Four-color multiparameter DNA flow cytometric method to study phenotypic intratumor heterogeneity in cervical cancer

Whole-transcriptome analysis of flow-sorted cervical cancer samples reveals that B cell expressed TCL1A is correlated with improved survival

Cervical cancer is typically well infiltrated by immune cells. Because of the intricate relationship between cancer cells and immune cells, we aimed to identify both cancer cell and immune cell expressed biomarkers. Using a novel approach, we isolated RNA from flow-sorted viable EpCAM⁺ tumor epithelial cells and CD45⁺ tumor-infiltrating immune cells obtained from squamous cell cervical cancer samples (n = 24). Total RNA was sequenced and differential gene expression analysis of the CD45⁺ immune cell fractions identified TCL1A as a novel marker for predicting improved survival (p = 0.007). This finding was validated using qRT-PCR (p = 0.005) and partially validated using immunohistochemistry (p = 0.083). Importantly, TCL1A was found to be expressed in a subpopulation of B cells (CD3⁻/CD19⁺/CD10⁺/CD34⁻) using multicolor immunofluorescence. A high TCL1A/CD20 (B cell) ratio, determined in total tumor samples from a separate patient cohort using qRT-PCR (n = 52), was also correlated with improved survival (p = 0.027). This is the first study demonstrating the prognostic value of separating tumor epithelial cells from tumor-infiltrating immune cells and determining their RNA expression profile for identifying putative cancer biomarkers. Our results suggest that intratumoral TCL1A⁺ B cells are important for controlling cervical cancer development.

Digital Sorting of Pure Cell Populations Enables Unambiguous Genetic Analysis of Heterogeneous Formalin-Fixed Paraffin-Embedded Tumors by Next Generation Sequencing

Precision medicine in oncology requires an accurate characterization of a tumor molecular profile for patient stratification. Though targeted deep sequencing is an effective tool to detect the presence of somatic sequence variants, a significant number of patient specimens do not meet the requirements needed for routine clinical application. Analysis is hindered by contamination of normal cells and inherent tumor heterogeneity, compounded with challenges of dealing with minute amounts of tissue and DNA damages common in formalin-fixed paraffin-embedded (FFPE) specimens. Here we present an innovative workflow using DEPArray™ system, a microchip-based digital sorter to achieve 100%-pure, homogenous subpopulations of cells from FFPE samples. Cells are distinguished by fluorescently labeled antibodies and DNA content. The ability to address tumor heterogeneity enables unambiguous determination of true-positive sequence variants, loss-of-heterozygosity as well as copy number variants. The proposed strategy overcomes the inherent trade-offs made between sensitivity and specificity in detecting genetic variants from a mixed population, thus rescuing for analysis even the smaller clinical samples with low tumor cellularity.

Cervical carcinoma-associated fibroblasts are DNA diploid and do not show evidence for somatic genetic alterations

Background

Cancer-associated fibroblasts (CAFs) have been recognized as important contributors to cancer development and progression. However, opposing evidence has been published whether CAFs, in addition to epigenetic, also undergo somatic genetic alterations and whether these changes contribute to carcinogenesis and tumour progression.

Methods

We combined multiparameter DNA flow cytometry, flow-sorting and 6K SNP-arrays to study DNA aneuploidy, % S-phase, loss of heterozygosity (LOH) and copy number alterations (CNAs) in cervical cancer-associated stromal cell fractions (n = 57) from formalin-fixed, paraffin-embedded (FFPE) samples. Tissue sections were examined for the presence of CAFs. Microsatellite analysis was used to confirm LOH findings.

Results

Smooth muscle actin and vimentin immunohistochemistry verified the presence of CAFs in all cases tested. However, we found no evidence for DNA aneuploidy, somatic genetic alterations in the vimentin-positive stromal cell fractions of any samples, while high frequencies of DNA content abnormalities (43/57) and substantial numbers of CNAs and LOH were identified in the keratin-positive epithelial cell fractions. LOH hot-spots on chromosomes 3p, 4p and 6p found were confirmed by microsatellite analysis.

Conclusion

From our study we conclude that stromal cell fractions from cervical carcinomas are DNA diploid, have a genotype undistinguishable from patient-matched normal tissue and are genetically stable. Using flow cytometry and SNP-arrays, stromal genetic changes do not seem to play a role during cervical carcinogenesis and progression. In addition, the stromal cell fraction of cervical carcinomas can be used as reference allowing large retrospective studies of archival FFPE tissues for which no normal reference tissue is available.

Electronic supplementary material

The online version of this article (doi:10.1007/s13402-011-0061-5) contains supplementary material, which is available to authorized users.

High-resolution multiparameter DNA flow cytometry for the detection and sorting of tumor and stromal subpopulations from paraffin-embedded tissues

This unit contains a detailed protocol for the simultaneous flow cytometric measurement of tumor cells, stromal cells, and DNA content of formalin-fixed, paraffin-embedded (FFPE) tissues. The vimentin-positive stromal cell fraction can be used as an internal reference for DNA content assessments. This allows clear detection of keratin-positive tumor cells with a DNA index lower than 1.0 and of keratin-positive tumor cells with a DNA close to 1.0 in overall DNA aneuploid samples, thus improved DNA ploidy assessment in FFPE carcinomas. Furthermore, the protocol is useful for studying molecular genetic alterations and intratumor heterogeneity in archival FFPE samples. Keratin-positive tumor cell fractions can be flow-sorted for further molecular genetic analysis, while DNA from the sorted vimentin-positive stromal cells can serve as a reference when normal tissue of the patient is not available.

Multichromatic phenotyping of HER receptor coexpression in breast tumor tissue samples using flow cytometry--possibilities and limitations

The prognostic significance of HER2 expression in human breast carcinomas is beyond dispute nowadays. The HER family of receptor tyrosine kinases comprises four members (HER1/ErbB1/EGFR, HER2/ErbB2, HER3/ErbB3, and HER4/ErbB4) that act in concert via transactivation and consequently compose a functional signaling unit. Besides HER2 overexpression, coexpression of other HER receptors has substantial impact on course of disease and potential therapeutic benefit. This observation is substantiated by numerous preclinical studies and retrospective studies done on patients with breast cancer. Against this background, the quantification of all HER receptor expressions at the same time would significantly extend the information content revealed by routine diagnosis of breast cancer tissues. Moreover, the knowledge of HER receptor coexpression profiles in primary tumor samples could provide the basis to design and develop highly specific antireceptor treatment strategies. Here, we report on a simultaneous flow cytometric detection of all four HER receptors on carcinoma cells isolated from primary breast cancer tissues and separated from nonepithelial cells by cytokeratin staining. Combined with DNA, i.e. ploidy quantification, the approach resulted in a six-parameter assay that could complement the diagnosis of a variety of diseases in which HER receptor expression has a pivotal impact on the degree of malignancy.

High-resolution multiparameter DNA flow cytometry for the detection and sorting of tumor and stromal subpopulations from paraffin-embedded tissues

This unit contains a detailed protocol for the simultaneous flow cytometric measurement of tumor cells, stromal cells, and DNA content of formalin-fixed, paraffin-embedded (FFPE) tissues. The vimentin-positive stromal cell fraction can be used as an internal reference for DNA content assessments. This allows clear detection of keratin-positive tumor cells with a DNA index lower than 1.0 and of keratin-positive tumor cells with a DNA close to 1.0 in overall DNA aneuploid samples, thus improved DNA ploidy assessment in FFPE carcinomas. Furthermore, the protocol is useful for studying molecular genetic alterations and intratumor heterogeneity in archival FFPE samples. Keratin-positive tumor cell fractions can be flow-sorted for further molecular genetic analysis, while DNA from the sorted vimentin-positive stromal cells can serve as a reference when normal tissue of the patient is not available.

The importance of the age factor in cancer vaccination at older age

Cancer is an age-related disease, and with the graying of the society there is an increasing need to optimize cancer management and therapy to elderly patients. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Therefore, research is needed to establish whether age-specific tumor-immunological variables permit optimal use of cancer vaccines and therapy in the elderly. This review summarizes the current knowledge of T cell unresponsiveness in cancer patients and elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, new directions that may lead to effective cancer vaccination at older age will be proposed.

Genome-wide allelic state analysis on flow-sorted tumor fractions provides an accurate measure of chromosomal aberrations

Chromosomal aberrations are a common characteristic of cancer and are associated with copy number abnormalities and loss of heterozygosity (LOH). Tumor heterogeneity, low tumor cell percentage, and lack of knowledge of the DNA content impair the identification of these alterations especially in aneuploid tumors. To accurately detect allelic changes in carcinomas, we combined flow-sorting and single nucleotide polymorphism arrays. Cells derived from archival cervical and colon cancers were flow-sorted based on differential vimentin and keratin expression and DNA content and analyzed on single nucleotide polymorphism arrays. A new algorithm, the lesser allele intensity ratio, was used to generate a molecular measure of chromosomal aberrations for each case. Flow-sorting significantly improved the detection of copy number abnormalities; 31.8% showed an increase in amplitude and 23.2% were missed in the unsorted fraction, whereas 15.9% were detected but interpreted differently. Integration of the DNA index in the analysis enabled the identification of the allelic state of chromosomal aberrations, such as LOH ([A]), copy-neutral LOH ([AA]), balanced amplifications ([AABB]), and allelic imbalances ([AAB] or [AAAB], etc.). Chromosomal segments were sharply defined. Fluorescence in situ hybridization copy numbers, as well as the high similarity between the DNA index and the allelic state index, which is the average of the allelic states across the genome, validated the method. This new approach provides an individual molecular measure of chromosomal aberrations and will likely have repercussions for preoperative molecular staging, classification, and prognostic profiling of tumors, particularly for heterogeneous aneuploid tumors, and allows the study of the underlying molecular genetic mechanisms and clonal evolution of tumor subpopulations.

Cancer vaccination: manipulation of immune responses at old age

The incidence of cancer has increased over the last decade, mainly due to an increase in the elderly population. Vaccine therapy for cancer is less toxic than chemotherapy or radiation and could be, therefore, especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T-cell unresponsiveness, a phenomenon also observed in cancer patients per se. This review summarizes the current knowledge of impaired T-cell responses in cancer patients and the elderly, and the results of cancer vaccination in preclinical models at young and old age. Finally, various approaches how to manipulate immune responses against cancer by vaccination at older age will be proposed.

Multi-parametric flow cytometric cell cycle analysis using TO-PRO-3 iodide (TP3): detailed protocols

TO-PRO-3 iodide (TP3), a monomeric cyanine nucleic acid stain with a peak absorbance at 642 nm and emission at 661 nm, is best excited by a helium-neon (HeNe) laser (633nm). It was tested in monocytes and different cell lines under conditions of different fixatives, dye concentrations, labeling kinetics and RNAse concentrations for mono-, bi- and tri-parametric flow cytometric cell cycle analysis to establish the best protocol for DNA analysis in terms of G1 peak CV, G2/G1 ratio and minimal amount of debris. A linear increase in G1 peak position was found from 0.1 to 2 microM TP3 concentrations. Fixatives 70% ethanol or 1% methanol-free formaldehyde, followed by 70% ethanol, resulted in the best DNA histograms. Although different protocols were found to be cell-type specific, in general, excellent results were obtained with 30 min incubation with 0.5 microM TP3 plus RNAse in almost all cell lines tested. These data show that TP3 is an alternative method to propidium iodide (PI), the most commonly used DNA-specific probe in flow cytometry. The most important advantage of using TP3 in combination with other fluorochromes, such as fluorescein isothiocyanate (FITC) or phycoerythrin (PE) in bi- or tri-parametric flow cytometric analysis, is that there is no need for fluorescence compensation for the TP3 signals.

High-resolution multi-parameter DNA flow cytometry enables detection of tumour and stromal cell subpopulations in paraffin-embedded tissues

The accuracy of DNA ploidy measurements of paraffin-embedded tissues is limited by the lack of resolution and the inability to identify the DNA diploid population unequivocally in bimodal DNA histograms. A multi-parameter DNA flow cytometric method has been developed that enables the simultaneous detection of neoplastic and stromal cells in samples from dewaxed 50 microm sections or 2 mm diameter punches of archival tissue blocks. The method combines heat pretreatment in sodium citrate buffer and subsequent enzymatic dissociation with a collagenase/dispase mixture. Cells were simultaneously stained for keratin (FITC), vimentin (R-PE), and DNA (PI) before flow cytometric analysis. The method was applied to 12 paraffin-embedded cervical carcinomas and four colorectal carcinomas. In all cervical cancers, distinct keratin-positive and vimentin-positive cell populations were observed. While the exclusive vimentin-positive cell fractions always yielded unimodal DNA content distributions, bimodal distributions were observed for the keratin-positive cell fractions in nine cervical carcinomas, whereas one cervical carcinoma showed three distinct G0G1 populations. Coefficients of variation of the G0G1 peaks ranged from 1.70% to 4.79%. Average background, aggregate, and debris values were 14.7% (vimentin-positive fraction) and 33.8% (keratin-positive fraction). Flow sorting confirmed that the exclusively vimentin-positive cell fractions represent different normal stromal and infiltrate cells that can serve as an internal ploidy reference enabling discrimination between DNA hypo-diploid and DNA hyper-diploid tumour cell subpopulations. The neoplastic origin of the keratin-vimentin co-expressing cells from two cervical carcinomas was confirmed by genotyping of flow-sorted samples revealing loss of heterozygosity (LOH) of 6p. This improved method obviates the need for fresh/frozen tumour tissue for high-resolution DNA ploidy measurements and enables the isolation of highly purified tumour subpopulations for subsequent genotyping.

DRAQ5-based DNA content analysis of hematolymphoid cell subpopulations discriminated by surface antigens and light scatter properties

BACKGROUND

Analysis of cell cycle kinetics offers important information regarding the behavior of normal and neoplastic cells. Most often, cell cycle determinations by flow cytometry (FCM) have been performed using whole-sample analysis with intercalating dyes like propidium iodide (PI). The cell cycle phase assessment in individual cell subsets in heterogeneous samples is best performed using combined antigen/scatter and DNA analysis. DRAQ5, a novel DNA binding dye that excites at 488 nm and emits in the far red spectra, rapidly penetrates intact live cells while preserving their light scatter properties and expression of surface antigens. We evaluated the ability of this dye to measure cell cycle phases in a variety of clinical hematolymphoid samples.

METHODS

We first compared whole sample DRAQ5 and PI cell cycle analyses in 26 clinical hematolymphoid samples. Next, we analyzed cell subpopulations in 39 samples of nonpathologic bone marrow by performing simultaneous CD45/CD34 and DRAQ5 staining. We assessed cell cycle characteristics specific to each population identified by CD45/CD34/side light scatter: lymphocytes, monocytes, immature and mature granulocytes, nucleated erythroid cells, and early precursors.

RESULTS

Whole sample DNA cell cycle analyses by DRAQ5 and PI showed no significant differences in S-phase. DRAQ5, however, produced slightly larger coefficients of variation. DRAQ5-based DNA content analysis was easily performed on the distinct marrow cell subpopulations, since light scatter and antigen expression were completely preserved. Significant differences in S-phase were noted between subpopulations of cells exhibiting different degrees of maturation.

CONCLUSIONS

Because of its simplicity of use, excitability with 488 nm lasers, and the ability to stain viable cells, DRAQ5 should prove most useful in the kinetic evaluation of normal and neoplastic hematolymphoid cell subsets identified by light scatter and antigenic expression.

Chemoinformatic Analysis of a Supertargeted Combinatorial Library of Styryl Molecules

Styryl dyes are fluorescent, lipophilic cations that have been used as specific labeling probes of mitochondria in living cells. For specific applications such as epifluorescence microscopy or flow cytometry, it is often desirable to synthesize fluorescent derivatives with optimized excitation, emission, and localization properties. Here, we present a chemoinformatic strategy suitable for multiparameter analysis of a combinatorial library of styryl molecules supertargeted to mitochondria. The strategy is based on a simple additive model relating the spectral and subcellular localization characteristics of styryl compounds to the two chemical building blocks that are used to synthesize the molecules. Using a cross-validation approach, the additive model predicts with a high degree of confidence the subcellular localization and spectral properties of the styryl product, from numerical scores that are independently associated with the individual building blocks of the molecule. The fit of the data indicates that more complex, nonadditive interactions between the two building blocks play a minor role in determining the molecule's optical or biological properties. Moreover, the observed additive relationship allows mechanistic inferences to be made regarding the structure-property relationship observed for this particular class of molecules. It points to testable, mechanistic hypotheses about how chemical structure, fluorescence, and localization properties are related.

Precise CD4 T-cell counting using red diode laser excitation: for richer, for poorer

BACKGROUND

Measuring CD4 T-cell counts at low cost is relevant in dealing with the human immunodeficiency virus (HIV) epidemic throughout the developing world. The recently introduced novel concepts in gating strategies and sample stabilization facilitate affordable immunophenotyping by flow cytometry. However, the impact of these developments is still limited by the high cost of currently available flow cytometers.

METHODS

Diode lasers emitting 10-15 mW at 635 nm are one-tenth the size and cost and require one thousandth the power of an equivalent 488-nm argon ion laser. We used the available 635-nm diode-based flow cytometers, including PA-II, Luminex 100, SuperMot, and FACSCalibur, to investigate whether these instruments can generate reliable CD4 counts when used with allophycocyanin (APC) and cyanin-5 (Cy5)-labeled CD4 antibodies.

RESULTS

We document the feasibility of obtaining leucocyte differential counts using orthogonal side scatter (SSC) without the need for forward scatter (FSC). Accurate CD4% values among lymphocytes and leucocytes can be obtained by primary CD4 gating using a single CD4 monoclonal antibody conjugated to APC or Cy5. Double immunofluorescence (IF) staining with CD4-APC (FL1) and CD45-APC-Cy7 (FL2) introduces pan-leucogating for a convenient assessment of absolute CD4 counts on double platforms. We demonstrate that small flow cytometers with laser diodes are capable of delivering absolute CD4 T-cell counts with a precision similar to the performance of the current state-of-the-art single-platform instruments (e.g., the CytoronAbsolute; R(2) = 0.961). In this respect, they appear to be superior to the nonflow CD4 counting techniques.

CONCLUSIONS

Accurate CD4 counts can be generated at minimal cost on red diode laser-operated flow cytometers, retaining the potential for high throughput capacity without compromising precision. With further improvements in volumetric technology and clinical software, these cytometers may develop into a new generation of inexpensive battery-operated laboratory hardware that combines cellular phenotyping with bead-based multiplexing immunoassays for (HIV) serology.

Software compensation improves the analysis of heterogeneous tumor samples stained for multiparameter DNA flow cytometry

BACKGROUND

High concentrations of propidium iodide (PI), in combination with fluorescein isothiocyanate (FITC) and R-phycoerythrin (RPE) used for multiparameter DNA flow cytometry (FCM), cause spectral cross-talk into the green fluorescence channel (FL1). We have evaluated the use of post-acquisition software compensation (N-Color Compensation) in order to correct this spectral cross-talk caused by PI.

METHOD

Cell mixtures were prepared consisting of keratin 8/18 FITC labeled, keratin 8/18 RPE labeled, and unlabeled MCF-7 breast carcinoma cells. DNA was stained with PI (100 microM). Post-acquisition software compensation was applied to correct the spectral cross-talk of PI fluorescence. Secondly, the distribution of the Ki-67 (FITC) protein during the cell cycle (PI) of SiHa cervical carcinoma cells (no software compensation) was compared to the Ki-67 expression pattern of SiHa cells, simultaneously stained for keratin 8 (RPE), after applying software compensation. Finally, software compensation was used to compare the relative levels of PCNA and p53 expression in two clinical ovarian cancer ascites specimens, stained for PCNA or p53 (FITC), keratin 8/18 (RPE), and DNA (PI), with a known p53 status (positive and negative, respectively).

RESULTS

The Ki-67 cell cycle-dependent pattern of a triply stained sample (Ki-67 (FITC), keratin 8 (RPE), and DNA (PI)) is restored after software compensation and the results are comparable to the Ki-67 distribution of a sample stained solely for Ki-67 and DNA. P53 expression could only be resolved after using software compensation in the p53 positive ovarian ascites (OA) sample.

CONCLUSIONS

We conclude that software compensation is a robust and reliable post-acquisition method for the correction of RPE/PI spectral cross-talk, permitting better identification of weakly expressed proteins in heterogeneous clinical tumor samples stained for multiple cellular antigens and DNA using PI.

Flow cytometric DNA-quantification of three-color immunophenotyped cells for subpopulation specific determination of aneuploidy and proliferation

A method is described for three-color immunophenotyping and simultaneous DNA-quantification using a flow cytometer equipped with a 488-nm argon laser and a mercury lamp (UV). The approach includes reproducible immunophenotyping comparing antigen expression before and after cell manipulation for DNA-measurement. The coefficients of variation after DNA-staining (CV=3.13 for T-cells in peripheral blood and CV=3.38 for T-cells in bone marrow) were adequate for exact DNA-analysis. For aneuploidy detection, a true internal standard was established measuring, for example, the DNA-content of T-cells in B-cell disease simultaneously with the DNA-content of the malignant cells. Using this method, aneuploidies could be unequivocally detected in 17 out of 24 patients with multiple myeloma. Furthermore, intratumor heterogeneities in DNA-content and antigen expression could be recognized, allowing an exact separation of tumor cells and normal hematopoiesis. The study also demonstrated the importance of exact immunophenotypic characterization of lymphocyte subpopulations and the determination of their specific proliferation, for example after proliferation induction in cell cultures. Future studies should address the applicability of this rather simple multiparameter approach for simultaneous immunophenotyping and DNA-measurement especially in the detection of minimal amounts of aneuploid cells after chemotherapy.

A unified procedure for conservative (morphology) and integral (DNA and immunophenotype) cell staining for flow cytometry

BACKGROUND

Current methods for multiparameter DNA flow cytometry suffer from several limitations. These include significant modifications of cell morphological parameters, the impossibility to counterstain cells with certain fluorochromes, and laborious tuning of the instrument that, for some procedures, must be equipped with an ultraviolet (UV) laser. To overcome these problems, we developed a novel method for the simultaneous analysis of morphological parameters, four-color immunophenotyping, and stoichiometric DNA labeling using a bench-top flow cytometer.

METHODS

The method consists of a mild permeabilization/fixation treatment at room temperature, followed by labeling with fluorochrome-conjugated monoclonal antibodies (mAbs) and with the DNA dye 7-aminoactinomycin D (7-AAD) at 56 degrees C.

RESULTS

Using this method, we analyzed resting peripheral blood mononucleated cells (PBMC), proliferating T cells cultured in the presence of interleukin-2 (IL-2), and lymphoblastoid B cells. Lymphocytes, monocytes, and lymphoblasts treated by this procedure retained differential light scattering (DLS) characteristics virtually identical to those of untreated cells. This allowed regions to be drawn on forward scatter (FSC) and side scatter (SSC) cytograms resolving different cell populations. DLS were preserved well enough to distinguish large lymphoblasts in the S or G2/M phases from small G0/G1 cells. Also, stainability with fluorescein-isothiocyanate (FITC), R-phycoerythrin (PE), allophycocyanin (APC)-conjugated mAbs was generally preserved. DNA labeling with 7-AAD was of quality good enough to permit accurate cell cycle analysis.

CONCLUSIONS

The method described here, which we called integral hot staining (IHS), represents a very simple, reproducible, and conservative assay for multiparameter DNA analysis using a bench-top flow cytometer. Last but not least, the cytometer tuning for multiparameter acquisition is straightforward.

Distinction between HLA class I-positive and -negative cervical tumor subpopulations by multiparameter DNA flow cytometry

BACKGROUND

The study of the molecular-genetic basis of heterogeneity of HLA class I expression in solid tumors is hampered by the lack of reliable rapid cell-by-cell isolation techniques. Hence, we studied the applicability of a flow cytometric approach (Corver et al.: Cytometry 2000;39;96-107).

METHODS

Cells were isolated from five fresh cervical tumors and simultaneously stained for CD45 or vimentin (fluorescein isothiocyanate fluorescence), Keratin (R-phycoerythrin fluorescence), HLA class I (APC fluorescence), and DNA (propidium iodide fluorescence). A dual-laser flow cytometer was used for fluorescence analysis. Tissue sections from the corresponding tumors were stained for HLA class I antigens, keratin, vimentin, or CD45.

RESULTS

Flow cytometry enabled the simultaneous measurement of normal stromal cells (vimentin positive), inflammatory cells (CD45 positive), epithelial cells (keratin positive), and DNA content readily. Normal stromal/inflammatory cells served as intrinsic HLA class I-positive as well as DNA-diploid references. Good DNA histogram quality was obtained (average coefficient of variation < 4%). Intratumor keratin positive subpopulations differing in HLA class I expression as well as DNA content could be clearly identified. Losses of allele-specific HLA class I expression found by immunohistochemistry were also detected by flow cytometry.

CONCLUSIONS

We conclude that multiparameter DNA flow cytometry is a powerful tool to study loss of HLA class I expression in human cervical tumors. The method enables flow-sorting of discrete tumor and normal cell subpopulations for further molecular genetic analysis.

Multiple genetic alterations cause frequent and heterogeneous human histocompatibility leukocyte antigen class I loss in cervical cancer

The nature and frequency of human histocompatibility leukocyte antigen (HLA) class I loss mechanisms in primary cancers are largely unknown. We used flow cytometry and molecular analyses to concurrently assess allele-specific HLA phenotypes and genotypes in subpopulations from 30 freshly isolated cervical tumor cell suspensions.Tumor-associated HLA class I alterations were present in 90% of the lesions tested, comprising four altered pheno/genotype categories: (a) HLA-A or -B allelic loss (17%), mostly associated with gene mutations; (b) HLA haplotype loss, associated with loss of heterozygosity at 6p (50%). This category included cases with additional loss of a (third) HLA-A or -B allele due to mutation, as well as one case with an HLA class I-negative tumor cell subpopulation, caused by a beta2-microglobulin gene mutation; (c) Total HLA class I antigen loss and retention of heterozygosity (ROH) at 6p (10%); and (d) B locus or HLA-A/B downregulation associated with ROH and/or allelic imbalance at 6p (10%). Normal HLA phenotypes and ROH at 6p were observed in 10% of the cases. One case could not be classified (3%). Altered HLA class I antigen expression occurs in most cervical cancers, is diverse, and is mainly caused by genetic changes. Combined with widespread tumor heterogeneity, these changes have profound implications for natural immunity and T cell-based immunotherapy in cervical cancer.