Differential integrity of TALE nuclease genes following adenoviral and lentiviral vector gene transfer into human cells

The array of genome editing strategies based on targeted double-stranded DNA break formation have recently been enriched through the introduction of transcription activator-like type III effector (TALE) nucleases (TALENs). To advance the testing of TALE-based approaches, it will be crucial to deliver these custom-designed proteins not only into transformed cell types but also into more relevant, chromosomally stable, primary cells. Viral vectors are among the most effective gene transfer vehicles. Here, we investigated the capacity of human immunodeficiency virus type 1- and adenovirus-based vectors to package and deliver functional TALEN genes into various human cell types. To this end, we attempted to assemble particles of these two vector classes, each encoding a monomer of a TALEN pair targeted to a bipartite sequence within the AAVS1 'safe harbor' locus. Vector DNA analyses revealed that adenoviral vectors transferred intact TALEN genes, whereas lentiviral vectors failed to do so, as shown by their heterogeneously sized proviruses in target cells. Importantly, adenoviral vector-mediated TALEN gene delivery resulted in site-specific double-stranded DNA break formation at the intended AAVS1 target site at similarly high levels in both transformed and non-transformed cells. In conclusion, we demonstrate that adenoviral, but not lentiviral, vectors constitute a valuable TALEN gene delivery platfor

Quantitative evaluation of chromosomal rearrangements in gene-edited human stem cells by CAST-Seq

Genome editing has shown great promise for clinical translation but also revealed the risk of genotoxicity caused by off-target effects of programmable nucleases. Here we describe chromosomal aberrations analysis by single targeted linker-mediated PCR sequencing (CAST-Seq), a preclinical assay to identify and quantify chromosomal aberrations derived from on-target and off-target activities of CRISPR-Cas nucleases or transcriptional activator-like effector nucleases (TALENs), respectively, in human hematopoietic stem cells (HSCs). Depending on the employed designer nuclease, CAST-Seq detected translocations in 0%–0.5% of gene-edited human CD34+ HSCs, and up to 20% of on-target loci harbored gross rearrangements. Moreover, CAST-Seq detected distinct types of chromosomal aberrations, such as homology-mediated translocations, that are mediated by homologous recombination and not off-target activity. CAST-Seq is a sensitive assay able to identify and quantify unintended chromosomal rearrangements in addition to the more typical mutations at off-target sites. CAST-Seq analyses may be particularly relevant for therapeutic genome editing to enable thorough risk assessment before clinical application of gene-edited products

Engineered zinc finger nickases induce homology-directed repair with reduced mutagenic effects

Engineered zinc finger nucleases (ZFNs) induce DNA double-strand breaks at specific recognition sequences and can promote efficient introduction of desired insertions, deletions or substitutions at or near the cut site via homology-directed repair (HDR) with a double- and/or single-stranded donor DNA template. However, mutagenic events caused by error-prone non-homologous end-joining (NHEJ)-mediated repair are introduced with equal or higher frequency at the nuclease cleavage site. Furthermore, unintended mutations can also result from NHEJ-mediated repair of off-target nuclease cleavage sites. Here, we describe a simple and general method for converting engineered ZFNs into zinc finger nickases (ZFNickases) by inactivating the catalytic activity of one monomer in a ZFN dimer. ZFNickases show robust strand-specific nicking activity in vitro. In addition, we demonstrate that ZFNickases can stimulate HDR at their nicking site in human cells, albeit at a lower frequency than by the ZFNs from which they were derived. Finally, we find that ZFNickases appear to induce greatly reduced levels of mutagenic NHEJ at their target nicking site. ZFNickases thus provide a promising means for inducing HDR-mediated gene modifications while reducing unwanted mutagenesis caused by error-prone NHEJ

AAV-mediated photoreceptor transduction of the pig cone-enriched retina

Recent success in clinical trials supports the use of adeno-associated viral (AAV) vectors for gene therapy of retinal diseases caused by defects in the retinal pigment epithelium (RPE). In contrast, evidence of the efficacy of AAV-mediated gene transfer to retinal photoreceptors, the major site of inherited retinal diseases, is less robust. In addition, although AAV-mediated RPE transduction appears efficient, independently of the serotype used and species treated, AAV-mediated photoreceptor gene transfer has not been systematically investigated thus so far in large animal models, which also may allow identifying relevant species-specific differences in AAV-mediated retinal transduction. In the present study, we used the porcine retina, which has a high cone/rod ratio. This feature allows to properly evaluate both cone and rod photoreceptors transduction and compare the transduction characteristics of AAV2/5 and 2/8, the two most efficient AAV vector serotypes for photoreceptor targeting. Here we show that AAV2/5 and 2/8 transduces both RPE and photoreceptors. AAV2/8 infects and transduces photoreceptor more efficiently than AAV2/5, similarly to what we have observed in the murine retina. The use of the photoreceptor-specific rhodopsin promoter restricts transgene expression to porcine rods and cones, and results in photoreceptor transduction levels similar to those obtained with the ubiquitous promoters tested. Finally, immunological, toxicological and biodistribution studies support the safety of AAV subretinal administration to the large porcine retina. The data presented here on AAV-mediated transduction of the cone-enriched porcine retina may affect the development of gene-based therapies for rare and common severe photoreceptor diseases

Risk factors of osteoporosis in healthy Moroccan men

<p>Abstract</p> <p>Background</p> <p>Although not as common as in women, osteoporosis remains a significant health care problem in men. Data concerning risk factors of osteoporosis are lacking for the male Moroccan population. The objective of the study was to identify some determinants associated to low bone mineral density in Moroccan men.</p> <p>Methods</p> <p>a sample of 592 healthy men aged 20-79 years was recruited from the area of Rabat, the capital of Morocco. Measurements were taken at the lumbar spine and proximal femurs using DXA (Lunar Prodigy Vision, GE). Biometrical, clinical, and lifestyle determinants were collected. Univariate, multivariate, and logistic regression analyses were performed.</p> <p>Results</p> <p>the mean (SD) age of the patients was 49 (17.2) years old. The prevalence of osteoporosis and osteopenia were 8.7% and 52.8%, respectively. Lumbar spine and hip BMD correlated significantly with age, weight and BMI. When comparing the subjects according to the WHO classification, significant differences were revealed between the three groups of subjects for age, weight and BMI, prevalence of low calcium intake and low physical activity. The multiple regression analysis found that only age, BMI, and high coffee consumption were independently associated to the osteoporotic status.</p> <p>Conclusion</p> <p>ageing and low BMI are the main risk factors associated with osteoporosis in Moroccan men.</p