S111: REPEATED INFUSIONS OF ESCALATING DOSES OF EXPANDED AND ACTIVATED AUTOLOGOUS NATURAL KILLER CELLS IN MINIMAL RESIDUAL DISEASE-POSITIVE PH+ ACUTE LYMPHOBLASTIC LEUKEMIA PATIENTS. A GIMEMA PHASE 1 TRIAL

Background: Due to age and co-morbidities, many Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) patients are ineligible to undergo high-dose chemotherapy or allogeneic transplant as consolidation treatment. Our group reported the promising results of the chemo-free scheme D-ALBA based on dasatinib/blinatumomab in induction/consolidation, underlying the potential role of immunotherapy in this setting (Foà et al, NEJM 2020;383:1616-23). Considerable interest has been raised by natural killer (NK) cells. We developed a GMP protocol for NK cell ex vivo expansion in the presence of IL-2 and IL-15, and report the results of a phase 1 protocol of adoptive immunotherapy with activated and expanded autologous NK cells for Ph+ ALL patients in complete hematologic remission (CHR) but with persistent/recurrent minimal residual disease (MRD) ≥60 years or ineligible for other post-CHR treatment modalities. Aims: The primary endpoint was to determine the maximum tolerated dose of NK cells and the recommended dose for subsequent studies. Secondary endpoints were the assessment of safety and tolerability of the treatment, the immunologic modifications induced by the procedure and the clinical response to treatment. Methods: The planned 6 patients were enrolled: 5 in 1st CHR and 1 in 2nd CHR. Patients underwent repeated infusions (maximum 5) of escalating doses of NK cells, ranging from 1x106 to 5x107/kg of body weight (BW). No conditioning therapies were administered before the infusion; patients were allowed to continue tyrosine kinase inhibitors. Patients underwent a comprehensive MRD monitoring by Q-RT-PCR with a one-year follow-up. Immunophenotypic analysis on the NK cell product was performed before and after the expansion. Intracellular cytokine production and PBMC cytotoxic activity against K562 cells, allogeneic and autologous blasts were evaluated after expansion and at time 0 and 7 days from each NK cell infusion. Results: NK cells presented a 12.3-fold ex vivo expansion. Expanded cells showed an increased expression of activating receptors and measurable cytotoxicity against primary allogeneic and autologous blasts. One patient received a maximum NK cell dose of 5x106 cells/kg, 2 patients 1x107 cells/kg and 3 5x107 cells/kg/BW. No patient experienced infusion-related toxicities. Two adverse events were recorded (grade 1 and 2), both judged not treatment-related, that resolved after TKI suspension. The higher cell dose infusion resulted in a significantly increased expression of natural cytotoxicity receptors, a greater cytokine production by NK, T and NKT cells, and in an increased capacity of PBMC to lyse K562 cells. These modifications appear persistent over time. At a 1-year follow-up from the last infusion, 5/6 patients are alive in CHR (Table 1). The MRD levels reduced over time and 4/6 patients reached a complete molecular response (CMR) or a positive-not-quantifiable (PNQ) status during the study period. At a median follow-up of 30.8 months from the last infusion, the 5 patients who received the NK treatment in 1st CHR are still in CMR or PNQ, though 1 patient required additional treatment. The patient in 2nd CHR at the time of the infusions showed a rise in MRD and died of disease progression. Image:Summary/Conclusion: This phase 1 study demonstrates that autologous NK cells can be efficiently expanded ex vivo from MRD-positive Ph+ ALL patients in CHR. The infusion of these expanded cells is safe and induces a marked in vivo host immune response, suggesting that this approach represents a tolerable and feasible model worthy of being investigated in larger clinical studies.