Study to Investigate Lifileucel Regimen Plus Pembrolizumab Compared With Pembrolizumab Alone in Participants With Untreated Advanced Melanoma.

Prior treatment

• Participant received more than 1 prior line of therapy.
• Participant received prior therapy for metastatic disease
• Participants with a BRAF V600 mutation-positive tumor received prior adjuvant/neoadjuvant ICI therapy only
• Participant had another primary malignancy within the previous 3 years (except for those that do not require treatment or were curatively treated \>1 year ago, and in the judgment of the investigator do not pose a significant risk of recurrence.)

Other illness

• Participant has an active medical illness(es) that, in the opinion of the investigator, would pose increased risks for study participation, such as systemic infections; seizure disorders; coagulation disorders; or other active major medical illnesses of the cardiovascular, respiratory, or immune systems.
• Participant has a history of allogeneic cell or organ transplant.
  • Other protocol defined inclusion/exclusion criteria could apply.

Other

• Participant has melanoma of uveal/ocular origin.
• Participant has symptomatic untreated brain metastases.
• Participant has any form of primary or acquired immunodeficiency (eg, SCID or AIDS).

• Participant has a histologically or pathologically confirmed diagnosis of Stage IIIC, IIID, or IV unresectable or metastatic melanoma.
• In the investigator's assessment, the participant has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 and an estimated life expectancy of \> 6 months.
• Participant is assessed as having at least one resectable lesion (or aggregate lesions) for lifileucel generation.
• Participant must have at least one measurable disease as defined by RECIST 1.1 following tumor resection.
• Participants must have adequate organ function.
• Participants of childbearing potential or those with partners of childbearing potential must be willing to practice an approved method of highly effective birth control.
• Participants who are \> 70 years of age may be allowed to enroll after the investigator discusses with the medical monitor.