The antibody used in this study is called anti-HER2 (Human Epidermal Growth Factor Receptor 2). This antibody sticks to GBM cells because of a substance on the outside of these cells called HER2. Up to 80% of GBMs are positive for HER2. HER2 antibodies have been used to treat people with HER2-positive cancers. For this study, the HER2 antibody has been changed so that instead of floating free in the blood it is now attached to T cells. When an antibody is joined to a T cell in this way it is called a chimeric receptor. These chimeric receptor-T cells seem to be able to kill tumors like GBM, but they don't last very long and so their chances of fighting the cancer are limited. Therefore, developing ways to prolong the life of these T cells should help them fight cancer.