Info
Background:
Despite the unprecedented success of immunotherapy in cancer, the longstanding conundrum of cancer heterogeneity and inability to assess the complexity of tumor immune microenvironment has limited its benefit to only a small fraction of patients1,2. Current biomarkers such as PD‑L1, TMB, dMMR, and MSI‑H rely on invasive, spatially restricted tissue or blood sampling that often fails to capture multifocal disease or predict therapeutic response3. Recent efforts have focused on imaging immune activation, including T‑cell–directed tracers that primarily reflect late responses and cannot reliably distinguish activated from nonactivated or immunosuppressive subsets4-7. Antigen presenting cells (APCs) bridge innate and adaptive immunity and are fundamental in orchestrating both early and late tumor immune responses8,9. Their activation is essential for the success of cancer immunotherapies. Yet, few studies have investigated non-invasive approaches for monitoring APC function in vivo. This study introduces αCD80 as a robust molecular marker for tracking activated APCs via whole-body immunoPET imaging, providing predictive insights into immunotherapy efficacy and immunological memory establishment.
Hypothesis/Objective:
Imaging activated APCs can predict response to immunotherapy. The in vivo PET imaging indicated αCD80 to be an optimal marker for immunoPET of activated APCs. Our objective was to establish αCD80 immunoPET for the prediction of the tumor response and long-term immune memory imparted by LPS immunotherapy.
Methods:
C57BL/6 mice received subcutaneous injections of lipopolysaccharide (LPS) to simulate immune activation. The antibodies (αCD80, αCD86, and αCD40) were labeled with Zirconium-89 (89Zr) using deferoxamine (DFO) as a chelating agent. Serial PET scans were conducted at defined time points, and radiotracer biodistribution activity was quantified at the endpoint. For tumor studies, KPC 689 pancreatic tumor-bearing mice were treated with LPS, followed by [89Zr]Zr-DFO-αCD80 injection and PET imaging. 18F-FDG PET imaging was performed at 3h in the LPS-treated KPC 689 pancreatic cancer model. Tumor sizes were correlated with tumor uptake to assess therapy response. For αCD80 immunoPET of immune memory, the responders to LPS therapy were rechallenged with tumor cells, and PET images were acquired 3 days post-rechallenge.
Results:
Longitudinal PET images showed that [89Zr]Zr-DFO-αCD80 (32.15 ± 15.8%ID/g) selectively accumulated at the LPS injection site, outperforming [89Zr]-DFO-αCD40 (15.3 ± 2.1%ID/g) and [89Zr]Zr-DFO-αCD86 (4.2 ± 0.11%ID/g) in the LPS-induced immune activation model. [89Zr]Zr-DFO-αCD80 displayed minimal uptake in clearance organs, conferring its high specificity. αCD80 immunoPET was employed in APC imaging and response assessment in KPC 689 subcutaneous pancreatic tumor with intratumoral LPS therapy (Fig.1A). The PET images (Fig.1B) showed higher tumor uptake of [89Zr]Zr-DFO-αCD80 compared to control and distinguished responders from non-responders (Fig.1C). The tumor uptake (Fig.1D) in responders was significantly higher than control and non-responders at 48h whereas no significant change in tumor uptake was observed between control and non-responders. Furthermore, a statistically significant decrease in relative tumor volume (Fig.1E) was seen as early as 7 days in responders compared to controls. Tumor uptake of [89Zr]Zr-DFO-αCD80 at 48h showed a strong Spearman correlation (Fig.1F) with tumor volume at day 7 (r = -0.6, p = 0.004) and endpoint (r = -0.64, p=0.0021). αCD80 immunoPET. 18F-FDG PET imaging results indicated no distinction between LPS-activated immune cells and non-activated immune cells. αCD80 immunoPET in rechallenge mice (Fig.1G) indicated a high uptake at the tumor site in rechallenged mice (18.9±2 %ID/g) compared to age-matched controls (9.8±2.7 %ID/g). All rechallenged mice showed tumor rejection compared to age-matched controls (Fig.1H).
Conclusion:
αCD80 immunoPET is effective for non-invasive imaging of activated APCs and can predict early and late response to immunotherapy. The study reports the first-ever αCD80 immunoPET for the prediction and visualization of immunological memory.
Image/Figure:
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Image/Figure Caption:
Figure 1. CD80-targeted ImmunoPET for tumor response assessment and immune memory visualization. Schematic (1A) for αCD80 immunoPET in the KPC 689 pancreatic cancer model. The representative PET images (1B) of [89Zr]Zr-DFO-αCD80 uptake and tumor volumes (1C) of KPC 689 pancreatic tumor-bearing mice treated with LPS immunotherapy. The difference in tumor uptake (1D) of [89Zr]Zr-DFO-αCD80 and relative tumor volume (1E) in responders and non-responders. Receiver operating characteristics (ROC) curve analysis (1F). αCD80 immunoPET (1G) for visualization of immune memory in rechallenged mice and tumor volumes (1H).
Author
Neetu Singh
University of Utah