Abstract: Cell transplantation faces significant hurdles: finding an abundant source of healthy cells, the risk of allograft transplantation rejection, and tumorigenicity of in vitro expanded cells. This study introduces a universal allogeneic donor ES cell line, Cloaked-FailSafe™ (CFS) cells, designed to tackle these issues. The cell line can be used to differentiate cells into various cell types and expanded in vitro using any established protocol. CFS cells are engineered with ‘cloaking’ offensive and defensive mechanisms to evade immune rejection. Furthermore, these cells contain a drug-inducible "kill-switch" to eliminate uncontrolled proliferating cells via the application of the drug ganciclovir. However, prior to clinical application, these cells need to be tested against human immune cells. Earlier, we tested the CFS cells and control H1 parent cells with human NK and T cell lines in addition to human PBMC to show suppression of immune responses by CFS cells. However, recognizing that in vitro testing using immune cells cannot fully replicate in vivo conditions, we proceeded to assess the engraftment or rejection of the CFS cells following their transplantation in a humanised mouse model. We subcutaneously injected 10^6 cells into humanised mice and compared these to the ‘uncloaked’ H1 control cells and assessed this over time using bioluminescent imaging. We showed that the CFS cells increased in number with time and formed visible lumps by 6 weeks at the injection site. On the other hand, the H1 cells reduced in number and resulted in either no or very small lumps, likely scar tissue, at the site of injection. For the mice injected with CFS cells, when the lumps reached 400-500mm^3 in size, ganciclovir was injected daily for between 1-2 weeks, resulting in a size reduction of the lumps and then tissue stabilization. In conclusion, the CFS cells show acceptance of transplanted cells in an allogeneic humanized mouse model, and their growth can be effectively regulated with a drug. This makes them a promising and safe universal cell source for in vitro differentiation into therapeutic cells aimed at addressing a wide range of degenerative diseases.
Funding Source: The work in this study was supported by the RGC European Union - Hong Kong Research and Innovation Cooperation Co-funding Mechanism (E-HKU703/18).
