Miletic et al. [9] and Matuskova et al. [21] demonstrated a potent bystander killing effect of HSV-TK expressing rat bone marrow (BM)-derived tumor-infiltrating progenitor cells on 9 L rat gliomas and human mesenchymal stem cells (hMSCs) on the human glioblastoma cell lines 8-MG-BA, 42-MG-BA and U-118 MG. The gene discussed is TKT; the disease is glioblastoma.