Less is more: Investigating the influence of cellular nanoparticle load on transfection outcomes in neural cells

Genetic engineering of cell transplant populations offers potential for delivery of neurotherapeutic factors to modify the regenerative microenvironment of the injured spinal cord. The use of magnetic nanoparticle (MNP) based vectors has reduced the traditional reliance on viral methods and their associated obstacles in terms of scale up and safety. Studies utilising magnetic assistive platforms for MNP‐mediated gene delivery have found transfection efficiency in astrocytes (a major transplant and homeostatic neural cell type) to be both frequency and amplitude‐dependent. It is widely assumed that increased intracellular particle load will enhance transfection efficiency in a cell population. Therefore, we tested repeat delivery of MNP:plasmid complexes in conjunction with oscillating magnetic field parameters‐ a process termed ‘magneto‐multifection’‐ in astrocytes of primary origin in an attempt to enhance transfection levels. We show i) levels of transfection using magneto‐multifection equal that seen with viral methods; ii) reporter protein expression using two reporter plasmids shows a diverse profile of single/dual transfected cells with implications for delivery of a ‘cocktail’ of neurotherapeutic proteins and, iii) contrary to expectation, an inverse relationship exists between particle load and reporter protein expression