The role of co-stimulation in regulation of chemokine receptor expression and HIV-1 infection in primary T lymphocytes

Kruppel-like factor 2 modulates CCR5 expression and susceptibility to HIV-1 infection

CCR5, a cell surface molecule critical for the transmission and spread of HIV-1, is dynamically regulated during T cell activation and differentiation. The molecular mechanism linking T cell activation to modulation of CCR5 expression remains undefined. Kruppel-like factor 2 (KLF2) is a transcription factor that promotes quiescence, survival, and in part by modulating chemokine receptor levels, induces homing to secondary lymphoid organs. Given the relationship between T cell activation and chemokine receptor expression, we tested whether the abundance of KLF2 after T cell activation regulates CCR5 expression and, thus, susceptibility of a T cell to CCR5-dependent HIV-1 strains (R5). We observed a strong correlation between T cell activation, expression of KLF2 and CCR5, and susceptibility to infection. To directly measure how KLF2 affects CCR5 regulation, we introduced small interfering RNA targeting KLF2 expression and demonstrated that reduced KLF2 expression also resulted in less CCR5. Chromatin immunoprecipitation assays identified KLF2 bound to the CCR5 promoter in resting but not CD3/28 activated T cells, suggesting that KLF2 directly regulates CCR5 expression. Introduction of KLF2 under control of a heterologous promoter could restore CCR5 expression and R5 susceptibility to CD3/28 costimulated T cells and some transformed cell lines. Thus, KLF2 is a host factor that modulates CCR5 expression in CD4 T cells and influences susceptibility to R5 infection.

Antigen presentation on artificial acellular substrates: modular systems for flexible, adaptable immunotherapy

BACKGROUND

Recent findings on T cells and dendritic cells have elucidated principles that can be used for a bottom-up approach to engineering artificial antigen presentation on synthetic substrates.

OBJECTIVE/METHODS

To compare the latest artificial antigen-presenting cell (aAPC) technology, focussing on acellular systems because they offer advantages such as easy tunability and rapid point-of-care application compared with cellular systems. We review acellular aAPC performance and discuss their promise for clinical applications.

RESULTS/CONCLUSION

Acellular aAPCs are a powerful alternative to natural-cell-based therapies, offering flexibility and modularity for incorporation oSf a variety of stimuli, hence increasing precision. Current technologies should adapt physiologically important signals within safe materials to more closely approximate their cellular counterparts. These constructs could be administered parenterally as APC replacements for active vaccines or used ex vivo for adoptive immunotherapy.

T-cell dysfunction in HIV-1 infection: targeting the inhibitors

Since AIDS emerged almost three decades ago, there have been considerable advances in the field of antiretroviral chemotherapy for those chronically infected with HIV-1. However, this therapy is noncurative and as our understanding of HIV-1 immunopathogenesis increases, it is becoming apparent that further therapeutic interventions are required to reverse the devastating effects of HIV-1 infection worldwide. While viral clearance remains the principle goal of HIV-1 treatment, this article describes immunotherapeutic options that target the immunological effects of the virus, to reduce its presence in the body and counteract viral-induced T-cell dysfunction and inhibition. Such approaches may augment existing antiretroviral therapy to overturn virus-induced T-cell anergy in the infected host, improving levels of immune control that reduce viremia and decrease the rate of transmission.

Adoptive immunotherapy: good habits instilled at youth have long-term benefits

Many recent advances in basic cell biology and immunology are a harbinger of progress in adoptive cell therapy (ACT) including (1) the finding that host lymphodepletion enhances engraftment and efficacy, (2) the recognition that in vitro T cell functions may not correlate with in vivo efficacy, and (3) the development of advanced ex vivo culture methods to expand lymphocytes to therapeutically effective numbers. In this article, we focus on the development of artificial antigen presenting cells (aAPCs) in our laboratory and their applicability to augment ACT protocols. We also describe how aAPCs can be used to broaden ACT to treat patients with a wide variety of cancers, chronic infectious diseases, and autoimmune manifestations.

Addition of deoxynucleosides enhances human immunodeficiency virus type 1 integration and 2LTR formation in resting CD4+ T cells

Resting CD4+ T cells restrict human immunodeficiency virus (HIV) infection at a step prior to integration. Despite this restriction, we showed previously that HIV integration occurs in resting CD4+ T cells in vitro, albeit at lower levels than in activated CD4+ T cells. Here we show that addition of deoxynucleosides enhanced integration and 2LTR formation in resting CD4+ T cells but that the kinetics were still significantly delayed compared to those of activated T cells. Thus, deoxynucleoside addition partially overcomes the restriction to HIV infection in resting CD4+ T cells.

Human immunodeficiency virus type 1 can establish latent infection in resting CD4+ T cells in the absence of activating stimuli

Resting CD4(+) T cells are the best-defined reservoir of latent human immunodeficiency virus type 1 (HIV-1) infection, but how the reservoir is formed is unclear. Understanding how the reservoir of latently infected cells forms is critical because it is a major barrier to curing HIV infection. The system described here may provide an in vitro model of latent HIV-1 infection in resting CD4(+) T cells. We demonstrated that HIV-1 integrates into the genomes of in vitro-inoculated resting CD4(+) T cells that have not received activating stimuli and have not entered cell cycle stage G(1b). A percentage of the resting CD4(+) T cells that contain integrated DNA produce virus upon stimulation, i.e., are latently infected. Our results show that latent HIV-1 infection occurs in unstimulated resting CD4(+) T cells and suggest a new route for HIV-1 reservoir formation.

Current status of gene therapy strategies to treat HIV/AIDS

Progress in developing effective gene transfer approaches to treat HIV-1 infection has been steady. Many different transgenes have been reported to inhibit HIV-1 in vitro. However, effective translation of such results to clinical practice, or even to animal models of AIDS, has been challenging. Among the reasons for this failure are uncertainty as to the most effective cell population(s) to target, the diffuseness of these target cells in the body, and ineffective or insufficiently durable gene delivery. Better understanding of the HIV-1 replicative cycle, host factors involved in HIV-1 infection, vector biology and application, transgene technology, animal models, and clinical study design have all contributed vastly to planning current and future strategies for application of gene therapeutic approaches to the treatment of AIDS. This review focuses on the newest developments in these areas and provides a strong basis for renewed optimism that gene therapy will have an important role to play in treating people infected with HIV-1.

Envelope variants from women recently infected with clade A human immunodeficiency virus type 1 confer distinct phenotypes that are discerned by competition and neutralization experiments

Women infected with clade A human immunodeficiency virus type 1 harbor a virus population that is genetically diverse in the envelope gene, a fact that contrasts with the homogeneous virus population identified in newly infected men. It is not known whether viral genetic diversity at this early stage of infection is manifested as phenotypic diversity. This is a significant question because phenotypic diversity in the viral population that establishes infection in women may have important implications for pathogenesis and therapeutic intervention. Thus, in this study we compared the biological properties of three pairs of chimeric viruses that contained envelope genes representative of variant groups in each of three infected women-Q23, Q45, and Q47. Envelope chimeras were evaluated for replication in stimulated and resting peripheral blood mononuclear cells alone and in competition, for coreceptor use, and for neutralization sensitivity. All viruses utilized CCR5 exclusively and had a non-syncytium-inducing phenotype on MT-2 cells and in primary culture. There were no significant differences in replication parameters between paired variants in individual cultures. However, in competition experiments, one chimera of each variant pair always dominated. The dominant virus from Q23 and Q47, but not from Q45, infected a significantly higher number of CCR5- and CD4-expressing GHOST cells than the weaker chimeras. Significantly, chimeric viruses from Q47 and Q45 showed markedly different neutralization sensitivity to antibodies to CCR5 and gp120, respectively. These data indicate that distinct envelope genotypes identified in clade A-infected women near seroconversion confer unique phenotypes that affect viral fitness and that may be due, in part, to different requirements for relative configuration of CD4 and CCR5 on infected cells.

Gene array and protein expression profiles suggest post-transcriptional regulation during CD8+ T cell differentiation

Peripheral CD8(+) T cells circulate in a quiescent naive state until they are primed by specific antigen and differentiate into effector cells. In the effector state, CD8(+) T cells acquire cytolytic activity and produce increased levels of cytokines such as interferon-gamma. They also exhibit increased T cell receptor sensitivity, decreased CD28 dependence, and become inhibitable by CTLA-4 and other negative regulatory pathways. We hypothesized that one mechanism by which these two states are regulated is via differential expression of specific genes. To this end, basal gene expression profiles of naive and effector 2C TCR transgenic x RAG2(-/-) CD8(+) T cells were analyzed using Affymetrix arrays representing 11,000 genes. Of the 177 differentially expressed known genes, 68 were expressed at higher levels in effector cells, but 109 were more abundant in naive cells, supporting the notion that the naive state is not passive. Expression of genes related to metabolism, actin cytoskeletal dynamics, and effector function increased with priming, whereas expression of putative anti-proliferative genes decreased. Semiquantitative reverse transcription-PCR was utilized as a secondary validation for selected transcripts, and Western blot analysis was used to examine protein expression for molecules of interest. Surprisingly, for 24 genes examined, 12 showed discordant protein versus mRNA expression. In summary, our study indicates that: 1) not only does the expression of some genes in naive CD8(+) T cells become up-regulated upon priming, but the expression of other genes is down-regulated as well and 2) the complexities of T cell differentiation include regulation at the post-transcriptional level.

Contribution of immune activation to the pathogenesis and transmission of human immunodeficiency virus type 1 infection

The life cycle of human immunodeficiency virus type 1 (HIV-1) is intricately related to the activation state of the host cells supporting viral replication. Although cellular activation is essential to mount an effective host immune response to invading pathogens, paradoxically the marked systemic immune activation that accompanies HIV-1 infection in vivo may play an important role in sustaining phenomenal rates of HIV-1 replication in infected persons. Moreover, by inducing CD4+ cell loss by apoptosis, immune activation may further be central to the increased rate of CD4+ cell turnover and eventual development of CD4+ lymphocytopenia. In addition to HIV-1-induced immune activation, exogenous immune stimuli such as opportunistic infections may further impact the rate of HIV-1 replication systemically or at localized anatomical sites. Such stimuli may also lead to genotypic and phenotypic changes in the virus pool. Together, these various immunological effects on the biology of HIV-1 may potentially enhance disease progression in HIV-infected persons and may ultimately outweigh the beneficial aspects of antiviral immune responses. This may be particularly important for those living in developing countries, where there is little or no access to antiretroviral drugs and where frequent exposure to pathogenic organisms sustains a chronically heightened state of immune activation. Moreover, immune activation associated with sexually transmitted diseases, chorioamnionitis, and mastitis may have important local effects on HIV-1 replication that may increase the risk of sexual or mother-to-child transmission of HIV-1. The aim of this paper is to provide a broad review of the interrelationship between immune activation and the immunopathogenesis, transmission, progression, and treatment of HIV-1 infection in vivo.

Naive CD4 T cells inhibit CD28-costimulated R5 HIV replication in memory CD4 T cells

Stimulation with antibodies to CD3 and CD28 coimmobilized on beads can be used to significantly expand T cells ex vivo. With CD4 T cells from HIV-infected patients, this expansion usually is accompanied by complete suppression of viral replication, presumed to be caused by down-regulation of the viral coreceptor CCR5 and up-regulation of CCR5 ligands. Here we show that this suppression occurs in total CD4 T cells acutely infected with R5 HIV, but not in purified CD62L(-) memory CD4 T cells. The lack of complete suppression in these memory cells, typically comprising 10-40% of total CD4 T cells, occurs despite high levels of CCR5 ligand secretion and down-regulation of CCR5. Significantly, adding back naive or CD62L(+) memory CD4 T cells inhibits the viral replication in the CD62L(-) cells, with the naive cells capable of completely repressing the virus. Although this inhibition was previously thought to be specific to bead-bound anti-CD3/CD28 stimulation, we show that the same suppression is obtained with sufficiently strong anti-CD3/B7.1 stimulation. Our results show that inhibitory mechanisms, expressed predominantly by strongly stimulated naive CD4 T cells and mediated independently of CCR5-binding chemokines, play a role in the inhibition of R5 HIV replication in CD4 T cells upon CD28 costimulation.

T-lymphocyte production of macrophage inflammatory protein-1α is critical to the recruitment of CD8+ T cells to the liver, lung, and spleen during graft-versus-host disease

To investigate the mechanism by which macrophage inflammatory protein-1α (MIP-1α) affects graft-versus-host disease (GVHD), the expression and function of MIP-1α in 2 murine models of GVHD were evaluated. In irradiated class I and class II disparate recipients, the expression of messenger RNA (mRNA) and protein for MIP-1α was significantly increased in GVHD target organs after transfer of allogeneic lymphocytes compared to syngeneic lymphocytes. When lymphocytes unable to make MIP-1α were transferred, there was a decrease in the production of MIP-1α in the liver, lung, and spleen of bm1 (B6.C-H2bm1/By) and bm12 (B6.C-H2bm12/KhEg) recipients compared to the transfer of wild-type splenocytes. At day 6 there was a 4-fold decrease in the number of transferred CD8+ T cells in the lung and approximately a 2-fold decrease in the number of CD8+ T cells in the liver and spleen in bm1 recipients after transfer of MIP-1α–deficient (MIP-1α−/−) splenocytes compared to wild-type (MIP-1α+/+) splenocytes. These differences persisted for 13 days after splenocyte transfer. In contrast, the number of donor CD4+ T cells found in the liver and lung was significantly increased after the transfer of MIP-1α−/− compared to wild-type splenocytes in bm12 recipients from day 6 through day 10. Thus, the transfer of allogeneic T cells was associated with the enhanced expression of MIP-1α in both a class I and class II mismatch setting. However, the increased expression only led to enhanced recruitment of CD8+, but not CD4+, donor T cells. Production of MIP-1α by donor T cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion.

T-lymphocyte production of macrophage inflammatory protein-1α is critical to the recruitment of CD8+ T cells to the liver, lung, and spleen during graft-versus-host disease

To investigate the mechanism by which macrophage inflammatory protein-1α (MIP-1α) affects graft-versus-host disease (GVHD), the expression and function of MIP-1α in 2 murine models of GVHD were evaluated. In irradiated class I and class II disparate recipients, the expression of messenger RNA (mRNA) and protein for MIP-1α was significantly increased in GVHD target organs after transfer of allogeneic lymphocytes compared to syngeneic lymphocytes. When lymphocytes unable to make MIP-1α were transferred, there was a decrease in the production of MIP-1α in the liver, lung, and spleen of bm1 (B6.C-H2bm1/By) and bm12 (B6.C-H2bm12/KhEg) recipients compared to the transfer of wild-type splenocytes. At day 6 there was a 4-fold decrease in the number of transferred CD8+ T cells in the lung and approximately a 2-fold decrease in the number of CD8+ T cells in the liver and spleen in bm1 recipients after transfer of MIP-1α–deficient (MIP-1α−/−) splenocytes compared to wild-type (MIP-1α+/+) splenocytes. These differences persisted for 13 days after splenocyte transfer. In contrast, the number of donor CD4+ T cells found in the liver and lung was significantly increased after the transfer of MIP-1α−/− compared to wild-type splenocytes in bm12 recipients from day 6 through day 10. Thus, the transfer of allogeneic T cells was associated with the enhanced expression of MIP-1α in both a class I and class II mismatch setting. However, the increased expression only led to enhanced recruitment of CD8+, but not CD4+, donor T cells. Production of MIP-1α by donor T cells is important in the occurrence of GVHD and functions in a tissue-dependent fashion.

Kinetics of CXCR4 and CCR5 up-regulation and human immunodeficiency virus expansion after antigenic stimulation of primary CD4+ T lymphocytes

The chemokine receptors CCR5 and CXCR4 are coreceptors for the human immunodeficiency virus (HIV) and determine the cell tropism of different HIV strains. Previous studies on their regulation were performed under conditions of unspecific T-lymphocyte stimulation and provided conflicting results. To mimick physiologic conditions, highly purified primary Staphylococcus enterotoxin B (SEB)-reactive CD4 T lymphocytes were stimulated in the presence of autologous antigen-presenting cells and the kinetics of CCR5 and CXCR4 surface expression and HIV replication were studied. Both chemokine receptors were transiently up-regulated with maximal expression at day 3 after stimulation. The stimulated T cells were equally susceptible to productive infection with R5-and X4-tropic virus strains. Thus, antigenic stimulation of T cells promotes efficient replication of both, T cell-tropic and macrophage-tropic HIV.

Kinetics of CXCR4 and CCR5 up-regulation and human immunodeficiency virus expansion after antigenic stimulation of primary CD4+ T lymphocytes

The chemokine receptors CCR5 and CXCR4 are coreceptors for the human immunodeficiency virus (HIV) and determine the cell tropism of different HIV strains. Previous studies on their regulation were performed under conditions of unspecific T-lymphocyte stimulation and provided conflicting results. To mimick physiologic conditions, highly purified primary Staphylococcus enterotoxin B (SEB)-reactive CD4 T lymphocytes were stimulated in the presence of autologous antigen-presenting cells and the kinetics of CCR5 and CXCR4 surface expression and HIV replication were studied. Both chemokine receptors were transiently up-regulated with maximal expression at day 3 after stimulation. The stimulated T cells were equally susceptible to productive infection with R5-and X4-tropic virus strains. Thus, antigenic stimulation of T cells promotes efficient replication of both, T cell-tropic and macrophage-tropic HIV.

The C-class chemokine, lymphotactin, impairs the induction of Th1-type lymphokines in human CD4+ T cells

Chemokines are involved in the regulation of leukocyte migration and for some of them, T-cell costimulation. To date, the only direct property of lymphotactin (Lptn), the unique member of the C class of chemokines, consists of T-cell chemoattraction. This report describes a novel function for Lptn in human T-lymphocyte biology, by demonstrating the direct ability of Lptn to both inhibit and costimulate CD4+ and CD8+ T-cell activation, respectively. Lptn but not RANTES inhibited CD4+ T-cell proliferation, through a decreased production of Th1 (interleukin [IL]-2, interferon [IFN]-γ) but not Th2 (IL-4, IL-13) lymphokines, and decreased IL-2R expression. Transfections in Jurkat cells showed a Lptn-mediated transcriptional down-regulation of gene-promoter activities specific for Th1-type lymphokines, as well as of nuclear factor of activated T cells (NF-AT) but not AP-1 or NF-ΚB enhancer activities. This suppressive action of Lptn could be compensated by overexpression of NF-ATc but not NF-ATp. CD4+ T-cell proliferation was completely restored by exogenous IL-2 or reversed by pertussis toxin, wortmannin, and genistein, suggesting the involvement of multiple partners in Lptn signaling. In contrast to CD4+ cells, Lptn exerted a potent costimulatory activity on CD8+ T-cell proliferation and IL-2 secretion. These data provide important insights into the role of Lptn in differential regulation of normal human T-cell activation and its possible implication in immune response disorders.

The C-class chemokine, lymphotactin, impairs the induction of Th1-type lymphokines in human CD4+ T cells

Chemokines are involved in the regulation of leukocyte migration and for some of them, T-cell costimulation. To date, the only direct property of lymphotactin (Lptn), the unique member of the C class of chemokines, consists of T-cell chemoattraction. This report describes a novel function for Lptn in human T-lymphocyte biology, by demonstrating the direct ability of Lptn to both inhibit and costimulate CD4+ and CD8+ T-cell activation, respectively. Lptn but not RANTES inhibited CD4+ T-cell proliferation, through a decreased production of Th1 (interleukin [IL]-2, interferon [IFN]-γ) but not Th2 (IL-4, IL-13) lymphokines, and decreased IL-2R expression. Transfections in Jurkat cells showed a Lptn-mediated transcriptional down-regulation of gene-promoter activities specific for Th1-type lymphokines, as well as of nuclear factor of activated T cells (NF-AT) but not AP-1 or NF-ΚB enhancer activities. This suppressive action of Lptn could be compensated by overexpression of NF-ATc but not NF-ATp. CD4+ T-cell proliferation was completely restored by exogenous IL-2 or reversed by pertussis toxin, wortmannin, and genistein, suggesting the involvement of multiple partners in Lptn signaling. In contrast to CD4+ cells, Lptn exerted a potent costimulatory activity on CD8+ T-cell proliferation and IL-2 secretion. These data provide important insights into the role of Lptn in differential regulation of normal human T-cell activation and its possible implication in immune response disorders.

CCR5 and CXCR4 chemokine receptor expression and beta-chemokine production during early T cell repopulation induced by highly active anti-retroviral therapy

Expression of chemokine receptors and beta-chemokine production by peripheral blood mononuclear cells (PBMC) were determined in HIV-1-infected individuals before and after highly active anti-retroviral therapy (HAART) and their relationship to viral load, T cell phenotype and the expression of immunological activation markers was examined. We found that the expression of CCR5 is up-regulated in HIV-1-infected individuals while CXCR4 appears down-regulated on both CD4 and CD8 T cells compared with normal controls. These alterations are associated with the high levels of viral load. In addition, a relationship was observed between the degree of immune activation and chemokine receptor expression on T cells. However, after 3 months of combined anti-retroviral regimen, expression of CXCR4 significantly increased while CCR5 decreased when compared with pretherapy determinations. This was seen in strict association with a dramatic decrease of viral load and an increase of both CD45RA+/CD62L+ (naive) and CD45RA-/CD62L+ or CD45RA+/CD62L- (memory) T cells accompanied by a significant decrease of the expression of immune activation markers such as HLA-DR and CD38. At enrolment, both spontaneous and lectin-induced RANTES, macrophage inflammatory protein-1alpha (MIP-1alpha) and MIP-1beta production by PBMC were higher in HIV-1-infected individuals compared with normal controls, although differences for MIP-1beta were not statistically significant. However, RANTES and MIP-1alpha production decreased during HAART at levels closer to that determined with normal controls, while MIP-1beta production was less consistently modified. These data indicate that the expression of chemokine receptors CCR5 and CXCR4 and the production of beta-chemokines are altered in HIV-infected individuals, and suggest that their early modifications during HAART reflect both the peripheral redistribution of naive/memory T cell compartments and the decrease in levels of T cell activation. Such modifications in the expression of host determinants of viral tropism and the production of anti-viral molecules may play a role in the emergence of virus variants when a failure of HAART occurs.

CD28 co-stimulation results in down-regulation of lymphotactin expression in human CD4(+) but not CD8(+) T cells via an IL-2-dependent mechanism

Chemokines are key molecules in promoting leukocyte migration and, for some of them, T cell adhesion and activation. Lymphotactin, which is the unique known member of the C class of chemokines, is produced by and acts on T lymphocytes, but the requirement of co-stimulatory pathways such as CD28 for its expression is largely unknown. CD28 plays a dominant role in the amplification of T cell proliferation, survival and cytokine production. In this report, we demonstrate that human lymphotactin expression, at both the mRNA and protein levels, is optimally induced by CD3/TCR activation alone, whereas CD28 co-stimulation turns off this expression. This down-regulation is not attributable to secondary activation via CTLA-4, the alternative counter-receptor of B7 ligands. Only the CD4(+) and not the CD8(+) subset is directly affected by this negative regulation. Transcript destabilization can be ruled out as a mechanism by which CD28 down-regulates lymphotactin expression. However, such down-regulation can be partly induced by IL-2 and abrogated by blocking IL-2/IL-2 receptor interaction. This particular profile of lymphotactin expression is not in line with the prevailing dogma of up-regulation of cytokine gene expression by CD28 co-stimulation, and represents a new CD28-mediated regulatory mechanism for lymphotactin expression.

Functional Gene Transfer of HIV DNA by an HIV Receptor-Independent Mechanism

HIV-1 enters target cells mainly via binding to CD4 and its coreceptors. The presence of HIV-1 in CD4− cells suggests, however, that there exist other mechanisms for viral entry. Here it is reported that HIV-1 DNA may be transferred from one cell to another by uptake of apoptotic bodies in a CD4-independent way. This was investigated by coculturing CD4−, chemokine receptor CCR5− and CXCR4− human fetal fibroblasts with apoptotic HIV-1-infected HuT78 cells or apoptotic PBMC isolated from HIV-1-infected patients. After 2 wk of coculture, fibroblasts contained HIV-1 DNA and expressed HIV-1 proteins p24 and gp120. Transfer of HIV-1 DNA was verified by coculturing fibroblasts with apoptotic bodies derived from cells infected with a defective HIV-1 virus. These cells contain one integrated copy of a reverse transcriptase (RT)-negative HIV-1 strain (8E5/LAV RT− cells) and consequently cannot produce free virus. Intracellular HIV-1 gag DNA was detected in both fibroblasts and dendritic cells after coculture with apoptotic 8E5/LAV RT− cells. Transfer of viral DNA after uptake of apoptotic bodies may explain HIV-1 infection of CD4− cells in vivo and furthermore may be relevant for Ag presentation.