Humanized immune system (HIS) mice provide researchers with a unique opportunity to study human immune responses in a living organism. Developed to address the lack of suitable in vivo models for diseases such as HIV/AIDS, these mice now serve a range of research areas, from oncology to autoimmunity.
Monika Buczek, PhD Director, Humanized Immune Model Core Taconic Biosciences
In this Innovation Spotlight, Monika Buczek, the director of the Humanized Immune Model Core for Taconic Biosciences, discusses the advantages and challenges of using HIS mice, highlighting advances in customization and donor selection that enhance these models’ utility and reproducibility.
What are HIS mice?
HIS mice are immunodeficient mice that have been transplanted with human immune cells or immune tissues. Most commonly, researchers use hematopoietic stem cells from human cord blood, bone marrow, peripheral blood, or liver tissue to reconstitute a functional human immune system in the mouse. This enables the study of how the human immune system develops, functions, and responds to disease, treatments, or infection within a mouse model.
Why were HIS mice developed?
HIS mice were first developed in the late 1980s to address the urgent need for in vivo models to study human immune function, particularly in the context of HIV. These models emerged from early experiments using severe combined immunodeficiency (SCID) mice engrafted with human immune cells. The field evolved dramatically with the development of advanced immunodeficient strains such as NOG and NSG mice in the early 2000s, which enabled robust, long-term engraftment of human hematopoietic stem cells and tissues. HIS mice are now essential tools for studying infectious diseases, cancer immunotherapy, autoimmunity, and drug development.
How are HIS mice created, and can they be customized?
Typically, creation of an HIS mouse involves two components, and each of these provide options for customization that influence what the resulting HIS mice can ultimately be used for. Firstly, the choice of the recipient immunocompromised mouse strain will influence the functionality and survival of the human cells. The second key factor is the type and source of human cells used for engraftment.
All HIS models are made using severely immunodeficient mouse strains (e.g., NOG, NSG, BRG, or NRG) that lack T, B, and natural killer (NK) cells and do not reject human cells. The addition of human cytokines by knock-in or transgenic expression improves reconstitution of specific immune subsets such as myeloid cells, NK cells, or regulatory T cells.
For example, the NOG-EXL strain, which stands for extended lineage, produces human versions of the cytokines IL-3 and GM-CSF that promote the expansion, survival, and function of human myeloid lineages, in particular, dendritic cells, granulocytes and mast cells. This makes the model invaluable for studying immune-modulating drugs that target these types of cells or for modeling autoimmune disorders, allergies, or even acute myeloid leukemia. Genetic editing techniques in the laboratory mouse have allowed us to fine tune these models to help researchers address very specific research goals and to understand disease and test therapies in a way that is very translatable to the clinic.
Of course, this direct translatability comes from the second component, the human cells themselves that we engraft into these mice. Most HIS models use one of two sources for human donor cells: either hematopoietic stem cells (HSCs), which can be harvested from the umbilical cord vein following birth, or peripheral blood mononuclear cells (PBMCs), which can be harvested from blood samples taken from adults. Both have their advantages and disadvantages, and there are reasons to choose one or the other.
For example, HSCs are immature pluripotent progenitor cells that can develop into any type of human blood cells within the mouse given the right signal. Once these cells engraft, differentiate, and expand in the mouse, they are typically very long-lived and, with some caveats, function as normal human immune cells alongside the host mouse tissues and will respond to drugs meant for the clinic. The downside of HSCs is that they are challenging to source, are available in limited quantities, and can be variable. Unlike HSCs, PBMCs are easy to come by, and a single adult donor could, in theory, be a source for unlimited cells to generate HIS mice. But PBMCs are very different from HSCs: they are mature immune cells that have developed in a human. As such, they will sense the recipient mouse tissues as foreign and may attack the recipient mouse. This limits the usable shelf life of a PBMC-based HIS mouse (typically only 3-6 weeks) although there are ways to mitigate this. Unlike HSC-based models, PBMC models typically have a narrower range of human immune cells present and are basically considered T cell-only models.
What applications are humanized immune system mice suitable for?
As HIS mice become more complex and more customizable, the applications of these models have expanded dramatically. We have come a long way since these were first used to study HIV infection. In terms of infectious disease, HIS mice continue to support HIV research (mucosal and systemic infection, viral latency and therapeutics) but have also been used for hepatitis B and C (especially for special liver humanized models) and SARS-CoV-2 research.
Probably the biggest growth has been seen with immuno-oncology applications of HIS mice. When HIS mice are also engrafted with a human tumor, including patient-derived xenografts (PDX), this enables studies of human tumor-immune interactions. Researchers widely use HIS models for studying checkpoint inhibitors, such as PD-1/PD-L1 or CTLA-4, and CAR T efficacy and safety. For targeting the tumor microenvironment, models such as the huNOG-EXL are ideal because these possess the relevant human myeloid and lymphoid cells.
Some other applications of humanized mice include the following.
Vaccines and Adjuvants
- Human B and T cell responses to novel antigens
- Evaluation of adjuvants on human immune maturation
- HLA-transgenic HIS mice for antigen-specific T cell responses
Autoimmune and Inflammatory Diseases
- Models of T and B cell autoreactivity
- Cytokine or HLA-driven autoimmunity (e.g., lupus-like models)
- Evaluation of biologics targeting IL-6, TNF-α, and IFN pathways
Tissue-Specific Immunity
- Mucosal immunity (e.g., gut, vaginal, rectal mucosa in BLT mice)
- Liver–immune system crosstalk (e.g., Hu-Hepato models)
- Skin graft rejection and tolerance
GvHD and Transplantation
- Hu-PBMC models to induce GvHD for testing immunosuppressants
- HSC-derived HIS mice to explore tolerance induction
Hematopoiesis and Cell Therapy
- Studying lineage commitment, thymic education, and immune reconstitution
- Tracking gene-modified stem cells or immune cells over time
What challenges are currently associated with working with humanized immune system mice?
Many researchers struggle with donor availability, variability, and reproducibility of data.
In terms of donor availability, cord blood cells are a limited resource, and the already finite supply is further affected by regulatory requirements, accessibility, quality of cell material, and volume at time of collection. Thus, the variability of donors is a direct result of the inability to return to a specific donor indefinitely and the requirement to utilize multiple donors, and their individual characteristics, to achieve the statistical power and conclusive data.
Donor-to-donor engraftment and efficacy have been well documented and remain a leading cause of inconclusive or incorrect data in preclinical trials.1 In addition to variation between donors, using uncharacterized donors can directly affect investigations using humanized mice, essentially adding innumerable variables to an experimental design. Different donors not only have different rates of engraftment but can also develop unique cell population ratios that can confound research studies.
The combination of low donor availability and donor-to-donor variability causes major problems for ensuring data reproducibility. Often, going back to the same donor for repeat or follow-on experiments is not possible, and requires researchers to re-validate new donors to support the N values of their research.
Additionally, in the clinic, failing to match HLAs between a donor and recipient can result in transplant failure, including graft versus host disease. When modeling complex human systems using xenograft studies, the difference between agent efficacy and allogenic tumor responses to mismatched HLA donors can quickly lead to spiraling costs in unexpectedly necessary subsequent experiments. Understanding the need for matching (or mismatching) HLA on an experimental design is crucial to interpreting results and making decisions.
huSelect allows researchers to customize HIS mice by selecting specific donor characteristics to improve model consistency, reduce variability, and accelerate translational research.
©iStock, JamesBrey
What is huSelect®, and how do scientists working with HIS mice benefit from this service?
huSelect® services are a panel of customizations customers can add to their humanized mouse orders to better suit their research needs and reduce the challenges typically faced when using HIS animals. These customizations range from the ability to select donors on specific criteria, screen donors for important characteristics, and reserve donors for future studies.
Researchers can select donors on criteria such as HLA types (Taconic has a library of over 400 donors with known HLA A, B, and C, DRB1, DRB3, DRB4, DRB5 DQB1, and DPB1 sequences), specific cell populations (T, B, NK, or myeloid lineages), and sex and ethnicity (where available).
Customers can also dive deeper into T, B, and myeloid cell populations using our pre-optimized immunophenotyping panels, which can also be customized by mixing and matching immune markers.
Taconic has pre-validated over 100 donors with engraftment levels tracked at 10 weeks post engraftment in the NOG-EXL background and have further pre-characterized an additional 10 high-titer donors extensively over the course of 30 weeks post engraftment with time-course engraftment kinetics, bodyweights, and health scores. This data can be available upon request and can reduce the unknowns when selecting a donor for high-value and time-sensitive experiments.
Finally, once a customer finds a donor that fits their study needs, they have the option to request that donor for a custom engraftment into the background mouse strain of their choice or reserve it for a period of time for later engraftment. Taconic will hold those donor cells aside for the next time the researcher needs them, giving them a known donor and model to return to, reducing the variability in their model system and allowing their experiments to progress with more certainty, efficiency, and speed.
- Belderbos ME, et al. Donor-to-donor heterogeneity in the clonal dynamics of transplanted human cord blood stem cells in murine xenografts. Biol Blood Marrow Transplant. 2020;26(1):16-25.
