The tropism for glioma cells was more specific with LCMV-GP lentiviral pseudotyped vectors, as VSV-G pseudotyped lentiviral vectors also transduced few normal brain cells in invasive areas. In previous studies using a rat glioma model, we also showed a more specific transduction of glioma cells by LCMV-GP pseudotyped vectors compared to VSV-G pseudotyped vectors [18, 19] . In fact, in these studies, the VSV-G pseudotyped vectors transduced normal brain cells at a much higher frequency than in this study. This can be explained by the mode of vector delivery, because in the previous studies, we injected the vectors both into the tumor core as well as into tumor border areas. In the present study, we injected the vectors into the tumor core only using convection enhanced delivery. We used this method because it results in a high distribution volume of drug and vector and is currently used as a delivery method in clinical studies [28] . In addition, the tumor model we apply here is highly invasive and lacks a sharply demarcated brain tumor/normal brain interface, present in the rat glioma model. Another explanation could be the species difference as we used human glioma cells in this study in contrast to rat glioma cells in the previous work. VSV-G pseudotyped vectors might have a higher tropism for human glioma cells than for rat normal host cells. However, as the receptor for VSV-G is unknown [29] , this remains a hypothesis. The targeting of cancer stem cells or cancer stem-like cells in human tumors including glioblastoma has recently evolved as a major aim in cancer therapy. These stem cells are suggested to initiate cancer and might be resistant to therapy, thus being responsible for tumor recurrence [30] [31] [32] . Yet, recent studies have initiated a controversial discussion whether cancer stem cells really exist [33, 34] . Therefore, we use the term ''cancer stem-like cells'' in our study to designate cells which have certain stem-like properties described previously. We showed that both lentiviral vectors transduced CD133-positive and CD133-negative cells. CD133-positive cells have been identified as cancer initiating cells and cancer stem cells in many different cancers including glioblastoma [30, 35] . However, more recent reports questioned these findings showing that CD133-negative popopulations can include cancer initiating cells as well [36, 37] . The efficient targeting of CD133-positive and CD133-negative glioma cells has also been described for adenoviral vectors [38, 39] .