DESIGN OF A PRIVATE PASSAGEWAY FUSION RECEPTOR FOR SENSITIVE CONTROL OF ADOPTIVE CELL THERAPIES

Most Adoptive Cell Therapies (ACT), including CAR T cell therapies, suffer failure because of the severe side effects due to loss-of-control of the therapeutic cells once they are inside the patient’s body, suggesting that novel strategies must be developed for a better in vivo control of these engineered cells. In the meantime, CAR T cell therapies targeting solid tumors have not experienced the remarkable success achieved with hematopoietic cancers, mainly due to continuous tumor antigen exposure and a suppressive tumor microenvironment. Here we designed a private passageway fusion receptor, which is composed of a ligand binding domain and a glycosylphosphatidylinositol (GPI) anchoring domain, to be expressed and localized to the surface of CAR T cells independently to the classical CAR T construct. These ligand binding domains preserve high binding affinity towards their cognate ligands and are only expressed on the CAR T cells that have been transduced. Therefore, cytotoxic drugs or immunosuppressants linked to the corresponding targeting ligands are shown to be specifically delivered to these fusion receptor positive CAR T cells for lowering the activity of the over-activated CAR T cells. On the other hand, we discovered that a potent TLR7 agonist is able to enhance the lysis effect of the exhausted CAR T cells in a co-culture model. Serial releasable and non-releasable targeted TLR7 agonists were prepared and tested. Based on these data, we suggest that our secret passageway fusion receptor platform provides a better control of the activity of CAR T cells using the corresponding targeting ligand-payload conjugates in a dose dependent manner and function as a doorway for the delivery of instructions to CAR T cells for versatile purposes.