PEP-CMV Vaccine Targeting CMV Antigen to Treat Newly Diagnosed Pediatric HGG and DIPG and Recurrent Medulloblastoma

This study is testing a vaccine (called PEP-CMV) that targets a protein from the cytomegalovirus (CMV) found in brain tumor cells. It is being tested in children and young adults with newly diagnosed high-grade brain tumors (HGG/DIPG) or with recurrent medulloblastoma — a type of brain cancer. **You may be eligible if...** - You are between 3 and 39 years old - You have been diagnosed with recurrent or progressive medulloblastoma with a measurable tumor on MRI, OR you have a newly diagnosed high-grade brain tumor (HGG) or DIPG - You have already received prior radiation and other standard therapies - Your performance/functional status meets minimum requirements **You may NOT be eligible if...** - Your tumor does not have the CMV protein that the vaccine targets - You have severe organ dysfunction - You are pregnant or breastfeeding - You have active uncontrolled infection - Your prior radiation was completed too recently (within the required washout period) Talk to your doctor to see if this trial is right for you.