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Microfluidic Co-Culture Models for Dissecting the Immune Response in in vitro Tumor Microenvironments

Complex disease models demand cutting-edge tools able to deliver physiologically and pathologically relevant, actionable insights, and unveil otherwise ...

Università Cattolica del Sacro Cuore

In most (if not all) solid tumors, malignant cells are outnumbered by their non-malignant counterparts, including immune, endothelial and stromal cells. However, while the mechanisms whereby cancer cells adapt to microenvironmental perturbations have been studied in great detail, relatively little is known on stress responses in non-malignant compartments of the tumor microenvironment. Here, we discuss the mechanisms whereby cancer-associated fibroblasts and other cellular components of the tumor stroma react to stress in the context of an intimate crosstalk with malignant, endothelial and immune cells, and how such crosstalk influences disease progression and response to treatment.

Stress responses in stromal cells and tumor homeostasis.

Tumor neantigens (TNAs) and tumor-associated antigens (TAAs) are crucial triggers of anticancer immune responses. Through major histocompatibility complex, such antigens activate T cells, which, by releasing interferon gamma (IFN-γ) and granzyme B (GRZB), act as crucial effectors against tumor onset and progression. However, in response to immune pressure, cancer cells use different strategies to favor the establishment of an immunosuppressive tumor microenvironment (TME). Elucidating the dynamics of tumor-host co-evolution provides novel opportunities for personalized cancer immunotherapies. The in sitro (in vitro+in situ) technology is an experimental approach involving the preparation of heterocellular cell suspensions from fresh tumors and their use in vitro. The in sitro experimental setup offers the possibility to (1) analyze immune-related parameters (e.g., quantification of cytokines released in the TME), (2) reveal the mechanism of action of drugs, and (3) unveil crucial cell-intrinsic and cell-extrinsic processes boosting anticancer immune responses. Nonetheless, the in sitro technology does not fully recapitulate the complexity of the tissue "in situ" nor models the patterns of infiltrating immune cell localization, and hence parallel experimentation should be scheduled. In this chapter we discuss in sitro technology to analyze and quantify IFN-γ and GRZB production by T cells either co-cultured with cancer cells in the presence of exogenous adjuvant stimuli (i.e., an antibody targeting the immune checkpoint programmed cell death protein 1, and recombinant calreticulin) and boosting with TAAs (i.e., the model SIINFEKL ovalbumin antigen). Specifically, we describe IFN-γ and GRZB quantification by flow cytometry, ELISA and ELISpot technologies.

Assessment of IFN-γ and granzyme-B production by in "sitro" technology.

Dendritic cells (DCs) are specialized antigen presenting cells (APCs) able to intake and crosspresent antigens (Ags) on major histocompatibility complex (MHC) class I and II molecules to T cells thus initiating primary and memory immune responses. DC-mediated Ag uptake and crosspresentation represent crucial steps toward cancer recognition and eventually elimination. Cytofluorometry is a standardized procedure to study phagocytosis. By fast and reproducible single cell measurements, flow cytometry allows for simultaneous biochemical and functional analyses of Ag intake. In this chapter, we discuss a two-color flow cytometric analysis of DC-mediated uptake of apoptotic bodies. We also show data on the adjuvanticity of Type-I-interferons (Type-I-IFNs) during Ag retention as we offer a guideline and a range of advice on sample preparation and acquisition.

Cytofluorometric assessment of dendritic cell-mediated uptake of cancer cell apoptotic bodies.

Cancer cell dormancy is a common feature of human tumors and represents a major clinical barrier to the long-term efficacy of anticancer therapies. Dormant cancer cells, either in primary tumors or disseminated in secondary organs, may reawaken and relapse into a more aggressive disease. The mechanisms underpinning dormancy entry and exit strongly resemble those governing cancer cell stemness and include intrinsic and contextual cues. Cellular and molecular components of the tumor microenvironment persistently interact with cancer cells. This dialog is highly dynamic, as it evolves over time and space, strongly cooperates with intrinsic cell nets, and governs cancer cell features (like quiescence and stemness) and fate (survival and outgrowth). Therefore, there is a need for deeper insight into the biology of dormant cancer (stem) cells and the mechanisms regulating the equilibrium quiescence--proliferation are vital in our pursuit of new therapeutic opportunities to prevent cancer from recurring. Here, we review and discuss microenvironmental regulations of cancer dormancy and its parallels with cancer stemness, and offer insights into the therapeutic strategies adopted to prevent a lethal recurrence, by either eradicating resident dormant cancer (stem) cells or maintaining them in a dormant state.

Tuning Cancer Fate: Tumor Microenvironment's Role in Cancer Stem Cell Quiescence and Reawakening.

Cancer stem cells (CSCs) are tumor subpopulations driving disease development, progression, relapse and therapy resistance, and their targeting ensures tumor eradication. CSCs display heterogeneous replication stress (RS), but the functionality/relevance of the RS response (RSR) centered on the ATR-CHK1 axis is debated. Here, we show that the RSR is efficient in primary CSCs from colorectal cancer (CRC-SCs), and describe unique roles for PARP1 and MRE11/RAD51. First, we demonstrated that PARP1 is upregulated in CRC-SCs resistant to several replication poisons and RSR inhibitors (RSRi). In these cells, PARP1 modulates replication fork speed resulting in low constitutive RS. Second, we showed that MRE11 and RAD51 cooperate in the genoprotection and mitosis execution of PARP1-upregulated CRC-SCs. These roles represent therapeutic vulnerabilities for CSCs. Indeed, PARP1i sensitized CRC-SCs to ATRi/CHK1i, inducing replication catastrophe, and prevented the development of resistance to CHK1i. Also, MRE11i + RAD51i selectively killed PARP1-upregulated CRC-SCs via mitotic catastrophe. These results provide the rationale for biomarker-driven clinical trials in CRC using distinct RSRi combinations.

Claudia Galassi

Istituto di Patologia Generale

Università Cattolica del Sacro Cuore

Microfluidic Co-Culture Models for Dissecting the Immune Response in in vitro Tumor Microenvironments