Expression of tdTomato and luciferase in a murine lung cancer alters the growth and immune microenvironment of the tumor

KPC-luciferase-expressing cells elicit an anti-tumor immune response in a mouse model of pancreatic cancer

Mouse models for the study of pancreatic ductal adenocarcinoma (PDAC) are well-established and representative of many key features observed in human PDAC. To monitor tumor growth, cancer cells that are implanted in mice are often transfected with reporter genes, such as firefly luciferase (Luc), enabling in vivo optical imaging over time. Since Luc can induce an immune response, we aimed to evaluate whether the expression of Luc could affect the growth of KPC tumors in mice by inducing immunogenicity. Although both cell lines, KPC and Luc transduced KPC (KPC-Luc), had the same proliferation rate, KPC-Luc tumors had significantly smaller sizes or were absent 13 days after orthotopic cell implantation, compared to KPC tumors. This coincided with the loss of bioluminescence signal over the tumor region. Immunophenotyping of blood and spleen from KPC-Luc tumor-bearing mice showed a decreased number of macrophages and CD4+ T cells, and an increased accumulation of natural killer (NK) cells in comparison to KPC tumor mice. Higher infiltration of CD8+ T cells was found in KPC-Luc tumors than in their controls. Moreover, the immune response against Luc peptide was stronger in splenocytes from mice implanted with KPC-Luc cells compared to those isolated from KPC wild-type mice, indicating increased immunogenicity elicited by the presence of Luc in the PDAC tumor cells. These results must be considered when evaluating the efficacy of anti-cancer therapies including immunotherapies in immunocompetent PDAC or other cancer mouse models that use Luc as a reporter for bioluminescence imaging.

Transplantable Subcutaneous Tumor Models

Mouse tumor models are essential in cancer research, especially in elucidating malignancy, developing prevention, diagnosis, and new therapeutic approaches. Nowadays, due to standardized ways of maintaining animal colonies and the availability of mouse strains with known genetic backgrounds and approaches to reduce the variability of tumor size between animals, transplantable mouse tumor models can be widely used in translational cancer research. Here, we describe the induction of different subcutaneous tumor models in mice, in particular xenograft and syngeneic that can be used as experimental tumor models.

Infection of tumor cells with Salmonella typhimurium mimics immunogenic cell death and elicits tumor-specific immune responses

Some properties of Salmonella-infected cells overlap with immunogenic cell death. In this study, we demonstrated that intracellular infection of melanoma with Salmonella typhimurium induced high immunogenicity in melanoma cells, leading to antitumor effects with melanoma-antigen-specific T-cell responses. Murine B16F10 melanoma cells were infected with tdTomato-expressing attenuated S. typhimurium (VNP20009; VNP-tdT), triggering massive cell vacuolization. VNP-tdT-infected B16F10 cells were phagocytosed efficiently, which induced the activation of antigen-presenting cells with CD86 expression in vitro. Subcutaneous coimplantation of uninfected and VNP-tdT-infected B16F10 cells into C57BL/6 mice significantly suppressed tumor growth compared with the implantation of uninfected B16F10 cells alone. Inoculation of mice with VNP-tdT-infected B16F10 cells elicited the proliferation of melanoma-antigen (gp100)-specific T cells, and it protected the mice from the second tumor challenge of uninfected B16F10 cells. These results suggest that Salmonella-infected tumor cells acquire effective adjuvanticity, leading to ideal antitumor immune responses.

Establishing a mouse model of lung metastases using ultrasound-guided right heart ventricle injection

We report a technique to generate a murine model of lung metastases by selectively injecting tumor cells into the right heart ventricle under ultrasound guidance. First, we describe cell preparation and reference animal preparation as previously described. We then detail the technique using a previously described 3D-printed instrument stabilization device. Finally, we describe tumor growth surveillance using bioluminescent imaging. For complete details on the use and execution of this protocol, please refer to Labora et al.1.

Genome editing in the mouse brain with minimally immunogenic Cas9 RNPs

Transient delivery of CRISPR-Cas9 ribonucleoproteins (RNPs) into the central nervous system (CNS) for therapeutic genome editing could avoid limitations of viral vector-based delivery including cargo capacity, immunogenicity, and cost. Here, we tested the ability of cell-penetrant Cas9 RNPs to edit the mouse striatum when introduced using a convection-enhanced delivery system. These transient Cas9 RNPs showed comparable editing of neurons and reduced adaptive immune responses relative to one formulation of Cas9 delivered using AAV serotype 9. The production of ultra-low endotoxin Cas9 protein manufactured at scale further improved innate immunity. We conclude that injection-based delivery of minimally immunogenic CRISPR genome editing RNPs into the CNS provides a valuable alternative to virus-mediated genome editing.

Generation of liver metastases in a mouse model using ultrasound-guided intravenous injection

Here, we present a protocol to generate a murine model of liver metastasis by directly injecting tumor cells into the portal vein under ultrasound guidance. We describe steps for animal and cell preparation and two techniques for injecting tumor cells. One technique is freehand, while the other technique is device-assisted using a 3D-printed prototype device. Finally, we describe tumor surveillance with bioluminescent imaging.

Diets Differently Regulate Tumorigenesis in Young E0771 Syngeneic Breast Cancer Mouse Model

Breast cancer (BC) is the most diagnosed cancer type, accounting for one in eight cancer diagnoses worldwide. Epidemiological studies have shown that obesity is associated with increased risk of BC in post-menopausal women, whereas adiposity reduces the risk of BC in premenopausal women. The mechanistic link between obesity and BC has been examined by combining murine BC models with high-fat diet (HFD) induced obesity. However, the effect of adiposity (not obesity) induced by a short period of HFD consumption on BC pathogenesis is not well understood. In the current study, we examined the effects of different diet compositions on BC pathogenesis using a young E0771 syngeneic BC mouse model fed on either an HFD or regular diet (RD: a low-fat high-carbohydrate diet) for a short period (4 weeks) before implanting mammary tumors in mice. We analyzed the effect of diet composition on the onset of tumor growth, metastasis, and metabolic and immune status in the tumor microenvironment (TME) using various methods including in vivo bioluminescence imaging and immunoblotting analyses. We showed for the first time that a short-term HFD delays the onset of tumorigenesis by altering the immune and metabolic signaling and energy mechanism in the TME. However, RD may increase the risk of tumorigenesis and metastasis by increasing pro-inflammatory factors in the TME in young mice. Our data suggest that diet composition, adipogenesis, and loss of body fat likely regulate the pathogenesis of BC in a manner that differs between young and post-menopausal subjects.

Validation of an orthotopic non-small cell lung cancer mouse model, with left or right tumor growths, to use in conformal radiotherapy studies

Orthotopic non-small cell lung cancer (NSCLC) mice models are important for establishing translatability of in vitro results. However, most orthotopic lung models do not produce localized tumors treatable by conformal radiotherapy (RT). Here we report on the performance of an orthotopic mice model featuring conformal RT treatable tumors following either left or right lung tumor cell implantation. Athymic Nude mice were surgically implanted with H1299 NSCLC cell line in either the left or right lung. Tumor development was tracked bi-weekly using computed tomography (CT) imaging. When lesions reached an appropriate size for treatment, animals were separated into non-treatment (control group) and RT treated groups. Both RT treated left and right lung tumors which were given a single dose of 20 Gy of 225 kV X-rays. Left lung tumors were treated with a two-field parallel opposed plan while right lung tumors were treated with a more conformal four-field plan to assess tumor control. Mice were monitored for 30 days after RT or after tumor reached treatment size for non-treatment animals. Treatment images from the left and right lung tumor were also used to assess the dose distribution for four distinct treatment plans: 1) Two sets of perpendicularly staggered parallel opposed fields, 2) two fields positioned in the anterior-posterior and posterior-anterior configuration, 3) an 180° arc field from 0° to 180° and 4) two parallel opposed fields which cross through the contralateral lung. Tumor volumes and changes throughout the follow-up period were tracked by three different types of quantitative tumor size approximation and tumor volumes derived from contours. Ultimately, our model generated delineable and conformal RT treatable tumor following both left and right lung implantation. Similarly consistent tumor development was noted between left and right models. We were also able to demonstrate that a single 20 Gy dose of 225 kV X-rays applied to either the right or left lung tumor models had similar levels of tumor control resulting in similar adverse outcomes and survival. And finally, three-dimensional tumor approximation featuring volume computed from the measured length across three perpendicular axes gave the best approximation of tumor volume, most closely resembled tumor volumes obtained with contours.

5-Azacytidine-Mediated Modulation of the Immune Microenvironment in Murine Acute Myeloid Leukemia

Cancer cells accumulate epigenetic modifications that allow escape from intrinsic and extrinsic surveillance mechanisms. In the case of acute myeloid leukemias (AML) and myelodysplastic syndromes, agents that disrupt chromatin structure, namely hypomethylating agents (HMAs), have shown tremendous promise as an alternate, milder treatment option for older, clinically non-fit patients. HMAs reprogram the epigenetic landscape in tumor cells through the reversal of DNA hypermethylation. Therapeutic effects resulting from these epigenetic changes are incredibly effective, sometimes resulting in complete remissions, but are frequently lost due to primary or acquired resistance. In this study, we describe syngeneic murine leukemias that are responsive to the HMA 5-azacytidine (5-Aza), as determined by augmented expression of a transduced luciferase reporter. We also found that 5-Aza treatment re-established immune-related transcript expression, suppressed leukemic burden and extended survival in leukemia-challenged mice. The effects of 5-Aza treatment were short-lived, and analysis of the immune microenvironment reveals possible mechanisms of resistance, such as simultaneous increase in immune checkpoint protein expression. This represents a model system that is highly responsive to HMAs and recapitulates major therapeutic outcomes observed in human leukemia (relapse) and may serve as a pre-clinical tool for studying acquired resistance and novel treatment combinations.

Development and Characterization of a Luciferase Labeled, Syngeneic Murine Model of Ovarian Cancer

Despite advances in surgery and targeted therapies, the prognosis for women with high-grade serous ovarian cancer remains poor. Moreover, unlike other cancers, immunotherapy has minimally impacted outcomes in patients with ovarian cancer. Progress in this regard has been hindered by the lack of relevant syngeneic ovarian cancer models to study tumor immunity and evaluate immunotherapies. To address this problem, we developed a luciferase labeled murine model of high-grade serous ovarian cancer, STOSE.M1 luc. We defined its growth characteristics, immune cell repertoire, and response to anti PD-L1 immunotherapy. As with human ovarian cancer, we demonstrated that this model is poorly sensitive to immune checkpoint modulators. By developing the STOSE.M1 luc model, it will be possible to probe the mechanisms underlying resistance to immunotherapies and evaluate new therapeutic approaches to treat ovarian cancer.

TNF-α-Secreting Lung Tumor-Infiltrated Monocytes Play a Pivotal Role During Anti-PD-L1 Immunotherapy

Immune checkpoint blockade (ICB) of the PD-1 pathway revolutionized the survival forecast for advanced non-small cell lung cancer (NSCLC). Yet, the majority of PD-L1⁺ NSCLC patients are refractory to anti-PD-L1 therapy. Recent observations indicate a pivotal role for the PD-L1⁺ tumor-infiltrating myeloid cells in therapy failure. As the latter comprise a heterogenous population in the lung tumor microenvironment, we applied an orthotopic Lewis Lung Carcinoma (LLC) model to evaluate 11 different tumor-residing myeloid subsets in response to anti-PD-L1 therapy. While we observed significantly reduced fractions of tumor-infiltrating MHC-II^low macrophages and monocytes, serological levels of TNF-α restored in lung tumor-bearing mice. Notably, we demonstrated in vivo and in vitro that anti-PD-L1 therapy mediated a monocyte-specific production of, and response to TNF-α, further accompanied by their significant upregulation of CD80, VISTA, LAG-3, SIRP-α and TIM-3. Nevertheless, co-blockade of PD-L1 and TNF-α did not reduce LLC tumor growth. A phenomenon that was partly explained by the observation that monocytes and TNF-α play a Janus-faced role in anti-PD-L1 therapy-mediated CTL stimulation. This was endorsed by the observation that monocytes appeared crucial to effectively boost T cell-mediated LLC killing in vitro upon combined PD-L1 with LAG-3 or SIRP-α blockade. Hence, this study enlightens the biomarker potential of lung tumor-infiltrated monocytes to define more effective ICB combination strategies.