CRISPR ribonucleoprotein-mediated genetic engineering in plants

CRISPR-derived biotechnologies have revolutionized the genetic engineering field and have been widely applied in basic plant research and crop improvement. Commonly used Agrobacterium- or particle bombardment-mediated transformation approaches for the delivery of plasmid-encoded CRISPR reagents can result in the integration of exogenous recombinant DNA and potential off-target mutagenesis. Editing efficiency is also highly dependent on the design of the expression cassette and its genomic insertion site. Genetic engineering using CRISPR ribonucleoproteins (RNPs) has become an attractive approach with many advantages: DNA/transgene-free editing, minimal off-target effects, and reduced toxicity due to the rapid degradation of RNPs and the ability to titrate their dosage while maintaining high editing efficiency. Although RNP-mediated genetic engineering has been demonstrated in many plant species, its editing efficiency remains modest, and its application in many species is limited by difficulties in plant regeneration and selection. In this review, we summarize current developments and challenges in RNP-mediated genetic engineering of plants and provide future research directions to broaden the use of this technology.

Full-Spectrum Targeted Mutagenesis in Plant and Animal Cells

Directed evolution is a powerful approach for protein engineering and functional studies. However, directed evolution outputs from bacterial and yeast systems do not always translate to higher organisms. In situ directed evolution in plant and animal cells has previously been limited by an inability to introduce targeted DNA sequence diversity. New hypermutation tools have emerged that can generate targeted mutations in plant and animal cells, by recruiting mutagenic proteins to defined DNA loci. Progress in this field, such as the development of CRISPR-derived hypermutators, now allows for all DNA nucleotides within user-defined regions to be altered through the recruitment of error-prone DNA polymerases or highly active DNA deaminases. The further engineering of these mutagenesis systems will potentially allow for all transition and transversion substitutions to be generated within user-defined genomic windows. Such targeted full-spectrum mutagenesis tools would provide a powerful platform for evolving antibodies, enzymes, structural proteins and RNAs with specific desired properties in relevant cellular contexts. These tools are expected to benefit many aspects of biological research and, ultimately, clinical applications.

Design and Testing of Vector-Producing HEK293T Cells Bearing a Genomic Deletion of the SV40 T Antigen Coding Region

The use of the human embryonic kidney (HEK) 293T cell line to manufacture vectors for in vivo applications raises safety concerns due to the presence of SV40 T antigen-encoding sequences. We used CRISPR-Cas9 genome editing to remove the SV40 T antigen-encoding sequences from HEK293T cells by transfecting them with a recombinant plasmid expressing Cas9 and two distinct single guide RNAs (sgRNAs) corresponding to the beginning and end of the T antigen coding region. Cell clones lacking T antigen-encoding sequences were identified using PCR. Whole-genome (WG) and targeted locus amplification (TLA) sequencing of the parental HEK293T cell line revealed multiple SV40 T antigen-encoding sequences replacing cellular sequences on chromosome 3. The putative T antigen null clones demonstrated a loss of sequence reads mapping to T antigen-encoding sequences. Western blot analysis of cell extracts prepared from the T antigen null clones confirmed that the SV40 large and small T antigen proteins were absent. Lentiviral vectors produced using the T antigen null clones exhibited titers up to 1.5 × 107 transducing units (TU)/mL, while the titers obtained from the parent HEK293T cell line were up to 4 × 107 TU/mL. The capacity of the T antigen-negative cells to produce high titer adeno-associated virus (AAV) vectors was also evaluated. The results obtained revealed that the lack of T antigen sequences did not impact AAV vector titers.

Oral lesions in haemopathic patients

This paper deals with the oral manifestations observed in patients with haemolymphopathies and oral complications associated with systemic cytotoxic chemotherapy and/or radiation therapy. We report the percentage of oral manifestations observed in 30 patients treated with cytotoxic drugs for malignant haemolymphopathies or other tumors after 2-4 cycles of systemic combinations chemotherapy. No sex or age differences were recorded except for abnormalities of taste present only in 13% treated patients older than 50. Stomatitis was more frequent in patients with malignant haemolymphopathies than in patient with other neoplastic diseases, probably due to the fact that in the former group neutropenia and thrombocytopenia induced by bone marrow infiltration or by more aggressive combination chemotherapy are most frequent. An oral care protocol for these patients is suggested.