Demographics and treatment outcomes in patients with EBV+ PTLD treated with off-the-shelf EBV-specific CTL under an ongoing expanded access program in Europe: First analyses.

7530 Background: Patients undergoing allogeneic hematopoietic cell transplant (HCT) or solid organ transplant (SOT) are at risk of developing Epstein–Barr virus driven post-transplant lymphoproliferative disorder (EBV+ PTLD), a rare hematologic malignancy, which is often aggressive and life-threatening. Patients with relapsed or refractory (r/r) EBV+ PTLD have few treatment options with poor outcomes, demonstrating a clear unmet medical need. Tabelecleucel is an investigational, off-the-shelf, allogeneic EBV-specific T-cell immunotherapy being studied in patients with serious EBV+ diseases (NCT04554914 & NCT03394365) that has demonstrated clinical benefit and favorable safety profile in the treatment of EBV+ PTLD after failure of rituximab (R) ± chemotherapy (Prockop, EBMT 2021, ATC 2021, ASH 2021). Methods: Atara Biotherapeutics supports an ongoing expanded access program (EAP) in Europe for patients with EBV+ diseases who have no other treatment options. Here we report demographics, efficacy and safety results of r/r EBV+ PTLD patients following SOT or HCT who presented between Jul 2020 and Nov 2021 and consented to research. Results: A total of 48 EAP requests from 9 countries for patients with EBV+ diseases were received. Twenty-two patients from 7 countries consented to this research: 16 EBV+ PTLD and 6 EBV+ non-PTLD. Of the 16 PTLD patients 15 received at least one dose of tabelecleucel. Overall, 9 out of 15 (60%) patients achieved a response as assessed by the treating physician, with 6 complete responses and 3 partial responses. Eight out of nine responses were seen after the first cycle. No adverse events were reported as related to tabelecleucel by the treating physician. Conclusions: The successful execution of this European EAP demonstrates the feasibility to deliver an off-the-shelf allogeneic EBV+ T-cell therapy in time-sensitive clinical situations when no other treatment options exist. These data show clinically meaningful outcomes for patients with r/r EBV+PTLD post-SOT or post-HCT treated with tabelecleucel consistent with previously reported favorable safety and efficacy profile (Prockop, ASH 2021).[Table: see text]