CD19-immunoPET for noninvasive visualization of CD19 expression in B-cell lymphoma patients

Cell- and antibody-based CD19-directed therapies have demonstrated great potential for treating B-cell non-Hodgkin lymphoma (B-NHL). However, all these approaches suffer from limited response rates and considerable toxicity. Until now, therapy decisions have been routinely based on histopathological CD19 staining of a single lesion at initial diagnosis or relapse, disregarding heterogeneity and temporal alterations in antigen expression. To visualize in vivo CD19 expression noninvasively, we radiolabeled anti-human CD19 monoclonal antibodies with copper-64 (64Cu-αCD19) for positron emission tomography (CD19-immunoPET). 64Cu-αCD19 specifically bound to subcutaneous Daudi xenograft mouse models in vivo. Importantly, 64Cu-αCD19 did not affect the anti-lymphoma cytotoxicity of CD19 CAR-T cells in vitro. Following our preclinical validation, 64Cu-αCD19 was injected into four patients with follicular lymphoma, diffuse large B-cell lymphoma or mantle zone lymphoma. We observed varying 64Cu-αCD19 PET uptake patterns at different lymphoma sites, both within and among patients, correlating with ex vivo immunohistochemical CD19 expression. Moreover, one patient exhibited enhanced uptake in the spleen compared to that in patients with prior B-cell-depleting therapy, indicating that 64Cu-αCD19 is applicable for identifying B-cell-rich organs. In conclusion, we demonstrated the specific targeting and visualization of CD19+ B-NHL in mice and humans by CD19-immunoPET. The intra- and interindividual heterogeneous 64Cu-αCD19 uptake patterns of lymphoma lesions indicate variability in CD19 expression, suggesting the potential of CD19-immunoPET as a novel tool to guide CD19-directed therapies.

Two birds with one stone: human SIRPα nanobodies for functional modulation and in vivo imaging of myeloid cells

Signal-regulatory protein α (SIRPα) expressed by myeloid cells is of particular interest for therapeutic strategies targeting the interaction between SIRPα and the "don't eat me" ligand CD47 and as a marker to monitor macrophage infiltration into tumor lesions. To address both approaches, we developed a set of novel human SIRPα (hSIRPα)-specific nanobodies (Nbs). We identified high-affinity Nbs targeting the hSIRPα/hCD47 interface, thereby enhancing antibody-dependent cellular phagocytosis. For non-invasive in vivo imaging, we chose S36 Nb as a non-modulating binder. By quantitative positron emission tomography in novel hSIRPα/hCD47 knock-in mice, we demonstrated the applicability of 64Cu-hSIRPα-S36 Nb to visualize tumor infiltration of myeloid cells. We envision that the hSIRPα-Nbs presented in this study have potential as versatile theranostic probes, including novel myeloid-specific checkpoint inhibitors for combinatorial treatment approaches and for in vivo stratification and monitoring of individual responses during cancer immunotherapies.

Acidosis-mediated increase in IFN-γ-induced PD-L1 expression on cancer cells as an immune escape mechanism in solid tumors

Immune checkpoint inhibitors have revolutionized cancer therapy, yet the efficacy of these treatments is often limited by the heterogeneous and hypoxic tumor microenvironment (TME) of solid tumors. In the TME, programmed death-ligand 1 (PD-L1) expression on cancer cells is mainly regulated by Interferon-gamma (IFN-γ), which induces T cell exhaustion and enables tumor immune evasion. In this study, we demonstrate that acidosis, a common characteristic of solid tumors, significantly increases IFN-γ-induced PD-L1 expression on aggressive cancer cells, thus promoting immune escape. Using preclinical models, we found that acidosis enhances the genomic expression and phosphorylation of signal transducer and activator of transcription 1 (STAT1), and the translation of STAT1 mRNA by eukaryotic initiation factor 4F (elF4F), resulting in an increased PD-L1 expression. We observed this effect in murine and human anti-PD-L1-responsive tumor cell lines, but not in anti-PD-L1-nonresponsive tumor cell lines. In vivo studies fully validated our in vitro findings and revealed that neutralizing the acidic extracellular tumor pH by sodium bicarbonate treatment suppresses IFN-γ-induced PD-L1 expression and promotes immune cell infiltration in responsive tumors and thus reduces tumor growth. However, this effect was not observed in anti-PD-L1-nonresponsive tumors. In vivo experiments in tumor-bearing IFN-γ-/- mice validated the dependency on immune cell-derived IFN-γ for acidosis-mediated cancer cell PD-L1 induction and tumor immune escape. Thus, acidosis and IFN-γ-induced elevation of PD-L1 expression on cancer cells represent a previously unknown immune escape mechanism that may serve as a novel biomarker for anti-PD-L1/PD-1 treatment response. These findings have important implications for the development of new strategies to enhance the efficacy of immunotherapy in cancer patients.

Advances in PET imaging of cancer

Molecular imaging has experienced enormous advancements in the areas of imaging technology, imaging probe and contrast development, and data quality, as well as machine learning-based data analysis. Positron emission tomography (PET) and its combination with computed tomography (CT) or magnetic resonance imaging (MRI) as a multimodality PET-CT or PET-MRI system offer a wealth of molecular, functional and morphological data with a single patient scan. Despite the recent technical advances and the availability of dozens of disease-specific contrast and imaging probes, only a few parameters, such as tumour size or the mean tracer uptake, are used for the evaluation of images in clinical practice. Multiparametric in vivo imaging data not only are highly quantitative but also can provide invaluable information about pathophysiology, receptor expression, metabolism, or morphological and functional features of tumours, such as pH, oxygenation or tissue density, as well as pharmacodynamic properties of drugs, to measure drug response with a contrast agent. It can further quantitatively map and spatially resolve the intertumoural and intratumoural heterogeneity, providing insights into tumour vulnerabilities for target-specific therapeutic interventions. Failure to exploit and integrate the full potential of such powerful imaging data may lead to a lost opportunity in which patients do not receive the best possible care. With the desire to implement personalized medicine in the cancer clinic, the full comprehensive diagnostic power of multiplexed imaging should be utilized.

In vivo imaging of CD8+ T cells in metastatic cancer patients: first clinical experience with simultaneous [89Zr]Zr-Df-IAB22M2C PET/MRI

Aim/Introduction: Despite the spectacular success of immune checkpoint inhibitor therapy (ICT) in patients with metastatic cancer, only a limited proportion of patients benefit from ICT. CD8⁺ cytotoxic T cells are important gatekeepers for the therapeutic response to ICT and are able to recognize MHC class I-dependent tumor antigens and destroy tumor cells. The radiolabeled minibody [⁸⁹Zr]Zr-Df-IAB22M2C has a high affinity for human CD8⁺ T cells and was successfully tested in a phase I study. Here, we aimed to gain the first clinical PET/MRI experience with the noninvasive assessment of the CD8⁺ T-cell distribution in cancer patients by in vivo [⁸⁹Zr]Zr-Df-IAB22M2C with a distinct focus of identifying potential signatures of successful ICT. Material and Methods: We investigated 8 patients with metastasized cancers undergoing ICT. Radiolabeling of Df-IAB22M2C with Zr-89 was performed according to Good Manufacturing Practice. Multiparametric PET/MRI was acquired 24 h after injection of 74.2±17.9 MBq [⁸⁹Zr]Zr-Df-IAB22M2C. We analyzed [⁸⁹Zr]Zr-Df-IAB22M2C uptake within the metastases and within primary and secondary lymphatic organs. Results: [⁸⁹Zr]Zr-Df-IAB22M2C injection was tolerated well without noticeable side effects. The CD8 PET/MRI data acquisitions 24 hours post-administration of [⁸⁹Zr]Zr-Df-IAB22M2C revealed good image quality with a relatively low background signal due to only low unspecific tissue uptake and marginal blood pool retention. Only two metastatic lesions showed markedly increased tracer uptake in our cohort of patients. Furthermore, we observed high interpatient variability in [⁸⁹Zr]Zr-Df-IAB22M2C uptake within the primary and secondary lymphoid organs. Four out of five ICT patients exhibited rather high [⁸⁹Zr]Zr-Df-IAB22M2C uptake in the bone marrow. Two of these four patients as well as two other patients yielded pronounced [⁸⁹Zr]Zr-Df-IAB22M2C uptake within nonmetastatic lymph nodes. Interestingly, cancer progression in ICT patients was associated with a relatively low [⁸⁹Zr]Zr-Df-IAB22M2C uptake in the spleen compared to the liver in 4 out of the 6 patients. Lymph nodes with enhanced [⁸⁹Zr]Zr-Df-IAB22M2C uptake revealed significantly reduced apparent diffusion coefficient (ADC) values in diffusion weighted MRI. Conclusion: Our first clinical experiences revealed the feasibility of [⁸⁹Zr]Zr-Df-IAB22M2C PET/MRI in assessing potential immune-related changes in metastases and primary and secondary lymphatic organs. According to our results, we hypothesize that alterations in [⁸⁹Zr]Zr-Df-IAB22M2C uptake in primary and secondary lymphoid organs might be associated with the response to ICT.

Abstract LB058: Imaging of CD8+ cytotoxic T-cells by Zr-89-Df-IAB22M2C PET/MRI: First clinical experience in patients with metastatic cancer

CD8+ cytotoxic T cells are key players in anti-cancer immune responses as they destroy MHC class I-dependent tumor cells. Therefore, the spatial distribution of CD8+ cytotoxic T cells might represent an important surrogate for the response to cancer immunotherapy including immune checkpoint inhibitor therapy ICT. The radiolabeled minibody [89Zr]Zr-Df-IAB22M2C is characterized by a high affinity to human CD8 and was already investigated in a phase I study. Here, we present our first experience with the non invasive in vivo assessment of the whole body CD8 T cell distribution in cancer patients using clinical [89Zr]Zr-Df-IAB22M2C PET/MRI. In total 8 patients with metastasized cancers (5 x malignant melanoma; 1 x choroidal melanoma, 1 x NSCLC and 1 x sarcoma) were studied before (n = 3) or during (n = 5) ICT. Multiparametric PET/MRI was performed 24 h after injection of 74.2±17.9 MBq [89Zr]Zr-Df-IAB22M2C (1.1 - 1.8 mg Df-IAB22M2C) on a Siemens Biograph mMR System (SiemensHealthineers, Erlangen, Germany). The whole body distribution of the [89Zr]Zr-Df-IAB22M2C tracer was analyzed with a special focus on tumors/metastases as well as primary and secondary lymphatic organs. The PET tracer [89Zr]Zr-Df-IAB22M2C was well tolerated without any reported side effects. The PET/MRI acquisitions 24h p.i. of [89Zr]Zr-Df-IAB22M2C revealed a comparably low background signal with only a minor blood pool and unspecific tissue retention. Regarding the primary and secondary lymphoid organs we observed a high interpatient variability of the tracer uptake. Four out of five patients with previous ICT exhibited a relatively high [89Zr]Zr-Df-IAB22M2C uptake in the bone marrow. Also a large number of non metastatic lymph nodes yielded a pronounced [89Zr]Zr-Df-IAB22M2C uptake in four patients. Strikingly, a low [89Zr]Zr-Df-IAB22M2C uptake in the spleen compared to the liver (liver/spleen ratio < 10) was observed in 4 out of the 5 patients with cancer progression during ICT. Interestingly, only one metastasis with an intense tracer was detected in this patient cohort. This first clinical experiences revealed the feasibility to assess potential immune-related changes by [89Zr]Zr-Df-IAB22M2C PET/MRI. Considering these results we hypothesize that the whole body distribution of CD8+ cytotoxic T-cells assessed by non-invasive in vivo [89Zr]Zr-Df-IAB22M2C PET/MRI might be associated with the response to cancer immunotherapy which needs to be investigated in subsequent prospective trials.

Citation Format: Johannes Schwenck, Dominik Sonanini, Walter Ehrlichmann, Gabriele Kienzle, Gerald Reischl, Pascal Krezer, Ian Wilson, Ron Korn, Irene Gonzalez-Menendez, Leticia Quintanilla-Martinez, Ferdinand Seith, Andrea Forschner, Thomas Eigentler, Lars Zender, Martin Röcken, Bernd Pichler, Lukas Flatz, Manfred Kneilling, Christian la Fougere. Imaging of CD8+ cytotoxic T-cells by Zr-89-Df-IAB22M2C PET/MRI: First clinical experience in patients with metastatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB058.

Translational immunoPET imaging using a radiolabeled GD2-specific antibody in neuroblastoma

Background: Antibodies targeting surface expressed disialoganglioside GD2 are increasingly used in neuroblastoma immunotherapy and might also have potential for use in radioimmunotherapy. As such targeted treatments might benefit from a dedicated theranostic approach, we studied the influence of radiolabeling on the binding characteristics of ch14.18 antibodies produced by Chinese hamster ovary (CHO) cells and evaluated the benefit of GD2-ImmunoPET as a potential tool for therapy planning.

Methods:⁶⁴Cu was used to reduce radiation burden, which is of high importance especially in a pediatric patient population. ⁶⁴Cu-labeling was accomplished using the chelators NOTA- or DOTAGA-NCS. Radiolabeled antibodies were characterized in vitro. [⁶⁴Cu]Cu-DOTAGA-ch14.18/CHO was studied in a neuroblastoma mouse model (subcutaneous CHP-134 xenografts). In vivo PET and MR images were acquired at 3 h, 24 h, and 48 h p.i. The specificity of binding was verified using GD2-negative tumors (HEK-293 xenografts), a control antibody and in vivo blocking. A first translational application was performed by PET/MRI in a patient with metastasized neuroblastoma.

Results: Radiolabeling at an antibody-to-chelator ratio ≥1:10 yielded a product with a radiochemical purity of ≥90% and a specific activity of 0.2-1.0 MBq/µg. Radiochelation was stable over 48 h in PBS, mouse serum or EDTA, and 50.8 ± 3.5% and 50.8 ± 2.0% of the radiolabeled conjugates, prepared at antibody-to-chelator ratios of 1:10 or 1:15, were immunoreactive. In vivo, highly specific accumulation (31.6 ± 5.8% ID/g) in neuroblastoma was shown preclinically. Clinical PET/MR scans using [⁶⁴Cu]Cu-NOTA-ch14.18/CHO (NOTA used for safety reasons) could visualize neuroblastoma metastases.

Conclusions:In vivo,⁶⁴Cu-labeled ch14.18/CHO is suitable for specific identification of neuroblastoma in PET. A first patient PET indicated the feasibility of the method for clinical translation and the potential utility in image-guided therapy.

Single-Domain Antibodies for Targeting, Detection, and In Vivo Imaging of Human CD4+ Cells

The advancement of new immunotherapies necessitates appropriate probes to monitor the presence and distribution of distinct immune cell populations. Considering the key role of CD4⁺ cells in regulating immunological processes, we generated novel single-domain antibodies [nanobodies (Nbs)] that specifically recognize human CD4. After in-depth analysis of their binding properties, recognized epitopes, and effects on T-cell proliferation, activation, and cytokine release, we selected CD4-specific Nbs that did not interfere with crucial T-cell processes in vitro and converted them into immune tracers for noninvasive molecular imaging. By optical imaging, we demonstrated the ability of a high-affinity CD4-Nb to specifically visualize CD4⁺ cells in vivo using a xenograft model. Furthermore, quantitative high-resolution immune positron emission tomography (immunoPET)/MR of a human CD4 knock-in mouse model showed rapid accumulation of ⁶⁴Cu-radiolabeled CD4-Nb1 in CD4⁺ T cell-rich tissues. We propose that the CD4-Nbs presented here could serve as versatile probes for stratifying patients and monitoring individual immune responses during personalized immunotherapy in both cancer and inflammatory diseases.

Low-dose total body irradiation facilitates antitumoral Th1 immune responses

CD4⁺ T helper cells are capable of mediating long-term antitumoral immune responses. We developed a combined immunotherapy (COMBO) using tumor antigen-specific T helper 1 cells (Tag-Th1), dual PD-L1/LAG-3 immune checkpoint blockade, and a low-dose total body irradiation (TBI) of 2 Gy, that was highly efficient in controlling the tumor burden of non-immunogenic RIP1-Tag2 mice with late-stage endogenous pancreatic islet carcinomas. In this study, we aimed to explore the impact of 2 Gy TBI on the treatment efficacy and the underlying mechanisms to boost CD4⁺ T cell-based immunotherapies. Methods: Heavily progressed RIP1-Tag2 mice underwent COMBO treatment and their survival was compared to a cohort without 2 Gy TBI. Positron emission tomography/computed tomography (PET/CT) with radiolabeled anti-CD3 monoclonal antibodies and flow cytometry were applied to investigate 2 Gy TBI-induced alterations in the biodistribution of endogenous T cells of healthy C3H mice. Migration and homing properties of Cy5-labeled adoptive Tag-Th1 cells were monitored by optical imaging and flow cytometric analyses in C3H and tumor-bearing RIP1-Tag2 mice. Splenectomy or sham-surgery of late-stage RIP1-Tag2 mice was performed before onset of COMBO treatment to elucidate the impact of the spleen on the therapy response. Results: First, we determined a significant longer survival of RIP1-Tag2 mice and an increased CD4⁺ T cell tumor infiltrate when 2 Gy TBI was applied in addition to Tag-Th1 cell PD-L1/LAG-3 treatment. In non-tumor-bearing C3H mice, TBI induced a moderate host lymphodepletion and a tumor antigen-independent accumulation of Tag-Th1 cells in lymphoid and non-lymphoid organs. In RIP1-Tag2, we found increased numbers of effector memory-like Tag-Th1 and endogenous CD4⁺ T cells in the pancreatic tumor tissue after TBI, accompanied by a tumor-specific Th1-driven immune response. Furthermore, the spleen negatively regulated T cell effector function by upregulation PD-1/LAG-3/TIM-3 immune checkpoints, providing a further rationale for this combined treatment approach. Conclusion: Low-dose TBI represents a powerful tool to foster CD4⁺ T cell-based cancer immunotherapies by favoring Th1-driven antitumoral immunity. As TBI is a clinically approved and well-established technique it might be an ideal addition for adoptive cell therapy with CD4⁺ T cells in the clinical setting.

Hydrojet-based delivery of footprint-free iPSC-derived cardiomyocytes into porcine myocardium

The reprogramming of patient´s somatic cells into induced pluripotent stem cells (iPSCs) and the consecutive differentiation into cardiomyocytes enables new options for the treatment of infarcted myocardium. In this study, the applicability of a hydrojet-based method to deliver footprint-free iPSC-derived cardiomyocytes into the myocardium was analyzed. A new hydrojet system enabling a rapid and accurate change between high tissue penetration pressures and low cell injection pressures was developed. Iron oxide-coated microparticles were ex vivo injected into porcine hearts to establish the application parameters and the distribution was analyzed using magnetic resonance imaging. The influence of different hydrojet pressure settings on the viability of cardiomyocytes was analyzed. Subsequently, cardiomyocytes were delivered into the porcine myocardium and analyzed by an in vivo imaging system. The delivery of microparticles or cardiomyocytes into porcine myocardium resulted in a widespread three-dimensional distribution. In vitro, 7 days post-injection, only cardiomyocytes applied with a hydrojet pressure setting of E20 (79.57 ± 1.44%) showed a significantly reduced cell viability in comparison to the cells applied with 27G needle (98.35 ± 5.15%). Furthermore, significantly less undesired distribution of the cells via blood vessels was detected compared to 27G needle injection. This study demonstrated the applicability of the hydrojet-based method for the intramyocardial delivery of iPSC-derived cardiomyocytes. The efficient delivery of cardiomyocytes into infarcted myocardium could significantly improve the regeneration.

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

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 CIT than in non-responders, and this relationship was independent of bone metastasis, even in the baseline scan. Conclusions: Thus, we are presenting the first translational study of solid tumors focusing on the metabolic patterns of primary and secondary lymphoid organs induced by the systemic immune response after CIT. We demonstrate that the widely available ¹⁸F-FDG-PET modality is an applicable translational tool that has high potential to stratify patients at an early time point.

The administration route of tumor-antigen-specific T-helper cells differentially modulates the tumor microenvironment and senescence

Cancer treatment with adoptively transferred tumor-associated antigen-specific CD4+ T-helper cells is a promising immunotherapeutic approach. In the pancreatic cancer model RIP-Tag2, the intraperitoneal (i.p.) application of Tag-specific TH1 cells exhibited a profound antitumoral efficiency. We investigated, whether an intravenous (i.v.) application of Tag-TH1 cells induces an equivalent therapeutic effect. Adoptively transferred fluorescent Tag-TH1 cells revealed a pronounced homing to the tumors after either i.p. or i.v. transfer, and both routes induced an almost equivalent therapeutic effect as demonstrated by magnetic resonance imaging, blood glucose level course and histology. The i.v. administration of Tag-TH1 cells induced p16INK4-positive/Ki67-negative tumor senescence more efficiently than i.p. administration. Both routes replenish host CD4+ T cells by transferred T cells and recruitment of B and dendritic cells to the tumors while reducing CD8+ T cells and depleting macrophages. Both administration routes efficiently induced a similar antitumoral efficiency despite the pronounced senescence induction after i.v. administration. Thus, a combinatory i.v./i.p. injection of therapeutic cells might overcome limitations of the individual routes and improve therapeutic efficacy in solid tumors.

The yin and yang of imaging tumor associated macrophages with PET and MRI

Tumor associated macrophages (TAM) are key players in the cancer microenvironment. Molecular imaging modalities such as MRI and PET can be used to track and monitor TAM dynamics in tumors non-invasively, based on specific uptake and quantification of MRI-detectable nanoparticles or PET-detectable radiotracers. Particular molecular signatures can be leveraged to target anti-inflammatory TAM, which support tumor growth, and pro-inflammatory TAM, which suppress tumor growth. In addition, TAM-directed imaging probes can be designed to include immune modulating properties, thereby leading to combined diagnostic and therapeutic (theranostic) effects. In this review, we will discuss the complementary role of TAM-directed radiotracers and iron oxide nanoparticles for monitoring cancer immunotherapies with PET and MRI technologies. In addition, we will outline how TAM-directed imaging and therapy is interdependent and can be connected towards improved clinical outcomes

Abstract 658: Translational theranostic imaging of lymphoma using radiolabeled αCD19-antibodies

CD19 proved to be an excellent target in B cell leukemia and lymphoma, especially in patients, refractory or not eligible to αCD20 monoclonal antibody (mAb) therapy. With the CD3-CD19 bispecific mAb Blinatumumab and αCD19 chimeric antigen receptor (CAR) T cells, two promising therapeutics have recently found their way into clinical application with impressive results. However, therapy decisions are mainly based on histological CD19 staining at initial diagnosis disregarding tumor heterogeneity and temporal expression alterations. To address these limitations, Theranostic Imaging approaches using radiolabeled antibodies are emerging tools to advance targeted cancer therapies. Positron-Emission-Tomography (PET) enables non-invasive whole-body visualization of specific target expression perfectly suitable for therapy stratification and to monitor response to targeted drugs. Furthermore, by following antibody biodistribution and tumor targeting in vivo over time modes of action and resistance mechanisms can be uncovered. We here report on the generation, preclinical characterization, and clinical evaluation of a radiolabeled αCD19 antibody for Theranostic Imaging of Non-Hodgkin lymphoma (NHL). Fc-optimized αCD19-mAb (4G7SDIE) with enhanced antibody-dependent cell cytotoxicity was manufactured at our university and successfully tested to treat minimal residual disease of childhood acute lymphoblastic leukemia. For Theranostic Imaging, this antibody was chelator conjugated with DOTAGA at an antibody-to-chelator ratio of 1:15. Radiolabeling with Copper-64 (64Cu) yielded radiochemical purity of >90 %. For clinical application, the radioimmunoconjugate was produced in accordance to GMP. In vitro cell labeling studies revealed specific binding to the target cells and immunoreactive fraction was 30 % after radiolabeling. Three different xenograft NHL mouse models were established in CD1 nude mice for in vivo imaging studies. PET/MRI was performed 6 h, 24 h, and 48 h after i.v. injection confirming specific targeting of 64Cu-DOTAGA-αCD19-mAb compared to CD19-negative tumors. Administration of the radioimmunoconjugate was then carried out in four NHL patients based on compassionate use program to evaluate eligibility of CD19-targeted therapy. Cervical, mediastinal, and abdominal lymphoma sites as well as bone marrow infiltration were detected by PET. Limited uptake was observed in some lesions including bulk tumors indicating partly insufficient amount of injected antibody. To our knowledge, we demonstrate for the first time the feasibility of a radiolabeled αCD19-mAb for lymphoma targeting in human. This theranostic approach might serve as a novel tool to predict response to upcoming CD19-targeting therapies including antibody-based or CAR T cell therapies. Further clinical studies will follow to test optimal dose regime and predosing strategies for enhanced tumor targeting.

Citation Format: Dominik Sonanini, Johannes Schwenck, Julia Schmitt, Andreas Maurer, Sergios Gatidis, Christian Seitz, Gerald Reischl, Manfred Kneilling, Gundram Jung, Peter Lang, Lothar Kanz, Konstantin Nikolaou, Rupert Handgretinger, Christian la Fougère, Bernd J. Pichler. Translational theranostic imaging of lymphoma using radiolabeled αCD19-antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 658.

Abstract LB-105: Combining CD4+ T cell transfer and immune checkpoint blockade demonstrates the power of combined immunotherapies for treatment of progressed solid carcinomas in mice

Tumor and immune cells express inhibitory immune checkpoints (ICP) that paralyze tumor infiltrating T cells. ICP-specific antibodies (mAbs) can block and restore T cell functions and promote anti-tumoral effects. Also, tumor-antigen specific IFN-y secreting CD4+ T cells (TA-Th1) mediate strong anti-tumoral effects and can induce senescence in cancer cells. Here, we report on the development and immunological characterization of a highly efficient TA-Th1 and checkpoint-inhibitor based combined immunotherapy (CIT) in a progressed endogenous cancer model. Mice bearing progressed pancreatic islet carcinomas (RIP1-Tag2) and symptomatic low blood glucose levels (BGL; ~80 mg/dl) were treated weekly with TA-Th1 and αPD-L1+αLAG-3 mAbs (PDL1/LAG3) after an initial preparative 2 Gy-whole body radiation. Therapy was monitored by BGL measurements. Additionally, we conducted baseline and follow-up 18F-FDG PET/MRI scans to uncover the splenic glucose metabolism as a consequence of immune cell activation. We performed ex vivo flow cytometry (FC), immunohistochemistry (IHC), and fluorescent microscopy (FM) of tumor tissue and lymphatic organs at early (1 wk) and late (3-4 wks; endpoint of SHAM treated mice) time point of treatment focusing on the immune cell composition, activation patterns and senescence induction. Treatment exclusively with TA-Th1 prolonged the median survival of the mice from 14 to 18 wks (n=14) while ICP blockade without TA-Th1 cells was not efficient at all (PDL1/LAG3; median survival=14wks, n=11). The combination of TA-Th1 and PDL1/LAG3 (CIT) was highly efficient and significantly extended the median survival to 20 wks (n=15, p=0.001). Thus, exclusively CIT-treated mice revealed very small tumors and a strong lymphocytic infiltrate. FC analysis demonstrated early and specific homing of highly activated (CD69) TA-Th1 into the draining LN without impairment of the endogenous CD8+ T cell population. After 4 wks of treatment, we determined an increase in endogenous effector CD4+ and CD8+ T cells exclusively in mice receiving TA-Th1, indicating cross-priming as a possible mechanism of T cell activation. Analysis of p16/Ki67 expression in tumors revealed a strongly enhanced p16 and reduced Ki67 expression exclusively in CIT-treated mice indicating tumor senescence which was not observed in control groups. 18F-FDG-PET/MRI of the spleen showed a significantly increased glucose metabolism in CIT treated mice when compared to SHAM-treatment. In conclusion, our newly developed CIT (2 Gy+TA-Th1+PDL1/LAG3) strongly promoted an anti-tumor immune response in mice with progressed solid cancer. Most importantly, only CIT was able to induce TA-Th1 mediated tumor senescence whereas TA-Th1 or PDL1/LAG3 mAbs alone were inefficient. Moreover, 18F-FDG-PET/MRI of the spleen might represent a novel powerful tool to stratify ICP-blocked responders. Thus, ICP-blockade is applicable to reinforce Th1-cell based immunotherapies and to prolong the lifespan of mice with progressed solid carcinomas.

Citation Format: Barbara F. Schörg, Dominik Sonanini, Johannes Schwenck, Christoph Griessinger, Birgit Fehrenbacher, Martin Schaller, Ursula Kohlhofer, Leticia Quintanilla-Martinez, Christian La Fourgère, Martin Röcken, Bernd J. Pichler, Manfred Kneilling. Combining CD4+ T cell transfer and immune checkpoint blockade demonstrates the power of combined immunotherapies for treatment of progressed solid carcinomas in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-105.