometry has proven its capability for rapid and quantitative analysis of individual cells and the separation of targeted biological samples from others. The emerging microfluidics technology makes it possible to develop portable microfluidic diagnostic devices for point-of-care testing (POCT) applications. Microfluidic flow cytometry (MFCM), where flow cytometry and microfluidics are combined to achieve similar or even superior functionalities on microfluidic chips, provides a powerful single-cell characterisation and sorting tool for various biological samples. In recent years, researchers have made great progress in the development of the MFCM including focusing, detecting, and sorting subsystems, and its unique capabilities have been demonstrated in various biological applications. Moreover, liquid biopsy using blood can provide various physiological and pathological information. Thus, biomarkers from blood are regarded as meaningful circulating transporters of signal molecules or particles and have great potential to be used as non (or minimally)-invasive diagnostic tools. In this review, we summarise the recent progress of the key subsystems for MFCM and its achievements in blood-based biomarker analysis. Finally, foresight is offered to highlight the research challenges faced by MFCM in expanding into blood-based POCT applications, potentially yielding commercialisation opportunities.

A role for microfluidic systems in precision medicine

Precision oncology continues to challenge the "one-size-fits-all" dogma. Under the precision oncology banner, cancer patients are screened for molecular tumor alterations that predict treatment response, ideally leading to optimal treatments. Functional assays that directly evaluate treatment efficacy on the patient's cells offer an alternative and complementary tool to improve the accuracy of precision oncology. Unfortunately, traditional Petri dish-based assays overlook much tumor complexity, limiting their potential as predictive functional biomarkers. Here, we review past applications of microfluidic systems for precision medicine and discuss the present and potential future role of functional microfluidic assays as treatment predictors.

Exponential magnetophoretic gradient for the direct isolation of basophils from whole blood in a microfluidic system

Despite their rarity in peripheral blood, basophils play important roles in allergic disorders and other diseases including sepsis and COVID-19. Existing basophil isolation methods require many manual steps and suffer from significant variability in purity and recovery. We report an integrated basophil isolation device (i-BID) in microfluidics for negative immunomagnetic selection of basophils directly from 100 μL of whole blood within 10 minutes. We use a simulation-driven pipeline to design a magnetic separation module to apply an exponentially increasing magnetic force to capture magnetically tagged non-basophils flowing through a microtubing sandwiched between magnetic flux concentrators sweeping across a Halbach array. The exponential profile captures non-basophils effectively while preventing their excessive initial buildup causing clogging. The i-BID isolates basophils with a mean purity of 93.9% ± 3.6% and recovery of 95.6% ± 3.4% without causing basophil degradation or unintentional activation. Our i-BID has the potential to enable basophil-based point-of-care diagnostics such as rapid allergy assessment.

Microfluidic-Based Technologies for CTC Isolation: A Review of 10 Years of Intense Efforts towards Liquid Biopsy

The selection of circulating tumor cells (CTCs) directly from blood as a real-time liquid biopsy has received increasing attention over the past ten years, and further analysis of these cells may greatly aid in both research and clinical applications. CTC analysis could advance understandings of metastatic cascade, tumor evolution, and patient heterogeneity, as well as drug resistance. Until now, the rarity and heterogeneity of CTCs have been technical challenges to their wider use in clinical studies, but microfluidic-based isolation technologies have emerged as promising tools to address these limitations. This review provides a detailed overview of latest and leading microfluidic devices implemented for CTC isolation. In particular, this study details must-have device performances and highlights the tradeoff between recovery and purity. Finally, the review gives a report of CTC potential clinical applications that can be conducted after CTC isolation. Widespread microfluidic devices, which aim to support liquid-biopsy-based applications, will represent a paradigm shift for cancer clinical care in the near future.

Multiphysics microfluidics for cell manipulation and separation: a review

Multiphysics microfluidics, which combines multiple functional physical processes in a microfluidics platform, is an emerging research area that has attracted increasing interest for diverse biomedical applications. Multiphysics microfluidics is expected to overcome the limitations of individual physical phenomena through combining their advantages. Furthermore, multiphysics microfluidics is superior for cell manipulation due to its high precision, better sensitivity, real-time tunability, and multi-target sorting capabilities. These exciting features motivate us to review this state-of-the-art field and reassess the feasibility of coupling multiple physical processes. To confine the scope of this paper, we mainly focus on five common forces in microfluidics: inertial lift, elastic, dielectrophoresis (DEP), magnetophoresis (MP), and acoustic forces. This review first explains the working mechanisms of single physical phenomena. Next, we classify multiphysics techniques in terms of cascaded connections and physical coupling, and we elaborate on combinations of designs and working mechanisms in systems reported in the literature to date. Finally, we discuss the possibility of combining multiple physical processes and associated design schemes and propose several promising future directions.

Efficient recovery of potent tumour-infiltrating lymphocytes through quantitative immunomagnetic cell sorting

Adoptive cell therapies require the recovery and expansion of highly potent tumour-infiltrating lymphocytes (TILs). However, TILs in tumours are rare and difficult to isolate efficiently, which hinders the optimization of therapeutic potency and dose. Here we show that a configurable microfluidic device can efficiently recover potent TILs from solid tumours by leveraging specific expression levels of target cell-surface markers. The device, which is sandwiched by permanent magnets, balances magnetic forces and fluidic drag forces to sort cells labelled with magnetic nanoparticles conjugated with antibodies for the target markers. Compared with conventional cell sorting, immunomagnetic cell sorting recovered up to 30-fold higher numbers of TILs, and the higher levels and diversity of the recovered TILs accelerated TIL expansion and enhanced their therapeutic potency. Immunomagnetic cell sorting also allowed us to identify and isolate potent TIL subpopulations, in particular TILs with moderate levels of CD39 (a marker of T-cell reactivity to tumours and T-cell exhaustion), which we found are tumour-specific, self-renewable and essential for the long-term success of adoptive cell therapies.

The Role of Circulating Biomarkers in Lung Cancer

Lung cancer is the leading cause of cancer morbidity and mortality worldwide and early diagnosis is crucial for the management and treatment of this disease. Non-invasive means of determining tumour information is an appealing diagnostic approach for lung cancers as often accessing and removing tumour tissue can be a limiting factor. In recent years, liquid biopsies have been developed to explore potential circulating tumour biomarkers which are considered reliable surrogates for understanding tumour biology in a non-invasive manner. Most common components assessed in liquid biopsy include circulating tumour cells (CTCs), cell-free DNA (cfDNA), circulating tumour DNA (ctDNA), microRNA and exosomes. This review explores the clinical use of circulating tumour biomarkers found in liquid biopsy for screening, early diagnosis and prognostication of lung cancer patients.

Relevance of Circulating Tumor Cells as Predictive Markers for Cancer Incidence and Relapse

Shedding of cancer cells from the primary site or undetectable bone marrow region into the circulatory system, resulting in clinically overt metastasis or dissemination, is the hallmark of unfavorable invasive cancers. The shed cells remain in circulation until they extravasate to form a secondary metastatic lesion or undergo anoikis. The circulating tumor cells (CTCs) found as single cells or clusters carry a plethora of information, are acknowledged as potential biomarkers for predicting cancer prognosis and cancer progression, and are supposed to play key roles in determining tailored therapies for advanced diseases. With the advent of novel technologies that allow the precise isolation of CTCs, more and more clinical trials are focusing on the prognostic and predictive potential of CTCs. In this review, we summarize the role of CTCs as a predictive marker for cancer incidence, relapse, and response to therapy.

A review of enrichment methods for circulating tumor cells: from single modality to hybrid modality

Circulating tumor cell (CTC) analysis as a liquid biopsy can be used for early diagnosis of cancer, evaluating cancer progression, and assessing treatment efficacy. The enrichment of CTCs from patient blood is important for CTC analysis due to the extreme rarity of CTCs. This paper updates recent advances in CTC enrichment methods. We first review single-modality methods, including biophysical and biochemical methods. Hybrid-modality methods, combining at least two single-modality methods, are gaining increasing popularity for their improved performance. Then this paper reviews hybrid-modality methods, which are categorized into integrated and sequenced hybrid-modality methods. The state of the art indicates that the CTC capture efficiencies of integrated hybrid-modality methods can reach 85% or higher by taking advantage of the superimposed and enhanced capture effects from multiple single-modality methods. Moreover, a hybrid method integrating biophysical with biochemical methods is characterized by both high processing rate and high specificity.

Circulating tumor cells: biology and clinical significance

Circulating tumor cells (CTCs) are tumor cells that have sloughed off the primary tumor and extravasate into and circulate in the blood. Understanding of the metastatic cascade of CTCs has tremendous potential for the identification of targets against cancer metastasis. Detecting these very rare CTCs among the massive blood cells is challenging. However, emerging technologies for CTCs detection have profoundly contributed to deepening investigation into the biology of CTCs and have facilitated their clinical application. Current technologies for the detection of CTCs are summarized herein, together with their advantages and disadvantages. The detection of CTCs is usually dependent on molecular markers, with the epithelial cell adhesion molecule being the most widely used, although molecular markers vary between different types of cancer. Properties associated with epithelial-to-mesenchymal transition and stemness have been identified in CTCs, indicating their increased metastatic capacity. Only a small proportion of CTCs can survive and eventually initiate metastases, suggesting that an interaction and modulation between CTCs and the hostile blood microenvironment is essential for CTC metastasis. Single-cell sequencing of CTCs has been extensively investigated, and has enabled researchers to reveal the genome and transcriptome of CTCs. Herein, we also review the clinical applications of CTCs, especially for monitoring response to cancer treatment and in evaluating prognosis. Hence, CTCs have and will continue to contribute to providing significant insights into metastatic processes and will open new avenues for useful clinical applications.

Negative enrichment of circulating tumor cells from unmanipulated whole blood with a 3D printed device

Reliable and routine isolation of circulating tumor cells (CTCs) from peripheral blood would allow effective monitoring of the disease and guide the development of personalized treatments. Negative enrichment of CTCs by depleting normal blood cells ensures against a biased selection of a subpopulation and allows the assay to be applied on different tumor types. Here, we report an additively manufactured microfluidic device that can negatively enrich viable CTCs from clinically-relevant volumes of unmanipulated whole blood samples. Our device depletes nucleated blood cells based on their surface antigens and the smaller anucleated cells based on their size. Enriched CTCs are made available off the device in suspension making our technique compatible with standard immunocytochemical, molecular and functional assays. Our device could achieve a ~ 2.34-log depletion by capturing > 99.5% of white blood cells from 10 mL of whole blood while recovering > 90% of spiked tumor cells. Furthermore, we demonstrated the capability of the device to isolate CTCs from blood samples collected from patients (n = 15) with prostate and pancreatic cancers in a pilot study. A universal CTC assay that can differentiate tumor cells from normal blood cells with the specificity of clinically established membrane antigens yet require no label has the potential to enable routine blood-based tumor biopsies at the point-of-care.

Systemic cytology. A novel diagnostic approach for assessment of early systemic disease

Recognition of low grade or asymptomatic systemic diseases suggests prevention of the worst, yet has been proven challenging ever since. Biomarker-based liquid biopsy has emerged in recent years as a practical platform for the assessment of systemic diseases yet, technical realizations were mainly focused on cancer, faced challenges in accuracy at early stage and are lacking provision of sufficient evidence of disease. In particular in cell-based cancer liquid biopsy, obstacles are rarity and heterogeneity of circulating tumor and tumor-associated rare cells. Evidence is mounting about an entire spectrum of distinct circulating rare cell types that denotes the systemic component of a certain physiological state. Therefore, circulating rare cells in combination may arise from yet, also account for systemic diseases, which we denote as multi-rare cell association and involves foremost bone marrow-derived progenitor and stem cells yet, also matured somatic cell types. One would expect immense diagnostic value in the read-out of the so called rare cell population which represents cytological evidence of abnormality. We hypothesize that comprehensive rare cell population profiling as contrasted to the biomarker screening approach may realize the premise of a biopsy as to confirm, characterize, grade, stage or predict a systemic disease. This novel approach represents the "missing link" in diagnostic care of in particular early or residual systemic disease and presumes a steady gain in knowledge about the clinical interpretation of rare cell population profiles thus, expecting the knowledge-driven transformation of cell-based liquid biopsy from suggestion to confirmation. We support our hypothesis by past findings made by others and us and provide insights how to interpret a certain rare cell population profile.