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quantify tumor CD8+ T-cell infiltration

Head-to-head comparison of nuclear imaging techniques to quantify tumor CD8+ T cell infiltration 

by Gerwin Sandker, René Raavé, Ines Antunes, Peter Wierstra, Iris Hagemans, Milou Boswinkel, Gerben Franssen, Janneke Molkenboer-Kuenen, Johan Bussink, Gosse Adema, Erik Aarntzen, Martijn Verdoes, Sandra Heskamp

EMIM 2022 Conference Abstract


CD8+ T cells are key effector cells in anti-tumor immune responses. Immunotherapies (re)activating these cells are promising cancer treatments. Prevalent immune-related adverse effects and high costs combined with limited treatment responses necessitate biomarkers predicting response. Previous studies have shown that nuclear imaging techniques with radiolabeled anti-CD8 antibodies, IL2 and ex vivo labeled cells can be used to noninvasively evaluate the whole-body and tumor residing distribution of CD8+ T cells over time. In this study, we perform a head-to-head comparison of these techniques.
C57BL/6 mice bearing B16F10/ova tumors were randomized in 3 groups (n=10) to receive either: 1) 89Zr-labeled DFO-conjugated Fc-silent anti-CD8 antibodies (89Zr-antiCD8lala), 2) from donor mice isolated and ex vivo 89Zr-oxine labeled OT1 T cells (89Zr-OT1), or 3) 18F-labeled RESCA-IL2 (18F-IL2). Mice were injected intravenously with 89Zr-antiCD8lala 72 hours, 89Zr-OT1 48 hours, and 18F-IL2 directly before PET/CT scanning and dissection. Additionally, 89Zr-OT1 mice were PET/CT scanned 24 hours after injection. Following dissection, relevant tissues were collected for ex vivo biodistribution analysis. Next, tumors were halved for subsequent immunohistochemistry and autoradiography evaluation, and flow cytometric analysis to evaluate the number of CD8+ T cells. 
Preliminary data analysis suggests tumor uptake of 89Zr-antiCD8lala, 89Zr-OT1 and 18F-IL2 above background levels. Furthermore, uptake of 89Zr-antiCD8lala and 89Zr-OT1 was observed in the spleen and lymph nodes. (Figure 1 A and B) 18F-IL2 accumulation was observed in spleen, lung and the excretory organs. (Figure 1 C) The uptake of 89Zr-antiCD8lala and 18F-IL2 in lymphoid organs indicates their target specificity, whereas the uptake of 89Zr-OT1 indicates that the OT1 T cells were viable and retained their migratory ability.
Preliminary data analysis suggests quantifiable tumor uptake of each tracer. Further analysis will investigate the correlations between the quantified PET signal and the number of CD8+ T cells in the tumor as determined by flow cytometry. Moreover, immunohistochemistry for CD8 will be performed to investigate the spatial correlation with autoradiographic images.