Radionuclide Imaging of Cytotoxic Immune Cell Responses to Anti-Cancer Immunotherapy

• Published in: Biomedicines Vol. 10; no. 5; p. 1074
• Main Authors: Lauwerys, Louis, Smits, Evelien, Van den Wyngaert, Tim, Elvas, Filipe
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 05-05-2022; MDPI
• Subjects: Antigens; Apoptosis; biomarkers; Biopsy; Cancer; Cancer immunotherapy; Cancer therapies; CD8 antigen; Cell division; Clinical medicine; Computed tomography; Cytotoxicity; Effector cells; Genes; Immunotherapy; in vivo imaging; Labeling; Lymphocytes; Lymphocytes T; molecular imaging; Morphology; Natural killer cells; Patients; Positron emission tomography; Radiation; Review; Single photon emission computed tomography; T cell imaging; Tomography; in vivo imaging; exhaustion markers; biomarkers; immunotherapy; activation markers; cell imaging; T cell imaging; molecular imaging; positron emission tomography; oncology
• ISSN: 2227-9059; 2227-9059
• DOI: 10.3390/biomedicines10051074

Cancer immunotherapy is an evolving and promising cancer treatment that takes advantage of the body's immune system to yield effective tumor elimination. Importantly, immunotherapy has changed the treatment landscape for many cancers, resulting in remarkable tumor responses and improvements in patient survival. However, despite impressive tumor effects and extended patient survival, only a small proportion of patients respond, and others can develop immune-related adverse events associated with these therapies, which are associated with considerable costs. Therefore, strategies to increase the proportion of patients gaining a benefit from these treatments and/or increasing the durability of immune-mediated tumor response are still urgently needed. Currently, measurement of blood or tissue biomarkers has demonstrated sampling limitations, due to intrinsic tumor heterogeneity and the latter being invasive. In addition, the unique response patterns of these therapies are not adequately captured by conventional imaging modalities. Consequently, non-invasive, sensitive, and quantitative molecular imaging techniques, such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) using specific radiotracers, have been increasingly used for longitudinal whole-body monitoring of immune responses. Immunotherapies rely on the effector function of CD8
T cells and natural killer cells (NK) at tumor lesions; therefore, the monitoring of these cytotoxic immune cells is of value for therapy response assessment. Different immune cell targets have been investigated as surrogate markers of response to immunotherapy, which motivated the development of multiple imaging agents. In this review, the targets and radiotracers being investigated for monitoring the functional status of immune effector cells are summarized, and their use for imaging of immune-related responses are reviewed along their limitations and pitfalls, of which multiple have already been translated to the clinic. Finally, emerging effector immune cell imaging strategies and future directions are provided.