A variety of filters assays have been described to enrich circulating tumor cells (CTC) based on differences in physical characteristics of blood cells and CTC. to the size of EpCAM+CK+CD45?DNA+ CTC from patients with metastatic breast colorectal and prostate cancer. The 8 μm track-etched filter and the 5 μm microsieve had the best performance on MDA-231 PC3-9 and SKBR-3 cells enriching >80% of cells from whole blood. TEM grids had poor recovery of ～25%. Median diameter of cell lines ranged from 10.9-19.0 μm compared to 13.1 10.7 and 11.0 μm for breast prostate and colorectal CTC respectively. The 11.4 μm COLO-320 cell line had the lowest recovery of 17%. The ideal filter for CTC enrichment is constructed of a stiff flat material is usually inert to blood cells has at least 100 0 regularly spaced 5 μm pores for 1 ml of blood with a ≤10% porosity. While cell size is an important factor in determining recovery other factors must be involved as well. To evaluate a filtration procedure cell lines with a median size of 11-13 μm should be used to challenge the system. Introduction Circulating tumor cells (CTC) predict survival in patients with various metastatic cancers [1]-[8]. Enumeration of these CTC is a great technological challenge [9]. The lack of a positive control complicates assay development as the number of CTC in patient samples is usually unknown. No detection of CTC in healthy controls and relatively high recovery of tumor cells spiked into blood DTP348 samples are frequently used to gauge the performance of a given assay yet without proof that this frequency of these cells relates to survival it remains uncertain whether “true” CTC are enumerated. CTC are extremely rare cells typically 1-10 CTC among ～6×106 leukocytes ～2×108 platelets and ～4×109 erythrocytes per ml of blood [10]. This implies that any assay for their enumeration must be able to handle a large number of cells. Examination of a large number of immunofluorescently labeled cells increases the influence of non-specific binding which is usually inherent to immunofluorescence staining of cells. A non-specific background of 0.01% may be acceptable for routine immunophenotyping but for rare event detection DTP348 this would result in detection of 100 “CTC” after analysis of 1 1 0 0 leukocytes. To increase the specificity of CTC detection the number of analyzed cells needs to be reduced. While some assays only perform an erythrocyte lysis DTP348 or density separation [11]-[15] other assays achieve enhanced enrichment by leukocyte depletion [16] [17] size based filtration [18]-[24] or antibody based enrichment [25]-[31]. Each approach has its drawback. CTC could be lost due to the effect of erythrocyte lysis brokers and CTC could be lost by employing a density separation as the range of densities of CTC is usually unknown. Size based filtration is antigen expression impartial but will miss smaller CTC and tumor micro particles both of which are clinically relevant [32]. Antibody based methods are insensitive to variations in size but don’t enrich tumor cells that have low expression of the target antigen. The epithelial cell adhesion molecule (EpCAM) is frequently used for CTC enrichment as it has little or no expression on leukocytes and is expressed by the CTC in most patients [12] [32] [33]. Filtration was recently proposed for CTC enrichment [18]-[24] and previously we have reported around the filtration parameters important for enrichment of CTC from whole blood by filtration [34]. In this study we investigate the properties of the ideal DTP348 Mouse monoclonal to CD4.CD4 is a co-receptor involved in immune response (co-receptor activity in binding to MHC class II molecules) and HIV infection (CD4 is primary receptor for HIV-1 surface glycoprotein gp120). CD4 regulates T-cell activation, T/B-cell adhesion, T-cell diferentiation, T-cell selection and signal transduction. filter for CTC recovery such as pore size spacing between pores number DTP348 of pores filter thickness and filter surface material. Filtration parameters such as dilution fixation DTP348 en flow rate are kept constant. In addition the size distribution of CTC in metastatic breast prostate and colorectal cancer and a variety of cell lines was decided to aid in choosing a cell line that can be used as an adequate model for optimization of filtration based CTC assays. Materials and Methods Blood Samples Healthy volunteers aged 20-55 provided informed consent prior to donating blood. The study protocol was approved by the METC Twente ethics committee. Healthy was defined as no prior history of cancer or blood.