A Clinical Study Investigating the Therapeutic Effects and Safety of an Investigational Cell Therapy Given With and Without an Additional Investigational Product in Males With Testicular Cancer or a Form of Cancer That Developed From Sperm

Key Inclusion Criteria: * Have a histologically confirmed diagnosis of a testicular or extragonadal GCT of extracranial origin. * Evidence of measurable disease by RECIST 1.1 or if RECIST 1.1 evaluation is not possible, elevation of serum tumor marker(s) (AFP or βhCG). * Participants with evidence of progressive or recurrent metastatic GCT defined as meeting at least one of the following criteria: * Tumor biopsy of new or growing or unresectable lesions demonstrating viable non-teratomatous GCT. In the event of an incomplete gross resection where viable GCT is found, participants will be considered eligible for this study. * Elevated serum tumor markers (AFP or ßhCG) that are increasing. Increase of an elevated lactate dehydrogenase alone does not constitute progressive disease. * Development of new or enlarging lesions in the setting of persistently elevated AFP or ßhCG, even if the markers are not continuing to rise. * Participants must have received prior high-dose chemotherapy with autologous stem cell transplantation or conventional dose chemotherapy as salvage therapy. There is no maximum limit for the number of prior treatments. * Have a CLDN6-positive tumor assessed using an analytically validated immunohistochemistry assay at a central laboratory. * Have an Eastern Cooperative Oncology Group performance status of 0 to 1. * Have laboratory tests of adequate organ function as defined in the protocol. Key Exclusion Criteria: * Had major surgery within the 4 we…