Cancer immunotherapy is accompanied by distinct metabolic patterns in primary and secondary lymphoid organs observed by non-invasive in vivo ¹⁸F-FDG-PET

Abstract

Purpose: Cancer immunotherapy depends on a systemic immune response, but the basic underlying mechanisms are still largely unknown. Despite the very successful and widespread use of checkpoint inhibitors in the clinic, the majority of cancer patients do not benefit from this type of treatment. In this translational study, we investigated whether noninvasive in vivo positron emission tomography (PET) imaging using 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) is capable of detecting immunotherapy-associated metabolic changes in the primary and secondary lymphoid organs and whether this detection enables the prediction of a successful anti-cancer immune response.Methods: RIP1-Tag2 mice with progressed endogenous insular cell carcinomas underwent a combined cancer immunotherapy consisting of CD4+ T cells plus monoclonal antibodies (mAbs) against programmed death ligand-1 (PD-L1) and lymphocyte activation gene-3 (LAG-3) or a sham treatment after radiation-mediated immune cell depletion. A second cohort of RIP1-Tag2 mice underwent exclusive checkpoint inhibitor therapy (CIT) using anti-PD-L1/LAG-3 mAbs or sham treatment without initial immune cell depletion to mimic the clinical situation.All mice were monitored by 18F-FDG-PET combined with anatomical magnetic resonance imaging (MRI). In addition, we retrospectively analyzed PET / computed tomography (CT) scans (PET/CT) regarding 18F-FDG uptake of CIT-treated metastatic melanoma patients in the spleen (n=23) and bone marrow (BM; n=20) as well as blood parameters (n=17-21).Results: RIP1-Tag2 mice with advanced insular cell carcinomas treated with combination immunotherapy exhibited significantly increased 18F-FDG uptake in the spleen compared to sham-treated mice. Histopathology of the spleens from treated mice revealed atrophy of the white pulp with fewer germinal centers and an expanded red pulp with hyperplasia of neutrophils than those of sham-treated mice. Immunohistochemistry and flow cytometry analyses of the spleens revealed a lower number of T cells and a higher number of neutrophils compared to those in the spleens of sham-treated mice. Flow cytometry of the BM showed enhanced activation of T cells following the treatment schemes that included checkpoint inhibitors. The ratio of 18F-FDG uptake at baseline to the uptake at follow-up in the spleens of exclusively CIT-treated RIP1-Tag2 mice was significantly enhanced, but the ratio was not enhanced in the spleens of the sham-treated littermates. Flow cytometry analysis confirmed a reduced number of T cells in the spleens of exclusively CIT-treated mice compared to that of sham-treated mice. A retrospective analysis of clinical 18F-FDG-PET/CT scans revealed enhanced 18F-FDG uptake in the spleens of some successfully CIT-treated patients with metastatic melanoma, but there were no significant differences between responders and non-responders. The analysis of the BM in clinical 18F-FDG-PET/CT scans with a computational segmentation tool revealed significantly higher baseline 18F-FDG uptake in patients who responded to C...

Is there a link between very early changes of primary and secondary lymphoid organs in 18F-FDG-PET/MRI and treatment response to checkpoint inhibitor therapy?

“…33 Nevertheless, the reported changes in FDG-uptake were small, the evaluation time points vary and although it may appear likely, the link between the metabolic activity of immune organs and an immune response has not been proven yet. The recently published translational study by Schwenck et al 22 and the correlation of the metabolic activity early after treatment initiation to baseline immune biomarkers observed in our study support the hypothesis, that 18 F-FDG-PET is a reliable tool to monitor an effective systemic immune response in patients treated with CIT. A further important observation from this longitudinal patient study is that the systemic immune response seems a highly dynamic process, also in 18 F-FDG-PET.…”

“…This may explain the differing results to our previous retrospective study with examination time points between 50 days before and 125 days after treatment initiation. 22 Invasive biopsies of the spleen or bone marrow under therapy are ethically not feasible and a detailed explanation of the observations in lymphoid organs regarding changes in cellular Figure 4 Left hand side: results of the evaluation of lymphoid organs demonstrated as relative changes in % to the baseline scan t 0 in the responder and non-responder group. Significant differences between the time points were found for SULmean at t 1 and for relative differences between t 0 and t 1 .…”

“…This may explain the differing results to our previous retrospective study with examination time points between 50 days before and 125 days after treatment initiation. 22 Invasive biopsies of the spleen or bone marrow under therapy are ethically not feasible and a detailed explanation of the observations in lymphoid organs regarding changes in cellular components of the immune system is beyond the scope of our work. In this connection, anti-CD8 immuno-PET might help gain a deeper understanding of the process of immune response under CIT in the future.…”

“…In a recently published translational study, the potential of 18 F-FDG-PET to evaluate primary (bone marrow) and secondary (spleen) lymphoid organs could be demonstrated by our group. 22 While in the preclinical experiments fewer T cells and a higher number of neutrophils in the spleen led to a significantly higher 18 F-FDG uptake in CIT-treated mice, the observed changes in the clinical data were small, and the examination time point varied due to the retrospective study setting. Preclinical studies in mice indicated that an antitumor immune response can be observed early after therapy start using the PET tracer (1-(2-deoxy-2-[ 18 F]fluoroarabinofuranosyl) cytosine, which is targeting the deoxyribonucleotide salvage pathway.…”

Tumor immune profiles noninvasively estimated by FDG PET with deep learning correlate with immunotherapy response in lung adenocarcinoma

“…In addition, metabolic interactions that occur in tumors and the microenvironment are becoming recognized as important in the anti-tumor immune reaction 16 . A previous study on FDG uptake patterns in primary and secondary lymphoid organs to stratify patients who receive immunotherapy also implicate potential role of FDG-PET in recognizing immune reaction in a patient 41 . Thus, we could assume that neural networks look at these complex metabolic profiles and interactions to define CytAct as a whole, though we should solve the issue of interpretability in the future.…”