Modeling human tumor-immune environments in vivo for the preclinical assessment of immunotherapies

Abstract

Despite the significant contributions of immunocompetent mouse models to the development and assessment of cancer immunotherapies, they inadequately represent the genetic and biological complexity of corresponding human cancers. Immunocompromised mice reconstituted with a human immune system (HIS) and engrafted with patient-derived tumor xenografts are a promising novel preclinical model for the study of human tumor-immune interactions. Whilst overcoming limitations of immunocompetent models, HIS-tumor models often rely on reconstitution with allogeneic immune cells, making it difficult to distinguish between anti-tumor and alloantigen responses. Models that comprise of autologous human tumor and human immune cells provide a platform that is more representative of the patient immune-tumor interaction. However, limited access to autologous tissues, short experimental windows, and poor retention of tumor microenvironment and tumor infiltrating lymphocyte components are major challenges affecting the establishment and application of autologous models. This review outlines existing preclinical murine models for the study of immuno-oncology, and highlights innovations that can be applied to improve the feasibility and efficacy of autologous models.

Keywords: Animal models; Autologous models; Cancer; Immune-system; Immunotherapies; Preclinical Safety-assessment/risk management.

Fig. 1

Schematic showing the generation of common preclinical murine cancer models. a. Carcinogen-Induced models are generated through the administration of cancer-causing agents to immunocompetent mouse strains. b. GEMMs promote tumor development through the promotion of oncogene expression or through deletion of tumor suppressors. c. Syngeneic models are generated through administration of murine-derived tumor cell lines, commonly carcinogen-induced cancers or transgenic tumor lines. d. CDX models are established through transplantation of human-derived 2D cancer cells into immunocompromised mice, either subcutaneously (under the skin) or orthotopically (in the corresponding organ). e. PDX models are established by transplantation of whole patient-derived tumor tissue either subcutaneously or orthotopically into immunocompromised mice, followed by in vivo passage of the tissue to create an experimental cohort

Fig. 2

Steps involved in establishing human immune system (HIS) models in vivo: a. The hu-PBL (human Peripheral Blood Leukocytes) model can be established through intravenous (IV) or Intraperitoneal (IP) injection of human peripheral blood mononuclear cells (PBMCs) in adult immunocompromised mice. b. The hu-SRC (human Stem Repopulating Cell) model is established through either IV or intrafemoral (IF) injection of haematopoietic stem cells (HSCs) into irradiated adult immunocompromised mice. HSCs are isolated from either umbilical cord blood, bone marrow (BM), fetal liver or mobilized peripheral blood HSCs. Hu-SRC models can also be established through IV, intracardiac (IC) or intrahepatic (IH) injection of HSCs into irradiated newborn immunocompromised mice. c. The hu-BLT (human Bone marrow, Liver, Thymus) model can be established through the transplantation of foetal thymus and liver fragments under the kidney capsule of irradiated adult immunocompromised mice, in addition to the IV injection of autologous HSCs. d. The hu-PDX (HIS patient-derived xenograft) model dually engrafts immunocompromised adult mice with early passage PDXs and a HIS. Most commonly, this is done with the use of immunocompromised mice engrafted with human CD34^+ve HSCs but can also be established with human lymphocytes such as PBMC or splenic mononuclear cells (SPMCs). e. Schematic showing the development of preclinical models for the in vivo assessment of cancer immunotherapies. Primary tumor tissue from the patient can be used to derive 2D cell lines and PDOs. A biopsy of primary tissue can also be expanded in vivo in immunocompromised mice to establish a PDX line. Patient derived (autologous) or allogeneic PBMCs, SPMCs or HSCs can be used to generate humanized mice. 2D cells, 3D cells or passaged xenograft tissue can be implanted or injected into the established HIS mice. Both HIS mice and tumor bearing HIS mice can be used to study cell fate, functional efficacy and safety and toxicity of immunotherapies.