Clinical applications of laser scanning cytometry

Cytomics--new technologies: towards a human cytome project

BACKGROUND

Molecular cell systems research (cytomics) aims at the understanding of the molecular architecture and functionality of cell systems (cytomes) by single-cell analysis in combination with exhaustive bioinformatic knowledge extraction. In this way, loss of information as a consequence of molecular averaging by cell or tissue homogenisation is avoided.

PROGRESS

The cytomics concept has been significantly advanced by a multitude of current developments. Amongst them are confocal and laser scanning microscopy, multiphoton fluorescence excitation, spectral imaging, fluorescence resonance energy transfer (FRET), fast imaging in flow, optical stretching in flow, and miniaturised flow and image cytometry within laboratories on a chip or laser microdissection, as well as the use of bead arrays. In addition, biomolecular analysis techniques like tyramide signal amplification, single-cell polymerase chain reaction (PCR), and the labelling of biomolecules by quantum dots, magnetic nanobeads, or aptamers open new horizons of sensitivity and molecular specificity at the single-cell level. Data sieving or data mining of the vast amounts of collected multiparameter data for exhaustive multilevel bioinformatic knowledge extraction avoids the inadvertent loss of information from unknown molecular relations being inaccessible to an a priori hypothesis.

CHALLENGE

It seems important to address the challenge of a human cytome project using hypothesis-driven molecular information collection from disease associated cell systems, supplemented by systematic and exhaustive knowledge extraction. This will allow the description of the molecular setup of normal and abnormal cell systems within a relational knowledge system, permitting the standardised discrimination of abnormal cell states in disease. As one of the consequences, individualised predictions of further disease course in patients (predictive medicine by cytomics) by characteristic discriminatory data patterns will permit individualised therapies, identification of new pharmaceutical targets, and establishment of a standardised framework of relevant molecular alterations in disease. This special issue of Cytometry, on new technologies in cytomics, focuses on prominent examples of this presently fast-moving scientific field, and represents one of the preconditions for the formulation of a human cytome project.

Scanning fluorescent microscopy analysis is applicable for absolute and relative cell frequency determinations

BACKGROUND

Flow cytometry (FCM) and laser scanning cytometry (LSC) are the routine techniques for fluorescent cell analysis. Recently, we developed a scanning fluorescent microscopy (SFM) technique. This study compares SFM to LSC (two slide-based cytometry, SBC, techniques) and FCM, in experimental and clinical settings.

METHODS

For the relative cell-frequency determinations, HT29 colorectal cancer cells and Ficoll separated blood mononuclear cells (FSBMCs) were serially diluted (from 1:1 to 1:1,000) and measured by each of the three techniques. For the absolute cell number determinations (only for SBC) FSBMCs were smeared on slides, then HT29 cells were placed on the slide with a micromanipulator (5-50 cells). Tumor cells circulating in the peripheral blood were isolated by magnetic separation from clinical blood samples of colorectal cancer patients. All samples were double-stained by CD45 ECD and CAM5.2 FITC antibodies. For slides, TOTO-3 and Hoechst 33258 DNA dyes were applied as nuclear counter staining.

RESULTS

In the relative cell frequency determinations, the correlations between the calculated value and measured values by SFM, LSC, and FCM were r(2) = 0.79, 0.62, and 0.84, respectively (for all P < 0.01). In the absolute cell frequency determinations, SFM and LSC correlated to a high degree (r(2) = 0.97; P < 0.01).

CONCLUSIONS

SFM proved to be a reliable alternative method, providing results comparable to LSC and FCM. SBC proved to be more suitable for rare-cell detection than FCM. SFM with digital slides may prove an acceptable adaptation of conventional fluorescent microscopes in order to perform rare-cell detection.

Scanning fluorescent microscopy is an alternative for quantitative fluorescent cell analysis

BACKGROUND

Fluorescent measurements on cells are performed today with FCM and laser scanning cytometry. The scientific community dealing with quantitative cell analysis would benefit from the development of a new digital multichannel and virtual microscopy based scanning fluorescent microscopy technology and from its evaluation on routine standardized fluorescent beads and clinical specimens.

METHODS

We applied a commercial motorized fluorescent microscope system. The scanning was done at 20 x (0.5 NA) magnification, on three channels (Rhodamine, FITC, Hoechst). The SFM (scanning fluorescent microscopy) software included the following features: scanning area, exposure time, and channel definition, autofocused scanning, densitometric and morphometric cellular feature determination, gating on scatterplots and frequency histograms, and preparation of galleries of the gated cells. For the calibration and standardization Immuno-Brite beads were used.

RESULTS

With application of shading compensation, the CV of fluorescence of the beads decreased from 24.3% to 3.9%. Standard JPEG image compression until 1:150 resulted in no significant change. The change of focus influenced the CV significantly only after +/-5 microm error.

CONCLUSIONS

SFM is a valuable method for the evaluation of fluorescently labeled cells.

Quantitative histology by multicolor slide-based cytometry

BACKGROUND

In lymphatic organs, the quantitative analysis of the spatial distribution of leukocytes by tissue cytometry would give relevant information about alterations during diseases (leukemia, HIV, AIDS) and their therapeutic regimen, as well as in experimental settings.

METHODS

We have developed a semiautomated analysis method for laser scanning cytometry (LSC) termed "multiple thresholding," which is suitable for archived or fresh biopsy material of human lymph nodes and tonsils. Sections are stained with PI for nuclear DNA and up to four antigens using direct or indirect immunofluorescence staining. Measurement is triggered on DNA-fluorescence (argon laser, Ar) or on specific cell labeling. Due to the heterogeneity of cell density, measurements are performed repeatedly at different threshold levels (low threshold: regions of low cellular density, germinal center; high threshold: dense regions, mantle zone). Data are acquired by single- (Ar) or dual-laser excitation (Ar-HeNe) in order to analyze single- (FITC) up to four-color (FITC/PE/PECy5/APC) stained specimen.

RESULTS

Percentage and cellular density of cell-subsets is quantified in different microanatomical regions of the specimen. These data were highly correlated with manual scoring of identical specimens (r(2) = 0.96, P < 0.0001). With LSC, semiautomated operator-independent immunophenotyping in tissue sections of lymphatic organs with up to three antibodies simultaneously is possible.

CONCLUSIONS

We expect this tissue cytometric approach to yield new insight into processes during diseases and help to quantify the success of therapeutic interventions.

Distinguishing modes of cell death using the ImageStream® multispectral imaging flow cytometer

BACKGROUND

Here we demonstrate the ability of the ImageStream 100 Multispectral Imaging Cytometer to discriminate between live, necrotic, and early and late apoptotic cells, using unique combinations of photometric and morphometric features.

METHODS

Live, necrotic, and early and late apoptotic cells were prepared and analyzed by immunofluorescence microscopy, conventional flow cytometry, and imaging flow cytometry, both as single populations and as a heterogeneous mixture of cells.

RESULTS

Live (annexin V(-), 7-AAD(-)) and early apoptotic (annexin V(+), 7-AAD(-)) cells were readily identifiable using either conventional or ImageStream based flow cytometric methods. However, inspection of multispectral images of cells demonstrated that the annexin V(+), 7-AAD(+) population contained both necrotic and late-stage apoptotic cells. Although these cells could not be distinguished using conventional flow cytometric techniques, they were separable using unique combinations of photometric and morphometric measures available using ImageStream technologies.

CONCLUSIONS

Using multispectral imagery, morphologically distinct cell populations can be distinguished using features not available with conventional flow cytometers. In particular, the ability to couple morphometric with photometric measures makes it possible to distinguish live cells from cells in the early phases of apoptosis, as well as late apoptotic cells from necrotic cells.

Diagnostic and prognostic use of DNA image cytometry in cervical squamous intraepithelial lesions and invasive carcinoma

In the fight against cervical malignancy and its precursors, several adjuvant diagnostic methods have been proposed to increase the accuracy of cytologic and histologic diagnoses. Because chromosomal aneuploidy has been accepted as an early key event in tumorigenesis caused by genetic instability, the cytometric equivalent of chromosomal aneuploidy detected by DNA image cytometry (DNA-ICM) may serve as a marker of neoplasia. During the last decade, the appearance of a new generation of hardware with high processing and storage capacities, together with the development of appropriate software, has facilitated the development of high-performance DNA-ICM systems. International consensus on the clinical application of DNA-ICM has been reached. According to the statements of Task Force 8 of the International Consensus Conference on the Fight Against Cervical Cancer, indications for DNA-ICM include the identification of prospectively malignant cells in squamous intraepithelial lesions (SILs) and atypical squamous cells of undetermined significance (ASCUS). The European Society of Analytical Cellular Pathology consensus reports on DNA-ICM have provided standardized technical details on performance, terms, and algorithms for diagnostic data interpretation and quality-assurance procedures. Increasing biologic evidence and clinical data have confirmed the utility of DNA-ICM as an adjuvant method suitable for determining the diagnosis and prognosis of cervical intraepithelial lesions and invasive carcinoma. Patients with ASCUS and low-grade SIL diagnoses that reveal DNA euploidy may return for normal screening intervals, whereas the detection of DNA aneuploidy indicates that these lesions should be removed. Formerly a research tool, today, standardized DNA-ICM has become a useful and low-cost laboratory method to establish objectively and reproducibly an early diagnosis of prospectively progressive cervical intraepithelial lesions at a high-quality level. DNA-ICM may further contribute to the monitoring of treatment in patients with invasive cervical malignancies.

Comparison of flow cytometry and laser scanning cytometry for the analysis of CD34+hematopoietic stem cells

BACKGROUND

Characterization of hematopoietic stem cells (HSCs) by laser scanning cytometry (LSC) was compared with conventional flow cytometry (FCM). The method was evaluated for application in the development of advanced cell culture substrates that were supposed to support the ex vivo expansion of HSC. For this purpose, adherent HSCs were grown in culture on thin polymer films coated with reconstituted collagen I fibrils and subsequently analyzed by LSC.

METHODS

CD34+ HSCs were isolated from cord blood by immunomagnetic separation and cultivated on polymer films coated with reconstituted collagen I fibrils. Cell surface antigens (CD34, CD29) were stained with antibodies, and nuclei were labeled with a DNA stain (TO-PRO-3 iodide) that does not interfere with the fluorochromes of the antibodies. Fluorescence intensity of the adherent cells was measured by means of LSC. Before and after in vitro expansion for time periods of up to 7 days, suspension cells were analyzed with LSC and FCM.

RESULTS

LSC-based analysis enabled reliable quantification of CD34+ cells with bright antigen expression before cell culture. At this stage, LSC and FCM data for CD34 expression at given HSC samples largely coincided. After in vitro expansion, LSC data deviated from FCM data for cells with dim CD34 antigen expression, whereas the fluorescence intensity of the CD29 antigen remained comparable. The deviation between LSC and FCM data for CD34dim was attributed to the better resolution of weak fluorescence by FCM. Based on the preceding evaluation of the method, LSC analysis could be applied to characterize HSCs cultivated on collagen I-coated polymer films without detachment of the cells from the substrate.

CONCLUSIONS

LSC-based analysis allows for the automated evaluation of adherent HSCs. Although resolution of weakly expressed antigens can be achieved more precisely with FCM, the method provides a valuable tool to study interactions of HSCs with bioartificial substrates.

Immunophenotypic analysis of human articular chondrocytes: Changes in surface markers associated with cell expansion in monolayer culture

Cartilage tissue engineering relies on in vitro expansion of primary chondrocytes. Monolayer is the chosen culture model for chondrocyte expansion because in this system the proliferative capacity of chondrocytes is substantially higher compared to non-adherent systems. However, human articular chondrocytes (HACs) cultured as monolayers undergo changes in phenotype and gene expression known as "dedifferentiation." To gain a better understanding of the cellular mechanisms involved in the dedifferentiation process, our research focused on the characterization of the surface molecule phenotype of HACs in monolayer culture. Adult HACs were isolated by enzymatic digestion of cartilage samples obtained post-mortem. HACs cultured in monolayer for different time periods were analyzed by flow cytometry for the expression of cell surface markers with a panel of 52 antibodies. Our results show that HACs express surface molecules belonging to different categories: integrins and other adhesion molecules (CD49a, CD49b, CD49c, CD49e, CD49f, CD51/61, CD54, CD106, CD166, CD58, CD44), tetraspanins (CD9, CD63, CD81, CD82, CD151), receptors (CD105, CD119, CD130, CD140a, CD221, CD95, CD120a, CD71, CD14), ectoenzymes (CD10, CD26), and other surface molecules (CD90, CD99). Moreover, differential expression of certain markers in monolayer culture was identified. Up-regulation of markers on HACs regarded as distinctive for mesenchymal stem cells (CD10, CD90, CD105, CD166) during monolayer culture suggested that dedifferentiation leads to reversion to a primitive phenotype. This study contributes to the definition of HAC phenotype, and provides new potential markers to characterize chondrocyte differentiation stage in the context of tissue engineering applications.

Eosinophilia in nasal polyposis: its objective quantification and clinical relevance

BACKGROUND

Eosinophilia within nasal polyps is often taken as a criterion for adjuvant medical treatment postoperatively such as topical steroids.

OBJECTIVE

This study was performed in order to validate a new technique for objective quantification of eosinophilia by using laser scanning cytometry (LSC), to compare these results with manual scoring and routine histopathology, and to correlate them with the history of allergy or recurrence.

METHODS

LSC was used for semi-automated analysis of single-cell preparations from representative ethmoidal polyps obtained during routine paranasal sinus surgery (n=41). This microscope-based instrument scans the cells after immobilization of cells on a glass slide and after triple staining of cytokeratin, eosinophilic granula, and DNA. The location of each cell is stored with the fluorescence data. Therefore, the morphology of every cell can be documented by re-staining with haemotoxylin and eosin and re-localization on the slide. Subsequently, slides were subjected to manual scoring. The remaining polyps were analysed by routine histopathology.

RESULTS

Data from LSC and manual scoring showed good correlation (r=0.81, P<0.001), whereas there were discrepancies with histopathology. Eosinophilia scored by LSC and histopathology was neither correlated with the history of allergy nor with recurrence as determined by Fisher's exact test independent of the definition of eosinophilia (> or =2%, > or =3%, or > or =5% of all cells).

CONCLUSION

Scoring eosinophilia by LSC in comparison with histopathology does not contribute to a more reliable basis for adjuvant medical therapy in nasal polyposis. Instead, functional parameters (cytokine production, apoptosis) may serve better.

Chromosomal aberrations accumulate in polyploid cells of high-grade squamous intraepithelial lesions (HSIL)

Persistant infection with human papillomavirus (HPV) of the uterine cervix is related with cytological atypia (SIL), the oncogenic potential of which is unclear in a given time point of monitoring. HPV-induced genetic instability result in polyploidization as well as in low frequency random chromosome aberrations in squamous cells. In the present work we analyzed whether highly polyploid/aneuploid cells reflect genomic changes at the chromosomal level. 13 samples with the cytological diagnosis of HSIL were analyzed for HPV type and nuclear DNA content measured by laser scanning cytometry (LSC). Hyperdiploid cells with >5c and with >9c DNA content were further analyzed for numerical aberrations of the chromosomes 3 and 17 by fluorescence in situ hybridization (FISH) following repositioning. Cells with >5c DNA content were found more frequently than cells with >9c DNA content (5-98 and 1-44 cells, respectively). The FISH analysis demonstrated frequent polysomies, however, the rate of aneusomy (other than 2, 4, 8 or 16 chromosome copies) was significantly higher in cells with >9c DNA content than in cells with >5c DNA content or the normal diploid cells. The imbalance of chromosome 3 and 17 copy number was also increased in cells with >9c DNA content. Moreover, in three out of the 13 analyzed HSIL samples, recurrent abnormal chromosome 3/17 ratio was demonstrated in a significant part of the cells, indicating a common origin of these cells. Highly polyploid/aneuploid cells in HSIL accumulate cytogenetic aberrations detectable by FISH analysis. These cells may reflect early changes with tumorigenic potential in a very concentrated fashion.

A suitable method for identifying cell aggregates in laser scanning cytometry listmode data for analyzing disaggregated cell suspensions obtained from human cancers

BACKGROUND

The presence of cell aggregates in cell suspensions obtained from human solid tumors can interfere with the measurement of cell DNA content of cell singlets, and can confound multiparameter analysis of other measurements on the same cells. Flow cytometric corrections for cell aggregates based on signal pulse shape have not proven to be reliable. Mathematical models have been developed to correct for cell aggregates in binned DNA histogram data, but they are not suitable for the correction of correlated non-DNA measurements obtained on the same cells.

METHODS

A total of 21 samples representing a variety of normal and malignant human cell types, including normal lymphocytes, normal sputum, human breast cancer cell lines, and mechanically disaggregated cell suspensions from primary breast cancers and nonsmall cell lung cancers, were studied by laser scanning cytometry (LSC) using the CompuCyte laser scanning cytometer (Cambridge, MA). Nuclear area, nuclear perimeter, and an LSC-based cell texture parameter were measured on approximately 400 cells in each sample, using an air-cooled, violet laser emitting at a wavelength of 405 nm for DAPI excitation, and each cell was classified as a singlet or aggregate by its appearance under direct observation. A "saddle function" provided by CompuCyte was used, together with an algorithm based on the measurements of nuclear area, perimeter, and cell texture (the APT algorithm), to identify cell aggregates and exclude them from the listmode data file.

RESULTS

Proportions of cell aggregates in the uncorrected samples ranging from 6 to 56% (mean, 20%) were reduced to proportions ranging from 0 to 7% (mean, 2.4%) after correction. The discriminant function was "tuned" to maintain both average cell singlet purity and average cell singlet yield at >70% over a broad range of cell DNA contents.

CONCLUSIONS

A combined approach to cell aggregate detection, which utilizes both the saddle function and the APT algorithm, produces list mode data files that exclude >80% of cell aggregates from samples of disaggregated cell suspensions of human tumors and other sources of clinical material. Such data files are suitable for multiparameter analysis.

Microscopy-based multicolor tissue cytometry at the single-cell level

Cytomics is a novel perspective from which to look at life. As with genomics and proteomics before, this discipline requires novel and innovative techniques and technologies to focus on its substrate of research--the cytome. With cytomics being the discipline that analyzes cellular systems and their interdependencies, advanced microscopy represents a key technology in cytomics research. Yet, conventional microscopy-based investigations, i.e., "look and conclude" analyses, do not meet the major cytomics criteria of 1) relating multiple parameters to each other, 2) within large populations of cells, 3) on a single-cell basis, and 4) in a quantitative and observer-independent manner. However, emerging improvements in the fields of fluorophore technology, sensitive fluorescence detection devices, and sophisticated image analysis procedures, are important and necessary steps into the cytomics era. Tissue represents an important class of cytomes, hence tissue cytometry--on the single cell level--can be expected to become an important cytomics technology. In this report, the techniques and technologies of microscopy-based multicolor tissue cytometry (MMTC) are outlined and applications are discussed, including the phenotypic characterization of tissue infiltrating leukocytes, in situ quantification of proliferation markers and tumor suppressors, and in situ quantification of apoptosis.

Slide-based cytometry for predicting malignancy in solid salivary gland tumors by fine needle aspirate biopsies

BACKGROUND

To minimize hospitalization and morbidity for a patient with a solid tumor of a salivary gland, malignancy must be confirmed or excluded as soon as possible. This information cannot be obtained preoperatively by existing standard procedures. Minimal-invasive approaches with adequate diagnostic analysis represent a promising precondition for optimized therapy.

METHODS

For fine needle aspirate biopsies (FNABs), laser scanning cytometry (LSC) offers a semi-automated slide-based technology for objective and quantitative analysis. We have established an assay for FNABs from salivary gland tumors. FNAB cells were stained for cytokeratin and DNA followed by LSC analysis. The cells were subsequently HE-stained and were relocalized on the slide. The LSC analysis quantitatively determines the DNA index (DI) of the tumor cells taking leukocytes as internal DNA diploid standard. Histograms with 0.95 < DI < 1.05 and 1.9 <DI <2.1 were defined as DNA euploid, whereas any other DI was defined as DNA aneuploid. The percentage of cytokeratin positive cells with DI > 2.5 (i.e., 5c exceeding rate, 5cER) was calculated. Samples with DNA aneuploid peaks or with 5cER > 5% were classified as malignant. Routine histopathology was performed as a control.

RESULTS

FNABs from 51 solid salivary gland tumors (41 parotid gland, six submandibular, four parapharyngeal) were analyzed with this assay. Eleven of 14 malignant tumors were DNA aneuploid by LSC analysis. All benign tumors showed diploid DNA content. The positive predictive value for malignancy was 1.0, the negative predictive value was 0.93, the correlation with routine histopathology was highly significant (p = 7.6 x 10(-9), Fisher's exact test). The calculated specificity of LSC analysis was 1.0 and the sensitivity was 0.79.

CONCLUSIONS

This pilot study demonstrates the validity of slide-based cytometry for the preoperative prediction of malignancy in solid tumors being inaccessible for incision biopsy but suitable for FNABs such as those of the parotid gland.

Cytomics in predictive medicine

Patient-specific, disease-course predictions with >95% or >99% accuracy during therapy would be highly valuable for everyday medicine. If these predictors were available, disease aggravation or progression, frequently accompanied by irreversible tissue damage or therapeutic side effects, could then potentially be avoided by early preventive therapy. The molecular analysis of heterogeneous cellular systems (cytomics) by cytometry in conjunction with pattern-oriented bioinformatic analysis of the multiparametric cytometric and other data provides a promising approach to individualized or personalized medical treatment or disease management. As a consequence, better patient care and new forms of inductive scientific hypothesis development based on the interpretation of predictive data patterns are at reach.

Automated subcellular localization and quantification of protein expression in tissue microarrays

The recent development of tissue microarrays-composed of hundreds of tissue sections from different tumors arrayed on a single glass slide-facilitates rapid evaluation of large-scale outcome studies. Realization of this potential depends on the ability to rapidly and precisely quantify the protein expression within each tissue spot. We have developed a set of algorithms that allow the rapid, automated, continuous and quantitative analysis of tissue microarrays, including the separation of tumor from stromal elements and the sub-cellular localization of signals. Validation studies using estrogen receptor in breast carcinoma show that automated analysis matches or exceeds the results of conventional pathologist-based scoring. Automated analysis and sub-cellular localization of beta-catenin in colon cancer identifies two novel, prognostically significant tumor subsets, not detected by traditional pathologist-based scoring. Development of automated analysis technology empowers tissue microarrays for use in discovery-type experiments (more typical of cDNA microarrays), with the added advantage of inclusion of long-term demographic and patient outcome information.

Near-infrared dyes for six-color immunophenotyping by laser scanning cytometry

BACKGROUND

To adequately analyze the complexity of the immune system and reduce the required sample volume for immunophenotyping in general, more measurable colors for the discrimination of leukocyte subsets are necessary. Immunophenotyping by the laser scanning cytometer (LSC), a slide-based cytometric technology, combines cell detection based on multiple colors with their subsequent visualization without the need for physical cell sorting. In the present study, the filter setting of the LSC was adapted for the measurement of the far-red emitting dye cyanine 7 (Cy7), thereby increasing the number of measurable commercially available fluorochromes.

METHODS

The optical filters of the LSC were replaced-photomultiplier (PMT) 3/allophycocyanin (APC): 740-nm dichroic long pass, and 670-/55-nm bandpass; PMT 4/Cy7: 810-/90-nm bandpass. Peripheral blood leukocytes were stained directly by fluorochrome-labeled antibodies or by indirect staining. The tandem dyes of Cy7 (phycoerythrin [PE]-Cy7, APC-Cy7) and the fluorochromes fluorescein isothiocyanate (FITC), PE, PE-Cy5, and APC were tested alone and in different combinations.

RESULTS

With the new filter combination and tandem fluorochromes, Cy7 was measurable at 488-nm (argon laser) or 633-nm (helium-neon laser) excitation. Resolution was in the range of FITC for PE-Cy7 but approximately 30% lower for APC-Cy7; spillover into the respective donor fluorochrome channel for both tandem dyes was prominent. A six-color panel for leukocyte subtyping was designed.

CONCLUSIONS

With this adaptation, it is possible to measure the tandem conjugates PE-Cy7 and APC-Cy7. This new setup opens the way for six-color immunophenotyping by LSC.