Final Report Summary - STROKECELLFUSION (Cell fusion as regenerative tool for stroke treatment) Ischemic stroke ranks among the leading cause of death and adult disability in developed countries. Upon an ischemic insult, an area called penumbra area is formed, which, although at risk, is still possible to recover. It was reported that bone marrow transplantation made 24hrs after the stroke leads to functional outcome. Cell fusion is one of the underlying mechanisms, but its true regenerative potential is hindered by the low frequency of fusion events, especially in the brain. StrokeCellFusion describes a strategy based in the co-administration of bone marrow derived cells (BMSCs) and the controlled release of fusogenic factors aimed to increase cell fusion events. Therefore, the objectives of the present project are: 1) identify new putative fusogenic factors in vitro; 2) develop a nanocarrier adequate for the sustained and controlled delivery of the selected fusogenic factors; 3) evaluate the in vivo efficacy of the developed system in a mouse model of stroke.From the developed nanocarriers poly(lactic) nanoparticles (PLA NPs) were the drug delivery system selected. PLA NPs were not cytotoxic, exhibited the physical/chemical properties and the release profile more appropriates for the current biomedical application. Furthermore, biodistribution studies of PLA NPs labeled with fluorophore rhodamine (Rho) revealed an overall body distribution and were not concentrated in kidney/liver. With the help of an in vitro cell fusion detection system and FACS analysis, interleukine-4 (IL-4) was indentified and selected as a putative fusogenic agent, as it increased the fusion events between neural cells with BMSCs. Later on, it was assessed the in vivo effect of IL-4 intracerebral administration in animals transplanted with BMSCs. Mice were sacrificed 15 days after IL-4 administration and it was observed a slight increase in the number of fused cells in comparison with sham control. However, under pathological conditions, such as stroke, the fusogenic effects of IL-4 might be potentiated due to the unique environment generated at the infracted area. Furthermore, it was confirmed that IL-4 effect was not due to the recruitment of activated microglia. The next step would be to test the effect of co-administrating IL4-loaded NPs together with intravenous bone marrow transplant in the mouse model of stroke. In summary, in StrokeCellFusion it was developed a delivery system that can be applied to other neurodegenerative conditions that involve the destruction/alteration of the blood brain barrier and that require a drug with a controlled pharmacokinetic profile. Furthermore, IL-4 has been identified as a fusogenic factor with potential to increment fusion events up to effective levels for therapy.