CD31 (PECAM-1) is a marker of recent thymic emigrants among CD4+ T-cells, but not CD8+ T-cells or gammadelta T-cells, in HIV patients responding to ART

Neonatal CD4+ T cells have a characteristic transcriptome and epigenome and respond to TCR stimulation with proliferation and yet a limited immune response

The adaptive immune response is coordinated by CD4+ T cells, which determine the type and strength of the immune response and the effector cells involved. It has been reported that CD4+ T cells are less responsive in neonates, leading to low activation of the cellular response and poor antibody production by B cells. This low response is essential for the tolerant window that favors birth transition from the sterile environment in the womb to the outside world but leaves neonates vulnerable to infection, which is still an important health issue. Neonates have a high morbidity and mortality rate due to infections, and the molecular reasons are still understudied. We asked whether the neonatal naive CD4+ T cells have a genomic program that predisposes them to a low response. Therefore, we evaluated the transcriptome and epigenome of human neonatal and adult naive CD4+ T cells. Our results point to a gene expression profile forming a distinct regulatory network in neonatal cells, which favors proliferation and a low T-cell response. Such expression profile is supported by a characteristic epigenetic landscape of neonatal CD4+ T cells, which correlates with the characteristic transcriptome of the neonatal cells. These results were confirmed by experiments showing a low response to activation signals, higher proliferation, and lower expression of cytokines of neonatal CD4+ T cells as compared to adult cells. Understanding this network could lead to novel vaccine formulations and better deal with life-threatening diseases during this highly vulnerable period of our lives.

A disrupted FOXP3 transcriptional signature underpins systemic regulatory T cell insufficiency in early pregnancy failure

Regulatory T (Treg) cell defects are implicated in disorders of embryo implantation and placental development, but the origins of Treg cell dysfunction are unknown. Here, we comprehensively analyzed the phenotypes and transcriptional profile of peripheral blood Treg cells in individuals with early pregnancy failure (EPF). Compared to fertile subjects, EPF subjects had 32% fewer total Treg cells and 54% fewer CD45RA+CCR7+ naive Treg cells among CD4+ T cells, an altered Treg cell phenotype with reduced transcription factor FOXP3 and suppressive marker CTLA4 expression, and lower Treg:Th1 and Treg:Th17 ratios. RNA sequencing demonstrated an aberrant gene expression profile, with upregulation of pro-inflammatory genes including CSF2, IL4, IL17A, IL21, and IFNG in EPF Treg cells. In silico analysis revealed 25% of the Treg cell dysregulated genes are targets of FOXP3. We conclude that EPF is associated with systemic Treg cell defects arising due to disrupted FOXP3 transcriptional control and loss of lineage fidelity.

Dominant CD4+ T cell receptors remain stable throughout antiretroviral therapy-mediated immune restoration in people with HIV

In people with HIV (PWH), the post-antiretroviral therapy (ART) window is critical for immune restoration and HIV reservoir stabilization. We employ deep immune profiling and T cell receptor (TCR) sequencing and examine proliferation to assess how ART impacts T cell homeostasis. In PWH on long-term ART, lymphocyte frequencies and phenotypes are mostly stable. By contrast, broad phenotypic changes in natural killer (NK) cells, γδ T cells, B cells, and CD4+ and CD8+ T cells are observed in the post-ART window. Whereas CD8+ T cells mostly restore, memory CD4+ T subsets and cytolytic NK cells show incomplete restoration 1.4 years post ART. Surprisingly, the hierarchies and frequencies of dominant CD4 TCR clonotypes (0.1%-11% of all CD4+ T cells) remain stable post ART, suggesting that clonal homeostasis can be independent of homeostatic processes regulating CD4+ T cell absolute number, phenotypes, and function. The slow restoration of host immunity post ART also has implications for the design of ART interruption studies.

Better safe than sorry: Naive T-cell dynamics in healthy ageing

It is well-known that the functioning of the immune system gradually deteriorates with age, and we are increasingly confronted with its consequences as the life expectancy of the human population increases. Changes in the T-cell pool are among the most prominent features of the changing immune system during healthy ageing, and changes in the naive T-cell pool in particular are generally held responsible for its gradual deterioration. These changes in the naive T-cell pool are thought to be due to involution of the thymus. It is commonly believed that the gradual loss of thymic output induces compensatory mechanisms to maintain the number of naive T cells at a relatively constant level, and induces a loss of diversity in the T-cell repertoire. Here we review the studies that support or challenge this widely-held view of immune ageing and discuss the implications for vaccination strategies.

Heterogeneity of circulating CD4+CD8+ double-positive T cells characterized by scRNA-seq analysis and trajectory inference

The frequency of CD4⁺CD8⁺ double-positive (DP) T cells is highly associated with a variety of diseases. Recently, we used high-throughput single-cell RNA sequencing to show that circulating DP T cells in cynomolgus monkeys comprise nine heterogeneous populations. To better understand the characteristics of DP T cells, we analyzed 7601 cells from a rhesus monkey and detected 14,459 genes. Rhesus monkey DP T cells comprised heterogeneous populations (naïve, Treg-, Tfh-, CCR9⁺ Th-, Th17-, Th2-, Eomes⁺ Tr1-, CTL-, PLZF⁺ innate- and Eomes⁺ innate-like cells) with multiple potential functions. We also identified two new subsets using aggregated scRNA-seq datasets from the rhesus and the cynomolgus monkey: CCR9⁺ Th-like cells expressing ICAM2 and ITGA1, and PLZF⁺ innate-like cells that display innate-associated gene signatures such as ZBTB16, TYROBP, MAP3K8, and KLRB1. Trajectory inference of cell differentiation status showed that most DP T cells in the rhesus monkey were found in the mid-to-late pseudotime, whereas DP T cells from the cynomolgus monkey were found in early pseudotime. This suggests that DP T cells in rhesus monkeys may exhibit more diverse differentiation states than those in cynomolgus monkeys. Thus, scRNA-seq and trajectory inference identified a more diverse subset of the circulating DP T cells than originally thought.

DJ-1 depletion prevents immunoaging in T-cell compartments

Decline in immune function during aging increases susceptibility to different aging-related diseases. However, the underlying molecular mechanisms, especially the genetic factors contributing to imbalance of naïve/memory T-cell subpopulations, still remain largely elusive. Here, we show that loss of DJ-1 encoded by PARK7/DJ-1, causing early-onset familial Parkinson's disease (PD), unexpectedly diminished signs of immunoaging in T-cell compartments of both human and mice. Compared with two gender-matched unaffected siblings of similar ages, the index PD patient with DJ-1 deficiency showed a decline in many critical immunoaging features, including almost doubled non-senescent T cells. The observation was further consolidated by the results in 45-week-old DJ-1 knockout mice. Our data demonstrated that DJ-1 regulates several immunoaging features via hematopoietic-intrinsic and naïve-CD8-intrinsic mechanisms. Mechanistically, DJ-1 depletion reduced oxidative phosphorylation (OXPHOS) and impaired TCR sensitivity in naïve CD8 T cells at a young age, accumulatively leading to a reduced aging process in T-cell compartments in older mice. Our finding suggests an unrecognized critical role of DJ-1 in regulating immunoaging, discovering a potent target to interfere with immunoaging- and aging-associated diseases.

FRugally Optimized DNA Octomer (FRODO) qPCR Measurement of HIV and SIV in Human and Nonhuman Primate Samples

Quantitative polymerase chain reactions (qPCRs) are commonly employed to enumerate genes of interest among particular biological samples. Insertion of PCR amplicons into plasmid DNA is a mainstay for creation of known quantities of target sequences to standardize qPCRs. Typically, one amplicon is inserted into one plasmid construct, and the plasmid is then amplified, purified, serially diluted, and quantified to be used to enumerate target sequences in unknown samples. As qPCR is often used to detect multiple amplicons simultaneously, individual qPCR standards are often desired to normalize one to another. Here we report a single plasmid containing eight amplicons, which can be used to quantify several different strains of simian immunodeficiency virus and human immunodeficiency virus, cell number equivalents for humans and nonhuman primates, T cell receptor excision circles, and bacterial 16S DNA. This FRugally Optimized DNA Octomer (FRODO) plasmid was created and standardized to quantify all eight PCR amplicons. © 2021 US Government. Basic Protocol 1: Total genomic DNA extraction from primary cells Basic Protocol 2: Quantitative PCR for viral, bacterial, and cell number equivalents Support Protocol: Purification, quantification, and storage of FRODO standard plasmid DNA.

Characterization of CD31 expression in CD4+ and CD8+T cell subpopulations in chronic untreated HIV infection

BACKGROUND

The platelet endothelial cell adhesion molecule-1 (PECAM-1) or CD31 has been involved in regulation of T-cell tolerance, activation, survival and homing in mice cells. However, there is limited knowledge about the expression pattern and role of this molecule in human T cells, particularly in conditions of chronic immune activation.

OBJECTIVES

We explored CD31 expression in T cell differentiation subsets of individuals with untreated HIV infection and in non-HIV-infected controls. We also assessed phenotypic differences between CD31+ and CD31- subsets in memory and terminally differentiated (TEMRA) CD4+ and CD8 + T cells.

METHODS

Forty-one individuals with untreated HIV infection and 34 non-HIV-infected controls were included in the study. We compared the expression of CD31 in CD4+ and CD8 + T cells across stages of differentiation in the two study groups by flow cytometry. We also analyzed the expression of CD57 (a marker of senescence), Ki67 (a marker of cycling cells), PD-1 (a marker of exhaustion), and CD38/HLA-DR (a marker of immune activation) on memory and TEMRA CD31+ and CD31- T cells.

RESULTS

CD31 expression was significantly higher in CD8 + T cells than in CD4 + T cells, measured as frequency, absolute numbers and median fluorescence intensity (MFI), in both study groups (p < 0.0001 in all cases). Intermediate differentiation subsets of CD4+ and CD8 + T cells expressed higher levels of CD31 in the context of HIV infection (p < 0.001 in all cases). CD31 expression frequency decreased with cellular differentiation of CD4+ and CD8 + T cells in both groups, but this decrease was steeper in individuals without HIV infection (CD4+: p < 0.001 and CD8+: p < 0.0001). As expected, memory and TEMRA CD4+ and CD8 + T cells expressed significantly higher levels of CD57, PD-1, Ki67 and CD38/HLA-DR in HIV-infected compared to non-HIV-infected individuals (p < 0.01 in all cases). CD31 expression was associated with lower activation of memory (but not TEMRA) CD4 + T cells in non-HIV-infected persons, an effect not observed in the HIV-infected group. CD31 expression on memory CD8 + T cells of HIV-infected individuals was associated higher levels of PD-1 (p = 0.0019) and CD38/HLADR (p = 0.0345), and higher PD-1 expression on CD8 + TEMRA (p = 0.0024), an effect not observed in non-HIV-infected individuals.

CONCLUSION

In the context of HIV-associated chronic immune activation, specifically on memory CD8 + T cells, CD31 expression was associated with higher PD-1 and CD38/HLA-DR co-expression, suggesting that CD31 expression may result from an insufficient attempt to contain T cell exhaustion and activation. CD31-targeted therapies may contribute to modulate these cellular responses.

Naïve CD4+ T Cell Lymphopenia and Apoptosis in Chronic Hepatitis C Virus Infection Is Driven by the CD31+ Subset and Is Partially Normalized in Direct-Acting Antiviral Treated Persons

Background

The mechanisms underlying naïve CD4+ lymphopenia during chronic Hepatitis C Virus (HCV) infection are unclear. Whether direct-acting antiviral (DAA) therapy restores peripheral naïve CD4+ T cell numbers and function is unknown.

Methods

We enumerated frequencies and counts of peripheral naïve CD4+, CD4+CD31+ and CD4+CD31- T cells by flow cytometry in a cross sectional analysis comparing chronic HCV infected (n=34), DAA-treated(n=29), and age-range matched controls (n=25), as well as in a longitudinal cohort of HCV DAA treated persons (n=16). The cross-sectional cohort was stratified by cirrhosis state. Cell apoptosis/survival (AnnexinV+7AAD+/BCL-2 labeling) and cell cycle entry (Ki67 expression) of CD31+ and CD31- naïve CD4+ T cells was analyzed directly ex vivo and following 3 and 5 days of in vitro culture with media, interleukin (IL) -7 or CD3/CD28 activator.

Results

In the cross-sectional cohort, naïve CD4+ proportions were lower in chronic HCV infected persons compared to controls and DAA-treated persons, an effect in part attributed to cirrhosis. Age was associated with naïve cell counts and proportions in HCV infected and treated persons as well. Naïve CD4+ cell proportions negatively correlated with plasma levels of soluble CD14 following therapy in DAA-treated persons. Naïve CD4+ cells from HCV infected persons exhibited greater direct ex vivo apoptosis and cell-cycling compared to cells from DAA-treated persons and controls, and this was localized to the CD4+CD31+ subset. On the other hand, no remarkable differences in expression of BCL-2 or IL-7 Receptor (CD127) at baseline or following in vitro media or IL7 containing culture were observed. In the longitudinal cohort, naïve CD4+CD31+/CD31- ratio tended to increase 24 weeks after DAA therapy initiation.

Conclusions

Activation and apoptosis of peripheral naïve CD4+CD31+ T cells appear to contribute to naïve CD4+ lymphopenia in chronic HCV infection, and this defect is partially reversible with HCV DAA therapy. Age and cirrhosis -associated naïve CD4+ lymphopenia is present both before and after HCV DAA therapy. These findings have implications for restoration of host immune function after DAA therapy.

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.

The immune system in infants: Relevance to xenotransplantation

Despite the improvement in surgical interventions in the treatment of congenital heart disease, many life-threatening lesions (eg, hypoplastic left heart syndrome) ultimately require transplantation. However, there is a great limitation in the availability of deceased human cardiac donors of a suitable size. Hearts from genetically engineered pigs may provide an alternative source. The relatively immature immune system in infants (eg, absence of anti-carbohydrate antibodies, reduced complement activation, reduced innate immune cell activity) should minimize the risk of early antibody-mediated rejection of a pig graft. Additionally, recipient thymectomy, performed almost routinely as a preliminary to orthotopic heart transplantation in this age-group, impairs the T-cell response. Because of the increasing availability of genetically engineered pigs (eg, triple-knockout pigs that do not express any of the three known carbohydrate antigens against which humans have natural antibodies) and the ability to diagnose congenital heart disease during fetal life, cardiac xenotransplantation could be preplanned to be carried out soon after birth. Because of these several advantages, prolonged graft survival and even the induction of tolerance, for example, following donor-specific pig thymus transplantation, are more likely to be achieved in infants than in adults. In this review, we summarize the factors in the infant immune system that would be advantageous in the success of cardiac xenotransplantation in this age-group.

T Lymphocytes in Patients With Nijmegen Breakage Syndrome Demonstrate Features of Exhaustion and Senescence in Flow Cytometric Evaluation of Maturation Pathway

Patients with Nijmegen Breakage Syndrome (NBS) suffer from recurrent infections due to humoral and cellular immune deficiency. Despite low number of T lymphocytes and their maturation defect, the clinical manifestations of cell-mediated deficiency are not as severe as in case of patients with other types of combined immune deficiencies and similar T cell lymphopenia. In this study, multicolor flow cytometry was used for evaluation of peripheral T lymphocyte maturation according to the currently known differentiation pathway, in 46 patients with genetically confirmed NBS and 46 sex and age-matched controls. Evaluation of differential expression of CD27, CD31, CD45RA, CD95, and CD197 revealed existence of cell subsets so far not described in NBS patients. Although recent thymic emigrants and naïve T lymphocyte cell populations were significantly lower, the generation of antigen-primed T cells was similar or even greater in NBS patients than in healthy controls. Moreover, the senescent and exhausted T cell populations defined by expression of CD57, KLRG1, and PD1 were more numerous than in healthy people. Although this hypothesis needs further investigations, such properties might be related to an increased susceptibility to malignancy and milder clinical course than expected in view of T cell lymphopenia in patients with NBS.

Cotrimoxazole reduces systemic inflammation in HIV infection by altering the gut microbiome and immune activation

Long-term cotrimoxazole prophylaxis reduces mortality and morbidity in HIV infection, but the mechanisms underlying these clinical benefits are unclear. Here, we investigate the impact of cotrimoxazole on systemic inflammation, an independent driver of HIV mortality. In HIV-positive Ugandan and Zimbabwean children receiving antiretroviral therapy, we show that plasma inflammatory markers were lower after randomization to continue (n = 144) versus stop (n = 149) cotrimoxazole. This was not explained by clinical illness, HIV progression, or nutritional status. Because subclinical enteropathogen carriage and enteropathy can drive systemic inflammation, we explored cotrimoxazole effects on the gut microbiome and intestinal inflammatory biomarkers. Although global microbiome composition was unchanged, viridans group Streptococci and streptococcal mevalonate pathway enzymes were lower among children continuing (n = 36) versus stopping (n = 36) cotrimoxazole. These changes were associated with lower fecal myeloperoxidase. To isolate direct effects of cotrimoxazole on immune activation from antibiotic effects, we established in vitro models of systemic and intestinal inflammation. In vitro cotrimoxazole had modest but consistent inhibitory effects on proinflammatory cytokine production by blood leukocytes from HIV-positive (n = 16) and HIV-negative (n = 8) UK adults and reduced IL-8 production by gut epithelial cell lines. Collectively we demonstrate that cotrimoxazole reduces systemic and intestinal inflammation both indirectly via antibiotic effects on the microbiome and directly by blunting immune and epithelial cell activation. Synergy between these pathways may explain the clinical benefits of cotrimoxazole despite high antimicrobial resistance, providing further rationale for extending coverage among people living with HIV in sub-Saharan Africa.

Efficacy of Antithymocyte Globulin Treatment for Severe Centrilobular Injury Following Pediatric Liver Transplant: Clinical Significance of Monitoring Lymphocyte Subset

OBJECTIVES

Central perivenulitis can occur in association with T-cell-mediated rejection and can sometimes require strong immunosuppressant therapy as refractory rejection. Furthermore, patients with central perivenulitis are more likely to have subsequent episodes of T-cell-mediated rejection and develop chronic rejection than those without central perivenulitis. We retrospectively analyzed clinical data of pediatric patients with episodes of T-cell-mediated rejection according to severity of central perivenulitis and monitored HLA-DR-positive CD8-positive T cells and recent thymic emigrants during treatment for T-cell-mediated rejection.

MATERIALS AND METHODS

We identified biopsy-proven T-cell-mediated rejection in 50 liver transplant recipients (45 with living-related donors, 5 with deceased donors) between September 2014 and August 2018. Lymphocyte subsets in peripheral blood samples were analyzed.

RESULTS

Of 50 pediatric patients, 30 were boys and 20 were girls (median age at transplant of 1.1 y; interquartile range, 0.6-6.2 y). Central perivenulitis was found in 46 patients (92%), which was mild in 13, moderate in 16, and severe in 17. Antithymocyte globulin was more frequently administered to patients with severe central perivenulitis than others (P < .05). Patients with antithymocyte globulin treatment were less likely to have subsequent episodes of T-cell-mediated rejection than those without this treatment (P < .05). The absolute number of CD8-positive HLA-DR-positive T cells in patients during treatment was significantly higher than in control patients (P < .05). The absolute number of recent thymic emigrants in patients with active infection was significantly lower than in patients without infection (P < .05).

CONCLUSIONS

Our results suggest the efficacy and safety of antithymocyte globulin for treating T-cell-mediated rejection with severe central perivenulitis in pediatric liver transplant recipients and suggest that antithymocyte globulin can prevent subsequent episodes of T-cell-mediated rejection. Analyzing lymphocyte subsets during treatment for rejection may help highlight viable therapeutic strategies for achieving a good outcome.

EuroFlow Standardized Approach to Diagnostic Immunopheneotyping of Severe PID in Newborns and Young Children

The EuroFlow PID consortium developed a set of flow cytometry tests for evaluation of patients with suspicion of primary immunodeficiency (PID). In this technical report we evaluate the performance of the SCID-RTE tube that explores the presence of recent thymic emigrants (RTE) together with T-cell activation status and maturation stages and discuss its applicability in the context of the broader EuroFlow PID flow cytometry testing algorithm for diagnostic orientation of PID of the lymphoid system. We have analyzed peripheral blood cells of 26 patients diagnosed between birth and 2 years of age with a genetically defined primary immunodeficiency disorder: 15 severe combined immunodeficiency (SCID) patients had disease-causing mutations in RAG1 or RAG2 (n = 4, two of them presented with Omenn syndrome), IL2RG (n = 4, one of them with confirmed maternal engraftment), NHEJ1 (n = 1), CD3E (n = 1), ADA (n = 1), JAK3 (n = 3, two of them with maternal engraftment) and DCLRE1C (n = 1) and 11 other PID patients had diverse molecular defects [ZAP70 (n = 1), WAS (n = 2), PNP (n = 1), FOXP3 (n = 1), del22q11.2 (DiGeorge n = 4), CDC42 (n = 1) and FAS (n = 1)]. In addition, 44 healthy controls in the same age group were analyzed using the SCID-RTE tube in four EuroFlow laboratories using a standardized 8-color approach. RTE were defined as CD62L+CD45RO-HLA-DR-CD31+ and the activation status was assessed by the expression of HLA-DR+. Naïve CD8+ T-lymphocytes and naïve CD4+ T-lymphocytes were defined as CD62L+CD45RO-HLA-DR-. With the SCID-RTE tube, we identified patients with PID by low levels or absence of RTE in comparison to controls as well as low levels of naïve CD4+ and naïve CD8+ lymphocytes. These parameters yielded 100% sensitivity for SCID. All SCID patients had absence of RTE, including the patients with confirmed maternal engraftment or oligoclonally expanded T-cells characteristic for Omenn syndrome. Another dominant finding was the increased numbers of activated CD4+HLA-DR+ and CD8+HLA-DR+ lymphocytes. Therefore, the EuroFlow SCID-RTE tube together with the previously published PIDOT tube form a sensitive and complete cytometric diagnostic test suitable for patients suspected of severe PID (SCID or CID) as well as for children identified via newborn screening programs for SCID with low or absent T-cell receptor excision circles (TRECs).

HIV-1 low-level viremia affects T cell activation rather than T cell development in school-age children, adolescents, and young adults during antiretroviral therapy

OBJECTIVES

Given the improvements in antiretroviral therapy (ART) in recent years, more pediatric HIV patients receiving ART are reaching adolescence and adulthood. This study investigated the influence of poor virological response (low-level viremia (LLV) and virological failure (VF)) on the immune system of these patients.

METHODS

HIV-infected, ART-experienced pediatric patients (n=206) were enrolled in this cross-sectional study. The patients were subdivided into school-age children/early adolescents, middle adolescents, and late adolescents/young adults according to their age, and further classified into virological suppression (VS), LLV, and VF groups according to plasma viral load (pVL) measurement. Thymic output, T cells subsets, and immune activation were analyzed by flow cytometry.

RESULTS

Compared with VS patients, VF patients displayed decreased CD4⁺ T cell counts, while LLV and VS patients had comparable CD4⁺ T cell counts regardless of age. Compared with VS patients, LLV and VF patients had higher percentages of CD8⁺HLA-DR⁺ and CD8⁺CD38^high T cells, and the immune activation was positively correlated with pVL in VF and LLV patients. Thymic output levels (CD31⁺) and regulatory T cell subpopulations in LLV and VF patients were comparable to those in VS patients. LLV patients showed comparable percentages of T cell subsets (T_N, T_CM, T_EMRA, and T_EM) as VS patients in all age groups.

CONCLUSIONS

LLV causes excessive immune activation although it does not impair T cell recovery or naïve-to-memory T cell conversion in pediatric patients living with HIV. Therefore, T cell immune activation should be monitored at the management of LLV during ART.

Restoration of recent thymic emigrant CD4+ T cells is associated with sustained adherence to antiretroviral treatment in HIV-infected children

To evaluate the levels of recent thymic emigrant (RTE) CD4⁺ T cells in HIV-infected children and to explore the associations among their frequency, antiretroviral treatment (ART) adherence, and CD4⁺ T cell restoration. The group evaluated comprised 85 HIV-infected patients classified as subjects with moderate or severe immunosuppression or as those with no evidence of immunosuppression. To evaluate the association between the frequency of RTE CD4⁺ T cells and ART adherence, 23 of the 85 patients were evaluated at two different time points during a one-year follow-up period. Children with severe immunosuppression had lower frequencies of RTE CD4⁺ T cells compared with children without evidence of immunosuppression (P < .001). The frequency of RTE CD4⁺ T cells in children with a high rate of adherence was significantly higher (P < .05) than that observed among those with suboptimal adherence. The latter group presented with infectious intercurrences on admission that decreased after initiation of treatment along with improved CD4⁺ and RTE naïve CD4⁺ T cells counts. The adequate ART adherence is essential for immune reconstitution, which might be reflected by the levels of RTE CD4⁺ T cells.

Different phenotypes of CD4+CD25+Foxp3+ regulatory T cells in recipients post liver transplantation

CD4⁺ regulatory T cells (Tregs) play an important role in inducing immune tolerance in organ transplantation, which can be divided into CD45RA⁺Tregs (resting Tregs, rTregs) and CD45RO⁺Tregs (activated Tregs, aTregs). Currently, the expressions and phenotypic changes of Tregs in recipients after liver transplantation (LT) is unknown. We therefore investigated the expression and transformation of rTregs and aTregs in 83 cases of recipients with normal status post-LT. The percentages of CD45RA, CD45RO, CD31 in CD4⁺Tregs were detected by flow cytometry and the effective factors were analyzed. In LT recipients, the percentage of CD45RO⁺Tregs in CD4⁺Tregs was higher than that of CD45RA⁺Tregs. There was significant difference in the ratio of positive Foxp3 between CD45RA⁺Tregs and CD45RO⁺Tregs. Percentage of CD45RA⁺Tregs was higher in pediatric group than that in adult group, whereas percentage of CD45RO⁺Tregs was lower in the pediatric group. However, it was different only in CD45RO⁺Tregs in various survival periods post-LT. In conclusion, Tregs pool in human was heterogeneous post-LT and contained different subsets in phenotypes. Upon stimulation by donor graft, percentages of CD4⁺Tregs and CD45RO⁺Tregs were increased post-LT and most of rTregs was transformed into aTregs in peripheral blood, and rTregs and aTregs were both related to recipients' ages.

Human Intestinal Allografts Contain Functional Hematopoietic Stem and Progenitor Cells that Are Maintained by a Circulating Pool

Human intestinal transplantation often results in long-term mixed chimerism of donor and recipient blood in transplant patients. We followed the phenotypes of chimeric peripheral blood cells in 21 patients receiving intestinal allografts over 5 years. Donor lymphocyte phenotypes suggested a contribution of hematopoietic stem and progenitor cells (HSPCs) from the graft. Surprisingly, we detected donor-derived HSPCs in intestinal mucosa, Peyer's patches, mesenteric lymph nodes, and liver. Human gut HSPCs are phenotypically similar to bone marrow HSPCs and have multilineage differentiation potential in vitro and in vivo. Analysis of circulating post-transplant donor T cells suggests that they undergo selection in recipient lymphoid organs to acquire immune tolerance. Our longitudinal study of human HSPCs carried in intestinal allografts demonstrates their turnover kinetics and gradual replacement of donor-derived HSPCs from a circulating pool. Thus, we have demonstrated the existence of functioning HSPCs in human intestines with implications for promoting tolerance in transplant recipients.

Incomplete functional T-cell reconstitution in immunological non-responders at one year after initiation of antiretroviral therapy possibly predisposes them to infectious diseases

BACKGROUND

Immunological non-responders (INR) represent a unique category of HIV-infected patients on antiretroviral therapy. These patients have suppressed viremia but a suboptimal increase in CD4 cell count, which might have opposing effects on functional immune reconstitution. Hence, the extent of immune reconstitution in INR patients was investigated in order to determine their susceptibility to opportunistic infections.

METHODS

Twenty-three INR patients (CD4 increase <50 cells/mm³, viral load <40 copies/ml), 40 age-, sex-, and baseline CD4 count-matched responders (CD4 increase >100 cells/mm³, viral load <40 copies/ml), and 18 treatment failures defined as per the national guidelines were enrolled at 1year of antiretroviral therapy. The following examinations were performed: haemogram, phenotypic characterization by flow cytometry, and assessment of functional immune status by ELISPOT and intracellular cytokine assays.

RESULTS

A higher percentage of INR patients had clinically symptomatic infections than the responders. CD8⁺ activation and innate immune parameters, including the absolute neutrophil count and natural killer (NK) cell frequency and functionality, were restored in the INR patients. They had significantly higher non-HIV antigen-specific T-cell responses and activated CD4⁺ cells, but significantly compromised T-cell functionality, as assessed after anti-CD3 stimulation, and lower CD31⁺ and CD62L⁺CD4⁺ cells.

CONCLUSIONS

INR patients showed lower thymic output, incomplete functional T-cell reconstitution, higher responses to HIV co-pathogens, and higher symptomatic events, indicating the need for close monitoring and intervention strategies to overcome their continuing immunocompromised status.

Human T Cell Development, Localization, and Function throughout Life

Throughout life, T cells coordinate multiple aspects of adaptive immunity, including responses to pathogens, allergens, and tumors. In mouse models, the role of T cells is studied in the context of a specific type of pathogen, antigen, or disease condition over a limited time frame, whereas in humans, T cells control multiple insults simultaneously throughout the body and maintain immune homeostasis over decades. In this review, we discuss how human T cells develop and provide essential immune protection at different life stages and highlight tissue localization and subset delineation as key determinants of the T cell functional role in immune responses. We also discuss how anatomic compartments undergo distinct age-associated changes in T cell subset composition and function over a lifetime. It is important to consider age and tissue influences on human T cells when developing targeted strategies to modulate T cell-mediated immunity in vaccines and immunotherapies.

Association of neutrophil-lymphocyte ratio and T lymphocytes with the pathogenesis and progression of HBV-associated primary liver cancer

Background

The neutrophil–lymphocyte ratio (NLR) is a new prognostic predictor for patients with liver cancer. The association of NLR and T lymphocytes with the pathogenesis and progression of liver cancer is poorly understood.

Methods

Seventy-three patients with hepatitis B virus (HBV)-associated primary liver cancer (HBV-PLC), 50 patients with HBV-associated liver cirrhosis (HBV-LC) and 37 patients with chronic HBV infection (CHB) were prospectively enrolled from July 1, 2013 to February 28, 2014 in Beijing Ditan Hospital, Capital Medical University (Beijing, China). The NLR, proportions and concentrations of neutrophils and lymphocytes, concentration of subpopulations of lymphocytes, and the expression of CD31 (index for recent thymic output) and HLA-DR (index for activation of T lymphocytes) of T cells in the peripheral blood samples of the patients were assessed and statistically compared between different groups.

Results

The NLR was significantly increased from patients with CHB, those with HBV-LC to those with HBV-PLC (P<0.05), along with significant increase of neutrophils and decrease of lymphocytes in the same way (P<0.05). The concentrations of T lymphocytes, natural killer cells, B cells, CD4⁺ T cells and CD8⁺ T cells were decreased from patients with CHB, those with HBV-LC to those with HBV-PLC, and were significantly reduced in patients with HBV-PLC compared with those in patients with CHB (P<0.05). The CD31 and HLA-DR expression of naive CD4⁺ and CD8⁺ T cells was significantly decreased and increased, respectively in patients with HBV-PLC compared with that in patients with CHB.

Conclusions

Elevated NLR, resulted from the increase of neutrophils and decrease of lymphocytes, is positively associated with the pathogenesis and progression of HBV-PLC. The reduced thymic output and hyperactivation of T lymphocytes may contribute to the decrease of T lymphocytes, which could be also related to the pathogenesis of HBV-PLC.

CD31 Expression on CD4+ Cells: A Simple Method for Quantitation of Recent Thymus Emigrant CD4 Cells

Measurements of CD4⁺CD31⁺ cells gave results consistent with those expected for recent thymus emigrant (RTE) CD4⁺ cells. The method was markedly simpler than established procedures for measurement of CD4⁺ RTE cells and is usable in locations with limited facilities and budgets.

Immune activation is associated with decreased thymic function in asymptomatic, untreated HIV-infected individuals

Background

Reduced thymic function causes poor immunological reconstitution in human immunodeficiency virus (HIV)-positive patients on combined antiretroviral therapy (cART). The association between immune activation and thymic function in asymptomatic HIV-positive treatment-naive individuals has thus far not been investigated.

Aims and objectives

To optimise a five-colour flow cytometric assay for measurement of thymic function by measuring recent thymic emigrants (RTEs) in treatment-naive HIV-infected patients and healthy controls and correlate results with levels of immune activation, CD4 counts and viral load.

Methods

Blood obtained from 53 consenting HIV-positive individuals and 32 controls recruited from HIV prevention and testing clinic in Cape Town, South Africa. RTEs were measured (CD3⁺/CD4⁺/CD45RA⁺/CD31⁺/CD62L⁺) and levels were correlated with CD4 counts of HIV-infected individuals, log viral load and levels of immune activation (CD8⁺/CD38⁺ T-cells).

Results

HIV-infected individuals had reduced frequencies of RTEs when compared to controls (p = 0.0035). Levels of immune activation were inversely correlated with thymic function (p = 0.0403), and the thymic function in HIV-infected individuals showed no significant correlation with CD4 counts (p = 0.31559) and viral load (p = 0.20628).

Conclusions

There was impaired thymic function in HIV-infected individuals, which was associated with increased levels of immune activation. The thymic dysfunction was not associated with CD4 counts and viral load. Immune activation may result in inflammatory damage to the thymus and subsequent thymic dysfunction, and CD4 counts and viral load may not necessarily reflect thymic dysfunction in HIV.

Recent Thymus Emigrant CD4+ T Cells Predict HIV Disease Progression in Patients With Perinatally Acquired HIV

BACKGROUND

Robust immune restoration in human immunodeficiency virus (HIV)-positive patients is dependent on thymic function. However, few studies have investigated thymic function and its correlation with disease progression over time in HIV-positive patients.

METHODS

In this longitudinal prospective study, we followed 69 HIV-positive patients who were perinatally infected. Peripheral blood mononuclear cells were stained with monoclonal anti-CD4 and anti-CD31 and recent thymic emigrants (CD4+recently emigrated from the thymus (RTE), CD4+CD31+) quantified by flow cytometry. Statistical analysis used Wilcoxon rank sum test, Kruskal-Wallis, Spearman correlation, and Kaplan-Meier estimates; Cox regression models were performed for the longitudinal analysis.

RESULTS

Median age of HIV positive patients enrolled was 13 years (interquartile range [IQR], 8.6). CD4+RTE% decreased with age and was higher in females. Median CD4+RTE% was 53.5%, IQR, 22.9. CD4+RTE% was closely related to CD4+% and absolute counts but independent of viral load and CD8+CD38+%. Antiretroviral compliance as well as higher nadir CD4+% were associated with higher CD4+RTE%. Low CD4+RTE% predicted poor progression of VL and CD4+% over time.

CONCLUSIONS

CD4+RTE% predicts disease progression and may reflect history of disease in HIV-positive patients and adolescents. They are easy to measure in the clinical setting and may be helpful markers in guiding treatment decisions.

Thymic Function Is Most Severely Impaired in Chronic HIV-1 Infection, but Individuals With Faster Disease Progression During Early HIV-1 Infection Expressed Lower Levels of RTEs

In HIV disease course, the decline of peripheral CD4 T-cell count correlates with rapid disease progression. The supply of peripheral naive T cells by the thymus requires precursor T-cell proliferation within the thymus. In the setting of HIV-1 infection, when both naive and memory T cells are progressively depleted, the contribution of thymic dysfunction in CD4 depletion needs to be studied. Previous research has shown that thymic function may also be impaired in HIV-1 infection. However, it is inconclusive regarding whether this impairment occurred at the early time or during the chronic phase. In addition, the relationship between thymic dysfunction and disease progression remains unknown. In this study, we examined the thymic function in 65 HIV-infected individuals. Among them, 17 were in acute phase, 15 were in early chronic phase, 15 were in chronic phase with no ART (antiretroviral therapy), and 18 were on ART. We also included 11 uninfected individuals as controls. We measured the peripheral blood levels of T-cell receptor rearrangement excision circles and PTK7 and CD31 expressions for the frequency of circulating recent thymic emigrants. We observed that the 2 indicators of thymic function, sj/β-TREC and PTK7, seemed to be lower in the chronic infection group than those in the acute and early chronic groups. Both indicators returned to the normal level after ART. However, after 1-year follow-up of patients with early HIV-1 infection, rapid progressors (n = 4) had lower PTK7 and CD31 expressions than chronic progressors (n = 6).

Thymic output: Assessment of CD4+ recent thymic emigrants and T-Cell receptor excision circles in infants

BACKGROUND

CD4⁺ recent thymic emigrants (CD4⁺ RTEs) constitute a subset of T cells recently generated in the thymus and exported into peripheral blood. CD4⁺ RTEs have increased copy numbers of T-cell receptor excision circles (TREC). They are characterized by the expression of CD31 on naïve CD4 T-cells. We aimed to validate a flow-cytometry assay to enumerate CD4⁺ RTEs and assess its performance in relation to TREC measurement.

METHODS

CD4⁺ RTEs cell count in peripheral blood was measured to determine sample stability, precision, linearity, and to establish reference ranges. TRECs were measured using qPCR assay performed with DNA isolated from peripheral blood. CD4⁺ RTEs, TRECs, and flow cytometry results for major T-cell markers were assessed in 50 infants less than 2 years of age.

RESULTS

Inter-and intra-assay precisions (% CV) were 1.5-12.2 and 1.5-7.0, respectively. Linearity studies showed that the results are linear over a range of 0.7 to 403.0 CD4⁺ RTEs/μL of blood. There was 84% agreement (42 of 50) between CD4⁺ RTEs and TRECs qualitative results for the infant samples. CD4⁺ RTEs reference ranges in 17 healthy children was in agreement with published data, while that of the healthy adults were 51-609 cells/μL of blood.

CONCLUSION

The validation results provide acceptable measures of the CD4⁺ RTEs test performance within CAP/CLIA frameworks. CD4⁺ RTEs and TRECs assays show high agreement in the infant population. The CD4⁺ RTEs test can be used as a confirmation for the TREC results along with or as an alternative to T-cell phenotyping in infants with repeatedly low TRECs concentrations. © 2015 International Clinical Cytometry Society.

Lymphocyte depletion and repopulation after chemotherapy for primary breast cancer

Background

Approximately 30 % of breast cancer patients receive chemotherapy, yet little is known about influences of current regimens on circulating lymphocyte levels and phenotypes. Similarly, clinico-pathological factors that modify these influences, and implications for future immune health remain mainly unexplored.

Methods

We used flow-cytometry to assess circulating lymphocyte levels and phenotypes in 88 primary breast cancer patients before chemotherapy and at time-points from 2 weeks to 9 months after chemotherapy completion. We examined circulating titres of antibodies against pneumococcal and tetanus antigens using ELISAs.

Results

Levels of B, T and NK cells were significantly reduced 2 weeks after chemotherapy (p < 0.001). B cells demonstrated particularly dramatic depletion, falling to 5.4 % of pre-chemotherapy levels. Levels of all cells recovered to some extent, although B and CD4⁺ T cells remained significantly depleted even 9 months post-chemotherapy (p < 0.001). Phenotypes of repopulating B and CD4⁺ T cells were significantly different from, and showed no sign of returning to pre-chemotherapy profiles. Repopulating B cells were highly depleted in memory cells, with proportions of memory cells falling from 38 % to 10 % (p < 0.001). Conversely, repopulating CD4⁺ T cells were enriched in memory cells, which increased from 63 % to 75 % (p < 0.001). Differences in chemotherapy regimen and patient smoking were associated with significant differences in depletion extent or repopulation dynamics. Titres of anti-pneumococcal and anti-tetanus antibodies were both significantly reduced post-chemotherapy and did not recover during the study (p < 0.001).

Conclusion

Breast cancer chemotherapy is associated with long-term changes in immune parameters that should be considered during clinical management.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0669-x) contains supplementary material, which is available to authorized users.

Reduced T-Cell Thymic Export Reflected by sj-TREC in Patients with Coronary Artery Disease

AIM

Immunologic dysfunction was recently found to be one of the most important mechanisms underlying the initiation and development of atherosclerosis. Thymus involution can contribute to immune disturbance and disequilibrium of T-cell subsets. This study aimed to explore whether recent thymic emigration (RTE) is impaired in patients with coronary artery disease (CAD).

METHODS

Content of signal-joint T cell receptor excision circles (sj-TREC) in T lymphocytes, a molecular marker of RTE, was assessed among CAD patients and age-matched controls. Monochrome multiplex quantitative PCR method was used to assess the samples' telomere length in order to exclude the potential influence of T cell proliferation on the dilution of sj-TREC. Patients were grouped according to Gensini score (GS) (low, GS ＜18; intermediate, GS 18-41; high, GS ＞41). Ordinary logistic regression models were used to determine potential risk factors for CAD and GS tertiles.

RESULTS

Average copy numbers of sj-TREC per 10(6) T lymphocytes among patients with unstable angina, stable angina, and controls were 726±429, 1213±465, and 1795±838, respectively (P＜0.001). However, there was no significant difference in telomere length among groups. Moreover, the content of sj-TREC in the high GS group was most significantly reduced than the low GS group (P＜0.001). Multivariate logistic regression analysis revealed that lower sj-TREC was independently associated with the progression of CAD (OR=0.44, P＜0.001) and higher GS (OR=0.4, P＜0.001).

CONCLUSION

Impaired RTE could be partly responsible for CAD development. Mechanisms may be involved in the disturbance of T lymphocyte compartment and interruption of maintained immune tolerance resulting from thymus involution.

Human T-Cell Development and Thymic Egress: An Infectious Disease Perspective

Emigration of mature naïve CD4 SP T cells from the human thymus to the periphery is not fully understood, although elucidation of the mechanisms that govern egress of T cells is crucial to understanding both basic immunology and the immune response in diseases such as HIV infection. Recent work has brought to light the requirement for sphingosine-1-phosphate (S1P) and its receptors in a variety of fields including mature naïve T-cell egress from the thymus of mice. We are examining the expression and function of this novel requisite T-cell egress receptor within the human thymus, characterizing changes observed in the expression and function of this receptor in infectious diseases. To perform this work, we use a variety of humanized murine models reviewed in this article. Future work in the field of T-cell egress, especially as it pertains to S1P receptors, should advance the fields of basic T-cell immunology and immunopathology and open new avenues for exploration into novel therapeutics.

Preventing or reversing immunosenescence: can exercise be an immunotherapy?

There is now a strong body of evidence demonstrating that aging is accompanied by severe alterations in the immune system, a process known as immunosenescence. Among these changes are alterations in T-cell subpopulation size, cytokine secretion pattern, cell replicative capacity and antibody production, all of which culminate in a proinflammatory state called 'inflammaging' and a diminished capacity to respond to new antigens. These alterations are closely related to the increased mortality and morbidity rates observed in this population. However, the role of exercise on the prevention or treatment of immunosenescence is virtually unknown. Data gathered from the literature regarding the effects of physical activity on immune system aging are still limited and conflicting, with existing reports either advocating benefits or asserting a lack of evidence. Exercise as part of a healthy lifestyle has already been shown to provide long-term benefits with regard to cardiovascular, cognitive, psychosocial and other aspects of the elderly. If positive effects are also observed for immunosenescence, exercise could be a highly cost-effective measure to improve human quality of life compared with other strategies currently being pursued.

Kinetics of homeostatic proliferation and thymopoiesis after rATG induction therapy in kidney transplant patients

BACKGROUND

Lymphocyte-depleting therapy is associated with long-lasting effects on repopulated T cells and subsequent increased rates of infections and malignancies. The mechanisms of T-cell repopulation and their posttransplantation kinetics are not fully understood.

METHODS

We studied thymopoiesis by CD31(+) naïve T cells (recent thymic emigrants) and homeostatic proliferation by Ki-67(+) T cells in rabbit antithymocyte globulin (rATG)-treated patients the first 6 months after transplantation. Patients receiving basiliximab or no induction therapy served as controls.

RESULTS

At 6 months after transplantation, T-cell numbers were lower than before transplantation in rATG-treated patients, whereas T-cell numbers remained stable in both control groups. In this time period, thymopoiesis was similar between the three treatment groups; CD8(+) T cells showed the highest percentage of recent thymic emigrants. At month 1, percentages of Ki-67(+) naïve and memory CD4(+) and CD8(+) T cells were the highest in rATG-treated patients, but these percentages declined in the months thereafter. When CD31 was used to distinguish between cytokine- and antigen-driven proliferation in naïve T cells, we found evidence for cytokine-dependent proliferation. Cytokine-dependent proliferation was also shown by in vivo increased percentages of phosphorylated STAT5 and high expression levels of the interleukin-7 receptor-α and interleukin-15 receptor-α by T cells.

CONCLUSION

These findings demonstrate that, in the first month after rATG therapy, cytokine-induced homeostatic proliferation is involved in T-cell repopulation of both naïve and memory T cells. At later time points, the contribution of homeostatic proliferation diminished, which explains the observed incomplete T-cell recovery.

Methods of detection of immune reconstitution and T regulatory cells by flow cytometry

Allogeneic hematopoietic stem cell therapy (HSCT) remains one of the few curative treatments for high-risk hematological malignancies (high-risk leukemia, myelodysplastic syndromes, advanced myeloproliferative disorders, high-risk lymphomas, and multiple myeloma) and is currently applied in more than 15,000 patients per year in Europe. Following HSCT, patients experience a period of reconstitution of the immune system, which seems to be highly dependent on conditioning, immunosuppression regimes, and the level of adverse events the patients experience. During this reconstitution period, the patient is immune compromised and susceptible to opportunistic infections and disease relapse. Consequently, a large number of clinical studies have been devoted to monitoring the recovery of the immune system following HSCT in the hopes of determining which cellular subsets are indicative of a favorable outcome. In this chapter we review the methods that have been employed to monitor the immune reconstitution and what clinical observations have been made. Of particular interest is the regulatory T cell (Treg) subset, which has been associated with tolerance and has been the subject of recent clinical trials as a possible cellular therapy for rejection reactions. Finally we will detail a proposed methodology for the flow cytometric assessment of cellular reconstitution post-HSCT.

T-cell subset distribution in HIV-1-infected patients after 12 years of treatment-induced viremic suppression

OBJECTIVE

Residual immune activation and skewed T cell maturation may contribute to excess comorbidity and mortality in successfully treated HIV-infected patients, and long-term effects of combination antiretroviral therapy (cART) on immune reconstitution remain a debated issue. Quantitative T cell reconstitution and activation and its association with residual viremia in patients with 12 years of viremic suppression were investigated.

DESIGN

Blood samples collected cross-sectionally from 71 HIV-infected patients with cART-induced viremic suppression through 12 years were compared with samples from 16 healthy controls.

METHODS

Several different subsets of naive, memory, and activated T cells were analyzed in fresh whole blood by 6-color flowcytometry, and ultrasensitive quantification of HIV RNA was performed.

RESULTS

HIV-infected patients had lower absolute and relative CD4 T cell counts and higher absolute and relative CD8 T cell counts than controls. HIV-infected patients had lower concentrations of naive CD4 cells than controls, but proportions were similar. HIV-infected patients had higher concentrations of CD8 T cells than controls in all the examined subsets but only a higher proportion of CD8 cells in the intermediately differentiated and activated subsets. Residual viremia did not correlate to proportions of naive CD4, CD4 recent thymic emigrants, or activated CD8 T cells.

CONCLUSIONS

This study demonstrated some degree of T cell imbalance even after 12 years of successful cART. Large longitudinal studies are needed to establish whether these discrete changes have clinical relevance.

Immunologic consequences of chemotherapy for acute myeloid leukemia

There are few data characterizing the immunologic consequences of chemotherapy for acute myeloid leukemia (AML) and almost nothing is known about the effects of chemotherapy in a pediatric AML cohort. We identified T-cell subsets, B-cell subsets, and used Enzyme-linked immunosorbent spot analyses to define the function of T cells and B cells in 7 pediatric patients with AML on chemotherapy. The data show that the effects of chemotherapy disproportionately target the B cell and depletion of B cells is associated with impaired responses to the inactivated influenza vaccine. Diminished T-cell numbers were also observed although the magnitude of the effect was less than what was seen for B cells. Furthermore, measures of T-cell function were largely intact. We conclude that humoral immunity is significantly affected by chemotherapy for AML.

Proportions of CD4+ memory T cells are altered in individuals chronically infected with Schistosoma haematobium

Characterisation of protective helminth acquired immunity in humans or experimental models has focused on effector responses with little work conducted on memory responses. Here we show for the first time, that human helminth infection is associated with altered proportions of the CD4+ memory T cells, with an associated alteration of T_H1 responses. The reduced CD4+ memory T cell proportions are associated with a significantly lower ratio of schistosome-specific IgE/IgG4 (marker for resistance to infection/re-infection) in uninfected older people. Helminth infection does not affect the CD8+ memory T cell pool. Furthermore, we show for the first time in a helminth infection that the CD4+ memory T cell proportions decline following curative anti-helminthic treatment despite increased CD4+ memory cell replication. Reduced accumulation of the CD4+ memory T cells in schistosome-infected people has implications for the development of natural or vaccine induced schistosome-specific protective immunity as well as for unrelated pathogens.

Reduced thymic output is a major mechanism of immune reconstitution failure in HIV-infected patients after long-term antiretroviral therapy

BACKGROUND

Approximately 20% of human immunodeficiency virus type 1 (HIV-1)--infected adults do not normalize their CD4(+) T lymphocytes after long-term effective highly active antiretroviral therapy (HAART). The mechanistic basis for this failure is unclear.

METHODS

Seventy-four patients were followed up regularly for 3-7 years. Patients with undetectable plasma viral load (<50 copies/mL) for over 12 months were further classified into 2 groups: (1) immunological nonresponders, whose CD4(+) T-cell count was < 200/μL or <20% compared with baseline; and (2) immunological responders, whose CD4(+) T-cell count was > 300/μL or >30% compared with baseline.

RESULTS

Compared with 17 immunological responders, 13 immunological nonresponders had a lower magnitude of naive CD4(+) T-cell increase, a lower percentage of recent thymic immigrants (CD31(+)%), and a higher percentage of activated CD8(+) T cells. Furthermore, unlike CD4(+) T cells, which increased along with the decrease of viral load, the percentage of recent thymic immigrants (CD31(+)%) had little change in the majority of patients. These data were fit into a mathematical model, , from which we deduced that the initial rate of CD4(+) T-cell restoration is associated significantly with the percentage of recent thymic immigrants (CD31(+)%).

CONCLUSIONS

Our data indicate that the failure to restore CD4(+) T-cell count following HAART was associated primarily with a defect in recent thymic immigrants, which suggests the existence of thymus exhaustion.

Helios expression is a marker of T cell activation and proliferation

Foxp3+ T-regulatory cells (Tregs) normally serve to attenuate immune responses and are key to maintenance of immune homeostasis. Over the past decade, Treg cells have become a major focus of research for many groups, and various functional subsets have been characterized. Recently, the Ikaros family member, Helios, was reported as a marker to discriminate naturally occurring, thymic-derived Tregs from those peripherally induced from naïve CD4+ T cells. We investigated Helios expression in murine and human T cells under resting or activating conditions, using well-characterized molecules of naïve/effector/memory phenotypes, as well as a set of Treg-associated markers. We found that Helios-negative T cells are enriched for naïve T cell phenotypes and vice versa. Moreover, Helios can be induced during T cell activation and proliferation, but regresses in the same cells under resting conditions. We demonstrated comparable findings using human and murine CD4+Foxp3+ Tregs, as well as in CD4+ and CD8+ T cells. Since Helios expression is associated with T cell activation and cellular division, regardless of the cell subset involved, it does not appear suitable as a marker to distinguish natural and induced Treg cells.

A prospective study of influenza vaccination and a comparison of immunologic parameters in children and adults with chromosome 22q11.2 deletion syndrome (digeorge syndrome/velocardiofacial syndrome)

Prior to the advent of cardiac bypass, most children with congenital cardiac anomalies and chromosome 22q11.2 deletion syndrome died. With improved technology, there is now a wave of young adults with chromosome 22q11.2 deletion syndrome requiring clinical care. Fifteen young children and 20 adults with chromosome 22q11.2 deletion had flow cytometry, functional T cell analyses, and functional B cell analyses to characterize their immune system. Subjects were vaccinated with the annual inactivated influenza vaccine, and responses were evaluated by hemagglutination inhibition titer assessment. The pattern of T cell subset abnormalities was markedly different between pediatric and adult patients. In spite of the cellular deficits observed in adults, titers produced after influenza vaccine administration were largely intact. We conclude that disruption to T cell production appears to have secondary consequences for T cell differentiation and B cell function although the clinical impact remains to be determined.

IL-7 dysregulation and loss of CD8+ T cell homeostasis in the monogenic human disease autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autoimmune disease that is caused by mutations in the AIRE gene. Murine studies have linked AIRE to thymocyte selection and peripheral deletional tolerance, but the pathogenesis of the human disease remains unclear. In this study, we show that APECED patients have elevated IL-7 levels and a drastically decreased expression of IL-7R on CD8(+) T cells. This is associated with increased proliferation and a decreased expression of the negative TCR regulator CD5 in the CD45RO(-) subset. The CD45RO(-) cells also display oligoclonal expansions, decreased expression of the lymph node homing factors CCR7 and CD62L, and increased expression of perforin, consistent with the accumulation of highly differentiated effector cells. The CD45RO(-)CCR7(+)CD8(+) population of cells with markers characteristic of naive phenotype is also skewed, as shown by decreased expression of CD5 and increased expression of perforin. The putative CD31(+) recent thymic emigrant population is likewise affected. These data are consistent with IL-7 dysregulation inducing a decreased threshold of TCR signaling and self-antigen-driven proliferation, probably in synergy with the failed thymic selection. The resultant loss of CD8(+) T cell homeostasis is likely to play a significant role in the pathogenesis of APECED. Our findings may also hold lessons for other diseases in which the IL-7-IL-7R pathway has emerged as a risk factor.

Thymic tissue is not evident on high-resolution computed tomography and [¹⁸F]fluoro-deoxy-glucose positron emission tomography scans of aviraemic HIV patients with poor recovery of CD4⁺ T cells

Some previously immunodeficient HIV patients responding to antiretroviral therapy display poor recovery of CD4⁺ T cells. Evaluation of the contribution of thymic function requires sensitive detection and quantitation of metabolically active thymic tissue. We describe patients with low but detectable thymopoiesis assessed as circulating CD4⁺ naive T cells expressing CD31. High-resolution computed tomography and PET scans found no residual thymic tissue even though metabolic activity was demonstrable by PET in lymph nodes.