Induced Pluripotent Stem Cell-Derived Gamma Delta CAR-T Cells for Cancer Immunotherapy

Introduction

Allogenic CAR-T cell therapies for cancer provide a new option to reduce barriers faced by autologous cell therapies, but several challenges remain. One challenge is the risk of graft versus host disease (GvHD) caused by the infused T cells. A potential solution is the use of a subset of gamma delta (γδ) CAR-T cells whose T cell receptors (TCRs) recognize invariant antigens rather than hypervariable MHC molecules. Here we describe an off-the-shelf, induced pluripotent stem cell (iPSC)-derived γδ CAR-T (γδ CAR-iT) for treatment of cancer and a process for deriving such cells.

Methods

T cell-derived iPSCs (TiPSC) are generated by reprogramming γδ T cells to yield pluripotent stem cells. For proof-of-concept studies, TiPSC were engineered using CRISPR gene editing to deliver a CD19 CAR transgene. TiPSC are then subjected to a two-stage differentiation process. First, TiPSC are differentiated into CD34-expressing hematopoietic progenitor cells (HPCs). HPCs are then exposed to a feeder-free differentiation process that results in uniform γδ CAR-iT cells. The purity and identity of γδ CAR-iT cells were assessed by flow cytometry and the ability of γδ CAR-iT cells to respond to homeostatic growth factors was determined by intracellular staining of phosphorylated signaling proteins and mRNA transcriptome analysis. Cytokine production by CAR-iT cells was measured by immunoassays following stimulation of the CAR. Tumor cell killing by γδ CAR-iT cells was performed using IncuCyte cytotoxicity assays. In vivo control of tumors by γδ CAR-iT in immunodeficient mice was determined using a NALM-6 B cell lymphoblastic xenograft model.

Results

A research-grade γδ TiPSC line was used to develop an iT differentiation process. This γδ TiPSC line was engineered to express a CD19 CAR molecule and then subjected to the differentiation process after which >95% of cells were CD3 ⁺ γδ TCR ⁺ CAR ⁺ iT cells. These γδ CAR-iT cells responded to IL-2 and IL-15. STAT5 phosphorylation levels were similar but STAT3 phosphorylation levels were greater in response to IL-15 compared to IL-2 at equimolar concentrations of cytokine. IL-2 and IL-15 elicited qualitatively similar transcriptional responses, but the magnitude of cytokine-induced gene expression was generally greater in IL-15-treated cells. Upon activation, γδ CAR-iT cells released markedly less IFN-γ and other inflammatory cytokines than conventional blood-derived ab CAR-T cells. In an IncuCyte serial killing assay, γδ CAR-iT cells exhibited sustained killing of NALM-6 tumor cells for at least one week in the presence of IL-15. In vivo, γδ CAR-iT cells caused a significant reduction in NALM-6 tumor burden with a single dose of γδ CAR-iT resulting in >95% tumor growth inhibition.

To establish an efficient method for derivation of clinical grade γδ TiPSC lines, we investigated methods to isolate, expand, and reprogram human γδ T cells. When γδ T cells were expanded by exposure to the chemical zoledronic acid (zoledronate) and IL-2, we found a large disparity between donors; some donors exhibit robust expansion while others are seemingly resistant to zoledronate. In order to enhance γδ T cell expansion we screened dozens of activation conditions and eventually established a universal activation protocol that can elicit robust expansion of γδ T cells from all donors tested. When expanded γδ T cells were subjected to reprogramming conditions, dozens to hundreds of individual TiPSC colonies were obtained from each donor. The identity of the rearranged γδ TCR locus was confirmed using molecular assays. New γδ TiPSC lines were engineered with a CD19 CAR molecule and killing activity was confirmed in an in vitro serial killing assay.

Conclusions

γδ CAR-iT cells provide a new opportunity to treat cancers with an off-the-shelf universal T cell platform without the risk for GvHD. γδ CAR-iT cells are readily manufacturable, and we have derived an end-to-end process that enables new TiPSC line reprogramming, genetic modification of TiPSC lines, and feeder-free differentiation. γδ CAR-iT cells exhibit potent antigen-specific tumor killing and they release less inflammatory cytokine than conventional CAR-T cells, potentially reducing the risk for cytokine-mediated toxicities. We believe that this off-the-shelf platform will enable safer and more accessible allogenic cell therapies for hematologic and solid cancers.