Circulating tumour cell enumeration, biomarker analyses, and kinetics in patients with colorectal cancer and other GI malignancies

Objective

Most of the work in terms of liquid biopsies in patients with solid tumors is focused on circulating tumor DNA (ctDNA). Our aim was to evaluate the feasibility of using circulating tumor cells (CTCs) in peripheral blood samples from patients with advanced or metastatic gastrointestinal (GI) cancers.

Methods

In this prospective study, blood samples were collected from each patient in 2 AccuCyte® blood collection tubes and each tube underwent CTC analysis performed utilizing the RareCyte® platform. The results from both tubes were averaged and a total of 150 draws were done, with 281 unique reported results. The cadence of sampling was based on convenience sampling and piggybacked onto days of actual clinical follow-ups and treatment visits. The CTC results were correlated with patient- and tumor-related variables.

Results

Data from a total of 59 unique patients were included in this study. Patients had a median age of 58 years, with males representing 69% of the study population. More than 57% had received treatment prior to taking blood samples. The type of GI malignancy varied, with more than half the patients having colorectal cancer (CRC, 54%) followed by esophageal/gastric cancer (17%). The least common cancer was cholangiocarcinoma (9%). The greatest number of CTCs were found in patients with colorectal cancer (Mean: 15.8 per 7.5 ml; Median: 7.5 per 7.5 ml). In comparison, patients with pancreatic cancer (PC) had considerably fewer CTCs (Mean: 4.2 per 7.5 ml; Median: 3 per 7.5 ml). Additionally, we found that patients receiving treatment had significantly fewer CTCs than patients who were not receiving treatment (Median 2.7 versus 0.7). CTC numbers showed noteworthy disparities between patients with responding/stable disease in comparison to those with untreated/progressive disease (Median of 2.7 versus 0). When CTCs were present, biomarker analyses of the four markers human epidermal growth factor receptor 2 (HER2)/programmed death-ligand 1 (PD-L1)/Kiel 67 (Ki-67)/epidermal growth factor receptor (EGFR) was feasible. Single cell sequencing confirmed the tumor of origin.

Conclusion

Our study is one of the first prospective real-time studies evaluating CTCs in patients with GI malignancies. While ctDNA-based analyses are more common in clinical trials and practice, CTC analysis provides complementary information from a liquid biopsy perspective that is of value and worthy of continued research.

Beyond Circulating Tumor Cell Enumeration: Cell-Based Liquid Biopsy to Assess Protein Biomarkers and Cancer Genomics Using the RareCyte® Platform

The practice of medicine has steadily employed less invasive methods to obtain information derived from the tumor to guide clinical management of patients. Liquid biopsy—the sampling of blood—is a non-invasive method for generating information previously only available from tissue biopsies of the tumor mass. Analysis of fragmented circulating tumor DNA in the plasma is clinically used to identify actionable mutations and detect residual or recurrent disease. Plasma analysis cannot, however, assess cancer phenotypes, including the expression of drug targets and protein biomarkers. Circulating tumor cells (CTCs) are intact cancer cells that have entered the blood that have the potential for distant metastasis. While enumeration of CTCs is prognostic of outcome, recently developed technology allows for the interrogation of protein biomarkers on CTCs that could be predictive of response. Furthermore, since CTCs contain intact whole cancer genomes, isolating viable CTCs detected during therapy could provide a rational approach to assessing mutational profiles of resistance. Identification, characterization and molecular analysis of CTCs together will advance the capacity of liquid biopsy to meet the requirements of twenty-first century medicine.

Human ovarian tumor ascites fluids rapidly and reversibly inhibit T cell receptor-induced NF-κB and NFAT signaling in tumor-associated T cells

Human memory T cells present in ovarian tumor ascites fluids fail to respond normally to stimulation via the T cell receptor (TCR). This immunosuppression is manifested by decreases in NF-κB and NFAT activation, IFN-γ production, and cell proliferation in response to TCR stimulation with immobilized antibodies to CD3 and CD28. The anergy of the tumor-associated T cells (TATs) is mediated by soluble factors present in ovarian tumor ascites fluids. The non-responsiveness of the T cells is quickly reversed when the cells are assayed in the absence of the ascites fluid, and is rapidly reestablished when a cell-free ascites fluid is added back to the T cells. Based upon the observed normal phosphorylation patterns of the TCR proximal signaling molecules, the inhibition of NF-κB, and NFAT activation in response to TCR stimulation, as well as the ability of the diacylglycerol analog PMA and the ionophore ionomycin to bypass the ascites fluid-induced TCR signaling arrest, the site of the arrest in the activation cascade appears to be at or just upstream of PLC-γ. An identical TCR signaling arrest pattern was observed when T cells derived from normal donor peripheral blood were incubated with either malignant or nonmalignant (cirrhotic) ascites fluids. The immunosuppressive activity of ascites fluids reported here suggests that soluble factors acting directly or indirectly upon T cells present within tumors contribute to the anergy that has previously been observed in T cells derived from malignant and nonmalignant inflammatory microenvironments. The soluble immunosuppressive factors represent potential therapeutic targets for ovarian cancer.

An introduction to mass cytometry: fundamentals and applications

Mass cytometry addresses the analytical challenges of polychromatic flow cytometry by using metal atoms as tags rather than fluorophores and atomic mass spectrometry as the detector rather than photon optics. The many available enriched stable isotopes of the transition elements can provide up to 100 distinguishable reporting tags, which can be measured simultaneously because of the essential independence of detection provided by the mass spectrometer. We discuss the adaptation of traditional inductively coupled plasma mass spectrometry to cytometry applications. We focus on the generation of cytometry-compatible data and on approaches to unsupervised multivariate clustering analysis. Finally, we provide a high-level review of some recent benchmark reports that highlight the potential for massively multi-parameter mass cytometry.

Image cytometry-based detection of aneuploidy by fluorescence in situ hybridization in suspension

Cytogenetic abnormalities are important diagnostic and prognostic criteria for hematologic malignancies. Karyotyping and fluorescence in situ hybridization (FISH) are the conventional methods by which these abnormalities are detected. The sensitivity of these microscopy-based methods is limited by the abundance of the abnormal cells in the samples and therefore these analyses are commonly not applicable to minimal residual disease (MRD) stages. A flow cytometry-based imaging approach was developed to detect chromosomal abnormalities following FISH in suspension (FISH-IS), which enables the automated analysis of several log-magnitude higher number of cells compared with the microscopy-based approaches. This study demonstrates the applicability of FISH-IS for detecting numerical chromosome aberrations, establishes accuracy, and sensitivity of detection compared with conventional FISH, and feasibility to study procured clinical samples of acute myeloid leukemia (AML). Male and female healthy donor peripheral blood mononuclear cells hybridized with combinations of chromosome enumeration probes (CEP) 8, X, and Y served as models for disomy, monosomy, and trisomy. The sensitivity of detection of monosomies and trisomies amongst 20,000 analyzed cells was determined to be 1% with a high level of precision. A high correlation (R(2) = 0.99) with conventional FISH analysis was found based on the parallel analysis of diagnostic samples procured from 10 AML patients with trisomy 8 (+8). Additionally, FISH-IS analysis of samples procured at the time of clinical remission demonstrated the presence of residual +8 cells indicating that this approach may be used to detect MRD and associated chromosomal defects.

CD81 is essential for the re-entry of hematopoietic stem cells to quiescence following stress-induced proliferation via deactivation of the Akt pathway

A protein that is thought to orchestrate the distribution of other signaling molecules on the cell membrane, CD81, is critical to maintaining the functional integrity of hematopoietic stem cells during their regeneration.

The regulatory mechanisms governing the cell cycle progression of hematopoietic stem cells (HSCs) are well characterized, but those responsible for the return of proliferating HSCs to a quiescent state remain largely unknown. Here, we present evidence that CD81, a tetraspanin molecule acutely responsive to proliferative stress, is essential for the maintenance of long-term repopulating HSCs. Cd81^−/− HSCs showed a marked engraftment defect when transplanted into secondary recipient mice and a significantly delayed return to quiescence when stimulated to proliferate with 5-fluorouracil (5FU). In addition, we found that CD81 proteins form a polarized patch when HSCs are returning to quiescence. Thus, we propose that the spatial distribution of CD81 during the HSC recovery phase drives proliferative HSC to quiescence, and is important to preserve the self-renewal properties. Here, we show that lack of CD81 leads to loss of HSC self-renewal, and the clustering of CD81 on HSC membrane results in deactivation of Akt, which subsequently leads to nuclear translocation of FoxO1a. Thus, CD81 functions as part of a previously undefined mechanism that prohibits excessive proliferation of HSCs exposed to environmental stress.

Hematopoietic stem cells (HSCs) remain dormant in the bone marrow until needed to replenish the hematopoietic system, at which point they are stimulated to proliferate extensively, undergoing both regeneration (self-renewal) and differentiation. Self-renewal is key to maintaining an adequate HSC reserve, and return to dormancy after such stimulation is critical, yet still poorly understood. In this study, we report that CD81, a transmembrane organizing protein, is a novel regulator involved in HSC self-renewal. Transplanting HSCs into mice that are lethally irradiated to remove their native HSCs stimulates the transplanted HSCs to proliferate to replenish the hematopoietic system, allowing us to examine whether and how HSCs return to quiescence. HSCs lacking CD81 take longer to return to quiescence after such stimulation, resulting in reduced stem cell function. Conversely, forced CD81 membrane clustering, using an antibody, promotes early return of proliferating stem cells to quiescence and nuclear localization of FoxO1a, a key protein that mediates the cell cycle arrest. CD81 clustering also constrains Akt activity, which orchestrates multiple pathways such as cell proliferation and responses to reactive oxygen species. Treatment of Cd81-deficient HSCs with an Akt inhibitor, perifosine, which bypasses the requirement for CD81 in this process, rescues the delay defect of Cd81-deficient HSCs. Together, our data demonstrate that CD81 is critical to maintaining the functional integrity of HSCs during regeneration, and it is acting through Akt to influence its downstream pathways that govern cell cycle progression.

Visualization and quantification of cytotoxicity mediated by antibodies using imaging flow cytometry

Conventional approaches for the detection of antibody dependent cell-mediated cytotoxicity (ADCC) activity rely on quantification of the release of traceable compounds from target cells or flow cytometry analysis of population-wide phenomena. We report a new method for the direct imaging and quantification of ADCC of cancer cells. The proposed method using imaging flow cytometry combines the statistical power of flow cytometry with the analytical advantages of cell imaging, providing a novel and more comprehensive perspective of effector/target cell interactions during ADCC events. With this method we can quantify and show in detail the morphological changes in target and effector cells, their apoptotic index, the physical interaction between effector and target cells, and a directional transfer of cytosolic contents from effector to target cells. As a model system we used the therapeutic anti-CD20 antibody rituximab to target CFSE labeled Ramos human Burkitt's lymphoma cells, to CMTPX-labeled human monocytic U-937 effector cells. We expect that similar studies using different effector and target cell populations may contribute to the pre-clinical evaluation of therapeutic antibodies and help to identify mechanisms that could be beneficial in the immunotherapy of cancer.

Flow cytometric analysis of microparticles

Cell-derived microparticles (MPs) are increasingly recognized as important cell-to-cell signaling mechanisms and may exhibit important functions in homeostasis but also in pathogenesis. Indeed, MPs are associated with a number of diseases inhibiting their production that protects against pathogenesis. MPs are distinct from exosomes and apoptotic bodies, often exhibiting the membrane proteins of the activated or apoptotic cell from which they are derived. Electron microscopic analyses have shown that MPs are produced by all cell types tested to date, and ELISA-based assays have established that increased numbers of MPs are produced following cell activation. These approaches do not, however, determine the exact number of MPs and distribution of functional proteins on their surface. Flow cytometry represents an obvious approach to analyze MPs, and we present here a method to assess the number and phenotype of MPs by using a conventional flow cytometer. We also present the caveats with this method and describe a new imaging flow cytometry approach that overcomes these limitations.

C1q deficiency leads to the defective suppression of IFN-alpha in response to nucleoprotein containing immune complexes

Almost all humans with homozygous deficiency of C1q develop systemic lupus erythematosus (SLE). The precise cellular mechanism(s) by which C1q prevents the development of SLE remains unclear. In this study, we tested the role of C1q in the regulation of IFN-α induced by immune complexes (ICs) in vitro, as well as the consequences of lack of C1q in vivo. Our experiments revealed that C1q preferentially promotes the binding of SLE ICs to monocytes rather than plasmacytoid dendritic cells, but this inhibition was not due to the induction of inhibitory soluble factors. The presence of C1q also altered the trafficking of ICs within monocytes such that ICs persisted in early endosomes. In patients with C1q deficiency, serum and cerebrospinal fluid levels of IFN-α and IFN-γ-inducible protein-10 levels were elevated and strongly correlated with Ro autoantibodies, demonstrating the clinical significance of these observations. These studies therefore associate C1q deficiency with defective regulation of IFN-α and provide a better understanding of the cellular mechanisms by which C1q prevents the development of IC-stimulated autoimmunity.

Immune modulation with sulfasalazine attenuates immunopathogenesis but enhances macrophage-mediated fungal clearance during Pneumocystis pneumonia

Although T cells are critical for host defense against respiratory fungal infections, they also contribute to the immunopathogenesis of Pneumocystis pneumonia (PcP). However, the precise downstream effector mechanisms by which T cells mediate these diverse processes are undefined. In the current study the effects of immune modulation with sulfasalazine were evaluated in a mouse model of PcP-related Immune Reconstitution Inflammatory Syndrome (PcP-IRIS). Recovery of T cell-mediated immunity in Pneumocystis-infected immunodeficient mice restored host defense, but also initiated the marked pulmonary inflammation and severe pulmonary function deficits characteristic of IRIS. Sulfasalazine produced a profound attenuation of IRIS, with the unexpected consequence of accelerated fungal clearance. To determine whether macrophage phagocytosis is an effector mechanism of T cell-mediated Pneumocystis clearance and whether sulfasalazine enhances clearance by altering alveolar macrophage phagocytic activity, a novel multispectral imaging flow cytometer-based method was developed to quantify the phagocytosis of Pneumocystis in vivo. Following immune reconstitution, alveolar macrophages from PcP-IRIS mice exhibited a dramatic increase in their ability to actively phagocytose Pneumocystis. Increased phagocytosis correlated temporally with fungal clearance, and required the presence of CD4(+) T cells. Sulfasalazine accelerated the onset of the CD4(+) T cell-dependent alveolar macrophage phagocytic response in PcP-IRIS mice, resulting in enhanced fungal clearance. Furthermore, sulfasalazine promoted a TH2-polarized cytokine environment in the lung, and sulfasalazine-enhanced phagocytosis of Pneumocystis was associated with an alternatively activated alveolar macrophage phenotype. These results provide evidence that macrophage phagocytosis is an important in vivo effector mechanism for T cell-mediated Pneumocystis clearance, and that macrophage phenotype can be altered to enhance phagocytosis without exacerbating inflammation. Immune modulation can diminish pulmonary inflammation while preserving host defense, and has therapeutic potential for the treatment of PcP-related immunopathogenesis.

High throughput, parallel imaging and biomarker quantification of human spermatozoa by ImageStream flow cytometry

Spermatid specific thioredoxin-3 protein (SPTRX-3) accumulates in the superfluous cytoplasm of defective human spermatozoa. Novel ImageStream technology combining flow cytometry with cell imaging was used for parallel quantification and visualization of SPTRX-3 protein in defective spermatozoa of five men from infertile couples. The majority of the SPTRX-3 containing cells were overwhelmingly spermatozoa with a variety of morphological defects, detectable in the ImageStream recorded images. Quantitative parameters of relative SPTRX-3 induced fluorescence measured by ImageStream correlated closely with conventional flow cytometric measurements of the same sample set and reflected the results of clinical semen evaluation. Image Stream quantification of SPTRX-3 combines and surpasses the informative value of both conventional flow cytometry and light microscopic semen evaluation. The observed patterns of the retention of SPTRX-3 in the sperm samples from infertility patients support the view that SPTRX3 is a biomarker of male infertility.

Numbers matter: quantitative and dynamic analysis of the formation of an immunological synapse using imaging flow cytometry

Activation of T lymphocytes by antigen-presenting cells (APC) results in the formation of an immunological synapse. Following contact with the target cell, key signaling and adhesion molecules polarize within minutes to hours to the T cell-APC interface. Multispectral imaging flow cytometry, a new technology which combines flow cytometry with imaging, was used to visualize and quantify the recruitment of the CD3epsilon and Lck signaling molecules during the evolution of an immune synapse. Using this technology, thousands of T cell/macrophage conjugates could be analyzed for each experimental time point. Following Ca++ triggered T cell activation, the dynamics of Lck and CD3epsilon recruitment to the synapse, analyzed by two independent methods, were comparable. However, CD3epsilon exhibited longer residence times (>8 min) at the synapse than Lck.

Human plasmacytoid dendritic cells preferentially conjugate with and fuse with acute or chronically HIV-IIIB infected cells. (131.7)

Plasmacytoid Dendritic Cells (PDC) produce copious amounts of IFN-a in response to TLR-7 or -9 stimulation and serve as a link between the innate and adaptive immune systems. In HIV infection, there is a gradual depletion of PDC as well as a functional deficiency in remaining circulating PDC. The mechanism of PDC depletion is not yet understood. We have demonstrated using imaging flow cytometry (ImageStream®) that PDC preferentially take up membrane and cytoplasm from HSV and Influenza infected cells in an endocytic process called "nibbling" that results in IFN-α production by the PDC. Using acutely HIVIIIB infected CD4 T cells or chronically HIVIIIB infected H9 T cells, PDC preferentially form conjugates with HIVIIIB infected vs uninfected T cells, but, rather than being nibbled, the majority of these encounters lead to PDC/infected T cell fusions. Acutely infected CD4 T cells but not chronically-infected H9 cells stimulated PDC to produce IFN-α, albeit it lower levels than other TLR7/9 inducers. Fusions were blocked with the addition of the specific fusion inhibitors (T-20 or AMD-3100), but there was no increase in conjugate formation or uptake of material. We hypothesize that this successful subversion of PDC nibbling and IFN-α production by HIV-infected cells contributes to loss of PDC and the deficient IFN-α production seen in HIV-infected patients. Supported by AI26806.

Numbers matter: quantitative and dynamic analysis of the formation of a mature immunological synapse using imaging flow cytometry (42.15)

Activation of T lymphocytes by antigen-presenting cells (APC) results in the formation of an immunological synapse. Following intercellular contact with the target cell, key signaling and adhesion molecules polarize within minutes to hours to the T cell-APC interface. We use multispectral imaging flow cytometry, a new technology which combines flow cytometry with imaging, to visualize and quantify the recruitment of signaling molecules CD3ε and Lck during the evolution of a mature immune synapse. We use two independent analysis methods to show that the dynamics of Lck and CD3ε recruitment are comparable; however, CD3ε exhibits longer residence times (> 8 min) following Ca++ triggered activation in the synapses of thousands of T cell-macrophage conjugates.

Measurement of cytoplasmic to nuclear translocation

A method is described for the quantitative assessment of the translocation of signaling molecules from the cytoplasm to the nucleus in cells. This method utilizes fluorochrome-conjugated antibodies to the signaling molecule and a nuclear dye, and it is based on imagery acquired rapidly in flow with the use of a multispectral imaging cytometer. The analysis correlates the spatial distribution of the stained translocating signaling molecule with nuclear staining, and it generates a quantitative score for each cell using Pearson's correlation coefficient. Examples described in this section use reagents that detect NFkappaB and IRF-7 and measure the translocation of these molecules under stimulating conditions. A protocol for combining cell surface phenotype with cytoplasm to nuclear translocation is also included.

Image-based study of interferongenic interactions between plasmacytoid dendritic cells and HSV-infected monocyte-derived dendritic cells

Plasmacytoid dendritic cells (pDC) are well-known for their ability to produce large quantities of interferon-alpha (IFN-alpha) in response to viruses. In addition, pDC produce IFN-alpha in response to HSV-infected cells. We demonstrate that both tonsil and PBMC contain pDC that respond to stimulation with HSV either in suspension or in tonsil tissue-fragment culture. We hypothesized that other DC subsets acquire virus in the periphery and deliver the interferongenic signals to the pDC in the draining lymphoid tissue. As a model for pDC/myeloid DC interaction, we studied the interaction of pDC derived from blood with HSV-infected and uninfected monocyte derived dendritic cells (MDDC). Infected, but not uninfected, MDDC induced IFN-alpha in pDC. To further study pDC/infected MDDC interactions, we labeled MDDC with fluorescent cell trackers PKH67 or CFSE prior to infection with HSV and co-cultured with pDC. Cells were then analyzed using conventional and imaging flow cytometry. In addition, we infected MDDC with a GFP-expressing HSV prior to co-culture with pDC. Using traditional flow cytometry, we observed that pDC became fluorescent after co-incubation with uninfected or infected, fluorescently labeled MDDC, indicating that MDDC transferred fluorescent protein and membrane to pDC. By imaging flow cytometry, we observed formation of conjugates between pDC and MDDC as well as transfer and internalization of cellular components from the labeled MDDC by pDC, with preferential uptake from, and association with, infected vs. uninfected MDDC. These studies demonstrate that MDDC infected with HSV are able to stimulate IFN-alpha and chemokine production by pDC through the transfer of cellular materials from the HSV-infected MDDC to the pDC. Together, these observations indicate that heterogeneous populations of DC interact to generate an effective IFN-alpha response.

Oncogenic CARD11 mutations in human diffuse large B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common form of non-Hodgkin's lymphoma. In the least curable (ABC) subtype of DLBCL, survival of the malignant cells is dependent on constitutive activation of the nuclear factor-kappaB (NF-kappaB) signaling pathway. In normal B cells, antigen receptor-induced NF-kappaB activation requires CARD11, a cytoplasmic scaffolding protein. To determine whether CARD11 contributes to tumorigenesis, we sequenced the CARD11 gene in human DLBCL tumors. We detected missense mutations in 7 of 73 ABC DLBCL biopsies (9.6%), all within exons encoding the coiled-coil domain. Experimental introduction of CARD11 coiled-coil domain mutants into lymphoma cell lines resulted in constitutive NF-kappaB activation and enhanced NF-kappaB activity upon antigen receptor stimulation. These results demonstrate that CARD11 is a bona fide oncogenein DLBCL, providing a genetic rationale for the development of pharmacological inhibitors of the CARD11 pathway for DLBCL therapy.

Autophosphorylation docking site Tyr-867 in Mer receptor tyrosine kinase allows for dissociation of multiple signaling pathways for phagocytosis of apoptotic cells and down-modulation of lipopolysaccharide-inducible NF-kappaB transcriptional activation

Efficient clearance of apoptotic cells is essential for tissue homeostasis, allowing for cellular turnover without inflammatory consequences. The Mer (Nyk and c-Eyk) receptor tyrosine kinase (Mertk) is involved in two aspects of apoptotic cell clearance by acting as a receptor for Gas6, a gamma-carboxylated phosphatidylserine-binding protein that bridges apoptotic and viable cells. First, Mertk acts in a bona fide engulfment pathway in concert with alphavbeta5 integrin by regulating cytoskeletal assemblages, and second, it acts as a negative regulator for inflammation by down-modulating pro-inflammatory signals mediated from bacterial lipopolysaccharide-Toll-like receptor 4 (TLR4) signaling, and hence recapitulating anti-inflammatory immune modulation by apoptotic cells. Here we describe Mertk post-receptor events that govern phagocytosis and cytoskeletal signaling are principally mediated by autophosphorylation site Tyr-867. Using the Mertk Y867F mutant and pharmacological inhibitors, we show that Tyr-867 is required for phosphatidylinositol 3-kinase and phospholipase Cgamma2 activation; their activation in turn elicits protein kinase C-dependent signals that act on the actin cytoskeleton. Although Mertk(Y867F) blocked the tyrosine phosphorylation of FAK on Tyr-861 and p130(cas) and also abrogated the phagocytosis of apoptotic cells, this mutant did not suppress lipopolysaccharide-inducible NF-kappaB transcription, nor was NF-kappaB activation dependent on the protein kinase C inhibitor, calphostin C. Finally, unlike the cytoskeletal events associated with Tyr-867 autophosphorylation, the trans-inhibition of NF-kappaB occurred in a postnuclear-dependent fashion independent of cytosolic IkappaB phosphorylation and p65/RelA sequestration. Taken together, these data suggest that Mertk has distinct and separable effects for phagocytosis and for resolving inflammation, providing a molecular rationale for how immune licensing and inflammation can be dissociated from phagocytosis in a single phagocytic receptor.

IFN-alpha is not sufficient to drive Th1 development due to lack of stable T-bet expression

During inflammatory immune responses, the innate cytokine IL-12 promotes CD4+ Th-1 development through the activation of the second messenger STAT4 and the subsequent expression of T-bet. In addition, type I IFN (IFN-alphabeta), secreted primarily during viral and intracellular bacterial infections, can promote STAT4 activation in human CD4+ T cells. However, the role of IFN-alphabeta in regulating Th1 development is controversial, and previous studies have suggested a species-specific pathway leading to Th1 development in human but not mouse CD4+ T cells. In this study, we found that although both IFN-alpha and IL-12 can promote STAT4 activation, IFN-alpha failed to promote Th1 commitment in human CD4+ T cells. The difference between these innate signaling pathways lies with the ability of IL-12 to promote sustained STAT4 tyrosine phosphorylation, which correlated with stable T-bet expression in committed Th1 cells. IFN-alpha did not promote Th1 development in human CD4+ T cells because of attenuated STAT4 phosphorylation, which was insufficient to induce stable expression of T-bet. Further, the defect in IFN-alpha-driven Th1 development was corrected by ectopic expression of T-bet within primary naive human CD4+ T cells. These results indicate that IL-12 remains unique in its ability to drive Th1 development in human CD4+ T cells and that IFN-alpha lacks this activity due to its inability to promote sustained T-bet expression.

Intracellular localization and trafficking using the ImageStream imaging flow cytometer (132.6)

Specific ligands or antibody-conjugated drugs can mediate their cellular effects by gaining entry into cells via receptor mediated endocytosis. Once internalized, molecules differ in their preferential endocytic pathway, and drug efficacy is highly dependant on the route of entry and interaction with cellular components. Evaluation of internalization and intracellular molecular trafficking events are traditionally performed using microscopy. These analyses are limited, because manual image acquistion and quantitative image analysis are time consuming processes. Here we describe a method for measuring internalized events using the ImageStream imaging flow cytometer, which automatically collects large numbers of images per data set and provides qunatitative image analysis tools. In addition, localization of internalized probes to endosomes and lysosomes is quantified in several model systems. Because the ImageStream collects multiple fluorescent images per cell, internalized marker colocalization to different cellular compartments can be done simultaneously in a quantitative manner.

Temporal Dissection of T-bet Functions

T-bet is a transcription factor of the T-box family that regulates the expression of numerous immune system-associated genes. T-bet directs the acquisition of the Th1-associated genetic program in differentiating CD4(+) lymphocytes. It also influences the development of NK and NKT cells through its regulation of the IL-2/IL-15Rbeta-chain (CD122) and the trafficking of these lymphocytes through CxCR3. The temporal requirements of T-bet activity for the production of IFN-gamma and the regulation of CD122 and CxCR3 expression remain undefined. We produced an ectopically controllable form of T-bet by fusing its C-terminal domain with a mutated ligand-binding domain of human estrogen receptor alpha. By temporally controlling the expression of T-bet-estrogen receptor alpha by the addition or removal of 4-hydroxytamoxifen (4-HT), we show that IFN-gamma, CD122, and CxCR3 are direct gene targets of T-bet whose expression are acutely regulated by T-bet activity.

Receptor cross-linking on human plasmacytoid dendritic cells leads to the regulation of IFN-alpha production

Plasmacytoid dendritic cells (PDC) are the natural type I IFN-producing cells that produce large amounts of IFN-alpha in response to viral stimulation. During attempts to isolate PDC from human PBMC, we observed that cross-linking a variety of cell surface receptors, including blood DC Ag (BDCA)-2, BDCA-4, CD4, or CD123 with Abs and immunobeads on PDC leads to inhibition of IFN-alpha production in response to HSV. To understand the mechanisms involved, a number of parameters were investigated. Cross-linking did not inhibit endocytosis of soluble Ag by PDC. Flow cytometry for annexin V and activated caspase-3 indicated that PDC are not undergoing apoptosis after receptor cross-linking. Cross-linking of CD123, but not the other receptors, caused the up-regulation of costimulatory molecules CD80 and CD86, as well as the down-regulation of CD62L, indicating PDC maturation. Thus, anti-CD123 Ab may be acting similar to the natural ligand, IL-3. Anti-phosphotyrosine Ab, as well as Ab to the IFN regulatory factor, IRF-7, was used in intracellular flow cytometry to elucidate the signaling pathways involved. Tyrosine phosphorylation occurred after cross-linking BDCA-2 and BDCA-4, but not CD4. Cross-linking did not affect IRF-7 levels in PDC, however, cross-linking BDCA-2, BDCA-4, and CD4, but not CD123, inhibited the ability of IRF-7 to translocate to the nucleus. Taken together, these results suggest that cross-linking BDCA-2, BDCA-4, and CD4 on PDC regulates IFN-alpha production at the level of IRF-7, while the decrease in IFN-alpha production after CD123 cross-linking is due to stimulation of the IL-3R and induction of PDC maturation.

Quantitative analysis of protein co-localization on B cells opsonized with rituximab and complement using the ImageStream multispectral imaging flow cytometer

Binding of the chimeric, humanized anti-CD20 mAb Rituximab (RTX) to B lymphocytes activates complement and promotes covalent deposition of C3 fragments (C3b/iC3b) on cells. Previous fluorescence microscopy studies, based on examination of B cell lines and of blood samples from RTX-treated CLL patients, suggest that C3b/iC3b is closely associated with cell-bound RTX. We examined Raji cells opsonized with serum and RTX with the ImageStream imaging flow cytometer. Cells were stained with fluorescently-labeled RTX and mAbs specific for C3b/iC3b fragments or for human IgG, and then imaged using the ImageStream cytometer and analyzed with an algorithm (Similarity Bright Detail Score, SBDS) which tests for co-localization of fluorescent probes. SBDS, calculated on 10,000 cells, verified that the majority of deposited C3b/iC3b is co-localized with bound RTX. In contrast, when cells were first opsonized in serum alone, washed and then reacted with RTX, SBDS confirmed that RTX and C3b/iC3b are poorly co-localized, thus demonstrating that cell-bound RTX directs deposition of C3b. In addition, a sulfhydryl-specific probe, maleimide conjugated to AF488, exhibited substantial co-localization with an anti-C3b/iC3b mAb on Raji cells opsonized with RTX and serum, thus validating maleimide labeling as an alternative for detecting cell-bound C3b/iC3b. The digital imaging method described should have wide applicability for quantitative analysis of co-localization.

Cutting edge: FADD is not required for antigen receptor-mediated NF-kappaB activation

Recently, it has been demonstrated that stimulated T cells bearing defects in caspase-8 fail to promote nuclear shuttling of NF-kappaB complexes. Such cells display strikingly similar proliferative and survival defects as T cells lacking Fas-associated death domain protein (FADD) function. We characterized NF-kappaB signaling in T cells bearing a dominant-negative FADD transgene (FADDdd). Whereas FADDdd T cells displayed proliferative defects following activation, these were not a consequence of aberrant NF-kappaB signaling, as measured by IKK/IkappaB phosphorylation and IkappaB degradation. There were no appreciable defects in nuclear translocation of p65/Rel using ImageStream, a flow-based imaging cytometer. Pretreatment with benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, a potent caspase inhibitor, also failed to impede canonical NF-kappaB signaling. Secretion of IL-2 and up-regulation of various activation markers occurred normally. Thus, FADD does not play an essential role in NF-kappaB activation, suggesting an alternative route by which this adaptor promotes the clonal expansion of T cells.

Quantitative measurement of nuclear translocation events using similarity analysis of multispectral cellular images obtained in flow

Nuclear translocation of NF-kappaB initiates transcription of numerous genes, many of which are critical to host defense. Fluorescent image-based methods that quantify this event have historically utilized adherent cells with large cytoplasm-to-nuclear area ratios. However, many immunologically relevant cells are naturally non-adherent and have small cytoplasm-to-nuclear area ratios. Using the ImageStream imaging flow cytometer, we have developed a novel method that measures nuclear translocation in large populations using cross-correlation analysis of nuclear and NF-kappaB images from each cell. This approach accurately measures NF-kappaB translocation in cells with small cytoplasmic areas in dose- and time-dependent manners. Further, NF-kappaB translocation was accurately measured in a subset of cells contained in a mixed population and the technique was successfully employed to measure IRF-7 translocation in plasmacytoid dendritic cells (PDC) obtained from human peripheral blood. The techniques described here provide an objective and statistically robust method for measuring cytoplasmic to nuclear molecular translocation events in a variety of immunologically relevant cell types with characteristically low cytoplasm-to-nuclear area ratios.

Sensitivity measurement and compensation in spectral imaging

BACKGROUND

The ImageStream system combines advances in CCD technologies with a novel optical architecture for high sensitivity and multispectral imaging of cells in flow. The sensitivity and dynamic range as well as a methodology for spectral compensation of imagery is presented.

METHODS

Multicolored fluorescent beads were run on the ImageStream and a flow cytometer. Four single color fluorescent control samples of cells were run to quantify spectral overlap. An additional sample, labeled with all colors was run and compensated in six spectral channels.

RESULTS

Analysis of empirical data for sensitivity and dynamic range matched theoretical predictions. The ImageStream system demonstrated fluorescence sensitivity comparable to a PMT-based flow cytometer. A methodology for addressing spectral overlap, individual pixel anomalies, and multiple imaging modalities was demonstrated for spectral compensation of K562 cells. Imagery is shown pre- and post-compensation.

CONCLUSIONS

Unlike intensity measurements made with conventional flow cytometers, object size impacts both dynamic range and fluorescence sensitivity in systems that utilize pixilated detection. Simultaneous imaging of alternate modalities can be employed to increase fluorescent sensitivity. Effective compensation of complex multimode imagery spanning six spectral bands is accomplished in a semi-automated manner.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mucosal CD8alpha+ DC, with a plasmacytoid phenotype, induce differentiation and support function of T cells with regulatory properties

Repetitive stimulation of naïve T cells by immature splenic dendritic cells (DC) can result in the differentiation of T-cell lines with regulatory properties. In the present study we identified a population of DC in the mucosae that exhibit the plasmacytoid phenotype, secrete interferon-alpha (IFN-alpha) following stimulation with oligodeoxynucleotides containing certain cytosine-phosphate-guanosine (CpG) motifs and can differentiate naïve T cells into cells that exhibit regulatory properties. Although these DC appear to be present in both spleen and mesenteric lymph nodes (MLN), only CpG-matured DC from the MLN (but not the spleen) were able to differentiate naïve T cells into T regulatory 1-like cells with regulatory properties. The activity of these DC failed to sustain robust T-cell proliferation and thereby enhanced the suppressive efficacy of CD4+ CD25+ T regulatory cells. These DC are the major CD8alpha+ DC population in the Peyer's patches (PP). Given their significant presence in mucosal tissue, we propose that these DC may provide a mechanistic basis for the homeostatic regulation in the gut by eliciting regulatory cell suppressor function and poorly supporting T helper cell proliferation at a site of high antigenic stimulation like the intestine.

High antigen dose and activated dendritic cells enable Th cells to escape regulatory T cell-mediated suppression in vitro

CD4+CD25+ regulatory T cells (Tregs) are critical for peripheral tolerance and prevention of autoimmunity. In vitro coculture studies have revealed that increased costimulation breaks Treg-mediated suppression in response to anti-CD3 or antigen. However, it was unclear whether loss of suppression arose from inactivation of Tregs or whether increased stimulation caused Th cells to escape suppression. We have investigated conditions that allow or override Treg-mediated suppression using DO11.10 TCR-transgenic T cells and chicken ovalbumin peptide 323-339-pulsed antigen-presenting cells. Treg suppression of Th proliferation is broken with potent stimulation, using activated spleen cells and high antigen dose, but is intact at low antigen dose. Costimulation with CD80 and CD86 expressed on activated dendritic cells was essential for Th cell escape from suppression at a high antigen dose. Potently stimulated Tregs were functional since they reduced levels of IL-2, IFN-gamma, IL-4 and Th CD25 expression in cocultures. Furthermore, Tregs responding to high antigen dose and activated splenocytes retained the ability to suppress proliferation, but only of Th cells responding to a sub-optimal dose of independent antigen. Together, our results demonstrate that under conditions of strong antigen-specific stimulation, Tregs remain functional, but Th cells escape Treg-mediated suppression.

Definition of additional functional ligands for Ly49I(B6) using FVBLy49I(B6) transgenic mice and B6 natural killer cell effectors

BACKGROUND

Natural killer (NK) cells use inhibitory Ly49 receptors to differentiate self from foreign cells based on interactions with major histocompatibility (MHC) class I molecules. Inhibitory receptors may recognize multiple MHC class I molecules. Studies to define ligands for the Ly49 receptors are complicated by the fact that receptors are expressed in overlapping subsets on NK cells. Binding studies can predict which MHC class I molecules are ligands for Ly49 receptors, but functional tests are required to substantiate results from binding studies.

METHODS

We developed Ly49 receptor transgenic mice and studied the function of Ly49I(B6) in FVB.Ly49I(B6) transgenic mice using bone marrow transplantation assays to determine additional functional ligands for Ly49I(B6). We have also used fluorescence-activated cell sorting to isolate specific populations of B6 NK cells bearing Ly49I for use as effectors in chromium-release assays against a panel of Concanavalin A blast targets.

RESULTS

Bone marrow transplantation studies indicate that H2-K(b), H2(s), and H2(v) serve as functional ligands for Ly49I(B6). In vitro cytotoxicity assays indicate that Ly49I recognizes H2(q), but not H2(d) or H2(k), target cells to inhibit NK killing.

CONCLUSIONS

These data add support to previous binding studies by showing functional interactions between the B6-strain Ly49I and H2-K(b), H2(s), H2(v), and H2(q) class I antigens.

B6 Strain Ly49I Inhibitory Gene Expression on T Cells in FVB.Ly49IB6 Transgenic Mice Fails to Prevent Normal T Cell Functions

Inhibitory Ly49 receptors expressed on NK cells provide a mechanism for tolerance to normal self tissues. The immunoregulatory tyrosine-based inhibitory motifs present in some Ly49s are able to transmit an inhibitory signal upon ligation by MHC class I ligands. In our system, as well as others, mice transgenic for inhibitory Ly49 receptors express these receptors on both NK and T cells. FVB (H2(q)) mice transgenic for the B6 strain Ly49I (Ly49I(B6)) express the inhibitory Ly49 receptor on the surface of both T and NK cells. Although Ly49I functions to prevent NK-mediated rejection of H2(b) donor bone marrow cells in this transgenic mouse strain, the T cells do not appear to be affected by the expression of the Ly49I transgene. FVB.Ly49I T cells have normal proliferative capabilities both in vitro and in vivo in response to the Ly49I ligand, H2(b). In vivo functional T cell assays were also done, showing that transgenic T cells were not functionally affected. T cells in these mice also appear to undergo normal T cell development and activation. Only upon stimulation with suboptimal doses of anti-CD3 in the presence of anti-Ly49I is T cell proliferation inhibited. These data are in contrast with findings in Ly49A, and Ly49G2 receptor transgenic models. Perhaps Ly49I-H2(b) interactions are weaker or of lower avidity than Ly49A-H-2D(d) interactions, especially in T cells.

Ly49I NK cell receptor transgene inhibition of rejection of H2b mouse bone marrow transplants

The Ly49 family of genes encode NK cell receptors that bind class I MHC Ags and transmit negative signals if the cytoplasmic domains have immunoregulatory tyrosine-based inhibitory motifs (ITIMs). 5E6 mAbs recognize Ly49C and Ly49I receptors and depletion of 5E6+ NK cells prevents rejection of allogeneic or parental-strain H2d bone marrow cell (BMC) grafts. To determine the function of the Ly49I gene in the rejection of BMC grafts, we transfected fertilized eggs of FVB mice with a vector containing DNA for B6 strain Ly49I (Ly49IB6). Ly49IB6 is ITIM+ and is recognized by 5E6 as well as Ly49I-specific 8H7 mAbs. Normal FVB H2q mice reject H2b but not H2d BMC allografts, and the rejection of H2b BMC was inhibited partially by anti-NK1.1 and completely by anti-asialo GM1, but not by anti-CD8, Abs. In FVB mice, NK1.1 is expressed on only 60% NK cells. FVB. Ly49IB6 hosts failed to reject H2d or H2b BMC, but did reject class I-deficient TAP-1-/- BMC, indicating that NK cells were functional. Nondepleting doses of anti-Ly49I Abs reversed the acceptance of H2b BMC by FVB.Ly49IB6 mice. FVB.Ly49IB6+/- mice were crossed and back-crossed with 129 mice-H2b, 5E6-, poor responders to H2d BMC grafts. While transgene-negative H2b/q F1 or first-generation back-crossed mice rejected H2b marrow grafts (hybrid resistance), transgene-positive mice did not. Thus B6 strain Ly49I receptors transmit inhibitory signals from H2b MHC class I molecules. Moreover, Ly49IB6 has no positive influence on the rejection of H2d allografts.

Tolerance and alloreactivity of the Ly49D subset of murine NK cells

Class I-specific stimulatory and inhibitory receptors expressed by NK cell subsets contribute to the alloreactive potential of the self-tolerant murine NK cell repertoire. In this report, we have studied potential mechanisms of tolerance to the function of the positive signaling Ly49D receptor in mice that express one of its ligands, H2-Dd. Our results demonstrate that H2-Dd-expressing mice possess a large Ly49D+ subset of NK cells that is functionally capable of rejecting bone marrow cell (BMC) allografts in vivo and lysing allogeneic Con A lymphoblasts in vitro. Also, we show that the Ly49D receptor is responsible for the ability of H2b/d F1 hybrid mice to reject H2d/d parental BMC (hybrid resistance). Thus, deletion or anergy of Ly49D+ cells in H2-Dd+ hosts cannot explain self tolerance. Our functional studies revealed that coexpression of the Dd-specific Ly49A or Ly49G2 inhibitory receptors by Ly49D+ cells resulted in tolerance to Dd+ targets, while coexpression of Kb-specific inhibitory receptors Ly49C/I resulted in tolerance to Kb+ targets. Only in H2d/d cells did Ly49C/I dominantly inhibit Ly49D-Dd stimulation. This correlated with an increased mean fluorescence intensity of Ly49C expression, as well as an increased percentage of Ly49C+ cells in the Ly49D+A/G2- compartment. Therefore, we conclude that self tolerance of the Ly49D subset can be achieved through coexpression of a sufficient level of self-specific inhibitory receptors.

Tolerance and Alloreactivity of the Ly49D Subset of Murine NK Cells

Class I-specific stimulatory and inhibitory receptors expressed by NK cell subsets contribute to the alloreactive potential of the self-tolerant murine NK cell repertoire. In this report, we have studied potential mechanisms of tolerance to the function of the positive signaling Ly49D receptor in mice that express one of its ligands, H2-Dd. Our results demonstrate that H2-Dd-expressing mice possess a large Ly49D+ subset of NK cells that is functionally capable of rejecting bone marrow cell (BMC) allografts in vivo and lysing allogeneic Con A lymphoblasts in vitro. Also, we show that the Ly49D receptor is responsible for the ability of H2b/d F1 hybrid mice to reject H2d/d parental BMC (hybrid resistance). Thus, deletion or anergy of Ly49D+ cells in H2-Dd+ hosts cannot explain self tolerance. Our functional studies revealed that coexpression of the Dd-specific Ly49A or Ly49G2 inhibitory receptors by Ly49D+ cells resulted in tolerance to Dd+ targets, while coexpression of Kb-specific inhibitory receptors Ly49C/I resulted in tolerance to Kb+ targets. Only in H2d/d cells did Ly49C/I dominantly inhibit Ly49D-Dd stimulation. This correlated with an increased mean fluorescence intensity of Ly49C expression, as well as an increased percentage of Ly49C+ cells in the Ly49D+A/G2− compartment. Therefore, we conclude that self tolerance of the Ly49D subset can be achieved through coexpression of a sufficient level of self-specific inhibitory receptors.

Positive Recognition of MHC Class I Molecules by the Ly49D Receptor of Murine NK Cells

Members of the murine Ly49 family of receptors have been shown to inhibit and activate NK cell function. Subsets of Ly49-expressing NK cells mediate the rejection of bone marrow cell allografts and the lysis of allogeneic lymphoblasts. In this report we have studied Ly49-mediated positive and negative signaling in an in vitro cytotoxicity assay using sorted NK cell subsets as effectors and a panel of 51Cr-labeled Con A lymphoblasts as targets in the presence or the absence of Abs to Ly49 and/or class I molecules. Our results demonstrate that the activating receptor Ly49D delivers stimulatory signals for target cell lysis upon interacting with H2-Dd, Dr, and Dsp2, but not H2b or H2k class I Ags. On the other hand, the inhibitory receptor Ly49G2 delivers negative signals for target cell lysis upon interacting with Dd, Dr, and H2k, but not H2b or Dsp2, class I Ags. Furthermore, Ly49-mediated negative signaling dominates Ly49D-mediated positive signaling. Thus, lysis of class I MHC-bearing targets by NK cells is not merely the consequence of the absence of an Ly49-mediated negative signal, but also requires positive recognition of class I molecules by certain Ly49 receptors. Activation of NK cells by nonself class I molecules was not predicted by the missing self hypothesis.

Positive recognition of MHC class I molecules by the Ly49D receptor of murine NK cells

Members of the murine Ly49 family of receptors have been shown to inhibit and activate NK cell function. Subsets of Ly49-expressing NK cells mediate the rejection of bone marrow cell allografts and the lysis of allogeneic lymphoblasts. In this report we have studied Ly49-mediated positive and negative signaling in an in vitro cytotoxicity assay using sorted NK cell subsets as effectors and a panel of 51Cr-labeled Con A lymphoblasts as targets in the presence or the absence of Abs to Ly49 and/or class I molecules. Our results demonstrate that the activating receptor Ly49D delivers stimulatory signals for target cell lysis upon interacting with H2-Dd, Dr, and Dsp2, but not H2b or H2k class I Ags. On the other hand, the inhibitory receptor Ly49G2 delivers negative signals for target cell lysis upon interacting with Dd, Dr, and H2k, but not H2b or Dsp2, class I Ags. Furthermore, Ly49-mediated negative signaling dominates Ly49D-mediated positive signaling. Thus, lysis of class I MHC-bearing targets by NK cells is not merely the consequence of the absence of an Ly49-mediated negative signal, but also requires positive recognition of class I molecules by certain Ly49 receptors. Activation of NK cells by nonself class I molecules was not predicted by the missing self hypothesis.