Capture and enrichment of CD34-positive haematopoietic stem and progenitor cells from blood circulation using P-selectin in an implantable device

Translational tissue-engineered vascular grafts: From bench to bedside

Cardiovascular disease is a primary cause of mortality worldwide, and patients often require bypass surgery that utilizes autologous vessels as conduits. However, the limited availability of suitable vessels and the risk of failure and complications have driven the need for alternative solutions. Tissue-engineered vascular grafts (TEVGs) offer a promising solution to these challenges. TEVGs are artificial vascular grafts made of biomaterials and/or vascular cells that can mimic the structure and function of natural blood vessels. The ideal TEVG should possess biocompatibility, biomechanical mechanical properties, and durability for long-term success in vivo. Achieving these characteristics requires a multi-disciplinary approach involving material science, engineering, biology, and clinical translation. Recent advancements in scaffold fabrication have led to the development of TEVGs with improved functional and biomechanical properties. Innovative techniques such as electrospinning, 3D bioprinting, and multi-part microfluidic channel systems have allowed the creation of intricate and customized tubular scaffolds. Nevertheless, multiple obstacles must be overcome to apply these innovations effectively in clinical practice, including the need for standardized preclinical models and cost-effective and scalable manufacturing methods. This review highlights the fundamental approaches required to successfully fabricate functional vascular grafts and the necessary translational methodologies to advance their use in clinical practice.

Nanoscopic Characterization of Cell Migration under Flow Using Optical and Electron Microscopy

Hematopoietic stem/progenitor cell (HSPC) and leukemic cell homing is an important biological phenomenon that takes place through essential interactions with adhesion molecules on an endothelial cell layer. The homing process of HSPCs begins with the tethering and rolling of the cells on the endothelial layer, which is achieved by the interaction between selectins on the endothelium to the ligands on HSPC/leukemic cells under shear stress of the blood flow. Although many studies have been based on in vitro conditions of the cells rolling over recombinant proteins, significant challenges remain when imaging HSPC/leukemic cells on the endothelium, a necessity when considering characterizing cell-to-cell interaction and rolling dynamics during cell migration. Here, we report a new methodology that enables imaging of stem-cell-intrinsic spatiotemporal details during its migration on an endothelium-like cell monolayer. We developed optimized protocols that preserve transiently appearing structures on HSPCs/leukemic cells during its rolling under shear stress for fluorescence and scanning electron microscopy characterization. Our new experimental platform is closer to in vivo conditions and will contribute to indepth understanding of stem-cell behavior during its migration and cell-to-cell interaction during the process of homing.

A sticky wicket: Defining molecular functions for CD34 in hematopoietic cells

The CD34 cell surface antigen is widely expressed in tissues on cells with progenitor-like properties and on mature vascular endothelia. In adult human bone marrow, CD34 marks hematopoietic stem and progenitor cells (HSPCs) starting from the bulk of hematopoietic stem cells with long-term repopulating potential (LT-HSCs) throughout expansion and differentiation of oligopotent and unipotent progenitors. CD34 protein surface expression is typically lost as cells mature into terminal effectors. Because of this expression pattern of HSPCs, CD34 has had a central role in the evaluation or selection of donor graft tissue in HSC transplant (HSCT). Given its clinical importance, it is surprising that the biological functions of CD34 are still poorly understood. This enigma is due, in part, to CD34's context-specific role as both a pro-adhesive and anti-adhesive molecule and its potential functional redundancy with other sialomucins. Moreover, there are also critical differences in the regulation of CD34 expression on HSPCs in humans and experimental mice. In this review, we highlight some of the more well-defined functions of CD34 in HSPCs with a focus on proposed functions most relevant to HSCT biology.

Heterogeneity of Circulating Tumor Cells in Breast Cancer: Identifying Metastatic Seeds

Metastasis being the main cause of breast cancer (BC) mortality represents the complex and multistage process. The entrance of tumor cells into the blood vessels and the appearance of circulating tumor cells (CTCs) seeding and colonizing distant tissues and organs are one of the key stages in the metastatic cascade. Like the primary tumor, CTCs are extremely heterogeneous and presented by clusters and individual cells which consist of phenotypically and genetically distinct subpopulations. However, among this diversity, only a small number of CTCs is able to survive in the bloodstream and to form metastases. The identification of the metastasis-initiating CTCs is believed to be a critical issue in developing therapeutic strategies against metastatic disease. In this review, we summarize the available literature addressing morphological, phenotypic and genetic heterogeneity of CTCs and the molecular makeup of specific subpopulations associated with BC metastasis. Special attention is paid to the need for in vitro and in vivo studies to confirm the tumorigenic and metastatic potential of metastasis-associating CTCs. Finally, we consider treatment approaches that could be effective to eradicate metastatic CTCs and to prevent metastasis.

Not just a marker: CD34 on human hematopoietic stem/progenitor cells dominates vascular selectin binding along with CD44

CD34 is routinely used to identify and isolate human hematopoietic stem/progenitor cells (HSPCs) for use clinically in bone marrow transplantation, but its function on these cells remains elusive. Glycoprotein ligands on HSPCs help guide their migration to specialized microvascular beds in the bone marrow that express vascular selectins (E- and P-selectin). Here, we show that HSPC-enriched fractions from human hematopoietic tissue expressing CD34 (CD34^pos) bound selectins, whereas those lacking CD34 (CD34^neg) did not. An unbiased proteomics screen identified potential glycoprotein ligands on CD34^pos cells revealing CD34 itself as a major vascular selectin ligand. Biochemical and CD34 knockdown analyses highlight a key role for CD34 in the first prerequisite step of cell migration, suggesting that it is not just a marker on these cells. Our results also entice future potential strategies to investigate the glycoforms of CD34 that discriminate normal HSPCs from leukemic cells and to manipulate CD34^neg HSPC-enriched bone marrow or cord blood populations as a source of stem cells for clinical use.

Engineering nanoscale surface features to sustain microparticle rolling in flow

Nanoscopic features of channel walls are often engineered to facilitate microfluidic transport, for instance when surface charge enables electro-osmosis or when grooves drive mixing. The dynamic or rolling adhesion of flowing microparticles on a channel wall holds potential to accomplish particle sorting or to selectively transfer reactive species or signals between the wall and flowing particles. Inspired by cell rolling under the direction of adhesion molecules called selectins, we present an engineered platform in which the rolling of flowing microparticles is sustained through the incorporation of entirely synthetic, discrete, nanoscale, attractive features into the nonadhesive (electrostatically repulsive) surface of a flow channel. Focusing on one example or type of nanoscale feature and probing the impact of broad systematic variations in surface feature loading and processing parameters, this study demonstrates how relatively flat, weakly adhesive nanoscale features, positioned with average spacings on the order of tens of nanometers, can produce sustained microparticle rolling. We further demonstrate how the rolling velocity and travel distance depend on flow and surface design. We identify classes of related surfaces that fail to support rolling and present a state space that identifies combinations of surface and processing variables corresponding to transitions between rolling, free particle motion, and arrest. Finally we identify combinations of parameters (surface length scales, particle size, flow rates) where particles can be manipulated with size-selectivity.

In vivo tissue engineering: mimicry of homing factors for self-endothelialization of blood-contacting materials

Thrombogenicity of foreign surfaces is the major obstacle in cardiovascular interventions. Despite enormous advances in biomaterials research, the hemocompatibility of blood-contacting materials is still not satisfactory and the native endothelium still represents the ideal surface for blood contact. Circulating adult endothelial progenitor cells (EPCs) in the human blood provide an excellent source of autologous stem cells for the in vivo self-endothelialization of blood-contacting materials. For this purpose, material surfaces can be coated with capture molecules mimicking natural homing factors to attract circulating EPCs. Hitherto, several ligands, such as aptamers, monoclonal antibodies, peptides, selectins and their ligands, or magnetic molecules, are used to biofunctionalize surfaces for the capturing of EPCs directly from patient's bloodstream onto blood-contacting materials. Subsequently, attracted EPCs can differentiate into endothelial cells and generate an autologous endothelium. The in vivo self-endothelialization of blood-contacting materials prevents the recognition of them as a foreign body; this opens up revolutionary new prospects for future clinical stem-cell and tissue engineering strategies.

The cancer stem cell hypothesis: a guide to potential molecular targets

Common cancer theories hold that tumor is an uncontrolled somatic cell proliferation caused by the progressive addition of random mutations in critical genes that control cell growth. Nevertheless, various contradictions related to the mutation theory have been reported previously. These events may be elucidated by the persistence of residual tumor cells, called Cancer Stem Cells (CSCs) responsible for tumorigenesis, tumor maintenance, tumor spread, and tumor relapse. Herein, we summarize the current understanding of CSCs, with a focus on the possibility to identify specific markers of CSCs, and discuss the clinical application of targeting CSCs for cancer treatment.

Modulation of selectin-mediated adhesion of flowing lymphoma and bone marrow cells by immobilized SDF-1

The α-chemokine, stromal-derived factor-1 (SDF-1), has been linked to the homing of circulating tumor cells to bone. SDF-1 is expressed by bone microvascular cells and osteoblasts and normally functions to attract blood-borne hematopoietic stem and progenitor cells to marrow. It has been shown that treatment of cancer cells with soluble SDF-1 results in a more aggressive phenotype; however, the relevance of the administration of the soluble protein is unclear. As such, a flow device was functionalized with P-selectin and SDF-1 to mimic the bone marrow microvasculature and the initial steps of cell adhesion. The introduction of SDF-1 onto the adhesive surface was found to significantly enhance the adhesion of lymphoma cells, as well as low-density bone marrow cells (LDBMC), both in terms of the number of adherent cells and the strength of cell adhesion. Thus, SDF-1 has a synergistic effect with P-selectin on cancer cell adhesion and may be sufficient to promote preferential metastasis to bone.

A cell rolling cytometer reveals the correlation between mesenchymal stem cell dynamic adhesion and differentiation state

This communication presents quantitative studies of the dynamic adhesion behavior of mesenchymal stem cells (MSCs) enabled by the combination of cell-surface receptor-ligand interactions and three-dimensional hydrodynamic control by microtopography.

Nanotechnology for the detection and kill of circulating tumor cells

Circulating tumor cells (CTCs) represent a surrogate biomarker of hematogenous metastases and thus could be considered as a 'liquid biopsy' which reveals metastasis in action. But it is absolutely a challenge to detect CTCs due to their extreme rarity. At present, the most common principle is to take advantage of the epithelial surface markers of CTCs which attach to a specific antibody. Antibody-magnetic nanobeads combine with the epithelial surface markers, and then the compound is processed by washing, separation, and detection. However, a proportion of CTC antigen expressions are down-regulated or lost in the process of epithelial-mesenchymal transition (EMT), and thus, this part of CTCs cannot be detected by classical detection methods such as CellSearch. To resolve this problem, some multiple-marker CTC detections have been developed rapidly. Additionally, nanotechnology is a promising approach to kill CTCs with high efficiency. Implantable nanotubes coated with apoptosis-promoting molecules improve the disease-free survival and overall survival. The review introduces some novel CTC detection techniques and therapeutic methods by virtue of nanotechnology to provide a better knowledge of the progress about CTC study.

P-selectin glycoprotein ligand-1 deficiency augments G-CSF induced myeloid cell mobilization

The effect of granulocyte colony-stimulating factor (G-CSF) was investigated in P-selectin glycoprotein ligand-1 (PSGL-1) deficient (PSGL-1(-/-)) and wild-type (PSGL-1(+/+)) mice to establish the role of this mucin in myeloid cell mobilization. G-CSF activates tissue proteases that cleave adhesion molecules, thus enhances the mobilization of myeloid cells and haematopoietic stem cells. Cytopenia was induced with a single dose of cyclophosphamide. In PSGL-1(-/-) animals, we observed a delayed extravasation of mature myeloid cells from the peripheral vessels into the tissue compartments and their faster mobilization from the bone marrow. Subsequently, animals received G-CSF twice a day for 4 days. Neutrophil and monocyte counts increased upon completion of G-CSF treatment and both values were significantly higher in PSGL-1(-/-) mice; 47.7 versus 28.3 G/l for neutrophils and 4.1 versus 2.0 G/l for monocytes. The ratio of atypical myeloid cells was also elevated. Analyzing the causes of the above differences, we identified a 4-fold increase in the colony-forming unit (CFU-GM) counts of the peripheral blood in PSGL-1(-/-) mice, compared to wild-type animals. A significantly elevated number of CFU-GM was detected also in the femurs of PSGL-1(-/-) mice, 4 and 5 days after cyclophosphamide treatment and these values paralleled with the elevation of CD34+/CD117+ stem cell counts in the peripheral blood. Our data suggest, that in the absence of PSGL-1, G-CSF was more potent in elevating absolute myeloid cell numbers by acting on cell release from the bone marrow, maturation from circulating precursor cells in the peripheral blood and prolonged retainment in the circulation.

Stem cell enrichment with selectin receptors: mimicking the pH environment of trauma

The isolation of hematopoietic stem and progenitor cells (HSPCs) is critical for transplantation therapy and HSPC research, however current isolation techniques can be prohibitively expensive, time-consuming, and produce variable results. Selectin-coated microtubes have shown promise in rapidly isolating HSPCs from human bone marrow, but further purification of HSPCs remains a challenge. Herein, a biomimetic device for HSPC isolation is presented to mimic the acidic vascular microenvironment during trauma, which can enhance the binding frequency between L-selectin and its counter-receptor PSGL-1 and HSPCs. Under acidic pH conditions, L-selectin coated microtubes enhanced CD34+ HSPC adhesion, as evidenced by decreased cell rolling velocity and increased rolling flux. Dynamic light scattering was utilized as a novel sensor to confirm an L-selectin conformational change under acidic conditions, as previously predicted by molecular dynamics. These results suggest that mimicking the acidic conditions of trauma can induce a conformational extension of L-selectin, which can be utilized for flow-based, clinical isolation of HSPCs.

Tuning of cell-biomaterial anchorage for tissue regeneration

Which mechanisms mediate cell attachment to biomaterials? What role does the surface charge or wettability play on cell-material anchorage? What are the currently investigated strategies to modify cell-matrix adherence spatiotemporally? Considering the development of scaffolds made of biocompatible materials to temporarily replace the structure and/or function of the extracellular matrix, focus is given to the analysis of the specific (i.e., cell adhesive peptide sequences) and unspecific (i.e., surface charge, wettability) mechanisms mediating cell-matrix interactions. Furthermore, because natural tissue regeneration is characterized by the dynamic attachment/detachment of different cell populations, the design of advanced scaffolds for tissue engineering, based in the spatiotemporal tuning of cell-matrix anchorage is discussed.

Exercise increases the frequency of circulating hematopoietic progenitor cells, but reduces hematopoietic colony-forming capacity

Circulating hematopoietic progenitor cells (CPCs) may be triggered by physical exercise and/or normobaric hypoxia from the bone marrow. The aim of the study was to investigate the influence of physical exercise and normobaric hypoxia on CPC number and functionality in the peripheral blood as well as the involvement of oxidative stress parameters as possibly active agents. Ten healthy male subjects (25.3±4.4 years) underwent a standardized cycle incremental exercise test protocol (40 W+20 W/min) under either normoxic (FiO2 ∼0.21) or hypoxic conditions (FiO2<0.15, equals 3,500 m, 3 h xposure) within a time span of at least 1 week. Blood was drawn from the cubital vein before and 10, 30, 60, and 120 min after exercise. The number of CPCs in the peripheral blood was analyzed by flow cytometry (CD34/CD45-positive cells). The functionality of cells present was addressed by secondary colony-forming unit-granulocyte macrophage (CFU-GM) assays. To determine a possible correlation between the mobilization of CPCs and reactive oxygen species, parameters for oxidative stress such as malondialdehyde (MDA) and myeloperoxidase (MPO) were obtained. Data showed a significant increase of CPC release under normoxic as well as hypoxic conditions after 10 min of recovery (P<0.01). Most interestingly, although CD34+/CD45dim cells increased in number, the proliferative capacity of CPCs decreased significantly 10 min after cessation of exercise (P<0.05). A positive correlation between CPCs and MDA/MPO levels turned out to be significant for both normoxic and hypoxic conditions (P<0.05/P<0.01). Hypoxia did not provoke an additional effect. Although the CPC frequency increased, the functionality of CPCs decreased significantly after exercise, possibly due to the influence of increased oxidative stress levels.

Cornering metastases: therapeutic targeting of circulating tumor cells and stem cells

The last decade has witnessed an evolution of our understanding of the biology of the metastatic cascade. Recent insights into the metastatic process show that it is complex, dynamic, and multi-directional. This process starts at a very early stage in the natural history of solid tumor growth leading to early development of metastases that grow in parallel with the primary tumor. The role of stem cells in perpetuating cancer metastases is increasingly becoming more evident. At the same time, there is a growing recognition of the crucial role circulating tumor cells (CTCs) play in the development of metastases. These insights have laid the biological foundations for therapeutic targeting of CTCs, a promising area of research that aims to reduce cancer morbidity and mortality by preventing the development of metastases at a very early stage. The hematogenous transport phase of the metastatic cascade provides critical access to CTCs for therapeutic targeting aiming to interrupt the metastatic process. Recent advances in the fields of nanotechnology and microfluidics have led to the development of several devices for in vivo targeting of CTC during transit in the circulation. Selectin-coated tubes that target cell adhesion molecules, immuno-magnetic separators, and in vivo photo-acoustic flow cytometers are currently being developed for this purpose. On the pharmacological front, several pharmacological and immunological agents targeting cancer stem cells are currently being developed. Such agents may ultimately prove to be effective against circulating tumor stem cells (CTSCs). Although still in its infancy, therapeutic targeting of CTCs and CTSCs offers an unprecedented opportunity to prevent the development of metastasis and potentially alter the natural history of cancer. By rendering cancer a "local" disease, these approaches could lead to major reductions in metastasis-related morbidity and mortality.

Inducing apoptosis in rolling cancer cells: a combined therapy with aspirin and immobilized TRAIL and E-selectin

Though metastasis is considered an inefficient process, over 90% of cancer related deaths are attributed to the formation of secondary tumors. Thus, eliminating circulating cancer cells could lead to improved patient survival. This study was aimed at exploiting the interactions of cancer cells with selectins under flow to selectively kill captured colon cancer cells. Microtubes functionalized with E-selectin and TRAIL were perfused with colon cancer cell line Colo205 either treated with 1 mM aspirin or untreated for 1 or 2 h. Cells were collected from the microtube and analyzed by flow cytometry. Aspirin treatment alone killed only 3% cells in culture. A 95% difference in the number of cells killed between control and TRAIL + ES surfaces was seen when aspirin treated cells were perfused over the functionalized surface for 2 h. We have demonstrated a novel biomimetic method to capture and neutralize cancer cells in flow, thus reducing the chances for the formation of secondary tumors.

The recombinant bifunctional protein αCD133-GPVI promotes repair of the infarcted myocardium in mice

BACKGROUND

Bone-marrow-derived progenitor cells are important in myocardial repair mechanisms following prolonged ischemia. Cell-based therapy of diseased myocardium is limited by a low level of tissue engraftment.

OBJECTIVES

The aim of this study was the development of the bifunctional protein αCD133-glycoprotein (GP)VI as an effective treatment for supporting vascular and myocardial repair mechanisms.

RESULTS

We have generated and characterized a bifunctional molecule (αCD133-GPVI) that binds both to the subendothelium of the injured microvasculature and to CD133(+) progenitor cells with high affinity. αCD133-GPVI enhances progenitor cell adhesion to extracellular matrix proteins and differentiation into mature endothelial cells. In vivo studies showed that αCD133-GPVI favors adhesion of circulating progenitor cells to the injured vessel wall (intravital microscopy). Also, treatment of mice undergoing experimental myocardial infarction with αCD133-GPVI-labeled progenitor cells reduces infarction size and preserves myocardial function.

CONCLUSIONS

The bifunctional trapping protein αCD133-GPVI represents a novel and promising therapeutic option for limiting heart failure of the ischemic myocardium.

Microtube Device for Selectin-Mediated Capture of Viable Circulating Tumor Cells from Blood

BACKGROUND

Circulating tumor cells (CTCs) can be used clinically to treat cancer. As a diagnostic tool, the CTC count can be used to follow disease progression, and as a treatment tool, CTCs can be used to rapidly develop personalized therapeutic strategies. To be effectively used, however, CTCs must be isolated at high purity without inflicting cellular damage.

METHODS

We designed a microscale flow device with a functionalized surface of E-selectin and antibody molecules against epithelial markers. The device was additionally enhanced with a halloysite nanotube coating. We created model samples in which a known number of labeled cancer cells were suspended in healthy whole blood to determine device capture efficiency. We then isolated and cultured primary CTCs from buffy coat samples of patients diagnosed with metastatic cancer.

RESULTS

Approximately 50% of CTCs were captured from model samples. Samples from 12 metastatic cancer patients and 8 healthy participants were processed in nanotube-coated or smooth devices to isolate CTCs. We isolated 20–704 viable CTCs per 3.75-mL sample, achieving purities of 18%–80% CTCs. The nanotube-coated surface significantly improved capture purities (P = 0.0004). Experiments suggested that this increase in purity was due to suppression of leukocyte spreading.

CONCLUSIONS

The device successfully isolates viable CTCs from both blood and buffy coat samples. The approximately 50% capture rate with purities &gt;50% with the nanotube coating demonstrates the functionality of this device in a clinical setting and opens the door for personalized cancer therapies.

Cell sorting by deterministic cell rolling

This communication presents the concept of "deterministic cell rolling", which leverages transient cell-surface molecular interactions that mediate cell rolling to sort cells with high purity and efficiency in a single step.

E-selectin liposomal and nanotube-targeted delivery of doxorubicin to circulating tumor cells

The presence of circulating tumor cells (CTCs) is believed to lead to the formation of secondary tumors via an adhesion cascade involving interaction between adhesion receptors of endothelial cells and ligands on CTCs. Many CTCs express sialylated carbohydrate ligands on their surfaces that adhere to selectin protein found on inflamed endothelial cells. We have investigated the feasibility of using immobilized selectin proteins as a targeting mechanism for CTCs under flow. Herein, targeted liposomal doxorubicin (L-DXR) was functionalized with recombinant human E-selectin (ES) and polyethylene glycol (PEG) to target and kill cancer cells under shear flow, both when immobilized along a microtube device or sheared in a cone-and-plate viscometer in a dilute suspension. Healthy circulating cells such as red blood cells were not targeted by this mechanism and were left to freely circulate, and minimal leukocyte death was observed. Halloysite nanotube (HNT)-coated microtube devices immobilized with nanoscale liposomes significantly enhanced the targeting, capture, and killing of cancer cells. This work demonstrates that E-selectin functionalized L-DXR, sheared in suspension or immobilized onto microtube devices, provides a novel approach to selectively target and deliver chemotherapeutics to CTCs in the bloodstream.

Glycomechanics of the metastatic cascade: tumor cell-endothelial cell interactions in the circulation

Hydrodynamic shear force plays an important role in the leukocyte adhesion cascade that involves the tethering and rolling of cells along the endothelial layer, their firm adhesion or arrest, and their extravasation or escape from the circulatory system by inducing passive deformation, or cell flattening, and microvilli stretching, as well as regulating the expression, distribution, and conformation of adhesion molecules on leukocytes and the endothelial layer. Similarly, the dissemination of circulating tumor cells (CTCs) from the primary tumor sites is believed to involve tethering, rolling, and firm adhesion steps before their eventual extravasation which leads to secondary tumor sites (metastasis). Of particular importance to both the leukocyte adhesion cascade and the extravasation of CTCs, glycoproteins are involved in all three steps (capture, rolling, and firm adhesion) and consist of a variety of important selectin ligands. This review article provides an overview of glycoprotein glycosylation associated with the abnormal glycan expression on cancer cell surfaces, where well-established and novel selectin ligands that are cancer related are discussed. An overview of computational approaches on the effects of fluid mechanical force on glycoprotein mediated cancer cell rolling and adhesion is presented with a highlight of recent flow-based and selectin-mediated cell capturing/enriching devices. Finally, as an important branch of the glycoprotein family, mucins, specifically MUC1, are discussed in the context of their aberrant expression on cancer cells and their role as cancer cell adhesion molecules. Since metastasis relies heavily on glycoprotein interactions in the bloodstream where the fluid shear stress highly regulates cell adhesion forces, it is important to study and understand the glycomechanics of all relevant glycoproteins (well-established and novel) as they relate to the metastatic cascade.

Suppression of prostate cancer cell rolling and adhesion to endothelium by 1α,25-dihydroxyvitamin D3

Adhesion of circulating prostate cancer (PCa) cells to the microvascular endothelium is a critical step during cancer metastasis. To study PCa cell rolling and adhesion behavior, we developed a dynamic flow-based microtube system to mimic the microvascular environment. We found that PCa cell rolling capacity is mediated by E-selectin and can be enhanced by stromal cell-derived factor-1 under different wall shear stresses. Using this device, we tested if the chemopreventive agent, vitamin D, could interfere with PCa cell adhesion. We found that 1α,25-dihydroxyvitamin D(3) (1,25-VD), the bioactive form of vitamin D, reduced PCa cell rolling numbers and increased rolling velocities resulting in a significant decreased number of PCa cells adhering to the microtube. The inhibitory effects of 1,25-VD on PCa cell heterotypic adhesion were further confirmed using microvascular endothelial cells in a static condition. Furthermore, we demonstrated that 1,25-VD can increase E-cadherin expression in PCa cells and promote the homotypic cell-cell aggregation, which can then hinder PCa cell adhesion to the endothelium. Blocking E-cadherin with a neutralizing antibody can reverse 1,25-VD-mediated suppression of PCa cell adhesion to the endothelium. Taken together, our data revealed that 1,25-VD promoted PCa cell aggregation by increasing E-cadherin expression, thus interfering with circulating PCa cell adhesion to microvascular endothelial cells and potentially reducing their metastatic potential.

Use of naturally occurring halloysite nanotubes for enhanced capture of flowing cells

The development of individualized treatments for cancer can be facilitated by more efficient methods for separating cancer cells from patient blood in such a way that they remain viable for live cell assays. We have previously shown that immobilized P-selectin protein can be used on the inner surface of a microscale flow system to induce leukemic cells and leukocytes to roll at different velocities and relative fluxes, thereby creating a means for rapid cell fractionation without inflicting cellular damage. In this study, we explore a method to more efficiently capture leukemic and epithelial cancer cells from flow by altering the nanoscale topography of the inner surface of P-selectin-coated microtubes. This functionalized topography is achieved by attaching naturally occurring halloysite nanotubes to the microtube surface via a monolayer of poly-L-lysine), followed by functionalization with recombinant human selectin protein. We have found that halloysite nanotube coatings promote increased capture of leukemic cells and have determined the key parameters for controlling cell capture under flow: halloysite content and selectin density. Ultimately, selectin-functionalized nanotube coatings should provide a means for enhanced cancer cell isolation from whole blood and other mixtures of cells.

Combination of intensive chemotherapy and anticancer vaccines in the treatment of human malignancies: the hematological experience

In vitro studies have demonstrated that cancer-specific T cell cytotoxicity can be induced both ex vivo and in vivo, but this therapeutic strategy should probably be used as an integrated part of a cancer treatment regimen. Initial chemotherapy should be administered to reduce the cancer cell burden and disease-induced immune defects. This could be followed by autologous stem cell transplantation that is a safe procedure including both high-dose disease-directed chemotherapy and the possibility for ex vivo enrichment of the immunocompetent graft cells. The most intensive conventional chemotherapy and stem cell transplantation are used especially in the treatment of aggressive hematologic malignancies; both strategies induce T cell defects that may last for several months but cancer-specific T cell reactivity is maintained after both procedures. Enhancement of anticancer T cell cytotoxicity is possible but posttransplant vaccination therapy should probably be combined with optimalisation of immunoregulatory networks. Such combinatory regimens should be suitable for patients with aggressive hematological malignancies and probably also for other cancer patients.

Clinical potential of adult vascular progenitor cells

Cell therapy to treat vascular and cardiovascular diseases has evolved over the past decade with improved understanding of progenitor cell mobilization, recruitment, and differentiation. The beneficial effects seen in several preclinical studies have prompted translation of adult vascular progenitor therapy to clinical trials. To date, progenitor cells isolated from bone marrow and peripheral blood have been tested in the context of acute myocardial infarction and chronic ischemic cardiomyopathy, with moderate benefit. This therapeutic effect occurs despite a relatively small number of injected progenitor cells and short-term residence in the target zone. Thus, indirect benefits, such as paracrine factors released from these cells, have been suggested as significant contributors to therapeutic efficacy. Several additional vascular progenitors of endothelial, smooth muscle, mesenchymal, and cardiac origin have been identified that may contribute to vasculogenesis. Indeed, a unifying paradigm for the most effective cell therapy strategies to date appears to be robust support of angiogenesis. Here we discuss a number of progenitor cells that currently show potential as cardiovascular therapeutics, either singly or in combination. We look at emerging cell types and disease targets that may be exploited for therapeutic benefit and future strategies that may maximize clinical efficacy.

Nanoparticle coatings for enhanced capture of flowing cells in microtubes

Recently, a flow-based selectin-dependent method for the capture and enrichment of specific types of cells (CD34+ hematopoetic stem and progenitor cells and human leukemia HL60) from peripheral blood was demonstrated. However, these devices depend on a monolayer of selectin protein, which has been shown to have a maximum binding efficiency as a function of surface area. A novel surface coating of colloidal silica nanoparticles was designed that alters the surface roughness resulting in increased surface area. The nanoparticles were adhered using either an inorganic titanate resinous coating or an organic polymer of poly-L-lysine. Using Alexa Fluor 647 conjugated P-selectin, an increase in protein adsorption of up to 35% when compared to control was observed. During perfusion experiments using P-selectin-coated microtubes, we observed increased cell capture and greatly decreased rolling velocity at equivalent protein concentration compared to nonparticle control. Atomic force microscopy showed increased surface roughness consistent with the nanoparticle mean diameter, suggesting a monolayer of particles. These results support the coating's potential to improve existing cell capture implantable devices for a variety of therapeutic and scientific uses.

In vivo tissue engineering of heart valves: evolution of a novel concept

Current tissue-engineering principles of heart valves include tissue- or stem cell-derived cells with subsequent in vitro incubation on various scaffolds prior to implantation. Limitations of this approach include a long in vitro culture, an accompanied risk of infection and sophisticated, cost-intensive infrastructures. An 'off-the-shelf' heart valve with in vivo endothelialization and tissue-regeneration potential would overcome these limitations. Additionally, the development of a heart valve with growth potential would be a huge improvement for pediatric patients. This article discusses different starter matrices, homing and immobilization strategies of host cells and masking approaches of inflammatory structures for in vivo surface and tissue engineering of heart valves. Novel concepts will be presented based on highly specific DNA-aptamers immobilized on the heart valve surface as capture molecules for endothelial progenitor cells circulating in the bloodstream.

Delivery of apoptotic signal to rolling cancer cells: a novel biomimetic technique using immobilized TRAIL and E-selectin

The survival rate for patients with metastases versus localized cancer is dramatically reduced, with most deaths being associated with the formation of secondary tumors. Circulating cancer cells interact with the endothelial lining of the vasculature via a series of adhesive interactions that facilitate tethering and firm adhesion of cancer cells in the initial steps of metastasis. TNF-related apoptosis-inducing ligand (TRAIL) holds promise as a tumor-specific cancer therapeutic, by inducing a death signal by apoptosis via the caspase pathway. In this study, we exploit this phenomenon to deliver a receptor-mediated apoptosis signal to leukemic cells adhesively rolling along a TRAIL and selectin-bearing surface. Results show that cancer cells exhibit selectin-mediated rolling in capillary flow chambers, and that the rolling velocities can be controlled by varying the selectin and selectin surface density and the applied shear stress. It was determined that a 1 h rolling exposure to a functionalized TRAIL and E-selectin surface was sufficient to kill 30% of captured cells compared to static conditions in which 4 h exposure was necessary to kill 30% of the cells. Thus, we conclude that rolling delivery is more effective than static exposure to a TRAIL immobilized surface. We have also verified that there is no significant effect of TRAIL on hematopoietic stem cells and other normal blood cells. This represents the first demonstration of a novel biomimetic method to capture metastatic cells from circulation and deliver an apoptotic signal.

Microcontact printing of P-selectin increases the rate of neutrophil recruitment under shear flow

The local variation of P-selectin expression on inflamed endothelial layers affects leukocyte recruitment in vivo. As an initial study of the spatially heterogeneous presentation of P-selectin in vitro, the influence of microcontact printing (microCP) of P-selectin on a planar surface in neutrophil recruitment was investigated using a parallel-plate flow chamber. Microline patterned and nonpatterned P-selectin were prepared using PDMS, Poly(dimethylsiloxane) (PMDS) stamps and isolated neutrophils perfused over the surface to quantify the level of neutrophil recruitment. We first found a significant increase in cell rolling flux and a decrease in cell rolling velocity on the microcontact printed P-selectin-surfaces compared with a randomly adsorbed P-selectin-surface. However, the increase in rolling adhesion under shear on the surfaces prepared by microCP was not proportional to the number of functional sites of P-selectin transferred using immunofluorescent labeling. Interestingly, the relative immunofluorescent intensities of the nonfunctional regions of microcontact printed P-selectin-surfaces were substantially lower than that that of randomly adsorbed P-selectin. Taken together, these data indicate that the microCP of selectin increases the transfer rate of the adhesion molecule on a surface in the functionally correct orientation and, consequently, improves the recruitment of leukocytes to the selectin surface under flow. It is concluded that microCP may be a more general technique to control protein orientation on a substrate.

Direct magnetic separation of immune cells from whole blood using bacterial magnetic particles displaying protein G

Direct separation of target cells from mixed population, such as peripheral blood, umbilical cord blood, and bone marrow, is an essential technique for various therapeutic or diagnosis applications. In this study, novel particles were fabricated, and direct magnetic separation of immune cells from whole blood using such particles was performed. The magnetotactic bacterium Magnetospirillum magneticum AMB-1 synthesizes intracellular bacterial magnetic particles (BacMPs), and protein G was expressed on the surface of the BacMPs by gene fusion techniques with anchor proteins isolated from BacMP membrane. The BacMPs displaying protein G (protein G-BacMPs) had high binding capabilities to a wide range of antibody types, and various versions of protein G-BacMPs binding with different anti-CD monoclonal antibodies were constructed. Consequently, direct magnetic separation of immune cells from whole blood using protein G-BacMPs binding with anti-CD monoclonal antibodies was demonstrated. B lymphocytes (CD19+ cells) or T lymphocytes (CD3+ cells), which represent less than 0.05% in whole blood cells, were successfully separated at a purity level of more than 96%. This level was superior to that from previous reports using other magnetic separation approaches. The results of this study demonstrate the utility of protein G-BacMP and this particle may become a powerful tool for various therapeutic or diagnosis applications.

Enrichment of cancer cells using aptamers immobilized on a microfluidic channel

This work describes the development and investigation of an aptamer modified microfluidic device that captures rare cells to achieve a rapid assay without pretreatment of cells. To accomplish this, aptamers are first immobilized on the surface of a poly(dimethylsiloxane) microchannel, followed by pumping a mixture of cells through the device. This process permits the use of optical microscopy to measure the cell-surface density from which we calculate the percentage of cells captured as a function of cell and aptamer concentration, flow velocity, and incubation time. This aptamer-based device was demonstrated to capture target cells with >97% purity and >80% efficiency. Since the cell capture assay is completed within minutes and requires no pretreatment of cells, the device promises to play a key role in the early detection and diagnosis of cancer where rare diseased cells can first be enriched and then captured for detection.

Separation of SSEA-4 and TRA-1-60 labelled undifferentiated human embryonic stem cells from a heterogeneous cell population using magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS)

A major concern in human embryonic stem cell (hESC)-derived cell replacement therapy is the risk of tumorigenesis from undifferentiated hESCs residing in the population of hESC-derived cells. Separation of these undifferentiated hESCs from the differentiated derivatives using cell sorting methods may be a plausible approach in overcoming this problem. We therefore explored magnetic activated cell sorting (MACS) and fluorescence activated cell sorting (FACS) to separate labelled undifferentiated hESCs from a heterogeneous population of hESCs and hepatocellular carcinoma cells (HepG2) deliberately mixed respectively at different ratios (10:90, 20:80, 30:70, 40:60 and 50:50) to mimic a standard in vitro differentiation protocol, instead of using a hESC-differentiated cell population, so that we could be sure of the actual number of cells separated. HES-3 and HES-4 cells were labelled in separate experiments for the stem cell markers SSEA-4 and TRA-1-60 using primary antibodies. Anti-PE magnetic microbeads that recognize the PE-conjugated SSEA-4 labelled hESCs was added to the heterogeneous cell mixture and passed through the MACS column. The cells that passed through the column ('flow-through' fraction) and those retained ('labelled' fraction') were subsequently analysed using FACS. The maximum efficacy of hESCs retention using MACS was 81.0 +/- 2.9% (HES-3) and 83.6 +/- 4.2% (HES-4). Using FACS, all the undifferentiated hESCs labelled with the two cell-surface markers could be removed by selective gating. Both hESCs and HepG2 cells in the 'flow-through' fraction following MACS separation were viable in culture whereas by FACS separation only the HepG2 cells were viable. FACS efficiently helps to eliminate the undifferentiated hESCs based on their cell-surface antigens expressed.

P-selectin-coated microtube for the purification of CD45+ hematopoietic cells directly from human peripheral blood

Purified samples of CD45+ hematopoietic cells are a prerequisite for chimerism analysis in transplantation therapies, and are useful in various research and clinical settings such as functional and molecular analysis or disease diagnosis. Recently, we have established a flow-based adhesion molecule-dependent process for the purification of these cells from human bone marrow. However, for practical purposes, it is desirable to apply this approach to process small volumes of human blood. CD45+ cell purities were >94% when PBMNCs and plasma depleted blood were perfused through P-selectin coated microtubes. However, P-selectin surface failed to capture CD45+ cells when fresh blood prior to washing was perfused. The process requires a pre-step of plasma removal which otherwise inhibits interactions of cell surface PSGL-1 with immobilized P-selectin due to the presence of soluble PSGL-1 in plasma. We conclude that P-selectin can be used in a compact flow device to isolate and purify CD45+ cells directly from human peripheral blood. The process is simple, rapid, cost effective and represents a physiologic approach to the capture and purification of CD45+ MNCs from peripheral blood.

Purification of CD45+ hematopoietic cells directly from human bone marrow using a flow-based P-selectin-coated microtube

Recently, a flow-based selectin-dependent method for capture and enrichment of specific type blood cells (CD34+ hematopoietic stem and progenitor cells) from bone marrow and peripheral blood has been described. Using a similar approach, here we show isolation of CD45+ blood cells directly from human bone marrow to a high purity (90%-97%). The process mimics a ubiquitous mechanism of cell trafficking in the body for the recruitment of neutrophils during inflammation. The method is straightforward, rapid, and may represent a practical alternative to CD45+ cell enrichment procedures required for chimerism analysis following allogenic stem-cell transplantation.