Syngeneic vs. Xenograft Cancer Models: Overview, Key Differences, and When To Use Each

August 07, 2023 /

Scientists have been investigating cancer for well over 100 years, with the first animal model of cancer being a squamous cell carcinoma induced on the ears of rabbits using coal tar.1,2 Since that time, many thousands of animal models of cancer have been developed, but they largely fall into one of two baskets: syngeneic models and xenograft models. Both types of models have been used by researchers for over 50 years.3,4 Understanding the differences between these models, the variations within each type of model, and how to select the most appropriate model is key to designing a successful study – one which will most accurately predict clinical relevance.

 

What is a Syngeneic Cancer Model?

In a syngeneic cancer model, the cancer is derived from a cell line which is derived from a tumor originating from the same inbred strain of mice being used in the study. Because the individuals in the inbred mouse strain are nearly genetically identical, and the major histocompatibility complex (MHC) is genetically identical, they do not have a graft-vs-host reaction to the implanted cells or tumor. This allows researchers working with syngeneic models to use immunocompetent mice.

Syngeneic models are sometimes also referred to as autograft models.

 

What is a Xenograft Cancer Model?

In a xenograft cancer model, a tumor cell line or tumor tissue of human origin is implanted into an immunodeficient mouse. For reasons of convenience and animal welfare, this implant is most often subcutaneous, however it has long been known5,6 that orthotopic tumors, which are implanted into the organ or tissue which matches the tumor histotype, are generally superior. More recent studies on the development of new xenograft models continue to demonstrate the superiority of orthotopic xenograft models.7,8,9 While not always the case, the therapeutic effects of an experimental treatment can differ between subcutaneous and orthotopic models.10 Orthotopic implantation allows the tumor to develop in an environment which more closely matches the original tumor microenvironment. Orthotopic tumors are therefore more pathologically relevant, demonstrating comparatively greater malignancy which more closely resembles metastasis in native tumors. Despite the disadvantages in pathology, subcutaneous xenografts may be appropriate for practical reasons in certain screening situations when throughput and cost per animal are more important than precise replication of the disease state.

Beyond the method of implantation, there is also the question of the source of the tumor tissue or cells. This further divides xenograft models along another axis: whether they are a Patient-Derived Xenograft (PDX) or a Cell line-Derived Xenograft (CDX). As the names imply, patient-derived xenografts are originally from the tumors of patients while cell line-derived xenografts can be from commercial or any other cell lines. While these are not mutually exclusive definitions, it is generally accepted that PDX, even when they are from cell lines, are more recent and have not been passaged nearly as much as more “standard” cell lines used in CDX models. PDX models may be more representative of naturally occurring cancers, however can have high degrees of variability between models. CDX models are generally cheaper and easier to obtain, but may sacrifice clinical relevance.

Differences Between Syngeneic vs. Xenograft Models

As can be surmised from the fact that both types of models are still used over half a century later, each has its own benefits and drawbacks. There are two main differences between syngeneic and xenograft models: the immune status of the mice used and the origin of the tumors.

In syngeneic mice, the tumors are of murine origin and from the same inbred line. Because of this, the mice can be immunocompetent. In xenograft mice, the tumors are of human origin. Because of the foreign nature of the xenograft, the mice must be immunodeficient to avoid graft vs. host rejection. Therefore, syngeneic models involve more relevant immune function while xenograft models involve more relevant tumor function.

Syngeneic Xenograft
  Immune Status     Immunocompetent     Immunodeficient  
Tumor Origin Murine Human

A notable limitation of syngeneic models is the relatively limited amount of available syngeneic murine tumor lines compared to the ready availability of a large number of characterized human tumor lines, the development of which only requires a tumor or immortalized cell line from any source. When assessing a new immuno-oncology therapy which targets a novel immune target or cancer type / subtype, additional characterization or model development may be required. Characterization of new xenograft models, when required, is comparatively fast and easy.

 

When Should You Use Syngeneic Models vs Xenograft Models?

The decision on whether to use a syngeneic model or xenograft model will depend largely on the type of therapy you are developing.

When developing cancer immunotherapies, syngeneic models must be used, as the immunodeficient mice used in xenograft models cannot replicate the necessary immune function. When selecting a syngeneic model, you should ensure that it has well-characterized responses to known immune checkpoint inhibitors (e.g., anti-PD-1, anti-PDL-1, anti-CTLA-4). Immunogenicity and the composition and extent of tumor-infiltrating leukocytes (TIL) should also inform your model selection.

For chemotherapies, or any therapies which do not rely on immune function, xenograft models are preferred. Orthotopic implants of human tumor cells into immunodeficient mice can provide a more clinically relevant assessment of the efficacy of a chemotherapy than would a syngeneic model utilizing mouse-derived tumors in immunocompetent mice.

 

Syngeneic and Xenograft Models Aren’t Your Only Options!

If you don’t want to choose between testing murine cell lines in immunocompetent mice or human cell lines in immunodeficient mice, you could also choose a humanized mouse model, a type of model most often used in immuno-oncology which we will discuss more in a later post.

 

References

  1. https://en.wikipedia.org/wiki/Yamagiwa_Katsusabur%C5%8D, retrieved July 12, 2023
  2. Yamagiwa, K., Ichikawa, K.. Experimental Study of the Pathogenesis of Carcinoma. The Journal of Cancer Research. 3 (1): 1–29 (1918).
  3. Abdolahi, S., Ghazvinian, Z., Muhammadnejad, S. et al. Patient-derived xenograft (PDX) models, applications and challenges in cancer research. J Transl Med 20, 206 (2022). doi: 10.1186/s12967-022-03405-8
  4. Day C.P., Merlino G., Van Dyke T. Preclinical mouse cancer models: a maze of opportunities and challenges. Cell. 2015 Sep 24;163(1):39-53. doi: 10.1016/j.cell.2015.08.068
  5. Killion, J.J., Radinsky, R. & Fidler, I.J. Orthotopic Models are Necessary to Predict Therapy of Transplantable Tumors in Mice. Cancer Metastasis Rev 17, 279–284 (1998). doi: 10.1023/A:1006140513233
  6. Bibby, M.C. Orthotopic models of cancer for preclinical drug evaluation: advantages and disadvantages. European Journal of Cancer. 40 (6): 852-857 (2004). doi: 10.1016/j.ejca.2003.11.021
  7. Zhang, Y., Zhang, G., Sun, X., Cao, K., Ma, C., Nan, N., Yang, G., Yu, M., Wang, X. Establishment of a murine breast tumor model by subcutaneous or orthotopic implantation. Oncology Letters. 15 (5): 6233-6240 (2018). doi: 10.3892/ol.2018.8113
  8. Zhang, W., Fan, W., Rachagani, S. et al. Comparative Study of Subcutaneous and Orthotopic Mouse Models of Prostate Cancer: Vascular Perfusion, Vasculature Density, Hypoxic Burden and BB2r-Targeting Efficacy. Sci Rep 9, 11117 (2019). doi: 10.1038/s41598-019-47308-z
  9. Du, Q., Jiang, L., Wang, X.Q., Pan, W., She, F.F., Chen, Y.L.. Establishment of and comparison between orthotopic xenograft and subcutaneous xenograft models of gallbladder carcinoma. Asian Pac J Cancer Prev. 2014;15(8):3747-52. doi: 10.7314/apjcp.2014.15.8.3747
  10. Tran Chau, V., Liu, W., Gerbé de Thoré, M. et al. Differential therapeutic effects of PARP and ATR inhibition combined with radiotherapy in the treatment of subcutaneous versus orthotopic lung tumour models. Br J Cancer 123, 762–771 (2020). doi: 10.1038/s41416-020-0931-6