FT538: Preclinical Development of an Off-the-Shelf Adoptive NK Cell Immunotherapy with Targeted Disruption of CD38 to Prevent Anti-CD38 Antibody-Mediated Fratricide and Enhance ADCC in Multiple Myeloma When Combined with Daratumumab

Monoclonal antibody (mAb) treatment is an effective therapeutic strategy for many cancer types, though there remains meaningful opportunity to improve mAb efficacy by optimizing the interaction with natural killer (NK) cells to enhance antibody-dependent cellular cytotoxicity (ADCC). NK cells are an ideal effector cell for combined use with tumor-targeting mAbs, as NK cells effect both innate tumoricidal capacity and ADCC. CD38-targeting mAbs, such as daratumumab, are effective in treating multiple myeloma (MM) and achieve their efficacy through multiple mechanisms, including ADCC. However, because activated NK cells express high levels of CD38, daratumumab induces NK cell depletion through fratricide, potentially reducing treatment effectiveness. Adoptive NK cell immunotherapy therefore has the potential to augment daratumumab's ADCC activity if fratricide can be reduced or prevented. FT538 is an off-the-shelf adoptive NK cell immunotherapy product candidate designed for enhanced cellular persistence and ADCC while avoiding anti-CD38 mAb induced fratricide. It is derived from induced pluripotent stem cells (iPSC) engineered to lack CD38 expression, which we have previously shown to eliminate daratumumab-induced fratricide among iPSC-derived NK cells, resulting in enhanced long-term daratumumab-mediated ADCC. FT538 is engineered to express an IL-15 receptor alpha fusion protein (IL-15RF; IL-15 tethered to IL-15 receptor α) to enhance persistence and a high-affinity non-cleavable CD16 (hnCD16, FcRγIII) to increase ADCC. To support the clinical translation of FT538, and to enable the repeatable and scalable cell production to support off-the-shelf availability of a uniform NK cell product, a clinical-grade master pluripotent stem cell line was developed. The FT538 master pluripotent stem cell line was created by reprogramming donor fibroblasts into iPSCs using our non-integrating cellular reprogramming platform, and cells were further genetically edited by targeting IL-15RF and hnCD16 to the CD38 locus. Clonal iPSC lines were generated and screened for precise knock-in and knock-out edits at the CD38 locus and a lack of off-target genome integration (15% total success rate for CD38-/-IL-15RF+CD16+). Selected engineered iPSC clones were confirmed to be free of reprogramming transgenes and to maintain genomic stability. Engineered iPSC clones were additionally tested for their NK cell differentiation potential and function, and a single clone was selected to serve as the renewable starting material for cGMP manufacturing and clinical development. Upon differentiation and expansion FT538 demonstrated a mature NK cell phenotype with expression of NK cell receptors including NKp30, NKp46, NKG2D, KIR, NKG2A, and DNAM-1. The functional impact of CD38 knockout on FT538 NK cells was confirmed in an in vitro fratricide assay, where peripheral blood (PB)-NK cells exhibited fratricide at a frequency of 33% after 3 hr culture with increasing daratumumab concentrations. In contrast, FT538 cells were entirely resistant ( Disclosures Bjordahl: Fate Therapeutics, Inc.: Employment. Gaidarova:Fate Therapeutics, Inc: Employment. Cichocki:Fate Therapeutics, Inc: Research Funding. Bonello:Fate Therapeutics, Inc.: Employment. Robinson:Fate Therapeutics, Inc.: Employment. Ruller:Fate Therapeutics, Inc.: Employment. Pribadi:Fate Therapeutics, Inc.: Employment. Dinella:Fate Therapeutics, Inc.: Employment. Fong:Fate Therapeutics, Inc.: Employment. Huffman:Fate Therapeutics, Inc.: Employment. Chu:FATE THERAPEUTICS: Employment. Lee:Fate Therapeutics, Inc.: Employment. Abujarour:Fate Therapeutics, Inc.: Employment. Kaufman:FATE Therapeutics: Consultancy, Research Funding. Malmberg:Fate Therapeutics, Inc.: Consultancy, Research Funding; Vycellix: Consultancy, Membership on an entity's Board of Directors or advisory committees. Miller:CytoSen: Membership on an entity's Board of Directors or advisory committees; Moderna: Membership on an entity's Board of Directors or advisory committees; OnKImmune: Membership on an entity's Board of Directors or advisory committees; GT BioPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Dr. Reddys Laboratory: Membership on an entity's Board of Directors or advisory committees; Fate Therapeutics, Inc: Consultancy, Research Funding. Valamehr:Fate Therapeutics, Inc: Employment.