We have recently demonstrated that the matrix metalloproteinase (MMP) 14 promoter drives gene expression specifically within the myeloid progeny of HSCs infiltrating brain metastases in contrast to the myeloid cells in other organs.17 Here, we used this promoter in HSC gene therapy to deliver TGFβ-blocking peptide to experimental GBM in combination with radiation therapy. Here, TGFB1 is linked to glioblastoma.