HIV-infected Patients with a Large Thymus Maintain Higher CD4 Counts in a 5-year Follow-up Study of Patients Treated with Highly Active Antiretroviral Therapy

CD4 recovery in HIV-infected patients treated with highly active antiretroviral therapy (HAART) is in part believed to be dependent on the degree of preserved thymic function. We investigated whether the thymus has a prolonged effect on CD4 recovery. Total and naïve CD4 counts as well as thymic output determined as the number of CD4 +  cells containing T-cell receptor-rearrangement excision DNA circles were measured prospectively in 25 HIV-infected patients with known thymic size during 5 years of HAART. Patients with larger thymic size had at all time points of follow-up significantly higher CD4 counts than patients with minimal thymic size ( P  = 0.0036). The CD4 increase from time of initiation of HAART until 6 months of follow-up differed significantly between the two thymic groups ( P  = 0.045), but did not at later time points. Thymic output remained significantly higher in patients with larger thymic size at follow-up. However, no difference in the increase in thymic output was seen between thymic groups. In conclusion, the importance of the thymus to the rate of cellular restoration seems primarily to lie within the first two years of HAART. However, patients with larger thymic size are able to maintain higher CD4 counts even after 5 years of HAART.     

Changes in thymus volume in adult HIV-infected patients under HAART: correlation with the T-cell repopulation

An important thymus role has been suggested in T‐cell repopulation after HAART in adult HIV‐1 infected patients. Thymus volume increase after treatment has been described in HIV‐1 infected children but not in adult patients. The objective of this work was to evaluate the effect of HAART on the thymic volume of adult HIV‐1 infected patients and its relation with the T‐cell repopulation. Twenty‐one adult patients following 24 weeks under HAART were included in the study. All patients underwent a thoracic computed tomography (CT) evaluation for the measurement of thymic volumes at weeks 0, 12 and 24. Baseline thymus volume showed a significant correlation with the patient's age. Thymic volume significantly increased after 24 weeks of HAART. Besides, a significant correlation between changes in the thymus volume and changes in both total and naïve CD4+ cell counts was found. Only patients with increases ≥100 CD4+ cell counts after treatment significantly increased the thymic volume. These data show the first evidence of an early change in thymic volume of adult HIV‐1 infected patients under HAART. This increase was related to the rise of both total and naïve CD4+ cell counts suggesting a functional role of thymic volume increase.     

A remarkable depletion of both naïve CD4+ and CD8+ with high proportion of memory T cells in an IPEX infant with a FOXP3 mutation in the forkhead domain

IPEX is a rare X-linked syndrome, with immune dysfunction, polyendocrinopathy and enteropathy. We describe an infant who died at the age of 11 months after developing eczema, severe diarrhoea, diabetes, hypothyroidism, thrombocytopenia and four episodes of septicaemia. Immunophenotyping of peripheral blood at 8 months revealed normal CD3+ T, CD4+ T and CD8+ T cell numbers, with low NK and B cells. CD4+ and CD8+ T lymphocytes showed remarkably low numbers and percentages of naïve cells and high numbers of memory CD4 and CD8 cells. At autopsy, an intense depletion of immune cells in thymus, spleen and lymph nodes was observed. No Hassall's corpuscles were found in thymus. Lymphocytic pancreatitis and intense villous atrophy with mucosal lymphocytic infiltration in small bowel were also seen. FOXP3 gene studies revealed a: C→G substitution 3 bp upstream of exon 10, which prevents splicing between exons 9 and 10, likely resulting in a functionally altered or deficient protein. Florid clinical findings are usually observed in association of forkhead DNA-binding domain mutations. The intense depletion of naïve T cells we report suggest that depletion of immune cells might take place due to uncontrolled activation due to the absence of regulatory T cells.     

Premature ageing of the immune system underlies immunodeficiency in ataxia telangiectasia

ATM kinase modulates pathways implicated in premature ageing and ATM genotype predicts survival, yet immunodeficiency in ataxia telangiectasia is regarded as mild and unrelated to age. We address this paradox in a molecularly characterised sequential adult cohort with classical and mild variant ataxia telangiectasia. Immunodeficiency has the characteristics of premature ageing across multiple cellular and molecular immune parameters. This immune ageing occurs without previous CMV infection. Age predicts immunodeficiency in genetically homogeneous ataxia telangiectasia, and in comparison with controls, calendar age is exceeded by immunological age defined by thymic naïve CD4+ T cell levels. Applying ataxia telangiectasia as a model of immune ageing, pneumococcal vaccine responses, characteristically deficient in physiological ageing, are predicted by thymic naïve CD4+ T cell levels. These data suggest inherited defects of DNA repair may provide valuable insight into physiological ageing. Thymic naïve CD4+ T cells may provide a biomarker for vaccine responsiveness in elderly cohorts.     

Low CD4+ T-cell counts in HIV patients receiving effective antiretroviral therapy are associated with CD4+ T-cell activation and senescence but not with lower effector memory T-cell function

The adverse effects of immune activation on CD4(+) T-cell recovery and the relationship between CD4(+) T-cell counts and effector T-cell function were examined in HIV-1 patients receiving long-term effective ART. Patients with nadir CD4(+) T-cell counts <100/microl, > 12 months on ART and >6 months with <50 HIV RNA copies/ml were stratified by current CD4(+) T-cell counts and patients from the lowest (n = 15) and highest (n = 12) tertiles were studied. We assessed proliferation (Ki67), activation (HLA-DR, CD38) and replicative senescence (CD57) by flow cytometry and CD4(+) T-cell responses to CMV by IFN-gamma ELISpot. Proportions of CD4(+) T-cells expressing HLA-DR or CD57 were strong univariate predictors of total (P = 0.0002 and P = 0.002) and naive (P < 0.0001 and P < 0.0001, respectively) CD4(+) T-cell counts, suggesting that CD4(+) T-cell activation drives the depletion of naive CD4(+) T-cells. This was clearest in patients with a small/undetectable thymus. IFN-gamma responses to CMV were similar in patients with low or high CD4(+) T-cell counts.     

Increases in CD4+ T lymphocytes occur without increases in thymic size in HIV-infected subjects receiving interleukin-2 therapy

OBJECTIVE: To examine the potential contribution of the thymus to CD4+ T-lymphocyte increases in HIV-infected patients receiving intermittent interleukin-2 (IL-2) therapy. DESIGN: Fifteen HIV-infected patients treated with antiretroviral regimens who were enrolled in a study of intermittent IL-2 therapy and were willing to undergo serial thymic computed tomography (CT) were prospectively studied. METHODS: Thymic CT was performed before and approximately 6 and 12-17 months after intermittent IL-2 therapy was started. Scans were graded in a blinded manner. Changes in lymphocyte subpopulations were determined by flow cytometry. RESULTS: Statistically significant increases in CD4+ T lymphocytes occurred with IL-2 administration, with a preferential increase in naive relative to memory CD4+ T cells. Despite this increase in naive CD4+ T cells, overall there was a modest decrease in thymic volume observed during the study period. No correlation was found between changes in thymic volume indices and total, naive, or memory CD4+ T-lymphocyte counts. CONCLUSIONS: These findings demonstrate that the profound CD4+ T-lymphocyte increases seen with intermittent IL-2 administration are not associated with increases in thymic volume and more likely are due to peripheral expansion rather than increased thymic output.     

Pathology of the thymus after allogeneic bone marrow transplantation in man. A histologic immunohistochemical study of 36 patients.

A major hypothesis to explain the immunodeficiency associated with bone marrow transplantation states that thymic epithelial damage due to graft-versus-host disease (GVHD) abrogates or delays the recovery of normal immunologic function. This study evaluated the thymus glands of 36 human bone marrow transplant recipients dying between 4 and 1742 days after transplant using histology, histochemistry, and immunohistology. The observations lead to a model of thymic damage by irradiation, chemotherapy, and GVHD in which early injury by all three of these agents results in profound thymic atrophy followed by long-delayed restitution. Patients undergoing total body irradiation showed more severe damage to thymic cortical and medullary epithelium than did patients undergoing chemotherapy alone as preparation for transplantation. Patients with GVHD showed additional damage in the form of individual thymic epithelial cell death and showed HLA-DR surface protein expression on thymic epithelium during GVHD. Longer-term survivors showed a profoundly delayed restitution of normal thymic epithelium and delayed evidence of restored lymphopoiesis. A few patients dying late after transplant showed evidence of reconstitution of normal thymic structure or nodules of lymphopoiesis in focal areas of epithelial-cell reconstitution. Evidence of such lymphopoiesis was seen at times ranging between 90 and 1742 days after grafting. The data are consistent with a model of long-standing thymic damage caused by GVHD which is reversible after the development of tolerance.     

Thymus transplantation

Thymus transplantation is a promising investigational therapy for infants born with no thymus. Because of the athymia, these infants lack T cell development and have a severe primary immunodeficiency. Although thymic hypoplasia or aplasia is characteristic of DiGeorge anomaly, in “complete” DiGeorge anomaly, there is no detectable thymus as determined by the absence of naive (CD45RA⁺, CD62L⁺) T cells. Transplantation of postnatal allogeneic cultured thymus tissue was performed in sixty subjects with complete DiGeorge anomaly who were under the age of 2 years. Recipient survival was over 70%. Naive T cells developed 3–5 months after transplantation. The graft recipients were able to discontinue antibiotic prophylaxis, and immunoglobulin replacement. Immunosuppression was used in a subset of subjects but was discontinued when naive T cells developed. The adverse events have been acceptable with thyroid disease being the most common. Research continues on mechanisms underlying immune reconstitution after thymus transplantation.     

FK506 attenuates thymic output in patients with myasthenia gravis

Introduction

Myasthenia gravis (MG) is an antibody-mediated, T-cell-dependent autoimmune disease. The symptoms are caused by high-affinity IgG against the muscle acetylcholine receptor (AChR) at the neuromuscular junction. The production of these antibodies in B-cells depends on AChR-specific CD4⁺ T-cells and the thymus gland seems to play a significant role in the pathogenesis of MG. Altered thymic T-cell export seems to be associated with a pathological mechanism in myasthenia gravis. Tacrolimus (FK506) has recently been used to treat MG.

Material and methods

We examined the effects of tacrolimus on thymic T-cell export in patients with MG. Sixteen patients with nonthymomatous and/or thymectomized MG were treated with oral administrations of tacrolimus. To assess the effect of tacrolimus on the thymic output, we assayed the levels of T-cell receptor excision circle (TREC), a molecular marker of thymus emigrants.

Results

T-cell receptor excision circle was not significantly different from those in age-matched controls before tacrolimus therapy, but they were partially decreased 4 months after tacrolimus therapy. T-cell receptor excision circle levels were significantly decreased in the thymomatous group (p < 0.05), but not in the nonthymomatous group. Tacrolimus treatment significantly attenuated TREC levels in cultured CD4^–CD8⁺ cells (p < 0.05), but total cell counts were not significantly changed.

Conclusions

These results indicate that TREC levels may become a marker of the curative effect of tacrolimus therapy for thymomatous MG, and that tacrolimus suppresses not only activating T-lymphocytes, but also naïve T-cells.     

胸腺在EAE 小鼠不同临床时期变化的研究

目的:探讨胸腺在EAE 小鼠不同临床时期的变化。方法:记录小鼠EAE 模型诱导后第0、10、15、20 天的胸腺指数和胸腺细胞数;应用流式细胞术观察胸腺细胞的凋亡比例和脾脏CD4+ CD44+ T 细胞的比例;应用PCR 和电泳技术观察凋亡因子p53 和Bcl-2 的含量变化。结果:EAE 小鼠在第0、10、15 天胸腺指数和胸腺细胞数相应地逐渐减少;第10、15 天胸腺细胞凋亡率升高,第10 天最高;CD4+ CD44+ T 细胞比例在第10、15 天升高,第10 天最高;EAE 诱导第10 天胸腺细胞p53 含量升高,而Bcl-2 含量降低。结论:EAE 小鼠诱导后第15 天胸腺萎缩最严重,第10 天凋亡率最高,并且与基因p53 和Bcl-2 调控有关;EAE 小鼠胸腺变化与小鼠发病关系密切,并且胸腺又先于临床症状恢复。     

Immune modulating peptides for the treatment and suppression of multiple sclerosis

The signaling pathways utilized by naïve and experienced effector CD4 T cells during activation and proliferation were evaluated. While inhibition of either mTOR or MAPK alone was able to inhibit naïve T cell proliferation, both mTOR and MAPK (ERK) pathway inhibition was required to efficiently block experienced, effector CD4 T cell proliferation. This was demonstrated both in vitro, and in vivo by treating mice with collagen-induced arthritis using mTOR and/or ERK inhibitors. The combination of mTOR and ERK inhibition prevented or treated disease more efficiently than either agent alone. These data illustrate the different requirements of naïve and experienced effector CD4 T cells in the use of the mTOR and MAPK pathways in proliferation, and suggest that therapies targeting both the mTOR and MAPK pathways may be more effective than targeting either pathway alone in the treatment of CD4 T cell-mediated autoimmunity.     

Induction of thymocyte apoptosis by systemic administration of concanavalin A in mice: role of TNF-alpha, IFN-gamma and glucocorticoids

Administration of concanavalin A (Con A) is a well-established model of acute immune-mediated hepatitis. Here, we demonstrate that intravenous injection of Con A in mice induces profound thymic atrophy. Compared to liver damage, the kinetics of Con A-induced thymic atrophy is slower and more prolonged; the nadir in thymocyte number is reached 4 days after Con A injection, whereas peak transaminase levels are observed at 12-24 h. Marked alterations in the ratio of CD4+ and CD8+cells in the thymus and spleen and significantly increased rates of thymocyte and splenocyte apoptosis are observed. Neutralization of the cytokines TNF-alpha or IFN-gamma, which protects mice from Con A-induced hepatitis, prevents thymic atrophy as well as alterations in CD4+ and CD8+ cell numbers and apoptosis rates. However, neither TNF-alpha nor IFN-gamma are detectable in thymocyte lysates after Con A injection, whereas both cytokines are present in liver, spleen and serum. Administration of the glucocorticoid receptor antagonist mifepristone does not prevent thymic atrophy, thus ruling out a possible contribution of endogenous glucocorticoids. Con A-induced thymic atrophy is accompanied by down-regulation of Bcl-2 expression in the thymus, which is prevented by neutralization of TNF-alpha or IFN-gamma. These data demonstrate that the thymus is a critical target organ of Con A-induced inflammation; the effects of Con A on the thymus are mediated by extrathymic production of TNF-alpha and IFN-gamma, but not by glucocorticoids.     

人脐带间充质干细胞联合番茄红素对衰老小鼠免疫功能的影响

背景：人脐带间充质干细胞、番茄红素均有延缓衰老的作用,而二者联合应用对衰老机体免疫功能影响的研究却未见报道。 目的：分析人脐带间充质干细胞联合番茄红素对D-半乳糖诱导衰老小鼠免疫功能的影响。 方法：ICR小鼠雌雄各半,随机分为正常对照组、模型组、番茄红素组、干细胞组及干细胞联合番茄红素组。模型组与各治疗组连续8周颈背部皮下注射D-半乳糖溶液,同时进行相应的治疗干预。造模结束后检测各组小鼠血液衰老相关T淋巴细胞百分比、血清白细胞介素2、白细胞介素4水平并观察脾脏、胸腺组织结构。 结果与结论：3个治疗组均能提高衰老小鼠血液CD3+、CD8+CD28+T细胞百分比及血清白细胞介素2、白细胞介素4水平(P < 0.01);与模型组相比,联合组初始性CD8+T细胞百分比升高,记忆性CD8+T细胞百分比降低(P < 0.05),干细胞及番茄红素组初始性及记忆性CD8+T细胞百分比变化不显著(P > 0.05);各组初始性及记忆性CD4+T细胞百分比变化均不显著(P > 0.05);胸腺、脾脏镜下观察发现：模型组胸腺小体缩小,脾脏淋巴小结明显增多,髓质淤血;正常对照组与3个治疗组胸腺、脾脏皮质髓质均未见明显病变。结果表明人脐带间充质干细胞、番茄红素均可以不同程度改善衰老小鼠免疫功能,且联合治疗效果更优。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

Robust interferon-α and IL-12 responses by dendritic cells are related to efficient CD4+ T-cell recovery in HIV patients on ART

Amongst HIV patients with successful virological responses to antiretroviral therapy (ART), poor CD4(+) T-cell recovery is associated with low nadir CD4(+) T-cell counts and persistent immune activation. These factors might be influenced by dendritic cell (DC) function. Interferon-α-producing plasmacytoid DC and IL-12-producing myeloid DC were quantified by flow cytometry after stimulation with agonists to TLR7/8 (CL075) or TLR9 (CpG-ODN). These were compared between patients who achieved CD4(+) T-cell counts above or below 200 cells/μL after 6 months on ART (High vs. Low groups). High Group patients had more DC producing interferon-α or IL-12 at Weeks 6 and 12 on ART than Low Group patients. The frequencies of cytokine-producing DC at Week 12 were directly correlated with CD4(+) T-cell counts at baseline and at Week 12. Patients with good recovery of CD4(+) T-cells had robust TLR-mediated interferon-α responses by plasmacytoid DC and IL-12 responses by myeloid DC during early ART (1-3 months).     

Thymic volume predicts CD4 T-cell decline in HIV-infected adults under prolonged treatment interruption

OBJECTIVE: To analyze the predictive capacity of thymic volume in CD4 T-cell loss after treatment interruption in HIV-infected patients with high nadir CD4 count. METHODS: Thirty-nine HIV-infected patients with CD4 counts greater than or equal to 500 cells/microL, nadir CD4 counts greater than or equal to 250 cells/microL, and plasma viral loads less than 50 copies/mL for at least the past 12 months began a treatment interruption program. The event of interest for this study was the decrease of CD4 count below 350 cells/microL. Kaplan-Meier curves were used for all time-to-event analyses, and log-rank tests were used for comparison between groups in the univariate analysis. All variables with statistical association with CD4 T-cell loss were analyzed using multivariate Cox proportional hazards regression models. RESULTS: Twenty-three percent of the patients had a decrease in CD4 count to less than 350 cells/microL. In the univariate analysis, only thymic volume was statistically significant with this event (P = 0.02). Nadir CD4 count nearly reached statistical significance. However, age, sex, HCV coinfection, CD4 count, T-cell receptor excision circle-bearing cells, and early viral load rebound did not show statistical differences. Thymic volume and CD4 T-cell loss were independently associated using Cox proportional hazards regression model (P = 0.04; relative risk, 0.76; 95% confidence interval, 0.59-0.99). CONCLUSIONS: In this study, we demonstrate for the first time that thymic volume predicts CD4 T-cell loss in patients with nadir CD4 count greater than or equal to 250 cells/muL under treatment interruption.     

Thymic volume is associated independently with the magnitude of short- and long-term repopulation of CD4+ T cells in HIV-infected adults after highly active antiretroviral therapy (HAART)

Age is one of the main factors involved in the rapidity and the magnitude of CD4(+) T cell repopulation in human immunodeficiency virus (HIV)-infected patients on highly active antiretroviral treatment (HAART). Improved thymic function has been suggested as the main factor associated with CD4(+) T cell restoration after HAART. This work was undertaken to determine, among host factors, the predictor variable at baseline involved in the magnitude of short- and long-term recovery of CD4(+) T cells after HAART. HIV-RNA levels and CD4(+) T cell numbers were determined in 54 HIV-infected adults at baseline and at weeks 4, 12, 48 and 96 after HAART. T cell subpopulations were determined by flow cytometry, thymic volume by computed tomography, T cell receptor excision circle (TREC)-bearing cells by quantitative polymerase chian reaction (PCR) and interleukin (IL)-7 levels by enzyme linked immunosorbent assay at baseline. The phenotype of patients' isolates was determined by infecting GHOST cells expressing CCR5 and CXCR4. The possible interference of phenotype with thymic function was also analysed. Baseline thymic volume was associated independently with the magnitude of short- and long-term recovery of CD4(+) T cells after HAART, despite the patients' viral phenotype. The measurement of thymic volume before therapy may predict the magnitude of T cell increase. This result could have important clinical implications not only in HIV-infected patients, but also in other scenarios of T cell depletion such as bone marrow transplantation and chemotherapy.     

Impaired Recovery of CD4+ Cell Counts Following Highly Active Antiretroviral Therapy in Drug-Naïve Patients Coinfected with Human Immunodeficiency Virus and Hepatitis C Virus

Coinfection with the human immunodeficiency virus (HIV) and the hepatitis C virus (HCV) is highly prevalent in southern Europe. However, there are few and contradictory data about the effect of HCV carriage on the response to highly active antiretroviral therapy (HAART). In this study, the recovery of CD4+ T cells following HAART among antiretroviral-naïve patients seropositive for HIV with and without HCV coinfection was investigated. Two hundred one HIV-infected patients without previous exposure to antiretroviral drugs were included in the study. HCV coinfection was detected in 123 (61%) patients. The time to recover 200 CD4+ cells/µl was longer in the HCV-positive group (P<0.001). In a Cox model, HCV infection and lack of persistent HIV viremia (defined as <200 copies/ml) were associated with the time to recover 200 CD4+ cells/µl. The mean increase in CD4+ cell counts was lower in the HCV-positive group during the first year of therapy. HIV/HCV-coinfected patients naïve for antiretroviral therapy show a delayed recovery of CD4+ cell counts after starting HAART.     

The perivascular space as a path of hematopoietic progenitor cells and mature T cells between the blood circulation and the thymic parenchyma

It is known that selected populations of lymphoid cells migrate into and from the adult thymus through blood vessels at the cortico-medullary junction and in the medulla. Here, we show that in the perivascular spaces (PVS) of mice surrounding large blood vessels, CD117-positive hematopoietic progenitor cells, CD4 single-positive (SP) and CD8SP T cells are located. However, developing thymocytes, CD25-positive cells and CD4 and CD8 double-positive cells, are not detectable in the PVS. After intravenous (i.v.) injection of CD117-positive bone marrow (BM) cells from C57BL/6 mice into non-irradiated RAG2 mutant mice i.v., donor-derived cells first preferentially migrate into the PVS within 30 min, and then the number of donor-derived cells in the thymic parenchyma increases. Likewise, newly developed mature T cells in the thymic parenchyma of RAG2 mutant mice transferred with wild-type BM cells migrate to the PVS, before leaving the thymus to the circulation. Accumulation of mature T cells was observed after treatment with sphingosine-1 phosphate receptor agonist FTY720 not only in the medulla but also in the thymic PVS. These results suggest that the PVS is a transit pathway for progenitor cells to immigrate into the thymus and for mature T cells to emigrate from the thymus.     

Increased Interleukin-7 Plasma Levels Are Associated with Recovery of CD4+ T Cells in HIV-Infected Children

To asses the role of interleukin 7 (IL-7) in the thymic reconstitution of CD4 T cells observed in children after successful antiretroviral therapy, a longitudinal study in five vertically HIV-1-infected children was carried out. Thymic function, IL-7 plasma levels, viral load, and T-lymphocytes subsets were determined every 2 or 3 months for about 90 months. In all the children, the drop in CD4+ T cells below 5–10% was associated with a marked increase in IL-7 plasma levels. The drastic decrease in viral load after treatment, led in all the cases to a recover of CD4 to levels higher than 30%, which was associated to an increase in thymic production of T cells and followed by a decrease in IL-7 to the normal levels. We conclude that the drop in CD4 in HIV children would induce an increase of IL-7 as part of a homeostatic mechanism. IL-7 would induce the thymus to produce new T cells to recover the normal levels of CD4 when the viral load was low and so the thymic function was not inhibited. The increase in the thymic production of new T cells recovers the CD4 population, and leads to a normalization of IL-7 levels.