Thymic output, T-cell diversity, and T-cell function in long-term human SCID chimeras.
ABSTRACT: Severe combined immunodeficiency (SCID) is a syndrome of diverse genetic cause characterized by profound deficiencies of T, B, and sometimes NK-cell function. Nonablative human leukocyte antigen-identical or rigorously T cell-depleted haploidentical parental bone marrow transplantation (BMT) results in thymus-dependent genetically donor T-cell development in the recipients, leading to long-term survival. We reported previously that normal T-cell numbers, function, and repertoire developed by 3 to 4 months after transplantation in SCID patients, and the repertoire remained highly diverse for the first 10 years after BMT. The T-cell receptor diversity positively correlated with T-cell receptor excision circle levels, a reflection of thymic output. However, the fate of thymic function in SCID patients beyond 10 to 12 years after BMT remained to be determined. In this greater than 25-year follow-up study of 128 patients with 11 different molecular types of SCID after nonconditioned BMT, we provide evidence that T-cell function, thymic output, and T-cell clonal diversity are maintained long-term.
Project description:SCID is a fatal syndrome caused by mutations in at least 13 different genes. It is characterized by the absence of T cells. Immune reconstitution can be achieved through nonablative related donor BMT. However, the first transplant may not provide sufficient immunity. In these cases, booster transplants may be helpful. A prospective/retrospective study was conducted of 49 SCID patients (28.7% of 171 SCIDs transplanted over 30 years) who had received booster transplants to define the long-term outcome, factors contributing to a need for a booster and factors that predicted success. Of the 49 patients, 31 (63%) are alive for up to 28 years. Age at initial transplantation was found to have a significant effect on outcome (mean of 194 days old for patients currently alive, versus a mean of 273 days old for those now deceased, P=0.0401). Persistent viral infection was present in most deceased booster patients. In several patients, the use of two parents as sequential donors resulted in striking T-and B-cell immune reconstitution. A majority of the patients alive today have normal or adequate T-cell function and are healthy. Nonablative booster BMT can be lifesaving for SCID.
Project description:Myeloablative conditioning results in thymic epithelial cell (TEC) injury, slow T-cell reconstitution, and a high risk of opportunistic infections. Keratinocyte growth factor (KGF) stimulates TEC proliferation and, when given preconditioning, reduces TEC injury. Thymocytes and TECs express androgen receptors, and exposure to androgen inhibits thymopoiesis. In this study, we have investigated whether TEC stimulation via preconditioning treatment with KGF and leuprolide acetate (Lupron), 2 clinically approved agents, given only before conditioning would circumvent the profound TEC and associated T-cell deficiency seen in allogeneic bone marrow transplant (BMT) recipients. Only combined treatment with KGF plus leuprolide acetate normalized TEC subset numbers and thymic architecture. Thymopoiesis and thymic output were supranormal, leading to the accelerated peripheral reconstitution of naive CD4 and CD8 T cells with a broad Vbeta repertoire and decreased homeostatic T-cell proliferation. Combined therapy facilitated T:B cooperativity and enabled a B-cell humoral response to a CD4 T cell-dependent neoantigen challenge soon after BMT. In vivo antigen-specific CD8 T-cell responses and clearance of a live pathogen was superior with combined versus individual agent therapy. Thus, KGF combined with androgen blockade represents a novel approach to restore thymic function and facilitates the rapid recovery of peripheral T-cell function after allogeneic BMT.
Project description:Restoring T cell competence is a significant clinical challenge in patients whose thymic function is severely compromised due to age or cytoreductive conditioning. Here, we demonstrate in mice that mesenteric LNs (MLNs) support extrathymic T cell development in euthymic and athymic recipients of bone marrow transplantation (BMT). Furthermore, in aged murine BMT recipients, the contribution of the MLNs to the generation of T cells was maintained, while the contribution of the thymus was significantly impaired. Thymic impairment resulted in a proportional increase in extrathymic-derived T cell progenitors. Extrathymic development in athymic recipients generated conventional naive TCR?? T cells with a broad V? repertoire and intact functional and proliferative potential. Moreover, in the absence of a functional thymus, immunity against known pathogens could be augmented using engineered precursor T cells with viral specificity. These findings demonstrate the potential of extrathymic T cell development for T cell reconstitution in patients with limited thymic function.
Project description:Thymic graft-versus-host disease (tGVHD) can contribute to profound T cell deficiency and repertoire restriction after allogeneic BM transplantation (allo-BMT). However, the cellular mechanisms of tGVHD and interactions between donor alloreactive T cells and thymic tissues remain poorly defined. Using clinically relevant murine allo-BMT models, we show here that even minimal numbers of donor alloreactive T cells, which caused mild nonlethal systemic graft-versus-host disease, were sufficient to damage the thymus, delay T lineage reconstitution, and compromise donor peripheral T cell function. Furthermore, to mediate tGVHD, donor alloreactive T cells required trafficking molecules, including CCR9, L selectin, P selectin glycoprotein ligand-1, the integrin subunits alphaE and beta7, CCR2, and CXCR3, and costimulatory/inhibitory molecules, including Ox40 and carcinoembryonic antigen-associated cell adhesion molecule 1. We found that radiation in BMT conditioning regimens upregulated expression of the death receptors Fas and death receptor 5 (DR5) on thymic stromal cells (especially epithelium), while decreasing expression of the antiapoptotic regulator cellular caspase-8-like inhibitory protein. Donor alloreactive T cells used the cognate proteins FasL and TNF-related apoptosis-inducing ligand (TRAIL) (but not TNF or perforin) to mediate tGVHD, thereby damaging thymic stromal cells, cytoarchitecture, and function. Strategies that interfere with Fas/FasL and TRAIL/DR5 interactions may therefore represent a means to attenuate tGVHD and improve T cell reconstitution in allo-BMT recipients.
Project description:Bone marrow (BM) transplantation (BMT) represents a curative treatment for various hematological disorders. Prior to BMT, a large amount of the relevant anticancer drug needed to be administered to eliminate cancer cells. However, during this pre?BMT cytotoxic conditioning regimen, hematopoietic stem cells in the BM and thymic epithelial cells were also destroyed. The T cell receptor (TCR) recognizes diverse pathogen, tumor and environmental antigens, and confers immunological memory and self?tolerance. Delayed thymus reconstitution following pre?BMT cytotoxic conditioning impedes de novo thymopoiesis and limits T cell?mediated immunity. Several cytokines, such as RANK ligand, interleukin (IL)?7, IL?22 and stem cell factor, were recently reported to improve thymopoiesis and immune function following BMT. In the present study, it was found that the co?transplantation of tonsil?derived mesenchymal stromal cells (T?MSCs) with BM?derived cells (BMCs) accelerated the recovery of involuted thymuses in mice following partial pre?BMT conditioning with busulfan?cyclophosphamide treatment, possibly by inducing FMS?like tyrosine kinase 3 ligand (FLT3L) and fibroblast growth factor 7 (FGF7) production in T?MSCs. The co?transplantation of T?MSCs with BMCs also replenished the CD3+ cell population by inhibiting thymocyte apoptosis following pre?BMT cytotoxic conditioning. Furthermore, T?MSC co?transplantation improved the recovery of the TCR repertoire and led to increased thymus?generated T cell diversity.
Project description:The development of T cell tolerance in the thymus requires the presentation of host proteins by multiple antigen-presenting cell (APC) types. However, the importance of transferring host antigens from transcription factor AIRE-dependent medullary thymic epithelial cells (mTECs) to bone marrow (BM) APCs is unknown. We report that antigen was primarily transferred from mTECs to CD8?+ dendritic cells (DCs) and showed that CD36, a scavenger receptor selectively expressed on CD8?+ DCs, mediated the transfer of cell-surface, but not cytoplasmic, antigens. The absence of CD8?+ DCs or CD36 altered thymic T cell selection, as evidenced by TCR repertoire analysis and the loss of allo-tolerance in murine allogeneic BM transplantation (allo-BMT) studies. Decreases in these DCs and CD36 expression in peripheral blood of human allo-BMT patients correlated with graft-versus-host disease. Our findings suggest that CD36 facilitates transfer of mTEC-derived cell-surface antigen on CD8?+ DCs to promote tolerance to host antigens during homeostasis and allo-BMT.
Project description:Cytoablative treatments lead to severe damages on thymic epithelial cells (TECs), which result in delayed <i>de novo</i> thymopoiesis and a prolonged period of T-cell immunodeficiency. Understanding the mechanisms that govern thymic regeneration is of paramount interest for the recovery of a functional immune system notably after bone marrow transplantation (BMT). Here, we show that RANK ligand (RANKL) is upregulated in CD4<sup>+</sup> thymocytes and lymphoid tissue inducer (LTi) cells during the early phase of thymic regeneration. Importantly, whereas RANKL neutralization alters TEC recovery after irradiation, <i>ex vivo</i> RANKL administration during BMT boosts the regeneration of TEC subsets including thymic epithelial progenitor-enriched cells, thymus homing of lymphoid progenitors, and <i>de novo</i> thymopoiesis. RANKL increases specifically in LTi cells, lymphotoxin ?, which is critical for thymic regeneration. RANKL treatment, dependent on lymphotoxin ?, is beneficial upon BMT in young and aged individuals. This study thus indicates that RANKL may be clinically useful to improve T-cell function recovery after BMT by controlling multiple facets of thymic regeneration.
Project description:<h4>Background</h4>The effect of pretransplantation conditioning on the long-term outcomes of patients receiving hematopoietic stem cell transplantation for severe combined immunodeficiency (SCID) has not been completely determined.<h4>Objective</h4>We sought to assess the outcomes of 23 mostly conditioned patients with SCID and compare their outcomes with those of 25 previously reported nonconditioned patients with SCID who underwent transplantation.<h4>Methods</h4>In the present study we reviewed the medical records of these 23 consecutive, mostly conditioned patients with SCID who underwent transplantation between 1998 and 2007.<h4>Results</h4>Eighteen patients (median age at transplantation, 10 months; range, 0.8-108 months) received haploidentical mismatched related donor, matched unrelated donor, or mismatched unrelated donor transplants, 17 of whom received pretransplantation conditioning (with 1 not conditioned); 13 (72%) patients engrafted with donor cells and survive at a median of 3.8 years (range, 1.8-9.8 year); 5 (38%) of 13 patients require intravenous immunoglobulin; and 6 of 6 age-eligible children attend school. Of 5 recipients (median age at transplantation, 7 months; range, 2-23 months) of matched related donor transplants, all 5 engrafted and survive at a median of 7.5 years (range, 1.5-9.5 year), 1 recipient requires intravenous immunoglobulin, and 3 of 3 age-eligible children attend school. Gene mutations were known in 16 cases: mutation in the common gamma chain of the IL-2 receptor (IL2RG) in 7 patients, mutation in the alpha chain of the IL-7 receptor (IL7RA) in 4 patients, mutation in the recombinase-activating gene (RAG1) in 2 patients, adenosine deaminase deficiency (ADA) in 2 patients, and adenylate kinase 2 (AK2) in 1 patient. Early outcomes and quality of life of the previous nonconditioned versus the present conditioned cohorts were not statistically different, but longer-term follow-up is necessary for confirmation.<h4>Conclusions</h4>Hematopoietic stem cell transplantation in patients with SCID results in engraftment, long-term survival, and a good quality of life for the majority of patients with or without pretransplantation conditioning.
Project description:T-cell production depends on the recruitment of hematopoietic progenitors into the thymus. T cells are among the last of the hematopoietic lineages to recover after bone marrow transplantation (BMT), but the reasons for this delay are not well understood. Under normal physiologic conditions, thymic settling is selective and either CCR7 or CCR9 is required for progenitor access into the thymus. The mechanisms of early thymic reconstitution after BMT, however, are unknown. Here we report that thymic settling is briefly CCR7/CCR9-independent after BMT but continues to rely on the selectin ligand PSGL-1. The CCR7/CCR9 independence is transient, and by 3 weeks after BMT these receptors are again strictly required. Despite the normalization of thymic settling signals, the rare bone marrow progenitors that can efficiently repopulate the thymus are poorly reconstituted for at least 4 weeks after BMT. Consistent with reduced progenitor input to the thymus, intrathymic progenitor niches remain unsaturated for at least 10 weeks after BMT. Finally, we show that thymic recovery is limited by the number of progenitors entering the thymus after BMT. Hence, T-lineage reconstitution after BMT is limited by progenitor supply to the thymus.
Project description:Thymus transplantation, in conjunction with bone marrow transplantation (BMT), has been attracting attention for the treatment of various diseases. Recently, donor lymphocyte infusion (DLI) has been used as a helpful tool for establishing donor chimerism and preventing a relapse of leukemia/lymphoma. However, the effects of DLI on transplanted and recipient thymuses have not been explored. We therefore performed DLI in the intrabone marrow-BMT + thymus transplantation setting. We have found that DLI leads to derangements in both recipient thymuses and transplanted thymuses; by 2 wk after BMT, we saw a decrease in total cell number, a lower percentage of CD4(+)CD8(+) cells, and the obliteration of the thymic corticomedullary junction. Four weeks later, the thymic impairment became more serious. However, when we depleted the CD4(+) T cells (CD4(-)-DLI), the recipient thymic recovery and transplanted thymic development were significantly restored by the treatment. In addition, there were much greater levels of TNF-? and Fas ligand, and a lower percentage of regulatory T cells in the DLI group than in the CD4(-)-DLI group. These findings indicate that inflammation induced by DLI, especially by CD4(+) T cells, plays a crucial role in the thymic impairment.