Thymic involvement in immune recovery during antiretroviral treatment of HIV infection in adults; comparison of CT and sonographic findings

In adult HIV-infected patients, thymic size evaluated from CT scans seems to be important to the degree of immune reconstitution obtainable during treatment with highly active antiretroviral therapy (HAART). To examine whether ultrasound is as reliable as CT for estimating thymic size and predicting immune recovery, CT and ultrasound scans were performed in 25 adult HIV-infected patients and 10 controls. CD4 counts and naive CD4 counts were measured in order to determine immune reconstitution. Furthermore, the CD4+ T-cell receptor excision circle (TREC) frequency and T-cell receptor (TCR) repertoire were determined. The study demonstrated no correlation between the 2 scanning methods (r = 0.201, p = 0.358 in patients and r = 0.457, p = 0.184 in controls). Among the patients, no association was found between the sonographically estimated thymic size and immunological parameters such as CD4 count (r = 0.083, p = 0.706), naive CD4 count (r = 0.067, p = 0.762), CD4 + TREC frequency (r = 0.028, p = 0.900) and CD4 + TCR repertoire (r = -0.057, p = 0.828). These findings show that CT remains superior for assessing thymic size in adults and is preferable to ultrasound when evaluating the importance of a large thymus to immune recovery during HAART.     

Effect of highly active antiretroviral therapy and thymic transplantation on immunoreconstitution in HIV infection

The purpose of this study was to determine whether thymic transplantation in addition to highly active antiretroviral therapy (HAART) will restore T cell function in HIV infection. Eight treatment-naive HIV-infected patients with CD4+ T cell counts of 200-500/mm3 were randomized into thymic transplantation and control arms. All patients received HAART (zidovudine, lamivudine, and ritonavir) for 6 weeks prior to transplantation. Thymic transplantation was done without immunosuppression, using postnatal HLA-unmatched cultured allogeneic thymus tissue. Patients were immunized every 6 months with the neoantigen keyhole limpet hemocyanin (KLH) and the recall antigen tetanus toxoid (TT). T cell phenotype and function and T cell receptor rearrangement excision circles (TRECs) were assessed. Thymic allografts were biopsied at 2 months. Six HIV-infected patients completed the study. Four patients received cultured allogeneic postnatal thymic grafts, two others were controls. CD4+ T cell counts increased and T cell-proliferative responses to Candida antigen and TT normalized in all patients. Proliferative responses to KLH developed in three of four transplant recipients and one of two controls. Patients responding to KLH after secondary immunization had greater TREC increases compared with the patients who did not respond. All thymic allografts were rejected within 2 months. In summary, four of six patients developed T cell-proliferative responses to the neoantigen KLH over the first 2 years of HAART. The transplanted thymus tissue, however, was rejected. There was no clear difference in restoration of T cell function in the transplant recipients compared with the controls. Increases in TRECs after initiation of HAART may correlate with improved immune function.     

Evidence of thymic function in heavily antiretroviral-treated human immunodeficiency virus type 1-infected adults with long-term virologic treatment failure

Thymic function was evaluated in 32 heavily antiretroviral-treated human immunodeficiency virus type 1 (HIV-1)-infected adults with long-term virologic treatment failure by measuring thymic volume, by determining the absolute number of naive T cell phenotypes, and by determining the number of cells carrying T cell receptor excision circles (TRECs). There was a significant inverse correlation between age and thymic volume (r=-0.415; P=.018), and there was a significant direct correlation between thymic volume and total naive T cell counts (r=0.529; P=.002), naive CD4(+) cell counts (r=0.437; P=.012), naive CD8(+) cell counts (r=0.467; P=.007), and TREC levels (r=0.391; P=.027). In conclusion, this study found clear evidence that the thymus of heavily antiretroviral-treated HIV-1-infected adults with long-term virologic treatment failure is actively engaged in thymopoiesis, which generates new naive T cells for the peripheral lymphocyte pool.     

Thymopoiesis in HIV-infected adults after highly active antiretroviral therapy.

The thymus of HIV-seropositive patients can enlarge as CD4+ T cell counts increase on highly active anti-retroviral therapy (HAART). This may indicate development of new T cells or represent mature peripheral T cells recirculating to the thymus. To define the etiology of the enlargement, the thymuses of two HIV-infected individuals on HAART were biopsied. For more than 3 years before initiation of HAART, both patients (38 and 41 years of age) had documented CD4+ T lymphopenia. Peripheral blood samples were obtained to assess circulating CD4+ CD45RA+ CD62L+ T cells, which were thought to have recently developed in the thymus. Peripheral blood T cells from both patients and thymocytes from the second patient were also tested for levels of DNA episomes formed during T cell receptor gene rearrangement (T cell receptor rearrangement excision circles, TRECs). With HAART, peripheral blood CD4+ T cell counts increased from approximately 60/mm(3) to 552/mm(3) and 750/mm(3) for patients 1 and 2, respectively. Thymic biopsies from both patients showed normal thymus histology with active thymopoiesis. Percentages of peripheral blood CD4+ CD45RA+ CD62L+ T cells and quantitation of T cell TRECs also reflected active thymopoiesis in both patients. Thus, in these two HIV-seropositive adults examined after initiation of HAART, thymic enlargement represented active thymopoiesis. Thymopoiesis in adult AIDS patients may contribute to immune reconstitution even after prolonged CD4+ T lymphopenia.     

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.     

Poor CD4 T cell restoration after suppression of HIV-1 replication may reflect lower thymic function

OBJECTIVE: To characterize immune phenotype and thymic function in HIV-1-infected adults with excellent virologic and poor immunologic responses to highly active antiretroviral therapy (HAART). METHODS: Cross-sectional study of patients with CD4 T cell rises of > or = 200 x 10(6) cells/l (CD4 responders; n = 10) or < 100 x 10(6) cells/l (poor responders; n = 12) in the first year of therapy. RESULTS: Poor responders were older than CD4 responders (46 versus 38 years; P < 0.01) and, before HAART, had higher CD4 cell counts (170 versus 35 x 106 cells/l; P = 0.11) and CD8 cell counts (780 versus 536 x 10(6) cells/l; P = 0.02). After a median of 160 weeks of therapy, CD4 responders had more circulating naive phenotype (CD45+CD62L+) CD4 cells (227 versus 44 x 10(6) cells/l; P = 0.001) and naive phenotype CD8 cells (487 versus 174 x 10(6) cells/l; P = 0.004) than did poor responders (after 130 weeks). Computed tomographic scans showed minimal thymic tissue in 11/12 poor responders and abundant tissue in 7/10 responders (P = 0.006). Poor responders had fewer CD4 cells containing T cell receptor excision circles (TREC) compared with CD4 responders (2.12 versus 27.5 x 10(6) cells/l; P = 0.004) and had shorter telomeres in CD4 cells (3.8 versus 5.3 kb; P = 0.05). Metabolic labeling studies with deuterated glucose indicated that the lower frequency of TREC-containing lymphocytes in poor responders was not caused by accelerated proliferation kinetics. CONCLUSION: Poor CD4 T cell increases observed in some patients with good virologic response to HAART may be caused by failure of thymic T cell production.     

Granulocyte colony-stimulating factor increases CD4+ T cell counts of human immunodeficiency virus-infected patients receiving stable, highly active antiretroviral therapy: results from a randomized, placebo-controlled trial

Thirty human immunodeficiency virus (HIV)-infected patients with CD4+ T cell counts <350 cells/mm3 who had received stable, highly active antiretroviral therapy (HAART) for at least 24 weeks were randomized to receive either placebo or granulocyte colony-stimulating factor (G-CSF; 0.3 mg/mL 3 times a week) for 12 weeks. Blood samples were collected at specified time points. G-CSF treatment enhanced the total lymphocyte count (P=.002) and increased CD3+ (P=.005), CD4+ (P=.03), and CD8+ (P=.004) T cell counts as well as numbers of CD3-CD16+CD56+ NK cells (P=.001). The increases in CD4+ and CD8+ cell counts resulted from increases in CD45RO+ memory T cells and cells expressing the CD38 activation marker. Lymphocyte proliferative responses to phytohemagglutinin and Candida antigen decreased, whereas NK cell activity and plasma HIV RNA did not change during G-CSF treatment. After 24 weeks, all immune parameters had returned to baseline values. This study suggests that G-CSF treatment of HIV-infected patients receiving stable HAART increases the concentration of CD4+, CD8+, and NK cells without inducing changes in the virus load.     

T-cell repopulation and thymic volume in HIV-1-infected adult patients after highly active antiretroviral therapy

The origin of T cells after highly active antiretroviral therapy (HAART) in patients infected with human immunodeficiency virus 1 (HIV-1) is now under discussion. The possibility of renewed lymphopoiesis in aged thymuses is still controversial. In this work we combine the analysis of na?ve T cells, T-cell receptor excision circles (TRECs), and computed tomography scanning of thymic tissue to further assess whether the thymus is involved in immune reconstitution. Fifteen antiretroviral-na?ve HIV-1-infected patients were evaluated during 48 weeks of HAART. At baseline, significant correlation was present among age and both thymic volume and TRECs, and between na?ve T cells and TRECs. After starting HAART, there was a significant increase at week 12 in na?ve CD4(+) and CD8(+) T cells, TRECs, and thymic volume. The initial net increases in na?ve T cells and TREC counts were significantly correlated. Changes in thymic volume and TRECs were also indirectly related; splitting the population into 2 groups of high and low baseline TREC levels, only the group with low TREC levels had significant increases in both TRECs and thymic volume. Thus, the increase in thymic volume might be functional, in response to depleted TREC levels. Taken together, our data strongly suggest a thymic role in immune reconstitution, at least in patients with depleted baseline TREC levels. (Blood. 2002;99:3702-3706)     

Evidence of thymic reconstitution after highly active antiretroviral therapy in HIV-1 infection

Objectives

We aimed to provide evidence of thymic reconstitution after highly active antiretroviral therapy (HAART) in HIV‐1 infected patients and to correlate this with the restoration of peripheral naïve T cells.

Methods

Positron emission tomography (PET) enables definitive evidence of thymic activity, indicating functional potential. In this case study, a single patient who initiatiated HAART demonstrated reconstitution of the naïve T‐cell pool and underwent thymic PET scans at baseline and 2 and 6 months following initiation of therapy. Two patients who failed to demonstrate such reconstitution acted as controls. These patients (mean age 27 years) had chronic HIV infection with low CD4 T‐cell counts (mean 82, range 9–160 cells/μL blood). Increased function of the thymus visualized by PET was correlated with phenotypic changes in CD4 and CD8 T cells in the periphery measured by flow cytometry, and with numbers of recent thymic emigrants measured by quantification of the numbers of T‐cell receptor excision circles (TRECs) in peripheral cells.

Results

In one patient, clear correlations could be drawn between visible activity within the thymus, as measured by increased [F18]fluorodeoxyglucose (FDG) uptake, and regeneration of naïve CD4 (CD45RA/CD62L) T cells, increased numbers of CD4 T cells, controlled viraemia and increased numbers of recent thymic emigrants. A second patient displayed no increase in peripheral CD4 count and no increase in thymic activity. The third patient elected to stop therapy following the 2‐month time point.

Conclusions

The use of PET suggests that thymic activity may increase after HAART, indicating that the thymus has the potential to be functional even in HIV‐1 infected persons with low CD4 T‐cell counts.

     

Discordant increases in CD4+ T cells in human immunodeficiency virus-infected patients experiencing virologic treatment failure: role of changes in thymic output and T cell death

Some patients infected with human immunodeficiency virus (HIV) who are experiencing antiretroviral treatment failure have persistent improvement in CD4+ T cell counts despite high plasma viremia. To explore the mechanisms responsible for this phenomenon, 2 parameters influencing the dynamics of CD4+ T cells were evaluated: death of mature CD4+ T cells and replenishment of the CD4+ T cell pool by the thymus. The improvement in CD4+ T cells observed in patients with treatment failure was not correlated with spontaneous, Fas ligand-induced, or activation-induced T cell death. In contrast, a significant correlation between the improvement in CD4+ T cell counts and thymic output, as assessed by measurement of T cell receptor excision circles, was observed. These observations suggest that increased thymic output contributes to the dissociation between CD4+ T cell counts and viremia in patients failing antiretroviral therapy and support a model in which drug-resistant HIV strains may have reduced replication rates and pathogenicity in the thymus.     

Thymic output during initial highly active antiretroviral therapy (HAART) and during HAART supplementation with interleukin 2 and/or with HIV type 1 immunogen (Remune)

The thymic output of patients receiving highly active antiretroviral therapy (HAART) was assessed by sjTREC (signal joint T cell receptor rearrangement excision circle) analysis to determine the thymic contribution to CD4(+) T cell reconstitution during initial therapy and during interleukin 2 (IL-2) and/or Remune supplementation of HAART. Levels of sjTRECs were observed to decline dramatically after the first 4 weeks of HAART and then increased without significant associated changes in CD4(+) T cell counts. HAART supplementation with IL-2 was observed to lead to rapid increases in CD4(+) T cells that were accompanied by sjTREC decreases. No notable changes in CD4(+) T cell counts and sjTRECs were seen in patients receiving HAART supplemented with Remune alone. The results indicate CD4(+) T cell maintenance during initial treatment of HIV-1 with HAART and early CD4(+) T cell reconstitution of patients receiving IL-2 with HAART is largely due to thymus-independent mechanisms, with the thymus making a limited contribution.     

Thymic size and lymphocyte restoration in patients with human immunodeficiency virus infection after 48 weeks of zidovudine, lamivudine, and ritonavir therapy

Human immunodeficiency virus (HIV) infection is associated with progressive loss of circulating CD4+ lymphocytes. Treatment with highly active antiretroviral therapy (HAART) has led to increases in CD4+ T lymphocytes of naive (CD45RA+62L+) and memory (CD45R0+RA-) phenotypes. Thymic computerized tomography scans were obtained on 30 individuals with HIV disease to investigate the role of the thymus in cellular restoration after 48 weeks of HAART. Individuals with abundant thymic tissue had higher naive CD4+ T lymphocyte counts at weeks 2-24 after therapy than individuals with minimal thymic tissue. Individuals with abundant thymic tissue had significantly larger increases in naive CD4+ cells during the first 4 weeks of therapy. These individuals were also more likely to experience viral rebound despite comparable initial declines in plasma HIV-1 RNA. These findings suggest that there is a complex relationship among the thymus, viral replication, and lymphocyte restoration after application of HAART in HIV disease.     

Dysregulation of CD4+CD25+CD127lowFOXP3+ regulatory T cells in HIV-infected pregnant women

Pregnancy represents a major challenge to immunologic tolerance. How the fetal "semiallograft" evades maternal immune attack is unknown. Pregnancy success may involve alteration of both central (thymic) and peripheral tolerance mechanisms. HIV infection is characterized by CD4(+) T-cell depletion, chronic immune activation, and altered lymphocyte subsets. We studied immunologic consequences of pregnancy in 20 HIV-infected women receiving highly active antiretroviral therapy (HAART), and for comparison in 16 HIV-negative women. Lymphocyte subsets, thymic output, and cytokine profiles were measured prospectively during pregnancy and postpartum. A significant expansion of CD4(+)CD25(+)CD127(low)FoxP3(+) regulatory T cells indicating alteration of peripheral tolerance was seen during second trimester, but only in HIV-negative women. HIV-infected women had lower CD4 counts, lower thymic output and Th-2 cytokines, and more immune activation at all time points compared with controls. Immune activation was decreased in HIV-infected patients during pregnancy. In contrast, CD4 counts were increased in both groups. In conclusion, the study does not indicate that pregnancy adversely affects the immunologic course of HIV infection. However, despite HAART during pregnancy, HIV-infected women display different immunologic profiles from HIV-negative women, which may have importance for the induction of fetal-maternal tolerance and in part explain the increased risk of abortion in HIV-infected women.     

Endogenous IL-7 is associated with increased thymic volume in adult HIV-infected patients under highly active antiretroviral therapy

OBJECTIVE: Immune reconstitution after highly active antiretroviral therapy (HAART) in HIV-infected patients has led to an increase in the number of new CD4 T lymphocytes. Neolymphopoiesis in the thymus has been proposed as a mechanism in T-cell regeneration. Nevertheless, factors involved in the regeneration of T cells by thymic-dependent pathways in HIV-infected patients under HAART are still unknown and might be of relevance in HIV infection. The aim of this work was to study the role of IL-7 in the thymic rebound of HIV-infected adults under HAART. DESIGN: To study the association between IL-7 and thymic function-related markers, these variables were measured in 49 antiretroviral-naive HIV-infected patients at baseline and at weeks 12, 24, 36 and 48 of treatment. METHODS: Thymic function-related markers: thymic volume, naive phenotype, and T-cell receptor excision circles (TREC) bearing-cells, were evaluated by computed tomography, flow cytometry, and quantitative polymerase chain reaction, respectively. IL-7 levels were evaluated using a high sensitivity colorimetric enzyme-linked immunosorbent assay. RESULTS: At baseline, we found an inverse correlation between IL-7 levels and thymic function-associated parameters: thymic volume, naive T cells and TREC-bearing cells. After 48 weeks of therapy increased levels of thymic function-related markers along with a significant decrease in IL-7 levels were found. IL-7 levels at baseline were the only independently associated variable with respect to changes in thymic volume at weeks 12, 24 and 48 of follow-up. CONCLUSION: These data suggest that IL-7 plays an important role in thymic rebound in adult HIV-infected patients under HAART.     

Entrapment of recent thymic emigrants in lymphoid tissues from HIV-infected patients: association with HIV cellular viral load

OBJECTIVE(S): Depletion of thymus derived naive T-cells is a feature of HIV infection. Here the impact of HIV infection on the compartmentalization of recent thymic emigrants of (RTE) and naive T-cells was examined. METHODS: Peripheral blood mononuclear cells (PBMC) and lymphoid tissue (LT) from 43 HIV-infected patients and 12 controls were examined for RTE distribution by measuring coding joint T-cell receptor excisional circles (cjTREC) by PCR and naive and memory T-cell subsets and adhesion molecules (L-selection, LFA-1) by flow cytometry. RESULTS: In HIV-infected patients, the RTE as quantified by cjTRECs in CD4 LT cells were significantly higher than in PBMC. Their values, however, were less than in control subjects, in both the LT and PBMC compartments. This was associated with an increase in L-selectin and LFA-1 expression on LT derived T cells. In PBMC, a significant positive relationship between TREC and naive CD4 cells and an inverse relationship between TREC and cellular viral load (CVL) was observed. Whereas in LT, there was a positive relationship between cjTREC and both naive CD4 cell percentage and CVL. CONCLUSIONS: Collectively, the data suggests that LT is a significant reservoir for RTE. The RTE appeared to be entrapped in LT from HIV-infected subjects. Such entrapment is probably a response to the high viral load in these tissues. These observations may partially explain the decline in RTE observed in the peripheral blood of HIV-infected patients, and the delay in recovery of naive cells in blood after initiation of HAART.     

Thymic function in severely immunodeficient HIV type 1-infected patients receiving stable and effective antiretroviral therapy

The role of the thymus in long-term immune reconstitution has not been addressed in HIV patients who were severely immunodeficient prior to successful treatment with combination antiretroviral therapy (ART). Adult HIV-1 patients (n = 78) with nadir CD4+ T cell counts <100 T cells/microl, at least 12 months on ART and 6 months of complete viral suppression (<50 HIV RNA copies/ml) were selected from a patient database. The cohort was divided according to current CD4+ T cell counts and patients from the lowest (n = 15) and highest (n = 12) tertiles were studied. Thymic volume was assessed by spiral computed tomography. Naive (CD45RA+CD62L+) and replicating (Ki67+) T cells were quantitated by flow cytometry, T cell receptor excision circles (TREC) were assessed by real-time PCR, and serum IL-7 and testosterone by immunoassay. Patients with low CD4+ T cell counts had smaller thymuses [0(0-5.3) vs. 3.5(0-15.6) cm(3), p = 0.04] and were more likely to have no detectable thymus. They had similar proportions of replicating cells, but fewer naive CD4+ and CD8+ T cells and less TREC in CD4+ and CD8+ T cells/ml of blood than patients with high CD4+ T cell counts. However, some patients with no detectable thymus had high numbers of naive and TREC-bearing T cells. Thus, the recovery of CD4+ T cells in severely immunodeficient HIV patients with a virological response to ART is probably limited by thymic function. However, the data are consistent with extrathymic T cell production contributing to the naive T cell pool in some patients.     

Structural normalization of the lymphoid tissue in asymptomatic HIV-infected patients after 48 weeks of potent antiretroviral therapy.

BACKGROUND: The hallmark of HIV infection is the involution and destruction of lymphoid tissue. However, very little information exists on the effect of highly active antiretroviral therapy (HAART) on lymphoid tissue structure. OBJECTIVE: To evaluate the effect of a HAART regimen after 48 weeks on the architecture and cell regeneration of tonsil lymphoid tissue in HIV-infected patients with CD4 T cell counts > or = 500/microl. METHODS: From June 1997 to February 1998 all asymptomatic HIV-infected patients with CD4 T cell counts > or = 500/microl seen at our unit were offered quadruple antiretroviral therapy. Tonsil biopsies were obtained at baseline and at 48 weeks. Tonsil tissue sections were examined to evaluate structural and immunohistochemical changes by two blinded and independent pathologists. Cell numbers were counted for selected markers in T-dependent zones. RESULTS: Eleven patients were evaluable, six were excluded because of insufficient or inadequate sampling in at least one of the biopsies. Cellular depletion, plasma cell accumulation and prominent vessels were observed in all cases; three excluded patients with evaluable baseline biopsies showed similar tissue lesions. Follow-up biopsies demonstrated some degree of improvement in all patients. Germinal centres appeared in seven cases that were not seen at baseline. CD4 cell counts increased and CD8 cell counts decreased significantly in lymphoid tissue. An increase in CD45RA+ cells was observed; however, the proportion of CD45+Ki67+ cells did not differ between baseline and 48 weeks. CONCLUSION: This study shows an unexpected range of moderate to severe lymphoid tissue lesions in mildly immunosuppressed HIV-infected patients, which was partly restored after 48 weeks of HAART.     

Short communication: decreasing soluble CD30 and increasing IFN-gamma plasma levels are indicators of effective highly active antiretroviral therapy

It was previously reported that without highly active antiretroviral therapy (HAART), secretion of Th1 cytokines and antiviral IFN-gamma in HIV-infected patients is decreased, whereas the production of Th2 cytokines, proinflammatory cytokines, and TNF-alpha is increased. We studied the effect of HAART on Th1-, Th2-, and monocyte-derived cytokines, and on the Th2-type immune response marker soluble (s)CD30 in HIV-1-infected hemophilia patients. Viral Load (VL), CD4+ lymphocyte counts, and plasma levels of sIL-1RA, IL-2, sIL-2R, IL-3, IL-4, IL-6, sIL-6R, IL-7, IL-10, TNF-alpha, TGF-beta2, IFN-gamma, and sCD30 were measured in 18 patients who received HAART. Nine patients were initially treatment-naive and were monitored after the initiation of HAART. sCD30 median levels were significantly higher in treatment-naive patients than in patients who were on HAART (77 vs. 30 U/ml, p = 0.005). A strong association was observed between sCD30 and VL (r = 0.85, p = 0.004). After the initiation of HAART, sCD30 levels decreased and remained low (at 1 year, 38; at 2 years, 41 U/ml; p = 0.012 and p = 0.021, respectively, as compared to baseline level) and this was accompanied by a decrease in VL and monocyte-derived IL-6 and an increase in CD4+ lymphocyte counts and Th1-derived IFN-gamma. One year after the initiation of HAART a strong inverse correlation was observed between IFN-gamma and VL (r = -0.83, p = 0.006). In contrast to sCD30 and IFN-gamma, CD4 counts and plasma IL-6 did not correlate with VL at any time. Our data suggest that decreasing sCD30 and increasing IFN-gamma plasma levels are indicators of effective HAART treatment and CD4 Th1 cell recovery in HIV-infected patients.     

Evaluation of T cell receptor gene rearrangement excision circles after antiretroviral therapy in children infected with human immunodeficiency virus

Immune reconstitution after antiretroviral therapy in human immunodeficiency virus (HIV)infected patients may result from the recovery of thymus function, peripheral redistribution, or decreased T cell destruction. This study investigated levels of T cell receptor gene rearrangement excision circles (TRECs) as a measure of recent thymic emigrant cells in peripheral blood lymphocytes of 50 HIV-infected infants and children who were followed-up for 40 months after the start or change of antiretroviral therapy. At baseline, patients exhibited fewer TRECs than did uninfected control subjects. The increase in TRECs after antiretroviral therapy was greater in infants than in older HIV-infected children. Of interest, patients who demonstrated discordant responses (i.e., increased CD4 T cell counts without significant virologic suppression) also had substantial gains in TRECs. Furthermore, TRECs correlated positively with the number of CD4 and naive T cells and negatively with age and virus load. Measurement of TRECs may serve as a useful tool for evaluating immune reconstitution in HIV-infected children receiving antiretroviral therapy.     

IL-2 therapy and thymic production of naive CD4 T cells in HIV-infected patients with severe CD4 lymphopenia

OBJECTIVES: IL-2 therapy increases memory and naive CD4 T cells in HIV-infected patients, but its effect on thymopoiesis is unknown. To investigate this effect, we quantified T-cell receptor rearrangement excision circles (TREC) in CD4 T cells from lymphopenic AIDS patients treated with highly active antiretroviral therapy and IL-2. METHODS: CD4 cell subsets were evaluated by flow cytometry using anti-CD45RO/RA, CD62L, Ki67 and CD95 monoclonal antibodies. The proportion of recent thymic emigrant had been quantified by a real-time polymerase chain reaction assay for signal joint TREC in peripheral blood mononuclear and purified CD4 T cells. RESULTS: At initiation of IL-2, TREC copies/microl of blood were correlated with naive T cell numbers and age. Both naive and TREC numbers/microl significantly increased over time in all patients, with a wide range of TREC increases. Higher percentages of CD4+CD45RO-negative cells positive for the Ki67 cell-cycle marker were found in patients with a low TREC increase, but remained stable under IL-2. TREC and naive cell recovery were correlated; they also correlated with the numbers of TREC and naive cells at the start of IL-2, and with age, suggesting a thymic origin for naive T-cell recovery. A mathematical model showing the linear recovery of naive cells and TREC under IL-2 also strongly suggested that a naive T-cell increase reflects thymic export and involves little net death and proliferation. CONCLUSION: Although we cannot rule out a mechanism of altered proliferation or death rate, the thymus plays an important role in the long-term recovery of naive T cells under IL-2 therapy.