Tissue engineering complex and mechanically active microenvironments for studies in asthma and cancer

The goals of tissue engineering include recapitulating specific tissue functions for regenerative medicine and developing in vitro models of human tissues to study human physiology and pathophysiology and for testing and screening drugs before expensive clinical trials. Success of these goals relies on the capability to recapitulate the complex interactions between cells and their microenvironments in vitro, which requires interdisciplinary approaches. Tissue engineering has evolved greatly in the past two decades, with notable progress in replacing function in tissues such as cartilage, bone, arteries, skin, and pancreatic islets. What is lacking, however, are examples of, and design principles for, engineering complex microenvironments to understand disease progression. The two particular examples addressed in this thesis are (1) airway remodeling in asthma and (2) tumor invasion and metastasis in cancer. These diseases involve complex interactions between different cell types as well as extracellular matrix remodeling, which, together with the mechanical environment that affects cell-cell and cell-matrix interactions and that can change in a diseased state (or in some cases induce the disease state), collectively cause the pathology. Such disease states are difficult to study in vivo because (a) one cannot easily tease out mechanisms or have much control over these complex interactions in an animal model, and (b) there are many differences between animal and human cells. The aim of this thesis was to engineer mechanically dynamic microenvironments for the study of two disease processes: viral infection in asthmatic remodeled airways and cancer metastasis to the lymph node. These involved multidisciplinary approaches and drew tools and methods from mechanobiology, materials science, cell biology, and molecular biology. First, we developed and characterized a relevant 3D in vitro model of the bronchial mucosa with a functional epithelial barrier, including improved epithelial differentiation, ciliogenesis, and mucociliary function and showed for the first time that dynamic compression, such as that seen in asthmatic bronchoconstriction, enhances viral infection of epithelial and subepithelial cells using lentiviral technology and may help explaining why asthmatic patients are more susceptible to viral infection. However, the strain device had deficiencies in reproducibility, ease of use, time to assemble, and most importantly, homogeneous distribution of strain (because collagen and other natural extracellular matrices are mechanically weak since they have >99% water and cannot retain residual strain). To address these problems, we engineered a completely different dynamic strain device, which includes an elastic porous superstructure to contain the collagen and which can modulate stress/strain to the entire culture system. We characterized this device and showed that we could impose dynamic strains to 3D soft, hydrated cultures over relatively long periods of time and with variable amplitude and frequency in a uniform way. The device has the potential to be used in a wide spectrum of applications, including the possibility to study the correlation between mechanostimulation and metastatic potential of tumor cells in the context of lung metastasis of many cancer types. Finally, we used this material as a supporting structure for tissue-generated stress such as that generated by myofibroblasts, and in particular the ones that build up the lymph node stroma in the paracortex. The importance of these cells relies on their ability to form conduits for chemokine transport to high endothelial venules, where lymphocytes enter the node, the ability to form a platform for directing immune cell migration and interactions, and the ability to secrete two chemokines that are important to regulate lymphocyte adhesion and migration: CCL19 and CCL21. Specifically, we found that lymph node stromal cells use this supporting composite to remodel and reorganize their surrounding matrix into physiologically relevant bundles. By giving these cells the relevant stimuli (matrix microenvironment and flow), we could recapitulate certain features of the lymph node microenvironment, including a physiological stromal structure and chemokine profile, that may be critical for understanding immune and cancer cell interactions there. Using this model we demonstrated for the first time that slow flow through the lymph node stroma can itself drive cell and stromal organization and upregulates CCL21 production. Finally, we incorporated this engineered lymph node model into a larger model of the tumor-lymphatic-lymph node pathway to model the relative modulation of tumor growth, migration within a lymphatic "channel" towards the lymph node, and behavior within this lymph node environment. We used human lymphatic endothelial cells and a mass of transduced tumor cells with engineered chemokine profiles. We showed how CCR7 signaling correlates with the ability of tumor cells to metastasize to the lymph node and to interact with lymph node stromal cells once they reach the node. Our findings demonstrate how a multidisciplinary tissue engineering approach allows creating complex microenvironments in vitro that include both physical and chemical cues and allows recapitulating tissue function in vitro and investigating dynamic pathophysiological diseases like asthma and cancer metastasis. It combines both the development of these model systems and some examples of their usefulness to gain insight into asthma pathophysiology and cancer biology.

The interplay between the VEGF-C/VEGFR-3 axis and CCL21/CCR7 axis in tumor cell invasion

Amine Issa

There are two main routes for tumor spread and metastasis, the blood vasculature and the lymphatic system. A wide range of human carcinomas, including lung, colon and breast cancer, spread to distant sites via the lymphatic system. Preclinical and clinical studies have demonstrated a positive correlation between the incidence of lymph node metastasis and the secretion of vascular endothelial growth factor-C (VEGF-C) by tumor cells. Indeed, VEGF-C is critical for the formation of new lymphatic vessels in a process called lymphangiogenesis, suggesting this mechanism as the main "escape route" for tumor cells. However, many studies have failed to identify functional lymphatic vessels inside tumors, and much research has demonstrated that metastasis can occur in the absence of lymphangiogenesis. Furthermore, there is growing evidence that many tumor cells may express vascular endothelial growth factor receptor-3 (VEGFR-3), the primary receptor for VEGF-C, suggesting that autologous VEGFR-3 signaling loops may enhance the invasive and metastatic potential of tumor cells. Other than lymphangiogenic factors, the lymphatic homing chemokine receptor CCR7 is strongly correlated to lymph node metastasis, suggesting that tumor cells mimic dendritic cells in sensing and homing to lymphatic vessels and lymph nodes. Potential mechanisms underlying these observations have not been elucidated. Using several in vitro 3D models, we examined the interactions between tumor and lymphatic endothelial cells (LECs) to gain insight into the mechanistic roles of VEGF-C and CCR7-mediated tumor cell invasion towards lymphatics as well as elucidate their potential interplay. All the designed experimental setups utilized a 3D matrix for a more physiologically relevant chemokine and growth factor signaling environment. For example, we designed one culture model where tumor cells are seeded in one gel compartment and lymphatic endothelial cells in a horizontally adjacent one, allowing both cell types to establish contact through soluble mediators without being initially mixed while simultaneously allowing direct visualization of their interactions. We first demonstrated that receptor expression patterns by cells are strongly influenced by the extracellular matrix (ECM). Indeed, while we failed to detect tumor expression of VEGFR-3 in 2D conditions, we found both expression and phosphorylation of VEGFR-3 in three of four tumor cell lines tested. Furthermore, in the three VEGFR-3 positive cell lines, invasive capacity and chemoattraction towards lymphatics was demonstrated to be dependent on both VEGF-C secretion and CCR7 expression by the tumor cells. We found that VEGF-C could act in both an autocrine manner, by enhancing the migratory and invasive capacity of tumor cells, and in a paracrine manner where it enhances CCL21 secretion by LECs to promote the chemoinvasion of tumor cells via CCL21 secretion. The same mechanism was also tested in vivo by injecting VEGF-C into mouse skin: VEGF-C, but not saline nor VEGF-A, caused marked upregulation of CCL21 associated with lymphatic vessels. In this way, VEGF-C and CCR7 act synergistically to promote the invasive phenotype of tumor cells. Additionally, we uncovered a new and critical role for VEGFR-3 on mammary epithelial cells. We demonstrated that the receptor is involved in epithelial tubulogenesis in a collagen matrix, and furthermore, it helps to preserve the integrity of a mammary cell layer (since blocking the receptor leads to increased epithelial permeability). In conclusion, this work highlights the importance of the VEGFR-3/VEGF-C and CCR7/CCL21 axis in promoting tumor cell migration and invasion. It also shows that VEGFR-3 may play many roles in the process of tumorigenesis and metastasis.

EPFL2009

Therapeutic Immunomodulation of the Lymphoid-like Tumor Environment Using Nanoparticulate Formulations

Iraklis Kourtis

Cancer is a leading cause of death worldwide. Understanding the underlying mechanisms that lead to tumor escape and evasion is pivotal for the design of new therapeutic applications. This thesis takes an immunobioengineering approach, and navigates through identifying the immunological parameters relevant in the tumor microenvironment, proposing and developing a strategy in response to address these parameters using nanosized drug and antigen carriers. It is widely accepted that changes in the immunological equilibriumof the tumor microenvironment are crucial for the progression, dissemination and metastasis of a developing tumor. Motivated by tumors' natural secretion of CCL21, a chemokine known for dendritic (DC) migration towards the lymphatics, and for attracting DC and T cells in the lymph node (LN), we perturbed the physiological secretion of CCL21 of B16-F10 melanomas, deriving both a knock-down (CCL21low) and an over-expressing (CCL21high) variant. Interestingly, in immunocompetent mice, growth in CCL21-secreting tumors had an advantage over the CCL21low sub-clones and was CCR7 dependent. CCL21low tumors harbored more antigen specific T cells, while CCL21-secreting, more T regulatory cells (Tregs), which also correlated with subsequent biochemical polarization. Moreover, CCL21-secreting tumors formed a reticular fibroblastic (FRC) network (ERTR7+gp38+CCL21+) reminiscent of the lymphoid tissue of the paracortex (T cell zone) within LNs. The lymphoidlike stroma was orchestrated by the recruitment of CCR7+ adult lymphoid tissue inducers (LTis), responsible for LN formation during embryogenesis, present only in the CCL21-secreting tumors. In mice lacking LTis (Rorc(γt)-deficient) control tumors displayed impaired growth, suggesting that tumor growth is stroma dependent. In addition, the stroma of control or CCL21high tumors was infiltrated by more myeloid suppressor cells (MDSCs) than in CCL21low variant. MDSCs are a heterogeneous population of immature myeloid precursor cells that repress T cell activation and antigen presentation in chronic inflammation and cancer, hampering the efficacy of anti-tumoral vaccinations. CCL21's ability to protect allografts was further demonstrated in non-syngeneic recipients and in ectopically CCL21 transduced βTC tumor models. By mimicking secondary lymphoid organs, tumors may hi-jack and modulate the immune response from immunogenic to tolerogenic to allow for growth and metastasis. Intrigued by the excessive stroma infiltration of MDSCs in CCL21-secreting tumors, we performed a detailed spatiotemporal biodistribution analysis of ultrasmall (sub 50 nm) nanoparticles (NPs) in naïve and tumor bearing mice. Intradermally administered NPs rapidly drained to the LNs and spleen and persistently targetedmajor phagocytic populations that play a key role in hosting an immune response in naïve and tumor bearing mice. Furthermore, tumor-induced myeloid compartments, mainlyMDSCs, were highly targeted naturally within the tumormicroenvironment and spleen (tumor macroenvironment) 12 h post administration, without the use of site specific ligand. Following the MDSCs' natural preference towards phagocytosing NPs, and taking advantage of their excessive reductive cytoplasm, we designed a macromolecular pro-drug formulation that bears a cytotoxic payload and can be released in highly reductive microenvironments. Specifically, we engineered a reducible delivery system of 6-tioguanine (TG) in various formulations. Remarkably, bothMDSC compartments were ablated, monocytic ∼20 fold (CD11b+Ly6c+), polymorphonuclear ∼100 fold (CD11b+Ly6g+), for at least 7 d after administration in tumor bearing mice. As the bioidstribution revealed that apart from MDSCs, other antigen presenting cells (APCs) have phagocytosed NPs, we observed only a ∼2 fold decrease in APCs, suggesting that the rest could be used for vaccination. Taking into account that cancer vaccines and cancer immunotherapy rely on the efficient antigen presentation and education of naïve T cells by professional APCs, we explored the ability of NPs to deliver antigens in the appropriate sub-cellular compartment for antigen presentation and activation of T cells. Using the model antigen ovalbumin, we illustrated that exogenous antigen coupled to NPs by reducible bonds were internalized by DCs in vivo and in vitro. The conjugated antigen was preferentially released from the NPs with a reducible formulation, and was successfully presented in the major histocompatibility complex (MHC) I and II, which lead to activation and proliferation of antigen specific CD8+ and CD4+ T cells in vivo, respectively. Taking together, the nanoparticle platformcould be used efficiently for both inducing cytotoxicity and invoking an immune response. From discovery of new suppressive niches to therapeutical applications, we envisioned a two prong strategy that combined I) a modulatory regime to upset the balance of theMDSC populations both within the tumor microenvoronent and systemically with II) a cancer vaccine with the potential to significantly improve anti-tumoral therapeutic applications. This thesis demonstrated that such an approach is both possible and probable.

EPFL2012

Intravital Immunofluorescence for Visualizing the Microcirculatory and Immune Microenvironments in the Mouse Ear Dermis

Witold Waldemar Kilarski, Amanda Waite Lund, Scott Oliver, Melody Swartz, Jeremy Teo

Visualizing the dynamic behaviors of immune cells in living tissue has dramatically increased our understanding of how cells interact with their surroundings, contributing important insights into mechanisms of leukocyte trafficking, tumor cell invasion, and T cell education by dendritic cells, among others. Despite substantial advances with various intravital imaging techniques including two-photon microscopy and the generation of multitudes of reporter mice, there is a growing need to assess cell interactions in the context of specific extracellular matrix composition and microvascular functions, and as well, simpler and more widely accessible methods are needed to image cell behaviors in the context of living tissue physiology. Here we present an antibody-based method for intravital imaging of cell interactions with the blood, lymphatic, and the extracellular matrix compartments of the living dermis while simultaneously assessing capillary permeability and lymphatic drainage function. Using the exposed dorsal ear of the anesthetized mouse and a fluorescence stereomicroscope, such events can be imaged in the context of specific extracellular matrix proteins, or matrix-bound chemokine stores. We developed and optimized the method to minimize tissue damage to the ear, rapidly immunostain for multiple extracellular or cell surface receptors of interest, minimize immunotoxicity with pre-blocking Fc gamma receptors and phototoxicity with extracellular antioxidants, and highlight the major dermal tissue structures with basement membrane markers. We demonstrate differential migration behaviors of bone marrow-derived dendritic cells, blood-circulating leukocytes, and dermal dendritic cells, with the latter entering sparse CCL21-positive areas of pre-collecting lymphatic vessels. This new method allows simultaneous imaging of cells and tissue structures, microvascular function, and extracellular microenvironment in multiple skin locations for 12 hours or more, with the flexibility of immunolabeling in addition to genetic-based fluorescent reporters.

Public Library of Science2013