Adding the selective BCL-2 inhibitor venetoclax to reduced intensity conditioning (RIC) chemotherapy (fludarabine and busulfan, FluBu2) may enhance anti-leukemic cytotoxicity and thereby reduce the risk of post-transplant relapse. This phase 1 study investigated the recommended phase 2 (RP2D) of venetoclax, a BCL-2 selective inhibitor, when added to FluBu2 in adult patients with high risk acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and MDS/myeloproliferative neoplasms (MPN) undergoing transplant. Patients received dose-escalated venetoclax (200-400 mg daily starting day -8 for 6-7 doses) in combination with fludarabine 30 mg/m2/day for four doses and busulfan 0.8 mg/kg twice daily for eight doses on day -5 to -2 (FluBu2). Transplant related-toxicity was evaluated from the first venetoclax dose on day -8 to +28. Twenty-two patients were treated. At study entry, 5 MDS and MDS/MPN patients had 5-10% marrow blasts and 18/22 (82%) had a persistent detectable mutation. Grade 3 adverse events included mucositis, diarrhea and liver transaminitis (N=3 each). Neutrophil/platelet recovery and acute/chronic GVHD rates were similar to standard FluBu2. No DLTs were observed. The RP2D of venetoclax was 400 mg daily for 7 doses. With a median follow-up of 14.7 months (8.6-24.8 months), median overall survival was not reached, and progression free survival was 12.2 months (95% CI: 6.0 months, not estimable). In high risk AML, MDS, and MDS/MPN patients, adding venetoclax to FluBu2 was feasible and safe. To further address relapse risk, assessment of maintenance therapy after venetoclax plus FluBu2 transplant is on-going. This study was registered at clinicaltrials.gov as #NCT03613532.

IDH2 (isocitrate dehydrogenase 2) mutations occur in approximately 15% of patients with acute myeloid leukemia (AML). The IDH2 inhibitor enasidenib was recently approved for IDH2-mutated relapsed or refractory AML. We conducted a multi-center, phase I trial of maintenance enasidenib following allogeneic hematopoietic cell transplantation (HCT) in patients with IDH2-mutated myeloid malignancies. Two dose levels, 50mg and 100mg daily were studied in a 3x3 dose-escalation design, with 10 additional patients treated at the recommended phase 2 dose (RP2D). Enasidenib was initiated between days 30 and 90 following HCT and continued for twelve 28-day cycles. Twenty-three patients were enrolled, of whom 19 initiated post-HCT maintenance. Two had myelodysplastic syndrome, and 17 had AML. All but 3 were in first complete remission. No dose limiting toxicities were observed, and the RP2D was established at 100 mg daily. Grade ≥3 toxicities attributable to enasidenib were rare, with the most common being cytopenias. Eight patients stopped maintenance therapy before completing 12 cycles, due to adverse events (n=3), pursuing treatment for graft versus host disease (GVHD) (n=2), clinician choice (n=1), relapse (n=1), and COVID-19 infection (n=1). No cases of grade ≥3 acute GVHD were seen, and the 12-month cumulative incidence of moderate/severe chronic GVHD was 42% (20-63%). Cumulative incidence of relapse was 16% (95% CI: 3.7-36%); only one subject relapsed while receiving maintenance enasidenib. Two-year progression-free and overall survival were 69% (95% CI: 39-86%) and 74% (950% CI, 44-90%), respectively. Enasidenib is safe, well-tolerated, with preliminary activity as maintenance therapy following HCT, and merits additional study. The study was registered at ClinicalTrials.gov (NCT03515512).

Vaccination using irradiated, adenovirus transduced autologous myeloblasts to secrete GM-CSF (GVAX) early after allogeneic hematopoietic stem cell transplantation (HSCT) can induce potent immune responses. We conducted a randomized phase II trial of GVAX after HSCT for MDS-EB or relapsed/refractory AML. Myeloblasts were harvested before HSCT to generate the vaccine. Randomization to GVAX vs. placebo (1:1) was stratified by disease, transplant center, and conditioning. GVHD prophylaxis included tacrolimus and methotrexate. GVAX or placebo started between day +30-45 if there was engraftment and no GVHD. Vaccines were administered SC/ID weekly x 3, then q2 wks x 3. Tacrolimus taper began after vaccine completion. 123 patients enrolled, 92 proceeded to HSCT, and 57 (GVAX 30, Placebo 27) received at least 1 vaccination. No CTC grade ≥ 3 vaccine related adverse events were reported, but injection site reactions were more common after GVAX (10 vs. 1, p=0.006). With a median follow up of 39 months (range, 9-89), 18-month PFS, OS and relapse incidence were 53% vs 55% (p=0.79), 63% vs. 59% (p= 0.86), and 30% vs. 37% (p=0.51) for GVAX and placebo, respectively. NRM at 18 months was 17% vs. 7.7% (p=0.18), Grade II-IV aGVHD at 12 months 34% vs. 12% (p=0.13), and cGVHD at 3 years 49% vs. 57% for GVAX and placebo, respectively, p=0.26. Reconstitution of T, B, and NK cells were not decreased or enhanced by GVAX. There were no differences in serum MICA/B or other immune biomarkers between GVAX and placebo. GVAX does not improve survival after HSCT for MDS/AML. (Clinicaltrials.gov identifier: NCT01773395)

Background Relapse of acute myeloid leukemia (AML) after allogeneic stem cell transplant has a poor prognosis with limited treatment options. Cytokine-induced memory like natural killer (CIML NK) cells are a novel therapy with enhanced cytotoxicity independent of KIR ligand interactions able to induce remission of relapsed/refractory AML (Romee et al, Science TM 2016). We are evaluating the safety and potential efficacy of donor-derived CIML NK cells in patients with relapsed myeloid malignancies after haploidentical donor transplant (haploSCT) in a phase 1/1b study (clinicaltrials.gov: NCT040247761). Here we report on manufacturing, safety, and in vivo correlative biology of the adoptively transferred CIML NK cells in the first 3 enrolled patients. Methods The primary endpoint is to identify the maximum-tolerated dose (MTD) of CIML NK cells in patients with MDS, MPN, or AML who relapsed after haplo-SCT. NK cells were enriched from donor-derived non-mobilized leukapheresis product via two-step CD3 depletion followed by selection of CD56+ cells using the CliniMACS reagent system (Miltenyi Biotec). The enriched NK cell product was cultured for 12-16 hours in X-VIVO 15 media containing rhIL-12, rhIL-15, and rhIL-18 to generate CIML NK cells (Figure 1A). Patients in the current cohort were lymphodepleted with fludarabine 25mg/m2 daily for 3-5 days and cyclophosphamide 60mg/kg daily for 2 days followed by CIML NK cells at a dose of 5-10 x 106 cells/kg and IL-2 106 IU/m2 QOD for 7 doses. Dose-limiting toxicities were evaluated for 6 weeks following NK cell infusion. Response to therapy was assessed at day+28 following CIML NK cell infusion. Results Patient #001 has FLT3-ITD AML that relapsed 5 months after a reduced intensity (RIC) haploSCT. She received 7.4x106 NK cells/kg followed by IL-2 106 IU/m2 QOD for 7 doses. Her day+28 bone marrow had no leukemia blasts although FLT3-ITD mutation remained detectable. Two months post-CIML NK the leukocyte and granulocyte chimerism were 88% and 89%, respectively. Patient #002 has AML with multiple pathogenic variants, including a potentially pathogenic variant in TP53. His disease relapsed 15 months post haplo-SCT with repeat marrow showing all the original mutations, including the TP53 variant (VAF 50.5%). He received 9.5x106 NK cells/kg followed by IL-2 106 IU/m2 QOD for 7 doses. His day+28 marrow had trilineage hematopoiesis without any mutations, including no TP53 mutation (Figure 1B). Two months post-CIML NK the leukocyte and granulocyte chimerism were both 99%. Patient #003 has MDS whose disease relapsed 8 months post RIC haploSCT with persistence of all her diagnostic pathogenic mutations. She received approximately 9.2x106 NK cells/kg and has only just completed IL-2 106 IU/m2 QOD for 7 doses. Among the 3 patients, the main toxicity was prolonged cytopenia requiring stem cell boost in one case. Donor NK cells demonstrated a dramatic shift from a predominantly CD56dimCD16hi (88% of NK cells) to a CD56dimCD16lo phenotype (49% of NK cells) as CIML NK cells. Infused CIML NK cells expanded massively, with approximately 50-fold, 10-fold, and 15-fold maximum in vivo expansion in the first three patients, respectively (Figure 1C). CIML NK cells were the major population in the day+28 marrows in both patients #001 and #002, with CD56+CD7+ cells constituting 89% of the cellularity in the former and 48% in the latter (Figure 1C). CIML NK cells persisted for 3 and 6 months post-infusion in the first two patients. The NK cells were predominantly mature, with most expressing CD16 and low levels of the inhibitory receptor NKG2A. PD-1 expression was much lower on the expanded NK cells vs the pre-infusion donor-derived NK cells. There was minimal concurrent expansion of CD4+CD25+ T-regulatory cells (Figure 1D). Conclusion We show with the first 3 patients in this trial that CIML NK cells can be generated and infused safely, can expand massively in the peripheral blood and bone marrow within the first 30 days post-infusion, and can persist for several months. In addition, CIML NK cell infusion can reduce the burden of pathogenic variant alleles to below the limit of detection, including the burden of high-risk mutations such as in TP53. Though our results are preliminary, the massive in vivo expansion and long-term persistence of adoptively transferred CIML NK cells underscores the unique biology of these cells that makes them an attractive option for cellular therapy protocols. Disclosures Nikiforow: Kite: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Nkarta: Membership on an entity's Board of Directors or advisory committees. Rambaldi:Equillium: Research Funding. Cutler:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kadmon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Jazz: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medsenic: Consultancy, Membership on an entity's Board of Directors or advisory committees; Generon: Consultancy, Membership on an entity's Board of Directors or advisory committees; Mesoblast: Consultancy, Membership on an entity's Board of Directors or advisory committees. Koreth:Cugene: Membership on an entity's Board of Directors or advisory committees; Regeneron: Other: Research Support; Clinigen: Other; Miltenyi: Other: Research Support; BMS: Other: Research Support; Therakos: Membership on an entity's Board of Directors or advisory committees; Equillium: Consultancy; EMD Serono: Consultancy; Biolojic Design Inc: Consultancy; Amgen: Consultancy; Moderna Therapeutics: Consultancy. Wu:Pharmacyclics: Research Funding; BionTech: Current equity holder in publicly-traded company. Soiffer:Juno: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; VOR Biopharma: Consultancy; Mana Therapeutics: Consultancy; Precision Bioscience: Consultancy; Cugene: Consultancy; Rheos Therapeutics: Consultancy; Kiadis: Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy; Celgene: Membership on an entity's Board of Directors or advisory committees; alexion: Consultancy; Be the Match/ National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees. Ritz:TScan Therapeutics: Consultancy; Talaris Therapeutics: Consultancy; Rheos Medicines: Consultancy; LifeVault Bio: Consultancy; Avrobio: Consultancy; Kite Pharma: Research Funding; Equillium: Research Funding; Amgen: Research Funding; Falcon Therapeutics: Consultancy; Infinity Pharmaceuticals: Consultancy.