Letetresgene Autoleucel Engineered T Cells in NY-ESO-1 Positive Participants With Advanced Myxoid/ Round Cell Liposarcoma

This trial will evaluate safety and efficacy of Letetresgene autoleucel (GSK3377794) in participants with advanced myxoid/round cell liposarcoma or high-grade myxoid liposarcoma.

New York esophageal antigen-1 (NY-ESO-1) and LAGE-1a antigens are tumor-associated proteins that have been found in several tumor types. Clinical trials using adoptively transferred T-cells directed against NY-ESO-1/LAGE-1a have shown objective responses. Letetresgene autoleucel (GSK3377794) is the first generation of NY-ESO-1 specific T-cell receptor (TCR) engineered T-cells. This protocol investigates Letetresgene autoleucel treatment in Human Leukocyte Antigen (HLA)-A\*02+ participants with NY-ESO1+ advanced myxoid/round cell liposarcoma or high-grade myxoid liposarcoma.

Eligibility Criteria:
Inclusion Criteria:

* Participant is greater than equal to (\>=)18 years of age at the time of signing the study informed consent.
* Participant has a diagnosis of advanced (metastatic or inoperable) high grade myxoid liposarcoma / myxoid round cell liposarcoma confirmed histologically and by the presence of the reciprocal chromosomal translocation t(12;16) (q13;p11) or t(12; 22) (q13;q12).
* Participant has measurable disease according to RECIST v1.1 criteria.
* Participant must have previously received or be intolerant to anthracycline based therapy for advanced (metastatic or inoperable) disease.
* Participants who received neoadjuvant/adjuvant anthracycline based therapy and progressed within 6 months of completion of therapy will be eligible.
* Participant must be HLA A\*02:01, HLA A\*02:05 and/or HLA-A\*02:06 positive.
* Participant's tumor (either the most recent archival specimen or a fresh biopsy) is positive for NY-ESO-1 expression by a designated central laboratory.
* Participant has an Eastern Cooperative Oncology Group (ECOG) Performance Status 0-1.
* Participant has a left ventricular ejection fraction \>=45%.
* Participant is fit for apheresis and has adequate venous access for the cell collection.
* Participants must satisfy pregnancy and contraceptive requirements per protocol and have adequate organ function per protocol specified values.

Exclusion Criteria:

* Any previous gene therapy using an integrating vector.
* Any previous allogeneic hematopoietic stem cell transplant.
* Participant has history of allergic reactions attributed to compounds of similar chemical or biologic composition to fludarabine, cyclophosphamide or other agents used in the study.
* Participant has history of chronic or recurrent (within the last year prior to screening) severe autoimmune or immune mediated disease requiring steroids or other immunosuppressive treatments.
* Participant has known active brain or leptomeningeal metastases.
* Participant has other prior malignancy that is not in complete remission.
* Participant has uncontrolled intercurrent illness including, but not limited to:
* (i) Ongoing or active infection.
* (ii) Clinically significant cardiac disease
* (iii) Interstitial lung disease (participants with existing pneumonitis as a result of radiation are not excluded, however, participants must not be oxygen dependent).
* Participant has active infection with Human Immunodeficiency Virus (HIV), Hepatitis B virus (HBV), ), Hepatitis C virus (HCV) or human T-lymphotropic virus (HTLV).