A Reproducible Method for Isolation and In Vitro Culture of Functional Human Lymphoid Stromal Cells from Tonsils

Deciphering the localization and trajectory of human natural killer cell development

Innate immune cells represent the first line of cellular immunity, comprised of both circulating and tissue-resident natural killer cells and innate lymphoid cells. These innate lymphocytes arise from a common CD34+ progenitor that differentiates into mature natural killer cells and innate lymphoid cells. The successive stages in natural killer cell maturation are characterized by increased lineage restriction and changes to phenotype and function. Mechanisms of human natural killer cell development have not been fully elucidated, especially the role of signals that drive the spatial localization and maturation of natural killer cells. Cytokines, extracellular matrix components, and chemokines provide maturation signals and influence the trafficking of natural killer cell progenitors to peripheral sites of differentiation. Here we present the latest advances in our understanding of natural killer and innate lymphoid cell development in peripheral sites, including secondary lymphoid tissues (i.e. tonsil). Recent work in the field has provided a model for the spatial distribution of natural killer cell and innate lymphoid cell developmental intermediates in tissue and generated further insights into the developmental niche. In support of this model, future studies using multifaceted approaches seek to fully map the developmental trajectory of human natural killer cells and innate lymphoid cells in secondary lymphoid tissues.

Mapping human natural killer cell development in pediatric tonsil by imaging mass cytometry and high-resolution microscopy

Natural killer (NK) cells develop from CD34+ progenitors in a stage-specific manner defined by changes in cell surface receptor expression and function. Secondary lymphoid tissues, including tonsil, are sites of human NK cell development. Here we present new insights into human NK cell development in pediatric tonsil using cyclic immunofluorescence and imaging mass cytometry. We show that NK cell subset localization and interactions are dependent on NK cell developmental stage and tissue residency. NK cell progenitors are found in the interfollicular domain in proximity to cytokine-expressing stromal cells that promote proliferation and maturation. Mature NK cells are primarily found in the T-cell rich parafollicular domain engaging in cell-cell interactions that differ depending on their stage and tissue residency. The presence of local inflammation results in changes in NK cell interactions, abundance, and localization. This study provides the first comprehensive atlas of human NK cell development in secondary lymphoid tissue.

A novel cryopreservation and biobanking strategy to study lymphoid tissue stromal cells in human disease

Nonhematopoietic lymph node stromal cells (LNSCs) regulate lymphocyte trafficking, survival, and function for key roles in host defense, autoimmunity, alloimmunity, and lymphoproliferative disorders. However, the study of LNSCs in human diseases is complicated by a dependence on viable lymphoid tissues, which are most often excised prior to establishment of a specific diagnosis. Here, we demonstrate that cryopreservation can be used to bank lymphoid tissue for the study of LNSCs in human disease. Using human tonsils and lymph nodes (LN), lymphoid tissue fragments were cryopreserved for subsequent enzymatic digestion and recovery of viable nonhematopoietic cells. Flow cytometry and single-cell transcriptomics identified comparable proportions of LN stromal cell types in fresh and cryopreserved tissue. Moreover, cryopreservation had little effect on transcriptional profiles, which showed significant overlap between tonsils and LN. The presence and spatial distribution of transcriptionally defined cell types were confirmed by in situ analyses. Our broadly applicable approach promises to greatly enable research into the roles of LNSCs in human disease.

PI16+ reticular cells in human palatine tonsils govern T cell activity in distinct subepithelial niches

Fibroblastic reticular cells (FRCs) direct the interaction and activation of immune cells in discrete microenvironments of lymphoid organs. Despite their important role in steering innate and adaptive immunity, the age- and inflammation-associated changes in the molecular identity and functional properties of human FRCs have remained largely unknown. Here, we show that human tonsillar FRCs undergo dynamic reprogramming during life and respond vigorously to inflammatory perturbation in comparison to other stromal cell types. The peptidase inhibitor 16 (PI16)-expressing reticular cell (PI16⁺ RC) subset of adult tonsils exhibited the strongest inflammation-associated structural remodeling. Interactome analysis combined with ex vivo and in vitro validation revealed that T cell activity within subepithelial niches is controlled by distinct molecular pathways during PI16⁺ RC-lymphocyte interaction. In sum, the topological and molecular definition of the human tonsillar stromal cell landscape reveals PI16⁺ RCs as a specialized FRC niche at the core of mucosal immune responses in the oropharynx.

A novel cryopreservation and biobanking strategy to study lymphoid tissue stromal cells in human disease

Non-hematopoietic lymph node stromal cells (LNSCs) regulate lymphocyte trafficking, survival, and function for key roles in host defense, autoimmunity, alloimmunity, and lymphoproliferative disorders. However, study of LNSCs in human diseases is complicated by a dependence on viable lymphoid tissues, which are most often excised prior to establishment of a specific diagnosis. Here, we demonstrate that cryopreservation can be used to bank lymphoid tissue for the study of LNSCs in human disease. Using human tonsils, lymphoid tissue fragments were cryopreserved for subsequent enzymatic digestion and recovery of viable non-hematopoietic cells. Flow cytometry and single-cell transcriptomics identified comparable proportions of LNSC cell types in fresh and cryopreserved tissue. Moreover, cryopreservation had little effect on transcriptional profiles, which showed significant overlap between tonsils and lymph nodes. The presence and spatial distribution of transcriptionally defined cell types was confirmed by in situ analyses. Our broadly applicable approach promises to greatly enable research into the roles of LNSC in human disease.

Lymph Node Fibroblastic Reticular Cells Attenuate Immune Responses Through Induction of Tolerogenic Macrophages at Early Stage of Transplantation

BACKGROUND

Fibroblastic reticular cells (FRCs) are a type of stromal cells located in the T zone in secondary lymphoid organs. Previous studies showed that FRCs possess the potential to promote myeloid differentiation. We aim to investigate whether FRCs in lymph nodes (LNs) could induce tolerogenic macrophage generation and further influence T-cell immunity at an early stage of allogeneic hematopoietic stem cell transplantation (allo-HSCT).

METHODS

LNs were assayed to confirm the existence of proliferating macrophages after allo-HSCT. Ex vivo-expanded FRCs and bone marrow cells were cocultured to verify the generation of macrophages. Real-time quantitative PCR and ELISA assays were performed to observe the cytokines expressed by FRC. Transcriptome sequencing was performed to compare the difference between FRC-induced macrophages (FMs) and conventional macrophages. Mixed lymphocyte reaction and the utilization of FMs in acute graft-versus-host disease (aGVHD) mice were used to test the inhibitory function of FMs in T-cell immunity in vitro and in vivo.

RESULTS

We found a large number of proliferating macrophages near FRCs in LNs with tolerogenic phenotype under allo-HSCT conditions. Neutralizing anti-macrophage colony-stimulating factor receptor antibody abolished FMs generation in vitro. Phenotypic analysis and transcriptome sequencing suggested FMs possessed immunoinhibitory function. Mixed lymphocyte reaction proved that FMs could inhibit T-cell activation and differentiation toward Th1/Tc1 cells. Injection of FMs in aGVHD mice effectively attenuated aGVHD severity and mortality.

CONCLUSIONS

This study has revealed a novel mechanism of immune regulation through the generation of FRC-induced tolerogenic macrophages in LNs at an early stage of allo-HSCT.

A synthetic human 3D in vitro lymphoid model enhancing B-cell survival and functional differentiation

To investigate B-cell differentiation and maturation occurring in the germinal center (GC) using in vitro culture systems, key factors and interactions of the GC reaction need to be accurately simulated. This study aims at improving in vitro GC simulation using 3D culture techniques. Human B-cells were incorporated into PEG-4MAL hydrogels, to create a synthetic extracellular matrix, supported by CD40L cells, human tonsil-derived lymphoid stromal cells, and cytokines. The differentiation and antibody production of CD19⁺B-cells was best supported in a 5.0%-PEG-4MAL, 2.0 mM-RGD-peptide composition. The 3D culture significantly increased plasmablast and plasma cell numbers as well as antibody production, with less B-cell death compared to 2D cultures. Class switching of naive CD19⁺IgD⁺B-cells toward IgG⁺ and IgA⁺B-cells was observed. The formation of large B-cell clusters indicates the formation of GC-like structures. In conclusion, a well-characterized and controllable hydrogel-based human 3D lymphoid model is presented that supports enhanced B-cell survival, proliferation, differentiation, and antibody production.

The influence of three-dimensional structure on naïve T cell homeostasis and aging

A breakdown in cellular homeostasis is thought to drive naïve T cell aging, however the link between naïve T cell homeostasis and aging in humans is poorly understood. To better address this, we developed a lymphoid organoid system that maintains resting naïve T cells for more than 2 weeks, in conjunction with high CD45RA expression. Deep phenotypic characterization of naïve T cells across age identified reduced CD45RA density as a hallmark of aging. A conversion from CD45RA^high naive cells to a CD45RA^low phenotype was reproduced within our organoid system by structural breakdown, but not by stromal cell aging or reduced lymphocyte density, and mediated by alternative CD45 splicing. Together, these data suggest that external influences within the lymph node microenvironment may cause phenotypic conversion of naïve T cells in older adults.

[3D Tumor organoid models produced by cellular capsules technology CCT]

Monolayer cultures of cell lines and derived-patient cells have long been the in vitro model of choice in oncology. In particular, these models have made it possible to decipher the mechanisms that determine tumor proliferation and invasion. However these 2D models are insufficient because they do not take into account the spatial organization of cells and their interactions with each other or with the extracellular matrix. In the context of cancer, there is a need to develop new 3D (tumoroid) models in order to gain a better understanding of the development of these pathologies but also to assess the penetration of drugs through a tissue and the associated cellular response. We present here the cell capsule technology (CCT), which allows the production of different tumoroid models: simple or more complex 3D culture models including co-culture of tumor cells with components of the microenvironment (fibroblasts, matrix, etc.). The development of these new 3D culture systems now makes it possible to propose refined physiopathological models that will allow the implementation of improved targeted therapeutic strategies.

Visualization and functional characterization of lymphoid organ fibroblasts

Fibroblastic reticular cells (FRCs) are specialized stromal cells of lymphoid organs that generate the structural foundation of the tissue and actively interact with immune cells. Distinct FRC subsets position lymphocytes and myeloid cells in specialized niches where they present processed or native antigen and provide essential growth factors and cytokines for immune cell activation and differentiation. Niche‐specific functions of FRC subpopulations have been defined using genetic targeting, high‐dimensional transcriptomic analyses, and advanced imaging methods. Here, we review recent findings on FRC‐immune cell interaction and the elaboration of FRC development and differentiation. We discuss how imaging approaches have not only shaped our understanding of FRC biology, but have critically advanced the niche concept of immune cell maintenance and control of immune reactivity.

Isolation of primary human B lymphocytes from tonsils compared to blood as alternative source for ex vivo application

B lymphocytes ('B cells') are components of the human immune system with obvious potential for medical and biotechnological applications. Here, we discuss the isolation of primary human B cells from both juvenile and adult tonsillar material using a two-step procedure based on gradient centrifugation followed by separation on a nylon wool column as alternative to the current gold standard, i.e., negative immunosorting from buffy coats by antibody-coated magnetic beads. We show that the nylon wool separation is a low-cost method well suited to the isolation of large amounts of primary B cells reaching purities ≥ 80%. More importantly, this method allows the preservation of all B cell subsets, while MACS sorting seems to be biased against a certain B cell subtype, namely the CD27⁺ B cells. Importantly, compared to blood, the excellent recovery yield during purification of tonsillar B cells provides high number of cells, hence increases the number of subsequent experiments feasible with identical cell material, consequently improving comparability of results. The cultivability of the isolated B cells was demonstrated using pokeweed mitogen (PWM) as a stimulatory substance. Our results showed for the first time that the proliferative response of tonsillar B cells to mitogens declines with the age of the donor. Furthermore, we observed that PWM treatment stimulates the proliferation of a dedicated subpopulation and induces some terminal differentiation with ASCs signatures. Taken together this indicates that the proposed isolation procedure preserves the proliferative capability as well as the differentiation capacity of the B cells.

Circulating ILC precursors expressing CD62L exhibit a type 2 signature distinctly decreased in psoriatic patients

Human CD117⁺CRTH2^neg innate lymphoid cells (ILC) comprise multipotent precursors (ILCp), which are able to differentiate into subtypes in response to different signals received in peripheral tissues. NKp46⁺ ILCp have been reported to associate with ILC3 whereas KLRG1⁺ILCp with ILC2, although the latter can also generate other ILC subsets, thus, maintaining a substantial plasticity. We here showed that CD62L is expressed by ILCp exclusively within KLRG1⁺ population and its expression marks a loss of their broad differentiation potential.

Analysis of cytokine production and relevant markers demonstrated that CD62L⁺ILCp mainly differentiate into ILC2 whereas CD62L^neg counterpart can also differentiate into other ILC subsets depending on the signals they receive. Remarkably, in peripheral blood of psoriatic patients, where ILC3 are usually enriched, CD62L⁺ILC were drastically reduced, whereas CD62L^negILC2 upregulated both RORγt and NKp46, thus, suggesting an ongoing conversion to ILC3. Therefore, CD62L now emerges as a potential marker to identify a skewing toward type 2 among ILCp.

Fibroblastic reticular cells at the nexus of innate and adaptive immune responses

Lymphoid organs guarantee productive immune cell interactions through the establishment of distinct microenvironmental niches that are built by fibroblastic reticular cells (FRC). These specialized immune‐interacting fibroblasts coordinate the migration and positioning of lymphoid and myeloid cells in lymphoid organs and provide essential survival and differentiation factors during homeostasis and immune activation. In this review, we will outline the current knowledge on FRC functions in secondary lymphoid organs such as lymph nodes, spleen and Peyer's patches and will discuss how FRCs contribute to the regulation of immune processes in fat‐associated lymphoid clusters. Moreover, recent evidence indicates that FRC critically impact immune regulatory processes, for example, through cytokine deprivation during immune activation or through fostering the induction of regulatory T cells. Finally, we highlight how different FRC subsets integrate innate immunological signals and molecular cues from immune cells to fulfill their function as nexus between innate and adaptive immune responses.

Differential cellular composition of human palatine and pharyngeal tonsils

OBJECTIVE

The goal of this study was to gain a better understanding of the potential functional specialization of palatine and pharyngeal tonsils, by comparing their cellular composition in paired specimens from a large cohort of adenotonsillectomy patients.

DESIGN

Resident B cell, T cell, dendritic cell, and stromal cell subsets were characterized using multicolor flow cytometry in palatine and pharyngeal tonsil specimens from 27 patients, age 2-34 years.

RESULTS

Paired comparisons showed highly significant intra-individual differences in resident cell subsets of palatine and pharyngeal tonsils. Palatine tonsils harbored higher fractions of germinal center B cells/plasmablasts and IgD- CD27- double-negative B cells, and conversely lower fractions of IgD + CD38- resting naïve B cells compared to pharyngeal tonsils. Palatine tonsils also showed lower fractions of plasmacytoid dendritic cells, and higher percentages of two subsets of stromal cells - fibroblastic reticular cells and lymphatic endothelial cells - compared to pharyngeal tonsils from the same individual.

CONCLUSIONS

Despite their physical proximity and histological similarities, palatine and pharyngeal tonsils display marked intra-individual differences in their cellular composition with regard to functionally important immune and stromal subsets. These differences are likely to have immunologic, pathologic, and physiologic significance.

Designed Surface Topographies Control ICAM-1 Expression in Tonsil-Derived Human Stromal Cells

Fibroblastic reticular cells (FRCs), the T-cell zone stromal cell subtype in the lymph nodes, create a scaffold for adhesion and migration of immune cells, thus allowing them to communicate. Although known to be important for the initiation of immune responses, studies about FRCs and their interactions have been impeded because FRCs are limited in availability and lose their function upon culture expansion. To circumvent these limitations, stromal cell precursors can be mechanotranduced to form mature FRCs. Here, we used a library of designed surface topographies to trigger FRC differentiation from tonsil-derived stromal cells (TSCs). Undifferentiated TSCs were seeded on a TopoChip containing 2176 different topographies in culture medium without differentiation factors, then monitored cell morphology and the levels of ICAM-1, a marker of FRC differentiation. We identified 112 and 72 surfaces that upregulated and downregulated, respectively, ICAM-1 expression. By monitoring cell morphology, and expression of the FRC differentiation marker ICAM-1 via image analysis and machine learning, we discovered correlations between ICAM-1 expression, cell shape and design of surface topographies and confirmed our findings by using flow cytometry. Our findings confirmed that TSCs are mechano-responsive cells and identified particular topographies that can be used to improve FRC differentiation protocols.

Secondary lymphoid organ fibroblastic reticular cells mediate trans-infection of HIV-1 via CD44-hyaluronan interactions

Fibroblastic reticular cells (FRCs) are stromal cells in secondary lymphoid organs, the major sites for HIV-1 infection of CD4⁺ T cells. Although FRCs regulate T cell survival, proliferation, and migration, whether they play any role in HIV-1 spread has not been studied. Here, we show that FRCs enhance HIV-1 spread via trans-infection in which FRCs capture HIV-1 and facilitate infection of T cells that come into contact with FRCs. FRCs mediate trans-infection in both two- and three-dimensional culture systems and in a manner dependent on the virus producer cells. This producer cell dependence, which was also observed for virus spread in secondary lymphoid tissues ex vivo, is accounted for by CD44 incorporated into virus particles and hyaluronan bound to such CD44 molecules. This virus-associated hyaluronan interacts with CD44 expressed on FRCs, thereby promoting virus capture by FRCs. Overall, our results reveal a novel role for FRCs in promoting HIV-1 spread.

Fibroblastic reticular cells (FRCs) are important regulators of T cell survival, proliferation, and migration in secondary lymphoid organs, but their role in HIV infection isn’t studied. Here, Murakami et al. show that FRCs enhance HIV spread via CD44- and hyaluronan-mediated trans-infection.

Dendritic Cell Migration to Skin-Draining Lymph Nodes Is Controlled by Dermatan Sulfate and Determines Adaptive Immunity Magnitude

For full activation of naïve adaptive lymphocytes in skin-draining lymph nodes (LNs), presentation of peptide:MHC complexes by LN-resident and skin-derived dendritic cells (DCs) that encountered antigens (Ags) is an absolute prerequisite. To get to the nearest draining LN upon intradermal immunization, DCs need to migrate from the infection site to the afferent lymphatics, which can only be reached by traversing a collagen-dense network located in the dermis of the skin through the activity of proteolytic enzymes. Here, we show that mice with altered collagen fibrillogenesis resulting in thicker collagen fibers in the skin display a reduced DC migration to the draining LN upon immune challenge. Consequently, the initiation of the cellular and humoral immune response was diminished. Ag-specific CD8+ and CD4+ T cells as well as Ag-specific germinal center B cells and serum immunoglobulin levels were significantly decreased. Hence, we postulate that alterations to the production of extracellular matrix, as seen in various connective tissue disorders, may in the end affect the qualitative outcome of adaptive immunity.