A severe reduction of blood flow to the brain causes cells to die. This is called a stroke. The after-effects of a stroke can range from recovery to permanent brain damage and death. A new emergency gene therapy treatment for people who are at risk of brain damage from a stroke was tested in mice. • The human granulocyte colony-stimulating factor, hG-CSF, is a protein that stimulates the production of stem cells in bone marrow. • mRNA coding for hG-CSF was obtained and used to make cDNA. • This cDNA was inserted into an adeno-associated virus (AAV) vector and given in eye drops to mice just after they experienced a stroke.