P574: CPX-351 COMBINED WITH HEMATOPOIETIC CELL TRANSPLANTATION WITH REGULATORY AND CONVENTIONAL T CELL IMMUNOTHERAPY FOR HIGH-RISK ACUTE MYELOID LEUKEMIA

Abstract

Background: Patients with newly diagnosed acute myeloid leukemia with myelodysplasia-related changes (MRC-AML) or therapy-related AML (t-AML) have an extremely poor prognosis. CPX-351, a dual-drug liposomal encapsulation of cytarabine and daunorubicin, improved significantly rates of remission and overall survival (Lancet JE et al, JCO 2018). Allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative strategy for such patients, but incidence of post-transplant relapse is still unacceptably high. We developed a novel HSCT strategy that combines an age-adapted myeloablative irradiation-based conditioning regimen with regulatory and conventional T-cell adoptive immunotherapy (Treg/Tcon HSCT). HLA-haploidentical Treg/Tcon HSCT ensured low relapse rate (4%) and resulted in an unprecedented chronic graft versus host disease/relapse free survival (CRFS, 75%) in AML patients (Pierini et al., Blood Adv. 2021). Aims: We report preliminary outcomes of the combination therapy with CPX-351 and Treg/Tcon HSCT for MRC-AML and t-AML at our center. Methods: We included in the study all patients with MRC-AML or t-AML who were referred at our center from September 2019 to January 2022 and could be treated with CPX-351. Treg/Tcon HSCT consisted of a myeloablative conditioning regimen with total marrow/lymphoid irradiation, thiotepa, fludarabine and cyclophosphamide followed by an infusion of 2x106/Kg donor Tregs on day -4, 1x106/Kg Tcons on day -1 and a megadose (>6x106/Kg) of purified CD34+ hematopoietic progenitor cells on day 0. No pharmacological GvHD prophylaxis was given post-transplant (clinicaltrials.gov: #NCT03977103). Results: Seventeen patients with a median age of 57.5 years (46-72) were treated with CPX-351: 13 with newly diagnosed AML (11 MRC-AML and 2 t-AML) and 4 patients who relapsed after a previous HSCT and who acquired novel cytogenetic abnormalities (2 complex karyotypes, CK). 9/13 patients with newly diagnosed AML had karyotype abnormalities: 4 monosomy 7, 1 CK, 1 t(3;3), 1 isolated del(20q) and 2 (both t-AML) t(11;20) which resulted in NUP98-TOP1 fusion. Nine patients achieved complete remission (CR), 2 partial response (PR) and 2 had persistent disease. No patient experienced grade>3 extrahematologic toxicity. Ten/13 patients underwent a first HSCT (8 in CR, 2 in PR). Eight underwent Treg/Tcon HSCT (3 from HLA-matched, 5 from HLA-haploidentical donor), while 2 unmanipulated haploidentical HSCT followed by post-transplant cyclophosphamide (PT-Cy). All patients achieved full-donor engraftment. No patients experienced non-relapse mortality (NRM). Three/10 patients had a grade ≥ III acute GvHD; all of them are alive and off immunosuppressive therapy. At a median follow up of 16.2 months (range 9-29 months), 9/10 patients are alive and in CR with no chronic GvHD. No relapse occurred in the 8 patients who underwent Treg/Tcon HSCT, while one patient who underwent HSCT followed by PT-CY relapsed. The 4 patients who were treated after one previous HSCT received one single induction cycle with CPX-351, achieved CR and experienced no grade>3 extra-hematologic toxicity. All of them could undergo a second HSCT. NRM occurred in 1 patient (septic shock), while 3 patients are alive to date. Summary/Conclusion: CPX-351 allowed most of MRC-AML and t-AML patients to reach HSCT in CR despite high risk genetics and even when used in patients who relapsed after a 1st HSCT. Combination of CPX-351 with Treg-Tcon HSCT is safe and exert powerful antileukemic activity. Thus, it appears to be a promising strategy to ensure high rate of CRFS in very high-risk AML.