%0 Journal Article %A James Mansfield %A Gang Ren %A Jeff Gaudet %A Yanrong Zhang %A Marco Gerosa %A Max Wintermark %A Patrick Goodwill %T Imaging cancer immunology: Systemic tracking of immune cells in vivo with magnetic particle imaging %D 2020 %J Journal of Nuclear Medicine %P 101-101 %V 61 %N supplement 1 %X 101Objectives: The rapid growth of research into immuno-oncology research has fueled a need to evaluate the existence, amount and phenotype of a variety of immune cells systemically. Tumor associated macrophages (TAM) plays a pivotal role in cancer immunotherapy. However, existing methods for qualitative and quantitative evaluation of TAM accumulation have generally been insufficient. Magnetic Particle Imaging (MPI) is a novel tomographic molecular imaging technique that can be used to non-invasively track phagocytotic cells, primarily macrophages, in 3D in vivo, with contrast similar to nuclear medicine but without the complex workflow, safety, and half-life limitations. A murine breast tumor model was established by injecting 3 x 105 4T1 cells into the 5th mammary fat pad of 8-10-week female Blab/c mice. Immunotherapy was initiated by the combination of CD47 mAb and PD-L1 mAb once the tumors become palpable. Single mAb treated and isotype matched mAb treated groups were used as controls. All mice were injected with an iron-oxide MPI tracer (Ferumoxytol, 30mg/kg) and then 3D MPI and MRI (T2-weighted multi-slice, multi-echo (MSME) sequences) images were acquired at 1, 3, 7 and 14 days after tracer injection. MPI and MRI images were co-registered and quantitated. Tumors, liver, spleen and draining lymph nodes were then harvested, imaged, fixed, and stained with Perls Prussian blue for analysis of iron content. Tumour-associated macrophage (TAM) accumulation has been shown qualitatively to increase following CD47 treatment. With the combination of antiPDL1 treatment, more Ferumoxytol accumulated at the tumor site as demonstrated by in vivo MPI studies. All mice showed an accumulation of Ferumoxytol in the tumor and liver following injection. For both groups, nanoparticles were predominately detected in the expanding margins of the tumour. There was a statistically significant difference in the accumulation of TAMs between the CD47-treated and untreated groups, with the combination treated group having the most increased TAM accumulation. The sensitivity, specificity and quantitation of MPI provides valuable non-invasive information on the development of a preclinical model that monitors the efficacy of the combination of CD47 mAb and PDL1 mAb cancer immunotherapies. When combined with the high spatial resolution provided by MRI, co-registered MRI-MPI can be utilized to evaluate the response of TAMs to the combination immunotherapy. %U