Flow cytometric analysis of cerebrospinal fluid samples and its usefulness in routine clinical practice

The influence of fixation and cryopreservation of cerebrospinal fluid on antigen expression and cell percentages by flow cytometric analysis

The pauci-cellular nature of cerebrospinal (CSF), particularly ventricular CSF, and the rapid cell death following sampling, incumbers the use of flow cytometric analysis of these samples in the investigation of central nervous system (CNS) pathologies. Developing a method that allows long-term storage and batched analysis of CSF samples without compromising cell integrity is highly desirable in clinical research, given that CSF is often sampled after hours creating logistical difficulties for fresh processing. We examined percentages and relative proportion of peripheral and brain-derived immune cells in cryopreserved and transfix-treated CSF, compared to freshly processed CSF. Cell proportions were more comparable between Fresh and Cryopreserved CSF (mean of differences = 3.19), than between fresh and transfix-treated CSF (mean of differences = 14.82). No significant differences in cell percentages were observed in fresh versus cryopreserved CSF; however significantly lower cell percentages were observed in transfix-treated CSF compared to Fresh CSF [(CD11b++ (p = 0.01), CD4+ (p = 0.001), CD8+ (p = 0.007), NK cells (p = 0.04), as well as CD69+ activation marker (p = 0.001)]. Furthermore, loss of marker expression of various lymphocyte sub-populations were observed in transfix-treated CSF. Cryopreservation is a feasible option for long-term storage of ventricular CSF and allows accurate immunophenotyping of peripheral and brain-derived cell populations by flow cytometry.

Is flow cytometry useful in determining central nervous system involvement in patients with hematological malignancy? Analysis with a prospective cohort

Central nervous system (CNS) involvement occurs in approximately 5-15% of patients in hematological malignancies. Early diagnosis and treatment is essential for a successful approach to CNS involvement. The gold standard method for diagnosis is cytological evaluation, but its sensitivity is low. Flow cytometry (FCM) from cerebrospinal fluid(CSF) is another method used to identify small groups of cells with abnormal phenotype. In our study, we compared FCM and cytological findings in the evaluation of CNS involvement in our patients with hematological malignancies. 90 patients [58 males, 32 females] were included in the study. CNS involvement was positive in 35(%38.9) patients, negative in 48(%53.3) patients, and suspicious (atypical) in 7(%7.8) patients by flow cytometry and ıt was positive in 24(%26.7) patients, negative in 63(%70) patients, and atypical in 3(%3.3) patients by cytology. While the sensitivity and specificity were found to be respectively 68.5% and 100% by cytology, it was found to be 94.2% and 85.4% by flow cytometry. Flow cytometry, cytology and MR findings were significantly correlated with each other in both prophylaxis (p < 0.001) and patients with prediagnosis of CNS involvement. Although the gold standard diagnostic method in the diagnosis of CNS involvement is cytological, its sensitivity is low and it can give false negative results at a rate of 20-60%. Flow cytometry is an ideal objective and quantitative method for identifying small groups of cells with abnormal phenotype. Flow cytometry can be used routinely in the diagnosis of CNS involvement in patients with hematological malignancies with cytology, since it can detect fewer malignant cells, has a higher sensitivity, and provides easy and faster results.

Stabilization of leukocytes from cerebrospinal fluid for central immunophenotypic evaluation in multicenter clinical trials

Analysis of cerebrospinal fluid (CSF) represents a valuable window into the pathogenesis of neuroinflammatory diseases, such as multiple sclerosis (MS). However, analysis of the cellular fraction of CSF is often neglected because CSF cells die rapidly ex vivo. Immunophenotyping of CSF cells in multicenter clinical trials requires sample preservation and shipping to a centralized lab. Yet, there is no consensus on the best method to preserve intact CSF cells and no detailed evaluation of subset-specific cell loss. We used flow cytometry to compare major leukocyte populations in fresh CSF (processed within 2 h) to cells fixed for 48 h with TransFix-EDTA® or cryopreserved and thawed after 96 h. We observed a statistically significant loss of total mononuclear cells, total T cells, CD3+ CD8- T cells, and CD3+ CD8+ T cells after cryopreservation compared to fresh or fixed (p < 0.001), with no significant difference between fresh and fixed. Thus, our results demonstrate that TransFix-EDTA® was superior to cryopreservation for preserving intact CSF T cells. Surprisingly, neither cryopreservation nor fixation had a significant effect on recovery of low frequency cell subsets in CSF, including B cells, NK cells, NKT-like cells, CD14+ monocytes, or CD123+ DCs, versus fresh CSF. To determine the effect of prolonged fixation on cell recovery, we analyzed major CSF cell subsets by flow cytometry after 24, 48, or 72 h of fixation with TransFix-EDTA®. We observed a consistent and progressive loss in the absolute counts of all subsets over time, although this effect was not statistically significant. We conclude that for immunophenotyping of major CSF cell subsets by flow cytometry, fixation with TransFix-EDTA®, shipment to a central lab, and analysis within 48 h is a feasible method to ensure stability of both absolute cell number and relative frequency. This method is a valuable alternative to fresh CSF analysis and can be implemented in multicenter clinical trials.

Flow Cytometric Detection of Malignant Blasts in Cerebrospinal Fluid: A Biomarker of Central Nervous System Involvement in Childhood Acute Lymphoblastic Leukemia

Despite the excellent prognosis for children and adolescents with acute lymphoblastic lymphoma (ALL), the involvement of the central nervous system (CNS) represents a major therapeutic challenge. Patients who develop CNS relapse have a very poor prognosis, and since current methods cannot reliably identify patients with CNS involvement or patients at high risk of CNS relapse, all children with ALL receive CNS-directed treatment. The current golden standard for detecting CNS involvement is the assessment of cytomorphology on cytospin slides of cerebrospinal fluid (CSF). This technique is inadequate due to low sensitivity and reproducibility. Flow cytometric analysis of CSF represent a novel, highly specific and sensitive technique for the detection of leukemic cells in the CNS. In prospective studies, CSF flow cytometry demonstrated two to three times higher rates of CNS involvement at diagnosis of childhood ALL than conventional cytospin, and especially demonstrated superior sensitivity in detecting low-level CNS disease. CNS involvement determined via flow cytometry has been linked to a higher risk of CNS relapse and poor outcomes in several studies. In this review, we discuss the central analytical concepts of CSF flow cytometry and summarize the current evidence supporting the use of flow cytometric detection of malignant blasts as a biomarker of CNS involvement in childhood ALL.

Cerebrospinal fluid findings in patients with hematologic neoplasms and meningeal infiltration

Neoplastic cell infiltration into the central nervous system (CNS) is a serious complication of hematological neoplasms. Cytomorphology (CM) and flow cytometry (FC) have been used to detect meningeal infiltration. The association between CSF findings with the results of CM and FC is still poorly understood. We retrospectively evaluated CSF findings in 72 patients with hematological neoplasm and meningeal infiltration detected either by CM or FC. We compared CSF cell count, total protein concentration, and lactate concentration according to the type of hematological neoplasm. We also compared these CSF findings according to the FC and CM results (FC + CM + , FC + CM-, and FC-CM +). The proportion of patients with positive FC was higher than with CM (FC - 91.7%; CM - 63.9%). Thirty-five (48.6%) patients with meningeal infiltration had normal CSF cell count, normal total protein concentration, and normal lactate concentration. The proportion of cases in which these CSF parameters were normal did not differ according to the type of hematological neoplasm. The positivity of CM was significantly higher in patients with > 3 cell/mm³ (P = 0.015) but the positivity of FC was not significantly different between patients with > 3 cell/mm³ or ≤ 3 cells/mm³. Patients with positive CM had more CSF cells (P = 0.0005) and higher lactate concentration (P = 0.0165) than patients with negative CM. The absence of CSF changes in cell count and total protein and lactate concentrations does not exclude the presence of meningeal infiltration. Although CM is considered the gold standard, the probability of positive CM is low in patients without CSF abnormalities in these parameters. Patients with hematological neoplasm with suspected meningeal infiltration should be investigated with both methods.

Targeting Neoepitopes to Treat Solid Malignancies: Immunosurgery

Successful outcome of immune checkpoint blockade in patients with solid cancers is in part associated with a high tumor mutational burden (TMB) and the recognition of private neoantigens by T-cells. The quality and quantity of target recognition is determined by the repertoire of ‘neoepitope’-specific T-cell receptors (TCRs) in tumor-infiltrating lymphocytes (TIL), or peripheral T-cells. Interferon gamma (IFN-γ), produced by T-cells and other immune cells, is essential for controlling proliferation of transformed cells, induction of apoptosis and enhancing human leukocyte antigen (HLA) expression, thereby increasing immunogenicity of cancer cells. TCR αβ-dependent therapies should account for tumor heterogeneity and availability of the TCR repertoire capable of reacting to neoepitopes and functional HLA pathways. Immunogenic epitopes in the tumor-stroma may also be targeted to achieve tumor-containment by changing the immune-contexture in the tumor microenvironment (TME). Non protein-coding regions of the tumor-cell genome may also contain many aberrantly expressed, non-mutated tumor-associated antigens (TAAs) capable of eliciting productive anti-tumor immune responses. Whole-exome sequencing (WES) and/or RNA sequencing (RNA-Seq) of cancer tissue, combined with several layers of bioinformatic analysis is commonly used to predict possible neoepitopes present in clinical samples. At the ImmunoSurgery Unit of the Champalimaud Centre for the Unknown (CCU), a pipeline combining several tools is used for predicting private mutations from WES and RNA-Seq data followed by the construction of synthetic peptides tailored for immunological response assessment reflecting the patient’s tumor mutations, guided by MHC typing. Subsequent immunoassays allow the detection of differential IFN-γ production patterns associated with (intra-tumoral) spatiotemporal differences in TIL or peripheral T-cells versus TIL. These bioinformatics tools, in addition to histopathological assessment, immunological readouts from functional bioassays and deep T-cell ‘adaptome’ analyses, are expected to advance discovery and development of next-generation personalized precision medicine strategies to improve clinical outcomes in cancer in the context of i) anti-tumor vaccination strategies, ii) gauging mutation-reactive T-cell responses in biological therapies and iii) expansion of tumor-reactive T-cells for the cellular treatment of patients with cancer.

Leptomeningeal involvement by relapsed follicular lymphoma detected by flow cytometry despite exceedingly low white blood cell counts in cerebrospinal fluid: A case report

Follicular lymphoma is usually an indolent non-Hodgkin lymphoma that rarely involves the central nervous system (CNS) and flow cytometric detection of such lymphoma in cerebrospinal fluid (CSF) is often challenging because of low cellularity and viability of CSF samples. Here, we report our experience in a 52-year-old man whose relapsed follicular lymphoma with leptomeningeal involvement was confirmed by flow cytometric analysis of CSF, despite an exceedingly low white blood cell count (3/cumm).

Multicentric MFI30 study: Standardization of flow cytometry analysis of CD30 expression in non-Hodgkin lymphoma

CD30 transmembrane receptor, a member of the tumor necrosis factor receptor family, is expressed in different lymphomas. Brentuximab vedotin (BV), a CD30 monoclonal antibody (Ab)-drug conjugate, is effective in CD30-positive lymphomas. However, the response to BV is not always correlated to CD30 expression detected by immunohistochemistry (IHC). The objectives of this study were to standardize and evaluate CD30 intensity by flow cytometry (FCM) in non-Hodgkin's lymphomas. Twelve centers analyzed 161 cases on standardized cytometers using normalized median fluorescence intensity (nMFI30) of three different Abs, of which one clone can recognize the same epitope as BV. FCM distinguished four groups of cases: negative group (n = 110) which showed no expression with the three clones; high positive group (n = 13) which gave nMFI30 > 5% with all tested clones; dim positive group (n = 17) which showed nMFI30 > 1% with all tested clones and <5% for at least one; discordant group (n = 21) with positive and negative expression of the different clones. In consistency with the literature, CD30 was positive in all anaplastic large cell lymphomas, in some diffuse large B-cell lymphomas (DLBCL), and in other rare lymphomas. FCM results were concordant with those of IHC in 77% of cases. Discrepancies could be explained by clones-related differences, microenvironment, or intracytoplasmic staining. Interestingly, FCM was more sensitive than IHC in 11% of cases, especially in DLBCL. Multicenter standardized FCM of specific CD30 could improve case detection and extend the treatment of BV to various CD30-positive lymphomas.

Intraocular leucocyte subpopulations analysis by multiparametric flow cytometry in human uveitis

PURPOSE

The aim of this study was to describe the cellular infiltrate in aqueous and vitreous samples of patients with uveitis analysed by multiparametric flow cytometry.

METHODS

This is a retrospective analysis of aqueous and vitreous samples analysed by flow cytometry for diagnostic purposes, in cases of masquerade syndromes and infectious and non-infectious uveitis. Data collected included demographics, anatomical classification of uveitis, phenotypic diagnosis, anterior chamber cells grading, vitreous haze and time of follow-up since presentation to sample obtained.

RESULTS

Thirty-one samples (17 aqueous and 14 vitreous fluids) from 31 patients, 18 men, were analysed. The mean age at the time of sample collection was 60.23±17.03 years. The most frequent anatomical classification was panuveitis (14 of 31). T cells accounted for the main cellular component in the majority of the samples (10 of 13 aqueous samples; 7 of 14 in vitreous samples). CD4:CD8 ratios ranged from 0.21 to 16.3 in the case of aqueous samples and from 0.5 to 9.7 in the case of vitreous samples.

DISCUSSION

Flow cytometry analysis of aqueous and vitreous samples from patients with uveitis could provide insight into the pathogenesis of human uveitis and help develop accurate animal models which better mimic human disease.

Examination and characterisation of burst spinal cord stimulation on cerebrospinal fluid cellular and protein constituents in patient responders with chronic neuropathic pain - A Pilot Study

INTRODUCTION

Patients with neuropathic pain have altered proteomic and neuropeptide constituents in cerebrospinal fluid (CSF) compared to controls. Tonic spinal cord stimulation (SCS) has demonstrated differential expression of neuropeptides in CSF before and after treatment suggesting potential mechanisms of action. Burst-SCS is an evidence-based paraesthesia free waveform utilised for neuropathic pain with a potentially different mechanistic action to tonic SCS. This study examines the dynamic biological changes of CSF at a cellular and proteome level after Burst-SCS.

METHODS

Patients with neuropathic pain selected for SCS had CSF sampled prior to implant of SCS and following 8 weeks of continuous Burst-SCS. Baseline and 8-week pain scores with demographics were recorded. T cell frequencies were analysed by flow cytometry, proteome analysis was performed using mass spectrometry and secreted cytokines, chemokines and neurotrophins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

4 patients (2 females, 2 males) with a mean age of 51 years (+/-SEM 2.74, SD 5.48) achieved a reduction in pain of >50% following 8 weeks of Burst-SCS. Analysis of the CSF proteome indicated a significant alteration in protein expression most related to synapse assembly and immune regulators. There was significantly lower expression of the proteins: growth hormone A1 (PRL), somatostatin (SST), nucleobindin-2 (NUCB2), Calbindin (CALB1), acyl-CoA binding protein (DBI), proSAAS (PCSK1N), endothelin-3 (END3) and cholecystokinin (CCK) after Burst-SCS. The concentrations of secreted chemokines and cytokines and the frequencies of T cells were not significantly changed following Burst-SCS.

CONCLUSION

This study characterised the alteration in the CSF proteome in response to burst SCS in vivo. Functional analysis indicated that the alterations in the CSF proteome is predominately linked to synapse assembly and immune effectors. Individual protein analysis also suggests potential supraspinal mechanisms.

Evaluation of the Idexx ProCyte Dx® for analysis of canine cerebrospinal fluid

OBJECTIVES

To assess the utility of the Idexx ProCyte Dx® haematology analyser for assessing total nucleated cell count and differential cell counts in canine cerebrospinal fluid.

MATERIALS AND METHODS

Seventy-three client-owned dogs undergoing investigations for pyrexia and/or neurological signs were prospectively included. Cerebrospinal fluid samples were assessed using an Idexx ProCyte Dx® analyser and the results were compared to those obtained with the external laboratory reference standard.

RESULTS

The Idexx ProCyte Dx® performed with good sensitivity (92.6%) and moderate specificity (67.4%) for total nucleated cell count when compared to the reference standard. Qualitative assessment of the Idexx ProCyte Dx® scatter plots, and quantitative assessment of differential cell counts where available, appeared to correlate well with the external laboratory manual differential cell counts, with a good-to-high agreement in 25 of 26 samples (96.2%).

CLINICAL SIGNIFICANCE

The Idexx ProCyte Dx® analyser performed well in determining the total nucleated cell count and differential cell counts in canine cerebrospinal fluid when compared to a reference standard of external laboratory analysis, except for cell counts higher than ~1000/μL. As the Idexx ProCyte Dx® currently only provides a cell count in 10 cells/μL increments, software modification may improve agreement between the two methods. As in human medicine, automated methods may prove useful in the future for cerebrospinal fluid analysis in addition to manual assessment, particularly in an emergency setting.

Lymphocyte Immunophenotyping and CD4/CD8 Ratio in Cerebrospinal Fluid for the Diagnosis of Sarcoidosis-related Uveitis

Background: This study aimed to assess the diagnostic relevance of CD4/CD8 ratio in cerebrospinal fluid (CSF) for the etiological diagnosis work-up of uveitis.Methods: We consecutively included patients who were referred to our department for the diagnostic workup of intermediate and/or posterior uveitis. Etiological diagnoses were established in a blind manner regarding CD4/CD8 ratio.Results: Fifty-two patients were included. A diagnosis of ocular sarcoidosis was made in 15 (29%) patients, 21% had another determined diagnosis while 50% remained of undetermined origin. Median CD4/CD8 ratio in CSF was 4.57 (IQR 3.39-5.47) in ocular sarcoidosis, 1.74 (1.60-3.18) in uveitis due to other determined cause (P = .008), and 2.83 (2.34-3.54) in those with uveitis of undetermined origin (P = .007). CD4/CD8 ratio >3.23 was associated with a diagnosis of ocular sarcoidosis.Conclusion: Determination of CD4/CD8 ratio in CSF can be useful for diagnosis work-up since a CD4/CD8 ratio >3.23 in CSF is associated with ocular sarcoidosis.

Optimization of CSF biological investigations for CNS lymphoma diagnosis

Diagnosis of lymphoma leptomeningeal dissemination is challenging and relies on a wide array of methods. So far, no consensus biological guidelines are available. This increases the chance of intra- and interpractice variations, despite the shared concern to perform the minimum amount of tests while preserving clinically relevant results.We evaluated a training cohort of 371 cerebrospinal fluid (CSF) samples from patients with putative lymphomatous central nervous system (CNS) localization using conventional cytology (CC), flow cytometry (FCM), molecular clonality assesment by PCR and cytokine quantification (CQ). This led us to propose a biological algorithm, which was then verified on a validation cohort of 197 samples. The samples were classified according to the clinical context and the results of each technique were compared. Using all four techniques was not useful for exclusion diagnosis of CNS lymphoma (CNSL), but they proved complementary for cases with suspected CNSL. This was particularly true for CQ in primary CNSL. Overall, diagnosis can be obtained with a two-step approach. The first step comprises CC and FCM, as results are available quickly and FCM is a sensitive method. Both PCR and CQ can be postponed and performed in a second step, depending on the results from the first step and the clinical context.The proposed algorithm missed none of the CNSL samples of the validation cohort. Moreover, applying this algorithm would have spared 30% of PCR tests and 20% of CQ over a one-year period, without compromising clinical management.

Monitoring of Measurable Residual Disease in Multiple Myeloma by Multiparametric Flow Cytometry

Recent interest in high sensitivity multiple myeloma (MM) measurable residual disease (MRD) testing is a direct consequence of the high-quality responses achieved using novel therapeutic agents and better treatment strategies. Traditional diagnostic measures such as immunohistochemistry and morphology have detection sensitivities of only 10^-2 - 10^-3, which do not reliably predict progression free survival (PFS) or overall survival (OS) after these treatments. Contemporary monitoring of MM MRD has switched to more sensitive platforms such as quantitative allele-specific oligonucleotide polymerase chain reaction (ASO-qPCR), next-generation sequencing (NGS), and multiparametric flow cytometry (MFC). Though both ASO-qPCR and NGS have excellent detection sensitivities (10^-5 - 10^-6), both technologies have lower applicability when compared to MFC. Conventional MFC can easily reach a detection sensitivity of 10^-4 and when optimized can achieve a sensitivity of 10^-5 - 10^-6. Current consensus guidelines require a minimum of 2 million and recommend 5 million events be acquired to reach a minimum sensitivity of 10^-5. As conventional immunophenotyping protocols are unable to attain these numbers, alternative MFC staining procedures are required. This manuscript describes two high-sensitivity MFC approaches that can be used for MM MRD testing.

Determinants for Neoantigen Identification

All tumors accumulate genetic alterations, some of which can give rise to mutated, non-self peptides presented by human leukocyte antigen (HLA) molecules and elicit T-cell responses. These immunogenic mutated peptides, or neoantigens, are foreign in nature and display exquisite tumor specificity. The correlative evidence suggesting they play an important role in the effectiveness of various cancer immunotherapies has triggered the development of vaccines and adoptive T-cell therapies targeting them. However, the systematic identification of personalized neoantigens in cancer patients, a critical requisite for the success of these therapies, remains challenging. A growing amount of evidence supports that only a small fraction of all tumor somatic non-synonymous mutations (NSM) identified represent bona fide neoantigens; mutated peptides that are processed, presented on the cell surface HLA molecules of cancer cells and are capable of triggering immune responses in patients. Here, we provide an overview of the existing strategies to identify candidate neoantigens and to evaluate their immunogenicity, two factors that impact on neoantigen identification. We will focus on their strengths and limitations to allow readers to rationally select and apply the most suitable method for their specific laboratory setting.

Detection of Central Nervous System Infiltration by Myeloid and Lymphoid Hematologic Neoplasms Using Flow Cytometry Analysis: Diagnostic Accuracy Study

Introduction

Infiltration of the central nervous system (CNS) by hematologic or lymphoid malignant cells can cause extensive neurological damage, be progressive and fatal. However, usually, the cerebrospinal fluid (CSF) has low cellularity and rapid cell degeneration, which can impair cytometry analysis. Storage and transport measures, sample preparation, and staining protocols can interfere with diagnostic accuracy.

Objective

To calculate the diagnostic performance of flow cytometry (FC) using a cell stabilizer for sample preservation compared to cytomorphology in the detection of CNS infiltration by lymphoid and hematologic neoplasms.

Methods

Cell samples from all consecutive patients with suspected infiltration by hematological malignancies evaluated between January 2014 and December 2016 were included. Cases were analyzed by FC using a cell preservation medium and cytomorphology. Sensitivity and specificity were calculated.

Results

From 414 CSF samples, 72 had a phenotype compatible with characteristics of infiltration by hematological disease, whereas cytology was positive for 35 cases. FC showed higher sensitivity and specificity when compared to cytomorphology, particularly in cases with cellularity under 5 leukocytes/mm³.

Conclusion

We demonstrated that collecting CSF in a medium that preserves the stability of the sample improves accuracy when compared to cytomorphology, particularly in low-volume and low-cellularity samples.

Diagnosis of Plasma Cell Dyscrasias and Monitoring of Minimal Residual Disease by Multiparametric Flow Cytometry

Plasma cell dyscrasia (PCD) is a heterogeneous disease that has seen a tremendous change in outcomes due to improved therapies. Over the past few decades, multiparametric flow cytometry has played an important role in the detection and monitoring of PCDs. Flow cytometry is a high-sensitivity assay for early detection of minimal residual disease (MRD) that correlates well with progression-free survival and overall survival. Before flow cytometry can be effectively implemented in the clinical setting, sample preparation, panel configuration, analysis, and gating strategies must be optimized to ensure accurate results. Current consensus methods and reporting guidelines for MRD testing are discussed.

Early Dynamics of Cerebrospinal CD14+ Monocytes and CD15+ Granulocytes in Patients after Severe Traumatic Brain Injury: A Cohort Study

In traumatic brain injury (TBI) the analysis of neuroinflammatory mechanisms gained increasing interest. In this context certain immunocompetent cells might play an important role. Interestingly, in the actual literature there exist only a few studies focusing on the role of monocytes and granulocytes in TBI patients. In this regard it has recently reported that the choroid plexus represents an early, selective barrier for leukocytes after brain injury. Therefore the aim of this study was to evaluate the very early dynamics of CD14+ monocytes and CD15+ granulocyte in CSF of patients following severe TBI with regard to the integrity of the BBB. Cytometric flow analysis was performed to analyze the CD14+ monocyte and CD15+ granulocyte population in CSF of TBI patients. The ratio of CSF and serum albumin as a measure for the BBB's integrity was assessed in parallel. CSF samples of patients receiving lumbar puncture for elective surgery were obtained as controls. Overall 15 patients following severe TBI were enrolled. 10 patients were examined as controls. In patients, the monocyte population as well as the granulocyte population was significantly increased within 72 hours after TBI. The BBB's integrity did not have a significant influence on the cell count in the CSF.

Consensus guidelines on plasma cell myeloma minimal residual disease analysis and reporting

BACKGROUND

Major heterogeneity between laboratories in flow cytometry (FC) minimal residual disease (MRD) testing in multiple myeloma (MM) must be overcome. Cytometry societies such as the International Clinical Cytometry Society and the European Society for Clinical Cell Analysis recognize a strong need to establish minimally acceptable requirements and recommendations to perform such complex testing.

METHODS

A group of 11 flow cytometrists currently performing FC testing in MM using different instrumentation, panel designs (≥ 6-color) and analysis software compared the procedures between their respective laboratories and reviewed the literature to propose a consensus guideline on flow-MRD analysis and reporting in MM.

RESULTS/CONCLUSION

Consensus guidelines support i) the use of minimum of five initial gating parameters (CD38, CD138, CD45, forward, and sideward light scatter) within the same aliquot for accurate identification of the total plasma cell compartment; ii) the analysis of potentially aberrant phenotypic markers and to report the antigen expression pattern on neoplastic plasma cells as being reduced, normal or increased, when compared to a normal reference plasma cell immunophenotype (obtained using the same instrument and parameters); and iii) the percentage of total bone marrow plasma cells plus the percentages of both normal and neoplastic plasma cells within the total bone marrow plasma cell compartment, and over total bone marrow cells. Consensus guidelines on minimal current and future MRD analyses should target a lower limit of detection of 0.001%, and ideally a limit of quantification of 0.001%, which requires at least 3 × 10(6) and 5 × 10(6) bone marrow cells to be measured, respectively.

Diagnostic and prognostic significance of flow cytometry immunophenotyping in patients with leptomeningeal carcinomatosis

Some patients with epithelial-cell cancers develop leptomeningeal carcinomatosis (LC), a severe complication difficult to diagnose and with an adverse prognosis. This study explores the contribution of flow cytometry immunophenotyping (FCI) to the diagnosis and prognosis of LC. Cerebrospinal fluid (CSF) samples from patients diagnosed with LC were studied using FCI. Expression of the epithelial-cell adhesion molecule (EpCAM) was the criterion used to identify the epithelial cells. To test the diagnostic precision, 144 patients (94 diagnosed with LC) were included. The prognostic value of FCI was evaluated in 72 patients diagnosed with LC and eligible for therapy. Compared with cytology, FCI showed greater sensitivity and negative predictive value (79.79 vs. 50%; 68.85 vs. 51.55%, respectively), but lower specificity and positive predictive value (84 vs. 100%; 90.36 vs. 100%, respectively). The multivariate analysis revealed that the percentage of CSF EpCAM+ cells predicted an increased risk of death (HR: 1.012, 95% CI 1.000-1.023; p=0.041). A cut-off value of 8% EpCAM+ cells in the CSF distinguished two groups of patients with statistically significant differences in overall survival (OS) (p=0.018). This cut-off value kept its statistical significance regardless of the absolute CSF cell-count. The FCI study of the CSF improved the sensitivity for diagnosing LC, but refinement of the technique is needed to improve specificity. Furthermore, quantification of CSF EpCAM+ cells was revealed to be an independent prognostic factor for OS in patients with LC eligible for therapy. An 8% cut-off value contributed to predicting clinical evolution before initiation of therapy.

Utility of Flow Cytometry of Cerebrospinal Fluid as a Screening Tool in the Diagnosis of Central Nervous System Lymphoma

Context.—Experiences at our institution show that flow cytometry analysis (FCA) has become routine clinical practice in the workup of patients with altered mental status, even if risk factors are low.

Objective.—To assess diagnostic accuracy of combined FCA and cytology in the diagnosis of central nervous system lymphoma in an unselected patient population with neurologic symptoms, including patients with no history of lymphoma or suspicious radiology.

Design.—Between 2001 and 2011, cerebrospinal fluid was submitted from 373 patients for lymphoma screening by FCA. The medical records were reviewed for patient symptomatology, history of malignancy, brain imaging, FCA results, cytology results, brain biopsy, and clinical follow-up.

Results.—A lymphoid malignancy was detected by FCA in 4% of cases. A positive diagnosis was more likely in patients with either a history of hematologic malignancy and/or a suspicious radiology result (P = .009). All patients with no history of lymphoma and no suspicious radiology (n = 102) had negative cytology, and none had a correspondingly positive FCA result. The positive and negative predictive values of combined cytology and FCA in the patients with history of lymphoma and/or abnormal imaging results were 92% and 89%, respectively, when compared with open brain tissue biopsy, and 89% and 86%, respectively, when compared with clinical follow-up. When low-risk patients were included, the positive predictive value remained at 92%, but the negative predictive value dropped to 52% with the open brain biopsy as the reference, and values did not change significantly for the group with clinical follow-up.

Conclusions.—Concurrent FCA and cytology are most useful in the appropriate clinical setting, and we propose a triage algorithm for how FCA on cerebrospinal fluid is best used.

Diagnostic strategies to investigate cerebrospinal fluid involvement in haematological malignancies

Central nervous system (CNS) involvement is a fatal complication of certain haematological malignancies with an incidence as high as 25% in specific leukaemia/lymphoma subtypes. It is often accompanied by 'occult' cerebrospinal fluid (CSF) involvement at diagnosis, which is frequently missed by conventional cytology examination. Unfortunately, a diagnostic gold standard is yet unavailable since CSF morphology may be negative for malignant cells in up to 45% of patients with suspected meningeal involvement. New technologies such as flow cytometry, molecular genetics and newer biomarkers may improve sensitivity and specificity facilitating the diagnosis of CNS involvement as well as effective prophylaxis and successful treatment.

Final results of a multicenter trial addressing role of CSF flow cytometric analysis in NHL patients at high risk for CNS dissemination

This prospective study compared diagnostic and prognostic value of conventional cytologic (CC) examination and flow cytometry (FCM) of baseline samples of cerebrospinal fluid (CSF) in 174 patients with newly diagnosed aggressive non-Hodgkin lymphoma (NHL). FCM detected a neoplastic population in the CSF of 18 of 174 patients (10%), CC only in 7 (4%; P < .001); 11 patients (14%) were discordant (FCM+/CC−). At a median follow-up of 46 months, there were 64 systemic progressions and 10 CNS relapses, including 2 patients with both systemic and CNS relapses. Two-year progression-free and overall survival were significantly higher in patients with FCM− CSF (62% and 72%) compared with those FCM+ CSF (39% and 50%, respectively), with a 2-year CNS relapse cumulative incidence of 3% (95% confidence interval [CI], 0-7) versus 17% (95% CI, 0-34; P = .004), respectively. The risk of CNS progression was significantly higher in FMC+/CC− versus FCM−/CC− patients (hazard ratio = 8.16, 95% CI, 1.45-46). In conclusion, FCM positivity in the CSF of patients with high-risk NHL is associated with a significantly higher CNS relapse risk and poorer outcome. The combination of IV drugs with a higher CNS bioavailability and intrathecal chemotherapy is advisable to prevent CNS relapses in FCM+ patients.

EuroFlow antibody panels for standardized n-dimensional flow cytometric immunophenotyping of normal, reactive and malignant leukocytes

Most consensus leukemia & lymphoma antibody panels consist of lists of markers based on expert opinions, but they have not been validated. Here we present the validated EuroFlow 8-color antibody panels for immunophenotyping of hematological malignancies. The single-tube screening panels and multi-tube classification panels fit into the EuroFlow diagnostic algorithm with entries defined by clinical and laboratory parameters. The panels were constructed in 2-7 sequential design-evaluation-redesign rounds, using novel Infinicyt software tools for multivariate data analysis. Two groups of markers are combined in each 8-color tube: (i) backbone markers to identify distinct cell populations in a sample, and (ii) markers for characterization of specific cell populations. In multi-tube panels, the backbone markers were optimally placed at the same fluorochrome position in every tube, to provide identical multidimensional localization of the target cell population(s). The characterization markers were positioned according to the diagnostic utility of the combined markers. Each proposed antibody combination was tested against reference databases of normal and malignant cells from healthy subjects and WHO-based disease entities, respectively. The EuroFlow studies resulted in validated and flexible 8-color antibody panels for multidimensional identification and characterization of normal and aberrant cells, optimally suited for immunophenotypic screening and classification of hematological malignancies.

Rapid, efficient functional characterization and recovery of HIV-specific human CD8+ T cells using microengraving

The nature of certain clinical samples (tissue biopsies, fluids) or the subjects themselves (pediatric subjects, neonates) often constrain the number of cells available to evaluate the breadth of functional T-cell responses to infections or therapeutic interventions. The methods most commonly used to assess this functional diversity ex vivo and to recover specific cells to expand in vitro usually require more than 10(6) cells. Here we present a process to identify antigen-specific responses efficiently ex vivo from 10(4)-10(5) single cells from blood or mucosal tissues using dense arrays of subnanoliter wells. The approach combines on-chip imaging cytometry with a technique for capturing secreted proteins--called "microengraving"--to enumerate antigen-specific responses by single T cells in a manner comparable to conventional assays such as ELISpot and intracellular cytokine staining. Unlike those assays, however, the individual cells identified can be recovered readily by micromanipulation for further characterization in vitro. Applying this method to assess HIV-specific T-cell responses demonstrates that it is possible to establish clonal CD8(+) T-cell lines that represent the most abundant specificities present in circulation using 100- to 1,000-fold fewer cells than traditional approaches require and without extensive genotypic analysis a priori. This rapid (<24 h), efficient, and inexpensive process should improve the comparative study of human T-cell immunology across ages and anatomic compartments.

Circulating plasma cells predict the outcome of relapsed or refractory multiple myeloma

Pretreatment detection of peripheral blood malignant circulating plasma cells (CPCs) has been shown to be of negative prognostic value in multiple myeloma (MM). We hypothesized that the assessment of CPC kinetics in response to one therapy cycle using six-color flow cytometry could be helpful in the early detection of MM refractoriness to treatment. Forty-two patients with refractory or relapsed (RR) MM were enrolled. Median time to tumor progression (TTP) of 51 days and median overall survival (OS) of 308 days was shortest in patients whose CPCs with aberrant phentoype (aCPCs) did not decrease after one therapy cycle compared to patients with decreasing (median TTP 258 days and OS 856 days) or undetectable (median TTP 581 days and OS 1006 days) aCPCs (p < 0.001 and p = 0.007 for TTP and OS, respectively). Non-reduction of aCPCs in patients with RR MM after the first cycle of therapy may be useful in early identification of patients resistant to a given therapy.

Flow cytometric immunophenotyping of cerebrospinal fluid specimens

Flow cytometric immunophenotyping (FCI) is recommended in the evaluation of cerebrospinal fluid (CSF) specimens for hematologic neoplasms. This study reviewed FCI of CSF specimens collected for primary diagnosis (n = 77) and follow-up for known malignancy (n = 153). FCI was positive in 11 (4.8%) of 230 specimens: acute myeloid leukemia, 6; precursor B-acute lymphoblastic leukemia, 2; B-cell lymphoma, 2; and T-cell lymphoma, 1. Positive results were obtained in low-cellularity specimens, including 2 with fewer than 100 events in the population of interest. FCI was indeterminate in 19 (8.3%) of 230 specimens, including 3 with only sparse events, 8 with possible artifact (apparent lack of staining, nonspecific or background staining, and aspirated air), and 8 with phenotypic findings considered insufficient for diagnosis. Indeterminate specimens were often limited by low cellularity and lacked normal cell populations to evaluate for appropriate staining. FCI may be of value in low-cellularity CSF specimens, although the results should be interpreted with caution.

Diagnosis of leptomeningeal disease in diffuse large B-cell lymphomas of the central nervous system by flow cytometry and cytopathology

Reliable detection of leptomeningeal disease has the potential of facilitating the diagnosis of central nervous system (CNS) lymphoma and is important for therapeutic considerations. Currently, the standard diagnostic procedure for the detection of lymphoma in the cerebrospinal fluid is cytopathology. To improve the limited specificity and sensitivity of cytopathology, flow cytometry has been suggested as an alternative. Here, we evaluated multi-parameter flow cytometry in combination with conventional cytopathology in cerebrospinal fluid (CSF) samples from 30 patients with primary CNS lymphoma and seven patients with secondary CNS lymphoma. Overall, in 11 of 37 (29.7%) patients with CNS lymphoma, lymphoma cells were detected in CSF by flow cytometry, while cytopathology was less sensitive displaying unequivocally malignant CSF cells in only seven of all 37 (18.9%) patients. Six (16.2%) patients showed cytopathological results suspicious of lymphoma; however, in only one of these patients, the diagnosis of CSF lymphoma cells could be confirmed by flow cytometry. In primary CNS lymphomas (PCNSL), seven of 30 (23.3%) patients were positive for CSF lymphoma cells in flow cytometry, in contrast to four (13.3%) patients with PCNSL with definitely positive cytopathology. In summary, our results suggest that multi-parameter flow cytometry increases the sensitivity and specificity of leptomeningeal disease detection in CNS lymphomas. Both methods should be applied concurrently for complementary diagnostic assessment in patients with CNS lymphoma.

Standardized MRD quantification in European ALL trials: proceedings of the Second International Symposium on MRD assessment in Kiel, Germany, 18-20 September 2008

Assessment of minimal residual disease (MRD) has acquired a prominent position in European treatment protocols for patients with acute lymphoblastic leukemia (ALL), on the basis of its high prognostic value for predicting outcome and the possibilities for implementation of MRD diagnostics in treatment stratification. Therefore, there is an increasing need for standardization of methodologies and harmonization of terminology. For this purpose, a panel of representatives of all major European study groups on childhood and adult ALL and of international experts on PCR- and flow cytometry-based MRD assessment was built in the context of the Second International Symposium on MRD assessment in Kiel, Germany, 18-20 September 2008. The panel summarized the current state of MRD diagnostics in ALL and developed recommendations on the minimal technical requirements that should be fulfilled before implementation of MRD diagnostics into clinical trials. Finally, a common terminology for a standard description of MRD response and monitoring was established defining the terms 'complete MRD response', 'MRD persistence' and 'MRD reappearance'. The proposed MRD terminology may allow a refined and standardized assessment of response to treatment in adult and childhood ALL, and provides a sound basis for the comparison of MRD results between different treatment protocols.

Naive and Memory CD4+T-cells in the Cerebrospinal Fluid of Children with Aseptic Meningitis Following Measles-Mumps-Rubella Vaccination and Enteroviral Meningitis

We investigated the distribution of memory (CD45RO+) and naive (CD45RA+CD62L+) CD4+ T-cells as well as CD8+ T-cells and total T-cells in the CSF of children with aseptic meningitis following measles-mumps-rubella (MMW) vaccination and those with enteroviral meningitis. Flow cytometric analysis of CSF cells was performed in 12 children with MMR vaccine-associated meningitis and 11 children with enteroviral meningitis. Percentages of total T-cells, CD4+ and CD8+ T-cells and monocytes in CSF of patients from the two groups were not significantly different. The majority of CD4+ T-cells in the CSF of both patient groups were of memory phenotype. Percentages of CSF naive CD4+ T-cells were increased in children with aseptic meningitis following MMR vaccination. Further studies focused on the more detailed immunophenotyping of CSF cells are needed to fully establish the usefulness of flow cytometry in the diagnostic workup of inflammatory CNS diseases in children.

Identification of Leptomeningeal Disease in Aggressive B-Cell Non-Hodgkin's Lymphoma: Improved Sensitivity of Flow Cytometry

Purpose

Here, we evaluate the sensitivity and specificity of a new 11-parameter flow cytometry (FCM) approach versus conventional cytology (CC) for detecting neoplastic cells in stabilized CSF samples from newly diagnosed aggressive B-cell non-Hodgkin's lymphoma (B-NHL) at high risk of CNS relapse, using a prospective, multicentric study design.

Patients and Methods

Moreover, we compared the distribution of different subpopulations of CSF leukocytes and the clinico-biologic characteristics of CSF+ versus CSF−, patients, in an attempt to define new algorithms useful for predicting CNS disease.

Results

Overall, 27 (22%) of 123 patients showed infiltration by FCM, while CC was positive in only seven patients (6%), with three other cases being suspicious (2%). CC+/FCM+ samples typically had more than 20% neoplastic B cells and/or ≥ one neoplastic B cell/μL, while FCM+/CC− samples showed lower levels (P < .0001) of infiltration. Interestingly, in Burkitt lymphoma, presence of CNS disease by FCM could be predicted with a high specificity when increased serum β2-microglobulin and neurological symptoms coexisted, while peripheral blood involvement was the only independent parameter associated with CNS disease in diffuse large B-cell lymphoma, with low predictive value.

Conclusion

FCM significantly improves the sensitivity of CC for the identification of leptomeningeal disease in aggressive B-NHL at higher risk of CNS disease, particularly in paucicellular samples.

Direct analysis of clinical relevant single bacterial cells from cerebrospinal fluid during bacterial meningitis by means of micro-Raman spectroscopy

Bacterial meningitis is a relevant public health concern. Despite the availability of modern treatment strategies it is still a life-threatening disease that causes significant morbidity and mortality. Therefore, an initial treatment approach plays an important role. For in-time identification of specific bacterial pathogens of the cerebrospinal fluid (CSF) and emerged antimicrobial and adjunctive treatment, microbiological examination is of major importance. This contribution spotlights the potential of micro-Raman spectroscopy as a biomedical assay for direct analysis of bacteria in cerebrospinal fluid of patients with bacterial meningitis. The influence of miscellaneous artificial environments on several bacterial species present during bacterial meningitis was studied by means of Raman spectroscopy. The application of chemometric data interpretation via hierarchical cluster analysis (HCA) allows for the differentiation of in vitro cultured bacterial cells and can also be achieved on a single cell level. Moreover as proof of principle the investigation of a CSF sample obtained from a patient with meningococcal meningitis showed that the cerebrospinal fluid matrix does not mask the Raman spectrum of a bacterial cell notably since via chemometric analysis with HCA an identification of N. meningitidis cells from patients with bacterial meningitis could be achieved.

Flow cytometric immunophenotyping of cerebrospinal fluid

Leptomeningeal disease is an important adverse complication occurring in patients with B and T cell lymphomas and acute leukemias of lymphoid and myeloid origin. Recent reports suggest that multiparameter flow cytometry immunophenotypic assessment of spinal fluid samples could improve the efficiency of detection of CNS involvement, due to its high specificity and greater sensitivity. However, spinal fluid samples are frequently paucicellular with a rapidly decreasing cell viability. Staining of spinal fluid therefore requires dedicated sample storage/transport, staining, and preparation protocols. The Basic Protocol in this unit outlines a consensus multiparameter (3- to 8-color) flow cytometry immunophenotypic protocol for the evaluation of CNS involvement of cerebrospinal fluid (CSF) samples by neoplastic cells. A Support Protocol describing the simultaneous assessment of surface and cytoplasmic antigens is also provided. Finally, in the Alternate Protocol, we describe a method to calculate absolute numbers of both normal and pathological cell subpopulations by adding counting beads to the assay.

CSF enrichment of highly differentiated CD8+ T cells in early multiple sclerosis

CD8+ T cells may play an important role in multiple sclerosis (MS). Whether these cells would be involved in early stages of MS is unclear. We enrolled 52 patients with suspected MS, determined the recruitment of their highly differentiated (CCR7-/CD45RA+ or -) T cells (T(HD)) in the CSF as compared to peripheral blood and followed them for 12+/-7.3 months. A ROC curve showed that a CD8+/CD4+ T(HD) cells ratio of 0.94 helped to distinguish relapsing-remitting (RR-MS) and possible MS (Po-MS) from primary-progressive MS (PP-MS) and other neurological diseases patients (OND) patients (p=0.039), risk ratio of 2.29 (95% CI: 1.13-4.66; p=0.006). The CSF enrichment in CD8+ T(HD) cells was greater than in CD4+ T(HD) cells in RR/Po-MS patients (p=0.024) and than in CD8+ T(HD) cells in PP-MS/OND patients (p=0.006). These data suggest that CD8+ T(HD) cells play a role in the early stages of RR-MS.

Detection of malignant hematopoietic cells in cerebral spinal fluid previously diagnosed as atypical or suspicious

BACKGROUND

Involvement of the cerebrospinal fluid (CSF) by hematopoietic malignancies may be difficult to document by morphology alone. In cases with low numbers of cells or ambiguous morphology, the diagnoses of "atypical" or "suspicious" may be used. The significance of these diagnostic terms in this scenario has not been well established.

METHODS

Between January 2000 and July 2004, 32 patients with known lymphoma or leukemia and an initial diagnosis of "atypical" or "suspicious" using morphologic criteria were identified. Subsequent flow cytometry (FC) and cytologic data from these patients were evaluated.

RESULTS

Of the 32 patients with an initial diagnosis of "atypical" or "suspicious," 40.6% (n = 13) had negative first and subsequent FC and morphologic evaluation of their CSF samples with follow-up up to 1 year. Nineteen patients (59.4%) had malignant hematopoietic cells identified in subsequent CSF samples by cytology and/or FC.

CONCLUSIONS

In patients with a previous history of lymphoma or a hematopoietic malignancy, a majority of the patients (59.4%) with an "atypical" or "suspicious" diagnosis on CSF will ultimately have malignant cells identified in the CSF by cytology and/or FC. Many of these patients can be identified more expediently with the concurrent utilization of flow cytometry.

Advantages of flow cytometry immunophenotyping for the diagnosis of central nervous system non-Hodgkin's lymphoma in AIDS patients

BACKGROUND

Neurological disorders are common in HIV-infected patients. Central nervous system (CNS) lymphoma should always be considered because it is an important cause of morbidity and mortality.

OBJECTIVES

To investigate the clinical utility of flow cytometry immunophenotyping (FCI) in diagnosing or discarding leptomeningeal involvement in HIV-infected patients and to compare its sensitivity with that of conventional cytological methods.

METHODS

Fifty-six cerebrospinal fluid (CSF) samples from 29 HIV-infected patients were independently evaluated by flow cytometry and cytology. The description of an aberrant immunophenotype was the criterion used to define the malignant nature of any CSF cell population.

RESULTS

FCI and cytology gave concordant results for 48 of the 56 CSF samples studied: 37 were negative for malignancy and 11 had evidence of CNS lymphoma. Discordant results were obtained for eight CSF samples, and the accuracy of the FCI findings could be demonstrated for four CSF samples described as positive for malignancy according to the FCI criteria.

CONCLUSIONS

A high level of agreement was found between the results obtained using the two methods, but FCI gave at least 25% higher sensitivity than conventional cytomorphological methods for the detection of malignant cells. This advantage suggests that, in case of negative flow cytometry results, disorders other than non-Hodgkin's lymphoma should be strongly considered.

B-lymphocyte and plasma cell clonal expansion in monosymptomatic optic neuritis cerebrospinal fluid

The CD19+ B-lymphocyte and CD138+ plasma cell repertoires in cerebrospinal fluid from four patients with monosymptomatic optic neuritis (ON) were analyzed by single-cell reverse transcriptase polymerase chain reaction. Amplified heavy (H)- and light (L)-chain antibody segments were sequenced and used to identify the rearranged germline and J segment of closest homology. Both the B-cell and plasma cell repertoires from ON cerebrospinal fluid demonstrated significant clonal expansion. Up to 75% of the amplified H- and L-chain sequences were contained in overrepresented populations and were somatically mutated, consistent with an antigen-targeted response. The relationship between clonal populations within the CD19+ B lymphocyte and CD138+ plasma cell populations suggests ongoing mutational pressure to refine antigen binding. Our observations demonstrate that an antigen-driven clonal B-lymphocyte and plasma cell response is prominent in the initial stages of central nervous system demyelination and suggest that detection of the disease-relevant antigens in ON may bear on the inciting antigens in chronic inflammatory disorders such as multiple sclerosis.

CSF B-cell expansion in opsoclonus-myoclonus syndrome: A biomarker of disease activity

Lack of a biomarker of disease activity has hindered the therapy of childhood opsoclonus-myoclonus syndrome (OMS), which is purported to be mediated humorally. To determine if the cerebrospinal fluid (CSF) B lymphocyte, which may traffic into the central nervous system (CNS) to produce antibody locally, is one such biomarker, B lymphocytes were immunophenotyped in the CSF and blood of 56 children with OMS and 26 pediatric controls by dual-laser flow cytometry. Neurological severity was rated blindly from videotapes using a validated 12-item motor evaluation scale. Children with OMS manifested a 4- to 7-fold higher percentage of total B-cells in CSF (P < 0.0001), including CD5(+) (P = 0.001) and CD5(-) (P = 0.0004) B-cell subsets, compared with controls, in whom the percentages were negligible and unchanging with age. CSF expansion of both B-cell subsets increased with disease severity and decreased with disease duration (P </= 0.0001, ANOVA). Previous treatment with conventional immunotherapies, chemotherapy, or tumor resection had not normalized B-cell percentages in those with lingering symptoms. These studies reveal that CSF B-cell expansion in OMS is characteristic and often persistent. Presence of the autoreactive CD5(+) B-cell subset and correlations with neurological severity and disease duration suggest CSF B-cell expansion is a biomarker of disease activity and possible target for B-cell-specific therapy. Immunophenotyping of CSF lymphocytes by flow cytometry yields valuable clinical information missed by routine studies and allows crucial treatment decisions to be made rapidly.