Generation of c-MycERTAM-transduced human late-adherent olfactory mucosa cells for potential regenerative applications

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.

Microcarrier expansion of c-MycERTAM -modified human olfactory mucosa cells for neural regeneration

Human olfactory mucosa cells (hOMCs) have potential as a regenerative therapy for spinal cord injury. In our earlier work, we derived PA5 cells, a polyclonal population that retains functional attributes of primary human OMCs. Microcarrier suspension culture is an alternative to planar two-dimensinal culture to produce cells in quantities that can meet the needs of clinical development. This study aimed to screen the effects of 10 microcarriers on PA5 hOMCs yield and phenotype. Studies performed in well plates led to a 2.9-fold higher cell yield on plastic compared to plastic plus microcarriers with upregulation of neural markers β-III tubulin and nestin for both conditions. Microcarrier suspension culture resulted in concentrations of 1.4 × 10⁵ cells/ml and 4.9 × 10⁴ cells/ml for plastic and plastic plus, respectively, after 7 days. p75^NTR transcript was significantly upregulated for PA5 hOMCs grown on Plastic Plus compared to Plastic. Furthermore, coculture of PA5 hOMCs grown on Plastic Plus with a neuronal cell line (NG108-15) led to increased neurite outgrowth. This study shows successful expansion of PA5 cells using suspension culture on microcarriers, and it reveals competing effects of microcarriers on cell expansion versus functional attributes, showing that designing scalable bioprocesses should not only be driven by cell yields.

Impact of Dual Cell Co-culture and Cell-conditioned Media on Yield and Function of a Human Olfactory Cell Line for Regenerative Medicine

Olfactory ensheathing cells (OECs) are a promising candidate therapy for neuronal tissue repair. However, appropriate priming conditions to drive a regenerative phenotype are yet to be determined. We first assessed the effect of using a human fibroblast feeder layer and fibroblast conditioned media on primary rat olfactory mucosal cells (OMCs). We found that OMCs cultured on fibroblast feeders had greater expression of the key OEC marker p75NTR (25.1 ± 10.7 cells/mm²) compared with OMCs cultured on laminin (4.0 ± 0.8 cells/mm², p = 0.001). However, the addition of fibroblast-conditioned media (CM) resulted in a significant increase in Thy1.1 (45.9 ± 9.0 cells/mm² versus 12.5 ± 2.5 cells/mm² on laminin, p = 0.006), an undesirable cell marker as it is regarded to be a marker of contaminating fibroblasts. A direct comparison between human feeders and GMP cell line Ms3T3 was then undertaken. Ms3T3 cells supported similar p75NTR levels (10.7 ± 5.3 cells/mm²) with significantly reduced Thy1.1 expression (4.8 ± 2.1 cells/mm²). Ms3T3 cells were used as feeder layers for human OECs to determine whether observations made in the rat model were conserved. Examination of the OEC phenotype (S100β expression and neurite outgrowth from NG108-15 cells) revealed that co-culture with fibroblast feeders had a negative effect on human OECs, contrary to observations of rat OECs. CM negatively affected rat and human OECs equally. When the best and worst conditions in terms of supporting S100β expression were used in NG108-15 neuron co-cultures, those with the highest S100β expression resulted in longer and more numerous neurites (22.8 ± 2.4 μm neurite length/neuron for laminin) compared with the lowest S100β expression (17.9 ± 1.1 μm for Ms3T3 feeders with CM). In conclusion, this work revealed that neither dual co-culture nor fibroblast-conditioned media support the regenerative OEC phenotype. In our case, a preliminary rat model was not predictive of human cell responses.