Automated rare single cell picking with the ALS cellcelector™

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.

From Efficiency to Yield: Exploring Recent Advances in CHO Cell Line Development for Monoclonal Antibodies

The increasing demand for biosimilar monoclonal antibodies (mAbs) has prompted the development of stable high-producing cell lines while simultaneously decreasing the time required for screening. Existing platforms have proven inefficient, resulting in inconsistencies in yields, growth characteristics, and quality features in the final mAb products. Selecting a suitable expression host, designing an effective gene expression system, developing a streamlined cell line generation approach, optimizing culture conditions, and defining scaling-up and purification strategies are all critical steps in the production of recombinant proteins, particularly monoclonal antibodies, in mammalian cells. As a result, an active area of study is dedicated to expression and optimizing recombinant protein production. This review explores recent breakthroughs and approaches targeted at accelerating cell line development to attain efficiency and consistency in the synthesis of therapeutic proteins, specifically monoclonal antibodies. The primary goal is to bridge the gap between rising demand and consistent, high-quality mAb production, thereby benefiting the healthcare and pharmaceutical industries.

Integrating single-cell transcriptomics with cellular phenotypes: cell morphology, Ca2+ imaging and electrophysiology

I review recent technological advancements in coupling single-cell transcriptomics with cellular phenotypes including morphology, calcium signaling, and electrophysiology. Single-cell RNA sequencing (scRNAseq) has revolutionized cell type classifications by capturing the transcriptional diversity of cells. A new wave of methods to integrate scRNAseq and biophysical measurements is facilitating the linkage of transcriptomic data to cellular function, which provides physiological insight into cellular states. I briefly discuss critical factors of these phenotypical characterizations such as timescales, information content, and analytical tools. Dedicated sections focus on the integration with cell morphology, calcium imaging, and electrophysiology (patch-seq), emphasizing their complementary roles. I discuss their application in elucidating cellular states, refining cell type classifications, and uncovering functional differences in cell subtypes. To illustrate the practical applications and benefits of these methods, I highlight their use in tissues with excitable cell-types such as the brain, pancreatic islets, and the retina. The potential of combining functional phenotyping with spatial transcriptomics for a detailed mapping of cell phenotypes in situ is explored. Finally, I discuss open questions and future perspectives, emphasizing the need for a shift towards broader accessibility through increased throughput.

A magnetic microneedle to isolate single immunomagnetically labeled cells

Immunomagnetic enrichment of cell populations from bodily fluids followed by immunofluorescent labeling is an established sample preparation method often used for the detection and enumeration of rare cells such as circulating tumor cells. For a detailed analysis of the heterogeneous characteristics of these cells, the cells need to be retrieved individually. Although several technologies are available to obtain 100% pure cells either individually or in bulk, these are often expensive, have low specificity, or suffer from high cell losses, either inherent to the technology or caused by sample transfer into special chips. To solve this issue, we introduce the magnetic micro-needle approach, which allows for the isolation of immunomagnetically labeled target cells by the use of a magnetized microneedle directly from glass slides. The magnetic microneedle approach makes use of the already present magnetic labeling used for enrichment, while the glass-slide-based open sample container allows for easy and loss-free sample loading. Additionally, the system facilitates not only the isolation but also the precise placement of cells. As the used parts are low cost, the technology provides researchers with an affordable and efficient method to pick up and isolate, as well as specifically place magnetically labeled cells from enriched fractions, thereby enabling the researchers to isolate or analyze these rare cells in more detail.

Quantification and Characterization of CTCs and Clusters in Pancreatic Cancer by Means of the Hough Transform Algorithm

Circulating Tumor Cells (CTCs) are considered a prognostic marker in pancreatic cancer. In this study we present a new approach for counting CTCs and CTC clusters in patients with pancreatic cancer using the Isoflux^TM System with the Hough transform algorithm (Hough-Isoflux^TM). The Hough-Isoflux^TM approach is based on the counting of an array of pixels with a nucleus and cytokeratin expression excluding the CD45 signal. Total CTCs including free and CTC clusters were evaluated in healthy donor samples mixed with pancreatic cancer cells (PCCs) and in samples from patients with pancreatic ductal adenocarcinoma (PDAC). The Isoflux^TM System with manual counting was used in a blinded manner by three technicians who used Manual-Isoflux^TM as a reference. The accuracy of the Hough-Isoflux^TM approach for detecting PCC based on counted events was 91.00% [84.50, 93.50] with a PCC recovery rate of 80.75 ± 16.41%. A high correlation between the Hough-Isoflux^TM and Manual-Isoflux^TM was observed for both free CTCs and for clusters in experimental PCC (R² = 0.993 and R² = 0.902 respectively). However, the correlation rate was better for free CTCs than for clusters in PDAC patient samples (R² = 0.974 and R² = 0.790 respectively). In conclusion, the Hough-Isoflux^TM approach showed high accuracy for the detection of circulating pancreatic cancer cells. A better correlation rate was observed between Hough-Isoflux^TM approach and with the Manual-Isoflux^TM for isolated CTCs than for clusters in PDAC patient samples.

LIFTOSCOPE: development of an automated AI-based module for time-effective and contactless analysis and isolation of cells in microtiter plates

BACKGROUND

The cultivation, analysis, and isolation of single cells or cell cultures are fundamental to modern biological and medical processes. The novel LIFTOSCOPE technology aims to integrate analysis and isolation into one versatile, fully automated device.

METHODS

LIFTOSCOPE's three core technologies are high-speed microscopy for rapid full-surface imaging of cell culture vessels, AI-based semantic segmentation of microscope images for localization and evaluation of cells, and laser-induced forward transfer (LIFT) for contact-free isolation of cells and cell clusters. LIFT transfers cells from a standard microtiter plate (MTP) across an air gap to a receiver plate, from where they can be further cultivated. The LIFT laser is integrated into the optical path of an inverse microscope, allowing to switch quickly between microscopic observation and cell transfer.

RESULTS

Tests of the individual process steps prove the feasibility of the concept. A prototype setup shows the compatibility of the microscope stage with the LIFT laser. A specifically designed MTP adapter to hold a receiver plate has been designed and successfully used for material transfers. A suitable AI algorithm has been found for cell selection.

CONCLUSION

LIFTOSCOPE speeds up cell cultivation and analysis with a target process time of 10 minutes, which can be achieved if the cell transfer is sped up using a more efficient path-finding algorithm. Some challenges remain, like finding a suitable cell transfer medium.

SIGNIFICANCE

The LIFTOSCOPE system can be used to extend existing cell cultivation systems and microscopes for fully automated biotechnological applications.

The Role of Circulating Tumor Cells in Ovarian Cancer Dissemination

Metastatic ovarian cancer is the main reason for treatment failures and consequent deaths. Ovarian cancer is predisposed to intraperitoneal dissemination. In comparison to the transcoelomic route, distant metastasis via lymph vessels and blood is less common. The mechanisms related to these two modes of cancer spread are poorly understood. Nevertheless, the presence of tumor cells circulating in the blood of OC patients is a well-established phenomenon confirming the significant role of lymphatic and hematogenous metastasis. Thus, the detection of CTCs may provide a minimally invasive tool for the identification of ovarian cancer, monitoring disease progression, and treatment effectiveness. This review focuses on the biology of ovarian CTCs and the role they may play in cancer diagnosis and therapy.

Characterization of a novel microfluidic platform for the isolation of rare single cells to enable CTC analysis from head and neck squamous cell carcinoma patients

Detailed examination of tumor components is leading‐edge to establish personalized cancer therapy. Accompanying research on cell‐free DNA, the cell count of circulating tumor cells (CTCs) in patient blood is seen as a crucial prognostic factor. The potential of CTC analysis is further not limited to the determination of the overall survival rate but sheds light on understanding inter‐ and intratumoral heterogeneity. In this regard, commercial CTC isolation devices combining an efficient enrichment of rare cells with a droplet deposition of single cells for downstream analysis are highly appreciated. The Liquid biopsy platform CTCelect was developed to realize a fully‐automated enrichment and single cell dispensing of CTCs from whole blood without pre‐processing. We characterized each process step with two different carcinoma cell lines demonstrating up to 87 % enrichment (n = 10) with EpCAM coupled immunomagnetic beads, 73 % optical detection and dispensing efficiency (n = 5). 40 to 56.7 % of cells were recovered after complete isolation from 7.5 ml untreated whole blood (n = 6). In this study, CTCelect enabled automated dispensing of single circulating tumor cells from HNSCC patient samples, qPCR‐based confirmation of tumor‐related biomarkers and immunostaining. Finally, the platform was compared to commercial CTC isolation technologies to highlight advantages and limitations of CTCelect. This system offers new possibilities for single cell screening in cancer diagnostics, individual therapy approaches and real‐time monitoring.

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.

Multi-Marker Immunofluorescent Staining and PD-L1 Detection on Circulating Tumour Cells from Ovarian Cancer Patients

Simple Summary

Circulating tumour cells (CTCs) have the potential to serve as a rich source of information for cancer diagnostic and therapeutic decisions. To fully exploit this minimally invasive diagnostic resource requires techniques that aid in enriching heterogenous populations of CTCs and markers to efficiently characterise these cells as tumour derived. In the present study we eva-luated the microfluidic enrichment of CTCs and a multi-marker staining methodology for the identification of heterogeneous CTCs in ovarian cancer (OC) patients and evaluation of PD-L1 expression. We showed, for the first time, the existence of hybrid CTCs with an epithelial/mesenchymal phenotype and their association with PD-L1 in OC. Incorporation of this method in future clinical trials can help predict immunotherapy responsiveness in OC patients.

Abstract

Detection of ovarian cancer (OC) circulating tumour cells (CTCs) is primarily based on targeting epithelial markers, thus failing to detect mesenchymal tumour cells. More importantly, the immune checkpoint inhibitor marker PD-L1 has not been demonstrated on CTCs from OC patients. An antibody staining protocol was developed and tested using SKOV-3 and OVCA432 OC cell lines. We targeted epithelial (cytokeratin (CK) and EpCAM), mesenchymal (vimentin), and OC-specific (PAX8) markers for detection of CTCs, and CD45/16 and CD31 were used for the exclusion of white blood and vascular endothelial cells, respectively. PD-L1 was used for CTC characterisation. CTCs were enriched using the Parsortix™ system from 16 OC patients. Results revealed the presence of CTCs in 10 (63%) cases. CTCs were heterogeneous, with 113/157 (72%) cells positive for CK/EpCAM (epithelial marker), 58/157 (37%) positive for vimentin (mesenchymal marker), and 17/157 (11%) for both (hybrid). PAX8 was only found in 11/157 (7%) CTCs. In addition, 62/157 (39%) CTCs were positive for PD-L1. Positivity for PD-L1 was significantly associated with the hybrid phenotype when compared with the epithelial (p = 0.007) and mesenchymal (p = 0.0009) expressing CTCs. Characterisation of CTC phenotypes in relation to clinical outcomes is needed to provide insight into the role that epithelial to mesenchymal plasticity plays in OC and its relationship with PD-L1.

Liquid biopsy for ovarian cancer using circulating tumor cells: Recent advances on the path to precision medicine

Ovarian cancer (OC) is the most lethal gynecologic malignance worldwide. Considering its metastasis nature, oncologists shift focus towards circulating tumor cells (CTCs), a progenitor that originates from primary tumor and undergoes morphologic/genetic alterations to enter bloodstream and invade nearby tissues. Mountains of evidence suggested that CTCs could provide deep insights into genomic, transcriptomic, and proteomic profiling of OC metastatic cascades. To pave the way for precision medicine, researchers exert great efforts to develop isolation/detection methodologies and construct CTCs-derived propagation platforms, including traditional cell cultures, patient-derived xenografts (PDXs), and organoids. From bench to bedside, CTCs provide minimally-invasive means to inform early diagnosis, predict prognosis, and guide treatment decisions. This review shined a spotlight on biology, detection technologies, and propagation platforms for CTCs. Of note, we also reviewed clinical applications of CTCs in liquid biopsy-based personalized cancer treatment and critically appraised limitations in routine clinical practice on the path to precision medicine.

Cartilaginous spheroid-assembly design considerations for endochondral ossification: towards robotic-driven biomanufacturing

Spheroids have become essential building blocks for biofabrication of functional tissues. Spheroid formats allow high cell-densities to be efficiently engineered into tissue structures closely resembling the native tissues. In this work, we explore the assembly capacity of cartilaginous spheroids (d∼ 150µm) in the context of endochondral bone formation. The fusion capacity of spheroids at various degrees of differentiation was investigated and showed decreased kinetics as well as remodeling capacity with increased spheroid maturity. Subsequently, design considerations regarding the dimensions of engineered spheroid-based cartilaginous mesotissues were explored for the corresponding time points, defining critical dimensions for these type of tissues as they progressively mature. Next, mesotissue assemblies were implanted subcutaneously in order to investigate the influence of spheroid fusion parameters on endochondral ossification. Moreover, as a step towards industrialization, we demonstrated a novel automated image-guided robotics process, based on targeting and registering single-spheroids, covering the range of spheroid and mesotissue dimensions investigated in this work. This work highlights a robust and automated high-precision biomanufacturing roadmap for producing spheroid-based implants for bone regeneration.

High-throughput and automation advances for accelerating single-cell cloning, monoclonality and early phase clone screening steps in mammalian cell line development for biologics production

Mammalian cell line development is a multistep process wherein timelines for developing clonal cells to be used as manufacturing cell lines for biologics production can commonly extend to 9 months when no automation or modern molecular technologies are involved in the workflow. Steps in the cell line development workflow involving single-cell cloning, monoclonality assurance, productivity and stability screening are labor, time and resource intensive when performed manually. Introduction of automation and miniaturization in these steps has reduced the required manual labor, shortened timelines from months to weeks, and decreased the resources needed to develop manufacturing cell lines. This review summarizes the advances, benefits, comparisons and shortcomings of different automation platforms available in the market for rapid isolation of desired clonal cell lines for biologics production.

Simple-to-Operate Approach for Single Cell Analysis Using a Hydrophobic Surface and Nanosized Droplets

Microfluidics-based technologies for single-cell analysis are becoming increasingly important tools in biological studies. With the increasing sophistication of microfluidics, cellular barcoding techniques, and next-generation sequencing, a more detailed picture of cellular subtype is emerging. Unfortunately, the majority of the methods developed for single-cell analysis are high-throughput and not suitable for rare cell analysis as they require a high input cell number. Here, we report a low-cost and reproducible method for rare single-cell analysis using a highly hydrophobic surface and nanosized static droplets. Our method allows rapid and efficient on-chip single-cell lysis and subsequent collection of genetic materials in nanoliter droplets using a micromanipulator or a laboratory pipette before subsequent genetic analysis. We show precise isolation of single cancer cells with high purity using two different strategies (i- cytospin and ii- static droplet array) for subsequent RNA analysis using droplet digital polymerase chain reaction (PCR) and real-time PCR. Our highly controlled isolation method opens a new avenue for the study of subcellular functional mechanisms, enabling the identification of rare cells of potential functional or pathogenic consequence.

A Review of Circulating Tumour Cell Enrichment Technologies

Simple Summary

Circulating tumour cells (CTCs) are cancer cells shed into the bloodstream from tumours and their analysis can provide important insights into cancer detection and monitoring, with the potential to direct personalised therapies for the patient. These CTCs are rare in the blood, which makes their detection and enrichment challenging and to date, only one technology (the CellSearch) has gained FDA approval for determining the prognosis of patients with advanced breast, prostate and colorectal cancers. Here, we review the wide range of enrichment technologies available to isolate CTCs from other blood components and highlight the important characteristics that new technologies should possess for routine clinical use.

Abstract

Circulating tumour cells (CTCs) are the precursor cells for the formation of metastatic disease. With a simple blood draw, liquid biopsies enable the non-invasive sampling of CTCs from the blood, which have the potential to provide important insights into cancer detection and monitoring. Since gaining FDA approval in 2004, the CellSearch system has been used to determine the prognosis of patients with metastatic breast, prostate and colorectal cancers. This utilises the cell surface marker Epithelial Cell Adhesion Molecule (EpCAM), to enrich CTCs, and many other technologies have adopted this approach. More recently, the role of mesenchymal-like CTCs in metastasis formation has come to light. It has been suggested that these cells are more aggressive metastatic precursors than their epithelial counterparts; however, mesenchymal CTCs remain undetected by EpCAM-based enrichment methods. This has prompted the development of a variety of ‘label free’ enrichment technologies, which exploit the unique physical properties of CTCs (such as size and deformability) compared to other blood components. Here, we review a wide range of both immunocapture and label free CTC enrichment technologies, summarising the most significant advantages and disadvantages of each. We also highlight the important characteristics that technologies should possess for routine clinical use, since future developments could have important clinical implications, with the potential to direct personalised therapies for patients with cancer.

Myocyte-specific enhancer factor 2c triggers transdifferentiation of adipose tissue-derived stromal cells into spontaneously beating cardiomyocyte-like cells

Cardiomyocyte regeneration is limited in adults. The adipose tissue-derived stromal vascular fraction (Ad-SVF) contains pluripotent stem cells that rarely transdifferentiate into spontaneously beating cardiomyocyte-like cells (beating CMs). However, the characteristics of beating CMs and the factors that regulate the differentiation of Ad-SVF toward the cardiac lineage are unknown. We developed a simple culture protocol under which the adult murine inguinal Ad-SVF reproducibly transdifferentiates into beating CMs without induction. The beating CMs showed the striated ventricular phenotype of cardiomyocytes and synchronised oscillation of the intracellular calcium concentration among cells on day 28 of Ad-SVF primary culture. We also identified beating CM-fated progenitors (CFPs) and performed single-cell transcriptome analysis of these CFPs. Among 491 transcription factors that were differentially expressed (≥ 1.75-fold) in CFPs and the beating CMs, myocyte-specific enhancer 2c (Mef2c) was key. Transduction of Ad-SVF cells with Mef2c using a lentiviral vector yielded CFPs and beating CMs with ~ tenfold higher cardiac troponin T expression, which was abolished by silencing of Mef2c. Thus, we identified the master gene required for transdifferentiation of Ad-SVF into beating CMs. These findings will facilitate the development of novel cardiac regeneration therapies based on gene-modified, cardiac lineage-directed Ad-SVF cells.

Image-Based Live Cell Sorting

Technologies capable of cell separation based on cell images provide powerful tools enabling cell selection criteria that rely on spatially or temporally varying properties. Image-based cell sorting (IBCS) systems utilize microfluidic or microarray platforms, each having unique characteristics and applications. The advent of IBCS marks a new paradigm in which cell phenotype and behavior can be explored with high resolution and tied to cellular physiological and omics data, providing a deeper understanding of single-cell physiology and the creation of cell lines with unique properties. Cell sorting guided by high-content image information has far-reaching implications in biomedical research, clinical medicine, and pharmaceutical development.

An Automated Fluorescence-Based Method to Isolate Bone Marrow-Derived Plasma Cells from Rhesus Macaques Using SIVmac239 SOSIP.664

Simian immunodeficiency virus (SIV) infection of Indian rhesus macaques (RMs) is one of the best-characterized animal models for human immunodeficiency virus (HIV) infection. Monoclonal antibodies (mAbs) have shown promise for prevention and treatment of HIV infection. However, it has been difficult to isolate mAbs that potently neutralize the highly pathogenic SIVmac239 strain. This has been largely due to the low frequency of circulating B cells encoding neutralizing Abs. Here we describe a novel technique to isolate mAbs directly from bone marrow-derived, Ab-secreting plasma cells. We employed an automated micromanipulator to isolate single SIVmac239 SOSIP.664-specific plasma cells from the bone marrow of a SIVmac239-infected RM with serum neutralization titers against SIVmac239. After picking plasma cells, we obtained 44 paired Ab sequences. Ten of these mAbs were SIV specific. Although none of these mAbs neutralized SIVmac239, three mAbs completely neutralized the related SIVmac316 strain. The majority of these mAbs bound to primary rhesus CD4+ T cells infected with SIVmac239 and induced Ab-dependent cellular cytotoxicity. This method is a first step in successful isolation of antigen-specific bone marrow-derived plasma cells from RMs.

PIC&RUN: An integrated assay for the detection and retrieval of single viable circulating tumor cells

Circulating tumor cells (CTCs) shed from solid tumors can serve as a minimally invasive liquid biopsy for monitoring disease progression. Because CTCs are rare and heterogeneous, their biological properties need to be investigated at the single cell level, which requires efficient ways to isolate and analyze live single CTCs. Current methods for CTC isolation and identification are either performed on fixed and stained cells or need multiple procedures to isolate pure live CTCs. Here, we used the AccuCyte-RareCyte system to develop a Protocol for Integrated Capture and Retrieval of Ultra-pure single live CTCs using Negative and positive selection (PIC&RUN). The positive selection module of PIC&RUN identifies CTCs based on detection of cancer surface markers and exclusion of immune markers. Combined with a two-step cell picking protocol to retrieve ultrapure single CTCs, the positive selection module is compatible for downstream single cell transcriptomic analysis. The negative selection module of PIC&RUN identifies CTCs based on a live cell dye and the absence of immune markers, allowing retrieval of viable CTCs that are suitable for ex vivo culture. This new assay combines the CTC capture and retrieval in one integrated platform, providing a valuable tool for downstream live CTC analyses.

Single-Cell Analysis of Circulating Tumor Cells: How Far Have We Come in the -Omics Era?

Tumor cells detach from the primary tumor or metastatic sites and enter the peripheral blood, often causing metastasis. These cells, named Circulating Tumor Cells (CTCs), display the same spatial and temporal heterogeneity as the primary tumor. Since CTCs are involved in tumor progression, they represent a privileged window to disclose mechanisms of metastases, while -omic analyses at the single-cell level allow dissection of the complex relationships between the tumor subpopulations and the surrounding normal tissue. However, in addition to reporting the proof of concept that we can query CTCs to reveal tumor evolution throughout the continuum of treatment for early detection of resistance to therapy, the scientific literature has also been highlighting the disadvantages of CTCs, which hampers a routine use of this approach in clinical practice. To date, an increasing number of CTC technologies, as well as -omics methods, have been employed, mostly lacking strong comparative analyses. The rarity of CTCs also represents a major challenge, because there is no consensus regarding the minimal criteria necessary and sufficient to define an event as CTC; moreover, we cannot often compare data from of one study with that of another. Finally, the availability of an individual tumor profile undermines the traditional histology-based treatment. Applying molecular data for patient benefit implies a collective effort by biologists, bioengineers, and clinicians, to create tools to interpret molecular data and manage precision medicine in every single patient. Herein, we focus on the most recent findings in CTC −omics to learn how far we have come.

Self-Seeding Microwells to Isolate and Assess the Viability of Single Circulating Tumor Cells

The availability of viable tumor cells could significantly improve the disease management of cancer patients. Here we developed and evaluated a method using self-seeding microwells to obtain single circulating tumor cells (CTC) and assess their potential to expand. Conditions were optimized using cells from the breast cancer cell line MCF-7 and blood from healthy volunteers collected in EDTA blood collection tubes. 43% of the MCF-7 cells (nucleus+, Ethidium homodimer-1-, Calcein AM+, α-EpCAM+, α-CD45-) spiked into 7.5 mL of blood could be recovered with 67% viability and these could be further expanded. The same procedure tested in metastatic breast and prostate cancer patients resulted in a CTC recovery of only 0–5% as compared with CTC counts obtained with the CellSearch^® system. Viability of the detected CTC ranged from 0–36%. Cell losses could be mainly contributed to the smaller size and greater flexibility of CTC as compared to cultured cells from cell lines and loss during leukocyte depletion prior to cell seeding. Although CTC losses can be reduced by fixation, to obtain viable CTC no fixatives can be used and pore size in the bottom of microwells will need to be reduced, filtration conditions adapted and pre-enrichment improved to reduce CTC losses.