Fibroblastic Reticular Network Research Articles

Diffuse Large B-Cell Lymphoma Remodels the Fibroblastic Reticular Network That Acquires Aberrant Immunosuppressive Capabilities; Implications for the Regulation of Anti-Tumor Immunity in the Immuno-Oncology Era

Abstract Immunotherapy has demonstrated potential to reactivate or transfer T cell immunity and regress tumors, offering hope to relapsed or refractory diffuse large B-cell lymphoma (DLBCL) patients. However, many DLBCL patients do not experience therapeutic benefit, likely owing to a lack of pre-existing anti-tumor immunity and/or poorly understood immunosuppressive mechanisms in the tumor microenvironment (TME). Understanding the different obstacles that cytotoxic T cells face in the DLBCL TME will help the development of novel therapeutic approaches to overcome them and optimize immunotherapy. Stroma-associated gene signatures reflecting fibroblast and immune cell activity as well as angiogenesis have been associated with outcome in DLBCL but the biology underlying these signatures has been understudied. Here we have examined beyond tumor 'effacement' and hypothesized that, rather than being sparse bystanders, lymph node stromal cells may be important players in driving immune suppression in lymphoma. Multiplex immunofluorescence (IF) confocal microscopy analysis of the major stromal cell subsets revealed a marked expansion and remodeling of podoplanin, PDPN+ fibroblastic reticular cells (FRCs) in DLBCL lymph node tissue TME biopsies across GCB and ABC subtypes (n=40) compared to reactive control tissues (n=10). FRC myofibroblasts were similarly remodeled in tumors from the transgenic mouse model of DLBCL (Iμ-HABCL6, n=10) compared to wild type littermates (n=5). These altered PDPNhigh, αSMAhigh FRC networks were interspersed within effaced lymph node tissues in close proximity to DLBCL tumor cells. To model the interactions between tumor cells and FRCs, we established 2D and 3D co-culture platforms that combined DLBCL cells (or non-malignant control B-cells) and PDPN+ FRCs derived from human or murine lymph node tissues. These quantitative assays have shown that tumor cells activate FRCs promoting their proliferation, increased expression of PDPN, marked elongation/stretching and subsequent reduced ability to contract 3D collagen matrix (non-contractile) (P<.01). Exposure to tumor cells caused uncoupling of PDPN from RHOA signaling and redistribution of PDPN into lipid rafts, permitting FRC stretching. FRCs purified from both human and murine tumor lymph nodes showed the same activated morphology and phenotype, demonstrating that our co-culture systems recapitulate in vivo findings. Screening experiments have shown that lymphoma-expressed membrane and soluble lymphotoxins (LTα1β2, LTα3) as well as TNFα significantly contribute to the remodeling of FRCs (P<.01). Co-culture assays have revealed evidence for mutualistic interaction as FRCs, that express BAFF, promote the survival of DLBCL cells in 3D matrix gels (P<.01). Expanded lymphoma PDPNhigh FRCs in situ co-expressed BAFF compared to a more restricted expression profile (marginal zone FRCs) in reactive lymph node tissues. Flow cytometry revealed that lymphoma FRCs exhibit a cancer-associated fibroblast (CAF)-like immunophenotype including upregulation of fibroblast activation protein (FAP) and αSMA, as well as immunomodulatory MHC class I, PD-L1 and PD-L2 molecules compared to control FRCs (P<.01). An important function of FRCs in regulating immunity is attracting and maintaining T cells by secreting chemokines and promoting their migration along the network. Functional assays revealed that T cells show significantly reduced chemotaxis as well motility (quantitative time-lapse movies) across 2D and 3D lymphoma FRC networks compared to control FRCs (P<.01). Multiplex IF analysis revealed reduced CCL19 and CCL21-expressing FRCs in DLBCL compared to the reactive control FRC network as well as low numbers of tumor-infiltrated CD8+ T cells, which localized closely with remodeled FRCs. We next determined whether lymphoma FRCs (CAFs) could negatively regulate T cell function. Triple culture autologous assays (murine and human) have shown that prior exposure of tumor-infiltrated CD8+ T cells to FRCs significantly decreased their cytolytic killing activity against tumor cells (P<.01). In conclusion our data indicate that DLBCL tumor cells convert FRCs into immunosuppressive CAFs, which exhibit altered immumomodulatory activities at different levels that we believe has important implications for the regulation of anti-tumor immunity as well as response to immunotherapy. Disclosures Vardi: Gilead: Research Funding; Janssen: Honoraria. Ramsay:Roche Glycart AG: Research Funding; MedImmune: Research Funding; Celgene Corporation: Research Funding.

Extracellular matrix in the CNS induced by neuropathogenic viral infection.

During the early phase of infection with an extremely neurovirulent murine coronavirus, cl‐2, the ER‐TR7 antigen (ERag)‐positive fibers (ERfibs) associated with laminin and collagen III show a rapid increase in expression levels in the meninges, followed by an appearance of the antigens in the ventricle and brain parenchyma. Then, cl‐2 invades the ventricle and ventricular wall along the newly assembled ERfibs after infection, using them as a pathway from the meninges, the initial site of infection. In the lymph nodes and spleen, ERag is mainly produced by fibroblastic reticular cells (FRCs), which play a key role in nursing the ERfibs to form a fibroblastic reticular network (FRN). The FRN functions as a conduit system to transfer antigens, cytokines or leukocytes in the lymphoid organs. In the brain parenchyma, astrocytes were found to produce the main components of mature ERfibs, such as collagen, laminin and ERag, which have been identified in the lymphoid organs. The producibility of these extracellular matrices (ECMs) by astrocytes was further confirmed by primary brain cultures, which disclosed the dissociation of laminin and ERag production, and the close association of ERag production with that of collagen, forming a fibrous structure. The pattern of ECM production in vitro indicated the process of forming mature ERfibs in the brain, that is, fibers made of collagen fibers and ERag are wrapped by laminin prepared as a sheet structure. In addition, the brain parenchymal cells that produce interferon β after infection in spite of their residence away from the sites of viral invasion were surrounded by ERfibs, which were closely associated with astrocytic fibers. These findings indicate that astrocytes play a central role in forming the astrocytic reticular network (ARN) in the brain parenchyma, as FRCs do to form FRN in the lymphoid organs.

Highly Neurovirulent Viruses Invade and Spread in the Brain Using the Host Reactions Triggered by Infection

Coronaviruses (CoVs) have relatively high mutation and RNA recombination rates and undergo rapid crossspecies transmission events in vitro and in vivo. The viruses have evolved diverse strategies to evade, blocking host immune responses, and resulting in an emergence of highly virulent CoVs to cause fatal diseases in human, such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). Among CoVs used for experimental studies, the cl-2 virus (cl-2), isolated from a neuropathogenic JHM viral strain (JHMV) of mouse hepatitis virus (MHV), shows extremely high virulence. All mice infected with cl-2 die within 3 days post-inoculation (dpi). Less virulent but still highly neurovirulent mutant viruses, soluble receptor resistant mutant virus (srr7) and Mu-3 virus (Mu-3), have been isolated from cl-2 and srr7, respectively. Although these viruses cause different pictures of neuropathologies with different distribution of viral antigens after infection, they use the same pathway to enter the brain before inducing lesions in the brain parenchyma. The pathway is formed as an astrocytic reticular network (ARN) after infection. The ARN functions as a conduit system in a similar way to a fibroblastic reticular network (FRN) in lymphoid organs. In addition, the viruses induce an immunosuppressive state in infected mice, mimicking endotoxin tolerance (ET), or lipopolysaccharide (LPS) tolerance. The immunosuppressive states are detected by; 1) pathological findings as 1a); a very low -level inflammatory response, 1b); the shrunken spleen, 1c); the refractory state to LPS challenge, and 1d); the local production of anti-inflammatory cytokines by neurons, and by 2) immunological studies, which showed 2a); the systemic production of anti-inflammatory cytokines by eliciting CD11b+Gra-1+ suppressor monocytes/macrophages (Mo/Mas).In addition, cultured splenic cells and Mo/Mas after infection exhibit 2b); low-level responses to stimulation of toll-like receptors (TLRs) 4 and 7, and 2c); the induction of Lewis X carbohydrate structure (Lex), which can trigger the C-type lectin-like receptor that initiates an immunosuppressive pathway, respectively.

Formation of fibroblastic reticular network in the brain after infection with neurovirulent murine coronavirus.

cl‐2 virus is an extremely neurovirulent murine coronavirus. However, during the initial phase of infection between 12 and 24 h post‐inoculation (hpi), the viral antigens are detected only in the meninges, followed by viral spread into the ventricular wall before invasion into the brain parenchyma, indicating that the viruses employ a passage between the meninges and ventricular wall as an entry route into the brain parenchyma. At 48 hpi, the passage was found to be constructed by ER‐TR7 antigen (ERag)‐positive fibers (ERfibs) associated with laminin and collagen III between the fourth ventricle and meninges at the cerebellopontine angle. The construct of the fibers mimics the reticular fibers of the fibroblastic reticular network, which comprises a conduit system in the lymphoid organs. In the meninges, ERfibs together with collagen fibers, lining in a striped pattern, made up a pile of thin sheets. In the brain parenchyma, mature ERfibs associated with laminin were found around blood vessels. Besides mature ERfibs, immature Erfibs without associations with other extracellular matrix components like laminin and collagen appeared after infection, suggesting that the CNS creates a unique conduit system for immune communication triggered by viral invasion.

Dendritic cells in remodeling of lymph nodes during immune responses.

A critical hallmark of adaptive immune responses is the rapid and extensive expansion of lymph nodes. During this process, the complex internal structure of the organs is maintained revealing the existence of mechanisms able to balance lymph node integrity with structural flexibility. This article reviews the extensive architectural remodeling that occurs within lymph nodes during adaptive immune responses and how it is regulated by dendritic cells (DCs). In particular we focus on previously unappreciated functions of DCs in coordinating remodeling of lymph node vasculature, expansion of the fibroblastic reticular network and maintenance of lymphoid stromal phenotypes. Our increased understanding of these processes indicates that DCs need to be viewed not only as key antigen-presenting cells for lymphocytes but also as broad-acting immune sentinels that convey signals to lymphoid organ stroma and thereby facilitate immune response initiation at multiple levels.

Dendritic cells control fibroblastic reticular network tension and lymph node expansion.

Following immunogenic challenge, infiltrating and dividing lymphocytes significantly increase lymph node (LN) cellularity leading to organ expansion1,2. Here we report that the physical elasticity of LNs is maintained in part by podoplanin (PDPN) signalling in stromal fibroblastic reticular cells (FRCs) and its modulation by CLEC-2 expressed on dendritic cells (DCs). We show that PDPN induces actomyosin contractility in FRCs via activation of RhoA/C and downstream Rho-kinase. Engagement by CLEC-2 causes PDPN clustering and rapidly uncouples PDPN from RhoA/C activation, relaxing the actomyosin cytoskeleton and permitting FRC stretching. Notably, administration of CLEC-2 protein to immunised mice augments LN expansion. In contrast, the latter is significantly constrained in mice selectively lacking CLEC-2 expression in DCs. Thus, the same DCs that initiate immunity by presenting antigens to T lymphocytes3 also initiate remodeling of LNs by delivering CLEC-2 to FRCs. CLEC-2 modulation of PDPN signalling permits FRC network stretching and allows for the rapid LN expansion driven by lymphocyte influx and proliferation that is the critical hallmark of adaptive immunity.

Drug Development Targeting Microenvironment for Malignant Lymphoma

Abstract Abstract 1661 Most cancer drug developments are focusing either in vitro target-based screening or cell-based phenotypic screening to identify potential compounds. The target-based screenings are powerful screening methods if the cancer relay on a single driver mutation. On the other hand, cell-based phenotypic screenings measure cell phenotypes such as growth inhibitory effect on established cancer cell lines. However, these established cell lines do not recapitulate human cancer in some aspects. For instance, most cell lines have the microenvironment-independent growth ability, while primary cancer cells can not survive in ex vivo culture. In this study, we established a new drug screening system targeting microenvironment-dependent primary lymphoma cells. First of all, we established primary lymphoma xenograft models, including three diffuse large B cell lymphoma (DLBCL), one follicular lymphoma, one intravascular large cell lymphoma (IVL), and one mantle cell lymphoma. Interestingly, lymphoma cells from the patient with severe extranodal invasion invaded extranodal organ also in mice. And pattern of invasion in tissue such as intravascular tumor invasion of IVL was maintained in the xenograft models. In addition, mRNA expression profiles were similar between primary lymphoma cells and the lymphoma cells obtained from NOG mice. Furthermore, the heterogeneity of primary tumor such as heterogenous expression of CD20 was maintained in the xenograft models. These data suggested that the lymphoma cells propagated in NOG mice kept the original patient's phenotype. Next, we investigated the microenvironment of lymphoma in primary lymphoma xenograft models. Fibroblastic reticular cell (FRC) and follicular dendritic cell (FDC) are reported to be important to support the survival of lymphoma cells in their microenvironment. In the spleen of DLBCL model mice, lymphoma cells colocalized with FRC, but FDC was not detected in NOG mouse. FRC is known to produce reticular fiber and forms fibroblastic reticular network (FRN). Lymphoma induced reticular fiber production and tumor formation on FRN were also observed in our system. Furthermore, co-culture with FRC cell line, BLS4, significantly enhanced viability of 2 out of 3 DLBCL cells obtained from primary lymphoma xenograft mice and enabled more than three weeks long-term ex vivo culture of them. These results indicated that FRC played an important role for lymphoma cell survival. Finally, we established a new drug screening system using this co-culture system. Primary DLBCL cells transplanted to NOG mice were collected and seeded on pre-seeded BLS4 in 96-well plates (lymphoma cell co-culture). Monoculture of BLS4 in 96-well plates was also prepared. Both lymphoma co-cultured cell and BLS4 monoculture cell were treated by 2613 kinds of pharmacologically active compounds for 72 h. DAPI-stained dead cells of lymphoma cells were counted by image analyzer, and the proliferation of BLS4 was measured by MTT assay. We calculated Drug Effect Index (DEI) by multiplication of dead cell number of lymphoma cells and MTT value of BLS4 and compared. The compound with the highest DEI was pyrvinium pamoate, oxyuricide. Pyrvinium pamoate aborogated the survival of lymphoma cells co-cultured with BLS4 dose-dependently. And subcutaneous tumor of primary lymphoma cells and BLS4 were diminished by single intratumoral injection of 20 mg/kg pyrvinium pamoate. These results indicated that our screening system could be performed in large scale and select drugs with anti-tumor activity to primary lymphoma cells. Screening against primary lymphoma cells sheds new light on lymphoma drug development. Disclosures: Sugimoto: Otsuka Pharmaceutical co ltd: Employment.

Influence of the Fibroblastic Reticular Network on Cell-Cell Interactions in Lymphoid Organs

Secondary lymphoid organs (SLO), such as lymph nodes and the spleen, display a complex micro-architecture. In the T cell zone the micro-architecture is provided by a network of fibroblastic reticular cells (FRC) and their filaments. The FRC network is thought to enhance the interaction between immune cells and their cognate antigen. However, the effect of the FRC network on cell interaction cannot be quantified to date because of limitations in immunological methodology. We use computational models to study the influence of different densities of FRC networks on the probability that two cells meet. We developed a 3D cellular automaton model to simulate cell movements and interactions along the FRC network inside lymphatic tissue. We show that the FRC network density has only a small effect on the probability of a cell to come into contact with a static or motile target. However, damage caused by a disruption of the FRC network is greatest at FRC densities corresponding to densities observed in the spleen of naïve mice. Our analysis suggests that the FRC network as a guiding structure for moving T cells has only a minor effect on the probability to find a corresponding dendritic cell. We propose alternative hypotheses by which the FRC network might influence the functionality of immune responses in a more significant way.

CCL21 Expression Pattern of Human Secondary Lymphoid Organ Stroma Is Conserved in Inflammatory Lesions with Lymphoid Neogenesis

CCL21 is a homeostatic lymphoid chemokine instrumental in the recruitment and organization of T cells and dendritic cells into lymphoid T areas. In human secondary lymphoid organs (SLOs), CCL21 is produced by cells distributed throughout the T zone, whereas high endothelial venules (HEVs) lack CCL21 mRNA. A critical question remains whether the development of ectopic lymphoid tissue (ELT) in chronic inflammation recapitulates the features of SLOs. Thus, we systematically investigated in situ the cellular sources of CCL21 in SLOs and ELTs in several human diseases characterized by lymphoid neogenesis. By in situ hybridization and the use of combinatorial cell markers, we show that CCL21-producing vessels in inflamed tissues systematically display typical markers of lymphatic vessels, whereas, as in SLOs, ectopic HEVs do not synthesize detectable levels of CCL21. We also provide first-time evidence that a common pattern of CCL21 expression by CD45-negative myofibroblast-like cells localized in extra-HEV position and organized in a fibroblastic reticular network similarly characterizes human SLOs and organized ELTs. Altogether, our results demonstrate that in humans the pattern of CCL21 production in SLOs is maintained during inflammation and that the phenotypic and functional properties of stromal cells, found in SLO T-cell areas, are reproduced at ectopic sites.