Résumé :
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Murine myoblast transplantation studies in mouse models have provided encouraging results but have underlined important limitations, such as acute cell death and poor migration capacity, beyond the immunological tolerance of the grafted cells. The specific nature and yield of implantation success have been less thoroughly investigated using cells of human origin. Therefore we evaluated the extent of cell survival and integration efficiency upon transplantation of human myoblasts into immunodeficient recipients. We injected low passages CD56-positive healthy human myoblasts into the Tibialis Anterior muscles of immunodeficient SCID mice, and the animals were sacrificed at regular intervals from day 0 to day 28. Human cells fate was assessed by co-detecting human cytoplasmic (COX2) and nuclear (Lamin A/C) antigens. Human cells were counted on serial sections and a mathematical model was written accounting the biological parameters to understand its dynamics. The relocation into the satellite cell niche was assessed by triple labelling of human cells (lamin A/C), and of murine muscle fibres and basal lamina delineated respectively by dystrophin and laminin edging. We observed a nonlinear but progressive loss of injected cells from day 0 to day 28. According to the mathematical model, 90% of cells had disappeared at day 14, correlating with the progressive erasing of human nuclei initially present in the interstitial spaces. This phenomenon was associated with a low capacity of cells to fuse with recipient fibres. Indeed, the number of cells integrated into the fibres seemed established at day 2 after cell injection, as indicated by specific human lamin A/C staining of donor nuclei within recipient fibres. Upon maturation, human cytoplasmic antigens were observed within these fibres. Although a few human cells held a satellite cell position on day 28, this suggested the preservation of the self renewal capacity of human myoblasts after transplantation. Finally, our mathematical model suggested an improvement of the cell survival by reducing the number of myoblasts injected, in agreement with recent proposals. In conclusion, our results demonstrate the low regenerative potential of human myoblasts in SCID mouse muscles. This was partly due to a lack of fusion with host fibres in absence of a damaging context. Elaborating around protocols to improve fusion represents future avenues for research in these models.
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