Phase I Trial of IL-21 Ex Vivo Expanded NK Cells Administration to Prevent Disease Relapse after Haploidentical Stem-Cell Transplantation for Myeloid Leukemias

Background: As outcomes of haploidentical stem cell transplantation (HaploSCT) have improved, disease relapse represents the most common cause of treatment failure. Methods: We initiated a phase I clinical trial (clinicaltrials.gov NCT01904136) using peripheral blood-derived NK cells expanded ex vivo for 14 days with K562 antigen presenting cells expressing membrane-bound (mb) IL21 to prevent disease relapse after HaploSCT for patients with myeloid malignancies (AML,CML,MDS). We hypothesized that infusion of expanded and activated NK cells would compensate for the lower NK cell function in the early post-transplant period, and higher NK cell numbers would enhance anti-tumor effects of the graft. The primary endpoints were safety and determining the maximum tolerated dose (MTD). Patients were treated with a melphalan-based conditioning regimen (Figure). All patients had a primary bone marrow graft. NK cells were generated from peripheral blood mononuclear cells of the same donor obtained prior to marrow harvest and infused on days -2, +7 and on/after +28. The first infusion was with fresh and the other two were with cryopreserved NK cells. The dose escalation was planned in cohorts of 2 patients starting at 1x105/kg up to 1x109/kg or more if MTD will not be reached. Predictive NK alloreactivity and/or donor KIR B genotyping was preferred but not required to participate on study, however, was evaluated in all patients (Table). Results: Ten patients have been enrolled and treated to date. Of these, 8 patients were beyond Day+30 and were evaluated, 5 with AML (3 in CR1 with intermediate and 1 with high-risk cytogenetics, and 1 in CR2 FLT3+ with persistent MRD by flow cytometry) and 3 with CML (2 in second chronic phase, one with clonal evolution who failed multiple TKIs). The median age was 39 years (range 18-59). Four patients were males and 4 females. The NK cells dose escalation was as follows: 1x105/kg (N=2), 1x106/kg (N=3) and 1x107/kg (N=2). One patient was treated with 1x104/kg before full evaluation of 1x105/kg was completed. All patients achieved primary engraftment (100%). All patients except the one who received the lowest dose (1x104/kg) had sustained engraftment and 100% donor chimerism on Day 30 post-transplant. The median time to neutrophil engraftment was 18 days and to platelet engraftment was 26 days. The first patient had a mixed chimerism, developed secondary graft failure and concurrent parainfluenza pneumonia. He was re-transplanted with a different donor but died of treatment-related mortality (TRM). Of 7 patients evaluable for aGVHD, the maximum aGVHD grade was gr II in 4 patients. No gr III-IV aGVHD or cGVHD was observed. Only 3/7 patients had CMV reactivation (43% compared with 71% in retrospective data with the same treatment without NK cells), 2 requiring a brief period of treatment of approximately 1 month. None developed BK virus hemorrhagic cystitis. All patients achieved CR after transplant. One patient (#2) treated at 1x105/kg NK cell dose relapsed, received salvage treatment and is alive at last follow-up. All other patients are alive and in remission (N=6) after a median follow-up of 6 months (range 1-12.5). NK cell phenotype and function early post-transplant will be presented at the meeting. Conclusions: Doses up to 1x107/kg of ex vivo expanded NK cells using the mbIL-21 method can be safely administered after HaploSCT. Administration of these cells in this setting in not associated with a higher incidence of aGVHD. There was a low rate of viral reactivation, suggesting that the infused NK cells may provide antiviral activity. MTD has not been reached, the study is ongoing. Disclosures Lee:Intrexon: Equity Ownership; Ziopharm: Equity Ownership; Cyto-sen: Equity Ownership. Rezvani:Pharmacyclics: Research Funding.