Targeting Aggressive Brain Tumours With Broadly Cytotoxic Expanded NK And CAR-Engineered NK Cells

Abstract

Glioblastoma multiforme (GBM) and medulloblastoma (MB) are both highly malignant brain tumours that are challenged by pervasive tumour recurrence and the potential for severe post-therapy complications, respectively. Cancer immunotherapy, and more specifically, adoptive cell therapy (ACT) has been increasingly explored in the context of these brain tumours, with a primary focus on αβ T cells. These cells are most conventionally employed in chimeric antigen receptor (CAR)-based immunotherapies, and have shown significant clinical efficacy against hematologic malignancies. Due to the challenges that arise with CAR-αβ T cells, including manufacturing delays and the potential for fatal immune overactivation, other cell sources, including Natural Killer (NK) cells, are increasingly being explored. NK cells are an emerging and viable cell source for allogeneic cell transfer given their potent antigen-independent intrinsic cytotoxicity, self-regulating inhibitory mechanisms, and low graft vs. host disease risk. For clinical use, these cells are upscaled, conventionally through ex vivo expansion approaches. Expansion with K562 feeder cells expressing membrane-bound IL-21 (K562-mb-IL-21) has been shown to lead to large-scale proliferation of highly activated and metabolically robust NK cells from peripheral blood. We found these cells to be adept at targeting both cell lines and patient-derived tumour cells of GBM and MB. To enhance the tumour-specific cytotoxicity of these cells, we engineered them with a CD70-CAR through clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and AAV-based viral transduction. CD70 is a promising immunogenic target owing to its minimal expression in healthy tissues and overexpression in GBM, where it contributes to recurrence and immune escape. Our CD70-targeting CAR-NK cells did not show preferential targeting of CD70 expressing brain tumours, both in vitro and in vivo, but further genetic modifications can enhance their clinical potential.