Unaltered NKG2D-CAR T cell function under hypoxia in osteosarcoma in vitro

Cancer is the leading cause of death among children and adolescents in high-income countries. Among solid tumors, osteosarcoma (OS) is the most prevalent primary bone cancer in the pediatric population. For patients who relapse or develop metastases, the survival rate remains at only 30%, with scarce improvement over the past 30 years. Immunotherapy, including chimeric antigen receptor (CAR) T cells, represents a promising approach to treating OS. We observed that despite robust in vitro cytotoxicity of NKG2D-CAR T at low effector-to-target ratios, NKG2D-CAR T cells failed to control tumor growth in our xenograft OS models, highlighting the suppressive tumor microenvironment (TME). In this regard, the hypoxic TME has been widely considered a barrier to effective immunotherapies. Here, we examined the impact of hypoxia on NKG2D-CAR T function in OS in vitro models. We confirmed HIF-1α is highly expressed in our OS models, indicating the potential of hypoxia as a CAR T disruptor. However, hypoxia was not responsible for lowering NKG2D ligands expression for CAR recognition, nor did it impact the expression of major activating or inhibitory immune checkpoints. Crucially, functional assays demonstrated that NKG2D-CAR T cell phenotype, activity, and cytokine secretion remained unaffected and its activity against three-dimensional OS-spheroids was preserved under in vitro hypoxic conditions. Although these findings challenge the idea that hypoxia alone compromises in vitro NKG2D-CAR T efficacy in OS, further studies are needed on how hypoxia interacts with multiple factors of the TME that could modulate CAR T cell behavior.