Near-infrared emitting quantum dots for cellular and vascular fluorescent labeling in in vivo multiplexed imaging studies

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 199-217).In vivo multimodal, multiplexed microscopy allows real-time observation of hematopoietic cells, their stem and progenitor cells and metastatic cancer cells in their native bone marrow (BM) environment. Multiplexing has made possible detailed studies of the BM's microarchitecture, which helps define the niche of these cells; it has nonetheless been limited by the paucity of suitable probes fluorescent in the near-infrared spectrum that is favored by tissue optics. This project attempts to address this problem by developing cellular and vascular fluorescent imaging probes comprised of semiconductor nanocrystals, or quantum dots (QDs), with tunable fluorescence between 65o-8oonm and exhibiting photostability, robust quantum yield and narrow fluorescence profiles that are critical for such applications. The synthesis of alloyed CdTexSe1 x QDs will be detailed in the thesis. Reproducibility and workability in subsequent steps are emphasized in the methods. Special attention is also paid to the difference between working with alloyed versus single semiconductor QDs, especially the need to achieve physical and spectral uniformity when composition and its gradient are also variable. The steps for creating biological probes from these QD fluorophores are also described. They include overcoating, water solubilization and functionalization for cellular uptake and vascular retention. Finally, the thesis returns to its motivation and reports novel methods, developed using NIR QD vascular imaging probes, for visualizing in vivo 3-D imaging data of the murine BM and characterizing the tissue's architecture. Measuring the Euclidean distance between BM osteoblasts and blood vessels is presented to exemplify a potential platform for describing the geographic relationships between cells, molecules and structural components in any tissue.by Juwell Wendy Wu.Ph.D

Three-color femtosecond source for simultaneous excitation of three fluorescent proteins in two-photon fluorescence microscopy

We demonstrate a fiber-based, three-color femtosecond source for simultaneous imaging of three fluorescent proteins (FPs) using two-photon fluorescence microscopy (2PM). The three excitation wavelengths at 775 nm, 864 nm and 950 nm, are obtained through second harmonic generation (SHG) of the 1550-nm pump laser and the 1728-nm and 1900-nm solitons generated through soliton self-frequency shift (SSFS) in a large-mode-area (LMA) fiber. These energetic pulses are well matched to the two-photon excitation peaks of red, cyan and yellow fluorescent proteins (TagRFPs, TagCFPs, and TagYFPs) for efficient excitation. We demonstrate simultaneous 2PM of human melanoma cells expressing a “rainbow” combination of these three fluorescent proteins

Defining Clonal Color in Fluorescent Multi-Clonal Tracking

Clonal heterogeneity and selection underpin many biological processes including development and tumor progression. Combinatorial fluorescent protein expression in germline cells has proven its utility for tracking the formation and regeneration of different organ systems. Such cell populations encoded by combinatorial fluorescent proteins are also attractive tools for understanding clonal expansion and clonal competition in cancer. However, the assignment of clonal identity requires an analytical framework in which clonal markings can be parameterized and validated. Here we present a systematic and quantitative method for RGB analysis of fluorescent melanoma cancer clones. We then demonstrate refined clonal trackability of melanoma cells using this scheme

Tracking Single Cells in Live Animals Using a Photoconvertible Near-Infrared Cell Membrane Label

We describe a novel photoconversion technique to track individual cells in vivo using a commercial lipophilic membrane dye, DiR. We show that DiR exhibits a permanent fluorescence emission shift (photoconversion) after light exposure and does not reacquire the original color over time. Ratiometric imaging can be used to distinguish photoconverted from non-converted cells with high sensitivity. Combining the use of this photoconvertible dye with intravital microscopy, we tracked the division of individual hematopoietic stem/progenitor cells within the calvarium bone marrow of live mice. We also studied the peripheral differentiation of individual T cells by tracking the gain or loss of FoxP3-GFP expression, a marker of the immune suppressive function of CD4+ T cells. With the near-infrared photoconvertible membrane dye, the entire visible spectral range is available for simultaneous use with other fluorescent proteins to monitor gene expression or to trace cell lineage commitment in vivo with high spatial and temporal resolution

Direct measurement of local oxygen concentration in the bone marrow of live animals

Characterizing how the microenvironment, or niche, regulates stem cell activity is central to understanding stem cell biology and to developing strategies for therapeutic manipulation of stem cells1. Low oxygen tension (hypoxia) is commonly thought to be a shared niche characteristic in maintaining quiescence in multiple stem cell types2–4. However, support for the existence of a hypoxic niche has largely come from indirect evidence such as proteomic analysis5, expression of HIF-1 and related genes6, and staining with surrogate hypoxic markers (e.g. pimonidazole)6–8. Here we perform direct in vivo measurements of local oxygen tension (pO2) in the bone marrow (BM) of live mice. Using two-photon phosphorescence lifetime microscopy (2PLM), we determined the absolute pO2 of the BM to be quite low (<32 mmHg) despite very high vascular density. We further uncovered heterogeneities in local pO2, with the lowest pO2 (~9.9 mmHg, or 1.3%) found in deeper peri-sinusoidal regions. The endosteal region, by contrast, is less hypoxic as it is perfused with small arteries that are often positive for the marker nestin. These pO2 values change dramatically after radiation and chemotherapy, pointing to the role of stress in altering the stem cell metabolic microenvironment

Intravital imaging of mouse bone marrow: Hemodynamics and vascular permeability

The bone marrow is a unique microenvironment where blood cells are produced and released into the circulation. At the top of the blood cell lineage are the hematopoietic stem cells (HSC), which are thought to reside in close association with the bone marrow vascular endothelial cells (Morrison and Scadden, Nature 505:327–334, 2014). Recent efforts at characterizing the HSC niche have prompted us to make close examinations of two distinct types of blood vessel in the bone marrow, the arteriolar vessels originating from arteries and sinusoidal vessels connected to veins. We found the two vessel types to exhibit different vascular permeabilites, hemodynamics, cell trafficking behaviors, and oxygen content (Itkin et al., Nature 532:323–328, 2016; Spencer et al., Nature 508:269–273, 2014). Here, we describe a method to quantitatively measure the permeability and hemodynamics of arterioles and sinusoids in murine calvarial bone marrow using intravital microscopy. © 2018, Springer Science+Business Media, LLC

Intravital imaging of mouse bone marrow: Hemodynamics and vascular permeability

The bone marrow is a unique microenvironment where blood cells are produced and released into the circulation. At the top of the blood cell lineage are the hematopoietic stem cells (HSC), which are thought to reside in close association with the bone marrow vascular endothelial cells (Morrison and Scadden, Nature 505:327–334, 2014). Recent efforts at characterizing the HSC niche have prompted us to make close examinations of two distinct types of blood vessel in the bone marrow, the arteriolar vessels originating from arteries and sinusoidal vessels connected to veins. We found the two vessel types to exhibit different vascular permeabilites, hemodynamics, cell trafficking behaviors, and oxygen content (Itkin et al., Nature 532:323–328, 2016; Spencer et al., Nature 508:269–273, 2014). Here, we describe a method to quantitatively measure the permeability and hemodynamics of arterioles and sinusoids in murine calvarial bone marrow using intravital microscopy

Intravital fluorescence microscopy with negative contrast.

Advances in intravital microscopy (IVM) have enabled the studies of cellular organization and dynamics in the native microenvironment of intact organisms with minimal perturbation. The abilities to track specific cell populations and monitor their interactions have opened up new horizons for visualizing cell biology in vivo, yet the success of standard fluorescence cell labeling approaches for IVM comes with a "dark side" in that unlabeled cells are invisible, leaving labeled cells or structures to appear isolated in space, devoid of their surroundings and lacking proper biological context. Here we describe a novel method for "filling in the void" by harnessing the ubiquity of extracellular (interstitial) fluid and its ease of fluorescence labelling by commonly used vascular and lymphatic tracers. We show that during routine labeling of the vasculature and lymphatics for IVM, commonly used fluorescent tracers readily perfuse the interstitial spaces of the bone marrow (BM) and the lymph node (LN), outlining the unlabeled cells and forming negative contrast images that complement standard (positive) cell labeling approaches. The method is simple yet powerful, offering a comprehensive view of the cellular landscape such as cell density and spatial distribution, as well as dynamic processes such as cell motility and transmigration across the vascular endothelium. The extracellular localization of the dye and the interstitial flow provide favorable conditions for prolonged Intravital time lapse imaging with minimal toxicity and photobleaching

Intravital fluorescence microscopy with negative contrast.

Advances in intravital microscopy (IVM) have enabled the studies of cellular organization and dynamics in the native microenvironment of intact organisms with minimal perturbation. The abilities to track specific cell populations and monitor their interactions have opened up new horizons for visualizing cell biology in vivo, yet the success of standard fluorescence cell labeling approaches for IVM comes with a "dark side" in that unlabeled cells are invisible, leaving labeled cells or structures to appear isolated in space, devoid of their surroundings and lacking proper biological context. Here we describe a novel method for "filling in the void" by harnessing the ubiquity of extracellular (interstitial) fluid and its ease of fluorescence labelling by commonly used vascular and lymphatic tracers. We show that during routine labeling of the vasculature and lymphatics for IVM, commonly used fluorescent tracers readily perfuse the interstitial spaces of the bone marrow (BM) and the lymph node (LN), outlining the unlabeled cells and forming negative contrast images that complement standard (positive) cell labeling approaches. The method is simple yet powerful, offering a comprehensive view of the cellular landscape such as cell density and spatial distribution, as well as dynamic processes such as cell motility and transmigration across the vascular endothelium. The extracellular localization of the dye and the interstitial flow provide favorable conditions for prolonged Intravital time lapse imaging with minimal toxicity and photobleaching

The Microanatomy of the Leukemic Stem Cell Niche in Murine Chronic Myelogenous Leukemia

Abstract Objectives and background: Constituents of the bone marrow microenvironment (BMM) influence the proliferation, differentiation and location of hematopoietic stem and progenitor cells (HSPC). Dependent on their maturation stage, different subsets of HSPC are localized at distinct sites in the BMM. This location depends on HSPC-intrinsic, as well as HSPC-extrinsic factors. The BMM protects leukemic stem cells (LSC) from treatment with tyrosine kinase inhibitors or chemotherapy. We, therefore, investigated the microanantomy of the LSC niche hypothesizing that it may differ from the normal HSPC niche. Methods: We used a combination of confocal and 2-photon intravital microscopy (IVM) of the murine calvarium and well-described retroviral models of BCR-ABL1+chronic myelogenous leukemia (CML) and B-cell acute lymphoblastic leukemia (B-ALL). Results: We show here that BCR-ABL1+Lin–c-Kit+Sca-1+ (LKS) CD150+CD48– (LKS SLAM) cells, which harbor the LSC fraction in the CML model, homed to locations further away from the endosteum than their normal counterparts. Prior in-vitro treatment of BCR-ABL1+ LKS with imatinib mesylate, considered standard of care in CML, reversed this phenotype and the cells were found closer to the endosteum. Native BCR-ABL1, as well as the imatinib-resistant BCR-ABL1 point mutants BCR-ABL1Y253F, BCR-ABL1E255K, BCR-ABL1T315I and BCR-ABL1M351T had similar intrinsic catalytic activity, but the BCR-ABL1Y253F, BCR-ABL1E255K, and BCR-ABL1T315I mutants increased the IL-3-independent proliferative capacity of 32D cells relative to native BCR-ABL1. BCR-ABL1Y253F and BCR-ABL1M351T caused increased transformation of primary BM B-lymphoid progenitors in vitro and led to accelerated induction of B-ALL in mice. In the CML model, BCR-ABL1Y253F and BCR-ABL1T315Iinduced myeloproliferative neoplasia with shortened survival and features of accelerated phase disease compared to native BCR-ABL1, whereas BCR-ABL1T315I LKS cells homed closer to osteoblastic cells than LKS cells expressing native BCR-ABL1. Sequential in vivo tracking of leukemic progenitor growth by IVM showed a similar nadir in the number of cells per leukemic cell ‘nest’ 11 days after irradiation and IV transplantation in recipients of DsRed+BCR-ABL1+ or empty vector control-transduced bone marrow. However, between days 18-25 after transplantation there was a significant increase in the number of cells per leukemic cell ‘nest’ compared to the empty vector control group. Sequential immunohistochemistry and TUNEL assays of leukemic bone sections in imatinib- or vehicle-treated recipient mice with CML showed that initial BCR-ABL1+ growth tends to occur at locations further away from the endosteum, whereas erythroid islands were found closer to the endosteum and trabeculae. Apoptosis in response to imatinib appeared most prominent in the metaphysis. Lastly, we could demonstrate by IVM in the CML model that treatment of mice with a combination of imatinib plus granulocyte colony-stimulating factor led to ‘emptying’ of the LSC niche and superior eradication of BCR-ABL1+ leukemic cells compared to treatment with imatinib alone. Conclusions: In summary, these data suggest that the microanatomy of the LSC niche in CML differs from the normal hematopoietic niche. BCR-ABL1 mutation status may affect the positioning of CML LSC in the microenvironment, and location in the niche may be altered pharmacologically, suggesting that niche location may influence clinical outcome. Disclosures Krause: Glycomimetics. Inc.: Research Funding