Background: Approximately 25% of patients (pts) with NPC develop RM disease, which has a poor prognosis (median overall survival [mOS]: 12–16 mo), despite standard treatments with radiation and/or chemotherapy. NPC is an EBV-associated cancer in which programmed cell death ligand 1 (PD-L1) expression is upregulated upon EBV activation. Pembro showed antitumor activity in a phase 1b study of pts with RM-NPC (objective response rate [ORR]: 26%; mOS: 16.5 mo) (Hsu, J Clin Oncol 2017;35:4050-56). Targeting RM EBV+ NPC with tab-cel immunotherapy (off-the-shelf, allogeneic EBV-specific T cells) in pts has also shown promise, with 2-yr OS rates of 84% (Prockop, ASCO 2016;34:3012). The favorable safety profile of tab-cel offers the opportunity for combination immunotherapy with pembro for increased efficacy. Methods: This multicenter, open-label, single-arm phase 1b/2 study evaluates safety and efficacy of tab-cel in combination with pembro. Study participants are ≥12 yrs of age with incurable, locally recurrent or metastatic EBV+ NPC previously treated with platinum-containing therapy. Pts are checkpoint-inhibitor naïve (phase 1b/2) or refractory to anti-PD-1 or anti-PD-L1 therapy (phase 1b). Tab-cel is selected from a bank based on matching ≥2 HLA alleles, including ≥1 restricting HLA allele, between pts and donors. Tab-cel will be administered intravenously (IV) on days 1, 8, and 15 of a 21-day cycle. Initial tab-cel dose is 2x10⁶ cells/kg and the de-escalated tab-cel dose (if needed) is 1x10⁶ cells/kg. Pembro is administered at 200 mg IV Q3W in adults and 2 mg/kg IV Q3W in pts aged 12 to 17 yrs. Primary outcomes of phase 1b are to characterize dose-limiting toxicities, identify the maximum tolerated dose (MTD) or in the absence of MTD, the recommended phase 2 dose, and assess safety. Primary outcomes for phase 2 are ORR and safety. Secondary endpoints include progression-free survival, OS, and duration of response. Enrollment is ongoing for 12-24 participants in the phase 1b portion of the study with a 6+6 design. Phase 2 is expected to enroll 36 pts. Clinical trial information: NCT03769467