Assembly of Baculovirus Vectors for Multiplexed Prime Editing.

Efficient genome editing by using CRISPR technologies requires simultaneous and efficient delivery of multiple genetically encoded components to mammalian cells. Amongst all editing approaches, prime editing (PE) has the unique potential to perform seamless genome rewriting, in the absence of DNA double-strand breaks (DSBs). The cargo capacity required for efficient PE delivery to mammalian cells stands at odd with the limited packaging capacity of traditional viral delivery vectors. By contrast, baculovirus (BV) has a large synthetic DNA capacity and can efficiently transduce mammalian cells. Here we describe a protocol for the assembly of baculovirus vectors for multiplexed prime editing in mammalian cells.

An engineered baculoviral protein and DNA co-delivery system for CRISPR-based mammalian genome editing.

CRISPR-based DNA editing technologies enable rapid and accessible genome engineering of eukaryotic cells. However, the delivery of genetically encoded CRISPR components remains challenging and sustained Cas9 expression correlates with higher off-target activities, which can be reduced via Cas9-protein delivery. Here we demonstrate that baculovirus, alongside its DNA cargo, can be used to package and deliver proteins to human cells. Using protein-loaded baculovirus (pBV), we demonstrate delivery of Cas9 or base editors proteins, leading to efficient genome and base editing in human cells. By implementing a reversible, chemically inducible heterodimerization system, we show that protein cargoes can selectively and more efficiently be loaded into pBVs (spBVs). Using spBVs we achieved high levels of multiplexed genome editing in a panel of human cell lines. Importantly, spBVs maintain high editing efficiencies in absence of detectable off-targets events. Finally, by exploiting Cas9 protein and template DNA co-delivery, we demonstrate up to 5% site-specific targeted integration of a 1.8 kb heterologous DNA payload using a single spBV in a panel of human cell lines. In summary, we demonstrate that spBVs represent a versatile, efficient and potentially safer alternative for CRISPR applications requiring co-delivery of DNA and protein cargoes.

Cytotoxicity of current adhesive systems: in vitro testing on cell cultures of primary murine macrophages.

OBJECTIVES: The aim of this study was to evaluate, in vitro, the potential cytotoxicity of dentinal adhesives on alveolar macrophages of Wistar rats, after diffusion through dentin. METHODS: The cytotoxicity of adhesives [single bond plus (SB), clearfil SE bond (CF) and Xeno V (XE)] applied to the occlusal surface of human dentin disks adapted to a dentin barrier test device were analyzed. The sets placed on a monolayer of cells were incubated for 24, 48 and 72h. Culture medium and Escherichia coli lipopolysaccharides (LPS) were used as negative and positive controls, respectively. Cellular cytotoxicity was evaluated by observing the cell survival rate (MTT assay) and nitric oxide production (NO). The data were analyzed by one-way factorial ANOVA and Tukey's and Tamhane's paired comparisons T2 (α=0.05). RESULTS: All the adhesive systems reduced the percentage of live cells by over 50%, compared with the control group. Within the same period of time, there was a statistically significant difference between the adhesives and LPS compared with the negative control group. SB presented a statistically significant difference between 24h and 72h, and XE between 48h and 72h. The quantity of NO produced in 24h did not differ statistically between the NC and adhesive groups. After 48h there was a significant difference between SB/CF and XE/NC. At 72h only CF showed a significant difference from each of the other groups. LPS differed statistically from all the other groups at all the evaluation times. SIGNIFICANCE: Components of the adhesives tested may permeate the dentin in sufficient concentrations to cause death and damage to cell metabolism in the alveolar macrophages of rats, which indicates potential cytotoxicity to pulpal cells.