Russell B. Foxall

Rate of Increase in Circulating IL-7 and Loss of IL-7Rα Expression Differ in HIV-1 and HIV-2 Infections: Two Lymphopenic Diseases with Similar Hyperimmune Activation but Distinct Outcomes

IL-7 is a nonredundant cytokine for T cell homeostasis. Circulating IL-7 levels increase in lymphopenic clinical settings, including HIV-1 infection. HIV-2 infection is considered a “natural” model of attenuated HIV disease given its much slower rate of CD4 decline than HIV-1 and limited impact on the survival of the majority of infected adults. We compared untreated HIV-1- and HIV-2-infected patients and found that the HIV-2 cohort demonstrated a delayed increase in IL-7 levels during the progressive depletion of circulating CD4 T cells as well as a dissociation between the acquisition of markers of T cell effector differentiation and the loss of IL-7Rα expression. This comparison of two persistent infections associated with progressive CD4 depletion and immune activation demonstrates that a better prognosis is not necessarily associated with higher levels of IL-7. Moreover, the delayed increase in IL-7 coupled with sustained expression of IL-7Rα suggests a maximization of available resources in HIV-2. The observation that increased IL-7 levels early in HIV-1 infection were unable to reduce the rate of CD4 loss and the impaired expression of the IL-7Rα irrespective of the state of cell differentiation raises concerns regarding the use of IL-7 therapy in HIV-1 infection.

Increased Frequency of Circulating CCR5+ CD4+ T Cells in Human Immunodeficiency Virus Type 2 Infection

ABSTRACT CCR5 expression determines susceptibility to infection, cell tropism, and the rate of human immunodeficiency virus type 1 (HIV-1) disease progression. CCR5 is also considered the major HIV-2 coreceptor in vivo, in spite of broad coreceptor use in vitro. Here we report a significantly increased proportion of memory-effector CD4 T cells expressing CCR5 in HIV-2-infected patients correlating with CD4 depletion. Moreover, HIV-2 proviral DNA was essentially restricted to memory-effector CD4, suggesting that this is the main target for HIV-2. Similar levels of proviral DNA were found in the two infection categories. Thus, the reduced viremia and slow rate of CD4 decline that characterize HIV-2 infection seem to be unrelated to coreceptor availability.

Major depletion of plasmacytoid dendritic cells in HIV-2 infection, an attenuated form of HIV disease.

Plasmacytoid dendritic cells (pDC) provide an important link between innate and acquired immunity, mediating their action mainly through IFN-α production. pDC suppress HIV-1 replication, but there is increasing evidence suggesting they may also contribute to the increased levels of cell apoptosis and pan-immune activation associated with disease progression. Although having the same clinical spectrum, HIV-2 infection is characterized by a strikingly lower viremia and a much slower rate of CD4 decline and AIDS progression than HIV-1, irrespective of disease stage. We report here a similar marked reduction in circulating pDC levels in untreated HIV-1 and HIV-2 infections in association with CD4 depletion and T cell activation, in spite of the undetectable viremia found in the majority of HIV-2 patients. Moreover, the same overexpression of CD86 and PD-L1 on circulating pDC was found in both infections irrespective of disease stage or viremia status. Our observation that pDC depletion occurs in HIV-2 infected patients with undetectable viremia indicates that mechanisms other than direct viral infection determine the pDC depletion during persistent infections. However, viremia was associated with an impairment of IFN-α production on a per pDC basis upon TLR9 stimulation. These data support the possibility that diminished function in vitro may relate to prior activation by HIV virions in vivo, in agreement with our finding of higher expression levels of the IFN-α inducible gene, MxA, in HIV-1 than in HIV-2 individuals. Importantly, serum IFN-α levels were not elevated in HIV-2 infected individuals. In conclusion, our data in this unique natural model of “attenuated” HIV immunodeficiency contribute to the understanding of pDC biology in HIV/AIDS pathogenesis, showing that in the absence of detectable viremia a major depletion of circulating pDC in association with a relatively preserved IFN-α production does occur.

Variable relationship between proviral DNA load and infectious virus titre in the peripheral blood mononuclear cells of HIV-1-infected individuals.

ObjectivesTo determine the relationship between infectious virus titre and proviral copy number in peripheral blood mononuclear cells (PBMC) of infected subjects and to ascertain which, if either, is most closely related to CD4+ cell loss and disease progression. Design and methodsCellular HIV-1 viraemia was quantified in 45 infected subjects who had not received antiretroviral therapy using limiting dilution tissue culture infective dose (PBMC TCID) and quantitative polymerase chain reaction (PCR) techniques. ResultsProviral DNA was detected in 44 (98%) and infectious virus in 38 (82%) of the 45 subjects. Viraemia as measured by both culture and PCR was inversely correlated with patient CD4 + cell count and associated with disease status. Measurement using both techniques correlated with each other (Spearmans rank correlation rho = 0.52; P = 0.0006). The ratio of proviral copies to PBMC TCID ranged from 1:1 to > 1000:1. ConclusionsThe ratio of provirus:PBMC TCID was highest when the PBMC TCID was low, and approached unity when PBMC TCID was high. This ratio could be influenced by a variety of factors but did not correlate significantly with patient disease status or CD4+ cell count.

Enteric Mucosa Integrity in the Presence of a Preserved Innate Interleukin 22 Compartment in HIV Type 1–Treated Individuals

BACKGROUND Interleukin 22 (IL-22) is emerging as a key cytokine for gut epithelial homeostasis and mucosal repair. Gut disruption is a hallmark of human immunodeficiency virus (HIV) infection. Here, we investigated IL-22 production and gut mucosal integrity in HIV type 1 (HIV-1)-infected individuals receiving long-term antiretroviral therapy (ART). METHODS Biopsy specimens from 37 individuals who underwent colonoscopy primarily for cancer screening and from 17 HIV-1-infected and 20 healthy age-matched controls were assessed. RESULTS We found significant depletion of sigmoid IL-22-producing CD4(+) T cells (T-helper type 22 [Th22] cells) even after prolonged ART, contrasting with the apparently normal compartments of regulatory and interleukin 17 (IL-17)-producing CD4(+) T cells, as well as total mucosal CD4(+) T cells. Despite the preferential Th22 cell depletion, IL-22 production by innate lymphoid cells (ILCs) was similar to that observed in HIV-1-seronegative subjects, and transcription of genes encoding molecules relevant for IL-22 production (ie, AHR, IL23, IL23R, IL1B, IL6, and TGFB1) was preserved. Remarkably, levels of transcripts of IL-22-target genes (ie, REG3G, DEFB4A, S100A9, MUC1, and MUC13) were unaltered, suggesting an adequate production of antimicrobial peptides and mucins. In agreement, enteric epithelial architecture was fully preserved. CONCLUSIONS Despite the reduced Th22 cell subset, innate IL-22-mediated mechanisms, essential for sigmoid mucosa integrity, were fully operational in long-term-treated HIV-1-infected individuals. Our data highlight IL-22 production by ILCs as an important target for therapies aimed at facilitating human mucosal reconstitution.

Regulatory T-Cell Development in the Human Thymus

The thymus generates a lineage-committed subset of regulatory T-cells (Tregs), best identified by the expression of the transcription factor FOXP3. The development of thymus-derived Tregs is known to require high-avidity interaction with MHC-self peptides leading to the generation of self-reactive Tregs fundamental for the maintenance of self-tolerance. Notwithstanding their crucial role in the control of immune responses, human thymic Treg differentiation remains poorly understood. In this mini-review, we will focus on the developmental stages at which Treg lineage commitment occurs, and their spatial localization in the human thymus, reviewing the molecular requirements, including T-cell receptor and cytokine signaling, as well as the cellular interactions involved. An overview of the impact of described thymic defects on the Treg compartment will be provided, illustrating the importance of these in vivo models to investigate human Treg development.

Memory and naive-like regulatory CD4+ T cells expand during HIV-2 infection in direct association with CD4+ T-cell depletion irrespectively of viremia

Objective:The dynamics of CD4+ regulatory T cells (Treg) during HIV-1 infection remains unclear. To further investigate Treg in this context, we characterized, for the first time, this population in HIV-2-positive individuals. Although both HIV infections are associated with hyperimmune activation and CD4+ T-cell lymphopenia, most HIV-2-positive individuals display slower disease progression and low-to-undetectable viremia. Design/methods:Samples were obtained from cohorts of untreated HIV-2-positive and HIV-1-positive, treated HIV-1-positive and seronegative individuals. The proportion of CD4+ T cells bearing a Treg phenotype, defined in terms of high-level CD25 or Foxp3 expression, was assessed by flow cytometry and correlated with markers of disease progression. The proportions of naive and memory-like subsets as well as cycling cells were determined. Results:We observed an increased proportion of Treg, associated with disease progression, as well as increased proportions of cycling (Ki67+) memory Treg, in untreated HIV-2-positive and HIV-1-positive individuals. We also noted an expansion of Treg that persisted over time in treated, immunologically discordant HIV-1-positive individuals, who, similarly to HIV-2-positive patients, present undetectable viremia and low CD4 T-cell count. Conclusion:Overall, we demonstrated that Treg frequency was increased in all lymphopenic HIV-2-positive and HIV-1-positive individuals irrespective of the presence or absence of viremia or antiretroviral treatment. This, in turn, suggests that the observed alterations in Treg frequency in HIV/AIDS are more directly related to the degree of CD4 depletion than to viremia.

PD-1 and its ligand PD-L1 are progressively up-regulated on CD4 and CD8 T-cells in HIV-2 infection irrespective of the presence of viremia.

Objective:Hyper-immune activation is a main determinant of HIV disease progression, potentially counter-acted by T-cell inhibitory pathways. Here we investigated, for the first time, inhibitory molecules in HIV-2 infection, a naturally occurring attenuated form of HIV disease, associated with reduced viremia and very slow rates of CD4 T-cell decline. Design:Programmed death (PD)-1/PD-L1, an important pathway in limiting immunopathology, and its possible relationship with T-cell immunoglobulin and mucin-domain containing molecule-3 (TIM-3), a recently identified inhibitory molecule, were studied in untreated HIV-2 and HIV-1 cohorts, matched for degree of CD4 T-cell depletion, and noninfected individuals. Methods:Flow cytometric analysis of T-cell expression of PD-1, PD-L1 and TIM-3, combined with markers of cell differentiation, activation, cycling and survival. Statistical analysis was performed using ANOVA, Mann–Whitney/Wilcoxon tests, Spearmans correlations, multiple linear regressions and canonical correlation analysis. Results:T-cell expression of PD-1 and PD-L1 was tightly associated and directly correlated with CD4 T-cell depletion and immune activation in HIV-2 infection. No such correlation was found for PD-L1 expression in HIV-1-positive patients. Central memory and intermediate memory cells, rather than terminally differentiated T-cells, expressed the highest levels of both PD-1 and PD-L1 molecules. Conversely, TIM-3 expression was independent of T-cell differentiation and dissociated from cell cycling, suggesting distinct induction mechanisms. Importantly, in contrast with HIV-1, no significant increases in TIM-3 expression were found in the HIV-2 cohort. Conclusions:Our data suggest that PD-1/PD-L1 molecules, rather than markers of T-cell exhaustion, may act as modulators of T-cell immune activation, contributing to the slower course of HIV-2 infection. These data have implications for the design of antiretroviral therapy-complementary immune-based strategies.

Human regulatory T-cell development is dictated by Interleukin-2 and -15 expressed in a non-overlapping pattern in the thymus

Thymus-derived FOXP3-expressing regulatory T-cells (tTregs) are master orchestrators of physiological and pathological immune responses, thus constituting ideal targets for the treatment of autoimmunity. Despite their clinical importance, the developmental program governing their differentiation in the human thymus remains poorly understood. Here, we investigated the role of common gamma-chain cytokines in human tTreg differentiation, by performing gain- and loss-of-function experiments in 3D and 2D postnatal thymic cultures. We identified IL-2 and IL-15 as key molecular determinants in this process and excluded a major function for IL-4, IL-7 and IL-21. Mechanistically, IL-2 and IL-15 were equally able to drive tTreg precursor differentiation into FOXP3(+) cells, and promote tTreg proliferation and survival. Both cytokines also increased the expression levels of molecules associated with effector function within FOXP3(+) subsets, supporting their involvement in tTreg functional maturation. Furthermore, we revealed that IL-2 and IL-15 are expressed in a non-overlapping pattern in the human thymus, with the former produced mainly by mature αβ and γδ thymocytes and the latter by monocyte/macrophages and B lymphocytes. Our results identify core mechanisms dictating human tTreg development, with IL-2 and IL-15 defining specific niches required for tTreg lineage stabilization and differentiation, with implications for their therapeutic targeting in autoimmune conditions.

Monocyte and Myeloid Dendritic Cell Activation Occurs Throughout HIV Type 2 Infection, an Attenuated Form of HIV Disease

Monocytes and myeloid dendritic cells (mDCs) are important orchestrators of innate and human immunodeficiency virus (HIV)-specific immune responses and of the generalized inflammation that characterizes AIDS progression. To our knowledge, we are the first to investigate monocyte and mDC imbalances in HIV type 2 (HIV-2)-positive patients, who typically feature reduced viremia and slow disease progression despite the recognized ability of HIV-2 to establish viral reservoirs and overcome host restriction factors in myeloid cells. We found a heightened state of monocyte and mDC activation throughout HIV-2 infection (characterized by CD14(bright)CD16(+) expansion, as well as increased levels of soluble CD14, HLA-DR, and CD86), together with progressive mDC depletion. Importantly, HIV-2-positive patients also featured overexpression of the inhibitory molecule PD-L1 on monocytes and mDCs, which may act by limiting the production of proinflammatory molecules. These data, from patients with a naturally occurring form of attenuated HIV disease, challenge current paradigms regarding the role of monocytes in HIV/AIDS and open new perspectives regarding potential strategies to modulate inflammatory states.