The graphic comprises promising targets for TAM imaging and related radiotracers. Target reactivity for mouse (m) and human (h) species is classified as fully developed tracer ( ), tracer development possible ( ) and no species specific target expression ( ). Tracer specificity for selective targeting of macrophages (MΦ) is listed for each target ranging from low (+) to high (+++) macrophage specific signal. Target specificity towards M1 or M2 phenotype was estimated based on existing literature and marked as black line.

Multi-tracer and multi-modality imaging for the characterization of the glioma immune microenvironment. (A) Gadolinium enhanced T1 weighted (T1 MRI Gd) of a human glioma model. PET-MR images for [¹⁸F]fluoroethyl tyrosine and the TSPO tracer [¹⁸F]DPA-714 provide complementary information of heterogeneous glioma tissues (arrows). (B) Immunofluorescence analysis reveals tumor-associated macrophages/microglia (Iba-1, red) as important source of TSPO (green) in this model. Scale bar: 50 µm. Image courtesy of: B. Zinnhardt, C. Foray, C. Barca, O. Grauer, M. Schäfers and A. H. Jacobs, unpublished.

Transverse (upper row) and coronal (middle row) PET/CT images of wild-type (left) and MMR-deficient (right) 3LL-R tumor-bearing mice 3 h after injection of ¹⁸F-FB-anti-MMR3.49. PET signals are encoded in color scale, CT image in gray scale. Arrows point to tumor (T), kidney (K), and bladder (B). Autoradiography performed on slices from 3LL-R tumors grown in WT (left) vs. MMR-deficient (right) mice are shown in the bottom row. max = maximum; min = minimum. Reproduced after permission from . Copyright © 2015 Society of Nuclear Medicine and Molecular Imaging.

Visualisation of ⁸⁹Zr-HDL nanotracer accumulation in tumor tissues by in vivo PET imaging. CT and PET/CT fusion sections of ⁸⁹Zr-AI-HDL (A) and ⁸⁹Zr-PL-HDL (B) obtained 24 h after injection in mice bearing orthotopic 4T1 tumors (indicated by arrows). Reproduced after permission from . Copyright © 2015 Society of Nuclear Medicine and Molecular Imaging.

Growth rate and MRI enhancement of human glioblastomas in representative NOD-SCID x RAG g/d dko mice. (A) Representative MR images with superimposed T2* relaxation time maps of anti-CD47 mAb treated tumor (upper row) and sham-treated control (lower row). (B) Corresponding tumor growth rates, calculated as % change in tumor size, and (C) T2* relaxation times of anti-CD47 mAb treated tumors (n=3) and sham-treated controls (n=5), displayed as means and standard deviations. Please note that ferumoxytol-induced T2*-signal enhancement is quantified by shortened T2* relaxation times (shorter T2* time = stronger contrast enhancement).

Ferumoxytol alters macrophage polarization in hepatic metastasis in vivo. a, Livers of the same mice described in Fig. were further analysed with FACS for infiltrating leukocyte populations. b, Accordingly, the relative number of GFP+ cells within the liver gate (%) was significantly reduced in ferumoxytol-treated livers compared with untreated controls. c, CD11blowF4/80high tissue-resident macrophages were increased in ferumoxytol-treated livers compared to controls and d, CD11bhighF4/80low peripheral-derived macrophages were increased in ferumoxytol-treated livers compared with controls. e,f, The polarization of both tissue-resident and infiltrating macrophages shifted towards the M1 phenotype as measured by CD80 and CD206 markers: median fluorescent intensity ratios (MFI) of M1/M2 associated markers (CD80/CD206) in CD11blowF4/80high tissue-resident macrophages (e) and infiltrating F4/80low CD11bhigh liver macrophages (f) isolated from ferumoxytol-treated livers and untreated controls. All quantitative data are displayed as the mean of seven livers per group ± standard deviation. *P < 0.05, indicates a statistically significant difference (Student's t-test) from untreated controls. Reproduced after permission from . Copyright © 2016 NPG.

Effect of FP-NPs on tumor cell proliferation and macrophage polarization. (A) B16F10 cells were incubated with FMT-NH2, PIC, or FP-NPs for 48 h and the cell viability was analyzed by CCK-8 assay. (B) B16F10 cells pre-labeled with CFSE co-cultured with RAW 264.7 at a ratio of 2:1 were incubated with FMT-NH2, PIC, or FP-NPs for 48 h and cell proliferation was then analyzed by FCM. (C) GFP-B16F10 cells co-cultured with RAW 264.7 at a ratio of 2:1 were incubated with FMT-NH2, PIC, or FP-NPs for 48 h and the fluorescence intensity of GFP was captured. (D) Left: Schematic diagram of the co-culture. Right: B16F10 cells co-cultured with RAW 264.7 at a ratio of 2:1 were incubated with FMT-NH2, PIC, or FP-NPs in a dual-chamber Transwell system for 48 h and the tumor cells in the lower chamber were stained with DAPI and analyzed by fluorescence microscopy. (E, F) RAW 264.7 were incubated with FMT-NH2, PIC, or FP-NPs for 12 h and the expression of macrophage M1 (iNOS, CD86) and M2 (Arg-1, CD206) related genes was analyzed by qRT-PCR. (G) RAW 264.7 cells were incubated with FMT-NH2, PIC, or FP-NPs for 15 min and the expression of target proteins was analyzed by WB. All representative data are from three independent experiments. Error bars, SD. *P < 0.05, **P < 0.01, ***P < 0.001. FCM: flow cytometry; FMT: ferumoxytol; FP-NPs: FMT-NH2-poly I:C; iNOS: inducible nitric oxide synthase; PIC: poly I:C, polyinosinic-polycytidylic acid. WB: western blotting. Reproduced after permission from . Copyright © 2018 Ivyspring International Publisher Pty Ltd.