<i>In vivo</i> nanoparticle-based T cell imaging can predict therapy response towards adoptive T cell therapy in experimental glioma

Abstract

<b>Rationale:</b> Intrinsic brain tumors, such as gliomas are largely resistant to immunotherapies including immune checkpoint blockade. Adoptive cell therapies (ACT) including chimeric antigen receptor (CAR) or T cell receptor (TCR)-transgenic T cell therapy targeting glioma-associated antigens are an emerging field in glioma immunotherapy. However, imaging techniques for non-invasive monitoring of adoptively transferred T cells homing to the glioma microenvironment are currently lacking. <b>Methods:</b> Ultrasmall iron oxide nanoparticles (NP) can be visualized non-invasively by magnetic resonance imaging (MRI) and dedicated MRI sequences such as <i>T</i>₂* mapping. Here, we develop a protocol for efficient <i>ex vivo</i> labeling of murine and human TCR-transgenic and CAR T cells with iron oxide NPs. We assess labeling efficiency and T cell functionality by flow cytometry and transmission electron microscopy (TEM). NP labeled T cells are visualized by MRI at 9.4 T <i>in vivo</i> after adoptive T cell transfer and correlated with 3D models of cleared brains obtained by light sheet microscopy (LSM). <b>Results:</b> NP are incorporated into T cells in subcellular cytoplasmic vesicles with high labeling efficiency without interfering with T cell viability, proliferation and effector function as assessed by cytokine secretion and antigen-specific killing assays <i>in vitro</i>. We further demonstrate that adoptively transferred T cells can be longitudinally monitored intratumorally by high field MRI at 9.4 Tesla in a murine glioma model with high sensitivity. We find that T cell influx and homogenous spatial distribution of T cells within the TME as assessed by <i>T</i>₂* imaging predicts tumor response to ACT whereas incomplete T cell coverage results in treatment resistance. <b>Conclusion:</b> This study showcases a rational for monitoring adoptive T cell therapies non-invasively by iron oxide NP in gliomas to track intratumoral T cell influx and ultimately predict treatment outcome.