In vivo and ex vivo gene transfer in thymocytes and thymocyte precursors.

The thymus provides a specialized environment allowing the differentiation of T lymphocytes from bone marrow-derived progenitor cells. We and others have demonstrated that gene transfer into distinct thymocyte populations can be obtained, both in vivo and ex vivo, using lentiviral vectors. Here, we describe techniques for intrathymic lentiviral transduction in mice, using a surgical approach wherein the thoracic cavity is exposed as well as a significantly less invasive strategy wherein virions are directly injected through the skin. Moreover, thymocyte differentiation from murine and human progenitors is now feasible in vitro, under conditions wherein the Notch and IL-7 signaling pathways are activated. We describe methods allowing transduction of murine and human progenitors and their subsequent differentiation into more mature thymocytes. Conditions for lentiviral gene transfer into more differentiated human thymocyte subsets are also presented. Optimization of technologies for HIV-based gene transfer into murine and human thymocyte progenitors will advance strategies aimed at modulating T-cell differentiation and function in-vivo; approaches potentially targeting patients with genetic and acquired immunodeficiencies as well as immune-sensitive tumors. Furthermore, this technology will foster the progression of basic research aimed at elucidating molecular aspects of T-cell differentiation in mice and humans.

Is the coexistence of thromboembolic events and Factor VII deficiency fortuitous?

Over 30 thromboembolic events have been reported in factor VII (FVII) deficiency either associated with previously asymptomatic forms or bleeding diathesis. Whether this coexistence is fortuitous or not is still a mater of debate. Nevertheless, it is well admitted that (i) thrombotic events occurring in FVII-deficient patients with any apparent triggering factors are very rare, (ii) surgical procedures, replacement therapy (especially containing activated factors) but also the presence of an antiphospholipid syndrome are frequently associated with these particular thrombotic events, (iii) in the same way, R304Q and A294V FVII variants appear to be more prevalent than other FVII equally frequent mutations and finally (iv) low FVII coagulant activity levels do not protect against thrombosis. Therefore, peri-operative thrombotic prophylaxis should be relevant for these particular FVII-deficient patients. However, safety, treatment modalities and specific indications of such an antithrombotic prophylaxis remain to be established.

A meta-analysis of human embryonic stem cells transcriptome integrated into a web-based expression atlas.

Microarray technology provides a unique opportunity to examine gene expression patterns in human embryonic stem cells (hESCs). We performed a meta-analysis of 38 original studies reporting on the transcriptome of hESCs. We determined that 1,076 genes were found to be overexpressed in hESCs by at least three studies when compared to differentiated cell types, thus composing a "consensus hESC gene list." Only one gene was reported by all studies: the homeodomain transcription factor POU5F1/OCT3/4. The list comprised other genes critical for pluripotency such as the transcription factors NANOG and SOX2, and the growth factors TDGF1/CRIPTO and Galanin. We show that CD24 and SEMA6A, two cell surface protein-coding genes from the top of the consensus hESC gene list, display a strong and specific membrane protein expression on hESCs. Moreover, CD24 labeling permits the purification by flow cytometry of hESCs cocultured on human fibroblasts. The consensus hESC gene list also included the FZD7 WNT receptor, the G protein-coupled receptor GPR19, and the HELLS helicase, which could play an important role in hESCs biology. Conversely, we identified 783 genes downregulated in hESCs and reported in at least three studies. This "consensus differentiation gene list" included the IL6ST/GP130 LIF receptor. We created an online hESC expression atlas, http://amazonia.montp.inserm.fr, to provide an easy access to this public transcriptome dataset. Expression histograms comparing hESCs to a broad collection of fetal and adult tissues can be retrieved with this web tool for more than 15,000 genes.