Tissue-Engineered Stromal Reticula to Study Lymph Node Fibroblastic Reticular Cells in Type I Diabetes

Fibril-Guided Three-Dimensional Assembly of Human Fibroblastic Reticular Cells

Fibroblastic reticular cells (FRCs) are stromal cells (SCs) that can be isolated from lymph node (LN) biopsies. Studies have shown that these nonhematopoietic cells have the capacity to shape and regulate adaptive immunity and can become a form of personalized cell therapy. Successful translational efforts, however, require the cells to be formulated as injectable units, with their native architecture preserved. The intrinsic reticular organization of FRCs, however, is lost in the monolayer cultures. Organizing FRCs into three-dimensional (3D) clusters would recapitulate their structural and functional attributes. Herein, we report a scaffolding method based on the self-assembling peptide (SAP) EAKII biotinylated at the N-terminus (EAKbt). Cross-linking with avidin transformed the EAKbt fibrils into a dense network of coacervates. The combined forces of fibrillization and bioaffinity interactions in the cross-linked EAKbt likely drove the cells into a cohesive 3D reticula. This facile method of generating clustered FRCs (clFRCs) can be completed within 10 days. In vitro clFRCs attracted the infiltration of T cells and rendered an immunosuppressive milieu in the cocultures. These results demonstrate the potential of clFRCs as a method for stromal cell delivery.

Pancreatic draining lymph nodes (PLNs) serve as a pathogenic hub contributing to the development of type 1 diabetes

Type 1 diabetes (T1D) is a chronic, progressive autoinflammatory disorder resulting from the breakdown of self-tolerance and unrestrained β cell-reactive immune response. Activation of immune cells is initiated in islet and amplified in lymphoid tissues, especially those pancreatic draining lymph nodes (PLNs). The knowledge of PLNs as the hub of aberrant immune response is continuously being replenished and renewed. Here we provide a PLN-centered view of T1D pathogenesis and emphasize that PLNs integrate signal inputs from the pancreas, gut, viral infection or peripheral circulation, undergo immune remodeling within the local microenvironment and export effector cell components into pancreas to affect T1D progression. In accordance, we suggest that T1D intervention can be implemented by three major ways: cutting off the signal inputs into PLNs (reduce inflammatory β cell damage, enhance gut integrity and control pathogenic viral infections), modulating the immune activation status of PLNs and blocking the outputs of PLNs towards pancreatic islets. Given the dynamic and complex nature of T1D etiology, the corresponding intervention strategy is thus required to be comprehensive to ensure optimal therapeutic efficacy.

Chitosan Scaffolds as Microcarriers for Dynamic Culture of Human Neural Stem Cells

Human neural stem cells (hNSCs) possess remarkable potential for regenerative medicine in the treatment of presently incurable diseases. However, a key challenge lies in producing sufficient quantities of hNSCs, which is necessary for effective treatment. Dynamic culture systems are recognized as a powerful approach to producing large quantities of hNSCs required, where microcarriers play a critical role in supporting cell expansion. Nevertheless, the currently available microcarriers have limitations, including a lack of appropriate surface chemistry to promote cell adhesion, inadequate mechanical properties to protect cells from dynamic forces, and poor suitability for mass production. Here, we present the development of three-dimensional (3D) chitosan scaffolds as microcarriers for hNSC expansion under defined conditions in bioreactors. We demonstrate that chitosan scaffolds with a concentration of 4 wt% (4CS scaffolds) exhibit desirable microstructural characteristics and mechanical properties suited for hNSC expansion. Furthermore, they could also withstand degradation in dynamic conditions. The 4CS scaffold condition yields optimal metabolic activity, cell adhesion, and protein expression, enabling sustained hNSC expansion for up to three weeks in a dynamic culture. Our study introduces an effective microcarrier approach for prolonged expansion of hNSCs, which has the potential for mass production in a three-dimensional setting.

New tools for immunologists: models of lymph node function from cells to tissues

The lymph node is a highly structured organ that mediates the body's adaptive immune response to antigens and other foreign particles. Central to its function is the distinct spatial assortment of lymphocytes and stromal cells, as well as chemokines that drive the signaling cascades which underpin immune responses. Investigations of lymph node biology were historically explored in vivo in animal models, using technologies that were breakthroughs in their time such as immunofluorescence with monoclonal antibodies, genetic reporters, in vivo two-photon imaging, and, more recently spatial biology techniques. However, new approaches are needed to enable tests of cell behavior and spatiotemporal dynamics under well controlled experimental perturbation, particularly for human immunity. This review presents a suite of technologies, comprising in vitro, ex vivo and in silico models, developed to study the lymph node or its components. We discuss the use of these tools to model cell behaviors in increasing order of complexity, from cell motility, to cell-cell interactions, to organ-level functions such as vaccination. Next, we identify current challenges regarding cell sourcing and culture, real time measurements of lymph node behavior in vivo and tool development for analysis and control of engineered cultures. Finally, we propose new research directions and offer our perspective on the future of this rapidly growing field. We anticipate that this review will be especially beneficial to immunologists looking to expand their toolkit for probing lymph node structure and function.

CCL21 and beta-cell antigen releasing hydrogels as tolerance-inducing therapy in Type I diabetes

Type-I Diabetes (T1D) is caused by defective immunotolerance mechanisms enabling autoreactive T cells to escape regulation in lymphoid organs and destroy insulin-producing β-cells in the pancreas, leading to insulin dependence. Strategies to promote β-cell tolerance could arrest T1D. We previously showed that secretion of secondary lymphoid chemokine CCL21 by CCL21 transgenic β-cells induced tolerance and protected non-obese diabetic (NOD) mice from T1D. T1D protection was associated with formation of lymph node-like stromal networks containing tolerogenic fibroblastic reticular cells (FRCs). Here, we developed a polyethylene glycol (PEG) hydrogel platform with hydrolytically degradable PEG-diester dithiol crosslinkers to provide controlled and sustained delivery of CCL21 and β-cell antigens for at least 28 days in vitro and recapitulate properties associated with the tolerogenic environment of CCL21 transgenic β-cells in our previous studies. CCL21 and MHC-II restricted antigens were tethered to gels via simple click-chemistry while MHC-I restricted antigens were loaded in PEG-based polymeric nanovesicles and incorporated in the gel networks. CCL21 and antigen release kinetics depended on the PEG gel tethering strategy and the linkers. Importantly, in vitro functionality, chemotaxis, and activation of antigen-specific T cells were preserved. Implantation of CCL21 and β-cell antigen gels under the kidney capsule of pre-diabetic NOD mice led to enrichment of adoptively transferred antigen-specific T cells, formation of gp38 + FRC-like stromal cell networks, and increased regulation of specific T cells with reduced accumulation within pancreatic islets. Thus, our platform for sustained release of β-cell antigens and CCL21 immunomodulatory molecule could enable the development of antigen-specific tolerance therapies for T1D.

LN-Derived Fibroblastic Reticular Cells and Their Impact on T Cell Response—A Systematic Review

Fibroblastic reticular cells (FRCs), usually found and isolated from the T cell zone of lymph nodes, have recently been described as much more than simple structural cells. Originally, these cells were described to form a conduit system called the “reticular fiber network” and for being responsible for transferring the lymph fluid drained from tissues through afferent lymphatic vessels to the T cell zone. However, nowadays, these cells are described as being capable of secreting several cytokines and chemokines and possessing the ability to interfere with the immune response, improving it, and also controlling lymphocyte proliferation. Here, we performed a systematic review of the several methods employed to investigate the mechanisms used by fibroblastic reticular cells to control the immune response, as well as their ability in determining the fate of T cells. We searched articles indexed and published in the last five years, between 2016 and 2020, in PubMed, Scopus, and Cochrane, following the PRISMA guidelines. We found 175 articles published in the literature using our searching strategies, but only 24 articles fulfilled our inclusion criteria and are discussed here. Other articles important in the built knowledge of FRCs were included in the introduction and discussion. The studies selected for this review used different strategies in order to access the contribution of FRCs to different mechanisms involved in the immune response: 21% evaluated viral infection in this context, 13% used a model of autoimmunity, 8% used a model of GvHD or cancer, 4% used a model of Ischemic-reperfusion injury (IRI). Another four studies just targeted a particular signaling pathway, such as MHC II expression, FRC microvesicles, FRC secretion of IL-15, FRC network, or ablation of the lysophosphatidic acid (LPA)-producing ectoenzyme autotaxin. In conclusion, our review shows the strategies used by several studies to isolate and culture fibroblastic reticular cells, the models chosen by each one, and dissects their main findings and implications in homeostasis and disease.

LN-Derived Fibroblastic Reticular Cells and Their Impact on T Cell Response-A Systematic Review

Fibroblastic reticular cells (FRCs), usually found and isolated from the T cell zone of lymph nodes, have recently been described as much more than simple structural cells. Originally, these cells were described to form a conduit system called the “reticular fiber network” and for being responsible for transferring the lymph fluid drained from tissues through afferent lymphatic vessels to the T cell zone. However, nowadays, these cells are described as being capable of secreting several cytokines and chemokines and possessing the ability to interfere with the immune response, improving it, and also controlling lymphocyte proliferation. Here, we performed a systematic review of the several methods employed to investigate the mechanisms used by fibroblastic reticular cells to control the immune response, as well as their ability in determining the fate of T cells. We searched articles indexed and published in the last five years, between 2016 and 2020, in PubMed, Scopus, and Cochrane, following the PRISMA guidelines. We found 175 articles published in the literature using our searching strategies, but only 24 articles fulfilled our inclusion criteria and are discussed here. Other articles important in the built knowledge of FRCs were included in the introduction and discussion. The studies selected for this review used different strategies in order to access the contribution of FRCs to different mechanisms involved in the immune response: 21% evaluated viral infection in this context, 13% used a model of autoimmunity, 8% used a model of GvHD or cancer, 4% used a model of Ischemic-reperfusion injury (IRI). Another four studies just targeted a particular signaling pathway, such as MHC II expression, FRC microvesicles, FRC secretion of IL-15, FRC network, or ablation of the lysophosphatidic acid (LPA)-producing ectoenzyme autotaxin. In conclusion, our review shows the strategies used by several studies to isolate and culture fibroblastic reticular cells, the models chosen by each one, and dissects their main findings and implications in homeostasis and disease.