cGMP Mass Production of FT538, a First-of-Kind, Off-the-Shelf, Multiplexed Engineered Natural Killer Cell Cancer Immunotherapy Derived from a Clonal Master Induced Pluripotent Stem Cell Line

FT538 is an investigational, off-the-shelf, multiplexed engineered natural killer (NK) cell cancer immunotherapy that is derived from a clonal master induced pluripotent stem cell (iPSC) line engineered with three functional components to enhance innate immunity: a novel high-affinity, non-cleavable CD16 (hnCD16) Fc receptor; an IL-15/IL-15 receptor fusion (IL-15RF); and the elimination of CD38 expression. The use of a clonal master engineered iPSC line as a starting cell source enables routine mass production of FT538 and supports off-the-shelf product availability to reach many patients.

The clonal master iPSC line for the manufacture of FT538 was made by reprogramming and engineering donor-consented human fibroblasts to induce pluripotency using a proprietary non-integrating system and to integrate a bicistronic cassette containing hnCD16 and IL-15RF into the CD38 locus, which resulted in complete disruption of the CD38 gene. The engineered iPSC population was then sorted to isolate single clones, and each engineered iPSC clone was screened for multiple critical quality attributes including pluripotency, identity, genomic stability, cassette integration, and off-target effects of engineering. Accordingly, a single engineered iPSC clone was selected as the FT538 clonal master iPSC line.

The clonal master engineered iPSC line serves as a renewable source for the routine cGMP mass production of FT538 drug product. Routine cGMP manufacture of FT538 drug product consists of three stages: 1) differentiation of the clonal master engineered iPSC line to CD34-expressing hematopoietic progenitor cells; 2) further differentiation to and expansion of NK cells; and 3) fill/finish and cryopreservation of the FT538 drug product. A cGMP manufacturing campaign yielded sufficient CD34-expressing hematopoietic progenitor cells to support at least 15 batches of NK cell differentiation, the first batch of which was used to produce a total of 3 × 10¹¹ FT538 NK cells filled into over 300 units of cryopreserved drug product. The cGMP campaign had a theoretical yield of 4.5 x 10¹² FT538 NK cells.

The FT538 drug product was characterized and found to be comprised of uniformly engineered CD56+ NK cells with homogeneous expression of hnCD16 and lacking expression of CD38. Importantly, there were no residual iPSCs detected in the FT538 drug product. Additionally, the FT538 drug product exhibited potent effector function in a candidate potency assay measuring IFN-γ release in response to RPMI 8226 target cells in the presence of daratumumab.

An Investigational New Drug application for FT538 has been cleared by the U.S. Food and Drug Administration (FDA) for the conduct of a multicenter, multi-dose Phase I clinical trial for the treatment of patients with relapsed/refractory (r/r) acute myelogenous leukemia (AML) and multiple myeloma (MM). The dose-escalation utilizes a 3+3 design to identify the maximum tolerated dose of three doses of FT538 on Days 1, 8, and 15 as a monotherapy in r/r AML (Regimen A) and in combination with daratumumab (Regimen B) or elotuzumab (Regimen C) in r/r MM. The trial will test up to five FT538 dose levels ranging from 50 million to 1.5 billion cells, and up to 105 patients will be enrolled. The trial is expected to begin patient enrollment in 2020.