Infusion of ex vivo-cultured allogeneic NK cells in acute myeloid leukemia patients not eligible for stem cell transplantation (a phase I dose escalation study)

Patients with acute myeloid leukemia (AML), older than 60 years, treated with
intensive chemotherapy achieve complete remission (CR) rates of about 50%.
However, over 75% of the patients relapse thereafter despite CR and only 15% of
those patients are still alive after 3 years. Although allogeneic stem cell
transplantation (SCT) can be curative, this option is unavailable for the
majority of patients due to age and co-morbidity. Interestingly, it has been
demonstrated that Natural Killer (NK) cell alloreactivity can control relapse
of AML without causing graft-versus-host disease (GVHD) in the setting of
HLA-mismatched haploidentical allogeneic SCT. Furthermore, in a non-transplant
setting it has been demonstrated that allogeneic NK cell infusions can induce
CR in poor-prognosis AML patients (Miller et al Blood 2005). In this study, we
plan to further investigate adoptive immunotherapy of NK cells in
poor-prognosis AML patients who are not eligible for allogeneic SCT due to age.
Unlike the procedure chosen by Miller et al. we will generate allogeneic NK
cell products ex vivo from CD34+ hematopoietic progenitor cells. Conform
GMP-regulations these CD34+ cells will be enriched from umbilical cord blood
(UCB) units from the Cord Blood Bank Nijmegen. NK cell therapy is a novel
experimental treatment for these AML patients.

The primary aim of our study is to evaluate safety and toxicity of ex
vivo-expanded NK cell infusions following a non-myeloablative conditioning
regimen in elderly AML patients who are no candidates for allogeneic SCT.
Moreover there is also a second aim; how long do the administered NK-cellen
remain in life and what is the impact on the sickness (AML).

The study is designed as a prospective phase I dose escalation study in a
series of 15 AML patients with age * 55 years who have successfully achieved CR
(i.e. <5% blasts in the bone marrow) after standard intensive chemotherapy.
Prior to NK cell infusion, patients will receive non-myeloablative
immunosuppression with cyclophosphamide and fludarabine on 4 consecutive days.
On day 0, four cohorts of 3 patients will receive 3x106, 10x106, 3x107 and
10x107 allogeneic NK cells per kg body weight generated ex vivo from CD34+
cells obtained from an allogeneic UCB unit.

Allogeneic NK cell products generated ex vivo from CD34+ UCB cells will be
transfused into patients in a single escalating dose up to 10x107 donor NK
cells/kg body weight after completing standard chemotherapy and preparative
immunosuppressive conditioning consisting of fludarabine (30 mg/m2/day) and
cyclophosphamide (900 mg/m2/day) on days -6, -5, -4, and -3 in order to
prevent rejection. Monitoring will be done for toxicity, biological parameters
and remission status.

In other clinical studies up to 2x107 allogeneic NK cells ex vivo purified and
activated with IL-2 have been administered to patients with several
malignancies including AML (Miller et al. Blood 2005; Shi et al. Br J Hematol
2008). The Hi-Cy/Flu regimen in the AML patients (n=19) induced transient
pancytopenia by the time of NK cell infusion (Miller et al. Blood 2005). The NK
cell infusions were well tolerated without evidence of induction of GVHD.
Toxicity was limited to constitutional symptoms consisting of low-grade fever,
chills and myalgias mostly due to low-dose IL-2 injections given post-NK cell
infusion. Therefore, in our study escalating dose NK cell infusions will be
given without IL-2 infusions. For follow-up peripheral blood will be collected
from patients (pre-study, at 4 hr, day 1, 2, 5, 7, 14, 28 and 56 after NK cell
infusion) and bone marrow aspirates (after concolidation treatments, and 7
days, 3 and 6 months after NK cell infusion). UCB units stored in the Cord
Blood Bank Nijmegen will be used to enrich CD34+ cells for ex vivo expansion
and differentiation of NK cells.