Human immunodeficiency virus (HIV)-based lentiviral vectors (LVs) hold immense promise for gene delivery applications because of their relatively large packaging capacity and their ability to infect a range of cell types. The genome of HIV non-specifically integrates into the host genome, and this promotes efficient, stable transgene expression in dividing cells. However, integration can also be problematic because of variations in gene expression among cells, possible gene silencing and, most importantly, insertional mutagenesis which can lead to undesirable effects such as malignant transformation. In order to alleviate these problems, we have developed a range of non-integrating LVs (NILVs) by introducing point mutations into the catalytic site, chromosome binding site, and viral DNA binding site of the viral integrase (IN). In addition, we have mutated the IN attachment (att) sites within the HIV long terminal repeats (LTRs). All of the vectors produced show efficient reverse transcription and transgene expression in dividing cells and prolonged expression in non-dividing myotubes. Finally, we show that NILV can be used for achieving highly effective gene transfer and expression in muscle in vivo.

Wiskott Aldrich syndrome (WAS) is caused by mutations in the WAS IntroductionWiskott-Aldrich syndrome (WAS) is a rare X-linked immunodeficiency caused by mutations of the WAS gene that is widely expressed within hematopoietic cells. 1 The clinical phenotype of WAS is characterized by congenital thrombocytopenia, combined immunodeficiency, and eczema. 1 The WAS protein (WASp) includes several functional domains that couple signal transduction to reorganization of the actin cytoskeleton. As a result, WASp has significant influence on processes such as cell adhesion, migration, assembly/turnover of cell surface receptors, and immunologic synapse formation. 1,2 Several studies in patients with WAS and in Was knock-out (WKO) mice have shown that WASp plays a critical role in the function of T and natural killer lymphocytes and dendritic cells. 1,3 However, the importance of WASp in B-cell development and function is less clearly defined. In vitro studies have shown that WASp-deficient B cells display defective actin polymerization on activation, 4 and impaired migration in response to CXCL13 5 ; however, calcium mobilization and proliferation after B-cell receptor ligation were found to be normal or only slightly reduced. 3 Studies in heterozygous Was ϩ/Ϫ mice have found progressive in vivo selection for WASp-expressing cells in T, B, and natural killer lineages. 6 Within the B-cell lineage, such selective advantage was especially prominent in marginal zone (MZ) B cells. 2,6 However, the in vivo effect of selective deficiency of WASp expression within a single lineage has not been analyzed so far and is of critical importance to understand WAS pathophysiology. Recently, with the use of a chimeric BM transplantation reconstitution model, Becker-Herman et al have provided evidence that lack of WASp expression in B lymphocytes causes immune dysregulation and may lead to fatal autoimmunity. 7 However, mixed chimerism in non-B lineages, irradiation-induced load of The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. 2819BLOOD, 22 MARCH 2012 ⅐ VOLUME 119, NUMBER 12For personal use only. on May 9, 2018. by guest www.bloodjournal.org From apoptotic bodies, and homeostatic B-cell proliferation may also have contributed to autoimmunity in that model.We describe here the generation of mice in which the Was locus has been floxed by homologous recombination. By crossing these mice to mb1-Cre knock-in mice, 8 which express the Cre recombinase under control of the CD79a promoter, the Was locus is selectively and efficiently deleted in B cells only, allowing analysis of the effect of B cell-restricted deficiency of WASp in vivo. Methods MiceAll mice were bred on a C57BL/6 background. WKO mice have been described. 3 Mb1-Cre mice 8 were a generous gift from Dr Michael Reth (Max Planck Institute of Immunobiology, ...

To more precisely identify the B-cell phenotype in Wiskott-Aldrich syndrome (WAS), we used 3 distinct murine in vivo models to define the cell intrinsic requirements for WAS protein (WASp) in central versus peripheral B-cell development. Whereas WASp is dispensable for early bone marrow B-cell development, WASp deficiency results in a marked reduction in each of the major mature peripheral B-cell subsets, exerting the greatest impact on marginal zone and B1a B cells. Using in vivo bromodeoxyuridine labeling and in vitro functional assays, we show that these deficits reflect altered peripheral homeostasis, partially resulting from an impairment in integrin function, rather than a developmental defect. Consistent with these observations, we also show that: (1) WASp expression levels increase with cell maturity, peaking in those subsets exhibiting the greatest sensitivity to WASp deficiency; (2) WASp+ murine B cells exhibit a marked selective advantage beginning at the late transitional B-cell stage; and (3) a similar in vivo selective advantage is manifest by mature WASp+ human B cells. Together, our data provide a better understanding of the clinical phenotype of WAS and suggest that gene therapy might be a useful approach to rescue altered B-cell homeostasis in this disease.

The Wiskott-Aldrich syndrome protein (WASp) is a key cytoskeletal regulator in hematopoietic cells. Covalent modification of a conserved tyrosine by phosphorylation has emerged as an important potential determinant of activity, although the physiological significance remains uncertain. In a murine knockin model, mutation resulting in inability to phosphorylate Y293 (Y293F) mimicked many features of complete WASp-deficiency. Although a phosphomimicking mutant Y293E conferred enhanced actin-polymerization, the cellular phenotype was similar due to functional dysregulation. Furthermore, steady-state levels of Y293E-WASp were markedly reduced compared to wild-type WASp and Y293F-WASp, although partially recoverable by treatment of cells with proteasome inhibitors. Consequently, tyrosine phosphorylation plays a critical role in normal activation of WASp in vivo, and is indispensible for multiple tasks including proliferation, phagocytosis, chemotaxis, and assembly of adhesion structures. Furthermore, it may target WASp for proteasome-mediated degradation, thereby providing a default mechanism for self-limiting stimulation of the Arp2/3 complex. actin polymerization ͉ immune deficiency ͉ Wiskott-Aldrich syndrome