Marker For Recent Thymic Emigrants Research Articles

A very low thymus function identifies patients with substantial increased risk for long-term mortality after kidney transplantation

BackgroundEnd-stage renal disease is associated with premature ageing of the T cell immune system but inter-individual variation is substantial. The hypothesis was tested that advanced immunological T cell ageing assessed by peripheral T cell differentiation increases the long-term mortality risk after renal transplantation.ResultsCirculating T cells of 211 recipients of a kidney from a living donor were analyzed before and in the first year after transplantation. The number of CD31-positive naive T cells (as a marker for recent thymic emigrants) and the differentiation status of the memory T cells was assessed. Thirty recipients died during follow-up of at least 5 years. Absolute numbers of naive CD4+ (living:258 cells/μl vs. deceased:101 cells/μl, p < 0.001) and naive CD8+ T cells (living:97 cells/μl vs. deceased:37 cells/μl, p < 0.001) were significantly lower in the deceased group prior to transplantation. In a multivariate proportional hazard analysis the number of naive CD4+ T cells remained associated with all-cause mortality (HR 0.98, CI 0.98–0.99, p < 0.001). The low number of naive T cells in the deceased patient group was primarily caused by a decrease in recent thymic emigrants (i.e. less CD31+ naive T cells) indicating a lowered thymus function. In addition, the physiological age-related compensatory increase in CD31− naïve T cells was not observed. Within the first year after transplantation, the number and characteristics of naive T cells remained stable.ConclusionsA severe reduction in circulating naïve T cells because of a decrease in recent thymic emigrants is highly associated with all-cause mortality after renal transplantation.

Maintained thymic output of conventional and regulatory T cells during human pregnancy

Maintained thymic output of conventional and regulatory T cells during human pregnancy

P40. Does IL8 (CXCL8) have a role in thymoma progression and as a marker for relapse

Thymomas are rare tumours of thymic epithelium for which surgical resection is the definitive treatment. The thymus is the organ in which T cells mature. During development in the thymus, T cells acquire their unique T cell receptor (TCR) through somatic recombination. Mature naive T cells that exit the thymus harbour small circles of DNA that are by-products of somatic recombination known as TCR excision circles (TRECs). Although stable, TRECs are not replicative and hence are a marker of recent thymic emigrants (RTEs). We have recently shown that thymocytes and subsequently RTEs, unlike more mature peripheral blood T cells, produce the cytokine interleukin 8 (IL8/CXCL8). This ability appears to be lost with repeated stimulation and expansion. Therefore, T cell production of IL8, like TREC levels, is a marker of RTEs and thymic activity. Our recent data proposes two questions in relation to this tumour type: (I) Could IL8 together with TREC levels act as a biomarker for tumour recurrence? (II) Does IL8 have a role as a growth factor for thymoma? After resection, macroscopic recurrence is usually detected in patients by active surveillance with serial axial imaging. There is some data in the literature to suggest that TREC levels are higher in patients with recurrence compared to those without. This raises the possibility of using RTEs to aid in surveillance and guide the judicious use of imaging. Our initial data suggests that even after R0 margins, both TRECs and IL8 producing T cells can be detected in the periphery, albeit at very low levels. However, we hypothesize that intra-patient monitoring of TREC levels and IL8 producing T cells may still be useful as a biomarker for recurrence. Moreover, the fact that IL-8 is associated with tumour maintenance through its functions in angiogenesis; cancer cell growth and survival; and modification of immune responses, indicates that this may be an important growth factor in thymoma. We hope to address this using resected material in comparison with normal thymuses.

Reduced thymic output in elite athletes

Athletes undergoing intensive training schedules have chronic exposure to stress-induced hormones such as cortisol that can depress immune function. We compared the circulating levels of T cell receptor excision circles (TREC), a marker of recent thymic emigrants, as well as the levels of naïve and memory subsets in a group of elite endurance athletes and in controls. The athletes showed a reduction in absolute numbers of naïve T cells, particularly in CD4 T cells. In contrast, memory cells were increased. TREC levels in the athletes were significantly reduced compared to age-matched controls. Such changes resemble premature ageing of the T cell component of the immune system. Since thymic production of T cells naturally decline with age, these results raise the concern that prolonging high intensity exercise into the 4th decade of life may have deleterious consequences for athletes' health.

Increased levels of circulating Helios+ FoxP3+ natural regulatory T cells in systemic lupus erythematosus

ObjectivesThe authors aimed to analyse the coexpression level of Helios, a member of the Ikaros transcription factor family, in FoxP3+ regulatory T cell (Treg) subsets to characterise the pool of...

Different Proliferative Potential and Migratory Characteristics of Human CD4+ Regulatory T Cells That Express either CD45RA or CD45RO

Although human naturally occurring regulatory T cells (Tregs) may express either CD45RA or CD45RO, we find in agreement with previous reports that the ( approximately 80%) majority of natural Tregs in adults are CD45RO(+). The proportion of CD45RA(+) Tregs decreases, whereas CD45RO(+) Tregs increase significantly with age. Nevertheless, a small proportion of CD45RA(+) Tregs are found even in old (>80 y) adults and a proportion of these express CD31, a marker for recent thymic emigrants. We found that CD45RO(+) Tregs were highly proliferative compared with their CD45RA(+) counterparts. This was due in part to the conversion of CD45RA Tregs to CD45RO expression after activation. Another difference between these two Treg populations was their preferential migration to different tissues in vivo. Whereas CD45RA(+) Tregs were preferentially located in the bone marrow, associated with increased CXCR4 expression, CD45RO(+) Tregs were preferentially located in the skin, and this was associated with their increased expression of CLA and CCR4. Our studies therefore show that proliferation features strongly in maintenance of the adult Treg pool in humans and that the thymus may make a minor contribution to the maintenance of the peripheral pool of these cells, even in older adults. Furthermore, the different tissue compartmentalization of these cells suggests that different Treg niches exist in vivo, which may have important roles for their maturation and function.

Distribution of CD31 on CD4 T-Cells from Cord Blood, Peripheral Blood and Tonsil at Different Stages of Differentiation~!2009-11-24~!2009-12-24~!2010-03-05~!

CD31+ is a marker for recent thymic emigrants. Nevertheless it is present in a proportion of memory cells. We looked at the distribution of CD31 on CD4 T-cell subpopulations. In cord blood, CD31 was present in the majority of the CD45RA high and 60% of the CD45RA low cells, and in adults over 70% of true naive and in 5-10% of all memory sub- populations (central memory, effector memory, follicular helper and T regulatory cells). No major differences were seen in the distribution of chemokine receptors between CD31+ and CD31- populations within the naive cells nor the memory populations except for CCR3 and CCR9, which were preferentially expressed in the CD31+ memory cells. The CD31 distribution and cytokine receptors was similar between HIV negative and positive individuals, and between adult blood and tonsils. There was a correlation between the levels of TRECs and the percentages of CD31 in all samples studied.

CD31 (PECAM‐1) is a marker of recent thymic emigrants among CD4+ T‐cells, but not CD8+ T‐cells or γδ T‐cells, in HIV patients responding to ART

Some severely immunodeficient HIV patients experience poor recovery of CD4(+) T-cell counts on antiretroviral therapy (ART). Evaluation of the function of thymopoiesis in T-cell production in individual patients requires a simple marker of T-cells that have recently emigrated from the thymus. Here, we address whether expression of CD31 on CD4(+) T-cells, CD8(+) T-cells, regulatory T-cells and gammadelta T-cells correlates with other indicators of thymus function. Adult HIV-1 patients (n=27) with nadir CD4(+) T-cell counts <100 per mul and a sustained virological response to ART and healthy controls (n=23) were studied. CD31 expression was assessed by flow cytometry, T-cell receptor excision circles content by real-time PCR and thymic volume by spiral computed tomography. Proportions of CD4(+) T-cells expressing CD45RA and CD31 declined with age in HIV patients (P=0.03) and healthy controls (P<0.0001), and correlated directly with other markers of thymus function. In controls, proportions of CD8(+) T-cells expressing CD45RA and CD31 declined with age (P=0.003) and correlated directly with some markers of thymus function, but this was not seen in HIV patients. Proportions of CD45RA(+) CD31(+) gammadelta T-cells were higher in patients than controls (P=0.007) and did not correlate with thymus volume. In controls, proportion of gammadelta T-cells co-expressing CD45RA and CD31 increased with age (P=0.002). These data support the use of CD31 as a marker of recent thymic origin in CD4(+) T-cells, but not CD8(+) T-cells in HIV patients receiving ART. In such patients, CD31 expression is unlikely to indicate thymic origin in gammadelta T-cells.

Effect of KGF (Palifermin) On Immune Reconstitution After Autologous Transplantation for Multiple Myeloma.

Abstract 1152Poster Board I-174 IntroductionHuman-keratinocyte growth factor 1(KGF) is currently being evaluated in clinical trials for its safety and efficacy in preventing mucosal damage from irradiation and after bone marrow transplantation (BMT). It has been suggested that, besides having preventive effects on oral mucositis, it may also have immunomodulating effects by uniquely protecting thymic epithelial cells. A potential clinical application of KGF is the amelioration of prolonged post BMT-immune deficiency in BMT recipients. In animal models of autologous and allogeneic BMT, KGF administration during BMT resulted in enhanced thymopoiesis and increased peripheral T-cell numbers. Therefore, a potential clinical application of KGF is the improvement of prolonged post BMT-immune deficiency in BMT recipients. Thymopoiesis can be assessed by analysis of T-cell receptor excision circles (TREC). This marker for recent thymic emigrants might be a novel prognostic factor for outcome after transplantation in multiple myeloma patients. We investigated the potential influence of KGF on immune reconstitution after autologous transplantation for myeloma using this marker. Materials and MethodsTwenty-four myeloma patients from a single institution were treated homogeneously with the induction combination bortezomib (Velcade®) plus dexamethasone (DXM), followed by high dose melphalan (140-200 mg/m2) and an autologous transplantation with peripheral blood stem cells. Patients were randomized for KGF treatment in 2 groups, 11 having received three doses of palifermin (Kepivance®) (60 μg/kg once daily i.v.) pre- and post-conditioning regimen (total six doses). Blood samples were drawn at diagnosis, before BMT, and at 1, 3, 6, 9, 12 and 18 months post BMT. We analysed signal joint (sj) TREC in peripheral blood lymphocytes using quantitative RT-PCR. The percentage and absolute numbers of lymphocyte populations were monitored by flow cytometry. Values were expressed as means ± SEM. Patient groups were compared by the Mann-Whitney test. ResultsBoth CD4+ and CD8+ naïve T cells (CD45RA+ CCR7+) were strongly decreased by pretransplantation bortezomib plus DXM treatment. SjTREC decreased sharply after transplantation and returned to baseline after 1 year without differences between the two groups of patients. Natural regulatory T lymphocytes (phenotypically assessed as CD4+ CD25 high, CD127 low) were not modified by KGF treatment either. Notably, the CD3+ cell population was significantly higher during the first 3 months post BMT in KGF treated patients (1518 ± 380 vs 821 ± 105 CD3+/blood mL, p = 0.032 at 1 month post BMT). This was related to a higher CD8+ cell counts, specifically in the CD8 effector memory cells (assessed as CD45 RA- CCR7-) (790 ± 320 vs 292 ± 55, p< 0.05 at 1 month post BMT). No correlation was found with documented infectious complications, relapse or survival. ConclusionsThese data suggest that, unexpectedly, the main effect of KGF on immunity in that autologous BMT setting, is not to be accounted by changes in thymic function but rather by the peripheral expansion of CD8+ effector memory cells which could be favoured by the treatment prior BMT and/or by the post-BMT lymphopenia. DisclosuresNo relevant conflicts of interest to declare.

Recent Thymic Emigrants Do Not Account for the Increased Number of TCells Seen in the Lungs of Stable Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) patients have an increased number of T cells within their lungs. It is unknown whether these T cells, remain there forever or if there is a continuous turnover from the blood. In the adult, there is a significant T lymphocytopoiesis from the thymus producing cells known as recent thymic emigrants (RTEs). T cell receptor excision circles (TREC) are a marker of RTEs. We investigated the number of TREC in blood from patients with untreated stable, mild to moderate COPD (n=6) compared with age-matched smokers with normal lung function (n=6) and nonsmokers (n=8). The results showed variable expression of TREC in each subject group and no sig- nificant difference between TREC expressions in any group of subjects. Changes in T-cell numbers in the lung of stable COPD patients may reflect prolonged survival or proliferation of these cells within the lung rather than continuous re- cruitment from the blood.

Relationship between Changes in Thymic Emigrants and Cell-Associated HIV-1 Dna in HIV-1-Infected Children Initiating Antiretroviral Therapy

To investigate the relationship between cell-associated HIV-1 dynamics and recent thymic T-cell emigrants, HIV-1 DNA and T-cell receptor rearrangement excision circles (TREC, a marker of recent thymic emigrants) were measured in peripheral blood mononuclear cells in 181 samples from 33 HIV-1-infected children followed for 96 weeks after antiretroviral therapy (ART) initiation. At baseline, HIV-1 DNA was higher in children with higher TREC (P=0.02) and was not related to age, CD4 or HIV-1 RNA in multivariate analyses (P>0.3). Overall, TREC increased and HIV-1 DNA decreased significantly after ART initiation, with faster HIV-1 DNA declines in children with higher baseline TREC (P=0.009). The greatest decreases in HIV-1 DNA occurred in children with the smallest increases in TREC levels during ART (P=0.002). However, this inverse relationship between changes in HIV-1 DNA and TREC tended to vary according to the phase of HIV-1 RNA decline (P=0.13); for the same increase in TREC, HIV-1 DNA decline was much smaller during persistent or transient viraemia compared with stable HIV-1 RNA suppression. Overall, these findings indicate that TREC levels predict HIV-1 DNA response to ART and suggest that immune repopulation by thymic emigrants adversely affects HIV-1 DNA decline in the absence of persistent viral suppression, possibly by providing a cellular source for viral infection and replication.

Impact of thymectomy on the peripheral T cell pool in rhesus macaques before and after infection with simian immunodeficiency virus

The goal of this study was to define, by surgical removal of the thymus in juvenile rhesus macaques, the role of the thymus in peripheral T cell homeostasis and to assess the significance of thymic output in SIV infection. By monitoring the changes in phenotypic T cell markers as well as in the numbers of TCR excisional circles--a recently described marker for recent thymic emigrants--following thymectomy, we present evidence that surgical thymectomy in juvenile macaques results in a faster decay of peripheral CD4(+) cells, but does not cause a substantial shift in CD45RA(+) and CD45RA(-) populations. We were able to measure a thymic output of 0.32% and 0.21% per day of CD4(+) and CD8(+) cells, respectively. No compensatory extra-thymic source was detected in lymphoid tissues, although there was a small compensatory increase in T cell proliferation in the peripheral T cell pool. After SIV infection, thymectomized animals did not have higher viral loads, greater T cell decay, or faster disease progression. We therefore conclude that peripheral destructive processes, rather than a loss of thymic output, appear to be the main causes of T cell depletion in SIV infection.

Differential expression of the cytokine receptors for human interleukin (IL)-12 and IL-18 on lymphocytes of both CD45RA+ and CD45RO+ phenotype from tonsils, cord and adult peripheral blood

The objective of this study was to demonstrate the variable expression of cytokine receptors on naive versus memory human CD4+ T cell subpopulations in tonsillar tissue, cord blood and adult blood. We prove that the receptors for both interleukin (IL)-12 and IL-18 are expressed exclusively on memory T cells. This observation was seen not only on the CD45RO+ memory T cells but also on a significant percentage of the CD45RA+, CD62L-, CD27- and CCR7- populations. Furthermore, CD45RA+ CD62L+, CD27+ or CCR7+ CD4+ T cells that expressed IL-12Rbeta1 and IL-18Ralpha did not express CD31, a marker for recent thymic emigrants. We reveal that cord blood lymphocytes do not express IL-12Rbeta1 whereas IL-18Ralpha expression was detected at low levels. Importantly, the IL-12Rbeta2 signalling chain, which is absent in all resting T cells, was up-regulated in both CD45RA+ and CD45RO+ T cells as a result of stimulation with anti-CD3 and anti-CD28 in vitro. This observed up-regulation was, however, restricted to 80% of the total CD4+ population. Finally, a very small proportion of the CD4+ CD45RO+ tonsillar T cells expressed the IL-12 and IL-18 receptors, thereby establishing the differential expression of these receptors between peripheral and tonsillar memory T cell subpopulations.

Recent thymic emigrants and prognosis in T- and B-cell childhood hematopoietic malignancies.

The concentration of T-cell receptor rearrangement excision DNA circles (TRECs) in peripheral blood mononuclear cells (PBMCs) is currently known to be a marker of recent thymic emigrants. We evaluated the hypothesis that TREC values would be lower in childhood T-cell hematopoietic malignancies than in childhood B-cell acute lymphoblastic leukemia (ALL) or healthy controls because the former category may reflect compromised thymic function. From the Greek national childhood leukemia/lymphoma database we obtained all 30 available T-cell leukemia/non-Hodgkin's lymphoma cases, 30 age- and sex-matched childhood B-cell origin cases of ALL and 60 healthy hospital controls. We compared TREC levels in PBMCs using a real-time PCR assay. There was highly significant reduction of TREC values in children with T-cell malignancies (median 3,100 TRECs/10(6) PBMCs), whereas children with B-cell origin ALL had slightly but nonsignificantly lower TREC values compared to healthy children (medians 19,300 and 22,500 TRECs/10(6) PBMCs, respectively). During a median follow-up period of about 19 months, only 4 children died. All of them had a T-cell hematopoietic malignancy and relatively low TREC values. The number of TRECs was higher among healthy girls than among healthy boys, and a similar pattern was evident in T-cell malignancies. It appears that there is a pattern of concordance of high TREC values with better disease prognosis in hematologic childhood malignancies. This applies to specific disease entities with better prognosis (B-cell origin ALL having higher TREC values than T-cell leukemia/lymphoma) and to gender, another important predictor of prognosis conditional on disease entity (girls having higher TREC values than boys); however, it may also be true for the survival of individual patients. These preliminary findings can be used as hypothesis-generating indications that should be confirmed in larger data sets.

Immune consequences of mutations in the human common γ-chain gene

A mutation (c.878T > A) in the common gamma chain (γ c) causes an X-linked combined immunodeficiency (XCID) in a large kindred of British origin. In the disease, γ c is expressed, but its binding to Jak3 is reduced. The immune deficiencies and clinical course were less marked in toddlers and school age children with XCID L293Q than in severe combined immunodeficiency (SCID). However, affected newborns were profoundly deficient in thymic size and T cells. In some affected infants, thymic size and numbers of T cells gradually increased during the first year. Their clinical course was relatively benign. In affected infants of one lineage, the number of blood T cells failed to increase substantially. They succumbed to opportunistic infections. T cell deficiencies in XCID L293Q progressively worsened during adolescence. Decreased thymic function, failure to rescue T cells from apoptosis, and replication senescence were possible causes. Blood T cells with the phenotype CD45RA +CD62L + (unstimulated T cells) were most depressed. CD4 + T cells were also deficient in a specific marker of recent thymic emigrants, episomal DNA deletion circles created during TcR gene rearrangements. Apoptosis of T cells was increased, but neither apoptosis nor cell death was age-related. In contrast, telomere shortening in T cells increased with age. Unlike murine γ c gene deletions, γδ T cells were prominent in affected adolescents and young adults. Furthermore, T cells with a Vδ2/Vγ9 specificity declined with age and were replaced in the oldest male with a Vδ1 specificity. Thus, the mutation provides many insights concerning the role of γ c in the biology of T cells.

Age-related changes in CCR9+ circulating lymphocytes: are CCR9+ naive T cells recent thymic emigrants?

The chemokine receptor CCR9 is reported to be predominantly expressed by thymocytes as well as by circulating gut-homing and resident T cells in the small intestinal mucosa. Its ligand thymus-expressed chemokine (TECK) is produced by thymic and small intestinal epithelium. Here we report that the proportion of circulating CCR9+ naive T cells (mostly CD4+) declines with age, from approximately 15% of all T cells at birth to around 1% in adults. The proportion of CCR9+ T cells lacking the classical gut-homing receptor alpha4beta7, was much higher in children than in adults. Therefore, circulating CD3+CCR9+CD45RA+ cells have most likely left the thymus quite recently. This notion was supported by the small number of CCR9+ naive T cells which was present shortly after thymectomy. Establishing a phenotypic marker for recent thymic emigrants might provide a powerful tool in the clinical assessment and follow-up after cancer chemotherapy, hematopoietic stem cell transplantation, and during antiretroviral treatment of human immunodeficiency virus (HIV)-infected patients.