FGFR4 Chimeric Antigen Receptor (CAR) T Cells in Children and Young Adults With Recurrent or Refractory Rhabdomyosarcoma

30 mg/m2 per day IV on days -5, -4, -3, -2

500 mg/m2 per day IV on days -4, -3, -2

"Participants Age \>=18 years, based on FDA approved dosing: Loading dose of 400 mg/m2 IV, followed by 250 mg/m2 IV weekly for a total of 4 doses.~Participants Age \<18 years, based on phase I data of cetuximab in children: Dose of 250 mg/m2 IV administered over 1 hour weekly for a total of 4 doses."

Single intravenous (IV) infusion on Day 0