Development and Applications of Patient-Derived Xenograft Models in Humanized Mice for Oncology and Immune-Oncology Drug Discovery

Personalized Treatment of Recurrent, Metastatic Head and Neck Cancer Guided by Patient-Derived Xenograft Models

Recurrent or metastatic head and neck squamous cell carcinoma (RMHNSCC) is associated with a poor prognosis and short survival duration. There is an urgent need to identify personalized predictors of drug response to guide the selection of the most effective therapy for each individual recurrence. We tested the feasibility of patient-derived xenografts (PDX) for guiding their RMHNSCC salvage treatment. Fresh tumor samples from eligible, consented patients were implanted into mice. Established tumors were expanded in mouse PDX cohorts to identify responses to candidate salvage drug treatments in parallel testing. Patients alive and suitable for chemotherapy were treated based on responses determined by PDX testing. Nine patient tumors were successfully engrafted in mice with an average time of 89.2±41.7 days. Four patients' PDX models underwent parallel drug testing. Two patients received PDX-guided therapy. In one of these patients, single agents of cetuximab and paclitaxel demonstrated the best responses in the PDX model, and this patient exhibited sequential partial responses to each drug, including a 17-month clinical response to cetuximab. The main limitation of PDX testing for RMHNSCC was the time delay in obtaining testing results. Despite this, parallel PDX testing may be feasible for a subset of patients and appears to correlate with clinical benefit.

Generation of Orthotopic Patient-Derived Xenografts in Humanized Mice for Evaluation of Emerging Targeted Therapies and Immunotherapy Combinations for Melanoma

Current methodologies for developing PDX in humanized mice in preclinical trials with immune-based therapies are limited by GVHD. Here, we compared two approaches for establishing PDX tumors in humanized mice: (1) PDX are first established in immune-deficient mice; or (2) PDX are initially established in humanized mice; then established PDX are transplanted to a larger cohort of humanized mice for preclinical trials. With the first approach, there was rapid wasting of PDX-bearing humanized mice with high levels of activated T cells in the circulation and organs, indicating immune-mediated toxicity. In contrast, with the second approach, toxicity was less of an issue and long-term human melanoma tumor growth and maintenance of human chimerism was achieved. Preclinical trials from the second approach revealed that rigosertib, but not anti-PD-1, increased CD8/CD4 T cell ratios in spleen and blood and inhibited PDX tumor growth. Resistance to anti-PD-1 was associated with PDX tumors established from tumors with limited CD8+ T cell content. Our findings suggest that it is essential to carefully manage immune editing by first establishing PDX tumors in humanized mice before expanding PDX tumors into a larger cohort of humanized mice to evaluate therapy response.

Experimental in vitro, ex vivo and in vivo models in prostate cancer research

Androgen deprivation therapy has a central role in the treatment of advanced prostate cancer, often causing initial tumour remission before increasing independence from signal transduction mechanisms of the androgen receptor and then eventual disease progression. Novel treatment approaches are urgently needed, but only a fraction of promising drug candidates from the laboratory will eventually reach clinical approval, highlighting the demand for critical assessment of current preclinical models. Such models include standard, genetically modified and patient-derived cell lines, spheroid and organoid culture models, scaffold and hydrogel cultures, tissue slices, tumour xenograft models, patient-derived xenograft and circulating tumour cell eXplant models as well as transgenic and knockout mouse models. These models need to account for inter-patient and intra-patient heterogeneity, the acquisition of primary or secondary resistance, the interaction of tumour cells with their microenvironment, which make crucial contributions to tumour progression and resistance, as well as the effects of the 3D tissue network on drug penetration, bioavailability and efficacy.

Autologous humanized mouse models to study combination and single-agent immunotherapy for colorectal cancer patient-derived xenografts

Designing studies of immunotherapy is limited due to a lack of pre-clinical models that reliably predict effective immunotherapy responses. To address this gap, we developed humanized mouse models of colorectal cancer (CRC) incorporating patient-derived xenografts (PDX) with human peripheral blood mononuclear cells (PBMC). Humanized mice with CRC PDXs were generated via engraftment of autologous (isolated from the same patients as the PDXs) or allogeneic (isolated from healthy donors) PBMCs. Human T cells were detected in mouse blood, tissues, and infiltrated the implanted PDXs. The inclusion of anti-PD-1 therapy revealed that tumor responses in autologous but not allogeneic models were more comparable to that of patients. An overall non-specific graft-vs-tumor effect occurred in allogeneic models and negatively correlated with that seen in patients. In contrast, autologous humanized mice more accurately correlated with treatment outcomes by engaging pre-existing tumor specific T-cell populations. As autologous T cells appear to be the major drivers of tumor response thus, autologous humanized mice may serve as models at predicting treatment outcomes in pre-clinical settings for therapies reliant on pre-existing tumor specific T-cell populations.

Establishment of Humanized Mice from Peripheral Blood Mononuclear Cells or Cord Blood CD34+ Hematopoietic Stem Cells for Immune-Oncology Studies Evaluating New Therapeutic Agents

The clinical success of immune checkpoint modulators and the development of next-generation immune-oncology (IO) agents underscore the need for robust preclinical models to evaluate novel IO therapeutics. Human immune system (HIS) mouse models enable in vivo studies in the context of the HIS via a human tumor. The immunodeficient mouse strains NOG (Prkdc^scid Il2rg^tm1Sug ) and triple-transgenic NOG-EXL [Prkdc^scid Il2rg^tm1Sug Tg (SV40/HTLV-IL3, CSF2)], which expresses human IL-3 and GM-CSF, allow for human CD34+ hematopoietic stem cell (huCD34+ HSC) engraftment and multilineage immune cell development by 12 to 16 weeks post-transplant and facilitate studies of immunomodulatory agents. A more rapid model of human immune engraftment utilizes peripheral blood mononuclear cells (PBMCs) transplanted into immunodeficient murine hosts, permitting T-cell engraftment within 2 to 3 weeks without outgrowth of other human immune cells. The PBMC-HIS model can be limited due to onset of xenogeneic graft-versus-host disease (xGVHD) within 3 to 5 weeks post-implantation. Host deficiency in MHC class I, as occurs in beta-2 microglobulin knockout in either NOG or NSG mice, results in resistance to xGVHD, which permits a longer therapeutic window. In this article, detailed processes for generating humanized mice by transplantation of HSCs from cord blood-derived huCD34+ HSCs or PBMCs into immunodeficient mouse strains to respectively generate HSC-HIS and PBMC-HIS mouse models are provided. In addition, the co-engraftment and growth kinetics of patient-derived and cell line-derived xenograft tumors in humanized mice and recovery of tumor-infiltrating lymphocytes from growing tumors to evaluate immune cell subsets by flow cytometry are described. © 2020 The Authors. Basic Protocol 1: Establishment of patient-derived xenograft tumors in CD34+ hematopoietic stem cell-humanized mice Basic Protocol 2: Establishment of patient-derived xenograft tumors in peripheral blood mononuclear cell-humanized mice Support Protocol 1: Flow cytometry assessment of humanization in mice Support Protocol 2: Flow cytometry assessment of tumor-infiltrating lymphocytes in tumor-bearing humanized mouse models.

Cancer Explant Models

Overcoming the challenges of understanding and treating cancer requires reliable patient-derived models of cancer (PDMCs). For decades, cancer research and therapeutic development relied primarily on cancer cell lines because of their prevalence, reproducibility, and simplicity to maintain. However, findings from research conducted in cell lines are rarely recapitulated in vivo and seldom directly translatable to patients. The tumor microenvironment (TME), tumor-stromal interactions, and associations with host immune cells produce profound changes in tumor phenotype and complexity not captured in traditional monolayer cell culture. In this chapter, we present various cancer explant models and discuss their applicability based on specific research aims. We discuss the appropriateness of these models for basic science questions, drug screening/development, and for personalized, precision medicine. We also consider logistical factors such as resource cost, technical difficulty, and accessibility. We finish this chapter with a practical guide intended to help the reader select the cancer explant model system(s) that best address their research aims.

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.

Roles of the immune system in cancer: from tumor initiation to metastatic progression

In this review, Gonzelez et al. provide an update of recent accomplishments, unifying concepts, and futures challenges to study tumor-associated immune cells, with an emphasis on metastatic carcinomas.

The presence of inflammatory immune cells in human tumors raises a fundamental question in oncology: How do cancer cells avoid the destruction by immune attack? In principle, tumor development can be controlled by cytotoxic innate and adaptive immune cells; however, as the tumor develops from neoplastic tissue to clinically detectable tumors, cancer cells evolve different mechanisms that mimic peripheral immune tolerance in order to avoid tumoricidal attack. Here, we provide an update of recent accomplishments, unifying concepts, and future challenges to study tumor-associated immune cells, with an emphasis on metastatic carcinomas.