Immune humanized mice have been valuable in the development of novel cancer immunotherapies as well as infectious disease. An immune humanized rat, built on the SRG Platform, the ImmunoRat, could provide several advantages over the currently available humanized mouse models, including supporting the growth of larger tumors for serial fine needle biopsies to assess immune infiltration and serial blood draws for assessing human immune development and tumor biomarkers in real-time throughout an efficacy study. Using the SRG (Sprague Dawley Rag2 -/- Il2rg -/- ) rat, Hera and collaborators have demonstrated PBMC engraftment and a novel autologous human skin and immune cells-humanized rat model. The SRG ImmunoRat is under development at Hera and is expected to launch commercially soon.

SRG ImmunoRats support development of adult-like, full-thickness human skin and human lymphoid organoids along with human immune cells. Methicillin-resistant Staphylococcus aureus inoculation in the human skin results in infection and skin pathology, thus recapitulating clinical outcomes. This model will enable in vivo mechanistic studies for development and evaluation of novel therapeutics for skin infectious disease and may also provide a model for establishing skin grafts of patient-derived melanoma tumors to investigate melanoma metastasis and response to therapies. In addition, engrafting the rat with human lymphoid organs and human immune cells may provide a similar platform to the BLT mouse for immunotherapy studies. Finally, we have demonstrated humanization of the rat immune system using human PBMCs. Human CD45+, CD3+, and CD20+ cells can be found in the peripheral blood, spleen, and bone marrow of engrafted rats. These immune humanized rat models may be beneficial for evaluating immunotherapies in human cancer models, including assessment of immune cell infiltration through fine needle biopsies.

PBMC engraftment in ImmunoRat: SRG rats demonstrate robust immune-system humanization with peripheral blood mononuclear cells.

Peripheral blood was analyzed for the presence of human CD45+, CD3+, CD4+, and CD8+ cells at 3, 7, 14, 28, 54, and 70 days post-injection. By 4 weeks post-transplant, recipients had an average of 29% circulating human CD45+ cells. As of 10 weeks post-transplant, recipients have up to 46% human CD45+ cells and remain healthy

 ImmunoRat supports the development of functional human T cells and skin engraftment.

Representative flow cytometry analysis of human T cells (hCD3+ cells) from the human thymus tissue of ImmunoRat at 36 weeks post-transplantation. (B). Flow cytometry analysis of cytokine response in human T cells from human thymus tissue following stimulation without (Vehicle) or with CD3/CD28 beads.

 Immunohistochemical analysis of the human skin and immune system in the humanized SRG

(A). Various human skin cells are reconstituted in the human skin, including keratinocytes (AE1/AE3+ cells, hCytokeratin+ cells), dermal fibroblast (TE7+ cells, hFibroblast+ cells), cutaneous immune cells (hCD45+ cells), and Langerhans cells (hCD207+). (B) Representative histological and immunohistochemical analysis of the human thymus (engrafted under the kidney capsule) demonstrate robust development of human thymus organoid at 9 months post transplantation, with human immune cells (Humans CD45+), including (C) high levels of T cells (hCD3+) and macrophages (hCD68+). (D) The rat spleen is also reconstituted with human immune cells (Humans CD45+); non-transplanted (NTP) SRG rat was used as a staining control. Scale bars: 200 μm.

  1. 2018 American Association for Cancer Research (AACR) Annual Meeting poster. The SRG™ rat: A novel SCID rat for humanization studies.
  2. 2019 AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics. A Rag2/Il2rg double-knockout rat supports engraftment of human immune system for immunotherapy-based cancer efficacy studies.