An effective immuno-PET imaging method to monitor CD8-dependent responses to immunotherapy

The rapidly advancing field of cancer immunotherapy is currently limited by the scarcity of noninvasive and quantitative technologies capable of monitoring the presence and abundance of CD8⁺ T cells and other immune cell subsets. In this study, we describe the generation of ⁸⁹Zr-desferrioxamine-labeled anti- CD8 cys-diabody (⁸⁹Zr-malDFO-169 cDb) for noninvasive immuno-PET tracking of endogenous CD8⁺ T cells. We demonstrate that anti-CD8 immuno-PET is a sensitive tool for detecting changes in systemic and tumor-infiltrating CD8 expression in preclinical syngeneic tumor immunotherapy models including antigen-specific adoptive T-cell transfer, agonistic antibody therapy (anti-CD137/4-1BB), and checkpoint blockade antibody therapy (anti-PD-L1). The ability of anti-CD8 immuno-PET to provide whole body information regarding therapy-induced alterations of this dynamic T-cell population provides new opportunities to evaluate antitumor immune responses of immunotherapies currently being evaluated in the clinic.