Background Acute Myeloid Leukemia (AML) is characterized by neoplastic myeloid cells which compromise normal hematopoiesis. In recent years, novel therapies and biologics have expanded treatment options for this challenging disease. Yet despite this, overall cure rates and therapeutic options remain limited.
Methods Here, we investigated expansion of autologous NK cells in AML. PBMCs from 14 AML patients (4 in remission, 4 treatment-naive, 6 relapsed/refractory (R/R)) were expanded in flasks supplemented with IL-2 and OKT-3. R/R and treatment-naive patients had blasts reduced in the PBMCs by MACS prior to culture; typically by CD33+ MACS where blasts robustly and homogenously expressed CD33.
Results From these cohorts, 3 of 4 (75%) remission, 2 of 4 (50%) treatment-naïve and 4 of 6 (66%) R/R patients successfully grew in culture; with mean total fold changes by day 20 of 424, 38 and 177 respectively. Mean NK Cell (CD3- CD56+) content of all cultures was 27% by day 20 of culture; increased from mean 14% of lymphocytes in starting PBMCs.
Next, these expanded cells were assayed in cytotoxicity assays 1:1 against K562 cells. Degranulation was seen in all 3 remission patients (mean 55% CD107a+ NK cells). One treatment-naive patient was assessed and also degranulated strongly and produced IFNg against both K562 (57% CD107a+, 46% IFNg+) and autologous blasts (45% CD107a+, 49% IFNg+). Conversely, of the 4 R/R patients, none degranulated against autologous blasts (mean 3% CD107a+) and degranulation against K562 cells was weaker (mean 43% CD107a+). Interestingly however, the three cohorts’ expanded cells did not differ significantly in terms of%NK which express natural cytotoxicity receptors (NKp30, NKp44, NKp46) or NKG2D.
These data suggest that in advanced AML, blasts may be too poorly immunogenic to elicit robust NK responses, and their presence during NK cell culturing negatively affects subsequent NK effector function.
Conclusions In conclusion, PBMCs from remission patients show promise and will be tested in future work in large-scale bioreactor expansions.
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