Defining an allogeneic CAR-T approach by shRNA-mediated knockdown of the T-cell receptor.

e14551 Background: An allogeneic approach for CAR T-Cell therapy can significantly streamline manufacturing, provide more accessible options to patients as well as enhance safety by reducing the possibility of graft-versus-host-disease. The T-Cell Receptor (TCR) is comprised of multiple subunits and functions to activate T-cells by a signal transduction cascade that is initiated upon antigen binding. Eliminating expression of the endogenous TCR on modified CAR-T-Cells may eliminate the ability to recognize major and minor histocompatibility antigens in the recipient. This study assessed if simultaneous expression of multiple short hairpin RNAs that knockdown levels of individual TCR subunits could result in the loss of TCR expression and TCR-mediated T-Cell activation. Methods: Recombinant DNA producing short hairpin RNAs against the TCR complex was transfected into T-cells. Cell surface TCR was analyzed by FACS. Following CD3 activation or co-culture with B-cells, T-Cell activation was quantified by measuring the levels of IL-2 by ELISA and QPCR. Results: When expressed individually, each shRNA inhibited it’s cognate TCR subunit by up to 93% of the endogenous levels. However, upon simultaneous expression of the shRNAs against the different subunits from the same vector, we observed a near complete depletion of the TCR complex from the cell surface ( > 99%) as measured by FACS analyses. Furthermore, TCR functionality was inhibited when treated cells were stimulated with either CD3 or in B cell co-cultures with Staphylococcal enterotoxins. IL-2 secretion was inhibited to undetectable levels by ELISA by the multi-shRNA treatment and > 98% by qPCR. Conclusions: Though knockdown of any single component of TCR never exceeded 93%, simultaneous knockdown of several TCR subunits abrogated surface TCR and downstream activation suggesting that disruption of stoichiometric expression the subunits prevented TCR formation. The small size of the shRNA expression cassette ( < 2 Kb) permits co-expression from the same lentiviral vector as the CAR. Altogether, these data point to a viable strategy towards generating a single vector approach for the production of allogeneic T-Cells for immunotherapies against certain cancers.