Preclinical PET imaging of bispecific antibody ERY974 targeting CD3 and glypican 3 reveals that tumor uptake correlates to T cell infiltrate

Molecular Imaging of B7-H3-Targeting Bispecific T Cell-Engaging Antibody MGD009 in Glioblastoma Models

Adults diagnosed with glioblastoma (GBM) face an extremely poor prognosis; it is the most aggressive and fatal form of a primary brain tumor. The development of CD3-targeting bispecific antibodies (CD3-bsAbs) has recently gained attention as a promising therapeutic approach for GBM. MGD009, a CD3-bsAb, promotes T-cell-mediated cancer cell death by linking B7-H3 on tumor cells with CD3ε on T cells. The efficacy and relative toxicity of this treatment are closely associated with the tumor uptake and metabolic profile of major organs. However, limited data on the biodistribution and GBM targeting of MGD009 have been reported. In this study, surface plasmon resonance (SPR), flow cytometry, and immunofluorescence assays were carried out to assess the in vitro binding affinities of MGD009 with glioma cells. MGD009 was also labeled with a near-infrared fluorescent dye to evaluate its tumor targeting capacity and biodistribution in subcutaneous GBM models. Moreover, MGD009 was labeled with PET isotope zirconium-89 (89Zr) to facilitate noninvasive molecular imaging in subcutaneous and orthotopic GBM models. The fluorescence intensity of Cy5.5-labeled MGD009 peaked at 24 h postinjection (p.i.), with a radiant efficiency of 8.98 × 109 D/s/cm2/sr and a prolonged retention time up to 120 h. Tumor uptake of 89Zr-labeled MGD009 peaked at 24 h p.i., with an uptake value of 10.77 ± 1.43% ID/g. In orthotopic U-87MG models, tumor uptake of 89Zr-labeled MGD009 reached 18.10 ± 0.87% ID/g at 24 h p.i. Additionally, the liver, spleen, and bone marrow also showed a relatively high radioactivity. These findings provide critical insights into the biodistribution and tumor-targeting of MGD009, supporting its potential clinical application in glioblastoma treatment.

Construction of Bispecific T-Cell Engager Radiotracer and Its Micro-PET Evaluation in Pancreatic Cancer

Mucin 17 (MUC17), a transmembrane mucin, is overexpressed in pancreatic cancer and is associated with tumor proliferation and metastasis. CD3 is an indispensable molecule on the surface of T lymphocytes, which is associated with T cell activation and participates in immune responses. Here, we developed a bispecific T-cell engager radiotracer, 89Zr-M17C3, targeting MUC17 and CD3, to enable noninvasive PET imaging of both tumor cells and T-cell infiltration in pancreatic cancer. 89Zr-M17C3 was synthesized by conjugating AMG199 with zirconium-89 and verified for its radiochemical purity and in vitro stability. The 89Zr-M17C3 probe demonstrated excellent radiochemical purity (>99%) and stability (maintained ≥99% over 120 h). Cellular uptake assays and binding affinity studies were conducted to evaluate the probe's specificity for MUC17 and CD3. Micro-PET/CT imaging and biodistribution studies were performed in MUC17-expressing nude mice and CD3 humanized mice to assess probe uptake in tumors and T-cell-infiltrated tissues. In MUC17-expressing AsPC-1 tumors, probe uptake was significantly higher than in MUC17-negative PANC-1 tumors (SUVmax: 2.26 ± 0.18 vs 1.13 ± 0.14, P < 0.001) and was confirmed to be MUC17-dependent through blocking studies. In CD3 humanized mice, the probe was able to visualize both T-cell infiltration and MUC17-positive tumors, with peak uptake in AsPC-1 tumors (SUVmax: 2.35 ± 0.46) and spleen (SUVmax: 2.19 ± 0.40) at 216 h. Immunohistochemical analysis confirmed the spatial correlation between MUC17 expression and CD3-positive T-cell infiltration in AsPC-1 tumors but not in PANC-1 tumors. In summary, the 89Zr-M17C3 radiotracer exhibited high affinity for MUC17 and CD3 and successfully differentiated MUC17-positive tumors from MUC17-negative tumors while simultaneously providing insight into the T-cell distribution. This study highlights the potential of 89Zr-M17C3 as a versatile imaging tool to support patient stratification and therapeutic monitoring in tumor-targeted immunotherapy, particularly for bispecific T-cell engager-based approaches such as AMG199.

Radiopharmaceuticals and their applications in medicine

Radiopharmaceuticals involve the local delivery of radionuclides to targeted lesions for the diagnosis and treatment of multiple diseases. Radiopharmaceutical therapy, which directly causes systematic and irreparable damage to targeted cells, has attracted increasing attention in the treatment of refractory diseases that are not sensitive to current therapies. As the Food and Drug Administration (FDA) approvals of [177Lu]Lu-DOTA-TATE, [177Lu]Lu-PSMA-617 and their complementary diagnostic agents, namely, [68Ga]Ga-DOTA-TATE and [68Ga]Ga-PSMA-11, targeted radiopharmaceutical-based theranostics (radiotheranostics) are being increasingly implemented in clinical practice in oncology, which lead to a new era of radiopharmaceuticals. The new generation of radiopharmaceuticals utilizes a targeting vector to achieve the accurate delivery of radionuclides to lesions and avoid off-target deposition, making it possible to improve the efficiency and biosafety of tumour diagnosis and therapy. Numerous studies have focused on developing novel radiopharmaceuticals targeting a broader range of disease targets, demonstrating remarkable in vivo performance. These include high tumor uptake, prolonged retention time, and favorable pharmacokinetic properties that align with clinical standards. While radiotheranostics have been widely applied in tumor diagnosis and therapy, their applications are now expanding to neurodegenerative diseases, cardiovascular diseases, and inflammation. Furthermore, radiotheranostic-empowered precision medicine is revolutionizing the cancer treatment paradigm. Diagnostic radiopharmaceuticals play a pivotal role in patient stratification and treatment planning, leading to improved therapeutic outcomes in targeted radionuclide therapy. This review offers a comprehensive overview of the evolution of radiopharmaceuticals, including both FDA-approved and clinically investigated agents, and explores the mechanisms of cell death induced by radiopharmaceuticals. It emphasizes the significance and future prospects of theranostic-based radiopharmaceuticals in advancing precision medicine.

Integrated Imaging Probe and Bispecific Antibody Development Enables In Vivo Targeting of Glypican-3-Expressing Hepatocellular Carcinoma

Glypican-3 (GPC3) is a proteoglycan with high sensitivity and specificity for hepatocellular carcinoma (HCC). We describe the integrated development and validation of a GPC3-targeting optical imaging probe and T cell-redirecting antibody (TRAB) as a theranostic strategy for the detection and treatment of HCC. A novel TRAB targeting GPC3 on HCC tumor cells and the CD3 T-cell receptor as well as a distinct GPC3-specific optical imaging probe were developed from a short peptide. The efficacy of GPC3/CD3 TRAB was evaluated in vitro using IFNγ release and calcein-AM assays. Patient-derived xenografts were used to assess the in vivo efficacy of GPC3/CD3 TRAB and the GPC3 imaging probe for the detection of GPC3+ HCC. GPC3/CD3 TRAB caused a dose-dependent escalation in IFNγ release from inactive peripheral blood T cells (P = 0.001) and higher tumor-cell lysis (P = 0.01) compared with controls in vitro. Intratumorally injected GPC3/CD3 TRAB resulted in significant prolongation of tumor doubling time in the GPC3+ tumors, with an associated reduction of tumor fluorescent signal from the HiLyte 488-conjugated GPC3-specific peptide on optical imaging. These data demonstrate that HCC cell targeting using a GPC3/CD3 TRAB derived from a small peptide enabled effective T-cell activation and induction of a cytotoxic response toward GPC3+ HCC tumor cells both in vitro and in vivo. GPC3-specific optical imaging enabled the detection of the GPC3+ HCC cells and noninvasive monitoring of tumor response to adoptive immunotherapy. The integrated development of a targeted therapeutic and molecular imaging probe provides a promising paradigm for the development of cancer theranostics.

Molecular imaging supports the development of multispecific cancer antibodies

Multispecific antibodies are engineered antibody derivatives that can bind to two or more distinct epitopes or antigens. Unlike mixtures of monospecific antibodies, the binding properties of multispecific antibodies enable two specific molecules to be physically linked, a characteristic with important applications in cancer therapy. The field of multispecific antibodies is highly dynamic and expanding rapidly; to date, 15 multispecific antibodies have been approved for clinical use, of which 11 were approved for oncological indications, and more than 100 new antibodies are currently in clinical development. Nevertheless, substantial challenges limit the applications of multispecific antibodies in cancer therapy, particularly inefficient targeting of solid tumours and substantial adverse effects. Both PET and single photon emission CT imaging can reveal the biodistribution and complex pharmacology of radiolabelled multispecific antibodies. This Review summarizes the insights obtained from preclinical and clinical molecular imaging studies of multispecific antibodies, focusing on their structural properties, such as molecular weight, shape, target specificity, affinity and avidity. The opportunities associated with use of molecular imaging studies to support the clinical development of multispecific antibody therapies are also highlighted.

Construction and preclinical evaluation of a 124I-labelled bispecific antibody targeting PD-L1 and PD-L2

PURPOSE

NB12 is a bispecific antibody that consists of two anti-programmed cell death-ligand 1 (PD-L1) nanobodies and two anti-programmed cell death-ligand 2 (PD-L2) nanobodies. The aim of this study was to design a novel tracer, [124I]I-NB12, targeting PD-L1/2 and perform preclinical evaluations to dynamically monitor PD-L1/2 expression for determining cancer patient responsiveness to ICI therapy.

METHODS

NB12 was labelled with the radionuclide 124I at room temperature (RT). An in vitro binding assay was performed to assess the affinity of [124I]I-NB12 for PD-L1 and PD-L2. Cellular uptake, pharmacokinetic, and biodistribution experiments were performed to evaluate the biological properties. Micro-PET/CT imaging with [124I]I-NB12 was conducted at different time points. Immunohistochemical and haematoxylin and eosin (HE) staining experiments were carried out using tumour tissues. Routine blood, biochemical indices and major organ pathology were used to evaluate the biosafety of the tracers.

RESULTS

The radiochemical yield of [124I]I-NB12 was 84.62 ± 3.90%, and the radiochemical purity (RCP) was greater than 99%. [124I]I-NB12 had a high affinity for the PD-L1 (Kd = 19.82 nM) and PD-L2 (Kd = 2.93 nM). Cellular uptake experiments confirmed that the uptake of [124I]I-NB12 by A549-PDL1/2 cells was greater than that by A549 cells. The half-lives of the distribution phase and elimination phase were 0.26 h and 4.08 h, respectively. Micro-PET/CT showed significant [124I]I-NB12 uptake in the tumour region of A549-PDL1/2 tumour-bearing mice compared with A549 tumour-bearing mice 24 h postinjection. Immunohistochemical and HE staining experiments confirmed that tumour-bearing mice was successfully constructed.

CONCLUSION

We constructed a bispecific antibody that targets PD-L1 and PD-L2, namely, [124I]I-NB12. Biological evaluation revealed its specificity and affinity for PD-L1/2, and micro-PET/CT confirmed the feasibility of visualizing tumour PD-L1/2 in vivo. Using [124I]I-NB12 may be a promising strategy for identifying cancer patients that can potentially benefit from ICI therapy.

Nuclear Imaging of Bispecific Antibodies on the Rise

Bispecific antibodies (bsAbs) are engineered to target 2 different epitopes simultaneously. About 75% of the 16 clinically approved bsAbs have entered the clinic internationally since 2022. Hence, research on biomedical imaging of various radiolabeled bsAb scaffolds may serve to improve patient selection for bsAb therapy. Here, we provide a comprehensive overview of recent advances in radiolabeled bsAbs for imaging via PET or SPECT. We compare direct targeting and pretargeting approaches in preclinical and clinical studies in oncologic research. Furthermore, we show preclinical applications of imaging bsAbs in neurodegenerative diseases. Finally, we offer perspectives on the future directions of imaging bsAbs based on their challenges and opportunities.

Recent Trends in Diagnostic Biomarkers of Tumor Microenvironment

The tumor microenvironment (TME) play critical roles in tumor survival, progression, and metastasis and can be considered potential targets for molecular imaging of cancer. The targeting agents for imaging of TME components (e.g., fibroblasts, mesenchymal stromal cells, immune cells, extracellular matrix, blood vessels) provide a promising strategy to target these biomarkers for the early diagnosis of cancers. Moreover, various cancer types have similar tumor immune microenvironment (TIME) features that targeting those biomarkers and offer clinically translatable molecular imaging of cancers. In this review, we categorize and summarize the components in TME which have been targeted for molecular imaging. Moreover, this review updated the recent progress in targeted imaging of TIME biological molecules by various modalities for the early detection of cancer.

Combination of T cell-redirecting bispecific antibody ERY974 and chemotherapy reciprocally enhances efficacy against non-inflamed tumours

Identifying a strategy with strong efficacy against non-inflamed tumours is vital in cancer immune therapy. ERY974 is a humanized IgG4 bispecific T cell-redirecting antibody that recognizes glypican-3 and CD3. Here we examine the combination effect of ERY974 and chemotherapy (paclitaxel, cisplatin, and capecitabine) in the treatment of non-inflamed tumours in a xenograft model. ERY974 monotherapy shows a minor antitumour effect on non-inflamed NCI-H446 xenografted tumours, as infiltration of ERY974-redirected T cells is limited to the tumour-stromal boundary. However, combination therapy improves efficacy by promoting T cell infiltration into the tumour centre, and increasing ERY974 distribution in the tumour. ERY974 increases capecitabine-induced cytotoxicity by promoting capecitabine conversion to its active form by inducing thymidine phosphorylase expression in non-inflamed MKN45 tumour through ERY974-induced IFNγ and TNFα in T cells. We show that ERY974 with chemotherapy synergistically and reciprocally increases antitumour efficacy, eradicating non-inflamed tumours.

Novel Nanotechnology Approaches to Overcome Drug Resistance in the Treatment of Hepatocellular Carcinoma: Glypican 3 as a Useful Target for Innovative Therapies

Hepatocellular carcinoma (HCC) is the second most lethal tumor, with a 5-year survival rate of 18%. Early stage HCC is potentially treatable by therapies with curative intent, whereas chemoembolization/radioembolization and systemic therapies are the only therapeutic options for intermediate or advanced HCC. Drug resistance is a critical obstacle in the treatment of HCC that could be overcome by the use of targeted nanoparticle-based therapies directed towards specific tumor-associated antigens (TAAs) to improve drug delivery. Glypican 3 (GPC3) is a member of the glypican family, heparan sulfate proteoglycans bound to the cell surface via a glycosylphosphatidylinositol anchor. The high levels of GPC3 detected in HCC and the absence or very low levels in normal and non-malignant liver make GPC3 a promising TAA candidate for targeted nanoparticle-based therapies. The use of nanoparticles conjugated with anti-GPC3 agents may improve drug delivery, leading to a reduction in severe side effects caused by chemotherapy and increased drug release at the tumor site. In this review, we describe the main clinical features of HCC and the common treatment approaches. We propose the proteoglycan GPC3 as a useful TAA for targeted therapies. Finally, we describe nanotechnology approaches for anti-GPC3 drug delivery systems based on NPs for HCC treatment.

Imaging ligands targeting glypican-3 receptor expression in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality. Early detection of HCC is important since potentially curative therapies exist in the initial stages of HCC; no curative therapies exist for late-stage HCC. However, the initial detection of HCC remains challenging due to the lack of symptoms during the early stage of the disease. Other methods of screening and detecting HCC, including blood serum tests and conventional imaging methods, remain inadequate due to genetic differences between patients and the high background activity of liver tissues. Thus, there is a need for an accurate imaging agent for the diagnosis, staging, and prognosis of HCC. Glypican-3 (GPC3) is an oncofetal receptor responsible for regulating cell division, growth, and survival. GPC3 is a clinically relevant biomarker for imaging and therapeutics, as its expression is HCC tumor-specific and absent from normal and other pathological liver tissues. The development of novel GPC3-targeting imaging agents has encompassed three classes of biomolecules: peptides, antibodies, and aptamers. These biomolecules serve as constructs for diagnostic imaging (demonstrating potential as positron emission tomography [PET], single-photon emission tomography [SPECT], and optical imaging agents) and HCC treatment delivery. More than 20 unique ligands have been identified in the literature as showing specificity for the GPC3 receptor. Although several ligands are currently under clinical investigation as therapies for HCC, clinical translation of GPC3-targeting ligands as imaging agents is lacking. This review highlights the current landscape of ligands targeting GPC3 and describes their promising possibilities as imaging agents for HCC.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Imaging immunity in patients with cancer using positron emission tomography

Immune checkpoint inhibitors and related molecules can achieve tumour regression, and even prolonged survival, for a subset of cancer patients with an otherwise dire prognosis. However, it remains unclear why some patients respond to immunotherapy and others do not. PET imaging has the potential to characterise the spatial and temporal heterogeneity of both immunotherapy target molecules and the tumor immune microenvironment, suggesting a tantalising vision of personally-adapted immunomodulatory treatment regimens. Personalised combinations of immunotherapy with local therapies and other systemic therapies, would be informed by immune imaging and subsequently modified in accordance with therapeutically induced immune environmental changes. An ideal PET imaging biomarker would facilitate the choice of initial therapy and would permit sequential imaging in time-frames that could provide actionable information to guide subsequent therapy. Such imaging should provide either prognostic or predictive measures of responsiveness relevant to key immunotherapy types but, most importantly, guide key decisions on initiation, continuation, change or cessation of treatment to reduce the cost and morbidity of treatment while enhancing survival outcomes. We survey the current literature, focusing on clinically relevant immune checkpoint immunotherapies, for which novel PET tracers are being developed, and discuss what steps are needed to make this vision a reality.

PET imaging of VEGFR and integrins in glioma tumor xenografts using 89Zr labelled heterodimeric peptide

Vascular endothelial growth factor receptor (VEGFR) and integrin αv are over-expressed in angiogenesis of variety malignant tumors with key roles in angiogenesis, and have been proven as valuable targets for cancer imaging and treatment. In this study, a heterodimeric peptide targeting VEGFR and integrin was designed, and radiolabeled with zirconium-89 (⁸⁹Zr) for PET imaging of glioma. ⁸⁹Zr-DFO-heterodimeric peptide, a the newly developed probe, was prepared with radiochemical yield of 88.7 ± 2.4%. Targeted binding capability of ⁸⁹Zr-DFO-heterodimeric peptide towards U87MG cells was investigated in murine glioma xenograft models, which shows that the designed probe has good binding ability to both targeting sites. Biodistribution indicated that kidney metabolism is the main pathway and tumor uptake of ⁸⁹Zr-DFO-heterodimeric peptide reached the peak of 0.62 ± 0.10% ID/g . U87MG xenograft could be clearly visualized by microPET/CT imaging through 1 to 3 h post-injection of ⁸⁹Zr-DFO-heterodimeric peptide. Importantly, the tumor radiouptake was significantly reduced after blocking, and the imaging effect of this radioactive compound was more obvious than that of monomeric peptide probes. ⁸⁹Zr-DFO-heterodimeric peptide has been demonstrated to show potential as a new radiopharmaceutical probe towards glioma, and multi-target probes do have advantages in tumor imaging.

Far-Red Light Triggered Production of Bispecific T Cell Engagers (BiTEs) from Engineered Cells for Antitumor Application

Bispecific T-cell engagers (BiTEs), which have shown potent antitumor activity in humans, are emerging as one of the most promising immunotherapeutic strategies for cancer treatment in recent years. However, the clinical application of BiTEs nowadays has been hampered by their short half-life in the circulatory system due to their low molecular weight and rapid renal clearance. Inevitable continuous infusion of BiTEs has become a routine operation in order to achieve effective treatment, although it is costly, inconvenient, time-consuming, and even painful for patients in some cases. To develop an on-demand, tunable, and reversible approach to overcome these limitations, we assembled a transcription-control device into mammalian cells based on a bacterial far-red light (FRL) responsive signaling pathway to drive the expression of a BiTE against Glypican 3 (GPC3), which is a highly tumor-specific antigen expressed in most hepatocellular carcinomas (HCC). As demonstrated in in vitro experiments, we proved that the FRL sensitive device spatiotemporally responded to the control of FRL illumination and produced a therapeutic level of BiTEs that recruited and activated human T cells to eliminate GPC3 positive tumor cells. By functionally harnessing the power of optogenetics to remotely regulate the production of BiTEs from bioengineered cells and demonstrating its effectiveness in treating tumor cells, this study provides a novel approach to achieve an in vivo supply of BiTEs, which could be potentially applied to other formats of bispecific antibodies and facilitate their clinical applications.

Combination Therapy of Hepatocellular Carcinoma by GPC3-Targeted Bispecific Antibody and Irinotecan is Potent in Suppressing Tumor Growth in Mice

Hepatocellular carcinoma (HCC) is a world leading cause of cancer-related mortality, and currently no curative treatment for advanced HCC is available. Glypican-3 (GPC3) is an attractive target for HCC immunotherapy. This study explored the efficacy of six GPC3-targeted bispecific antibodies, alone or in combination with chemotherapeutic drug Irinotecan, for the treatment of HCC. The bispecific antibodies were constructed using three different structures, knob-into-hole (KH), scFv-scFv-hFc, and scFv-hFc-scFv, where CD3-targeting mAb OKT3 (scFv) was paired with two representative GPC3 mAbs hYP7 (scFv) and HN3 (VH only) that target different epitopes. The In vitro cell killing assay revealed that all bispecific antibodies efficiently killed GPC3 positive cancer cells, with hYP7-KH, hYP7-OKT3-hFc, and HN3-KH being most potent. In vivo xenograft mouse studies demonstrated that all bispecific antibodies suppressed tumor growth similarly, with hYP7-OKT3-hFc performing slightly better. Combination of hYP7-OKT3-hFc with Irinotecan dramatically improved the efficacy and arrested tumor growth of HepG2, Hep3B, and G1 in xenograft mice. Our results demonstrated that the cell surface proximal bispecific antibody hYP7-OKT3-hFc was superior in terms of potency and the GPC3-targeted bispecific antibody combined with Irinotecan was much potent to control HCC growth.

Identification of a Glypican-3 Binding Peptide From a Phage-Displayed Peptide Library for PET Imaging of Hepatocellular Carcinoma

Tumor-targeting peptides functioned as molecular probes are essential for multi-modality imaging and molecular-targeting therapy in caner theronostics. Here, we performed a phage-displayed bio-panning to identify a specific binding peptide targeting Glypican-3 (GPC-3), a promising biomarker in hepatocellular carcinoma (HCC). After screening in the cyclic peptide library, a candidate peptide named F3, was isolated and showed specific binding to HCC cell lines. In a bio-distribution study, higher accumulation of F3 peptide was observed in HepG-2 tumors compared to PC-3 tumors in xenograft models. After labeling with radioactive ⁶⁸Ga, the F3 peptide tracer enabled the specific detection of tumors in HCC tumor models with PET imaging. More importantly, the expression of GPC-3 in human tissue samples may be distinguished by an F3 fluorescent peptide probe indicating its potential for clinical application. This cyclic peptide targeting GPC-3 has been validated, and may be an alternative to serve as an imaging probe or a targeting domain in the drug conjugate.

Next Generation Imaging Techniques to Define Immune Topographies in Solid Tumors

In recent years, cancer immunotherapy experienced remarkable developments and it is nowadays considered a promising therapeutic frontier against many types of cancer, especially hematological malignancies. However, in most types of solid tumors, immunotherapy efficacy is modest, partly because of the limited accessibility of lymphocytes to the tumor core. This immune exclusion is mediated by a variety of physical, functional and dynamic barriers, which play a role in shaping the immune infiltrate in the tumor microenvironment. At present there is no unified and integrated understanding about the role played by different postulated models of immune exclusion in human solid tumors. Systematically mapping immune landscapes or "topographies" in cancers of different histology is of pivotal importance to characterize spatial and temporal distribution of lymphocytes in the tumor microenvironment, providing insights into mechanisms of immune exclusion. Spatially mapping immune cells also provides quantitative information, which could be informative in clinical settings, for example for the discovery of new biomarkers that could guide the design of patient-specific immunotherapies. In this review, we aim to summarize current standard and next generation approaches to define Cancer Immune Topographies based on published studies and propose future perspectives.

Current Perspectives on 89Zr-PET Imaging

⁸⁹Zr is an emerging radionuclide that plays an essential role in immuno-positron emission tomography (PET) imaging. The long half-life of ⁸⁹Zr (t_1/2 = 3.3 days) is favorable for evaluating the in vivo distribution of monoclonal antibodies. Thus, the use of ⁸⁹Zr is promising for monitoring antibody-based cancer therapies. Immuno-PET combines the sensitivity of PET with the specificity of antibodies. A number of studies have been conducted to investigate the feasibility of ⁸⁹Zr immuno-PET imaging for predicting the efficacy of radioimmunotherapy and antibody therapies, imaging target expression, detecting target-expressing tumors, and the monitoring of anti-cancer chemotherapies. In this review, we summarize the current status of PET imaging using ⁸⁹Zr in both preclinical and clinical studies by highlighting the use of immuno-PET for the targets of high clinical relevance. We also present ⁸⁹Zr-PET applications other than immuno-PET, such as nanoparticle imaging and cell tracking. Finally, we discuss the limitations and the ongoing research being performed to overcome the remaining hurdles.