Developing high-efficiency base editors by combining optimized synergistic core components with new types of nuclear localization signal peptide

The clustered regularly interspaced short palindromic repeats(CRISPR)–CRISPR-associated protein(Cas) system has been widely used for genome editing. In this system, the cytosine base editor(CBE) and adenine base editor(ABE) allow generating precise and irreversible base mutations in a programmable manner and have been used in many different types of cells and organisms. However, their applications are limited by low editing efficiency at certain genomic target sites or at specific target cytosine(C) or adenine(A) residues. Using a strategy of combining optimized synergistic core components, we developed a new multiplex super-assembled ABE(sABE) in rice that showed higher base-editing efficiency than previously developed ABEs. We also designed a new type of nuclear localization signal(NLS) comprising a FLAG epitope tag with four copies of a codon-optimized NLS(F4NLS^(r2)) to generate another ABE named F4NLS-sABE. This new NLS increased editing efficiency or edited additional A at several target sites. A new multiplex super-assembled CBE(sCBE) and F4NLS^(r2) involved F4NLS-sCBE were also created using the same strategy. F4NLS-sCBE was proven to be much more efficient than sCBE in rice. These optimized base editors will serve as powerful genome-editing tools for basic research or molecular breeding in rice and will provide a reference for the development of superior editing tools for other plants or animals.

ANTI-TUMOR ACTIVITY AND IMMUNE RESPONSES INDUCED BY HUMAN CANCER-ASSOCIATED MUCIN CORE PEPTIDE

Objective: To investigate the immune responses induced by apomucin which is a mixture of mucin core peptide, in mice for elucidating the role of mucin core peptide in the modulation of cancers. Methods: Apomucin was isolated from human pancreatic cancer cell line SW1990. The mice were immunized with this apomucin (10μg/time×6) plus DETOX. Results: When immunized, all mice developed delayedtype hypersensitivity (DTH) after challenged with apomucin or synthetic peptide MUC2 or MUC3, while the mice immunized with apomucin alone did not develop DTH. No antibodies were detected by ELISA after immunization. When the spleen cells of vaccinated mice were cocultured with this apomucin (10—50μg/ml) and rhIL2(50U/ml) in vitro, the proliferated lymphocytes showed cytotoxicity against human cancer cells, including colon cancer, gastric cancer, pancreatic cancer and leukemia as measured by Cr51 release assay. Antibodies against MUC2 and MUC3 could block the cytotoxicity. Conclusion: It was identified that a vaccine combined of apomucin and immune adjuvant DETOX can induce cellular immune response and antitumor cytotoxicity in mice.