The purpose of this study is to determine the clinical benefit and characterize the safety profile of tabelecleucel for the treatment of Epstein-Barr virus-associated post-transplant lymphoproliferative disease (EBV+ PTLD) in the setting of (1) solid organ transplant (SOT) after failure of rituximab (SOT-R) and rituximab plus chemotherapy (SOT-R+C) or (2) allogeneic hematopoietic cell transplant (HCT) after failure of rituximab.

This is a multicenter, open-label, phase 3 study to assess the efficacy and safety of tabelecleucel for the treatment of EBV+ PTLD in the setting of SOT-R and SOT-R+C (Cohort [C]-SOT) or HCT after failure of rituximab (C-HCT).

SOT-R further included participants:

1. who did not receive chemotherapy and did not have a documented medical reason not to receive chemotherapy (SOT-Ro) or
2. who were considered chemotherapy ineligible/inappropriate (SOT-R-Ci)

Combined population (SOT-R-Ci, SOT-R+C, and HCT) and (SOT-R-Ci and SOT-R+C) who received commercial product, or a product manufactured using a comparable process version (PV) were also used for analysis of outcomes.

Enrollment will be preceded by confirmation of availability of partially human leukocyte antigen (HLA) matched and restricted tabelecleucel for the participant.

Study procedures and product administration will be the same for each cohort. Tabelecleucel will be administered in cycles lasting 5 weeks (35 days). During each cycle, participants will receive intravenous tabelecleucel at a dose of 2 × 10^6 cells/kg on Days 1, 8, and 15, followed by observation through Day 35. Treatment will continue until maximal response, unacceptable toxicity, initiation of non protocol therapy, or failure of tabelecleucel with up to 2 different HLA restrictions (C-SOT) or up to 4 different HLA restrictions (C-HCT). The study includes a total of 5 years of follow-up for disease and survival status for participants enrolled before or after 09 October 2023 to reach the initial sample size of 33 participants in both cohorts. For all other participants enrolled after 09 October 2023 and after the initial sample of 33 participants in both cohorts has been reached in both cohorts, the follow-up will be every 3 months, up to 12 months, as assessed on anniversary of Cycle 1 Day 1. For responders, the follow-up will be 12 months from the date of initial response.

Inclusion Criteria:

1. Prior SOT of kidney, liver, heart, lung, pancreas, small bowel, or any combination of these (C-SOT); or prior allogeneic HCT (C-HCT).

2. A diagnosis of locally assessed, biopsy-proven EBV+ PTLD.

3. Availability of appropriate partially HLA-matched and restricted tabelecleucel has been confirmed by the sponsor.

4. Measurable, 18F-deoxyglucose (FDG)-avid (Deauville score ≥ 3) systemic disease using Lugano Classification response criteria by positron emission tomography (PET)-diagnostic computed tomography (CT), except when contraindicated or mandated by local practice, then magnetic resonance imaging (MRI) may be used. For participants with treated central nervous system (CNS) disease, a head CT and/or brain/spinal MRI as clinically appropriate will be required to follow CNS disease response per Lugano Classification response criteria.

5. Treatment failure of rituximab or interchangeable commercially available biosimilar monotherapy (C-SOT-R or C-HCT) or rituximab plus any concurrent or sequentially administered chemotherapy regimen (C-SOT-R+C) for treatment of PTLD.

6. Males and females of any age.

7. Eastern Cooperative Oncology Group performance status ≤ 3 for participants aged ≥ 16 years; Lansky score ≥ 20 for participants < 16 years.

8. For C-HCT only: If allogeneic HCT was performed as treatment for an acute lymphoid or myeloid malignancy, the underlying primary disease for which the participant underwent transplant must be in morphologic remission.

9. Adequate organ function.

   1. Absolute neutrophil count ≥ 1000/μL, (C-SOT) or ≥ 500/μL (C-HCT), with or without cytokine support.
   2. Platelet count ≥ 50,000/μL, with or without transfusion or cytokine support. For C-HCT, platelet count < 50,000/μL but ≥ 20,000/μL, with or without transfusion support, is permissible if the participant has not had grade ≥ 2 bleeding in the prior 4 weeks (where grading of the bleeding is determined per the National Cancer Institute's Common Terminology Criteria for Adverse Events [CTCAE], version 5.0).
   3. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and total bilirubin each < 5 × the upper limit of normal; however, ALT, AST, and total bilirubin each ≤ 10 × upper limit of normal is acceptable if the elevation is considered by the investigator to be due to EBV and/or PTLD involvement of the liver as long as there is no known evidence of significant liver dysfunction.

10. Participant or participant's representative is willing and able to provide written informed consent.

Exclusion Criteria:

1. Currently active Burkitt, T-cell, NK/T-cell lymphoma/LPD, Hodgkin, plasmablastic, transformed lymphoma, active hemophagocytic lymphohistiocytosis, or other malignancies requiring systemic therapy.
2. Daily steroids of > 0.5 mg/kg prednisone or glucocorticoid equivalent, ongoing methotrexate, or extracorporeal photopheresis.
3. Untreated CNS PTLD or CNS PTLD for which the participant is actively receiving CNS-directed chemotherapy (systemic or intrathecal) or radiotherapy at enrollment. NOTE: Participants with previously treated CNS PTLD may enroll if CNS-directed therapy is complete.
4. Suspected or confirmed grade ≥ 2 graft-versus-host disease (GvHD) per the Center for International Blood and Marrow Transplant Research consensus grading system at enrollment.
5. Ongoing or recent use of a checkpoint inhibitor agent (eg, ipilimumab, pembrolizumab, nivolumab) within 3 drug half-lives from the most recent dose to enrollment.
6. For C-HCT: active adenovirus viremia.
7. Need for vasopressor or ventilatory support.
8. Antithymocyte globulin or similar anti-T cell antibody therapy ≤ 4 weeks prior to enrollment.
9. Treatment with Epstein-Barr virus cytotoxic T lymphocytes or chimeric antigen receptor T cells directed against B cells within 8 weeks of enrollment (C-SOT or C-HCT), or unselected donor lymphocyte infusion within 8 weeks of enrollment (C-HCT only).
10. Female who is breastfeeding or pregnant or female of childbearing potential or male with a female partner of childbearing potential unwilling to use a highly effective method of contraception.
11. Inability to comply with study-related procedures.
12. Any medical condition or organ system dysfunction that in the investigator';s opinion, could compromise the participant's safety or ability to complete the study.