Thymopoiesis in HIV-infected adults after highly active antiretroviral therapy

Thymic Parenchymal Hyperplasia

Thymic hyperplasia is a rare condition generally caused by lymphoid follicular hyperplasia associated with autoimmune disorders. True thymic parenchymal hyperplasia unassociated with lymphoid follicular hyperplasia is extremely rare and may give rise to difficulties in diagnosis. We have studied 44 patients with true thymic hyperplasia (38 females and 6 males) aged 7 months to 64 years (mean, 36 years). Eighteen patients presented with symptoms of chest discomfort or shortness of breath; in 20 patients, the lesions were discovered incidentally. Imaging studies demonstrated enlargement of the mediastinum by a mass lesion suspicious for malignancy. All patients were treated with complete surgical excision. The tumors measured from 3.5 to 24 cm (median, 10 cm; mean, 10.46 cm). Histologic examination showed lobules of thymic tissue displaying well-developed corticomedullary architecture, with scattered Hassall corpuscles separated by mature adipose tissue and bounded by a thin fibrous capsule. No cases showed evidence of lymphoid follicular hyperplasia, cytologic atypia, or confluence of the lobules. Immunohistochemical studies showed a normal pattern of distribution for keratin-positive thymic epithelial cells against a background rich in CD3/TdT/CD1a+ lymphocytes. Twenty-nine cases had an initial clinical or pathological diagnosis of thymoma or thymoma vs thymic hyperplasia. Clinical follow-up in 26 cases showed that all patients were alive and well between 5 and 15 years after diagnosis (mean, 9 years). Thymic parenchymal hyperplasia causing significant enlargement of the normal thymus that is sufficient to cause symptoms or worrisome imaging findings should be considered in the differential diagnosis of anterior mediastinal masses. The criteria for distinguishing such lesions from lymphocyte-rich thymoma are presented.

Immune reconstitution inflammatory syndrome-associated Graves disease in HIV-infected patients: clinical characteristics and response to radioactive iodine therapy

OBJECTIVES

We aimed to describe the clinical characteristics and the response to radioactive iodine (RAI) treatment of immune reconstitution inflammatory syndrome-associated Graves disease (IRIS-GD) in comparison to Graves disease (GD) seen in HIV-uninfected patients.

METHODS

We retrospectively reviewed the medical records of patients treated with RAI for GD. We obtained clinical, biochemical and HIV-related information of patients from their medical records. We compared patient characteristics and response to RAI treatment between patients with IRIS-GD and GD seen in HIV-uninfected patients.

RESULTS

A total of 253 GD patients, including 51 patients with IRIS-GD, were included. Among IRIS-GD patients, CD4 cell nadir was 66 cells/µL (range: 37-103) with a peak HIV viral load of 60 900 copies/mL (range: 36 542-64 500). At the time of diagnosis of IRIS-GD, all patients had a completely suppressed HIV viraemia with a CD4 cell count of 729 cells/µL (range: 350-1279). The median interval between the commencement of HIV treatment and the onset of GD was 63 months. At 3 months follow-up, the proportion of patients with IRIS-GD achieving a successful RAI treatment outcome (euthyroid/hypothyroid state) was lower than that of HIV-uninfected patients (35.3% vs. 63.4%, respectively; p < 0.001). The response rate remained lower (60.8%) among patients with IRIS GD than among HIV-uninfected GD patients (80.2%, p = 0.004) at 6 months follow-up. After correcting for differences in age, gender and pre-treatment thyroid-stimulating hormone level, there was no significant difference in RAI treatment response between the two groups.

CONCLUSIONS

After correcting for possible confounders, the response to RAI treatment was not different between patients with IRIS-GD and GD in HIV-uninfected patients.

First case of acute granulomatous interstitial nephritis with immune reconstitution inflammatory syndrome in a patient with HIV coinfected with disseminated Mycobacterium kansasii

Restoration of immune response by highly active antiretroviral therapy (HAART) effectively improved the overall prognosis of HIV infection. However, 25%-31.7% of patients experience paradoxical worsening of pre-existing infections or unmasking of subclinical infections after starting HAART therapy, which is termed as immune reconstitution inflammatory syndrome (IRIS). Acute granulomatous interstitial nephritis as a consequence of IRIS has never been reported with Mycobacteriumkansasiicoinfection. Here, we describe an HIV/AIDS patient coinfected with disseminated M. kansasii infection, who presented with acute kidney injury 4.5 months after initiation of HAART. The diagnostic workup revealed IRIS was the cause of acute kidney injury. Short-term course of prednisone (1 mg/kg/day) along with antimycobacterial and HAART regimen achieved significant improvement.

Immunologic basis for revaccination of HIV-infected children receiving HAART

With increasing access to antiretroviral therapy for children infected with HIV, especially in sub-Saharan Africa, better understanding of the development and maintenance of memory T- and B-cell responses to pathogens after immune reconstitution is needed to assess the risk of infection. Knowledge of long-term immune responses after starting HAART is of particular importance for policies on revaccination of HIV-infected children, who may lose protective immunity to prior infections and immunizations. We review normal development of T- and B-cell memory responses to viruses and vaccines against viral pathogens, and contrast the immunological effects of perinatal HIV transmission with HIV infection acquired later in life. We then explore the potential benefits of antiretroviral therapy and revaccination, using measles virus as a model.

CD4+ T cell depletion, immune activation and increased production of regulatory T cells in the thymus of HIV-infected individuals

Mechanisms by which HIV affects the thymus are multiple and only partially known, and the role of thymic dysfunction in HIV/AIDS immunopathogenesis remains poorly understood. To evaluate the effects of HIV infection on intra-thymic precursors of T cells in HIV-infected adults, we conducted a detailed immunophenotypic study of thymic tissue isolated from 7 HIV-infected and 10 HIV-negative adults who were to undergo heart surgery. We found that thymuses of HIV-infected individuals were characterized by a relative depletion of CD4+ single positive T cells and a corresponding enrichment of CD8+ single positive T cells. In addition, thymocytes derived from HIV-infected subjects showed increased levels of activated and proliferating cells. Our analysis also revealed a decreased expression of interleukin-7 receptor in early thymocytes from HIV-infected individuals, along with an increase in this same expression in mature double- and single-positive cells. Frequency of regulatory T cells (CD25+FoxP3+) was significantly increased in HIV-infected thymuses, particularly in priorly-committed CD4 single positive cells. Our data suggest that HIV infection is associated with a complex set of changes in the immunophenotype of thymocytes, including a reduction of intrathymic CD4+ T cell precursors, increased expression of activation markers, changes in the expression pattern of IL-7R and enrichment of T regulatory cells generation.

Treatment with recombinant growth hormone is associated with modest improvement in CD4 lymphocyte reconstitution in HIV-infected persons on antiretroviral therapy: results of ACTG A5174

Pilot studies have suggested that treatment with recombinant human growth hormone (rhGH) is associated with increased T-lymphocyte restoration and enhanced thymic output. We evaluated the immunologic effects of rhGH on HIV(+) subjects with incomplete immune reconstitution on antiretroviral therapy (ART). Sixty subjects were randomized to receive rhGH 1.5 mg scqd and ART for 48 weeks (Arm A) or continue ART alone for 24 weeks then add rhGH 3.0 mg scqd for 24 weeks (Arm B). Median baseline CD4 for Arms A and B were 223 and 219, respectively. There was little difference between Arm A and Arm B in change in total or naive CD4 cells or percentage from baseline to week 24. Only one subject in Arm A met the primary endpoint, an increase in naive CD4 percentage of at least 10 percentage points. By week 48 both Arms had statistically significant increases in naive CD4 cell count and percentage and thymus size. Within Arm B, treatment with rhGH was associated with significant increases in naive CD4(+) cell count and percentage compared with ART alone. Treatment with rhGH +ART may be associated with modest increases in CD4 lymphocytes over ART alone in subjects with CD4 <350, yet the origin of these naive cells and their impact on immune function require further investigation.

Human T cell reconstitution in DiGeorge syndrome and HIV-1 infection

The thymus is essential for proper development and maintenance of a broad T cell repertoire capable of recognizing a wide-range of foreign antigens. Recent advances in multicolor flow cytometry, non-invasive imaging techniques, and molecular assessments of thymic function have enabled a more comprehensive characterization of human thymic output in clinical settings than in the past. These techniques have been particularly valuable in monitoring human T cells after therapeutic thymic grafting for complete DiGeorge syndrome and during HIV-1 infection and AIDS. By defining the degree and mechanisms of T cell reconstitution in these settings, clinical investigators and primary caregivers have been able to better diagnose, treat and care for individuals with congenital or acquired immune deficiencies associated with loss of thymic function.

Recent thymic emigrants in lymphoma patients with and without human immunodeficiency virus infection candidates for autologous peripheral stem cell transplantation

Signal joint T cell receptor excision circles (sjTRECs) have been reported as a clinical marker to measure the potential for recovery of the immune system after immunosuppressive treatments. The aim of this study was to investigate the thymic regenerative potential in 55 human immunodeficiency virus (HIV)-1 infected (HIV(+)) and non-infected (HIV(-)) lymphoma patients, candidates for autologous stem cell transplantation (ASCT). Moreover, the possible associations between sjTRECs and other immunological and clinical parameters were examined. SjTRECs levels in peripheral blood mononuclear cells (PBMCs) were quantified by real-time polymerase chain reaction and T lymphocyte subsets were analysed by flow cytometry. Our data showed that sjTRECs were reduced in lymphoma patients compared to healthy controls, although a weak significant association between low sjTRECs levels and increasing age was maintained [odds ratio (OR) = 4.00; 95% confidence interval (CI) 1.09-17.17]. We found that different chemotherapeutic treatments seem to induce similar effects on the thymic reservoir, independently from their intensity (type and number of cycles of previous chemotherapy). Results from multivariate models including adjustment for patients' sex, type of lymphoma and type of chemotherapy showed that thymic output was independent from HIV infection (OR, 0.95; 95% CI 0.20-4.48). SjTRECs levels correlated with naive T cell subsets in overall lymphoma patients and after stratification by HIV infection (r > 0.37). HIV replication should be maximally suppressed to properly evaluate thymic output by sjTREC markers. Our results suggested that de novo T cell generation is maintained partially in pretreated recurrent lymphoma patients, candidates for ASCT, and could contribute to restore the immune function after transplantation.

Acutely dysregulated, chronically disabled by the enemy within: T-cell responses to HIV-1 infection

Human immunodeficiency virus (HIV) infection causes chronic progressive immunodeficiency and immune dysregulaton. Although simple depletion of the major target of HIV infection, the CD4+ T cell, can explain much of the immunosuppression seen, there are multiple other factors contributing to the immune dysregulation. CD4+ T-cell depletion induces a range of homeostatic mechanisms that contribute to immune activation and cell turnover, providing a milieu conducive to further viral replication and cell destruction, resulting in functional defects in various lymphoid organs. These changes are progressive and in turn compromise the homeostatic processes. Further, the infection, like any other viral infection, provokes an active immune response consisting of both CD4+ and CD8+ T-cell responses. Both appear compromised, displaying aberrant memory cell production. While some of these defects result from viral variation and the chronicity of antigen presentation, other defects of memory cell production appear very early during the primary immune response limiting the viral specific T-cell responses from the outset. This, combined with the ability of the virus to escape any successful immune responses, results in an attenuated immune response that eventually becomes exhausted, characterized by progressive deficits in T-cell repertoire. Furthermore, negative regulatory mechanisms that normally control the immune response may be aberrantly invoked, perhaps directly by the virus, further compromising the efficacy of the immune response. Rational design of effective immunotherapies depends on a clear understanding of the processes compromising the immune response to HIV.

Longitudinal assessment of de novo T cell production in relation to HIV-associated T cell homeostasis failure

Loss of circulating CD4+ T cells in HIV-1 disease is balanced by CD8+ lymphocytosis to maintain normal CD3+ T cell counts [blind T cell homeostasis (TCH)]. However, for unknown reasons TCH generally fails 1.5-2.5 years before clinically defined AIDS. We investigated whether TCH failure was associated with changes in thymic production of T cells. Using specimens stored prospectively in the Multicenter AIDS Cohort Study (MACS), we measured expression of signal-joint T cell receptor excision circles (sjTRECs), a marker for thymic T cell production, and the fraction of proliferating naive and memory T cells during a 6-8 year period bracketing TCH failure. Segmented regression modeling assessed (1) rates of change in TREC levels before and after TCH failure, and (2) whether these were affected by cellular proliferation, which may dilute sjTREC levels. TCH failure was associated with a large decline in sjTREC (median 1109-fold, p = 0.028); the rate of this decline was only slightly affected when increased proliferation of naive T cells or other peripheral lymphocytes was taken into account. Preferential loss of naive CD4+ T cells was also noted before TCH failure, as has been seen in other studies. These results suggest that deficits in de novo T cell production, either through the decline of thymic function or the destruction of naive T cells, are likely to play an important role in TCH failure and progression of HIV-1 disease.

IL-7 induces immunological improvement in SIV-infected rhesus macaques under antiviral therapy

Despite efficient antiretroviral therapy (ART), CD4+ T cell counts often remain low in HIV-1-infected patients. This has led to IL-7, a crucial cytokine involved in both thymopoiesis and peripheral T cell homeostasis, being suggested as an additional therapeutic strategy. We investigated whether recombinant simian IL-7-treatment enhanced the T cell renewal initiated by ART in rhesus macaques chronically infected with SIVmac251. Six macaques in the early chronic phase of SIV infection received antiretroviral treatment. Four macaques also received a 3-wk course of IL-7 injections. Viral load was unaffected by IL-7 treatment. IL-7 treatment increased the number of circulating CD4+ and CD8+ memory T cells expressing activation (HLA-DR+, CD25+) and proliferation (Ki-67+) markers. It also increased naive (CD45RAbrightCD62L+) T cell counts by peripheral proliferation and enhanced de novo thymic production. The studied parameters returned to pretreatment values by day 29 after the initiation of treatment, concomitantly to the appearance of anti-IL-7 neutralizing Abs, supporting the need for a nonimmunogenic molecule for human treatment. Thus, IL-7, which increases T cell memory and de novo renewal of naive T cells may have additional benefits in HIV-infected patients receiving ART.

Immune reconstitution and predictors of virologic failure in adolescents infected through risk behaviors and initiating HAART: week 60 results from the PACTG 381 cohort

The responses to HAART in HIV-infected adolescents infected through risk behaviors are not well defined. PACTG 381 collected intensive immunologic and virologic data on youth naive to or with minimal exposure to antiretroviral therapy who began HAART. Subjects were evaluated according to their weeks 16-24 virologic response. Comparisons with a cohort of HIV-uninfected adolescents from the REACH cohort were performed. Cox proportional hazards models were used to identify baseline and week 24 predictors of virologic failure. Only 69 of 120 subjects (58%) achieved virologic suppression by weeks 16-24, whereas 55 of 69 (80%) demonstrated control to week 60. Higher CD4+ naive T cells (CD4+/62L+/RA+: hazard ratio [HR], 2.13; p = 0.018), higher CD8+ activated T cells (CD8+/CD38+/DR+: HR, 1.40, p = 0.028 per 100 cells/mm3) and higher CD8+ naive T cells (CD8+/62L+/RA+: HR, 1.72; p = 0.005) at weeks 16-24 in subjects with early viral success were predictive of subsequent failure. By week 60, total CD4+ T cells remained significantly lower than in uninfected controls. Adolescents beginning HAART achieve moderate rates of viral suppression by weeks 16-24. In those who do achieve early virologic control, suppression to week 60 is high although total CD4+ T cells remain significantly lower than in uninfected controls. Several T cell markers were predictive of subsequent virologic failure in subjects achieving short-term success. Further study is warranted to determine whether these predictors provide any benefit to clinical management.

Graves' Disease as an Immune Reconstitution Syndrome in an HIV-1–Positive Patient Commencing Effective Antiretroviral Therapy: Case Report and Literature Review

Combination antiretroviral therapy (cART) reduces morbidity and mortality in human immunodeficiency virus (HIV) infection, but it may also alter the clinical course of subclinical opportunistic infections and can even induce autoimmune disease. These atypical presentations are known as immune restoration disease (IRD), immune reconstitution syndrome/immune recovery syndrome (IRS), or immune restoration inflammatory syndrome (IRIS). We report the case of a 27-year-old, HIV-1-positive woman who developed hyperthyroidism attributable to Graves' disease (GD) after commencing potent cART. At the initiation of cART, her CD4 T cell count was 15 cells/microL and plasma HIV RNA 35 000 copies/mL. Her commencement of cART resulted in complete viral suppression and subsequent improvement of the CD4 T-cell count. Three years later, the diagnosis of GD was established based on a typical clinical picture and the results of hormonal and immunological analyses. It coincided with a 58-fold rise of the CD4 T cells. Retrospective analysis of serum samples revealed normal thyroid function and lack of anti-thyroid peroxidase (anti-TPO), anti- thyroid-stimulating hormone receptor (anti-TSHR), and anti-thyroglobulin (anti-TG) autoantibodies at the beginning of cART. HLA class II gene examination did not reveal susceptibility for the GD development in this patient. We suggest that GD in our patient was an IRD, and advise this as a possible differential diagnosis in patients presenting with hyperthyroidism on cART. To provide further details relevant to this case, we also review the literature concerning IRD-GD.

Naïve T Cells Are Maintained in the Periphery During the First3 Months of Acute HIV-1 Infection: Implications for Analysis of Thymus Function

A key determinant of T cell dynamics in HIV-1 infection is the status of thymic function. To date, most studies of the impact of HIV-1 on the thymus during early HIV-1 infection have been done in samples collected in the interval of 3-12 months after infection. In this study, we have probed the status of thymic function and peripheral naive T cells in patients with acute HIV-1 infection diagnosed 18-72 days after the onset of symptoms. We found that peripheral CD4 and CD8 T cell proliferation was initially elevated, then waned over time. The fall in T cell proliferation correlated with a reduction in HIV-1 viral RNA levels and a rise in peripheral blood CD4+ CD25+ T cells. In spite of elevated T cell proliferation early on in primary HIV-1 infection, levels of naive phenotype CD4 and CD8 T cells and T cell receptor excision circle positive cells (sjTREC(+)) remained constant. Taken together with the observation that T cell proliferation normally dilutes peripheral T cell episomal sjTREC levels, these data suggested that thymopoiesis contributes to maintenance of the naive T cell pool during the earliest stages of HIV-1 infection (18-72 days).

Multiparameter evaluation of human thymic function: interpretations and caveats

After the provision of highly active antiretroviral therapy (HAART), the level of circulating CD4+ T cells increases in many adults infected with the human immunodeficiency virus, type 1 (HIV). To study factors involved in immune reconstitution, we have measured thymic abundance by CT scans, circulating naive-phenotype CD4+ T cells by flow cytometry, and T cell receptor (TCR) rearrangement excision circles (TRECs) by quantitative PCR in 40 virologically suppressed, HIV-infected adults and 33 age-matched, HIV-uninfected controls. In HIV-uninfected subjects, naive T cell numbers, thymic abundance, and the frequency of circulating naive CD4+ T cells bearing TRECs decreased with age, as expected. When corrected for this relationship with age, naive T cell numbers correlated significantly with naive T cell TREC frequencies. Virologically suppressed HIV-infected subjects had higher TREC frequencies, and subjects over the age of 39 were more likely to have abundant thymus compared to age-matched, HIV-uninfected adults. Nevertheless, all HIV-infected subjects had reduced absolute numbers of naive T cells, irrespective of thymic size, age, or TREC frequencies. These data illustrate the complex relationship between these measures of thymic size and function and underscore the need to develop more definitive measures of thymic function in the future.

Disease progression in macaques with low SIV replication levels: on the relevance of TREC counts

BACKGROUND

An attenuated immunodeficiency virus has been long considered innocuous. Nevertheless, converging data suggest that low levels of viral replication can still provoke AIDS. Pathogenesis of these attenuated infections is not understood.

OBJECTIVES

To determine the pathogenicity of a long-term attenuated infection and to delineate T-cell dynamics during such an infection.

METHODS

This is a cross-sectional study of 12 rhesus macaques infected with SIV Delta nef for 8 years. We evaluated apoptosis (annexin V), activation (HLA-DR, Ki67), and newly generated T cells (TCR excision circle: TREC).

RESULTS

Infection with SIV Delta nef induced pathological CD4 T-cell depletion after 8 years of infection. Virus replication and CD8 T-cell activation positively correlated with the rate of disease progression. The frequency of TREC within CD8+CD45RA+ cells increased in SIV Delta nef-infected animals compared to age-matched non-infected controls. Moreover, in the cohort of infected animals, TREC+CD45RA+CD4+ T-cell counts correlated strongly with non-progression to AIDS. The animal with the lowest rate of disease progression exhibited a 115-fold increase in TREC+CD45RA+CD4+ T-cell counts compared to age-matched non-infected controls. In contrast, the animal showing the fastest rate of progression to AIDS displayed 600-fold lower TREC+CD45RA+CD4+ T-cell counts compared to age-matched non-infected controls.

CONCLUSIONS

Our results suggest that the thymus plays a major role in the pathogenesis of an attenuated SIV infection and that a sustained thymic output could maintain CD4 T-cell homeostasis in the context of low viral loads.

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.

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.

Assessing thymopoiesis in patients with common variable immunodeficiency as measured by T-cell receptor excision circles

BACKGROUND

Common variable immunodeficiency (CVID) is one of the most common primary immune deficiencies. The immunologic hallmark of CVID is failure of B-cell differentiation and impaired secretion of immunoglobulins. However, there is mounting evidence of accompanying T-cell dysregulation, which could be due to abnormal thymic function because the thymus plays a crucial role in T-cell development. Recently, it was shown that the human thymus remains functional well into adulthood. Current data show that the level of T-cell receptor excision circles (TRECs) correlates well with active thymopoiesis.

OBJECTIVE

To determine whether thymic dysfunction contributes to the pathogenesis of CVID.

METHODS

We evaluated 15 patients, aged 19 to 65 years, previously diagnosed as having CVID. Genomic DNA was isolated from peripheral blood mononuclear cells of each patient. Thymic output was evaluated by measuring coding joint TRECs in the total T-cell population using real-time polymerase chain reaction.

RESULTS

Results were compared with known age-matched reference values. The median TREC level in patients with CVID (82,034 copies/microg of DNA) was significantly higher than that in the healthy cohort (43,000 copies/microg of DNA) (P < .001). In examining the relationship between TREC levels and age, we noted that TREC levels significantly declined faster with age in patients with CVID vs the healthy cohort.

CONCLUSIONS

In these patients, thymic dysregulation may be a factor in CVID, with an accelerated rate of TREC loss with age compared with healthy adults.

Graves' disease after interleukin-2 therapy in a patient with human immunodeficiency virus infection

Interleukin-2 (IL-2) is a cytokine that regulates the proliferation and differentiation of lymphocytes, and is currently used clinically in the treatment of assorted malignancies. Additionally, IL-2 is being actively investigated in clinical trials for treatment of human immunodeficiency virus (HIV) infection. Patients treated with IL-2 are susceptible to autoimmune thyroid disease (AITD), presenting as thyroiditis, which leads to either thyrotoxicosis or hypothyroidism, if not correctly and promptly identified and treated. IL-2-induced hypothyroidism can also sometimes follow a thyrotoxic phase. However, the development of Graves' disease (GD) in this clinical setting has not been reported to date. Here, we report the case of a 39-year-old HIV-infected man in whom GD developed after IL-2 therapy. We correlated the immunologic parameters pertinent to the patient's HIV infection status with clinical, hormonal, and serologic evidence of GD during its emergence. This revealed an association between peripheral blood cell numbers of specific lymphocyte subpopulations (CD4(+), CD3(+)CD25(+), and naïve T-cells) and serum levels of markers for AITD (free thyroxine [T(4)] and thyroid-stimulating immunoglobulin). Interestingly, no association was found between natural killer (NK) cell numbers and AITD markers. The immunopathogenesis of GD in this patient may be similar to that hypothesized for the GD that occurs in immune-reconstituted patients after combination antiretroviral therapy. From a practical standpoint, we propose that patients who have received or are receiving treatment with IL-2 who show signs of hyperthyroidism need to be carefully evaluated for GD.

Graves' disease during immune reconstitution after highly active antiretroviral therapy for HIV infection: evidence of thymic dysfunction

A patient with HIV infection who experienced immune reconstitution after highly active antiretroviral therapy (HAART) [increase in CD4 T cell count from <1/microl to >600/microl] presented with severe Graves' disease 32 months after commencing HAART. A comprehensive clinical and laboratory study demonstrated pronounced regional lymphadenopathy and thymic enlargement at presentation, and that the onset of thyrotropin receptor antibody production was associated with increased production of soluble CD30 (a marker of type 2 immune responses). Blood naive CD8 T cell counts and TREC levels in both CD4 and CD8 T cells were increased at multiple time points compared with carefully selected controls. We conclude that the Graves' disease in this patient was associated with abnormally high blood counts of thymus-derived T cells, and propose that Graves' disease after HAART in this and other HIV patients may result from failure to delete autoreactive T cell clones in the regenerating thymus.

Histologic and molecular assessment of human thymus

Most work describing the histopathology of normal human thymus has focused on pediatric thymus because of tissue availability and high thymopoietic activity. However, pathologic examination of the thymus can provide information about immune status that is relevant to the clinical care of patients of all ages. Understanding age-related changes in the relative abundance and composition of anatomic compartments within the thymus is critical for evaluation of the thymus in normal adults and patients with diseases that affect the thymus. The purpose of this review is to acquaint diagnostic pathologists with some of the newer histologic, flow cytometric, and molecular techniques for assessment of non-neoplastic thymus. Diagnostic criteria are presented for assessment of thymic function and for determining the mechanisms underlying thymic hyperplasia. Accurate assessment of thymic function is critical for the diagnosis and treatment of patients with complete DiGeorge syndrome and can complement the clinical care of patients with a variety of disorders that affect the immune system.

Changes in levels of immune activation and reconstitution markers among HIV-1-infected Africans receiving antiretroviral therapy

OBJECTIVE

To describe changes in immune activation and reconstitution markers among HIV-1-infected patients receiving antiretroviral therapy (ART) in Abidjan, Côte d'Ivoire.

METHODS

Between November 1998 and February 2001, we analyzed changes in immune activation and reconstitution markers among 52 patients. Good virologic responders (n = 26) were defined as those who had suppressed and maintained plasma viral load (VL) below the detection limit of the assay for at least 12 months. Poor virologic responders (n = 26) were defined as those with a detectable VL at 6 and 12 months after beginning ART.

RESULTS

Of the 26 good virologic responders, 20 (77%) were on highly active antiretroviral therapy (HAART) compared with one (4%) of the poor responders. Among the 26 good responders, baseline median levels of CD38+CD8+ T cells were elevated, but had decreased significantly at 6 months (P < 0.001) and at 12 months of therapy (P < 0.001). Median levels of HLA-DR+CD8+ T cells also decreased from baseline at 6 months (P < 0.001) and at 12 months of therapy (P < 0.001). Levels of CD62L+CD4+ T cells increased steadily during the 6 and 12 months of therapy and reached levels observed among HIV-negative blood donors (P = 0.07). Among the 26 poor responders, median levels of CD38+CD8+ T cells decreased significantly at 12 months of therapy (P = 0.006), but were higher than levels in blood donors (P = 0.005). Levels of HLA-DR+CD8+ T cells decreased significantly at 12 months of therapy (P < 0.001). Levels of CD62L+CD4+ decreased over time.

CONCLUSION

Our results suggest that HAART can be successfully used in African populations with elevated baseline immune activation markers.

Reconstitution of thymic function in HIV-1 patients treated with highly active antiretroviral therapy

The extent to which highly active antiretroviral therapy can restore thymic function in HIV-1 infected patients is not known. We simulate treatment using a temporal model of thymopoiesis during HIV-1 infection, tracking thymic function by the number of recent thymic emigrants (RTE) exported to the periphery per day. Our results suggest that suppressing viral load in peripheral blood and improving inherent thymic function are necessary for the reconstitution of RTE levels in adult thymic infection with either R5 or X4 HIV-1 strains. This is also the case in pediatric thymic infection with R5 strains. However, recovery of RTE levels during pediatric infection with X4 strains also depends on high drug efficacy within the thymus. We further predict that protease inhibitors have high levels of efficacy directly suppressing viral replication within the thymus, while reverse transcriptase inhibitors have low efficacy.

Diverse repertoire of HIV-1 p24-specific, IFN-gamma-producing CD4+ T cell clones following immune reconstitution on highly active antiretroviral therapy

HIV-1 Ag-specific CD4(+) T cell proliferative responses in human subjects with advanced, untreated HIV-1 disease are often weak or undetectable. Conversely, HIV-1-specific CD4(+) T cell proliferation is occasionally detected following suppression of HIV-1 replication with highly active antiretroviral therapy (HAART). These observations suggest that unchecked HIV-1 replication may lead to depletion or dysfunction of HIV-1-specific CD4(+) T cells, and that these defects may be partially corrected by viral suppression and subsequent immune reconstitution. However, the impact of this immune reconstitution on the repertoire of HIV-1-specific CD4(+) T cells has not been thoroughly evaluated. To examine the HIV-1-specific CD4(+) T cell repertoire in this clinical setting, we established HIV-1 p24-specific CD4(+) T cell clones from a successfully HAART-treated subject whose pretreatment peripheral CD4 count was 0 cells/ micro l. Eleven different p24-specific CD4(+) T cell clonotypes were distinguished among 13 clones obtained. Most clones produced both IFN-gamma and IL-4 upon Ag stimulation. Clones targeted eight distinct epitopes that varied in their conservancy among HIV-1 strains, and responses were restricted by one of three MHC II molecules. Clones showed a range of functional avidities for both protein and peptide Ags. Additional studies confirmed that multiple HIV-1 p24-derived epitopes were targeted by IFN-gamma-producing CD4(+) cells from subjects first treated with HAART during advanced HIV-1 disease (median, 4.5 peptides/subject; range, 3-6). These results suggest that in HAART-treated subjects whose peripheral CD4(+) T cell pools were once severely depleted, the HIV-1-specific CD4(+) T cell repertoire may include a diverse array of clonotypes targeting multiple HIV-1 epitopes.

Dynamics of T cells and TCR excision circles differ after treatment of acute and chronic HIV infection

We quantified T cell proliferation and thymic function in primary HIV infection (PHI; n = 19) and chronic HIV infection (CHI; n = 14) by measuring Ki67 staining and TCR excision circle (TREC) number. After antiretroviral therapy of PHI there is a profound decrease in the number and percentage of Ki67(+) T cells (<6% Ki67(+)) with no significant increase in TREC per million cells and a transient increase in TREC per milliliter. In contrast, after antiretroviral therapy of CHI there is a reduction in the percentage but little change in the total number of Ki67(+)CD4(+) T cells associated with increases in both TREC per million cells and TREC per milliliter. Using a mathematical model that accounts for proliferation, death, and redistribution of T cells, we find that redistribution is consistent with the TREC changes observed during treatment of PHI and that an increase in thymic output is needed to explain the increase in TREC during treatment of CHI. Consideration of TREC per milliliter shows that changes in proliferation alone cannot explain the changes in TREC. In addition, although increased proliferation of memory cells in HIV infection has been established, we find no difference in TREC per million CD45RA(-) "memory" T cells between healthy and infected individuals (p = 0.154 for CD4(+); p = 0.383 for CD8(+)). Finally, although the number of TREC per million cells is always much lower in memory T cells than in naive T cells, in the setting of HIV infection, given that memory cells make up a larger proportion of total T cells, we find that 50% of TREC per milliliter in CD4(+) T cells is harbored in the CD45RA(-) "memory" subset of our infected subjects.

Deficiency in Bak and Bax perturbs thymic selection and lymphoid homeostasis

Bak and Bax are required and redundant regulators of an intrinsic mitochondrial cell death pathway. To analyze this pathway in T cell development and homeostasis, we reconstituted mice with Bak(-/-)Bax<(-/-) hematopoietic cells. We found that the development and selection of Bak(-/-)Bax(-/-) thymocytes was disrupted, with altered representation of thymic subsets and resistance to both death-by-neglect and antigen receptor-induced apoptosis. Elimination of Bak(-/-)Bax(-/-) T cells that responded to endogenous superantigen was also reduced. Despite more efficient early reconstitution and apoptotic resistance of Bak(-/-)Bax(-/-) thymocytes, thymic cellularity declined over time. Reduced thymic cellularity resulted from a progressive cessation of thymopoiesis. However, animals developed splenomegaly as a result of accumulated memory T cells that were not deleted after antigen-driven expansion. These data indicate that Bak and Bax are required for thymic selection and peripheral lymphoid homeostasis and suggest that thymopoiesis can be negatively regulated by the accumulation of cells that would normally be eliminated by pro-apoptotic Bcl-2-related genes.

Immune reconstitution in patients with HIV infection

The peripheral T cell pool is damaged by HIV-1 infection and can be regenerated by production of new T lymphocytes either from the thymus or from proliferation of post-thymic T cells. A critical question for AIDS patients is whether treatment with antiretroviral drugs can restore the capability to produce new T lymphocytes. The development of a new assay of thymus function in adults (the measurement of T cell receptor excision circles, TRECs), and studies of thymus biopsies in untreated and treated HIV-1-infected patients, have suggested that in select patients the thymus can regenerate on antiretroviral therapy. New strategies to overcome the thymic atrophy of aging are needed to improve thymic function in the majority of AIDS patients.

The human thymus during aging

The human thymus is required for establishment of a normal T cell repertoire in fetal development, as children born without a thymus (DiGeorge Syndrome) lack thymus-derived (T) and T cell immunity. While the function of the thymus in children for production of new T cells is clear, it has not been obvious that the adult thymus can produce significant numbers of new T cells. Until recently, no assays were available to directly evaluate postnatal thymic function. This paper reviews work on human thymic aging at Duke University School of Medicine and discusses the relevance of this work to devising new strategies for T cell immune reconstitution in man.