Fc-engineered anti-CD33 monoclonal antibody potentiates cytotoxicity of membrane -bound interleukin-21 expanded natural killer cells in acute myeloid leukemia

Background: Qualitative and quantitative defects in natural killer (NK) cells have been noted in patients with acute myeloid leukemia (AML), providing rationale for infusion of donor -derived NK cells. We previously showed that decitabine enhances expression of NKG2D ligands in AML with additive cytotoxicity when NK cells and Fc (fragment crystallizable region) -engineered CD33 monoclonal antibody (CD33mAb) was used. We conducted a phase 1 study evaluating decitabine and haploidentical NK cells in relapsed AML. Using patient samples from this study, we evaluated whether ex vivo donor -derived expanded NK cells with or without CD33mAb was effective in decitabine-treated AML. Methods: Bone marrow aspirates were collected from patients at pre- and post-NK cell infusion. NK cells from healthy donors were expanded for 14 days using irradiated K562 feeder cells displaying membrane -bound IL -21 (mbIL-21). Patient samples were used to test in vitro activity of mbIL-21 NK cells ? CD33m Ab-dependent cellular cytotoxicity (ADCC) and AML patient derived xenograft (PDX) mice were developed to test in vivo activity. Results: Upon incubation with primary AML blasts, mbIL-21 NK cells showed variable donor -dependent intra-cellular interferon - g production, which increased with CD33mAb-coated AML. ADCC assays revealed mbIL-21 NK cells effectively lysed primary AML blasts with higher activity on CD33mAb-coated AML. Impor- tantly, CD33mAb-dependent enhanced cytotoxicity by mbIL-21 NK cells was maintained in AML cells from patients even 24 days post-decitabine treatment. In vivo infusion of mbIL-21 NK cells in AML PDX mice, treated with CD33mAb, reduced the tumor burden. Discussion: These data show the therapeutic utility of mbIL-21 NK cells that can be further potentiated by addition of CD33mAb in AML.