The possible systemic toxic effect of the immunotoxin tested in this study against malignant glioma cells could be minor because it does not have the B chain of abrin, a galactose-specific lectin that facilitates cell entry [49] and because it is chemically bound by the SMPT crosslinker to IgY, which only recognizes CD133+ cells. This evidence concerns the gene PROM1 and malignant glioma.