The Jackson Laboratory presents its versatile set of mouse modeling tools capable of supporting broad functional components of the human immune system.
Although many mammals have immune systems that share important characteristics with humans, certain cell types and immune phenomena are unique to us. As a result, it has been difficult to design and conduct empirical studies that help researchers accurately predict clinical responses to therapeutic drugs, infectious diseases, cancers, and other stimuli that may trigger an immune response. In particular, system-wide immune disorders such as cytokine release syndrome (CRS) and host graft disease (GvHD) have remained incredibly difficult to study, prevent, and treat. . In vitro studies do not capture the cascading effects that the immune system can have on a wide range of tissues, while in vivo studies in animals such as rodents and nonhuman primates have historically been unable to predict toxicities linked to unique cell types. human immune cells. (Eastwood et al., 2010).
To solve these problems, the Jackson Laboratory (JAX) has developed a set of versatile mouse model tools capable of supporting broad functional components of the human immune system. These mice provide a preclinical research platform that provides sensitive and reproducible results for examining drug candidates for inflammatory responses. The platform also provides information on the progression of immune disorders and the potential efficacy of drugs intended to treat them.
Humanization of mice for immunology studies
To create our humanized mouse platform to study T-cell-based immune responses, we grafted immunodeficient mice (NOD-scid IL2rgnull or NSG) with human donor peripheral blood mononuclear cells (PBMCs). PBMCs include a variety of immune cells, but this graft model is dominated by T cells that allow us to recreate a human T cell-mediated immune response in mice.
In validation studies, we found that we could reliably induce a dose-dependent CRS response in these humanized mouse models using compounds known to cause CRS clinically, and that there was no CRS response to immunotherapies known to be clinically safe. Our results also captured the variation in cytokine release observed in individual human PBMC donors, with greater sensitivity and more reproducible results than in vitro assays performed with cells from the same donors (Ye et al. , 2020).
Examining how CRS affects organs
CRS occurs when the immune system overreacts to a stimulus such as a drug or disease. Activated white blood cells flood the body with an excess of cytokine signaling proteins, which activate more white blood cells and create a dangerous snowball effect that can lead to fever, organ failure, and even death.
With our humanized mouse model, we were able to measure not only the levels of various human cytokines released into the bloodstream after drug administration, but we were also able to observe the downstream effects these cytokines have on the body over time. of time. We observed changes in body weight and collected serum to analyze kidney and liver enzyme levels. We also collected liver and lung tissue samples for histopathology studies by hematoxylin and eosin (H&E) staining, caspase 3 staining, and detection of single cell necrosis in hepatocytes.
Figure 1. Comparison of the clinical serum half-life of three therapeutic antibodies with the corresponding half-life in a) WT mice or b) humanized mice with FcRn (Tg32), respectively. The R square of the linear regression model is shown in the graph, indicating a strong correlation between the human PK of these molecules and that of mice humanized with FcRn but not in WT animals.
As expected, depending on cytokine release levels, humanized mice treated with compounds known to cause CRS showed reduced body mass and experienced severe organ damage that reduced their functionality. We can continue to refine these studies to provide a better understanding of how factors such as dose variation can alter the effects of organs downstream of CRS.
Modeling the progression of GvHD
We also created humanized mice to model GvHD, which affects whole organ systems and can be developed from CRS that is not treated for too long. We generated these models by treating NSG mice with irradiation and then grafting them with human PBMCs, a process similar to that of our studies. However, it was important that PBMC donors for this particular study had already been specifically characterized specifically for their response to GvHD.
We observed that the progression and severity of GvHD in humanized mouse models are specific to individual PBMC donors and closely reflect the diversity and severity of GvHD responses observed in human transplant recipients. This indicates that, as with CRS, this platform could one day be used to help make individualized predictions about how patients’ immune systems will respond to treatment.
We conducted an initial study to demonstrate the usefulness of this platform for preclinical testing of new drugs designed to treat complications of immune transplantation such as GvHD. We used the model to compare Abatacept, an immunomodulator known to slow the progression of GvHD, with high and low doses of a bispecific antibody designed to achieve the same.
Figure 1. Comparison of the clinical serum half-life of three therapeutic antibodies with the corresponding half-life in a) WT mice or b) humanized mice with FcRn (Tg32), respectively. The R square of the linear regression model is shown in the graph, indicating a strong correlation between the human PK of these molecules and that of mice humanized with FcRn but not in WT animals.
In humans with GvHD, Abatacept decreases T cell expansion and cytokine release and improves survival. Compared to controls, both Abatacept and bispecific antibody doses demonstrated these three effects. The high dose of the bispecific antibody worked better than Abatacept in the last weeks of the study; this result demonstrates that this humanized mouse platform can provide nuanced information about the efficacy and mode of action of any new drug intended to treat GvHD.
References
Eastwood D, Findlay L, Poole S, Bird C, Wadhwa M, Moore M, Burns C, Thorpe R, Stebbings R. The failure of the TGN1412 monoclonal antibody assay explained by species differences in expression CD28 in CD4 + effector memory T cells. Br J Pharmacol. October 2010; 161 (3): 512-26. doi: 10.1111 / j.1476-5381.2010.00922.x. PMID: 20880392
Ye C, Yang H, Cheng M, Shultz L, Greiner D, Brehm M, Keck J. A humanized murine model of fast, sensitive, and reproducible in vivo PBMC to determine therapy-related cytokine release syndrome. FASEB J. 2020 August 09; 34: 12963-12975. doi: 10.1096 / fj.202001203R