Association of syncytium-inducing phenotype of HIV-1 with CD4 cell count, viral load and sociodemographic characteristics

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.

HIV-1 non-R5 tropism correlates with a larger size of the cellular viral reservoir and a detectable residual viremia in patients under suppressive ART

BACKGROUND

The influence of HIV-1 co-receptor usage on the course of therapy in subjects fully responding to ART has been poorly investigated.

OBJECTIVES

To explore the relationship between co-receptor tropism and cellular reservoir size, residual viremia and subsequent virological outcome in ART-treated patients with HIV-1 RNA stable <50 copies/mL.

STUDY DESIGN

Viral co-receptor usage was predicted by viral env DNA sequencing with geno2pheno interpretation (FPR20%) and classified as R5 and non-R5. Total blood-associated HIV-1 DNA levels (log₁₀ copies/10⁶ leukocytes) were measured by qRT-PCR (5'LTR). Residual plasma viremia was categorized as detectable (1-49 cps/mL) or undetectable (<1 copy/mL). Virological rebounds (any HIV-1 RNA >50 copies/mL) were evaluated over 96 weeks.

RESULTS

The study included 116 subjects. Patients with R5 virus (n = 59) and non-R5 virus (n = 57) were homogeneous for the main characteristics except for the lower nadir CD4 cell count in the non-R5 group. Patients with non-R5 variants showed higher levels of HIV-1 DNA as compared to patients with R5 virus: mean 2.47 (95% CI 2.37-2.56) vs 2.17 (2.08-2.26) (p < 0.001). Moreover, a higher proportion of patients in the non-R5 group displayed detectable residual viremia with respect to the R5-group (54.4% vs 32.2%, p = .016). Detectable residual viremia was found to be significantly associated with viral rebounds.

CONCLUSION

The presence of non-R5 viral DNA variants is related to a higher probability of residual viremia and to a larger size of the cellular viral reservoir in this setting. These data highlight a potential role of viral tropism in the monitoring of HIV-1 infection in virologically controlled subject.

Chemokine co-receptor usage in HIV-1-infected treatment-naïve voluntary counselling and testing clients in Southern Taiwan

OBJECTIVE

The goal of this present study was to determine the proportion of CCR5-tropic and CXCR4-tropic viruses and impact of tropism test on clinical presentation, CD4 cell counts, viral load and genotypic drug resistance from drug-naïve, voluntary counselling and testing (VCT) clients in southern Taiwan.

DESIGN

This was a cross-sectional study. Plasma samples were collected from HIV-1-infected patients from January 2013 to December 2013; subjects were recruited from free VCT centres in southern Taiwan.

SETTING

Taiwan.

PARTICIPANTS

Plasma samples from 108 HIV-1-infected, treatment-naïve, VCT clients were analysed. HIV-1 strains were sequenced, genotype resistance was determined by a commercial kit (Viro-seq) and co-receptor tropism (CRT) was predicted by an internet tool geno2pheno[coreceptor], with a 10% false-positive rate as the cut-off. Differences in progression markers, patient characteristics, VCT questionnaires and HIV subtype distribution were evaluated statistically.

RESULTS

All the 108 VCT clients were male with 90% between the ages of 20 and 40 years. Eighty-eight per cent of the patients were men who have sex with men (MSM). The median (IQR) CD4 cell count was 342 cells/µL (221-454) and the viral load was 4.6 log (4.0-5.0). HIV-transmitted drug resistance was found in 9.3% (10/108) of the patients. CRT predictions indicated that 74% of the patients had only R5-tropic strains. CRT was not associated with CD4 cell counts, patient characteristics, VCT questionnaire and transmitted drug resistance. There was a significant difference with regard to viral load at the time of presentation, showing that patients with R5 more often had a higher viral load as compared with those with X4/DM strains (4.6±0.6 log vs 4.33±0.7 log, p=0.036).

CONCLUSIONS

We found that 74% of the VCT clients were infected with R5-tropic virus strains. HIV-transmitted drug resistance was not associated with CRT predictions. Higher viral load at presentation was predictive of R5 co-receptor usage.

Identification of interdependent variables that influence coreceptor switch in R5 SHIV(SF162P3N)-infected macaques

Background

We previously reported that adoption of an “open” envelope glycoprotein (Env) to expose the CD4 binding site for efficient receptor binding and infection of cell targets such as macrophages that express low levels of the receptor represents an early event in the process of coreceptor switch in two rapidly progressing (RP) R5 SHIV_SF162P3N-infected rhesus macaques, releasing or reducing Env structural constraints that have been suggested to limit the pathways available for a change in coreceptor preference. Here we extended these studies to two additional RP monkeys with coreceptor switch and three without to confirm and identify additional factors that facilitated the process of phenotypic conversion.

Results

We found that regardless of coreceptor switching, R5 viruses in SHIV_SF162P3N-infected RP macaques evolved over time to infect macrophages more efficiently; this was accompanied by increased sCD4 sensitivity, with structural changes in the CD4 binding site, the V3 loop and/or the fusion domain of their Envs that are suggestive of better CD4 contact, CCR5 usage and/or virus fusion. However, sCD4-sensitive variants with improved CD4 binding were observed only in RPs with coreceptor switch. Furthermore, cumulative viral load was higher in RPs with than in those without phenotypic switch, with the latter maintaining a longer period of seroconversion.

Conclusions

Our data suggest that the increased virus replication in the RPs with R5-to-X4 conversion increased the rate of virus evolution and reduction in the availability of target cells with optimal CD4 expression heightened the competition for binding to the receptor. In the absence of immunological restrictions, variants that adopt an “open” Env to expose the CD4 binding site for better CD4 use are selected, allowing structural changes that confer CXCR4-use to be manifested. Viral load, change in target cell population during the course of infection and host immune response therefore are interdependent variables that influence R5 virus evolution and coreceptor switch in SHIV_SF162P3N-infected rhesus macaques. Because an "open" Env conformation also renders the virus more susceptible to antibody neutralization, our findings help to explain the infrequent and late appearance of X4 virus in HIV-1 infection when the immune system deteriorates.

Prevalence and clinical associations of CXCR4-using HIV-1 among treatment-naive subtype C-infected women in Botswana

HIV-1 coreceptor use was determined using a phenotypic assay in plasma samples from treatment-naive women infected with subtype C virus who had CD4 cell counts below 200 cells/mm3. Of 148 women, 14.9% were infected with dual/mixed virus; the remainder had R5 virus. A greater proportion of women in the lowest CD4 cell count stratum had dual/mixed virus (P = 0.026); change in coreceptor use after antiretroviral therapy exposure was uncommon. CXCR4-using HIV-1 was less common in subtype C-infected women than reported in subtype B cohorts but was most prevalent in women with the lowest CD4 cell counts.

Decreased CD4 and wide-ranging expression of other immune receptors after HIV-envelope-mediated formation of syncytia in vitro

In human HIV infection, multinucleated cells (syncytia) are formed by fusion of HIV-infected cells with CD4+ cells. In order to examine possible functional implications of syncytia formation for the immune response, the expression of important surface molecules by T-cell syncytia and surrounding cells that remain unfused (bystander cells) was analyzed in cocultures of HIV-Env- and CD4-expressing E6 Jurkat T cells. Fusion partners were differentially labeled with lipophilic probes, and syncytia and bystander cells were identified by flow cytometry. The cellular phenotype and response to activation stimulus after fusion were analyzed with antibodies coupled to third-party fluorochromes. Cocultured unfused E6 cells showed a marked decrease in CD4 expression, suggesting the selective recruitment of cells strongly expressing CD4 into syncytia. However, the incorporated CD4 was not detected in the syncytia, whereas the range of expression of CD28, ICAM-1, CXCR4 and CD3 was wider than that of unfused cells. Limited expression of CD4 in the bystander unfused population, as well as in the newly formed syncytia, would result in limitation of further viral entry and a failure to identify these cells, and it could partially contribute to functional impairment and a decrease in the number of CD4+ T cells in AIDS. Most of the syncytia were viable and expressed CD25 and IL-2 in response to activation by phorbol myristate acetate (PMA) and ionomicyn. Thus, syncytia populations harboring widely heterogeneous levels of receptors would constitute a potential source of anomalous immune function.

CD4-dependent characteristics of coreceptor use and HIV type 1 V3 sequence in a large population of therapy-naive individuals

We investigated the associations between coreceptor use, V3 loop sequence, and CD4 count in a cross-sectional analysis of a large cohort of chronically HIV-infected, treatment-naive patients. HIV coreceptor usage was determined in the last pretherapy plasma sample for 977 individuals initiating HAART in British Columbia, Canada using the Monogram Trofile Tropism assay. Relative light unit (RLU) readouts from the Trofile assay, as well as HIV V3 loop sequence data, were examined as a function of baseline CD4 cell count for 953 (97%) samples with both phenotype and genotype data available. Median CCR5 RLUs were high for both R5 and X4-capable samples, while CXCR4 RLUs were orders of magnitude lower for X4 samples (p < 0.001). CCR5 RLUs in R5 samples (N = 799) increased with decreasing CD4 count (p < 0.001), but did not vary with plasma viral load (pVL) (p = 0.74). In X4 samples (N = 178), CCR5 RLUs decreased with decreasing CD4 count (p = 0.046) and decreasing pVL (p = 0.097), while CXCR4 RLUs increased with decreasing pVL (p = 0.0008) but did not vary with CD4 (p = 0.96). RLUs varied with the presence of substitutions at V3 loop positions 11, 25, and 6-8. The prevalence and impact of substitutions at codons 25 and 6-8 were CD4 dependent as was the presence of amino acid mixtures in the V3; substitutions at position 11 were CD4 independent. Assay RLU measures predictably vary with both immunological and virological parameters. The ability to predict X4 virus using genotypic determinants at positions 25 and 6-8 of the V3 loop is CD4 dependent, while position 11 appears to be CD4 independent.

HIV-1 biological phenotype and predicted coreceptor usage based on V3 loop sequence in paired PBMC and plasma samples

Paired PBMCs and plasma samples from 34 HIV-infected patients were studied to verify the relationship between coreceptor use based on genotyping of V3 region of HIV-1 envelope gp120 and biological phenotype with virus isolation and subsequent correlation to clinical characteristics. The "11/25" rule, geno2pheno and PSSM were compared. All SI patients were HIV-1 subtype B (p=0.04) and had a lower CD4 count than NSI patients (p=0.01), while no differences were observed in mean HIV-RNA (log) (p=0.6). SI phenotype was not associated with AIDS-defining events (p=0.1) or with concurrent antiretroviral therapy (p=0.4). With geno2pheno, which shows the highest sensibility (83%), an X4 or X4/R5 genotype in PBMC DNA was also associated to B-subtype and lower CD4 count (p=0.01) compared to R5 isolates. Based on plasma RNA sequences, the predicted coreceptor usage agreed with PBMC DNA in 79% of cases with the "11/25" rule, 82% with geno2pheno, and 82% with PSSM. A X4 virus in plasma (but not in PBMCs) was significantly associated with HAART in all three methods (p=0.01 for "11/25" rule, p=0.01 for geno2pheno and p=0.03 for PSSM). Due to viral mixtures and/or difficulties in genotype interpretation, current V3 sequence-based methods cannot accurately predict HIV-1 coreceptor use.

Discriminating in vitro cell fusion from cell aggregation by flow cytometry combined with fluorescence resonance energy transfer

Expression of fusion proteins in the plasma membrane enables cells to bind and fuse with surrounding cells to form syncytia. Cell fusion can have important functional outcomes for the interacting cells, as syncytia formation does in AIDS pathogenesis. Studies on cell fusion would be facilitated by a quantitative method able to discriminate between cellular aggregates and bona fide fused cells in a cell population. Flow cytometry with fluorescence resonance energy transfer is applied here for analyzing fusion of HIV-1 envelope-expressing cells with CD4+ Jurkat cells. Fusion partners were labeled with the vital lipophilic fluorescent probes DiO (green) and DiI (red) and FRET is manifested by an enhancement of the DiI red fluorescence intensity in double fluorescent cells, thus allowing discrimination between fused and aggregated cells. The inhibitory effect of anti-CD4 monoclonal antibodies and the inhibitory peptide T-20 upon cell fusion were readily quantified by this technique. This method allows the distinction of fused and aggregated cells even when they are at low frequencies.

[Identification of factors influencing the response of antiretroviral treatment]

OBJECTIVE

The authors had an aim to define the ideal patient profile by determining the factors responsible for an initial variation of CD4 lymphocytes and viral load, and the effect of these factors on the therapeutic response after 12 months of treatment in HIV infected patients.

PATIENTS AND METHOD

A retrospective study was made on data concerning the clinical stage, the HIV phenotype strain, the therapeutic status, and the type of treatment. This data was compared to the CD4 count and the viral load before and after 12 months of treatment.

RESULTS

Initially, CD4 lymphocytes values were low in case of: phenotype SI (p = 0.012), patient in clinical stage C (p < 0.0001), or treated with protease inhibitor (p < 0.0002). The viral loads were high for patients in stage C (p < 0.0002) and treated with protease inhibitor (p < 0.0001). After 12 months of treatment, the increase of CD4 count was lower in patients with phenotype SI (p = 0.05). Furthermore, the viral load was statistically more important in naive patient (p < 0.0001).

CONCLUSION

According to our study, the ideal patient is naive and presents with phenotype NSI.

Does patient sex affect human immunodeficiency virus levels?

We undertook a critical epidemiological review of the available evidence concerning whether women have lower levels of human immunodeficiency virus (HIV) RNA than do men at similar stages of HIV infection. The 13 studies included in this analysis reported viral load measurements in HIV-infected men and women at a single point in time (cross-sectional studies) or over time (longitudinal studies). Seven of the 9 cross-sectional studies demonstrated that women had 0.13-0.35 log(10) ( approximately 2-fold) lower levels of HIV RNA than do men, despite controlling for CD4(+) cell count. Four longitudinal studies revealed that women had 0.33-0.78 log(10) (2- to 6-fold) lower levels of HIV RNA than do men, even when controlling for time since seroconversion. Adjustment for possible confounders of the relationship between sex and viral load, including age, race, mode of virus transmission, and antiretroviral therapy use, did not change this outcome. This finding is significant, because viral loads are frequently used to guide the initiation and modification of antiretroviral therapy.

HAART in HIV-infected patients: restoration of antigen-specific CD4 T-cell responses in vitro is correlated with CD4 memory T-cell reconstitution, whereas improvement in delayed type hypersensitivity is related to a decrease in viraemia

OBJECTIVE

To analyse prospectively the effect of highly active antiretroviral treatment (HAART) on CD4 T-cell responses in vitro and in vivo in HIV-infected patients.

DESIGN

Prospective study with 49 protease inhibitor-naive adult patients. Data were collected at baseline and after 3 and 6 months of HAART.

METHODS

In vitro CD4 T-cell reactivity was analysed by stimulation of peripheral blood mononuclear cells with several antigens. In vivo CD4 T-cell reactivity (delayed type hypersensitivity) was assessed by Multitest Merieux. Both measurements were correlated to CD4 (memory) T-cell count and HIV-1 viraemia.

RESULTS

Restoration of specific CD4 T-cell proliferation was observed in most patients. The in vitro T-cell response was restored more frequently against antigens to which the immune system is constantly exposed (Candida albicans, Mycobacterium tuberculosis, M. avium) as compared with a low-exposure antigen (tetanus toxoid). Overall, delayed type hypersensitivity detection rate increased under HAART. Multivariate analysis showed improvement of antigen-specific T-cell proliferation to be significantly associated with an increase in memory CD4 T-cells, whereas improvement of the delayed type hypersensitivity response was associated with a decrease in plasma HIV-1 RNA.

CONCLUSIONS

HAART for 6 months restored antigen-specific CD4 T-cell response to several antigens. In vitro immune reconstitution was closely correlated with an increase in memory CD4 cells. Restoration of delayed type hypersensitivity was associated with suppression of viraemia. It appears that in addition to expansion of memory CD4 cells, suppression of viraemia following HAART may allow an improved inflammatory reaction, thus providing even stronger immune reconstitution.