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

Metabolism-dependent ferroptosis promotes mitochondrial dysfunction and inflammation in CD4+ T lymphocytes in HIV-infected immune non-responders

BACKGROUND

HIV immune non-responders (INRs) are described as a failure to reestablish a pool of CD4⁺ T lymphocytes (CD4 cells) after antiretroviral therapy (ART), which is related to poor clinical results. Ferroptosis is a newly discovered form of cell death characterised by iron-dependent lipid peroxidation and the accumulation of reactive oxygen species (ROS). The mechanism of unrecoverable CD4 cells in INRs and whether ferroptosis plays a role are not fully understood.

METHODS

Ninety-two people living with HIV (PLHIVs) who experienced four-year ART with sustained viral suppression, including 27 INRs, 34 partial responders (PRs), and 31 complete responders (CRs); and 26 uninfected control participants (UCs) were analysed for 16 immune parameters with flow cytometry. Then plasma lipid, iron and oxidation, and antioxidant indicators were detected by ELISA, and CD4 cells were sorted out and visualised under transmission electron microscopy. Finally, ferroptosis inhibitors were added, and alterations in CD4 cell phenotype and function were observed.

FINDINGS

We found decreased recent thymic emigrants (RTE), over-activation and over-proliferation phenotypes, diminished killing function, decreased IL-7R and more severe inflammation; increased lipid peroxidation in the mitochondria and disruptions of the mitochondrial structure, showing typical features of ferroptosis in CD4 cells in INRs. Additionally, ferroptosis inhibitors could reduce inflammation and repair mitochondrial damage. Meanwhile, ELISA results showed increased plasma free fatty acids (FFA) and an imbalance of oxidative and antioxidant systems in INRs. Flow cytometry results displayed alterations of both transferrin receptor (CD71) and lipid transporter (CD36) expressions on the surface of CD4 cells. Mechanistically, there was a stronger correlation between CD36 expression and mitochondrial lipid peroxidation production, ferroptosis makers, and inflammation indicators; while amino acid transporter (CD98) was more related to killing functions; and CD71 was more closely related to activation status in CD4 cells.

INTERPRETATION

Cellular metabolism was closely correlated with its diverse functions in INRs. Ferroptosis was observed in CD4 cells of INRs, and inhibiting ferroptosis through modulating mitochondrial disorders and inflammation may offer an alternative immunological strategy for reinvigorating CD4 cells in INRs.

FUNDING

This research was supported by the 13th Five-year Plan, Ministry of Science and Technology of China (2018ZX10302-102), Beijing Municipal Administration of Hospitals' Ascent Plan (DFL20191802), and Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (ZYLX202126).

Aging, trends in CD4+/CD8+ cell ratio, and clinical outcomes with persistent HIV suppression in a dynamic cohort of ambulatory HIV patients

BACKGROUND

Age blunts CD4+ lymphocyte cell count/μl (CD4+) improvements observed with antiretroviral therapy (ART)-induced viral suppression among people with HIV (PWH). Prolonged viral suppression reduces immune dysregulation, reflected by rising CD4+/CD8+ ratios (CD4+/CD8+). We studied CD4+/CD8+ over time to determine whether it predicts risk for select comorbidities and mortality among aging PWH with viral suppression.

METHODS

We studied HIV Outpatient Study (HOPS) participants prescribed ART during 2000-2018 who achieved a viral load less than 200 copies/ml on or after 1 January 2000, and remained virally suppressed at least 1 year thereafter. We modeled associations of CD4+/CD8+ with select incident comorbidities and all-cause mortality using Cox regression and controlling for demographic and clinical factors.

RESULTS

Of 2480 eligible participants,1145 (46%) were aged less than 40 years, 835 (34%) 40-49 years, and 500 (20%) ≥ 50 years. At baseline, median CD4+/CD8+ was 0.53 (interquartile range: 0.30-0.84) and similar among all age groups (P = 0.18). CD4+/CD8+ values and percentage of participants with CD4+/CD8+ at least 0.70 increased within each age group (P < 0.001 for all). CD4+/CD8+ increase was greatest for PWH aged less than 40 years at baseline. In adjusted models, most recent CD4+/CD8+less than 1.00 and less than 0.70 were independently associated with higher risk of non-AIDS cancer and mortality, respectively.

CONCLUSION

Pretreatment immune dysregulation may persist as indicated by CD4+/CD8+ less than 0.70. Persistent viral suppression can improve immune dysregulation over time, reducing comorbidity, and mortality risk. Monitoring CD4+/CD8+ among ART-treated PWH with lower values provide a means to assess for mortality and comorbidity risk.

Study of thymus volume and density in COVID-19 patients: Is there a correlation in terms of pulmonary CT severity score?

Background

Thymus has a pivotal role in combating infectious diseases. Although some reviews have been published about its critical role in COVID-19, there is not enough research. In this study, the size and density of thymus related to computed tomography pulmonary severity score (CT-SS) were researched.

Results

A total of 196 patients were analyzed with a mean age of 52.54 ± 18.78 years; 97 (49.5%) of them were RT-PCR (−) and 99 (50.5%) were RT-PCR (+). Within RT-PCR (+) group 62 (62.6%) of them had pneumonia with a mean CT-SS of 9.37 ± 8.83; within RT-PCR (−) group 20 (20.6%) of them had pneumonia with the mean CT-SS of 12.00 ± 10.18. CT-SS had moderate negative correlation with thymus volume and thymus maximum diameter in patients having nodular-type thymus (R  = −0.591, P  = 0.02; R  = −0.515, P  = 0.049, respectively). Homogenous fat infiltration was more commonly seen in RT-PCR (−) group while reticular and nodular types were commonly seen in RT-PCR (+) group (p  = 0.015). The mean volume and maximum diameter of thymus were statistically significantly higher in RT-PCR (+) group (p  = 0.027 and p  = 0.048, respectively).

Conclusion

This study showed the higher thymic volume and maximum diameter and more involution in COVID-19 patients. CT-SS had a moderate negative correlation with thymus volume and thymus maximum diameter. Pneumonia was more frequent in COVID patients, but mean CT-SS of the non-COVID cases was higher.

Relationship between Pneumonia and the Thymus Gland in Children with COVID-19: A Volumetric Computed Tomography Study

Objective Many studies showed that less-severe disease symptoms and fewer mortality rates have been reported in pediatric novel coronavirus disease 2019 (COVID-19) patients. In this study, we aimed to reveal the relationship between the volume of thymus gland, which provides T lymphocyte maturation in children, with the severity of lung involvement and blood laboratory values in pediatric patients with COVID-19 infection.

Methods Thymus density and thymus and cardiac volumes were measured in pediatric COVID-19 patients and a control group that underwent thoracic tomography for reasons other than infection. Thymus/heart ratios were calculated to index the thymus volumes of the patients to their body dimensions. The severity of pneumonia was demonstrated by proportioning the involved lung parenchymal volume to the total lung volume in patients with typical involvement in thoracic tomography. The relationship between volumetric and blood laboratory values was statistically evaluated.

Results Thymus density (p = 0.015) and thymus/heart ratio (p = 0.04) significantly differed between patients with COVID-19 infection and the control group. A correlation was observed between the pneumonia involvement rate and C-reactive protein (CRP) (k: 0.451, p = 0.08) and white blood cell (WBC; k: 0.419, p = 0.015) values in the thoracic tomography of the COVID-19 group.

Conclusion The thymus gland is enlarged as an indicator of activation in COVID-19 infection. We hope that our study will guide new studies on the prognostic value of thymus size in lymphopenic patients with severe disease.

Associations between recent thymic emigrants and CD4+ T-cell recovery after short-term antiretroviral therapy initiation

Supplemental Digital Content is available in the text

Objective:

Around 20–30% of HIV-infected individuals (HIV+) on successful antiretroviral therapy (ART) fail to normalize their CD4⁺ T-cell counts. Various factors could contribute to the lack of immune reconstitution, one of them being thymic insufficiency. We aimed to explore associations between recent thymic emigrants (RTEs) and CD4⁺ T-cell recovery.

Design:

ART-naive HIV+ individuals who started ART with advanced AIDS were selected. Good versus poor immune reconstitution was defined by CD4⁺ gains above or below 100 CD4⁺ T cells/μl. The follow-up period was 6 months.

Methods:

Peripheral blood mononuclear cells were isolated and flow cytometry was used to characterize RTEs as the fraction of naive CD4⁺ T cells expressing CD31⁺, the platelet endothelial cell adhesion molecule. Markers of cellular activation, senescence, exhaustion and cycling were also assessed.

Results:

After 6 months on ART, HIV+ individuals with good immune reconstitution had higher absolute numbers of RTEs, compared with those with poor immune reconstitution, and these strongly correlated with CD4⁺ gains in those individuals with good immune reconstitution but not with poor immune reconstitution. We also found that CD8⁺ T-cell immune activation decreased as early as 2 months post-ART initiation in individuals with good immune reconstitution, but only at month 6 post-ART in individuals with poor immune reconstitution. Levels of immune activation were inversely correlated with the absolute numbers of RTEs in both groups, but more strongly so in individuals with poor immune reconstitution.

Conclusion:

We show that RTEs are linked to CD4⁺ T-cell recovery and that the degree of immune reconstitution is not directly linked to persistent immune activation.

Metcalf Lecture Award: Applying niche biology to engineer T-cell regenerative therapies

The processes generating cells of adaptive immunity render them less amenable to the single cytokine signals used so effectively to regenerate myeloid cells. T-cell neogenesis begins in the bone marrow, where specific sets of late osteolineage cells govern the specification of hematopoietic cells capable of migrating to the thymus where differentiation is completed. Osteocalcin-expressing bone marrow stromal cells producing Dll4 serve as a progenitor niche enabling this T-competent cell production. Biocompatible alginate-based cryogels containing bone morphogenetic proteins (BMP-2) and the Notch ligand Dll4 were engineered to recapitulate the endogenous niche. These cryogels are highly pliable and can be injected under the skin of animals undergoing bone marrow transplantation. The result in mice is an ectopic niche fostering T-competent progenitor generation that results in improved T-cell numbers and receptor diversity. The recipients can generate neoantigen vaccine responses while having improved tolerance manifest by reduced graft-versus-host disease upon allogeneic transplant. Through emerging details of niches in the bone marrow, therapeutics more complex than those necessary for myeloid reconstitution are possible. Niche biology-guided bioengineered design offers the possibility of regenerative therapies for T lymphoid cells.

Targeting T-cell malignancies using anti-CD4 CAR NK-92 cells

Peripheral T-cell lymphomas (PTCLs) are a group of very aggressive non-Hodgkin's lymphomas (NHLs) with poor prognoses and account for a majority of T-cell malignancies. Overall, the standard of care for patients with T-cell malignancies is poorly established, and there is an urgent clinical need for a new approach. As demonstrated in B-cell malignancies, chimeric antigen receptor (CAR) immunotherapy provides great hope as a curative treatment regimen. Because PTCLs develop from mature T-cells, these NHLs are commonly CD4+, and CD4 is highly and uniformly expressed. Therefore, CD4 is an ideal target for PTCL CAR immunotherapy. To that effect, we created a robust third-generation anti-CD4 CAR construct (CD4CAR) and introduced it into clonal NK cells (NK-92). CD4CAR NK-92 cells specifically and robustly eliminated diverse CD4+ human T-cell leukemia and lymphoma cell lines (KARPAS-299, CCRF-CEM, and HL60) and patient samples ex vivo. Furthermore, CD4CAR NK-92 cells effectively targeted KARPAS-299 cells in vivo that modeled difficult-to-access lymphoma nodules, significantly prolonging survival. In our study, we present novel targeting of CD4 using CAR-modified NK cells, and demonstrate efficacy. Combined, our data support CD4CAR NK cell immunotherapy as a potential new avenue for the treatment of PTCLs and CD4+ T-cell malignancies.

Alcohol Types and HIV Disease Progression Among HIV-Infected Drinkers Not Yet on Antiretroviral Therapy in Russia and Uganda

In HIV-infected drinkers, alcohol types more likely to cause inflammation could plausibly increase the risk of HIV disease progression. We therefore assessed the association between alcohol type and plasma HIV RNA level (HIV viral load) among HIV-infected drinkers not on antiretroviral therapy (ART) in Russia and Uganda. We analyzed the data of participants from cohorts in Russia and Uganda and assessed their HIV viral load at enrollment by the alcohol type predominantly consumed. We defined predominant alcohol type as the alcohol type contributing >50% of total alcohol consumption in the 1 month (Russia) or 3 months (Uganda) prior to enrollment. Using multiple linear regression, we compared log₁₀ HIV viral load by predominant alcohol type, controlling for age, gender, socioeconomic status, total number of standard drinks, frequency of drinking ≥6 drinks/occasion, and in Russia, history of injection drug use. Most participants (99.2% of 261 in Russia and 98.9% of 352 in Uganda) predominantly drank one alcohol type. In Russia, we did not find evidence for differences in viral load levels between drinkers of fortified wine (n = 5) or hard liquor (n = 49), compared to drinkers of beer/low-ethanol-content cocktails (n = 163); however, wine/high-ethanol-content cocktail drinkers (n = 42) had higher mean log₁₀ viral load than beer/low-ethanol-content cocktail drinkers (β = 0.38, 95% CI 0.07-0.69; p = 0.02). In Uganda, we did not find evidence for differences in viral load levels between drinkers of locally-brewed beer (n = 41), commercially-distilled spirits (n = 38), or locally-distilled spirits (n = 43), compared to drinkers of commercially-made beer (n = 218); however, wine drinkers (n = 8) had lower mean log₁₀ HIV viral load (β = -0.65, 95% CI -1.36 to 0.07, p = 0.08), although this did not reach statistical significance. Among HIV-infected drinkers not yet on ART in Russia and Uganda, we observed an association between the alcohol type predominantly consumed and the HIV viral load level in the Russia sample. These exploratory results suggest that, in addition to total number of drinks and drinking patterns, alcohol type might be a dimension of alcohol use that merits examination in studies of HIV and alcohol related outcomes.

Thymic hyperplasia after chemotherapy in adults with mature B cell lymphoma and its influence on thymic output and CD4(+) T cells repopulation

To investigate the thymic regenerative potential in adults accepting chemotherapy for lymphoma. The dynamics of thymic activity in 54 adults from baseline to 12 mo post-chemotherapy was analyzed by assessing thymic structural changes with serial computed tomography (CT) scans, and correlating these with measurements of thymic output by concurrent analysis of single-joint (sj) T-cell receptor excision circles (sjTREC) and CD31⁺ recent thymic emigrants (RTE) in peripheral blood. Furthermore, the consequence of thymic renewal on peripheral CD4⁺ T cell recovery after chemotherapy was evaluated. Time-dependent changes of thymic size and thymic output assessed by both sjTREC levels and CD31⁺ RTE counts in peripheral blood were observed during and after chemotherapy. Enlargement of thymus over baseline following chemotherapy regarded as rebound thymic hyperplasia (TH) was identified in 20 patients aged 18−53 y (median 33 y). By general linear models repeated measure analysis, it was found that, patients with TH (n = 20) had a faster recovery of sjTREC levels and CD31⁺ RTE counts after chemotherapy than patients with comparable age, gender, diagnosis, disease stage, thymic volume and output function at baseline but without TH (n = 18) (p = 0.035, 0.047); besides, patients with TH had a faster repopulation of both naïve CD4⁺ T cell and natural regulatory CD4⁺ T cell subsets than those without TH (p = 0.042, 0.038). These data suggested that adult thymus retains the capacity of regeneration after chemotherapy, especially in young adults. The presence of TH could contribute to the renewal of thymopoiesis and the replenishment of peripheral CD4⁺ T cell pool following chemotherapy in adults.

Poor immune reconstitution in HIV-infected patients associates with high percentage of regulatory CD4+ T cells

CD4⁺ regulatory T cells (Tregs) are essential for the maintenance of the immune system's equilibrium, by dampening the activation of potential auto-reactive T cells and avoiding excessive immune activation. To correctly perform their function, Tregs must be maintained at the right proportion with respect to effector T cells. Since this equilibrium is frequently disrupted in individuals infected with the human immunodeficiency virus (HIV), we hypothesize that its deregulation could hamper immune reconstitution in patients with poor CD4⁺ T cell recovery under highly active antiretroviral therapy (HAART). We analysed Tregs percentages amongst CD4⁺ T cells in 53 HIV-infected patients under HAART, with suppression of viral replication and distinct levels of immune reconstitution. As controls, 51 healthy individuals were also analysed. We observed that amongst the patients with Nadir values (the lowest CD4⁺ T cell counts achieved) <200 cells/µL, the individuals with high Tregs percentages (≥10% of total CD4⁺ T cells) had the worse CD4⁺ T cell reconstitution. In accordance, the well-described direct correlation between the Nadir value and CD4⁺ T cell reconstitution is clearly more evident in individuals with high Tregs proportions. Furthermore, we observed a strong negative correlation between Tregs percentages and CD4⁺ T cell recovery among immunological non-responder HIV⁺ individuals. All together, this work shows that high Tregs frequency is an important factor associated with sub-optimal CD4⁺ T cell recovery. This is particularly relevant for immunological non-responders with low Nadir values. Our results suggest that the Tregs proportion might be of clinical relevance to define cut-offs for HAART initiation.

Thymopoietic and bone marrow response to murine Pneumocystis pneumonia

CD4(+) T cells play a key role in host defense against Pneumocystis infection. To define the role of naïve CD4(+) T cell production through the thymopoietic response in host defense against Pneumocystis infection, Pneumocystis murina infection in the lung was induced in adult male C57BL/6 mice with and without prior thymectomy. Pneumocystis infection caused a significant increase in the number of CCR9(+) multipotent progenitor (MPP) cells in the bone marrow and peripheral circulation, an increase in populations of earliest thymic progenitors (ETPs) and double negative (DN) thymocytes in the thymus, and recruitment of naïve and total CD4(+) T cells into the alveolar space. The level of murine signal joint T cell receptor excision circles (msjTRECs) in spleen CD4(+) cells was increased at 5 weeks post-Pneumocystis infection. In thymectomized mice, the numbers of naïve, central memory, and total CD4(+) T cells in all tissues examined were markedly reduced following Pneumocystis infection. This deficiency of naïve and central memory CD4(+) T cells was associated with delayed pulmonary clearance of Pneumocystis. Extracts of Pneumocystis resulted in an increase in the number of CCR9(+) MPPs in the cultured bone marrow cells. Stimulation of cultured bone marrow cells with ligands to Toll-like receptor 2 ([TLR-2] zymosan) and TLR-9 (ODN M362) each caused a similar increase in CCR9(+) MPP cells via activation of the Jun N-terminal protein kinase (JNK) pathway. These results demonstrate that enhanced production of naïve CD4(+) T lymphocytes through the thymopoietic response and enhanced delivery of lymphopoietic precursors from the bone marrow play an important role in host defense against Pneumocystis infection.

Different profiles of immune reconstitution in children and adults with HIV-infection after highly active antiretroviral therapy

Background

Recent advances in characterizing the immune recovery of HIV-1-infected people have highlighted the importance of the thymus for peripheral T-cell diversity and function. The aim of this study was to investigate differences in immune reconstitution profiles after highly active antiretroviral therapy (HAART) between HIV-children and adults.

Methods

HIV patients were grouped according to their previous clinical and immunological status: 9 HIV-Reconstituting-adults (HIV-Rec-adults) and 10 HIV-Reconstituting-children (HIV-Rec-children) on HAART with viral load (VL) ≤400 copies/ml and CD4⁺ ≥500 cells/μL at least during 6 months before the study and CD4⁺ ≤300 cells/μL anytime before. Fifteen healthy-adults and 20 healthy-children (control subjects) were used to calculate Z-score values to unify value scales between children and adults to make them comparable.

Results

HIV-Rec-children had higher T-cell receptor excision circles (TREC) and lower interleukin (IL)-7 levels than HIV-Rec-adults (p < 0.05). When we analyzed Z-score values, HIV-Rec-children had higher TREC Z-score levels (p = 0.03) than HIV-Rec-adults but similar IL-7 Z-score levels. Regarding T-cell subsets, HIV-Rec-children had higher naïve CD4⁺ (CD4⁺CD45RA ^hi+CD27⁺), naïve CD8⁺ (CD8⁺CD45RA ^hi+CD27⁺), and memory CD8⁺ (CD8⁺CD45RO⁺) cells/μl than HIV-Rec-adults, but similar memory CD4⁺ (CD4⁺CD45RO⁺) counts. HIV-Rec-children had lower naïve CD8⁺ Z-score values than HIV-Rec-adults (p = 0.05).

Conclusion

Our data suggest that HIV-Rec-children had better thymic function than HIV-Rec-adults and this fact affects the peripheral T-cell subsets. Thus, T-cell recovery after HAART in HIV-Rec-adults could be the consequence of antigen-independent peripheral T-cell expansion while in HIV-Rec-children thymic output could play a predominant role in immune reconstitution.

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.

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.

High Thymic Volume Is Associated With Viral Replication and Immunologic Impairment Only Early After HAART Interruption in Chronic HIV Infection

One of the strategies that has been investigated to reduce antiretroviral treatment toxicity in patients infected with human immunodeficiency virus (HIV) is structured treatment interruption (STI). Our aim was to analyze early viral and immune dynamics after interruption of highly active antiretroviral therapy (HAART) and to determine whether thymic function-related markers play a role in preventing CD4 count decline caused by increased viral replication. This was a prospective study of an open cohort of 47 HIV-infected patients with a median 969 CD4 count and prolonged viral suppression. They were followed every 4 weeks though week 24. Thymic volume and TREC level were analyzed at baseline. Increased thymic volume was associated with higher plasma viral load and greater CD4 count decline early after interruption. Three virologic patterns were observed: rapid/high (RH), delayed/high (DH), and low/slow (LS) viral replication. RH correlated with higher thymic volume at baseline and with higher CD4 count decline at week 4. Patients with greater thymic volume was associated with an immune and virologic impairment only early after interruption, probably because of infection of the increased number of available target cells. As the long-term consequences of these observations are unknown, the safety of treatment interruption must be further studied.

Age-dependent incidence, time course, and consequences of thymic renewal in adults

Homeostatic regulation of T cells involves an ongoing balance of new T cell generation, peripheral expansion, and turnover. The recovery of T cells when this balance is disrupted provides insight into the mechanisms that govern homeostasis. In a long-term, single cohort study, we assessed the role of thymic function after autologous transplant in adults, correlating serial computed tomography imaging of thymic size with concurrent measurements of peripheral CD4(+) T cell populations. We established the age-dependent incidence, time course, and duration of thymic enlargement in adults and demonstrated that these changes were correlated with peripheral recovery of naive CD45RA(+)CD62L(+) and signal-joint TCR rearrangement excision circle-bearing CD4(+) populations with broad TCR diversity. Furthermore, we demonstrated that renewed thymopoiesis was critical for the restoration of peripheral CD4(+) T cell populations. This recovery encompassed the recovery of normal CD4(+) T cell numbers, a low ratio of effector to central memory cells, and a broad repertoire of TCR Vbeta diversity among these memory cells. These data define the timeline and consequences of renewal of adult thymopoietic activity at levels able to quantitatively restore peripheral T cell populations. They further suggest that structural thymic regrowth serves as a basis for the regeneration of peripheral T cell populations.

Long-term changes in circulating CD4 T lymphocytes in virologically suppressed patients after 6 years of highly active antiretroviral therapy

Highly active antiretroviral therapy (HAART) initiated in advanced HIV disease is associated with CD4 lymphocyte increases (200-300 cells/mm3 after 2-4 years), although longer-term cellular dynamics have not been studied. We observed a significant median CD4 lymphocyte increase of 126 cells/mm3 and 54 naive CD4 lymphocytes from year 3 to 6 of HAART among 20 individuals with pre-HAART CD4 cell counts of 100-300 cells/mm3. This cohort represents the longest prospective immunological follow-up of virologically suppressed patients on HAART.

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.