Improved Outcomes for Patients Receiving High-Doses of IL-21 Ex Vivo Expanded NK Cells after Haploidentical Transplantation (haploSCT): Long-Term Follow-up of a Phase 1/2 Clinical Trial with Comparison to CIBMTR Controls
Authors: Ciurea Stefan O. , Bassett Roland , Soebbing Doris , Rondon Gabriela , Cao Kai , Olson Amanda L. , Bashir Qaiser , Shpall Elizabeth J. , Devine Steven , Pasquini Marcelo C. , St. Martin Andrew , Lee Dean Anthony , Champlin Richard E 
Published: February 2020

Background: Disease relapse following allogeneic stem-cell transplantation remains unacceptably high and there is an urgent need for new therapies that decrease relapse rates and improve survival post-transplant. Natural killer (NK) cells have potent antitumor effects, particularly those expended with mb-IL21 from peripheral blood. Preliminary data from a phase-1 dose-escalation study of up to 1x108 NK cells/Kg/dose and multiple dosing yielded promising results and a favorable safety profile (Ciurea SO.Blood.2017;130:18657). This report presents long-term follow-up from a phase-1/2 clinical trial in patients with high-risk myeloid malignancies (AML/MDS/CML) (clinicaltrials.gov NCT01904136) and a comparison with CIBMTR controls.
Methods: Patients received conditioning with fludarabine 160 mg/m2, melphalan 140 mg/m2 and 2GyTBI, post-transplant cyclophosphamide-based GVHD prophylaxis and bone marrow graft from a haploidentical donor. Ex vivo expanded NK cells were generated from peripheral blood mononuclear cells of the same donor with a K562 feeder cells expressing mb-IL21 and 41BB and infused fresh on Day-2, and cryopreserved on Day+7 and +28 (up to Day+90). 1x108/Kg/dose was chosen for the phase 2 trial. An independent matched-pair analysis was done using controls from the CIBMTR database stratified by conditioning intensity.
Results: 24/26 patients treated to date were evaluable (one short follow-up and one excluded as ineligible). 80% (19/24) of patients received all 3 doses of NK cells. The median age was 45 years (range 18-59), median follow-up was 43.6 months (range 15.1-60.9). Thirteen patients (54%) were females. 5 patients had donor-specific anti-HLA antibodies (DSA). The median HCT-CI was 2 (range 0-8), 12 patients (50%) had HCT-CI&gt;3. 17 patients (72%) had AML/MDS and 7 (28%) advanced CML. Of AML/MDS patients, 10 (59%) had high-risk cytogenetics, 7 (41%) had measurable residual disease, 9 (53%) had intermediate/adverse-risk ELN2017 and 5 (29.4%) had primary induction failure. No infusion reactions or significant adverse events were observed to date.
All patients (100%) achieved engraftment after a median of 19 days (range 14-42). The cumulative incidence (CI) of grade 2-4 aGVHD was 29.2% at Day100 and 41.7% at 1-year post-transplant. Only one patient developed severe grade 3-4 aGVHD and one patient had extensive cGVHD. Only one patient relapsed (a patient with DSA who did not receive desensitization prior to transplantation), 1-year CI of relapse was 5.9%. The CI of TRM at 1-year for patients without DSA was 21%. The median overall survival and progression-free survival (PFS) were not reached. The 1-year and 3-year PFS for all patients and patients without DSA was 70.8% and 66.1%, and 79% and 72.9% for patients without DSA, respectively (Figure 1). One-year and 3-years GRFS for all patients and patients without DSA was 70.8% and 66.1%, and 79% and 72.9%, respectively.
An independent matched-pair analysis (at least 1:1) was conducted by CIBMTR after the first 18 patients treated on study in 07/2018 with RIC (N=57) or MAC (N=61) controls. The relapse was 1/18 vs 25/57 for RIC (p=0.037) and 15/61 for MAC (p=0.07), while the 1-year PFS was 82% vs 49% for RIC and 64% for MAC (p=0.21) (Figure 1). Updated results of this analysis will be presented at the meeting.
Conclusions: Results from this long-term follow-up analysis confirm very low relapse rate and excellent GRFS after haploSCT for patients treated with high-doses of NK cells expanded with mbIL21 stimulation. A prospective multi-center phase 2 BMTCTN study will evaluate the safetly and efficacy of high doses of NK cells for the prevention of relapse in patents with AML/MDS receiving haploSCT.
Figure 1

Disclosures
Ciurea: Miltenyi: Research Funding; Kiadis Pharma: Membership on an entity's Board of Directors or advisory committees, Other: stock holder; MolMed: Membership on an entity's Board of Directors or advisory committees; Spectrum: Membership on an entity's Board of Directors or advisory committees. Bashir:Kite: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; StemLine: Research Funding; Acrotech: Research Funding; Celgene: Research Funding; Imbrium: Membership on an entity's Board of Directors or advisory committees; Spectrum: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Pasquini:Novartis: Research Funding; Kite Pharmaceuticals: Research Funding; BMS: Research Funding; Medigene: Consultancy; Amgen: Consultancy; Pfizer: Consultancy. Lee:Kiadis Pharma: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding.