Exploring Veto Activity: DNAM-1-CD155 Axis in Overcoming NK Cell-Mediated Allo-Rejection and Applications for CAR-T Cell Therapy

As Miller et al. defined veto activity, it enables cells to target host cytotoxic T lymphocyte (CTL) precursors specific to veto cells' antigens, selectively eliminating anti- donor T cell clones without inducing rejection. By leveraging this unique immune property, two key research aims were proposed: “Exploration of the Impact of Veto Activity on Natural Killer (NK) Cell-Mediated Allo-rejection” and “Development of Off-the- shelf Chimeric Antigen Receptor (CAR)-T Therapy: Engineering Anti-Viral Veto CD8+ T Cells”. As demonstrated in our previous research, in a murine model with mild conditioning, anti-third-party central memory CD8+ veto T cells (veto Tcm) can prevent T cell- mediated graft rejection without causing significant graft-versus-host disease (GvHD). These veto Tcm eliminate donor-specific T cell clones via a Fas-FasL-signaling pathway. However, the underlying mechanism of their interaction with alloreactive NK cells remains elusive. By transplanting nude mice with allogeneic T cell-depleted bone marrow cells (TDBM), we demonstrated that veto Tcm cells effectively overcome NK cell-mediated rejection. We also discovered that veto Tcm cells upregulate CD155, a primary ligand for the activating receptor DNAM-1. Later in vitro studies further indicated that conjugation between veto Tcm cells and alloreactive NK cells induces NK cell anergy by enhancing the internalization and degradation of DNAM-1, a process significantly linked to the activation of the Cbl protein in alloreactive NK cells. Next, we aim to develop off-the-shelf CAR-T cells to translate this approach into human clinical applications using this novel platform. By triggering veto activity of cytotoxic CD8 T cells and selectively expanding clones specific to viral peptides, we can effectively address the challenges of graft rejection and GvHD. CD19 Veto CAR-T cells, generated via retroviral transduction, demonstrated promising anti-tumor effects in vitro and in vivo without inducing GvHD. These findings highlight that veto Tcm can serve as a promising platform for CAR-T cell therapy, potentially avoiding the need for extensive gene editing to mitigate the risks of bi-directional alloreactivity.