Multiparameter analysis and sorting of mammalian cells

Flow cytometry: retrospective, fundamentals and recent instrumentation

Flow cytometry is a complete technology given to biologists to study cellular populations with high precision. This technology elegantly combines sample dimension, data acquisition speed, precision and measurement multiplicity. Beyond the statistical aspect, flow cytometry offers the possibility to physically separate sub-populations. These performances come from the common endeavor of physicists, biophysicists, biologists and computer engineers, who succeeded, by providing new concepts, to bring flow cytometry to current maturity. The aim of this paper is to present a complete retrospective of the technique and remind flow cytometry fundamentals before focusing on recent commercial instrumentation.

Flow cytometry: retrospective, fundamentals and recent instrumentation

Flow cytometry is a complete technology given to biologists to study cellular populations with high precision. This technology elegantly combines sample dimension, data acquisition speed, precision and measurement multiplicity. Beyond the statistical aspect, flow cytometry offers the possibility to physically separate sub-populations. These performances come from the common endeavor of physicists, biophysicists, biologists and computer engineers, who succeeded, by providing new concepts, to bring flow cytometry to current maturity. The aim of this paper is to present a complete retrospective of the technique and remind flow cytometry fundamentals before focusing on recent commercial instrumentation.

Automatic cytometric device using multiple wavelength excitations

Precise identification of eosinophils, basophils, and specific subpopulations of blood cells (B lymphocytes) in an unconventional automatic hematology analyzer is demonstrated. Our specific apparatus mixes two excitation radiations by means of an acousto-optics tunable filter to properly control fluorescence emission of phycoerythrin cyanin 5 (PC5) conjugated to antibodies (anti-CD20 or anti-CRTH2) and Thiazole Orange. This way our analyzer combining techniques of hematology analysis and flow cytometry based on multiple fluorescence detection, drastically improves the signal to noise ratio and decreases the spectral overlaps impact coming from multiple fluorescence emissions.

Recent advances in the isolation of liver cells

The development of new and refined separation techniques--including FACS, FFE, CFE and isopyknic gradients--has had a profound impact on the ability of investigators to isolate specific cell types from the liver. Although some of these techniques, such as FFE, may be of limited preparative value, they are nonetheless important analytical tools that detect subtle differences among cell subpopulations. The isolation of highly purified preparations of liver cells in large yields requires the use of more conventional purification methods such as CFE and isopyknic centrifugation. Immunological approaches represent a key development for the isolation of specific liver cell types, especially when they are used in combination with other techniques. Excellent, reliable and relatively simple techniques now exist to isolate highly purified preparations of hepatocytes, cholangiocytes, KCs, SCs, FSC, myofibroblasts and pit cells. Additional work is necessary to refine techniques for the isolation of dendritic cells and lymphocytes.

The use of flow microfluorometry for pharmaceutical testing

The techniques and procedures of rapid flow microfluorometry (FMF) in the development and testing of pharmaceuticals can be useful in the following ways: (1) cell identification and use of more precise and accurate endpoints of cell viability in cytotoxicity screening assays; (2) faster methods for determining total cellular protein, diameter, and volume in fixed cells and lymphocytes obtained in clinical studies, and adjustment of dosing regimens may be made rapidly based on such analyses; (3) studies of cellular nucleic acid content, mitotic cell progression, and growth in drug-treated cell populations, and investigations conducted on whether a particular drug is acting on a sensitive cell population or whether its effects are consistent throughout a particular group of cells or tissues; (4) measurement of drug penetration, uptake, concentration, resistance, and cell cycle specificity in cells and tissues, and (5) automated scoring of chromosome number, ploidy, and aberrations in treated cells as additional evidence of toxic activity of pharmaceutical substances. The binding of drugs to cellular macromolecules and other structures can result in a multiplicity of effects on cell growth, metabolism, chromosome content, morphology, and neoplastic potential. The methods and results described in this review can be used individually and in combination, along with commonly used techniques. It is hoped that an integrated approach to basic cellular biology, pharmacology, physiology, genetics, and toxicology as applied to drug development and testing can be furthered through use of FMF. Caution must be exercised, however, in extrapolating results found in one study of chemotherapeutic efficacy to other circumstances of clinical practice, since interindividual differences in response are not abrogated by this new technology. The introduction of flow microfluorometry is likely to engender a significant delay in its validation by the Food and Drug Administration as a means of generating data suitable for support of approval of the pharmaceutical products and processes that it regulates. This is due to the complex theoretical considerations associated with FMF and the attendant need for instrument familiarization and training of Food and Drug Administration reviewers. As with any new technology, time must pass and further experimentation be conducted before a laboratory method can become a universally accepted, commercially useful, and viable technique.

A conjugate of adriamycin and monoclonal antibodies to Thy-1 antigen inhibits human neuroblastoma cells in vitro

Antibodies to the differentation antigen Thy-1 were linked via a dextran-hydrazide bridge to adriamycin. These monoclonal antibodies, which were previously prepared against first-trimester human fetal cells, reacted with several human brain tissue tumors such as neuroblastoma, glioma, and leiomyosarcoma through a common differentiation antigen, Thy-1. The conjugates were tested in vitro for their cytotoxic effects on a neuroblastoma cell line LA-N-I. The conjugate maintained its full drug and antibody activities. Moreover, the specific conjugate exhibited a higher efficacy in inhibition of RNA synthesis and was more cytotoxic than the nonspecific Ig-drug conjugate. Fluorescent microscopy showed that the specific conjugate was able to penetrate the cell membrane. Both the specific antibody and the drug were also observed to accumulate in the cell nucleus. Flow microfluorometric analysis of cellular DNA traverse showed that the specific antibody-drug conjugate caused a higher accumulation of neuroblastoma cells in stage G2 of the cell cycle than did the free drug, perhaps indicating a more efficient prevention of the progression of cells through mitosis.

Signal processing electronics for multiple electronic and optical measurements on cells

Processing electronics for flow cytometry applications requiring simultaneous or sequential analysis of multiple electrical and optically sensed signals has been developed. A maximum of six analog signals are input to the processor. A measurement mode selector determines what signals are to be analyzed and the initial timing sequence of sense gates for acquiring signal crest values. Processor signal-triggering and sense gate time delays are selectable. Logic coincidence-anticoincidence circuits determine constraints on incoming signals. Gated peak-sense and hold signals are routed to computer interface electronics for digitizing and are then displayed as frequency distribution histograms using an LSI-11 computer. Signals also are processed as single parameters, ratios, and gated single parameters for output to a multichannel pulse-height analyzer and cell sorting electronics. The functional features of the processor are described along with examples illustrating simultaneous and sequential analysis of cultured cells stained with fluorescent dyes.

Quantitation of cell concentration using the flow cytometer

A simple procedure has been developed to simultaneously measure cell concentration and analyze marker positive cell populations using the flow cytometer. Fluorescent latex particles of known concentration are added to the sample to be analyzed. Marker positive cells and fluorescent particles are then analyzed using flow cytometric methods. Since the particle concentration is known, the number of particles that have accumulated gives the exact volume of the sample analyzed. The concentration of total and marker positive cells that were analyzed then can be calculated. The method will be illustrated using single, dual, and triple laser excitation of cells stained for DNA content in combination with green or red fluorescent spheres. The usefulness of the procedure is demonstrated by counting cells from highly necrotic tumors where large amounts of debris are present.

High resolution optics combined with high spatial reproducibility in flow

Accurate sizing in flow using optical methods generally requires high resolution optics and specially designed flow systems. Flow systems developed by this group have following features: (a) double sheath configuration for optical index match, (b) no curved optical surface in the sensing area, (c) gradual hydrodynamic focusing over a long distance to minimize mechanical shearing, (d) precision spatial positioning of cells by reducing suspension fluid diameter to a cell diameter or less, (e) total thickness between outer surfaces of the flow chamber at the viewing area of 1.5 mm or less. Cells intersect a laser light beam focussed go circular as well as elliptical cross-sections or 1 micron or less in diameter. Cellular extinction is monitored during transit through the beam. Cell length is derived from the time for flight measurement and corrected for absolute values by continuous velocity reference using a second laser beam intersecting the cell stream at a predetermined distance. This second spot may be circular or elliptical, of a different polarization and/or frequency. Simultaneous fluorescence intensity and diameter measurements were performed on test particles using different optical geometries. The influence of the particle structure on fluorescence measurements is demonstrated where high resolution sizing is required at the same time.

Rapid cell cycle analysis by measurement of the radioactivity per cell in a narrow window in S phase (RCSi)

A new rapid method for the cell cycle analysis of asynchronously growing cells is presented. The new method is an alternative to the more time consuming and subjective fraction of labeled mitoses (FLM) method. Like the FLM method, all cells in the S phase of the cell cycle are marked by pulse labeling with a radioactive DNA precursor. The subsequent progress of the cohort of cells thus labeled is monitored through a narrow window in the cell cycle. The window is defined by a narrow range of DNA contents corresponding to cells in mid-S phase and is designated Si. The cellular DNA content is measured by flow cytometry and the cells in the window Si are selected by electronic cell sorting. The radioactivity per cell in Si (RCSi) is determined by liquid scintillation counting. The duration of S phase and of the total cycle and the dispersions therein are determined from the oscillation of the RCSi values with time. The complete cell cycle analysis can be accomplished in as little as 1 day following the collection of samples. Exponentially growing Chinese hamster ovary (CHO) cells were analyzed according to the RCSi method and the FLM method. It is demonstrated that the two techniques give essentially the same results.