SPEARHEAD-3 Pediatric Study

Who May Qualify: - Subject has diagnosed by tissue sample (biopsy-confirmed) diagnosis of any one of the following cancers: (A) Synovial Sarcoma (SS), (B) MPNST, (C) Neuroblastoma, or (D) Osteosarcoma (OS). - Age: (A) Synovial Sarcoma: 2 to 17 years (B) MPNST, Neuroblastoma and Osteosarcoma: 2 to 21 years - Body weight ≥ 10 kg - Must have previously received a systemic chemotherapy - Measurable disease prior to lymphodepletion according to RECIST v1.1 (or INCR, 2017 Neuroblastoma only). - HLA-A\*02 positive - Tumor shows MAGE-A4 expression confirmed by central laboratory. - Performance Status: (A) Subjects ≥16: Eastern Cooperative Oncology Group (ECOG) 0 or 1 (B) Subjects 2 to 16: Lansky score ≥ 80 • Subject has anticipated expected to live at least 3 months in the opinion of the investigator. Who Should NOT Join This Trial: - Positive for HLA-A\*02:05 in either allele; or any A\*02 having same protein sequence as HLA-A\*02:05 - History of allergic reactions attributed to compounds of similar chemical or biologic composition to fludarabine, cyclophosphamide. - History of autoimmune or immune mediated disease - Known central nervous system (CNS) metastases. - Other prior malignancy that is not considered by the Investigator to be in complete remission - Clinically significant cardiovascular disease - Active infection with human weakened immune system virus, hepatitis B virus, hepatitis C virus, or human T cell leukemia virus - Pregnant or breastfeeding - Experiencing ongoing rapid disease progression that in the opinion of the Investigator significantly increases the subjects risk associated with treatment. Always talk to your doctor about whether this trial is right for you.