NKAML: a pilot study to determine the safety and feasibility of haploidentical natural killer cell transplantation in childhood acute myeloid leukemia

Abstract

PURPOSE To conduct a pilot study to determine the safety, feasibility, and engraftment of haploidentical natural killer (NK) cell infusions after an immunosuppressive regimen in children with acute myeloid leukemia (AML). PATIENTS AND METHODS Ten patients (0.7 to 21 years old) who had completed chemotherapy and were in first complete remission of AML were enrolled on the Pilot Study of Haploidentical Natural Killer Cell Transplantation for Acute Myeloid Leukemia (NKAML) study. They received cyclophosphamide (60 mg/kg on day -7) and fludarabine (25 mg/m(2)/d on days -6 through -2), followed by killer immunoglobulin-like receptor-human leukocyte antigen (KIR-HLA) mismatched NK cells (median, 29 x 10(6)/kg NK cells) and six doses of interleukin-2 (1 million U/m(2)). NK cell chimerism, phenotyping, and functional assays were performed on days 2, 7, 14, 21, and 28 after transplantation. Results All patients had transient engraftment for a median of 10 days (range, 2 to 189 days) and a significant expansion of KIR-mismatched NK cells (median, 5,800/mL of blood on day 14). Nonhematologic toxicity was limited, with no graft-versus-host disease. Median length of hospitalization was 2 days. With a median follow-up time of 964 days (range, 569 to 1,162 days), all patients remain in remission. The 2-year event-free survival estimate was 100% (95% CI, 63.1% to 100%). CONCLUSION Low-dose immunosuppression followed by donor-recipient inhibitory KIR-HLA mismatched NK cells is well tolerated by patients and results in successful engraftment. We propose to further investigate the efficacy of KIR-mismatched NK cells in a phase II trial as consolidation therapy to decrease relapse without increasing mortality in children with AML.

Fig 1.

Natural killer (NK) cell engraftment and cytotoxicity. (A) Number of NK cells per microliter of blood. (B) Cytotoxicity against K562 cells with a target:effector cell ratio of 1:2. (C) Absolute number of killer immunoglobulin-like receptor (KIR)–mismatched NK cells. (D) Percentage of KIR-mismatched NK cells on days 2, 7, 14, 21, or 28. Gray areas in (A) and (B) represent the normal range established by analyzing donor blood before transplantation.

Fig 2.

Patterns of natural killer (NK) cell engraftment. (A and D) Absolute number of NK cells per milliliter of blood for each patient. (B and E) Cytotoxicity against K562 cells with a target:effector cell ratio of 1:2. (C and F) Absolute number of killer immunoglobulin-like receptor (KIR)–mismatched NK cells for each patient. Unique patient number [UPN] 1 did not have a KIR-mismatched donor; donors for all other patients were KIR mismatched (Table 1).