Assessing Oximetry Response to Chimeric Antigen Receptor T-cell Therapy against Glioma with F-19 MRI in a Murine Model

Purpose: To assess the cell-specific, intracellular partial pressure of oxygen (Po-2) dynamics of both tumor and chimeric antigen receptor (CAR) T cells in a murine immunotherapy model. Materials and Methods: Human glioblastoma cells or human T cells were intracellularly labeled with perfluorocarbon nanoemulsion droplet sensors prior to in vivo injection in severe combined immunodeficient mice to measure Po-2 in the two cell types in response to treatment. Two main sets of experiments were performed: (a) mice were injected in the flank with perfluorocarbon-labeled human glioblastoma cells and were then inoculated with either CAR T cells or untransduced T cells or were untreated 5 days after tumor inoculation; and (b) mice with unlabeled glioblastoma tumors were inoculated with perfluorocarbon-labeled CAR T cells or untransduced T cells 5 days after tumor inoculation. Longitudinal fluorine 19 (F-19) spin-lattice relaxation time measurements of the tumor mass were used to ascertain absolute Po-2 in vivo. Results were analyzed for significance using an analysis of variance, a linear mixed-effect model, and a Pearson correlation coefficient test, as appropriate. Results: The intracellular tumor cell Po-2 temporal dynamics exhibited delayed, transient hyperoxia at 3 days after infusion of CAR T cells, commensurate with significant tumor cell killing and CAR T-cell infiltration, as observed by bioluminescence imaging and histologic findings. Conversely, no significant changes were detected in CAR or untransduced T-cell intracellular Po-2 over time in tumor using these same methods. Moreover, it was observed that the total F-19 tumor cell signal quenches with treatment, consistent with rapid tissue clearance of probe from apoptotic tumor cells. Conclusion: Cell-specific Po-2 measurements using perfluorocarbon probes can provide insights into effector cell function and tumor response in cellular immunotherapeutic cancer models.