High-grade gliomas are the most common brain tumors in humans and are essentially incurable. The defining hallmark of these high-grade gliomas is the presence within the tumor mass of highly tumorigenic cellular subpopulations that fuel tumor aggressiveness. Identification of the molecular mechanisms remains elusive. Therefore, there is a need for diagnostic markers to accurately determine the type of glioma and appropriate treatment. Gene delivery vehicles are provided that comprise an oncogene, IRES-Cre-ER cassette and a gene encoding an oligonucleotide that inhibits p53 including shp53. Methods are also provided for determining a diagnosis and for treatment of non-aggressive and aggressive gliomas.