Syncytium-inducing Research Articles

Examining HIV progression mechanisms via mathematical approaches


 
 
 The progression of HIV infection to AIDS is unclear and under examined. Many mechanisms have been proposed, including a decline in immune response, increase in replication rate, involution of the thymus, syncytium inducing capacity, activation of the latently infected cell pool, chronic activation of the immune system, and the ability of the virus to infect other immune system cells. The significance of each mechanism in combination has not been studied. We develop a simple HIV viral dynamics model incorporating proposed mechanisms as parameters that are allowed to vary. In the entire parameter space, we derive two formulae for the basic reproduction number (R0) by considering the infection starting with a single infected CD4 T cell and a single virion, respectively. We show that both formulae are equivalent. We derive analytical conditions for the occurrence of backward and forward bifurcations. To investigate the influence of the proposed mechanisms to the HIV progression, we perform uncertainty and sensitivity analysis for all parameters and conduct a bifurcation analysis on all parameters that are shown to be significant, in combination, to explore various HIV/AIDS progression dynamics.
 
 

Isolation and biological characterization of human immunodeficiency virus type 1 from Cubans asymptomatic patients

Isolation and biological characterization of human immunodeficiency virus type 1 from Cubans asymptomatic patients

HIV Progression to AIDS: Bioinformatics Approach to Determining the Mechanism of Action

The mechanism by which HIV infection transforms into AIDS disease is unclear. Several factors such as the decline in immune response, increase in replication rate, Syncytium inducing capacity and ability of the viruses to infect tumour cell lines are found to be associated with HIV progression to AIDS. What has not been investigated is the role of an increase in affinity for the CD4+ T cells by the HIV-1 T cell lymphocyte-loving (T-tropic) viruses. They are known to be mutants of the Macrophage-loving (M-tropic) viruses and dominate the late stage of the HIV infection in the disease progression. To elucidate the mechanism by which HIV is transformed into AIDS, this role is examined by using the Resonant Recognition Model (RRM). This is achieved by comparing the degree of affinity between the host CD4 and the gp120 from the HIV-1 M-tropic and HIV-1 T-tropic viruses as well as the isolates of HIV-2 and Simian immunodeficiency virus (SIV). The results reveal that only HIV-1 T-tropic viruses bind effectively to the CD4 suggesting that T-tropic viruses, which were identified to have mutated from the M-tropic viruses, acquire enhanced and long-lasting attachment to the CD4. This sustained affinity brings about continued attack on the diminishing CD4 until the immune system of the host collapses, which manifests clinically as AIDS. The findings therefore suggest an approach that should target the Variable region 3 (V3) of the HIV-1 gp120 at the early stage of the infection as a part of the HIV/AIDS management procedure. This procedure is essential as early initiation of HIV/AIDS therapy is generally assumed to prevent the spread of the virus and deterioration of the host immunity. The study is expected to help better understand the HIV pathogenesis and re-strategise pharmaceutical approaches to designing new HIV/AIDS therapeutic interventions.

HIV Progression to AIDS: Bioinformatics Approach to Determining the Mechanism of Action

The mechanism by which HIV infection transforms into AIDS disease is unclear. Several factors such as the decline in immune response, increase in replication rate, Syncytium inducing capacity and ability of the viruses to infect tumour cell lines are found to be associated with HIV progression to AIDS. What has not been investigated is the role of an increase in affinity for the CD4+ T cells by the HIV-1 T cell lymphocyte-loving (T-tropic) viruses. They are known to be mutants of the Macrophage-loving (M-tropic) viruses and dominate the late stage of the HIV infection in the disease progression. To elucidate the mechanism by which HIV is transformed into AIDS, this role is examined by using the Resonant Recognition Model (RRM). This is achieved by comparing the degree of affinity between the host CD4 and the gp120 from the HIV-1 M-tropic and HIV-1 T-tropic viruses as well as the isolates of HIV-2 and Simian immunodeficiency virus (SIV). The results reveal that only HIV-1 T-tropic viruses bind effectively to the CD4 suggesting that T-tropic viruses, which were identified to have mutated from the M-tropic viruses, acquire enhanced and long-lasting attachment to the CD4. This sustained affinity brings about continued attack on the diminishing CD4 until the immune system of the host collapses, which manifests clinically as AIDS. The findings therefore suggest an approach that should target the Variable region 3 (V3) of the HIV-1 gp120 at the early stage of the infection as a part of the HIV/AIDS management procedure. This procedure is essential as early initiation of HIV/AIDS therapy is generally assumed to prevent the spread of the virus and deterioration of the host immunity. The study is expected to help better understand the HIV pathogenesis and re-strategise pharmaceutical approaches to designing new HIV/AIDS therapeutic interventions. Keywords: CD4, gp120, Macrophage-loving viruses, Resonant Recognition Model, and T-cell lymphocyte-loving viruses, HIV, CF, immune, V3

Subtype-specific differences in human immunodeficiency virus type 1 co-receptor usage in Northern Kenya

Background HIV-1 phenotype variability plays an important role in HIV-1 transmission and pathogenesis of AIDS. The basis of heterogeneity between the phenotypes is known to be the differential use of chemokine receptors as co-receptors for viral entry. Beta Chemokine receptor-5 (CCR5) using variants are associated with acute infections, macrophage tropism, non syncytium inducing (NSI) phenotype and slow progression to AIDS. Alpha chemokine receptor-4 (CXCR4) using variants evolve later in infection in about 50 % of the patients and are associated with T cell lines tropism, syncytium induction, accelerated T cell depletion and Rapid progression to AIDS. HIV-1 co-receptor usage and phenotypes are mapped in the third variable region (V3) of the gp120 env gene. Methods One hundred and thirty five (135) whole blood samples were collected from HIV-1 infected patients in Northern Kenya. Proviral DNA was extracted using DNazol and ethanol precipitation. HIV-1 V3 region was amplified by nested PCR using C2V3 primers. Amplicons were sequenced directly using Big Dye technology in the ABI Prism Genetic Analyzer to generate gp120 V3 loop sequences. Bioinformatics tools were used to determine co-receptor usage from the sequences obtained. Results CXCR4 usage was most dominant with 94 out of 135 samples(69.6 %) using this co-receptor compared to CCR5 which was used by 29 of the 135 (21.8 %) samples and dual co-receptor usage found in 12 of the 135(8.6%) samples tested. Conclusion Most patients were inferred to be in late stages of infection and likely to be rapidly progressing to AIDS. Based on these results from co-receptor usage data, HIV-1 incidence rate was likely to be low. Co-receptor usage was observed to be associated with HIV-1 subtypes. Poor alignment of the Northern Kenya sequences with the training data for the classifier software necessitates the need for development of Bioinformatic software relevant for locally circulating HIV-1 subtypes.

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.

Performance of Genotypic Algorithms for Predicting HIV-1 Tropism Measured against the Enhanced-Sensitivity Trofile Coreceptor Tropism Assay

The objectives of this study were to assess the performance of genotypic algorithms for predicting CXCR4-using virus, with enhanced sensitivity Trofile HIV coreceptor tropism assay (ES Trofile) as the reference, and to compare the concordance/accuracy of genotypic tests with ES Trofile and with the original Trofile assay. Paired phenotypic and genotypic determinations of HIV-1 coreceptor usage were compared in plasma samples from HIV-1-infected patients. Sequencing of the third hypervariable (V3) loop of the viral gene and phenotypic assays were performed for each sample. Genotypic rules used to predict tropism were Geno2pheno (false-positive rate at 1 to 20%), position-specific scoring matrix X4R5 (PSSM(X4R5)) and PSSM(sinsi) (where "sinsi" stands for syncytium inducing and non-syncytium inducing), and the 11/25, 11/24/25, and net charge rules. Two hundred forty-four phenotypic and genotypic samples were tested. Coreceptor usage was obtained from ES Trofile for 145 (59%) samples and from Trofile for 99 (41%) samples. The highest concordance (82.6%) was obtained with PSSM(X4R5) when ES Trofile was used as the reference. Geno2pheno at a 20% false-positive rate showed the highest sensitivity (76.7%) for CXCR4-using virus detection with ES Trofile. Samples from naïve subjects and those with CD4 cell counts between 200 and 500 cells/mm(3) showed the best predictive performance. Overall, the accuracy of the bioinformatics tools to detect CXCR4-using virus was similar for ES Trofile and Trofile; however, the negative predictive values for genotypic tools with ES Trofile were slightly higher than they were with Trofile. The accuracy of genotypic algorithms for detecting CXCR4-using viruses is high when using ES Trofile as the reference. Results are similar to those obtained with Trofile. The concordance with ES Trofile is better with higher CD4 cell counts and nonexposure to antiretroviral therapy.

Short Communication: Biological and Genetic Characterization of HIV Type 1 Subtype B and Nonsubtype B Transmitted Viruses: Usefulness for Vaccine Candidate Assessment

Due to the extraordinary degree of genetic diversity of HIV-1 and the structural complexity of its envelope glycoproteins, designing an effective vaccine is difficult, requiring the development of viral reagents to assess vaccine-elicited neutralizing antibodies. The aim of this study was to improve on our previously developed panel of HIV-1 strains of different genetic forms, focusing on strains from acute and recently acquired infections as the most representative of the transmitted viruses. HIV-1 primary isolates were expanded in peripheral blood mononuclear cells. Viral stocks of 40 ml each were produced. Syncytium-inducing (SI) phenotype, coreceptor use, and TCID(50)/ml were determined. Near full-length HIV-1 genomes were amplified by RT-nested PCR in four overlapping segments. Phylogenetic analyses were performed with neighbor-joining trees and bootscanning. Forty-four HIV-1 strains were included in the panel. Twenty-four (54.1%) strains were from early infections (16 acute and 8 recent); of them, 21 (87%) were sexually transmitted. NSI/R5 phenotype was detected in 37 (84.1%) viruses and SI/R5,X4 in another 7 (15.9%). TCID(50)/ml ranged between 10(4) and 10(6.6). Twelve different genetic forms constituted this panel: subtypes A1, B, C, F1, and G; circulating recombinant forms CRF02_AG, CRF14_BG, and CRF24_BG; and unique recombinant forms CRF02_AG/A3, BF1, CRF12_BF/B, and DF1G. In conclusion, in this study, we report the development of a comprehensive and well-characterized panel of HIV-1 isolates for assessing neutralization in HIV vaccine research. This panel is available for distribution through the Programme EVA Centre for AIDS Reagents, National Institute for Biological Standard and Control (NIBSC).

Construction and characterization of a full-length infectious clone from a fast-replicating, X4-tropic HIV-1 subtype B′ isolate

In HIV-1 epidemics in China, HIV-1 subtype B' is the most predominant subtype circulating in intravenous drug users. In this study, we constructed an HIV-1 full-length infectious molecular clone based on the primary virus LWJ, which was isolated from an HIV-infected patient in Fujian Province, China. Phylogenetic and bootscanning analysis of the viral sequence revealed that the isolate LWJ belonged to HIV-1 subtype B'. The infectious clone was designated as "pLWJ". The virus (LWJ-c) produced from this infectious clone by in vitro transfection of 293T cells could infect both human peripheral blood mononuclear cells (PBMCs) and human the T cell line MT4. Interestingly, the cloned LWJ-c virus utilized CXCR4 as its co-receptor and could replicate in vitro with similar efficiency and kinetics compared to its parental primary isolate LWJ as well as the clade B reference virus NL4-3. The LWJ-c virus could also cause cytopathic effects in both PBMCs and MT cells. Sequence analysis of the envelope glycoprotein of pLWJ showed that a conserved GPGR motif and an arginine at position 11 were present in the V3 loop, which was consistent with previous reports regarding CXCR4 co-receptor usage and syncytium-inducing (SI) phenotype. Thus, the infectious clone represents a fast-replicating, high-producing, CXCR4-tropic and syncytium-inducing isolate. Given the prevalence of HIV-1 subtype B' in China, this infectious clone can be a very useful tool to provide a versatile molecular model for research focusing on the biological properties of this subtype.

HIV-1 with Predicted CXCR4 Genotype Identified in Clade C from India

HIV-1 uses co-receptors CCR5 and CXCR4 in addition to CD4 for viral entry into cells. CCR5 is used in the early stages of HIV-1 infection, but viruses that utilize CXCR4 for viral entry emerge in the later stages. This is not common among clade C strains, with previous data from India showing the absence of the emergence of CXCR4-using strains. Sequence analysis has demonstrated that the V3 loop plays a very important role in determining the syncytium-inducing (SI) phenotype. The V3 region of the SI variants were observed to have positively charged amino acids at positions 11 and/or 25 and also a overall higher charge. This study looked at co-receptor usage among HIV-1 strains in India from individuals who were antiretroviral therapy (ART) naïve and those not responding to ART. Amplification and sequencing of the HIV-1 env gp120 V3 region was done on 40 ART-naïve individuals, who were selected for the study based on their CD4 counts, and eight patients who had not responded to ART. The sequences were submitted to Geno2Pheno and Web PSSM. The pol gene sequences of these strains were submitted to the REGA HIV-1 subtyping tool. Forty-seven strains were identified as clade C and one strain as clade A1. Geno2Pheno identified three CXCR4-using strains, and the Web PSSM clade C matrix identified two. We report, for the first time, CXCR4-using strains among HIV-1 clade C strains circulating in India.

TR1.3 Viral Pathogenesis and Syncytium Formation Are Linked to Env-Gag Cooperation

Infection with murine leukemia virus (MLV) TR1.3 or the related molecular construct W102G causes severe neuropathology in vivo. Infection is causally linked to the development of extensive syncytia in brain capillary endothelial cells (BCEC). These viruses also induce cell fusion of murine cell lines, such as SC-1 and NIH 3T3, which are otherwise resistant to MLV-induced syncytium formation. Although the virulence of these viruses maps within the env gene, the mechanism of fusion enhancement is not fully determined. To this end, we examined the capacity of the syncytium-inducing (SI) TR1.3 and W102G MLVs to overcome the fusion inhibitory activity inherent in the full-length Env cytoplasmic tail. These studies showed that the TR1.3 and W102G Envs did not induce premature cleavage of p2E, nor did they override p2E fusion inhibition. Indeed, in the presence of mutations that disrupt p2E function, the TR1.3 and W102G Envs significantly increased the extent of cell fusion compared to that with the non-syncytium-inducing MLV FB29. Surprisingly, we also observed that TR1.3 and W102G Envs failed to elicit syncytium formation in these in vitro assays. Coexpression of gag-pol with env restored syncytium formation, and accordingly, mutations within gag-pol were used to examine the minimal functional requirements for the SI phenotype. The results indicate that both gag-dependent particle budding and cleavage of p2E are required to activate the SI phenotype of TR1.3 and W102G viruses. Collectively, these data suggest that the TR1.3 and W102G viruses induce cell fusion by the fusion-from-without pathway.

R5 to X4 coreceptor switch of human immunodeficiency virus type 1 B’ and Bʼ/C recombinant subtype isolates in China

he chemokine receptors CCR5 and CXCR4 play an important role as coreceptors for human immunodeficiency virus type 1 (HIV-1) entring into cells. HIV-1 isolates can be distinguished by the chemokine coreceptors. Nonsyncytium inducing (NSI), macrophage tropic viruses utilizing CCR5, are called R5 viruses; syncytium inducing (SI) isolates use CXCR4 and known as X4 viruses. R5 viruses generally are associated with latent stage of infection and X4 viruses with later, more severe stages of infection. This phenotypic switch from R5 to X4 correlated with the decreased CD4

Association of IL-7 with disease progression in Chinese HIV-1 seropositive individuals

Elevated levels of interleukin-7 (IL-7) have been correlated with CD4(+) T cell depletion and the emergence of syncytium-inducing (SI) variants in human immunodeficiency virus type-1 (HIV-1) infection, and suggested as an indicator of acquired immunodeficiency syndrome (AIDS) disease progression. Therefore, we investigated the effects of IL-7 on disease progression and virus phenotype in Chinese HIV/AIDS patients. In a cross-sectional study of 71 untreated HIV-1 seropositive individuals and 12 healthy donors, plasma IL-7 levels were determined by an ultra sensitive enzyme-linked immunosorbent assay (ELISA), and its relations to CD4(+) T cells, CD8(+) T cells, plasma viral loads and HIV phenotypes were analyzed. Significant higher IL-7 levels were found in Chinese HIV/AIDS patients [(3.33 +/- 3.60) pg/ml] than those of health controls [(1.2 +/- 0.81) pg/ml] (P < 0.05), and IL-7 levels were inversely associated with CD4(+) T cell counts (r = -0.497, P < 0.01). Furthermore, IL-7 levels were significant higher in patients with SI variants [(9.12 +/- 4.55) pg/ml] than those with non-syncytium-inducing variants [(1.50 +/- 2.69) pg/ml] (P < 0.01). Increased IL-7 levels were found in Chinese HIV/AIDS patients and significantly associated with disease progression, thus increased IL-7 plasma levels may indicate disease progression.

Isolation and biological characterization of HIV-1 BG intersubtype recombinants and other genetic forms circulating in Galicia, Spain

The biological characteristics of HIV-1 primary isolates of different recombinant forms (RFs) and non-B subtypes from Galicia, Spain, were investigated and the relationships between biological phenotype and evolution of infection were determined. Peripheral blood mononuclear cells (PBMCs) were obtained during the follow-up of 32 patients infected with HIV-1 non-subtype B genetic forms, characterized in partial sequences of pol (protease-reverse transcriptase) and env V3 region: 12 (37.5%) circulating RFs (CRFs), 9 (28.1%) unique RFs (URFs), and 11(34.4%) non-B subtypes. Primary isolates were obtained by coculture with donor PBMCs. Syncytium-inducing (SI) phenotype was examined in MT2 cell line and coreceptor use in GHOST and U87.CD4 cells. Fifty percent of tissue culture infective dose (TCID(50)) and viral phenotype based on V3 net charge and Geno2pheno(coreceptor) bioinformatic method were determined. Fifty-four HIV-1 primary isolates were obtained. CRF14_BG and BG URFs represented the largest group, being all SI/X4, independently of the CD4+ cell count, viral load, or the duration of infection. By contrast, 10 of 11 CRF02_AG viruses were NSI/R5. The prediction of co-receptor use was concordant with biological characterization in all NSI/R5 and in 23 of 26 SI/X4 isolates. The presence of SI/X4 or SI/X4,R5 isolates at early stages of the infection in addition to a decrease in CD4+ counts below 500 cells/microl between 2 and 6 years since diagnosis was observed in all patients infected with CRF14_BG and BG URFs. These data contrast with the usual progression in B subtype infections, in which SI/X4 viruses rarely predominate in the early years of HIV-1 infection.

Single-Round HIV Type 1 Neutralization Measured by ELISPOT Technique in Primary Human Cells

To accurately quantify HIV-1 neutralizing antibody titers in primary human cells, we developed a single round, focus-forming unit (FFU) reduction assay in human peripheral blood mononuclear cells (PBMC). Infected PBMC were enumerated by a reverse ELISPOT technique in which they were incubated under agarose in the presence of a protease inhibitor in anti-p24 antibody-coated microtiter plates. Viral p24, secreted in the immediate vicinity of infected cells and captured by immobilized antibodies, was subsequently stained using gold-labeled anti-p24-antibody and a precipitating silver substrate. The resulting spots were counted visually, without the aid of a microscope, and percent neutralization titers were determined using curve-fitting software. Results of this ELISPOT neutralization assay (ENA) for 15 HIV-positive human specimens were compared with results from a standard PBMC neutralization assay (standard assay) that measured neutralization as a function of p24 concentration by enzyme immunoassay (EIA). The ENA measures FFU reduction of both syncytium-inducing (SI) and non-syncytium-inducing (NSI) primary isolates. Completed assay plates may be retained as a physical record of results or saved as an image using a flat-bed computer scanner.

Indian primary HIV-2 isolates and relationship between V3 genotype, biological phenotype and coreceptor usage

The chemokine coreceptors play a significant role in HIV entry and pathogenesis. The V3 region of HIV envelope glycoprotein is considered as a principal determinant for viral phenotype and tropism. The present study describes lack of association between the V3 genotype and viral phenotype of 18 Indian HIV-2 isolates. The viruses were isolated, confirmed by PCR and the HIV subtypes were determined by sequencing V3 region of the env gene. The coreceptor usage and syncytium inducing (SI) capacity of isolates was determined. Our study indicated that CCR5 coreceptor usage and NSI phenotype is predominant among Indian HIV-2 isolates obtained from patients in the early stage of infection. Two of the four HIV-2 isolates obtained from the late stage patients were SI and dual tropic. Phylogenetic analysis of these isolates revealed close relatedness to the isolates from western and southern India.

Differential effects of R5 and X4 human immunodeficiency virus type 1 infection on CD4+ cell proliferation and activation

Human immunodeficiency virus type 1 (HIV-1) isolates can be distinguished by their chemokine coreceptor usage. Non-syncytium-inducing (NSI), macrophage-tropic viruses utilize CCR5 and are called R5 viruses; syncytium-inducing (SI) isolates use CXCR4 and are known as X4 viruses. R5 and X4 HIV isolates are both transmitted but, in most cases, R5 viruses predominate in the blood prior to the development of AIDS-related pathogenesis. The reason for the selective growth of the R5 strain is not known, but could reflect a replication advantage of R5 viruses over X4 viruses in CD4+ cells. To explore this possibility, eight phenotypically distinct viruses were used to infect CD4+ cells and cellular proliferation and activation were evaluated. In unstimulated CD4+ cells, R5 virus isolates increased the level of cell activation compared with X4 virus isolates and uninfected control cells. In CD4+ cells that were stimulated with interleukin 2, both R5 and X4 viruses were found to decrease the level of cell proliferation and reduce the majority of the activation markers studied when compared with uninfected control CD4+ cells from the same donors. However, although equal amounts of CD4+ cells were infected, R5 virus-infected CD4+ cells showed a two- to fourfold increase in cellular proliferation over X4 viruses, as measured by [3H]thymidine incorporation (P=0.001) and nuclear expression of Ki67 (P=0.001). In addition, a larger proportion of CD4+ T cells infected with R5 viruses had significantly higher levels of activation-marker expression (e.g. CD25, CD71 and HLA-DR) than CD4+ T lymphocytes infected with X4 viruses (P<0.02). Taken together, these results indicate that CD4+ cells infected with R5 virus isolates may have a selective advantage over X4 virus-infected CD4+ T cells for survival and, hence, virus spread.

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

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. 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. 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. 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.

High IL-7 plasma levels may induce and predict the emergence of HIV-1 virulent strains in pediatric infection

HIV-1 infection results in severe immunodeficiency when T-cell loss cannot be compensated. IL-7 is one of the main cytokines involved in the maintenance of T-cell homeostasis. However, IL-7 can also enhance HIV-1 replication in vivo and lead to an accelerated progression of AIDS. The aim of our study was to evaluate if the increase of IL-7 levels in response to CD4+ T cell depletion could favor the emergence of HIV-1 strains with more aggressive phenotypes in pediatric infection. Plasma IL-7 levels were measured in 42 HIV-1 vertically infected infants at different times of infection, and HIV-1 isolates were obtained from primary cell cultures to determine replication rate and syncytium-inducing (SI) capability on MT-2 cell line. IL-7 levels were significantly higher in infants harboring HIV-1 SI strains compared to those with non-syncytium-inducing (NSI) viruses (p<0.0001). Likewise, IL-7 levels were higher in infants with rapid replicating viral strains versus those with slow replicating viruses (p=0.0006). Despite the strong negative correlation between IL-7 levels and CD4+ T lymphocyte counts (r=-0.55, p=0.0001), covariance analysis demonstrated that the high levels of IL-7 were associated with more virulent phenotype features (SI and rapid replicating strains) independently of CD4+ T cell depletion. In 19 of the 42 infants, longitudinal follow-up studies showed that SI to NSI phenotype switch can occur after HAART administration, with a reduction in IL-7 levels and an increase in CD4+ T cell counts. IL-7 response to T-cell depletion may enhance T-cell production, but at the same time may foster HIV-1 disease progression favoring the emergence of more virulent HIV-1 strains characterized by SI capability and rapid replication rate.

Longitudinal Assessment of Immune Response and Viral Characteristics in HIV-Infected Patients with Prolonged CD4+/Viral Load Discordance

Although suppression of HIV-1 RNA below the limit of detection is associated with optimal outcomes, many patients can maintain or increase their CD4(+) count for prolonged time periods in the presence of persistent low-level viremia. We followed seven patients with prolonged (>5 years) discordant CD4(+)/viral load (VL) responses on protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) prospectively for 1 year to assess evolution of immune function, viral phenotype, replication capacity (RC), and resistance profile. Immune function was assessed by qualitative and quantitative measurement of cellular activation (CD38(+)HLA-DR(+) and CD38 antibodies bound per cell), and the interferon (IFN)-() ELISpot assay. Presence of syncytium-inducing (SI) or nonsyncytium-inducing (NSI) viral strains was determined by MT-2 cell culture. RC was measured by a modified rapid recombinant virus assay. The resistance profile was characterized by both genotypic and phenotypic analysis. Over the year of follow-up, IFN-() production to gag persisted, responses to other HIV antigens increased, and markers of cellular activation did not change. NSI virus predominated. The genotypic (GSS) and phenotypic (PSS) susceptibility scores remained stable. Evolution of RC was variable over the year of follow-up, but the RC of viruses remained well below that of wild-type clinical isolates. Thus, CD4(+)/VL discordance can be maintained for periods exceeding 5 years in some patients receiving PI-based HAART without significant evolution of HIV resistance.