Thymic Function Research Articles

Zinc Status Affects T Cell Reconstitution in Patients Receiving Naïve T Cell Depleted Allogeneic HSCT

Delayed immune reconstitution (IR) is a major clinical problem contributing to post-allogeneic hematopoietic stem cell transplant (allo-HSCT) morbidity and mortality. Specifically, CD4 T cell reconstitution is linked with improved clinical outcomes. As the primary organ of T cell production, the thymus is a crucial contributor to T cell reconstitution after HSCT generating a broad T cell receptor (TCR) repertoire selected through central tolerance However, T cell reconstitution can be hindered by poor thymus function as a consequence of age, transplant conditioning, or graft versus host disease (GVHD). At present, no drugs are available to boost T cell recovery, while many of the factors limiting IR are still unknown. Zinc (Zn), the second most abundant trace element in our body, is important for normal T cell development. Zn deficiency (ZD) in humans and mice is characterized by poor circulating T cells and depressed thymic function, which are both restorable after reintroduction of Zn with the diet. Despite having multiple risk factors for ZD, there are no published data focusing on ZD prevalence among allo-HSCT recipients. Based on our previous observations, we hypothesized that peri-HSCT Zn levels correlate with IR. In this study, we analyzed serum Zn levels of allo-HSCT patients who received naïve T cell (T N) depleted grafts as a strategy to prevent aGVHD (Bleakley et al., 2022, NCT00914940). This population is particularly interesting for studying IR because in these patients, circulating T N at d+365 after HSCT will primarily be of donor hematopoietic stem cell origin generated in the recipient thymus. Samples and clinical data were prospectively collected. Fifty-two patients had peri-HSCT serum samples available for Zn measures, as pre-HSCT and/or day +80 samples. Zn measures were performed through mass-spectrometry at the University of Washington Hospital-Biochemistry Lab. ZD was defined for Zn<70ug/dL as defined by the WHO. T cell populations (CD4 +, CD8 +, T N CD4 + and CD8 +, T regulatory cells, NK cells, B cells) were analyzed by flow cytometry at day+365. DNA was extracted from PBMC pellets collected at d+365 and were analyzed in qPCR for the expression of signal-joint T cell receptor excision circles (sjTRECs), being the gold standard for measuring thymic-derived T cells. We studied the association between Zn levels at baseline and day+80 and parameters of IR through linear regression. Comparisons between two groups were analyzed by t-test. Median age at transplant was 47 (range 6-61). Twenty-eight patients received myeloablative conditioning with total body irradiation (TBI) of 13.2 Gy (53.8%) and 24 (46.2%) received an intermediate intensity conditioning regimen with 4Gy TBI. Forty-one patients (78.8%) had pre-HSCT and 46 (88.5%) had day+80 Zn measures; 38 patients (73.1%) had both pre-HSCT and day+80 Zn measures. Median pre-HSCT and day+80 Zn levels were, respectively, 71 (range 60-105) and 80 (range 36-112); at baseline, 13 patients (25%) had ZD (<70ug/dL, according to WHO), whereas seven (13.3%) were ZD at day+80. Median sjTRECs at day +365 were 3.33/mg of DNA (range 0.00-16,704.54). As expected, sjTRECs at day+365 significantly correlated with age at transplant (r 2=0,3824; p<0.0001), whereas Zn levels preHCT or day80 did not. The number of circulating CD4 + and CD8 + T N at day+365 showed significant correlation with age. Zinc levels did not correlate with IR of absolute CD4 +, CD8 +, NK, T regs, and B cells at day+365, although we observed a trend for lower CD4 + counts at day 365 with lower day+80 Zn levels. Day+80 serum Zn levels was associated with sjTRECs at day+365 (Figure 1A. r 2=0.2643; p=0.0019) and lower pre-HSCT Zn significantly correlated with worse CD8 +T N reconstitution at day+365 (Figure 1B. r 2=0.1433; p= 0.0327), with clear trends in the same direction also for pre-HSCT Zn and CD4 + T N and day+80 Zn and CD4 + T N. In conclusion, we found that a non-negligible population of patients undergo allo-HSCT with unrecognized ZD. Peri-transplant Zinc status negatively affects IR, especially on the thymic-derived T cell compartment. Early recognition of ZD and zinc supplementation might help prevent morbidity related to poor IR in a proportion of patients. A multivariable analysis looking at other clinical data and outcomes is ongoing. Validation of these findings is needed on a larger number of patients, including a cohort of patients receiving T N-replete HSCT.

Ligustilide prevents thymic immune senescence by regulating Thymosin β15-dependent spatial distribution of thymic epithelial cells

BackgroundThymus is the most crucial organ connecting immunity and aging. The progressive senescence of thymic epithelial cells (TECs) leads to the involution of thymus under aging, chronic stress and other factors. Ligustilide (LIG) is a major active component of the anti-aging Chinese herbal medicine Angelica sinensis (Oliv.) Diels, but its role in preventing TEC-based thymic aging remains elusive. PurposeThis study explored the protective role of Ligustilide in alleviating ADM (adriamycin) -induced thymic immune senescence and its underlying molecular mechanisms. MethodThe protective effect of Ligustilide on ADM-induced thymic atrophy was examined by mouse and organotypic models, and conformed by SA-β-gal staining in TECs. The abnormal spatial distribution of TECs in the senescent thymus was analyzed using H&E, immunofluorescence and flow cytometry. The possible mechanisms of Ligustilide in ADM-induced thymic aging were elucidated by qPCR, fluorescence labeling and Western blot. The mechanism of Ligustilide was subsequently validated through actin polymerization inhibitor, genetic engineering to regulate Thymosin β15 (Tβ15) and Tβ4 expression, molecular docking and β Thymosin-G-actin cross-linking assay. ResultsAt a 5 mg/kg dose, Ligustilide markedly ameliorated ADM-induced weight loss and limb grip weakness in mice. It also reversed thymic damage and restored positive selection impaired by ADM. In vitro, ADM disrupted thymic structure, reduced TECs number and hindered double negative (DN) T cell differentiation. Ligustilide counteracted these effects, promoted TEC proliferation and reticular differentiation, leading to an increase in CD4+ single positive (CD4SP) T cell proportion. Mechanistically, ADM diminished the microfilament quantity in immortalized TECs (iTECs), and lowered the expression of cytoskeletal marker proteins. Molecular docking and cross-linking assay revealed that Ligustilide inhibited the protein binding between G-actin and Tβ15 by inhibiting the formation of the Tβ15-G-actin complex, thus enhancing the microfilament assembly capacity in TECs. ConclusionThis study, for the first time, reveals that Ligustilide can attenuate actin depolymerization, protects TECs from ADM-induced acute aging by inhibiting the binding of Tβ15 to G-actin, thereby improving thymic immune function. Moreover, it underscores the interesting role of Ligustilide in maintaining cytoskeletal assembly and network structure of TECs, offering a novel perspective for deeper understanding of anti thymic aging.

Naive CD4 T Cells Highly Expressing the Inflammatory Chemokine Receptor CXCR3 Increase with Age and Radiation Exposure in Atomic Bomb Survivors.

The numbers of naive T cells that react to novel pathogens not yet encountered by an immune system, decrease during aging, mainly due to age-associated involution of the thymus. CD45RA+ naive CD4 T cells consist of heterogeneous populations, including highly CXCR3-expressing cells that appear during the homeostatic proliferation of naive T cells and exhibit enhanced type-1 inflammatory phenotypes. Based on previous evidence of radiation-associated reductions in thymic function and peripheral blood naive CD4 T cells, we hypothesized that the homeostatic proliferation of naive CD4 T cells compensates for deficits in peripheral T-cell populations after radiation injury, which may increase the proportion of CXCR3high cells in naive CD4 T cells and enhance inflammation. The statistical models employed in this study revealed positive associations between the number of CXCR3high naive CD4 T cells and age as well as radiation dose among 580 Hiroshima atomic bomb survivors. In addition, the CXCR3high cells in these survivors increased not only with the levels of homeostatic cytokines, IL6 and IL7, but also with those of inflammatory indicators, CXCL10 and CRP. These results suggest that thymic T-cell production deficiency due to radiation and aging results in enhanced homeostatic proliferation that drives the appearance of CXCR3high naive CD4 T cells poised for an inflammatory response. Molecular mechanisms and clinical relevance of increasing CXCR3high cells in naive CD4 T populations should be further investigated in the context of inflammatory disease development long after radiation exposure.

The alarmin IL33 orchestrates type 2 immune-mediated control of thymus regeneration

As the primary site of T-cell development, the thymus dictates immune competency of the host. The rates of thymus function are not constant, and thymus regeneration is essential to restore new T-cell production following tissue damage from environmental factors and therapeutic interventions. Here, we show the alarmin interleukin (IL) 33 is a product of Sca1+ thymic mesenchyme both necessary and sufficient for thymus regeneration via a type 2 innate immune network. IL33 stimulates expansion of IL5-producing type 2 innate lymphoid cells (ILC2), which triggers a cellular switch in the intrathymic availability of IL4. This enables eosinophil production of IL4 to re-establish thymic mesenchyme prior to recovery of thymopoiesis-inducing epithelial compartments. Collectively, we identify a positive feedback mechanism of type 2 innate immunity that regulates the recovery of thymus function following tissue injury.

Accelerating Immune Reconstitution in HSCT Patients through iPSC-Derived Thymic Epithelial Cells

T cells are central to host defense and tolerance, yet the critical role of the thymus in facilitating T cell development and TCR repertoire selection is often overlooked. Thymic function declines in the second decade of life and is susceptible to a wide range of pathogenic insults. Compromise of thymic function is a frequent complication after HSCT as a result of radiation, anti-thymocyte globulin, CMV infection and acute GVHD. Thymic injury can lead to delayed immune reconstitution, opportunistic infections, autoimmunity and chronic GVHD. Reconstituting thymic function, e.g. through induced pluripotent stem cell (iPSC)-derived thymic epithelial cells (TECs), holds great therapeutic promise. However, the regenerative potential of the thymus remains clinically untapped as the signals that drive thymic ontogeny beyond the anterior foregut are incompletely understood. In this study, we elucidated pathways instructing commitment and specialization of the human thymic epithelial stroma through orthogonal single cell transcriptomic analysis strategies. First, we inferred inductive cues that contribute to the initiation of thymic organogenesis by comparing gene regulatory networks expressed in human fetal epithelial cells of the thymus and other anterior foregut-derived organs. Then we defined lineage trajectories within the thymic epithelium by evaluating human thymus samples sequentially across embryonic, fetal, and early postnatal stages. Our data revealed that responses to types I and II interferon distinguish epithelial cells of the thymus from other anterior foregut-derived organs. We further found that the downstream effects of interferon extend differentially within the cortical and medullary lineages, reflected in characteristic NFκB and IRF signatures (Figure 1A). We have translated the core set of gene regulatory networks identified in our transcriptomic study into a morphogen-based approach to advance the differentiation of iPSCs into TECs. TECs derived from this protocol demonstrate high transcriptional fidelity with primary human fetal intertypic TECs that can give rise to cortical and medullary lineages (Fig. 1B). To test the functional capacity of iPSC-derived TECs to give rise to human T cells, and specifically to execute positive and negative selection, we transplanted iPSC-derived TECs into humanized athymic NSG-nude mice (NSG-Foxn1 Null) (Figure 1C). 12 weeks after transplantation, flowcytometric analysis of dissociated TEC grafts showed robust human T cell development recapitulating the physiologic progression from double-negative to double-positive to TCRab-rearranged single CD4 and CD8 positive T cells observed in primary human thymus. (Figure 1D) These results provide proof of concept that transplantable iPSC-derived TECs can promote T cell development in vivo and have potential as a regenerative thymic replacement therapy for patients suffering from complications of defective T cell immune reconstitution after HSCT.

MSCs-IL33-ILC2s-AREG-Tecs Axis Promotes the Remodeling of Thymic Function in Acute Gvhd

Background: Previous studies suggested that mesenchymal stromal cells (MSCs) administrated at the acute graft versus host disease (aGVHD) phase effectively decreased the incidence and severity of chronic GVHD (cGVHD) by boosting thymic regeneration. Our research has found that MSCs expressing interleukin 33 (IL33) may participate in thymus regeneration from aGVHD damage through type 2 innate lymphoid cells (ILC2s)-mediated tissue recovery. However, the mechanism for ILC2s repairing the damaged thymus caused by aGVHD is unclear. Here, we further explored the mechanisms on how ILC2s promote thymus recovery post-BMT. Methods: We carried out studies in a aGVHD mice model of fully MHC-mismatched myeloablative bone marrow transplantation (C57BL/6 to BALB/c). IL33 knocked-down (MSC/IL33 -) and empty-load MSCs (MSC/Control) were generated by lentivirus transfection, and then administrated intravenously at day 7 post-BMT to intervene in aGVHD and assess the effect of IL33 from MSCs on ILC2s (Lin-CD45+iCD3-CD127+GATA3+) in the thymus by flow cytometery at day 14 post-BMT. Clinical scores and survival were recorded once every days. Furthermore, we isolated, purified and amplified ILC2s from C57BL/6 mouse thymus by immunomagnetic bead sorting and flow cytometry for aGVHD intervention and studied whether ILC2s can home to thymus by fluorescence tracing and the effects of ILC2s on TECs by immunofluorescence. To study the potential mechanism of ILC2s affecting TECs by using transcriptome sequencing (RNA-seq) and related molecular biology experiments. Finally, the potential target amphiregulin (AREG) was found from RNA-seq analyses and the murine recombinant AREG was used as an intervention to evaluate its effect on aGVHD mouse. Results: In this study, we found that knocking down the expression of IL33 in MSCs partially blocked the repair effect of MSCs on thymus and decreased the expansion of thymic ILC2s in aGVHD mice compared with the MSC/Control group. Then, we found that exogenous infusion of thymic ILC2s is very effective in treating thymic tissue injury, and can home to the recipient thymus and further migrate to the thymic medulla region. Furthermore, we found that ILC2s may home to the thymus and migrate to the thymic medulla region through CCR7 and MSCs promote the high expression of AREG in ILC2s through RNA-seq. Importantly, we found that the expression level of intrathymic AREG in No-GVHD, MSCs-GVHD and ILC2s-GVHD group was significantly increased than aGVHD group on day 14 post-BMT and exogenous administration of AREG after transplantation can significantly increase the proliferation of thymic epithelial cells, especially the regeneration of thymic medulla and the generation of new thymus-derived CD4/CD8 double-positive T cells. Conclusion: In conclusion, we demonstrate that MSCs infusion may rely on the MSCs-IL33-ILC2s-AREG-TECs axis mediated by ILC2s to remodeling the thymic microenvironment homeostasis, thus promoting the reconstruction of T cell immune homeostasis. Importantly, the results presented in this report identify a previously unrecognized role for the epidermal growth factor family member AREG in promoting the remodeling of thymus tissue. and providing new insights for the mechanism of MSCs treatment for GVHD.

Low CD117 Expression Identifies Hematopoietic Stem Cell Subsets with Enhanced Lymphoid Potential in Mice and Humans

Background: Hematopoietic stem cells (HSCs) with multilineage potential are critical for effective de novo T-cell generation and thymic recovery, restoring the adaptive immune system after Hematopoietic Cell Transplantation (HCT). Recent studies have brought new insights into functional heterogeneity within HSCs, revealing an organized and predictable framework governing the adoption of lineage-restricted fates. However, the gene-regulatory networks underlying lymphoid determination and their conservation with aging in HSCs need to be elucidated. This study aims to comprehensively investigate the molecular profile of young and old HSCs and identify HSC subsets with multilineage transcriptional programs. Results: We conducted single-cell multiomic RNA and ATAC sequencing of young and old HSCs defined by Lineage-CD34-CD48-CD150+Sca-1+Kit+. We identified two CD117 (Kit) HSC subsets, Kit lo and Kit hi, with unique transcriptional profiles. Kit hi HSCs were characterized by quiescence, platelet bias, and low-output gene signatures, while Kit lo HSCs enriched for multi-lineage and high-output gene signatures. We observed a decreased frequency of Kit lo HSCs in aged mice. Although Kit lo HSCs have been previously described to exhibit increased self-renewal (Shin et al. JEM, 2014), their T-cell potential and the molecular underpinnings governing lymphoid differentiation programs are unknown. We performed in vitro studies, S17 stromal assay, and artificial thymic organoids (ATOs), which revealed an enhanced output of lymphoid progenitors and T-cells from Kit lo HSCs, consistent across all age cohorts. We next compared Kit lo vs. Kit hi HSCs in a competitive allogeneic HCT model. Kit lo HSCs demonstrated improved thymic recovery and post-HCT T-cell reconstitution, independent of age. To orthogonally evaluate post-HCT thymic function, we assessed Recent Thymic Emigrants (RTEs) output, which further substantiated superior recovery in mice receiving Kit lo HSCs. We further observed that Kit lo HSC-derived T-cells exhibited better proliferation in response to an acute Listeria monocytogenes infection. Next, we transplanted middle-aged mice to evaluate the rejuvenation potential of different Kit HSC subsets. We observed that Kit lo HSCs partly mitigated age-related changes in the thymic microenvironment, specifically by enhancing the regeneration of thymic epithelial cells (TECs) in middle-aged mice, thereby reversing the decline in T-cell production. We found differential expression and activity of key transcription factors (TFs), including Runx3, Zbtb7a, and Ezh1, associated with lymphoid differentiation through integrative transcriptional and chromatin accessibility analyses of Kit lo HSCs. These TFs notably showed distinct patterns in Kit lo HSCs independent of age, indicating their potential role in driving their enhanced T-cell potential. To establish the existence of a comparable human subset, we interrogated a human BM CITE-Seq dataset (Sommarin et al. Biorxiv 2021) for the mouse Kit lo gene signature. In concordance with our findings in mice, we observed an enrichment of the Kit lo gene program in young HSCs and decreased frequency of Kit lo HSCs in old BM. Next, we used ATOs to validate differential lymphoid potential. We found increased T-cell output originating from Kit lo HSCs, thus underscoring their enhanced lymphoid capacity and potential clinical relevance. Conclusion: Collectively, we demonstrate a distinct HSC subset, Kit lo HSC, with an age-conserved lymphoid gene program that enhances T-cell production and facilitates thymic regeneration. Importantly, we demonstrate the presence of an analogous HSC subset in humans, revealing the relevance of these insights to human health and disease. Thus, Kit lo HSCs have therapeutic potential to counteract age-associated immune senescence and treatment-related immune suppression.

Altered T cell development in an animal model of multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease that affects the central nervous system (CNS), leading to demyelination and axonal degeneration. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS that has significantly improved our understanding of MS. Studies have observed early thymic involution in MS patients, suggesting the potential involvement of the thymus in CNS autoimmunity. However, our knowledge of the thymus's role in autoimmune disorders affecting the CNS remains limited. In this study, we examined the effects of EAE induction on thymopoiesis and observed alterations in T cell development. These changes were characterized by increased apoptosis and decreased proliferation of thymocytes at the EAE peak stage. We also identified a blockade in the transition from CD4−CD8− double-negative thymocytes to CD4+CD8+ double-positive cells, as evidenced by the accumulation of double-negative stage 1 thymocytes at both the EAE onset and peak stages. Furthermore, positive selection was disrupted in the thymus of EAE mice at both stages, leading to an elevated proportion and number of CD4+CD8− and CD4−CD8+ single-positive cells. Meanwhile, we observed an augmented production of regulatory T cells in the thymus of EAE mice. Moreover, peripheral blood analysis of EAE mice at the onset stage showed expanded T cell subsets but not at the peak stage. We also observed altered expression patterns in thymus-derived CD4+CD8− and CD4−CD8+ single-positive cells between MS patients and healthy controls. Our findings demonstrate a modified T cell development in EAE/MS, providing valuable insights into the potential of modulating thymic function as a targeted therapeutic approach to MS/EAE.

Cryopreservation of mouse thymus depletes thymocytes but supports immune reconstitution on transplantation.

Cryopreservation of mouse thymus depletes donor thymocytes but preserves thymus function when transplanted after thawing into athymic mice. No differences in immune reconstitution were observed between fresh and frozen/thawed transplants suggesting that donor thymocyte depletion does not affect outcome. Thus, cryopreservation of thymus may improve outcomes in thymus transplant patients.

Genetically determined thymic function affects strength and duration of immune response in COVID patients with pneumonia.

Thymic activation improves the outcome of COVID-19 patients with severe pneumonia. The rs2204985 genetic polymorphism within the TCRA-TCRD locus, which affects thymic output in healthy individuals, was found here to modify SARS-CoV-2-specific immunity and disease severity in COVID-19 patients with severe pneumonia. Forty patients with severe COVID-19 pneumonia were investigated. The GG genotype at the rs2204985 locus was associated, independently of age and sex, with stronger and long-lasting anti-SARS-CoV-2 helper and cytotoxic T cell responses 6 months after recovery. The GG genotype was also associated with less severe lung involvement, higher thymic production, and higher counts of blood naïve T lymphocytes, including recent thymic emigrants, and a larger population of activated stem cell memory CD4+ T cells. Overall, GG patients developed a more robust and sustained immunity to SARS-CoV-2. Polymorphism at rs2204985 locus should be considered as an additional predictive marker of anti-SARS-CoV-2 immune response.

Nitric oxide-dependent immunosuppressive function of thymus-derived mesenchymal stromal/stem cells

BackgroundThe thymus is required for T cell development and the formation of the adaptive immunity. Stromal cells, which include thymic epithelial cells (TECs) and mesenchymal stromal cells (MSCs), are essential for thymic function. However, the immunomodulatory function of thymus-derived MSCs (T-MSCs) has not been fully explored.MethodsMSCs were isolated from mouse thymus and their general characteristics including surface markers and multi-differentiation potential were characterized. The immunomodulatory function of T-MSCs stimulated by IFN-γ and TNF-α was evaluated in vitro and in vivo. Furthermore, the spatial distribution of MSCs in the thymus was interrogated by using tdTomato-flox mice corssed to various MSC lineage Cre recombinase lines.ResultsA subset of T-MSCs express Nestin, and are mainly distributed in the thymic medulla region and cortical-medulla junction, but not in the capsule. The Nestin-positive T-MSCs exhibit typical immunophenotypic characteristics and differentiation potential. Additionally, when stimulated with IFN-γ and TNF-α, they can inhibit activated T lymphocytes as efficiently as BM-MSCs, and this function is dependent on the production of nitric oxide (NO). Additionally, the T-MSCs exhibit a remarkable therapeutic efficacy in acute liver injury and inflammatory bowel disease (IBD).ConclusionsNestin-positive MSCs are mainly distributed in medulla and cortical-medulla junction in thymus and possess immunosuppressive ability upon stimulation by inflammatory cytokines. The findings have implications in understanding the physiological function of MSCs in thymus.

Mesenchymal stromal cells ameliorate chronic GVHD by boosting thymic regeneration in a CCR9-dependent manner in mice.

Chronic graft-versus-host disease (cGVHD) is a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Mature donor T cells within the graft contribute to severe damage of thymic epithelial cells (TECs), which are known as key mediators in the continuum of acute GVHD (aGVHD) and cGVHD pathology. Mesenchymal stromal cells (MSCs) are reportedly effective in the prevention and treatment of cGVHD. In our previous pilot clinical trial in patients with refractory aGVHD, the incidence and severity of cGVHD were decreased, along with an increase in levels of blood signal joint T-cell receptor excision DNA circles after MSCs treatment, which indicated an improvement in thymus function of patients with GVHD, but the mechanisms leading to these effects remain unknown. Here, we show in a murine GVHD model that MSCs promoted the quantity and maturity of TECs as well as elevated the proportion of Aire-positive medullary TECs, improving both CD4+CD8+ double-positive thymocytes and thymic regulatory T cells, balancing the CD4:CD8 ratio in the blood. In addition, CCL25-CCR9 signaling axis was found to play an important role in guiding MSC homing to the thymus. These studies reveal mechanisms through which MSCs ameliorate cGVHD by boosting thymic regeneration and offer innovative strategies for improving thymus function in patients with GVHD.

TGF-β Promotes the Postselection Thymic Development and Peripheral Function of IFN-γ-Producing Invariant NKT cells.

IFN-γ-producing invariant NKT (iNKT)1 cells are lipid-reactive innate-like lymphocytes that are resident in the thymus and peripheral tissues where they protect against pathogenic infection. The thymic functions of iNKT1 cells are not fully elucidated, but subsets of thymic iNKT cells modulate CD8 T cell, dendritic cell, B cell, and thymic epithelial cell numbers or function. In this study, we show that a subset of murine thymic iNKT1 cells required TGF-β-induced signals for their postselection development, to maintain hallmark TGF-β-induced genes, and for expression of the adhesion receptors CD49a and CD103. However, the residency-associated receptor CD69 was not TGF-β signaling-dependent. Recently described CD244+ c2 thymic iNKT1 cells, which produce IFN-γ without exogenous stimulation and have NK-like characteristics, reside in this TGF-β-responsive population. Liver and spleen iNKT1 cells do not share this TGF-β gene signature, but nonetheless TGF-β impacts liver iNKT1 cell phenotype and function. Our findings provide insight into the heterogeneity of mechanisms guiding iNKT1 cell development in different tissues and suggest a close association between a subset of iNKT1 cells and TGF-β-producing cells in the thymus that support their development.

Clinical relevance of thymic and bone marrow outputs in multiple sclerosis patients treated with alemtuzumab

Thymic and bone marrow outputs were evaluated in 13 sequential samples of 68 multiple sclerosis patients who initiated alemtuzumab and were clinically followed for 48 months. Three months after alemtuzumab infusions, the levels of new T lymphocytes were significantly reduced, but progressively increased reaching the highest values at 36 months, indicating the remarkable capacity of thymic function recovery. Newly produced B cells exceeded baseline levels as early as 3 months after alemtuzumab initiation. Heterogeneous patterns of new T- and B-cell recovery were identified, but without associations with age, sex, previous therapies, development of secondary autoimmunity or infections, and disease re-emergence.Trial registration version 2.0–27/01/2016.

Aire drives steroid hormone biosynthesis by medullary thymic epithelial cells.

Thymic epithelial cells (TECs) produce glucocorticoids, which antagonize negative selection of autoreactive thymocytes and promote a competent T cell antigen-specific repertoire. To characterize their source, we generated a knock-in reporter mouse in which endogenous Cyp11b1, the final enzyme in de novo production of active glucocorticoids, was fluorescently tagged with mScarlet. Here, we find that Cyp11b1 is expressed in medullary TECs (mTECs) but not cortical TECs or other cells in the thymus. A distinct characteristic of mTECs is the presence of Aire, a transcription factor that drives expression of tissue-restricted antigens (TRAs) important for establishing immune tolerance. Cyp11b1 expression was highest in Aire+ mTECs, lower in post-Aire mTECs, and absent in mTECs of Aire-deficient mice. Transcriptomic analyses found that multiple enzymatic biosynthetic pathways are expressed specifically in mTECs and are also Aire dependent. In particular, we found that the thymus expresses messenger RNA for enzymes that catalyze production of many bioactive steroids and that glucocorticoids and sex steroids were secreted by cultured thymi. Expression of the transcripts for these genes and production of their final steroid products were markedly reduced in the absence of Aire. Thus, in addition to its well-established role in inducing TRAs that promote negative selection, Aire has an additional and contrary function of inducing glucocorticoids that antagonize negative selection, which together may expand and enhance the TCR repertoire. Furthermore, because Aire drives expression of multiple enzymes responsible for production of other non-gene-encoded bioactive molecules, it might have yet other roles in thymus development and function.

Thymus-derived hormonal and cellular control of cancer.

The thymus gland is a central lymphoid organ in which developing T cell precursors, known as thymocytes, undergo differentiation into distinct type of mature T cells, ultimately migrating to the periphery where they exert specialized effector functions and orchestrate the immune responses against tumor cells, pathogens and self-antigens. The mechanisms supporting intrathymic T cell differentiation are pleiotropically regulated by thymic peptide hormones and cytokines produced by stromal cells in the thymic microenvironment and developing thymocytes. Interestingly, in the same way as T cells, thymic hormones (herein exemplified by thymosin, thymulin and thymopoietin), can circulate to impact immune cells and other cellular components in the periphery. Evidence on how thymic function influences tumor cell biology and response of patients with cancer to therapies remains unsatisfactory, although there has been some improvement in the knowledge provided by recent studies. Herein, we summarize research progression in the field of thymus-mediated immunoendocrine control of cancer, providing insights into how manipulation of the thymic microenvironment can influence treatment outcomes, including clinical responses and adverse effects of therapies. We review data obtained from clinical and preclinical cancer research to evidence the complexity of immunoendocrine interactions underpinning anti-tumor immunity.

The use of alpha 1 thymosin as an immunomodulator of the response against SARS-Cov2

BackgroundSince the beginning of SARS-CoV2 pandemic, the mortality rate among elderly patients (60–90 years) has been around 50%, so age has been a determining factor of a worse COVID-19 prognosis. Associated with age, the thymic function involution and depletion plays an important role, that could be related to a dysregulated and ineffective innate and adaptive immune response against SARS-CoV2. Our study aims to further in vitro effect of human Thymosin-alpha-1 (α1Thy) treatment on the immune system in population groups with different thymic function levels in the scenario of SARS-CoV2 infection.ResultsActivation markers such as CD40, CD80 and TIM-3 were upregulated in α1Thy presence, especially in plasmacytoid dendritic cells (pDCs) and, with increased TNFα production was observed compared to untreated condition. Co-cultures of CD4 + and CD8 + T cells with DCs treated with α1Thy in response to SARS-CoV2 peptides showed a decrease in the cytokine production compared to the condition without α1Thy pre-treated. A decrease in CD40L activation co-receptor expression in CD8 + LTs was also observed, as well as an increase in PD1 in CD4 + TLs expression in both age groups. In fact, there are no age-related differences in the immunomodulatory effect of the hormone, and it seems that effector memory and terminally differentiated memory T lymphocyte subsets were the most actively influenced by the immunomodulatory α1Thy effect. Finally, the polyfunctionality measured in SARS-CoV2 Specific-T cells response was maintained in α1Thy presence in total and memory subpopulations CD4 + and CD8 + T-cells, despite decreased proinflammatory cytokines production.ConclusionThe hormone α1Thy could reduce, through the modulation of DCs, the amount of proinflammatory cytokines produced by T cells. Moreover, α1Thy improve lymphocyte functionality and could become a beneficial therapeutic alternative as an adjuvant in SARS-CoV2 treatment either in the acute phase after infection or reinfection. In addition, the effect on the T immune response means that α1Thy can be incorporated into the vaccination regimen, especially in the most immunologically vulnerable individuals such as the elderly.SubjectsThymosin alpha 1, Dendritic cells, SARS-CoV2-specific T cells response, Immunomodulation

Intrathymic somatotropic circuitry: consequences upon thymus involution.

Growth hormone (GH) is a classic pituitary-derived hormone crucial to body growth and metabolism. In the pituitary gland, GH production is stimulated by GH-releasing hormone and inhibited by somatostatin. GH secretion can also be induced by other peptides, such as ghrelin, which interacts with receptors present in somatotropic cells. It is well established that GH acts directly on target cells or indirectly by stimulating the production of insulin-like growth factors (IGFs), particularly IGF-1. Notably, such somatotropic circuitry is also involved in the development and function of immune cells and organs, including the thymus. Interestingly, GH, IGF-1, ghrelin, and somatostatin are expressed in the thymus in the lymphoid and microenvironmental compartments, where they stimulate the secretion of soluble factors and extracellular matrix molecules involved in the general process of intrathymic T-cell development. Clinical trials in which GH was used to treat immunocompromised patients successfully recovered thymic function. Additionally, there is evidence that the reduction in the function of the somatotropic axis is associated with age-related thymus atrophy. Treatment with GH, IGF-1 or ghrelin can restore thymopoiesis of old animals, thus in keeping with a clinical study showing that treatment with GH, associated with metformin and dehydroepiandrosterone, could induce thymus regeneration in healthy aged individuals. In conclusion, the molecules of the somatotrophic axis can be envisioned as potential therapeutic targets for thymus regeneration in age-related or pathological thymus involution.

Autoantibodies targeting type I interferons: Prevalence, mechanisms of induction, and association with viral disease susceptibility.

The type I IFN (IFN-I) system is essential to limit severe viral disease in humans. Thus, IFN-I deficiencies are associated with serious life-threatening infections. Remarkably, some rare individuals with chronic autoimmune diseases develop neutralizing autoantibodies (autoAbs) against IFN-Is thereby compromising their own innate antiviral defenses. Furthermore, the prevalence of anti-IFN-I autoAbs in apparently healthy individuals increases with age, such that ∼4% of those over 70 years old are affected. Here, I review the literature on factors that may predispose individuals to develop anti-IFN-I autoAbs, such as reduced self-tolerance caused by defects in the genes AIRE, NFKB2, and FOXP3 (among others), or by generally impaired thymus function, including thymic involution in the elderly. In addition, I discuss the hypothesis that predisposed individuals develop anti-IFN-I autoAbs following "autoimmunization" with IFN-Is generated during some acute viral infections, systemic inflammatory events, or chronic IFN-I exposure. Finally, I highlight the enhanced susceptibility that individuals with anti-IFN-I autoAbs appear to have towards viral diseases such as severe COVID-19, influenza, or herpes (e.g., varicella-zoster virus, herpes simplex virus, cytomegalovirus), as well as adverse reactions to live-attenuated vaccines. Understanding the mechanisms underlying development and consequences of anti-IFN-I autoAbs will be key to implementing effective prophylactic and therapeutic measures.

Association of T cell infiltration and morphological change of thymus gland with the aggravation of pulmonary emphysema in testosterone deficiency

Chronic obstructive pulmonary disease is an inflammatory lung disease characterized by chronic bronchitis and emphysema. Our previous study revealed that testosterone depletion induced T cell infiltration in the lungs and aggravated pulmonary emphysema in orchiectomized (ORX) mice exposed to porcine pancreatic elastase (PPE). However, the association between T cell infiltration and emphysema remains unclear. The aim of this study was to determine whether thymus and T cells are involved in the exacerbation of PPE-induced emphysema in ORX mice. The weight of thymus gland in ORX mice was significantly greater than that of sham mice. The pretreatment of anti-CD3 antibody suppressed PPE-induced thymic enlargement and T cell infiltration in the lungs in ORX mice, resulting in improved expansion of the alveolar diameter, a marker of emphysema exacerbation. These results suggest that increased thymic function due to testosterone deficiency and the associated increased pulmonary infiltration of T cells may trigger the development of emphysema.