T lymphocytes must be produced throughout life, yet the thymus, where T lymphocytes are made, exhibits accelerated atrophy with age. Even in advanced atrophy, however, the thymus remains plastic, and ...can be regenerated by appropriate stimuli. Logically, thymic atrophy is thought to reflect senescent cell death, while regeneration requires proliferation of stem or progenitor cells, although evidence is scarce. Here we use conditional reporters to show that accelerated thymic atrophy reflects contraction of complex cell projections unique to cortical epithelial cells, while regeneration requires their regrowth. Both atrophy and regeneration are independent of changes in epithelial cell number, suggesting that the size of the thymus is regulated primarily by rate-limiting morphological changes in cortical stroma, rather than by their cell death or proliferation. Our data also suggest that cortical epithelial morphology is under the control of medullary stromal signals, revealing a previously unrecognized endocrine-paracrine signaling axis in the thymus.
Summary
The thymus is the most rapidly aging tissue in the body, with progressive atrophy beginning as early as birth and not later than adolescence. Latent regenerative potential exists in the ...atrophic thymus, because certain stimuli can induce quantitative regrowth, but qualitative function of T lymphocytes produced by the regenerated organ has not been fully assessed. Using a genome‐wide computational approach, we show that accelerated thymic aging is primarily a function of stromal cells, and that while overall cellularity of the thymus can be restored, many other aspects of thymic function cannot. Medullary islet complexity and tissue‐restricted antigen expression decrease with age, representing potential mechanisms for age‐related increases in autoimmune disease, but neither of these is restored by induced regrowth, suggesting that new T cells produced by the regrown thymus will probably include more autoreactive cells. Global analysis of stromal gene expression profiles implicates widespread changes in Wnt signaling as the most significant hallmark of degeneration, changes that once again persist even at peak regrowth. Consistent with the permanent nature of age‐related molecular changes in stromal cells, induced thymic regrowth is not durable, with the regrown organ returning to an atrophic state within 2 weeks of reaching peak size. Our findings indicate that while quantitative regrowth of the thymus is achievable, the changes associated with aging persist, including potential negative implications for autoimmunity.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Although autoimmune disorders are a significant source of morbidity and mortality in older individuals, the mechanisms governing age-associated increases in susceptibility remain incompletely ...understood. Central T cell tolerance is mediated through presentation of self-antigens by cells constituting the thymic microenvironment, including epithelial cells, dendritic cells, and B cells. Medullary thymic epithelial cells (mTECs) and B cells express distinct cohorts of self-antigens, including tissue-restricted self-antigens (TRAs), such that developing T cells are tolerized to antigens from peripheral tissues. We find that expression of the TRA transcriptional regulator Aire, as well as Aire-dependent genes, declines with age in thymic B cells in mice and humans and that cell-intrinsic and cell-extrinsic mechanisms contribute to the diminished capacity of peripheral B cells to express Aire within the thymus. Our findings indicate that aging may diminish the ability of thymic B cells to tolerize T cells, revealing a potential mechanistic link between aging and autoimmunity.
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•Expression of Aire and self-antigen genes decreases with age in thymic B cells•B cell-intrinsic and B cell-extrinsic mechanisms contribute to this decline in expression•The phenotype and transcriptome of thymic B cells change with age•T-bet expression and frequency of IgG2a expression increase in aged thymic B cells
Mechanisms governing age-associated increases in autoimmunity remain elusive. Expression of Aire and downstream self-antigens by thymic B cells helps tolerize developing T cells. Cepeda et al. report age-associated declines in expression of Aire and self-antigen genes in thymic B cells concomitant with increases in T-bet and IgG2a expression.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
T lymphocytes are essential mediators of immunity that are produced by the thymus in proportion to its size. The thymus atrophies rapidly with age, resulting in progressive diminution of new T cell ...production. This decreased output is compensated by duplication of existing T cells, but it results in gradual dominance by memory T cells and decreased ability to respond to new pathogens or vaccines. Here, we show that accelerated and irreversible thymic atrophy results from stromal deficiency in the reducing enzyme catalase, leading to increased damage by hydrogen peroxide generated by aerobic metabolism. Genetic complementation of catalase in stromal cells diminished atrophy, as did chemical antioxidants, thus providing a mechanistic link between antioxidants, metabolism, and normal immune function. We propose that irreversible thymic atrophy represents a conventional aging process that is accelerated by stromal catalase deficiency in the context of an intensely anabolic (lymphoid) environment.
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•The thymus exhibits accelerated atrophy with age due to changes in stromal cells•Global transcriptome analysis reveals that stromal cells are deficient in catalase•Stromal cells showed elevated H2O2 levels and multiple hallmarks of oxidative damage•Genetic or biochemical restoration of antioxidant activity ameliorates thymic atrophy
Thymic function is essential for maintenance of immunity but decreases with age. Griffith et al. show that stromal deficiency in catalase leads to mitochondrial dysfunction and DNA damage in stromal cells and that atrophy is ameliorated by genetic complementation of catalase or biochemical antioxidants.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
BackgroundDespite numerous therapeutic options, safe and curative therapy is unavailable for most patients with chronic lymphocytic leukemia (CLL). A drawback of current therapies such as the ...anti-CD20 monoclonal antibody (mAb) rituximab is the elimination of all healthy B cells, resulting in impaired humoral immunity. We previously reported the identification of a patient-derived, CLL-binding mAb, JML-1, and identified sialic acid-binding immunoglobulin-like lectin-6 (Siglec-6) as the target of JML-1. Although little is known about Siglec-6, it appears to be an attractive target for cancer immunotherapy due to its absence on most healthy cells and tissues.MethodsWe used a target-specific approach to mine for additional patient-derived anti-Siglec-6 mAbs. To assess the therapeutic utility of targeting Siglec-6 in the context of CLL, T cell-recruiting bispecific antibodies (T-biAbs) that bind to Siglec-6 and CD3 were engineered into single-chain variable fragment–Fc and dual-affinity retargeting (DART)–Fc constructs. T-biAbs were evaluated for their activity in vitro, ex vivo, and in vivo.ResultsWe discovered the anti-Siglec-6 mAbs RC-1 and RC-2, which bind with higher affinity than JML-1 yet maintain similar specificity. Both JML-1 and RC-1 T-biAbs were effective at activating T cells and killing Siglec-6+ target cells. The RC-1 clone in the DART–Fc format was the most potent T-biAb tested and was the only anti-Siglec-6 T-biAb that eliminated Siglec-6+ primary CLL cells via autologous T cells at pathological T-to-CLL cell ratios. Tested at healthy T-to-B cell ratios, it also eliminated a Siglec-6+ fraction of primary B cells from healthy donors. The subpicomolar potency of the DART–Fc format was attributed to the reduction in the length and flexibility of the cytolytic synapse. Furthermore, the RC-1 T-biAb was effective at clearing MEC1 CLL cells in vivo and demonstrated a circulatory half-life of over 7 days.ConclusionSiglec-6-targeting T-biAbs are highly potent and specific for eliminating Siglec-6+ leukemic and healthy B cells while sparing Siglec-6− healthy B cells, suggesting a unique treatment strategy for CLL with diminished suppression of humoral immunity. Our data corroborate reports that T-biAb efficacy is dependent on synapse geometry and reveal that synapse architecture can be tuned via antibody engineering. Our fully human anti-Siglec-6 antibodies and T-biAbs have potential for cancer immunotherapy.Trial registration numberNCT00923507.
BACKGROUND On-demand therapy may offer an effective approach to the long-term management of gastro-oesophageal reflux disease (GORD) without oesophagitis.
AIM To examine the efficacy of the novel ...proton pump inhibitor esomeprazole as on-demand therapy in endoscopy-negative GORD.
PATIENTS AND METHODS Endoscopy-negative GORD patients who achieved complete resolution of heartburn after short-term esomeprazole or omeprazole treatment (n = 721) were randomized to esomeprazole 20 mg (n = 282), 40 mg (n = 293) or placebo (n = 146) on demand (maximum one dose/day) for 6 months. The primary and secondary efficacy endpoints were time to study discontinuation due to (i) unwillingness to continue and (ii) inadequate control of heartburn, respectively.
RESULTS Both doses of esomeprazole were more effective than placebo. During the 6-month period, 42% of placebo recipients discontinued treatment due to unwillingness to continue, compared with 8% and 11% of esomeprazole 20 mg and 40 mg recipients, respectively. Overall, more patients treated with esomeprazole were free from gastrointestinal symptoms after 6 months of on-demand therapy.
CONCLUSIONS Esomeprazole 20 mg was superior to placebo for on-demand treatment of GORD; a higher dose did not confer additional clinical benefit. Over 90% of patients were willing to continue on-demand treatment with esomeprazole 20 mg over a 6-month period.
Abstract
T lymphocytes develop in the thymus, where mutually inductive signaling between lymphoid progenitors and thymic stromal cells (TSCs) directs the progenitors along a well-characterized ...program of differentiation. However, the biology of the TSCs comprising the lymphopoietic thymic microenvironment remains relatively under-characterized because stromal cells are rare and difficult to isolate. Using a deconvolution technique to study gene expression essentially in situ, we previously identified a deficiency in the H202 quenching enzyme catalase (CAT) in TSCs, and found that CAT deficiency results in high H202 levels in this population, eventually leading to thymic atrophy. Our current studies address the possibility that high H202 levels serve physiological functions in TSCs in the young, steady state thymus. TSCs exhibit high basal levels of autophagy at the steady state, which is critical for self-antigen presentation and T cell selection. The mechanisms governing high basal autophagy in TSCs are unknown, however autophagy is induced by many stressors, including high H202 levels. Our data indicate that catalase overexpression targeted to mitochondria in transgenic mice (mCAT Tg) results in diminished autophagy in TSCs and causes diminished negative selection in the thymus, eventually leading to autoimmunity. The effects on negative selection in mCAT Tg mice are rescued by increased basal autophagy on the beclin 1 knock-in (Becn1F121A/F121A) background. Our results suggest that the high basal autophagy level required in TSCs for T cell negative selection is promoted by physiologically low levels of catalase expression in the steady state thymus.
Abstract
The primary site for the development of T lymphocytes is the thymus, where cross-talk between thymic stromal cells (TSCs) and T cell progenitors mediates the development and maintenance of ...both populations. However, the thymus begins to atrophy relatively early in life, resulting in diminished T cell output, and corresponding immunodeficiencies in aged individuals. Our previous studies revealed that thymic stromal cells express conspicuously low levels of the peroxide quenching enzyme catalase (CAT), which results in high reactive oxygen species (ROS) levels and accumulated oxidative damage in thymic stromal cells, ultimately promoting thymic atrophy. In our current studies, we find that when catalase deficiency is complemented by overexpression targeted to mitochondria in transgenic mice (mCAT Tg), stromal function declines in young mice relative to non-transgenic littermates. TSC transcriptome analysis reveals decreased expression of tissue-restricted antigen (TRA) genes in young mCat Tg mice relative to controls. Stromal TRA expression is required for self-antigen presentation, and therefore promotes negative selection of potentially auto-reactive T cells. We propose that oxidative stress generated by low catalase levels in stromal cells promotes this key physiological function in the young, steady state thymus; in contrast however, the resulting accumulated oxidative damage ultimately impairs function in the aged thymus.
Abstract
T lymphocytes develop in the thymus, where mutually inductive signaling between lymphoid progenitors and thymic stromal cells directs the progenitors along a well-characterized program of ...differentiation. However, the biology of the stromal cells comprising the lymphopoietic thymic microenvironment remains relatively under-characterized because stromal cells are rare and difficult to isolate. Using a deconvolution technique to study gene expression essentially in situ, we previously identified a deficiency in the peroxide quenching enzyme catalase (CAT) in thymic stromal cells, and found that CAT deficiency results in high reactive oxygen (ROS) levels in this population, eventually leading to thymic atrophy. Our current studies address the possibility that high ROS levels serve physiological functions in stromal cells in the young, steady-state thymus. Autophagy is critical for self-antigen presentation and T cell selection in the thymus, and is induced by many stressors, including oxidative stress. Our preliminary data indicate that catalase overexpression targeted to mitochondria in transgenic mice (mCAT Tg) results in diminished autophagy in thymic stromal cells and causes diminished negative selection in the thymus. Our results suggest that, while accumulated oxidative damage ultimately undermines healthy thymus function, a high ROS environment in stromal cells promotes autophagy critical for stromal induction of T cell tolerance in the young, steady-state thymus.
Supported by N.I.H. grants R01AI121367 and R21AI103685
Abstract
T lymphocytes develop in the thymus, where mutually inductive signaling between lymphoid progenitors and thymic stromal cells directs the progenitors along a well-characterized program of ...differentiation. However, the biology of the stromal cells comprising the lymphopoietic thymic microenvironment remains relatively under-characterized because stromal cells are rare and difficult to isolate. Using a deconvolution technique to study gene expression essentially in situ, we previously identified a deficiency in the peroxide quenching enzyme catalase (CAT) in thymic stromal cells, and found that CAT deficiency results in high reactive oxygen (ROS) levels in this population, eventually leading to thymic atrophy. Here, we address the possibility that high ROS levels serve physiological functions in stromal cells in the young, steady state thymus. Our preliminary data indicate that when catalase deficiency is complemented by overexpression targeted to mitochondria in transgenic mice (mCAT Tg), both ROS levels and stromal function are diminished in young mice relative to non-transgenic littermates. We find evidence of diminished tissue-restricted antigen (TRA) expression and autophagy in mCAT Tg mice, both of which are critical for establishing a self-tolerant T cell repertoire. We propose that a high ROS environment in stromal cells promotes promiscuous gene expression and autophagy critical for stromal induction of T cell tolerance in the young thymus, while accumulated oxidative damage ultimately undermines healthy thymus function.
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