Immuno-PET Monitoring of CD8+ T Cell Infiltration Post ICOS Agonist Antibody Treatment Alone and in Combination with PD-1 Blocking Antibody Using a 89Zr Anti-CD8+ Mouse Minibody in EMT6 Syngeneic Tumor Mouse

Abstract

Purpose The presence and functional competence of intratumoral CD8+ T cells is often a barometer for successful immunotherapeutic responses in cancer. Despite this understanding and the extensive number of clinical-stage immunotherapies focused on potentiation (co-stimulation) or rescue (checkpoint blockade) of CD8+ T cell antitumor activity, dynamic biomarker strategies are often lacking. To help fill this gap, immuno-PET nuclear imaging has emerged as a powerful tool for in vivo molecular imaging of antibody targeting. Here, we took advantage of immuno-PET imaging using 89Zr-IAB42M1-14, anti-mouse CD8 minibody, to characterize CD8+ T-cell tumor infiltration dynamics following ICOS (inducible T-cell co-stimulator) agonist antibody treatment alone and in combination with PD-1 blocking antibody in a model of mammary carcinoma. Procedures. Female BALB/c mice with established EMT6 tumors received 10 µg, IP of either IgG control antibodies, ICOS agonist monotherapy, or ICOS/PD-1 combination therapy on days 0, 3, 5, 7, 9, 10, or 14. Imaging was performed at 24 and 48 h post IV dose of 89Zr IAB42M1-14. In addition to 89Zr-IAB42M1-14 uptake in tumor and tumor-draining lymph node (TDLN), 3D radiomic features were extracted from PET/CT images to identify treatment effects. Imaging mass cytometry (IMC) and immunohistochemistry (IHC) was performed at end of study. Results 89Zr-IAB42M1-14 uptake in the tumor was observed by day 11 and was preceded by an increase in the TDLN as early as day 4. The spatial distribution of 89Zr-IAB42M1-14 was more uniform in the drug treated vs. control tumors, which had spatially distinct tracer uptake in the periphery relative to the core of the tumor. IMC analysis showed an increased percentage of cytotoxic T cells in the ICOS monotherapy and ICOS/PD-1 combination group compared to IgG controls. Additionally, temporal radiomics analysis demonstrated early predictiveness of imaging features. Conclusion To our knowledge, this is the first detailed description of the use of a novel immune-PET imaging technique to assess the kinetics of CD8+ T-cell infiltration into tumor and lymphoid tissues following ICOS agonist and PD-1 blocking antibody therapy. By demonstrating the capacity for increased spatial and temporal resolution of CD8+ T-cell infiltration across tumors and lymphoid tissues, these observations underscore the widespread potential clinical utility of non-invasive PET imaging for T-cell-based immunotherapy in cancer.

Whole-body bioluminescence imaging of T-cell response in PDAC models

“…Nagasaki et al., 2022 found that the addition of anti-PD-1 therapy promotes the infiltration, into the TME, of tumor-attacking exhausted T-cells clonotypes from the TDLN’s. In other cases, increased T-cell presence in the TDLN’s have been detected several times in the literature to occur when tumor cells are treated with checkpoint blockers ( 23 , 29 , 31 , 36 , 37 ). In particular, imaging active T-cells, using an anti-OX40 radiotracer, in a model of cancer treated with CpG vaccination/adjuvant therapy, clearly showed the TDLN persistent enhanced signal throughout the treatment period (on days 2 and 9 after treatment) ( 38 ).…”

“…It can be combined with a modality like PET/SPECT that can provide additional information regarding where the T-cells are in the tumor; as well as being more translatable to clinical settings ( 20 – 22 ). Currently the available methods to monitor responses to immunotherapy in the clinic are mainly based on ex vivo analyses of tissues or of blood ( 23 ). Bensch et al., 2018 found that when comparing patient response predictions with their in vivo PET tracer versus IHC or RNA seq.…”

“…By imaging on the right dorsal side, in the treatment experiment, we could use TbiLuc to look not only at the tumor but also at the axial lymph node next to the tumor which can be considered as a tumor-draining lymph node (TDLN) ( Figures 4 , 5 ) ( 30 ). Imaging T-cells in secondary lymphoid organs, using targeted imaging techniques such as those employed by TbiLuc, can significantly improve a model’s ability to infer, and possibly predict, the success rates of specific treatments ( 23 , 29 , 31 , 32 ). For example, using CD8+ T-cell radiolabeled with 89Zr, Alsaid and colleagues found that the number of CD8 T-cells increased in the TDLN’s, already 4 days after the start of ICOS/anti-PD-1 treatment, and in the tumor 11 days after ( 23 ).…”

“…Imaging T-cells in secondary lymphoid organs, using targeted imaging techniques such as those employed by TbiLuc, can significantly improve a model’s ability to infer, and possibly predict, the success rates of specific treatments ( 23 , 29 , 31 , 32 ). For example, using CD8+ T-cell radiolabeled with 89Zr, Alsaid and colleagues found that the number of CD8 T-cells increased in the TDLN’s, already 4 days after the start of ICOS/anti-PD-1 treatment, and in the tumor 11 days after ( 23 ). This CD8 minibody is now in phase 2 clinical trials in patients treated with immune checkpoint blockers (NCT03802123 and NCT05013099) ( 33 , 34 ).…”