Abstract A038: Effective rerouting of NK cell cytotoxicity against B-cell malignancies upon TCR gene transfer

T-cell receptor (TCR) gene transfer involves ex-vivo introduction of a tumour-reactive TCR into patient-derived CD8 T-cells enabling specific-targeting of tumour cells. Competition for expression with CD3 from the endogenous TCR and the potential for TCR mixed- dimer formation necessitate optimisation of cellular therapeutics with sustained potency and increased safety. NK-cells (CD3-CD56+) are potent short-lived effector cells that lyse abnormal or stressed cells independent of antigen. Efficacy and safety of adoptive NK therapy has been demonstrated in the treatment of hematologic malignancies in both the autologous and allogeneic setting. Here,we aimed to exploit NK-cell cytotoxicity and redirect it toward antigen-specific recognition of tumors without the limitation of TCR mixed- dimer formation and competition for CD3.Firstly, peripheral blood derived NK-cells were expanded and retrovirally transduced to express BOB1-specific TCR, restricted to HLA- B*07:02, in combination with CD3 alongside CD8 co-receptor.BOB1 is a B-cell restricted transcription factor, important for B-cell survival. Purified BOB1-TCR expressing NK-cells demonstrated antigen-specific binding of BOB1-specific pMHC-tetramer and proliferated upon co-culture with HLA-B*07:02 positive B-lymphoblastic cell lines (B-LCL) but not with HLA-B*07:02 negative B-LCL. Furthermore, BOB1-TCR expressing NK-cells demonstrated in vitro cytotoxicity against HLA-B*07:02 positive B-LCL, multiple myeloma and B-ALL cell lines. Conversely, these tumor cell lines remained resistant to NK-cell mediated lysis when co-cultured with mock transduced NK-cells. Finally, NK sensitive cell line K562 was comparably lysed by both BOB1-TCR or mock transduced NK-cells demonstrating retained NK-cell mediated activity.These data demonstrated that NK-cell cytotoxicity can be redirected toward antigen-specific recognition of tumors and is TCR-dependent. Retention of NK-cell function in genetically modified cells allows for a double-hit therapeutic approach that can offer advantages over current cellular approaches. Citation Format: Laura T. Morton, Anne K. Wouters, Dennis F. Remst, Renate S. Hagedoorn, Marleen M. Van Loenen, Renate de Boer, J. H.F. Falkenberg, Mirjam H.M. Heemskerk. Effective rerouting of NK cell cytotoxicity against B-cell malignancies upon TCR gene transfer [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A038.