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Simple Summary Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies, with an approximate 10% five-year survival rate despite therapy. A plausible reason for this observation may be that other, redundant, immune-suppressive mechanisms are at play. Thus, effective treatment of PDAC is a medical challenge and warrants the development of a pre-clinical model whereby the patient’s tumor immune phenotype is characterized and the immune response within the tumor microenvironment tested prior to therapy. These studies present a pre-clinical organoid model that may be used to test the efficacy of combinatorial therapies and targeted therapies, based on modulating the tumor microenvironment, to improve cancer patient response and survival. Abstract Purpose: Pancreatic ductal adenocarcinoma (PDAC) has the lowest five-year survival rate of all cancers in the United States. Programmed death 1 receptor (PD-1)-programmed death ligand 1 (PD-L1) immune checkpoint inhibition has been unsuccessful in clinical trials. Myeloid-derived suppressor cells (MDSCs) are known to block anti-tumor CD8+ T cell immune responses in various cancers including pancreas. This has led us to our objective that was to develop a clinically relevant in vitro organoid model to specifically target mechanisms that deplete MDSCs as a therapeutic strategy for PDAC. Method: Murine and human pancreatic ductal adenocarcinoma (PDAC) autologous organoid/immune cell co-cultures were used to test whether PDAC can be effectively treated with combinatorial therapy involving PD-1 inhibition and MDSC depletion. Results: Murine in vivo orthotopic and in vitro organoid/immune cell co-culture models demonstrated that polymorphonuclear (PMN)-MDSCs promoted tumor growth and suppressed cytotoxic T lymphocyte (CTL) proliferation, leading to diminished efficacy of checkpoint inhibition. Mouse- and human-derived organoid/immune cell co-cultures revealed that PD-L1-expressing organoids were unresponsive to nivolumab in vitro in the presence of PMN-MDSCs. Depletion of arginase 1-expressing PMN-MDSCs within these co-cultures rendered the organoids susceptible to anti-PD-1/PD-L1-induced cancer cell death. Conclusions: Here we use mouse- and human-derived autologous pancreatic cancer organoid/immune cell co-cultures to demonstrate that elevated infiltration of polymorphonuclear (PMN)-MDSCs within the PDAC tumor microenvironment inhibit T cell effector function, regardless of PD-1/PD-L1 inhibition. We present a pre-clinical model that may predict the efficacy of targeted therapies to improve the outcome of patients with this aggressive and otherwise unpredictable malignancy.

In vitro studies of gastric wound repair typically involves the use of gastric cancer cell lines in a scratch-wound assay of cellular proliferation and migration. One critical limitation of such assays, however, is their homogenous assortment of cellular types. Repair is a complex process which demands the interaction of several cell types. Therefore, to study a culture devoid of cellular subtypes, is a concern that must be overcome if we are to understand the repair process. The gastric organoid model may alleviate this issue whereby the heterogeneous collection of cell types closely reflects that of the gastric epithelium or other native tissues in vivo. Demonstrated here is a novel, in vitro scratch-wound assay derived from human or mouse 3-dimensional organoids which can then be transferred to a gastric epithelial monolayer as either intact organoids or as a single cell suspension of dissociated organoids. The goal of the protocol is to establish organoid-derived gastric epithelial monolayers that can be used in a novel scratch-wound assay system to study gastric regeneration.

Organoid cultures generated from gastrointestinal tissues have been an invaluable advancement for in vitro studies of physiological function and disease. Here we present a comprehensive protocol for the establishment and culture of human- and mouse-derived 3-dimensional gastric organoids transferred to 2-dimensional gastric epithelial cell monolayers. We introduce two methods that include the establishment of monolayers from: (1) intact organoids, and (2) single cells dissociated from intact organoids.

The interaction between the receptor, programmed cell death protein 1 (PD-1) and ligand, programmed cell death 1 (PD-L1) is known to inhibit CD8+ cytotoxic T lymphocyte proliferation, survival, and effector function. The result of this interaction leads to evasion of immune surveillance by tumors and subsequently cancer cell proliferation. Immunotherapy via PD-L1 blockade is used for a variety of malignancies, yet the prognostic value of immune checkpoint inhibition for the treatment of gastric cancer remains controversial. Thus, preclinical models that would predict the efficacy of such therapy in a subgroup of gastric cancer patients would be an advancement in the personalized treatment of this disease. Three-dimensional organoid cultures have not only been used to investigate the mechanisms regulating development and disease, but have also been used for high-throughput drug screening for targeted personalized therapy. Here we present the methodology for the co-culture of mouse-derived gastric cancer organoids with autologous immune cells specifically for the study of PD-L1/PD-1 interactions within the tumor microenvironment in vitro.

Background & Aims Our goal was to develop an initial study for the proof of concept whereby gastric cancer organoids are used as an approach to predict the tumor response in individual patients. Methods Organoids were derived from resected gastric cancer tumors (huTGOs) or normal stomach tissue collected from sleeve gastrectomies (huFGOs). Organoid cultures were treated with standard-of-care chemotherapeutic drugs corresponding to patient treatment: epirubicin, oxaliplatin, and 5-fluorouracil. Organoid response to chemotherapeutic treatment was correlated with the tumor response in each patient from whom the huTGOs were derived. HuTGOs were orthotopically transplanted into the gastric mucosa of NOD scid gamma mice. Results Whereas huFGOs exhibited a half maximal inhibitory concentration that was similar among organoid lines, divergent responses and varying half maximal inhibitory concentration values among the huTGO lines were observed in response to chemotherapeutic drugs. HuTGOs that were sensitive to treatment were derived from a patient with a near complete tumor response to chemotherapy. However, organoids resistant to treatment were derived from patients who exhibited no response to chemotherapy. Orthotropic transplantation of organoids resulted in the engraftment and development of human adenocarcinoma. RNA sequencing revealed that huTGOs closely resembled the patient's native tumor tissue and not commonly used gastric cancer cell lines and cell lines derived from the organoid cultures. Conclusions The treatment of patient-derived organoids alongside patients from whom cultures were derived will ultimately test their usefulness to predict individual therapy response and patient outcome., Graphical abstract

Tumor cells expressing programmed cell death ligand 1 (PD-L1) interact with PD-1 on CD8+ cytotoxic T lymphocytes (CTLs) to inhibit CTL effector function. In gastric cancer, the mechanism regulating PD-L1 is unclear. The Hedgehog (Hh) signaling pathway is reactivated in various cancers including gastric. Here we tested the hypothesis that Hh-induced PD-L1 inactivates effector T cell function and allows gastric cancer cell proliferation. Mouse organoids were generated from tumors of a triple-transgenic mouse model engineered to express an activated GLI2 allele, GLI2A, in Lgr5-expressing stem cells, (mTGOs) or normal mouse stomachs (mGOs). Bone marrow-derived dendritic cells (DCs) were pulsed with conditioned media collected from normal (mGOCM) or cancer (mTGOCM) organoids. Pulsed DCs and CTLs were then co-cultured with either mGOs or mTGOs in the presence of PD-L1 neutralizing antibody (PD-L1Ab). Human-derived gastric cancer organoids (huTGOs) were used in drug and xenograft assays. Hh/Gli inhibitor, GANT-61 significantly reduced the expression of PD-L1 and tumor cell proliferation both in vivo and in vitro. PD-L1Ab treatment induced tumor cell apoptosis in mTGO/immune cell co-cultures. GANT-61 treatment sensitized huTGOs to standard-of-care chemotherapeutic drugs both in vivo and in vitro. Thus, Hh signaling mediates PD-L1 expression in gastric cancer cells and subsequently promotes tumor proliferation.