Preliminary Minimal Residual Disease Analysis of the Australasian Leukaemia & Lymphoma Group (ALLG) ALL8 Study of Front-Line Blinatumomab with Chemotherapy in Adults with Ph Negative B-Cell Acute Lymphoblastic Leukaemia

Background - Conventional chemotherapy for adults with Acute Lymphoblastic Leukaemia (ALL) is associated with considerable treatment-related toxicity. Blinatumomab is a CD19/CD3 targeting bi-specific T-cell engager that has demonstrated promising efficacy in relapsed/refractory ALL, and in combination with chemotherapy in newly diagnosed patients. Preliminary studies also suggest less toxicity and good efficacy (CR/CRh 66%) when delivered as induction to older adults (median age 75) with newly diagnosed B-ALL (Advani, ASH 2018). Of responders, Minimal Residual Disease (MRD) negativity in this trial was achieved in 92%. Given this, the Australasian Leukaemia & Lymphoma Group (ALLG) has explored the potential for upfront Blinatumomab as induction for younger adults with Ph- B-lineage Acute Lymphoblastic Leukaemia, alternating with CNS-directed chemotherapy cycles.

Aim - To assess response to therapy of the first 10 patients enrolled on this study by molecular MRD analysis as a surrogate measure of short-term efficacy of this combination.

Method - The ALLG ALL8 study (ACTRN12617000084381) is a phase II proof-of-concept front-line study for patients fit for treatment with a Hyper-CVAD-like regimen (between 40-65 years) with newly diagnosed Ph- B-lineage ALL. Those with CNS positive disease are excluded. Patients receive a steroid pre-phase (Prednisolone 100mg daily for 7 days) followed by a disease debulking phase of cyclophosphamide 150mg/m² BD day 1-3, vincristine 2mg day 1 & 11 and dexamethasone 10mg/m² day 1-4 and 11-14. Patients then receive alternating cycles of Blinatumomab (at 9mcg/d for the first 7 days of cycle 1 followed by 28mcg/d until day 28) with B-cycles of Hyper-CVAD (Methotrexate 1g/m² day 1, Cytarabine 3g/m² BD day 2,3, Methylprednisolone 50mg BD day 1-3) (figure 1). All patients receive intrathecal prophylaxis with methotrexate, cytarabine and hydrocortisone prior to blinatumomab treatment blocks and day 1 and 8 of each B-cycle until a total of 8 doses were administered. At the completion of therapy, high-risk patients (MLL translocations, hypodiploid, complex karyotype or MRD positive at TP3) are recommend to proceed to allogeneic stem cell transplant while others receive 24 months of POMP maintenance. Minimal residual disease analysis was performed at a centralised EuroMRD accredited laboratory utilising Taqman probes and patient specific PCR primers targeted at immunoglobulin heavy chain or T-cell receptor (Ig/TCR) gene rearrangements. MRD positivity was defined as a detectable level of ≥ 1 x 10^-4.

Results - The following results are based upon the first 10 patients enrolled on ALL8. Median age of 54.7 years (range 43 to 66 years) and 70% were male. Median ECOG PS was 0 (range 0 - 2). 6 patients had an abnormal karyotype, 2 high-risk (one with hypodiploid karyotype, one with t(1;19). Median white cell count at diagnosis was 3.36 x 10⁹/L (range 1.95 - 12.05 x 10⁹/L). All patients (10/10) attained CR/CRi following induction therapy with no treatment related deaths. At the end of the induction phase (MRD TP1) 4 out of 10 had attained MRD negativity, 2 had detectable unquantifiable MRD and 4 were MRD positive. By the end of the 1^st consolidation cycle (MRD TP2) 1 additional patient had become MRD negative and 1 MRD positive patient had become MRD unquantifiable. 1 patient was not evaluable at TP2 being withdrawn prior to this, 2 do not have TP2 available at this time (1 being MRD negative at TP1, 1 with unquantifiable low-level MRD). One patient had MRD increase between TP1 and TP2, this subject had a hypodiploid karyotype. Thus, by completion of 1^st consolidation an aggregate of 7 out of 10 patients were MRD negative or had unquantifiable low-level MRD, 3 remaining MRD positive (with 1 MRD progression). Updated results will be presented at the meeting.

Conclusion - Front-line therapy with Blinatumomab in combination with chemotherapy is feasible in adults and results in high levels of MRD response by the end of the first consolidation block with the majority of MRD negative responses attained after the first treatment block. Despite early incorporation of Blinatumomab into this treatment protocol, MRD progression was seen in one patient with high-risk cytogenetic abnormalities.

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