Fate of Immortalized Human Neuronal Progenitor Cells Transplanted in Rat Spinal Cord

Abstract

Background: Replacement of neurons and glia by transplantation has been proposed as a therapy for neurodegenerative diseases, including amyotrophic lateral sclerosis. This strategy requires using human motor neuronal progenitor cells or xenografts of animal cells, but there is little evidence that xenografted neuronal cells can survive in spinal cord despite immunosuppression. Objective: To clarify the mechanisms responsible for the death of xenografted neurons in spinal cord. Methods: Cells from an immortalized, neuronally committed, human embryonic spinal cord-derived cell line (HSP1) that expresses motor neuronal properties in vitro were transplanted into adult rat spinal cord. The rats were killed at intervals up to 8 weeks and serial sections through the graft sites were processed for immunofluorescence using primary antibodies against human nuclear and mitochondrial antigens, microtubule-associated protein 2, TUJ1, CD5, natural killer cells, and activated microglia-macrophages, caspase-3 and caspase-9. Results: Grafted cells did not migrate and underwent partial differentiation along a neuronal pathway. They were rejected after 4 weeks despite cyclosporine immunosuppression. Cells died by apoptosis via the cytochrome c/caspase-9/caspase-3 pathway. The host response included natural killer cells and activated microglia-macrophages but few T cells. Conclusions: Intraspinal neuronal xenotransplantation failed because of apoptotic cell death. Neither T cells nor the spinal cord environment, which favors gliogenesis, are likely to have been responsible, but natural killer cells may have been involved.

Bax siRNA promotes survival of cultured and allografted granule cell precursors through blockade of caspase-3 cleavage

“…On the other hand, the transplantation of immortalized neuronal precursors into the spinal cord may result in graft rejection even if immunosuppression had been performed. 37 In the present study, we have observed that Bax repression strongly increases the total transplant volume in 24 h following their introduction. In addition, cleaved caspase-3 immunoreactivity was strongly reduced in siBax-transfected precursors, while density of grafted cells, which were visualized by BrdU, did not change in comparison to that of non-transfected precursors.…”

“…16 The death pathways activated upon allografting have not yet been completely understood. Proinflammatory cytokines, 34 necrosis, 35 and caspase-mediated apoptosis 16,36,37 have been mentioned by different authors as a main reason of transplanted precursor cell death. Several strategies have been used to increase the yield of grafted cells survival.…”

“…Several strategies have been used to increase the yield of grafted cells survival. 17,37,38 According to Cicchetti et al, 17 simultaneous inhibition of caspases and complement system significantly improves survival of striatal neurons grafted into the rat brain. In a recent study, Niranjan et al 38 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 320 300 280 260 240 220 200 180 160 140 120 100 80 60 40 neural progenitors in both normal and tumour-bearing brain through an unknown mechanism.…”

“…Taken together, these data indicate that survival of precursors within the critical hours followed by their transplantation could be favoured by their transfection with siRNA interacting with Bax gene prior to transplantation. This approach consisting in allotransplantation of precursors transfected by a specific siRNA has several advantages: (i), the treatment is targeted to a single specific gene and is thus focused on a particular mechanism, unlike the strategy of brain irradiation, 38 (ii) the precursors stay in a modified state only within a limited time period, in contrast to the immortalized cells, 37 and (iii) the transient apoptosis blockade, which also takes place in normal conditions in the regulation of cell cycle, may restrict some undesirable side-effects such as tumorigenesis. 39 In conclusion, our results indicate that Bax plays a key role in the apoptosis of immature granule neurons.…”

Harvested human neurons engineered as live nervous tissue constructs: implications for transplantation

“…These efforts, however, have been hampered by poor long-term survival of transplanted neurons derived from these cells, limited differentiation into neuronal phenotypes following transplantation, and the risk of tumor formation from non-neuronal cells. 1,2,12 Although an alternative strategy is to transplant neurons harvested from animals into humans, there is a high risk of rejection or transmission of pathogens. 7,14,16 Nonetheless, there remains another source of transplantable neurons that has been generally overlooked.…”