Engineering High Affinity and Cleavage Resistant CD16 to Augment ADCC of Placental Hematopoietic Stem Cells-Derived Natural Killer Cells

Abstract

Background: Celularity, Inc. is developing human placental hematopoietic stem cells-derived, cryopreserved, off-the-shelf, ex-vivo expanded and allogenic natural killer (PNK) cells for various hematological malignancies and solid tumors. NK cells play a central role in antibody dependent cell mediated cytotoxicity (ADCC) through Fc receptor CD16 in monoclonal antibody mediated anti-tumor therapies. Two allelic forms of CD16 have been identified. The 158Val/Val form has shown to have higher IgG binding affinity compared to the 158Phe/Phe form.1 The high IgG binding allele are found in about 10-20% of the normal population.2,3 In addition, activation of NK cells induces CD16 shedding by matrix metalloprotease ADAM17 at 197Ser, thus limiting ADCC responses. A single mutation (Ser197Pro) prevents CD16 shedding and increases ADCC activity in NK cells.4 Since the antibody binding affinity and CD16 expression of PNK could vary with different donors, we hypothesize that expressing a high affinity (158Val) and proteinase cleavage resistant (197Pro) CD16 variant (CD16VP) augments anti-tumor ADCC activity. Methods: Lentivirus expressing CD16VP was used to transduce human placental CD34+ cells. After transduction, the cells were cultured in the presence of cytokines including thrombopoietin, SCF, Flt3 ligand, IL-7, IL-15 and IL-2, for 35 days to generate PNK-CD16VP cells. Non-transduced PNK cells (NT) served as a control. Expression of CD16VP was evaluated by activating cells with PMA/ionomycin to induce CD16 cleavage (CD16 shedding assay) followed by immunostaining with CD16 antibody and analyzed using flowcytometry. ADCC of PNK-CD16VP cells was assessed against Daratumumab (anti-CD38) or Rituximab (anti-CD20) opsonized lymphoma cell lines at various effector to target (E:T) ratios. IgG was used as ADCC control. In vivo anti-tumor activity was assessed in a Daudi disseminated Xenograft model in NSG mice. Luciferase-expressing Daudi cells (3x106) were intravenously (IV) administered at day 0, followed by PNK-CD16VP cells (10x106) IV at day 1 and day 3, and Daratumumab at day 3. Tumor burden in mice was monitored by Bioluminescence Imaging (BLI). Statistical differences between the groups were calculated using paired t-test using Prism. Results: Lentiviral transduction of CD16VP achieved high expression efficiency in multiple placental CD34+ donors. These cells expanded [7095 ± 2998 folds (n=8)] and differentiated into PNK cells (>90% CD56+CD3-) at day 35. PNK-CD16VP expressed 64.6 ± 10.3% (n=8) of CD16, while the NT expressed 12.1 ± 3.3% (n=8) CD16. PMA/ionomycin induced >89% shedding of CD16 in NT cells, while significantly less (<11%) CD16 shedding was observed in PNK-CD16VP cells. These results indicated that CD16VP was expressed and maintained throughout the culture process. In vitro ADCC assay demonstrated improved anti-tumor activity of PNK-CD16VP cells over NT cells against Daratumumab or Rituximab opsonized lymphoma cell lines. At 10:1 E:T ratio PNK-CD16VP cells elicited higher cytotoxicity compared to NT: 47 ± 13% against Daratumumab opsonized Daudi cells versus 25 ± 5% (n=5; p<0.05); 30 ± 13% against Daratumumab opsonized HS-Sultan cells versus 21 ± 14% (n=3; p<0.05); 30 ± 7% against Daratumumab opsonized Sudhl6 cells versus 16 ± 10% (n=3; p<0.05). Improved ADCC activities in PNK-CD16VP were also observed in other cell lines including Raji and Sudhl4 with Daratumumab and Rituximab antibodies. PNK-CD16VP were used to test anti-tumor ADCC in vivo using a disseminated Daudi Xenograft model. The preliminary data demonstrated that PNK-CD16VP combined with Daratumumab reduced BLI signal (>50%) compared to vehicle or Daratumumab alone at day 10 after treatment. This observation suggested that PNK-CD16VP demonstrated in vivo ADCC anti-tumor activity. Conclusions: In this study, we genetically modified PNK to express high affinity and cleavage resistant CD16 variant using lentivirus. The PNK-CD16VP cells demonstrated enhanced ADCC function against lymphoma cell lines in vitro and in vivo. Further development of PNK-CD16VP for immune-oncology therapeutics is warranted.