Atara presents updated clinical data from Phase 3 trial of tab-cel

Atara Biotherapeutics announced updated interim analysis and safety results from its Phase 3 multicenter ALLELE study investigating tabelecleucel for the treatment of relapsed/refractory Epstein-Barr virus positive post-transplant lymphoproliferative disease following solid organ transplant or hematopoietic cell transplant. The Phase 3 ALLELE study findings, along with updated efficacy and safety data from two single-center, open-label studies as well as a multicenter expanded access program investigating tab-cel including patients with Epstein-Barr virus positive leiomyosarcomas, were featured among four poster presentations at the 64th American Society of Hematology Annual Meeting taking place December 10-13, 2022, in New Orleans. In the ongoing Phase 3 ALLELE study, 43 patients – 14 HCT recipients and 29 SOT recipients – were treated with tab-cel and were included in the analysis. Patients received a median of 2 cycles of tab-cel. The median age of evaluable patients for both SOT and HCT was 48.5 years who had received a median of 1 prior systemic treatments. Responses per clinical and radiographic assessment were measured by independent oncologic response adjudication assessment. Results as of November 2021 data cutoff showed: An objective response rate of 51.2% was observed for both HCT and SOT groups, 51.7% for patients following SOT and 50.0% for HCT patients with a best overall response of Complete Response or Partial Response. The median time to response in all patients was 1.0 month and median duration of response in 22 responders was 23.0 months, with 12/22 responders having a DOR greater than6 months. Median overall survival of 18.4 months in all patients, 16.4 months in SOT and not yet reached in HCT. One-year survival rates were 61.1%, 56.2% in SOT and 70.1% in HCT. Patients responding to tab-cel had longer one-year survival compared to the non-responders, with a one-year survival rate of 84.4% versus 34.8% for non-responders. In addition, Atara presented updated efficacy and safety data investigating the potential of tab-cel in patients with EBV+ LMS who have received at least one therapy. EBV+ LMS is a rare, aggressive, and potentially fatal solid tumor that responds poorly to radiation and chemotherapy. Among 18 patient-treatments, median age was 8.9 years and 44.4% of patients were male Results showed: A clinical benefit rate of 77.8%, and ORR of 22.2% was observed. Median follow-up for all patients was 18.9 months. The estimated median OS was 77.4 months and the median progression-free survival was 12.5 months. Median DOR was 6.2 months with a one-year DOR rate of 37.5%. The one-year survival rate was 86.7% and the estimated two-year survival rate was 78.0%. In both the ALLELE and LMS studies, tab-cel was well tolerated and the safety profile consistent with previous data. There was no evidence of tumor flare reaction, infusion reactions, cytokine release syndrome, transmission of infectious diseases, and no events of graft versus host disease or organ rejection related to tab-cel. In separate posters, Atara also presented the methodology of using T-cell receptor beta sequencing to identify allogeneic cell product clones post-infusion and data confirming the absence of clinical manifestation of immunogenicity following tab-cel administration in patients enrolled in the ALLELE study.