Immune checkpoint inhibitors (ICIs), by reinvigorating CD8+ T cell mediated immunity, have revolutionized cancer therapy. Yet, the systemic CD8+ T cell distribution, a potential biomarker of ICI response, remains poorly characterized. We assessed safety, imaging dose and timing, pharmacokinetics and immunogenicity of zirconium-89-labeled, CD8-specific, one-armed antibody positron emission tomography tracer 89ZED88082A in patients with solid tumors before and ~30 days after starting ICI therapy (NCT04029181). No tracer-related side effects occurred. Positron emission tomography imaging with 10 mg antibody revealed 89ZED88082A uptake in normal lymphoid tissues, and tumor lesions across the body varying within and between patients two days after tracer injection (n = 38, median patient maximum standard uptake value (SUVmax) 5.2, IQI 4.0–7.4). Higher SUVmax was associated with mismatch repair deficiency and longer overall survival. Uptake was higher in lesions with stromal/inflamed than desert immunophenotype. Tissue radioactivity was localized to areas with immunohistochemically confirmed CD8 expression. Re-imaging patients on treatment showed no change in average (geometric mean) tumor tracer uptake compared to baseline, but individual lesions showed diverse changes independent of tumor response. The imaging data suggest enormous heterogeneity in CD8+ T cell distribution and pharmacodynamics within and between patients. In conclusion, 89ZED88082A can characterize the complex dynamics of CD8+ T cells in the context of ICIs, and may inform immunotherapeutic treatments.

Purpose Immune checkpoint inhibitors can induce a T cell–mediated anti-tumor immune response in patients with melanoma. Visualizing T cell activity using positron emission tomography (PET) might allow early insight into treatment efficacy. Activated tumor–infiltrating T cells express the high-affinity interleukin-2 receptor (IL-2R). Therefore, we performed a pilot study, using fluorine-18-labeled IL-2 ([18F]FB-IL2 PET), to evaluate whether a treatment-induced immune response can be detected. Methods Patients with metastatic melanoma received ~ 200 MBq [18F]FB-IL2 intravenously, followed by a PET/CT scan before and during immune checkpoint inhibitor therapy. [18F]FB-IL2 uptake was measured as standardized uptake value in healthy tissues (SUVmean) and tumor lesions (SUVmax). Response to therapy was assessed using RECIST v1.1. Archival tumor tissues were used for immunohistochemical analyses of T cell infiltration. Results Baseline [18F]FB-IL2 PET scans were performed in 13 patients. SUVmean at baseline was highest in the kidneys (14.2, IQR: 11.6–18.0) and liver (10.6, IQR: 8.6–13.4). In lymphoid tissues, uptake was highest in spleen (10.9, IQR: 8.8–12.4) and bone marrow (2.5, IQR: 2.1–3.0). SUVmax in tumor lesions (n = 41) at baseline was 1.9 (IQR: 1.7–2.3). In 11 patients, serial imaging was performed, three at week 6, seven at week 2, and one at week 4. Median [18F]FB-IL2 tumor uptake decreased from 1.8 (IQR: 1.7–2.1) at baseline to 1.7 (IQR: 1.4–2.1) during treatment (p = 0.043). Changes in [18F]FB-IL2 tumor uptake did not correlate with response. IL-2R expression in four archival tumor tissues was low and did not correlate with baseline [18F]FB-IL2 uptake. No [18F]FB-IL2-related side effects occurred. Conclusion PET imaging of the IL-2R, using [18F]FB-IL2, is safe and feasible. In this small patient group, serial [18F]FB-IL2-PET imaging did not detect a treatment-related immune response. Trial registration Clinicaltrials.gov: NCT02922283; EudraCT: 2014-003387.20

First-in-human study of the biodistribution and pharmacokinetics of 89Zr-CX-072, a novel immunopet tracer based on an anti-PD-L1 probody de Ruijter,