Subcutaneous delivery of mesenchymal stromal cells induces immunoregulatory effects in the lymph node prior to their apoptosis.

Background: Mesenchymal stromal cell (MSC) therapy commonly involves systemic infusion of MSCs, which undergo apoptosis in the lung and induce immunoregulatory macrophages that reduce disease. The relevance of this mode of action, however, is yet to be determined for MSCs administered via other routes. Here, we administered MSCs via subcutaneous (SC) injection into inflamed tissue and investigated the immunomodulatory effects on the local lymph node (LN), which is a major site for the initiation and regulation of immune responses.

Fibroblastic reticular cells provide a supportive niche for lymph node-resident macrophages.

The lymph node (LN) is home to resident macrophage populations that are essential for immune function and homeostasis, but key factors controlling this niche are undefined. Here, we show that fibroblastic reticular cells (FRCs) are an essential component of the LN macrophage niche. Genetic ablation of FRCs caused rapid loss of macrophages and monocytes from LNs across two in vivo models.

Secondary Lymphoid Organs in Mesenchymal Stromal Cell Therapy: More Than Just a Filter.

Mesenchymal stromal cells (MSCs) have demonstrated therapeutic potential in inflammatory models of human disease. However, clinical translation has fallen short of expectations, with many trials failing to meet primary endpoints. Failure to fully understand their mechanisms of action is a key factor contributing to the lack of successful commercialisation.

Mesenchymal stromal cell apoptosis is required for their therapeutic function.

Multipotent mesenchymal stromal cells (MSCs) ameliorate a wide range of diseases in preclinical models, but the lack of clarity around their mechanisms of action has impeded their clinical utility. The therapeutic effects of MSCs are often attributed to bioactive molecules secreted by viable MSCs. However, we found that MSCs underwent apoptosis in the lung after intravenous administration, even in the absence of host cytotoxic or alloreactive cells.

Biological Considerations in Scaling Up Therapeutic Cell Manufacturing.

Cell therapeutics - using cells as living drugs - have made advances in many areas of medicine. One of the most clinically studied cell-based therapy products is mesenchymal stromal cells (MSCs), which have shown promising results in promoting tissue regeneration and modulating inflammation. However, MSC therapy requires large numbers of cells, the generation of which is not feasible conventional planar tissue culture methods.

Thymospheres Are Formed by Mesenchymal Cells with the Potential to Generate Adipocytes, but Not Epithelial Cells.

Evidence suggests that a stem-cell-driven differentiation hierarchy maintains the dynamic thymic epithelial cell (TEC) network that governs T lymphocyte development. The identification of TEC stem/progenitor cells has been a major focus in the field, and several candidates with contrasting phenotypes have been described. We sought to determine the provenance and function of the only population reported to exhibit TEC stem cell properties in the adult, a Foxn1 EpCAM cell that generates so-called thymospheres.

Lymph node fibroblastic reticular cell transplants show robust therapeutic efficacy in high-mortality murine sepsis.

Sepsis is an aggressive inflammatory syndrome and a global health burden estimated to kill 7.3 million people annually. Single-target molecular therapies have not addressed the multiple disease pathways triggered by septic injury.

Alveolar macrophages are critical for the inhibition of allergic asthma by mesenchymal stromal cells.

Multipotent mesenchymal stromal cells (MSCs) possess reparative and immunoregulatory properties, making them attractive candidates for cellular therapy. However, the majority of MSCs administered i.v.

The transcriptional landscape of αβ T cell differentiation.

The differentiation of αβT cells from thymic precursors is a complex process essential for adaptive immunity. Here we exploited the breadth of expression data sets from the Immunological Genome Project to analyze how the differentiation of thymic precursors gives rise to mature T cell transcriptomes. We found that early T cell commitment was driven by unexpectedly gradual changes.

Identification of transcriptional regulators in the mouse immune system.

The differentiation of hematopoietic stem cells into cells of the immune system has been studied extensively in mammals, but the transcriptional circuitry that controls it is still only partially understood. Here, the Immunological Genome Project gene-expression profiles across mouse immune lineages allowed us to systematically analyze these circuits. To analyze this data set we developed Ontogenet, an algorithm for reconstructing lineage-specific regulation from gene-expression profiles across lineages.

Impact of sex steroid ablation on viral, tumour and vaccine responses in aged mice.

Recent evidence suggests that the decline in resistance to viral infections with age occurs predominantly as a result of a gradual loss of naïve antigen-specific T cells. As such, restoration of the naïve T cell repertoire to levels seen in young healthy adults may improve defence against infection in the aged. We have previously shown that sex steroid ablation (SSA) rejuvenates the ageing thymus and increases thymic export of naïve T cells, but it remains unclear whether T cell responses are improved.

Sex steroid ablation enhances immune reconstitution following cytotoxic antineoplastic therapy in young mice.

Cytotoxic antineoplastic therapy is used to treat malignant disease but results in long-term immunosuppression in postpubertal and adult individuals, leading to increased incidence and severity of opportunistic infections. We have previously shown that sex steroid ablation (SSA) reverses immunodeficiencies associated with age and hematopoietic stem cell transplantation in both autologous and allogeneic settings. In this study, we have assessed the effects of SSA by surgical castration on T cell recovery of young male mice following cyclophosphamide treatment as a model for the impact of chemotherapy.

Getting back at nature: understanding thymic development and overcoming its atrophy.

T cell development is a complex and tightly regulated process involving reciprocal interactions between the thymic stroma and differentiating thymocytes. Normal thymic function is critical for immunity and microenvironmental defects predispose to dysregulation in the T cell compartment. Thymic structure and function are also severely damaged by chemotherapy and pre-transplant conditioning.

Stem cells--meet immunity.

The ability of stem cells to differentiate into various different cell types holds great promise for the treatment of irreversible tissue damage that occurs in many debilitating conditions. With stem cell research advancing at a tremendous pace, it is becoming clear that one of the greatest hurdles to successful stem cell-derived therapies is overcoming immune rejection of the transplant. Although the use of immunosuppressive drugs can decrease the incidence of acute graft rejection, the burden of problems associated with prolonged immunosuppression must be reduced.

The Immunological Genome Project: networks of gene expression in immune cells.

The Immunological Genome Project combines immunology and computational biology laboratories in an effort to establish a complete 'road map' of gene-expression and regulatory networks in all immune cells.

Enhanced immune system regeneration in humans following allogeneic or autologous hemopoietic stem cell transplantation by temporary sex steroid blockade.

Purpose: To determine if temporarily blocking sex steroids prior to stem cell transplantation can increase thymus function and thus enhance the rate of T cell regeneration.

Experimental Design: This was a pilot study of luteinizing hormone-releasing hormone agonist (LHRH-A) goserelin given 3 weeks prior to allogeneic or autologous hemopoietic stem cell transplantation and administered up to 3 months posttransplantation. Patients (with or without LHRH-A administration) were assessed from 1 week to 12 months posttransplantation for multiple immunologic variables by flow cytometry (particularly naïve T cells), quantitative PCR to assess T-cell receptor excision circle levels (as a correlate of thymus function), CDR3 length analysis to determine the variability of the TCR repertoire, and in vitro assays to determine functional T cell responses.

De novo production of antigen-specific suppressor cells in vivo.

Foxp3-expressing regulatory T cells (Treg) play an essential role in maintaining tolerance to self antigens and are generated under physiological conditions when developing T cells encounter antigens expressed by thymic epithelial cells. We have addressed the possibility that Treg can be exploited to prevent or even suppress ongoing immune responses to foreign antigens. To this end, one must develop methods that permit the de novo generation of Treg specific for foreign antigens in peripheral lymphoid tissue.

Sex steroid ablation enhances lymphoid recovery following autologous hematopoietic stem cell transplantation.

Background: Autologous hematopoietic stem cell transplantation (auto-HSCT) patients experience long-term immunosuppression, which increases susceptibility to infection and relapse rates due to minimal residual disease (MRD). Sex steroid (SS) ablation is known to reverse age-related thymic atrophy and decline in B-cell production

Methods: This study used a congenic HSCT mouse model to analyze the effects of SS ablation (through surgical castration) on immune reconstitution and growth factor production following auto-HSCT. Bone marrow (BM) and thymic stromal cell (TSCs) populations were analyzed using RT-PCR and were tested for the production of growth factors previously implicated in immune reconstitution or age-relate immune degeneration

Results: Castration increased bone marrow (BM), thymic, and splenic cellularity following auto-HSCT.

Effects of castration on thymocyte development in two different models of thymic involution.

Age-associated thymic involution is accompanied by decreased thymic output. This adversely affects general immune competence and T cell recovery following cytoreductive treatments such as chemotherapy. A causal link between increasing sex steroids and age-related thymic atrophy is well established.

Activation of thymic regeneration in mice and humans following androgen blockade.

The thymus undergoes age-related atrophy, coincident with increased circulating sex steroids from puberty. The impact of thymic atrophy is most profound in clinical conditions that cause a severe loss in peripheral T cells with the ability to regenerate adequate numbers of naive CD4+ T cells indirectly correlating with patient age. The present study demonstrates that androgen ablation results in the complete regeneration of the aged male mouse thymus, restoration of peripheral T cell phenotype and function and enhanced thymus regeneration following bone marrow transplantation.