Donor-Derived Memory-like NK Cells for the Treatment of Children and Young Adults with Relapsed AML Following Allo-HCT

Leukemia recurrence is the most common type of treatment failure after allogeneic hematopoietic cell transplantation (allo-HCT) for pediatric AML. We have advanced memory-like (ML) NK cells as a cellular therapy for AML. NK cells differentiated to ML NK cells after stimulation with interleukins-12, -15, and -18 display significantly enhanced anti-leukemia functionality and in vivo persistence. We performed a prospective clinical trial utilizing donor lymphocyte (DLI) and ML NK cell infusions to treat relapsed AML after allo-HCT. Here we present the complete clinical cohort as an update to the previous report (Bednarski et al. Blood 2022; n=9) with 9 additional patients treated, including 4 patients who received 2 ML NK cell infusions.Eighteen patients with a median age of 8 years were enrolled. 7 patients had 2 prior transplants. Most patients received 1 salvage therapy (range 0-4) prior to study enrollment. All patients had active disease, with a median bone marrow (BM) blast percentage of 35%. Patients received fludarabine, cytarabine, and G-CSF followed by DLI and donor ML NK cell infusions 2 weeks later.ML NK cells were successfully manufactured from all donor types. Complete responses were observed in 8 patients (44%), of whom 3 (37.5%) were MRD negative. One of 8 responders received allo-HCT as consolidative therapy. Of the other 7 patients, 1 remains disease free without additional intervention (>4 years of follow up) and 6 remained in remission for a median of 100 days after ML NK cell infusion. 1-year overall survival was 37% for the entire cohort and 71% for responders (Fig 1). After protocol amendment, 4 patients received a second ML NK cell infusion. Patient 19 remained in MRD negative remission for 5 months after second infusion without further disease directed therapy. Patients 18 and 20 were treated for CBFA2T3-GLIS2 AML. Patient 18 remained in CR for 7 weeks following second infusion. Patient 20 developed extramedullary disease 4 weeks from second infusion while maintaining low level BM MRD (0.1%). ML NK cells were well tolerated without organ toxicity, cytokine release syndrome or neurotoxicity. De novo GVHD occurred in one patient (5.6%) who received 2 ML NK and DLI infusions.NK cells expanded following infusion and comprised a substantial frequency in peripheral blood (Fig 2A). Following a second infusion, peripheral NK cells expanded further (Fig 2B). The frequency of Ki67+ NK cells in the BM was substantially increased within 14 days from infusion, indicating in vivo activation and proliferation in the AML microenvironment (Fig 3). Full correlative immunology assessments will be presented at the meeting. ML NK therapy for relapsed AML after allo-HCT is feasible, safe and demonstrates promising efficacy in the largest cohort reported to date (8 of 18 with CR). An upcoming clinical trial will explore combinatorial TCRab depleted haplo-HCT and ML NK cell infusion for relapse prevention.