Image-guided adaptable CAR T cell therapy for solid tumors

About This Grant

PROJECT SUMMARY Despite promising results in treating B cell malignancies, over 50% of patients undergoing chimeric antigen receptor (CAR) T cell therapy experience tumor relapse, and CAR T cells have not consistently shown effectiveness against solid tumors. Antigen escape, T cell exhaustion, and severe toxicities remain major obstacles. This proposal addresses these challenges by developing an image-guided, universal, adaptable CAR (A-CAR) system comprising a tumor-targeting adaptor molecule fused with a C-terminal tag and a tag-specific CAR on T cells. Our stepwise approach to image-guided CAR T cell therapy involves: (1) Imaging: PET assessment of adaptor biodistribution using radiolabeled VHH adaptors; (2) Treatment: a single infusion of autologous tag-specific CAR T cells with optimized VHH adaptors that coat tumor cells for CAR T recognition; and (3) Assessment: monitoring tumor response and CAR T distribution via ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/CT. The clinically approved radiotracer ⁶⁸Ga-DOTATATE tracks CAR T cell expansion and activity at on- and off-tumor sites through binding to somatostatin receptor 2 (SSTR2) co-expressed on CAR T cells. The high specificity, affinity, and favorable kinetics of VHHs make them ideal for PET imaging and as CAR T cell adaptors, enabling non-invasive detection of antigen expression, patient selection, and prediction of homing sites and offtumor toxicity prior to treatment. This project comprehensively investigates VHHs as CAR T adaptors, including pharmacokinetic and biodistribution characterization, optimization of delivery (intermittent cyclic tumor tagging vs. continuous infusion) and dosing, and the potential to mitigate T cell exhaustion and overcome antigen escape through multi-antigen targeting. Mouse xenograft and syngeneic tumor models are essential for this work, as they are the only systems in which VHH adaptor biodistribution, CAR T cell trafficking, tumor targeting, and toxicity can be evaluated together in a living organism. These in vivo models enable optimization of adaptor and CAR T dosing, assessment of antigen escape and exhaustion under physiological conditions, and validation of PET imaging as a predictive tool — none of which are achievable in cell culture. By refining VHH and CAR T delivery guided by quantitative imaging, we seek to enhance efficacy and minimize off-tumor toxicity, with the ultimate goal of advancing A-CAR therapy against solid cancers.