Abstract B18: Noninvasive imaging of antitumor immune responses

Abstract

Abstract By using the body's own immune response, immunotherapy may prove to be a turning point in the treatment of cancer. Predictors of a patient's response to immunotherapy remain to be defined, as actual responses are heterogeneous and difficult to study in real-time. Is it possible to predict the outcome of therapy for an individual patient? What is the behavior and what are the dynamics of immune cells in the tumor microenvironment? We need new methods to noninvasively explore the microenvironment of tumors and enumerate relevant cell types. Imaging the extent of infiltration of immune cells into tumors and identifying the relevant lymphocyte subsets is therefore essential. We developed single domain antibodies (VHHs, ~15 kDa) against a variety of lymphocyte surface antigens to image antitumor immune responses. VHHs were engineered to contain a sortase recognition tag, X-LPETGG, at their C-terminus to enable site-specific modification with tags of choice. We synthesized a substrate that contains both a click handle and a metal chelator, where the click handle can be used to attach a polymer, and the chelator is used to chelate a radiometal onto the VHH of interest. We thus produced VHHs equipped with a polyethyleneglycol (PEG) molecule to increase circulatory half-life and a chelator. C57/BL6 mice were injected with 89Zr-PEGylated VHHs, and images were acquired 24 h post injection. Images of the PEGylated-VHHs showed specific staining with low background in kidney and intestine. When we used 89Zr-labeled PEGylated-VHHs specific for CD8 or Class II MHC, secondary lymphoid structures, including the mesenteric lymph node, were clearly visible. Knock-out mice were used to establish specificity of PET imaging. Mice bearing panc02 tumors were imaged at 24 h p.i. and showed CD8 T cells infiltrating the tumor. We monitored the CD8-T cell response to immunotherapy in the B16 melanoma model by using the antiCD8 VHH. For animals that showed a response that led to regression of the tumor, the distribution of the signal was homogeneous throughout the tumor. It is thus possible to monitor antitumor immune responses. Noninvasive monitoring could therefore change how therapy is applied. Citation Format: Mohammad Rashidian, Michael Dougan, Jessica Ingram, Hidde Ploegh. Noninvasive imaging of antitumor immune responses. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B18.