October 14, 2022 /
If you’ve been keeping up with the latest advancements in cancer research, you might come across the usage of humanized mouse models as a promising tool in cancer management and treatment.
This trend is driven by advances in the development of new rodent models which enabled scientists to further investigate and harness the power of immunotherapies in fighting tumors by replacing the mouse’s immune system with a functioning human one, hence the term “humanized”.
But first, what is a humanized mouse model?
A humanized mouse model is established by modifying specific genes that render it immunodeficient, lacking T, B, and NK cells, and replacing them with human functioning immune cells. This model serves as a preclinical tool in biomedical research by receiving transplantation of human tumor tissue known as “xenograft” derived from the patient’s cell line to explore cancer’s pathogenesis and evaluate different therapeutic effects.
Here, we highlight three different types of humanized mice models that are used in immuno-oncology studies:
- Humanized (hu) CD34+ Mouse Models
- Humanized (hu) PBMC Mouse Models
- Knock-in Humanized Mouse Models
CD34+ humanized mouse models are preferably used in long-term oncology studies.
Due to their ability to stably ingraft with huCD34+ hematopoietic stem cells, and their capacity in producing multi-lineage human immune cells that are viable up to nine months post-production, severely immune-deficient mice are exposed to whole-body irradiation followed by the injection of human CD34+ cells, this process makes the models ready for tumor implantation.
PBMC humanized mouse models are cost-effective in short-term oncology studies.
Because of their rapid engraftment with human immune cells, humanized PBMC mouse models are used in studies that aim to evaluate compounds for T cell immune modulation. This is done post the intravenous engraftment of human peripheral blood monocyte cells (PBMCs) in severely immune-deficient mice before or following the implantation of the xenograft. This allows for quick evaluation of a novel immuno-therapeutic with human, specifically with a focus on T cell immunology. From study planning to start, PBMC models can be accomplished is just a few weeks. This makes the model well suited for rapid results. However, PBMC models are limited in duration by GVHD onset within 4 to 8 weeks. For longer duration models, CD34+ humanized models are a better choice.
Knock-in humanized mouse models offer a distinctive anti-tumor response in research.
By expressing chimeric proteins made of a humanized extracellular domain, knock-in mouse models with fully functioning immune systems are primarily used to evaluate the anti-tumor response of the immune checkpoint inhibitors related to human targets. First generation humanized mice broadly supported human T cell engraftment. Recent advances permitted the addition of human cytokines such as GM-CSF, IL-3 and/or IL-15 creating 2nd generation humanized mice models. Second, generation mice support an even more completed human immune system with increase in the engraftment of granulocytes, macrophages, NK and dendritic cells.
Regardless of 1st or 2nd generation model type, humanized mice models have the capacity of bearing both the human immune system and human tumors, but their successful engraftment of human immune cells depends strongly on the immunodeficiency of the recipient mice.
While ectomy procedures, radiotherapy, and chemotherapy remain the most effective methods for treating tumors, the five-year survival rate post-operation remains insufficient. The significant progress in onco-immunology enabled immunotherapy to attack a tumor by potentiating functioning lymphocytes instead of killing it directly which marked the forward leap in cancer treatment.
In addition, recent studies demonstrated that humanized mouse models opened new perspectives in immunotherapy by bearing both human immune cells and human tumors. This is translated through the model’s ability to be engrafted with tumors either in a form of cell-line-derived xenograft (CDX) or patient-derived xenograft (PDX), with the later method being extensively used in cancer research today. Even though CDXs consume less time, studies showed that in vitro culture, a step before engraftment may cause a substantial loss of features in primary tumors. PDXs on the other hand, are fragments of fresh human tumors engrafted directly onto the recipient mouse model which makes them challenging to establish and may lead to potential loss of their associated human stroma over time.
Using humanized mouse model as a preclinical application for cancer immunotherapies requires the reproduction of the tumor microenvironment (TME) in the hu-PDX mice model. TME comprises varying elements such as blood vessels, lymph vessels, stromal cells, immunocytes, fibroblasts, and the extracellular matrix (ECM). The establishment of this complex milieu is a dominant factor in oncobiology studies as it not only offers the environment for tumor development and metastasis but also aids in its diagnosis, prevention, and prognosis. Due to its major role in tumorigenesis and cancer development alongside the interplay between immunocytes and tumor cells post mice humanization and PDX implantation, TME can provide new strategies for future therapy.
Pairing humanized mice with an accomplished flow cytometry core is essential to understand the TME. Pharmalegacy (PL) is fortunately to have an excellent cytometry core with multiple cytometers supporting up to 16 color staining. If you need to study T cell exhaustion markers, or a specialized subset of DC1 cells, PL can design a FACS panel to track all your cell populations of interest.
Additionally, the usage of humanized mice model to engineer genetic-modified T cells was reported to be of beneficial value in cancer patients receiving adoptive cellular therapy (ACT) which denotes expanding immunocompetent cells in vitro followed by reinjecting them back to the patients. The procedure of ACT infusion is based on T cells engineered to express transgenic T cell receptors (TCRs) or chimeric antigen receptors (CARs), which aids in improving the affinity with tumor-associated antigens (TAAs).
Also, a humanized mouse model was helpful in immune checkpoint blockade therapy. Several signaling pathways and inhibitory receptors grouped under immune checkpoints like programmed cell death protein-1 (PD-1), cytotoxic T-lymphocytes-associated protein-4 (CTLA-4), lymphocyte activation gene-3 (LAG-3), and T cell immunoglobulin-3 (TIM-3), all suppress excessively activated T cells preventing a self-tissue attack, hence eliminating the occurrence of autoimmune effects. The blockage of some immune checkpoints was marked as a unique setup in cancer treatment when PD-1 and CTLA-4 inhibitors won the Nobel Prize in physiology and medicine in 2018. The remarkable superiority of the humanized mice model in studying immune checkpoint inhibitors was established to test the effectiveness of individual clinical consultations for cancer patients.
First generation humanized mice have been highly predictive of human clinical success for check point therapies. Next generation of immune-oncology therapies will target processes beyond check point blockade. Future therapies will require a more complete TME that includes additional immune cell types commonly found in ‘cold’ tumors that do not respond to check point treatment. Second generation humanized mice promise to be the models of the future. Specifically, therapies that target NK cells, MDSC, and TAM can all benefit from 2nd generation humanized mice.
Current studies are undergoing tremendous efforts to ensure the reliable usage of humanized mouse models as a representative tool in preclinical immune-oncology studies by tackling its major setbacks. At PharmaLegacy, we understand that the need for humanized models is of utmost importance; This is why our team of experts are always hard at work to provide you with reliable and cost-effective models that fit your studies. Additionally, we manufacture our own humanized mice. This allows for customization to meet our client’s needs. We can transfect lentivirus expressing cytokines, screen donor CD34 stems cells, or additionally customize the model systems based on our customer’s needs.