Abstract: Disclosed are mammalian cells and mammalian cell lines that have a reduced load of remnants of past viral/retroviral infections and methods of producing and using the same.

Abstract: Disclosed are mammalian cells and mammalian cell lines that have a reduced load of remnants of past viral/retroviral infections and methods of producing and using the same.

Abstract: Disclosed are cells that have stably integrated into their genomes exogenous nucleic acid sequences, such as transgenes, within or proximal to the integration site of a sequence comprising at least part of an endogenous retrovirus (ERV) or a LTR-retrotransposon (LTR-RT), or instead of a sequence encompassing an ERV or a LTR-RT that is part or was part of the genome of the cell, as well as method of producing and using such cells. Advantageously, a high level and/or stable production of the transgene expression product(s) can be achieved. Transgene integration and expression may be furthered by modulating the DNA repair pathways of the cell, e.g., by transiently expressing a gene encoding a protein that forms part of a DNA repair pathway during transgene integration.

Abstract: Type-C endogenous retroviruses (ERVs) embedded in Chinese hamster ovary (CHO) cells were altered to modify the release of retroviral and/or retroviral-like particles in the culture supernatant. Although evidence for the infectivity of these particles is missing, their presence has raised safety concerns. 173 type-C ERV sequences that clustered into functionally conserved groups were identified. Transcripts from one type-C ERV group were identified to be full-length with intact open reading frames, and to have corresponding viral RNA genomes that were loaded into retroviral-like particles. Also, sequence analysis of the genomic RNA from viral particles indicated that they may result from few expressed ERV sequences. Disclosed herein is the disruption/alteration of the gag gene of the expressed ERV group using CRISPR-Cas9 genome editing.

Abstract: Disclosed are mammalian cells and mammalian cell lines that have a reduced load of remnants of past viral/retroviral infections and methods of producing and using the same.