Study to Evaluate Safety and Antitumor Activity of Lete-Cel (GSK3377794) in HLA-A2+ Participants With NY-ESO-1 Positive Previously Treated Advanced (Metastatic or Unresectable) Synovial Sarcoma or Myxoid/Round Cell Liposarcoma

Inclusion Criteria: * Participant must be ≥10 years of age at the time of signing the informed consent. * Participant scheduled to receive clinical drug product supply must also weigh ≥40 kg. * Participant has a diagnosis of synovial sarcoma or myxoid/round cell liposarcoma, confirmed by local histopathology with evidence of disease-specific translocation. * Participant has advanced (metastatic or unresectable) synovial sarcoma or myxoid/round cell liposarcoma. Unresectable refers to a tumor lesion in which clear surgical excision margins cannot be obtained without leading to significant functional compromise. * Male or female. Contraception requirements will apply at the time of leukapharesis and treatment. * Life expectancy ≥24 weeks * Participant has confirmed evidence of a relevant disease-specific translocation per below: * For synovial sarcoma, presence of a translocation involving chromosome 18 (SYT gene) and/or chromosome X (SSX1, SSX2 or SSX4 genes). * For myxoid/round cell liposarcoma, presence of a translocation involving chromosome 12 (DDIT3 gene) and/or chromosome 16 (FUS gene) and/or chromosome 22 (EWSR1 gene). * Participant is either currently being treated with or has completed at least one standard-of-care treatment including anthracycline-containing regimens (e.g., doxorubicin alone, doxorubicin with ifosfamide) for advanced (metastatic or inoperable) disease. Participants who are intolerant to anthracycline may receive ifosfamide alone unless intolerant to…