Nelly Noraz

Insulin-like growth factor induces the survival and proliferation of myeloma cells through an interleukin-6-independent transduction pathway

Multiple myeloma (MM) is a B‐cell neoplasia that is associated with an increased level of bone resorption. One important mediator of bone remodelling, insulin‐like growth factor (IGF‐I), has been shown to stimulate the proliferation of human myeloma cells. However, the mechanisms of action of IGF‐I in these cells have not been determined. Using interleukin (IL)‐6‐dependent myeloma cell lines, we show IGF‐I to be as potent a survival and proliferation factor as IL‐6. We demonstrated that IGF‐I functions independently of the IL‐6 transducer gp130 and that these two cytokines have additive effects. Moreover, inhibition of the IGF‐I pathway did not modulate the proliferative effect of IL‐6. Accordingly, we found that IL‐6 and IGF‐I activated distinct downstream signalling molecules: IL‐6 activated STAT3 phosphorylation, whereas IGF‐I treatment resulted in the phosphorylation of IRS‐1. Interestingly, these signalling pathways appear to converge as both cytokines activated the ras/MAPK pathway. Thus, IGF‐I acts as a potent survival and proliferation factor for myeloma cells by stimulating an IL‐6‐independent signalling cascade. These data, together with the finding that, in vivo, IGF‐I is normally expressed in close proximity to myeloma cells within the bone matrix, strongly suggest a role for this cytokine in the pathophysiology of multiple myeloma.

ZAP‐70 kinase regulates HIV cell‐to‐cell spread and virological synapse formation

HIV efficiently spreads in lymphocytes, likely through virological synapses (VSs). These cell–cell junctions share some characteristics with immunological synapses, but cellular proteins required for their constitution remain poorly characterized. We have examined here the role of ZAP‐70, a key kinase regulating T‐cell activation and immunological synapse formation, in HIV replication. In lymphocytes deficient for ZAP‐70, or expressing a kinase‐dead mutant of the protein, HIV replication was strikingly delayed. We have characterized further this replication defect. ZAP‐70 was dispensable for the early steps of viral cycle, from entry to expression of viral proteins. However, in the absence of ZAP‐70, intracellular Gag localization was impaired. ZAP‐70 was required in infected donor cells for efficient cell‐to‐cell HIV transmission to recipients and for formation of VSs. These results bring novel insights into the links that exist between T‐cell activation and HIV spread, and suggest that HIV usurps components of the immunological synapse machinery to ensure its own spread through cell‐to‐cell contacts.

IL-7 differentially regulates cell cycle progression and HIV-1-based vector infection in neonatal and adult CD4+ T cells

Differences in the immunological reactivity of umbilical cord (UC) and adult peripheral blood (APB) T cells are poorly understood. Here, we show that IL-7, a cytokine involved in lymphoid homeostasis, has distinct regulatory effects on APB and UC lymphocytes. Neither naive nor memory APB CD4+ cells proliferated in response to IL-7, whereas naive UC CD4+ lymphocytes underwent multiple divisions. Nevertheless, both naive and memory IL-7-treated APB T cells progressed into the G1b phase of the cell cycle, albeit at higher levels in the latter subset. The IL-7-treated memory CD4+ lymphocyte population was significantly more susceptible to infection with an HIV-1-derived vector than dividing CD4+ UC lymphocytes. However, activation through the T cell receptor rendered UC lymphocytes fully susceptible to HIV-1-based vector infection. These data unveil differences between UC and APB CD4+ T cells with regard to IL-7-mediated cell cycle progression and HIV-1-based vector infectivity. This evidence indicates that IL-7 differentially regulates lymphoid homeostasis in adults and neonates.

Defective expression of p56lck in an infant with severe combined immunodeficiency.

Severe combined immune deficiency (SCID) is a heterogeneous disorder characterized by profound defects in cellular and humoral immunity. We report here an infant with clinical and laboratory features of SCID and selective CD4 lymphopenia and lack of CD28 expression on CD8(+) T cells. T cells from this patient showed poor blastogenic responses to various mitogens and IL-2. Other T cell antigen receptor- induced responses, including upregulation of CD69, were similarly inhibited. However, more proximal T cell antigen receptor signaling events, such as anti-CD3 induced protein tyrosine phosphorylation, phosphorylation of mitogen-associated protein kinase, and calcium mobilization were intact. Although p59fyn and ZAP-70 protein tyrosine kinases were expressed at normal levels, a marked decrease in the level of p56lck was noted. Furthermore, this decrease was associated with the presence of an alternatively spliced lck transcript lacking the exon 7 kinase encoding domain. These data suggest that a deficiency in p56lck expression can produce a SCID phenotype in humans.

Green Fluorescent Protein as a Selectable Marker of Fibronectin-Facilitated Retroviral Gene Transfer in Primary Human T Lymphocytes

The success of gene therapy strategies for congenital and acquired blood disorders requires high levels of gene transfer into hematopoietic cells. Retroviral vectors have been extensively used to deliver foreign genes to mammalian cells and improvement of transduction protocols remains dependent on markers that can be rapidly monitored and used for efficient selection of transduced cells. The enhanced green fluorescent protein (EGFP) is a suitable reporter molecule for gene expression because of its lack of cytotoxicity and stable fluorescence signal that can be readily detected by flow cytometry. However, attempts to adapt the GFP system to stable transduction of human lymphocytes have not been satisfactory. In this article, transductions of primary human T lymphocytes were performed using cell-free supernatants from a PG13 packaging cell line in which a retroviral vector expressing EGFP was pseudotyped with the gibbon ape leukemia virus (GALV) envelope. Using this system combined with a fibronectin-facilitated protocol, primary lymphocytes were transduced with a mean gene transfer efficiency of 27.5% following a 2-day stimulation with either PHA or anti-CD3/CD28 antibodies. Conditions that increased the entry of lymphocytes into cell cycle did not consistently correlate with enhanced gene transfer, indicating that factors other than proliferation are important for optimal retroviral gene transfer. These results demonstrate the utility of EGFP as a marker for human T cell transduction and will enable further optimization of T cell gene therapy protocols.

Ex vivo isolation protocols differentially affect the phenotype of human CD4+ T cells.

Leukemic T cell lines have facilitated signal transduction studies but their physiological relevance is restricted. The use of primary T lymphocytes overcomes this limitation but it has long been speculated that methodological aspects of blood collection and the isolation procedure modify the phenotype of the cell. Here we demonstrate that several characteristics of human peripheral T cells are affected by the selection conditions. A significantly higher induction of the chemokine receptor CXCR4 was observed on CD4+ lymphocytes isolated by sheep red blood cell (SRBC) rosetting and CD4 MicroBeads as compared with positively selected CD4+ cells where the antibody/bead complex was immediately detached. These latter cells expressed CXCR4 at levels equivalent to that observed on CD4+ lymphocytes obtained by negative antibody-mediated selection. Furthermore, CD4+ cells isolated by SRBC rosetting and CD4 MicroBeads formed aggregates upon in vitro culture. CD4+ lymphocytes obtained by SRBC rosetting as well as those isolated following positive selection demonstrated basal phosphorylation of the extracellular signal-regulated kinase (ERK)-2. Altogether these data suggest that certain discrepancies concerning signal transduction in primary human T cells can be attributed to the selection conditions. Thus, it is essential to establish the parameters influenced by the isolation protocol in order to fully interpret T cell responses to antigens, chemokines, and cytokines.