Thymic Function Impacts the Peripheral CD4/CD8 Ratio of HIV-Infected Subjects

The persistence of low CD4/CD8 ratio in chronic HIV-infection, despite ART suppression and normal CD4 levels, is associated with pre-therapy values of inflammation and thymic function

BACKGROUND

Persistence of a low CD4/CD8 ratio is associated with an increased morbimortality in people living with HIV (PLWH) under effective antiretroviral therapy. We aimed to explore the immunological significance of a persistently low CD4/CD8 ratio, even despite normal CD4 levels, and assess whether these features vary from those associated to a low nadir-CD4, another well-established predictor of disease progression.

METHODS

CD4-recovered PLWH were classified by CD4/CD8 ratio after three-years of ART (viral suppression, CD4≥500; R < 0.8, n = 24 and R > 1.2, n = 28). sj/β-TRECs ratio and inflammatory-related markers were quantified. PBMCs were immunophenotyped by CyTOF and functionally characterized by ELISPOT. Subjects were also reclassified depending on nadir-CD4 (N ≤ 350/N > 350).

RESULTS

R < 0.8 showed a differential inflammatory profile compared to R > 1.2 (increased β2-microglobulin, D-dimers and IP-10 before ART). R < 0.8 presented lower baseline thymic function, being inversely correlated with post-ART inflammation. R < 0.8 at follow-up showed most alterations in CD8 subsets (increasing frequency and exhibiting a senescent phenotype [e.g., CD57+, CD95+]) and enhanced T-cell IFNγ/IL-2 secretion. However, comparing N ≤ 350 to N > 350, the main features were altered functional markers in CD4 T-cells, despite no differences in maturational subsets, together with a restricted T-cell cytokine secretion pattern.

CONCLUSION

Persistence of low CD4/CD8 ratio in successfully-treated PLWH, with normal CD4 counts, is associated with baseline inflammation and low thymic function, and it features post-therapy alterations specific to CD8 T-cells. Differently, subjects recovered from low nadir-CD4 in this setting feature post-therapy alterations on CD4 T-cells. Hence, different mechanisms of disease progression could underlie these biomarkers, potentially requiring different clinical approaches.

SARS-CoV-2 infection of thymus induces loss of function that correlates with disease severity

BACKGROUND

Lymphopenia, particularly when restricted to the T-cell compartment, has been described as one of the major clinical hallmarks in patients with coronavirus disease 2019 (COVID-19) and proposed as an indicator of disease severity. Although several mechanisms fostering COVID-19-related lymphopenia have been described, including cell apoptosis and tissue homing, the underlying causes of the decline in T-cell count and function are still not completely understood.

OBJECTIVE

Given that viral infections can directly target thymic microenvironment and impair the process of T-cell generation, we sought to investigate the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on thymic function.

METHODS

We performed molecular quantification of T-cell receptor excision circles and κ-deleting recombination excision circles to assess, respectively, T- and B-cell neogenesis in SARS-CoV-2-infected patients. We developed a system for in vitro culture of primary human thymic epithelial cells (TECs) to mechanistically investigate the impact of SARS-CoV-2 on TEC function.

RESULTS

We showed that patients with COVID-19 had reduced thymic function that was inversely associated with the severity of the disease. We found that angiotensin-converting enzyme 2, through which SARS-CoV-2 enters the host cells, was expressed by thymic epithelium, and in particular by medullary TECs. We also demonstrated that SARS-CoV-2 can target TECs and downregulate critical genes and pathways associated with epithelial cell adhesion and survival.

CONCLUSIONS

Our data demonstrate that the human thymus is a target of SARS-CoV-2 and thymic function is altered following infection. These findings expand our current knowledge of the effects of SARS-CoV-2 infection on T-cell homeostasis and suggest that monitoring thymic activity may be a useful marker to predict disease severity and progression.

Factors associated with the humoral response after three doses of COVID-19 vaccination in kidney transplant recipients

Introduction

Kidney transplant recipients showed a weak humoral response to the mRNA COVID-19 vaccine despite receiving three cumulative doses of the vaccine. New approaches are still needed to raise protective immunity conferred by the vaccine administration within this group of high-risk patients.

Methods

To analyze the humoral response and identify any predictive factors within these patients, we designed a prospective monocentric longitudinal study of Kidney transplant recipients (KTR) who received three doses of mRNA-1273 COVID-19 vaccine. Specific antibody levels were measured by chemiluminescence. Parameters related to clinical status such as kidney function, immunosuppressive therapy, inflammatory status and thymic function were analyzed as potential predictors of the humoral response.

Results

Seventy-four KTR and sixteen healthy controls were included. One month after the administration of the third dose of the COVID-19 vaccine, 64.8% of KTR showed a positive humoral response. As predictive factors of seroconversion and specific antibody titer, we found that immunosuppressive therapy, worse kidney function, higher inflammatory status and age were related to a lower response in KTR while immune cell counts, thymosin-a1 plasma concentration and thymic output were related to a higher humoral response. Furthermore, baseline thymosin-a1 concentration was independently associated with the seroconversion after three vaccine doses.

Discussion

In addition to the immunosuppression therapy, condition of kidney function and age before vaccination, specific immune factors could also be relevant in light of optimization of the COVID-19 vaccination protocol in KTR. Therefore, thymosin-a1, an immunomodulatory hormone, deserves further research as a potential adjuvant for the next vaccine boosters.

Predictive value of CD8+ T cell and CD4/CD8 ratio at two years of successful ART in the risk of AIDS and non-AIDS events

BACKGROUND

While increased CD8 counts and low CD4/CD8 ratio during treated HIV correlate with immunosenescence, their additional predictive values to identify individuals with HIV at higher risk of clinical events remain controversial.

METHODS

We selected treatment-naive individuals initiating ART from ACTG studies 384, 388, A5095, A5142, A5202, and A5257 who had achieved viral suppression at year 2. We examined the effect of CD8+ T cell counts and CD4/CD8 at year 2 on the probability of AIDS and serious non-AIDS events in years 3-7. We used inverse probability weighting methods to address informative censoring, combined with multivariable logistic regression models.

FINDINGS

We analyzed 5133 participants with a median age of 38 years; 959 (19%) were female, pre-ART median CD4 counts were 249 (Q1-Q3 91-372) cell/µL. Compared to participants with CD8 counts between 500/µL and 1499/µL, those with >1500/µL had a higher risk of clinical events during years 3-7 (aOR 1.75; 95%CI 1.33-2.32). CD4/CD8 ratio was not predictive of greater risk of events through year 7. Additional analyses revealed consistent CD8 count effect sizes for the risk of AIDS events and noninfectious non-AIDS events, but opposite effects for the risk of severe infections, which were more frequent among individuals with CD8 counts <500/µL (aOR 1.70; 95%CI 1.09-2.65).

INTERPRETATION

The results of this analysis with pooled data from clinical trials support the value of the CD8 count as a predictor of clinical progression. People with very high CD8 counts during suppressive ART might benefit from closer monitoring and may be a target population for novel interventions.

FUNDING

This research was supported by NIH/NIAID awards UM1 AI068634, UM1 AI068636, and UM1 AI106701 and Carlos III Health Institute and FEDER funds (BA21/00017 and BA21/00022).

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.

Effect of Coxsackievirus B4 Infection on the Thymus: Elucidating Its Role in the Pathogenesis of Type 1 Diabetes

The thymus gland is a primary lymphoid organ for T-cell development. Various viral infections can result in disturbance of thymic functions. Medullary thymic epithelial cells (mTECs) are important for the negative selection of self-reactive T-cells to ensure central tolerance. Insulin-like growth factor 2 (IGF2) is the dominant self-peptide of the insulin family expressed in mTECs and plays a crucial role in the intra-thymic programing of central tolerance to insulin-secreting islet β-cells. Coxsackievirus B4 (CVB4) can infect and persist in the thymus of humans and mice, thus hampering the T-cell maturation and differentiation process. The modulation of IGF2 expression and protein synthesis during a CVB4 infection has been observed in vitro and in vivo in mouse models. The effect of CVB4 infections on human and mouse fetal thymus has been studied in vitro. Moreover, following the inoculation of CVB4 in pregnant mice, the thymic function in the fetus and offspring was disturbed. A defect in the intra-thymic expression of self-peptides by mTECs may be triggered by CVB4. The effects of viral infections, especially CVB4 infection, on thymic cells and functions and their possible role in the pathogenesis of type 1 diabetes (T1D) are presented.

Immunological features beyond CD4/CD8 ratio values in older individuals

The CD4/CD8 T-cell ratio is emerging as a relevant marker of evolution for many pathologies and therapies. We aimed to explore immunological features beyond CD4/CD8 ratio values in older subjects (>65 years old) who were classified as having lower (<1.4), intermediate (1.4-2), or higher (>2) ratio values. The lower group showed a lower thymic output (sj/β-TREC ratio) and frequency of naïve T-cells, concomitant with increased mature T-cells. In these subjects, the CD4 T-cell subset was enriched in CD95+ but depleted of CD98+ cells. The regulatory T-cell (Treg) compartment was enriched in CTLA-4+ cells. The CD8 T-cell pool exhibited increased frequencies of CD95+ cells but decreased frequencies of integrin-β7+ cells. Interestingly, in the intermediate group, the CD4 pool showed greater differences than the CD8 pool, mostly for cellular senescence. Regarding inflammation, only hsCRP was elevated in the lower group; however, negative correlations between the CD4/CD8 ratio and β2-microglobulin and sCD163 were detected. These subjects displayed trends of more comorbidities and less independence in daily activities. Altogether, our data reveal different thymic output and immune profiles for T-cells across CD4/CD8 ratio values that can define immune capabilities, affecting health status in older individuals. Thus, the CD4/CD8 ratio may be used as an integrative marker of biological age.

Dynamics of thymus function and T cell receptor repertoire breadth in health and disease

T cell recognition of unknown antigens relies on the tremendous diversity of the T cell receptor (TCR) repertoire; generation of which can only occur in the thymus. TCR repertoire breadth is thus critical for not only coordinating the adaptive response against pathogens but also for mounting a response against malignancies. However, thymic function is exquisitely sensitive to negative stimuli, which can come in the form of acute insult, such as that caused by stress, infection, or common cancer therapies; or chronic damage such as the progressive decline in thymic function with age. Whether it be prolonged T cell deficiency after hematopoietic cell transplantation (HCT) or constriction in the breadth of the peripheral TCR repertoire with age; these insults result in poor adaptive immune responses. In this review, we will discuss the importance of thymic function for generation of the TCR repertoire and how acute and chronic thymic damage influences immune health. We will also discuss methods that are used to measure thymic function in patients and strategies that have been developed to boost thymic function.

Thymic Involution and Altered Naive CD4 T Cell Homeostasis in Neuromyelitis Optica Spectrum Disorder

Circulating T helper cells with a type 17-polarized phenotype (TH17) and expansion of aquaporin-4 (AQP4)-specific T cells are frequently observed in patients with neuromyelitis optica spectrum disorder (NMOSD). However, naive T cell populations, which give rise to T helper cells, and the primary site of T cell maturation, namely the thymus, have not been studied in these patients. Here, we report the alterations of naive CD4 T cell homeostasis and the changes in thymic characteristics in NMOSD patients. Flow cytometry was performed to investigate the naive CD4⁺ T cell subpopulations in 44 NMOSD patients and 21 healthy controls (HC). On immunological evaluation, NMOSD patients exhibited increased counts of CD31^+thymic naive CD4⁺ T cells and CD31^-cental naive CD4⁺ T cells along with significantly higher fraction and absolute counts of peripheral blood CD45RA⁺ CD62L⁺ naive CD4⁺ T cells. Chest computed tomography (CT) images of 60 NMOSD patients and 65 HCs were retrospectively reviewed to characterize the thymus in NMOSD. Thymus gland of NMOSD patients exhibited unique morphological characteristics with respect to size, shape, and density. NMOSD patients showed exacerbated age-dependent thymus involution than HC, which showed a significant association with disease duration. These findings broaden our understanding of the immunological mechanisms that drive severe disease in NMOSD.

Brain cancer induces systemic immunosuppression through release of non-steroid soluble mediators

Immunosuppression of unknown aetiology is a hallmark feature of glioblastoma and is characterized by decreased CD4 T-cell counts and downregulation of major histocompatibility complex class II expression on peripheral blood monocytes in patients. This immunosuppression is a critical barrier to the successful development of immunotherapies for glioblastoma. We recapitulated the immunosuppression observed in glioblastoma patients in the C57BL/6 mouse and investigated the aetiology of low CD4 T-cell counts. We determined that thymic involution was a hallmark feature of immunosuppression in three distinct models of brain cancer, including mice harbouring GL261 glioma, B16 melanoma, and in a spontaneous model of diffuse intrinsic pontine glioma. In addition to thymic involution, we determined that tumour growth in the brain induced significant splenic involution, reductions in peripheral T cells, reduced MHC II expression on blood leucocytes, and a modest increase in bone marrow resident CD4 T cells. Using parabiosis we report that thymic involution, declines in peripheral T-cell counts, and reduced major histocompatibility complex class II expression levels were mediated through circulating blood-derived factors. Conversely, T-cell sequestration in the bone marrow was not governed through circulating factors. Serum isolated from glioma-bearing mice potently inhibited proliferation and functions of T cells both in vitro and in vivo. Interestingly, the factor responsible for immunosuppression in serum is non-steroidal and of high molecular weight. Through further analysis of neurological disease models, we determined that the immunosuppression was not unique to cancer itself, but rather occurs in response to brain injury. Non-cancerous acute neurological insults also induced significant thymic involution and rendered serum immunosuppressive. Both thymic involution and serum-derived immunosuppression were reversible upon clearance of brain insults. These findings demonstrate that brain cancers cause multifaceted immunosuppression and pinpoint circulating factors as a target of intervention to restore immunity.

Impaired Thymic Output Can Be Related to the Low Immune Reconstitution and T Cell Repertoire Disturbances in Relapsing Visceral Leishmaniasis Associated HIV/AIDS Patients

Background: Visceral leishmaniasis/HIV-co-infected patients (VL/HIV) accounts for around 8% of VL reported cases in Brazil. Relapses of Leishmania infection after anti-leishmanial treatment constitute a great challenge in the clinical practice because of the disease severity and drug resistance. We have shown that non-relapsing-VL/HIV (NR-) evolved with increase of CD4⁺ T-cell counts and reduction of activated CD4⁺ and CD8⁺ T cells after anti-leishmanial treatment. This immune profile was not observed in relapsing-VL/HIV patients (R-), indicating a more severe immunological compromising degree. Elevated activation status may be related to a deficient immune reconstitution and could help to explain the frequent relapses in VL/HIV co-infection. Our aim was to evaluate if this gain of T cells was related to changes in the peripheral TCRVβ repertoire and inflammatory status, as well as the possible thymus involvement in the replenishment of these newly formed T lymphocytes.

Methods: VL/HIV patients, grouped into non-relapsing (NR- = 6) and relapsing (R- = 12) were evaluated from the active phase up to 12 months post-treatment (mpt). HIV-infected patients (non-VL) and healthy subjects (HS) were included. The TCRVβ repertoire was evaluated ex vivo by flow cytometry, whereas the plasmatic cytokine levels were assessed by Luminex assay. To evaluate the thymic output, DNA was extracted from PBMCs for TCR rearrangement excision circles (TREC) quantification by qPCR.

Results: VL/HIV cases presented an altered mobilization profile (expansions or retractions) of the TCRVβ families when compared to HS independent of the follow-up phase (p < 0.05). TCRVβ repertoire on CD4⁺ T-cells was more homogeneous in the NR-VL/HIV cases, but heterogeneous on CD8⁺ T-cells, since different Vβ-families were mobilized. NR-VL/HIV had the inflammatory pattern reduced after 6 mpt. Importantly, VL/HIV patients showed number of TREC copies lower than controls during all follow-up. An increase of recent thymic emigrants was observed in NR-VL/HIV individuals at 10 mpt compared to R- patients (p < 0.01), who maintained lower TREC contents than the HIV controls.

Conclusions: VL/HIV patients that maintain the thymic function, thus generating new T-cells, seem able to replenish the T lymphocyte compartment with effector cells, then enabling parasite control.

Dynamic study of oral Candida infection and immune status in HIV infected patients during HAART

OBJECTIVE

To dynamically monitor oral Candida infection, CD4⁺ T lymphocyte counts, CD8⁺ T lymphocyte counts and CD4/CD8 ratios in HIV/AIDS patients during their first year of HAART and to preliminarily explore the relationships between them.

DESIGN

Forty-six patients with HIV/AIDS receiving HAART at the Infection Department of Chongqing Red Cross Hospital were followed for one year. At baseline and 3, 6, and 12 months after HAART initiation, oral rinses were collected and cultured to identify Candida species. Further, blood samples were collected to detect CD4⁺ T lymphocyte counts, CD8⁺ T lymphocyte counts and CD4/CD8 ratios.

RESULTS

The prevalence of OC decreased after HAART initiation (P ＜ 0.05), and Candida albicans was the dominant species isolated from the oral cavity (66/93). At 3, 6 and 12 months after HAART initiation, CD4⁺ T lymphocyte counts were 327.91 ± 138.82, 329.65 ± 142.66 and 319.98 ± 97.90 cells/mm³, respectively, which were significantly higher than the level at baseline (263.39 ± 126.01 cells/mm³) (P = 0.016, P = 0.014, and P = 0.035, respectively). During the first year of HAART, CD4/CD8 ratios increased gradually, and CD8⁺ T lymphocyte counts decreased continually. OC was associated with low CD4⁺ T lymphocyte counts and a low CD4/CD8 ratio. CD4⁺ T lymphocyte counts <200 cells/mm³ and Candida load ≥300 CFU/mL were risk factors for OC (P ＜ 0.05), and oral Candida load was negatively correlated with CD4⁺ T lymphocyte counts and the CD4/CD8 ratio.

CONCLUSION

OC might be a useful marker for the evaluation of immune status in patients with HIV/AIDS.

Incomplete immune reconstitution in HIV/AIDS patients on antiretroviral therapy: Challenges of immunological non-responders

The morbidity and mortality of HIV type-1 (HIV-1)-related diseases were dramatically diminished by the grounds of the introduction of potent antiretroviral therapy, which induces persistent suppression of HIV-1 replication and gradual recovery of CD4⁺ T-cell counts. However, ∼10-40% of HIV-1-infected individuals fail to achieve normalization of CD4⁺ T-cell counts despite persistent virological suppression. These patients are referred to as "inadequate immunological responders," "immunodiscordant responders," or "immunological non-responders (INRs)" who show severe immunological dysfunction. Indeed, INRs are at an increased risk of clinical progression to AIDS and non-AIDS events and present higher rates of mortality than HIV-1-infected individuals with adequate immune reconstitution. To date, the underlying mechanism of incomplete immune reconstitution in HIV-1-infected patients has not been fully elucidated. In light of this limitation, it is of substantial practical significance to deeply understand the mechanism of immune reconstitution and design effective individualized treatment strategies. Therefore, in this review, we aim to highlight the mechanism and risk factors of incomplete immune reconstitution and strategies to intervene.

Immunological recovery failure in cART-treated HIV-positive patients is associated with reduced thymic output and RTE CD4+ T cell death by pyroptosis

Despite more than three decades of studies and advances in combination antiretroviral therapy (cART) against human immunodeficiency virus (HIV), the mechanisms that precisely determine immune reconstitution failure have not been completely elucidated yet. Thus, this study aimed to investigate the thymic function, immune activation, and cell death by pyroptosis and apoptosis in virologically suppressed HIV-positive patients receiving cART. Immunophenotyping analyses were performed in 57 cART-treated HIV-infected patients with undetectable plasma viral load, who were classified as immunological nonresponders (INR = 29) and immunologic responders (IR = 28). Sociodemographic and clinical data were also assessed from medical records. Twelve healthy volunteers were also included in this study. The INR showed lower pretreatment CD4+ T cell count that remained low even after 1 yr of treatment, lower CD4/CD8 ratio, lower percentage of recent thymic emigrant (RTE) CD4+ T cell (CD45RA+CD31+) and naïve CD4+ T cell (CD45RA+CD62L+), higher levels of effector memory CD4+ T cells (CD45RA-CD62L-), and higher pyroptosis levels of RTE CD4+ T cells (CD31+FLICA-Caspase1+) when compared with IR. Our findings indicate that reduced thymic function and RTE CD4+ T cell death by pyroptosis are the major mechanisms of immunological recovery failure in HIV-infected patients receiving cART.

Thymus Imaging Detection and Size Is Inversely Associated With Metabolic Syndrome and Frailty in People With HIV

BACKGROUND

People with HIV (PWH) may experience accentuating aging in relation to immuno-activation. Little is known regarding thymus (THY) involution in this process. We sought to investigate the relationship between THY imaging detection/size and clinically relevant aging outcomes such as metabolic syndrome (MetS), multimorbidity (MM), and frailty in PWH.

METHODS

This was a cross-sectional observational study including 665 HIV patients (81% males; median age, 53 years) attending Modena HIV Metabolic Clinic from 2014 to 2017. They underwent thoracic computed tomography scan as part of the medical assessment for cardiovascular disease, in which THY detection and size were reported using a semiquantitative score. Outcome measures were MetS, MM, and frailty.

RESULTS

THY was detected in 27.0% of subjects; 71.1% showed THY size of grade 1-2, and 28.9% exhibited grade ≥3. Covariates that inversely correlated with THY detection were age, male gender, body mass index (BMI), and HIV duration. Covariates that inversely correlated with MetS were age, HIV duration, BMI, and THY grade 1-2. Covariates that inversely correlated with MM were age, HIV duration, and CD4 nadir. Covariates that inversely correlated with frailty were age, HIV duration, CD4 nadir, BMI, and THY detection.

CONCLUSIONS

THY is inversely associated with MetS and frailty in PWH.

Managing antiretroviral therapy in the elderly HIV patient

Introduction: Owing to more effective and less toxic antiretroviral therapy (ART), people living with HIV (PLWH) live longer, a phenomenon expected to grow in the next decades. With advancing age, effectively treated PLWH experience not only a heightened risk for non-infective comorbidities and multimorbidity, but also for geriatric syndromes and frailty. In addition, older adults living with HIV (OALWH) have a higher prevalence of so-called iatrogenic triad described as polypharmacy (PP), potentially inappropriate medication use, and drug-drug interactions. Areas covered: This review will focus the management of ART in OALWH. We will discuss iatrogenic triad and best way to address PP. Special focus will be given to pharmacokinetic and pharmacodynamic aspects of ART in the elderly, evaluation of ART toxicities, and specific ART strategies commonly used in this population. Expert commentary: Research should be focused on recruiting more OALWH, frail individuals in particular, into the clinical trials and specific geriatric outcome need to be considered together with traditional viroimmunological outcomes.

Reduction in terminally differentiated T cells in virologically controlled HIV-infected aging patients on long-term antiretroviral therapy

Several studies have shown an increased accumulation of terminally differentiated T cells during HIV infection, suggestive of exhaustion/senescence, causing dysregulation of T cell homeostasis and function and rapid HIV disease progression. We have investigated whether long-term antiretroviral therapy (ART), which controls viremia and restores CD4 T cell counts, is correlated with reduction in terminally differentiated T cells, improved ratios of naïve to memory and function of T cells in 100 virologically controlled HIV-infected patients. We show that while the median frequencies of terminally differentiated CD4⁺ and CD8⁺ T cells (CD28^-, CD27^-, CD57⁺ and CD28^-CD57⁺), were higher in the virologically controlled HIV-infected patients’ cohort compared with uninfected individuals’ cohort, the frequencies of these cells significantly decreased with increasing CD4 T cell counts in HIV-infected patients. Although, the naïve CD4⁺ and CD8⁺ T cells were lower in HIV patients’ cohort than uninfected cohort, there was a significant increase in both naïve CD4⁺ and CD8⁺ T cells with increasing CD4 T cell counts in HIV-infected patients. The underlying mechanism behind this increased naïve CD4⁺ and CD8⁺ T cells in HIV-infected patients was due to an increase in recent thymic emigrants, CD4⁺CD31⁺, as compared to CD4⁺CD31^-. The CD4⁺ T cells of HIV-infected patients produced cytokines, including IL-2, IL-10 and IFN-γ comparable to uninfected individuals. In conclusion, virologically controlled HIV-infected patients on long-term ART show a significant reduction in terminally differentiated T cells, suggestive of decreased exhaustion/senescence, and improvement in the ratios of naïve to memory and function of T cells.

Thymic Function Failure Is Associated With Human Immunodeficiency Virus Disease Progression

Background

Thymic function has been mainly analyzed with surrogate peripheral markers affected by peripheral T-cell expansion, making it difficult to assess the role of thymic failure in human immunodeficiency virus (HIV) disease progression. The assay of signal-joint/DβJβ T-cell rearrangement excision circles (sj/β-TREC ratio) overcomes this limitation but has only been assayed in small cohorts. Thus, the aim of this study was to determine the role of thymic function, measured by the sj/β-TREC ratio, on CD4 T-cell maintenance in prospective HIV cohorts that include patients with a wide age range and different immunological phenotypes.

Methods

Seven hundred seventy-four patients including typical progressors, long-term nonprogressors (LTNPs), and vertically HIV-infected subjects were analyzed. Thymic function was quantified in peripheral blood samples using the sj/β-TREC ratio. Associations between thymic function and CD4 T-cell dynamics and combination antiretroviral therapy (cART) onset were analyzed using linear, logistic, and Cox proportional hazard models.

Results

Thymic function failure (sj/β-TREC ratio <10) was independently associated with HIV progression. In agreement, patients with distinctive high CD4 T-cell levels and low progression rates (vertically HIV-infected patients and LTNPs, including HIV controllers) had significantly higher thymic function levels whereas patients with thymic function failure had lower CD4 T-cell levels, lower nadir, and faster CD4 T-cell decay.

Conclusions

This work establishes the relevance of thymic function, measured by sj/β-TREC ratio, in HIV disease progression by analyzing a large number of patients in 3 cohorts with different HIV disease progression phenotypes. These results support and help to understand the mechanisms underlying the rationale of early cART onset.

A Lower Baseline CD4/CD8 T-Cell Ratio Is Independently Associated with Immunodiscordant Response to Antiretroviral Therapy in HIV-Infected Subjects

We explored if baseline CD4/CD8 T-cell ratio is associated with immunodiscordant response to antiretroviral therapy in HIV-infected subjects. Comparing immunodiscordant and immunoconcordant subjects matched by pretreatment CD4 counts, we observed a lower pretreatment CD4/CD8 T-cell ratio in immunodiscordant subjects. Furthermore, pretreatment CD4/CD8 T-cell ratio, but not CD4 counts, correlated with the main immunological alterations observed in immunodiscordants, including increased regulatory T-cell (Treg) frequency and T-cell turnover-related markers. Then, in a larger cohort, only baseline CD4/CD8 T-cell ratio was independently associated with immunodiscordance, after adjusting by the viral CXCR4-tropic HIV variants. Our results suggest that the CD4/CD8 T-cell ratio could be an accurate biomarker of the subjacent immunological damage triggering immunodiscordance.