hTERT-Driven Immortalization of RDEB Fibroblast and Keratinocyte Cell Lines Followed by Cre-Mediated Transgene Elimination

Viral integration promotes SV40T-induced immortalization by disturbing the expression of DNA/chromosome- and ECM-associated functional genes

Lentivirus containing simian virus 40 large T antigen (SV40T) is routinely used to induce cell immortalization. However, the roles of viral integration itself in this progress is still controversial. Here, we transformed primary mouse embryonic fibroblasts (MEFs) with SV40T lentivirus and studied the roles of viral integration in the immortalization using RNA sequencing (RNA-seq) and whole genome sequencing (WGS). During the immortalization, differentially expressed genes (DGEs) are enriched in viral infection and several diverse activities. However, DEGs between immortalized and aging cells are significantly enriched in DNA/chromosome- and extracellular matrix (ECM)-associated activities. Gene regulatory network (GRN) analysis shows that although p53 is a key regulatory factor, many other transcription factors also play critical roles in the process, like STAT1. Of these DEGs, 32 genes have viral integration in their coding and/or regulatory regions. Our findings suggest that viral integration may promote SV40T-mediated immortalization by disturbing the expression of DNA/chromosome- and ECM-associated genes.

Construction and Characterization of Immortalized Fibroblast Cell Line from Bactrian Camel

Immortalized cell lines with many advantages are widely used in various experimental contexts by many different labs. However, the absence of available cell lines poses difficulties for research in some species, such as camels. To establish an immortalized Bactrian camel fibroblast (iBCF) cell line and understand its biological characteristics, primary fibroblast cells from Bactrian camels were isolated and purified using enzymatic digestion in this study, and telomerase reverse transcriptase (hTERT) vectors were introduced into primary BCF (pBCF) for continuous passage to 80 generations after screening with G418. The cell morphology of different generations was examined under a microscope. Cell cycle and viability were evaluated by flow cytometry and CCK-8 assay, respectively. Cellular genes expression was monitored by qPCR, immunofluorescence, and Western blot, respectively. Chromosomes were determined by karyotyping. The results showed that like most other cells, both pBCF and iBCF were sensitive to nutrient concentrations and adapted to culture in the medium with 4.5 g/L glucose and 10% fetal bovine serum (FBS) concentration. hTERT gene was introduced and stably expressed in iBCF cells, which promoted BCF cell immortalization. The fibroblast specific marker vimentin (VIM) is expressed in both pBCF and iBCF, but epithelial marker cytokeratin18 (CK18) expression is weak in BCF cells. Proliferation and viability detection showed that hTERT-induced iBCF exhibits faster growth rates and higher viability than pBCF. Karyotyping showed that iBCF maintained the same number and morphology of chromosomes as the pBCF. This study demonstrated that we have successfully constructed an immortalized Bactrian camel fibroblast cell line, which was named BCF23. The establishment of the BCF23 cell line provides a foundation for expanding camel-related research.

Immortalization Reversibility in the Context of Cell Therapy Biosafety

Immortalization (genetically induced prevention of replicative senescence) is a promising approach to obtain cellular material for cell therapy or for bio-artificial organs aimed at overcoming the problem of donor material shortage. Immortalization is reversed before cells are used in vivo to allow cell differentiation into the mature phenotype and avoid tumorigenic effects of unlimited cell proliferation. However, there is no certainty that the process of de-immortalization is 100% effective and that it does not cause unwanted changes in the cell. In this review, we discuss various approaches to reversible immortalization, emphasizing their advantages and disadvantages in terms of biosafety. We describe the most promising approaches in improving the biosafety of reversibly immortalized cells: CRISPR/Cas9-mediated immortogene insertion, tamoxifen-mediated self-recombination, tools for selection of successfully immortalized cells, using a decellularized extracellular matrix, and ensuring post-transplant safety with the use of suicide genes. The last process may be used as an add-on for previously existing reversible immortalized cell lines.