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-positron emission tomography (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.

A new tripodal tris(hydroxypyridinone) bifunctional chelator for gallium allows easy production of (68)Ga-labelled proteins rapidly under mild conditions in high yields at exceptionally high specific activity and low concentration.

Significance Anti-CD8 immuno-PET imaging agents provide the potential to monitor the localization, migration, and expansion of CD8-expressing cells noninvasively in vivo. Shown here is the successful generation of functional anti-CD8 imaging agents based on engineered antibodies for use in a variety of preclinical disease and immunotherapeutic models.

A novel bifunctional chelator combines a dithiocarbamate group for binding the positron‐emitter 64Cu (red spheres) for PET imaging and a bisphosphonate group (green ellipsoids) for strong binding to several inorganic materials, such as MRI contrast agents based on superparamagnetic iron oxide nanoparticles and rare‐earth metal oxides. The dual PET–MR imaging capabilities of this approach are demonstrated in vivo by imaging lymph nodes using both imaging modalities.