Patient-Derived Tumor Xenografts Are Susceptible to Formation of Human Lymphocytic Tumors

PDX Models in Theranostic Applications: Generation and Screening for B Cell Lymphoma of Human Origin

This MIB guide briefly summarizes the generation of patient-derived xenografts (PDXs) and highlights the importance of validating PDX models for the presence of B cell lymphoma of human origin before their use in radiotheranostic applications. The use of this protocol will allow researchers to learn different methods for screening PDX models for Epstein-Barr virus (EBV)-infected B cell lymphoma.

Assessment of Patient-Derived Xenograft Growth and Antitumor Activity: The NCI PDXNet Consensus Recommendations

Although patient-derived xenografts (PDX) are commonly used for preclinical modeling in cancer research, a standard approach to in vivo tumor growth analysis and assessment of antitumor activity is lacking, complicating the comparison of different studies and determination of whether a PDX experiment has produced evidence needed to consider a new therapy promising. We present consensus recommendations for assessment of PDX growth and antitumor activity, providing public access to a suite of tools for in vivo growth analyses. We expect that harmonizing PDX study design and analysis and assessing a suite of analytical tools will enhance information exchange and facilitate identification of promising novel therapies and biomarkers for guiding cancer therapy.

Patient-Derived-Xenografts in Mice: A Preclinical Platform for Cancer Research

The use of patient-derived xenografts (PDXs) has dramatically improved drug development programs. PDXs (1) reproduce the pathological features and the genomic profile of the parental tumors more precisely than other preclinical models, and (2) more faithfully predict therapy response. However, PDXs have limitations. These include the inability to completely capture tumor heterogeneity and the role of the immune system, the low engraftment efficiency of certain tumor types, and the consequences of the human-host interactions. Recently, the use of novel mouse strains and specialized engraftment techniques has enabled the generation of "humanized" PDXs, partially overcoming such limitations. Importantly, establishing, characterizing, and maintaining PDXs is costly and requires a significant regulatory, administrative, clinical, and laboratory infrastructure. In this review, we will retrace the historical milestones that led to the implementation of PDXs for cancer research, review the most recent innovations in the field, and discuss future avenues to tackle deficiencies that still exist.

Hemangiosarcoma Cells Promote Conserved Host-derived Hematopoietic Expansion

Hemangiosarcoma and angiosarcoma are soft-tissue sarcomas of blood vessel-forming cells in dogs and humans, respectively. These vasoformative sarcomas are aggressive and highly metastatic, with disorganized, irregular blood-filled vascular spaces. Our objective was to define molecular programs which support the niche that enables progression of canine hemangiosarcoma and human angiosarcoma. Dog-in-mouse hemangiosarcoma xenografts recapitulated the vasoformative and highly angiogenic morphology and molecular characteristics of primary tumors. Blood vessels in the tumors were complex and disorganized, and they were lined by both donor and host cells. In a series of xenografts, we observed that the transplanted hemangiosarcoma cells created exuberant myeloid hyperplasia and gave rise to lymphoproliferative tumors of mouse origin. Our functional analyses indicate that hemangiosarcoma cells generate a microenvironment that supports expansion and differentiation of hematopoietic progenitor populations. Furthermore, gene expression profiling data revealed hemangiosarcoma cells expressed a repertoire of hematopoietic cytokines capable of regulating the surrounding stromal cells. We conclude that canine hemangiosarcomas, and possibly human angiosarcomas, maintain molecular properties that provide hematopoietic support and facilitate stromal reactions, suggesting their potential involvement in promoting the growth of hematopoietic tumors.

SIGNIFICANCE

We demonstrate that hemangiosarcomas regulate molecular programs supporting hematopoietic expansion and differentiation, providing insights into their potential roles in creating a permissive stromal-immune environment for tumor progression.

Representation of genomic intratumor heterogeneity in multi-region non-small cell lung cancer patient-derived xenograft models

Patient-derived xenograft (PDX) models are widely used in cancer research. To investigate the genomic fidelity of non-small cell lung cancer PDX models, we established 48 PDX models from 22 patients enrolled in the TRACERx study. Multi-region tumor sampling increased successful PDX engraftment and most models were histologically similar to their parent tumor. Whole-exome sequencing enabled comparison of tumors and PDX models and we provide an adapted mouse reference genome for improved removal of NOD scid gamma (NSG) mouse-derived reads from sequencing data. PDX model establishment caused a genomic bottleneck, with models often representing a single tumor subclone. While distinct tumor subclones were represented in independent models from the same tumor, individual PDX models did not fully recapitulate intratumor heterogeneity. On-going genomic evolution in mice contributed modestly to the genomic distance between tumors and PDX models. Our study highlights the importance of considering primary tumor heterogeneity when using PDX models and emphasizes the benefit of comprehensive tumor sampling.

Co-clinical Trial of Novel Bispecific Anti-HER2 Antibody Zanidatamab in Patient-Derived Xenografts

Zanidatamab is a bispecific human epidermal growth factor receptor 2 (HER2)-targeted antibody that has demonstrated antitumor activity in a broad range of HER2-amplified/expressing solid tumors. We determined the antitumor activity of zanidatamab in patient-derived xenograft (PDX) models developed from pretreatment or postprogression biopsies on the first-in-human zanidatamab phase I study (NCT02892123). Of 36 tumors implanted, 19 PDX models were established (52.7% take rate) from 17 patients. Established PDXs represented a broad range of HER2-expressing cancers, and in vivo testing demonstrated an association between antitumor activity in PDXs and matched patients in 7 of 8 co-clinical models tested. We also identified amplification of MET as a potential mechanism of acquired resistance to zanidatamab and demonstrated that MET inhibitors have single-agent activity and can enhance zanidatamab activity in vitro and in vivo. These findings provide evidence that PDXs can be developed from pretreatment biopsies in clinical trials and may provide insight into mechanisms of resistance.

SIGNIFICANCE

We demonstrate that PDXs can be developed from pretreatment and postprogression biopsies in clinical trials and may represent a powerful preclinical tool. We identified amplification of MET as a potential mechanism of acquired resistance to the HER2 inhibitor zanidatamab and MET inhibitors alone and in combination as a therapeutic strategy. This article is featured in Selected Articles from This Issue, p. 695.

Generation of Orthotopic and Subcutaneous Patient-Derived Xenograft Models from Diverse Clinical Tissue Samples of Pediatric Extracranial Solid Tumors

Realistic and renewable laboratory models that accurately reflect the distinct clinical features of childhood cancers have enormous potential to speed research progress. These models help us to understand disease biology, develop new research methods, advance new therapies to clinical trial, and implement personalized medicine. This chapter describes methods to generate patient-derived xenograft models of neuroblastoma and rhabdomyosarcoma, two tumor types for which children with high-risk disease have abysmal survival outcomes and survivors have lifelong-debilitating effects from treatment. Further, this protocol addresses model development from diverse clinical tumor tissue samples, subcutaneous and orthotopic engraftment, and approaches to avoid model loss.

Establishment and characterization of a non-gestational choriocarcinoma patient-derived xenograft model

BACKGROUND

Non-gestational choriocarcinoma (NGC) is a rare subtype of malignant germ cell tumour and there is no consensus on its treatment. The lack of suitable preclinical models for NGC is a challenge in drug discovery research. Patient-derived xenograft (PDX) models recapitulate the tumour microenvironment of the original cancer tissue. Therefore, they have received considerable attention for studies on rare cancer. Here, we aimed to establish a PDX model from a patient with recurrent NGC.

METHODS

Fresh NGC tumour tissue was immediately transplanted into a severely immune-deficient mouse (NOD.Cg-Prkdcscid1l2rgtm1Wjl/SzJ) and maintained for more than three in vivo passages. Subsequently, we evaluated the molecular characteristics of the PDX model using immunohistochemistry, polymerase chain reaction, and RNA sequencing. Moreover, the PDX tumours were transplanted into BALB/c nude mice, and we evaluated their sensitivity for cisplatin and methotrexate.

RESULTS

The PDX tumour maintained the morphological features of NGC. Moreover, Immunohistochemistry revealed that the human chorionic gonadotropin, cytokeratin 7, and EpCAM expression levels were similar to those in the primary tumour. Furthermore, serum human chorionic gonadotropin levels were elevated in both the primary tumour and the PDX models. Additionally, using PCR analysis with species-specific primers, we confirmed that the PDX tumour contained human genes and was derived from human tissue. Moreover, the gene expression profile of the NGC was compared with that of epithelial ovarian cancer samples and cell lines, and 568 dysregulated genes in the NGC were extracted. The expression of the dysregulated genes in PDX was significantly correlated with that in the primary tumour (R2 = 0.873, P < 0.001). Finally, we demonstrated that the PDX tumour was sensitive to cisplatin and methotrexate; therefore, its clinical response to the agents was similar to that of the primary tumour.

CONCLUSIONS

We successfully established a PDX model of NGC, to the best of our knowledge, for the first time. The established PDX retained the molecular and transcriptome characteristics of the primary tumour and can be used to predict drug effects. It may facilitate further research and the development of novel therapeutic agents for NGC.

Phenotyping of lymphoproliferative tumours generated in xenografts of non-small cell lung cancer

Background

Patient-derived xenograft (PDX) models involve the engraftment of tumour tissue in immunocompromised mice and represent an important pre-clinical oncology research method. A limitation of non-small cell lung cancer (NSCLC) PDX model derivation in NOD-scid IL2Rgammanull (NSG) mice is that a subset of initial engraftments are of lymphocytic, rather than tumour origin.

Methods

The immunophenotype of lymphoproliferations arising in the lung TRACERx PDX pipeline were characterised. To present the histology data herein, we developed a Python-based tool for generating patient-level pathology overview figures from whole-slide image files; PATHOverview is available on GitHub (https://github.com/EpiCENTR-Lab/PATHOverview).

Results

Lymphoproliferations occurred in 17.8% of lung adenocarcinoma and 10% of lung squamous cell carcinoma transplantations, despite none of these patients having a prior or subsequent clinical history of lymphoproliferative disease. Lymphoproliferations were predominantly human CD20+ B cells and had the immunophenotype expected for post-transplantation diffuse large B cell lymphoma with plasma cell features. All lymphoproliferations expressed Epstein-Barr-encoded RNAs (EBER). Analysis of immunoglobulin light chain gene rearrangements in three tumours where multiple tumour regions had resulted in lymphoproliferations suggested that each had independent clonal origins.

Discussion

Overall, these data suggest that B cell clones with lymphoproliferative potential are present within primary NSCLC tumours, and that these are under continuous immune surveillance. Since these cells can be expanded following transplantation into NSG mice, our data highlight the value of quality control measures to identify lymphoproliferations within xenograft pipelines and support the incorporation of strategies to minimise lymphoproliferations during the early stages of xenograft establishment pipelines.

A Genomically and Clinically Annotated Patient-Derived Xenograft Resource for Preclinical Research in Non-Small Cell Lung Cancer

Patient-derived xenograft (PDX) models are an effective preclinical in vivo platform for testing the efficacy of novel drugs and drug combinations for cancer therapeutics. Here we describe a repository of 79 genomically and clinically annotated lung cancer PDXs available from The Jackson Laboratory that have been extensively characterized for histopathologic features, mutational profiles, gene expression, and copy-number aberrations. Most of the PDXs are models of non-small cell lung cancer (NSCLC), including 37 lung adenocarcinoma (LUAD) and 33 lung squamous cell carcinoma (LUSC) models. Other lung cancer models in the repository include four small cell carcinomas, two large cell neuroendocrine carcinomas, two adenosquamous carcinomas, and one pleomorphic carcinoma. Models with both de novo and acquired resistance to targeted therapies with tyrosine kinase inhibitors are available in the collection. The genomic profiles of the LUAD and LUSC PDX models are consistent with those observed in patient tumors from The Cancer Genome Atlas and previously characterized gene expression-based molecular subtypes. Clinically relevant mutations identified in the original patient tumors were confirmed in engrafted PDX tumors. Treatment studies performed in a subset of the models recapitulated the responses expected on the basis of the observed genomic profiles. These models therefore serve as a valuable preclinical platform for translational cancer research.

SIGNIFICANCE

Patient-derived xenografts of lung cancer retain key features observed in the originating patient tumors and show expected responses to treatment with standard-of-care agents, providing experimentally tractable and reproducible models for preclinical investigations.

Facts and Hopes in the Relationship of EBV with Cancer Immunity and Immunotherapy

Epstein-Barr virus (EBV), the first identified human tumor virus, infects and takes up residency in almost every human. However, EBV genome-positive tumors arise in only a tiny minority of infected people, presumably when the virus-carrying tumor cells are able to evade immune surveillance. Traditional views regard viral antigens as the principal targets of host immune surveillance against virus-infected cells. However, recent findings indicate that EBV-infected/-transformed B cells elicit both cytotoxic CD8+ and CD4+ T-cell responses against a wide range of overexpressed cellular antigens known to function as tumor-associated antigens (TAA), in addition to various EBV-encoded antigens. This not only broadens the ways by which the immune system controls EBV infection and prevents it from causing cancers, but also potentially extends immune protection toward EBV-unrelated cancers by targeting shared TAAs. The goal of this review is to incorporate these new findings with literature data and discuss future directions for improved understanding of EBV-induced antitumor immunity, as well as the hopes for rational immune strategies for cancer prevention and therapy.

Machine-learning aided in situ drug sensitivity screening predicts treatment outcomes in ovarian PDX tumors

Long-term treatment outcomes for patients with high grade ovarian cancers have not changed despite innovations in therapies. There is no recommended assay for predicting patient response to second-line therapy, thus clinicians must make treatment decisions based on each individual patient. Patient-derived xenograft (PDX) tumors have been shown to predict drug sensitivity in ovarian cancer patients, but the time frame for intraperitoneal (IP) tumor generation, expansion, and drug screening is beyond that for tumor recurrence and platinum resistance to occur, thus results do not have clinical utility. We describe a drug sensitivity screening assay using a drug delivery microdevice implanted for 24 h in subcutaneous (SQ) ovarian PDX tumors to predict treatment outcomes in matched IP PDX tumors in a clinically relevant time frame. The SQ tumor response to local microdose drug exposure was found to be predictive of the growth of matched IP tumors after multi-week systemic therapy using significantly fewer animals (10 SQ vs 206 IP). Multiplexed immunofluorescence image analysis of phenotypic tumor response combined with a machine learning classifier could predict IP treatment outcomes against three second-line cytotoxic therapies with an average AUC of 0.91.

Spontaneous xenogeneic GvHD in Wilms' tumor Patient-Derived xenograft models and potential solutions

Severely immunocompromised NOD.Cg-Prkdc^scid Il2rg^tm1Sug (NOG) mice are among the ideal animal recipients for generation of human cancer models. Transplantation of human solid tumors having abundant tumor-infiltrating lymphocytes (TILs) can induce xenogeneic graft-versus-host disease (xGvHD) following engraftment and expansion of the TILs inside the animal body. Wilms' tumor (WT) has not been recognized as a lymphocyte-predominant tumor. However, 3 consecutive generations of NOG mice bearing WT patient-derived xenografts (PDX) xenotransplanted from a single donor showed different degrees of inflammatory symptoms after transplantation before any therapeutic intervention. In the initial generation, dermatitis, auto-amputation of digits, weight loss, lymphadenopathy, hepatitis, and interstitial pneumonitis were observed. Despite antibiotic treatment, no response was noticed, and thus the animals were prematurely euthanized (day 47 posttransplantation). Laboratory and histopathologic evaluations revealed lymphoid infiltrates positively immunostained with anti-human CD3 and CD8 antibodies in the xenografts and primary tumor, whereas no microbial infection or lymphoproliferative disorder was found. Mice of the next generation that lived longer (91 days) developed sclerotic skin changes and more severe pneumonitis. Cutaneous symptoms were milder in the last generation. The xenografts of the last 2 generations also contained TILs, and lacked lymphoproliferative transformation. The systemic immunoinflammatory syndrome in the absence of microbial infection and posttransplant lymphoproliferative disorder was suggestive of xGvHD. While there are few reports of xGvHD in severely immunodeficient mice xenotransplanted from lymphodominant tumor xenografts, this report for the first time documented serial xGvHD in consecutive passages of WT PDX-bearing models and discussed potential solutions to prevent such an undesired complication.

Establishment of an Ex Vivo Tissue Culture Model for Evaluation of Antitumor Efficacy in Clear Cell Renal Cell Carcinoma

There are many potential immunotherapeutic targets for cancer immunotherapy, which should be assessed for efficacy before they enter clinical trials. Here we established an ex vivo cultured patient-derived tumor tissue model to evaluate antitumor effectiveness of one VISTA inhibitor, given that our previous study showed that VISTA was selectively highly expressed in human clear cell renal cell carcinoma (ccRCC) tumors. We observed that all the tested patients responded to the anti-VISTA monoclonal antibody as manifested by TNF-α production, but only a small fraction were responders to the anti-PD-1 antibody. Co-blockade of VISTA and PD-1 resulted in a synergistic effect in 20% of RCC patients. Taken together, these findings indicate that this ex vivo tumor slice culture model represents a viable tool to evaluate antitumor efficacies for the inhibitors of immune checkpoints and further supports that VISTA could serve as a promising target for immunotherapy in ccRCC.

Patient-derived tumor models are attractive tools to repurpose drugs for ovarian cancer treatment: Pre-clinical updates

Despite advances in understanding of ovarian cancer biology, the progress in translation of research findings into new therapies is still slow. It is associated in part with limitations of commonly used cancer models such as cell lines and genetically engineered mouse models that lack proper representation of diversity and complexity of actual human tumors. In addition, the development of de novo anticancer drugs is a lengthy and expensive process. A promising alternative to new drug development is repurposing existing FDA-approved drugs without primary oncological purpose. These approved agents have known pharmacokinetics, pharmacodynamics, and toxicology and could be approved as anticancer drugs quicker and at lower cost. To successfully translate repurposed drugs to clinical application, an intermediate step of pre-clinical animal studies is required. To address challenges associated with reliability of tumor models for pre-clinical studies, there has been an increase in development of patient-derived xenografts (PDXs), which retain key characteristics of the original patient’s tumor, including histologic, biologic, and genetic features. The expansion and utilization of clinically and molecularly annotated PDX models derived from different ovarian cancer subtypes could substantially aid development of new therapies or rapid approval of repurposed drugs to improve treatment options for ovarian cancer patients.

Murine Models of Chronic Viral Infections and Associated Cancers

Viruses are now recognized as bona fide etiologic factors of human cancer. Carcinogenic viruses include Epstein– Barr virus (EBV), high-risk human papillomaviruses (HPVs), hepatitis B virus (HBV), hepatitis C virus (HCV), human T-cell leukemia virus type 1 (HTLV-1), human immunodeficiency virus type 1 (HIV-1, indirectly), and several candidate human cancer viruses. It is estimated that 15% of all human tumors worldwide are caused by viruses. Tumor viruses establish long-term persistent infections in humans, and cancer is an accidental side effect of viral replication strategies. Viruses are usually not complete carcinogens, supporting the concept that cancer results from the accumulation of multiple cooperating events, in which human cancer viruses display different, often opposing roles. The laboratory mouse Mus musculus is one of the best in vivo experimental systems for modeling human pathology, including viral infections and cancer. However, mice are unsusceptible to infection with the known carcinogenic viruses. Many murine models were developed to overcome this limitation and to address various aspects of virus-associated carcinogenesis, from tumors resulting from xenografts of human tissues and cells, including cancerous and virus infected, to genetically engineered mice susceptible to viral infections and associated cancer. The review considers the main existing models, analyzes their advantages and drawbacks, describes their applications, outlines the prospects of their further development.

Patient-Derived Xenografts of High-Grade Serous Ovarian Cancer Subtype as a Powerful Tool in Pre-Clinical Research

(1) Background. PDX models have become the preferred tool in research laboratories seeking to improve development and pre-clinical testing of new drugs. PDXs have been shown to capture the cellular and molecular characteristics of human tumors better than simpler cell line-based models. More recently, however, hints that PDXs may change their characteristics over time have begun to emerge, emphasizing the need for comprehensive analysis of PDX evolution. (2) Methods. We established a panel of high-grade serous ovarian carcinoma (HGSOC) PDXs and developed and validated a 300-SNP signature that can be successfully utilized to assess genetic drift across PDX passages and detect PDX contamination with lymphoproliferative tissues. In addition, we performed a detailed histological characterization and functional assessment of multiple PDX passages. (3) Results. Our data show that the PDXs remain largely stable throughout propagation, with marginal genetic drift at the time of PDX initiation and adaptation to mouse host. Importantly, our PDX lines retained the major histological characteristics of the original patients' tumors even after multiple passages in mice, demonstrating a strong concordance with the clinical responses of their corresponding patients. (4) Conclusions. Our data underline the value of defined HGSOC PDXs as a pre-clinical tumor model.

Epstein-Barr Virus+ B Cells in Breast Cancer Immune Response: A Case Report

EBV-specific T cells have been recently described to be involved in fatal encephalitis and myocarditis in cancer patients after immune checkpoint therapies. Here, we report the study of a human triple-negative breast cancer tumor (TNBC) and EBV-transformed B cells obtained from a patient-derived xenograft (PDX) that progressed into a lymphocytic neoplasm named xenograft-associated B-cell lymphoma (XABCL). T-cell receptor (TCR) high-throughput sequencing was performed to monitor the T-cell clonotypes present in the different samples. Forty-three T-cell clonotypes were found infiltrating the XABCL tissue after three passes in mice along 6 months. Eighteen of these (42%) were also found in the TNBC biopsy. TCR infiltrating the XABCL tissue showed a very restricted T-cell repertoire as compared with the biopsy-infiltrating T cells. Consequently, T cells derived from the TNBC biopsy were expanded in the presence of the B-cell line obtained from the XABCL (XABCL-LCL), after which the TCR repertoire obtained was again very restricted, i.e., only certain clonotypes were selected by the B cells. A number of these TCRs had previously been reported as sequences involved in infection, cancer, and/or autoimmunity. We then analyzed the immunopeptidome from the XABCL-LCL, to identify putative B-cell-associated peptides that might have been expanding these T cells. The HLA class I and class II-associated peptides from XABCL-LCL were then compared with published repertoires from LCL of different HLA typing. Proteins from the antigen processing and presentation pathway remained significantly enriched in the XABCL-LCL repertoire. Interestingly, some class II-presented peptides were derived from cancer-related proteins. These results suggest that bystander tumor-infiltrating EBV+ B cells acting as APC may be able to interact with tumor-infiltrating T cells and influence the TCR repertoire in the tumor site.

The HROC-Xenobank-A High Quality Assured PDX Biobank of >100 Individual Colorectal Cancer Models

Simple Summary

Considering recent research, it was established that the best experimental models to conserve biological features of human tumors and to predict individual clinical treatment success are patient-derived xenografts (PDX). Their recognized and growing importance for translational research, especially for late-stage preclinical testing of novel therapeutics, necessitates a high number of well-defined PDX models from individual patients’ tumors. The starting platform for the Hansestadt Rostock colorectal cancer (HROC)-Xenobank was the assortment of colorectal tumor and normal tissue samples from patients stored in our university biobank.

Abstract

Based on our research group’s large biobank of colorectal cancers (CRC), we here describe the ongoing activity of establishing a high quality assured PDX biobank for more than 100 individual CRC cases. This includes sufficient numbers of vitally frozen (n > 30 aliquots) and snap frozen (n > 5) backups, “ready to use”. Additionally, PDX tumor pieces were paraffin embedded. At the current time, we have completed 125 cases. This resource allows histopathological examinations, molecular characterizations, and gene expression analysis. Due to its size, different issues of interest can be addressed. Most importantly, the application of low-passage, cryopreserved, and well-characterized PDX for in vivo studies guarantees the reliability of results due to the largely preserved tumor microenvironment. All cases described were molecularly subtyped and genetic identity, in comparison to the original tumor tissue, was confirmed by fingerprint analysis. The latter excludes ambiguity errors between the PDX and the original patient tumor. A cancer hot spot mutation analysis was performed for n = 113 of the 125 cases entities. All relevant CRC molecular subtypes identified so far are represented in the Hansestadt Rostock CRC (HROC)-Xenobank. Notably, all models are available for cooperative research approaches.

Cancer animal models in thrombosis research

The cancer-thrombosis relationship has been established for decades, in both cancer biology and in the clinical signs and symptoms seen in cancer patients (thrombosis in cancer patients has been associated with a worse prognosis and survival). As the link between the pathologies becomes clearer, so does the need to develop models that enable researchers to study them simultaneously in vivo. Mouse models have often been used, and they have helped determine molecular pathways between cancer spread and thrombosis in humans. This review is a summary of the current literature that describes the use of cancer mouse models in thrombosis research. We included cancer models that are not yet used in thrombosis research, but that can positively impact this area of research in the near future. We describe the most commonly used techniques to generate thrombosis as well as the mouse strains and cancer cell types that are commonly used along with inoculation techniques. We endeavoured to create a compendium of the different mouse models that are beneficial for cancer-thrombosis research, as understanding these mechanisms is crucial for creating better and more effective treatments for thrombosis in cancer patients.

In Vivo and Ex Vivo Patient-Derived Tumor Xenograft Models of Lymphoma for Drug Discovery

In the hemato-oncology field, remarkable scientific progress has been achieved, primarily propelled by the discovery of new technologies, improvement in genomics, and novel in vitro and in vivo models. The establishment of multiple cell line collections and the development of instrumental mouse models enhanced our ability to discover effective therapeutics. However, cancer models that faithfully mimic individual cancers are still imperfect. Patient-derived tumor xenografts (PDTXs) have emerged as a powerful tool for identifying the mechanisms which drive tumorigenesis and for testing potential therapeutic interventions. The recognition that PDTXs can maintain many of the donor samples' properties enabled the development of new strategies for discovering and implementing therapies. Described in this article are protocols for the generation and characterization of lymphoma PDTXs that may be used as the basis of shared procedures. Universal protocols will foster the model utilization, enable the integration of public and private repositories, and aid in the development of shared platforms. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Tissue handling and cryopreservation of primary and PDTX samples Basic Protocol 2: Performing tumor implant in immunocompromised mice PDTX models Alternate Protocol 1: Intra-medullary femoral injection Alternate Protocol 2: Intravenous injection Alternate Protocol 3: Intraperitoneal injection Support Protocol 1: Phenotypical characterization of PDTXs by flow cytometry Support Protocol 2: Biological and molecular characterization of PDTX tumors by PCR detection of IGK, IGH, and TCR rearrangements Basic Protocol 3: Harvesting PDTX-derived tumor cells for ex vivo experiments Basic Protocol 4: In vivo testing of multiple compounds in a PDTX mouse model.

Characterization of the large-scale Japanese patient-derived xenograft (J-PDX) library

The use of patient‐derived xenografts (PDXs) has recently attracted attention as a drug discovery platform with a high predictive clinical efficacy and a preserved tumor heterogeneity. Given the racial differences in genetic variations, it would be desirable to establish a PDX library from Japanese cancer patients on a large scale. We thus tried to construct the Japanese PDX (J‐PDX) library with a detailed clinical information for further clinical utilization. Between August 2018 and May 2020, a total of 1126 cancer specimens from 1079 patients were obtained at the National Cancer Center Hospital and National Cancer Center Hospital East, Japan, and were immediately transplanted to immunodeficient mice at the National Cancer Center Research Institute. A total of 298 cross‐cancer PDXs were successfully established. The time to engraftment varied greatly by cancer subtypes, especially in the first passage. The engraftment rate was strongly affected by the clinical stage and survival time of the original patients. Approximately 1 year was needed from tumor collection to the time when coclinical trials were conducted to test the clinical utility. The 1‐year survival rates of the patients who were involved in establishing the PDX differed significantly, from 95.6% for colorectal cancer to 56.3% for lung cancer. The J‐PDX library consisting of a wide range of cancer subtypes has been successfully established as a platform for drug discovery and development in Japan. When conducting coclinical trials, it is necessary to consider the target cancer type, stage, and engraftment rate in light of this report.

Spontaneous mouse lymphoma in patient-derived tumor xenografts: The importance of systematic analysis of xenografted human tumor tissues in preclinical efficacy trials

Patient-derived tumor xenograft (PDX) is now largely recognized as a key preclinical model for cancer research, mimicking patient tumor phenotype and genotype. Immunodeficient mice, well-known to develop spontaneous lymphoma, are required for PDX growth. As for all animal models used for further clinical translation, a robust experimental design is strongly required to lead to conclusive results. Here we briefly report unintentional co-engraftment of mouse lymphoma during expansion of well-established PDXs to illustrate the importance of systematic check of the PDX identity to avoid misinterpretation. Besides, this quality control based on complementary approaches deserves a more detailed description in materials and methods section to ensure experimental validity and reproducibility.

Presence of complete murine viral genome sequences in patient-derived xenografts

Patient-derived xenografts are crucial for drug development but their use is challenged by issues such as murine viral infection. We evaluate the scope of viral infection and its impact on patient-derived xenografts by taking an unbiased data-driven approach to analyze unmapped RNA-Seq reads from 184 experiments. We find and experimentally validate the extensive presence of murine viral sequence reads covering entire viral genomes in patient-derived xenografts. The existence of viral sequences inside tumor cells is further confirmed by single cell sequencing data. Extensive chimeric reads containing both viral and human sequences are also observed. Furthermore, we find significantly changed expression levels of many cancer-, immune-, and drug metabolism-related genes in samples with high virus load. Our analyses indicate a need to carefully evaluate the impact of viral infection on patient-derived xenografts for drug development. They also point to a need for attention to quality control of patient-derived xenograft experiments.

The Promise of Patient-Derived Preclinical Models to Accelerate the Implementation of Personalised Medicine for Children with Neuroblastoma

Patient-derived preclinical models are now a core component of cancer research and have the ability to drastically improve the predictive power of preclinical therapeutic studies. However, their development and maintenance can be challenging, time consuming, and expensive. For neuroblastoma, a developmental malignancy of the neural crest, it is possible to establish patient-derived models as xenografts in mice and zebrafish, and as spheroids and organoids in vitro. These varied approaches have contributed to comprehensive packages of preclinical evidence in support of new therapeutics for neuroblastoma. We discuss here the ethical and technical considerations for the creation of patient-derived models of neuroblastoma and how their use can be optimized for the study of tumour evolution and preclinical therapies. We also discuss how neuroblastoma patient-derived models might become avatars for personalised medicine for children with this devastating disease.

Establishment of a Patient-Derived Xenograft Model of Colorectal Cancer in CIEA NOG Mice and Exploring Smartfish Liquid Diet as a Source of Omega-3 Fatty Acids

Cancer patient-derived xenografts (PDXs) better preserve tumor characteristics and microenvironment than traditional cancer cell line derived xenografts and are becoming a valuable model in translational cancer research and personalized medicine. We have established a PDX model for colorectal cancer (CRC) in CIEA NOG mice with a 50% engraftment rate. Tumor fragments from patients with CRC (n = 5) were engrafted in four mice per tumor (n = 20). Mice with established PDXs received a liquid diet enriched with fish oil or placebo, and fatty acid profiling was performed to measure fatty acid content in whole blood. Moreover, a biobank consisting of tissue and blood samples from patients was established. Histology, immunohistochemistry and in situ hybridization procedures were used for staining of tumor and xenograft tissue slides. Results demonstrate that key histological characteristics of the patients’ tumors were retained in the established PDXs, and the liquid diets were consumed as intended by the mice. Some of the older mice developed lymphomas that originated from human Ki67⁺, CD45⁺, and EBV⁺ lymphoid cells. We present a detailed description of the process and methodology, as well as possible issues that may arise, to refine the method and improve PDX engraftment rate for future studies. The established PDX model for CRC can be used for exploring different cancer treatment regimes, and liquid diets enriched with fish oil may be successfully delivered to the mice through the drinking flasks.

Early stability and late random tumor progression of a HER2-positive primary breast cancer patient-derived xenograft

We established patient-derived xenografts (PDX) from human primary breast cancers and studied whether stability or progressive events occurred during long-term in vivo passages (up to 4 years) in severely immunodeficient mice. While most PDX showed stable biomarker expression and growth phenotype, a HER2-positive PDX (PDX-BRB4) originated a subline (out of 6 studied in parallel) that progressively acquired a significantly increased tumor growth rate, resistance to cell senescence of in vitro cultures, increased stem cell marker expression and high lung metastatic ability, along with a strong decrease of BCL2 expression. RNAseq analysis of the progressed subline showed that BCL2 was connected to three main hub genes also down-regulated (CDKN2A, STAT5A and WT1). Gene expression of progressed subline suggested a partial epithelial-to-mesenchymal transition. PDX-BRB4 with its progressed subline is a preclinical model mirroring the clinical paradox of high level-BCL2 as a good prognostic factor in breast cancer. Sequential in vivo passages of PDX-BRB4 chronically treated with trastuzumab developed progressive loss of sensitivity to trastuzumab while HER2 expression and sensitivity to the pan-HER tyrosine kinase inhibitor neratinib were maintained. Long-term PDX studies, even though demanding, can originate new preclinical models, suitable to investigate the mechanisms of breast cancer progression and new therapeutic approaches.

Progress towards non-small-cell lung cancer models that represent clinical evolutionary trajectories

Non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related deaths worldwide. Although advances are being made towards earlier detection and the development of impactful targeted therapies and immunotherapies, the 5-year survival of patients with advanced disease is still below 20%. Effective cancer research relies on pre-clinical model systems that accurately reflect the evolutionary course of disease progression and mimic patient responses to therapy. Here, we review pre-clinical models, including genetically engineered mouse models and patient-derived materials, such as cell lines, primary cell cultures, explant cultures and xenografts, that are currently being used to interrogate NSCLC evolution from pre-invasive disease through locally invasive cancer to the metastatic colonization of distant organ sites.

Patient-derived tumour models for personalized therapeutics in urological cancers

Preclinical knowledge of dysregulated pathways and potential biomarkers for urological cancers has undergone limited translation into the clinic. Moreover, the low approval rate of new anticancer drugs and the heterogeneous drug responses in patients indicate that current preclinical models do not always reflect the complexity of malignant disease. Patient-derived tumour models used in preclinical uro-oncology research include 3D culture systems, organotypic tissue slices and patient-derived xenograft models. Technological innovations have enabled major improvements in the capacity of these tumour models to reproduce the clinical complexity of urological cancers. Each type of patient-derived model has inherent advantages and limitations that can be exploited, either alone or in combination, to gather specific knowledge on clinical challenges and address unmet clinical needs. Nevertheless, few opportunities exist for patients with urological cancers to benefit from personalized therapeutic approaches. Clinical validation of experimental data is needed to facilitate the translation and implementation of preclinical knowledge into treatment decision making.

Mouse models of high-risk neuroblastoma

Informative and realistic mouse models of high-risk neuroblastoma are central to understanding mechanisms of tumour initiation, progression, and metastasis. They also play vital roles in validating tumour drivers and drug targets, as platforms for assessment of new therapies and in the generation of drug sensitivity data that can inform treatment decisions for individual patients. This review will describe genetically engineered mouse models of specific subsets of high-risk neuroblastoma, the development of patient-derived xenograft models that more broadly represent the diversity and heterogeneity of the disease, and models of primary and metastatic disease. We discuss the research applications, advantages, and limitations of each model type, the importance of model repositories and data standards for supporting reproducible, high-quality research, and potential future directions for neuroblastoma mouse models.

PDX: Moving Beyond Drug Screening to Versatile Models for Research Discovery

Patient-derived xenografts (PDXs) are tools of the trade for many researchers from all disciplines and medical specialties. Most endocrinologists, and especially those working in oncology, commonly use PDXs for preclinical drug testing and development, and over the last decade large collections of PDXs have emerged across all tumor streams. In this review, we examine how the field has evolved to include PDXs as versatile resources for research discoveries, providing evidence for guidelines and changes in clinical practice.

A Biobank of Colorectal Cancer Patient-Derived Xenografts

Colorectal cancer (CRC) is a challenging disease, with a high mortality rate and limited effective treatment options, particularly for late-stage disease. Patient-derived xenografts (PDXs) have emerged as an informative, renewable experimental resource to model CRC architecture and biology. Here, we describe the generation of a biobank of CRC PDXs from stage I to stage IV patients. We demonstrate that PDXs within our biobank recapitulate the histopathological and mutation features of the original patient tumor. In addition, we demonstrate the utility of this resource in pre-clinical chemotherapy and targeted treatment studies, highlighting the translational potential of PDX models in the identification of new therapies that will improve the overall survival of CRC patients.

Chemogenomic profiling of breast cancer patient-derived xenografts reveals targetable vulnerabilities for difficult-to-treat tumors

Subsets of breast tumors present major clinical challenges, including triple-negative, metastatic/recurrent disease and rare histologies. Here, we developed 37 patient-derived xenografts (PDX) from these difficult-to-treat cancers to interrogate their molecular composition and functional biology. Whole-genome and transcriptome sequencing and reverse-phase protein arrays revealed that PDXs conserve the molecular landscape of their corresponding patient tumors. Metastatic potential varied between PDXs, where low-penetrance lung micrometastases were most common, though a subset of models displayed high rates of dissemination in organotropic or diffuse patterns consistent with what was observed clinically. Chemosensitivity profiling was performed in vivo with standard-of-care agents, where multi-drug chemoresistance was retained upon xenotransplantation. Consolidating chemogenomic data identified actionable features in the majority of PDXs, and marked regressions were observed in a subset that was evaluated in vivo. Together, this clinically-annotated PDX library with comprehensive molecular and phenotypic profiling serves as a resource for preclinical studies on difficult-to-treat breast tumors.

Patient-Derived Urothelial Cancer Xenograft Models: A Systematic Review and Future Perspectives

BACKGROUND: Lack of appropriate models that recapitulate the diversity, heterogeneity, and tumor microenvironment of urothelial cancer (UC) is a limitation to preclinical models. Patient-derived xenograft (PDX) models are a promising tool to overcome some of these issues, and thus we present an up-to-date and comprehensive overview of UC PDX models to aid in their future use. OBJECTIVE: To provide an overview on methodology, applications and limitations as well as future perspectives on bladder cancer PDX models. METHODS: Literature searches using PubMed and Web of Science databases were performed for relevant articles according to the following MeSH terms: “urothelial carcinoma(s)” OR “urothelial cancer” OR “urothelial tumor” OR “bladder cancer(s)” OR “bladder carcinoma(s)” OR “transitional cell carcinoma(s)” AND “xenograft(s)” OR “xenotransplant” at December 6th, 2019. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. RESULTS: Of the 49 studies extracted, 41 studies after the year 2000 were finally analyzed. Published studies show that (1) UC PDX platforms retained the histology and genomic characteristics of the corresponding patient tumors. (2) UC PDX can be applied to ask various questions including to study the mechanisms of disease progression and treatment resistance, to develop novel drugs and biomarkers, as well as to potentially realize personalized drug selection. Recent topics of research using PDX have included the development of humanized mice as well as the use of 3D culture to complement some of the limitations of PDX models. CONCLUSIONS: UC PDX models serve as tools for understanding cancer biology, drug development and empowering precision medicine. The improvement of experimental systems using humanized mice to recapitulate the immune microenvironment of tumors will optimize UC PDX to study future questions in the field of immunotherapy.

Establishment and Use of Patient-Derived Xenograft Models for Drug Testing in Head and Neck Squamous Cell Carcinoma

This protocol provides the steps required for the establishment of patient-derived xenograft (PDX) tumors for head and neck squamous cell carcinomas (HNSCCs) and their utility in examining drug responses. PDXs recapitulate the heterogeneity observed in the corresponding human tumors, which makes them an ideal pre-clinical model system. This protocol outlines the detailed steps required for (1) the generation of HNSCC-PDXs, (2) the processing of tumor tissues, and (3) the expansion of PDX models into cohorts for (4) drug testing.

For complete details on the use and execution of this protocol please refer to Karamboulas et al. (2018).

•

Patient-derived xenograft tumors are successfully generated from HNSCC tissue

•

Bulk single-cell suspensions of PDX tumors are used to create larger mouse cohorts

•

Tumor response to candidate drugs can be assessed across several PDX models

Spectrum of Posttransplant Lymphoproliferations in NSG Mice and Their Association With EBV Infection After Engraftment of Pediatric Solid Tumors

Pediatric patients receiving solid organ transplants may develop lymphoproliferative diseases, including graft-versus-host disease (GvHD) and posttransplant lymphoproliferative diseases (PTLDs). We characterized lesions in 11 clinically ill NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice that received pediatric-patient-derived solid tumors (PDXs) and developed immunodeficiency-associated lymphoproliferations comparable to GvHD and PTLDs over a period of 46 to 283 days after implantation. Lymphoproliferations were diffusely positive for human-specific biomarkers, including NUMA1, CD45, and CD43, but lacked immunoreactivity for murine CD45. Human immune cells were CD3-positive, with subsets having immunoreactivity for CD4 and CD8 as well as PAX5, CD79a, and IRF4, resulting from populations of human T and B cells present within the xenotransplants. Tissues and organs infiltrated included mucocutaneous zones (oral cavity and perigenital and perianal regions), haired skin, tongue, esophagus, forestomach, thyroid, salivary glands, lungs, liver, kidneys, spleen, lymph nodes, bone marrow, and brain. In 4 of 5 mice with PTLD, Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) were detected by in situ hybridization in PAX5+ human B cells associated with the PDX (n = 1/4) or with engrafted human immune cells at other anatomic locations (n = 4/11). One of the 4 mice had an EBV-associated human large B-cell lymphoma. NSG mice receiving xenotransplants can develop combinations of GvHD, EBV-driven PTLD, and B-cell lymphoma similar to those occurring in human pediatric patients. Therefore, pediatric xenotransplants should undergo histopathologic and immunohistochemical assessment upon collection to ensure that the specimen is not a lymphoma and does not contain lymphoma cells because these neoplasms can morphologically mimic small round blue cell pediatric solid tumors.

Mouse models of colorectal cancer: Past, present and future perspectives

Colorectal cancer (CRC) is the third most common diagnosed malignancy among both sexes in the United States as well as in the European Union. While the incidence and mortality rates in western, high developed countries are declining, reflecting the success of screening programs and improved treatment regimen, a rise of the overall global CRC burden can be observed due to lifestyle changes paralleling an increasing human development index. Despite a growing insight into the biology of CRC and many therapeutic improvements in the recent decades, preclinical in vivo models are still indispensable for the development of new treatment approaches. Since the development of carcinogen-induced rodent models for CRC more than 80 years ago, a plethora of animal models has been established to study colon cancer biology. Despite tenuous invasiveness and metastatic behavior, these models are useful for chemoprevention studies and to evaluate colitis-related carcinogenesis. Genetically engineered mouse models (GEMM) mirror the pathogenesis of sporadic as well as inherited CRC depending on the specific molecular pathways activated or inhibited. Although the vast majority of CRC GEMM lack invasiveness, metastasis and tumor heterogeneity, they still have proven useful for examination of the tumor microenvironment as well as systemic immune responses; thus, supporting development of new therapeutic avenues. Induction of metastatic disease by orthotopic injection of CRC cell lines is possible, but the so generated models lack genetic diversity and the number of suited cell lines is very limited. Patient-derived xenografts, in contrast, maintain the pathological and molecular characteristics of the individual patient’s CRC after subcutaneous implantation into immunodeficient mice and are therefore most reliable for preclinical drug development – even in comparison to GEMM or cell line-based analyses. However, subcutaneous patient-derived xenograft models are less suitable for studying most aspects of the tumor microenvironment and anti-tumoral immune responses. The authors review the distinct mouse models of CRC with an emphasis on their clinical relevance and shed light on the latest developments in the field of preclinical CRC models.

Biliary tract cancer patient-derived xenografts: Surgeon impact on individualized medicine

BACKGROUND & AIMS

Biliary tract tumors are uncommon but highly aggressive malignancies with poor survival outcomes. Due to their low incidence, research into effective therapeutics has been limited. Novel research platforms for pre-clinical studies are desperately needed. We sought to develop a patient-derived biliary tract cancer xenograft catalog.

METHODS

With appropriate consent and approval, surplus malignant tissues were obtained from surgical resection or radiographic biopsy and implanted into immunocompromised mice. Mice were monitored for xenograft growth. Established xenografts were verified by a hepatobiliary pathologist. Xenograft characteristics were correlated with original patient/tumor characteristics and oncologic outcomes. A subset of xenografts were then genomically characterized using Mate Pair sequencing (MPseq).

RESULTS

Between October 2013 and January 2018, 87 patients with histologically confirmed biliary tract carcinomas were enrolled. Of the 87 patients, 47 validated PDX models were successfully generated. The majority of the PDX models were created from surgical resection specimens (n = 44, 94%), which were more likely to successfully engraft when compared to radiologic biopsies (p = 0.03). Histologic recapitulation of original patient tumor morphology was observed in all xenografts. Successful engraftment was an independent predictor for worse recurrence-free survival. MPseq showed genetically diverse tumors with frequent alterations of CDKN2A, SMAD4, NRG1, TP53. Sequencing also identified worse survival in patients with tumors containing tetraploid genomes.

CONCLUSIONS

This is the largest series of biliary tract cancer xenografts reported to date. Histologic and genomic analysis of patient-derived xenografts demonstrates accurate recapitulation of original tumor morphology with direct correlations to patient outcomes. Successful development of biliary cancer tumografts is feasible and may be used to direct subsequent therapy in high recurrence risk patients.

LAY SUMMARY

Patient biliary tract tumors grown in immunocompromised mice are an invaluable resource in the treatment of biliary tract cancers. They can be used to guide individualized cancer treatment in high-risk patients.

Upregulation of CD20 Positive B-Cells and B-Cell Aggregates in the Tumor Infiltration Zone is Associated with Better Survival of Patients with Pancreatic Ductal Adenocarcinoma

Patients with pancreatic ductal adenocarcinoma (PDAC) normally have a poor long-term prognosis. However, some rare cases of long-term survivors have been reported. The tumor microenvironment, consisting of cellular and stromal components, possibly plays an important role and might influence prognosis. In this context, the role of tumor-infiltrating B-cells and its impact on the survival in patients with PDAC remains controversial. We therefore aimed to assess the prognostic value of CD20-positive B-cells and CD20-positive B-cell aggregates as well as CD138, IgM, Pax5, and Ki67 on the survival of patients with PDAC using immunohistochemistry of FFPE pancreatectomy tissue sections from patients that underwent primary surgery for pT3- and R0-pancreatic adenocarcinoma between 1995 and 2016. Patients with PDAC were matched and grouped in 16 long-term-survivors (LTS, median overall survival (OS): 96 months [range: 61–177 months]) and 16 short-term-survivors (STS, median OS: 16 months [range: 7–32 months]). CD20-positive B-cells and B-cell aggregates in the tumor infiltration zone were significantly upregulated in the LTS-group compared to the STS-group (p = 0.0499 respectively p = 0.0432). Regarding the entire patient cohort (n = 32) CD20 positive B-cell aggregates in the tumor infiltration zone were an independent prognostic marker for overall survival in multivariate analysis (HR 9.2, CI 1.6–51.4, p = 0.012). These results underline the importance of tumor-associated B-cells for prognosis of patients with PDAC. The detailed role of B cells in the pathomechanism of PDAC should be further investigated for predicting outcome, identifying appropriate treatment regimens, and developing novel therapeutic options.

Accelerating development of high-risk neuroblastoma patient-derived xenograft models for preclinical testing and personalised therapy

Background

Predictive preclinical models play an important role in the assessment of new treatment strategies and as avatar models for personalised medicine; however, reliable and timely model generation is challenging. We investigated the feasibility of establishing patient-derived xenograft (PDX) models of high-risk neuroblastoma from a range of tumour-bearing patient materials and assessed approaches to improve engraftment efficiency.

Methods

PDX model development was attempted in NSG mice by using tumour materials from 12 patients, including primary and metastatic solid tumour samples, bone marrow, pleural fluid and residual cells from cytogenetic analysis. Subcutaneous, intramuscular and orthotopic engraftment were directly compared for three patients.

Results

PDX models were established for 44% (4/9) of patients at diagnosis and 100% (5/5) at relapse. In one case, attempted engraftment from pleural fluid resulted in an EBV-associated atypical lymphoid proliferation. Xenogeneic graft versus host disease was observed with attempted engraftment from lymph node and bone marrow tumour samples but could be prevented by T-cell depletion. Orthotopic engraftment was more efficient than subcutaneous or intramuscular engraftment.

Conclusions

High-risk neuroblastoma PDX models can be reliably established from diverse sample types. Orthotopic implantation allows more rapid model development, increasing the likelihood of developing an avatar model within a clinically useful timeframe.

The fidelity of cancer cells in PDX models: Characteristics, mechanism and clinical significance

Patient-derived xenograft (PDX) models are widely used as preclinical cancer models and are considered better than cell culture models in recapitulating the histological features, molecular characteristics and intratumoral heterogeneity (ITH) of human tumors. While the PDX model is commonly accepted for use in drug discovery and other translational studies, a growing body of evidence has suggested its limitations. Recently, the fidelity of cancer cells within a PDX has been questioned, which may impede the future application of these models. In this review, we will focus the variable phenotypes of xenograft tumors and the genomic instability and molecular inconsistency of PDX tumors after serial transplantation. Next, we will discuss the underlying mechanism of ITH and its clinical relevance. Stochastic selection bias in the sampling process and/or deterministic clonal dynamics due to murine selective pressure may have detrimental effects on the results of personalized medicine and drug screening studies. In addition, we aim to identify a possible solution for the issue of fidelity in current PDX models and to discuss emerging next-generation preclinical models.

Corruption of neuroblastoma patient derived xenografts with human T cell lymphoma

BACKGROUND

Patient derived xenografts (PDXs) provide a unique opportunity for investigators to study tumor cell activity, response to therapeutics, and resistance patterns without exposing the human patient to experimental compounds, and thereby play a crucial role in pre-clinical evaluation of new therapies. It has been reported that PDXs may undergo a transformation to lymphoma, most commonly associated with Epstein Barr virus (EBV). If the character of a xenograft becomes compromised and remains undetected, it could have a detrimental impact on the research community as a whole. Our lab has established a number of pediatric solid tumor PDXs which accurately recapitulate the human tumors following several passages. One particular neuroblastoma PDX was noted to grow quickly and with an unusual phenotype, leading us to hypothesize that this PDX had undergone a transformation.

METHODS

The PDX in question was investigated with histology, immunohistochemistry (IHC), EBER in situ hybridization, and PCR to determine its identity.

RESULTS

Histology on the tumor revealed a small, round blue cell tumor similar to the original neuroblastoma from which it was derived. IHC staining showed that the tumor was composed of lymphocytes that were CD3 positive, <5% CD4 positive, and CD20 negative. The cells were Epstein Barr virus negative. PCR demonstrated that the tumor was human and not murine in origin.

CONCLUSION

These findings indicate that a human T Cell lymphoma developed in place of this neuroblastoma PDX. Changes in PDX identity such as this one will significantly impact studies utilizing pediatric PDXs and the mechanism by which this occurred warrants further investigation.

Pathological Pattern of Intrahepatic HBV in HCC is Phenocopied by PDX-Derived Mice: a Novel Model for Antiviral Treatment

BACKGROUND

Hepatitis B virus (HBV) is one of the most prominent risk factors for hepatocellular carcinoma (HCC) development and virus-mediated cases represents more than 80% of HCC in East Asia, where it is endemic. Currently, the HBV status of pathological HCC is not fully clarified, especially by comparison to nontumorous tissues. Lack of clinicopathological animal models of HCC impedes clinical application of antiviral treatment in the field.

MATERIALS AND METHODS

A cohort sample of 14 HCC and corresponding stroma tissues were analyzed for pathological patterns of HBV antigens using immunohistochemistry; 10 fresh primary tumor tissues were inoculated into NOD/SCID mice and risk factors for patient-derived xenograft (PDX) model were identified by the univariate F test. Consistency of HBV features and cellular biomarkers between patient tissues and tumor grafts were examined.

RESULTS

In HCC, HBV surface antigen (HBsAg) was mainly absent. Only 9.9% of samples showed HBsAg positivity in the tumor tissue that was limited to benign hepatocytes. In contrast, HBV core antigen (HBcAg) exhibited positive staining in all HCC tissues, located mainly in the cytoplasm of tumor cells. Of 14 HCC cases, three were diagnosed as occult infection of HBV based on HBcAg expression. The successful rate for the PDX model was 20% (2/10). Tumor lesions on hepatic lobes of V and VI, severe liver dysfunction and higher CA125 showed p-values of 0.01, 0.035, and 0.01, respectively. HBsAg absence in original tumors of #6 and 8 patients were faithfully reproduced by engraftments. Mixed distribution of HBcAg in cellular compartments of original tumor cells was also observed in mice. ki67 was dramatically increased in tumor grafts.

CONCLUSION

We delineated pathological HBV profiles of HCC specimens and perilesional areas, which provided evidence for virus-based therapy in the future. PDX mice may phenocopy virological and cellular features of patient tissues, which is novel in the virus-related hepatocarcinogenesis field.

Bone sarcoma patient-derived xenografts are faithful and stable preclinical models for molecular and therapeutic investigations

Standard therapy of osteosarcoma (OS) and Ewing sarcoma (EW) rests on cytotoxic regimes, which are largely unsuccessful in advanced patients. Preclinical models are needed to break this impasse. A panel of patient-derived xenografts (PDX) was established by implantation of fresh, surgically resected osteosarcoma (OS) and Ewing sarcoma (EW) in NSG mice. Engraftment was obtained in 22 of 61 OS (36%) and 7 of 29 EW (24%). The success rate in establishing primary cell cultures from OS was lower than the percentage of PDX engraftment in mice, whereas the reverse was observed for EW; the implementation of both in vivo and in vitro seeding increased the proportion of patients yielding at least one workable model. The establishment of in vitro cultures from PDX was highly efficient in both tumor types, reaching 100% for EW. Morphological and immunohistochemical (SATB2, P-glycoprotein 1, CD99, caveolin 1) studies and gene expression profiling showed a remarkable similarity between patient’s tumor and PDX, which was maintained over several passages in mice, whereas cell cultures displayed a lower correlation with human samples. Genes differentially expressed between OS original tumor and PDX mostly belonged to leuykocyte-specific pathways, as human infiltrate is gradually replaced by murine leukocytes during growth in mice. In EW, which contained scant infiltrates, no gene was differentially expressed between the original tumor and the PDX. A novel therapeutic combination of anti-CD99 diabody C7 and irinotecan was tested against two EW PDX; both drugs inhibited PDX growth, the addition of anti-CD99 was beneficial when chemotherapy alone was less effective. The panel of OS and EW PDX faithfully mirrored morphologic and genetic features of bone sarcomas, representing reliable models to test therapeutic approaches.

Tumor characteristics associated with engraftment of patient-derived non-small cell lung cancer xenografts in immunocompromised mice

BACKGROUND

Patient-derived xenograft (PDX) models increasingly are used in translational research. However, the engraftment rates of patient tumor samples in immunodeficient mice to PDX models vary greatly.

METHODS

Tumor tissue samples from 308 patients with non-small cell lung cancer were implanted in immunodeficient mice. The patients were followed for 1.5 to approximately 6 years. The authors performed histological analysis of PDXs and some residual tumor tissues in mice with failed PDX growth at 1 year after implantation. Quantitative polymerase chain reaction and enzyme-linked immunoadsorbent assay were performed to measure the levels of Epstein-Barr virus genes and human immunoglobulin G in PDX samples. Patient characteristics were compared for PDX growth and overall survival as outcomes using Cox regression analyses. Disease staging was based on the 7th TNM staging system.

RESULTS

The overall engraftment rate for PDXs from patients with non-small cell lung cancer was 34%. Squamous cell carcinomas had a higher engraftment rate (53%) compared with adenocarcinomas. Tumor samples from patients with stage II and stage III disease and from larger tumors were found to have relatively high engraftment rates. Patients whose tumors successfully engrafted had worse overall survival, particularly those individuals with adenocarcinoma, stage III or stage IV disease, and moderately differentiated tumors. Lymphoma formation was one of the factors associated with engraftment failure. Human CD8-positive and CD20-positive cells were detected in residual samples of tumor tissue that failed to generate a PDX at 1 year after implantation. Human immunoglobulin G was detected in the plasma of mice that did not have PDX growth at 14 months after implantation.

CONCLUSIONS

The results of the current study indicate that the characteristics of cancer cells and the tumor immune microenvironment in primary tumors both can affect engraftment of a primary tumor sample.

Genomic data analysis workflows for tumors from patient-derived xenografts (PDXs): challenges and guidelines

BACKGROUND

Patient-derived xenograft (PDX) models are in vivo models of human cancer that have been used for translational cancer research and therapy selection for individual patients. The Jackson Laboratory (JAX) PDX resource comprises 455 models originating from 34 different primary sites (as of 05/08/2019). The models undergo rigorous quality control and are genomically characterized to identify somatic mutations, copy number alterations, and transcriptional profiles. Bioinformatics workflows for analyzing genomic data obtained from human tumors engrafted in a mouse host (i.e., Patient-Derived Xenografts; PDXs) must address challenges such as discriminating between mouse and human sequence reads and accurately identifying somatic mutations and copy number alterations when paired non-tumor DNA from the patient is not available for comparison.

RESULTS

We report here data analysis workflows and guidelines that address these challenges and achieve reliable identification of somatic mutations, copy number alterations, and transcriptomic profiles of tumors from PDX models that lack genomic data from paired non-tumor tissue for comparison. Our workflows incorporate commonly used software and public databases but are tailored to address the specific challenges of PDX genomics data analysis through parameter tuning and customized data filters and result in improved accuracy for the detection of somatic alterations in PDX models. We also report a gene expression-based classifier that can identify EBV-transformed tumors. We validated our analytical approaches using data simulations and demonstrated the overall concordance of the genomic properties of xenograft tumors with data from primary human tumors in The Cancer Genome Atlas (TCGA).

CONCLUSIONS

The analysis workflows that we have developed to accurately predict somatic profiles of tumors from PDX models that lack normal tissue for comparison enable the identification of the key oncogenic genomic and expression signatures to support model selection and/or biomarker development in therapeutic studies. A reference implementation of our analysis recommendations is available at https://github.com/TheJacksonLaboratory/PDX-Analysis-Workflows .

Hepatocellular Carcinoma Xenografts Established From Needle Biopsies Preserve the Characteristics of the Originating Tumors

Hepatocellular carcinoma (HCC) is the second leading cause of cancer‐related deaths worldwide. Treatment options for patients with advanced‐stage disease are limited. A major obstacle in drug development is the lack of an in vivo model that accurately reflects the broad spectrum of human HCC. Patient‐derived xenograft (PDX) tumor mouse models could overcome the limitations of cancer cell lines. PDX tumors maintain the genetic and histologic heterogeneity of the originating tumors and are used for preclinical drug development in various cancers. Controversy exists about their genetic and molecular stability through serial passaging in mice. We aimed to establish PDX models from human HCC biopsies and to characterize their histologic and molecular stability during serial passaging. A total of 54 human HCC needle biopsies that were derived from patients with various underlying liver diseases and tumor stages were transplanted subcutaneously into immunodeficient, nonobese, diabetic/severe combined immunodeficiency gamma‐c mice; 11 successfully engrafted. All successfully transplanted HCCs were Edmondson grade III or IV. HCC PDX tumors retained the histopathologic, transcriptomic, and genomic characteristics of the original HCC biopsies over 6 generations of retransplantation. These characteristics included Edmondson grade, expression of tumor markers, tumor gene signature, tumor‐associated mutations, and copy number alterations. Conclusion: PDX mouse models can be established from undifferentiated HCCs, with an overall success rate of approximately 20%. The transplanted tumors represent the entire spectrum of the molecular landscape of HCCs and preserve the characteristics of the originating tumors through serial passaging. HCC PDX models are a promising tool for preclinical personalized drug development.

Testicular germ cell tumor: a comprehensive review

Testicular tumors are the most common tumors in adolescent and young men and germ cell tumors (TGCTs) account for most of all testicular cancers. Increasing incidence of TGCTs among males provides strong motivation to understand its biological and genetic basis. Gains of chromosome arm 12p and aneuploidy are nearly universal in TGCTs, but TGCTs have low point mutation rate. It is thought that TGCTs develop from premalignant intratubular germ cell neoplasia that is believed to arise from the failure of normal maturation of gonocytes during fetal or postnatal development. Progression toward invasive TGCTs (seminoma and nonseminoma) then occurs after puberty. Both inherited genetic factors and environmental risk factors emerge as important contributors to TGCT susceptibility. Genome-wide association studies have so far identified more than 30 risk loci for TGCTs, suggesting that a polygenic model fits better with the genetic landscape of the disease. Despite high cure rates because of its particular sensitivity to platinum-based chemotherapy, exploration of mechanisms underlying the occurrence, progression, metastasis, recurrence, chemotherapeutic resistance, early diagnosis and optional clinical therapeutics without long-term side effects are urgently needed to reduce the cancer burden in this underserved age group. Herein, we present an up-to-date review on clinical challenges, origin and progression, risk factors, TGCT mouse models, serum diagnostic markers, resistance mechanisms, miRNA regulation, and database resources of TGCTs. We appeal that more attention should be paid to the basic research and clinical diagnosis and treatment of TGCTs.

Rituximab Decreases Lymphoproliferative Tumor Formation in Hepatopancreaticobiliary and Gastrointestinal Cancer Patient-Derived Xenografts

High engraftment rates are critical to any patient-derived xenograft (PDX) program and the loss of PDX models due to the development of lymphoproliferative tumors (LTs) is costly and inefficient. We hypothesized that routine injection of rituximab, an anti-CD20 antibody, at the time of implantation would reduce the incidence of LTs. Rituximab injection was added to the standard PDX engraftment protocol. Univariate analysis and multivariate logistic regression were used to determine the significance of various factors. A total of 811 generations of PDX were implanted with 406 receiving rituximab with implantation. On multivariable analysis, rituximab was an independent factor for decreased LT formation across the entire cohort (OR 0.465, 95% CI 0.271–0.797, p = 0.005). Hepatocellular carcinomas (OR 0.319, 95% CI 0.107–0.949, p = 0.040) and cholangiocarcinomas (OR 0.185, 95% CI 0.049–0.696, p = 0.113) were the specific malignant histologic subtypes that demonstrated the greatest benefit. The frequency of LTs decreased across the entire cohort with rituximab administration and PDX tumors that are traditionally associated with higher rates of LT formation, HCCs and CCAs, appear to benefit the most from rituximab treatment. Routine use of rituximab at the time of tumor implantation may have significant programmatic benefits for laboratories that utilize PDX models.