Viral phenotype affects the thymic production of new T cells in HIV-1-infected children

Viral Tropism in Human Immunodeficiency Virus Type 1-Infected Children and Adolescents in Thailand

BACKGROUND

Maraviroc, a C-C chemokine receptor 5 (CCR5) antagonist, has been used as an alternative antiretroviral drug in treatment-experienced adults and children infected by CCR5-tropic human immunodeficiency virus type 1 (HIV-1) isolates. Prior to widespread use of this drug, rates of HIV-1 coreceptor tropism and factors associated with coreceptor tropism had to be determined.

METHODS

HIV-1-infected individuals aged <20 years with HIV-1 viral loads >1000 RNA copies/mL who were treatment-experienced or treatment-naive were enrolled. HIV-1 coreceptor tropism was determined using a genotypic test in which V3 sequences were analyzed with GENO2PHENO version 2.5 and a false discovery rate of 5%.

RESULTS

Fifty-two HIV-1-infected patients were recruited. The median age of participants was 14.9 years (interquartile range [IQR], 8.9-16.8 years). The median CD4 cell count was 396.0 cells/µL (IQR, 72.0-630.3 cells/µL). The median HIV-1 viral load was 43 339 RNA copies/mL (IQR, 8874-197 055 copies/mL). Thirty-nine patients (75%) were treatment-experienced. The most prevalent HIV-1 subtype in this population was CRF01_AE (36 patients, 69.2%). Based on analyses of V3 loop sequences, 5 of 13 treatment-naive patients (38.5%) and 11 of 39 treatment-experienced patients (28.2%) were infected by R5 viruses, while 7 of 13 treatment-naive patients (53.8%) and 19 of 39 treatment-experienced patients (48.7%) were infected by X4 viruses. The only factor associated with the presence of X4 viruses was HIV-1 subtype CRF01_AE.

CONCLUSIONS

X4-tropic viruses are associated with the CRF01_AE subtype. Hence, testing of HIV tropism should be performed before treatment with CCR5 inhibitors in children in areas where CRF01_AE predominates.

A Novel HIV-1 Nef Mutation in a Primary Pediatric Isolate Impairs MHC-Class I Downregulation and Cytopathicity

HIV-1-induced cytopathicity of thymocytes is a major cause of reduced peripheral T cells and rapid disease progression observed in HIV-1-infected infants. Understanding the virulence factors responsible for thymocyte depletion has paramount importance in addressing the pathogenesis of disease progression in children. In this study, thymocyte depletion was analyzed following infection with two primary CXCR4-tropic HIV-1 pediatric isolates (PI), PI-2 and PI-2.1, which were serially derived from an in utero-infected infant. Although highly similar to each other, PI-2 showed markedly decreased thymocyte depletion in vitro compared with PI-2.1. Further analysis showed a novel deletion in the Nef protein (NefΔK7S) of PI-2, which was absent in PI-2.1. This deletion inhibited Nef-mediated major histocompatibility complex class I (MHC-I) downregulation in infected thymocytes in vitro and in vivo; in contrast, the mutated Nef continued to downregulate CD4 surface expression in vitro. These results suggest that HIV-1 Nef contributes to thymic damage in infants through selective functions.

Young adults HIV-1 infected by vertical transmission in southern Brazil - Clinical, demographic, and virological features

Combination antiretroviral therapy promotes longer life expectancy, making it possible for perinatally HIV-infected patients to achieve adulthood. Past therapy was not always optimized, suggesting that virological and host features may also play a role in survival. The aim of this study is to describe characteristics of HIV disease progression associated with virological features in adolescents perinatally that were HIV infected. A case series was conducted including 81 patients that were in follow-up at Hospital de Clínicas/Universidade Federal do Paraná, Curitiba, Brazil. Venous blood was collected to conduct tropism and viral subtype assays. The median age was 19 years old (interquartile range 18-21), and a majority of patients were female (54.3%). Viral subtype was obtained for 66 (82%) patients, and subtypes B and C were found in 34% and 59%, respectively. Tropism assay was conducted in 55 (67%) patients: 71% were R5 and 29% X4. Distribution of viral tropism and subtype shows a significant association of subtype C with R5 tropism. Subtype C is more prevalent in southern Brazil and also in the population infected with HIV by vertical transmission. Both R5 tropism and subtype C are associated with slower progression to AIDS. The survival of these patients may be related to virological features present in a benign pattern of disease progression.

Association of X4 tropism with disease progression in antiretroviral-treated children and adolescents living with HIV/AIDS in São Paulo, Brazil

Management of children with HIV/AIDS is specially challenging. Age-related issues do not allow for direct transposition of adult observations to this population. CXCR4 tropism has been associated with disease progression in adults. The geno2pheno web-base is a friendly tool to predict viral tropism on envelope V3 sequences, generating a false positive rate for a CXCR4 prediction. We evaluated the association of HIV-1 tropism prediction with clinical and laboratory outcome of 73 children with HIV/AIDS in São Paulo, Brazil. The CXCR4 tropism was strongly associated with a lower (nadir) CD4 documented during follow-up (p < 0.0001) and with disease severity (clinical event and/or CD4 below 200 cells/mm³) at the last observation, using commonly applied clinical cutoffs, such as ^10%FPR_clonal (p = 0.001). When variables obtained during follow-up are included, both treatment adherence and viral tropism show a significant association with disease severity. As for viremia suppression, 30% (22/73) were undetectable at the last observation, with only adherence strongly associated with suppression after adjustment. The study brings further support to the notion that antiretroviral treatment adherence is pivotal to management of HIV disease, but suggests that tropism prediction may provide an additional prognostic marker to monitor HIV disease in children.

Detectable viral load aggravates immunosenescence features of CD8 T-cell subsets in vertically HIV-infected children

BACKGROUND

CD8 T cells are crucial in the immune responses against HIV infection, but HIV-infected adults suffer a naive CD8 T-cell depletion and accelerated senescence caused by chronic antigen stimulation. Although HIV-infected children preserve a better immune reconstitution capacity their CD8 responses are defective. We wanted to know, whether HIV vertical transmission produces a premature aging of the CD8 population due to antigen exposition to HIV from birth and persistent chronic activation.

METHODS

We conducted a multicentre cross-sectional study that compared vertically HIV-infected children with detectable (viremic) or undetectable (aviremic) viral load and age-matched healthy children. Using multiparameter flow cytometry, we studied within the CD8 population the frequencies of naive, memory, effector memory (effector memory), and TemRA subsets and measured markers of senescence, activation, and proliferation in these cells.

RESULTS

We found that naive subset in viremic children was markedly decreased and had a replicative senescence phenotype. Furthermore, viremic children showed increased frequencies of memory, TEM and TemRA CD8 T cells, with a more activated and replicative senescence phenotype. We found that HIV-infected children with undetectable viral load have an increased senescence in memory and effector CD8 T cells, but the frequencies and phenotype of the CD8 subsets analyzed are comparable to healthy children.

CONCLUSIONS

[corrected] Our study shows that CD8 T cells of HIV-infected children have a more senescent phenotype when compared with age-matched healthy children. Interestingly enough, our results support the importance of maintaining undetectable viral load in HIV-infected children to avoid the premature ageing and dysfunction of CD8 T cells.

Relevance of early detection of HIV type 1 SI/CXCR4-using viruses in vertically infected children

The aim of the study was to investigate the prevalence and persistence of syncytium-inducing (SI) strains in HIV-1-infected children along time of infection and to evaluate the influence of antiretroviral therapy and host factors on viral tropism. This is a retrospective analysis carried out in 267 HIV-1 vertically infected children from an Argentinean cohort. The viral phenotype was screened in MT-2 cells and coreceptor usage confirmed by the GHOST cell assay. Also, CD4(+) T cell count, viral load, antiretroviral therapy, and human CCR5-Δ32 and CCR2-64I genotypes were analyzed. A high frequency of HIV-1 SI/CXCR4-using variants (22%) was found among children within the first trimester of life, reaching 46% after 10 years of infection. At acute infection, zidovudine prophylaxis did not significantly affect the proportions of SI HIV-1 strains, while their presence was favored by the CCR5(+)/Δ32 genotype. Interestingly, the majority of the early SI strains did not persist over time, probably due to a higher susceptibility to antiretroviral (ARV) treatment or immunologic pressure. At the chronic stage, SI variants emerged even in the presence of HAART reaching 36% at 120 months of infection. Also the HIV-1 SI phenotype was associated with lower CD4(+) T cell counts all along the course of infection. These findings highlight the need to evaluate the presence of SI/CXCR4 variants early at primary infection. This will make it possible to optimize the use of CCR5 inhibitors in children who are apparently carriers of the R5 virus preventing early therapeutic failure due to the reemergence of SI strains from reservoirs.

Preterm neonates show marked leukopenia and lymphopenia that are associated with increased regulatory T-cell values and diminished IL-7

INTRODUCTION

Current advances in neonatology have improved survival among preterm and low-birth-weight infants. However, the risk of neonatal death in preterm infants is much greater than in full-term neonates and is frequently associated with infections.

METHODS

Little is known about the immune status of preterm neonates; therefore, we analyzed the frequency and absolute counts of different immune populations in 211 cord blood samples taken from very-preterm to full-term neonates.

RESULTS

We found that absolute counts of all the immune subsets analyzed (i.e., monocytes, granulocytes, B cells, natural killer (NK) cells, CD4(+), and CD8(+) T cells) were markedly lower in preterm infants than in full-term infants. Surprisingly, we observed that regulatory T cells (Tregs) were the only cell subset that did not decrease in preterm infants, and their frequency was even higher than in full-term infants.

DISCUSSION

Tregs are crucial to maternal-fetal tolerance, but their suppressive role could be also implicated in the leukopenia observed in preterm infants. We did not observe differences in thymic function, but we found that plasma levels of interleukin (IL)-7 and the frequency of its receptor were significantly decreased in preterm infants. Our results could help to identify leukopenia and to implement immune therapies that significantly diminish mortality in preterm neonates.

HIV-1 envelope-dependent restriction of CXCR4-using viruses in child but not adult untransformed CD4+ T-lymphocyte lines

Phytohemagglutin-stimulated child and adult leukocytes equally supported CCR5-dependent (R5) and CXCR4-dependent (X4) HIV-1 replication. In contrast, when phytohemagglutin-stimulated leukocytes from either healthy or congenitally immunodeficient children were cultured on feeder cells, they well supported R5, but not X4 HIV-1 replication, whereas both viruses equally spread in adult cells maintained in similar conditions. Both child and adult cells showed similar levels of proliferation and surface expression of CD4, CCR5, CXCR4, CD25, CD69, and HLA-DR. Lack of X4 HIV-1 replication in child versus adult cells was not caused by a differential expression of several known HIV-1 restriction factors. Similar levels of HIV DNA synthesis occurred in child cells infected with R5 and X4 viruses up to 48 hours after infection when R5 HIV-1 showed a significantly superior capacity to spread in culture than X4 virus. Cultured child cells well supported single round vescicular stomatitis virus-G pseudotyped virus replication, whereas superinfection of R5-infected cells with X4 HIV-1 (or vice versa) rescued the replication of this latter virus. Thus, child cells exposed to feeder cell culture represent a novel model system in which the superior capacity of R5 versus X4 viruses to spread can be investigated in primary, untransformed CD4+ cells.

CCR5: From Natural Resistance to a New Anti-HIV Strategy

The C-C chemokine receptor type 5 (CCR5) is a key player in HIV infection due to its major involvement in the infection process. Investigations into the role of the CCR5 coreceptor first focused on its binding to the virus and the molecular mechanisms leading to the entry and spread of HIV. The identification of naturally occurring CCR5 mutations has allowed scientists to address the CCR5 molecule as a promising target to prevent or limit HIV infection in vivo. Naturally occurring CCR5-specific antibodies have been found in exposed but uninfected people, and in a subset of HIV seropositive people who show long-term control of the infection. This suggests that natural autoimmunity to the CCR5 coreceptor exists and may play a role in HIV control. Such natural immunity has prompted strategies aimed at achieving anti-HIV humoral responses through CCR5 targeting, which will be described here.

HIV-1 clade B Tat, but not clade C Tat, increases X4 HIV-1 entry into resting but not activated CD4+ T cells

CXCR4-using human immunodeficiency virus, type 1 (HIV-1) variants emerge late in the course of infection in >40% of individuals infected with clade B HIV-1 but are described less commonly with clade C isolates. Tat is secreted by HIV-1-infected cells where it acts on both uninfected bystander cells and infected cells. In this study, we show that clade B Tat, but not clade C Tat, increases CXCR4 surface expression on resting CD4+ T cells through a CCR2b-dependent mechanism that does not involve de novo protein synthesis. The expression of plectin, a cytolinker protein that plays an important role as a scaffolding platform for proteins involved in cellular signaling including CXCR4 signaling and trafficking, was found to be significantly increased following B Tat but not C Tat treatment. Knockdown of plectin using RNA interference showed that plectin is essential for the B Tat-induced translocation of CXCR4 to the surface of resting CD4+ T cells. The increased surface CXCR4 expression following B Tat treatment led to increased function of CXCR4 including increased chemoattraction toward CXCR4-using-gp120. Moreover, increased CXCR4 surface expression rendered resting CD4+ T cells more permissive to X4 but not R5 HIV-1 infection. However, neither B Tat nor C Tat was able to up-regulate surface expression of CXCR4 on activated CD4+ T cells, and both proteins inhibited the infection of activated CD4+ T cells with X4 but not R5 HIV-1. Thus, B Tat, but not C Tat, has the capacity to render resting, but not activated, CD4+ T cells more susceptible to X4 HIV-1 infection.

Premature immunosenescence in HIV-infected patients on highly active antiretroviral therapy with low-level CD4 T cell repopulation

OBJECTIVES

To analyse the role of thymic function and its association with cellular immunosenescence markers in patients with low-level CD4 T cell repopulation, despite complete HIV RNA replication control on highly active antiretroviral therapy (HAART).

METHODS

Cellular immunosenescence markers comparing patients with CD4 T cell counts <or=250 cells/mm(3) for >or=48 weeks (n = 11) and patients with a CD4 T cell count >or=500 cells/mm(3) (n = 11) were investigated. Both groups were also compared with 11 healthy volunteers of similar age. Naive CD4 T cell counts, beta- and delta-T cell rearrangement excision circles, recent thymic emigrants, replicative senescence marker, cell activation, and rate of apoptosis were analysed. The Mann-Whitney U-test was used to compare parameters between both low-level and high-level CD4 T cell repopulation groups, and healthy volunteers.

RESULTS

Our results showed a lower thymic activity in patients with low-level CD4 T cell repopulation, leading to a decline in CD4 T cell production. On the other hand, a higher activation along with a higher replicative senescence of CD4 T cells contributed to a higher rate of apoptotic CD4 T cells in this group of patients.

CONCLUSIONS

We propose a model with several different related mechanisms involved in premature immune senescence in HIV-infected patients with low-level CD4 repopulation on HAART. The understanding of such different mechanisms could help find effective strategies to prevent immune decay.

Relationship between HIV coreceptor tropism and disease progression in persons with untreated chronic HIV infection

OBJECTIVE

To assess the effect of HIV coreceptor tropism (CRT) on the relative risk of progression to a composite outcome of CD4 count < or =350 cells per microliter, treatment initiation, or death.

METHODS

CRT assays were performed after study closure in baseline samples obtained from enrollees in a prospectively monitored cohort of treatment-naive adults with > or =450 CD4 cells per microliter and > or =1000 HIV-1 RNA copies per milliliter.

RESULTS

Dual/mixed (D/M) and R5 CRT were detected in 32 and 282 patients, respectively. The baseline CD4 count (617 versus 694 cells/microL; P = 0.05) differed in patients with D/M versus R5 CRT. Otherwise, baseline laboratory characteristics were similar.The relative risk of progression to the composite end point was 2.15 (P = 0.002) for D/M versus R5 CRT, 2.07 per 1.0 log10 higher viral load (P < 0.001) and 0.87 per 50 cells per microliter higher CD4 cell count (P < 0.001). The effect of D/M CRT was also significant in separate analyses of time to initiation of antiretroviral therapy or CD4 cell count < or =350 cells per microliter.

CONCLUSIONS

Untreated patients with D/M rather than R5 CRT had a faster rate of disease progression, whether assessed by a composite outcome of time to CD4 count < or =350 cells per microliter, treatment initiation, or death or by separate analyses of time to CD4 count < or =350 cells per microliter or treatment initiation.

Chemokine receptors and co-stimulatory molecules: unravelling feline immunodeficiency virus infection

Feline immunodeficiency virus (FIV) infection of the domestic cat induces an immunodeficiency characterised by a gradual depletion of CD4+ T-helper lymphocytes. The virus targets T-helper cells by way of an interaction between its envelope glycoprotein (Env) and the cell surface molecule CD134 (OX40), a member of the nerve growth factor receptor/tumour necrosis factor receptor superfamily. The Env-CD134 interaction is a necessary prerequisite for the subsequent interaction with CXCR4, the only chemokine receptor identified to date to act as a co-receptor for FIV. As T-helper cell expression of CD134 and CXCR4 is restricted to activated cells, FIV targets selectively antigen-specific T-helper cells. With disease progression the cell tropism of the virus expands; this may be the result of changes in the way in which Env interacts with CD134, a less stringent Env-CD134 interaction enabling the Env to interact more readily with CXCR4 and thus broadening the cell tropism of virus. In contrast, viruses that are present in early infection may have a narrower cell tropism, reflecting a more stringent interaction with CD134. Accordingly, "early" viruses may target CD134-expressing cells more efficiently and be more resistant to neutralising antibody. It is these early viruses that may be transmitted and should be considered as candidates for the development of vaccine regimes and novel therapeutic agents.

Prevalence of X4 tropic HIV-1 variants in patients with differences in disease stage and exposure to antiretroviral therapy

Viral tropism plays an important role in HIV pathogenesis. However, its correlation with the clinical outcome and following exposure to antiretroviral drugs are still unclear. HIV-1 co-receptor usage was examined in 206 infected individuals: 67 seroconverters, 52 chronically drug-naïve, and 87 antiretroviral-experienced patients. The V3 loop was sequenced from plasma HIV-RNA and co-receptor usage was inferred using a phenotype predictor software (http://genomiac2.ucsd.edu:8080/wetcat/v3.html), which classifies V3 sequences as R5 or X4. The overall prevalence of X4 viruses was 26.2%, with significant differences among groups: 13.4% in seroconverters, 25% in drug-naïve, and 36.8% in antiretroviral- experienced patients (P = 0.001). The presence of X4 variants in the latter group was associated with higher viral load (P = 0.002) but not with lower CD4 counts. There was no association between HIV tropism and gender, transmission route or age. Neither with the CCR5 Delta32 genotype. Moreover, no association was found between HIV-1 tropism and drug resistance mutations nor with failure to regimens based on either protease inhibitors or non-nucleoside reverse transcriptase inhibitors. Finally, no significant association was found between IL-7 plasma levels with HIV-1 tropism. In summary, X4 viruses are particularly frequent among antiretroviral-experienced patients with high viral loads, irrespective of the CD4 count. Thus, CCR5 antagonists should be used with special caution in this subset of patients.

Differential Biological Role of CD3 Chains Revealed by Human Immunodeficiencies

The biological role in vivo of the homologous CD3gamma and delta invariant chains within the human TCR/CD3 complex is a matter of debate, as murine models do not recapitulate human immunodeficiencies. We have characterized, in a Turkish family, two new patients with complete CD3gamma deficiency and SCID symptoms and compared them with three CD3gamma-deficient individuals belonging to two families from Turkey and Spain. All tested patients shared similar immunological features such as a partial TCR/CD3 expression defect, mild alphabeta and gammadelta T lymphocytopenia, poor in vitro proliferative responses to Ags and mitogens at diagnosis, and very low TCR rearrangement excision circles and CD45RA(+) alphabeta T cells. However, intrafamilial and interfamilial clinical variability was observed in patients carrying the same CD3G mutations. Two reached the second or third decade in healthy conditions, whereas the other three showed lethal SCID features with enteropathy early in life. In contrast, all reported human complete CD3delta (or CD3epsilon) deficiencies are in infants with life-threatening SCID and very severe alphabeta and gammadelta T lymphocytopenia. Thus, the peripheral T lymphocyte pool was comparatively well preserved in human CD3gamma deficiencies despite poor thymus output or clinical outcome. We propose a CD3delta >> CD3gamma hierarchy for the relative impact of their absence on the signaling for T cell production in humans.

Fusion-induced apoptosis contributes to thymocyte depletion by a pathogenic human immunodeficiency virus type 1 envelope in the human thymus

The mechanisms of CD4(+) T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection remain incompletely characterized. Of particular importance is how CD4(+) T cells are depleted within the lymphoid organs, including the lymph nodes and thymus. Herein we characterize the pathogenic mechanisms of an envelope from a rapid progressor (R3A Env) in the NL4-3 backbone (NL4-R3A) which is able to efficiently replicate and deplete CD4(+) thymocytes in the human fetal-thymus organ culture (HF-TOC). We demonstrate that uninterrupted replication is required for continual thymocyte depletion. During depletion, NL4-R3A induces an increase in thymocytes which uptake 7AAD, a marker of cell death, and which express active caspase-3, a marker of apoptosis. While 7AAD uptake is observed predominantly in uninfected thymocytes (p24(-)), active caspase-3 is expressed in both infected (p24(+)) and uninfected thymocytes (p24(-)). When added to HF-TOC with ongoing infection, the protease inhibitor saquinavir efficiently suppresses NL4-R3A replication. In contrast, the fusion inhibitors T20 and C34 allow for sustained HIV-1 production. Interestingly, T20 and C34 effectively prevent thymocyte depletion in spite of this sustained replication. Apoptosis of both p24(-) and p24(+) thymocytes appears to be envelope fusion dependent, as T20, but not saquinavir, is capable of reducing thymocyte apoptosis. Together, our data support a model whereby pathogenic envelope-dependent fusion contributes to thymocyte depletion in HIV-1-infected thymus, correlated with induction of apoptosis in both p24(+) and p24(-) thymocytes.

T-Cell Immune Reconstitution after Hematopoietic Stem Cell Transplantation for HIV-Associated Lymphoma

BACKGROUND

One of the major concern for high-dose chemotherapy and hematopoietic stem cell transplantation (HSCT) for HIV-associated lymphoma is that posttransplant immunosuppression might worsen immune defects of HIV individuals. Since the introduction of highly active antiretroviral therapy has made HSCT possible also in these patients, we analyzed whether the immune system already compromised by HIV infection might support an efficient T-cell recovery after HSCT.

METHODS

The kinetics and the extent of T-cell reconstitution were investigated before and after HSCT in four patients with HIV-related lymphoma (one with Hodgkin's Disease and three with non-Hodgkin's lymphoma) by measuring the thymic output, the level of IL-7 and the heterogeneity of T-cell repertoire. T-cell competence was gauged at two functional levels: by determining the number of T-cell divisions and by measuring IFN-gamma production.

RESULTS

The thymus of transplanted patients can be capable of generating new T cells, but there is no relationship between increasing number of newly produced lymphocytes and modification of IL-7 level. Various T-cell subsets, expressing different T-cell receptor variable beta genes, were preferentially expanded in CD8 population and most of them showed a restricted diversity. Furthermore, CD3 lymphocytes showed heterogeneous behaviors in terms of proliferative capability and IFN-gamma production.

CONCLUSIONS

High-dose therapy and HSCT in HIV patients under highly active antiretroviral therapy does not worsen the immune defects. On the contrary, in the presence of some conditions (including the type of hematologic malignancy, the therapy compliance, and the immune status before transplantation), high-dose therapy and HSCT might support the improvement of immune conditions.

Role of antiretroviral therapies in mucocutaneous manifestations in HIV-infected children over a period of two decades

BACKGROUND

Human immunodeficiency virus (HIV) infection causes a severe cellular immunodeficiency, which results in a greater susceptibility to infectious, inflammatory and malignant conditions. Among these, pathologies of the skin seem to be those most frequently observed in HIV+ patients. However, there are few reports on how antiretroviral therapy affects skin disorders in HIV-infected children.

OBJECTIVE

To study the incidence and prevalence of skin disorders in a cohort of HIV-infected children, in relation to the antiviral therapy [nontreated, monotherapy, combined therapy and highly active antiretroviral therapy (HAART)] received, and their impact on immunological and virological markers. The treatments were those available in different calendar periods in the history of antiviral treatment.

MATERIALS AND METHODS

A retrospective, observational study in a cohort of 210 HIV-infected children was carried out. These children were followed up every 3 months throughout 22 years. The viral load (HIV RNA copies mL(-1)) was quantified using reverse transcriptase-polymerase chain reaction and the viral phenotype of HIV-1 isolates was determined by in vitro culture. T-lymphocyte subsets in peripheral blood were quantified by flow cytometry.

RESULTS

Mucocutaneous manifestations were diagnosed in 17% of the untreated infected children. Of the treated children in different treatment periods, 22% in the monotherapy period, 25% in the combined therapy period but only 10% on HAART had some type of mucocutaneous manifestation, concordant with a higher number of CD4+ T cells, a lower viral load and less cytopathic virus in the last group. Mucocutaneous manifestations of infectious aetiology were most frequently observed; they were detected in 13% of the children during the first calendar period (untreated children), 16% during the second and third periods (monotherapy and combined therapy) and only 5% in the last period (HAART). Interestingly, syncytium-inducing virus was present in 69% of all children with mucocutaneous manifestations of infectious aetiology.

CONCLUSION

Only in the last calendar period (HAART) was a significant decrease observed in the prevalence of mucocutaneous manifestations with HIV infection associated with an increase in CD4+ T cells. In addition, we found a strong association between children who had mucocutaneous manifestations with an infectious aetiology and a more cytopathic (X4/SI) viral phenotype.

Immunological changes after highly active antiretroviral therapy with lopinavir-ritonavir in heavily pretreated HIV-infected children

We evaluated the effect of salvage antiretroviral therapy with lopinavir/ritonavir (LPV/r) on the immune system of heavily antiretroviral pretreated HIV-infected children. We carried out a longitudinal study in 20 antiretroviral experienced HIV-infected children to determine the changes in several immunological parameters (T cell subsets, thymic function) every 3 months during 18 months of follow-up on salvage therapy with LPV/r. Statistical analyses were performed with the Wilcoxon test, taking as a reference the basal value at the entry in the study. HIV-infected children showed an increase of CD4+ T cells, a decrease in CD8+ T cells, and an increase in T cell rearrangement excision circle (TRECs) levels. The percentage of HIV children with undetectable viral load (VL < or = 400 copies/ml) increased significantly (p = 0.007) and the percentage with SI viral phenotype decreased significantly (p = 0.002) at the end of the study. Thus, the viral phenotype changed to NSI/R5 after salvage therapy with LPV/r. Interestingly, we observed a significant decrease of memory (CD4+ CD45RO+) and a moderate decrease of activated (CD4+ HLA-DR+, CD4+ HLA-DR+CD38, CD4+, CD45RO+HLA-DR+) CD4+ T cells during the follow-up. On the other hand, memory (CD8+ CD45RO+ and CD8+ CD45RO+CD38+), activated (CD8+ HLA-DR+CD38+, CD8+ HLA-DR+, CD8+ CD38+), and effector (CD8+ CD57+, CD8+ CD28(-)CD57+) CD8+ T cells had a very significant decrease during follow-up. Our data indicate an immune system reconstitution in heavily pretreated HIV-infected children in response to salvage therapy with LPV/r as a consequence of a decrease in immune system activation and an increase in thymic function.

R5 to X4 Switch of the Predominant HIV-1 Population in Cellular Reservoirs During Effective Highly Active Antiretroviral Therapy

HIV-1 coreceptor usage plays a critical role for virus tropism and pathogenesis. A switch from CCR5 to CXCR4-using viruses can occur in the natural course of infection and correlates with subsequent disease progression. To investigate whether HIV-1 genetic evolution might lead to changes in virus coreceptor usage during highly active antiretroviral therapy (HAART), a longitudinal genotypic analysis of the virus found in cellular reservoirs was conducted in 32 patients with undetectable viral loads on HAART for 5 years. The genotype of the 3rd variable region of the env gene predicting coreceptor usage was retrospectively determined in the plasma or in peripheral blood mononuclear cells (PBMC) at baseline and then in PBMCs at months 30 and 60 of HAART. There was a switch from R5 to X4 variants in 11 of the 23 patients who harbored a majority virus population of R5 variants at baseline. X4 variants remained predominant in the 9 patients who harbored mainly X4 variants at baseline. The patients harboring predominantly X4 variants during HAART, either from baseline or after an R5 to X4 switch, tended to have lower CD4+ T-cell counts on HAART than did patients harboring continuously a majority population of R5 variants. These results suggest that potent antiretroviral therapy produces the conditions necessary for the gradual emergence of X4 variants in cellular reservoirs.

Homeostatic role of IL-7 in HIV-1 infected children on HAART: association with immunological and virological parameters

AIM

To investigate the role of IL-7 in HIV-infected children on highly active antiretroviral therapy (HAART) and its association with laboratory parameters related to disease progression.

PATIENTS AND METHODS

A cross-sectional study in 31 vertically HIV-infected children (median age 8.4 y) treated with HAART, and a longitudinal study in four of those same children was carried out. In both studies, viral load, CD4+ T-cell counts, thymic production of T cells by TCR rearrangement excision circles (TRECs), IL-7 plasma levels and viral phenotype were determined.

RESULTS

IL-7 levels were higher in HIV-infected children than in age-matched, uninfected controls. In addition, HIV children with CD4+ T cells between 200 and 500 T cells/mm3 had higher IL-7 levels and lower TREC values than HIV-infected children with CD4+ T cells >500 T cells/mm3. IL-7 levels were higher in children with syncytium-inducing (SI) phenotype than in those with non-syncytium-inducing (NSI) variants. During the follow-up of four HIV children, the decrease in viral load after HAART was always associated with a recovery of CD4+ T cells and TRECs, which was followed by a decrease in IL-7 returning to the levels present prior to the drop in CD4+ T cells. The four HIV-infected children had SI/X4 isolates in PBMC before HAART, and the viral phenotype switched to NSI/R5 after HAART.

CONCLUSION

Our data suggest that IL-7 plays a key role in the maintenance of T-cell homeostasis in HIV-infected children on HAART, both through peripheral expansion and through a thymus-dependent mechanism.

[Changes in CD4+ and CD8+ T-cell subsets in HIV-infected children differently correlate with viral replication and thymic function]

BACKGROUND AND OBJECTIVE

We intended to study the relationship between T-cell subsets with plasmatic detectable viral load (VL) and T-receptor excision circles (TREC).

PATIENTS AND METHOD

Twenty HIV-infected children on highly active antiretroviral therapy (HAART) were recruited in a 1-year longitudinal retrospective study. We analyzed the relationship between changes in peripheral blood T-cell subsets, VL and TREC markers by lineal regression.

RESULTS

Memory and activated CD4+ T-cells increases had a negative association with log10 TRECs increases. However, naive CD4+ T-cells increases had a positive association with log10 TRECs increases. In contrast, memory, activated and effector CD8+ T-cells increases positively correlated with log10 VL increases. On the other hand, naive CD8+ T-cells increases had a negative association with log10 VL increases.

CONCLUSIONS

CD4+ and CD8+ T-cells subsets change in a different way as a response to the changes produced by HAART in HIV vertically infected children. CD4+ T-cells are more dependent on thymic function and CD8+ T-cells are more dependent on viral replication. Thus, the decline in cellular activation would allow the production of more naive T-cells by the thymus.

HIV-infected children with moderate/severe immune-suppression: changes in the immune system after highly active antiretroviral therapy

The objective of this study was to monitor the changes in the immune system of HIV-infected children with moderate or severe immunodeficiency after highly active antiretroviral therapy (HAART), comprising a follow-up study in 14 HIV-infected children on HAART at two time points separated approximately by 11.8 +/- 0.4 (9.9; 15.4) months. HIV-infected children had significantly lower TREC levels than the control group, but 1 year after HAART the levels increased significantly (P < 0.05). In contrast, viral load (VL) did not change significantly. A positive correlation between T cell receptor excision circle (TREC) levels and both CD4(+) T cell absolute counts (r = 0.558; P = 0.05) and percentages (r = 0.625; P = 0.030) was found. During follow-up on HAART, the percentages and absolute counts of naive CD4(+) and CD8(+) T cell subsets were increased significantly (P < 0.05). CD4(+) CD45RA(hi+) CD62L(+), CD4(+) CD45RA(+) and CD4(+) CD38(+) percentages, and the CD8(+) CD45RA(hi+) CD62L(+) counts reached similar values to the control group. Also, CD8(+) CD45RO(+) CD38(+) and CD8(+) CD45RO(+) percentages, and CD8(+) CD45RO(+) CD38(+) absolute counts (P < 0.05) decreased with respect to the baseline. Lymphoproliferative responses to pokeweed mitogen (PWM) before HAART were lower in HIV-infected children than the control group, but they recovered to normal levels after a year on HAART. Tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma production by PHA-activated peripheral blood mononuclear cells (PBMC) was lower before HAART (P < 0.001), but reached similar levels to the control group 1 year after HAART. In HIV-infected children IgG, IgG(1) and IgG(3) plasma levels decreased significantly after HAART. The immune system reconstitution induced by HAART in HIV-infected children seems to be the consequence of decreased immune system activation and naive T cell reconstitution, mainly of thymic origin.

Increased interleukin-7 plasma levels are associated with recovery of CD4+ T cells in HIV-infected children

To asses the role of interleukin 7 (IL-7) in the thymic reconstitution of CD4 T cells observed in children after successful antiretroviral therapy, a longitudinal study in five vertically HIV-1-infected children was carried out. Thymic function, IL-7 plasma levels, viral load, and T-lymphocytes subsets were determined every 2 or 3 months for about 90 months. In all the children, the drop in CD4+ T cells below 5-10% was associated with a marked increase in IL-7 plasma levels. The drastic decrease in viral load after treatment, led in all the cases to a recover of CD4 to levels higher than 30%, which was associated to an increase in thymic production of T cells and followed by a decrease in IL-7 to the normal levels. We conclude that the drop in CD4 in HIV children would induce an increase of IL-7 as part of a homeostatic mechanism. IL-7 would induce the thymus to produce new T cells to recover the normal levels of CD4 when the viral load was low and so the thymic function was not inhibited. The increase in the thymic production of new T cells recovers the CD4 population, and leads to a normalization of IL-7 levels.

Virological phenotype switches under salvage therapy with lopinavir-ritonavir in heavily pretreated HIV-1 vertically infected children

OBJECTIVE

To investigate the effects of salvage therapy with lopinavir-ritonavir on HIV-1 phenotype in heavily antiretroviral experienced HIV-infected children.

DESIGN

Twenty antiretroviral experienced HIV-infected children were studied during a mean of time of 16.1 months from initiation of the treatment with lopinavir-ritonavir.

METHODS

Besides CD4 T cells, viral load and clinical status, we analyzed 91 serial viral isolates to study the phenotype, and biological clones derived from co-cultivation techniques.

RESULTS

We observed an increase in CD4 T cells, a statistically significant decrease in viral load and clinical benefits from 3 months after treatment. Ninety per cent of children had SI/X4 bulk isolates in peripheral blood mononuclear cells at study entry. The viral phenotype changed to non syncitium-inducing (NSI)/R5 in 94% of the children after a mean of 5.7 months (95% confidence interval, 2.1-9.3 months) of salvage therapy. The remaining 10% of children had NSI/R5 isolates at entry and at all follow-up study. Similar results were found at the clonal level. Thus, at study entry in PBMC of three children with bulk syncitium-inducing (SI) phenotype, we recovered 65 biologic clones, 56 being SI and nine NSI. After salvage therapy bulk isolates changed to NSI and of 40 biologic clones recovered only five were SI and the rest were NSI.

CONCLUSIONS

Our data suggest that lopinavir-ritonavir salvage therapy led not only to a viral load decrease but also to a phenotypic change. X4 virus appeared to be preferentially suppressed. Shifts in co-receptor usage may thereby contribute to the clinical efficacy of anti-HIV drugs in vertically infected infants.

The CCR5 and CXCR4 coreceptors--central to understanding the transmission and pathogenesis of human immunodeficiency virus type 1 infection

In this review, we will discuss what is known, what is suspected, and what still remains obscure about the central role played by coreceptor expression and usage in the transmission and pathogenic consequences of human immunodeficiency virus type 1 (HIV-1) infection. An emphasis will be on the HIV-1 phenotypic variants that are defined by their usage of the CCR5 or CXCR4 coreceptors, and how the different cellular tropism of these variants influences how and where HIV-1 replicates in vivo. We will also review what might happen when coreceptor antagonists are used clinically to treat HIV-1 infection.

T cell dynamics in HIV-1 infection

In the absence of antiretroviral treatment, HIV-1 establishes a chronic, progressive infection of the human immune system that invariably, over the course of years, leads to its destruction and fatal immunodeficiency. Paradoxically, while viral replication is extensive throughout the course of infection, deterioration of conventional measures of immunity is slow, including the characteristic loss of CD4(+) T cells that is thought to play a key role in the development of immunodeficiency. This conundrum suggests that CD4(+) T cell-directed viral cytopathicity alone cannot explain the course of disease. Indeed, recent advances now indicate that HIV-1 pathogenesis is likely to result from a complex interplay between the virus and the immune system, particularly the mechanisms responsible for T cell homeostasis and regeneration. We review these data and present a model of HIV-1 pathogenesis in which the protracted loss of CD4(+) T cells results from early viral destruction of selected memory T cell populations, followed by a combination of profound increases in overall memory T cell turnover, damage to the thymus and other lymphoid tissues, and physiological limitations in peripheral CD4(+) T cell renewal.

Characterizing the immune system after long-term undetectable viral load in HIV-1-infected children

Thirty two HIV-infected children, on highly active antiretroviral therapy (HAART) and > 500 CD4+ T cells/mm3, were rated according to the time-course of viral load (VL) during the whole follow-up period (> 18 months) in a longitudinal retrospective study. (a) uVL group: 15 children with VL below 400 copies/mL; (b) dVL group: 17 children with higher VL. The uVL group showed higher memory (CD4+CD45RO+) T cells than did dVL group, and higher number of memory activated CD4+CD45RO+HLA-DR+ than did control group (healthy age-matched uninfected children), whereas CD4+CD45RA(hi)+CD62L+ was similar. However, TCR rearrangement excision circles (TRECs) were higher in uVL group than in dVL group. uVL Group showed CD8+CD45RO+ and CD8+CD45RO+CD38- higher number than the control group, but lower than the dVL group. The percentage of CD8+CD45RA(hi)+CD62L+, CD8+CD45RA+, CD8+CD62L-, and CD8+CD28+ was higher in uVL group than in dVL group, and lower than in control group. The uVL group showed higher number of activated (HLA-DR+CD38+, HLA-DR+, HLA-DR+CD38-) CD4+ T cells and lower percentages of CD4+HLA-DR-CD38+ than dVL group. In activated CD8- T cell, the uVL group had lower CD8+HLA-DR+CD38+, CD8+HLA-DR+, and CD8+CD38+ than the dVL group. Preeffector (CD8+CD57-CD28- and CD8+CD45RA-CD62L-) T cells were lower in the uVL group than in dVL group. In the effector (CD8+CD57+, CD8+CD57+CD28-, and CD8+CD45RA+CD62L-) T cells, HIV-infected-children had higher values than control group. HIV-infected-children who respond to HAART had TRECs reconstitution, decreased immune activation, and lower effector CD8+ T cells. Moreover, successful HAART allow the increment of activated CD4+ T cells.

Positive regulation of CXCR4 expression and signaling by interleukin-7 in CD4+ mature thymocytes correlates with their capacity to favor human immunodeficiency X4 virus replication

The emergence of X4 human immunodeficiency virus type 1 (HIV-1) variants in infected individuals is associated with poor prognosis. One of the possible causes of this emergence might be the selection of X4 variants in some specific tissue compartment. We demonstrate that the thymic microenvironment favors the replication of X4 variants by positively modulating the expression and signaling of CXCR4 in mature CD4(+) CD8(-) CD3(+) thymocytes. Here, we show that the interaction of thymic epithelial cells (TEC) with these thymocytes in culture induces an upregulation of CXCR4 expression. The cytokine secreted by TEC, interleukin-7 (IL-7), increases cell surface expression of CXCR4 and efficiently overcomes the downregulation induced by SDF-1 alpha, also produced by TEC. IL-7 also potentiates CXCR4 signaling, leading to actin polymerization, a process necessary for virus entry. In contrast, in intermediate CD4(+) CD8(-) CD3(-) thymocytes, the other subpopulation known to allow virus replication, TEC or IL-7 has little or no effect on CXCR4 expression and signaling. CCR5 is expressed at similarly low levels in the two thymocyte subpopulations, and neither its expression nor its signaling was modified by the cytokines tested. This positive regulation of CXCR4 by IL-7 in mature CD4(+) thymocytes correlates with their high capacity to favor X4 virus replication compared with intermediate thymocytes or peripheral blood mononuclear cells. Indeed, we observed an enrichment of X4 viruses after replication in thymocytes initially infected with a mixture of X4 (NL4-3) and R5 (NLAD8) HIV strains and after the emergence of X4 variants from an R5 primary isolate during culture in mature thymocytes.

Preserved immune system in long-term asymptomatic vertically HIV-1 infected children

The objective of this study was to study immune system status in long-term asymptomatic (LTA) HIV-1-infected children. A cross-sectional study was used, involving HIV-1-infected children over 7 years of age who were rated into two groups according to their clinical and immunological classification: (a) LTA: 7 asymptomatic HIV-1-infected children in A1; (b) Rapid progressor (RP): 14 age-matched C3 HIV-1-infected children. The control group consisted of 17 age-matched uninfected children. The characterization of CD4+ T-cell subsets was determined by three-colour flow cytometry. The proliferative response and cytokine production by activated peripheral blood T-cells were also measured. IL-7 levels were measured in serum. Thymic production of T-cells was quantified by TCR rearrangement excision circles (TRECs). The LTA children showed similar proliferative responses to PHA, PWM and anti-CD3+ anti-CD28, but lower responses to tetanus toxoid and streptokinase, in comparison with the controls but always higher responses in comparison with the RP group. The production of TNF-alpha and IFN-gamma was similar in the LTA and control groups, and both were higher than the levels in the RP group. The LTA group showed a lower percentage of memory CD4+ T-cells (CD4+ CD45RO+, CD4+ CD45RA-CD62L+) than the control and RP groups. The LTA group also showed lower percentages of CD4+ CD7- cells than the controls. As for naïve CD4+ T-cells (CD4+ CD45RA+ CD62L+), CD4+ CD45RA+ and CD4+ CD62L+ cells, the LTA group showed higher values than the control and RP groups. The LTA group showed higher percentages of CD4+ HLA-DR+ CD38+ than the controls, but lower values than the RP group. In contrast, the LTA group had percentages of CD4+ HLA-DR-CD38+ T-cells higher than both the control and RP groups, whereas CD4+ CD38+ levels were only higher in the LTA group in comparison with the controls. CD4+ HLA-DR+ CD38- and CD4+ HLA-DR+ cell numbers were lower in the LTA group in comparison with the RP group. We found almost normal values of TRECs and IL-7 in the LTA group, but lower values in the RP group. Moreover, we found an inverse relation between TREC levels and IL-7 in plasma from HIV-infected children. Asymptomatic HIV-1 infected children have a well preserved immune system similar to that of control uninfected children in spite of HIV-infection for more than 7 years. Moreover, our results identified new markers of HIV disease, such as TRECs and IL-7, that could be used to monitor disease.

[Complete immune and clinical recovery after highly active antiretroviral therapy in advanced vertically HIV-1 infected children]

BACKGROUND AND OBJECTIVE

The aim of this study was to evaluate the ability of long-term highly active antiretroviral therapy (HAART) to fully reconstitute the immune system in children with severe AIDS.

PATIENT AND METHOD

Lymphoproliferative responses (LPR) were evaluated by incorporation of [3H]-thymidine. Cytokine production in culture (IFN- gamma, IL-5) was quantified using commercially available specific ELISA assays. T-cells subsets were determined by 3-color flow cytometry and thymic production of T-cells was assessed by quantification of TCR rearrangement excision circles (TRECs).

RESULTS

We present a vertically HIV-1-infected child at clinical category C, with long-standing CD4+ T-cells below 50/l, who was monitored during 3-years after starting HAART by quantifying the viral load (VL), naïve, memory, and activated T-cell subsets, and thymical function as well as clinical events. VL was suppressed to undetectable levels since the beginning of HAART with d4T, 3TC, nelfinavir, and efavirenz resulting in a dramatic immune reconstitution, achieving normal CD4+ T-cells counts after 6 months (25%, 597 CD4+ T-cells/l) and perdurable undetectable VL levels. Naïve CD4 and CD8 T-cells increased in parallel to TCR rearrangement excision circles (TRECs) levels, with a concomitant decrease in T-cell activation markers. Interestingly, the patient showed an increase in the lymphoproliferative responses to PHA; the IFN-gamma production by PBMCs increased with HAART while the production of IL-5 diminished, thus indicating a switch of type 2 to type 1 response. He recovered clinically and immunologically (up to normal levels) and remains asymptomatic at present.

CONCLUSION

This report demonstrates that at least in these children, an immune and clinical recovery from an advanced stage of HIV-disease can be possible throught HAART.

Low blood CD8+ T-lymphocytes and high circulating monocytes are predictors of HIV-1-associated progressive encephalopathy in children

OBJECTIVE

Human immunodeficiency virus type 1 (HIV-1)-associated progressive encephalopathy (PE) is a common and devastating complication of HIV-1 infection in children, whose risk factors have not yet been clearly defined. Regardless of the age of presentation, PE shortens life expectancy. Paradoxically, as survival of patients has been prolonged as a result of the use of antiretroviral therapy, the prevalence of PE has increased. Therefore, a predictive marker of PE emergence is critical. The objective of this study was to determine in an observational study whether any immunologic (CD4(+) and CD8(+) T-lymphocyte counts, monocyte counts) or virologic (viral load [VL], biological characteristics of viral isolates) marker might be predictive of PE and whether any particular marker may be involved in the timing of clinical onset of PE.

METHODS

A total of 189 children who were vertically infected with HIV-1 were studied retrospectively, 58 of whom fulfilled criteria of the American Academy of Neurology for PE. T-lymphocyte subsets and monocytes in peripheral blood were quantified by flow cytometry. HIV-1 RNA was measured in plasma using a quantitative reverse transcriptase polymerase chain reaction assay. Demographic, clinical, and viro-immunologic characteristics in infants were compared with control groups using logistic regression. Proportions were compared using the chi(2) test or Fisher exact test. For each child, immunologic and virologic markers were analyzed in parallel closely before clinical onset of PE and closely after PE onset and compared by using the Student t test for paired samples.

RESULTS

Overall, mortality of 58 HIV-1-infected children who developed PE was significantly higher than of children who did not develop this complication. Blood CD8(+) T-lymphocytes <25% in the first months of life suggested a relative risk of progressing to PE 4-fold higher than those with CD8(+) >25% (95% confidence interval: 1.2-13.9) and remained statistically significant after adjustment for treatment. When we compared the PE-positive group with the acquired immunodeficiency syndrome (AIDS)/PE-negative group (children who developed clinical category C and without neurologic manifestations) in a cross-sectional study within 12 months before PE or AIDS diagnosis, respectively, the %CD8(+) T-lymphocytes were significantly lower in the PE-positive group. Normalized absolute counts of CD8(+) T-lymphocytes with respect to seroreverting children were significantly lower in the group of children with encephalopathy with respect to the AIDS/PE-negative group (data not shown). It is interesting that a statistically significant increase was observed in circulating monocyte percentages and absolute counts shortly before the first neurologic symptoms compared with values after PE was established and with those from HIV-1-infected controls. With respect to AIDS-related events, PE was strongly associated with anemia and lymphoid interstitial pneumonitis in the PE-positive group with respect to a group of children with AIDS but without PE.

CONCLUSION

HIV-1 infection of the central nervous system (CNS) remains an important clinical concern. The first step toward PE prevention in HIV-1-infected children should be directed at predicting risk of PE and thus the prompt and reliable identification of infants who are at risk for CNS disease progression. Low blood CD8(+) T-lymphocytes is a strong early predictive marker of PE emergence in vertical HIV-1 infection. Indeed, among all of the immunologic and virologic variables assessed in this observational study, the only significant difference during the first months of life are the CD8(+) T-lymphocytes. A peak of significantly higher peripheral monocytes before the onset of PE with respect to established PE has not been previously described, and strengthens the growing evidence that an increased traffic of monocytes to the brain may be a key factor in triggering neurologic symptoms. The suppression of HIV-1 replication is dependent on the presence of a relatively small number of HIV-1-specifof HIV-1-specific CD8(+) T-lymphocytes, and it is possible that the duration of the neurologically asymptomatic phase for any given child may depend mostly on the magnitude of specific CD8(+) T-lymphocyte responses. Thus, a decrease of CD8(+) T-lymphocytes would diminish the host capacity to control viral infection, as reported in animal models, enabling infected macrophages to cross the blood-brain barrier. Our results advocate the use of CD8(+) T-lymphocyte and monocyte counts to follow-up HIV-1-infected children. We suggest that CD8(+) T-lymphocytes may be the nexus for many different aspects of the disease, namely loss of control of HIV-1 replication determining higher VL, increased traffic of activated and/or infected monocytes, spread of infection to immune sanctuaries, and finally clinical neurologic emergence of PE. Moreover, we suggest that CD8(+) T-lymphocytes or/and monocytes may be used as putative biological markers of neuropathogenicity. This might suggest their use in decision making of when to start more effective antiretroviral regimens for HIV-1 infection of the CNS and the need of new therapies either to preserve or to augment an adequate CD8(+) T-lymphocyte immune response. Early detection of children who are at risk for developing PE is particularly important because aggressive highly active antiretroviral therapy improves neurologic symptoms, allows possible use of neuroprotective treatment to prevent further development of encephalopathy, and emphasizes the relevance of developing therapies aimed to enhance CD8(+) T-lymphocyte function. In conclusion, the surrogate markers routinely used in clinical practice for HIV-1 infection (ie, CD4(+) T-lymphocyte counts and VL) seem to be insufficient to evaluate the clinical involvement of the CNS. Other systemic markers, as the recent proposed markers for PE evolution (cerebrospinal fluid VL by lumbar puncture and brain atrophy by cerebral magnetic resonance imaging) are undoubtedly more invasive than measuring CD8(+) T-lymphocyte and monocyte counts, when the neurologic manifestations of PE are still preventable.

Characterizing immune reconstitution after long-term highly active antiretroviral therapy in pediatric AIDS

In this study, we sought to characterize the T lymphocyte recovery in vertically HIV-1-infected children who respond to long-term highly active antiretroviral therapy (HAART). A 3-year longitudinal retrospective study was used to perform a cross-sectional study of 32 children rated according to the time course of CD4(+) T cell percentages in response to antiretroviral therapy and CDC clinical classification: (1) long-term asymptomatic (LTA group): 8 children in A1 during the whole follow-up period; (2) responsive to HAART (Rec group): 13 children in C3 before HAART who achieved CD4(+) T cell counts of > 500 cells/mm(3) after 3 years of HAART; and (3) nonresponsive to HAART (Non-Rec group): 11 children in C3 during the whole follow-up period despite 3 years of HAART. We also studied 17 healthy age-matched uninfected children as controls. Lymphoproliferative responses (LPRs) were evaluated by incorporation of [(3)H]thymidine, identification of T cell subsets by three-color flow cytometry, and determination of thymic production of T cells by quantification of T cell receptor rearrangement excision circles (TRECs). Interestingly, the Rec group showed an increase in percentage of CD4(+) T cells and a decrease in viral load, and recovered LPRs to mitogens and recall antigens, with values similar to those of the LTA group. Moreover, the Rec group produced similar percentages and absolute counts of naive (CD45RA(+)CD62L(+)) CD4(+) and CD8(+) T cells, and TRECs similar to those of the LTA group. In particular, the Rec group produced similar percentages of CD8(+)CD28(-)CD57(+) and CD8(+)CD28(-)CD57(-) T cell subsets compared with controls. Our data indicate that among children who have already progressed to AIDS and severe immunodeficiency but who respond to HAART, the immune system can recover and resemble those of nonprogressors or even uninfected children, in quantitative as well as in functional terms.

The effects of different HIV type 1 strains on human thymic function

Studies of HIV-1-infected humans indicate that the thymus can be infected by HIV-1. In some of these patients, there is a significant CD4(+) T cell decline and a faster disease progression. This phenomenon is more evident in pediatric patients who depend heavily on their thymus for generation of new T cells. We hypothesize that HIV-1 causes T cell regenerative failure within the thymus, which has a profound impact on disease progression. Building on our established human thymopoiesis model, we include dynamic interactions between different HIV-1 strains (R5 and X4) and thymocytes. Our results predict that thymic infection with different HIV-1 strains induces thymic dysfunction to varying degrees, contributing to differences in disease progression as observed in both HIV-1-infected children and adults. Thymic infection in children is more severe than in adults, particularly during X4 infection. This outcome is likely due to both a higher viral load and a more active thymus in pediatric patients. Our results also indicate that a viral strain switch from R5 to X4 induces further deterioration in thymopoiesis. We predict that both viral and host factors play key roles in controlling thymic infection, including strain virulence and health status of the thymus.

Immune recovery in HIV disease: role of the thymus and T cell expansion in immune reconstitution strategies

While the progressive depletion of CD4(+) T cells is the hallmark of the impact of HIV on the immune system, considerable data also point to the loss of T cell function. The question is: Can the immune system recover from this insult and what are the therapeutic strategies available to us to mediate this immune recovery? This review will focus on our current knowledge of immune recovery following treatment with highly active antiretroviral therapy (HAART). Enhancement of thymic function in generating de novo T cell synthesis post-HAART has also emerged as a viable immune recovery strategy. Advances in molecular (T cell receptor excision circle assay) and conventional (computed tomography scans of the thymus) approaches to evaluate the role of the thymus in immune recovery as well as potential agents that might enhance thymic output (interleukin-7, IL-7) will contribute greatly to the assessment of the success of these approaches as immune recovery strategies. In this review, we will integrate this new information in the context of the current strategies for HIV therapy leading to long-term immune reconstitution.

Decreased levels of recent thymic emigrants in peripheral blood of simian immunodeficiency virus-infected macaques correlate with alterations within the thymus

The thymus is responsible for de novo production of CD4(+) and CD8(+) T cells and therefore is essential for T-cell renewal. The goal of this study was to assess the impact of simian immunodeficiency virus (SIV) infection on the production of T cells by the thymus. Levels of recent thymic emigrants within the peripheral blood were assessed through quantification of macaque T-cell receptor excision circles (TREC). Comparison of SIV-infected macaques (n = 15) to uninfected macaques (n = 23) revealed stable or increased TREC levels at 20 to 34 weeks postinfection. Further assessment of SIV-infected macaques (n = 4) determined that TREC levels decreased between 24 and 48 weeks postinfection. Through the assessment of longitudinal time points in three additional SIVmac239-infected macaques, the SIV infection was divided into two distinct phases. During phase 1 (16 to 30 weeks), TREC levels remained stable or increased within both the CD4 and CD8 T-cell populations. During phase 2 (after 16 to 30 weeks), TREC levels declined in both T-cell populations. As has been described for human immunodeficiency virus (HIV)-infected patients, this decline in TREC levels did at times correlate with an increased level of T-cell proliferation (Ki67(+) cells). However, not all TREC decreases could be attributed to increased T-cell proliferation. Further evidence for thymic dysfunction was observed directly in a SIVmac239-infected macaque that succumbed to simian AIDS at 65 weeks postinfection. The thymus of this macaque contained an increased number of memory/effector CD8(+) T cells and an increased level of apoptotic cells. In summary, reduced levels of TREC can be observed beginning at 16 to 30 weeks post-SIV infection and correlate with changes indicative of dysfunction within the thymic tissue. SIV infection of macaques will be a useful model system to elucidate the mechanisms responsible for the thymic dysfunction observed in HIV-infected patients.

Effects of highly active antiretroviral therapy on thymical reconstitution of CD4 T lymphocytes in vertically HIV-infected children

CD4 T-cell percentages, viral load and thymic function measured as T-cell receptor rearrangement excision circle (TREC) levels were determined every 2-3 months in six treated HIV-infected children for 4 years. All children experienced a marked increase in CD4 cell count after therapy, accompanied by a concomitantly marked increase in TREC levels. In children, the decrease in viral load caused by antiviral therapy leads to an increase in CD4 T cells, mainly because of a recovery in the thymic production of new T cells.