Two-photon imaging of intratumoral CD8+ T cell cytotoxic activity during adoptive T cell therapy in mice

Cell-associated galectin 9 interacts with cytotoxic T cells confers resistance to tumor killing in nasopharyngeal carcinoma through autophagy activation

Immune effector cells, including cytotoxic T lymphocytes (CTLs) play essential roles in eliminating cancer cells. However, their functionality is often compromised, even when they infiltrate the tumor microenvironment (TME) or are transferred to cancer patients adoptively. In this study, we focused on galectin 9 (G9), an inhibitory ligand that we observed to be predominately positioned on the plasma membrane and readily interacts with CD8 + CTL in the TME of nasopharyngeal carcinoma (NPC). We discovered that cell-cell contact between activated effector CTLs and target tumor cells (TarTC) with G9 overexpression led to cellular death defects. Despite the formation of CTL-TarTC conjugates, there is no impact on the cell number nor viability of CTL, and the release of cytolytic content and associated activity were not completely abrogated. Instead, this interaction promoted autophagy and restricted necrosis in the TarTC. Furthermore, reducing G9 expression in tumor cells enhanced the suppressive effect on tumor growth upon adoptive transfer of activated effector CTL. Additionally, inhibiting autophagy effectively controlled tumor growth in cases of G9 overexpression. Therefore, we highlight the contribution of G9 in facilitating the resistance of NPC to CTL-mediated killing by inducing a selection-cell death state in tumor cells, characterized by increased autophagy and decreased necrosis.

Emerging insights into intravital imaging, unraveling its role in cancer immunotherapy

Cancer immunotherapy has attracted great attention as a potential therapeutic approach for advanced malignancies due to its promising survival benefits. Comprehension of intricate interactions between the tumor microenvironment (TME) and immune checkpoint inhibitors (ICIs) is crucial for optimizing and improving immunotherapies. Currently, several experimental strategies are available to monitor this complexity but most of them fail to facilitate real-time monitoring of the immune response such as cellular phagocytosis and cytolysis. Consequently, the application of intravital imaging has been extensively studied in the domain of cancer immunotherapy. Intravital imaging has been proven to be a powerful real-time imaging modality that provides insights into intratumoral immune responses, cellular metabolic signatures, tumor vasculature, and cellular functions. This review aims to provide a comprehensive overview of the latest research on intravital imaging in cancer immunotherapy, especially addressing how intravital imaging sheds light on essential features of tumor immunity, immune infiltrations, tumor angiogenesis, and aids in the clarification of underlying immunotherapeutic mechanisms. Moreover, a variety of labeling tools, imaging windows and models for real-time visualizations of TME are also summarized. We will also investigate the full potential of using intravital imaging to circumvent the limitations of currently available imaging modalities, which hold promise to advent efficient immunotherapy for cancer patients.

Optimized Spheroid Model of Pancreatic Cancer Demonstrates Influence of Macrophage-T Cell Interaction for Intratumoral T Cell Motility

BACKGROUND

Most spheroid models use size measurements as a primary readout parameter; some models extend analysis to T cell infiltration or perform caspase activation assays. However, to our knowledge, T cell motility analysis is not regularly included as an endpoint in imaging studies on cancer spheroids.

METHODS

Here, we intend to demonstrate that motility analysis of macrophages and T cells is a valuable functional endpoint for studies on molecular interventions in the tumor microenvironment. In particular, T cell migration analysis represents the final step of effector function, as T cells engage with targets cells upon cytotoxic interaction, which is represented by an arrest within the spheroid volume. Therefore, T cell arrest is a novel readout parameter of T cell effector function in spheroids.

RESULTS

Here, we demonstrate that incubation of macrophages with nigericin for NLRP3 activation increases T cell velocity, but results in decreased T cellular arrest. This is paralleled by reduced rejection kinetics of pancreatic cancer spheroids in the presence of antigen-dependent T cells and nigericin-treated macrophages. Our model demonstrates consistent changes in T cell motility upon coculturing of T cells and tumors cells with macrophages, including influences of molecular interventions such as NLRP3 activation.

CONCLUSIONS

Motility analysis using a spheroid model of pancreatic cancer is a more sophisticated alternative to in vitro cytotoxicity assays measuring spheroid size. Ultimately, an optimized spheroid model might replace at least some aspects of animal experiments investigating T cell effector function.

Myeloid effector cells in cancer

The role of myeloid cells in tumor immunity is multifaceted. While dendritic cells support T cell-mediated tumor control, the highly heterogenous populations of macrophages, neutrophils, and immature myeloid cells were generally considered immunosuppressive. This view has led to effective therapies reinvigorating tumor-reactive T cells; however, targeting the immunosuppressive effects of macrophages and neutrophils to boost the cancer immunity cycle was clinically less successful. Recent studies interrogating the role of immune cells in the context of successful immunotherapy affirm the key role of T cells, but simultaneously challenge the idea that the cytotoxic function of T cells is the main contributor to therapy-driven tumor regression. Rather, therapy-activated intra-tumoral T cells recruit and activate or reprogram several myeloid effector cell types, the presence of which is necessary for tumor rejection. Here, we reappreciate the key role of myeloid effector cells in tumor rejection as this may help to shape future successful immunotherapies.

T lymphocyte recruitment to melanoma brain tumors depends on distinct venous vessels

To improve immunotherapy for brain tumors, it is important to determine the principal intracranial site of T cell recruitment from the bloodstream and their intracranial route to brain tumors. Using intravital microscopy in mouse models of intracranial melanoma, we discovered that circulating T cells preferably adhered and extravasated at a distinct type of venous blood vessel in the tumor vicinity, peritumoral venous vessels (PVVs). Other vascular structures were excluded as alternative T cell routes to intracranial melanomas. Anti-PD-1/CTLA-4 immune checkpoint inhibitors increased intracranial T cell motility, facilitating migration from PVVs to the tumor and subsequently inhibiting intracranial tumor growth. The endothelial adhesion molecule ICAM-1 was particularly expressed on PVVs, and, in samples of human brain metastases, ICAM-1 positivity of PVV-like vessels correlated with intratumoral T cell infiltration. These findings uncover a distinct mechanism by which the immune system can access and control brain tumors and potentially influence other brain pathologies.

Agent-Based Modeling of Virtual Tumors Reveals the Critical Influence of Microenvironmental Complexity on Immunotherapy Efficacy

Since the introduction of the first immune checkpoint inhibitor (ICI), immunotherapy has changed the landscape of molecular therapeutics for cancers. However, ICIs do not work equally well on all cancers and for all patients. There has been a growing interest in using mathematical and computational models to optimize clinical responses. Ordinary differential equations (ODEs) have been widely used for mechanistic modeling in immuno-oncology and immunotherapy. They allow rapid simulations of temporal changes in the cellular and molecular populations involved. Nonetheless, ODEs cannot describe the spatial structure in the tumor microenvironment or quantify the influence of spatially-dependent characteristics of tumor-immune dynamics. For these reasons, agent-based models (ABMs) have gained popularity because they can model more detailed phenotypic and spatial heterogeneity that better reflect the complexity seen in vivo. In the context of anti-PD-1 ICIs, we compare treatment outcomes simulated from an ODE model and an ABM to show the importance of including spatial components in computational models of cancer immunotherapy. We consider tumor cells of high and low antigenicity and two distinct cytotoxic T lymphocyte (CTL) killing mechanisms. The preferred mechanism differs based on the antigenicity of tumor cells. Our ABM reveals varied phenotypic shifts within the tumor and spatial organization of tumor and CTLs despite similarities in key immune parameters, initial simulation conditions, and early temporal trajectories of the cell populations.

Identification of a clinically efficacious CAR T cell subset in diffuse large B cell lymphoma by dynamic multidimensional single-cell profiling

Chimeric antigen receptor (CAR) T cells used for the treatment of B cell malignancies can identify T cell subsets with superior clinical activity. Here, using infusion products of individuals with large B cell lymphoma, we integrated functional profiling using timelapse imaging microscopy in nanowell grids with subcellular profiling and single-cell RNA sequencing to identify a signature of multifunctional CD8+ T cells (CD8-fit T cells). CD8-fit T cells are capable of migration and serial killing and harbor balanced mitochondrial and lysosomal volumes. Using independent datasets, we validate that CD8-fit T cells (1) are present premanufacture and are associated with clinical responses in individuals treated with axicabtagene ciloleucel, (2) longitudinally persist in individuals after treatment with CAR T cells and (3) are tumor migrating cytolytic cells capable of intratumoral expansion in solid tumors. Our results demonstrate the power of multimodal integration of single-cell functional assessments for the discovery and application of CD8-fit T cells as a T cell subset with optimal fitness in cell therapy.

Cancer-on-a-chip model shows that the adenomatous polyposis coli mutation impairs T cell engagement and killing of cancer spheroids

Evaluating the ability of cytotoxic T lymphocytes (CTLs) to eliminate tumor cells is crucial, for instance, to predict the efficiency of cell therapy in personalized medicine. However, the destruction of a tumor by CTLs involves CTL migration in the extra-tumoral environment, accumulation on the tumor, antigen recognition, and cooperation in killing the cancer cells. Therefore, identifying the limiting steps in this complex process requires spatio-temporal measurements of different cellular events over long periods. Here, we use a cancer-on-a-chip platform to evaluate the impact of adenomatous polyposis coli (APC) mutation on CTL migration and cytotoxicity against 3D tumor spheroids. The APC mutated CTLs are found to have a reduced ability to destroy tumor spheroids compared with control cells, even though APC mutants migrate in the extra-tumoral space and accumulate on the spheroids as efficiently as control cells. Once in contact with the tumor however, mutated CTLs display reduced engagement with the cancer cells, as measured by a metric that distinguishes different modes of CTL migration. Realigning the CTL trajectories around localized killing cascades reveals that all CTLs transition to high engagement in the 2 h preceding the cascades, which confirms that the low engagement is the cause of reduced cytotoxicity. Beyond the study of APC mutations, this platform offers a robust way to compare cytotoxic cell efficiency of even closely related cell types, by relying on a multiscale cytometry approach to disentangle complex interactions and to identify the steps that limit the tumor destruction.

NFIL3 contributes to cytotoxic T lymphocyte-mediated killing

Cytotoxic T lymphocytes (CTLs) are key effectors of the adaptive immune system that recognize and eliminate virally infected and cancerous cells. In naive CD8+ T cells, T-cell receptor (TCR) engagement drives a number of transcriptional, translational and proliferation changes over the course of hours and days leading to differentiation into CTLs. To gain a better insight into this mechanism, we compared the transcriptional profiles of naive CD8+ T cells to those of activated CTLs. To find new regulators of CTL function, we performed a selective clustered regularly interspaced short palindromic repeats (CRISPR) screen on upregulated genes and identified nuclear factor IL-3 (NFIL3) as a potential regulator of cytotoxicity. Although NFIL3 has established roles in several immune cells including natural killer, Treg, dendritic and CD4+ T cells, its function in CD8+ CTLs is less well understood. Using CRISPR/Cas9 editing, we found that removing NFIL3 in CTLs resulted in a marked decrease in cytotoxicity. We found that in CTLs lacking NFIL3 TCR-induced extracellular signal-regulated kinase phosphorylation, immune synapse formation and granule release were all intact while cytotoxicity was functionally impaired in vitro. Strikingly, NFIL3 controls the production of cytolytic proteins as well as effector cytokines. Thus, NFIL3 plays a cell intrinsic role in modulating cytolytic mechanisms in CTLs.

Mathematical model predicts tumor control patterns induced by fast and slow cytotoxic T lymphocyte killing mechanisms

Immunotherapy has dramatically transformed the cancer treatment landscape largely due to the efficacy of immune checkpoint inhibitors (ICIs). Although ICIs have shown promising results for many patients, the low response rates in many cancers highlight the ongoing challenges in cancer treatment. Cytotoxic T lymphocytes (CTLs) execute their cell-killing function via two distinct mechanisms: a fast-acting, perforin-mediated process and a slower, Fas ligand (FasL)-driven pathway. Evidence also suggests that the preferred killing mechanism of CTLs depends on the antigenicity of tumor cells. To determine the critical factors affecting responses to ICIs, we construct an ordinary differential equation model describing in vivo tumor-immune dynamics in the presence of active or blocked PD-1/PD-L1 immune checkpoint. Specifically, we identify important aspects of the tumor-immune landscape that affect tumor size and composition in the short and long term. We also generate a virtual cohort of mice with diverse tumor and immune attributes to simulate the outcomes of immune checkpoint blockade in a heterogeneous population. By identifying key tumor and immune characteristics associated with tumor elimination, dormancy, and escape, we predict which fraction of a population potentially responds well to ICIs and ways to enhance therapeutic outcomes with combination therapy.

Heterogeneity in killing efficacy of individual effector CD8+ T cells against Plasmodium liver stages

Vaccination strategies in mice inducing high numbers of memory CD8+ T cells specific to a single epitope are able to provide sterilizing protection against infection with Plasmodium sporozoites. We have recently found that Plasmodium-specific CD8+ T cells cluster around sporozoite-infected hepatocytes but whether such clusters are important in elimination of the parasite remains incompletely understood. Here, we used our previously generated data in which we employed intravital microscopy to longitudinally image 32 green fluorescent protein (GFP)-expressing Plasmodium yoelii parasites in livers of mice that had received activated Plasmodium-specific CD8+ T cells after sporozoite infection. We found significant heterogeneity in the dynamics of the normalized GFP signal from the parasites (termed 'vitality index' or VI) that was weakly correlated with the number of T cells near the parasite. We also found that a simple model assuming mass-action, additive killing by T cells well describes the VI dynamics for most parasites and predicts a highly variable killing efficacy by individual T cells. Given our estimated median per capita kill rate of k = 0.031/h we predict that a single T cell is typically incapable of killing a parasite within the 48 h lifespan of the liver stage in mice. Stochastic simulations of T cell clustering and killing of the liver stage also suggested that: (i) three or more T cells per infected hepatocyte are required to ensure sterilizing protection; (ii) both variability in killing efficacy of individual T cells and resistance to killing by individual parasites may contribute to the observed variability in VI decline, and (iii) the stable VI of some clustered parasites cannot be explained by measurement noise. Taken together, our analysis for the first time provides estimates of efficiency at which individual CD8+ T cells eliminate intracellular parasitic infection in vivo.

Immunomodulation under the lens of real-time in vivo imaging

Modulation of cells and molecules of the immune system not only represents a major opportunity to treat a variety of diseases including infections, cancer, autoimmune, and inflammatory disorders but could also help understand the intricacies of immune responses. A detailed mechanistic understanding of how a specific immune intervention may provide clinical benefit is essential for the rational design of efficient immunomodulators. Visualizing the impact of immunomodulation in real-time and in vivo has emerged as an important approach to achieve this goal. In this review, we aim to illustrate how multiphoton intravital imaging has helped clarify the mode of action of immunomodulatory strategies such as antibodies or cell therapies. We also discuss how optogenetics combined with imaging will further help manipulate and precisely understand immunomodulatory pathways. Combined with other single-cell technologies, in vivo dynamic imaging has therefore a major potential for guiding preclinical development of immunomodulatory drugs.

Leishmania major drives host phagocyte death and cell-to-cell transfer depending on intracellular pathogen proliferation rate

The virulence of intracellular pathogens relies largely on the ability to survive and replicate within phagocytes but also on release and transfer into new host cells. Such cell-to-cell transfer could represent a target for counteracting microbial pathogenesis. However, our understanding of the underlying cellular and molecular processes remains woefully insufficient. Using intravital 2-photon microscopy of caspase-3 activation in the Leishmania major-infected (L. major-infected) live skin, we showed increased apoptosis in cells infected by the parasite. Also, transfer of the parasite to new host cells occurred directly without a detectable extracellular state and was associated with concomitant uptake of cellular material from the original host cell. These in vivo findings were fully recapitulated in infections of isolated human phagocytes. Furthermore, we observed that high pathogen proliferation increased cell death in infected cells, and long-term residency within an infected host cell was only possible for slowly proliferating parasites. Our results therefore suggest that L. major drives its own dissemination to new phagocytes by inducing host cell death in a proliferation-dependent manner.

Tumor-intrinsic sensitivity to the pro-apoptotic effects of IFN-γ is a major determinant of CD4+ CAR T-cell antitumor activity

CD4+ T cells and CD4+ chimeric antigen receptor (CAR) T cells display highly variable antitumor activity in preclinical models and in patients; however, the mechanisms dictating how and when CD4+ T cells promote tumor regression are incompletely understood. With the help of functional intravital imaging, we report that interferon (IFN)-γ production but not perforin-mediated cytotoxicity was the dominant mechanism for tumor elimination by anti-CD19 CD4+ CAR T cells. Mechanistically, mouse or human CD4+ CAR T-cell-derived IFN-γ diffused extensively to act on tumor cells at distance selectively killing tumors sensitive to cytokine-induced apoptosis, including antigen-negative variants. In anti-CD19 CAR T-cell-treated patients exhibiting elevated CAR CD4:CD8 ratios, strong induction of serum IFN-γ was associated with increased survival. We propose that the sensitivity of tumor cells to the pro-apoptotic activity of IFN-γ is a major determinant of CD4+ CAR T-cell efficacy and may be considered to guide the use of CD4+ T cells during immunotherapy.

Cytotoxic T Lymphocytes Control Growth of B16 Tumor Cells in Collagen-Fibrin Gels by Cytolytic and Non-Lytic Mechanisms

Cytotoxic T lymphocytes (CTLs) are important in controlling some viral infections, and therapies involving the transfer of large numbers of cancer-specific CTLs have been successfully used to treat several types of cancers in humans. While the molecular mechanisms of how CTLs kill their targets are relatively well understood, we still lack a solid quantitative understanding of the kinetics and efficiency by which CTLs kill their targets in vivo. Collagen-fibrin-gel-based assays provide a tissue-like environment for the migration of CTLs, making them an attractive system to study T cell cytotoxicity in in vivo-like conditions. Budhu.et al. systematically varied the number of peptide (SIINFEKL)-pulsed B16 melanoma cells and SIINFEKL-specific CTLs (OT-1) and measured the remaining targets at different times after target and CTL co-inoculation into collagen-fibrin gels. The authors proposed that their data were consistent with a simple model in which tumors grow exponentially and are killed by CTLs at a per capita rate proportional to the CTL density in the gel. By fitting several alternative mathematical models to these data, we found that this simple "exponential-growth-mass-action-killing" model did not precisely describe the data. However, determining the best-fit model proved difficult because the best-performing model was dependent on the specific dataset chosen for the analysis. When considering all data that include biologically realistic CTL concentrations (E≤107cell/mL), the model in which tumors grow exponentially and CTLs suppress tumor's growth non-lytically and kill tumors according to the mass-action law (SiGMA model) fit the data with the best quality. A novel power analysis suggested that longer experiments (∼3-4 days) with four measurements of B16 tumor cell concentrations for a range of CTL concentrations would best allow discriminating between alternative models. Taken together, our results suggested that the interactions between tumors and CTLs in collagen-fibrin gels are more complex than a simple exponential-growth-mass-action killing model and provide support for the hypothesis that CTLs' impact on tumors may go beyond direct cytotoxicity.

Mathematical modeling identifies LAG3 and HAVCR2 as biomarkers of T cell exhaustion in melanoma

Cytotoxic T lymphocytes (CTLs) control tumors via lysis of antigen-presenting targets or through secretion of cytokines such as interferon-γ (IFNG), which inhibit tumor cell proliferation. Improved understanding of CTL interactions within solid tumors will aid the development of immunotherapeutic strategies against cancer. In this study, we take a systems biology approach to compare the importance of cytolytic versus IFNG-mediated cytostatic effects in a murine melanoma model (B16F10) and to dissect the contribution of immune checkpoints HAVCR2, LAG3, and PDCD1/CD274 to CTL exhaustion. We integrated multimodal data to inform an ordinary differential equation (ODE) model of CTL activities inside the tumor. Our model predicted that CTL cytotoxicity played only a minor role in tumor control relative to the cytostatic effects of IFNG. Furthermore, our analysis revealed that within B16F10 melanomas HAVCR2 and LAG3 better characterize the development of a dysfunctional CTL phenotype than does the PDCD1/CD274 axis.

Modulation of T cell function and survival by the tumor microenvironment

Cancer immunotherapy is shifting paradigms in cancer care. T cells are an indispensable component of an effective antitumor immunity and durable clinical responses. However, the complexity of the tumor microenvironment (TME), which consists of a wide range of cells that exert positive and negative effects on T cell function and survival, makes achieving robust and durable T cell responses difficult. Additionally, tumor biology, structural and architectural features, intratumoral nutrients and soluble factors, and metabolism impact the quality of the T cell response. We discuss the factors and interactions that modulate T cell function and survive in the TME that affect the overall quality of the antitumor immune response.

Semi-supervised analysis of myeloid and T cell behavior in ex vivo ovarian tumor slices reveals changes in cell motility after treatments

Studies of the high-grade serous ovarian cancer (HGSOC) tumor microenvironment, the most lethal gynecological cancer, aim to enhance the efficiency of established therapies. Cell motility is an important process of anti-tumor response. Using ex vivo human and mouse HGSOC tumor slices combined with time-lapse imaging, we assessed the motility of CD8+ T and myeloid cells. We developed a semi-supervised analysis of cell movements, identifying four cell behaviors: migrating, long migrating, static, and wobbling. Tumor slices were maintained 24h ex vivo, retaining viability and cell movements. Ex vivo treatments with lipopolysaccharide altered CD8+ T and myeloid cell behavior. In vivo chemotherapy reduced ex vivo cell movements in human and mouse tumors and differentially affected CD8+ T and myeloid cells in chemo-sensitive and chemo-resistant mouse models. Ex vivo tumor slices can extend in vivo mouse studies to human, providing a stepping stone to translate mouse cancer studies to clinical trials.

Barriers to immune cell infiltration in tumors

Increased immune cell infiltration into tumors is associated with improved patient survival and predicts response to immune therapies. Thus, identification of factors that determine the extent of immune infiltration is crucial, so that methods to intervene on these targets can be developed. T cells enter tumor tissues through the vasculature, and under control of interactions between homing receptors on the T cells and homing receptor ligands (HRLs) expressed by tumor vascular endothelium and tumor cell nests. HRLs are often deficient in tumors, and there also may be active barriers to infiltration. These remain understudied but may be crucial for enhancing immune-mediated cancer control. Multiple intratumoral and systemic therapeutic approaches show promise to enhance T cell infiltration, including both approved therapies and experimental therapies. This review highlights the intracellular and extracellular determinants of immune cell infiltration into tumors, barriers to infiltration, and approaches for intervention to enhance infiltration and response to immune therapies.

Mathematical modeling suggests cytotoxic T lymphocytes control growth of B16 tumor cells in collagin-fibrin gels by cytolytic and non-lytic mechanisms

Cytotoxic T lymphocytes (CTLs) are important in controlling some viral infections, and therapies involving transfer of large numbers of cancer-specific CTLs have been successfully used to treat several types of cancers in humans. While molecular mechanisms of how CTLs kill their targets are relatively well understood we still lack solid quantitative understanding of the kinetics and efficiency at which CTLs kill their targets in different conditions. Collagen-fibrin gel-based assays provide a tissue-like environment for the migration of CTLs, making them an attractive system to study the cytotoxicity in vitro. Budhu et al. [1] systematically varied the number of peptide (SIINFEKL)- pulsed B16 melanoma cells and SIINFEKL-specific CTLs (OT-1) and measured remaining targets at different times after target and CTL co-inoculation into collagen-fibrin gels. The authors proposed that their data were consistent with a simple model in which tumors grow exponentially and are killed by CTLs at a per capita rate proportional to the CTL density in the gel. By fitting several alternative mathematical models to these data we found that this simple "exponential-growth-mass-action-killing" model does not precisely fit the data. However, determining the best fit model proved difficult because the best performing model was dependent on the specific dataset chosen for the analysis. When considering all data that include biologically realistic CTL concentrations ( E ≤ 10 ⁷ cell/ml) the model in which tumors grow exponentially and CTLs suppress tumor's growth non-lytically and kill tumors according to the mass-action law (SiGMA model) fitted the data with best quality. Results of power analysis suggested that longer experiments (∼ 3 - 4 days) with 4 measurements of B16 tumor cell concentrations for a range of CTL concentrations would best allow to discriminate between alternative models. Taken together, our results suggest that interactions between tumors and CTLs in collagen-fibrin gels are more complex than a simple exponential-growth- mass-action killing model and provide support for the hypothesis that CTLs impact on tumors may go beyond direct cytotoxicity.

CD4+ T cells in cancer

Cancer immunology and immunotherapy are driving forces of research and development in oncology, mostly focusing on CD8⁺ T cells and the tumor microenvironment. Recent progress highlights the importance of CD4⁺ T cells, corresponding to the long-known fact that CD4⁺ T cells are central players and coordinators of innate and antigen-specific immune responses. Moreover, they have now been recognized as anti-tumor effector cells in their own right. Here we review the current status of CD4⁺ T cells in cancer, which hold great promise for improving knowledge and therapies in cancer.

In vivo imaging of inflammatory response in cancer research

Inflammation can contribute to the development and progression of cancer. The inflammatory responses in the tumor microenvironment are shaped by complex sequences of dynamic intercellular cross-talks among diverse types of cells, and recapitulation of these dynamic events in vitro has yet to be achieved. Today, intravital microscopy with two-photon excitation microscopes (2P-IVM) is the mainstay technique for observing intercellular cross-talks in situ, unraveling cellular and molecular mechanisms in the context of their spatiotemporal dynamics. In this review, we summarize the current state of 2P-IVM with fluorescent indicators of signal transduction to reveal the cross-talks between cancer cells and surrounding cells including both immune and non-immune cells. We also discuss the potential application of red-shifted indicators along with optogenetic tools to 2P-IVM. In an era of single-cell transcriptomics and data-driven research, 2P-IVM will remain a key advantage in delivering the missing spatiotemporal context in the field of cancer research.

IL18 Receptor Signaling Inhibits Intratumoral CD8+ T-Cell Migration in a Murine Pancreatic Cancer Model

In pancreatic ductal adenocarcinoma (PDAC), the infiltration of CD8⁺ cytotoxic T cells (CTLs) is an important factor in determining prognosis. The migration pattern and interaction behavior of intratumoral CTLs are pivotal to tumor rejection. NLRP3-dependent proinflammatory cytokines IL-1β and IL-18 play a prominent role for CTL induction and differentiation. Here, we investigate the effects of T-cellular IL-1R and IL-18R signaling for intratumoral T-cell motility. Murine adenocarcinoma cell line Panc02 was stably transfected with ovalbumin (OVA) and fluorophore H2B-Cerulean to generate PancOVA H2B-Cerulean tumor cells. Dorsal skinfold chambers (DSFC) were installed on wild-type mice, and PancOVA H2B-Cerulean tumor cells were implanted into the chambers. PancOVA spheroids were formed using the Corning^® Matrigel^®-based 3D cell culture technique. CTLs were generated from OT-1 mice, Il1r^-/- OT-1 mice, or Il18r^-/- OT-1 mice and were marked with fluorophores. This was followed by the adoptive transfer of CTLs into tumor-bearing mice or the application into tumor spheroids. After visualization with multiphoton microscopy (MPM), Imaris software was used to perform T-cell tracking. Imaris analysis indicates a significantly higher accumulation of Il18r^-/- CTLs in PancOVA tumors and a significant reduction in tumor volume compared to wild-type CTLs. Il18r^-/- CTLs covered a longer distance (track displacement length) in comparison to wild-type (WT) CTLs, and had a higher average speed (mean track speed). The analysis of instantaneous velocity suggests a higher percentage of arrested tracks (arrests: <4 μm/min) for Il18r^-/- CTLs. Our data indicate the contribution of IL-18R signaling to T-cell effector strength, warranting further investigation on phenomena such as intratumoral T-cell exhaustion.

CAR T-cell behavior and function revealed by real-time imaging

Adoptive transfer of T-cells expressing chimeric antigen receptors (CAR) has shown remarkable clinical efficacy against advanced B-cell malignancies. Nonetheless, the field of CAR T-cells is currently facing several major challenges. In particular, the CAR T-cell strategy has not yet produced favorable clinical responses when targeting solid tumors. In this context, it is of paramount importance to understand the determinants that limit the efficacy of T-cell-based immunotherapy. Characterization of CAR T-cells is usually based on flow cytometry and whole-transcriptome profiling. These approaches have been very valuable to determine intrinsic elements that condition T-cell ability to proliferate and expand. However, they do not take into account spatial and kinetic aspects of T-cell responses. In particular, in order to control tumor growth, CAR T-cells need to enter into the tumor, migrate within a complex tumor environment, and form productive conjugates with their targets. Advanced imaging techniques combined with innovative preclinical models represent promising tools to uncover the dynamics of CAR T-cells. In this review, we will discuss recent results on the biology of engineered T-cells that have been obtained with real-time imaging microscopy. Important notions have emerged from these imaging-based studies, such as the multi-killing potential of CAR T-cells. Finally, we will highlight how imaging techniques combined with other tools can solve remaining unresolved questions in the field of engineered T-cells.

Chimeric antigen receptor T cells as adjuvant therapy for unresectable adenocarcinoma

Incomplete surgery of solid tumors is a risk factor for primary treatment failure. Here, we have investigated whether chimeric antigen receptor T cells (CARTs) could be used as an adjuvant therapy to clear residual cancer cells. We tested the feasibility of this approach in two partial resection xenograft models using mesothelin-specific CARTs. In addition, we developed a previously unexplored in vivo toxicity model to evaluate safety and effects on wound healing in immunocompetent C57BL/6 mice. We found that the local delivery of CARTs in a fibrin glue-based carrier was effective in clearing residual cancer cells following incomplete surgery. This resulted in significantly longer overall survival when compared to mice treated with surgery and CARTs without fibrin glue. On-target off-tumor toxicity was diminished, and wound healing complications were not seen in any of the mice. On the basis of these observations, a clinical trial in patients with locally advanced breast cancer is planned.

MAST: a hybrid Multi-Agent Spatio-Temporal model of tumor microenvironment informed using a data-driven approach

Motivation

Recently, several computational modeling approaches, such as agent-based models, have been applied to study the interaction dynamics between immune and tumor cells in human cancer. However, each tumor is characterized by a specific and unique tumor microenvironment, emphasizing the need for specialized and personalized studies of each cancer scenario.

Results

We present MAST, a hybrid Multi-Agent Spatio-Temporal model which can be informed using a data-driven approach to simulate unique tumor subtypes and tumor-immune dynamics starting from high-throughput sequencing data. It captures essential components of the tumor microenvironment by coupling a discrete agent-based model with a continuous partial differential equations-based model.The application to real data of human colorectal cancer tissue investigating the spatio-temporal evolution and emergent properties of four simulated human colorectal cancer subtypes, along with their agreement with current biological knowledge of tumors and clinical outcome endpoints in a patient cohort, endorse the validity of our approach.

Availability and implementation

MAST, implemented in Python language, is freely available with an open-source license through GitLab (https://gitlab.com/sysbiobig/mast), and a Docker image is provided to ease its deployment. The submitted software version and test data are available in Zenodo at https://dx.doi.org/10.5281/zenodo.7267745.

Supplementary information

Supplementary data are available at Bioinformatics Advances online.

Interdependence of sequential cytotoxic T lymphocyte and natural killer cell cytotoxicity against melanoma cells

Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells recognize and eliminate cancer cells. However, immune evasion, downregulation of immune function by the tumour microenvironment and resistance of cancer cells are major problems. Although CTL and NK cells are both important to eliminate cancer, most studies address them individually. We quantified sequential primary human CTL and NK cell cytotoxicity against the melanoma cell line SK-Mel-5. At high effector-to-target ratios, NK cells or melan-A (MART-1)-specific CTL eliminated all SK-Mel-5 cells within 24 h, indicating that SK-Mel-5 cells are not resistant initially. However, at lower effector-to-target ratios, which resemble numbers of the immune contexture in human cancer, a substantial number of SK-Mel-5 cells survived. Pre-exposure to CTL induced resistance in surviving SK-Mel-5 cells to subsequent CTL or NK cell cytotoxicity, and pre-exposure to NK cells induced resistance in surviving SK-Mel-5 cells to NK cells. Higher human leucocyte antigen class I expression or interleukin-6 levels were correlated with resistance to NK cells, whereas reduction in MART-1 antigen expression was correlated with reduced CTL cytotoxicity. The CTL cytotoxicity was rescued beyond control levels by exogenous MART-1 antigen. In contrast to the other three combinations, CTL cytotoxicity against SK-Mel-5 cells was enhanced following NK cell pre-exposure. Our assay allows quantification of sequential CTL and NK cell cytotoxicity and might guide strategies for efficient CTL-NK cell anti-melanoma therapies. KEY POINTS: Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells eliminate cancer cells. Both CTL and NK cells attack the same targets, but most studies address them individually. In a sequential cytotoxicity model, the interdependence of antigen-specific CTL and NK cell cytotoxicity against melanoma is quantified. High numbers of antigen-specific CTL and NK cells eliminate all melanoma cells. However, lower numbers induce resistance if secondary CTL or NK cell exposure follows initial CTL exposure or if secondary NK cell exposure follows initial NK cell exposure. On the contrary, if secondary CTL exposure follows initial NK cell exposure, cytotoxicity is enhanced. Alterations in human leucocyte antigen class I expression and interleukin-6 levels are correlated with resistance to NK cells, whereas a reduction in antigen expression is correlated with reduced CTL cytotoxicity; CTL cytotoxicity is rescued beyond control levels by exogenous antigen. This assay and the results on interdependencies will help us to understand and optimize immune therapies against cancer.

T cell-mediated additive cytotoxicity - death by multiple bullets

Immune effector cells, including cytotoxic T cells (CTLs), induce apoptosis and eliminate target cells by direct cell-cell contacts. In vivo, CTLs fail to efficiently kill solid tumor cells by individual contacts but rely upon multihit interactions by many CTLs (swarming). Recent evidence has indicated that multihit interactions by CTLs induce a series of sublethal damage events in target cells, including perforin-mediated membrane damage, induction of reactive oxygen species (ROS), nuclear envelope rupture, and DNA damage. Individual damage can be repaired, but when induced in rapid sequence, sublethal damage can accumulate and induce target cell death. Here, we summarize the sublethal damage and additive cytotoxicity concepts for CTL-induced and other cell stresses and discuss the implications for improving immunotherapy and multitargeted anticancer therapies.

Intravital microscopy for real-time monitoring of drug delivery and nanobiological processes

Intravital microscopy (IVM) expands our understanding of cellular and molecular processes, with applications ranging from fundamental biology to (patho)physiology and immunology, as well as from drug delivery to drug processing and drug efficacy testing. In this review, we highlight modalities, methods and model organisms that make up today's IVM landscape, and we present how IVM - via its high spatiotemporal resolution - enables analysis of metabolites, small molecules, nanoparticles, immune cells, and the (tumor) tissue microenvironment. We furthermore present examples of how IVM facilitates the elucidation of nanomedicine kinetics and targeting mechanisms, as well as of biological processes such as immune cell death, host-pathogen interactions, metabolic states, and disease progression. We conclude by discussing the prospects of IVM clinical translation and examining the integration of machine learning in future IVM practice.

Store-Operated Ca2+ Entry Is Up-Regulated in Tumour-Infiltrating Lymphocytes from Metastatic Colorectal Cancer Patients

Simple Summary

Store-operated Ca²⁺ entry (SOCE) has long been known to regulate the differentiation and effector functions of T cells as well as to be instrumental to the ability of cytotoxic T lymphocytes to target cancer cells. Currently, no information is available regarding the expression and function of SOCE in tumour-infiltrating lymphocytes (TILs) that have been expanded in vitro for adoptive cell therapy (ACT). This study provides the first evidence that SOCE is up-regulated in ex vivo-expanded TILs from metastatic colorectal cancer (mCRC) patients. The up-regulation of SOCE mainly depends on diacylglycerol kinase (DGK), which prevents the protein kinase C-dependent inhibition of Ca²⁺ entry in normal T cells. Of note, the pharmacological blockade of SOCE with the selective inhibitor, BTP-2, during target cell killing significantly increases cytotoxic activity at low TIL density, i.e., when TILs-mediated cancer cell death is rarer. This study, albeit preliminary, could lay the foundation to propose an alternative strategy to effect ACT. It has been shown that ex vivo-expanded TILs did not improve the disease-free survival rate in mCRC patients. Our results strongly suggest that pre-treating autologous TILs with a SOCE or DGK inhibitor before being infused into the patient could improve their cytotoxic activity against cancer cells.

Abstract

(1) Background: Store-operated Ca²⁺ entry (SOCE) drives the cytotoxic activity of cytotoxic T lymphocytes (CTLs) against cancer cells. However, SOCE can be enhanced in cancer cells due to an increase in the expression and/or function of its underlying molecular components, i.e., STIM1 and Orai1. Herein, we evaluated the SOCE expression and function in tumour-infiltrating lymphocytes (TILs) from metastatic colorectal cancer (mCRC) patients. (2) Methods: Functional studies were conducted in TILs expanded ex vivo from CRC liver metastases. Peripheral blood T cells from healthy donors (hPBTs) and mCRC patients (cPBTs) were used as controls. (3) Results: SOCE amplitude is enhanced in TILs compared to hPBTs and cPBTs, but the STIM1 protein is only up-regulated in TILs. Pharmacological manipulation showed that the increase in SOCE mainly depends on tonic modulation by diacylglycerol kinase, which prevents the protein kinase C-dependent inhibition of SOCE activity. The larger SOCE caused a stronger Ca²⁺ response to T-cell receptor stimulation by autologous mCRC cells. Reducing Ca²⁺ influx with BTP-2 during target cell killing significantly increases cytotoxic activity at low target:effector ratios. (4) Conclusions: SOCE is enhanced in ex vivo-expanded TILs deriving from mCRC patients but decreasing Ca²⁺ influx with BTP-2 increases cytotoxic activity at a low TIL density.

High resolution microfluidic assay and probabilistic modeling reveal cooperation between T cells in tumor killing

Cytotoxic T cells are important components of natural anti-tumor immunity and are harnessed in tumor immunotherapies. Immune responses to tumors and immune therapy outcomes largely vary among individuals, but very few studies examine the contribution of intrinsic behavior of the T cells to this heterogeneity. Here we show the development of a microfluidic-based in vitro method to track the outcome of antigen-specific T cell activity on many individual cancer spheroids simultaneously at high spatiotemporal resolution, which we call Multiscale Immuno-Oncology on-Chip System (MIOCS). By combining parallel measurements of T cell behaviors and tumor fates with probabilistic modeling, we establish that the first recruited T cells initiate a positive feedback loop to accelerate further recruitment to the spheroid. We also provide evidence that cooperation between T cells on the spheroid during the killing phase facilitates tumor destruction. Thus, we propose that both T cell accumulation and killing function rely on collective behaviors rather than simply reflecting the sum of individual T cell activities, and the possibility to track many replicates of immune cell-tumor interactions with the level of detail our system provides may contribute to our understanding of immune response heterogeneity.

Anti-cancer cytotoxic T cell responses largely vary among individuals. Here authors show, by stochastic modeling on high throughput T cell behavior and matched tumor spheroid fate data generated by a microfluidics system, that tumor killing is dependent on T cell cooperativity, which might contribute to the heterogeneity of T cell responses.

Current Strategies for the Treatment of Hepatocellular Carcinoma by Modulating the Tumor Microenvironment via Nano-Delivery Systems: A Review

Liver cancer remains a global health challenge with a projected incidence of over one million cases by 2025. Hepatocellular carcinoma (HCC) is a common primary liver cancer, accounting for about 90% of all liver cancer cases. The tumor microenvironment (TME) is the internal and external environment for tumor development, which plays an important role in tumorigenesis, immune escape and treatment resistance. Knowing that TME is a unique setting for HCC tumorigenesis, exploration of strategies to modulate TME has attracted increasing attention. Among them, the use of nano-delivery systems to deliver therapeutic agents to regulate TME components has shown great potential. TME-modulating nanoparticles have the advantages of protecting therapeutic agents from degradation, enhancing the ability of targeting HCC and reducing systemic toxicity. In this article, we summarize the TME components associated with HCC, including cancer-associated fibroblasts (CAFs), extracellular matrix (ECM), endothelial cells and immune cells, discuss their impact on the HCC progression, and highlight recent studies on nano-delivery systems that modulate these components. Finally, we also discuss opportunities and challenges in this field.

Greek Fire, Poison Arrows, and Scorpion Bombs: How Tumor Cells Defend Against the Siege Weapons of Cytotoxic T Lymphocytes

CD8⁺ cytotoxic T lymphocytes (CTLs) are the main cellular effectors of the adaptive immune response against cancer cells, which in turn have evolved sophisticated cellular defense mechanisms to withstand CTL attack. Herein we provide a critical review of the pertinent literature on early and late attack/defense events taking place at the CTL/target cell lytic synapse. We examine the earliest steps of CTL-mediated cytotoxicity (“the poison arrows”) elicited within seconds of CTL/target cell encounter, which face commensurately rapid synaptic repair mechanisms on the tumor cell side, providing the first formidable barrier to CTL attack. We examine how breach of this first defensive barrier unleashes the inextinguishable “Greek fire” in the form of granzymes whose broad cytotoxic potential is linked to activation of cell death executioners, injury of vital organelles, and destruction of intracellular homeostasis. Herein tumor cells deploy slower but no less sophisticated defensive mechanisms in the form of enhanced autophagy, increased reparative capacity, and dysregulation of cell death pathways. We discuss how the newly discovered supra-molecular attack particles (SMAPs, the “scorpion bombs”), seek to overcome the robust defensive mechanisms that confer tumor cell resistance. Finally, we discuss the implications of the aforementioned attack/defense mechanisms on the induction of regulated cell death (RCD), and how different contemporary RCD modalities (including apoptosis, pyroptosis, and ferroptosis) may have profound implications for immunotherapy. Thus, we propose that understanding and targeting multiple steps of the attack/defense process will be instrumental to enhance the efficacy of CTL anti-tumor activity and meet the outstanding challenges in clinical immunotherapy.

Tumour immunotherapy: lessons from predator-prey theory

With the burgeoning use of immune-based treatments for cancer, never has there been a greater need to understand the tumour microenvironment within which immune cells function and how it can be perturbed to inhibit tumour growth. Yet, current challenges in identifying optimal combinations of immunotherapies and engineering new cell-based therapies highlight the limitations of conventional paradigms for the study of the tumour microenvironment. Ecology has a rich history of studying predator-prey dynamics to discern factors that drive prey to extinction. Here, we describe the basic tenets of predator-prey theory as applied to 'predation' by immune cells and the 'extinction' of cancer cells. Our synthesis reveals fundamental mechanisms by which antitumour immunity might fail in sometimes counterintuitive ways and provides a fresh yet evidence-based framework to better understand and therapeutically target the immune-cancer interface.

Group 1 ILCs regulate T cell-mediated liver immunopathology by controlling local IL-2 availability

Group 1 innate lymphoid cells (ILCs), which comprise both natural killer (NK) cells and ILC1s, are important innate effectors that can also positively and negatively influence adaptive immune responses. The latter function is generally ascribed to the ability of NK cells to recognize and kill activated T cells. Here, we used multiphoton intravital microscopy in mouse models of hepatitis B to study the intrahepatic behavior of group 1 ILCs and their cross-talk with hepatitis B virus (HBV)-specific CD8⁺ T cells. We found that hepatocellular antigen recognition by effector CD8⁺ T cells triggered a prominent increase in the number of hepatic NK cells and ILC1s. Group 1 ILCs colocalized and engaged in prolonged interactions with effector CD8⁺ T cells undergoing hepatocellular antigen recognition; however, they did not induce T cell apoptosis. Rather, group 1 ILCs constrained CD8⁺ T cell proliferation by controlling local interleukin-2 (IL-2) availability. Accordingly, group 1 ILC depletion, or genetic removal of their IL-2 receptor a chain, considerably increased the number of intrahepatic HBV-specific effector CD8⁺ T cells and the attendant immunopathology. Together, these results reveal a role for group 1 ILCs in controlling T cell-mediated liver immunopathology by limiting local IL-2 concentration and have implications for the treatment of chronic HBV infection.

Ultrarapid lytic granule release from CTLs activates Ca2+-dependent synaptic resistance pathways in melanoma cells

Human cytotoxic T lymphocytes (CTLs) exhibit ultrarapid lytic granule secretion, but whether melanoma cells mobilize defense mechanisms with commensurate rapidity remains unknown. We used single-cell time-lapse microscopy to offer high spatiotemporal resolution analyses of subcellular events in melanoma cells upon CTL attack. Target cell perforation initiated an intracellular Ca²⁺ wave that propagated outward from the synapse within milliseconds and triggered lysosomal mobilization to the synapse, facilitating membrane repair and conferring resistance to CTL induced cytotoxicity. Inhibition of Ca²⁺ flux and silencing of synaptotagmin VII limited synaptic lysosomal exposure and enhanced cytotoxicity. Multiplexed immunohistochemistry of patient melanoma nodules combined with automated image analysis showed that melanoma cells facing CD8⁺ CTLs in the tumor periphery or peritumoral area exhibited significant lysosomal enrichment. Our results identified synaptic Ca²⁺ entry as the definitive trigger for lysosomal deployment to the synapse upon CTL attack and highlighted an unpredicted defensive topology of lysosome distribution in melanoma nodules.

Imaging the different timescales of germinal center selection

Germinal centers (GCs) are the site of antibody affinity maturation, a fundamental immunological process that increases the potency of antibodies and thereby their ability to protect against infection. GC biology is highly dynamic in both time and space, making it ideally suited for intravital imaging. Using multiphoton laser scanning microscopy (MPLSM), the field has gained insight into the molecular, cellular, and structural changes and movements that coordinate affinity maturation in real time in their native environment. On the other hand, several limitations of MPLSM have had to be overcome to allow full appreciation of GC events taking place across different timescales. Here, we review the technical advances afforded by intravital imaging and their contributions to our understanding of GC biology.

Nitric oxide controls proliferation of Leishmania major by inhibiting the recruitment of permissive host cells

Nitric oxide (NO) is an important antimicrobial effector but also prevents unnecessary tissue damage by shutting down the recruitment of monocyte-derived phagocytes. Intracellular pathogens such as Leishmania major can hijack these cells as a niche for replication. Thus, NO might exert containment by restricting the availability of the cellular niche required for efficient pathogen proliferation. However, such indirect modes of action remain to be established. By combining mathematical modeling with intravital 2-photon biosensors of pathogen viability and proliferation, we show that low L. major proliferation results not from direct NO impact on the pathogen but from reduced availability of proliferation-permissive host cells. Although inhibiting NO production increases recruitment of these cells, and thus pathogen proliferation, blocking cell recruitment uncouples the NO effect from pathogen proliferation. Therefore, NO fulfills two distinct functions for L. major containment: permitting direct killing and restricting the supply of proliferation-permissive host cells.

•

Direct killing of L. major by NO occurs only during the peak of the immune response

•

Efficient L. major proliferation requires newly recruited monocyte-derived cells

•

Loss of NO production increases both pathogen proliferation and monocyte recruitment

•

NO dampens L. major proliferation indirectly, limiting the pathogen’s cellular niche

Visualizing murine breast and melanoma tumor microenvironment using intravital multiphoton microscopy

Intravital multiphoton imaging of the tumor milieu allows for the dissection of intricate and dynamic biological processes in situ. Herein, we present a step-by-step protocol for setting up an experimental cancer imaging model that has been optimized for solid tumors such as breast cancer and melanoma implanted in the flanks of mice. This protocol can be utilized for dissecting tumor-immune cell dynamics in vivo or other tumor-specific biological questions.

For complete details on the use of this protocol for intravital imaging of breast cancer, please refer to Tikoo et al. (2021a), and for intravital imaging of melanoma, please refer to Tikoo et al. (2021b).

•

Detailed protocol for setting up high-resolution intravital imaging of murine tumors

•

3D printing of custom stage inserts for tumor stabilization

•

Procedures for cannulation of blood vessels

•

Surgical preparation and tissue stabilization for imaging tumor milieu in vivo

Cytotoxic T cells are able to efficiently eliminate cancer cells by additive cytotoxicity

Lethal hit delivery by cytotoxic T lymphocytes (CTL) towards B lymphoma cells occurs as a binary, "yes/no" process. In non-hematologic solid tumors, however, CTL often fail to kill target cells during 1:1 conjugation. Here we describe a mechanism of "additive cytotoxicity" by which time-dependent integration of sublethal damage events, delivered by multiple CTL transiting between individual tumor cells, mediates effective elimination. Reversible sublethal damage includes perforin-dependent membrane pore formation, nuclear envelope rupture and DNA damage. Statistical modeling reveals that 3 serial hits delivered with decay intervals below 50 min discriminate between tumor cell death or survival after recovery. In live melanoma lesions in vivo, sublethal multi-hit delivery is most effective in interstitial tissue where high CTL densities and swarming support frequent serial CTL-tumor cell encounters. This identifies CTL-mediated cytotoxicity by multi-hit delivery as an incremental and tunable process, whereby accelerating damage magnitude and frequency may improve immune efficacy.

Rational design of genetically encoded reporter genes for optical imaging of apoptosis

Apoptosis is a process in which cells are genetically regulated to cause a series of changes in morphology and metabolic activity, which ultimately lead to cell death. Apoptosis plays a vital role in the entire life cycle of an organism. Too much or too little apoptosis can cause a variety of diseases. Therefore, efficient and convenient methods for detecting apoptosis are necessary for clinical treatment and drug development. Traditional methods for detecting apoptosis may cause damage to the body during sample collection, such as for flow cytometry analysis. So it is necessary to monitor apoptosis without invasion in vivo. Optical imaging technique provides a more sensitive and economical way for apoptosis visualization. A subset of engineered reporter genes based on fluorescent proteins or luciferases are currently developed to monitor the dynamic changes in apoptotic markers, such as activation of caspases and exposure of phosphatidylserine on the surface of dying cells. These reporters detect apoptosis when cells have not undergone significant morphological changes, providing conditions for early diagnosis of tumors. In addition, these reporters show considerable value in high-throughput screening of apoptosis-related drugs and evaluation of their efficacy in treating tumors. In this review, we will discuss the recent research progress in the optical imaging of apoptosis based on the genetically encoded reporter genes.

Functional heterogeneity of cytotoxic T cells and tumor resistance to cytotoxic hits limit anti-tumor activity in vivo

Cytotoxic T cells (CTLs) can eliminate tumor cells through the delivery of lethal hits, but the actual efficiency of this process in the tumor microenvironment is unclear. Here, we visualized the capacity of single CTLs to attack tumor cells in vitro and in vivo using genetically encoded reporters that monitor cell damage and apoptosis. Using two distinct malignant B-cell lines, we found that the majority of cytotoxic hits delivered by CTLs in vitro were sublethal despite proper immunological synapse formation, and associated with reversible calcium elevation and membrane damage in the targets. Through intravital imaging in the bone marrow, we established that the majority of CTL interactions with lymphoma B cells were either unproductive or sublethal. Functional heterogeneity of CTLs contributed to diverse outcomes during CTL-tumor contacts in vivo. In the therapeutic settings of anti-CD19 CAR T cells, the majority of CAR T cell-tumor interactions were also not associated with lethal hit delivery. Thus, differences in CTL lytic potential together with tumor cell resistance to cytotoxic hits represent two important bottlenecks for anti-tumor responses in vivo.

Engineering Nano-Therapeutics to Boost Adoptive Cell Therapy for Cancer Treatment

Although adoptive transfer of therapeutic cells to cancer patients is demonstrated with great success and fortunately approved for the treatment of leukemia and B-cell lymphoma, potential issues, including the unclear mechanism, complicated procedures, unfavorable therapeutic efficacy for solid tumors, and side effects, still hinder its extensive applications. The explosion of nanotechnology recently has led to advanced development of novel strategies to address these challenges, facilitating the design of nano-therapeutics to improve adoptive cell therapy (ACT) for cancer treatment. In this review, the emerging nano-enabled approaches, that design multiscale artificial antigen-presenting cells for cell proliferation and stimulation in vitro, promote the transducing efficiency of tumor-targeting domains, engineer therapeutic cells for in vivo imaging, tumor infiltration, and in vivo functional sustainability, as well as generate tumoricidal T cells in vivo, are summarized. Meanwhile, the current challenges and future perspectives of the nanostrategy-based ACT for cancer treatment are also discussed in the end.

Recent advances in intravital microscopy for investigation of dynamic cellular behavior in vivo

Currently, most biological research relies on conventional experimental techniques that allow only static analyses at certain time points in vitro or ex vivo. However, if one could visualize cellular dynamics in living organisms, that would provide a unique opportunity to study key biological phenomena in vivo. Intravital microscopy (IVM) encompasses diverse optical systems for direct viewing of objects, including biological structures and individual cells in live animals. With the current development of devices and techniques, IVM addresses important questions in various fields of biological and biomedical sciences. In this mini-review, we provide a general introduction to IVM and examples of recent applications in the field of immunology, oncology, and vascular biology. We also introduce an advanced type of IVM, dubbed real-time IVM, equipped with video-rate resonant scanning. Since the real-time IVM can render cellular dynamics with high temporal resolution in vivo, it allows visualization and analysis of rapid biological processes.

The Dynamic Entropy of Tumor Immune Infiltrates: The Impact of Recirculation, Antigen-Specific Interactions, and Retention on T Cells in Tumors

Analysis of tumor infiltration using conventional methods reveals a snapshot view of lymphocyte interactions with the tumor environment. However, lymphocytes have the unique capacity for continued recirculation, exploring varied tissues for the presence of cognate antigens according to inflammatory triggers and chemokine gradients. We discuss the role of the inflammatory and cellular makeup of the tumor environment, as well as antigen expressed by cancer cells or cross-presented by stromal antigen presenting cells, on recirculation kinetics of T cells. We aim to discuss how current cancer therapies may manipulate lymphocyte recirculation versus retention to impact lymphocyte exclusion in the tumor.

Circulating clonally expanded T cells reflect functions of tumor-infiltrating T cells

Understanding the relationship between tumor and peripheral immune environments could allow longitudinal immune monitoring in cancer. Here, we examined whether T cells that share the same TCRαβ and are found in both tumor and blood can be interrogated to gain insight into the ongoing tumor T cell response. Paired transcriptome and TCRαβ repertoire of circulating and tumor-infiltrating T cells were analyzed at the single-cell level from matched tumor and blood from patients with metastatic melanoma. We found that in circulating T cells matching clonally expanded tumor-infiltrating T cells (circulating TILs), gene signatures of effector functions, but not terminal exhaustion, reflect those observed in the tumor. In contrast, features of exhaustion are displayed predominantly by tumor-exclusive T cells. Finally, genes associated with a high degree of blood-tumor TCR sharing were overexpressed in tumor tissue after immunotherapy. These data demonstrate that circulating TILs have unique transcriptional patterns that may have utility for the interrogation of T cell function in cancer immunotherapy.

A cross-talk between CAR T cell subsets and the tumor microenvironment is essential for sustained cytotoxic activity

Chimeric antigen receptor (CAR) T cell therapy relies on the activity of a large pool of tumor-targeting cytotoxic effectors. Whether CAR T cells act autonomously or require interactions with the tumor microenvironment (TME) remains incompletely understood. Here, we report an essential cross-talk between CAR T cell subsets and the TME for tumor control in an immunocompetent mouse B cell lymphoma model of anti-CD19 CAR T cell therapy. Using single-cell RNA sequencing, we revealed substantial modification of the TME during CAR T cell therapy. Interferon-γ (IFN-γ) produced by CAR T cells not only enhanced endogenous T and natural killer cell activity but was also essential for sustaining CAR T cell cytotoxicity, as revealed by intravital imaging. CAR T cell-derived IFN-γ facilitated host interleukin-12 production that supported host immune and CAR T cell responses. Compared with CD8⁺ CAR T cells, CD4⁺ CAR T cells were more efficient at host immune activation but less capable of direct tumor killing. In summary, CAR T cells do not act independently in vivo but rely instead on cytokine-mediated cross-talk with the TME for optimal activity. Invigorating CAR T cell interplay with the host represents an attractive strategy to prevent relapses after therapy.

Designed improvement to T-cell immunotherapy by multidimensional single cell profiling

BACKGROUND

Adoptive cell therapy based on the infusion of chimeric antigen receptor (CAR) T cells has shown remarkable efficacy for the treatment of hematologic malignancies. The primary mechanism of action of these infused T cells is the direct killing of tumor cells expressing the cognate antigen. However, understanding why only some T cells are capable of killing, and identifying mechanisms that can improve killing has remained elusive.

METHODS

To identify molecular and cellular mechanisms that can improve T-cell killing, we utilized integrated high-throughput single-cell functional profiling by microscopy, followed by robotic retrieval and transcriptional profiling.

RESULTS

With the aid of mathematical modeling we demonstrate that non-killer CAR T cells comprise a heterogeneous population that arise from failure in each of the discrete steps leading to the killing. Differential transcriptional single-cell profiling of killers and non-killers identified CD137 as an inducible costimulatory molecule upregulated on killer T cells. Our single-cell profiling results directly demonstrate that inducible CD137 is feature of killer (and serial killer) T cells and this marks a different subset compared with the CD107apos (degranulating) subset of CAR T cells. Ligation of the induced CD137 with CD137 ligand (CD137L) leads to younger CD19 CAR T cells with sustained killing and lower exhaustion. We genetically modified CAR T cells to co-express CD137L, in trans, and this lead to a profound improvement in anti-tumor efficacy in leukemia and refractory ovarian cancer models in mice.

CONCLUSIONS

Broadly, our results illustrate that while non-killer T cells are reflective of population heterogeneity, integrated single-cell profiling can enable identification of mechanisms that can enhance the function/proliferation of killer T cells leading to direct anti-tumor benefit.