Insertional mutagenesis combined with acquired somatic mutations causes leukemogenesis following gene therapy of SCID-X1 patients

X-linked SCID (SCID-X1) is amenable to correction by gene therapy using conventional gammaretroviral vectors. Here, we describe the occurrence of clonal T cell acute lymphoblastic leukemia (T-ALL) promoted by insertional mutagenesis in a completed gene therapy trial of 10 SCID-X1 patients. Integration of the vector in an antisense orientation 35 kb upstream of the protooncogene LIM domain only 2 (LMO2) caused overexpression of LMO2 in the leukemic clone. However, leukemogenesis was likely precipitated by the acquisition of other genetic abnormalities unrelated to vector insertion, including a gain-of-function mutation in NOTCH1, deletion of the tumor suppressor gene locus cyclin-dependent kinase 2A (CDKN2A), and translocation of the TCR-beta region to the STIL-TAL1 locus. These findings highlight a general toxicity of endogenous gammaretroviral enhancer elements and also identify a combinatorial process during leukemic evolution that will be important for risk stratification and for future protocol design.

Intracellular thiols regulate activation of nuclear factor kappa B and transcription of human immunodeficiency virus

The activation of nuclear factor kappa B (NF-kappa B) has been implicated in the regulation of transcription of a variety of genes and has been shown to be essential for the expression of genes controlled by the long terminal repeat of human immunodeficiency virus (HIV LTR). We show here that intracellular thiol levels play a key role in regulating this process. That is, stimulation with tumor necrosis factor alpha and/or phorbol 12-myristate 13-acetate activates NF-kappa B and markedly decreases intracellular thiols; N-acetyl-L-cysteine, an efficient thiol source, prevents this thiol decrease and blocks the activation of NF-kappa B; and the lack of activated NF-kappa B prevents the activation of the HIV LTR and the transcription of genes under its control. These findings reveal a previously unrecognized genetic regulatory mechanism in which cytokine-induced shifts in intracellular thiol levels are crucial in the control of NF-kappa B activity and thereby influence the spectrum of genes expressed by cytokine-stimulated cells.

Separation of oxidant-initiated and redox-regulated steps in the NF-kappa B signal transduction pathway

Studies presented here show that overall NF-kappa B signal transduction begins with a parallel series of stimuli-specific pathways through which cytokines (tumor necrosis factor alpha), oxidants (hydrogen peroxide and mitomycin C), and phorbol ester (phorbol 12-myristate 13-acetate) individually initiate signaling. These initial pathways culminate in a common pathway through which all of the stimulating agents ultimately signal NF-kappa B activation. We distinguish the stimuli-specific pathways by showing that the oxidative stimuli trigger NF-kappa B activation in only one of two human T-cell lines (Wurzburg but not Jurkat), whereas tumor necrosis factor alpha and phorbol 12-myristate 13-acetate readily stimulate in both lines. We propose the common pathway as the simplest way of accounting for the common requirements and properties of the signaling pathway. We include a redox-regulatory mechanism(s) in this common pathway to account for the previously demonstrated redox regulation of NF-kappa B activation in Jurkat cells (in which oxidants don't activate NF-kappa B); we put tyrosine phosphorylation in the common pathway by showing that kinase activity (inhibitable by herbimycin A and tyrphostin 47) is required for NF-kappa B activation by all stimuli tested in both cell lines. Since internal sites of oxidant production have been shown to play a key role in the cytokine-stimulated activation of NF-kappa B, and since tyrosine kinase and phosphatase activities are known to be altered by oxidants, these findings suggest that intracellular redox status controls NF-kappa B activation by regulating tyrosine phosphorylation event(s) within the common step of the NF-kappa B signal transduction pathway.

Cytokine-stimulated human immunodeficiency virus replication is inhibited by N-acetyl-L-cysteine

We show that the stimulation of human immunodeficiency virus (HIV) brought about by tumor necrosis factor alpha and phorbol 12-myristate 13-acetate can be inhibited by adding N-acetyl-L-cysteine (NAC). NAC, which replenishes intracellular glutathione, effectively inhibits the tumor necrosis factor alpha- or phorbol ester-stimulated replication of HIV in acutely infected cell cultures. NAC also inhibits the cytokine-enhanced HIV long terminal repeat-directed expression of beta-galactosidase in in vitro HIV model systems. These results show that intracellular thiol levels influence HIV production. Furthermore, because NAC reverses tumor necrosis factor alpha toxicity both in cells and in animals and is a well-known drug that can be administered orally without known toxicity in humans, these results suggest that NAC is a possible therapeutic agent in AIDS.

Vector integration is nonrandom and clustered and influences the fate of lymphopoiesis in SCID-X1 gene therapy

Recent reports have challenged the notion that retroviruses and retroviral vectors integrate randomly into the host genome. These reports pointed to a strong bias toward integration in and near gene coding regions and, for gammaretroviral vectors, around transcription start sites. Here, we report the results obtained from a large-scale mapping of 572 retroviral integration sites (RISs) isolated from cells of 9 patients with X-linked SCID (SCID-X1) treated with a retrovirus-based gene therapy protocol. Our data showed that two-thirds of insertions occurred in or very near to genes, of which more than half were highly expressed in CD34(+) progenitor cells. Strikingly, one-fourth of all integrations were clustered as common integration sites (CISs). The highly significant incidence of CISs in circulating T cells and the nature of their locations indicate that insertion in many gene loci has an influence on cell engraftment, survival, and proliferation. Beyond the observed cases of insertional mutagenesis in 3 patients, these data help to elucidate the relationship between vector insertion and long-term in vivo selection of transduced cells in human patients with SCID-X1.

Gammaretrovirus-mediated correction of SCID-X1 is associated with skewed vector integration site distribution in vivo

We treated 10 children with X-linked SCID (SCID-X1) using gammaretrovirus-mediated gene transfer. Those with sufficient follow-up were found to have recovered substantial immunity in the absence of any serious adverse events up to 5 years after treatment. To determine the influence of vector integration on lymphoid reconstitution, we compared retroviral integration sites (RISs) from peripheral blood CD3(+) T lymphocytes of 5 patients taken between 9 and 30 months after transplantation with transduced CD34(+) progenitor cells derived from 1 further patient and 1 healthy donor. Integration occurred preferentially in gene regions on either side of transcription start sites, was clustered, and correlated with the expression level in CD34(+) progenitors during transduction. In contrast to those in CD34(+) cells, RISs recovered from engrafted CD3(+) T cells were significantly overrepresented within or near genes encoding proteins with kinase or transferase activity or involved in phosphorus metabolism. Although gross patterns of gene expression were unchanged in transduced cells, the divergence of RIS target frequency between transduced progenitor cells and post-thymic T lymphocytes indicates that vector integration influences cell survival, engraftment, or proliferation.

Wnt signaling is required for thymocyte development and activates Tcf-1 mediated transcription

T cell factor / lymphocyte enhancer factor (Tcf/Lef) transcription factors complex with the transcriptional co-activator beta-catenin to transduce Wnt signals in a variety of developmental systems. The prototypic family member Tcf-1 is highly expressed in T lineage cells. Tcf1-/- mice are defective in cell cycling of early thymocyte stages. Here, we show that the interaction of beta-catenin with Tcf-1 is required for full thymocyte development. This interaction may be established by signals mediated by Wnt1 and Wnt4, leading to increased Tcf-dependent transcriptional activity in thymocytes, as demonstrated in Tcf-LacZ reporter mice. Transduction of fetal thymocytes with Wnt1 and Wnt4 results in increased survival in an in vitro cell culture system. Retroviral expression of soluble Wnt receptor mutants that block Wnt signaling inhibits thymocyte development. These results imply an important role for the Wnt cascade in thymocyte development.

Redox regulation of signal transduction: tyrosine phosphorylation and calcium influx

Studies presented here show that altering the intracellular redox balance by decreasing glutathione levels profoundly affects early signal transduction events in human T cells. In a T-cell receptor (TCR) signaling model, short-term pretreatment with buthionine sulfoximine, which specifically decreases intracellular glutathione, essentially abrogates the stimulation of calcium influx by anti-CD3 antibodies without significantly impairing other aspects of TCR-initiated signal transduction, such as overall levels of TCR-stimulated tyrosine phosphorylation. In an inflammatory-cytokine signaling model, the failure of tumor necrosis factor alpha to stimulate more than minimal tyrosine phosphorylation in lymphocytes is overcome by buthionine sulfoximine pretreatment--i.e., tumor necrosis factor alpha stimulates extensive tyrosine phosphorylation in glutathione-depleted lymphocytes. These redox-dependent changes in T-cell responsiveness suggest that the glutathione deficiency that we and others have demonstrated in human immunodeficiency virus-infected individuals may contribute significantly to the immunodeficiency and the increased inflammatory reactions in these individuals.

Morbidly obese human subjects have increased peripheral blood CD4+ T cells with skewing toward a Treg- and Th2-dominated phenotype

Obesity is associated with local T-cell abnormalities in adipose tissue. Systemic obesity-related abnormalities in the peripheral blood T-cell compartment are not well defined. In this study, we investigated the peripheral blood T-cell compartment of morbidly obese and lean subjects. We determined all major T-cell subpopulations via six-color flow cytometry, including CD8+ and CD4+ T cells, CD4+ T-helper (Th) subpopulations, and natural CD4+CD25+FoxP3+ T-regulatory (Treg) cells. Moreover, molecular analyses to assess thymic output, T-cell proliferation (T-cell receptor excision circle analysis), and T-cell receptor-β (TCRB) repertoire (GeneScan analysis) were performed. In addition, we determined plasma levels of proinflammatory cytokines and cytokines associated with Th subpopulations and T-cell proliferation. Morbidly obese subjects had a selective increase in peripheral blood CD4+ naive, memory, natural CD4+CD25+FoxP3+ Treg, and Th2 T cells, whereas CD8+ T cells were normal. CD4+ and CD8+ T-cell proliferation was increased, whereas the TCRB repertoire was not significantly altered. Plasma levels of cytokines CCL5 and IL-7 were elevated. CD4+ T-cell numbers correlated positively with fasting insulin levels. The peripheral blood T-cell compartment of morbidly obese subjects is characterized by increased homeostatic T-cell proliferation to which cytokines IL-7 and CCL5, among others, might contribute. This is associated with increased CD4+ T cells, with skewing toward a Treg- and Th2-dominated phenotype, suggesting a more anti-inflammatory set point.

N-acetylcysteine: a new approach to anti-HIV therapy

Several investigators have implicated depletion of glutathione (GSH) and production of reactive oxygen intermediates (ROIs) in the regulation of the human immunodeficiency virus (HIV). We have shown directly that N-acetylcysteine (NAC) blocks HIV expression in chronic and acute infection models, and HIV replication in normal peripheral blood mononuclear cells. NAC is a cysteine prodrug which maintains intracellular thiol levels during oxidative stress and replenishes depleted GSH. The observed antiviral effect of NAC is due to inhibition of viral stimulation by ROIs, which are produced in response to inflammatory cytokines. We have also shown that HIV-infected individuals have decreased intracellular GSH levels in their circulating T cells. Since GSH is the major protection against the production of ROIs, we hypothesize that the observed decrease is due to a chronic oxidative stress induced by continual exposure to elevated levels of inflammatory cytokines. Together, these results provide a rationale for clinical trials testing the efficacy of GSH-replenishing drugs such as NAC in the treatment of AIDS. NAC is different than many other antiviral drugs in that it inhibits host-mediated stimulation of viral replication arising in normal immune responses, and may thereby extend latency. In addition, it inhibits the action of inflammatory cytokines which may mediate cachexia, thereby raising the possibility that it may alleviate the deleterious wasting that accompanies late stage AIDS.

Intracellular glutathione levels in T cell subsets decrease in HIV-infected individuals

The authors have shown previously that intracellular glutathione (GSH) plays an important role in the regulation of human immunodeficiency virus (HIV) transcription and replication in vitro, through modulation of signal transduction by inflammatory cytokines. Moreover, intracellular GSH levels are known to regulate T-lymphocyte function. In multiparameter FACS studies presented here, we show that relative GSH levels in CD4+ and CD8+ T cells from HIV+ individuals are significantly lower than in corresponding subsets from uninfected controls. These studies define the relative intracellular glutathione (GSH) levels in CD4+ T cells, CD8+ T cells, B cells, and monocytes from 134 HIV-infected individuals and 31 uninfected controls. The greatest decreases in intracellular GSH occur in subsets of T cells in individuals in the later stages of the HIV infection. In AIDS patients, GSH levels are 63% of normal in CD4+ T cells (p less than 0.0001) and are 62% of normal in CD8+ T cells (p less than 0.0001). Similarly, in AIDS-related complex (ARC) patients, GSH levels are 66% of normal in CD4+ T cells (p less than 0.003) and are 69% of normal in CD8+ T cells (p less than 0.003). These findings suggest that low intracellular GSH levels may be an important factor in HIV infection and in the resulting immunodeficiency.

CD4 and CD8 T cells with high intracellular glutathione levels are selectively lost as the HIV infection progresses

Maintenance of intracellular glutathione (GSH) levels has been implicated in blocking cytokine-stimulated HIV replication in vitro, in both acute and latent infection models. We demonstrate here that subsets of human peripheral blood mononuclear cells differ substantially in mean GSH levels, as measured on a cell-by-cell basis with the fluorescence-activated cell sorter (FACS): B cells have the lowest GSH levels; T cells are intermediate; and monocytes and macrophages have the highest levels. Furthermore, GSH levels subdivide the CD4 and CD8 T cell subsets into two classes each: high- and low-GSH cells, which cannot be distinguished by cell size or by currently known surface markers. Significantly, the high-GSH T cells are selectively depleted early during the HIV infection, and are effectively missing in all ARC and AIDS patients.

Antioxidants inhibit stimulation of HIV transcription

In studies presented here, we demonstrate that antioxidants regulate NF-kappa B activation and signal transduction pathways leading to HIV expression. We show (1) that N-acetyl-L-cysteine (NAC), an antioxidant and an efficient glutathione (GSH) precursor, inhibits NF-kappa B activation and HIV expression under conditions in which GSH is depleted and NAC cannot be converted to GSH, (2) that the D-stereoisomer of NAC and a wide variety of chemically unrelated antioxidants also inhibit NF-kappa B activation and/or transcription directed by the HIV LTR, and (3) that depletion of GSH, the principal intracellular antioxidant, augments HIV production in an acute infection model. Taken together, these findings suggest direct antioxidant action as the mechanism for inhibition of HIV transcription by NAC. They also confirm that GSH, acting in its capacity as an antioxidant, regulates HIV expression and that exogenous antioxidants can potentiate this regulation.

Tcf-1-mediated transcription in T lymphocytes: differential role for glycogen synthase kinase-3 in fibroblasts and T cells

Beta-catenin is the vertebrate homolog of the Drosophila segment polarity gene Armadillo and plays roles in both cell-cell adhesion and transduction of the Wnt signaling cascade. Recently, members of the Lef/Tcf transcription factor family have been identified as protein partners of beta-catenin, explaining how beta-catenin alters gene expression. Here we report that in T cells, Tcf-1 also becomes transcriptionally active through interaction with beta-catenin, suggesting that the Wnt signal transduction pathway is operational in T lymphocytes as well. However, although Wnt signals are known to inhibit the activity of the negative regulatory protein kinase glycogen synthase kinase-3beta (GSK-3beta), resulting in increased levels of beta-catenin, we find no evidence for involvement of GSK-3beta in Tcf-mediated transcription in T cells. That is, a dominant negative GSK-3beta does not specifically activate Tcf transcription and stimuli (lithium or phytohemagglutinin) that inhibit GSK-3beta activity also do not activate Tcf reporter genes. Thus, inhibition of GSK-3beta is insufficient to activate Tcf-dependent transcription in T lymphocytes. In contrast, in C57MG fibroblast cells, lithium inactivates GSK-3beta and induces Tcf-controlled transcription. This is the first demonstration that lithium can alter gene expression of Tcf-responsive genes, and points to a difference in regulation of Wnt signaling between fibroblasts and lymphocytes.

N-acetylcysteine inhibits latent HIV expression in chronically infected cells

The progression of the human immunodeficiency virus (HIV) infection from its early latent (asymptomatic) stage to active, late-stage acquired immunodeficiency syndrome (AIDS) apparently begins with the production of inflammatory cytokines that stimulate the expression and replication of the latent virus. We have shown that N-acetylcysteine, a cysteine precursor that is converted intracellularly into glutathione, blocks cytokine-stimulated HIV replication in an acutely infected T-cell line and in acutely infected peripheral blood mononuclear cells from normal individuals. In this report, we show that N-acetylcysteine also inhibits stimulated HIV expression in chronically infected monocyte and T-cell lines which are used as models for latent infection in AIDS. Furthermore, we show that N-acetylcysteine blocks viral production in monocyte cell lines more effectively than it blocks viral production in T cells. Since monocytes are a major reservoir for HIV in infected individuals, these results suggest that N-acetylcysteine may slow the change from latency to the later stages of AIDS in HIV-infected individuals.

Tcf/Lef transcription factors during T-cell development: unique and overlapping functions

The founding members of the TCF family are T-cell factor-1 (Tcf-1) and lymphoid enhancing factor-1 (Lef-1). In adult mammals, Tcf-1 is uniquely expressed in T lymphocytes, while Lef-1 is expressed in T cells and early B cells. During murine development, however, expression of Tcf-1 and Lef-1 occurs in complex overlapping patterns in many tissues. The unique in vivo function of Tcf-1 and Lef-1 have been explored by gene disruption experiments. Tcf-1-/- knockout mice are severely impaired in the generation of T cells, but are otherwise normal. Lef-1-/- mice lack hair, teeth, mammary glands and trigeminal nuclei and as a consequence die around birth. As deduced from direct analyses and from transplantation experiments, the Lef-1 mutation has no major effects on the immune system. In Tcf-1/Lef-1 double knockout mice, development of T cells is completely abrogated, indicating that Lef-1 can substitute for Tcf-1 in T-cell differentiation. Factors of the TCF/LEF HMG domain family (TCFs) exist throughout the animal kingdom. It has become evident that the TCFs interact with the vertebrate Wnt effector beta-catenin to mediate axis formation in Xenopus. Likewise, Armadillo (the Drosophila ortholog of beta-catenin) is genetically upstream of Drosophila TCF in the Wingless pathway. Upon Wingless/Wnt signaling, Armadillo/beta-catenin associate with nuclear TCFs and contribute a trans-activation domain to the resulting bipartite transcription factor. In the absence of Wnt signaling, Tcf factors associate with proteins of the Groucho family of transcriptional repressors to strongly repress target gene transcription.

Transcriptional Control of T Lymphocyte Differentiation

Initiation of gene transcription by transcription factors (TFs) is an important regulatory step in many developmental processes. The differentiation of T cell progenitors in the thymus is tightly controlled by signaling molecules, ultimately activating nuclear TFs that regulate the expression of T lineage-specific genes. During the last 2 years, significant progress has been made in our understanding of the signaling routes and TFs operating during the earliest stages of thymic differentiation at the CD4(-)CD8(-) double negative stage. Here we will review the TF families that play an important role in differentiation of thymocytes, particularly focusing on recent new information with respect to the Tcf, bHLH, GATA, and CBF/HES TF families.

CD4+ T-cell counts and interleukin-8 and CCL-5 plasma concentrations discriminate disease severity in children with RSV infection

BACKGROUND

Current tools to predict the severity of respiratory syncytial virus (RSV) infection might be improved by including immunological parameters. We hypothesized that a combination of inflammatory markers would differentiate between severe and mild disease in RSV-infected children.

METHODS

Blood and nasopharyngeal samples from 52 RSV-infected children were collected during acute infection and after recovery. Retrospectively, patients were categorized into three groups based on disease severity: mild (no supportive treatment), moderate (supplemental oxygen and/or nasogastric feeding), and severe (mechanical ventilation). Clinical data, number of flow-defined leukocyte subsets, and cytokine concentrations were compared.

RESULTS

Children with severe RSV infection were characterized by young age; lymphocytopenia; increased interleukin (IL)-8, granulocyte colony-stimulating factor (G-CSF), and IL-6 concentrations; and decreased chemokine (C-C motif) ligand (CCL-5) concentrations in plasma. The combination of plasma levels of IL-8 and CCL-5, and CD4+ T-cell counts, with cutoff values of 67 pg/ml, 13 ng/ml, and 2.3 × 10(6)/ml, respectively, discriminated severe from mild RSV infection with 82% sensitivity and 96% specificity.

CONCLUSION

This study demonstrates that the combination of CD4+ T-cell counts and IL-8 and CCL-5 plasma concentrations correlates with disease severity in RSV-infected children. In addition to clinical features, these immunological markers may be used to assess severity of RSV infection and guide clinical management.

N-acetylcysteine: potential for AIDS therapy

The observations that people infected with HIV suffer not only from an inflammatory stress but also from depleted glutathione levels have led to a general hypothesis that these two are causally related, and that treatment of AIDS should include thiol-replenishment therapy. In particular, inflammatory stimulations are dependent on intracellular thiol levels, as they are potentiated at low glutathione levels (oxidative stress) and inhibited at high glutathione levels. Inflammatory stress may itself lead to decreased levels of glutathione. HIV has taken advantage of inflammatory signals to regulate its own replication; thus, the HIV infection is exacerbated by low levels of glutathione. We have shown that N-acetylcysteine can inhibit inflammatory stimulations, including that of HIV replication. Since N-acetylcysteine can replenish depleted glutathione levels in vivo, we suggest that it be used as an adjunct in the treatment of AIDS.

Successful Preclinical Development of Gene Therapy for Recombinase-Activating Gene-1-Deficient SCID

Recombinase-activating gene-1 (RAG1)-deficient severe combined immunodeficiency (SCID) patients lack B and T lymphocytes due to the inability to rearrange immunoglobulin and T cell receptor genes. Gene therapy is an alternative for those RAG1-SCID patients who lack a suitable bone marrow donor. We designed lentiviral vectors with different internal promoters driving codon-optimized RAG1 to ensure optimal expression. We used Rag1 -/- mice as a preclinical model for RAG1-SCID to assess the efficacy of the various vectors. We observed that B and T cell reconstitution directly correlated with RAG1 expression. Mice with low RAG1 expression showed poor immune reconstitution; however, higher expression resulted in phenotypic and functional lymphocyte reconstitution comparable to mice receiving wild-type stem cells. No signs of genotoxicity were found. Additionally, RAG1-SCID patient CD34+ cells transduced with our clinical RAG1 vector and transplanted into NSG mice led to improved human B and T cell development. Considering this efficacy outcome, together with favorable safety data, these results substantiate the need for a clinical trial for RAG1-SCID.

Glutathione and HIV infection: reduced reduced, or increased oxidized?

Glutathione is the main intracellular defence against oxidative stress and regulates the cellular redox potential. HIV infection is accompanied by severe metabolic and immune dysfunctions. Several laboratories have demonstrated that the intracellular redox balance is disturbed in CD4+ T cells from HIV-seropositive subjects, which may potentiate HIV replication and partly explain the immunological abnormalities associated with HIV disease. The importance of glutathione for immune function, regulation of gene expression, as well as therapeutic interventions with redox-active drugs are discussed in this commentary.

The role of cortistatin in the human immune system

Cortistatin (CST) is a recently described neuropeptide that shares high homology with somatostatin (somatotropin release-inhibiting factor, SRIF) and binds with high affinity to all somatostatin (sst) receptor subtypes. CST is currently known to have a widespread distribution in many human organs including the immune system. The activities specific to CST may be partially attributable to its binding to the growth hormone secretagogue (GHS)-receptor (GHS-R) and the orphan G-protein-coupled receptor MrgX2. Human immune cells produce CST, whereas macrophage lineage and activated endothelium express sst2, and human lymphocytes express sst3. The human thymus expresses sst1, 2, 3, MrgX2 and almost all immune cells express GHS-R. Moreover, at this very moment promising research with CST in experimental animal models is being performed. On the basis of these promising results, studies aiming to further evaluate the possibilities of CST as a therapeutic agent in human immune-mediated inflammatory diseases are warranted.