Clinical strategies to enhance T cell reconstitution

Donor natural killer cells trigger production of β-2-microglobulin to enhance post-bone marrow transplant immunity

Allogeneic hematopoietic transplantation is a powerful treatment for hematologic malignancies. Posttransplant immune incompetence exposes patients to disease relapse and infections. We previously demonstrated that donor alloreactive natural killer (NK) cells ablate recipient hematopoietic targets, including leukemia. Here, in murine models, we show that infusion of donor alloreactive NK cells triggers recipient dendritic cells (DCs) to synthesize β-2-microglobulin (B2M) that elicits the release of c-KIT ligand and interleukin-7 that greatly accelerate posttransplant immune reconstitution. An identical chain of events was reproduced by infusing supernatants of alloreactive NK/DC cocultures. Similarly, human alloreactive NK cells triggered human DCs to synthesize B2M that induced interleukin-7 production by thymic epithelial cells and thereby supported thymocyte cellularity in vitro. Chromatography fractionation of murine and human alloreactive NK/DC coculture supernatants identified a protein with molecular weight and isoelectric point of B2M, and mass spectrometry identified amino acid sequences specific of B2M. Anti-B2M antibody depletion of NK/DC coculture supernatants abrogated their immune-rebuilding effect. B2M knock-out mice were unable to undergo accelerated immune reconstitution, but infusion of (wild-type) NK/DC coculture supernatants restored their ability to undergo accelerated immune reconstitution. Similarly, silencing the B2M gene in human DCs, before coculture with alloreactive NK cells, prevented the increase in thymocyte cellularity in vitro. Finally, human recombinant B2M increased thymocyte cellularity in a thymic epithelial cells/thymocyte culture system. Our studies uncover a novel therapeutic principle for treating posttransplant immune incompetence and suggest that, upon its translation to the clinic, patients may benefit from adoptive transfer of large numbers of cytokine-activated, ex vivo-expanded donor alloreactive NK cells.

Tumor Arrests DN2 to DN3 Pro T Cell Transition and Promotes Its Conversion to Thymic Dendritic Cells by Reciprocally Regulating Notch1 and Ikaros Signaling

Tumor progression in the host leads to severe impairment of intrathymic T-cell differentiation/maturation, leading to the paralysis of cellular anti-tumor immunity. Such suppression manifests the erosion of CD4⁺CD8⁺ double-positive (DP) immature thymocytes and a gradual increase in CD4^-CD8^- double negative (DN) early T-cell progenitors. The impact of such changes on the T-cell progenitor pool in the context of cancer remains poorly investigated. Here, we show that tumor progression blocks the transition of Lin^-Thy1.2⁺CD25⁺CD44⁺c-Kit^lowDN2b to Lin^-Thy1.2⁺CD25⁺CD44^-c-Kit^-DN3 in T-cell maturation, instead leading to DN2-T-cell differentiation into dendritic cells (DC). We observed that thymic IL-10 expression is upregulated, particularly at cortico-medullary junctions (CMJ), under conditions of progressive disease, resulting in the termination of IL-10R^high DN2-T-cell maturation due to dysregulated expression of Notch1 and its target, CCR7 (thus restricting these cells to the CMJ). Intrathymic differentiation of T-cell precursors in IL-10^-/- mice and in vitro fetal thymic organ cultures revealed that IL-10 promotes the interaction between thymic stromal cells and Notch1^low DN2-T cells, thus facilitating these DN2-T cells to differentiate toward CD45⁺CD11c⁺MHC-II⁺ thymic DCs as a consequence of activating the Ikaros/IRF8 signaling axis. We conclude that a novel function of thymically-expressed IL-10 in the tumor-bearing host diverts T-cell differentiation toward a DC pathway, thus limiting the protective adaptive immune repertoire.

Advances in Ex Vivo T Cell Depletion - Where Do We Stand?

Graft-versus-host (GVHD) is an important cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). As donor T cells are recognized as key drivers of GVHD, some approaches to prevent GVHD have focused on T cell depletion of the allograft. In this review we summarize methods and outcomes of ex vivo T cell depleted (TCD) HCT with a focus on CD34+ selection. This platform is efficacious in preventing acute and chronic GVHD across a wide range of hematologic malignancies, and with the exception of chronic myeloid leukemia, is not associated with adverse relapse or survival outcomes compared to conventional GVHD prophylaxis platforms. In retrospective comparisons recipients of CD34+ selected HCT have higher rates of GVHD-free relapse-free survival (GRFS) than conventional HCT counterparts. Although CD34+ selected allografts require myeloablative and antithymocyte-globulin based conditioning to support engraftment, abrogation of calcineurin inhibitors and methotrexate in this approach reduces its toxicity such that it can be considered in select older and more comorbid patients who could benefit from ablative HCT. A trial comparing GVHD prophylaxis regimens (BMT CTN 1301, NCT02345850) has completed accrual and will be the first to compare CD34+ selected HCT with conventional HCT in a randomized prospective setting. Its findings have potential to establish CD34+ selected HCT as a new standard-of-care platform for GVHD prevention.

Characteristic analysis of TCR β-chain CDR3 repertoire for pre- and post-liver transplantation

Liver cirrhosis of hepatitis B is an immune-related disease in which liver cells die during the body’s immune system activation to clear the virus, and the progress is closely related to T lymphocytes. T lymphocyte cells recognise antigens, specifically by major histocompatibility complex (MHC), through a membrane protein T cell receptor (TCR). Here, we used high throughput immune repertoire sequencing technique to study the characteristics and diversity of the TCR repertoire between patients who underwent liver transplantation and healthy controls (NC). We sequenced the TCR β-chain complementary-determining region 3 (CDR3) repertoire in peripheral blood mononuclear cells (PBMCs) from 6 liver transplantation patients before transplantation (Pre) and on the first (Post1) and seventh days (Post7) after transplantation along with 6 NC. We observed that the distributions of CDR3, VD indel, and DJ indel lengths were similar among the Pre, Post1, Post7 and NC groups. We found that the TCR repertoire diversity of transplantation groups was relatively lower compared to NC group. The Pre-group had more highly expanded T cell clones compared to Post1, Post7 and NC groups, and the diversity of the T cell repertoire of the Post7 group was significantly decreased compared to the Pre, Post1 and NC groups. In addition, we found our results also show that various TRBV expression increased and some public sequences at different time points after liver transplantation, and the expression levels of 3 TRBV segments and 2 TRBJ segments were also significantly different in Pre, Post1, Post7 and NC groups. Moreover, 1 aa sequence shared by all liver transplantation patients and 2 aa sequences shared by at least two groups, which may serve as biomarkers to monitor the immune status of liver transplant patients.

Interleukin-7 and Immunosenescence

The age of an individual is an important, independent risk factor for many of the most common diseases afflicting modern societies. Interleukin-7 (IL-7) plays a central, critical role in the homeostasis of the immune system. Recent studies support a critical role for IL-7 in the maintenance of a vigorous healthspan. We describe the role of IL-7 and its receptor in immunosenescence, the aging of the immune system. An understanding of the role that IL-7 plays in aging may permit parsimonious preventative or therapeutic solutions for diverse conditions. Perhaps IL-7 might be used to "tune" the immune system to optimize human healthspan and longevity.

Engineering Cell Surfaces with Polyelectrolyte Materials for Translational Applications

Engineering cell surfaces with natural or synthetic materials is a unique and powerful strategy for biomedical applications. Cells exhibit more sophisticated migration, control, and functional capabilities compared to nanoparticles, scaffolds, viruses, and other engineered materials or agents commonly used in the biomedical field. Over the past decade, modification of cell surfaces with natural or synthetic materials has been studied to exploit this complexity for both fundamental and translational goals. In this review we present the existing biomedical technologies for engineering cell surfaces with one important class of materials, polyelectrolytes. We begin by introducing the challenges facing the cell surface engineering field. We then discuss the features of polyelectrolytes and how these properties can be harnessed to solve challenges in cell therapy, tissue engineering, cell-based drug delivery, sensing and tracking, and immune modulation. Throughout the review, we highlight opportunities to drive the field forward by bridging new knowledge of polyelectrolytes with existing translational challenges.

T cell repertoire following kidney transplantation revealed by high-throughput sequencing

Delayed T cell recovery and restricted T cell receptor (TCR) diversity after kidney transplantation are associated with increased risks of infection and malignancy. Technical challenges limit the faithful measurement of TCR diversity after kidney transplantation. In this study, we used a combination of multiplex-PCR, Illumina sequencing and IMGT/HighV-QUEST to directly assess millions of TCRs per individual before and at two time points after kidney transplantation (1days and 7days after transplantation) in a cohort of 10 patients compared to a normal control (NC) group (n=10). We identified the most commonly observed CDR3 length, VD indel length, and DJ indel length in transplantation group and normal group. In addition, we found that the TCR repertoire diversity of transplantation groups was relatively lower compared to NC group. T cell depletion in Post-1 group can be observed, which resulted in the altered distribution characteristics of clonotype abundance. A modest proportion of high abundance clones were shared among the pre-1 group, post-1 group and post-7 group, and it did not exist in the NC group, which exhibited a signature of antigen selection. Moreover, our results also demonstrated that various TRBV expression increased and some public sequences at different time points after kidney transplantation, which may provide biomarkers to monitor the immune status of transplant patients.

Sex steroid ablation: an immunoregenerative strategy for immunocompromised patients

Age-related decline in thymic function is a well-described process that results in reduced T-cell development and thymic output of new naïve T cells. Thymic involution leads to reduced response to vaccines and new pathogens in otherwise healthy individuals; however, reduced thymic function is particularly detrimental in clinical scenarios where the immune system is profoundly depleted such as after chemotherapy, radiotherapy, infection and shock. Poor thymic function and restoration of immune competence has been correlated with an increased risk of opportunistic infections, tumor relapse and autoimmunity. Apart from their primary role in sex dimorphism, sex steroid levels profoundly affect the immune system in general and, in fact, age-related thymic involution has been at least partially attributed to the increase in sex steroids at puberty. Subsequently it has been demonstrated that the removal of sex steroids, or sex steroid ablation (SSA), triggers physiologic changes that ultimately lead to thymic re-growth and improved T-cell reconstitution in settings of hematopoietic stem cell transplant (HSCT). Although the cellular and molecular process underlying these regenerative effects are still poorly understood, SSA clearly represents an attractive therapeutic approach to enhance thymic function and restore immune competence in immunodeficient individuals.

Improving cell-based therapies by nanomodification

Cell-based therapies are emerging as a promising approach for various diseases. Their therapeutic efficacy depends on rational control and regulation of the functions and behaviors of cells during their treatments. Different from conventional regulatory strategy by chemical adjuvants or genetic engineering, which is restricted by limited synergistic regulatory efficiency or uncertain safety problems, a novel approach based on nanoscale artificial materials can be applied to modify living cells to endow them with novel functions and unique properties. Inspired by natural "nano shell" and "nano compass" structures, cell nanomodification can be developed through both external and internal pathways. In this review, some novel cell surface engineering and intracellular nanoconjugation strategies are summarized. Their potential applications are also discussed, including cell protection, cell labeling, targeted delivery and in situ regulation. It is believed that these novel cell-material complexes can have great potentials for biomedical applications.

Efficacy and safety of CDX-301, recombinant human Flt3L, at expanding dendritic cells and hematopoietic stem cells in healthy human volunteers

Fms-like tyrosine kinase-3 ligand (Flt3L) uniquely binds the Flt3 (CD135) receptor expressed on hematopoietic stem cells (HSCs), early progenitor cells, immature thymocytes and steady-state dendritic cells (DCs) and induces their proliferation, differentiation, development and mobilization in the bone marrow, peripheral blood and lymphoid organs. CDX-301 has an identical amino-acid sequence and comparable biological activity to the previously tested rhuFlt3L, which ceased clinical development over a decade ago. This Phase 1 trial assessed the safety, pharmacokinetic, pharmacodynamic and immunologic profile of CDX-301, explored alternate dosing regimens and examined the impact of rhuFlt3L on key immune cell subsets. Thirty healthy volunteers received CDX-301 (1-75 μg/kg/day) over 5-10 days. One event of Grade 3 community-acquired pneumonia occurred. There were no other infections, dose-limiting toxicities or serious adverse events. CDX-301 resulted in effective peripheral expansion of monocytes, hematopoietic stem and progenitor cells and key subsets of myeloid DCs and plasmacytoid DCs, with no clear effect on regulatory T cells. These data from healthy volunteers support the potential for CDX-301, as monotherapy or in combination with other agents, in various indications including allogeneic HSC transplantation and immunotherapy, but the effects of CDX-301 will need to be investigated in each of these patient populations.

IL-18 acts in synergy with IL-7 to promote ex vivo expansion of T lymphoid progenitor cells

Although IL-18 has not previously been shown to promote T lymphopoiesis, results obtained via a novel data mining algorithm (global microarray meta-analysis) led us to explore a predicted role for this cytokine in T cell development. IL-18 is a member of the IL-1 cytokine family that has been extensively characterized as a mediator of inflammatory immune responses. To assess a potential role for IL-18 in T cell development, we sort-purified mouse bone marrow-derived common lymphoid progenitor cells, early thymic progenitors (ETPs), and double-negative 2 thymocytes and cultured these populations on OP9-Delta-like 4 stromal layers in the presence or absence of IL-18 and/or IL-7. After 1 wk of culture, IL-18 promoted proliferation and accelerated differentiation of ETPs to the double-negative 3 stage, similar in efficiency to IL-7. IL-18 showed synergy with IL-7 and enhanced proliferation of both the thymus-derived progenitor cells and the bone marrow-derived common lymphoid progenitor cells. The synergistic effect on the ETP population was further characterized and found to correlate with increased surface expression of c-Kit and IL-7 receptors on the IL-18-treated cells. In summary, we successfully validated the global microarray meta-analysis prediction that IL-18 affects T lymphopoiesis and demonstrated that IL-18 can positively impact bone marrow lymphopoiesis and T cell development, presumably via interaction with the c-Kit and IL-7 signaling axis.

TNFα polymorphism as marker of immunosenescence for rheumatoid arthritis patients

BACKGROUND

Expansion of CD4(+)CD28(null), a common feature of immunosenescence, which has been reported in rheumatoid arthritis (RA) patients, may also be associated with a CD4(+) imbalance. Although the increase of CD4(+)CD28(null) cells has been related to TNFα exposure, nothing is known about the possible role of genetic variants of this cytokine.

METHODS

Participants were genotyped for TNFA rs1800629 (-308 G>A) and frequency of the CD4(+)CD28(null), regulatory T cells and Th1 cells subsets were quantified in peripheral blood samples by flow cytometry in 129 RA patients and 33 healthy controls.

RESULTS

The expansion of CD4(+)CD28(null) cells in RA patients was associated with TNFA genotype, even at diagnosis, and linked to markers of aggressive disease in patient carriers of the minor allele. Analysis of regulatory T cells and IFNγ-CD4(+) expression suggested that defective suppression and/or Th1-shift could underlie the expansion of this population in these patients. Finally, although treatment with TNFα-blockers reduced CD4(+)CD28(null) cells in most patients, only those carriers of the common GG genotype reached values within the range of HC and showed a disease activity improvement correlated to this decrease.

CONCLUSIONS

Our results provide evidence for a genetic basis of the premature immunosenescence of RA patients and highlight its potential role in clinical outcome after TNFα blockade.

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.

Umbilical cord-derived mesenchymal stem cells regulate thymic epithelial cell development and function in Foxn1(-/-) mice

Thymic microenvironments are essential for the maturation of thymocytes, which can be anatomically compartmentalized into cortical and medullar regions. The absence of the gene encoding the transcription factor forkhead box n1 (Foxn1) causes epithelial differentiation to stall in the precursor stage, resulting in the formation of an abnormal thymus. In this study, we used human umbilical cord-derived mesenchymal stem cells (UC-MSCs) to treat Foxn1(-/-) mice, and then analyzed the maturation and distribution of thymic epithelial cells in the Foxn1(-/-) thymic rudiment and the thymopoiesis of this newly developed rudiment. Our data showed a well-organized cortex-medulla architecture and an obvious improvement in the maturation of thymic epithelial cells along with the appearance of UEA-1(+)MHCII(hi) thymic epithelial cells in the rudiment. We further demonstrated improved thymopoiesis and the enhanced export of mature T cells with increased numbers of regulatory T cells into the peripheral blood. Furthermore, we observed that MSCs can engraft into thymic tissue and express many cytokines or proteins, particularly keratinocyte growth factor (KGF) and CD248, which are essential for thymic development. Collectively, our data identified a new mechanism for MSCs, which may provide a proper microenvironment for the reconstitution and functional maturation of the thymus in Foxn1(-/-) mice. Additionally, we elicited additional insights into the therapeutic efficacy of MSCs in several autoimmune diseases.

Human proT-cells generated in vitro facilitate hematopoietic stem cell-derived T-lymphopoiesis in vivo and restore thymic architecture

Hematopoietic stem cell transplantation (HSCT) is followed by a period of immune deficiency due to a paucity in T-cell reconstitution. Underlying causes are a severely dysfunctional thymus and an impaired production of thymus-seeding progenitors in the host. Here, we addressed whether in vitro-derived human progenitor T (proT)-cells could not only represent a source of thymus-seeding progenitors, but also able to influence the recovery of the thymic microenvironment. We examined whether co-transplantation of in vitro-derived human proT-cells with hematopoietic stem cells (HSCs) was able to facilitate HSC-derived T-lymphopoiesis posttransplant. A competitive transfer approach was used to define the optimal proT subset capable of reconstituting immunodeficient mice. Although the 2 subsets tested (proT1, CD34(+)CD7(+)CD5(-); proT2, CD34(+)CD7(+)CD5(+)) showed thymus engrafting function, proT2-cells exhibited superior engrafting capacity. Based on this, when proT2-cells were coinjected with HSCs, a significantly improved and accelerated HSC-derived T-lymphopoiesis was observed. Furthermore, we uncovered a potential mechanism by which receptor activator of nuclear factor κb (RANK) ligand-expressing proT2-cells induce changes in both the function and architecture of the thymus microenvironment, which favors the recruitment of bone marrow-derived lymphoid progenitors. Our findings provide further support for the use of Notch-expanded progenitors in cell-based therapies to aid in the recovery of T-cells in patients undergoing HSCT.

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.

Thymic rejuvenation and aging

The thymus is a vital organ for homeostatic maintenance of the peripheral immune system. It is within this mediastinal tissue that T cells develop and are extensively educated and exported to the periphery for establishment of a functional and effective immune system. A striking paradoxical feature of this critical lymphoid tissue is that it undergoes profound age-associated involution. Thymic decline is of minimal consequence to healthy individuals, but the reduced efficacy of the immune system with age has direct etiological linkages with an increase in diseases including opportunistic infections, autoimmunity, and incidence/burden of cancer. Furthermore the inability of adults to restore immune function following insult induced by chemotherapy, ionizing radiation exposure or therapy, and infections (e.g. HIV-1) leads to increased morbidity and often mortality in the elderly. For these reasons, it is important that investigators strive to translate their understanding of mechanisms that drive thymic involution, and develop safe and effective strategies to rejuvenate the thymus in settings of clinical need. In this review, we present a discussion of the current status of thymic rejuvenation efforts associated with: sex steroid ablation, cytokines, growth factors, and hormones.

Quantitative assessment of T cell repertoire recovery after hematopoietic stem cell transplantation

Delayed T-cell recovery and restricted T-cell receptor (TCR) diversity after allogeneic hematopoietic stem cell transplantation (allo-HSCT) are associated with increased risks of infection and cancer relapse. Technical challenges have limited faithful measurement of TCR diversity following allo-HSCT. Here we combined 5′-RACE PCR with deep sequencing, to quantify TCR diversity in 28 allo-HSCT recipients using a single oligonucleotide pair. Analysis of duplicate blood samples confirmed that the frequency of individual TCRs was accurately determined. After 6 months, cord blood graft recipients approximated the TCR diversity of healthy individuals, whereas recipients of T-cell-depleted peripheral blood stem cell grafts had a 28-fold and 14-fold lower CD4⁺ and CD8⁺ T-cell diversity, respectively. After 12 months, these deficiencies had improved for the CD4⁺, but not the CD8⁺ T-cell compartment. Overall, this method provides unprecedented views of T-cell repertoire recovery after allo-HSCT and may identify patients at high risk of infection or relapse.

Persistent viral infections and immune aging

Immunosenescence comprises a set of dynamic changes occurring to both, the innate as well as the adaptive immune system that accompany human aging and result in complex manifestations of still poorly defined deficiencies in the elderly population. One of the most prominent alterations during aging is the continuous involution of the thymus gland which is almost complete by the age of 50. Consequently, the output of naïve T cells is greatly diminished in elderly individuals which puts pressure on homeostatic forces to maintain a steady T cell pool for most of adulthood. In a great proportion of the human population, this fragile balance is challenged by persistent viral infections, especially Cytomegalovirus (CMV), that oblige certain T cell clones to monoclonally expand repeatedly over a lifetime which then occupy space within the T cell pool. Eventually, these inflated memory T cell clones become exhausted and their extensive accumulation accelerates the age-dependent decline of the diversity of the T cell pool. As a consequence, infectious diseases are more frequent and severe in elderly persons and immunological protection following vaccination is reduced. This review therefore aims to shed light on how various types of persistent viral infections, especially CMV, influence the aging of the immune system and highlight potential measures to prevent the age-related decline in immune function.

Greater than the sum of their parts: combination strategies for immune regeneration following allogeneic hematopoietic stem cell transplantation

Cytoreductive conditioning regimes designed to allow for successful allogeneic hematopoietic stem cell transplantation (allo-HSCT) paradoxically are also detrimental to recovery of the immune system in general but lymphopoiesis in particular. Post-transplant immune depletion is particularly striking within the T cell compartment which is exquisitely sensitive to negative regulation, evidenced by the profound decline in thymic function with age. As a consequence, regeneration of the immune system remains a significant unmet clinical need. Over the past decade studies have revealed several promising therapeutic strategies to address ineffective lymphopoiesis and post-transplant immune deficiency. These include the use of cytokines such as IL-7, IL-12 and IL-15; growth factors and hormones like keratinocyte growth factor (KGF), insulin-like growth factor (IGF)-1 and growth hormone (GH); adoptive transfer of ex vivo-generated precursor T cells (pre-T) and sex steroid ablation (SSA). Moreover, recently several novel approaches have been proposed to generate whole thymii ex vivo using stem cell technologies and bioscaffolds. Increasingly, however, when transferred to the clinic, these strategies alone are not sufficient to restore thymopoiesis in all patients leading to the potential of combination strategies as a way to reign in non-responders. Synergistic enhancement in combination may be due to differential targets may therefore be effective in improving clinical outcomes in the transplant settings as well as in other lymphopenic states induced by high dose chemotherapy/radiation therapy or HIV, and may also be useful in improving responses to vaccination and augmenting anti-tumor immunotherapy.

Enhancing Cell therapies from the Outside In: Cell Surface Engineering Using Synthetic Nanomaterials

Therapeutic treatments based on the injection of living cells are in clinical use and preclinical development for diseases ranging from cancer to cardiovascular disease to diabetes. To enhance the function of therapeutic cells, a variety of chemical and materials science strategies are being developed that engineer the surface of therapeutic cells with new molecules, artificial receptors, and multifunctional nanomaterials, synthetically endowing donor cells with new properties and functions. These approaches offer a powerful complement to traditional genetic engineering strategies for enhancing the function of living cells.

Aging and immune function: molecular mechanisms to interventions

Abstract The immune system of an organism is an essential component of the defense mechanism aimed at combating pathogenic stress. Age-associated immune dysfunction, also dubbed "immune senescence," manifests as increased susceptibility to infections, increased onset and progression of autoimmune diseases, and onset of neoplasia. Over the years, extensive research has generated consensus in terms of the phenotypic and functional defects within the immune system in various organisms, including humans. Indeed, age-associated alterations such as thymic involution, T cell repertoire skewing, decreased ability to activate naïve T cells and to generate robust memory responses, have been shown to have a causative role in immune decline. Further, understanding the molecular mechanisms underlying the generation of proteotoxic stress, DNA damage response, modulation of ubiquitin proteasome pathway, and regulation of transcription factor NFκB activation, in immune decline, have paved the way to delineating signaling pathways that cross-talk and impact immune senescence. Given the role of the immune system in combating infections, its effectiveness with age may well be a marker of health and a predictor of longevity. It is therefore believed that a better understanding of the mechanisms underlying immune senescence will lead to an effective interventional strategy aimed at improving the health span of individuals. Antioxid. Redox Signal. 14, 1551-1585.

Age-associated remodeling of neural and nonneural thymic catecholaminergic network affects thymopoietic productivity

Ageing is associated with a progressive decline in thymic cytoarchitecture followed by a less efficient T cell development and decreased emigration of naïve T cells to the periphery. These thymic changes are linked to increased morbidity and mortality from infectious, malignant and autoimmune diseases in old age. Therefore, it is of paramount importance to understand the thymic homeostatic processes across the life span, as well as to identify factors and elucidate mechanisms driving or contributing to the thymic involution. Catecholamines (CAs) derived from sympathetic nerves and produced locally by thymic cells represent an important component of the thymic microenvironment. In young rats, they provide a subtle tonic suppressive influence on T cell development acting via β(2)- and α(1)-adrenoceptors (ARs) expressed on thymic nonlymphoid cells and thymocytes. In the face of thymic involution, a progressive increase in the thymic noradrenaline level, reflecting a rise in the density of noradrenergic nerve fibers and CA-synthesizing cells, occurs. In addition, the density of β(2)- and α(1)-AR-expressing thymic nonlymphoid cells and the α(1)-AR thymocyte surface density also exhibit a pronounced increase with age. The data obtained from studies investigating effects of AR blockade on T cell development indicated that age-related changes in CA-mediated thymic communications, certainly those involving α(1)-ARs, may contribute to diminished thymopoietic efficiency in the elderly. Having in mind thymic plasticity in the course of ageing, and broadening possibilities for pharmacological modulation of CA signaling, we here present and discuss the progress in research related to a role of CAs in thymic homeostasis and age-related decay in the thymic naïve T cell output.

Key players for T-cell regeneration

PURPOSE OF REVIEW

The thymus provides a unique and essential microenvironment for T-cell precursors to develop into mature functionally competent T lymphocytes. Ageing causes architectural changes in the thymus resulting in a loss of thymic epithelial space required for thymopoiesis - a process known as thymic involution. Additionally, cytoablative regimens used to treat malignancies also destroy thymic architecture. The net result of both processes is diminished thymic output and function that may lead to impaired immunity. Thus, immunocompromised individuals would benefit from strategies aimed at enhancing T-cell reconstitution.

RECENT FINDINGS

Here we discuss strategies such as the use of sex steroid ablation, keratinocyte growth factor, interleukin-7, and in-vitro-generated progenitor T cells as candidates for restoring T-cell immunity. Using various animal models of ageing or hematopoietic stem cell transplantation, these strategies have been shown to restore thymic architecture and cellularity, resulting in increased output and T-cell function in the periphery.

SUMMARY

These candidate approaches are currently being tested in clinical trials, with preliminary evidence showing encouraging effects on T-cell reconstitution. Nevertheless, although these strategies show clear promise in animal models, and in early human trials, further data are needed to determine their efficacy in patients.

IL-7 and lymphopenia

Interleukin-7 (IL-7) is a growth and anti-apoptotic factor for T-lymphocytes, with potential for clinical use in the treatment of immunodeficiencies due to loss of T-cells. Lymphopenia induced by disease (HIV infection, hemodialysis or Idiopathic CD4+ lymphopenia) or by treatment (high dose chemotherapy or depleting antibodies) for cancer or auto-immune diseases results in increased circulating levels of IL-7 which decline with T-cell recovery, however, the mechanism of such response remains to be elucidated. Furthermore, IL-7 is a major player in the regulation of peripheral T-cell homeostasis and as such is an important candidate cytokine for therapy aimed at improving T-cell reconstitution following lymphopenia. Anti- IL-7 is on the other hand proposed to treat conditions where IL-7 may play a more direct role in pathogenesis such as autoimmune disease like Rheumatoid Arthritis, Multiple Sclerosis or Inflammatory Bowel disease.

Rheumatoid arthritis: a role for immunosenescence?

Aging is accompanied by a progressive decline in the integrity of the immune system, a process known as immunosenescence. Pathological features typical of immune dysfunction in older adults, encompassing dysregulation of innate and adaptive immune responses, characterize rheumatoid arthritis (RA), an autoimmune disease whose incidence increases with age. Recent evidence suggests that certain features of immunosenescence, such as the decrease in T-cell generation and diversity, may contribute to the development of RA. Thus, physiological immunosenescence may render older adults susceptible to RA, and premature immunosenescence may contribute to the development of RA in young adults. In addition, other features of immunosenescence may result from the chronic immune stimulation that occurs in RA and lead to worsening of the disease. This article reviews the immunopathological features common to aging and RA and discusses the mechanisms by which immunosenescence may contribute to the development or progression of RA.

Allogeneic haematopoietic stem cell transplantation: individualized stem cell and immune therapy of cancer

The year 2009 marked the fiftieth anniversary of the first successful allogeneic haematopoietic stem cell transplant (HSCT). The field of HSCT has pioneered some of the most exciting areas of research today. HSCT was the original stem cell therapy, the first cancer immune therapy and the earliest example of individualized cancer therapy. In this Timeline article we review the history of the development of HSCT and major advances made in the past 50 years. We highlight accomplishments made by researchers who continue to strive to improve outcomes for patients and increase the availability of this potentially life-saving therapy for patients with otherwise incurable malignancies.

Postnatal tissue-specific disruption of transcription factor FoxN1 triggers acute thymic atrophy

The transcription factor FoxN1 is essential for differentiation of thymic epithelial cell (TEC) progenitors during thymic organogenesis. However, limited information is available on the postnatal contribution of FoxN1 to thymic maintenance. To address this question, we generated a loxP-floxed FoxN1 (fx) mouse with three different promoter-driven inducible CreER(T) transgenes. Postnatal ubiquitous deletion of FoxN1 caused dramatic thymic atrophy in 5 days and more severe deterioration in medullary TECs (mTECs) than in cortical TECs (cTECs). Induction of FoxN1 deletion selectively in K5 promoter-driven somatic epithelial cells (mostly mTECs and possibly some adult epithelial stem cells) was sufficient to cause significant thymic atrophy, whereas FoxN1 deletion in K18 promoter-driven somatic epithelial cells (mostly cTECs) was not. Thymic atrophy resulted from increased apoptosis and was associated with activation of the p53 gene in mature mTECs. Although FoxN1 is required for the development of both mTECs and cTECs in thymic organogenesis, it is most important for the maintenance of mTECs in the postnatal thymus, which are in turn necessary to prevent thymic atrophy.

21st century endocrinology

Recent developments in the field of diabetes and endocrinology have led to greater understanding of the body's complex hormonal axes. This article reviews the latest significant treatments which have the potential to impact greatly on a wide variety of disease states in the not too distant future.

Impaired CD4-cell immune reconstitution upon HIV therapy in patients with toxoplasmic encephalitis compared to patients with pneumocystis pneumonia as AIDS indicating disease

OBJECTIVES

There is only little data on immune reconstitution in antiretroviral naive AIDS-patients with toxoplasmosis. The observation of several cases with reduced increase of CD4-cells upon start of antiretroviral treatment (ART) prompted us to investigate the topic using the ClinSurv cohort.

METHODS

17 German HIV treatment centers contribute to ClinSurv, a multicentre observational cohort under the auspices of the Robert Koch Institute. We retrospectively selected all antiretroviral-naive patients with toxoplasmic encephalitis (TE) and - as comparator group - with pneumocystosis (PCP) between January 1999 and December 2005.

RESULTS

A total of 257 patients were included in the analysis, 61 with TE and 196 with PCP. Demographic baseline data showed differences with regard to gender, transmission group, and baseline CD4 superset+ counts (60.9 vs. 44.7/microl, p = 0.022). After ART-initiation the increase in CD4 superset+ lymphocytes was lower in the TE- versus the PCP-group in the first, second and fourth three-month-period (74.4 vs. 120.3/microl, p = 0.006; 96.6 vs. 136.2/microl, p = 0.021; 156.5 vs. 211.5/microl, p = 0.013). Viral load (VL) was higher in the PCP-group at baseline (4.46 log subset10cop/ml vs. 5.00 log subset10cop/ml, p = 0.008), while virological success of ART was equal.

CONCLUSIONS

Our data show for the first time that the average CD4 superset+ T-cell increase of patients with toxoplasmosis is impaired compared to PCP-patients. Most clinicians would not be prepared to discontinue follow-up TE-therapy unless CD4 superset+ counts of 200/microl are reached. Explanation for our finding might be the myelosuppressive side effect of pyrimethamine, possible interactions of toxoplasmosis therapy with ART, or an unknown direct biological influence of toxoplasmosis on immune restoration.

Rejuvenation of the aging T cell compartment

The elderly face significant risk for susceptibility to infection and cancer because of declining immune function. Various agents used in the setting of bone marrow transplantation and aging studies represent promising approaches to combating T cell defects in the aging population. Preclinical and clinical studies on the T cell reconstitution effects of sex steroid ablation, keratinocyte growth factor, the growth hormone pathway, and the cytokines interleukin-7, interleukin-12, and interleukin-15 indicate that these strategies may be used to alleviate the effects of T cell deficiencies in the elderly.

Role of ovarian hormones in age-associated thymic involution revisited

A commonly held view that ovarian hormones are causally involved in age-associated thymic involution has been recently challenged. In particular, their relevance in the progression of thymic involution has been disputed. To reassess this issue 10-month-old rats with well advanced thymic involutive changes were ovariectomized (Ovx), and after 1 month thymic cellularity, thymocyte development and levels of recent thymic emigrants (RTEs) were examined in peripheral blood and spleen. In addition, the distribution of major conventional and regulatory T-cell subsets was analyzed in the same peripheral lymphocyte compartments. Ovariectomy increased thymic weight and cellularity above the levels in both 10-month-old and age-matched controls indicating that ovarian hormone ablation not only prevented further progression of thymic involution, but also reversed it. The increased thymic cellularity was accompanied by altered thymocyte differentiation/maturation culminating in increased thymic output of naïve T cells as indicated by elevated levels of both CD4+ and CD8+ RTEs in peripheral blood and spleen. The changes in T-cell development produced: (i) a disproportional increase in cellularity across thymocyte subsets, so that relative proportions of cells at all maturational stages preceding the CD4+CD8+ T cell receptor (TCR)alphabeta(low) stage were reduced; the relative numbers of CD4+CD8+ TCRalphabeta(low) cells entering positive selection and their immediate CD4+CD8+ TCRalphabeta(high) descendents were increased, while those of the most mature CD4+CD8- and CD4-CD8+ TCRalphabeta(high) cells remained unaltered; (ii) enhanced cell proliferation across all thymocyte subsets and (iii) reduced apoptosis of cells within the CD4+CD8+ thymocyte subset. The augmented thymic output of naïve T cells in Ovx rats most likely reflected an early disinhibition of thymocyte development followed by increased positive/reduced negative selection, at least partly, due to raised thymocyte surface Thy-1 expression. The greater number of CD4+CD25+Foxp3+ cells in both thymus and peripheral blood suggested augmented thymic production of these cells. In addition, an increased CD4+/CD8+ cell ratio was found in the spleen of Ovx rats. Thus, ovarian hormone ablation led not only to increased diversity of the T-cell repertoire, but also to a new balance among distinct T-cell subsets in the periphery.

Thymic function in juvenile idiopathic arthritis

OBJECTIVE

Thymic function declines exponentially with age. Impaired thymic function has been associated with autoimmune disease in adults but has never been formally assessed in childhood autoimmunity. Therefore, thymic function in children with the autoimmune disease juvenile idiopathic arthritis (JIA) was determined.

METHODS

Thymic function was measured in 70 children and young adults with JIA (age range 2.1-30.8 (median 10.4)) and 110 healthy age-matched controls using four independent assays. T cell receptor excision circles (WBLogTREC/ml) and the proportion of CD4(+) CD45RA(+)CD31(+) T cells (representing recent thymic emigrants; %RTEs) were quantified and intrathymic proliferation measured by calculating the alphaTREC/SigmabetaTREC ratio. Lastly, regulatory T cells (T(Reg)) of thymic origin (CD4(+)FOXP3(+)) were quantified in peripheral blood to assess the ability of the thymus in JIA to generate this T cell subset.

RESULTS

Thymic function was equivalent by all four parameters in JIA when compared with the control population. Furthermore, there was no consistent effect of JIA subtype on thymic function, although intrathymic proliferation was higher in the small rheumatoid factor (RF)(+) polyarticular group. There were no significant effects of disease-modifying antirheumatic drugs (DMARDs) or oral corticosteroids on thymic function, although those with the worst prognostic ILAR (International League of Associations for Rheumatology) subtypes were also those most likely to be on a DMARD.

CONCLUSIONS

It is demonstrated that children and young adults with JIA, unlike adults with autoimmune diseases, have thymic function that is comparable with that of healthy controls. The varied pathologies represented by the term "JIA" suggest this observation may not be disease specific and raises interesting questions about the aetiology of thymic impairment in adult autoimmunity.

Thymopoiesis in elderly human is associated with systemic inflammatory status

Immunosenescence studies of age-related immune system damage focused on clinical lymphopenic situations or androgenic blockade have revealed new insights about adult human immune reconstitution. However, as far as we know, the extent of lymphopoiesis in the thymus of elderly humans remains unclear. To this effect, we have analyzed 65 adult human thymuses (from 36 to 81 years; median age 68.6 years) obtained from patients who underwent cardiac surgery. Our results show a correlation between CD4(+)CD8(+) double-positive (DP) cells and both the age (inverse) and percentage (direct) of peripheral naive T cells, indicating that the thymus is still able to affect the peripheral lymphocyte pool even in the elderly. We also found significant correlation between the degree of thymopoiesis and the inflammation markers, as shown by the inverse correlations between DP and the percentage of neutrophils and IL-6 levels and the percentage of peripheral lymphocytes. Furthermore, in a multivariate linear regression the percentage of DP and IL-7 levels, but not age, were independently associated with the percentage of neutrophils. In conclusion, the thymus maintains, even in the elderly, an active thymopoiesis that rejuvenates the peripheral naive T-cell pool. Moreover, age-related thymopoietic decay is associated with the peripheral inflammation markers.

The drug monosodium luminol (GVT) preserves thymic epithelial cell cytoarchitecture and allows thymocyte survival in mice infected with the T cell-tropic, cytopathic retrovirus ts1

A mutant of MoMuLV, called ts1, causes an AIDS-like syndrome in susceptible strains of mice. In mice infected at birth, thymic atrophy, CD4+ T cell loss, body wasting, and death occur by approximately 30-40 days postinfection (dpi). We have shown previously that the death of ts1-infected cells is not caused by viral replication per se, but by oxidative stress and apoptosis following their accumulation the ts1 viral envelope precursor protein, gPr80(env). In infected mice treated with the antioxidant monosodium alpha-luminol (GVT), T cell loss and thymic atrophy are delayed for many weeks, and body wasting and death do not occur until long after infected, untreated control mice have died. We show here that GVT treatment of ts1-infected mice maintains the thymic epithelial cell (TEC) cytoarchitecture and cytokeratin gradients required for thymocyte differentiation. It also suppresses thymocyte reactive oxygen species (ROS) levels, upregulates and stabilizes levels of the antioxidant-regulating transcription factor Nrf2, and prevents accumulation of gPr80(env) in thymocytes. We conclude that GVT treatment can make ts1 a non-cytopathic virus for thymocytes, although it cannot prevent thymocyte infection. Since oxidative stress also contributes to the loss of T cells in HIV-AIDS, the antioxidant effects of GVT may make it a useful therapeutic adjunct to HAART treatment.

The ageing immune system: is it ever too old to become young again?

Ageing is accompanied by a decline in the function of the immune system, which increases susceptibility to infections and can decrease the quality of life. The ability to rejuvenate the ageing immune system would therefore be beneficial for elderly individuals and would decrease health-care costs for society. But is the immune system ever too old to become young again? We review here the promise of various approaches to rejuvenate the function of the immune system in the rapidly growing ageing population.

Keratinocyte growth factor enhances DNA plasmid tumor vaccine responses after murine allogeneic bone marrow transplantation

Keratinocyte growth factor (KGF), which is given exogenously to allogeneic bone marrow transplantation (allo-BMT) recipients, supports thymic epithelial cells and increases thymic output of naive T cells. Here, we demonstrate that this improved T-cell reconstitution leads to enhanced responses to DNA plasmid tumor vaccination. Tumor-bearing mice treated with KGF and DNA vaccination have improved long-term survival and decreased tumor burden after allo-BMT. When assayed before vaccination, KGF-treated allo-BMT recipients have increased numbers of peripheral T cells, including CD8(+) T cells with vaccine-recognition potential. In response to vaccination, KGF-treated allo-BMT recipients, compared with control subjects, generate increased numbers of tumor-specific CD8(+) cells, as well as increased numbers of CD8(+) cells producing interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). We also found unanticipated benefits to antitumor immunity with the administration of KGF. KGF-treated allo-BMT recipients have an improved ratio of T effector cells to regulatory T cells, a larger fraction of effector cells that display a central memory phenotype, and effector cells that are derived from a broader T-cell-receptor repertoire. In conclusion, our data suggest that KGF can function as a potent vaccine adjuvant after allo-BMT through its effects on posttransplantation T-cell reconstitution.

The immunopathology of thymic GVHD

The clinical success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the appropriate reconstitution of the host's immune system. While recovery of T-cell immunity may occur in transplant recipients via both thymus-dependent and thymus-independent pathways, the regeneration of a population of phenotypically naive T cells with a broad receptor repertoire relies entirely on the de novo generation of T-cells in the thymus. Preclinical models and clinical studies of allogeneic HSCT have identified the thymus as a target of graft-versus-host disease (GVHD), thus limiting T-cell regeneration. The present review focuses on recent insight into how GVHD affects thymic structure and function and how this knowledge may aid in the design of new strategies to improve T-cell reconstitution following allogeneic HSCT.

Determination of thymic function directly from peripheral blood: a validated modification to an established method

The thymus contributes naïve, self MHC reactive, self tolerant T cells to the peripheral immune system throughout life, albeit with a log-linear decline with age. Quantification of thymic function is clinically relevant in the setting of lymphoablation, but a phenotypic marker distinguishing recent thymic emigrants from long lived naïve T cells remains elusive. T cell receptor excision circles (TREC) are present in thymocytes exiting the thymus and quantification of the most frequent of these, the deltarec-psiJalpha rearrangement has been widely used as a measure of recent thymic function. However, interpretation of results presented as TREC per cell has been criticised on the basis that extra-thymic cellular proliferation impacts on peripherally determined TREC numbers. TREC/ml is now considered to be more representative of thymic function than TREC/cell, especially where significant cellular proliferation occurs (e.g. during reconstitution following stem cell transplantation). Here we describe the validation of a novel variation to the established assay, directly quantifying TREC/ml from 300 microl whole blood. We show the assay to be reproducible, robust and stable longitudinally and we show equivalence of performance when compared with more standard assays. This assay particularly lends itself to the measurement of thymic function in children and where monitoring clinical variables is limited by tissue availability.