Advances in intranasal mesenchymal stem cell therapy for neonatal brain injury: from clinical translation to optimized therapeutic strategies

Neonatal hypoxic-ischemic (HI) brain injury is a major cause of long-term neurological morbidity and affects several brain regions, including the cortex, hippocampus, basal ganglia and, as more recently shown, the mammillary bodies. Current treatment options are limited to therapeutic hypothermia, which offers only partial protection. Mesenchymal stem cell (MSC) therapy has emerged as a promising strategy, demonstrating safety in humans and regenerative effects in preclinical studies. However, before intranasal MSC delivery can be widely translated to the clinic, key questions remain regarding optimal cell type and validation of the delivery route in anatomically relevant models. Additionally, strategies are needed to further enhance therapeutic efficacy. The overall aim of this thesis was therefore to advance the clinical translation of intranasal MSC therapy for infants affected by HI brain injury and to explore approaches to improve MSC therapeutic potency. We showed that intranasally delivered Wharton’s jelly–derived MSCs reach the neonatal mouse brain, promote neurorepair, reduce neuroinflammation and lesion size, and improve motor outcomes. Their combination with therapeutic hypothermia further enhanced recovery, supporting MSC-based combination therapies for improving outcomes in affected newborns. Using a newly established non-human primate model, we confirmed MSC migration to widespread brain regions without requiring hyaluronidase pretreatment in animals whose nasal structure more closely resembles that of human infants. We also identified early and persistent mammillary body damage that was not alleviated by current treatments, highlighting the need for targeted neuroprotection. Finally, we evaluated two MSC preconditioning strategies: hypoxic preconditioning enhanced MSC migration and therapeutic efficacy through distinct proteomic changes, whereas osteopontin preconditioning improved in vitro neurotrophic properties without enhancing in vivo benefits. In conclusion, this work provides essential preclinical evidence supporting intranasal MSC therapy and identifies avenues to optimize its regenerative potential. With continued refinement, MSC-based therapies hold strong promise for improving outcomes in infants affected by hypoxic-ischemic brain injury.