Humanized Mice as a Valuable Pre-Clinical Model for Cancer Immunotherapy Research

Abstract

Immunotherapy with checkpoint inhibitors opened new horizons in cancer treatment. Clinical trials for novel immunotherapies or unexplored combination regimens either need years of development or are simply impossible to perform like is the case in cancer patients with limited life expectancy. Thus, the need for preclinical models that rapidly and safely allow for a better understanding of underlying mechanisms, drug kinetics and toxicity leading to the selection of the best regimen to be translated into the clinic, is of high importance. Humanized mice that can bear both human immune system and human tumors, are increasingly used in recent preclinical immunotherapy studies and represent a remarkably unprecedented tool in this field. In this review, we describe, summarize, and discuss the recent advances of humanized mouse models used for cancer immunotherapy research and the challenges faced during their establishment. We also highlight the lack of preclinical studies using this model for radiotherapy-based research and argue that it can be a great asset to understand and answer many open questions around radiation therapy such as its presumed associated "abscopal effect".

Keywords: cancer; humanized mice; immunotherapy; oncoimmunology; preclinical model.

Figure 1

Mouse humanization models. Schematic representation of the four humanization methods described, and graphs of their immune reconstitution in peripheral blood (PB) over time showing human CD45⁺ immune cells out of all blood leukocytes and human CD19/20⁺ B cells, human CD3⁺ T cells, and human CD14⁺ monocytes/macrophages out of human CD45⁺ cells. Immune reconstitution data showed on the graphs are gathered from different studies (–14). (A) Generation of peripheral blood mononuclear cells (PBMCs) humanized mouse: Human PBMCs isolated from peripheral blood are engrafted into a low dose whole body irradiated or non-irradiated immunocompromised mouse by intraperitoneal (IP), intravenous (IV) or intrasplenic (IS) administration. (B) Generation of hematopoietic stem cells (HSCs) humanized mouse: Human HSCs isolated from either adult peripheral blood, bone marrow or umbilical cord blood, or from fetal liver are engrafted into a low dose irradiated immunocompromised mouse by IP or IV administration. (C) Generation of bone, liver, thymus (BLT) humanized mouse: Human fetal bone, thymus and liver tissue are co-transplanted under the kidney capsule of an immunocompromised mouse which is then irradiated and injected IV with human HSCs isolated from fetal liver. (D) Generation of spleen mononuclear cell (SPMC) humanized mouse: Human SPMC isolated from an adult spleen are engrafted into a low dose irradiated immunocompromised mouse by IP administration.

Figure 2

Novel immunotherapy settings tested in humanized mice. (A) Immune checkpoint inhibitors (ICI) prevent engagement of inhibitory receptors and allow activation of anti-tumoral immune activity. ICI were tested in humanized mice to target EBV⁺ nasopharyngeal carcinoma and other EBV-associated malignancies, melanoma, B cell lymphoma, osteosarcoma lung metastases, non-small cell lung carcinoma (NSCLC), and ovarian cancer. (B) Bispecific antibodies form a bridge between two target cells and were tested in humanized mice to target B cell lymphoma, pancreatic adenocarcinoma, NSCLC, gastric adenocarcinoma, and prostate cancer. (C) Therapeutic cancer vaccines boost the anti-tumor activity by injecting TAAs or TAA-encoding constructs to the patient. They were tested in humanized mice to target HPV16⁺ cervical tumors. (D) Adoptive transfer of ex vivo modified immune cells to improve their anti-tumor activity has been tested in humanized mice to target melanoma, pancreatic adenocarcinoma, lung carcinoma, ovarian cancer, and EBV-associated malignancies. (E) Oncolytic viruses specifically infect cancer cells and induce immunogenic cell death. They were tested in humanized mice to target pancreatic adenocarcinoma and lung carcinoma. Major histocompatibility complex (MHC); tumor associated antigen (TAA); T cell receptor (TCR); antigen presenting cell (APC); programmed cell death 1 (PD1); programmed death-ligand 1 (PD-L1); cytotoxic T lymphocyte antigen 4 (CTLA4); Epstein-Barr virus (EBV); cluster of differentiation (CD); dendritic cells (DCs); T cell bispecific (TCB); tumor infiltrating lymphocytes (TILs); prostate-specific membrane antigen (PSMA); human papillomavirus (HPV); natural killer (NK); chimeric antigen receptor (CAR); human epidermal growth factor receptor 2 (HER2); invariant natural killer T (iNKT); interleukin (IL); Torque Teno virus (TTV).