Humanized mice in studying efficacy and mechanisms of PD-1-targeted cancer immunotherapy

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.

RX-5902, a novel β-catenin modulator, potentiates the efficacy of immune checkpoint inhibitors in preclinical models of triple-negative breast Cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with limited systemic treatment options. RX-5902 is a novel anti-cancer agent that inhibits phosphorylated-p68 and thus attenuates nuclear β-catenin signaling. The purpose of this study was to evaluate the ability of β-catenin signaling blockade to enhance the efficacy of anti-CTLA-4 and anti-PD-1 immune checkpoint blockade in immunocompetent, preclinical models of TNBC.

METHODS

Treatment with RX-5902, anti-PD-1, anti-CTLA-4 or the combination was investigated in BALB/c mice injected with the 4 T1 TNBC cell line. Humanized BALB/c-Rag2nullIl2rγnullSIRPαNOD (hu-CB-BRGS) mice transplanted with a human immune system were implanted with MDA-MB-231 cells. Mice were randomized into treatment groups according to human hematopoietic chimerism and treated with RX-5902, anti-PD-1 or the combination. At sacrifice, bone marrow, lymph nodes, spleen and tumors were harvested for flow cytometry analysis of human immune cells.

RESULTS

The addition of RX-5902 to CTLA-4 or PD-1 inhibitors resulted in decreased tumor growth in the 4 T1 and human immune system and MDA-MB-231 xenograft models. Immunologic analyses demonstrated a significant increase in the number of activated T cells in tumor infiltrating lymphocytes (TILs) with RX-5902 treatment compared to vehicle (p < 0.05). In the RX-5902/nivolumab combination group, there was a significant increase in the percentage of CD4+ T cells in TILs and increased systemic granzyme B production (p < 0.01).

CONCLUSIONS

Conclusions: RX-5902 enhanced the efficacy of nivolumab in a humanized, preclinical model of TNBC. Several changes in immunologic profiles were noted in mice treated with RX-5902 and the combination, including an increase in activated TILs and a decrease in human myeloid populations, that are often associated with immunosuppression in a tumor microenvironment. RX-5902 also was shown to potentiate the effects of checkpoint inhibitors of CTLA4 and the PD-1 inhibitor in the 4 T-1 murine TNBC model. These findings indicate that RX-5902 may have important immunomodulatory, as well as anti-tumor activity, in TNBC when combined with a checkpoint inhibitor.

BRCA1 and BRCA2 associated breast cancer and the roles of current modelling systems in drug discovery

For a drug candidate to be fully developed takes years and investment of hundreds of millions of dollars. There is no doubt that drug development is difficult and risky, but vital to protecting against devastating disease. This difficulty is clearly evident in BRCA1 and BRCA2 related breast cancer, with current treatment options largely confined to invasive surgical procedures, as well as chemotherapy and radiotherapy regimes which damage healthy tissue and can leave remnant disease. Consequently, patient survival and relapse rates are far from ideal, and new candidate treatments are needed. The preclinical stages of drug discovery are crucial to get right for translation to hospital beds. Disease models must take advantage of current technologies and be accurate for rapid and translatable treatments. Careful selection of cell lines must be coupled with high throughput techniques, with promising results trialled further in highly accurate humanised patient derived xenograft models. Traditional adherent drug screening should transition to 3D culture systems amenable to high throughput techniques if the gap between in vitro and in vivo studies is to be partially bridged. The possibility of organoid, induced pluripotent stem cell, and conditionally reprogrammed in vitro models is tantalising, however protocols are yet to be fully established. This review of BRCA1 and BRCA2 cancer biology and current modelling systems will hopefully guide the design of future drug discovery endeavours and highlight areas requiring improvement.

The Tumor Milieu Promotes Functional Human Tumor-Resident Plasmacytoid Dendritic Cells in Humanized Mouse Models

Particular interest to harness the innate immune system for cancer immunotherapy is fueled by limitations of immune checkpoint blockade. Plasmacytoid dendritic cells (pDC) are detected in a variety of solid tumors and correlate with poor clinical outcome. Release of type I interferons in response to toll-like-receptor (TLR)7 and TLR9 activation is the pDC hallmark. Mouse and human pDC differ substantially in their biology concerning surface marker expression and cytokine production. Here, we employed humanized mouse models (HIS) to study pDC function. We performed a comprehensive characterization of transgenic, myeloid-enhanced mouse strains (NOG-EXL and NSG-SGM3) expressing human interleukin-3 (hIL-3) and granulocyte-macrophage colony stimulating factor (GM-CSF) using identical humanization protocols. Only in HIS-NOG-EXL mice sufficient pDC infiltration was detectable. Therefore, we selected this strain for subsequent tumor studies. We analyzed pDC frequency in peripheral blood and tumors by comparing HIS-NOG-EXL with HIS-NOG mice bearing three different ovarian and breast tumors. Despite the substantially increased pDC numbers in peripheral blood of HIS-NOG-EXL mice, we detected TLR7/8 agonist responsive and thus functional pDCs only in certain tumor models independent of the mouse strain employed. However, HIS-NOG-EXL mice showed in general a superior humanization phenotype characterized by reconstitution of different myeloid subsets, NK cells and B cells producing physiologic IgG levels. Hence, we provide first evidence that the tumor milieu but not genetically introduced cytokines defines intratumoral (i.t.) frequencies of the rare pDC subset. This study provides model systems to investigate in vivo pro- and anti-tumoral human pDC functions.

The Development of Next-generation PBMC Humanized Mice for Preclinical Investigation of Cancer Immunotherapeutic Agents

Investigation of the efficacy and mechanisms of human immuno-oncology agents has been hampered due to species-specific differences when utilizing preclinical mouse models. Peripheral blood mononuclear cell (PBMC) humanized mice provide a platform for investigating the modulation of the human immune-mediated antitumor response while circumventing the limitations of syngeneic model systems. Use of humanized mice has been stymied by model-specific limitations, some of which include the development of graft versus host disease, technical difficulty and cost associated with each humanized animal, and insufficient engraftment of some human immune subsets. Recent advances have addressed many of these limitations from which have emerged humanized models that are more clinically relevant. This review characterizes the expanded usage, advantages and limitations of humanized mice and provides insights into the development of the next generation of murine humanized models to further inform clinical applications of cancer immunotherapeutic agents.

PD1 blockade enhances K+ channel activity, Ca2+ signaling, and migratory ability in cytotoxic T lymphocytes of patients with head and neck cancer

BACKGROUND

Immunotherapy has emerged as a promising treatment modality for head and neck squamous cell carcinoma (HNSCC). Pembrolizumab, an anti-programmed death 1 antibody, is an immunotherapy agent currently approved for metastatic HNSCC and curative intent clinical trials. Although clinical responses to pembrolizumab are promising, many patients fail to respond. However, it is well known that T cell cytotoxicity and chemotaxis are critically important in the elimination of HNSCC tumors. These functions depend on ion channel activity and downstream Ca2+ fluxing abilities, which are defective in patients with HNSCC. The purpose of this study was to elucidate the effects of pembrolizumab on potassium (K+) channel (KCa3.1 and Kv1.3) activity, Ca2+ fluxes, and chemotaxis in the cytotoxic T cells of patients with HNSCC and to determine their correlation with treatment response.

METHODS

Functional studies were conducted in CD8+ peripheral blood T cells (PBTs) and tumor infiltrating lymphocytes (TILs) from patients with HNSCC treated with pembrolizumab. Untreated patients with HNSCC were used as controls. The ion channel activity of CD8+ T cells was measured by patch-clamp electrophysiology; single-cell Ca2+ fluxing abilities were measured by live microscopy. Chemotaxis experiments were conducted in a three-dimensional collagen matrix. Pembrolizumab patients were stratified as responders or non-responders based on pathological response (percent of viable tumor remaining at resection; responders: ≤80% viable tumor; non-responders: >80% viable tumor).

RESULTS

Pembrolizumab increased K+ channel activity and Ca2+ fluxes in TILs independently of treatment response. However, in PBTs from responder patients there was an increased KCa3.1 activity immediately after pembrolizumab treatment that was accompanied by a characteristic increase in Kv1.3 and Ca2+ fluxes as compared with PBTs from non-responder patients. The effects on Kv1.3 and Ca2+ were prolonged and persisted after tumor resection. Chemotaxis was also improved in responder patients' PBTs. Unlike non-responders' PBTs, pembrolizumab increased their ability to chemotax in a tumor-like, adenosine-rich microenvironment immediately after treatment, and additionally they maintained an efficient chemotaxis after tumor resection.

CONCLUSIONS

Pembrolizumab enhanced K+ channel activity, Ca2+ fluxes and chemotaxis of CD8+ T cells in patients with HNSCC, with a unique pattern of response in responder patients that is conducive to the heightened functionality of their cytotoxic T cells.

Immunotherapy for Metastatic Prostate Cancer: Current and Emerging Treatment Options

The advent of immunotherapy has revolutionized cancer treatment. Prostate cancer has an immunosuppressive microenvironment and a low tumor mutation burden, resulting in low neoantigen expression. The consensus was that immunotherapy would be less effective in prostate cancer. However, recent studies have reported that prostate cancer does have a high number of DNA damage and repair gene defects. Immunotherapies that have been tested in prostate cancer so far have been mainly vaccines and checkpoint inhibitors. A combination of genomically targeted therapies, with approaches to alleviate immune response and thereby make the tumor microenvironment immunologically hot, is promising.

Humanized Rodent Models for Cancer Research

As one of the most popular laboratory animal models, rodents have been playing crucial roles in mechanistic investigations of oncogenesis as well as anticancer drug or regimen discoveries. However, rodent tumors show different or no responses to therapies against human cancers, and thus, in recent years, increased attention has been given to mouse models with xenografted or spontaneous human cancer cells. By combining with the human immune system (HIS) mice, these models have become more sophisticated and robust, enabling in vivo exploration of human cancer immunology and immunotherapy. In this review, we summarize the pros and cons of these humanized mouse models, with a focus on their potential as an in vivo platform for human cancer research. We also discuss the strategies for further improving these models.

Heat Shock Proteins and PD-1/PD-L1 as Potential Therapeutic Targets in Myeloproliferative Neoplasms

Simple Summary

Myeloproliferative neoplasms (MPN), which are a heterogeneous group of rare disorders that affect blood cell production in bone marrow, present many significant challenges for clinicians. Though considerable progress has been made, in particular with the JAK1/2 inhibitor ruxolitinib, more effective alternative therapeutic approaches are needed. In the search for new and more efficient therapies, heat shock proteins, also known as stress proteins, and the programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1) immune checkpoint axis have been found to be of great interest in hematologic malignancies. Here, we review the therapeutic potential of stress protein inhibitors in the management of patients diagnosed with MPN and summarize the accumulating evidence of the role of the PD-1/PD-L1 axis in MPN in order to provide perspectives on future therapeutic opportunities relative to the inhibition of these targets.

Abstract

Myeloproliferative neoplasms (MPN) are a group of clonal disorders that affect hematopoietic stem/progenitor cells. These disorders are often caused by oncogenic driver mutations associated with persistent Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling. While JAK inhibitors, such as ruxolitinib, reduce MPN-related symptoms in myelofibrosis, they do not influence the underlying cause of the disease and are not curative. Due to these limitations, there is a need for alternative therapeutic strategies and targets. Heat shock proteins (HSPs) are cytoprotective stress-response chaperones involved in protein homeostasis and in many critical pathways, including inflammation. Over the last decade, several research teams have unraveled the mechanistic connection between STAT signaling and several HSPs, showing that HSPs are potential therapeutic targets for MPN. These HSPs include HSP70, HSP90 (chaperoning JAK2) and both HSP110 and HSP27, which are key factors modulating STAT3 phosphorylation status. Like the HSPs, the PD-1/PD-L1 signaling pathway has been widely studied in cancer, but the importance of PD-L1-mediated immune escape in MPN was only recently reported. In this review, we summarize the role of HSPs and PD-1/PD-L1 signaling, the modalities of their experimental blockade, and the effect in MPN. Finally, we discuss the potential of these emerging targeted approaches in MPN therapy.

High accuracy gene expression profiling of sorted cell subpopulations from breast cancer PDX model tissue

Intratumor Heterogeneity (ITH) is a functionally important property of tumor tissue and may be involved in drug resistance mechanisms. Although descriptions of ITH can be traced back to very early reports about cancer tissue, mechanistic investigations are still limited by the precision of analysis methods and access to relevant tissue sources. PDX models have provided a reproducible source of tissue with at least a partial representation of naturally occurring ITH. We investigated the properties of phenotypically distinct cell populations by Fluorescence activated cell sorting (FACS) tissue derived cells from multiple tumors from a triple negative breast cancer patient derived xenograft (PDX) model. We subsequently subjected each population to in depth gene expression analysis. Our findings suggest that process related gene expression changes (caused by tissue dissociation and FACS sorting) are restricted to Immediate Early Genes (IEGs). This allowed us to discover highly reproducible gene expression profiles of distinct cellular compartments identifiable by cell surface markers in this particular tumor model. Within the context of data from a previously published model our work suggests that gene expression profiles associated with hypoxia, stemness and drug resistance may reside in tumor subpopulations predictably growing in PDX models. This approach provides a novel opportunity for prospective mechanistic studies of ITH.

Personalized cancer therapy prioritization based on driver alteration co-occurrence patterns

Identification of actionable genomic vulnerabilities is key to precision oncology. Utilizing a large-scale drug screening in patient-derived xenografts, we uncover driver gene alteration connections, derive driver co-occurrence (DCO) networks, and relate these to drug sensitivity. Our collection of 53 drug-response predictors attains an average balanced accuracy of 58% in a cross-validation setting, rising to 66% for a subset of high-confidence predictions. We experimentally validated 12 out of 14 predictions in mice and adapted our strategy to obtain drug-response models from patients’ progression-free survival data. Our strategy reveals links between oncogenic alterations, increasing the clinical impact of genomic profiling.

The link between kidney disease and cancer: complications and treatment

Acute and chronic kidney disease encompasses a complex set of diseases that can both lead to, and result from, cancer. In particular, kidney disease can arise from the use of chemotherapeutic agents. Many of the current and newly developed cancer chemotherapeutic agents are nephrotoxic and can promote kidney dysfunction, which frequently manifests during the terminal stages of cancer. Given the link between kidney disease and cancer development and treatment, the aim of this Review is to highlight the importance of multidisciplinary collaboration between oncologists and nephrologists to predict and prevent chemotherapeutic-induced nephrotoxicity. As new therapies are introduced to treat cancer, new renal toxicities require proper diagnosis and management. We anticipate that multidisciplinary collaborations will lead to the development and implementation of guidelines for clinicians to improve the therapeutic management of patients with both cancer and renal impairment.

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.

Mouse Tumor Models for Advanced Cancer Immunotherapy

Recent advances in the development of new methods of cancer immunotherapy require the production of complex cancer animal models that reliably reflect the complexity of the tumor and its microenvironment. Mice are good animals to create tumor models because they are low cost, have a short reproductive cycle, exhibit high tumor growth rates, and can be easily genetically modified. However, the obvious problem of these models is the high failure rate observed in human clinical trials after promising results obtained in mouse models. In order to increase the reliability of the results obtained in mice, the tumor model should reflect the heterogeneity of the tumor, contain components of the tumor microenvironment, in particular immune cells, to which the action of immunotherapeutic drugs are directed. This review discusses the current immunocompetent and immunocompromised mouse models of human tumors that are used to evaluate the effectiveness of immunotherapeutic agents, in particular chimeric antigen receptor (CAR) T-cells and immune checkpoint inhibitors.

Revolutionizing the landscape of colorectal cancer treatment: The potential role of immune checkpoint inhibitors

Colorectal cancer (CRC) represents the third cause of cancer-related mortalities worldwide. The progression of CRC to the metastatic phase significantly compromises the overall survival rates. Despite the advances in the therapeutic protocols, CRC treatment is still challenging. Cancer immunotherapy joined the ranks of surgery, chemotherapy, radiotherapy and targeted therapy as the fifth pillar in the foundation of cancer therapeutics. Interruption of the immunosuppressive signals within the tumor microenvironment and reactivation of antitumor immunity via targeting the molecular immune checkpoints generated promising therapeutic outcomes in several types of hard-to-treat cancers. The year 2017 witnessed the first US Food and Drug Administration (FDA) approval of immune checkpoint inhibitor (ICI) immunotherapy for the management of CRC. The approval was granted to pembrolizumab (anti-PD-1) for the treatment of patients with advanced/metastatic solid malignancies with mismatch-repair deficiency including CRCs. Such natively immunogenic tumors constitute only a minor percentage of all CRCs. Therefore, it is imperative to utilize novel combinatorial regimens to enhance the response of a wider range of CRC tumors to cancer immunotherapy and help in extending the survival rates in patients with advanced/metastatic disease. This review highlights the novel approaches under clinical development to overcome the resistance of CRCs to immunotherapy and improve the therapeutic outcomes.

Conditional reprogramming: Modeling urological cancer and translation to clinics

Patient-derived models, including cell models (organoids and conditionally reprogrammed cells [CRCs]) and patient-derived xenografts, are urgently needed for both basic and translational cancer research. Conditional reprogramming (CR) technique refers to a co-culture system of primary human normal or tumor cells with irradiated murine fibroblasts in the presence of a Rho-associated kinase inhibitor to allow the primary cells to acquire stem cell properties and the ability to proliferate indefinitely in vitro without any exogenous gene or viral transfection. Considering its robust features, the CR technique may facilitate cancer research in many aspects. Under in vitro culturing, malignant CRCs can share certain genetic aberrations and tumor phenotypes with their parental specimens. Thus, tumor CRCs can promisingly be utilized for the study of cancer biology, the discovery of novel therapies, and the promotion of precision medicine. For normal CRCs, the characteristics of normal karyotype maintenance and lineage commitment suggest their potential in toxicity testing and regenerative medicine. In this review, we discuss the applications, limitations, and future potential of CRCs in modeling urological cancer and translation to clinics.

Autologously Humanized Mice for Immune-Oncologic Studies

With the rapid approval of immune checkpoint inhibitors for lung, melanoma, breast, genitourinary, and hematological malignancies, the hematopoietic cells in the tumor microenvironment (TME) are now considered an important, if not essential, consideration for cancer scientists. In many instances, syngeneic murine models have not been highly predictive for responsiveness in clinical trials. Our limited understanding of the human TME have, therefore, precluded a rational translation of immunotherapeutic combinations. This has led to the adoption of hematopoietic humanized murine models for the study of human tumor immunology in vivo. However, concerns about chimerism rates, HLA mismatching, and incomplete reconstitution of the innate immune system have driven a quest for improvements in these allogeneic humanized murine systems. Presented in this article is a completely autologous xenotransplantation method for reconstituting the human tumor immune microenvironment in vivo without the use of a patient's peripheral blood which is known to be associated with low engraftment rates. With this new approach, the current limitations of allogeneic humanized models are avoided by using matched bone marrow cells (BMCs) and derived tumor xenoplants (PDXs) from solid tumors in cancer patients. This autologous system provides a platform for studying endogenous lymphocytic and myeloid cell infiltration into the human tumor in vivo. © 2020 Wiley Periodicals LLC. Basic Protocol: Autologous reconstitution of human tumors Support Protocol 1: Transduction of BMCs and/or tumor cells prior to autologous reconstitution Support Protocol 2: Modeling immunotherapeutic agents in an autologously humanized model.

Uveal melanoma pathobiology: Metastasis to the liver

Uveal melanoma (UM) is a type of intraocular tumor with a propensity to disseminate to the liver. Despite the identification of the early driver mutations during the development of the pathology, the process of UM metastasis is still not fully comprehended. A better understanding of the genetic, molecular, and environmental factors participating to its spread and metastatic outgrowth could provide additional approaches for UM treatment. In this review, we will discuss the advances made towards the understanding of the pathogenesis of metastatic UM, summarize the current and prospective treatments, and introduce some of the ongoing research in this field.

Patient-derived xenografts as compatible models for precision oncology

Cancer is a very heterogeneous disease, displaying heterogeneity between patients (inter-tumoral heterogeneity) and heterogeneity within a patient (intra-tumoral heterogeneity). Precision oncology is a diagnostic and therapeutic approach for cancers based on the stratification of patients using genomic and molecular profiling of tumors. To develop diagnostic and therapeutic tools for the application of precision oncology, appropriate preclinical mouse models that reflect tumor heterogeneity are required. Patient-derived xenograft (PDX) models are generated by the engraftment of patient tumors into immunodeficient mice that retain several aspects of the patient’s tumor characteristics, including inter-tumoral heterogeneity and intra-tumoral heterogeneity. Therefore, PDX models can be applied in various developmental steps of cancer diagnostics and therapeutics, such as biomarker development, companion diagnostics, drug efficacy testing, overcoming drug resistance, and co-clinical trials. This review summarizes the diverse aspects of PDX models, addressing the factors considered for PDX generation, application of PDX models for cancer research, and future directions of PDX models.

Multiplexed drug testing of tumor slices using a microfluidic platform

Current methods to assess the drug response of individual human cancers are often inaccurate, costly, or slow. Functional approaches that rapidly and directly assess the response of patient cancer tissue to drugs or small molecules offer a promising way to improve drug testing, and have the potential to identify the best therapy for individual patients. We developed a digitally manufactured microfluidic platform for multiplexed drug testing of intact cancer slice cultures, and demonstrate the use of this platform to evaluate drug responses in slice cultures from human glioma xenografts and patient tumor biopsies. This approach retains much of the tissue microenvironment and can provide results rapidly enough, within days of surgery, to guide the choice of effective initial therapies. Our results establish a useful preclinical platform for cancer drug testing and development with the potential to improve cancer personalized medicine.

A microfluidic platform for functional testing of cancer drugs on intact tumor slices

Present approaches to assess cancer treatments are often inaccurate, costly, and/or cumbersome. Functional testing platforms that use live tumor cells are a promising tool both for drug development and for identifying the optimal therapy for a given patient, i.e. precision oncology. However, current methods that utilize patient-derived cells from dissociated tissue typically lack the microenvironment of the tumor tissue and/or cannot inform on a timescale rapid enough to guide decisions for patient-specific therapy. We have developed a microfluidic platform that allows for multiplexed drug testing of intact tumor slices cultured on a porous membrane. The device is digitally-manufactured in a biocompatible thermoplastic by laser-cutting and solvent bonding. Here we describe the fabrication process in detail, we characterize the fluidic performance of the device, and demonstrate on-device drug-response testing with tumor slices from xenografts and from a patient colorectal tumor.

Osteogenesis and bone remodeling: A focus on growth factors and bioactive peptides

Bone is one of the most frequently transplanted tissues. The bone structure and its physiological function and stem cells biology were known to be closely related to each other for many years. Bone is considered a home to the well-known systems of postnatal mesenchymal stem cells (MSCs). These bone resident MSCs provide a range of growth factors (GF) and cytokines to support cell growth following injury. These GFs include a group of proteins and peptides produced by different cells which are regulators of important cell functions such as division, migration, and differentiation. GF signaling controls the formation and development of the MSCs condensation and plays a critical role in regulating osteogenesis, chondrogenesis, and bone/mineral homeostasis. Thus, a combination of both MSCs and GFs receives high expectations in regenerative medicine, particularly in bone repair applications. It is known that the delivery of exogenous GFs to the non-union bone fracture site remarkably improves healing results. Here we present updated information on bone tissue engineering with a specific focus on GF characteristics and their application in cellular functions and tissue healing. Moreover, the interrelation of GFs with the damaged bone microenvironment and their mechanistic functions are discussed.

The humanized mouse: Emerging translational potential

The humanized mouse (HM) has emerged as a valuable animal model in cancer research. Engrafted with components of a human immune system and subsequently implanted with tumor tissue from cell lines or in the form of patient-derived xenografts, the HM provides a unique platform in which the tumor microenvironment (TME) can be evaluated in vivo. This model may also be beneficial in the assessment of potential cancer treatments including immune checkpoint inhibitors. However, to maximize its utility, researchers need to understand the critical factors necessary to ensure that the tumor immune interactions in the HM are representative of those within cancer patients. In most current HM models, the human T cells residing in the HM are educated in a murine thymus, allogeneic to implanted tumor tissue, and/or alloreactive to mouse tissues, making their interaction and reactivity with tumor cells suspect. There are several strategies underway to harmonize the immune-tumor environment in the HM. Once the essential components of the HM-tumor TME interface have been identified and understood, the HM model will permit not only the discovery of effective immunotherapy treatments, but it can be used to predict patient responses to great clinical benefit.

Patient-derived cancer modeling for precision medicine in colorectal cancer: beyond the cancer cell line

Since effective immunotherapeutic agents such as immune checkpoint blockade to treat cancer have emerged, the need for reliable preclinical cancer models that can evaluate and discover such drugs became stronger than ever before. The traditional preclinical cancer model using a cancer cell line has several limitations to recapitulate intra-tumor heterogeneity and in-vivo tumor activity including interactions between tumor-microenvironment. In this review, we will go over various preclinical cancer models recently discovered including patient-derived xenografts, humanized mice, organoids, organotypic-tumor spheroids, and organ-on-a-chip models. Moreover, we will discuss the future directions of preclinical cancer research.

Direct genome editing of patient-derived xenografts using CRISPR-Cas9 enables rapid in vivo functional genomics

Patient-derived xenografts are high fidelity in vivo tumor models that accurately reflect many key aspects of human cancer. In contrast to either cancer cell lines or genetically engineered mouse models, the utility of PDXs has been limited by the inability to perform targeted genome editing of these tumors. To address this limitation, we have developed methods for CRISPR-Cas9 editing of PDXs using a tightly regulated, inducible Cas9 vector that does not require in vitro culture for selection of transduced cells. We demonstrate the utility of this platform in PDXs (1) to analyze genetic dependencies by targeted gene disruption and (2) to analyze mechanisms of acquired drug resistance by site-specific gene editing using templated homology-directed repair. This flexible system has broad application to other explant models and substantially augments the utility of PDXs as genetically programmable models of human cancer.

Pre-clinical models of small cell lung cancer and the validation of therapeutic targets

Introduction: Small-cell lung cancer (SCLC) is an aggressive form of lung cancer that has a dismal prognosis. One of the factors hindering therapeutic developments for SCLC is that most SCLC is not surgically resected resulting in a paucity of material for analysis. To address this, significant efforts have been made by investigators to develop pre-clinical models of SCLC allowing for downstream target identification in this difficult to treat cancer.Areas covered: In this review, we describe the current pre-clinical models that have been developed to interrogate SCLC, and outline the benefits and limitations associated with each. Using examples we show how each has been used to (i) improve our knowledge of this intractable cancer, and (ii) identify and validate potential therapeutic targets that (iii) are currently under development and testing within the clinic.Expert opinion: The large numbers of preclinical models that have been developed have dramatically improved the ways in which we can examine SCLC and test therapeutic targets/interventions. The newer models are rapidly providing novel avenues for the design and testing of new therapeutics. Despite this many of these models have inherent flaws that limit the possibility of their use for individualized therapy decision-making for SCLC.

Patient-derived xenografts (PDXs) as model systems for human cancer

Patient-derived xenografts (PDXs) are obtained by transplanting fragments of a patient's tumour into immunodeficient mice. Growth and propagation of PDXs allows correlating therapeutic response in vivo with extensive, multi-dimensional molecular annotation, leading to identification of predictive biomarkers. PDXs are increasingly recognised as clinically relevant models of cancer for several reasons, of which the main is the possibility of studying the behaviour of cancer cells in a natural microenvironment, where they interact with stromal components accrued from the mouse host. PDXs maintain close similarities with the tumour of origin, in terms of tissue architecture, molecular features and response to treatments. Indeed, preclinical trials in PDXs have been shown to match and also anticipate data obtained in patients. Exploration of more complex processes like metastatic evolution and antitumour immune responses is actively pursued with PDXs, as new generations of host models emerge on the horizon.

PD-L1/PD-1 axis as a potent therapeutic target in breast cancer

Although both the incidence and the mortality rate of breast cancer is rising, there is no potent and practical option for the treatment of these patients, particularly in advanced stages. One of the most critical challenges for treatment is the presence of complicated and extensive tumor escape mechanisms in the tumor microenvironment. Immune checkpoint molecules are of the main immunosuppressive mechanisms used by cancerous cells to block anti-cancer immune responses. Among these molecules, PD-1 (Programmed cell death) and PD-L1 (programmed cell death-ligand 1) have been considered as worthy therapeutic targets for breast cancer therapy. In this review, we intend to discuss the immunobiology and signaling of the PD-1/PD-L1 axis and highlight its importance as a worthy therapeutic target in breast cancer. We believe that the prognostic value of PD-L1 depends on the breast cancer subtype. Moreover, the combination of PD-1/PD-L1 targeting with immune-stimulating vaccines can be considered as an effective therapeutic strategy in breast cancer.

Patient-Derived Xenograft Models in Urological Malignancies: Urothelial Cell Carcinoma and Renal Cell Carcinoma

The engraftment of human tumor tissues into immunodeficient host mice to generate patient-derived xenograft (PDX) models has become increasingly utilized for many types of cancers. By capturing the unique genomic and molecular properties of the parental tumor, PDX models enable analysis of patient-specific clinical responses. PDX models are an important platform to address the contribution of inter-tumoral heterogeneity to therapeutic sensitivity, tumor evolution, and the mechanisms of treatment resistance. With the increasingly important role played by targeted therapies in urological malignancies, the establishment of representative PDX models can contribute to improved facilitation and adoption of precision medicine. In this review of the evolving role of the PDX in urothelial cancer and kidney cancer, we discuss the essential elements of successful graft development, effective translational application, and future directions for clinical models.

Patient Derived Models to Study Head and Neck Cancer Radiation Response

Patient-derived model systems are important tools for studying novel anti-cancer therapies. Patient-derived xenografts (PDXs) have gained favor over the last 10 years as newer mouse strains have improved the success rate of establishing PDXs from patient biopsies. PDXs can be engrafted from head and neck cancer (HNC) samples across a wide range of cancer stages, retain the genetic features of their human source, and can be treated with both chemotherapy and radiation, allowing for clinically relevant studies. Not only do PDXs allow for the study of patient tissues in an in vivo model, they can also provide a renewable source of cancer cells for organoid cultures. Herein, we review the uses of HNC patient-derived models for radiation research, including approaches to establishing both orthotopic and heterotopic PDXs, approaches and potential pitfalls to delivering chemotherapy and radiation to these animal models, biological advantages and limitations, and alternatives to animal studies that still use patient-derived tissues.

Patient-derived explants (PDEs) as a powerful preclinical platform for anti-cancer drug and biomarker discovery

Preclinical models that can accurately predict outcomes in the clinic are much sought after in the field of cancer drug discovery and development. Existing models such as organoids and patient-derived xenografts have many advantages, but they suffer from the drawback of not contextually preserving human tumour architecture. This is a particular problem for the preclinical testing of immunotherapies, as these agents require an intact tumour human-specific microenvironment for them to be effective. In this review, we explore the potential of patient-derived explants (PDEs) for fulfilling this need. PDEs involve the ex vivo culture of fragments of freshly resected human tumours that retain the histological features of original tumours. PDE methodology for anti-cancer drug testing has been in existence for many years, but the platform has not been widely adopted in translational research facilities, despite strong evidence for its clinical predictivity. By modifying PDE endpoint analysis to include the spatial profiling of key biomarkers by using multispectral imaging, we argue that PDEs offer many advantages, including the ability to correlate drug responses with tumour pathology, tumour heterogeneity and changes in the tumour microenvironment. As such, PDEs are a powerful model of choice for cancer drug and biomarker discovery programmes.

Development of an Adrenocortical Cancer Humanized Mouse Model to Characterize Anti-PD1 Effects on Tumor Microenvironment

CONTEXT

Although the development of immune checkpoint inhibitors has transformed treatment strategies of several human malignancies, research models to study immunotherapy in adrenocortical carcinoma (ACC) are lacking.

OBJECTIVE

To explore the effect of anti-PD1 immunotherapy on the alteration of the immune milieu in ACC in a newly generated preclinical model and correlate with the response of the matched patient.

DESIGN, SETTING, AND INTERVENTION

To characterize the CU-ACC2-M2B patient-derived xenograft in a humanized mouse model, evaluate the effect of a PD-1 inhibitor therapy, and compare it with the CU-ACC2 patient with metastatic disease.

RESULTS

Characterization of the CU-ACC2-humanized cord blood-BALB/c-Rag2nullIl2rγnullSirpaNOD model confirmed ACC origin and match with the original human tumor. Treatment of the mice with pembrolizumab demonstrated significant tumor growth inhibition (60%) compared with controls, which correlated with increased tumor infiltrating lymphocyte activity, with an increase of human CD8+ T cells (P < 0.05), HLA-DR+ T cells (P < 0.05) as well as Granzyme B+ CD8+ T cells (<0.001). In parallel, treatment of the CU-ACC2 patient, who had progressive disease, demonstrated a partial response with 79% to 100% reduction in the size of target lesions, and no new sites of metastasis. Pretreatment analysis of the patient's metastatic liver lesion demonstrated abundant intratumoral CD8+ T cells by immunohistochemistry.

CONCLUSIONS

Our study reports the first humanized ACC patient-derived xenograft mouse model, which may be useful to define mechanisms and biomarkers of response and resistance to immune-based therapies, to ultimately provide more personalized care for patients with ACC.

Microfluidics for interrogating live intact tissues

The intricate microarchitecture of tissues - the "tissue microenvironment" - is a strong determinant of tissue function. Microfluidics offers an invaluable tool to precisely stimulate, manipulate, and analyze the tissue microenvironment in live tissues and engineer mass transport around and into small tissue volumes. Such control is critical in clinical studies, especially where tissue samples are scarce, in analytical sensors, where testing smaller amounts of analytes results in faster, more portable sensors, and in biological experiments, where accurate control of the cellular microenvironment is needed. Microfluidics also provides inexpensive multiplexing strategies to address the pressing need to test large quantities of drugs and reagents on a single biopsy specimen, increasing testing accuracy, relevance, and speed while reducing overall diagnostic cost. Here, we review the use of microfluidics to study the physiology and pathophysiology of intact live tissues at sub-millimeter scales. We categorize uses as either in vitro studies - where a piece of an organism must be excised and introduced into the microfluidic device - or in vivo studies - where whole organisms are small enough to be introduced into microchannels or where a microfluidic device is interfaced with a live tissue surface (e.g. the skin or inside an internal organ or tumor) that forms part of an animal larger than the device. These microfluidic systems promise to deliver functional measurements obtained directly on intact tissue - such as the response of tissue to drugs or the analysis of tissue secretions - that cannot be obtained otherwise.

Improved chemotherapy modeling with RAG-based immune deficient mice

We have previously characterized an acute myeloid leukemia (AML) chemotherapy model for SCID-based immune deficient mice (NSG and NSGS), consisting of 5 days of cytarabine (AraC) and 3 days of anthracycline (doxorubicin), to simulate the standard 7+3 chemotherapy regimen many AML patients receive. While this model remains tractable, there are several limitations, presumably due to the constitutional Pkrdc^scid (SCID, severe combined immune deficiency) mutation which affects DNA repair in all tissues of the mouse. These include the inability to combine preconditioning with subsequent chemotherapy, the inability to repeat chemotherapy cycles, and the increased sensitivity of the host hematopoietic cells to genotoxic stress. Here we attempt to address these drawbacks through the use of alternative strains with RAG-based immune deficiency (NRG and NRGS). We find that RAG-based mice tolerate a busulfan preconditioning regimen in combination with either AML or 4-drug acute lymphoid leukemia (ALL) chemotherapy, expanding the number of samples that can be studied. RAG-based mice also tolerate multiple cycles of therapy, thereby allowing for more aggressive, realistic modeling. Furthermore, standard AML therapy in RAG mice was 3.8-fold more specific for AML cells, relative to SCID mice, demonstrating an improved therapeutic window for genotoxic agents. We conclude that RAG-based mice should be the new standard for preclinical evaluation of therapeutic strategies involving genotoxic agents.

The development of human immune system mice and their use to study tolerance and autoimmunity

Autoimmune diseases evolve from complex interactions between the immune system and self-antigens and involve several genetic attributes, environmental triggers and diverse cell types. Research using experimental mouse models has contributed key knowledge on the mechanisms that underlie these diseases in humans, but differences between the mouse and human immune systems can and, at times, do undermine the translational significance of these findings. The use of human immune system (HIS) mice enables the utility of mouse models with greater relevance for human diseases. As the name conveys, these mice are reconstituted with mature human immune cells transferred directly from peripheral blood or via transplantation of human hematopoietic stem cells that nucleate the generation of a complex human immune system. The function of the human immune system in HIS mice has improved over the years with the stepwise development of better models. HIS mice exhibit key benefits of the murine animal model, such as small size, robust and rapid reproduction and ease of experimental manipulation. Importantly, HIS mice also provide an applicable in vivo setting that permit the investigation of the physiological and pathological functions of the human immune system and its response to novel treatments. With the gaining popularity of HIS mice in the last decade, the potential of this model has been exploited for research in basic science, infectious diseases, cancer, and autoimmunity. In this review we focus on the use of HIS mice in autoimmune studies to stimulate further development of these valuable models.

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Human immune system (HIS) mice bear components of the human immune system.

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HIS mice engraft with human blood or hematopoietic stem cells, and sometimes thymus.

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HIS mice are used to investigate development and function of the human immune system.

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Immunological tolerance and autoimmune responses can be studied in HIS mice.

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HIS models of autoimmunity vary in complexity and in ability to represent disease.

Humanized mice for immune checkpoint blockade in human solid tumors

Immunotherapy, specifically research involving immune checkpoint blockers (ICBs), has become a popular trend in anticancer research over the last three years. Due to the difficulties and often poor translation of results from in-vitro models, in-vivo models have become more relevant than ever. With the discovery of NOD, Prkdcscid , and Il2rγ-/- mutations, patient-derived xenograft (PDX) mouse models were developed, providing an ideal environment for ICBs testing. By implanting a PDX with either CD34+ or peripheral blood mononuclear cells, we can create a human immune system capable of mounting a response against tumor burden. These animal models are currently being used to study molecular mechanisms, test drug efficacy, and trial drug combinations. Others have found use for these humanized mouse models as surrogates to represent otherwise uncommon diseases. Limitations remain with regards to what the models are capable of, but in the short amount of time between the development of these models and heightened interest in ICBs, these mice have already shown utility for future developments in the field of immunotherapy.

Preclinical models of breast cancer: Two-way shuttles for immune checkpoint inhibitors from and to patient bedside

The Food and Drug Administration has lately approved atezolizumab, anti-programmed death ligand 1 (PD-L1), to be used together with nanoparticle albumin-bound (nab) paclitaxel in treating patients with triple negative breast cancer (BC) expressing PD-L1. Nonetheless, immune checkpoint inhibitors (ICIs) are still challenged by the resistance and immune-related adverse effects evident in a considerable subset of treated patients without conclusive comprehension of the underlying molecular basis, biomarkers and tolerable therapeutic regimens capable of unleashing the anti-tumour immune responses. Stepping back to preclinical models is thus inevitable to address these inquiries. Herein, we comprehensively review diverse preclinical models of BC exploited in investigating ICIs underscoring their pros and cons as well as the learnt and awaited lessons to allow full exploitation of ICIs in BC therapy.

The Tumor-Immune Response Is Not Compromised by Mesenchymal Stromal Cells in Humanized Mice

Therapeutic uses of mesenchymal stromal cells (MSCs) have emerged over the past decade. Yet, their effect on tumor growth remains highly debated, particularly in an immune competent environment. In this study, we wanted to investigate the impact of human umbilical cord-derived MSCs (hUC-MSCs) on tumor growth in humanized mice generated by the human adoptive transfer of PBMCs or the cotransplantation of hematopoietic stem cells and human thymic tissue (human BLT [Hu-BLT]). Our results showed that the growth and immune rejection of engineered human fibroblastic tumors was not altered by the injection of hUC-MSCs in immune-deficient or humanized mice, respectively. This was observed whether tumor cells were injected s.c. or i.v. and independently of the injection route of the hUC-MSCs. Moreover, only in Hu-BLT mice did hUC-MSCs have some effects on the tumor-immune infiltrate, yet without altering tumor growth. These results demonstrate that hUC-MSCs do not promote fibroblastic tumor growth and neither do they prevent tumor infiltration and rejection by immune cells in humanized mice.

Eluted 25-hydroxyvitamin D3 from radially aligned nanofiber scaffolds enhances cathelicidin production while reducing inflammatory response in human immune system-engrafted mice

Vitamin D₃ modulates immune response, induces endogenous antimicrobial peptide production, and enhances innate immunity to defend against infections. These findings suggest that incorporating vitamin D₃ into medical devices or scaffolds could positively modulate host immune response and prevent infections. In the current study, we evaluated host responses and endogenous antimicrobial peptide production using 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds in human immune system-engrafted mice. We transformed traditional 2D electrospun nanofiber membranes into radially aligned PCL nanofiber scaffolds using the concept of solid of revolution and an innovative gas-foaming technique. Such scaffolds can promote rapid cellular infiltration and neovascularization. The infiltrating immune cells within subcutaneously implanted 25(OH)D₃-containing scaffolds mainly consisted of human macrophages in the M1 phase (CCR7⁺), mice macrophages in the M2 phase (CD206⁺), and human cytotoxic T cells (CD8⁺) other than few human T-helper cells (CD4⁺). The 25(OH)D₃-eluting nanofiber scaffolds significantly inhibited the production of pro-inflammatory cytokines (TNF-α, IL-6), while accelerating the production of anti-inflammatory cytokines (IL-4, IL-10) within the scaffolds. Additionally, we observed increased expression of human cathelicidin LL-37 within the 25(OH)D₃-eluting scaffolds, while no LL-37 expression was observed in the control. Together, these findings support further work in the design of vitamin D₃-eluting medical devices or scaffolds for modulating immune response and promoting antimicrobial peptide production. This could potentially reduce the inflammatory response, prevent infections, and eventually improve success rates of implants. STATEMENT OF SIGNIFICANCE: Transplant failure of medical devices, grafts, scaffolds, and tissue-engineered constructs due to inflammation and infection causes not only economic losses but also sufferings of second operation to the patient. Positive modulation of the host response to implants, scaffolds, and tissue-engineered constructs is likely to reduce the failure rate. Vitamin D₃ plays an important role in modulating the immune response. It is able to not only reduce inflammation and induce endogenous antimicrobial peptide production but also prevent multidrug resistance and other side effects of traditional antibiotics. In this study, host responses to 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds were evaluated in human immune system-engrafted mice. The 25(OH)D₃-eluting medical devices or scaffolds were able to modulate positive immune response and promote antimicrobial peptide production. This work presented an innate immunity-enhancing approach for reducing the inflammatory response and preventing infections, likely resulting in improvement of success rates of implants.

The Evolving Landscape of Biomarkers for Anti-PD-1 or Anti-PD-L1 Therapy

The administration of antibodies blocking the immune checkpoint molecules programmed cell death protein 1 (PD-1) or programmed cell death 1 ligand 1 (PD-L1) has evolved as a very promising treatment option for cancer patients. PD-1/PD-L1 inhibition has significantly enhanced expansion, cytokine secretion, and cytotoxic activity of CD4⁺ and CD8⁺ T lymphocytes, resulting in enhanced antitumor responses. Anti-PD-1 or anti-PD-L1 therapy has induced tumor regression and improved clinical outcome in patients with different tumor entities, including melanoma, non-small-cell lung cancer, and renal cell carcinoma. These findings led to the approval of various anti-PD-1 or anti-PD-L1 antibodies for the treatment of tumor patients. However, the majority of patients have failed to respond to this treatment modality. Comprehensive immune monitoring of clinical trials led to the identification of potential biomarkers distinguishing between responders and non-responders, the discovery of modes of treatment resistance, and the design of improved immunotherapeutic strategies. In this review article, we summarize the evolving landscape of biomarkers for anti-PD-1 or anti-PD-L1 therapy.

Frontline Science: Exhaustion and senescence marker profiles on human T cells in BRGSF-A2 humanized mice resemble those in human samples

This work sought to confirm the human-like expression of exhaustion and senescence markers in a mouse model with a humanized immune system (HIS): the Balb/c Rag2^KO IL2rgc^KO Sirpα^NOD Flk2^KO HLA-A2^HHD (BRGSF-A2) mouse reconstituted with human CD34⁺ cord blood cells. With regard to senescence markers, the percentage of CD57⁺ T cells was higher in the bone marrow (BM) than in the spleen or blood. The same was true for KLRG1⁺ hCD8⁺ T cells. With regard to exhaustion markers, the percentage of programmed death 1 (PD-1⁺ ) T cells was higher in the BM than in the spleen or blood; the same was true for TIGIT⁺ hCD4⁺ cells. These tissue-specific differences were related to both higher proportions of memory T cells in BM and intrinsic differences in expression within the memory fraction. In blood samples from HIS mice and healthy human donors (HDs), we found that the percentage of KLRG1⁺ cells among hCD8⁺ T cells was lower in HIS compared to HDs. The opposite was true for CD4⁺ T cells. Unexpectedly, a high frequency of KLRG1⁺ cells was observed among naive T cells in HIS mice. CD57 expression on T cells was similar in blood samples from HIS mice and HDs. Likewise, PD-1 expression was similar in the two systems, although a relatively low proportion of HIS hCD4⁺ T cells expressed TIGIT. The BRGSF-A2 HIS mouse's exhaustion and senescence profile was tissue specific and relatively human like; hence, this mouse might be a valuable tool for determining the preclinical efficacy of immunotherapies.

An Improved Patient-Derived Xenograft Humanized Mouse Model for Evaluation of Lung Cancer Immune Responses

Human tumor xenograft models do not replicate the human immune system and tumor microenvironment. We developed an improved humanized mouse model, derived from fresh cord blood CD34+ stem cells (CD34+ HSC), and combined it with lung cancer cell line-derived human xenografts or patient-derived xenografts (Hu-PDX). Fresh CD34+ HSCs could reconstitute detectable mature human leukocytes (hCD45+) in mice at four weeks without the onset of graft-versus-host disease (GVHD). Repopulated human T cells, B cells, natural killer (NK) cells, dendritic cells (DC), and myeloid-derived suppressor cells (MDSC) increased in peripheral blood, spleen, and bone marrow over time. Although cultured CD34+ HSCs labeled with luciferase could be detected in mice, the cultured HSCs did not develop into mature human immune cells by four weeks, unlike fresh CD34+ HSCs. Ex vivo, reconstituted T cells, obtained from the tumor-bearing humanized mice, secreted IFNγ upon treatment with phorbol myristate acetate (PMA) or exposure to human A549 lung tumor cells and mediated antigen-specific CTL responses, indicating functional activity. Growth of engrafted PDXs and tumor xenografts was not dependent on the human leukocyte antigen status of the donor. Treatment with the anti-PD-1 checkpoint inhibitors pembrolizumab or nivolumab inhibited tumor growth in humanized mice significantly, and correlated with an increased number of CTLs and decreased MDSCs, regardless of the donor HLA type. In conclusion, fresh CD34+HSCs are more effective than their expanded counterparts in humanizing mice, and do so in a shorter time. The Hu-PDX model provides an improved platform for evaluation of immunotherapy.

Efficacy and safety profiles of programmed cell death-1/programmed cell death ligand-1 inhibitors in the treatment of triple-negative breast cancer: A comprehensive systematic review

Triple-negative breast cancer (TNBC) is associated with worse prognosis, with limited treatment regiments available and higher mortality rate. Immune checkpoint inhibitors targeting programmed cell death-1 (PD-1) or programmed cell death-ligand 1 (PD-L1) showed great potentials in treating malignancies and may serve as potential therapies for TNBC. This systematic review aims to evaluate the efficacy and safety profiles of PD-1/PD-L1 inhibitors in the treatment of TNBC. Literature search was performed via PubMed, EBSCOhost, Scopus, and CENTRAL databases, selecting studies which evaluated the use of anti-PD-1/PDL1 for TNBC from inception until February 2019. Risk of bias was assessed by the Newcastle-Ottawa Scale (NOS). Overall, 7 studies evaluating outcomes of 1395 patients with TNBC were included in this systematic review. Anti-PD-1/PD-L1 showed significant antitumor effect, proven by their promising response (objective response rate (ORR), 18.5-39.4%) and survival rates (median overall survival (OS), 9.2-21.3 months). Moreover, anti- PD-1/PD-L1 yielded better outcomes when given as first-line therapy, and overexpression of PD-L1 in tumors showed better therapeutic effects. On the other hands, safety profiles were similar across agents and generally acceptable, with grade ≥3 treatment- related adverse effects (AEs) ranging from 9.5% to 15.6% and no new AEs were experienced by TNBC patients. Most grade ≥3 AEs are immune-mediated, which are manifested as neutropenia, fatigue, peripheral neuropathy, and anemia. PD-1/PD-L1 inhibitors showed promising efficacy and tolerable AEs, and thus may benefit TNBC patients. Further studies of randomized controlled trials with larger populations are needed to better confirm the potential of these agents.

Fidelity of a PDX-CR model for bladder cancer

Patient-derived xenografts (PDXs) are widely recognised as a more physiologically relevant preclinical model than standard cell lines, but are expensive and low throughput, have low engraftment rate and take a long time to develop. Our newly developed conditional reprogramming (CR) technology addresses many PDX drawbacks, but lacks many in vivo factors. Here we determined whether PDXs and CRCs of the same cancer origin maintain the biological fidelity and complement each for translational research and drug development. Four CRC lines were generated from bladder cancer PDXs. Short tandem repeat (STR) analyses revealed that CRCs and their corresponding parental PDXs shared the same STRs, suggesting common cancer origins. CRCs and their corresponding parental PDXs contained the same genetic alterations. Importantly, CRCs retained the same drug sensitivity with the corresponding downstream signalling activity as their corresponding parental PDXs. This suggests that CRCs and PDXs can complement each other, and that CRCs can be used for in vitro fast, high throughput and low cost screening while PDXs can be used for in vivo validation and study of the in vivo factors during translational research and drug development.

Patient-Derived Xenograft Models of Breast Cancer and Their Application

Recently, patient-derived xenograft (PDX) models of many types of tumors including breast cancer have emerged as a powerful tool for predicting drug efficacy and for understanding tumor characteristics. PDXs are established by the direct transfer of human tumors into highly immunodeficient mice and then maintained by passaging from mouse to mouse. The ability of PDX models to maintain the original features of patient tumors and to reflect drug sensitivity has greatly improved both basic and clinical study outcomes. However, current PDX models cannot completely predict drug efficacy because they do not recapitulate the tumor microenvironment of origin, a failure which puts emphasis on the necessity for the development of the next generation PDX models. In this article, we summarize the advantages and limitations of current PDX models and discuss the future directions of this field.

Humanized mouse models of immunological diseases and precision medicine

With the increase in knowledge resulting from the sequencing of the human genome, the genetic basis for the underlying differences in individuals, their diseases, and how they respond to therapies is starting to be understood. This has formed the foundation for the era of precision medicine in many human diseases that is beginning to be implemented in the clinic, particularly in cancer. However, preclinical testing of therapeutic approaches based on individual biology will need to be validated in animal models prior to translation into patients. Although animal models, particularly murine models, have provided significant information on the basic biology underlying immune responses in various diseases and the response to therapy, murine and human immune systems differ markedly. These fundamental differences may be the underlying reason why many of the positive therapeutic responses observed in mice have not translated directly into the clinic. There is a critical need for preclinical animal models in which human immune responses can be investigated. For this, many investigators are using humanized mice, i.e., immunodeficient mice engrafted with functional human cells, tissues, and immune systems. We will briefly review the history of humanized mice, the remaining limitations, approaches to overcome them and how humanized mouse models are being used as a preclinical bridge in precision medicine for evaluation of human therapies prior to their implementation in the clinic.

Toward a comprehensive view of cancer immune responsiveness: a synopsis from the SITC workshop

Tumor immunology has changed the landscape of cancer treatment. Yet, not all patients benefit as cancer immune responsiveness (CIR) remains a limitation in a considerable proportion of cases. The multifactorial determinants of CIR include the genetic makeup of the patient, the genomic instability central to cancer development, the evolutionary emergence of cancer phenotypes under the influence of immune editing, and external modifiers such as demographics, environment, treatment potency, co-morbidities and cancer-independent alterations including immune homeostasis and polymorphisms in the major and minor histocompatibility molecules, cytokines, and chemokines. Based on the premise that cancer is fundamentally a disorder of the genes arising within a cell biologic process, whose deviations from normality determine the rules of engagement with the host's response, the Society for Immunotherapy of Cancer (SITC) convened a task force of experts from various disciplines including, immunology, oncology, biophysics, structural biology, molecular and cellular biology, genetics, and bioinformatics to address the complexity of CIR from a holistic view. The task force was launched by a workshop held in San Francisco on May 14-15, 2018 aimed at two preeminent goals: 1) to identify the fundamental questions related to CIR and 2) to create an interactive community of experts that could guide scientific and research priorities by forming a logical progression supported by multiple perspectives to uncover mechanisms of CIR. This workshop was a first step toward a second meeting where the focus would be to address the actionability of some of the questions identified by working groups. In this event, five working groups aimed at defining a path to test hypotheses according to their relevance to human cancer and identifying experimental models closest to human biology, which include: 1) Germline-Genetic, 2) Somatic-Genetic and 3) Genomic-Transcriptional contributions to CIR, 4) Determinant(s) of Immunogenic Cell Death that modulate CIR, and 5) Experimental Models that best represent CIR and its conversion to an immune responsive state. This manuscript summarizes the contributions from each group and should be considered as a first milestone in the path toward a more contemporary understanding of CIR. We appreciate that this effort is far from comprehensive and that other relevant aspects related to CIR such as the microbiome, the individual's recombined T cell and B cell receptors, and the metabolic status of cancer and immune cells were not fully included. These and other important factors will be included in future activities of the taskforce. The taskforce will focus on prioritization and specific actionable approach to answer the identified questions and implementing the collaborations in the follow-up workshop, which will be held in Houston on September 4-5, 2019.