Fc engineered anti-CD33mAb potentiates cytotoxicity of mbIL-21 expanded NK-cells against primary AML pre-treated with decitabine

Abstract

Background & Aim Natural killer (NK) cells are limited in number and require cytokines for in vivo expansion. Recipient NK cells are shown to have both qualitative and quantitative defects in acute myeloid leukemia (AML) patients, providing rationale for infusion of donor-derived NK cells. We showed that decitabine (DAC) enhances expression of NKG2D ligands in AML blasts and renders the blasts susceptible to killing by NK cells (Vasu et al. 2016). We conducted a phase I trial giving 5-day DAC in relapsed, refractory AML patients followed by haploidentical NK cells on day 0 and six doses of IL-2, where we demonstrated short term engraftment of donor-derived NK cells (up to 48 hours) can be achieved by fludarabine and DAC. Here, we report preclinical studies using membrane bound IL-21 (mbIL-21) expanded NK cells, which can be given without extraneous cytokine support. Methods, Results & Conclusion NK cells from healthy donors were expanded for 14 days using irradiated K562 feeder cells displaying mbIL-21 and 4-1BBL (CSTX002) to derive mbIL-21 NK cells. These cells have minimal senescence despite robust proliferation with the feasibility to infuse multiple NK cell doses of 1 × 108/kg (Denman et al. 2012). We investigated if mbIL-21 NK cells exhibit natural killer activity alone or in the presence of Fc-engineered anti-CD33 antibody [antibody-dependent cellular cytotoxicity (ADCC)] against primary AML samples from patients who received DAC, pre-NK cell infusion (day-1) and at 24 days post haplo-NK infusion (Post-NK infusion). Upon incubation with primary AML blasts, mbIL-21 NK cells displayed an activation profile as evidenced by surface CD107a induction (p=0.0051) and variable donor-dependent intra-cellular IFNγ production, which was further increased with CD33mAb coated AML cells (p=0.0018). ADCC assays using chromium-51 (Cr51) labelled primary AML blasts revealed mbIL-21 NK cells lysed primary AML blasts alone which was significantly enhanced with CD33mAb coated target cells (p=0.0004). Importantly, CD33mAb dependent enhanced-cytotoxicity by mbIL-21 NK cells was maintained in AML cells from patients even 24 days post DAC treatment. Further, in-vivo infusion of mbIL-21 NK cells in AML patient derived xenograft (AML PDX) mice, treated with CD33mAb, reduced the tumor burden. These data show the therapeutic utility of mbIL-21 NK cells that can be further potentiated by addition of Fc engineered anti-CD33 antibody in AML.