PROJECT SUMMARY/ABSTRACT Despite the unprecedented effects of immunotherapy in treating cancer, over 50–80% of patients will not respond to treatment and will endure severe adverse and life-threatening events due to treatment. Approaches to select or guide immunotherapeutic strategies are urgently needed. We propose to develop ultrasound-based approaches to characterize an overlooked attribute of tissue immuno-imaging; the vasculature and associated endothelium. In cancer, tumor blood vessels and associated endothelial cells are highly abnormal and immunosuppressive. These also differ extensively on a patient-by-patient basis. Approaches to modulate vascular and endothelial immunity have been developed, where anti-angiogenic agents are used to directly target these and enhance the effects of immunotherapy. However, timing and dosing of anti-angiogenics with immunotherapy remains a major challenge to maximize benefits to all patients. As such, the tools we propose to develop will help 1) select patients that are most likely to respond to immunotherapy and reduce adverse effects and costs to non-responders, and 2) provide imaging feedback for guiding combined anti-angiogenic and immunotherapy treatment regimens so that more patients may benefit from the unparalleled effects of these treatments. In order to achieve our goals, we will: 1) develop unique molecular ultrasound probes for imaging endothelial cell immunosuppressive surface markers, and 2) develop image-guidance to optimize immunotherapeutic strategies by exploring the quantitative ultrasound parameter space. Equipped with these initial developments, our goal will be to initiate a larger research program designed to further develop quantitative ultrasound approaches for imaging tissue, vascular and endothelial aspects of the immune system.