SPEARHEAD-3 Pediatric Study

Inclusion Criteria:

* Subject has histologically 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 life expectancy of greater than 3 months in the opinion of the investigator.

Exclusion Criteria:

* 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 immunodeficiency 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.