To overcome the myelosuppression that is a common side effect of chemotherapy, Adair et al. modified ex vivo the haematopoietic stem cells (HSCs) from three patients with glioblastoma to express a mutant form of 6-O-methylguanine-DNA methyltransferase (MGMT). This enzyme enhances the repair of DNA lesions caused by alkylating chemotherapies. Re-injection of the MGMT-modified HSCs, which successfully engrafted, enabled the patients to tolerate higher doses of chemotherapy, with some evidence of disease stabilization and improved survival.