Evaluating Efficacy of B7-H3-CAR T Cells Administered at the End of Upfront Map Chemotherapy in Patients With Newly Diagnosed High-Risk Osteosarcoma

The purpose of this study is to assess the safety, feasibility, and effectiveness of a consolidative B7-H3 CAR T cell therapy in patients with newly diagnosed high-risk osteosarcoma who have undergone upfront standard chemotherapy. Primary Objectives: \- To evaluate 1-year RFS from the time of SJCARB7H3-41BBL infusion for patients with newly diagnosed metastatic osteosarcoma who received standard chemotherapy. Secondary Objectives: * To evaluate the OS from time of SJCARB7H3-41BBL infusion for patients with newly diagnosed metastatic osteosarcoma who received standard chemotherapy. * To evaluate the feasibility of delivering SJCARB7H3-41BBL at the end of standard therapy in patients with newly diagnosed metastatic osteosarcoma. * To describe the safety of autologous SJCARB7H3-41BBL therapy when delivered at the end of standard therapy in patients with newly diagnosed metastatic osteosarcoma.

Inclusion Criteria: 1. Participant and/or legally authorized representative has signed the Informed Consent Form for this study 2. Prior cancer therapy: * Regimen A only: Completed all planned cycles of consolidation therapy between 14-28 days prior. * Regimen B only: has completed all planned cycles of consolidation chemotherapy at least 14 days prior and if clinically indicated, participant has undergone pulmonary metastasectomy. They must have recovered from any surgical complications with no ongoing sequelae of category 2 or higher by the Clavien-Dindo classification system and less than 6 weeks must have passed from time of pulmonary metastasectomy. 3. No evidence of progressive disease since enrolled on study 4. Lansky performance status score of ≥ 50 for participants \