The presently disclosed subject matter provides compositions, methods, and kits for transfecting adipose-derived mesenchymal stem cells (AMSCs) in freshly extracted adipose tissue using nanoparticles comprising biodegradable polymers self-assembled with nucleic acid molecules. The presently disclosed subject matter also provides methods for treating a neurological disease in a patient in need thereof, the method comprising administering the AMSCs transfected with the nucleic acid molecules to the patient, wherein the nucleic acid molecules encode one or more bioactive molecules functional in the treatment of a neurological disease, particularly wherein the neurological disease is a brain tumor.