Tumors are often surrounded and invaded by bone marrow-derived cells. Imaging the infiltration of such immune cells into tumors may therefore be an attractive means of detecting tumors or of tracking the response to anticancer therapy. We developed alpaca-derived antibody fragments specific for mouse class II MHC and CD11b products, expressed on the surface of a variety of myeloid cells. We validated these reagents by flow cytometry and two-photon microscopy to obtain images at cellular resolution. To enable noninvasive imaging of the targeted cell populations, we developed a method to site-specifically label VHHs [the variable domain (VH) of a camelid heavy-chain only antibody] with 18F or 64Cu. Radiolabeled VHHs rapidly cleared the circulation (t1/2 ~15min) and clearly visualized lymphoid organs. We used VHHs to explore the possibility of imaging inflammation in both xenogeneic and syngeneic tumor models, which resulted in detection of tumors with remarkable specificity. We also imaged the infiltration of myeloid cells upon injection of complete Freund's adjuvant. Both anti-class II MHC and anti-CD11b VHHs detected inflammation with excellent specificity. Given the ease of manufacture and labeling of VHHs, we believe that this method could transform the manner in which antitumor responses and/or infectious events may be tracked. The ability to monitor the immune response in the course of therapy will enable early determination of the efficacy of treatment and will inform decisions as to whether treatment should be stopped or continued. Noninvasive monitoring could therefore change how therapies are applied and assessed, to the benefit of many patients.
Citation Format: Mohammad Rashidian. Noninvasive imaging of immune responses. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B106.
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