Abstract CT180: Phase I clinical trial of CD19CAR -T cells secreting PD-1-targeting IL-21 in advanced relapsed/refractory acute lymphoblastic leukemia

Abstract Background/Purpose: Chimeric antigen receptor (CAR) T cell therapy has shown remarkable responses in hematologic malignancies. However, suboptimal clinical outcomes have been associated with decreased expansion and persistence of adoptive transferred CAR-T cells, antigen-negative relapses, and impairment by an immunosuppressive tumor microenvironment. We previously developed CD19CAR-T cells secreting PD-1Ab21 fusion protein composed of anti-PD-1 single chain antibody and IL-21 (PD-1Ab21-CD19CAR-T). This investigator-initiated clinical trial is designed to assess the safety and efficacy of the novel CAR-T cells in advanced relapsed/refractory acute Lymphoblastic leukemia (ALL). Methods: This study recruited 10 patients with advanced relapsed/refractory B-ALL and half of them relapsed after allogeneic hematopoietic stem cell transplantation (allo-HSCT). All patients received fludarabine and cyclophosphamide before a single infusion of PD-1Ab21-CD19CAR-T cells at dose of 0. 3, 1 or 3 x 106 cells/kg of body weight. The patients were monitored for adverse events, clinical response, as well as expansion of CAR-T and lymphocytes. Results: All five non-post-transplant patients achieved complete remission (CR), including two active CNS diseases, and three of them pursued consolidative allo-HSCT. Among the five post-transplant patients, one patient, who had undergone autologous, allogeneic CAR-T cell therapies and allo-HSCT, achieved CR and remained leukemia-free for 5 months, which was longer than the duration of remission (4 monthes) after allo-HSCT. The last treated patient achieved CR. Three other post-transplant patients, including two active CNS diseases, eventually died of the infection. One of the patients achieved minimal residual disease negative CR. The other two patients did not undergo laboratory evaluation, but their CNS symptoms disappeared. Once the expansion of CAR-T cells was detected, the proportion of CD8+T cell in CD3+T cells increased dramatically, rapidly reaching 77. 8~91. 2% and maintaining above 50% for a long time in all treated patients. Except for the three patients who died from infection, other patients experienced no or mild cytokine release syndrome (CRS) (grade ≤2). None of the patients had neurotoxic side effects. Conclusion: This study demonstrates that PD-1Ab21-secreting CAR-T cells are safe and effective therapeutic platform, even in cancer patients with CNS invasion. Our data also suggest that PD-1Ab21-secreting CAR-T therapy can activate endogenous anti-tumor CD8+ T cell responses. Citation Format: Yu Jing, Ying Li, Liping Dou, Shengjuan Zhang, Ran Tian, Guojing Wang, Xiangrui Cheng, Jitao Zhao, Hang Li, Yueyi An, Naibo Yang, Shengdian Wang. Phase I clinical trial of CD19CAR -T cells secreting PD-1-targeting IL-21 in advanced relapsed/refractory acute lymphoblastic leukemia abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT180.