Dasatinib-Blinatumomab Combination for the Front-Line Treatment of Adult Ph+ ALL Patients. Updated Results of the Gimema LAL2116 D-Alba Trial

Background. The management of adult patients with Ph+ acute lymphoblastic leukemia (Ph+ ALL), including the elderly, has changed since the introduction of tyrosine kinase inhibitors (TKI). A significantly better survival is observed in patients who become minimal residual disease (MRD)-negative.

Aims. To increase the rate of MRD-negative patients, we designed a front-line chemo-free induction-consolidation trial (D-ALBA, GIMEMA LAL2116) based on the combination of the second-generation TKI dasatinib with the bispecific monoclonal antibody blinatumomab. The primary endpoint of the study was the rate of patients who achieved a complete molecular remission (CMR) or a positive non-quantifiable (PNQ) disease after at least two cycles of blinatumomab. Secondary endpoints included disease-free survival (DFS), overall survival (OS), cumulative incidence of relapse (CIR) and safety. We also sought to evaluate the prognostic impact of additional genomic lesions - performed on diagnostic samples - and the potential changes in the immunologic compartment, in terms of T cells and T-regulatory cells (Tregs), evaluated by flow cytometry (CD3+/CD4+, CD3+/CD8+ and CD3+/CD4+/CD25+/FOXp3+, respectively).

Methods. This multicenter phase II study enrolled Ph+ ALL patients aged 18 years or older, with no upper age limit. Prior to dasatinib, patients received a 7-day steroids pre-phase: steroids were continued for further 24 days and stopped at day 31. Dasatinib (140 mg/day) was administered as induction for 85 days. Thereafter, patients who obtained a complete hematologic response (CHR) received a post-induction consolidation treatment with blinatumomab at a flat dose of 28 μg/day. A minimum of 2 cycles was mandatory, while the administration of up to 3 additional cycles was allowed based on the response to blinatumomab and medical decision. Dasatinib was continued during treatment with blinatumomab. CNS prophylaxis was carried out during the whole treatment. Post-consolidation treatment was open.

Results. Between May 2017 and January 2019, 63 patients have been enrolled. Median age was 54.5 years (range: 24.1-81.7), 54% were female, the median white blood cell count (WBC) was 42 x10⁹/l (range: 0.63-63.5) and 65.1% carried the p190 fusion. Copy number aberration analysis showed that the most frequent lesion was, as expected, IKZF1 deletion (54%): 23.9% of patients were thus classified as IKZF1plus (i.e. IKZF1 and/or PAX5 and/or CDKN2A/B deletions). The median follow-up is 10 months (range: 0.9-21.5). So far, 61 patients have completed induction, 55 the 1^st cycle of blinatumomab, 47 the 2^nd cycle, 33 the 3^rd, 26 the 4^th and 17 the 5^th. Two patients have gone off protocol for medical decision and toxicity, and 1 died during induction. At the end of the induction with dasatonib, 17/58 pts (29.3%) had a molecular response (6 CMR and 11 PNQ). At the primary endpoint (end of the 2^nd cycle of blinatumomab), 27/47 (56.3%) had a molecular response (17 CMR and 10 PNQ). The rates of molecular responses further increased after subsequent cycles of blinatumomab: 65.7% after the 3^rd cycle and 80% after the 4^th cycle. ABL1 mutational analysis was carried out in 15 patients with evidence of a MRD increase: 8 cases were WT, while mutations were detected in 7 (6 T315I, and 1 E255K). All mutations but 1 occurred prior to the start of blinatumomab and all were "cleared" by blinatumomab. The analysis of the immunologic compartment carried out in 12 patients who completed all 5 cycles of blinatumomab showed a significant increase in the rate of CD8+ T cells (19.8% before the start of blinatumomab and 29% after the 5^th cycle, p=0.04) and a significant reduction in the rate of Tregs (11% before blinatumomab and 3.7% after the 5^th cycle, p=0.02). Overall, 5 relapses have been recorded (2 hematologic, 2 isolated CNS and 1 nodal). The 12-month OS and DFS are 94.2% and 87.8%. A significantly inferior DFS (61.4%, p=0.01) was observed in IKZF1plus cases: these patients were prone to develop deleterious mutations. So far, 12 patients have been allografted and no transplant-related mortality has been recorded.

Conclusions. In the first chemo-free induction-consolidation protocol for adult Ph+ ALL patients of all ages based on a combination of a targeted and immunotherapeutic strategy, the rates of molecular responses and survival are highly promising; patients harboring IKZF1 plus represent, also in this setting, a clinical challenge.