Data from Using CD69 PET Imaging to Monitor Immunotherapy-Induced Immune Activation

<div>Abstract<p>Immune checkpoint inhibitors (ICI) have been effective in treating a subset of refractory solid tumors, but only a small percentage of treated patients benefit from these therapies. Thus, there is a clinical need for reliable tools that allow for the early assessment of response to ICIs, as well as a preclinical need for imaging tools that aid in the future development and understanding of immunotherapies. Here we demonstrate that CD69, a canonical early-activation marker expressed on a variety of activated immune cells, including cytotoxic T cells and natural killer (NK) cells, is a promising biomarker for the early assessment of response to immunotherapies. We have developed a PET probe by radiolabeling a highly specific CD69 mAb, H1.2F3, with Zirconium-89 (⁸⁹Zr), [⁸⁹Zr]-deferoxamine (DFO)-H1.2F3. [⁸⁹Zr]-DFO-H1.2F3 detected changes in CD69 expression on primary mouse T cells <i>in vitro</i> and detected activated immune cells in a syngeneic tumor immunotherapy model. <i>In vitro</i> uptake studies with [⁸⁹Zr]-DFO-H1.2F3 showed a 15-fold increase in CD69 expression for activated primary mouse T cells, relative to untreated resting T cells. <i>In vivo</i> PET imaging showed that tumors of ICI-responsive mice had greater uptake than the tumors of nonresponsive and untreated mice. <i>Ex vivo</i> biodistribution, autoradiography, and IHC analyses supported the PET imaging findings. These data suggest that the CD69 PET imaging approach detects CD69 expression with sufficient sensitivity to quantify immune cell activation in a syngeneic mouse immunotherapy model and could allow for the prediction of therapeutic immune responses to novel immunotherapies.</p></div>