Effects of Castration on Thymocyte Development in Two Different Models of Thymic Involution

Rebuilding and rebooting immunity with stem cells

Advances in modern medicine have enabled a rapid increase in lifespan and, consequently, have highlighted the immune system as a key driver of age-related disease. Immune regeneration therapies present exciting strategies to address age-related diseases by rebooting the host's primary lymphoid tissues or rebuilding the immune system directly via biomaterials or artificial tissue. Here, we identify important, unanswered questions regarding the safety and feasibility of these therapies. Further, we identify key design parameters that should be primary considerations guiding technology design, including timing of application, interaction with the host immune system, and functional characterization of the target patient population.

Primary and secondary defects of the thymus

The thymus is the primary site of T-cell development, enabling generation, and selection of a diverse repertoire of T cells that recognize non-self, whilst remaining tolerant to self- antigens. Severe congenital disorders of thymic development (athymia) can be fatal if left untreated due to infections, and thymic tissue implantation is the only cure. While newborn screening for severe combined immune deficiency has allowed improved detection at birth of congenital athymia, thymic disorders acquired later in life are still underrecognized and assessing the quality of thymic function in such conditions remains a challenge. The thymus is sensitive to injury elicited from a variety of endogenous and exogenous factors, and its self-renewal capacity decreases with age. Secondary and age-related forms of thymic dysfunction may lead to an increased risk of infections, malignancy, and autoimmunity. Promising results have been obtained in preclinical models and clinical trials upon administration of soluble factors promoting thymic regeneration, but to date no therapy is approved for clinical use. In this review we provide a background on thymus development, function, and age-related involution. We discuss disease mechanisms, diagnostic, and therapeutic approaches for primary and secondary thymic defects.

Disorganization of secondary lymphoid organs and dyscoordination of chemokine secretion as key contributors to immune aging

Aging is characterized by progressive loss of organ and tissue function, and the immune system is no exception to that inevitable principle. Of all the age-related changes in the body, reduction of the size of, and naïve T (Tn) cell output from, the thymus occurs earliest, being prominent already before or by the time of puberty. Therefore, to preserve immunity against new infections, over much of their lives, vertebrates dominantly rely on peripheral maintenance of the Tn cell pool in the secondary lymphoid organs (SLO). However, SLO structure and function subsequently also deteriorate with aging. Several recent studies have made a convincing case that this deterioration is of major importance to the erosion of protective immunity in the last third of life. Specifically, the SLO were found to accumulate multiple degenerative changes with aging. Importantly, the results from adoptive transfer and parabiosis studies teach us that the old microenvironment is the limiting factor for protective immunity in old mice. In this review, we discuss the extent, mechanisms, and potential role of stromal cell aging in the age-related alteration of T cell homeostatic maintenance and immune function decline. We use that discussion to frame the potential strategies to correct the SLO stromal aging defects - in the context of other immune rejuvenation approaches, - to improve functional immune responses and protective immunity in older adults.

Sex biased human thymic architecture guides T cell development through spatially defined niches

Within the thymus, regulation of the cellular cross-talk directing T cell development is dependent on spatial interactions within specialized niches. To create a holistic, spatially defined map of tissue niches guiding postnatal T cell development we employed the multidimensional imaging platform CO-detection by indEXing (CODEX), as well as CITE-seq and ATAC-seq. We generated age-matched 4-5-month-old postnatal thymus datasets for male and female donors, and identify significant sex differences in both T cell and thymus biology. We demonstrate a crucial role for JAG ligands in directing thymic-like dendritic cell development, reveal important functions of a novel population of ECM- fibroblasts, and characterize the medullary niches surrounding Hassall's corpuscles. Together, these data represent a unique age-matched spatial multiomic resource to investigate how sex-based differences in thymus regulation and T cell development arise, and provide an essential resource to understand the mechanisms underlying immune function and dysfunction in males and females.

Restored Thymic Output after Androgen Blockade Participates in Antitumor Immunity

The thymus is a hormone-sensitive organ, which involutes with age in response to production of sex steroids. Thymic involution leads to a decrease in the generation of recent thymic emigrants (RTEs), resulting in a reduced response to immune challenges such as cancer. Interestingly, the standard of care for prostate cancer patients is androgen deprivation therapy (ADT), which leads to thymic regeneration and an increase in thymic output. It remains unknown whether these newly produced T cells can contribute to the antitumor immune response. This study defines the kinetics of thymic regeneration in response to ADT in mice, determining that thymic epithelial cell proliferation is critical for the increase in RTE output. Using a mouse model to track RTE in vivo, we demonstrate that these newly generated RTEs can traffic to tumors, where they become activated and produce effector cytokines at levels similar to more mature T cells. Collectively, these data suggest that RTEs produced from ADT-induced thymic regeneration could be harnessed for the antitumor immune response.

The potential role of the thymus in immunotherapies for acute myeloid leukemia

Understanding the factors which shape T-lymphocyte immunity is critical for the development and application of future immunotherapeutic strategies in treating hematological malignancies. The thymus, a specialized central lymphoid organ, plays important roles in generating a diverse T lymphocyte repertoire during the infantile and juvenile stages of humans. However, age-associated thymic involution and diseases or treatment associated injury result in a decline in its continuous role in the maintenance of T cell-mediated anti-tumor/virus immunity. Acute myeloid leukemia (AML) is an aggressive hematologic malignancy that mainly affects older adults, and the disease's progression is known to consist of an impaired immune surveillance including a reduction in naïve T cell output, a restriction in T cell receptor repertoire, and an increase in frequencies of regulatory T cells. As one of the most successful immunotherapies thus far developed for malignancy, T-cell-based adoptive cell therapies could be essential for the development of a durable effective treatment to eliminate residue leukemic cells (blasts) and prevent AML relapse. Thus, a detailed cellular and molecular landscape of how the adult thymus functions within the context of the AML microenvironment will provide new insights into both the immune-related pathogenesis and the regeneration of a functional immune system against leukemia in AML patients. Herein, we review the available evidence supporting the potential correlation between thymic dysfunction and T-lymphocyte impairment with the ontogeny of AML (II-VI). We then discuss how the thymus could impact current and future therapeutic approaches in AML (VII). Finally, we review various strategies to rejuvenate thymic function to improve the precision and efficacy of cancer immunotherapy (VIII).

The transcriptome pattern of liver, spleen and hypothalamus provides insights into genetic and biological changes in roosters in response to castration

Chicken is widely accepted by consumers because of its delicate taste and abundant animal protein. The rooster after castration (capon) is believed to show better flavor, however, the molecular changes of the underpinned metabolism after castration is not yet understood. In this study, we aimed to figure out the alternation of meat quality and underpinned molecular mechanism via transcriptomic profiling of liver, spleen and hypothalamus as targeted organs in response to the castration. We identified differential expressed genes and their enriched functions and pathways in these organs between capon and rooster samples through RNA-seq analysis. In the liver, the lipid metabolism with targeted FABP1gene was found significantly enriched, which may be as one of the factors contributing to increased fat deposition and thus better meat flavor in capons than roosters, as predicted by the significantly lower shear force in capons than in roosters in meat quality experiments. However, the ability to xenobiotic detoxification and excretion, vitamin metabolism, and antioxidative effect of hemoglobin evidenced of the capon may be compromised by the alternation of SULT, AOX1, CYP3A5, HBA1, HBBA, and HBAD. Besides, in both the spleen and hypothalamus, PTAFR, HPX, CTLA4, LAG3, ANPEP, CD24, ITGA2B, ITGB3, CD2, CD7, and BLB2 may play an important role in the immune system including function of platelet and T cell, development of monocyte/macrophage and B cell in capons as compared to roosters. In conclusion, our study sheds lights into the possible molecular mechanism of better meat flavor, fatty deposit, oxidative detoxification and immune response difference between capons and roosters.

Thymus Reconstitution in Young and Aged Mice Is Facilitated by In Vitro-Generated Progenitor T Cells

The prolonged lag in T cell recovery seen in older patients undergoing hematopoietic stem cell transplant (HSCT), after chemo-/radiotherapy, can lead to immune dysfunction. As a result, recovering patients may experience a relapse in malignancies and opportunistic infections, leading to high mortality rates. The delay in T cell recovery is partly due to thymic involution, a natural collapse in the size and function of the thymus, as individuals age, and partly due to the damage sustained by the thymic stromal cells through exposure to chemo-/radiotherapy. There is a clear need for new strategies to accelerate intrathymic T cell reconstitution when treating aged patients to counter the effects of involution and cancer therapy regimens. Adoptive transfer of human progenitor T (proT) cells has been shown to accelerate T cell regeneration in radiation-treated young mice and to restore thymic architecture in immunodeficient mice. Here, we demonstrate that the adoptive transfer of in vitro-generated proT cells in aged mice (18-24 months) accelerated thymic reconstitution after treatment with chemotherapy and gamma irradiation compared to HSCT alone. We noted that aged mice appeared to have a more limited expansion of CD4-CD8- thymocytes and slower temporal kinetics in the development of donor proT cells into mature T cells, when compared to younger mice, despite following the same chemo/radiation regimen. This suggests a greater resilience of the young thymus compared to the aged thymus. Nevertheless, newly generated T cells from proT cell engrafted aged and young mice were readily present in the periphery accelerating the reappearance of new naïve T cells. Accelerated T cell recovery was also observed in both aged and young mice receiving both proT cells and HSCT. The strategy of transferring proT cells can potentially be used as an effective cellular therapy in aged patients to improve immune recovery and reduce the risk of opportunistic infections post-HSCT.

Role of thymus in health and disease

The thymus is a primary lymphoid organ, essential for the development of T-cells that will protect from invading pathogens, immune disorders, and cancer. The thymus decreases in size and cellularity with age referred to as thymus involution or atrophy. This involution causes decreased T-cell development and decreased naive T-cell emigration to the periphery, increased proportion of memory T cells, and a restricted, altered T-cell receptor (TCR) repertoire. The changes in composition and function of the circulating T cell pool as a result of thymic involution led to increased susceptibility to infectious diseases including the recent COVID and a higher risk for autoimmune disorders and cancers. Thymic involution consisting of both structural and functional loss of the thymus has a deleterious effect on T cell development, T cell selection, and tolerance. The mechanisms which act on the structural (cortex and medulla) matrix of the thymus, the gradual accumulation of genetic mutations, and altered gene expressions may lead to immunosenescence as a result of thymus involution. Understanding the molecular mechanisms behind thymic involution is critical for identifying diagnostic biomarkers and targets for treatment help to develop strategies to mitigate thymic involution-associated complications. This review is focused on the consequences of thymic involution in infections, immune disorders, and diseases, identifying potential checkpoints and potential approaches to sustain or restore the function of the thymus particularly in elderly and immune-compromised individuals.

Quantitative restoration of immune defense in old animals determined by naive antigen-specific CD8 T-cell numbers

Older humans and animals often exhibit reduced immune responses to infection and vaccination, and this often directly correlates to the numbers and frequency of naive T (Tn) cells. We found such a correlation between reduced numbers of blood CD8+ Tn cells and severe clinical outcomes of West Nile virus (WNV) in both humans naturally exposed to, and mice experimentally infected with, WNV. To examine possible causality, we sought to increase the number of CD8 Tn cells by treating C57BL/6 mice with IL-7 complexes (IL-7C, anti-IL-7 mAb bound to IL-7), shown previously to efficiently increase peripheral T-cell numbers by homeostatic proliferation. T cells underwent robust expansion following IL-7C administration to old mice increasing the number of total T cells (>fourfold) and NS4b:H-2D^b -restricted antigen-specific CD8 T cells (twofold). This improved the numbers of NS4b-specific CD8 T cells detected at the peak of the response against WNV, but not survival of WNV challenge. IL-7C-treated old animals also showed no improvement in WNV-specific effector immunity (neutralizing antibody and in vivo T-cell cytotoxicity). To test quantitative limits to which CD8 Tn cell restoration could improve protective immunity, we transferred graded doses of Ag-specific precursors into old mice and showed that injection of 5400 (but not of 1800 or 600) adult naive WNV-specific CD8 T cells significantly increased survival after WNV. These results set quantitative limits to the level of Tn reconstitution necessary to improve immune defense in older organisms and are discussed in light of targets of immune reconstitution.

Targeting the spectrum of immune checkpoints in prostate cancer

Introduction: The proven efficacy of the cellular vaccine sipuleucel-T in 2010 led to optimism about immunotherapeutic approaches for the treatment of prostate cancer. Some surmised that prostate cancer might be an ideal target for immune-mediated killing given that the prostate is not an essential organ and expresses unique proteins including prostate-specific antigen, prostate-specific membrane antigen, and prostatic acid phosphatase that could be targeted without side effects. Subsequently, antibodies that inhibit the T cell checkpoints PD1 and CTLA4 were shown to stimulate antitumor immune responses, leading to tumor regression in several cancer types. These therapies have since been tested in several studies as treatments for prostate cancer, but appear to have limited efficacy in molecularly unselected patients.Areas covered: In this review, we discuss these studies and evaluate features of prostate cancer and its host environment that may render it generally resistant to CTLA4 and PD1 blockade. We provide an overview of alternate immune checkpoints that may hold greater significance in this disease.Expert opinion: Combination therapies to target multiple layers of alternate immune checkpoints may be required for an effective immune response to prostate cancer. We discuss combination therapies currently being investigated.

End-Stage Renal Disease-Related Accelerated Immune Senescence: Is Rejuvenation of the Immune System a Therapeutic Goal?

End-stage renal disease (ESRD) patients exhibit clinical features of premature ageing, including frailty, cardiovascular disease, and muscle wasting. Accelerated ageing also concerns the immune system. Patients with ESRD have both immune senescence and chronic inflammation that are resumed in the so-called inflammaging syndrome. Immune senescence is particularly characterised by premature loss of thymic function that is associated with hyporesponsiveness to vaccines, susceptibility to infections, and death. ESRD-related chronic inflammation has multiple causes and participates to accelerated cardiovascular disease. Although, both characterisation of immune senescence and its consequences are relatively well-known, mechanisms are more uncertain. However, prevention of immune senescence/inflammation or/and rejuvenation of the immune system are major goal to ameliorate clinical outcomes of ESRD patients.

Recent Advancements in Regenerative Approaches for Thymus Rejuvenation

The thymus plays a key role in adaptive immunity by generating a diverse population of T cells that defend the body against pathogens. Various factors from disease and toxic insults contribute to the degeneration of the thymus resulting in a fewer output of T cells. Consequently, the body is prone to a wide host of diseases and infections. In this review, first, the relevance of the thymus is discussed, followed by thymic embryological organogenesis and anatomy as well as the development and functionality of T cells. Attempts to regenerate the thymus include in vitro methods, such as forming thymic organoids aided by biofabrication techniques that are transplantable. Ex vivo methods that have shown promise in enhancing thymic regeneration are also discussed. Current regenerative technologies have not yet matched the complexity and functionality of the thymus. Therefore, emerging techniques that have shown promise and the challenges that lie ahead are explored.

Potential of Mesenchymal Stem Cells in the Rejuvenation of the Aging Immune System

Rapid growth of the geriatric population has been made possible with advancements in pharmaceutical and health sciences. Hence, age-associated diseases are becoming more common. Aging encompasses deterioration of the immune system, known as immunosenescence. Dysregulation of the immune cell production, differentiation, and functioning lead to a chronic subclinical inflammatory state termed inflammaging. The hallmarks of the aging immune system are decreased naïve cells, increased memory cells, and increased serum levels of pro-inflammatory cytokines. Mesenchymal stem cell (MSC) transplantation is a promising solution to halt immunosenescence as the cells have excellent immunomodulatory functions and low immunogenicity. This review compiles the present knowledge of the causes and changes of the aging immune system and the potential of MSC transplantation as a regenerative therapy for immunosenescence.

In Pursuit of Adult Progenitors of Thymic Epithelial Cells

Peripheral T cells capable of discriminating between self and non-self antigens are major components of a robust adaptive immune system. The development of self-tolerant T cells is orchestrated by thymic epithelial cells (TECs), which are localized in the thymic cortex (cortical TECs, cTECs) and medulla (medullary TECs, mTECs). cTECs and mTECs are essential for differentiation, proliferation, and positive and negative selection of thymocytes. Recent advances in single-cell RNA-sequencing technology have revealed a previously unknown degree of TEC heterogeneity, but we still lack a clear picture of the identity of TEC progenitors in the adult thymus. In this review, we describe both earlier and recent findings that shed light on features of these elusive adult progenitors in the context of tissue homeostasis, as well as recovery from stress-induced thymic atrophy.

Dynamics of thymus function and T cell receptor repertoire breadth in health and disease

T cell recognition of unknown antigens relies on the tremendous diversity of the T cell receptor (TCR) repertoire; generation of which can only occur in the thymus. TCR repertoire breadth is thus critical for not only coordinating the adaptive response against pathogens but also for mounting a response against malignancies. However, thymic function is exquisitely sensitive to negative stimuli, which can come in the form of acute insult, such as that caused by stress, infection, or common cancer therapies; or chronic damage such as the progressive decline in thymic function with age. Whether it be prolonged T cell deficiency after hematopoietic cell transplantation (HCT) or constriction in the breadth of the peripheral TCR repertoire with age; these insults result in poor adaptive immune responses. In this review, we will discuss the importance of thymic function for generation of the TCR repertoire and how acute and chronic thymic damage influences immune health. We will also discuss methods that are used to measure thymic function in patients and strategies that have been developed to boost thymic function.

Curcumin protects thymus against D-galactose-induced senescence in mice

Senescence-related decline of thymus affects immune function in the elderly population and contributes to the prevalence of many relevant diseases like cancer, autoimmune diseases, and other chronic diseases. In this study, we investigated the therapeutic effects of curcumin, an agent that could counter aging, and explored its optimal intake and the alteration of autoimmune regulator (Aire) after curcumin treatment in the D-galactose (D-gal)-induced accelerated aging mice. ICR mice were intraperitoneally injected with D-gal for 8 weeks to establish the accelerated aging model and given curcumin with 50, 100, and 200 mg/kg body weight per day by gavage, respectively, for 6 weeks. It indicated that the D-gal-treated mice developed structural changes in the thymi compared with the control group without D-gal and curcumin treatment. As the supplements of curcumin, it resulted in a restoration of the normal thymic anatomy with an increase of proliferating cells and a reduction of apoptotic cells in the thymi of the D-gal-induced aging model mice. Curcumin administration could also expand the expression level of Aire from mRNA level and protein level. The current study demonstrated that curcumin could ameliorate senescence-related thymus involution via upregulating Aire expression, suggesting that curcumin can rejuvenate senescence-associated alterations of thymus induced by D-gal accumulation.

The role of the thymus in allogeneic bone marrow transplantation and the recovery of the peripheral T-cell compartment

As the thymus represents the primary site of T-cell development, optimal thymic function is of paramount importance for the successful reconstitution of the adaptive immunity after allogeneic hematopoietic stem cell transplantation. Thymus involutes as part of the aging process and several factors, including previous chemotherapy treatments, conditioning regimen used in preparation to the allograft, occurrence of graft-versus-host disease, and steroid therapy that impair the integrity of the thymus, thus affecting its role in supporting T-cell neogenesis. Although the pathways governing its regeneration are still poorly understood, the thymus has a remarkable capacity to recover its function after damage. Measurement of both recent thymic emigrants and T-cell receptor excision circles is valuable tools to assess thymic output and gain insights on its function. In this review, we will extensively discuss available data on factors regulating thymic function after allogeneic hematopoietic stem cell transplantation, as well as the strategies and therapeutic approaches under investigation to promote thymic reconstitution and accelerate immune recovery in transplanted patients, including the use of cytokines, sex-steroid ablation, precursor T-cells, and thymus bioengineering. Although none of them is routinely used in the clinic, these approaches have the potential to enhance thymic function and immune recovery, not only in patients given an allograft but also in other conditions characterized by immune deficiencies related to a defective function of the thymus.

Vaccine-Induced CD8+ T Cell Responses in Children: A Review of Age-Specific Molecular Determinants Contributing to Antigen Cross-Presentation

Infections are most common and most severe at the extremes of age, the young and the elderly. Vaccination can be a key approach to enhance immunogenicity and protection against pathogens in these vulnerable populations, who have a functionally distinct immune system compared to other age groups. More than 50% of the vaccine market is for pediatric use, yet to date vaccine development is often empiric and not tailored to molecular distinctions in innate and adaptive immune activation in early life. With modern vaccine development shifting from whole-cell based vaccines to subunit vaccines also comes the need for formulations that can elicit a CD8⁺ T cell response when needed, for example, by promoting antigen cross-presentation. While our group and others have identified many cellular and molecular determinants of successful activation of antigen-presenting cells, B cells and CD4⁺ T cells in early life, much less is known about the ontogeny of CD8⁺ T cell induction. In this review, we summarize the literature pertaining to the frequency and phenotype of newborn and infant CD8⁺ T cells, and any evidence of induction of CD8⁺ T cells by currently licensed pediatric vaccine formulations. In addition, we review the molecular determinants of antigen cross-presentation on MHC I and successful CD8⁺ T cell induction and discuss potential distinctions that can be made in children. Finally, we discuss recent advances in development of novel adjuvants and provide future directions for basic and translational research in this area.

T cell regeneration after immunological injury

Following periods of haematopoietic cell stress, such as after chemotherapy, radiotherapy, infection and transplantation, patient outcomes are linked to the degree of immune reconstitution, specifically of T cells. Delayed or defective recovery of the T cell pool has significant clinical consequences, including prolonged immunosuppression, poor vaccine responses and increased risks of infections and malignancies. Thus, strategies that restore thymic function and enhance T cell reconstitution can provide considerable benefit to individuals whose immune system has been decimated in various settings. In this Review, we focus on the causes and consequences of impaired adaptive immunity and discuss therapeutic strategies that can recover immune function, with a particular emphasis on approaches that can promote a diverse repertoire of T cells through de novo T cell formation.

Thymic Engraftment by in vitro-Derived Progenitor T Cells in Young and Aged Mice

T cells play a critical role in mediating antigen-specific and long-term immunity against viral and bacterial pathogens, and their development relies on the highly specialized thymic microenvironment. T cell immunodeficiency can be acquired in the form of inborn errors, or can result from perturbations to the thymus due to aging or irradiation/chemotherapy required for cancer treatment. Hematopoietic stem cell transplant (HSCT) from compatible donors is a cornerstone for the treatment of hematological malignancies and immunodeficiency. Although it can restore a functional immune system, profound impairments exist in recovery of the T cell compartment. T cells remain absent or low in number for many months after HSCT, depending on a variety of factors including the age of the recipient. While younger patients have a shorter refractory period, the prolonged T cell recovery observed in older patients can lead to a higher risk of opportunistic infections and increased predisposition to relapse. Thus, strategies for enhancing T cell recovery in aged individuals are needed to counter thymic damage induced by radiation and chemotherapy toxicities, in addition to naturally occurring age-related thymic involution. Preclinical results have shown that robust and rapid long-term thymic reconstitution can be achieved when progenitor T cells, generated in vitro from HSCs, are co-administered during HSCT. Progenitor T cells appear to rely on lymphostromal crosstalk via receptor activator of NF-κB (RANK) and RANK-ligand (RANKL) interactions, creating chemokine-rich niches within the cortex and medulla that likely favor the recruitment of bone marrow-derived thymus seeding progenitors. Here, we employed preclinical mouse models to demonstrate that in vitro-generated progenitor T cells can effectively engraft involuted aged thymuses, which could potentially improve T cell recovery. The utility of progenitor T cells for aged recipients positions them as a promising cellular therapy for immune recovery and intrathymic repair following irradiation and chemotherapy, even in a post-involution thymus.

Evaluating Thymic Function After Human Hematopoietic Stem Cell Transplantation in the Personalized Medicine Era

Hematopoietic stem cell transplantation (HSCT) is an effective treatment option for several malignant and non-malignant hematological diseases. The clinical outcome of this procedure relies to a large extent on optimal recovery of adaptive immunity. In this regard, the thymus plays a central role as the primary site for de novo generation of functional, diverse, and immunocompetent T-lymphocytes. The thymus is exquisitely sensitive to several insults during HSCT, including conditioning drugs, corticosteroids, infections, and graft-vs.-host disease. Impaired thymic recovery has been clearly associated with increased risk of opportunistic infections and poor clinical outcomes in HSCT recipients. Therefore, better understanding of thymic function can provide valuable information for improving HSCT outcomes. Recent data have shown that, besides gender and age, a specific single-nucleotide polymorphism affects thymopoiesis and may also influence thymic output post-HSCT, suggesting that the time of precision medicine of thymic function has arrived. Here, we review the current knowledge about thymic role in HSCT and the recent work of genetic control of human thymopoiesis. We also discuss different transplant-related factors that have been associated with impaired thymic recovery and the use of T-cell receptor excision circles (TREC) to assess thymic output, including its clinical significance. Finally, we present therapeutic strategies that could boost thymic recovery post-HSCT.

The Effects of Androgens on T Cells: Clues to Female Predominance in Autoimmune Liver Diseases?

The immune system responds differently in women and in men. Generally speaking, adult females show stronger innate and adaptive immune responses than males. This results in lower risk of developing most of the infectious diseases and a better ability to clear viral infection in women (1–5). On the other hand, women are at increased risk of developing autoimmune diseases (AID) such as rheumatoid arthritis, multiple sclerosis (MS), systemic lupus erythematosus (SLE), Sjögren's syndrome, and the autoimmune liver diseases autoimmune hepatitis (AIH) and primary biliary cholangitis (PBC) (6). Factors contributing to the female sex bias in autoimmune diseases include environmental exposure, e.g., microbiome, behavior, and genetics including X chromosomal inactivation of genes. Several lines of evidence and clinical observations clearly indicate that sex hormones contribute significantly to disease pathogenesis, and the role of estrogen in autoimmune diseases has been extensively studied. In many of these diseases, including the autoimmune liver diseases, T cells are thought to play an important pathogenetic role. We will use this mini-review to focus on the effects of androgens on T cells and how the two major androgens, testosterone and dihydrotestosterone, potentially contribute to the pathogenesis of autoimmune liver diseases (AILD).

Decreased Naïve T-cell Production Leading to Cytokine Storm as Cause of Increased COVID-19 Severity with Comorbidities

Aging, type 2 diabetes, and male gender are major risk factors leading to increased COVID-19 morbidity and mortality. Thymic production and the export of naïve T cells decrease with aging through the effects of androgens in males and in type 2 diabetes. Furthermore, with aging, recovery of naïve T-cell populations after bone marrow transplantation is delayed and associated with an increased risk of chronic graft vs. host disease. Severe COVID-19 and SARS infections are notable for severe T-cell depletion. In COVID-19, there is unique suppression of interferon signaling by infected respiratory tract cells with intact cytokine signaling. A decreased naïve T-cell response likely contributes to an excessive inflammatory response and increases the odds of a cytokine storm. Treatments that improve naïve T-cell production may prove to be vital COVID-19 therapies, especially for these high-risk groups.

Phosphate Transporter Profiles in Murine and Human Thymi Identify Thymocytes at Distinct Stages of Differentiation

Thymocyte differentiation is dependent on the availability and transport of metabolites in the thymus niche. As expression of metabolite transporters is a rate-limiting step in nutrient utilization, cell surface transporter levels generally reflect the cell's metabolic state. The GLUT1 glucose transporter is upregulated on actively dividing thymocytes, identifying thymocytes with an increased metabolism. However, it is not clear whether transporters of essential elements such as phosphate are modulated during thymocyte differentiation. While PiT1 and PiT2 are both phosphate transporters in the SLC20 family, we show here that they exhibit distinct expression profiles on both murine and human thymocytes. PiT2 expression distinguishes thymocytes with high metabolic activity, identifying immature murine double negative (CD4⁻CD8⁻) DN3b and DN4 thymocyte blasts as well as immature single positive (ISP) CD8 thymocytes. Notably, the absence of PiT2 expression on RAG2-deficient thymocytes, blocked at the DN3a stage, strongly suggests that high PiT2 expression is restricted to thymocytes having undergone a productive TCRβ rearrangement at the DN3a/DN3b transition. Similarly, in the human thymus, PiT2 was upregulated on early post-β selection CD4⁺ISP and TCRαβ⁻CD4^hiDP thymocytes co-expressing the CD71 transferrin receptor, a marker of metabolic activity. In marked contrast, expression of the PiT1 phosphate importer was detected on mature CD3⁺ murine and human thymocytes. Notably, PiT1 expression on CD3⁺DN thymocytes was identified as a biomarker of an aging thymus, increasing from 8.4 ± 1.5% to 42.4 ± 9.4% by 1 year of age (p < 0.0001). We identified these cells as TCRγδ and, most significantly, NKT, representing 77 ± 9% of PiT1⁺DN thymocytes by 1 year of age (p < 0.001). Thus, metabolic activity and thymic aging are associated with distinct expression profiles of the PiT1 and PiT2 phosphate transporters.

Androgen Receptors in Epithelial Cells Regulate Thymopoiesis and Recent Thymic Emigrants in Male Mice

Androgens have profound effects on T cell homeostasis, including regulation of thymic T lymphopoiesis (thymopoiesis) and production of recent thymic emigrants (RTEs), i. e., immature T cells that derive from the thymus and continue their maturation to mature naïve T cells in secondary lymphoid organs. Here we investigated the androgen target cell for effects on thymopoiesis and RTEs in spleen and lymph nodes. Male mice with a general androgen receptor knockout (G-ARKO), T cell-specific (T-ARKO), or epithelial cell-specific (E-ARKO) knockout were examined. G-ARKO mice showed increased thymus weight and increased numbers of thymic T cell progenitors. These effects were not T cell-intrinsic, since T-ARKO mice displayed unaltered thymus weight and thymopoiesis. In line with a role for thymic epithelial cells (TECs), E-ARKO mice showed increased thymus weight and numbers of thymic T cell progenitors. Further, E-ARKO mice had more CD4+ and CD8+ T cells in spleen and an increased frequency of RTEs among T cells in spleen and lymph nodes. Depletion of the androgen receptor in epithelial cells was also associated with a small shift in the relative number of cortical (reduced) and medullary (increased) TECs and increased CCL25 staining in the thymic medulla, similar to previous observations in castrated mice. In conclusion, we demonstrate that the thymic epithelium is a target compartment for androgen-mediated regulation of thymopoiesis and consequently the generation of RTEs.

Gender Disparity Impacts on Thymus Aging and LHRH Receptor Antagonist-Induced Thymic Reconstitution Following Chemotherapeutic Damage

One of the main consequences of thymus aging is the decrease in naïve T cell output. This condition accelerates at the onset of puberty, and presents as a major clinical complication for cancer patients who require cytoablative therapy. Specifically, the extensive use of chemotherapeutics, such as cyclophosphamide, in such treatments damage thymic structure and eliminate the existing naïve T cell repertoire. The resulting immunodeficiency can lead to increased incidence of opportunistic infections, tumor growth relapse and/or autoimmune diseases, particularly in older patients. Thus, strategies aimed at rejuvenating the aged thymus following chemotherapeutic damage are required. Previous studies have revealed that sex hormone deprivation in male mice is capable of regenerating the thymic microenvironment following chemotherapy treatment, however, further investigation is crucial to identify gender-based differences, and the molecular mechanisms involved during thymus regeneration. Through phenotypic analyzes, we identified gender-specific alterations in thymocytes and thymic epithelial cell (TEC) subsets from the onset of puberty. By middle-age, females presented with a higher number of thymocytes in comparison to males, yet a decrease in their Aire+ medullary TEC/thymocyte ratio was observed. This reduction could be associated with an increased risk of autoimmune disease in middle-aged women. Given the concurrent increase in female Aire+ cTEC/thymocyte ratio, we proposed that there may be an impediment in Aire+ mTEChi differentiation, and Aire+ cTEChi as its upstream precursor. The regenerative effects of LHRH receptor antagonist, degarelix, on TEC subsets was also less pronounced in middle-aged females compared to males, possibly due to slower progression of thymic involution in the former, which presented with greater TEChi proportions. Furthermore, following cyclophosphamide treatment, degarelix enhanced thymocyte and mature TEC subset recovery, with faster recovery kinetics observed in females. These events were found to involve both reactivation and proliferation of thymic epithelial progenitor cells. Taken together, the findings from this study portray a relationship between gender disparity and thymus aging, and highlight the potential benefits of LHRH receptor antagonist treatment for thymic regeneration. Further research is required, however, to determine how gender may impact on the mechanisms underpinning these events.

Effects of Castration on miRNA, lncRNA, and mRNA Profiles in Mice Thymus

Thymic degeneration and regeneration are regulated by estrogen and androgen. Recent studies have found that long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) are involved in organ development. In this study, RNA sequencing (RNA-seq) results showed that ovariectomy significantly affected 333 lncRNAs, 51 miRNAs, and 144 mRNAs levels (p < 0.05 and |log2fold change| > 1), and orchiectomy significantly affected 165 lncRNAs, 165 miRNAs, and 208 mRNA levels in the thymus. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that differentially expressed genes (DEGs) were closely related to cell development and immunity. Next, we constructed two lncRNA–miRNA–mRNA networks using Cytoscape based on the targeting relationship between differentially expressed miRNAs (DEMs) and DEGs and differentially expressed lncRNAs (DELs) analyzed by TargetScan and miRanda. Besides, we screened DEGs that were significantly enriched in GO and in ceRNA networks to verify their expression in thymocytes and thymic epithelial cells (TECs). In addition, we analyzed the promoter sequences of DEGs, and identified 25 causal transcription factors. Finally, we constructed transcription factor-miRNA-joint target gene networks. In conclusion, this study reveals the effects of estrogen and androgen on the expression of miRNAs, lncRNAs, and mRNAs in mice thymus, providing new insights into the regulation of thymic development by gonadal hormones and non-coding RNAs.

Contributions of Age-Related Thymic Involution to Immunosenescence and Inflammaging

Immune system aging is characterized by the paradox of immunosenescence (insufficiency) and inflammaging (over-reaction), which incorporate two sides of the same coin, resulting in immune disorder. Immunosenescence refers to disruption in the structural architecture of immune organs and dysfunction in immune responses, resulting from both aged innate and adaptive immunity. Inflammaging, described as a chronic, sterile, systemic inflammatory condition associated with advanced age, is mainly attributed to somatic cellular senescence-associated secretory phenotype (SASP) and age-related autoimmune predisposition. However, the inability to reduce senescent somatic cells (SSCs), because of immunosenescence, exacerbates inflammaging. Age-related adaptive immune system deviations, particularly altered T cell function, are derived from age-related thymic atrophy or involution, a hallmark of thymic aging. Recently, there have been major developments in understanding how age-related thymic involution contributes to inflammaging and immunosenescence at the cellular and molecular levels, including genetic and epigenetic regulation, as well as developments of many potential rejuvenation strategies. Herein, we discuss the research progress uncovering how age-related thymic involution contributes to immunosenescence and inflammaging, as well as their intersection. We also describe how T cell adaptive immunity mediates inflammaging and plays a crucial role in the progression of age-related neurological and cardiovascular diseases, as well as cancer. We then briefly outline the underlying cellular and molecular mechanisms of age-related thymic involution, and finally summarize potential rejuvenation strategies to restore aged thymic function.

Immune System Sex Differences May Bridge the Gap Between Sex and Gender in Fibromyalgia

The fibromyalgia syndrome (FMS) is characterized by chronic widespread pain, sleep disturbances, fatigue, and cognitive alterations. A limited efficacy of targeted treatment and a high FMS prevalence (2–5% of the adult population) sums up to high morbidity. Although, altered nociception has been explained with the central sensitization hypothesis, which may occur after neuropathy, its molecular mechanism is not understood. The marked female predominance among FMS patients is often attributed to a psychosocial predisposition of the female gender, but here we will focus on sex differences in neurobiological processes, specifically those of the immune system, as various immunological biomarkers are altered in FMS. The activation of innate immune sensors is compatible with a neuropathy or virus-induced autoimmune diseases. Considering sex differences in the immune system and the clustering of FMS with autoimmune diseases, we hypothesize that the female predominance in FMS is due to a neuropathy-induced autoimmune pathophysiology. We invite the scientific community to verify the autoimmune hypothesis for FMS.

Racial Differences in Immunological Landscape Modifiers Contributing to Disparity in Prostate Cancer

Prostate cancer affects African Americans disproportionately by exhibiting greater incidence, rapid disease progression, and higher mortality when compared to their Caucasian counterparts. Additionally, standard treatment interventions do not achieve similar outcome in African Americans compared to Caucasian Americans, indicating differences in host factors contributing to racial disparity. African Americans have allelic variants and hyper-expression of genes that often lead to an immunosuppressive tumor microenvironment, possibly contributing to more aggressive tumors and poorer disease and therapeutic outcomes than Caucasians. In this review, we have discussed race-specific differences in external factors impacting internal milieu, which modify immunological topography as well as contribute to disparity in prostate cancer.

Lymph nodes as barriers to T-cell rejuvenation in aging mice and nonhuman primates

In youth, thymic involution curtails production of new naïve T cells, placing the onus of T-cell maintenance upon secondary lymphoid organs (SLO). This peripheral maintenance preserves the size of the T-cell pool for much of the lifespan, but wanes in the last third of life, leading to a dearth of naïve T cells in blood and SLO, and contributing to suboptimal immune defense. Both keratinocyte growth factor (KGF) and sex steroid ablation (SSA) have been shown to transiently increase the size and cellularity of the old thymus. It is less clear whether this increase can improve protection of old animals from infectious challenge. Here, we directly measured the extent to which thymic rejuvenation benefits the peripheral T-cell compartment of old mice and nonhuman primates. Following treatment of old animals with either KGF or SSA, we observed robust rejuvenation of thymic size and cellularity, and, in a reporter mouse model, an increase in recent thymic emigrants (RTE) in the blood. However, few RTE were found in the spleen and even fewer in the lymph nodes, and SSA-treated mice showed no improvement in immune defense against West Nile virus. In parallel, we found increased disorganization and fibrosis in old LN of both mice and nonhuman primates. These results suggest that SLO defects with aging can negate the effects of successful thymic rejuvenation in immune defense.

Testosterone Protects Against Atherosclerosis in Male Mice by Targeting Thymic Epithelial Cells-Brief Report

Supplemental Digital Content is available in the text.

Objective—

Androgen deprivation therapy has been associated with increased cardiovascular risk in men. Experimental studies support that testosterone protects against atherosclerosis, but the target cell remains unclear. T cells are important modulators of atherosclerosis, and deficiency of testosterone or its receptor, the AR (androgen receptor), induces a prominent increase in thymus size. Here, we tested the hypothesis that atherosclerosis induced by testosterone deficiency in male mice is T-cell dependent. Further, given the important role of the thymic epithelium for T-cell homeostasis and development, we hypothesized that depletion of the AR in thymic epithelial cells will result in increased atherosclerosis.

Approach and Results—

Prepubertal castration of male atherosclerosis-prone apoE^−/− mice increased atherosclerotic lesion area. Depletion of T cells using an anti-CD3 antibody abolished castration-induced atherogenesis, demonstrating a role of T cells. Male mice with depletion of the AR specifically in epithelial cells (E-ARKO [epithelial cell-specific AR knockout] mice) showed increased thymus weight, comparable with that of castrated mice. E-ARKO mice on an apoE^−/− background displayed significantly increased atherosclerosis and increased infiltration of T cells in the vascular adventitia, supporting a T-cell–driven mechanism. Consistent with a role of the thymus, E-ARKO apoE^−/− males subjected to prepubertal thymectomy showed no atherosclerosis phenotype.

Conclusions—

We show that atherogenesis induced by testosterone/AR deficiency is thymus- and T-cell dependent in male mice and that the thymic epithelial cell is a likely target cell for the antiatherogenic actions of testosterone. These insights may pave the way for new therapeutic strategies for safer endocrine treatment of prostate cancer.

Immunotherapy for metastatic prostate cancer: immuno-cold or the tip of the iceberg?

PURPOSE OF REVIEW

Metastatic castration-resistant prostate cancer is in critical need of new and innovative treatment strategies. Since the approval of sipuleucel-T, the investigatory climate of prostate cancer immunotherapy has been rapidly evolving with promising developments in vaccine and immune checkpoint therapies.

RECENT FINDINGS

Sipuleucel-T remains the first and only therapeutic cancer vaccine approved for its survival benefit in metastatic castration-resistant prostate cancer. Additional cancer vaccines are currently being evaluated, with the most promising being a peptide vaccine encoding prostate-specific antigen, known as prostate-specific antigen-TRICOM. Emerging data supports combinatorial strategies for vaccine therapy and a potential role for implementation in earlier stages of advanced disease. Immune checkpoint therapies have demonstrated limited success in prostate cancer with negative late phase trials for ipilimumab monotherapy and discouraging early phase results for programmed cell death protein 1 blockade. Novel immune-modulatory targets and rational combination strategies aim to produce more favorable results. Recent progress has been made to determine biologic predictors for response and toxicity in prostate cancer immunotherapy aiming to improve patient selection and safety.

SUMMARY

Steady progress is anticipated in the field of prostate cancer immunotherapy including ongoing development of novel cancer vaccines, immune checkpoint therapies, and combinatorial strategies.

Thymic stromal cells: Roles in atrophy and age-associated dysfunction of the thymus

Atrophy of the thymus, the primary site of T lymphocyte generation, is a hallmark of the aging immune system. Age-associated thymic atrophy results in diminished output of new, naïve T cells, with immune sequelae that include diminished responses to novel pathogenic challenge and vaccines, as well as diminished tumor surveillance. Although a variety of stimuli are known to regulate transient thymic atrophy, mechanisms governing progressive age-associated atrophy have been difficult to resolve. This has been due in part to the fact that one of the primary targets of age-associated thymic atrophy is a relatively rare population, thymic stromal cells. This review focuses on changes in thymic stromal cells during aging and on the contributions of periodic, stochastic, and progressive causes of thymic atrophy.

Intrathymic Deletion of IL-7 Reveals a Contribution of the Bone Marrow to Thymic Rebound Induced by Androgen Blockade

Despite the well-documented effect of castration in thymic regeneration, the singular contribution of the bone marrow (BM) versus the thymus to this process remains unclear. The chief role of IL-7 in pre- and intrathymic stages of T lymphopoiesis led us to investigate the impact of disrupting this cytokine during thymic rebound induced by androgen blockade. We found that castration promoted thymopoiesis in young and aged wild-type mice. In contrast, only young germline IL-7–deficient (Il7−/−) mice consistently augmented thymopoiesis after castration. The increase in T cell production was accompanied by the expansion of the sparse medullary thymic epithelial cell and the peripheral T cell compartment in young Il7−/− mice. In contrast to young Il7−/− and wild-type mice, the poor thymic response of aged Il7−/− mice after castration was associated with a defect in the expansion of BM hematopoietic progenitors. These findings suggest that BM-derived T cell precursors contribute to thymic rebound driven by androgen blockade. To assess the role of IL-7 within the thymus, we generated mice with conditional deletion of IL-7 (Il7 conditional knockout [cKO]) in thymic epithelial cells. As expected, Il7cKO mice presented a profound defect in T cell development while maintaining an intact BM hematopoietic compartment across life. Unlike Il7−/− mice, castration promoted the expansion of BM precursors and enhanced thymic activity in Il7cKO mice independently of age. Our findings suggest that the mobilization of BM precursors acts as a prime catalyst of castration-driven thymopoiesis.

Interventions to restore appropriate immune function in the elderly

Advanced age is one indicator of likely immune dysfunction. As worldwide, the global population contains progressively more and more older individuals there is likelihood of an increased prevalence and incidence of infectious diseases due to common and emergent pathogens. The resultant increase in mortality and morbidity would be matched by the risk of functional decline and disability. Maintaining immune function at a plateau throughout life may therefore be associated with considerable cost savings. The aim of improving immune function in older individuals may be achieved through considering a therapeutic approach to rejuvenate, stimulate or support the indigenous immune system to perform in a more optimal manner. In terms of cost effectiveness a therapeutic approach may prove difficult because of issues associated with; identifying those who would benefit the most from this treatment, identifying the type of treatment which would suit them and identifying whether the treatment was successful. The alternative of supporting or providing a stronger stimulus through vaccination, whilst more cost effective, may be a more valuable option in the short term. Both approaches will be addressed in this review.

Hormones and fish monosex farming: A spotlight on immunity

Aquaculture is a promising and developing industry worldwide. One of the first step in monosex culturing, particularly in Nile tilapia, is the production of all-male fry; hormones are widely used in this respect. It is known that exogenous treatment with hormones disrupts various systems in the body including the immune and endocrine systems. There has been a growing interest in how hormones shape the biology of the fish. Many researchers all over the world explored how androgen can interact with many of the body systems; however, rarely any of them tried to improve the hormonal method or to find an alternative. The gate is open for research in this field. This review focusses on the potential effects of hormones, particularly androgens on fish immunity, and the up to date solutions (however, they are rare).

AIRE: a missing link to explain female susceptibility to autoimmune diseases

Women are more susceptible to autoimmune diseases than men. Autoimmunity results from tolerance breakdown toward self-components. Recently, three transcription modulators were identified in medullary thymic epithelial cells that orchestrate immune central tolerance processes: the autoimmune regulator (AIRE), FEZ family zinc finger 2 (FEZF2 or FEZ1), and PR domain zinc finger protein 1 (PRDM1). Interestingly, these three transcription modulators regulate nonredundant tissue-specific antigen subsets and thus cover broad antigen diversity. Recent data from different groups demonstrated that sex hormones (estrogen and testosterone) are involved in the regulation of thymic AIRE expression in humans and mice through direct transcriptional modulation and epigenetic changes. As a consequence, AIRE displays gender-biased thymic expression, with females showing a lower expression compared with males, a finding that could explain the female susceptibility to autoimmune diseases. So far, FEZF2 has not been related to an increased gender bias in autoimmune disease. PRDM1 expression has not been shown to display gender-differential thymic expression, but its expression level and its gene polymorphisms are associated with female-dependent autoimmune disease risk. Altogether, various studies have demonstrated that increased female susceptibility to autoimmune diseases is in part a consequence of hormone-driven reduced thymic AIRE expression.

Genetic and non-genetic determinants of thymic epithelial cell number and function

The thymus is the site of T cell development in vertebrates. In general, the output of T cells is determined by the number of thymic epithelial cells (TECs) and their relative thymopoietic activity. Here, we show that the thymopoietic activity of TECs differs dramatically between individual mouse strains. Moreover, in males of some strains, TECs perform better on a per cell basis than their counterparts in females; in other strains, this situation is reversed. Genetic crosses indicate that TEC numbers and thymopoietic capacity are independently controlled. Long-term analysis of functional parameters of TECs after castration provides evidence that the number of Foxn1-expressing TECs directly correlates with thymopoietic activity. Our study highlights potential complications that can arise when comparing parameters of TEC biology across different genetic backgrounds; these could affect the interpretation of the outcomes of interventions aimed at modulating thymic activity in genetically diverse populations, such as humans.

FLT3 ligand regulates thymic precursor cells and hematopoietic stem cells through interactions with CXCR4 and the marrow niche

Impaired immune reconstitution after hematopoietic stem cell transplantation (HSCT) is attributed in part to impaired thymopoiesis. Recent data suggest that precursor input may be a point of regulation for the thymus. We hypothesized that administration of FLT3 ligand (FLT3L) would enhance thymopoiesis after adoptive transfer of aged, FLT3L-treated bone marrow (BM) to aged, Lupron-treated hosts by increasing murine HSC (Lin^[minus]Sca1⁺c-Kit⁺ [LSK] cells) trafficking and survival. In murine models of aged and young hosts, we show that FLT3L enhances thymopoiesis in aged, Lupron-treated hosts through increased survival and export of LSK cells via CXCR4 regulation. In addition, we elucidate an underlying mechanism of FLT3L action on BM LSK cells-FLT3L drives LSK cells into the stromal niche using Hoescht (Ho) dye perimortem. In summary, we show that FLT3L administration leads to: (1) increased LSK cells and early thymocyte progenitor precursors that can enhance thymopoiesis after transplantation and androgen withdrawal, (2) mobilization of LSK cells through downregulation of CXCR4, (3) enhanced BM stem cell survival associated with Bcl-2 upregulation, and (4) BM stem cell enrichment through increased trafficking to the BM niche. Therefore, we show a mechanism by which FLT3L activity on hematopoeitic and thymic progenitor cells may contribute to thymic recovery. These data have potential clinical relevance to enhance thymic reconstitution after cytoreductive therapy.

A comprehensive review of immunotherapies in prostate cancer

Prostate cancer is the second most common malignant neoplasm in men worldwide and the fifth cause of cancer-related death. Although multiple new agents have been approved for metastatic castration resistant prostate cancer over the last decade, it is still an incurable disease. New strategies to improve cancer control are needed and agents targeting the immune system have shown encouraging results in many tumor types. Despite being attractive for immunotherapies due to the expression of various tumor associated antigens, the microenvironment in prostate cancer is relatively immunosuppressive and may be responsible for the failures of various agents targeting the immune system in this disease. To date, sipuleucel-T is the only immunotherapy that has shown significant clinical efficacy in this setting, although the high cost and potential trial flaws have precluded its widespread incorporation into clinical practice. Issues with patient selection and trial design may have contributed to the multiple failures of immunotherapy in prostate cancer and provides an opportunity to tailor future studies to evaluate these agents more accurately. We have reviewed all the completed immune therapy trials in prostate cancer and highlight important considerations for the next generation of clinical trials.

Effect of gonadotropin-releasing hormone vaccination on T lymphocyte changes in male rats

The aim of this study was to detect the effect of immunization against gonadotropin-releasing hormone (GnRH) on cell-meditated immunity. Three-week-old male Sprague-Dawley rats (n=32) were randomly and equally assigned to two groups: 1) GnRH-tandem-ovalbumin immunized group; and 2) the control group (injected with an equivalent Al(OH)₃ adjuvant). Blood samples were collected at two-week intervals to assess the level of GnRH-specific antibodies and testosterone. Moreover, blood and thymus samples were also collected to analyze the T lymphocyte subpopulations one and two months after the last booster immunization. T lymphocyte immunity against GnRH was activated during the first month post-immunization as exhibited by increased numbers of CD3+ (P<0.05) and CD4+ (P<0.05)T lymphocytes following testosterone suppression (P<0.01), which was then restored and maintained at appropriate levels in the second month. In contrast, the differentiation of T lymphocytes in the thymus was reduced during the first month after immunization as exhibited by the significant decreased number of CD3+ (P<0.05) cells, followed by the restoration and heightened numbers at later time points for both the number of CD3+ (P<0.05) and CD4+ (P<0.01)T lymphocytes. These results suggest that immunization against GnRH interferes with the number of lymphocytes during the early time points following immunization. The number of T lymphocytes initially decreased in the peripheral blood following immunization, but was replenished by newly exported cells from the thymus which eventually restored the T lymphocytes to normal levels.

Medullary thymic epithelial stem cells: role in thymic epithelial cell maintenance and thymic involution

The thymus consists of two distinct anatomical regions, the cortex and the medulla; medullary thymic epithelial cells (mTECs) play a crucial role in establishing central T-cell tolerance for self-antigens. Although the understanding of mTEC development in thymic organogenesis as well as the regulation of their differentiation and maturation has improved, the mechanisms of postnatal maintenance remain poorly understood. This issue has a central importance in immune homeostasis and physiological thymic involution as well as autoimmune disorders in various clinicopathological settings. Recently, several reports have demonstrated the existence of TEC stem or progenitor cells in the postnatal thymus, which are either bipotent or unipotent. We identified stem cells specified for mTEC-lineage that are generated in the thymic ontogeny and may sustain mTEC regeneration and lifelong central T-cell self-tolerance. This finding suggested that the thymic medulla is maintained autonomously by its own stem cells. Although several issues, including the relationship with other putative TEC stem/progenitors, remain unclear, further examination of mTEC stem cells (mTECSCs) and their regulatory mechanisms may contribute to the understanding of postnatal immune homeostasis. Possible relationships between decline of mTECSC activity and early thymic involution as well as various autoimmune disorders are discussed.

Integrating Immunotherapies in Prostate Cancer

In recent years, immunotherapy has emerged as a viable and promising treatment for prostate cancer. Beyond sipulecuel-T, phase III trials are evaluating multiple vaccine and immune-based therapies in men with this disease. Evidence suggests that many of these therapies are effective at augmenting immune responses and slowing tumor growth rates. Yet prospective data evaluating these responses as surrogates for survival are still needed. In the absence of validated intermediate markers of response, growing data suggests that patients with more indolent disease are more likely to benefit from immunotherapies. In order to further optimize immunotherapy use, ongoing trials are evaluating its combination with traditional as well as other immune-based treatments. Preliminary data from these trials are promising and are shedding new light on this area.

Thymus: the next (re)generation

As the primary site of T-cell development, the thymus plays a key role in the generation of a strong yet self-tolerant adaptive immune response, essential in the face of the potential threat from pathogens or neoplasia. As the importance of the role of the thymus has grown, so too has the understanding that it is extremely sensitive to both acute and chronic injury. The thymus undergoes rapid degeneration following a range of toxic insults, and also involutes as part of the aging process, albeit at a faster rate than many other tissues. The thymus is, however, capable of regenerating, restoring its function to a degree. Potential mechanisms for this endogenous thymic regeneration include keratinocyte growth factor (KGF) signaling, and a more recently described pathway in which innate lymphoid cells produce interleukin-22 (IL-22) in response to loss of double positive thymocytes and upregulation of IL-23 by dendritic cells. Endogenous repair is unable to fully restore the thymus, particularly in the aged population, and this paves the way toward the need for exogenous strategies to help regenerate or even replace thymic function. Therapies currently in clinical trials include KGF, use of the cytokines IL-7 and IL-22, and hormonal modulation including growth hormone administration and sex steroid inhibition. Further novel strategies are emerging in the preclinical setting, including the use of precursor T cells and thymus bioengineering. The use of such strategies offers hope that for many patients, the next regeneration of their thymus is a step closer.

Estrogen-mediated downregulation of AIRE influences sexual dimorphism in autoimmune diseases

Autoimmune diseases affect 5% to 8% of the population, and females are more susceptible to these diseases than males. Here, we analyzed human thymic transcriptome and revealed sex-associated differences in the expression of tissue-specific antigens that are controlled by the autoimmune regulator (AIRE), a key factor in central tolerance. We hypothesized that the level of AIRE is linked to sexual dimorphism susceptibility to autoimmune diseases. In human and mouse thymus, females expressed less AIRE (mRNA and protein) than males after puberty. These results were confirmed in purified murine thymic epithelial cells (TECs). We also demonstrated that AIRE expression is related to sexual hormones, as male castration decreased AIRE thymic expression and estrogen receptor α-deficient mice did not show a sex disparity for AIRE expression. Moreover, estrogen treatment resulted in downregulation of AIRE expression in cultured human TECs, human thymic tissue grafted to immunodeficient mice, and murine fetal thymus organ cultures. AIRE levels in human thymus grafted in immunodeficient mice depended upon the sex of the recipient. Estrogen also upregulated the number of methylated CpG sites in the AIRE promoter. Together, our results indicate that in females, estrogen induces epigenetic changes in the AIRE gene, leading to reduced AIRE expression under a threshold that increases female susceptibility to autoimmune diseases.