A Donor-Dependent In Vivo Model For Single Agent And Drug Combination Cytokine Release Syndrome Safety Evaluation.

2612 Background: Although antibodies and CART cells therapies have been successfully used for cancer therapy, they can have lethal adverse effects such as cytokine release syndrome (CRS). The animal models and in vitro human PBMC assays presently in use can’t reliably predict the CRS in patients. A predictive marker for identifying patients at risk for developing CRS upfront would improve the safety of immune-oncology drug development. Methods: We have developed a rapid, sensitive and reproducible in vivo humanized mouse model for quantitating CRS. The NSG mouse and its derivatives are engrafted with human PBMCs. On day 6 we induced cytokines release with pembrolizumab, avelumab, atezolizumab, ipilimumab, anti-CD28, ATG and OKT3 in single dose; as well as combination treatments involving pembrolizumab, lenalidomide, ATG and anti-CD28. Furthermore, we compared our method versus the in vitro PBMC assay. The cytokine levels were also compared to the dose response. Results: There are about 10-15% CD45+ human cells on day 5 of engraftment; and among of them, there were approximately 70% CD3 T cells and 25% CD56 NK cells. All tested cytokines, human IFN-γ, IL-2, IL-4, IL-6, IL-10 and TNF were upregulated after 2 and 6 hours of OKT3, ATG, anti-CD28, pembrolizumab, avelumab and atezolizumab drug treatment. Mouse’s rectal temperatures dropped from 37-38 °C to about 36 °C at 6 hours’ time point in the treated groups. There is various cytokines release levels, low to high response in different donors with anti-CD28 treatment. All donors showed high response to OKT3. The cytokine release levels were consistent with a dose response or variable PBMC engraftment. The cytokine levels were also higher in some drug combination studies such as pembrolizumab combined with lenalidomide or ATG; anti-CD28 combined with ATG. Our in vivo method was able to determine CRS missed in the in vitro testing method. Conclusions: We have developed a rapid, sensitive and reproducible novel in vivo PBMC humanized mouse model that is able to differentiate human PBMC donors based on individual safety response to single agent and combination therapeutics of immune checkpoint inhibitors and possibly CAR-T therapy. This assay could be employed in future drug development.