Intramedullary mesenchymal stromal cell transplantation in humans: Procedural safety and oncological risk...

Intramedullary cellular transplantation within the human spinal cord has historically been regarded as a highly experimental intervention associated with substantial theoretical risk. However, cumulative clinical evidence progressively challenges this perception. Multiple early-phase clinical studies have demonstrated the technical feasibility and procedural tolerability of intramedullary and intralesional cellular delivery in spinal cord injury (SCI), employing heterogeneous cellular products, including bone marrow-derived mononuclear cells, mesenchymal stromal cells (MSCs), and neural stem cells. Despite considerable heterogeneity in cellular composition, dosing strategies, injection volumes, and delivery paradigms, severe injection-related complications remain uncommon. Reported adverse events are predominantly mild and transient, while procedure-induced neurological deterioration has not emerged as a reproducible safety signal. These observations suggest that controlled spinal cellular administration may represent a biologically tolerated intervention rather than an intrinsically destabilizing procedure. Beyond procedural considerations, long-term biological safety remains a central dimension of translational evaluation. While theoretical concerns persist - particularly regarding tumorigenesis, clonal selection, and potential genomic instability associated with ex vivo MSC expansion - currently available clinical data have not identified reproducible or causally attributable neoplastic transformation signals within currently reported follow-up durations. Interpretation of long-term safety outcomes therefore requires careful distinction between theoretical biological plausibility and empirical clinical observations. In parallel, minimally manipulated autologous cellular products such as freshly isolated stromal vascular fraction (SVF) introduce a complementary translational framework. By preserving physiological cellular heterogeneity and eliminating risks associated with ex vivo expansion, SVF-based approaches further emphasize the need to reinterpret cellular variability as an intrinsic biological property rather than a marker of product instability. Collectively, available evidence supports consideration of multidimensional safety frameworks integrating procedural, short-term biological, and long-term theoretical domains. Future progress will depend on harmonized reporting standards, extended longitudinal evaluation, and large-scale collaborative datasets capable of refining biologically grounded safety models for spinal cellular therapies.