Precision Metrology Meets Cosmology: Improved Constraints on Ultralight Dark Matter from Atom-Cavity Frequency Comparisons

We conduct frequency comparisons between a state-of-the-art strontium optical lattice clock, a cryogenic crystalline silicon cavity, and a hydrogen maser to set new bounds on the coupling of ultralight dark matter to standard model particles and fields in the mass range of 10^{-16}-10^{-21}  eV. The key advantage of this two-part ratio comparison is the differential sensitivity to time variation of both the fine-structure constant and the electron mass, achieving a substantially improved limit on the moduli of ultralight dark matter, particularly at higher masses than typical atomic spectroscopic results. Furthermore, we demonstrate an extension of the search range to even higher masses by use of dynamical decoupling techniques. These results highlight the importance of using the best-performing atomic clocks for fundamental physics applications, as all-optical timescales are increasingly integrated with, and will eventually supplant, existing microwave timescales.

Engineering Quantum States of Matter for Atomic Clocks in Shallow Optical Lattices

We investigate the effects of stimulated scattering of optical lattice photons on atomic coherence times in a state-of-the art ^{87}Sr optical lattice clock. Such scattering processes are found to limit the achievable coherence times to less than 12 s (corresponding to a quality factor of 1×10^{16}), significantly shorter than the predicted 145(40) s lifetime of ^{87}Sr's excited clock state. We suggest that shallow, state-independent optical lattices with increased lattice constants can give rise to sufficiently small lattice photon scattering and motional dephasing rates as to enable coherence times on the order of the clock transition's natural lifetime. Not only should this scheme be compatible with the relatively high atomic density associated with Fermi-degenerate gases in three-dimensional optical lattices, but we anticipate that certain properties of various quantum states of matter-such as the localization of atoms in a Mott insulator-can be used to suppress dephasing due to tunneling.

Imaging Optical Frequencies with 100 μHz Precision and 1.1 μm Resolution

We implement imaging spectroscopy of the optical clock transition of lattice-trapped degenerate fermionic Sr in the Mott-insulating regime, combining micron spatial resolution with submillihertz spectral precision. We use these tools to demonstrate atomic coherence for up to 15 s on the clock transition and reach a record frequency precision of 2.5×10^{-19}. We perform the most rapid evaluation of trapping light shifts and record a 150 mHz linewidth, the narrowest Rabi line shape observed on a coherent optical transition. The important emerging capability of combining high-resolution imaging and spectroscopy will improve the clock precision, and provide a path towards measuring many-body interactions and testing fundamental physics.

A Fermi-degenerate three-dimensional optical lattice clock

Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 × 10¹⁷ Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 × 10^-19 in 1 hour of averaging time.

Coherent magnon optics in a ferromagnetic spinor Bose-Einstein condensate

We measure the dispersion relation, gap, and magnetic moment of a magnon in the ferromagnetic F = 1 spinor Bose-Einstein condensate of (87)Rb. From the dispersion relation we measure an average effective mass 1.033(2)(stat)(10)(sys) times the atomic mass, as determined by interfering standing and running coherent magnon waves within the dense and trapped condensed gas. The measured mass is higher than theoretical predictions of mean-field and beyond-mean-field Beliaev theory for a bulk spinor Bose gas with s-wave contact interactions. We observe a magnon energy gap of h × 2.5(1)(stat)(2)(sys) Hz, which is consistent with the predicted effect of magnetic dipole-dipole interactions. These dipolar interactions may also account for the high magnon mass. The effective magnetic moment of -1.04(2)(stat)(8)(sys) times the atomic magnetic moment is consistent with mean-field theory.

Ibrutinib-induced lymphocytosis in patients with chronic lymphocytic leukemia: correlative analyses from a phase II study

Ibrutinib and other targeted inhibitors of B-cell receptor signaling achieve impressive clinical results for patients with chronic lymphocytic leukemia (CLL). A treatment-induced rise in absolute lymphocyte count (ALC) has emerged as a class effect of kinase inhibitors in CLL and warrants further investigation. We here report correlative studies in 64 patients with CLL treated with ibrutinib. We quantified tumor burden in blood, lymph nodes, spleen, and bone marrow, assessed phenotypic changes of circulating cells, and measured whole blood viscosity. With just one dose of ibrutinib the average increase in ALC was 66%, and in over 40% of patients the ALC peaked within 24 hours of initiating treatment. Circulating CLL cells on day 2 showed increased Ki67 and CD38 expression, indicating an efflux of tumor cells from the tissue compartments into the blood. The kinetics and degree of the treatment-induced lymphocytosis was highly variable; interestingly in patients with a high baseline ALC the relative increase was mild and resolution rapid. After two cycles of treatment the disease burden in lymph node, bone marrow, and spleen decreased irrespective of the relative change in ALC. Whole blood viscosity was dependent on both ALC and hemoglobin. No adverse events were attributed to the lymphocytosis.

Enhanced and reduced atom number fluctuations in a BEC splitter

We measure atom number statistics after splitting a gas of ultracold 87Rb atoms in a purely magnetic double-well potential created on an atom chip. Well below the critical temperature for Bose-Einstein condensation Tc, we observe reduced fluctuations down to -4.9 dB below the atom shot noise level. Fluctuations rise to more than +3.8 dB close to Tc, before reaching the shot noise level for higher temperatures. We use two-mode and classical field simulations to model these results. This allows us to confirm that the supershot noise fluctuations directly originate from quantum statistics.

Human peripheral blood B-cell compartments: a crossroad in B-cell traffic

A relatively high number of different subsets of B-cells are generated through the differentiation of early B-cell precursors into mature B-lymphocytes in the bone marrow (BM) and antigen-triggered maturation of germinal center B-cells into memory B-lymphocytes and plasmablasts in lymphoid tissues. These B-cell subpopulations, which are produced in the BM and lymphoid tissues, recirculate through peripheral blood (PB), into different tissues including mucosa and the BM, where long-living plasma cells produce antibodies. These circulating PB B-cells can be classified according to their maturation stage into i) immature/transitional, ii) naïve, and iii) memory B-lymphocytes, and iv) plasmablasts/plasma cells. Additionally, unique subsets of memory B-lymphocytes and plasmablasts/plasma cells can be identified based on their differential expression of unique Ig-heavy chain isotypes (e.g.: IgM, IgD, IgG, IgA). In the present paper, we review recent data reported in the literature about the distribution, immunophenotypic and functional characteristics of these cell subpopulations, as well as their distribution in PB according to age and seasonal changes. Additional information is also provided in this regard based on the study of a population-based cohort of 600 healthy adults aged from 20 to 80 years, recruited in the Salamanca area in western Spain. Detailed knowledge of the distribution and traffic of B-cell subsets through PB mirrors the immune status of an individual subject and it may also contribute to a better understanding of B-cell disorders related to B-cell biology and homeostasis, such as monoclonal B-cell lymphocytosis (MBL).

Detection of unseparated human lymphocytes by flow cytometry

The protocol for flow cytometry analysis presented here has been specifically developed for studies of human peripheral blood cells. In this protocol, analysis is performed on unseparated cells in whole peripheral blood, rather than on Ficoll-Hypaque-purified mononuclear cells. The advantage of this approach is that it requires less time, uses smaller blood volumes, and eliminates possible differential blood loss as a result of cell separation techniques. In this regard, B cell recovery using the whole blood method is significantly greater than that obtained using Ficoll-Hypaque-purified mononuclear cells. However, because lymphocytes generally represent a minority of peripheral cells (especially in adults), careful gating of the test samples for lymphocytes is a more critical requirement in this procedure than in other procedures using purified cells.

Discrepancy in measuring CD4 expression on T-lymphocytes using fluorescein conjugates in comparison with unimolar CD4-phycoerythrin conjugates

BACKGROUND

Numerous methods for quantitative fluorescence calibration (QFC) have been developed to quantify receptor expression on lymphocytes. However, the results from the use of these different QFC methods vary considerably in the literature. To better identify the causes of these discrepancies, we measured CD4 expression using FITC and phycoerythrin (PE) conjugates to stain CYTO-TROL Control Cells and T-lymphocytes in whole blood and isolated cell preparations. We further examined pH of the cellular microenvironment as a cause of discordant results obtained with the FITC conjugate.

METHODS

Calibration with Quantibrite PE-labeled microspheres and the use of unimolar CD4-PE conjugates provided direct measurement of the antibody bound per cell value (ABC) for CD4 expression on normal T-lymphocytes. Calibration for CD4-FITC monoclonal antibody (Mab) labeled CYTO-TROL Control Cells and normal T-lymphocytes was based on molecules of equivalent soluble fluorochrome (MESF) as determined by FITC-labeled microspheres traceable to NIST RM 8640. The MESF value for CD4-FITC Mab was determined that enabled the conversion of the MESF values obtained for CYTO-TROL cells to ABC. We investigated the likely pH change in the fluorescein microenvironments within FITC-labeled Mab and cells stained with FITC-labeled Mab using a pH sensitive indicator.

RESULTS

The mean ABC value for T-lymphocytes prepared from fresh whole blood using CD4-PE conjugate (48,321) was consistent with previous results, and it was much higher than the mean ABC using CD4-FITC Mab (22,156). The mean ABC value for CYTO-TROL cells using CD4-PE conjugate (43,090) was also higher than that using CD4-FITC conjugate (34,734), although the discrepancy was not as great. Further studies suggested the discrepancy in CYTO-TROL results may be accounted for by the low pH of the membrane microenvironment, but the greater discrepancy in T-lymphocytes could not be fully explained.

CONCLUSION

CD4 expression on fresh normal whole blood samples and CYTO-TROL cells can be consistently quantified in ABC units using Quantibrite PE quantification beads and unimolar CD4-PE conjugates. Quantification with CD4-FITC conjugate is not as consistent, but may be improved by the use of CD4 T-cells as biological calibrators. This approximation is valid only for surface receptors with consensus ABC values measured by different QFC methods serving as biological standards.

CD69 expression as an index of T-cell function: assay standardization, validation and use in monitoring immune recovery

BACKGROUND

CD69 is a surrogate marker of T-cell responsiveness to mitogen and Ag stimulus and can be used as a measure of T-lymphocyte activation. Quantitative flow cytometric determination of CD69 expression on T lymphocytes has several advantages over traditional lymphocyte proliferation assays, but this method has not yet been standardized for clinical applications.

METHODS

We qualified a commercially available assay using the manufacturer's procedures for measurement of T-cell response to a mitogen (PHA), superantigen (Staphylococcus endotoxin B; SEB) and Ca(2+) ionophore (phorbyl myristate acetate; PMA) with peripheral blood from healthy volunteers. Following this, we tested the usefulness of the assay in determining T-cell responses to PHA and SEB for six immunocompromised patients.

RESULTS

Healthy volunteers showed 17-fold increases in T-cell CD69 Ab bound per cell (ABC) with PHA stimulation compared with the baseline. SEB was also an effective T-cell activating agent, increasing CD69 ABC by 5-fold, comparable with results obtained with PMA stimulation. PHA- and SEB-stimulated T-cell CD69 ABC for patients 100 days post-BM transplant were generally below 1 SD of that from healthy volunteers. SEB-stimulated T-cell CD69 expression was significantly depressed for CD8(+) T cells while CD4(+) T-cell responses to SEB were generally within 1 SD of the mean for healthy volunteers.

DISCUSSION

These results suggest that quantitative measurement of CD69 surface expression by flow cytometry is a useful diagnostic tool for detailed assessment of T-lymphocyte and subset activation.

Structure Sensitivity of Vibrational Spectra of Mesoporous Silica SBA-15 and Pt/SBA-15

The vibrational properties of mesoporous silica (SBA-15) were investigated by deep ultraviolet (UV) Raman and infrared spectroscopies with and without the presence of platinum nanoparticles in the mesopores that were incorporated by sonication. Raman and IR spectral line assignments were made by comparison to amorphous silicas. This procedure permitted identification of vibrations of longitudinal (LO) and transverse (TO) optical lattice modes, the presence of Si-OH, and vibrational modes associated with the presence of three-, four-, and six-membered siloxane rings. Hydraulic pressing of the mesoporous silica with pressure in the range 3-7 tons cm(-2) destroys the X-ray diffraction pattern and strongly decreases the Raman peak (D2) associated with three-membered rings at the surface. In the presence of platinum nanoparticles in the silica mesopores, a peak attributed to a Pt-O stretching vibration appears at between 530 and 580 cm(-1) in the UV-Raman spectrum, which can be used to monitor the presence of the platinum particles and their interaction with the support. The D2 feature in the UV-Raman spectra also decreases with increasing Pt loading, which is attributed to interactions of the Pt nanoparticles with the silica surface.

Studies in NZB IL-10 knockout mice of the requirement of IL-10 for progression of B-cell lymphoma

NZB mice develop an age-related malignant expansion of a subset of B cells, B-1 cells, with autocrine production of IL-10. IL-10, a pleiotropic cytokine with anti-inflammatory properties, is a potent growth and survival factor for malignant B cells. To further examine the in vivo requirement for IL-10 in the development and expansion of malignant B-1 clones in NZB mice, we developed a strain of homozygous IL-10 knockout (KO) mice on an NZB background. The NZB IL-10 KO mice develop peritoneal B-1 cells with approximately the same frequency as heterozygous and wild-type littermates. In contrast, the development of malignant B-1 cells in the peripheral blood and spleen, observed in wild-type NZB, rarely occurred in the NZB IL-10 KO. Phenotypic analysis of surface marker expression in splenic B cells indicated that, in contrast to the NZB with malignant B-1 splenic lymphoma, the surface marker expression of NZB IL-10 KO splenic B cells indicated that the majority of the B cells were typical B-2 cells. In the absence of IL-10, spontaneously activated B cells and antiapoptotic gene expression were reduced and lymphoma incidence was decreased. These results indicate that IL-10 is a critical factor for the progression of this B-cell malignant disease.

Clinical characteristics of familial B-CLL in the National Cancer Institute Familial Registry

In an ongoing study, families with two or more living cases of B-CLL in first-degree relatives have been recruited through physician and self-referral. Since 1967, 28 kindreds with 73 cases of B-CLL have been enrolled within the National Cancer Institute (NCI) Familial B-CLL Registry. Medical, clinical, and demographic information have been obtained from private physicians, patient interview, hospital records, and death certificates. We used SEER Registry data to compare characteristics of sporadic B-CLL to familial B-CLL. The mean age at diagnosis was approximately 10 years younger among familial cases (57.9 +/- 12.1) than that observed in sporadic cases (70.1 +/- 11.9). A higher percentage of second primary tumors among familial CLL cases compared to reports in sporadic was also observed (16% vs. 8.8%). However, the transformation rate to non-Hodgkin's lymphoma does not appear to be different from that reported for sporadic cases. In conclusion, we observed some differences between familial and sporadic cases; whether any of these characteristics affect survival time or severity of disease is unknown. The study of families with multiple B-CLL cases will aid in delineating the genes and environmental factors that may play a role in the development of both forms of B-CLL.

Analysis of expressed immunoglobulin heavy chain genes in familial B-CLL

In this study, we wished to determine whether familial chronic lymphocytic leukemia of B-cell phenotype (CLL) shares with sporadic B-CLL the same immunoglobulin (Ig) heavy chain variable region (VH) gene usage and occurrence of somatic mutation, to gain insight into the pathogenetic relatedness of these epidemiologically distinct forms of CLL. We therefore analyzed the expressed Ig heavy chain genes in 23 cases (11 families) of familial CLL, and compared these results with data previously reported for sporadic CLL. In addition, we assessed the relationship of the occurrence of somatic mutation to several clinical and phenotypic features. The distribution of V genes among these cases was similar to that observed in sporadic CLL: VH3 > VH1 > VH4. Thirteen of the 23 cases (57%) showed germ line VH gene sequences, whereas somatic mutations were detected in 10 cases (43%). The average mutation frequency of these latter 10 cases of was 6.7% (ranging from 1.7% to 8.8%), and evidence of antigen selection was noted in 6. Intraclonal variation, followed by clonal evolution and the appearance of a second clone over a 20-year period was observed in 1 case, suggesting that mutations can continue to accumulate after neoplastic transformation. The presence of somatic mutations correlated with age at presentation, low white blood cell (WBC) count, and low fluorescence intensity of surface CD5, and the potential significance of these relationships is discussed. Our data indicate that familial and sporadic B-CLL display a similar pattern of immunoglobulin gene usage and frequency of somatic mutation, and are consistent with a common ontogeny and immunogenetic origin for these 2 epidemiologically distinct forms of CLL. (Blood. 2000;95:1413-1419)

Distinct types of diffuse large B-cell lymphoma identified by gene expression profiling

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin's lymphoma, is clinically heterogeneous: 40% of patients respond well to current therapy and have prolonged survival, whereas the remainder succumb to the disease. We proposed that this variability in natural history reflects unrecognized molecular heterogeneity in the tumours. Using DNA microarrays, we have conducted a systematic characterization of gene expression in B-cell malignancies. Here we show that there is diversity in gene expression among the tumours of DLBCL patients, apparently reflecting the variation in tumour proliferation rate, host response and differentiation state of the tumour. We identified two molecularly distinct forms of DLBCL which had gene expression patterns indicative of different stages of B-cell differentiation. One type expressed genes characteristic of germinal centre B cells ('germinal centre B-like DLBCL'); the second type expressed genes normally induced during in vitro activation of peripheral blood B cells ('activated B-like DLBCL'). Patients with germinal centre B-like DLBCL had a significantly better overall survival than those with activated B-like DLBCL. The molecular classification of tumours on the basis of gene expression can thus identify previously undetected and clinically significant subtypes of cancer.

CD5 is A potential selecting ligand for B-cell surface immunoglobulin: a possible role in maintenance and selective expansion of normal and malignant B cells

Although the function of CD5 on B cells is unknown, previous studies suggested that CD5 interaction with V(H) framework regions of surface immunoglobulins (Igs) may contribute to survival and expansion of B cells. Here we used B-chronic lymphocytic leukemia (B-CLL) cells and transformed B-cell lines from normal and B-CLL patients to study CD5-Ig interactions. Immobilized Ig binds and permits isolation of CD5 from lysates of CD5-expressing cell lines. Immunoglobulins or Fab fragments of different V(H) families varied in their effectiveness as inhibitors of anti-CD5 staining of CLL cells, appendix and tonsil tissue sections. Human Ig also binds to purified recombinant CD5. We show here for the first time that the unconventional Ig-CD5 interaction maps to the extracellular CD5-D2 domain whereas conventional epitopes recognized by anti-CD5 antibodies are localized in the D1 domain of CD5. We propose that interactions of VH framework regions with CD5 as a ligand may maintain, select or expand normal, autoimmune or transformed B cells and also contribute to skewing of the normal V(H) repertoire.

Standardizing flow cytometry: a classification system of fluorescence standards used for flow cytometry

The growing number of standards commercially available in the field of flow cytometry makes it difficult to know which standards to use to obtain a desired level of quality assurance. A classification system of fluorescence standards has been developed on the basis of their physical characteristics. In turn, these physical characteristics determine the ability of the specific standards to perform selected functions, such as alignment, target referencing, compensation, and calibration. Knowing the properties and limitations of specific standards will help flow cytometer users to select the appropriate standard for the application that they will be performing, especially in regard to intra- and interlaboratory quality assurance. Common protocols used in conjunction with specific classifications of reference standards can provide unified analysis regions or window of analysis across different instruments and/or laboratories. In addition, specific classifications of calibration standards can help select those standards that will provide independent and direct comparison of instrument performance parameters, especially in studies involving multiple laboratories. Knowledge and understanding of the classification system can guide flow cytometer users in more efficient and accurate instrument setup and quality control when conducting research, as well as clinical applications.

Quantitative flow cytometry: inter-laboratory variation

Quantitative flow cytometry (QFCM) offers a means of standardization within and between flow cytometers. QFCM parameters were set by determining the antibody-binding capacity (ABC) of CD4, CD8, and CD3 cells from 10 normal donors with the use of eight FACScan flow cytometers. QC3 beads and a certified blank bead were used to set up the instruments. Fluorescein isothiocyanate (FITC) conjugated to molecular equivalents of soluble fluorochrome (MESF) microbead standards was used before and after the donor samples were run to ensure that the machines were operating consistently. Lyophilized cells (Cytotrol) were used as a target, to control for antigen expression in the cell preparation. Quantitative Simply Cellular (QSC) beads were used to establish a standard calibration curve for each of the FITC and phycoerythrin antibody conjugates on each of the instruments. Single-parameter fluorescent histograms derived from list-mode files were used to calculate the slope (coefficient of response), intercept (zero channel), number of channels per decade, and ABC or MESF threshold (blank bead). The fluorescence intensity (geometric mean) of the positive and negative donor cell populations was compared with the standard curves, and the ABCs were calculated. The results show consistent instrument performance between laboratories. However, after standardization of CD3, CD4, and CD8 ABCs to microbeads, large variations were noted between donors and laboratories. The source of this variation does not appear to be in the instrumentation but may be due to the lack of an unified set-up protocol, introducing issues of antibody saturation, methods for whole blood lysis and fixation, and the behavior of the microbead standards.

Terminology and nomenclature for standardization in quantitative fluorescence cytometry

Terminology in any field is a complex mix of established conventions, accepted usages, disputed terms, and occasional misnomers. The terminology that has evolved for quantitative fluorescence cytometry (QFCM) is especially multifarious, in part because QFCM encompasses a range from subjective visual assessments to objective photon counts. Thus, while descriptive terms such as "dim" and "bright" are still quite useful, quantitative terms such as "binding capacity" should be used with collective understanding of their exact meanings. This article reviews current usage and proposes definitions that, with refinement from suppliers and users of QFCM technology, can provide the required clarity.

Flow cytometric enumeration of CD34+ hematopoietic stem and progenitor cells. European Working Group on Clinical Cell Analysis

The need for a rapid and reliable marker for the engraftment potential of hematopoietic stem and progenitor cell (HPC) transplants has led to the development of flow cytometric assays to quantitate such cells on the basis of their expression of CD34. The variability associated with enumeration of low-frequency cells (i.e., as low as 0.1% or 5 cells/microl) is exceedingly large, but recent developments have improved the accuracy and precision of the assay. Here, we review and compare the major techniques. Based on the current state of the art, we recommend 1) bright fluorochrome conjugates of class II or III monoclonal antibodies (mAbs) that detect all glycoforms of CD34, 2) use of a vital nucleic acid dye to exclude platelets, unlysed red cells, and debris or use of 7-amino actinomycin D to exclude dead cells during data acquisition, 3) counterstaining with CD45 mAb to be included in the definition of HPC, 4) during list mode data analysis, Boolean gating to resolve the CD34+ HPCs from irrelevant cell populations on the basis of the low levels of CD45 expression and low sideward light-scatter signals of HPCs, 5) inclusion of CD34dim and CD34bright populations in the CD34+ cell count, 6) omission of the negative control staining, and 7) for apheresis products, enumeration of at least 100 CD34+ cells to ensure a 10% precision. Unresolved technical questions are 1) the replacement of conventional dual-platform by single-platform assay formats, i.e., derivation of absolute CD34+ cell counts from a single flow cytometric assessment instead of from combined flow cytometer (percent CD34+) and hematology analyzer (absolute leukocyte count) data, 2) the cross-calibration of the available single-platform assays, and 3) the optimal method for sample preparation. An important clinical question to be addressed is the definition of the precise phenotypes and required numbers of HPCs responsible for short- and long-term recovery to optimize HPC transplant strategies.

Comparative analysis of whole blood lysis methods for flow cytometry

We performed a parallel evaluation of six whole blood lysis methods comparing light scatter and quantitative fluorescence intensity based on quantitative flow cytometry, of selected lymphocyte subsets and CD34+ cells. Leukocytes prepared with FACS Lysing Solution (BDIS), Immunolyse (Coulter) and Optilyse B (Immunotech) consistently gave lower forward scatter values than those prepared with ACK (BioWhitaker), Ortho-mune (Ortho) and ImmunoPrep (Coulter). Debris, defined as CD45 negative events with the threshold off, accounted approximately 80% of all events with ACK and Ortho-mune. The other lysing methods consistently yielded less debris (approximately 50%) with Immunolyse generating only approximately 16% debris. Optilyse and FACS lyse consistently displayed the lowest percentage of lymphoid cells (CD45+/CD14-) in the three part differential. The percentage of CD3+, CD20+, CD5+, and CD16/CD56+ cells was consistent with all methods but CD4 and CD8 determinants showed inconsistent variation with ACK and Ortho-mune. In addition, the fluorescence intensity of CD14 PE and CD8 PE staining was markedly decreased on cells prepared with ImmunoPrep. Finally, the clearest separation of CD34+ cells was observed with ACK and Ortho-mune. Our data demonstrate that the method used for red cell lysis can have definite impact on immunophenotyping and selected methods appear to be more suitable for specific applications.

Immunization with meningococcal membrane-bound lipooligosaccharide accelerates granulocyte recovery and enhances lymphocyte proliferation in myelosuppressed mice

Protective effects of detergent-treated outer membrane vesicles (D-OMVs) prepared from the parent group B M986 strain and the nonencapsulated M986-NCV mutant in myelosuppressed mice were investigated in models of experimental septic shock. The effects of D-OMVs on expansion of the myeloid compartment, on spleen cell proliferation to mitogen stimulation, and on cytokines induced during this period were investigated. On 3 consecutive days, mice were injected with 1 microgram/kg of lipooligosaccharide (LOS) or lipopolysaccharide, or 75 micrograms/kg D-OMV followed by a single dose of cyclophosphamide (200 mg/kg) 24 h later. Eight weeks after the last injection, animals were challenged with a combination of galactosamine (400 mg/kg) and live Neisseria meningitidis. More than 90% of control mice died within 24 h when challenged with 10(5) CFU of bacteria. Mice immunized with LOS or D-OMV were rendered neutropenic but were protected against bacterial challenge of at least 10(7) CFU. At different time intervals, peripheral blood samples were obtained to characterize changes in circulating blood cells. The rise in absolute granulocyte numbers occurred 24 h earlier with peak cell counts about 3 times higher than those seen in the placebo groups. Peripheral blood cells from D-OMV-treated animals expressed about twofold more Gr-1 antigen (myeloid surface cell marker) than placebo-treated controls. The proliferative responses to both B and T cells were reduced in all treatment groups due to the effects of cyclophosphamide. D-OMV treatment afforded the greatest protection for mitogen-activated lymphocytes from the lethal effects of cyclophosphamide and also enhanced T and B cell proliferation. Low IL-1 beta levels and increases in serum IL-6 were detected in all treatment groups. In contrast, significant IFN-gamma and IL-3 levels were only detected in D-OMV-treated groups. These results indicate that D-OMVs, which have reduced toxicity, have prophylactic potential in inducing specific cytokines that accelerate granulocyte recovery following cytoreductive therapy by promoting both proliferation and maturation of myeloid precursors as well as augmenting the immune system.

Requirement for increased IL-10 in the development of B-1 lymphoproliferative disease in a murine model of CLL

Malignant B-1 cells derived from NZB mice, a murine model of spontaneous autoimmunity and B cell lymphoproliferative disease, produce significantly higher levels of IL-10 mRNA than normal B-1 or B cells. IL-10 may act as an autocrine growth factor for the expansion of malignant B-1 cells. In order to determine if elevated endogenous production of IL-10 was a required element for the malignant transformation of B-1 cells in NZB mice, backcross animals were studied for the linkage between elevated IL-10 expression and the presence of lymphoid malignancy. The phenotypes of aged (NZB x DBA/2)F1 x NZB animals were determined and a strong correlation was found between the elevated levels of IL-10 mRNA and the development of B-1 malignant clones. In contrast, an increased level of IL-10 message was not associated with elevated serum IgM or the presence of anemia or reticulocytosis which is mainly seen in response to autoantibody production. These results indicate that, at least in NZB, the autoimmunity and lymphoproliferation phenotypes are not linked genetically. IL-10 may enhance proliferation and the development of B-1 cell malignancy rather than antibody production by the B-1 cell subpopulation. Thus, IL-10 plays an important role in B-1 malignancies, and downregulation of IL-10 could be a likely site for intervention in B cell malignancies.

Hematotoxicity among Chinese workers heavily exposed to benzene

Benzene is a well-established hematotoxin. However, reports of its effects on specific blood cells have been somewhat inconsistent and the relative toxicity of benzene metabolites on peripheral blood cells in humans has not been evaluated. We compared hematologic outcomes in a cross-sectional study of 44 workers heavily exposed to benzene (median: 31 parts permillion [ppm] as an 8-hr time-weighted average [TWA] and 44 age and gender-matched unexposed controls from Shanghai, China. All hematologic parameters (total white blood cells [WBC], absolute lymphocyte count, platelets, red blood cells, and hematocrit) were decreased among exposed workers compared to controls, with the exception of the red blood cell mean corpuscular volume (MCV), which was higher among exposed subjects. In a subgroup of workers who were not exposed to more than 31 ppm benzene on any of 5 sampling days (n = 11, median 8 hr TWA = 7.6 ppm, range = 1-20 ppm), only the absolute lymphocyte count was significantly different between exposed workers (mean [sd]1.6 [0.4] x 10(3) mu L) and controls (1.9 [0.4] x l0(3) uL, p = 0.03). Among exposed subjects, a dose response relationship with various measures of current benzene exposure (i.e., personal air monitoring, benzene metabolites in urine) was present only for the total WBC count, the absolute lymphocyte count, and the MCV. Correlations between benzene metabolites and hematologic parameters were generally similar, although hydroquinone was somewhat more strongly associated with a decrease in the absolute lymphocyte count, and catechol was more strongly associated with an increase in MCV. Morphologic review of peripheral blood slides demonstrated an excess of red blood cell abnormalities (i.e., stomatocytes and target cells) only in the most heavily exposed workers, with no differences in granulocyte, lymphocyte, or platelet morphology noted. Although benzene can affect all the major peripheral blood elements, our results support the use of the absolute lymphocyte count as the most sensitive indicator of benzene-induced hematotoxicity.

The natural history of a lymphoproliferative disorder in aged NZB mice

The molecular lesions of human familial and common B-CLL remain unknown. As an approach to this problem, aged NZB mice with a B cell lymphoproliferative disorder were chosen as a murine model. Three groups of NZB mice (2 months, 6 months and > 18 months) for a total of nineteen were studied. A complete autopsy including a CBC was performed on each mouse. Spleen cells were immunophenotyped and cell cycle analysis was performed. Spleen weight, peritoneal cell counts and absolute lymphocytes counts were all elevated in the oldest group. All mice showed evidence of extramedulary hematopoiesis and the older group showed lymphocytic infiltrates in the lacrymal glands, kidneys, liver and lungs. Two of the seven aged mice had a malignant lymphoma. One was a marginal zone lymphoma and the other a lymphocytic lymphoma. Splenic immunophenotyping showed a loss of T cells with an increase in B cells as the mice age. Cell cycle analysis revealed hyperdiploidy in all of the aged mice with a decrease in the percentage G0G1 cells. This disease appears to involve an absolute lymphocytosis of the peritoneum and the peripheral blood compartment. This is associated with splenic aneuploidy. The infiltration of the spleen by malignant cells of varying morphology is a late event. The aged NZB mouse continues to be a model for human B-CLL.

Regulatory review of cellular and gene therapies: an overview of the process

Cell and gene therapies, using several different approaches, have been proposed for a variety of genetic diseases, cancer and AIDS. The major regulatory review process in the US consists of an institutional review board, the recombinant DNA advisory committee (RAC) and the Food and Drug Administration (FDA). Within the Center for Biologics Evaluation and Research, the Division of Cellular and Gene Therapies has been formed to primarily review investigational new drug applications (INDs) for cellular and gene therapies. Several appropriate "points to consider" documents have been prepared and the RAC has approved over 40 clinical protocols. Advances in biotechnology and the scientific basis for these advances are changing rapidly. Although a flexible, case-by-case approach is necessitated by these rapid changes, regulatory concerns common to all biologicals administered to human subjects remain unchanged. These include safety, efficacy, purity, potency, quality control and assessment, and reproducibility of individual lots. The goal of the review process is a prompt, complete and meticulous review. The emphasis of a pre-IND meeting is toward a working relationship between the sponsor and the FDA prior to the phase I, II and III clinical trials. A timely and ongoing evaluation of pre-clinical testing cannot be overemphasized in this rapidly growing and changing field. The development of a working relationship at this stage will ensure a seamless integration of the IND process with the product and establishment license applications. Because replication-competent retrovirus (RCR) represents a potential for pathogenicity, the FDA is recommending a conservative approach to RCR testing.

Artifactual staining of monoclonal antibodies in two-color combinations is due to an immunoglobulin in the serum and plasma

Two-color whole blood lysis is the assay of choice for lymphocyte immunophenotyping because of the additional information it provides. Recently, artifactual double-staining of some specimens has been observed with this assay. In these cases, the samples appear to be uncompensated for spectral overlap or to inappropriately coexpress two antigens simultaneously. This artifact can result in the apparent coexpression of CD4 and CD8 (observed in lymphoblastic processes) or of CD5 and CD20 (characteristic of chronic lymphocytic leukemia) in normal persons, leading to an erroneous diagnosis. Using plasma, serum, or immunoglobulin preparations from donors who exhibit this artifact we sought to determine 1) the source of the artifact and 2) ways to overcome it. This staining is apparently due to an immunoglobulin in the donors' serum and plasma which does not have specific reactivity with mouse immunoglobulin. Washing whole blood samples or blocking with mouse immunoglobulin is a convenient way of avoiding this artifact.

Heterotransplantation of human Burkitt's lymphoma cell lines in athymic nude mice: tumor-host relationships

We have explored the factors which influence tumorigenicity of Burkitt's lymphoma (BL) cell lines in athymic nude mice. Four cell lines, Namalwa, CA46, JD38, and ST486 revealed tumor incidence of 63.5, 69.0, 45.5 and 10.0%, respectively, in nude mice, but there was no correlation between tumor incidence and growth rate in vivo. Thus, growth rate and tumorigenicity are dependent upon different biochemical pathways. Evidence of tumor cell heterogeneity was demonstrated in the CA46 parent cell line. Five subclones derived from CA46 revealed varying degrees of tumor incidence (but very similar growth rates) that were consistently less than the parent CA46 line. Line 5, for example, produced 5.7-fold less tumors than the parent line. None of the BL cell lines or clones produced any metastatic lesions in liver, lung, brain, bone marrow or spleen in athymic nude mice. Northern blot analysis of c-myc mRNA levels in different BL cell lines revealed a possible relationship between percent tumor takes (but not growth rates) and the level of c-myc oncogene expression. However, no correlation was observed between c-myc mRNA levels and tumor incidence or growth rates among the CA46 clones. There was no correlation between the ability of the cell lines and the subclones to either secrete growth factors or to respond to growth factors secreted by Epstein-Barr virus-induced lymphoblastoid cells or lipopolysaccharide-activated monocytes, and their growth rates or percent tumor takes in mice. Comparison of tumor incidence and growth rates in irradiated and unirradiated mice showed that host factors influenced the growth of BL in nude mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigenic expression of B-cell chronic lymphocytic leukemic cell lines

A flow cytometric analysis of five B cell chronic lymphocytic leukemic (B-CLL) cell lines was undertaken using 129 unknown reagents from the blind panel (BP) and 72 reagents from the known CD panel obtained from the Fourth International Leucocyte Differentiation Conference and Workshop, B cell section (Vienna, 1989). The five cell lines examined were: SeD (PNAS 75, 5706, 1978), B-CLL-LCL (BLOOD 71, 9, 1988), JVM-HH and JVM-2(INT J CAN 38, 531, 1986), and WR#1 (TH and BD). The reagents were #1-129 (blinded panel) and reagents 1-44 and 53-84 (CD panel with CD23 reagents missing). Positivity was defined as greater than 30% of the cells having a three fold increase or more in mean channel fluorescence. Fourty-three reagents of the blinded panel were negative by these criteria while all remaining reagents were positive on all five lines. SeD showed the lowest reactivity; B-CLL-LCL and JVM-2 showed the most reactivity; JVM-HH and WR#1 were intermediate. The known CD panel confirmed the reactivity of the blinded panel. An average immunophenotype was constructed and compared to published normal EBV lymphoblastoid cell lines and several differences were noted. There was an absence or significant decrease in the expression of CD19, CD21, CD22 and CD37 while there was an increased expression of CD38, CD54, CD74 and CD76. The heterogeneity observed between the B-CLL lines may in part be due to polymorphisms but is more likely to represent the underlying heterogeneity seen in common and familial B-CLL.2+öff

CD20 and CD5 expression in B-chronic lymphocytic leukemia

In order to quantitate a previously noted decrease in CD20 fluorescence intensity (FI) on B-CLL lymphocytes, binding capacities [BC x 10(3) +/- 1SD = number of antibodies bound per cell] were calculated. The mean (N = 5) BC x 10(3) +/- 1SD of CD20 reagents for normal B-PBL and B-CLL lymphocytes confirmed this observation. B-PBL and B-CLL were 56 +/- 11 and 61 +/- 14, and 19 +/- 15 and 18 +/- 16, respectively, for Leu 16 and B1. Although adequate compensation standards for the determination of CD5 and CD20 coexpression are not available, qualitatively, the density of CD5 on both normal B-PBL and B-CLL is less compared to the expression of CD5 by normal T cells. CD5 expression on B-CLL seems to be linked to the lower levels of CD20, whereas CD5 expression may appear to be absent on CLL lymphocytes expressing normal levels of CD20. Levels of CD20 in B-CLL suggest involvement of one or two genes (alleles) whose decreased expression may be linked to CD5 expression.

Flow cytometric analysis of whole blood lysis, three anticoagulants, and five cell preparations

We studied the effects of anticoagulants and cell preparation methods on lymphocyte forward-angle scatter (FSC), autofluorescence, and immunofluorescent staining for CD45, CD14, and CD13. Blood samples collected in ethylenediaminetetracetic acid (EDTA), heparin, and acid citrate dextrose (ACD) were processed by using conventional Hypaque-Ficoll (HF) separation and four whole blood (WB) lysis techniques: Immuno-lyse, Q-Prep, FACS Lyse, and Gen Trak Lysis. Lymphocytes prepared by using three of the four whole blood methods gave FCS values comparable to those isolated by HF, while one method (FACS Lyse) gave consistently lower values. Autofluorescence values were comparable by all methods except Immuno-lyse, which showed consistently higher values in blood stored for 24 h with any anticoagulant. Immunofluorescent values for CD45-stained cells were quite consistent across all methods, and among the whole blood methods, FACS Lyse and Q-Prep uniformly gave the highest purity of CD45-positive cells in the lymphocyte light scatter gates. Additionally, propidium iodide (PI) analyses of CD45-stained whole blood, and analyzed without lysis, confirmed that ACD and heparin were superior to EDTA for maintaining viable leucocytes overnight. Future studies should focus on other commonly used reagents, a wide variety of abnormal samples, and cell viability.

Effects of 8-chloroadenosine 3',5'-monophosphate and N6-benzyl-cyclic adenosine 5'-monophosphate on cell cycle kinetics of HL-60 leukemia cells

Site-selective cyclic AMP (cAMP) analogues have been shown to inhibit growth and induce differentiation in several human leukemia cell lines. However, detailed studies of the effects exerted by cAMP analogues on cell cycle kinetics have been lacking. We have examined the effects of 8-Cl-cAMP and N6-benzyl-cAMP on the cell cycle kinetics of the HL-60 human promyelocytic leukemia cell line. A cell cycle study was performed by univariate DNA analysis after 24-72 h of treatment with noncytotoxic concentrations of 8-Cl-cAMP and N6-benzyl-cAMP capable of inducing 50-60% growth inhibition in these cells. HL-60 cells treated with 5 microM 8-Cl-cAMP showed no significant change in the cell distribution in the cycle as compared to the untreated control cells, whereas the treatment with 10 microM N6-benzyl-cAMP transiently increased the percentage of cells in the G0/G1 phase after 48 h, followed by a partial recovery at 72 h. Combined treatment with low doses of 8-Cl-cAMP and N6-benzyl-cAMP, each of which alone produced 20% growth inhibition, exerted a growth inhibitory effect of 65% and delayed increase of the G0/G1 phase by 72 h. To better understand the cell cycle effects induced by 8-Cl-cAMP, flow cytometric analysis of bromodeoxyuridine incorporation was also performed. 8-Cl-cAMP treatment exhibited a slowing down of the cell cycle; thus, the delayed appearance of the G0/G1 cell accumulation after combined treatment could be due to this effect of 8-Cl-cAMP on the HL-60 cell cycle. At a toxic dose, 8-Cl-cAMP brought about a G2M block, whereas N6-benzyl-cAMP brought about an increase of the G0/G1 compartment. G2M block produced by toxic doses of 8-Cl-cAMP was not related to its adenosine metabolite since 8-Cl-adenosine did not produce any specific block in the cell cycle. Our results show, for the first time, that these site-selective cAMP analogues could affect cell cycle kinetics at different points. These data may provide the basis for combination treatments involving cAMP analogues and other agents in the treatment of human leukemia.

Antigenic expression of B-cell chronic lymphocytic leukemic lymphocytes

A flow cytometric analysis of lymphocytes in B-cell chronic lymphocytic leukemia (B-CLL) samples and in monocyte-depleted and T-cell-depleted normal peripheral blood (B-PBL) samples was undertaken using 129 reagents from the blind panel (BP) and 72 reagents from the cluster designation (CD) panel obtained from the Fourth International Leucocyte Differentiation Conference and Workshop, B-Cell Section. After determining the average mean channel fluorescence and the average percentage of positive cells for the B-CLL and the normal B-PBL preparations, a combined ratio and difference analysis was performed for each monoclonal antibody reactivity. This analysis confirmed the intense expression of class II antigens on B-CLL and the preferential expression of CD19, CD20, CD23 and CD24 antigens. In addition, three new clustered and three new unclustered antigens were also preferentially expressed on B-CLL lymphocytes. Cluster analysis of these differences suggests the existence of at least three overlapping immunophenotypic subpopulations, composed of CD19, CD20, CD21, CD22, CD23, CD24, CD75, CD76 and CDw78.

Expression of interleukin-2 receptor beta subunit in hematopoietic malignancies

The expression of the interleukin-2 (IL-2) receptor was studied in neoplastic cells derived from acute leukemias, T-cell lymphoblastic lymphomas, peripheral T-cell lymphomas, chronic lymphocytic leukemias, well-differentiated lymphocytic lymphomas, and established cell lines by both flow cytometric analysis and sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) after affinity crosslinking of radiolabeled IL-2. Cells from most acute leukemias (19 of 22), irrespective of their subtype (T, common or nonlymphoid leukemias), as well as T-cell lymphoblastic lymphomas and peripheral T-cell lymphomas expressed only the p70-75 beta subunit of the IL-2 receptor. Cells from the more mature B-cell neoplasms, chronic lymphocytic leukemia, and well-differentiated lymphocytic lymphoma, expressed predominantly alpha beta IL-2 receptors (11 of 14). In contrast to these results, most cell lines established from hematopoietic malignancies do not express either chain of the IL-2 receptor. Further studies are necessary to determine the exact function of the IL-2R p70-75 beta subunit in immature hematopoietic cells, but its wide distribution throughout the hematopoietic system suggests that IL-2 may play a role in the early stages of hematopoiesis.

Lymphocyte analysis in a patient with X-linked agammaglobulinemia and isolated growth hormone deficiency after development of echovirus dermatomyositis and meningoencephalitis

A previously described patient with X-linked agammaglobulinemia and growth hormone deficiency developed an echovirus-associated meningoencephalitis and dermatomyositis-like syndrome while being treated with intramuscular gamma globulin and human growth hormone. Initiation of high-dose intravenous gamma globulin resulted in resolution of the clinical symptoms and the patient has remained asymptomatic over the past 55 months. Lymphocyte phenotype analysis at the time of presentation with echovirus infection revealed an increase in CD2+, CD16+, HNK-1+ lymphocytes, a decrease in CD4+ T cells as well as absence of B cells. This elevation in the LGL/NK phenotype resolved with clinical improvement. In addition, there was evidence of lymphocyte activation following the development of echovirus infection (increase in HLA-DR expression and elevated serum IL-2 receptor levels) which resolved with clinical improvement. A muscle biopsy obtained during the period of the dermatomyositis-like syndrome demonstrated a CD8+ lymphocytic infiltrate very similar to the observations in classical dermatomyositis. Taken together, these findings suggest that growth hormone therapy in this patient failed to alter the humoral immunodeficiency. In addition, serum IL-2 receptor levels and lymphocyte phenotyping may be useful adjuncts for monitoring echovirus disease in immunodeficient patients.

Polyclonal B-cell lymphocytosis and hypergammaglobulinemia in patients with Gaucher disease

Sera from 23 individuals with Gaucher disease (GD) were analyzed for hypergammaglobulinemia and oligoclonal and monoclonal gammopathies. Serum IgG level was elevated in 15/23 (65%) patients, and a diffuse hypergammaglobulinemia was present in 10/23 (43%) patients. An oligoclonal gammopathy was noted in six patients, and a monoclonal gammopathy in two. Lymphocyte subset analysis was also carried out in eight individuals with GD. Four of five individuals showed increased surface Ig-positive lymphocytes, while 7/7 were positive for either increased CD19- and/or CD20-positive lymphocytes. An eighth patient was found to have a B-cell leukemia. Statistical analysis of kappa and lambda histograms were suggestive of a monoclonal excess. However, restriction enzyme analysis of four individuals with GD and increased B cells failed to show any evidence of Ig gene rearrangements. Serum Ig abnormalities and perhaps B-cell lymphocytosis appear to be common in the GD patient population and are not associated with circulating monoclonal lymphocytes.

Flow cytometric analysis of platelet surface antigens

A flow cytometric analysis of human platelet surface antigens was carried out using a panel of monoclonal antibody reagents. The reagents used were specific either for the GPIb or the GP IIb/IIIa complex, surface immunoglobulin, or von Willebrand factor (vWf). Indirect surface immunophenotypes were determined using an EPICS V flow cytometer and the monoclonal antibodies 6D1, 10E5, Plt-1, UR1663, anti-IgG, and anti-vWf. Platelets were obtained from normal individuals or patients with either Bernard-Soulier syndrome (BSS) or Glanzmann's thrombasthenia (GT). Normal platelets were positive for 10E5, 6D1, Plt-1, and UR1663 and showed negligible activity for anti-IgG and anti-vWf. Platelets from individuals with BSS showed a marked reduction in 6D1, while the platelets of a patient with GT showed a marked reduction in binding of 10E5, Plt-1, and UR1663. Differences between histograms for normal platelets and for platelets from individuals with BSS or GT were evaluated using the Kolmogorov-Smirnov test. Compared to normal platelets, the BSS and GT platelets contain at least 35-fold less of the GPIb and GP IIb/IIIa complex respectively. Flow cytometry is a useful and precise method for the study of normal and abnormal surface platelet phenotypes.

Two-color flow cytometric analysis of monocyte depleted human blood lymphocyte subsets

Peripheral blood mononuclear cells (PBMC) from normal individuals were examined using 16 pairs of FITC and phycoerythrin (PE) directly conjugated monoclonal antibodies. Each pair of reagents was used to evaluate a conventional lymphocyte gate as well as open (non) gate of monocyte depleted PBMC. Parallel studies using the same panel of monoclonal antibodies were carried out on selected, nonmonocyte depleted samples. The major findings of this analysis were that 1,000-1,200 lymphocytes in a 10,000 cell analysis are found outside the lymphocyte gate and of these approximately 2/5 are CD16 positive LGL/NK cells, 2/5 are CD3 positive T cells, and 1/5 are CD19/CD20 positive B cells. Thus, it appears that 10-15% of the lymphoid cells fall outside of the conventional lymphocyte gate, and in certain settings monocyte depletion may be useful to perform more complete evaluation of the total lymphoid cell population obtained after ficoll-hypaque separation.

Application of lymphocyte immunophenotyping in selected diseases

The results of lymphocyte immunophenotyping in a variety of autoimmune disorders confirm major T cell immunoregulatory defects. The defects associated with autoreactive T cells appear to exist at the level/interface of the CD4 inducer of suppression and the CD8 effector cell. Although activated CD4 cells are occasionally found, subpopulations of activated CD8 cells are seen more commonly. A similar observation has been made in a subpopulation of patients with common variable hypogammaglobulinemia. In conjunction with antigen-specific T cell clones, we anticipate that flow cytometry will continue to aid in the further dissection of these HLA-restricted, anti-idiotype-controlled and pharmacological-mediated reactions. The known immunological distinction between AML and ALL are such that blast immunophenotyping will confirm and complement the clinical and morphological diagnosis in the vast majority of patients. With regards to chronic lymphocytosis in general and CLL in particular, flow cytometry offers an unusual opportunity to characterize lineage, monoclonality, stage of differentiation, presence or absence of activation antigens, aneuploidy and oncogene expression. Flow cytometry will continue to contribute to our understanding of the etiology and pathogenesis of CLL.