Interleukin-7 in plasma correlates with CD4 T-cell depletion and may be associated with emergence of syncytium-inducing variants in human immunodeficiency virus type 1-positive individuals

Identifying physiological tissue niches that support the HIV reservoir in T cells

Successful antiretroviral therapy (ART) can efficiently suppress Human Immunodeficiency Virus-1 (HIV-1) replication to undetectable levels, but rare populations of infected memory CD4+ T cells continue to persist, complicating viral eradication efforts. Memory T cells utilize distinct homing and adhesion molecules to enter, exit, or establish residence at diverse tissue sites, integrating cellular and environmental cues that maintain homeostasis and life-long protection against pathogens. Critical roles for T cell receptor and cytokine signals driving clonal expansion and memory generation during immunity generation are well established, but whether HIV-infected T cells can utilize similar mechanisms for their own long-term survival is unclear. How infected, but transcriptionally silent T cells maintain their recirculation potential through blood and peripheral tissues, or whether they acquire new capabilities to establish unique peripheral tissue niches, is also not well understood. In this review, we will discuss the cellular and molecular cues that are important for memory T cell homeostasis and highlight opportunities for HIV to hijack normal immunological processes to establish long-term viral persistence.

Immunomodulation with IL-7 and IL-15 in HIV-1 infection

Immunomodulating agents are substances that modify the host immune responses in diseases such as infections, autoimmune conditions and cancers. Immunomodulators can be divided into two main groups: 1) immunostimulators that activate the immune system such as cytokines, toll-like receptor agonists and immune checkpoint blockers; and 2) immunosuppressors that dampen an overactive immune system such as corticosteroids and cytokine-blocking antibodies. In this review, we have focussed on the two primarily T and natural killer (NK) cell homeostatic cytokines: interleukin-7 (IL-7) and -15 (IL-15). These cytokines are immunostimulators which act on immune cells independently of the presence or absence of antigen. In vivo studies have shown that IL-7 administration enhances proliferation of circulating T cells whereas IL-15 agonists enhance the proliferation and function of NK and CD8+ T cells. Both IL-7 and IL-15 therapies have been tested as single interventions in HIV-1 cure-related clinical trials. In this review, we explore whether IL-7 and IL-15 could be part of the therapeutic approaches towards HIV-1 remission.

Schlafen 12 restricts HIV-1 latency reversal by a codon-usage dependent post-transcriptional block in CD4+ T cells

Latency is a major barrier towards virus elimination in HIV-1-infected individuals. Yet, the mechanisms that contribute to the maintenance of HIV-1 latency are incompletely understood. Here we describe the Schlafen 12 protein (SLFN12) as an HIV-1 restriction factor that establishes a post-transcriptional block in HIV-1-infected cells and thereby inhibits HIV-1 replication and virus reactivation from latently infected cells. The inhibitory activity is dependent on the HIV-1 codon usage and on the SLFN12 RNase active sites. Within HIV-1-infected individuals, SLFN12 expression in PBMCs correlated with HIV-1 plasma viral loads and proviral loads suggesting a link with the general activation of the immune system. Using an RNA FISH-Flow HIV-1 reactivation assay, we demonstrate that SLFN12 expression is enriched in infected cells positive for HIV-1 transcripts but negative for HIV-1 proteins. Thus, codon-usage dependent translation inhibition of HIV-1 proteins participates in HIV-1 latency and can restrict the amount of virus release after latency reversal.

Cellular and molecular insights into incomplete immune recovery in HIV/AIDS patients

Highly active antiretroviral therapy (ART) can effectively inhibit virus replication and restore immune function in most people living with human immunodeficiency virus (HIV). However, an important proportion of patients fail to achieve a satisfactory increase in CD4⁺ T cell counts. This state is called incomplete immune reconstitution or immunological nonresponse (INR). Patients with INR have an increased risk of clinical progression and higher rates of mortality. Despite widespread attention to INR, the precise mechanisms remain unclear. In this review, we will discuss the alterations in the quantity and quality of CD4⁺ T as well as multiple immunocytes, changes in soluble molecules and cytokines, and their relationship with INR, aimed to provide cellular and molecular insights into incomplete immune reconstitution.

Plasma interleukin-7 correlation with human immunodeficiency virus RNA and CD4+ T cell counts, and interleukin-5 with circulating hepatitis B virus DNA may have implications in viral control

Chronic viral infections represent a leading cause of global morbidity and mortality. Chronic HBV, HCV, and HIV infections result in cytokine perturbations that may hold key implications in understanding the complex disease mechanisms driving virus persistence and/or resolution. Here, we determined the levels of various plasma cytokines using a commercial Bio-Plex Luminex cytokine array in chronic HBV (n = 30), HCV (n = 15), and HIV (n = 40) infections and correlated with corresponding plasma viral loads (PVLs) and liver parameters. We observed differential perturbations in cytokine profiles among the study groups. The cytokines levels positively correlated with PVL and liver transaminases. The monocyte-derived cytokines viz., MIP-1β, IL-8, and TNF-α, and Th2 cytokines like IL-4, IL-5, and IL-13 showed a better correlation with liver enzymes as compared to their corresponding PVLs. Our investigation also identified two cytokines viz., IL-5 and IL-7 that inversely correlated with HBV DNA and HIV PVLs, respectively. Regression analysis adjusted for age showed that every increase of IL-5 by one unit was associated with a reduction in HBV PVL by log10 0.4, whereas, every elevation by a unit of IL-7 was associated with decreased HIV PVL by log10 2.5. We also found that IL-7 levels correlated positively with absolute CD4+ T cell counts in HIV-infected patients. We concluded that plasma IL-5 and IL-7 may likely have a key role on viral control in HBV and HIV infections, respectively. A noteworthy increase in cytokines appears to bear protective and pathological significance, and indeed is reflective of the host's versatile immune armory against viral persistence.

CD8 T Cell Virus Inhibition Assay Protocol

The human immunodeficiency virus (HIV)-1 viral inhibition assay (VIA) measures CD8⁺ T cell-mediated inhibition of HIV replication in CD4⁺ T cells and is increasingly used for clinical testing of HIV vaccines and immunotherapies. Different VIAs that differ in length of CD8:CD4 T cell culture periods (6-13 days), purity of CD4 cultures [isolated CD4⁺ T cells or CD8⁺ depleted peripheral blood mononuclear cells (PBMCs)], HIV strains (laboratory strains, isolates, reporter viruses) and read-outs of virus inhibition (p24 ELISA, intracellular measurement of p24, luciferase reporter expression, and viral gag RNA) have been reported. Here, we describe multiple modifications to a 7-day VIA protocol, the most impactful being the introduction of independent replicate cultures for both HIV infected-CD4 (HIV-CD4) and HIV-CD4:CD8 T cell cultures. Virus inhibition was quantified using a ratio of weighted averages of p24⁺ cells in replicate cultures and the corresponding 95% confidence intervals. We identify methodological and analysis changes that could be incorporated into other protocols to improve assay reproducibility. We found that in people living with HIV (PLWH) on antiretroviral therapy (ART), CD8 T cell virus inhibition was largely stable over time, supporting the use of this assay and/or analysis methods to examine therapeutic interventions. Graphic abstract.

Characteristics of suboptimal immune response after initiating antiretroviral therapy among people living with HIV with a pre-treatment CD4 T cell count <200 ​cells/mm3 in Thailand

Background

Complete recovery of the CD4 T cell count is uncommon among chronically HIV-infected individuals with very low pre-treatment CD4 count. We studied the prevalence of chronically immune recovery and its associated factors including immune characteristics chronic HIV-infected Thais.

Methods

Treatment-naïve participants (n ​= ​375) from the HIV-NAT 006 cohort with a pre-treatment CD4 T cell count after initiating antiretroviral therapy (ART) and having achieved a suppressed viremia (HIV-RNA level ​< ​400 copies/mL) were retrospectively followed at the Thai Red Cross AIDS Research Centre, Bangkok, Thailand. Suboptimal immune recovery (SIR) was defined as having a CD4⁺ T cell count <200 ​cells/mm³ for 3 years after ART initiation. A case-control sub-study matched for age, sex and pre-ART CD4 T cell count was conducted to compare immunological characteristics between SIR (n ​= ​17) and non-SIR (n ​= ​24) participants. Immunological biomarkers such as interleukin-7 (IL-7) and soluble CD14 (sCD14) and other covariates including cytomegalovirus (CMV) DNA level, baseline hemoglobin level, hepatitis B and C co-infections, and T cell subsets associated with immune activation and exhaustion were evaluated.

Results

Among 375 participants with pre-ART CD4 T cell counts < 200 ​cells/mm³, the prevalence of SIR was 39.7%, 19.7% and 7.7% at years 1, 2 and 3 after starting ART, respectively. In a multivariate analysis, a pre-ART CD4 T cell count ≤100 ​cells/mm³ (adjusted odds ratio [aOR] 9.45, 95% CI 2.92–30.61, p ​< ​0.001), older age (aOR 1.07, 95% CI 1.01–1.13, p ​= ​0.029) and baseline HIV-RNA level (aOR 0.36, 95% CI 0.21–0.59, p ​< ​0.001) were independently associated with SIR at year 3 after ART initiation. In the matched case-control sub-study (cases ​= ​17, controls ​= ​24), there was a higher prevalence of hepatitis C co-infection (18.8% vs. 0%, p ​= ​0.05), lower sCD14 levels (mean, 6.23 vs. 6.27 log₁₀ ​pg/mL, p ​= ​0.04), lower CD8 T cell counts (mean, 514 vs. 876, p ​= ​0.0003), lower CD4/CD8 T cell ratio (mean, 0.27 vs. 0.41, p ​= ​0.01) and higher expression of PD1 on CD8⁺ T cells (74.2% vs. 65.1%, p ​= ​0.02) observed in SIR participants compared to their non-SIR counterparts at year 3 after ART initiation.

Conclusions

Nearly 10% of the study participants who had achieved virological suppression failed to recover a CD4 T cell count > 200 cells/mm³ after 3 years of ART which was with a very low pre-ART CD4 T cell count and older age. The long-term clinical outcomes of SIR participants need to be further explored.

The Effect of Antiretroviral Therapy on IL-6, IL-1β, TNF-α, IFN-γ Levels and their Relationship with HIV-RNA and CD4+ T Cells in HIV Patients

BACKGROUND

Serum cytokine levels over the course of HIV infection usually increase with immunosuppression and decrease after antiretroviral treatment (ART).

OBJECTIVES

The aim of the study is to compare cytokine levels between HIV-infected patients (HIP) and controls and investigate the relationship between CD4+T cell count, HIV-RNA levels, and cytokine levels.

METHODS

The study subjects comprised ART-naive HIP (n=30) with no comorbidities and age-and sex-matched healthy controls. We measured levels of IL-6, IL-1β, TNF-α, and IFN-γ in serum samples of HIP at the beginning and at month 6 of ART and in controls.

RESULTS

The mean age of the study subjects was 38.7 ±10.3 years, with men making up 86.7% of the study subjects (n=26). IL-6, IL-1β, and TNF-α levels were significantly higher in both ART-naive (p<0.001, p=0.002, p=0.001) and ART-experienced HIP (p<0.001) than controls. The IFN-γ level was lower in both ART-naive and ART-experienced HIP compared to controls (p=0.082 and p=0.002). There was a positive correlation between the CD4+T cell count and serum concentration of IFN- γ(r=0.320, p<0.05). While the serum IFN-γ concentration showed a negative correlation with the HIVRNA level(r=-0.412, p<0.001), the serum IL-1β, IL-6, and TNF-α concentrations showed a positive correlation with the HIV-RNA level (r=0.349, p<0.001; r:0.54, p<0.001; r:0.438, p<0.00).

CONCLUSION

Although serum concentrations of IL-6, IL-1β and TNF-α showed a significant decrease after ART, they were still significantly higher than the controls. IFN-γ responded differently to ART compared to the other cytokines, indicating that it may play a distinct and important role in the pathogenesis of HIV infection.

Cytokine levels of interleukin-2 and 7 amongst antiretroviral therapy success and failure HIV patients attending the University Teaching Hospital, Yaoundé, Cameroon

BACKGROUND

Immune reconstitution complications (IRC) are a major problem faced by HIV treated patients world wide. Interleukin (IL)-2 and IL-7 play vital roles in peripheral T-cell homeostasis. Our study objective was to measure and compare the blood plasma levels of IL-2 and IL-7 amongst antiretroviral therapy (ART) patients attending the Yaoundé University Teaching Hospital, Cameroon.

METHODS

We performed a cross-sectional study with 296 HIV positive patients enrolled between July 2017 and May 2018 at the Yaoundé University Teaching Hospital. IL-2, IL-7, T-cell profile counts and plasma viral load were measured on whole blood specimens. Data obtained were analyzed using Graph Pad Prism 5.0 and Epi info 7.0. Software.

RESULTS

IL-2 and IL-7 plasma concentration levels were higher in patients with ART failure compared to ART success, with a mean SD of 19.4±8 and 17.1±6 pg /ml, 35.26±11 and 21.5±5 pg/ml, with p < 0.001 and < 0.001. There was a direct and significant correlation between viral load, IL-2 and IL-7 with p values = 0.028, and 0.020, respectively. There was an association between IL-2, IL-7 and viral load in relation to the duration on treatment (DT), with p values = 0.003 (R²=0.041, CI= 0.069 - 0.34) ,0.017 (R²=0.027, CI=-0.30 - 0.030), and 0.001 (R²=0.048, CI=-0.047-0.76).

CONCLUSION

Considering that limited surrogate markers are availiable for monitoring immune reconstitution and high associated mortality rates, IL-2 and IL-7 could be a good immunological predictor for ART failure and success in HIV infected individuals.

Lymphocyte-Sparing Radiotherapy: The Rationale for Protecting Lymphocyte-rich Organs When Combining Radiotherapy With Immunotherapy

There is now strong clinical and preclinical evidence that lymphocytes, for example, CD8+ T cells, are key effectors of immunotherapy and that irradiation of large blood vessels, the heart, and lymphoid organs (including nodes, spleen, bones containing bone marrow, and thymus in children) causes transient or persistent lymphopenia. Furthermore, there is extensive clinical evidence, across multiple cancer sites and treatment modalities, that lymphopenia correlates strongly with decreased overall survival. At the moment, we lack quantitative evidence to establish the relationship between dose-volume and dose-rate to critical normal structures and lymphopenia. Therefore, we propose that data should be systematically recorded to characterise a possible quantitative relationship. This might enable us to improve the efficacy of radiotherapy and develop strategies to predict and prevent treatment-related lymphopenia. In anticipation of more quantitative data, we recommend the application of the principle of As Low As Reasonably Achievable to lymphocyte-rich regions for radiotherapy treatment planning to reduce the radiation doses to these structures, thus moving toward "Lymphocyte-Sparing Radiotherapy."

Delineation of Homeostatic Immune Signatures Defining Viremic Non-progression in HIV-1 Infection

Viremic non-progressors (VNPs), a distinct group of HIV-1-infected individuals, exhibit no signs of disease progression and maintain persistently elevated CD4+ T cell counts for several years despite high viral replication. Comprehensive characterization of homeostatic cellular immune signatures in VNPs can provide unique insights into mechanisms responsible for coping with viral pathogenesis as well as identifying strategies for immune restoration under clinically relevant settings such as antiretroviral therapy (ART) failure. We report a novel homeostatic signature in VNPs, the preservation of the central memory CD4+ T cell (CD4+ T_CM) compartment. In addition, CD4+ T_CM preservation was supported by ongoing interleukin-7 (IL-7)-mediated thymic repopulation of naive CD4+ T cells leading to intact CD4+ T cell homeostasis in VNPs. Regulatory T cell (Treg) expansion was found to be a function of preserved CD4+ T cell count and CD4+ T cell activation independent of disease status. However, in light of continual depletion of CD4+ T cell count in progressors but not in VNPs, Tregs appear to be involved in lack of disease progression despite high viremia. In addition to these homeostatic mechanisms resisting CD4+ T cell depletion in VNPs, a relative diminution of terminally differentiated effector subset was observed exclusively in these individuals that might ameliorate consequences of high viral replication. VNPs also shared signatures of impaired CD8+ T cell cytotoxic function with progressors evidenced by increased exhaustion (PD-1 upregulation) and CD127 (IL-7Rα) downregulation contributing to persistent viremia. Thus, the homeostatic immune signatures reported in our study suggest a complex multifactorial mechanism accounting for non-progression in VNPs.

Comprehensive Analysis of the Kinetics of Radiation-Induced Lymphocyte Loss in Patients Treated with External Beam Radiation Therapy

Radiation-induced lymphopenia (RIL) is associated with worse survival in patients with solid tumors, as well as lower response rates to checkpoint inhibitors. While single-fraction total-body irradiation is known to result in exponential decreases in the absolute lymphocyte count (ALC), the kinetics of lymphocyte loss after focal fractionated exposures have not previously been characterized. In the current study, lymphocyte loss kinetics was analyzed among patients undergoing focal fractionated radiotherapy for clinical indications. This registry-based study included 419 patients who received either total-body irradiation (TBI; n = 30), stereotactic body radiation therapy (SBRT; n = 73) or conventionally fractionated chemoradiation therapy (CFRT; n = 316). For each patient, serial ALCs were plotted against radiotherapy fraction number. The initial three weeks of treatment for CFRT patients and the entirety of treatment for SBRT and TBI patients were fit to exponential decay in the form ALC(x) = ae^-bx, where ALC(x) is the ALC after x fractions. From those fits, fractional lymphocyte loss (FLL) was calculated as FLL = (1 - e^-b) * 100, and multivariable regression was performed to identify significant correlates of FLL. Median linearized R² when fitting the initial fractions was 0.98, 0.93 and 0.97 for patients receiving TBI, SBRT and CFRT, respectively. In CFRT patients, apparent ALC loss rate slowed after week 3. Fitting ALC loss over the entire CFRT course therefore required the addition of a constant term, "c". For TBI and SBRT patients, treatment ended during the pure exponential decay phase. Initial FLL varied significantly with treatment technique. Mean FLL was 35.5%, 24.3% and 10.77% for patients receiving TBI, SBRT and CFRT, respectively (P < 0.001). Significant correlates of FLL varied by site and included field size, dose per fraction, mean spleen dose, chemotherapy backbone and age. Finally, total percentage ALC loss during radiotherapy was highly correlated with FLL (P < 0.001). Lymphocyte depletion kinetics during the initial phase of fractionated radiotherapy are characterized by pure exponential decay. Initial FLL is strongly correlated with radiotherapy planning parameters and total percentage ALC loss. The two groups with the highest FLL received no concurrent chemotherapy, suggesting that ALC loss can be a consequence of radiotherapy alone. This work may assist in selecting patients for adaptive radiotherapy approaches to mitigate RIL risk.

The role of integration and clonal expansion in HIV infection: live long and prosper

Integration of viral DNA into the host genome is a central event in the replication cycle and the pathogenesis of retroviruses, including HIV. Although most cells infected with HIV are rapidly eliminated in vivo, HIV also infects long-lived cells that persist during combination antiretroviral therapy (cART). Cells with replication competent HIV proviruses form a reservoir that persists despite cART and such reservoirs are at the center of efforts to eradicate or control infection without cART. The mechanisms of persistence of these chronically infected long-lived cells is uncertain, but recent research has demonstrated that the presence of the HIV provirus has enduring effects on infected cells. Cells with integrated proviruses may persist for many years, undergo clonal expansion, and produce replication competent HIV. Even proviruses with defective genomes can produce HIV RNA and may contribute to ongoing HIV pathogenesis. New analyses of HIV infected cells suggest that over time on cART, there is a shift in the composition of the population of HIV infected cells, with the infected cells that persist over prolonged periods having proviruses integrated in genes associated with regulation of cell growth. In several cases, strong evidence indicates the presence of the provirus in specific genes may determine persistence, proliferation, or both. These data have raised the intriguing possibility that after cART is introduced, a selection process enriches for cells with proviruses integrated in genes associated with cell growth regulation. The dynamic nature of populations of cells infected with HIV during cART is not well understood, but is likely to have a profound influence on the composition of the HIV reservoir with critical consequences for HIV eradication and control strategies. As such, integration studies will shed light on understanding viral persistence and inform eradication and control strategies. Here we review the process of HIV integration, the role that integration plays in persistence, clonal expansion of the HIV reservoir, and highlight current challenges and outstanding questions for future research.

Pathological roles of the homeostatic chemokine CXCL12

CXCL12 is a CXC chemokine that traditionally has been classified as a homeostatic chemokine. It contributes to physiological processes such as embryogenesis, hematopoiesis and angiogenesis. In contrast to these homeostatic functions, increased expression of CXCL12 in general, or of a specific CXCL12 splicing variant has been demonstrated in various pathologies. In addition to this increased or differential transcription of CXCL12, also upregulation of its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3 (ACKR3) contributes to the onset or progression of diseases. Moreover, posttranslational modification of CXCL12 during disease progression, through interaction with locally produced molecules or enzymes, also affects CXCL12 activity, adding further complexity. As CXCL12, CXCR4 and ACKR3 are broadly expressed, the number of pathologies wherein CXCL12 is involved is growing. In this review, the role of the CXCL12/CXCR4/ACKR3 axis will be discussed for the most prevalent pathologies. Administration of CXCL12-neutralizing antibodies or small-molecule antagonists of CXCR4 or ACKR3 delays disease onset or prevents disease progression in cancer, viral infections, inflammatory bowel diseases, rheumatoid arthritis and osteoarthritis, asthma and acute lung injury, amyotrophic lateral sclerosis and WHIM syndrome. On the other hand, CXCL12 has protective properties in Alzheimer's disease and multiple sclerosis, has a beneficial role in wound healing and has crucial homeostatic properties in general.

A systematic review of the influence of radiation-induced lymphopenia on survival outcomes in solid tumors

Lymphopenia is a common accompaniment of multimodal cancer therapy. As the most radiosensitive cells of the hematopoietic system, lymphocytes residing within or circulating through a radiation portal are frequently depleted by radiation therapy. The recognition that radiation-induced reduction of circulating lymphocyte counts and eventual lymphocyte infiltration of tumors have a tangible impact on overall survival outcomes has revived the interest in understanding the causes of treatment-associated lymphopenia and developing strategies to predict, prevent and ameliorate this well-documented phenomenon. In this systematic review, we have performed a comprehensive search of the literature to elucidate the studies that document a correlation between radiation-associated lymphopenia and survival outcomes in solid malignancies. We also summarize potential unifying paradigms that account for radiation-induced lymphopenia across studies and lay the groundwork for attempting to explain and/or counter this phenomenon.

Impact of Hepatitis C Virus on the Circulating Levels of IL-7 in HIV-1 Coinfected Women

OBJECTIVES

Hepatitis C virus (HCV) infection causes an alteration in T-cell maturation and activation in patients coinfected with human immunodeficiency virus (HIV). Because interleukin 7 (IL-7) is a major cytokine controlling T-cell homeostasis, we analyzed the potential influence of HCV coinfection on circulating IL-7 levels in HIV-infected women before and after highly active antiretroviral therapy (HAART).

DESIGN AND METHODS

This prospective study included 56 HIV monoinfected, 55 HIV/HCV coinfected without HCV viremia, 132 HIV/HCV coinfected with HCV viremia, and 61 HIV/HCV-uninfected women for whom plasma levels of IL-7 were determined by enzyme-linked immunosorbent assay at 1 or more follow-up visits before and after HAART. Cross-sectional analyses of the associations between plasma IL-7 levels and HCV infection, demographic, clinical, and immunologic characteristics were evaluated using univariate and multivariate linear regression models before and after HAART.

RESULTS

In multivariate models, IL-7 levels were significantly higher in coinfected HCV viremic women than in HIV monoinfected women (multiplicative effect = 1.48; 95% confidence interval: 1.01 to 2.16; P = 0.04) before HAART, but were similar between these two groups among women after HAART. In addition to HCV viremia, higher IL-7 levels were associated with older age (P = 0.02), lower CD4(+) T-cell count (P = 0.0007), and higher natural killer T-cell count (P = 0.02) in women before HAART. Among HAART-treated women, only lower CD4(+) T-cell count was significantly associated with IL-7 level (P = 0.006).

CONCLUSIONS

Our data demonstrate that in HIV-infected women, circulating levels of IL-7 are strongly associated with CD4 T-cell depletion both before and after HAART. Our data also demonstrate that HCV viremia increases circulating IL-7 levels before HAART but not after HAART in coinfected women. This suggests that the effect of HCV on lymphopenia is abrogated by HAART.

Pre-radiation lymphocyte harvesting and post-radiation reinfusion in patients with newly diagnosed high grade gliomas

Radiation (RT), temozolomide (TMZ), and dexamethasone in newly diagnosed high grade gliomas (HGG) produces severe treatment-related lymphopenia (TRL) that is associated with early cancer-related deaths. This TRL may result from inadvertent radiation to circulating lymphocytes. This study reinfused lymphocytes, harvested before chemo-radiation, and assessed safety, feasibility, and trends in lymphocyte counts. Patients with newly diagnosed HGG and total lymphocyte counts (TLC) ≥ 1000 cells/mm(3) underwent apheresis. Cryopreserved autologous lymphocytes were reinfused once radiation was completed. Safety, feasibility, and trends in TLC, T cell subsets and cytokines were studied. Serial TLC were also compared with an unreinfused matched control group. Ten patients were harvested (median values: age 56 years, dexamethasone 3 mg/day, TLC/CD4 1980/772 cells/mm(3)). After 6 weeks of RT/TMZ, TLC fell 69 % (p < 0.0001) with similar reductions in CD4, CD8 and NK cells but not Tregs. Eight patients received lymphocyte reinfusions (median = 7.0 × 10(7) lymphocytes/kg) without adverse events. A post-reinfusion TLC rise of ≥300 cells/mm(3) was noted in 3/8 patients at 4 weeks and 7/8 at 14 weeks which was similar to 23 matched controls. The reduced CD4/CD8 ratio was not restored by lymphocyte reinfusion. Severe lymphopenia was not accompanied by elevated serum interleukin-7 (IL-7) levels. This study confirms that severe TRL is common in HGG and is not associated with high plasma IL-7 levels. Although lymphocyte harvesting/reinfusion is feasible and safe, serial lymphocyte counts are similar to unreinfused matched controls. Studies administering higher lymphocyte doses and/or IL-7 should be considered to restore severe treatment-related lymphopenia in HGG.

Interleukin 7 up-regulates CD95 protein on CD4+ T cells by affecting mRNA alternative splicing: priming for a synergistic effect on HIV-1 reservoir maintenance

Interleukin-7 (IL-7) has been used as an immunoregulatory and latency-reversing agent in human immunodeficiency virus type 1 (HIV-1) infection. Although IL-7 can restore circulating CD4(+) T cell counts in HIV-1-infected patients, the anti-apoptotic and proliferative effects of IL-7 appear to benefit survival and expansion of HIV-1-latently infected memory CD4(+) T lymphocytes. IL-7 has been shown to elevate CD95 on CD4(+) T cells in HIV-1-infected individuals and prime CD4(+) T lymphocytes to CD95-mediated proliferative or apoptotic signals. Here we observed that through increasing microRNA-124, IL-7 down-regulates the splicing regulator polypyrimidine tract binding protein (PTB), leading to inclusion of the transmembrane domain-encoding exon 6 of CD95 mRNA and, subsequently, elevation of CD95 on memory CD4(+) T cells. Moreover, IL-7 up-regulates cellular FLICE-like inhibitory protein (c-FLIP) and stimulates c-Jun N-terminal kinase (JNK) phosphorylation, which switches CD95 signaling to survival mode in memory CD4(+) T lymphocytes. As a result, co-stimulation through IL-7/IL-7R and FasL/CD95 signal pathways augments IL-7-mediated survival and expansion of HIV-1-latently infected memory CD4(+) T lymphocytes. Collectively, we have demonstrated a novel mechanism for IL-7-mediated maintenance of HIV-1 reservoir.

The two human CXCR4 isoforms display different HIV receptor activities: consequences for the emergence of X4 strains

CXCR4 is a chemokine receptor that plays key roles with its specific ligand, CXCL12, in stem cell homing and immune trafficking. It is also used as a coreceptor by some HIV-1 strains (X4 strains), whereas other strains (R5 strains) use an alternative coreceptor, CCR5. X4 strains mainly emerge at late stages of the infection and are linked to disease progression. Two isoforms of this coreceptor have been described in humans: CXCR4-A and CXCR4-B, corresponding to an unspliced and a spliced mRNA, respectively. In this study, we show that CXCR4-B, but not CXCR4-A, mediates an efficient HIV-1 X4 entry and productive infection. Yet, the chemotactic activity of CXCL12 on both isoforms was similar. Furthermore, HIV-R5 infection favored CXCR4-B expression over that of CXCR4-A. In vitro infection with an R5 strain increased CXCR4-B/CXCR4-A mRNA ratio in PBMCs, and this ratio correlated with HIV RNA plasma level in R5-infected individuals. In addition, the presence of the CXCR4-B isoform favored R5 to X4 switch more efficiently than did CXCR4-A in vitro. Hence, the predominance of CXCR4-B over CXCR4-A expression in PBMCs was linked to the ability of circulating HIV-1 strains to use CXCR4, as determined by genotyping. These data suggest that R5 to X4 switch could be favored by R5 infection-induced overexpression of CXCR4-B. Finally, we achieved a specific small interfering RNA-mediated knockdown of CXCR4-B. This represents a proof of concept for a possible gene-therapeutic approach aimed at blocking the HIV coreceptor activity of CXCR4 without knocking down its chemotactic activity.

Effects of different antigenic stimuli on thymic function and interleukin-7/CD127 system in patients with chronic HIV infection

BACKGROUND

We tested if an increase in immune activation and a decrease in CD4⁺ T cells induced by different antigenic stimuli could be associated with changes in the thymic function and the interleukin (IL)-7/CD127 system.

METHODS

Twenty-six HIV-infected patients under combined antiretroviral therapy (cART) were randomized to receive, during 12 months, a complete immunization schedule (7 vaccines and 15 doses) or placebo. Thereafter, cART was interrupted during 6 months. Changes in the thymic function and the IL-7/CD127 system after 3 different antigenic stimuli (vaccines, episodes of low-level intermittent viremia before cART interruption, or viral load rebound after cART interruption) were assessed.

RESULTS

During the period on cART, neither vaccines nor low-level viremia influenced thymic function or IL-7/CD127 system parameters. By analyzing the cohort as a whole while on cART, a significant improvement was observed in the thymic function as measured by an increase in the thymic volume (P = 0.024), T-cell receptor excision circle-bearing cells (P = 0.012), and naive CD4⁺ and CD8⁺ T cells (P = 0.069 both). No significant changes were observed in the IL-7/CD127 system. After cART interruption, a decrease in T-cell receptor excision circles (P < 0.001) and naive CD8⁺ T cells (P < 0.001), an increase in IL-7 and expression of CD127 on naive and memory CD4⁺ T cells (P = 0.028, P = 0.088, and P = 0.04, respectively), and a significant decrease in CD127 on naive and memory CD8⁺ T cells (P = 0.01, P = 0.006, respectively) were observed.

CONCLUSIONS

Low-level transient antigenic stimuli during cART were not associated with changes in the thymic function or the IL-7/CD127 system. Conversely, viral load rebound very early after cART interruption influenced the thymic function and the IL-7/CD127 system. Clinical Trials.gov number NCT00329251.

Immune interventions in HIV infection

Immune-based therapy (IBT) interventions have found a window of opportunity within some limitations of the otherwise successful combined antiretroviral therapy (cART). Two major paradigms drove immunotherapeutic research to combat human immunodeficiency virus (HIV) infection. First, IBTs were proposed either to help restore CD4(+) T-cell counts in cases of therapeutic failures with cytokines, interleukin-2 (IL-2) or IL-7, or to better control HIV and disease progression during treatment interruptions with anti-HIV therapeutic candidate vaccines. The most widely used candidates were HIV-recombinant live vector-based alone or combined with other vaccine compounds and dendritic cell (DC) therapies. A more recent and current paradigm aims at achieving HIV cure by combining IBT with cART using either cytokines to reactivate virus production in latently infected cells and/or therapeutic immunization to boost HIV-specific immunity in a 'shock and kill' strategy. This review summarizes the rationale, hopes, and mechanisms of successes and failures of these cytokine-based and vaccine-based immune interventions. Results from these first series of IBTs have been so far somewhat disappointing in terms of clinical relevance, but have provided lessons that are discussed in light of the future combined strategies to be developed toward an HIV cure.

Genetic modification of hematopoietic stem cells as a therapy for HIV/AIDS

The combination of genetic modification and hematopoietic stem cell (HSC) transplantation may provide the necessary means to develop an alternative treatment option to conventional antiretroviral therapy. As HSCs give rise to all hematopoietic cell types susceptible to HIV infection, modification of HSCs is an ideal strategy for the development of infection-resistant immune cell populations. Although promising results have been obtained in multiple animal models, additional evidence is needed to convincingly demonstrate the feasibility of this approach as a treatment of HIV-1 infected patients. Here, we review the potential of HSC transplantation and the recently identified limitations of this approach. Using the Berlin Patient as a model for a functional cure, we contrast the confines of autologous versus allogeneic transplantation. Finally, we suggest that although autologous, gene-modified HSC-transplantation may significantly reduce plasma viremia, reaching the lower detection limits currently obtainable through daily HAART will remain a challenging endeavor that will require innovative combinatorial therapies.

Accelerated in vivo proliferation of memory phenotype CD4+ T-cells in human HIV-1 infection irrespective of viral chemokine co-receptor tropism

CD4⁺ T-cell loss is the hallmark of HIV-1 infection. CD4 counts fall more rapidly in advanced disease when CCR5-tropic viral strains tend to be replaced by X4-tropic viruses. We hypothesized: (i) that the early dominance of CCR5-tropic viruses results from faster turnover rates of CCR5⁺ cells, and (ii) that X4-tropic strains exert greater pathogenicity by preferentially increasing turnover rates within the CXCR4⁺ compartment. To test these hypotheses we measured in vivo turnover rates of CD4⁺ T-cell subpopulations sorted by chemokine receptor expression, using in vivo deuterium-glucose labeling. Deuterium enrichment was modeled to derive in vivo proliferation (p) and disappearance (d*) rates which were related to viral tropism data. 13 healthy controls and 13 treatment-naive HIV-1-infected subjects (CD4 143–569 cells/ul) participated. CCR5-expression defined a CD4⁺ subpopulation of predominantly CD45R0⁺ memory cells with accelerated in vivo proliferation (p = 2.50 vs 1.60%/d, CCR5⁺ vs CCR5⁻; healthy controls; P<0.01). Conversely, CXCR4 expression defined CD4⁺ T-cells (predominantly CD45RA⁺ naive cells) with low turnover rates. The dominant effect of HIV infection was accelerated turnover of CCR5⁺CD45R0⁺CD4⁺ memory T-cells (p = 5.16 vs 2.50%/d, HIV vs controls; P<0.05), naïve cells being relatively unaffected. Similar patterns were observed whether the dominant circulating HIV-1 strain was R5-tropic (n = 9) or X4-tropic (n = 4). Although numbers were small, X4-tropic viruses did not appear to specifically drive turnover of CXCR4-expressing cells (p = 0.54 vs 0.72 vs 0.44%/d in control, R5-tropic, and X4-tropic groups respectively). Our data are most consistent with models in which CD4⁺ T-cell loss is primarily driven by non-specific immune activation.

Loss of CD4⁺ T-cells is the cardinal feature of HIV/AIDS, resulting in pathological susceptibility to opportunistic infections. Mechanisms underlying CD4-depletion remain unclear, although the role of chronic immune activation is now well-recognized. Selectivity of the virus for its co-receptor target (either chemokine-receptor CCR5 or CXCR4) is also pivotal. We explored the relationship between these two factors by directly measuring in vivo proliferation rates of CD4⁺ T-cell subpopulations according to their expression of chemokine-receptors and the tropism of circulating virus in clinically-well people with HIV infection, and healthy human controls. We used stable isotope labeling with deuterium-labeled glucose to quantify proliferation and disappearance rate constants of CD4⁺ T-cells sorted by CCR5, CXCR4 and CD45R0/RA expression. We found that CCR5-expression defines a high turnover subpopulation which is therefore likely to be preferentially infected and produce more (CCR5-tropic) virus. CXCR4-tropic viruses induced a similar pattern of proliferation as R5-tropic strains, with no apparent selectivity for viral strains to induce proliferation in their targeted subpopulations. This study is significant in providing directly-measured in vivo human data supporting postulates generated in ex vivo human studies and SIV models suggesting that non-specific factors, such as immune activation, rather than cell-specific cytotoxicity, are dominant drivers for HIV pathogenesis.

Interleukin-7 facilitates HIV-1 transmission to cervico-vaginal tissue ex vivo

The majority of HIV-1 infections in women occur through vaginal intercourse, in which virus-containing semen is deposited on the cervico-vaginal mucosa. Semen is more than a mere carrier of HIV-1, since it contains many biological factors, in particular cytokines, that may affect HIV-1 transmission. The concentration of interleukin (IL)-7, one of the most prominent cytokines in semen of healthy individuals, is further increased in semen of HIV-1-infected men. Here, we investigated the potential role of IL-7 in HIV-1 vaginal transmission in an ex vivo system of human cervico-vaginal tissue. We simulated an in vivo situation by depositing HIV-1 on cervico-vaginal tissue in combination with IL-7 at concentrations comparable with those measured in semen of HIV-1-infected individuals. We found that IL-7 significantly enhanced virus replication in ex vivo infected cervico-vaginal tissue. Similarly, we observed an enhancement of HIV-1 replication in lymphoid tissue explants. Analysis of T cells isolated from infected tissues showed that IL-7 reduced CD4⁺ T cell depletion preventing apoptosis, as shown by the decrease in the number of cells expressing the apoptotic marker APO2.7 and the increase in the expression of the anti-apoptotic protein B-cell lymphoma (Bcl)-2. Also, IL-7 increased the fraction of cycling CD4⁺ T cells, as evidenced by staining for the nuclear factor Ki-67. High levels of seminal IL-7 in vivo may be relevant to the survival of the founder pool of HIV-1-infected cells in the cervico-vaginal mucosa at the initial stage of infection, promoting local expansion and dissemination of HIV infection.

Male-to-female HIV-1 transmission occurs predominantly through vaginal intercourse when the virus is transmitted with seminal fluid. The identification of the determinants of HIV-1 transmission to the female lower genital tract is of pivotal importance for understanding the basic mechanisms of HIV-1 infection. This understanding is necessary for the development of new strategies to prevent or contain this infection. Semen of HIV-1-infected individuals is highly enriched with IL-7, a crucial cytokine for the life cycle of CD4⁺ T cells, the primary target of HIV-1. Here, we utilized a system of human cervico-vaginal and lymphoid tissues ex vivo to study the effect of IL-7 on HIV-1 transmission and dissemination. Our results show that IL-7 at concentrations comparable to those found in semen of HIV-1-infected individuals enhanced HIV-1 replication by preventing the death and by stimulating the proliferation of CD4⁺ T cells. This allows sustained viral production by infected cells and provides new cellular targets for propagation of infection. The concentration of IL-7 in semen of HIV-1-infected men may be a key determinant of the efficiency of HIV-1 transmission to an uninfected female partner through vaginal intercourse.

Perspectives on interleukin-7 therapy in HIV infection

PURPOSE OF REVIEW

HIV infection is characterized by depletion of CD4 T cells and altered immune function, leading to severe immune deficiency. Mechanisms leading to this T-cell depletion are not completely understood. Potent antiretroviral therapy restores T-cell counts and improves prognosis. Apart from antiviral therapy for the infection, immunotherapies such as interleukin-7 that influence T-cell homeostatic mechanisms are undergoing clinical evaluation. Because of its pleiotropic effects on developing and mature T cells, interleukin-7 may help to restore immune function during HIV infection.

RECENT FINDINGS

Recent studies explored the therapeutic use of interleukin-7 in simian immunodeficiency virus models and in HIV-infected patients. Interleukin-7 can help to restore CD4 T-cell number and function.

SUMMARY

Numerous recent findings highlight the importance of interleukin-7 pathway impairment in the pathogenesis of HIV infection. Notably, interleukin-7 levels increased with advancing CD4 T-cell lymphopenia, whereas interleukin-7 receptor expression is downregulated mainly on CD8 T cells. Therapeutic trials conducted in monkeys and in humans (phase I) have provided evidence on the role of interleukin-7 in thymopoiesis and in restoration of T-cell functions. Interleukin-7 appeared to be well tolerated and to have no deleterious effects on viral load. These results should be confirmed in larger phase I/II studies.

Thirty Years with HIV Infection-Nonprogression Is Still Puzzling: Lessons to Be Learned from Controllers and Long-Term Nonprogressors

In the early days of the HIV epidemic, it was observed that a minority of the infected patients did not progress to AIDS or death and maintained stable CD4+ cell counts. As the technique for measuring viral load became available it was evident that some of these nonprogressors in addition to preserved CD4+ cell counts had very low or even undetectable viral replication. They were therefore termed controllers, while those with viral replication were termed long-term nonprogressors (LTNPs). Genetics and virology play a role in nonprogression, but does not provide a full explanation. Therefore, host differences in the immunological response have been proposed. Moreover, the immunological response can be divided into an immune homeostasis resistant to HIV and an immune response leading to viral control. Thus, non-progression in LTNP and controllers may be due to different immunological mechanisms. Understanding the lack of disease progression and the different interactions between HIV and the immune system could ideally teach us how to develop a functional cure for HIV infection. Here we review immunological features of controllers and LTNP, highlighting differences and clinical implications.

Hepatitis C coinfection enhances sensitization of CD4(+) T-cells towards Fas-induced apoptosis in viraemic and HAART-controlled HIV-1-positive patients

BACKGROUND

Recently, we identified increased rates of CD4(+) T-cell apoptosis in HCV-infected HIV-positive patients as a potential mechanism for enhanced mortality in patients with HIV/HCV coinfection. Since this effect might be attributed to changes in receptor-induced apoptosis, we studied expression and function of Fas ligand (FasL) and its death receptor Fas on CD4(+) T-cells in HIV/HCV coinfection.

METHODS

In this cross-sectional study, we simultaneously analysed surface expression of Fas and FasL on CD4(+) T-cells and serum levels of soluble FasL in HCV/HIV-coinfected, HIV-monoinfected and HCV-monoinfected patients. Susceptibility to FasL-induced apoptosis was analysed by incubating isolated peripheral blood mononuclear cells with rhFasL followed by measuring CD4(+) T-cell apoptosis.

RESULTS

HIV and HCV monoinfection were associated with significantly enhanced surface expression of Fas. Highest Fas expression was detected in HIV/HCV-coinfected patients and correlated with low CD4(+) T-cell counts. By contrast, elevated levels of soluble and cellular FasL were found only in patients with HIV infection, but not in patients with HCV infection. Importantly, enhanced Fas expression in HCV/HIV coinfection rendered CD4(+) T-cells more susceptible towards FasL-induced apoptosis. While effective HAART normalized expression and secretion of FasL in HIV-infected and HIV/HCV-coinfected patients, expression of Fas decreased only slightly and still remained significantly elevated as compared with healthy controls.

CONCLUSIONS

Our findings suggest a synergistic mechanism in HIV/HCV coinfection between up-regulation of Fas expression on CD4(+) T-cells and HIV-induced elevated levels of cellular and soluble FasL. Together, both effects contribute to enhanced apoptosis of CD4(+) T-cells in HIV/HCV coinfection.

Elevated cytokine and chemokine levels in the placenta are associated with in-utero HIV-1 mother-to-child transmission

OBJECTIVE

To determine whether there is an association between cytokine and chemokine levels in plasma isolated from the placenta and HIV-1 mother-to-child transmission (MTCT).

DESIGN

We designed a case-control study of HIV-infected, pregnant women enrolled in the Malaria and HIV in Pregnancy cohort. Participants were recruited in Blantyre, Malawi, from 2000 to 2004. Patients were women whose children were HIV-1 DNA-positive at birth (in-utero MTCT) or HIV-1 DNA-negative at birth and HIV-1 DNA-positive at 6 weeks postpartum (intrapartum MTCT); controls were women whose children were HIV-1 DNA-negative both at birth and 6 weeks postpartum.

METHODS

After delivery, blood was isolated from an incision on the basal plate of the placenta. We used a Bio-Plex human cytokine assay (Bio-Rad, Hercules, California USA) to simultaneously quantify 27 cytokines, chemokines and growth factors in placental plasma. HIV-1 RNA copies were quantified with the Roche Amplicor kit.

RESULTS

Levels of interleukin (IL) 4, IL-5, IL-6, IL-7, IL-9, eotaxin, IL-1Ra and interferon gamma-induced protein 10 (IP-10) were significantly elevated in placental plasma isolated from cases of in-utero HIV-1 MTCT. In contrast, only granulocyte colony-stimulating factor was elevated in placental plasma isolated from cases of intrapartum MTCT. After adjusting for maternal age, gestational age and peripheral CD4(+) T-cell count, every log(10) increase in placental IP-10 was associated with a three-fold increase in the prevalence of in-utero HIV-1 MTCT.

CONCLUSION

Elevated cytokine and chemokine levels in placental plasma were associated with in-utero and not intrapartum MTCT. IP-10, which is both a T-cell chemokine and potentiator of HIV-replication, was robustly and independently associated with prevalent, in-utero MTCT.

Incomplete immune recovery in HIV infection: mechanisms, relevance for clinical care, and possible solutions

Treatment of HIV-infected patients with highly active antiretroviral therapy (HAART) usually results in diminished viral replication, increasing CD4+ cell counts, a reversal of most immunological disturbances, and a reduction in risk of morbidity and mortality. However, approximately 20% of all HIV-infected patients do not achieve optimal immune reconstitution despite suppression of viral replication. These patients are referred to as immunological nonresponders (INRs). INRs present with severely altered immunological functions, including malfunction and diminished production of cells within lymphopoetic tissue, perturbed frequencies of immune regulators such as regulatory T cells and Th17 cells, and increased immune activation, immunosenescence, and apoptosis. Importantly, INRs have an increased risk of morbidity and mortality compared to HIV-infected patients with an optimal immune reconstitution. Additional treatment to HAART that may improve immune reconstitution has been investigated, but results thus far have proved disappointing. The reason for immunological nonresponse is incompletely understood. This paper summarizes the known and unknown factors regarding the incomplete immune reconstitution in HIV infection, including mechanisms, relevance for clinical care, and possible solutions.

Emergence of exhausted B cells in asymptomatic HIV-1-infected patients naïve for HAART is related to reduced immune surveillance

Alterations of B cell subpopulations have been described up to date as characterizing advanced stage of HIV-1 infection. However, whether such defects are relevant in subjects with a preserved number of CD4⁺ T cells (>350 cells/μL) is unclear. In a cross-sectional study, we investigated if signs of B cells exhaustion and impaired viral immune surveillance are present in a cohort of 43 asymptomatic HIV-1-infected patients with preserved CD4⁺ T cell counts (>350 cells/μL) and highly active antiretroviral therapy (HAART) untreated. A dramatic expansion of exhausted tissue-like memory B cells (CD10⁻CD21^lowCD27⁻) was observed. B cells alteration was related to an increase in Torque teno virus (TTV) load, used as surrogate marker of immune function. Successfully HAART-treated patients showed normalization of B cell subpopulations frequency and TTV load. These results provide new insights on B cell in HIV-1 infection and show that development of B cell abnormalities precedes CD4⁺ T cell decline.

Rapid down-regulation of γc on T cells in early SIV infection correlates with impairment of T-cell function

The common γ(c) subunit molecule is shared among all γ(c) cytokines and clearly involved in T-cell function, but its role in HIV infection and immunity is not well understood. Here, we examined expression and function of γ(c) on T cells during SIV infection in Rhesus macaques. Surface γ(c) distribution was differentially expressed on CD4(+) and CD8(+) T cells, and CD4(+) naive/memory cell populations in various lymphoid tissues of normal macaques. However, surface γ(c) expression was rapidly and significantly down-regulated on T cells in acute infection with pathogenic SIV, compared to infection with a less virulent SHIV or controls and did not recover on CD8(+) T cells in the chronic stage. Moreover, the peripheral and CD4(+)T cell loss was inversely correlated with γ(c)(+) CD8(+) T cells in individual tissues. γ(c)(+) T cells were mainly functional as evidenced by higher cytokine secretion and proliferative capacity. Further in vitro experiments found that surface γ(c) expression could be down-regulated following high level of IL-7 treatment by both internalization and shedding. Down-regulation of γ(c) during early HIV/SIV infection may inhibit T-cell function, particularly of CD8(+) T cells, and, may be linked with immune failure and loss of viral containment.

Longitudinal assessment of interleukin 7 plasma levels in HIV-infected patients in the absence of and under antiretroviral therapy

BACKGROUND

Cross-sectional studies in HIV-positive patients have suggested that interleukin 7 (IL-7) may increase in parallel to CD4 decline during the natural course of HIV infection. We tested this hypothesis in a longitudinal study examining the evolution of IL-7 and CD4 counts in 2 different scenarios.

METHODS

IL-7 and CD4 counts were regularly monitored in 30 drug-naive patients during a follow-up period of 46 ± 14 months in the absence of therapy and in 42 patients who started highly active antiretroviral therapy and maintained undetectable viremia for 2 years. Multivariate linear regression analysis was used to ascertain what factors were associated with IL-7 variations during follow-up.

RESULTS

In antiretroviral therapy-naive patients, CD4 counts significantly decreased (P < 0.0001), whereas plasma HIV-RNA and IL-7 levels remained fairly stable. In patients on highly active antiretroviral therapy, CD4 counts significantly increased (P < 0.0001) and IL-7 tended to decrease (P = 0.1). There was no correlation between CD4 and IL-7 variations either in the naive or in the treated population. The only parameter significantly associated with IL-7 variation during follow-up was its baseline level that showed a negative correlation.

CONCLUSIONS

In HIV patients with low or moderate degree of immunodeficiency, CD4 counts and plasma IL-7 levels do not evolve in parallel, suggesting that other factors different from CD4 counts must be involved in the upregulation of IL-7 observed in HIV infection.

Sustained high levels of serum interferon-γ during HIV-1 infection: a specific trend different from other cytokines

The expression levels of various cytokines increase with the progression of HIV-1 infection. However, the effects of antiretroviral therapy (ART) on serum cytokine levels have not been fully determined. In this study we measured serum cytokine levels of 35 HIV-1-infected Japanese adults. We first performed a cross-sectional study and observed that TNF-α, IL-6, IL-10, IL-18, and IL-7 levels all showed significant increases in those with advanced disease, and that this had a significant negative correlation with the CD4 cell count. However, IFN-γ levels did not show this relationship. A longitudinal study in 18 HIV-1-infected patients with a CD4 cell count <350/μL revealed that the introduction of ART reduced cytokine levels. Significant reductions of IL-7, IL-10, IFN-γ, and IL-18 levels were observed on days 30, 60, 90, and 90 after the initiation of ART, respectively. These results indicate a discrepancy between cross-sectional and longitudinal studies of serum levels of IFN-γ. To clarify this, we investigated serum IFN-γ levels in each patient. In 5 of the 15 patients IFN-γ levels did not decrease, even after ART initiation, and remained at 5 pg/mL or higher on day 120 after ART initiation. Higher IFN-γ levels (>5 pg/mL) were also observed in 2 of 7 asymptomatic patients, and 2 of 11 patients who underwent ART for 1 year or longer. These data demonstrate that IFN-γ levels in some patients increased and remained high even after the initiation of ART, which was a specific observation different from those of the other cytokines.

Interleukin-7 enhances memory CD8(+) T-cell recall responses in health but its activity is impaired in human immunodeficiency virus infection

Memory CD8(+) T cells regain function during a recall response, but the requirement of signals in addition to antigen during a secondary immune response is unknown. In this study, the ability of interleukin-7 (IL-7) to enhance memory CD8(+ ) CD45RA(- ) CD127(+) T-cell responses in health and in human immunodeficiency virus (HIV) infection was investigated. CD8(+) T-cell-depleted peripheral blood mononuclear cells (PBMCs) from HIV(-) and untreated HIV(+) donors were pulsed with a cytomegalovirus/Epstein-Barr virus/influenza (CEF) peptide pool, and co-cultured with autologous memory CD8(+) T cells in the presence of IL-7. Cell survival and the function of memory CD8(+) T-cell subsets were then evaluated. Memory CD8(+) T-cell proliferation and interferon-γ (IFN-γ) production was enhanced by the presence of antigen, and the addition of IL-7 further enhanced antigen-induced proliferation. In HIV(+) individuals, the presence of antigen enhanced IFN-γ production to a small degree but did not enhance proliferation. Lastly, IL-7 did not enhance antigen-mediated proliferation of memory CD8(+) T cells from HIV(+) individuals. IL-7 therefore appears to have a role in secondary immune responses and its activity is impaired in memory CD8(+) T cells from HIV(+) individuals. These results further our understanding of the signals involved in secondary immune responses, and provide new insight into the loss of CD8(+) T-cell function in HIV infection.

IL-7 and lymphopenia

Interleukin-7 (IL-7) is a growth and anti-apoptotic factor for T-lymphocytes, with potential for clinical use in the treatment of immunodeficiencies due to loss of T-cells. Lymphopenia induced by disease (HIV infection, hemodialysis or Idiopathic CD4+ lymphopenia) or by treatment (high dose chemotherapy or depleting antibodies) for cancer or auto-immune diseases results in increased circulating levels of IL-7 which decline with T-cell recovery, however, the mechanism of such response remains to be elucidated. Furthermore, IL-7 is a major player in the regulation of peripheral T-cell homeostasis and as such is an important candidate cytokine for therapy aimed at improving T-cell reconstitution following lymphopenia. Anti- IL-7 is on the other hand proposed to treat conditions where IL-7 may play a more direct role in pathogenesis such as autoimmune disease like Rheumatoid Arthritis, Multiple Sclerosis or Inflammatory Bowel disease.

Impact of gamma-chain cytokines on T cell homeostasis in HIV-1 infection: therapeutic implications

CD4(+) T cell lymphocytes are a major target for human immunodeficiency virus type-1 (HIV-1) infection. During this chronic infection, CD4(+) T cell loss (induced through direct viral replication), generalized immune activation and increased susceptibility to apoptosis result in impaired T cell homeostasis with subsequent development of opportunistic infections and cancers. Highly active antiretroviral therapy (HAART) has a well-defined, beneficial effect on HIV-1-related clinical outcome; however, it does not lead to normalization of immune dysregulation. In order to boost both CD4(+) T cell restoration and HIV-1 specific immunity, immunotherapy with gamma-chain cytokines has been used in HIV-1-infected patients during concomitant HAART. In this review, we summarize the role of gamma-chain cytokines, especially interleukin (IL)-2 and IL-7, in influencing T cell homeostasis and proliferation, and discuss how immunotherapy with these cytokines may be beneficial to reconstitute the T cell compartment in the context of HIV-1 infection. The intriguing results of two large trials evaluating the efficacy of IL-2 in restoring immune function during HIV-1 infection are also discussed. In addition, we consider the promises and caveats of the first phase I/II clinical trials with IL-7 in HIV-1-infected patients and the knowledge that is still lacking in the field of T cell reconstitution through gamma-chain cytokines.

Immunotherapies in HIV-1 infection

PURPOSE OF REVIEW

The purpose of this review is to describe the current status of immunotherapies for the treatment of HIV-1 infection. This review is timely, as the results of the phase III clinical trials of recombinant interleukin-2 (rIL-2) as adjuncts to combination antiretroviral therapy are about to be released.

RECENT FINDINGS

For many years, the use of rIL-2 in HIV-infected individuals has been explored. Although the results of the clinical endpoint studies of rIL-2 are awaited, there are now further data for rIL-2 as a stand-alone therapy for the treatment of HIV. Maraviroc, a recently approved anti-HIV agent, is a small molecule antagonist of human chemokine receptor-5. The recent observation that maraviroc-treated patients achieved higher CD4 and CD8 T-cell counts compared with comparator regimens (without a chemokine receptor-5 antagonist) for equivalent viral load reductions has fueled interest in using these host-directed therapies to enhance immune restoration.

SUMMARY

This review summarizes the most recent clinical data for rIL-2 and reviews other immunotherapies in earlier development including cytokines rIL-7, rIL-15, rIL-21, new therapeutic vaccination approaches including infusion of overlapping HIV peptides and dendritic cell immunotherapy and novel agents including luteinizing hormone-releasing hormone analogues and vitamin D3-binding protein macrophage activating factor.

HIV reservoir size and persistence are driven by T cell survival and homeostatic proliferation

HIV persists in a reservoir of latently infected CD4(+) T cells in individuals treated with highly active antiretroviral therapy (HAART). Here we identify central memory (T(CM)) and transitional memory (T(TM)) CD4(+) T cells as the major cellular reservoirs for HIV and find that viral persistence is ensured by two different mechanisms. HIV primarily persists in T(CM) cells in subjects showing reconstitution of the CD4(+) compartment upon HAART. This reservoir is maintained through T cell survival and low-level antigen-driven proliferation and is slowly depleted with time. In contrast, proviral DNA is preferentially detected in T(TM) cells from aviremic individuals with low CD4(+) counts and higher amounts of interleukin-7-mediated homeostatic proliferation, a mechanism that ensures the persistence of these cells. Our results suggest that viral eradication might be achieved through the combined use of strategic interventions targeting viral replication and, as in cancer, drugs that interfere with the self renewal and persistence of proliferating memory T cells.

Enhanced T cell recovery in HIV-1-infected adults through IL-7 treatment

HIV infection results in CD4+ T cell deficiency, but efficient combination antiretroviral therapy (c-ART) restores T cells and decreases morbidity and mortality. However, immune restoration by c-ART remains variable, and prolonged T cell deficiency remains in a substantial proportion of patients. In a prospective open-label phase I/IIa trial, we evaluated the safety and efficacy of administration of the T cell regulator IL-7. The trial included 13 c-ART-treated HIV-infected patients whose CD4+ cell counts were between 100 and 400 cells/microl and plasma HIV RNA levels were less than 50 copies/ml. Patients received a total of 8 subcutaneous injections of 2 different doses of recombinant human IL-7 (rhIL-7; 3 or 10 microg/kg) 3 times per week over a 16-day period. rhIL-7 was well tolerated and induced a sustained increase of naive and central memory CD4+ and CD8+ T cells. In the highest dose group, 4 patients experienced transient increases in viral replication. However, functional assays showed that the expanded T cells responded to HIV antigen by producing IFN-gamma and/or IL-2. In conclusion, in lymphopenic HIV-infected patients, rhIL-7 therapy induced substantial functional and quantitative changes in T cells for 48 weeks. Therefore, patients may benefit from intermittent therapy with IL-7 in combination with c-ART.

Pharmaceutical approaches to eradication of persistent HIV infection

Highly active antiretroviral therapy (HAART) has markedly decreased morbidity and mortality in human immunodeficiency virus type 1 (HIV-1)-infected individuals in the developed world. Successful therapy often results in stable plasma levels of HIV-1 RNA below the limits of detection of commercial assays. Nonetheless, HIV-1 has not been cured by HAART. The causes of persistence of HIV infection in the face of current therapy appear to be multifactorial: latent but replication-competent provirus in resting CD4+ T cells, cryptic viral expression below the limits of detection of clinical assays, and viral sanctuary sites might all contribute to persistence. Clearance of HIV infection will almost certainly require a multimodality approach that includes potent suppression of HIV replication, therapies that reach all compartments of residual HIV replication and depletion of any reservoirs of persistent, quiescent proviral infection. This review highlights the basic mechanisms for the establishment and maintenance of viral reservoirs and pharmaceutical approaches towards their elimination.

Priming of T cells to Fas-mediated proliferative signals by interleukin-7

T-cell depletion associated with HIV infection or cytoreductive therapies triggers potential T-cell regenerative mechanisms such as peripheral T-lymphocyte expansion to weak antigenic stimuli and the increased availability of interleukin-7 (IL-7), a cytokine with potent antiapoptotic and proliferative activities. Deleterious mechanisms also associated with lymphopenia, such as increased Fas expression and apoptosis of T cell, however, may result in opposing effects. In this study, we show that Fas molecules, primarily associated with T-cell depletion in lymphopenic settings, may also contribute to compensatory T-cell expansion through transmitting costimulatory signals to suboptimally activated T cells. Proliferation of T lymphocytes in response to concomitant Fas and T-cell receptor (TCR) triggering was shown to be increased in HIV-infected individuals compared with noninfected controls. As IL-7 levels are often elevated in lymphopenic individuals in association with increased Fas expression, we analyzed whether IL-7 would influence Fas-mediated proliferative signals in T cells. We show that IL-7 is able to increase the efficacy of Fas to induce proliferation of suboptimally activated T cells. Thus, high IL-7 levels associated with lymphopenic conditions may simultaneously induce sensitivity to Fas-mediated apoptosis in nonactivated T cells and increase Fas-induced costimulatory signals in T cells recognizing low-affinity antigens.

CD127 and CD25 expression defines CD4+ T cell subsets that are differentially depleted during HIV infection

Decreased CD4(+) T cell counts are the best marker of disease progression during HIV infection. However, CD4(+) T cells are heterogeneous in phenotype and function, and it is unknown how preferential depletion of specific CD4(+) T cell subsets influences disease severity. CD4(+) T cells can be classified into three subsets by the expression of receptors for two T cell-tropic cytokines, IL-2 (CD25) and IL-7 (CD127). The CD127(+)CD25(low/-) subset includes IL-2-producing naive and central memory T cells; the CD127(-)CD25(-) subset includes mainly effector T cells expressing perforin and IFN-gamma; and the CD127(low)CD25(high) subset includes FoxP3-expressing regulatory T cells. Herein we investigated how the proportions of these T cell subsets are changed during HIV infection. When compared with healthy controls, HIV-infected patients show a relative increase in CD4(+)CD127(-)CD25(-) T cells that is related to an absolute decline of CD4(+)CD127(+)CD25(low/-) T cells. Interestingly, this expansion of CD4(+)CD127(-) T cells was not observed in naturally SIV-infected sooty mangabeys. The relative expansion of CD4(+)CD127(-)CD25(-) T cells correlated directly with the levels of total CD4(+) T cell depletion and immune activation. CD4(+)CD127(-)CD25(-) T cells were not selectively resistant to HIV infection as levels of cell-associated virus were similar in all non-naive CD4(+) T cell subsets. These data indicate that, during HIV infection, specific changes in the fraction of CD4(+) T cells expressing CD25 and/or CD127 are associated with disease progression. Further studies will determine whether monitoring the three subsets of CD4(+) T cells defined based on the expression of CD25 and CD127 should be used in the clinical management of HIV-infected individuals.

Disruption of the gamma c cytokine network in T cells during HIV infection

The common gamma chain (gammac)-sharing cytokines (IL's-2, 4, 7, 9, 15, and 21) play a vital role in the survival, proliferation, differentiation and function of T lymphocytes. As such, disruption of their signaling pathways would be expected to have severe consequences on the integrity of the immune system. Indeed, it appears that the signaling network of these cytokines is both disrupted and exploited by HIV at various stages of infection. IL-2 secretion and signaling downstream of its receptor are impaired in T cells from chronically-infected HIV+ patients. Elevated plasma IL-7 levels and decreased IL-7Ralpha expression in patient T cells results in significantly decreased responsiveness to this critical cytokine. Interestingly, IL-2 and IL-15 are also able to render CD4+ T cells permissive to HIV infection through their influence on the activity of the APOBEC3G deaminase enzyme. Herein, we describe the current state of knowledge on how the gammac cytokine network is affected during HIV infection, with a focus on how this impairs CD4+ and CD8+ T cell function while also benefiting the virus itself. We also address the use of cytokines as adjuncts to highly active antiretroviral therapy to bolster immune reconstitution in infected patients.

Importance of interleukin-7 in the development of experimental graft-versus-host disease

Interleukin (IL)-7 promotes both thymopoiesis and mature T lymphocyte survival and proliferation in experimental murine models of hematopoietic stem cell (HSC) transplantation. Because HSC products for transplantation also may contain IL-7-responsive mature T lymphocytes, we examined whether IL-7 is necessary for the induction of GVHD after allogeneic bone marrow transplantation (BMT). Lethally irradiated C57BL6J (B6) and B6.IL-7(-/-) (both H2K(b)) recipient mice were co-transplanted with T cell-depleted (TCD) bone marrow cells and lymph nodes (LNs) from either congenic B6.SJL (CD45.1(+)) or allogeneic BALB/c (H2K(d)) donor mice. After transplantation, the recipient mice were subcutaneously injected with either human recombinant IL-7 or phosphate-buffered saline (PBS) for 60 days. No evidence of GVHD was detected in the congenic recipients or in the allogeneic B6/IL-7(-/-) recipients treated with PBS; in contrast, significantly increased rates of GVHD-related mortality and morbidity were found in the allogeneic B6.IL-7(-/-) recipients treated with IL-7. The proliferation and number of donor T cells were significantly lower at day 30 post-BMT in the PBS-treated B6.IL-7(-/-) recipients compared with the IL-7-treated B6.IL-7(-/-) mice. These experiments demonstrate that IL-7 is an important factor in the development of GVHD, presumably by supporting the survival, proliferation, and possibly activation of alloreactive donor-derived T cells in the recipients.

Low CD4 T-cell counts despite low levels of circulating HIV: Insights from the comparison of HIV-1 infected patients with a discordant response to antiretroviral therapy to patients with untreated advanced HIV-2 disease

A significant proportion of HIV-1+ patients with suppression of viremia under antiretroviral therapy fail to recover CD4(+) T-cell counts (ART-Discordants). Similarly, untreated HIV-2+ patients can also exhibit major CD4 depletion in spite of undetectable viremia. We characterize here the immunological disturbances associated with major CD4-lymphopenia in these two scenarios as compared to untreated viremic HIV-1+ patients with similar CD4-lymphopenia and HIV-1+ patients with successful immunological and virological responses under ART. Low CD4 counts were associated with major naive CD4 and CD8 depletion, irrespective of type of infection or ART-exposure. However, ART-Discordants exhibited lower levels of T-cell activation as compared to both untreated HIV-2 and HIV-1 cohorts, and a less marked increase in circulating IL-7 despite similar CD4 depletion. Nevertheless, ART-Discordants showed a preserved Bcl-2 expression, suggesting increased IL-7 consumption, which in conjunction with the relatively lower T-cell activation may contribute to their CD4 count stability and low rate of opportunistic infections.