B7-H3-Specific Chimeric Antigen Receptor Autologous T-Cell Therapy for Pediatric Patients With Solid Tumors (3CAR)

This trial is testing a personalized immune cell therapy (CAR-T cell therapy targeting a protein called B7-H3) for children and young adults with solid tumors that have returned or stopped responding to standard first-line treatment. B7-H3 is a protein found on the surface of many childhood cancers. **You may be eligible if...** - You are 21 years old or younger - You have a solid tumor that expresses the B7-H3 protein (confirmed by testing) - Your cancer has relapsed or become resistant to standard first-line therapy - Your expected survival is more than 8 weeks - You have adequate heart, kidney, lung, and liver function - You have adequate blood counts - Females of childbearing age must not be pregnant and agree to use birth control **You may NOT be eligible if...** - You have a known immune deficiency disease or HIV - You have an active serious infection (like hepatitis B or C) - You have had an allergic reaction to mouse-protein-based products in the past - You are on high-dose steroids within 7 days before the infusion - Your disease is rapidly progressing at the time of treatment Talk to your doctor to see if this trial is right for you.