Abstract
For the past several decades, chimeric antigen receptor T cell (CAR T) therapies have shown promise in the treatment of cancers. These treatments would greatly benefit from companion imaging biomarkers to follow the trafficking and activation of T cells in vivo. Using synthetic biology, we engineered T cells with a chimeric receptor SyNthetic Intramembrane Proteolysis Receptor (SNIPR) that induces overexpression of an exogenous reporter gene cassette upon recognition of specific tumor markers. We then applied a SNIPR-based positron emission tomography (PET) reporter system to two cancer-relevant antigens, human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor variant III (EGFRvIII), commonly expressed in breast and glial tumors respectively. Antigen-specific reporter induction of the SNIPR-PET T cells was confirmed in vitro using GFP fluorescence, luciferase luminescence, and the HSV-TK PET reporter with [18F]FHBG. Tumors were successfully imaged using PET in dual xenograft HER2+/HER2- and EGFRvIII+/EGFRvIII- animal models, with > 10-fold higher [18F]FHBG signals seen in antigen-expressing tumors versus the corresponding controls. The main innovation described is therefore PET detection of therapeutic T cells via specific antigen-induced signals, in contrast to reporter systems relying on constitutive gene expression.
Competing Interest Statement
I.Z. and K.T.R. are co-inventors on patents for synthetic receptors (PRV 62/905,258, 62/905,262, 62/905,266, 62/905,268, 62/905,251, 62/905,263). K.T.R. is a cofounder of Arsenal Biosciences, consultant, SAB member, and stockholder. K.T.R. is an inventor on patents for synthetic Notch receptors (WO2016138034A1, PRV/2016/62/333,106) and receives licensing fees and royalties. The patents were licensed by Cell Design Labs and are now part of Gilead. He was a founding scientist/consultant and stockholder in Cell Design Labs, now a Gilead Company. K.T.R. holds stock in Gilead. K.T.R. is on the SAB of Ziopharm Oncology and an Advisor to Venrock.
Footnotes
↵□ email: kole.roybal{at}ucsf.edu, david.m.wilson{at}ucsf.edu, thea.tlsty{at}ucsf.edu