Results of a phase I trial with Haploidentical mbIL-21 ex vivo expanded NK cells for patients with multiply relapsed and refractory AML

Natural killer (NK)-cells have potent anti-tumor effects, yet it remains unclear if they are effective for patients with relapsed acute myeloid leukemia (AML). In a phase I clinical trial, we treated 12 patients (median age 60 years) with refractory AML (median 5 lines of prior therapy, median bone marrow blast count of 47%) with fludarabine/cytarabine followed by 6 infusions of NK-cells expanded from haploidentical donors using K562 feeder cells expressing membrane-bound IL21 and 4-1BBL. Patients received 106-107/kg/dose. No toxicity or graft-versus-host disease (GVHD) was observed and MTD was not reached. Seven patients (58.3%) responded and achieved a complete remission (CR) with/without count recovery. Median time to best response was 48 days. Five responding patients proceeded to a haploidentical transplant from the same donor. After a median follow-up of 52 months, 1-year overall survival (OS) for the entire group was 41.7%, better for patients who responded with CR/CRi (57.14%), and for patients who responded and underwent transplantation (60%). Persistence and expansion of donor-derived NK-cells were identified in patients' blood, and serum IFNγ levels rose concurrently with NK cell infusions. A higher count-functional inhibitory KIR was associated with higher likelihood of achieving CR/CRi. In conclusion, we observed a significant response to ex vivo expanded NK-cell administration in refractory AML patients without adverse effects.

Decrease post-transplant relapse using donor-derived expanded NK-cells

In this phase I/II clinical trial, we investigated the safety and efficacy of high doses of mb-IL21 ex vivo expanded donor-derived NK cells to decrease relapse in 25 patients with myeloid malignancies receiving haploidentical stem-cell transplantation (HSCT). Three doses of donor NK cells (1 × 10⁵-1 × 10⁸ cells/kg/dose) were administered on days -2, +7, and +28. Results were compared with an independent contemporaneously treated case-matched cohort of 160 patients from the CIBMTR database.After a median follow-up of 24 months, the 2-year relapse rate was 4% vs. 38% (p = 0.014), and disease-free survival (DFS) was 66% vs. 44% (p = 0.1) in the cases and controls, respectively. Only one relapse occurred in the study group, in a patient with the high level of donor-specific anti-HLA antibodies (DSA) presented before transplantation. The 2-year relapse and DFS in patients without DSA was 0% vs. 40% and 72% vs. 44%, respectively with HR for DFS in controls of 2.64 (p = 0.029). NK cells in recipient blood were increased at day +30 in a dose-dependent manner compared with historical controls, and had a proliferating, mature, highly cytotoxic, NKG2C+/KIR+ phenotype.Administration of donor-derived expanded NK cells after haploidentical transplantation was safe, associated with NK cell-dominant immune reconstitution early post-transplant, preserved T-cell reconstitution, and improved relapse and DFS. TRIAL REGISTRATION: NCT01904136 ( https://clinicaltrials.gov/ct2/show/NCT01904136 ).

Enhanced antitumor effect and lower viral reactivation with high doses of ex vivo expanded NK cells administered after haploidentical transplantation

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Background: NK cells have potent antitumor and antiviral effects. We hypothesized that multiple infusions of high doses of mb-IL21 ex vivo expanded NK cells administered peri-transplant will enhance graft-versus-leukemia effect and decrease viral reactivation. Methods: In the phase 1 dose escalation study patients received NK cells starting at 1x105 to 1x108/Kg/dose (N = 13). No dose limiting toxicities were observed. In the phase 2 study, 12 patients with myeloid malignancies received mbIL-21 ex vivo expanded NK cells at dose 1x108NK cells/kg with a K562 feeder cell system and with 41BB. NK cells were generated from peripheral blood mononuclear cells of the same donor and infused fresh on day -2, and cryopreserved on day +7 and +28. Conditioning regimen consisted of melphalan, fludarabine and TBI. All patients had bone marrow graft. Here we report updated results of all patients treated to date on this study. Results: Twenty-five patients (18 AML/MDS and 7 CML) were treated to date. The median age was 45 years, the median follow-up of survivors was 28 months. 16/18 AML/MDS patients had high-risk disease. No adverse effects occurred. Engraftment was achieved in all 24 evaluable patients after a median of 19 days. The cumulative incidence (CI) of grade 2 aGVHD was 38% at day 100. No chronic GVHD was observed. The CI of TRM was 21% at 2 years. The CI of relapse at 1 year was 8%. The 2-years PFS was 66%. Ten patients reactivated CMV. Immunologic reconstitution of T cell subsets showed a 5.7 fold higher number of NK cells on day 28 in patients who received highest NK cell doses vs. others. A matched-pair analysis done with an independent CIBMTR cohort of patients who received either MAC (N = 61) or RIC (N = 57), showed a significantly improvement in relapse rate and PFS in favor of patients treated on trial. Conclusions: Administration of higher doses of NK cells was associated with higher NK cell numbers early post-transplant, suggesting that a dose-dependent effect could be achieved. A low relapse rate and lower viral reactivation post-transplant continues to be seen, suggesting that NK cells exert both anti-tumor and antiviral effects in this setting. Clinical trial information: NCT01904136.