The Potential of <i>In Vivo</i> Imaging for Optimization of Molecular and Cellular Anti-cancer Immunotherapies

This review aims to emphasize the potential of in vivo imaging to optimize current and upcoming anti-cancer immunotherapies: spanning from preclinical to clinical applications. Immunotherapies are an emerging class of treatments for a variety of diseases. The agents include molecular and cellular therapeutics, which aim to treat the disease through re-education of the host immune system, often via complex mechanisms of action. In vivo imaging has the potential to contribute in several different ways: (1) as a drug development tool to improve our understanding of their complex mechanisms of action, (2) as a tool to predict efficacy, for example, to stratify patients into probable responders and likely non-responders, and (3) as a non-invasive treatment response biomarker to guide efficient immunotherapy use and to recognize early signs of potential loss of efficacy or resistance in patients. Areas where in vivo imaging is already successfully implemented in onco-immunology research will be discussed and domains where its use offers great potential will be highlighted. The focus of this article is on anti-cancer immunotherapy as it currently is the most advanced immunotherapy area. However, the described concepts can also be paralleled in other immune-mediated disorders and for conditions requiring immunotherapeutic intervention. Importantly, we introduce a new study group within the European Society of Molecular Imaging with the goal to facilitate and enhance immunotherapy development through the use of in vivo imaging

PD-L1 microSPECT/CT Imaging for Longitudinal Monitoring of PD-L1 Expression in Syngeneic and Humanized Mouse Models for Cancer

Antibodies that block the interaction between programmed death ligand 1 (PD-L1) and PD-1 have shown impressive responses in subgroups of patients with cancer. PD-L1 expression in tumors seems to be a prerequisite for treatment response. However, PD-L1 is heterogeneously expressed within tumor lesions and may change upon disease progression and treatment. Imaging of PD-L1 could aid in patient selection. Previously, we showed the feasibility to image PD-L1(+) tumors in immunodeficient mice. However, PD-L1 is also expressed on immune cell subsets. Therefore, the aim of this study was to assess the potential of PD-L1 micro single-photon emission tomography/computed tomography (microSPECT/CT) using radiolabeled PD-L1 antibodies to (i) measure PD-L1 expression in two immunocompetent tumor models (syngeneic mice and humanized mice harboring PD-L1 expressing immune cells) and (ii) monitor therapy-induced changes in tumor PD-L1 expression. We showed that radiolabeled PD-L1 antibodies accumulated preferentially in PD-L1(+) tumors, despite considerable uptake in certain normal lymphoid tissues (spleen and lymph nodes) and nonlymphoid tissues (duodenum and brown fat). PD-L1 microSPECT/CT imaging could also distinguish between high and low PD-L1-expressing tumors. The presence of PD-L1(+) immune cells did not compromise tumor uptake of the human PD-L1 antibodies in humanized mice, and we demonstrated that radiotherapy-induced upregulation of PD-L1 expression in murine tumors could be monitored with microSPECT/CT imaging. Together, these data demonstrate that PD-L1 microSPECT/CT is a sensitive technique to detect variations in tumor PD-L1 expression, and in the future, this technique may enable patient selection for PD-1/PD-L1-targeted therapy

Characterization of Intrinsically Radiolabeled Poly(lactic-co-glycolic acid) Nanoparticles for ex Vivo Autologous Cell Labeling and in Vivo Tracking

With the advent of novel immunotherapies, interest in ex vivo autologous cell labeling for in vivo cell tracking has revived. However, current clinically available labeling strategies have several drawbacks, such as release of radiolabel over time and cytotoxicity. Poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are clinically used biodegradable carriers of contrast agents, with high loading capacity for multimodal imaging agents. Here we show the development of PLGA-based NPs for ex vivo cell labeling and in vivo cell tracking with SPECT. We used primary amine-modified PLGA polymers (PLGA-NH2) to construct NPs similar to unmodified PLGA NPs. PLGA-NH2 NPs were efficiently radiolabeled without chelator and retained the radionuclide for 2 weeks. Monocyte-derived dendritic cells labeled with [111In]In-PLGA-NH2 showed higher specific activity than those labeled with [111In]In-oxine, with no negative effect on cell viability. SPECT/CT imaging showed that radiolabeled THP-1 cells accumulated at the Staphylococcus aureus infection site in mice. In conclusion, PLGA-NH2 NPs are able to retain 111In, independent of chelator presence. Furthermore, [111In]In-PLGA-NH2 allows cell labeling with high specific activity and no loss of activity over prolonged time intervals. Finally, in vivo tracking of ex vivo labeled THP-1 cells was demonstrated in an infection model using SPECT/CT imaging

Skin-test infiltrating lymphocytes early predict clinical outcome of dendritic cell-based vaccination in metastatic melanoma

Item does not contain fulltextThe identification of responding patients early during treatment would improve the capability to develop effective new immunotherapies more rapidly. Here, we describe a bioassay that may link early T-cell-mediated immune responses to later clinical benefits. This bioassay rests upon the tenet of immunotherapy that tumor-specific effector T cells capable of invading peripheral tissue can recognize tumor antigens and exert cytotoxic functions there. To show its utility, we conducted a retrospective study of a large cohort of metastatic melanoma patients (n = 91) enrolled in dendritic cell (DC)-based vaccination protocols to examine a hypothesized correlation of posttreatment skin-infiltrating lymphocytes (SKIL) with overall survival (OS). Stringent immunologic criteria were defined to identify long-term survivors. The presence of tumor-associated antigen (TAA)-specific CD8(+) T cell populations within SKILs (criterion I) was highly predictive for long-term survival. Further restriction by selecting for the presence of TAA-specific CD8(+) T cells specifically recognizing tumor peptide (criterion II) was also associated with improved OS. Recognition of naturally processed antigen (criterion III) maximized the accuracy of the test, with a median OS of 24.1 versus 9.9 months (P = 0.001). Our results show that detailed characterization of SKILs can permit an accurate selection of metastatic melanoma patients who benefit most from DC-based vaccination. This simple and robust bioassay integrates multiple aspects of cellular functions that mediate effective immune responses, thereby offering an effective tool to rapidly identify patients who are responding to immunotherapy at an early stage of treatment. Cancer Res; 72(23); 6102-10. (c)2012 AACR

Circulating CD4+ T cells that produce IL4 or IL17 when stimulated by Melan-A but not by NY-ESO-1 have negative impacts on survival of patients with stage IV melanoma

Purpose: We initially observed that the presence of circulating NY-ESO-1– and/or Melan-A–specific T cells in patients with stage IV melanoma was significantly associated with prolonged survival. Here, we report the ways in which the phenotypes and functions of these T cells differentially affect survival in patients preselected for NY-ESO-1 and/or Melan-A reactivity.\ud \ud Experimental Design: We assayed functional antigen-reactive T cells recognizing NY-ESO-1 and/or Melan-A after in vitro stimulation using overlapping peptide pools. After restimulation, we assayed six cytokines simultaneously by intracellular cytokine staining. This allowed us to analyze the functional antigen response of both CD4+ and CD8+ T cells at the single-cell level.\ud \ud Results: We observed that NY-ESO-1 stimulated mainly CD4+ T cells, whereas Melan-A more often stimulated CD8+ T cells. NY-ESO-1 reactivity was not associated with an additional impact on survival, whether CD4+ T cells, CD8+ T cells, or both types of T cells were responding. In contrast, recognition of Melan-A by CD4+ T cells was associated with reduced survival in our cohort of patients preselected for NY-ESO-1 and/or Melan-A reactivity (that is, in patients with exceptionally long survival). We further observed a negative effect on survival in patients with CD4+ T cells producing IL4 and IL17 upon Melan-A stimulation. Their prognosis was comparable to patients without any Melan-A reactivity.\ud \ud Conclusions: The nature and prognostic impact of specific T-cell responses is different according to targeted antigen. Independent from phenotype and functional aspects, NY-ESO-1 reactivity is associated with good prognosis. In terms of Melan-A, antigen-specific CD8+ but not CD4+ responses are associated with prolonged survival

Functional T cells targeting NY-ESO-1 or Melan-A are predictive for survival of patients with distant melanoma metastasis.

Item does not contain fulltextPURPOSE: To analyze the prognostic relevance of circulating T cells responding to NY-ESO-1, Melan-A, MAGE-3, and survivin in patients with melanoma with distant metastasis. PATIENTS AND METHODS: We examined 84 patients with follow-up after analysis (cohort A), 18 long-term survivors with an extraordinarily favorable course of disease before analysis (> 24 months survival after first occurrence of distant metastases; cohort B), and 14 healthy controls. Circulating antigen-reactive T cells were characterized by intracellular cytokine staining after in vitro stimulation. RESULTS: In cohort A patients, the presence of T cells responding to peptides from NY-ESO-1, Melan-A, or MAGE-3 and the M category according to the American Joint Committee on Cancer classification were significantly associated with survival. T cells responding to NY-ESO-1 and Melan-A (hazard ratios, 0.29 and 0.18, respectively) remained independent prognostic factors in Cox regression analysis and were superior to the M category in predicting outcome. Median survival of patients possessing T cells responding to NY-ESO-1, Melan-A, or both was 21 months, compared with 6 months for all others. NY-ESO-1-responsive T cells were detected in 70% of cohort A patients surviving > 18 months and in 50% of cohort B patients. Melan-A responses were found in 42% and 47% of patients in cohorts A and B, respectively. In contrast, the proportion was only 22% for NY-ESO-1 and 23% for Melan-A in those who died within 6 months. CONCLUSION: The presence of circulating T cells responding to Melan-A or NY-ESO-1 had strong independent prognostic impact on survival in advanced melanoma. Our findings support the therapeutic relevance of Melan-A and NY-ESO-1 as targets for immunotherapy

Targeting of 111In-Labeled Dendritic Cell Human Vaccines Improved by Reducing Number of Cells

Item does not contain fulltextPURPOSE: Anticancer dendritic cell (DC) vaccines require the DCs to relocate to lymph nodes (LN) to trigger immune responses. However, these migration rates are typically very poor. Improving the targeting of ex vivo generated DCs to LNs might increase vaccine efficacy and reduce costs. We investigated DC migration in vivo in humans under different conditions. EXPERIMENTAL DESIGN: HLA-A*02:01 patients with melanoma were vaccinated with mature DCs loaded with tyrosinase and gp100 peptides together with keyhole limpet hemocyanin (NCT00243594). For this study, patients received an additional intradermal vaccination with 111In-labeled mature DCs. The injection site was pretreated with nonloaded, activated DCs, TNFalpha, or Imiquimod; granulocyte macrophage colony-stimulating factor was coinjected or smaller numbers of DCs were injected. Migration was measured by scintigraphy and compared with an intrapatient control vaccination. In an ex vivo tissue model, we measured CCL21-directed migration of 19F-labeled DCs over a period of up to 12 hours using 19F MRI to supplement our patient data. RESULTS: Pretreatment of the injection site induced local inflammatory reactions but did not improve migration rates. Both in vitro and in vivo, reduction of cell numbers to 5 x 106 or less cells per injection improved migration. Furthermore, scintigraphy is insufficient to study migration of such small numbers of 111In-labeled DCs in vivo. CONCLUSION: Reduction of cell density, not pretreatment of the injection site, is crucial for improved migration of DCs to LNs in vivo. Clin Cancer Res; 19(6); 1525-33. (c)2013 AACR

Natural human plasmacytoid dendritic cells induce antigen-specific T-cell responses in melanoma patients

Item does not contain fulltextVaccination against cancer by using dendritic cells has for more than a decade been based on dendritic cells generated ex vivo from monocytes or CD34(+) progenitors. Here, we report on the first clinical study of therapeutic vaccination against cancer using naturally occurring plasmacytoid dendritic cells (pDC). Fifteen patients with metastatic melanoma received intranodal injections of pDCs activated and loaded with tumor antigen-associated peptides ex vivo. In vivo imaging showed that administered pDCs migrated and distributed over multiple lymph nodes. Several patients mounted antivaccine CD4(+) and CD8(+) T-cell responses. Despite the limited number of administered pDCs, an IFN signature was observed after each vaccination. These results indicate that vaccination with naturally occurring pDC is feasible with minimal toxicity and that in patients with metastatic melanoma, it induces favorable immune responses. Cancer Res; 73(3); 1063-75. (c)2012 AACR