9 Decreased expression of MHC delays the onset of xenogeneic graft versus host disease in PBMC humanized NCG mice providing an enhanced model for oncology studies

Background

Humanized mice are specialized animal models that are used to assess the efficacy of human immunotherapies on tumors. Humanized mice incorporate components of the human immune system and are created by injecting human CD34⁺hematopoietic stem cells (HSCs) or human peripheral blood mononuclear cells (PBMCs) into an immunodeficient mouse. PBMC humanized (HuPBMC) mice recapitulate a robust human T cell population. One challenge when using HuPBMC mice is the onset of graft versus host disease (GvHD), limiting their lifespan compared to hCD34⁺ HSC humanized mice. The development of xenogeneic GvHD is dependent on the expression of major histocompatibility complex (MHC) on host cells and lowering MHC expression can delay the onset of GvHD. We examine two mouse strains, the NCG-B2m-KO and NCG-MHC-dKO, to determine the effects of MHC expression on GvHD. NCG-B2m-KO mice lack beta-2 microglobulin, a component of MHC I, and have lower cell surface expression of MHC I molecules. NCG-MHC-dKO mice lack the expression of MHC I and MHC II molecules.

Methods

We compared the onset of GvHD and human immune cell engraftment rates between HuPBMC NCG-MHC-dKO mice, HuPBMC NCG-B2m-KO mice and HuPBMC NCG mice. Mice were injected with 1x10⁷ PBMCs from individual donors. Animals were weighed three times a week to monitor for changes in body weight and general health status. Peripheral blood was collected at day 10, 20, 30, 40, 60 and 90 post injection for flow cytometric screening of human immune cell engraftment (hCD45⁺, hCD3⁺, hCD4⁺ and hCD8⁺). PBMC donor variability was also compared between these three PBMC humanized models by evaluating multiple donors and assessing additional collections from the same donor. HuPBMC mice were injected with RKO human colon carcinoma cells and tumor kinetics were compared between groups.

Results

Increased survival was observed in the HuPBMC NCG-MHC-dKO mice compared to the NCG-B2m-KO mice. Both HuPBMC NCG-MHC-dKO mice and NCG-B2m-KO mice survived longer than HuPBMC NCG mice. Lower levels of engraftment were observed in both the HuPBMC NCG-MHC-dKO mice and HuPBMC NCG-B2m-KO mice compared to HuPBMC NCG mice.

Conclusions

HuPBMC models have limited study duration due to the onset of GvHD. The deficiency of MHC delays the onset of GvHD allowing for the potential use in longer term tumor studies before the results are confounded by GvHD. PBMC humanized mice are an important model for translational research using immunotherapies and the PBMC humanized NCG-MHC-dKO and NCG-B2m-KO models provide an expanded study window ideal for oncology studies.

Ethics Approval

Animal procedures were reviewed and approved by CRL IACUC and performed in an AAALAC accredited facility.