641. Highly Efficient, ZFN-Driven Knockout of Surface Expression of the T-Cell Receptor and HLA Class I Proteins in Human T-Cells for Enhancing Allogeneic Adoptive Cell Therapies

While adoptive transfer of T-cells modified to express a chimeric antigen receptor or tumor antigen specific T-cell receptor (TCR) has shown great promise for the treatment of malignant cancers, most current clinical applications are limited by the use of autologous T-cell products. Targeting of the TCR and HLA Class I genes in primary T-cells thus represent attractive targets for genome editing in order to produce universal T cells from allogeneic donors. Elimination of the native TCR and HLA class I proteins on T-cells would, respectively, reduce the risk of graft-versus-host disease and host-versus-graft clearance mediated by the adaptive immune system. We have developed clinical grade zinc finger nuclease (ZFN) reagents that can efficiently target the T-cell receptor alpha constant (TRAC) and beta-2-microglobulin (B2M) loci. ZFN encoding mRNAs were introduced into purified T-cells by electroporation. Without selection, T-cells treated with TRAC specific ZFNs showed modification of up to 89% of alleles as gauged by deep sequencing. Flow analysis showed 91% of treated cells were negative for CD3 expression. Results from ZFN mRNA dose titration studies showed that the level of TRAC gene modification by deep sequencing was highly correlated with the percentage of cells that stain negative for CD3 expression by FACS (Spearman rho = 0.96; p u003c 0.0001). B2M is a subunit in all HLA class I molecules, and represents a conserved target for eliminating HLA class I presentation in cells from different donors. Analysis of T-cells transfected with mRNAs encoding B2M specific ZFNs showed up to 94% of alleles were modified, as determined by deep sequencing. FACS analysis showed that 89% of treated cells were negative for expression of HLA-A, B, C. Similar to TRAC modified cells, a marked correlation was observed between the percentage of B2M alleles modified and percentage of cells lacking surface expression of HLA-A,B, and C (Spearman rho = 0.57; p u003c 0.0001). ZFN mediated genome editing was well tolerated. T-cells treated with TRAC or B2M specific ZFNs showed similar viability and growth characteristics as mock transfected cells. Together, these highly efficient ZFN reagents permit the highly efficient double knockout of TCR and HLA class I surface expression in primary human T-cells for potential use in the development of allogeneic cell therapies.