The present disclosure relates to a method for introducing a hematopoietic cell into the brain of a mammal, by administering bone marrow-derived progenitor cells into the body of the mammal by intravenous injection. The bone marrow-derived cell is preferably a cell that differentiates into a glial cell. The disclosure also relates to a method for delivery of therapeutic protein molecules into the brain of a mammal, by administering to a mammal an effective amount of bone marrow-derived progenitor cells which contain a gene having a nucleic acid sequence that encodes a functional therapeutic protein. Isolated recombinant cells and a pharmaceutical composition are also provided.