Insights into thymic aging and regeneration

Lipid-Laden Multilocular Cells in the Aging Thymus Are Phenotypically Heterogeneous

Intrathymic lipid-laden multilocular cells (LLMC) are known to express pro-inflammatory factors that might regulate functional activity of the thymus. However, the phenotype of age-associated intrathymic LLMC is still controversial. In this study, we evaluated LLMC density in the aging thymus and better characterized their distribution, ultrastructure and phenotype. Our results show an increased density of LLMC in the thymus from 03 to 24 months of age. Morphologically, intrathymic LLMC exhibit fibroblastoid fusiform, globular or stellate shapes and can be found in the subcapsular region as well as deeper in the parenchyma, including the perivascular area. Some parenchymal LLMC were like telocytes accumulating lipids. We identified lipid droplets with different electrondensities, lipofuscin granules and autolipophagosome-like structures, indicating heterogeneous lipid content in these cells. Autophagosome formation in intrathymic LLMC was confirmed by positive staining for beclin-1 and perilipin (PLIN), marker for lipid droplet-associated proteins. We also found LLMC in close apposition to thymic stromal cells, endothelial cells, mast cells and lymphocytes. Phenotypically, we identified intrathymic LLMC as preadipocytes (PLIN⁺PPARγ2⁺), brown adipocytes (PLIN⁺UCP1⁺), macrophages (PLIN⁺Iba-1⁺) or pericytes (PLIN⁺NG2⁺) but not epithelial cells (PLIN^- panCK⁺). These data indicate that intrathymic LLMC are already present in the young thymus and their density significantly increases with age. We also suggest that LLMC, which are morphologically distinct, establish direct contact with lymphocytes and interact with stromal cells. Finally, we evidence that intrathymic LLMC correspond to not only one but to distinct cell types accumulating lipids.

Efficient in vitro generation of functional thymic epithelial progenitors from human embryonic stem cells

Thymic epithelial cells (TECs) are the major components of the thymic microenvironment for T cell development. TECs are derived from thymic epithelial progenitors (TEPs). It has been reported that human ESCs (hESCs) can be directed to differentiate into TEPs in vitro. However, the efficiency for the differentiation is low. Furthermore, transplantation of hESC-TEPs in mice only resulted in a very low level of human T cell development from co-transplanted human hematopoietic precursors. We show here that we have developed a novel protocol to efficiently induce the differentiation of hESCs into TEPs in vitro. When transplanted into mice, hESC-TEPs develop into TECs and form a thymic architecture. Most importantly, the hESC-TECs support the long-term development of functional mouse T cells or a higher level of human T cell development from co-transplanted human hematopoietic precursors. The hESC-TEPs may provide a new approach to prevent or treat patients with T cell immunodeficiency.

A high density of tertiary lymphoid structure B cells in lung tumors is associated with increased CD4+ T cell receptor repertoire clonality

T and B cell receptor (TCR and BCR, respectively) Vβ or immunoglobulin heavy chain complementarity-determining region 3 sequencing allows monitoring of repertoire changes through recognition, clonal expansion, affinity maturation, and T or B cell activation in response to antigen. TCR and BCR repertoire analysis can advance understanding of antitumor immune responses in the tumor microenvironment. TCR and BCR repertoires of sorted CD4⁺, CD8⁺ or CD19⁺ cells in tumor, non-tumoral distant tissue (NT), and peripheral compartments (blood/draining lymph node [P]) from 47 non-small cell lung cancer (NSCLC) patients (age_median = 68 y) were sequenced. The clonotype spectra were assessed among different tissues and correlated with clinical and immunological parameters. In all tissues, CD4⁺ and CD8⁺ TCR repertoires had greater clonality relative to CD19⁺ BCR. CD4⁺ T cells exhibited greater clonality in NT compared to tumor (p = 0.002) and P (p < 0.001), concentrated among older patients (age > 68). Younger patients exhibited greater CD4⁺ T cell diversity in P compared to older patients (p = 0.05), and greater CD4⁺ T cell clonality in tumor relative to P (p < 0.001), with fewer shared clonotypes between tumor and P than older patients (p = 0.04). More interestingly, greater CD4⁺ and CD8⁺ T cell clonality in tumor and P, respectively (both p = 0.05), correlated with high density of tumor-associated tertiary lymphoid structure (TLS) B cells, a biomarker of higher overall survival in NSCLC. Results indicate distinct adaptive immune responses in NSCLC, where peripheral T cell diversity is modulated by age, and tumor T cell clonal expansion is favored by the presence of TLSs in the tumor microenvironment.

Menarche increases relapse risk in pediatric multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) predominantly affects women with a sex ratio of 3:1 in contrast with a 1:1 sex ratio seen in pre-pubertal onset. Thus, puberty may influence MS risk differentially in males and females. How puberty may be associated with MS clinical features and disease course remains unknown.

OBJECTIVE

The objective of this paper is to determine the association of menarche with disease course in girls with MS.

METHODS

This is a longitudinal retrospective study from the UCSF Regional Pediatric MS Center database. We categorized patients by time of disease onset: pre-menarche, peri-menarche and post-menarche. Poisson regression models were used for within-subject relapse analyses offset by follow-up time.

RESULTS

Seventy-six girls were included (pre-menarche onset = 17; peri-menarche onset = 9; post-menarche onset = 50). Age of menarche was similar in all groups (Kruskal-Wallis p = 0.19). Relapse rate was the same in all three groups during the first two years of follow-up. In girls with follow-up overlapping at least two time periods, within-subject analyses showed increased relapses during the peri-menarche compared to post-menarche period (adjusted IRR = 8.5, 95% CI 2.5-28.7, p = 0.001).

CONCLUSION

Pubertal status may influence MS course at least in female patients. Understanding how puberty influences MS clinical features may offer new insights into important factors regulating disease processes.

The expansion of thymopoiesis in neonatal mice is dependent on expression of high mobility group a 2 protein (Hmga2)

Cell number in the mouse thymus increases steadily during the first two weeks after birth. It then plateaus and begins to decline by seven weeks after birth. The factors governing these dramatic changes in cell production are not well understood. The data herein correlate levels of High mobility group A 2 protein (Hmga2) expression with these temporal changes in thymopoiesis. Hmga2 is expressed at high levels in murine fetal and neonatal early T cell progenitors (ETP), which are the most immature intrathymic precursors, and becomes almost undetectable in these progenitors after 5 weeks of age. Hmga2 expression is critical for the initial, exponential expansion of thymopoiesis, as Hmga2 deficient mice have a deficit of ETPs within days after birth, and total thymocyte number is repressed compared to wild type littermates. Finally, our data raise the possibility that similar events occur in humans, because Hmga2 expression is high in human fetal thymic progenitors and falls in these cells during early infancy.

Premature thymic involution is independent of structural plasticity of the thymic stroma

The thymus is the organ devoted to T-cell production. The thymus undergoes multiple rounds of atrophy and redevelopment before degenerating with age in a process known as involution. This process is poorly understood, despite the influence the phenomenon has on peripheral T-cell numbers. Here we have investigated the FVB/N mouse strain, which displays premature thymic involution. We find multiple architectural and cellular features that precede thymic involution, including disruption of the epithelial–endothelial relationship and a progressive loss of pro-T cells. The architectural features, reminiscent of the human thymus, are intrinsic to the nonhematopoietic compartment and are neither necessary nor sufficient for thymic involution. By contrast, the loss of pro-T cells is intrinsic to the hematopoietic compartment, and is sufficient to drive premature involution. These results identify pro-T-cell loss as the main driver of premature thymic involution, and highlight the plasticity of the thymic stroma, capable of maintaining function across diverse interstrain architectures.

Concise review: engineering the fusion of cytokines for the modulation of immune cellular responses in cancer and autoimmune disorders

As our understanding of the basic precepts of immunobiology continue to advance at a rapid pace, translating such discoveries into meaningful therapies for patients has proved challenging. This is especially apparent in the use of cytokine-based immunotherapies for cancer. Unanticipated and serious side effects, as well as low objective response rates seen in clinical trials, have dealt setbacks to the field. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and common γ-chain (γ-c) interleukins are cytokines that have been used as stand-alone immunotherapies with moderate success. Our group has found that the fusion of GM-CSF to members of γ-c interleukins results in the generation of novel proteins with unique signaling properties and unheralded biological effects. These fusion proteins, termed GIFT (GM-CSF interleukin fusion transgenes) fusokines, are the result of combining GM-CSF and a γ-c interleukin into a single, bifunctional polypeptide. In our experience, GIFT fusokines often confer immune cells with a gain of function that cannot be explained by the mere sum of their constituent moieties. They act as bispecific ligands, coupling activated GM-CSF and interleukin receptors together to drive unique downstream signaling events. The synergy that arises from these fusions has shown great promise in its ability to modulate the immune response and overcome maladaptive biological processes that underlie diseases such as cancer and autoimmune conditions. In this review, we discuss the ways in which the GIFT fusokines are able to alter the immune response, particularly in disease states, with a special emphasis on how these novel molecules may be translated into effective therapies in the clinical setting.

Ghrelin augments murine T-cell proliferation by activation of the phosphatidylinositol-3-kinase, extracellular signal-regulated kinase and protein kinase C signaling pathways

Thymic atrophy occurs during normal aging, and is accelerated by exposure to chronic stressors that elevate glucocorticoid levels and impair the naïve T cell output. The orexigenic hormone ghrelin was recently shown to attenuate age-associated thymic atrophy. Here, we report that ghrelin enhances the proliferation of murine CD4+ primary T cells and a CD4+ T-cell line. Ghrelin induced activation of the ERK1/2 and Akt signaling pathways, via upstream activation of phosphatidylinositol-3-kinase and protein kinase C, to enhance T-cell proliferation. Moreover, ghrelin induced expression of the cell cycle proteins cyclin D1, cyclin E, cyclin-dependent kinase 2 (CDK2) and retinoblastoma phosphorylation. Finally, ghrelin activated the above-mentioned signaling pathways and stimulated thymocyte proliferation in young and older mice in vivo.

Sex steroid blockade enhances thymopoiesis by modulating Notch signaling

Velardi et al. show that sex steroids regulate thymopoiesis by directly modulating Notch signaling, and provide a novel clinical strategy to boost immune regeneration.

Paradoxical to its importance for generating a diverse T cell repertoire, thymic function progressively declines throughout life. This process has been at least partially attributed to the effects of sex steroids, and their removal promotes enhanced thymopoiesis and recovery from immune injury. We show that one mechanism by which sex steroids influence thymopoiesis is through direct inhibition in cortical thymic epithelial cells (cTECs) of Delta-like 4 (Dll4), a Notch ligand crucial for the commitment and differentiation of T cell progenitors in a dose-dependent manner. Consistent with this, sex steroid ablation (SSA) led to increased expression of Dll4 and its downstream targets. Importantly, SSA induced by luteinizing hormone-releasing hormone (LHRH) receptor antagonism bypassed the surge in sex steroids caused by LHRH agonists, the gold standard for clinical ablation of sex steroids, thereby facilitating increased Dll4 expression and more rapid promotion of thymopoiesis. Collectively, these findings not only reveal a novel mechanism underlying improved thymic regeneration upon SSA but also offer an improved clinical strategy for successfully boosting immune function.

Three different patterns of CD4 recovery in a cohort of Chinese HIV patients following antiretroviral therapy - a five-year observational study

To explore the heterogeneity of CD4 responses following highly active antiretroviral therapy, the patterns of CD4 recovery of HIV-1-infected Chinese patients who have been on their first antiretroviral regimen for ≥5 years were analysed. The CD4 trajectories were traced, smoothed and differentiated into three defined profiles. Half (56.3%) were 'satisfactory responders', with CD4 gain of >100 cells/μL and a peak of >350 cells/μL, plateauing before the end of Year 5. Thirty-three (24.4%) were 'continuing responders' whose CD4 rise persisted at Year 4-5. The remaining 26 (19.3%) were 'poor responders'. Presentation with AIDS before therapy was common not just among 'poor' but also paradoxically the 'continuing' responders. While a majority had responded well to antiretroviral therapy, older patients and those with AIDS diagnosis before initiation of therapy may never achieve a satisfactory level even with effective treatment. Categorization of HIV patients by their CD4 trajectory may support the prediction of immunological outcome over time, and ultimately inform treatment choices.

Response of thymus lymphocytes to streptozotocin-induced diabetes and exogenous vitamin C administration in rats

Diabetes causes oxidative stress, which in turn generates excessive free radicals resulting in cellular damage. Vitamin C is an antioxidant that protects tissues and organs from oxidative stress. The thymus is one of the most important lymphoid organs, which regulates T-lymphocyte proliferation and maturation. The aim of this study is to investigate the protective effects of vitamin C on the thymus of streptozotocin (STZ)-induced diabetic rats. The mitotic activity and cell integrity of thymic lymphocytes were explored. Wistar Albino rats were divided into three groups: control (Group 1), STZ-diabetes (Group 2) and vitamin C-treated STZ-diabetics (Group 3). Rats received a single intraperitoneal injection of 45 mg/kg STZ to induce diabetes. Vitamin C (20 mg/kg) was administered intragastrically. Semithin and ultrathin sections were examined under a light or an electron microscope, respectively. Considerable numbers of mitotic lymphocytes were observed in the thymus of control rats. In the diabetic rats, however, numbers of mitotic lymphocytes decreased to ∼57% of controls, and cell division abnormalities were observed. Additionally, diabetic rats showed degeneration in the structure of the thymus including trabecular thickening, accumulation of lipid vacuoles, heterochromatic nuclei and loss of mitochondrial cristae. Degradation of medullar and cortical integrity was also detected. In the vitamin C-treated STZ-diabetic group, the structure of the thymus and mitotic activity of the lymphocytes were similar to the control group. These results suggest that vitamin C protects the thymus against injury caused by diabetes and restores thymocyte mitotic activity.

Diversity and clonal selection in the human T-cell repertoire

T-cell receptor (TCR) diversity, a prerequisite for immune system recognition of the universe of foreign antigens, is generated in the first two decades of life in the thymus and then persists to an unknown extent through life via homeostatic proliferation of naïve T cells. We have used next-generation sequencing and nonparametric statistical analysis to estimate a lower bound for the total number of different TCR beta (TCRB) sequences in human repertoires. We arrived at surprisingly high minimal estimates of 100 million unique TCRB sequences in naïve CD4 and CD8 T-cell repertoires of young adults. Naïve repertoire richness modestly declined two- to fivefold in healthy elderly. Repertoire richness contraction with age was even less pronounced for memory CD4 and CD8 T cells. In contrast, age had a major impact on the inequality of clonal sizes, as estimated by a modified Gini-Simpson index clonality score. In particular, large naïve T-cell clones that were distinct from memory clones were found in the repertoires of elderly individuals, indicating uneven homeostatic proliferation without development of a memory cell phenotype. Our results suggest that a highly diverse repertoire is maintained despite thymic involution; however, peripheral fitness selection of T cells leads to repertoire perturbations that can influence the immune response in the elderly.

Thyrotropin acts as a T-cell developmental factor in mice and humans

Using gene expression profiling, we detected differential thyrotropin receptor (TSH-R) expression during human T-cell development in the thymus. This expression pattern indicated a potential role for the TSH-R within the thymus, independent of its function in the thyroid gland. Here, we demonstrate that TSH-R expression is thymus-specific within the immune system. TSH was able to bind and activate the TSH-R present on thymocytes, thereby activating calcium signaling and cyclic adenosine monophosphate signaling pathways. Mice lacking functional TSH-R expression (hyt/hyt mice) were shown to have lower frequencies of DP and SP thymocytes compared to their heterozygous littermates. Moreover, addition of TSH to co-cultures of human thymocytes enhanced T-cell development. Thus, TSH acts as a previously unrecognized growth factor for developing T cells, with potential clinical use to enhance thymic output and thereby the functional T-cell repertoire in the periphery. The direct effects of TSH on thymocytes may also explain the thus far enigmatic thymic hyperplasia in Graves' disease.

Neuro-immune modulation of the thymus microenvironment (review)

The thymus is the primary site for T-cell lympho-poiesis. Its function includes the maturation and selection of antigen specific T cells and selective release of these cells to the periphery. These highly complex processes require precise parenchymal organization and compartmentation where a plethora of signalling pathways occur, performing strict control on the maturation and selection processes of T lymphocytes. In this review, the main morphological characteristics of the thymus microenvironment, with particular emphasis on nerve fibers and neuropeptides were assessed, as both are responsible for neuro-immune‑modulation functions. Among several neurotransmitters that affect thymus function, we highlight the dopaminergic system as only recently has its importance on thymus function and lymphocyte physiology come to light.

Meis1 is required for the maintenance of postnatal thymic epithelial cells

Most epithelial tissues retain stem/progenitor cells to maintain homeostasis of the adult tissues; however, the existence of a thymic epithelial cell (TEC) progenitor capable of maintaining homeostasis of the postnatal thymus remains unclear. Here, we show that a cell population expressing high levels of Meis1, a homeodomain transcription factor, is enriched in TECs with an immature cellular phenotype. These TECs selectively express genes involved in embryonic thymic organogenesis and epithelial stem cell maintenance, and also have the potential to proliferate and differentiate into mature TEC populations. Furthermore, postnatal inactivation of Meis1 in TECs caused disorganization of the thymic architecture, which ultimately leads to premature disappearance of the thymus. There was an age-associated reduction in the proportion of the TEC population expressing high levels of Meis1, which may also be related to thymic involution. These findings indicate that Meis1 is potentially involved in the maintenance of postnatal TECs with progenitor activity that is required for homeostasis of the postnatal thymus.

Thymus and aging: morphological, radiological, and functional overview

Aging is a continuous process that induces many alterations in the cytoarchitecture of different organs and systems both in humans and animals. Moreover, it is associated with increased susceptibility to infectious, autoimmune, and neoplastic processes. The thymus is a primary lymphoid organ responsible for the production of immunocompetent T cells and, with aging, it atrophies and declines in functions. Universality of thymic involution in all species possessing thymus, including human, indicates it as a long-standing evolutionary event. Although it is accepted that many factors contribute to age-associated thymic involution, little is known about the mechanisms involved in the process. The exact time point of the initiation is not well defined. To address the issue, we report the exact age of thymus throughout the review so that readers can have a nicely pictured synoptic view of the process. Focusing our attention on the different stages of the development of the thymus gland (natal, postnatal, adult, and old), we describe chronologically the morphological changes of the gland. We report that the thymic morphology and cell types are evolutionarily preserved in several vertebrate species. This finding is important in understanding the similar problems caused by senescence and other diseases. Another point that we considered very important is to indicate the assessment of the thymus through radiological images to highlight its variability in shape, size, and anatomical conformation.

Mechanisms shaping the naïve T cell repertoire in the elderly - thymic involution or peripheral homeostatic proliferation?

The ability of the human immune system to repel infections is drastically diminished with age. Elderly individuals are more susceptible to new threats and are less able to control endogenous infections. The thymus, which is the sole source of new T cells, has been proposed as a target for regenerative efforts to improve immune competence, as thymic activity is dramatically reduced after puberty. In this review, we review the role of the thymus in the maintenance of T cell homeostasis throughout life and contrast the differences in mice and humans. We propose that in humans, lack of thymic T cell generation does not explain a decline in T cell receptor diversity nor would thymic rejuvenation restore diversity. Initial studies using next generation sequencing are beginning to establish lower boundaries of T cell receptor diversity. With increasing sequencing depth and the development of new statistical models, we are now in the position to test this model and to assess the impact of age on T cell diversity and clonality.

Chemical castration of melanoma patients does not increase the frequency of tumor-specific CD4 and CD8 T cells after peptide vaccination

Peptide vaccination against tumor-associated antigens remains one of the most common methods of immunization in cancer vaccine clinical trials. Although peptide vaccination has been reported to increase circulating antigen-specific T-cells, they have had limited clinical efficacy and there is a necessity to increase their capacity to generate strong antitumor responses. We sought to improve the clinical efficacy of peptide-based vaccines in cancer immunotherapy of metastatic melanoma using a LHRH agonist (leuprolide) as adjuvant. Seventy HLA-A*0201 stage IIb-IV melanoma patients were vaccinated with class I HLA-A*0201-restricted gp100209-2M peptide and stratified for HLA-DP4 restriction. HLA-DP4 patients were also vaccinated with class II HLA-DP4-restricted MAGE-3243-258 peptide. Patients from both groups were randomized to receive 2 doses of leuprolide or not. Here we report the increase in PBMC TREC levels at week 24 after peptide vaccination, which was independent of the leuprolide treatment. This change was mirrored by a small increase in the TREC-enriched CD8CD45RAROCD27CD103, but not the TREC-enriched CD4CD45RAROCD31 T-cell population. Serum concentration of 2 important factors for thymopoiesis was measured: insulin growth factor 1 (IGF-1) levels were not changed, whereas a moderate increase in IL-7 levels was noted in the sera of all patients 6 weeks after vaccination. Increased expression of CD127 (IL-7 receptor-α) at week 24, compared with baseline, was only seen in the CD8CD45RAROCD27CD103 T-cell population. Our results suggest that leuprolide has no effect on thymic output when used as peptide vaccine adjuvant, but IFA-based peptide vaccination may unexpectedly affect the thymus by increasing thymic output of new T cells.

Immunosenescence and immune response in organ transplantation

The immune system undergoes a complex and continuous remodeling with aging. Immunosenescence results into both quantitative and qualitative changes of specific cellular subpopulations that have major impact on allorecognition and alloresponse, and consequently on graft rejection and tolerance. Here, we are going to review the immunological changes associated with the aging process relevant for transplantation. Interventions to selectively target changes associated with the senescence process seem promising therapeutic strategies to improve transplantation outcome.

The effect of age on thymic function

Age-related regression of the thymus is associated with a decline in naïve T cell output. This is thought to contribute to the reduction in T cell diversity seen in older individuals and linked with increased susceptibility to infection, autoimmune disease, and cancer. Thymic involution is one of the most dramatic and ubiquitous changes seen in the aging immune system, but the mechanisms which underlying this process are poorly understood. However, a picture is emerging, implicating the involvement of both extrinsic and intrinsic factors. In this review we assess the role of the thymic microenvironment as a potential target that regulates thymic involution, question whether thymocyte development in the aged thymus is functionally impaired, and explore the kinetics of thymic involution.

Perspectives on immunotherapy in prostate cancer and solid tumors: where is the future?

The goals of any cancer therapy are to improve disease control, palliate pain and improve overall survival. We are fortunate to have in our cancer armamentarium two new immune-directed therapies which not only impact on disease control but also on overall survival. The first, sipuleucel-T, a cellular-based vaccine, was approved for prostate cancer and was shown to be safe with minimal toxicity. The second, ipilimumab, a monoclonal antibody directed to an immunologic checkpoint molecule, showed a survival benefit in patients with advanced melanoma. Benefit appeared to correlate in some cases with the development of autoimmune events, signaling that the immune system is in overdrive against the cancer. Where we are and where we will likely go are the topics to be discussed in this review.

Ovarian hormone withdrawal in prepubertal developmental stage does not prevent thymic involution in rats

The study was undertaken to assess the effects of ovarian hormone withdrawal in prepubertal age on thymopoiesis in 2- (young) and 11-month-old (middle-aged) rats. In ovariectomized (Ox) rats, irrespective of age, thymic weight and cellularity were greater than in age-matched controls, but the values of both parameters exhibited the age-related decline. In addition, although thymopoietic efficiency was increased in both groups of Ox rats when compared with age-matched controls, thymopoiesis exhibited the age-related decline mirrored in the lower numbers of both CD4+ and CD8+ recent thymic emigrants in peripheral blood. This reflected the prethymic changes affecting bone marrow progenitor generation/entry and the thymic alterations encompassing the impaired progenitor progression through early pre-T-cell receptor developmental stages (defined by CD45RC/CD2 expression) and, possibly, a more pronounced decrease in the proliferation of the most mature thymocytes. Apart from the changes at thymocyte level, in Ox rats the age-related alterations in thymic stroma (substantiated in a prominent loss of thymic epithelial cells) were registered. Ovariectomy-induced changes in thymic lymphoid and epithelial component, most probably, influenced each other leading to the increase in thymic expression of interleukin-6 and interleukin-7 mRNAs along with time after ovariectomy. Collectively, the study showed that the withdrawal of ovarian hormones in prepubertal age increases the efficiency of thymopoiesis in young adult rats, but does not prevent decline in thymopoiesis occurring with age.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Zinc: dietary intake and impact of supplementation on immune function in elderly

The diet in the elderly does not provide a sufficient level of nutrients needed to maintain an adequate healthy status leading to micronutrient deficiencies and impaired immune response with subsequent development of degenerative diseases. Nutrient "zinc" is a relevant micronutrient involved in maintaining a good integrity of many body homeostatic mechanisms, including immune efficiency, owing to its requirement for the biological activity of many enzymes, proteins and for cellular proliferation and genomic stability. Old people aged 60-65 years and older have zinc intakes below 50% of the recommended daily allowance on a given day. Many causes can be involved: among them, altered intestinal absorption, inadequate mastication, psychosocial factors, drugs interactions, altered subcellular processes (zinc transporters (Zip and ZnT family), metallothioneins, divalent metal transporter-1). Zinc supplementation may remodel the immune alterations in elderly leading to healthy ageing. Several zinc trials have been carried out with contradictory data, perhaps due to incorrect choice of an effective zinc supplementation in old subjects showing subsequent zinc toxic effects on immunity. Old subjects with specific IL-6 polymorphism (GG allele carriers; named C-) are more prone for zinc supplementation than the entire old population, in whom correct dietary habits with foods containing zinc (Mediterranean diet) may be sufficient in restoring zinc deficiency and impaired immune response. We summarise the main causes of low zinc dietary intake in elderly reporting an update on the impact of zinc supplementation upon the immune response also on the basis of individual IL-6 polymorphism.

Ultrasound measurement of the transverse diameter of the fetal thymus in pregnancies complicated by the preterm prelabor rupture of membranes

PURPOSE

To determine whether the measurement of the transverse diameter of the fetal thymus is of value in the identification of either histologic chorioamnionitis or funisitis in pregnancies complicated by preterm prelabor rupture of membranes (PPROM).

METHODS

The transverse diameter of the fetal thymus was measured in 216 fetuses from PPROM pregnancies. A small thymus was defined as a transverse thymic diameter below the fifth percentile according to a previously published nomogram. The placenta, the fetal membranes, and the umbilical cord were assessed for the presence of inflammation.

RESULTS

A small thymus was identified in 69% (150/216) of fetuses. A small thymus was present in 80% (106/133) and 88% (36/41) of women with histologic chorioamnionitis or funisitis, respectively. The presence of a small thymus had a sensitivity of 79%, specificity of 47%, positive predictive value of 71%, negative predictive value of 59% for the identification of chorioamnionitis (p < 0.0001; odds ratio 3.5) and a sensitivity of 88%, specificity of 35%, positive predictive value of 24%, and negative predictive value of 92% in the identification of funisitis (p = 0.004; odds ratio 4.4).

CONCLUSIONS

The sonographic finding of a small thymus is a sensitive indicator of histologic chorioamnionitis or funisitis; low specificity excludes it as a possible clinical implication in the management of PPROM pregnancies.

Medullary thymic epithelial cells, the indispensable player in central tolerance

Crosstalk between thymocytes and thymic epithelial cells is critical for T cell development and the establishment of central tolerance. Medullary thymic epithelial cells (mTECs) play important roles in the late stage of T cell development, especially negative selection and Treg generation. The function of mTECs is highly dependent on their characteristic features such as ectopic expression of peripheral tissue restricted antigens (TRAs) and their master regulator-autoimmune regulator (Aire), expression of various chemokines and cytokines. In this review, we summarize the current understanding of cellular and molecular mechanisms of mTEC development and its functions in T cell development and the establishment of central tolerance. The open questions in this field are also discussed. Understanding the function and underlying mechanisms of mTECs will contribute to the better control of autoimmune diseases and the improvement of immune reconstitution during aging or after infection, chemotherapy or radiotherapy.

Understanding the immune response to seasonal influenza vaccination in older adults: a systems biology approach

Annual vaccination against seasonal influenza is recommended to decrease disease-related mortality and morbidity. However, one population that responds suboptimally to influenza vaccine is adults over the age of 65 years. The natural aging process is associated with a complex deterioration of multiple components of the host immune system. Research into this phenomenon, known as immunosenescence, has shown that aging alters both the innate and adaptive branches of the immune system. The intricate mechanisms involved in immune response to influenza vaccine, and how these responses are altered with age, have led us to adopt a more encompassing systems biology approach to understand exactly why the response to vaccination diminishes with age. Here, the authors review what changes occur with immunosenescence, and some immunogenetic factors that influence response, and outline the systems biology approach to understand the immune response to seasonal influenza vaccination in older adults.

Does senescence affect lymph node number and morphology? A systematic review

BACKGROUND

Immunosenescence may contribute to an observed increase in infections and specific cancers in the elderly. Lymph nodes play a key role in the body's immune system. A systematic review was undertaken to investigate the effects of senescence on lymph node number and morphology.

METHODS

Electronic databases Ovid MEDLINE, Embase and Google Scholar were searched for relevant articles examining normal lymph node number and morphology with senescence. Data on lymph node number, gross anatomy and histo-architecture were collated and analysed.

RESULTS

A total of 20 articles (15 human and 5 animal studies) were eligible for inclusion; many were limited by poorly standardized methods and relatively small sample sizes. However, there is evidence to suggest both a decrease in lymph node number and histological lymph node degeneration with senescence, at least in some lymph node basins. Degenerative changes include loss of lymphoid tissue from both the cortex and the medulla of lymph nodes, a reduction in the number and size of germinal centres, and changes such as hyalinization, fibrosis, fat deposition, a decrease in high endothelial venules and 'transparency'.

CONCLUSION

In this first systematic review to examine changes in lymph nodes with senescence, evidence was accrued to suggest a decline in lymph node number and morphological degeneration in older age groups. These changes might adversely affect immune function and the prognosis of infections and selected cancers in the elderly. Further research is required to confirm these morphological changes and to explore their potential immunological and functional effects.

Targeting thymic epithelia AR enhances T-cell reconstitution and bone marrow transplant grafting efficacy

Although thymic involution has been linked to the increased testosterone in males after puberty, its detailed mechanism and clinical application related to T-cell reconstitution in bone marrow transplantation (BMT) remain unclear. By performing studies with reciprocal BMT and cell-specific androgen receptor (AR) knockout mice, we found that AR in thymic epithelial cells, but not thymocytes or fibroblasts, played a more critical role to determine thymic cellularity. Further dissecting the mechanism using cell-specific thymic epithelial cell-AR knockout mice bearing T-cell receptor transgene revealed that elevating thymocyte survival was due to the enhancement of positive selection resulting in increased positively selected T-cells in both male and female mice. Targeting AR, instead of androgens, either via genetic knockout of thymic epithelial AR or using an AR-degradation enhancer (ASC-J9®), led to increased BMT grafting efficacy, which may provide a new therapeutic approach to boost T-cell reconstitution in the future.

The polyfunctionality of human memory CD8+ T cells elicited by acute and chronic virus infections is not influenced by age

As humans age, they experience a progressive loss of thymic function and a corresponding shift in the makeup of the circulating CD8+ T cell population from naïve to memory phenotype. These alterations are believed to result in impaired CD8+ T cell responses in older individuals; however, evidence that these global changes impact virus-specific CD8+ T cell immunity in the elderly is lacking. To gain further insight into the functionality of virus-specific CD8+ T cells in older individuals, we interrogated a cohort of individuals who were acutely infected with West Nile virus (WNV) and chronically infected with Epstein Barr virus (EBV) and Cytomegalovirus (CMV). The cohort was stratified into young (<40 yrs), middle-aged (41-59 yrs) and aged (>60 yrs) groups. In the aged cohort, the CD8+ T cell compartment displayed a marked reduction in the frequency of naïve CD8+ T cells and increased frequencies of CD8+ T cells that expressed CD57 and lacked CD28, as previously described. However, we did not observe an influence of age on either the frequency of virus-specific CD8+ T cells within the circulating pool nor their functionality (based on the production of IFNγ, TNFα, IL2, Granzyme B, Perforin and mobilization of CD107a). We did note that CD8+ T cells specific for WNV, CMV or EBV displayed distinct functional profiles, but these differences were unrelated to age. Collectively, these data fail to support the hypothesis that immunosenescence leads to defective CD8+ T cell immunity and suggest that it should be possible to develop CD8+ T cell vaccines to protect aged individuals from infections with novel emerging viruses.

Pathogenesis of pediatric multiple sclerosis

Onset of multiple sclerosis in childhood occurs in 3-5% of patients. There is limited, but growing knowledge about the underlying pathobiology of pediatric MS. It is crucial to better understand this area in order to address central questions in the field: 1) Can pediatric multiple sclerosis inform us about factors related to disease initiation and propagation? 2) What are the biomarkers of disease course in pediatric multiple sclerosis; 3) Does pediatric multiple sclerosis pathogenesis differ from adult-onset multiple sclerosis; 4) How can we optimize treatment in pediatric demyelinating diseases? 5) Can pediatric multiple sclerosis provide insights into the environmental risk factors for multiple sclerosis in general? Here we review the current knowledge of the pathogenesis of multiple sclerosis in children, and address the five questions raised above.

Changes in primary lymphoid organs with aging

Aging is associated with decreased immune function that leads to increased morbidity and mortality in the elderly. Immune senescence is accompanied by age-related changes in two primary lymphoid organs, bone marrow and thymus, that result in decreased production and function of B and T lymphocytes. In bone marrow, hematopoietic stem cells exhibit reduced self-renewal potential, increased skewing toward myelopoiesis, and decreased production of lymphocytes with aging. These functional sequelae of aging are caused in part by increased oxidative stress, inflammation, adipocyte differentiation, and disruption of hypoxic osteoblastic niches. In thymus, aging is associated with tissue involution, exhibited by a disorganization of the thymic epithelial cell architecture and increased adiposity. This dysregulation correlates with a loss of stroma-thymocyte 'cross-talk', resulting in decreased export of naïve T cells. Mounting evidence argues that with aging, thymic inflammation, systemic stress, local Foxn1 and keratinocyte growth factor expression, and sex steroid levels play critical roles in actively driving thymic involution and overall adaptive immune senescence across the lifespan. With a better understanding of the complex mechanisms and pathways that mediate bone marrow and thymus involution with aging, potential increases for the development of safe and effective interventions to prevent or restore loss of immune function with aging.

Immune reconstitution after anti-thymocyte globulin-conditioned hematopoietic cell transplantation

BACKGROUND AIMS

Anti-thymocyte globulin (ATG) is being used increasingly to prevent graft-versus-host disease (GvHD); however, its impact on immune reconstitution is relatively unknown. We (i) studied immune reconstitution after ATG-conditioned hematopoietic cell transplantation (HCT), (ii) determined the factors influencing the reconstitution, and (iii) compared it with non-ATG-conditioned HCT.

METHODS

Immune cell subset counts were determined at 1-24 months post-transplant in 125 HCT recipients who received ATG during conditioning. Subset counts were also determined in 46 non-ATG-conditioned patients (similarly treated).

RESULTS

(i) Reconstitution after ATG-conditioned HCT was fast for innate immune cells, intermediate for B cells and CD8 T cells, and very slow for CD4 T cells and invariant natural killer T (iNKT) (iNKT) cells. (ii) Faster reconstitution after ATG-conditioned HCT was associated with a higher number of cells of the same subset transferred with the graft in the case of memory B cells, naive CD4 T cells, naive CD8 T cells, iNKT cells and myeloid dendritic cells; lower recipient age in the case of naive CD4 T cells and naive CD8 T cells; cytomegalovirus recipient seropositivity in the case of memory/effector T cells; an absence of GvHD in the case of naive B cells; lower ATG serum levels in the case of most T-cell subsets, including iNKT cells; and higher ATG levels in the case of NK cells and B cells. (iii) Compared with non-ATG-conditioned HCT, reconstitution after ATG-conditioned HCT was slower for CD4 T cells, and faster for NK cells and B cells.

CONCLUSIONS

ATG worsens the reconstitution of CD4 T cells but improves the reconstitution of NK and B cells.

Aging and neoteny in the B lineage

Aging and the physiologic decline of tissues and cells were once thought to be irreversible. However, recent studies suggest that various tissues, especially parts of the hematopoietic system, can be rejuvenated. Here we review potential mechanisms for this process and how they may be used to reverse age-related disorders and aging in general. We propose the novel hypothesis that altering the homeostatic process during cellular depletion can reverse aging in the hematopoietic system.

Deletion of FoxN1 in the thymic medullary epithelium reduces peripheral T cell responses to infection and mimics changes of aging

Aging increases susceptibility to infection, in part because thymic involution culminates in reduced naïve T-lymphocyte output. Thymic epithelial cells (TECs) are critical to ensure normal maturation of thymocytes and production of peripheral T cells. The forkhead-class transcription factor, encoded by FoxN1, regulates development, differentiation, and function of TECs, both in the prenatal and postnatal thymus. We recently showed that expression of FoxN1, by keratin 14 (K14)-expressing epithelial cells is essential for maintenance of thymic medullary architecture, and deletion of FoxN1 in K14 promoter-driven TECs inhibited development of mature TECs and reduced the number of total thymocytes. These findings are reminiscent of changes observed during normal thymic aging. In the current report, we compared the effects of K14-driven FoxN1 deletion on peripheral T cell function in response to influenza virus infection with those associated with normal aging in a mouse model. FoxN1-deleted mice had reduced numbers of peripheral CD62L+CD44− naïve T-cells. In addition, during influenza infection, these animals had reduced antigen-specific CD8+ T-cell and IgG responses to influenza virus, combined with increased lung injury, weight loss and mortality. These findings paralleled those observed in aged wild type mice, providing the first evidence that K14-mediated FoxN1 deletion causes changes in T-cell function that mimic those in aging during an immune response to challenge with an infectious agent.

Effects of subchronic inhalation exposure to ethyl tertiary butyl ether on splenocytes in mice

Ethyl tertiary-butyl ether (ETBE) is a motor fuel oxygenate used in reformulated gasoline. The current use of ETBE in gasoline or petrol is modest but increasing. To investigate the effects of ETBE on splenocytes, mice were exposed to 0 (control), 500 ppm, 1750 ppm, or 5000 ppm of ETBE by inhalation for 6 h/day for 5 days/wk over a 6- or 13-week period. Splenocytes were harvested from the control and exposed mice, and the following cell phenotypes were quantified by flow cytometry: (1) B cells (PerCP-Cy5.5-CD45R/B220), (2) T cells (PerCP-Cy5-CD3e), (3) T cell subsets (FITC-CD4 and PE-CD8a), (4) natural killer (NK) cells (PE-NK1.1), and (5) macrophages (FITC-CD11b). Body weight and the weight of the spleen were also examined. ETBE-exposure did not affect the weight of the spleen or body weight, while it transiently increased the number of RBC and the Hb concentration. The numbers of splenic CD3+, CD4+, and CD8+ T cells, the percentage of CD4+ T cells and the CD4+/CD8+ T cell ratio in the ETBE-exposed groups were significantly decreased in a dose-dependent manner. However, ETBE exposure did not affect the numbers of splenic NK cells, B cells, or macrophages or the total number of splenocytes. The above findings indicate that ETBE selectively affects the number of splenic T cells in mice.

The earliest thymic T cell progenitors sustain B cell and myeloid lineage potential

The stepwise commitment from hematopoietic stem cells in the bone marrow (BM) to T lymphocyte-restricted progenitors in the thymus represents a paradigm for understanding the requirement for distinct extrinsic cues during different stages of lineage restriction from multipotent to lineage restricted progenitors. However, the commitment stage at which progenitors migrate from the BM to the thymus remains unclear. Here we provide functional and molecular evidence at the single cell level that the earliest progenitors in the neonatal thymus possessed combined granulocyte-monocyte, T and B lymphocyte, but not megakaryocyte-erythroid lineage potential. These potentials were identical to those of thymus-seeding progenitors in the BM, which were closely related at the molecular level. These findings establish the distinct lineage-restriction stage at which the T lineage commitment transits from the BM to the remote thymus.

Thymic involution in pregnancy: a universal finding?

The thymus is a lymphatic organ that plays a vital role in the development of immunity in childhood. The thymus involutes during periods of stress and may acutely decrease in size but usually recovers to its normal size. The thymus also involutes during pregnancy, a process that is possibly hormonally mediated and thought to be necessary for fetal survival. This report describes two pregnant patients with signs and symptoms suggestive of pulmonary embolism who were incidentally found to have thymic enlargement on computed tomography. Follow-up imaging postpartum in both cases demonstrates a significant reduction in thymus size, suggesting thymic hyperplasia. Both patients delivered healthy babies at term. Thymic involution does not universally occur in pregnancy, challenging the theory of its necessity to fetal survival.

Towards segmentation of the thymus in fat and water parametric MR images

The thymus, an organ responsible for the development, selection, and maintenance of the peripheral T-cell population, is an important regulator of the immune system. Despite its physiological significance, it has received little attention in the medical image analysis literature. In practice, the anatomical location and variable shape of this gland pose challenges both in the image acquisition and analysis processes. We present an automated method for segmenting the thymus from water and fat parametric MR images that permits further analysis of volumetrics and tissue characterization. We compute fat ratio and water ratio parametric images and introduce the use of a stochastic edge detector that is embedded in a geometric variational segmentation model. Validation experiments of the proposed algorithm against manual delineations of the thymus indicate the applicability of our approach.

Defective CD8 T cell responses in aged mice are due to quantitative and qualitative changes in virus-specific precursors

Aging is associated with suboptimal CD8 T cell responses to viral infections. It is not clear whether these poor responses are due to environmental influences or quantitative and qualitative changes in the pool of responding CD8 T cells. Our studies demonstrated several deleterious age-related changes in the pool of Ag-specific CD8 T cells that respond to infection. The majority of CD8 T cells from uninfected aged mice was CD44(Hi) and had increased expression of inhibitory receptors including PD1, LAG3, 2B4, and CD160. These aged CD44(Hi) CD8 T cells were transcriptionally similar to exhausted CD8 T cells found during chronic infections. In addition, the number of virus-specific precursors in aged mice prior to infection was decreased up to 10-fold, and many of these Ag-specific precursors had high expression of CD44 and PD1. Finally, TCR transgenic studies demonstrated that the CD44(Hi) Ag-specific CD8 T cells from unimmunized aged and young mice were qualitatively inferior compared with CD44(Lo) CD8 T cells from aged or young donors. Thus, a decrease in precursor frequency as well as qualitative changes of CD8 T cells during aging are directly related to impaired immunity.

Interdisciplinary critique of sipuleucel-T as immunotherapy in castration-resistant prostate cancer

Sipuleucel-T was approved by the US Food and Drug Administration on April 29, 2010, as an immunotherapy for late-stage prostate cancer. To manufacture sipuleucel-T, mononuclear cells harvested from the patient are incubated with a recombinant prostatic acid phosphatase (PAP) antigen and reinfused. The manufacturer proposes that antigen-presenting cells exogenously activated by PAP induce endogenous T-cells to attack PAP-bearing prostate cancer cells. However, the lack of demonstrable tumor responses has prompted calls for scrutiny of the design of the trials in which sipuleucel-T demonstrated a 4-month survival benefit. Previously unpublished data from the sipuleucel-T trials show worse overall survival in older vs younger patients in the placebo groups, which have not been shown previously to be prognostic for survival in castration-resistant prostate cancer patients receiving chemotherapy. Because two-thirds of the cells harvested from placebo patients, but not from the sipuleucel-T arm, were frozen and not reinfused, a detrimental effect of this large repeated cell loss provides a potential alternative explanation for the survival "benefit." Patient safety depends on adequately addressing this alternative explanation for the trial results.

Consensus statement: evaluation of new and existing therapeutics for pediatric multiple sclerosis

New therapies are being evaluated by clinical trials and, if efficacious, introduced for the treatment of adult MS. The role of these new and existing agents in the management of pediatric MS has yet to be defined. Pediatric investigation plans are now required by the Food and Drug Administration and European Medicines Agency for approval of new biological agents, providing an important opportunity to gather much-needed data for clinicians caring for children and adolescents with MS. However, challenges include the small number of patients, and the need for efficient yet comprehensive study designs incorporating factors necessary to inform the clinical care of children with MS. The elected Steering committee of the International Pediatric MS Study Group (IPMSSG) conducted a structured review of existing data on the disease-modifying therapies in pediatric MS and developed a consensus statement, which was further modified by the IPMSSG general membership, using an online survey tool. Fifty-one IPMSSG members from 21 countries responded to the survey, and 50 approved the final statement. Consensus recommendations regarding use of existing first- and second-line therapies, as well as a proposed definition for inadequate treatment response, are presented. Recommendations for the use and evaluation of emerging therapies (currently in phase III clinical trials or recently approved for adult MS) are discussed. The IPMSSG endorses the inclusion of pediatric MS patients in trials evaluating appropriate new and emerging therapies. Mechanisms for conducting high-impact, multicenter studies, including long-term follow-up in pediatric MS, are required to ensure that all MS patients, irrespective of age, benefit from advances in MS therapeutics.