Development of an antigen-based approach to noninvasively image CAR T cells in real time and as a predictive tool.

CAR T cell therapy has revolutionized the treatment of a spectrum of blood-related malignancies. However, treatment responses vary among cancer types and patients. Accurate monitoring of CAR T cell dynamics is crucial for understanding and evaluating treatment efficacy. Positron emission tomography (PET) offers a comprehensive view of CAR T cell homing, especially in critical organs such as lymphoid structures and bone marrow. This information will help assess treatment response and predict relapse risk. Current PET imaging methods for CAR T require genetic modifications, limiting clinical use. To overcome this, we developed an antigen-based imaging approach enabling whole-body CAR T cell imaging. The probe detects CAR T cells in vivo without affecting their function. In an immunocompetent B cell leukemia model, CAR-PET signal in the spleen predicted early mortality risk. The antigen-based CAR-PET approach allows assessment of CAR T therapy responses without altering established clinical protocols. It seamlessly integrates with FDA-approved and future CAR T cell generations, facilitating broader clinical application.

A CAR enhancer increases the activity and persistence of CAR T cells.

Although chimeric antigen receptor (CAR) T cell therapies have demonstrated promising clinical outcomes, durable remissions remain limited. To extend the efficacy of CAR T cells, we develop a CAR enhancer (CAR-E), comprising a CAR T cell antigen fused to an immunomodulatory molecule. Here we demonstrate this strategy using B cell maturation antigen (BCMA) CAR T cells for the treatment of multiple myeloma, with a CAR-E consisting of the BCMA fused to a low-affinity interleukin 2 (IL-2). This selectively induces IL-2 signaling in CAR T cells upon antigen-CAR binding, enhancing T cell activation and antitumor activity while reducing IL-2-associated toxicities. We show that the BCMA CAR-E selectively binds CAR T cells and increases CAR T cell proliferation, clearance of tumor cells and development of memory CAR T cells. The memory cells retain the ability to re-expand upon restimulation, effectively controlling tumor growth upon rechallenge. Mechanistic studies reveal the involvement of both CAR and IL-2 receptor endodomains in the CAR-E mechanism of action. The CAR-E approach avoids the need for specific engineering and enables CAR T cell therapy with lower cell doses.