CD40 Ligand Dysregulation in HIV Infection: HIV Glycoprotein 120 Inhibits Signaling Cascades Upstream of CD40 Ligand Transcription

CD40L protects against mouse hepatitis virus-induced neuroinflammatory demyelination

Neurotropic mouse hepatitis virus (MHV-A59/RSA59) infection in mice induces acute neuroinflammation due to direct neural cell dystrophy, which proceeds with demyelination with or without axonal loss, the pathological hallmarks of human neurological disease, Multiple sclerosis (MS). Recent studies in the RSA59-induced neuroinflammation model of MS showed a protective role of CNS-infiltrating CD4⁺ T cells compared to their pathogenic role in the autoimmune model. The current study further investigated the molecular nexus between CD4⁺ T cell-expressed CD40Ligand and microglia/macrophage-expressed CD40 using CD40L^-/- mice. Results demonstrate CD40L expression in the CNS is modulated upon RSA59 infection. We show evidence that CD40L^-/- mice are more susceptible to RSA59 induced disease due to reduced microglia/macrophage activation and significantly dampened effector CD4⁺ T recruitment to the CNS on day 10 p.i. Additionally, CD40L^-/- mice exhibited severe demyelination mediated by phagocytic microglia/macrophages, axonal loss, and persistent poliomyelitis during chronic infection, indicating CD40-CD40L as host-protective against RSA59-induced demyelination. This suggests a novel target in designing prophylaxis for virus-induced demyelination and axonal degeneration, in contrast to immunosuppression which holds only for autoimmune mechanisms of inflammatory demyelination.

MS is primarily considered an autoimmune CNS disease, but its potential viral etiology cannot be ignored. Myelin-specific CD40L⁺CD4⁺ T cells migration into the CNS and resultant neuroinflammation is considered pathogenic in autoimmune MS. In contrast, CD40L⁺CD4⁺ T infiltration into the MHV-induced inflamed CNS and their interaction with CD40⁺ microglia/macrophages are shown to be protective in our study. Considering differential etiology but comparable demyelination and axonal loss, immunosuppressive treatments may not necessarily ameliorate MS in all patients. MHV-induced demyelination in this study indicates that the interaction between CD40L on CD4⁺T cells and CD40 on microglia/macrophage plays an important protective role against MHV-induced chronic progressive demyelination.

Differential Plasma Protein Regulation and Statin Effects in Human Immunodeficiency Virus (HIV)-Infected and Non-HIV-Infected Patients Utilizing a Proteomics Approach

BACKGROUND

People with human immunodeficiency virus (PWH) demonstrate increased atherosclerotic cardiovascular disease (ASCVD). Statins are being studied to prevent ASCVD in human immunodeficiency virus (HIV), but little is known regarding the effects of statins on a broad range of inflammatory and cardiovascular proteins in this population.

METHODS

We used a highly specific discovery proteomic approach (Protein Extension Assay), to determine statin effects on over 350 plasma proteins in relevant ASCVD pathways among HIV and non-HIV groups. Responses to pitavastatin calcium were assessed in 89 PWH in the INTREPID trial and 46 non-HIV participants with features of central adiposity and insulin resistance. History of cardiovascular disease was exclusionary for both studies.

RESULTS

Among participants with HIV, PCOLCE (enzymatic cleavage of type I procollagen) significantly increased after pitavastatin therapy and PLA2G7 (systemic marker of arterial inflammation) decreased. Among participants without HIV, integrin subunit alpha M (integrin adhesive function) and defensin alpha-1 (neutrophil function) increased after pitavastatin therapy and PLA2G7 decreased. At baseline, comparing participants with and without HIV, differentially expressed proteins included proteins involved in platelet and endothelial function and immune activation.

CONCLUSIONS

Pitavastatin affected proteins important to platelet and endothelial function and immune activation, and effects differed to a degree within PWH and participants without HIV.

Multi-Donor Longitudinal Antibody Repertoire Sequencing Reveals the Existence of Public Antibody Clonotypes in HIV-1 Infection

Characterization of single antibody lineages within infected individuals has provided insights into the development of Env-specific antibodies. However, a systems-level understanding of the humoral response against HIV-1 is limited. Here, we interrogated the antibody repertoires of multiple HIV-infected donors from an infection-naive state through acute and chronic infection using next-generation sequencing. This analysis revealed the existence of "public" antibody clonotypes that were shared among multiple HIV-infected individuals. The HIV-1 reactivity for representative antibodies from an identified public clonotype shared by three donors was confirmed. Furthermore, a meta-analysis of publicly available antibody repertoire sequencing datasets revealed antibodies with high sequence identity to known HIV-reactive antibodies, even in repertoires that were reported to be HIV naive. The discovery of public antibody clonotypes in HIV-infected individuals represents an avenue of significant potential for better understanding antibody responses to HIV-1 infection, as well as for clonotype-specific vaccine development.

Induction of Th1-Biased T Follicular Helper (Tfh) Cells in Lymphoid Tissues during Chronic Simian Immunodeficiency Virus Infection Defines Functionally Distinct Germinal Center Tfh Cells

Chronic HIV infection is associated with accumulation of germinal center (GC) T follicular helper (Tfh) cells in the lymphoid tissue. The GC Tfh cells can be heterogeneous based on the expression of chemokine receptors associated with T helper lineages, such as CXCR3 (Th1), CCR4 (Th2), and CCR6 (Th17). However, the heterogeneous nature of GC Tfh cells in the lymphoid tissue and its association with viral persistence and Ab production during chronic SIV/HIV infection are not known. To address this, we characterized the expression of CXCR3, CCR4, and CCR6 on GC Tfh cells in lymph nodes following SIVmac251 infection in rhesus macaques. In SIV-naive rhesus macaques, only a small fraction of GC Tfh cells expressed CXCR3, CCR4, and CCR6. However, during chronic SIV infection, the majority of GC Tfh cells expressed CXCR3, whereas the proportion of CCR4(+) cells did not change, and CCR6(+) cells decreased. CXCR3(+), but not CXCR3(-), GC Tfh cells produced IFN-γ (Th1 cytokine) and IL-21 (Tfh cytokine), whereas both subsets expressed CD40L following stimulation. Immunohistochemistry analysis demonstrated an accumulation of CD4(+)IFN-γ(+) T cells within the hyperplastic follicles during chronic SIV infection. CXCR3(+) GC Tfh cells also expressed higher levels of ICOS, CCR5, and α4β7 and contained more copies of SIV DNA compared with CXCR3(-) GC Tfh cells. However, CXCR3(+) and CXCR3(-) GC Tfh cells delivered help to B cells in vitro for production of IgG. These data demonstrate that chronic SIV infection promotes expansion of Th1-biased GC Tfh cells, which are phenotypically and functionally distinct from conventional GC Tfh cells and contribute to hypergammaglobulinemia and viral reservoirs.

Altered Monocyte Phenotype in HIV-1 Infection Tends to Normalize with Integrase-Inhibitor-Based Antiretroviral Therapy

Background

Monocytes are increasingly implicated in the inflammatory consequences of HIV-1 disease, yet their phenotype following antiretroviral therapy (ART) initiation is incompletely defined. Here, we define more completely monocyte phenotype both prior to ART initiation and during 48 weeks of ART.

Methods

Cryopreserved peripheral blood mononuclear cells (PBMCs) were obtained at baseline (prior to ART initiation) and at weeks 12, 24, and 48 of treatment from 29 patients participating in ACTG clinical trial A5248, an open label study of raltegravir/emtricitibine/tenofovir administration. For comparison, cryopreserved PBMCs were obtained from 15 HIV-1 uninfected donors, each of whom had at least two cardiovascular risk factors. Thawed samples were stained for monocyte subset markers (CD14 and CD16), HLA-DR, CCR2, CX3CR1, CD86, CD83, CD40, CD38, CD36, CD13, and CD163 and examined using flow cytometry.

Results

In untreated HIV-1 infection there were perturbations in monocyte subset phenotypes, chiefly a higher frequency and density (mean fluorescence intensity–MFI) of HLA-DR (%-p = 0.004, MFI-p = .0005) and CD86 (%-p = 0.012, MFI-p = 0.005) expression and lower frequency of CCR2 (p = 0.0002) expression on all monocytes, lower CCR2 density on inflammatory monocytes (p = 0.045) when compared to the expression and density of these markers in controls’ monocytes. We also report lower expression of CX3CR1 (p = 0.014) on patrolling monocytes at baseline, compared to levels seen in controls. After ART, these perturbations tended to improve, with decreasing expression and density of HLA-DR and CD86, increasing CCR2 density on inflammatory monocytes, and increasing expression and density of CX3CR1 on patrolling monocytes.

Conclusions

In HIV-1 infected patients, ART appears to attenuate the high levels of activation (HLA-DR, CD86) and to increase expression of the chemokine receptors CCR2 and CX3CR1 on monocyte populations. Circulating monocyte phenotypes are altered in untreated infection and tend to normalize with ART; the role of these cells in the inflammatory environment of HIV-1 infection warrants further study.

Restoration of CMV-specific-CD4 T cells with ART occurs early and is greater in those with more advanced immunodeficiency

Objectives

Restoration of Cytomegalovirus-specific-CD4 T cell (CMV-Sp-CD4) responses partly accounts for the reduction of CMV-disease with antiretroviral-therapy (ART), but CMV-Sp-CD4 may also drive immune activation and immunosenescence. This study characterized the dynamics of CMV-Sp-CD4 after ART initiation and explored associations with CD4 T cell recovery as well as frequency of naïve CD4 T cells at week 96.

Methods

Fifty HIV-infected, ART-naïve Thai adults with CD4 T cell count ≤350cells/µL and starting ART were evaluated over 96 weeks (ClinicalTrials.gov identifier NCT01296373). CMV-Sp-CD4 was detected by co-expression of CD25/CD134 by flow cytometry after CMV-antigen stimulation.

Results

All subjects were CMV sero-positive, 4 had quantifiable CMV-DNA (range 2.3-3.9 log₁₀ copies/mL) at baseline but none had clinically apparent CMV-disease. Baseline CMV-Sp-CD4 response was positive in 40 subjects. Those with CD4 T cell count <100cells/µL were less likely to have positive baseline CMV-Sp-CD4 response (P=0.003). Positive baseline CMV-Sp-CD4 response was associated with reduced odds of quantifiable CMV-DNA (P=0.022). Mean CD4 T cell increase at week 96 was 213 cells/µL. This was associated positively with baseline HIV-VL (P=0.001) and negatively with age (P=0.003). The frequency of CMV-Sp-CD4 increased at week 4 (P=0.008), then declined. Those with lower baseline CMV-Sp-CD4 (P=0.009) or CDC category C (P<0.001) had greater increases in CMV-Sp-CD4 at week 4. At week 96, CD4 T cell count was positively (P<0.001) and the frequency of CMV-Sp-CD4 was negatively (P=0.001) associated with the percentage of naïve CD4 T cells.

Conclusions

Increases in CMV-Sp-CD4 with ART occurred early and were greater in those with more advanced immunodeficiency. The frequency of CMV-Sp-CD4 was associated with reduced naïve CD4 T cells, a marker associated with immunosenescence.

Highly active antiretroviral therapy in patients infected with human immunodeficiency virus increases CD40 ligand expression and IL-12 production in cells ex vivo

Highly active anti-retroviral therapy (HAART) restores CD4(+) T-cell numbers in the periphery; however, its efficacy in restoring functional immunity is not fully elucidated. Here we evaluated longitudinal changes in the expression of several key markers of T-cell activation, namely CD40 ligand (CD154), OX40 (CD134), or CD69, after anti-CD3/CD28 activation, as well as levels of IL-12 production after Staphylococcus aureus Cowan stimulation in 28 HIV-infected adult patients. Patients were followed up to 12 mo post-HAART initiation. Viral burdens and CD4 cell counts were measured at the same time points. A control group of 15 HIV-uninfected adult subjects was included for comparison. Significant increases in CD40L and OX40 expression, but not of CD69 expression, were observed over time in the overall patient population, and more particularly in patients with baseline CD4 counts lower than or equal to 200 cells/μL, or those with baseline viral loads lower than or equal to 10(5) RNA copies/mL. Similar increases were seen for IL-12 production. Viral loads were inversely associated with CD40L expression or IL-12 production in a mixed linear model analysis, while CD4 counts were directly associated. CD40L expression and IL-12 production were significantly correlated. In conclusion, HAART-mediated control of viral replication led to partial restoration of CD40L upregulation/expression, and to increased IL-12 production, but the magnitude of the response depended on the baseline characteristics of the treated patients.

Impaired CD4 T cell memory response to Streptococcus pneumoniae precedes CD4 T cell depletion in HIV-infected Malawian adults

OBJECTIVE

Invasive pneumococcal disease (IPD) is a leading cause of morbidity and mortality in HIV-infected African adults. CD4 T cell depletion may partially explain this high disease burden but those with relatively preserved T cell numbers are still at increased risk of IPD. This study evaluated the extent of pneumococcal-specific T cell memory dysfunction in asymptomatic HIV infection early on in the evolution of the disease.

METHODS

Peripheral blood mononuclear cells were isolated from asymptomatic HIV-infected and HIV-uninfected Malawian adults and stained to characterize the underlying degree of CD4 T cell immune activation, senescence and regulation. Pneumococcal-specific T cell proliferation, IFN-γ, IL-17 production and CD154 expression was assessed using flow cytometry and ELISpot.

RESULTS

We find that in asymptomatic HIV-infected Malawian adults, there is considerable immune disruption with an increase in activated and senescent CD4+CD38+PD-1+ and CD4+CD25(high)Foxp3+ Treg cells. In the context of high pneumococcal exposure and therefore immune stimulation, show a failure in pneumococcal-specific memory T cell proliferation, skewing of T cell cytokine production with preservation of interleukin-17 but decreased interferon-gamma responses, and failure of activated T cells to express the co-stimulatory molecule CD154.

CONCLUSION

Asymptomatic HIV-infected Malawian adults show early signs of pneumococcal- specific immune dysregulation with a shift in the balance of CD4 memory, T helper 17 cells and Treg. Together these data offer a mechanistic understanding of how antigen-specific T cell dysfunction occurs prior to T cell depletion and may explain the early susceptibility to IPD in those with relatively preserved CD4 T cell numbers.

CD4+ T-cell differentiation, regulatory T cells and gag-specific T lymphocytes are unaffected by CD4-guided treatment interruption and therapy resumption

OBJECTIVES

Despite limiting exposure to antiretroviral drugs, structured treatment interruptions can influence multiple aspects of T-cell immunity, particularly those regarding CD4(+) T lymphocytes. We evaluated the impact of CD4-guided treatment interruption (CD4-GTI) and treatment resumption on regulatory T cells (Tregs), T-lymphocyte activation, differentiation and polyfunctional gag-specific response.

METHODS

Patients were analyzed just prior to treatment interruption, at 2 and 6 months after treatment interruption, just prior to treatment resumption and at 2 and 6 months after treatment resumption. Thawed peripheral blood mononuclear cells were stained immediately for phenotype analysis or stimulated with HIV-gag peptides and analyzed by polychromatic flow cytometry.

RESULTS

Treatment interruption resulted in a CD4(+) cell count decrease and plasma viral load (pVL) increase, but did not preclude a good immune reconstitution and a complete suppression of pVL after treatment resumption. Treatment interruption did not influence CD4(+) T-cell differentiation and Treg subsets. During treatment interruption, gag-specific CD4(+) T cells were not lost, although the frequency of HIV-specific CD8(+) cells increased. Most gag-specific CD4(+) T cells were potentially cytotoxic (CD107a(+)) and were not influenced by pVL or by HAART. Most helper (CD154(+)) gag-specific CD4(+) T lymphocytes did not produce interferon-γ or interleukin-2.

CONCLUSION

CD4-GTI did not cause depletion of memory cells, Tregs or HIV-specific CD4(+) cells and, on the contrary, could induce HIV-specific responses. If guided by CD4(+) T-cell count, treatment interruption does not provoke irreversible immune damages.

The CD40-autophagy pathway is needed for host protection despite IFN-Γ-dependent immunity and CD40 induces autophagy via control of P21 levels

Autophagy degrades pathogens in vitro. The autophagy gene Atg5 has been reported to be required for IFN-γ-dependent host protection in vivo. However, these protective effects occur independently of autophagosome formation. Thus, the in vivo role of classic autophagy in protection conferred by adaptive immunity and how adaptive immunity triggers autophagy are incompletely understood. Employing biochemical, genetic and morphological studies, we found that CD40 upregulates the autophagy molecule Beclin 1 in microglia and triggers killing of Toxoplasma gondii dependent on the autophagy machinery. Infected CD40(-/-) mice failed to upregulate Beclin 1 in microglia/macrophages in vivo. Autophagy-deficient Beclin 1(+/-) mice, mice with deficiency of the autophagy protein Atg7 targeted to microglia/macrophages as well as CD40(-/-) mice exhibited impaired killing of T. gondii and were susceptible to cerebral and ocular toxoplasmosis. Susceptibility to toxoplasmosis occurred despite upregulation of IFN-γ, TNF-α and NOS2, preservation of IFN-γ-induced microglia/macrophage anti-T. gondii activity and the generation of anti-T. gondii T cell immunity. CD40 upregulated Beclin 1 and triggered killing of T. gondii by decreasing protein levels of p21, a molecule that degrades Beclin 1. These studies identified CD40-p21-Beclin 1 as a pathway by which adaptive immunity stimulates autophagy. In addition, they support that autophagy is a mechanism through which CD40-dependent immunity mediates in vivo protection and that the CD40-autophagic machinery is needed for host resistance despite IFN-γ.

B cells require "nurturing" by CD4 T cells during development in order to respond in chronic graft-versus-host model of systemic lupus erythematosus

The murine chronic GVH (cGVH) model of SLE is induced by allo-recognition of foreign major histocompatibility complex (MHC) class II determinants. Previous studies have shown that syngeneic CD4(+) T cells are needed during B cell development in order to induce cGVH response in CD4KO mice. Our present studies show that B cells require "nurturing" by CD4 T cells through much of their ontogeny in order to respond to allo-signaling and become autoreactive. The nurturing process does not require antigen-specific cognate interactions between CD4 T cells and B cells. It is mediated by IL-4, but not IL-10, IL-6 and IFN-gamma. The CD4 T cell nurturing may be supplanted by large doses of IL-4 and/or by agonistic anti-CD40 mAb. Understanding the mechanism of this "nurturing" process may yield clues to the role of CD4 T cells in lupus and in host defense in general.

CD40, autophagy and Toxoplasma gondii

Toxoplasma gondii represents a pathogen that survives within host cells by preventing the endosomal-lysosomal compartments from fusing with the parasitophorous vacuoles. The dogma had been that the non-fusogenic nature of these vacuoles is irreversible. Recent studies revealed that this dogma is not correct. Cell-mediated immunity through CD40 re-routes the parasitophorous vacuoles to the lysosomal compartment by a process called autophagy. Autophagosome formation around the parasitophorous vacuole results in killing of the T. gondii. CD40-induced autophagy likely contributes to resistance against T. gondii particularly in neural tissue.

Autophagy in immunity against Toxoplasma gondii

A decisive outcome during host-pathogen interaction is governed by whether pathogen-containing vacuoles fuse with lysosomes. Fusion with lysosomes typically kills microbes. Toxoplasma gondii represents a classical example of an intracellular pathogen that survives within host cells by preventing the endosomal-lysosomal compartments from fusing with the vacuoles that contain the pathogen. Thus, T. gondii provides an excellent model to determine if the immune system can target a pathogen for lysosomal degradation. CD40, a major regulator of cell-mediated immunity, activates macrophages to kill T. gondii through a process that requires recruitment of autophagosomes around the parasitophorous vacuole, leading to lysosomal degradation of the parasite. These studies demonstrate that cell-mediated immunity can activate autophagy to kill a pathogen. CD40-induced autophagy likely contributes to resistance against T. gondii, particularly in neural tissues, the main sites affected by this pathogen.

IL-23 and IL-12p70 production by monocytes and dendritic cells in primary HIV-1 infection

IL-12 enhances protective responses against HIV replication. Its production after in vitro stimulation is defective in chronic HIV infection, but higher responses can be found. IL-23 shares the p40 chain and some properties with IL-12 and enhances Th17 responses, but its role in HIV infection is unknown. The production of IL-12 and IL-23 and the respective contribution of monocytes and myeloid conventional DC (cDCs) during primary HIV infection were determined. Sixteen patients included in the French PRIMO-ANRS Cohort without antiretroviral treatment were followed prospectively and compared with uninfected donors. Intracellular p40 expression by monocytes and cDCs, analyzed by flow cytometry, was transiently increased in monocytes and cDCs in response to LPS and more consistently, in monocytes in response to LPS + IFN-gamma. IL-23 production, measured by ELISA after PBMC stimulation, was induced by LPS in strong correlation with VLs. IL-12p70 production required the addition of IFN-gamma and was transiently increased in patients compared with controls in correlation with VLs, whereas IL-23 was increased sustainedly. Therefore, an apparent domination of IL-23 over IL-12 responses occurred throughout primary HIV infection, and a potential restoration of IL-12 responses might be expected from a treatment mimicking activated T cell signals.

CD40 and the immune response to parasitic infections

The interaction between CD40 and CD154 regulates many aspects of cellular and humoral immunity. The CD40-CD154 pathway is important for resistance against a variety of parasites. Studies done with these pathogens have provided important insight into the various mechanisms by which this pathway enhances host protection, mechanisms by which pathogens subvert CD40 signaling, conditions in which the CD40-CD154 pathway promotes disease and on modulation of this pathway for immunotherapy.

Altered T cell costimulation during chronic hepatitis B infection

T-cell response to hepatitis B virus (HBV) is vigorous, polyclonal and multi-specific in patients with acute hepatitis who ultimately clear the virus, whereas it is narrow and inefficient in patients with chronic disease, where inappropriate early activation events could account for viral persistence. We investigated the induction of activation receptors and cytokine production in response to HBcAg and crosslinking of CD28 molecules, in CD4+ cells from a group of chronically infected patients (CIP) and naturally immune subjects (NIS). We demonstrated that CD4+ cells from CIP did not increase levels of CD40L and CD69 following stimulation with HBcAg alone or associated to CD28 crosslinking, in contrast to subjects that resolved the infection (p<0.01). Furthermore, CD4+ cells from CIP produced elevated levels of IL-10 in response to HBcAg. These results suggest that a predominant inhibitory environment may be responsible for altered T cell costimulation, representing a pathogenic mechanism for viral persistence.

Immune dysregulation in human immunodeficiency virus infection: know it, fix it, prevent it?

Infection of humans by the human immunodeficiency virus (HIV) causes a progressive, multifactorial impairment of the immune system eventually leading to the acquired immunodeficiency syndrome (AIDS). No cure or vaccine exists yet against HIV infection. More worrisome is the fact that despite having identified HIV as the cause of the AIDS, we still do not understand what pathogenic mechanisms lead to the debacle of the immune system. In this review we consider the extent and the limits of our knowledge of HIV pathogenesis, and how this knowledge may be used to design preventive and therapeutic approaches.

Human immunodeficiency virus type 1-anchored CD40 ligand induces secretion of the chemokine interleukin-8 by human primary macrophages

CD40 ligand (CD40L) is mainly expressed in activated CD4(+)T cells and interacts with CD40 on antigen-presenting cells to regulate both humoral and cellular immune responses. We previously reported that CD40L is acquired by emerging HIV-1 particles. Here we demonstrate that both wild-type and a non-functional mutated form of CD40L are incorporated within HIV-1. Importantly, we show that wild-type CD40L remains functional since CD40L-bearing virions mediate NF-kappaB activation in a CD40-expressing reporter cell line and induce secretion of the chemokine IL-8 by monocyte-derived macrophages. These results suggest a possible means exploited by HIV-1 to attract susceptible target cells to the site of infection, a process that might promote viral dissemination.

Engagement of the CD4 receptor affects the redistribution of Lck to the immunological synapse in primary T cells: implications for T-cell activation during human immunodeficiency virus type 1 infection

Understanding the molecular mechanisms underlying dysregulated immune responses in human immunodeficiency virus type 1 (HIV-1) infection is crucial for the control of HIV/AIDS. Despite the postulate that HIV envelope glycoprotein gp120-CD4 interactions lead to impaired T-cell responses, the precise mechanisms underlying such association are not clear. To address this, we analyzed Lck and F-actin redistribution into the immunological synapse in stimulated human primary CD4(+) T cells from HIV-1-infected donors. Similar experiments were performed with CD4(+) T cells from HIV-uninfected donors, which were exposed to anti-CD4 domain 1 antibodies, as an in vitro model of gp120-CD4 interactions, or aldithriol-inactivated HIV-1 virions before stimulation. CD4(+) T cells from HIV-infected patients exhibited a two- to threefold inhibition of both Lck and F-actin recruitment into the synapse, compared to cells from uninfected donors. Interestingly, defective recruitment of Lck was ameliorated following suppressive highly active antiretroviral therapy. Engagement of the CD4 receptor on T cells from HIV-uninfected donors before anti-CD3/CD28 stimulation led to similar defects. Furthermore, the redistribution of Lck into lipid rafts was abrogated by CD4 preengagement. Our results suggest that the engagement of CD4 by HIV gp120 prior to T-cell receptor stimulation leads to dysregulation of early signaling events and could consequently play an important role in impaired CD4(+) T-cell function.

Chimpanzee CD4+ T cells are relatively insensitive to HIV-1 envelope-mediated inhibition of CD154 up-regulation

CD40-CD154 interaction forms a key event in regulation of crosstalk between dendritic cells and CD4 T cells. In human immunodeficiency virus (HIV)-1 infected patients CD154 expression is impaired, and the resulting loss of immune responsiveness by CD4+ T cells contributes to a progressive state of immunodeficiency in humans. Although chimpanzees are susceptible to chronic HIV-1/SIVcpz infection, they are relatively resistant to the onset of AIDS. This relative resistance is characterized by maintenance of CD4+ T cell populations and function, which is highly compromised in human patients. In our cohort of chronically HIV-1- and SIVcpz-infected chimpanzees, we demonstrated the capacity to produce IL-2, following CD3/CD28 stimulation, as well as preserved CD154 up-regulation. Cross-linking of CD4 with mAb was found to inhibit CD3/CD28-induced up-regulation of CD154 equally in chimpanzees and humans. However, specific cross-linking with trimeric recombinant HIV-1 gp140 revealed reduced sensitivity for inhibition of CD154 up-regulation in chimpanzees, requiring fourfold higher concentrations of viral protein. Chimpanzee CD4+ T cells are thus less sensitive to the immune-suppressive effect of low-dose HIV-1 envelope protein than human CD4+ T cells.

A splenic marginal zone-like peripheral blood CD27+B220- B cell population is preferentially depleted in HIV type 1-infected individuals

Peripheral blood CD27(+) B cells are reduced in HIV-1-infected individuals. In healthy individuals, the human peripheral blood CD27(+) B cell pool consists of two subsets defined by the expression, or lack thereof, of the CD45 isoform B220. We investigated the presence of circulating B220(+) and B220(-) memory B cells in HIV(+) individuals and found that the reduction in CD27(+) memory B cells occurs primarily among CD27(+)B220(-) B cells. Studies conducted using healthy controls indicate that CD27(+)B220(-) B cells have a splenic marginal zone like the immunophenotype IgM(hi)IgD(lo)CD21(+)CD23(-), express TLR9, and proliferate and secrete IgG and IgM in response to B cell-specific ODN. CD27(+)B220(+) B cells have the immunophenotype IgM(lo)IgD(hi)CD21(+)CD23(+), express activation-induced cytidine deaminase, and proliferate in response to SAC but do not secrete immunoglobulin. The AICD expression, along with CD86 expression, by CD27(+)B220(+) suggests these cells are of germinal center origin. The preferential depletion of CD27(+)B220(-) B cells mirrors alterations in spleen morphology and resident B cell populations due to HIV infection reported by other investigators and may play an important role in the defective B cell immunity against T-independent pathogens such as pneumococcus observed in HIV-1-infected individuals.

Identification of a strongly activating human anti-CD40 antibody that suppresses HIV type 1 infection

We characterized the functional properties of a novel set of human anti-CD40 monoclonal antibodies originating from a human phage display library and identified an antibody that strongly activates cells via the CD40 receptor for potential use in HIV therapy. The anti-CD40 antibodies were converted from a single chain antibody fragment format (scFv) to an IgG format and produced in HEK293 cells, and the binding characteristics were evaluated. Next, their ability to (1) rescue a human B cell line from induced apoptosis, (2) stimulate B cell proliferation, and (3) block the CD40-CD40L interaction was determined. Finally, the most activating anti-CD40 antibody was tested for its ability to block HIV-1 infection in a monocyte-derived cell line. The different anti-CD40 antibodies, A24, B44, E30, F33, and A2-54, displayed a wide variety of binding and functional properties. In particular, B44 showed a very strong ability to activate normal human B cells and, in addition, did not block the CD40-CD40L interaction. This antibody was able to suppress HIV-1 infection in a human cell line (MonoMac 1) and may be a potential therapeutic candidate in HIV infection.

Cell isolation and expansion using Dynabeads

This chapter describes the use of Dynabeads for cell isolation and expansion. Dynabeads are uniform polystyrene spherical beads that have been made magnetisable and superparamagnetic, meaning they are only magnetic in a magnetic field. Due to this property, the beads can easily be resuspended when the magnetic field is removed. The invention of Dynabeads made, by Professor John Ugelstad, has revolutionized the separation of many biological materials. For example, the attachment of target-specific antibodies to the surface of the beads allows capture and isolation of intact cells directly from a complex suspension such as blood. This is all accomplished under the influence of a simple magnetic field without the need for column separation techniques or centrifugation. In general, magnetic beads coated with specific antibodies can be used either for isolation or depletion of various cell types. Positive or negative cell isolation can be performed depending on the nature of the starting sample, the cell surface markers and the downstream application in question. Positive cell isolation is the method of choice for unprocessed samples, such as whole blood, and for downstream molecular applications. Positive cell isolation can also be used for any downstream application after detachment and removal of the beads. Negative cell isolation is the method of choice when it is critical that cells of interest remain untouched, i.e., no antibodies have been bound to any cell surface markers on the cells of interest. Some cell populations can only be defined by multiple cell surface markers. Such populations of cells can be isolated by the combination of negative and positive cell isolation. By coupling Dynabeads with antibodies directed against cell surface activation molecules, the beads can be used both for isolation and expansion of the cells. Dynabeads are currently used in two major clinical applications: 1) In the Isolex 300i Magnetic Cell Selection System for CD34 Stem Cell Isolation--2) For ex vivo T cell isolation and expansion using Dynabeads ClinExVivo CD3/CD28 for clinical trials in novel adoptive immunotherapy.

Live-cell assay to detect antigen-specific CD4+ T-cell responses by CD154 expression

This protocol details a method to identify CD4+ T cells that respond to antigens. The method relies on detection of CD154, a costimulatory cell surface protein that is expressed by CD4+ T cells upon activation, and can be used to purify live CD4+ T cells of diverse function. To detect CD154, fluorescently labeled antibodies are cultured with cell samples, peptides (or whole antigens) and monensin during a 6- to 24-h stimulation period. (Note that the assay is not compatible with brefeldin A.) After stimulation, cells are stained with any other antibodies of interest and then are analyzed by flow cytometry or purified by cell sorting. Unlike other assays, this method allows simultaneous assessment of other cell phenotypes or functions, is compatible with downstream RNA-based assays and preserves cell viability. This protocol can be completed in 9 h.

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

Deregulated expression of CD40 ligand in HTLV-I infection: distinct mechanisms of downregulation in HTLV-I-transformed cell lines and ATL patients

HTLV-I infection is associated with the development of adult T cell leukemia (ATL) and the neuroinflammatory disease HAM/TSP. There are quantitative and qualitative differences in the antiviral cytotoxic T cell (CTL) response in ATL and HAM/TSP although the underlying mechanisms are unclear. Here, we demonstrate that the HTLV-I Tax trans-activating protein is a transcriptional activator of CD40 ligand (CD40L), a critical regulator of dendritic cell maturation and adaptive immunity. Tax activates CD40L expression via a cyclosporin A insensitive pathway that is also independent of NF-kappaB. Although Tax upregulates CD40L gene expression, CD40L expression is absent in Tax-expressing HTLV-I-transformed cell lines via an epigenetic mechanism involving methylation. T lymphocytes cultured ex vivo from ATL patients, but not HAM/TSP or normal controls, exhibit a potent block in the induction of CD40L, but not CD69. However, the CD40L gene is not silenced by methylation in ATL patients, thus CD40L is downregulated by distinct mechanisms in HTLV-I-transformed cell lines and ATL patients.

Role of CD40-Dependent Down-Regulation of CD154 in Impaired Induction of CD154 in CD4+ T Cells from HIV-1-Infected Patients

CD40-CD154 interaction is pivotal for cell-mediated immunity. There are contradictory reports on whether HIV-1 infection impairs CD154 induction. The interaction between CD40 and CD154 is important not only because it results in activation of APCs but also because it controls CD154 by diminishing expression of this molecule. Compared with healthy controls, CD4(+) T cells from HIV-1(+) patients had impaired induction of CD154 when T cell activation was mediated by CD40(+) APCs. In contrast, T cell activation in the absence of these cells resulted in normal CD154 expression. CD154 induction in HIV-1(+) patients and controls were similar upon blockade of CD40-CD154 binding. Defective regulation of CD154 appeared to occur downstream of the control of mRNA levels because up-regulation of CD154 mRNA was not impaired by HIV-1 infection. This work identifies CD40 as a mediator of impaired CD154 induction in HIV-1 infection and explains why this defect was not detected by studies where T cell activation was triggered independently of CD40(+) APCs. In addition, dysregulation of CD154 in HIV-1 infection likely contributes to immunodeficiency because diminished expression of CD154 induced by CD40 is of functional relevance, resulting in decreased dendritic cell maturation.

Role of gp120 in dendritic cell dysfunction in HIV infection

Only a limited fraction of circulating virions are demonstrably infectious; therefore, exposure to inactivated viruses may mimic the most frequent type of CD4-HIV interactions that occur in vivo. Several studies have recently underscored the crucial role that those noninfectious viruses could play in defective immune function in HIV-infected individuals and in particular, in the dysregulation of dendritic cell (DC) function. In this review, we discuss how interactions between DC and HIV gp120 or inactivated virus, which harbor intact surface gp120, lead to impaired DC function through direct (direct contact) or indirect mechanisms (as a consequence of primary CD4+ T cell dysregulation, followed by defective CD4-DC interactions). It is important that these functionally impaired DCs fail to give optimal signal to T cells but appear to favor the emergence of regulatory T cells. gp120-mediated impairment of DC function could therefore play an important role in the pathogenesis of HIV disease.

HIV-1-driven regulatory T-cell accumulation in lymphoid tissues is associated with disease progression in HIV/AIDS

Regulatory T (Treg) cells accumulate in the lymphoid tissues of human immunodeficiency virus (HIV)-infected individuals, contributing to the inability of the immune system to control virus replication. We investigate here Treg-cell numbers and functional markers (FOXP3, CTLA-4, IDO, and TGF-beta1) in lymphoid tissues from untreated infected hosts with progressive or nonprogressive disease (HIV-infected humans and simian immunodeficiency virus [SIV]-infected macaques). We found that increased numbers of FOXP3(+) T cells as well as increased expression of Treg-cell-associated functional markers were detected only during progressive disease. Such increases were not correlated with immune activation. Of importance, a high-perforin/FOXP3 ratio was associated with nonprogressive disease, suggesting that the immune control of virus replication represents a balance between cell-mediated immune responses and Treg-cell-mediated counter regulation of such responses. Furthermore, using an in vitro model of Treg-cell-HIV interactions, we showed that exposure of Treg cells to HIV selectively promoted their survival via a CD4-gp120-dependent pathway, thus providing an underlying mechanism for the accumulation of Treg cells in infected hosts with active viral replication. Considered together, our findings imply that therapeutic manipulation of Treg-cell number and/or function could improve immune control of HIV infection.

CD8+ lymphocyte-mediated injury of dorsal root ganglion neurons during lentivirus infection: CD154-dependent cell contact neurotoxicity

Neuronal damage in dorsal root ganglia (DRGs) with accompanying axonal injury is a key feature of human immunodeficiency virus (HIV)-related distal sensory polyneuropathy (DSP). In a model of HIV-related DSP, we observed numerous CD3+ T lymphocytes (p < 0.05) in DRGs from feline immunodeficiency virus (FIV)-infected animals, which also exhibited low CD4+ and high CD8+ lymphocyte levels in blood accompanied by a selective loss of small-diameter sural nerve axons (p < 0.05). FIV-infected lymphocytes cocultured with syngeneic DRGs caused neuronal damage, indicated by neurite retraction, neuronal soma atrophy, and loss (p < 0.05). In contrast, supernatants from FIV-infected or uninfected lymphocytes were minimally neurotoxic, despite high FIV virion levels. Among lymphocyte subsets cocultured with DRG cultures, CD8+ T cells from both FIV-infected and uninfected lymphocytes selectively caused DRG neuronal injury (p < 0.05). FIV-infected CD8+ T cells showed markedly increased CD154 expression (p < 0.05), whereas neurons were the predominant cells expressing CD40 in DRGs. Blocking CD154 on activated CD8+ T cells protected DRG neurons (p < 0.05). These findings indicated that CD8+ T cells were principal effectors of DRG neuronal injury after FIV infection through a CD40-CD154 interaction in a cell contact-dependent manner.

Failure of HIV-exposed CD4+ T cells to activate dendritic cells is reversed by restoration of CD40/CD154 interactions

Because interactions between activated CD4+ T cells and antigen-presenting cells (APCs) are crucial for optimal APC function, defective CD4+ T-cell activation may contribute to APC dysregulation in HIV infection. Here, we show that CD4+ T cells exposed during stimulation to noninfectious HIV having functional envelope glycoproteins failed to provide activation signals to autologous dendritic cells (DCs). Consequently, important DC functions, including production of immunoregulatory cytokines (interleukin-12 p40 and interleukin-10) and up-regulation of costimulatory molecules (CD86, CD40, CD83), as well as the capacity to stimulate naive allogeneic T cells, were all adversely affected. The blunted up-regulation of CD154 in CD4+ T cells that were activated in the presence of noninfectious viruses is likely to be the major underlying mechanism for these defects. Addition of recombinant trimeric CD154 could restore production of cytokines by DCs cocultured with HIV-exposed T cells. Moreover, the functional defects mediated by coculture with HIV-exposed T cells were similar to those following antibody blockade of CD40-CD154 interactions. HIV-mediated blunted CD154 expression may thus play an important role in the suppression of cell-mediated immunity seen in HIV infection.

Expression of CD154 by a simian immunodeficiency virus vector induces only transitory changes in rhesus macaques

Human immunodeficiency virus infection is characterized by dysregulation of antigen-presenting cell function and defects in cell-mediated immunity. Recent evidence suggests that impaired ability of CD4+ T cells to upregulate the costimulatory molecule CD154 is at the core of this dysregulation. To test the hypothesis that increased expression of CD154 on infected CD4+ T cells could modulate immune function, we constructed a replication-competent simian immunodeficiency virus (SIV) vector that expressed CD154. We found that this recombinant vector directed the expression of CD154 on the surface of infected CD4+ T cells and that expression of CD154 resulted in activation of B cells present in the same cultures. Experimental infection of rhesus macaques resulted in very low viral loads for the CD154-expressing virus and the control virus, indicating that expression of CD154 did not result in increased viral replication. Analyses of the anti-SIV immune responses and the phenotype of lymphocytes in blood and lymphoid tissues showed changes that occurred during the acute phase of infection only in animals infected with the CD154-expressing SIV, but that became indistinguishable from those seen in animals infected with the control virus at later time points. We conclude that the level of expression of CD154 in itself is not responsible for affecting the immune response to an attenuated virus. Considering that the CD154-expressing SIV vector and the virus control did not carry an active nef gene, our results suggest that, in CD4+ T cells infected with wild-type virus, Nef is the viral factor that interferes with the immune mechanisms that regulate expression of CD154.

Immunomodulatory effects of the HIV-1 gp120 protein on antigen presenting cells: implications for AIDS pathogenesis

Antigen presenting cell (APC) function is central to the development of an effective anti-viral immune response. Among APC, monocytes, macrophages and dendritic cells (DC) form the principal non-T cell compartment involved in in vivo HIV infection, and these cells play important and well-established roles in multiple aspects of viral pathogenesis. HIV infection may result in APC defects, which could ultimately contribute to the loss of CD4+ T cell responses observed early in HIV infection, when the CD4+ T cell number is still within the normal range. Extensive in vitro studies have demonstrated that the envelope glycoproteins of HIV-1 exert profound influences on various cell populations of the immune system, including hematopoietic progenitors, T and B lymphocytes, monocytes/ macrophages and DC, as well as on neuronal cells. The demonstration of the presence of envelope proteins both free in the circulation and bound to the surface of CD4+ cells suggests that gp120 interactions with non-infected cells can influence cellular functions in vivo, thus contributing to the immunopathogenesis of AIDS. This paper provides an overview of the present knowledge on gp120 binding, signal transduction triggering and interference with macrophage and DC functions and it highlights the importance of this interaction in the pathogenesis of AIDS.

Cutting Edge: The Prevalence of Regulatory T Cells in Lymphoid Tissue Is Correlated with Viral Load in HIV-Infected Patients

Inadequate local cell-mediated immunity appears crucial for the establishment of chronic HIV infection. Accumulation of regulatory T cells (Treg) at the site of HIV replication, the lymphoid organs, may influence the outcome of HIV infection. Our data provide the first evidence that chronic HIV infection changes Treg tissue distribution. Several molecules characteristics of Treg (FoxP3, CTLA-4, glucocorticoid-induced TNFR family-related receptor, and CD25) were expressed more in tonsils of untreated patients compared with antiretroviral-treated patients. Importantly, most FoxP3+ cells expressed CTLA-4, but not CD69. Furthermore, a direct correlation between FoxP3 levels and viral load was evident. In contrast, FoxP3 expression was decreased in circulating T cells from untreated patients, but normalized after initiation of treatment. Functional markers of Treg activity (indoleamine 2,3-dioxygenase, TGF-beta, and CD80) were markedly increased in the tonsils of untreated patients. Our data could provide a new basis for immune-based therapies that counteract in vivo Treg and thereby reinforce appropriate antiviral immunity.

HIV may produce inhibitory microRNAs (miRNAs) that block production of CD28, CD4 and some interleukins

It is well-known that HIV-1 infection results in a gradual decline of the CD4+ T-lymphocytes, but the underlying mechanism of this decline is not completely understood. Research has shown that HIV-1 infection of CD4+ T cells results in decreased CD28 expression, but the mechanism of this repression is unknown. There is also substantial evidence demonstrating regulatory involvement of microRNA (miRNA) during protein expression in plants and some animals, and reports have recently been published confirming the existence of viral-encoded miRNAs. Based on these findings, we hypothesize that viral-encoded miRNA from HIV-1 may directly alter T cell, macrophage and dendritic cell activity. To investigate a potential correlation between the genomic complementarity of HIV-1 and host cell protein expression, a local alignment search was performed to assess for regions of complementarity between the HIV-1 proviral genome and the mRNA coding sequence of various proteins expressed by CD+ T cells and macrophages. Regions of complementarity with strong correlations to the currently established criteria for miRNA:target mRNA activity were found between HIV-1 and CD28, CTLA-4 and some interleukins, suggesting that HIV-1 may produce translational repression in host cells.

CXCR4-tropic HIV-1 envelope glycoprotein functions as a viral chemokine in unstimulated primary CD4+ T lymphocytes

Interaction of HIV-1 envelope glycoprotein gp120 with the chemokine receptor CXCR4 triggers not only viral entry but also an array of signal transduction cascades. Whether gp120 induces an incomplete or aberrant set of signals, or whether it can function as a full CXCR4 agonist, remains unclear. We report that, in unstimulated human primary CD4(+) T cells, the spectrum of signaling responses induced by gp120 through CXCR4 paralleled that induced by the natural ligand stromal cell-derived factor 1/CXCL12. gp120 activated heterotrimeric G proteins and the major G protein-dependent pathways, including calcium mobilization, phosphoinositide-3 kinase, and Erk-1/2 MAPK activation. Interestingly, gp120 caused rapid actin cytoskeleton rearrangements and profuse membrane ruffling, as evidenced by dynamic confocal imaging. This coordinated set of events resulted in a bona fide chemotactic response. Inactivated HIV-1 virions that harbored conformationally intact envelope glycoproteins also caused actin polymerization and chemotaxis, while similar virions devoid of envelope glycoproteins did not. Thus gp120, in monomeric as well as oligomeric, virion-associated form, elicited a complex cellular response that mimicked the effects of a chemokine. HIV-1 has therefore the capacity to dysregulate the vast CD4(+) T cell population that expresses CXCR4. In addition, HIV-1 may exploit its chemotactic properties to retain potential target cells and locally perturb their cytoskeleton, thereby facilitating viral transmission.